Published by Australian Academy of Science

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Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

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A

accelerator mass spectrometry (AMS). A highly sensitive technique that is used to measure the relative amount of different ions (and often isotopes) in a sample. Accelerated ions are separated by their mass to charge ratio. AMS can be used as a form of carbon dating. By measuring the different isotopes of carbon in a sample, the age of the sample can be determined.
Excuse me! The problem with methane gas

acidification. The lowering of the pH of oceans due to increasing levels of carbon dioxide. Ocean acidification affects certain types of microscopic algae (phytoplankton), corals and other marine organisms with calcium carbonate skeletal structures.
A sense of things to come – smart sensors and the environment

acid rain. A form of acid deposition. When fossil fuels are burnt, sulfur dioxide (SO₂) and oxides of nitrogen (NO_x ) are released into the atmosphere. They can react with water vapour (or chemicals derived from it) to form acids. If these attach to particulates in the air, they may fall as acid soot close to the source of the pollution. This is acid deposition. The acid can also fall in rain, snow or hail (collectively known as acid precipitation) often far away from the original pollution (eg, Canada receives acid rain from US pollution).
Local air pollution begins at home

active ingredient. The ingredient that is responsible for producing the desired effect of a mixture of ingredients and for giving the product its main characteristic. The active ingredient is not necessarily the most common ingredient in a product.
Putting on a good face – the chemistry of cosmetics

adrenaline and noradrenaline. Hormones, released by the adrenal glands, that are the first line of defence during any sudden stress. These hormones increase heart rate and blood pressure, and therefore increase blood flow to the muscles, allowing a 'flight or fight' response. These hormones are also called epinephrine and norepinephrine.
Bitumen battles – the phenomenon of road rage

adsorption. The binding of molecules or particles to the surface of a solid or liquid, as opposed to absorption, the filling of pores within a solid. The binding to the surface is usually weak and reversible unless a chemical bond is formed.
The quest to make hydrogen the fuel of the future

Advanced Mobile Phone System (AMPS). Analogue systems of mobile phones send information over radio waves as an electrical copy of the sounds picked up by the phone's microphone (in this case the human voice). The information is sent as a continuous flow of energy, so that only one conversation at a time is possible on any one frequency. More information on analogue and digital systems can be found at Sound into pulses: The benefits of digital transmission (Telstra Learning Centre, Australia) and What is the difference between analog and digital cell phones? (How Stuff Works, USA).
Mobile phones – communications on the go

afforestation. Establishing trees on previously unforested land.
Carbon currency – the credits and debits of carbon emissions trading

airways. A general term for the system of tubes that runs from the back of the mouth and nose into the lungs. The largest is the trachea or windpipe. In the chest, the trachea divides into two smaller tubes called bronchi. Each bronchus then supplies one lung. After entering the lung, the bronchi divide further into narrower tubes called bronchioles and these supply the air sacs of the lung. The airways contain a thin lining on the inside moistened with a little mucus. Barring choking or drowning, from the moment you are born your airways are kept clear and, unless you smoke, fairly clean. Asthma sufferers find that periodically their airways narrow and they can't breathe normally. The smooth muscle is contracting and so narrowing the airway, and at the same time the inner lining becomes inflamed and reddened. It may also swell. Extra mucus is produced, sometimes thicker than usual, and it can partially clog or obstruct the airway.
The rise and rise of asthma

albedo effect. A measure of how much of the Sun's energy is reflected off an object back out to space compared to how much is trapped in Earth's atmosphere. Snow, ice and clouds have a relatively high albedo so generally reflect more of the Sun's energy back to space which has a cooling effect on the Earth. However, cirrus clouds have a lower albedo transmitting more radiation through to Earth's surface and trapping Earth's reflected radiation. This increases the temperature on Earth.
Flying beyond our means – air travel and the environment

algae. A large group of simple organisms, ranging from single celled phytoplankton to the larger seaweeds. Like plants they are photosynthetic, but they generally have a simpler structure than plants. Algae are found in water as well as on land.
The quest to make hydrogen the fuel of the future

algorithm. A logical, step-by-step procedure used to solve problems in mathematics and computer programming. In the case of biometrics the algorithm refers to a computer program designed to turn raw data into code that can be used more easily by identification/verification software.
Good prospects ahead for data mining
Putting a finger on it – the loops and whorls of biometrics

allele. Genes can exist in more than one form. Each different form of the same gene is called an allele. For example, in the case of seed shape, there is one allele that determines wrinkled seeds and another allele that determines round seeds.
The Human Genome Project – discovering the human blueprint
Malaria – a growing threat
Conservation genetics – molecular detectives at work

allergens. An allergen is any substance that triggers an allergic reaction. Common respiratory allergens are grass pollen, mould spores or house dust mite faeces (present in dust); other allergens may affect the skin or the digestive system.
The rise and rise of asthma
Weeds – the real alien invaders

allergic reaction. Allergies are inappropriate reactions of the immune response to substances (allergens) that normally wouldn’t cause any noticeable effects. Most allergic reactions involve the allergen binding on to special immune system cells and causing these cells to release compounds that affect the surrounding tissue. One such compound is histamine. It causes itching and inflammation. Chemicals that block the effect of histamine are called antihistamines, and they are standard allergy medication. However, they are not particularly effective in asthma.
The rise and rise of asthma
Weeds – the real alien invaders

alloy. A substance made of two or more metals, or a metal and one or more non-metals, that has mostly metallic properties. Alloys are often created to improve the properties of metals such as strength, resistance to corrosion and hardness. For example, steel is an alloy of iron with up to two per cent carbon and often small amounts of other elements. The properties of steel such as strength, malleability and machinability can be changed by adjusting the amounts of its component elements.
Rocking on with hot rocks geothermal energy
Making light of metals

alloys. Metal mixtures with greater strength, hardness or malleability than their component metals. The ratio of each component determines the properties of the alloy. Modern alloys may be created by adding just a few per cent of another metal.
Probing past and future materials with neutrons

alternative energy sources. Energy sources different from those in widespread use at the moment (which are referred to as conventional). Alternative energy usually includes solar, wind, wave, tidal, hydroelectric and geothermal energy. Although they each have their own drawbacks, none of these energy sources produces significant air pollution, unlike conventional sources.
Harnessing direct solar energy – a progress report

alumina. (aluminium oxide). A compound that occurs naturally and can also be produced from the mineral ore bauxite. Aluminium is produced from alumina via electrolysis
Making light of metals

amino acid. The basic building block of protein. All amino acids contain an amino (NH₂ ) end, a carboxyl end (COOH) and a side group (R). In proteins, amino acids are joined together when the NH₂ group of one forms a bond with the COOH group of the adjacent amino acid. The side group is what distinguishes each of the amino acids from the others.

There are 20 common amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine.
More food, cleaner food – gene technology and plants
Driver fatigue – an accident waiting to happen
Who will win the drugs race?

amphiphilic (`loving both'). One end of an amphiphilic molecule is polar and hydrophilic (water loving) and the other is non-polar and hydrophobic (water hating). The hydrophilic ends of the molecule point outwards into the solution and the hydrophobic ends point inwards away from the water, so they tend to self-assemble in water. Amphiphilic materials are already widely used, but research into their use for drug delivery and ultrasound imaging is relatively new.
It’s an advanced material world

amygdala. An almond-shaped structure of the vertebrate brain, involved in the generation of emotions. It also plays a role in the development of memories.
Bitumen battles – the phenomenon of road rage

anabolic steroids. Compounds that promote the growth or synthesis (anabolism) of tissue, especially muscle. More information can be found at What are anabolic steroids? (National Institute on Drug Abuse, USA).
Who will win the drugs race?

anaerobic. Requiring no oxygen.
Biomass – the growing energy resource

angiogram. An X-ray visualisation of blood vessels showing their condition. To be able to see blood vessels in an X-ray image, the vessels are injected with dye.
The shocking truth about road trauma

anion. A negatively charged atom or group of atoms. Anions have more electrons (negatively charged) than protons (positively charged) which gives them a net negative charge.
Cleaner production – a solution to pollution?

anode. The negative electrode in an electrochemical cell. The anode is the source of electrons to provide electrical energy.
Fuelling the 21st century

anode and cathode. The two electrodes in an electrochemical cell. The anode is the source of electrons, which flow to the cathode. The flow of electrons generates an electrical current. For more information see What is a battery? (Glenn Research Center, NASA, USA)
A fair cop! Accurate breath analysis and speed detection

Antarctic Bottom Water and Antarctic Intermediate Water. Water does not have the same composition throughout the ocean. The different masses of water can be described by their chemical and physical properties – temperature and salinity are used most frequently. These two properties affect the density of water.

Antarctic Bottom Water forms close to Antarctica and is the most dense of the water masses. (Its high density is a result of its coldness and high levels of salinity.) It flows northwards from Antarctica under other water masses, hugging the sea floor.

Antarctic Intermediate Water also forms in the Antarctic region then sinks and spreads northwards. Antarctic Intermediate Water is less saline than Antarctic Bottom Water because it receives fresh water from melting ice shelves and glaciers.

More information about Antarctic water masses can be found at Antarctic circumpolar current (Tasmanian Parks and Wildlife Service).
The Southern Ocean and global climate

anthropogenic. Caused or induced by humans; of human origin.
Enhanced greenhouse effect – a hot international topic
Carbon currency – the credits and debits of carbon emissions trading
Predicting natural events

antibiotic. A substance produced by bacteria or fungi that destroys or prevents the growth of other bacteria and fungi. Antibiotics are not effective against viruses.
When bugs have you on the run
Bird flu – the pandemic clock is ticking

antibody. A protein produced by the body’s immune system in response to a foreign substance (antigen). An antibody reacts specifically with the antigen that induced its formation and inactivates the antigen. Our bodies fight off an infection by producing antibodies.
Malaria – a growing threat
Immunisation – protecting our children from disease
Kissing the Epstein-Barr virus goodbye?
Nanoscience – working small, thinking big
Bird flu – the pandemic clock is ticking
Cancer immunotherapy – redefining vaccines

antigen. Any foreign substance, usually a protein, that stimulates the body's immune system to produce antibodies. (The name antigen reflects its role in stimulating an immune response – antibody generating.)
Malaria – a growing threat
Immunisation – protecting our children from disease
Kissing the Epstein-Barr virus goodbye?
Bird flu – the pandemic clock is ticking
Cancer immunotherapy – redefining vaccines

antisense gene. A gene which produces RNA molecules complementary to the normal messenger RNA of the target gene. Antisense genes prevent expression of the target gene and are used to selectively turn off production of certain proteins.
More food, cleaner food – gene technology and plants

antivirals. Drugs that are used to prevent or cure a disease caused by a virus, by interfering with the ability of the virus to multiply in number or spread from cell to cell.
Bird flu – the pandemic clock is ticking

aquifer. A layer of rock or sand that contains water. For more information see Aquifers (Tasmanian Department of Primary Industries and Water, Australia).
Getting into hot water – global warming and rising sea levels
The water down under

aquifer. A layer of rock or sediment underground that holds a substantial source of water.
Capturing the greenhouse gang

arable land. Capable of being used for crop production.
Population and environment – what's the connection?

archaea. Single-celled organisms similar to bacteria as they do not have their genetic material enclosed within a nucleus. Archaea are prokaryotic but genetically similar to eukaryotes so are placed in a separate kingdom 'the archaea'.
Life on Mars?

artesian. Describes a source of groundwater or aquifer that is under pressure. If an artesian aquifer is tapped by a well, water rises above the surface of the aquifer without the need for pumping. The Great Artesian Basin in Australia is one of the largest artesian basins in the world lying under 22 per cent of the country.
Rocking on with hot rocks geothermal energy

ASCII. This acronym (pronounced asky) stands for American Standard Code for Information Interchange. It is an alphanumeric code commonly used in computers to represent letters, numerals and symbols.

ASCII uses a 7-bit code which produces 128 different combinations to represent different symbols. The decimal numbers 0 to 47 code for symbols and computer commands. Decimal numbers 48 to 57 code for the numerals (0-9), decimal numbers 65 to 90 code for capital letters (A-Z), and decimal numbers 97 to 122 code for lower case letters (a-z). For example, in a computer using the ASCII code, 'A' is represented by the decimal number 65. The computer 'reads' this as the binary number 01000001 and encodes the letter A.

Most computers use an 8-bit code (extended ASCII) which produces 256 different combinations to represent symbols. In addition to the regular character set represented by ASCII (in the decimal range from 0 to 127), extended ASCII has an additional 128 codes that can be used to represent additional symbols (eg, non-English characters or graphical symbols).

For more information see ASCII – What is it and why should I care? (Tela Communications, USA)
Communicating with light – fibre optics

asexual reproduction. A type of reproduction that involves only one parent and produces offspring that are genetically identical to the parent.
The mammal copiers – advances in cloning

asteroid. A small body that orbits the sun. Most asteroids are thought to be the result of debris left over from the formation of the solar system. Most asteroids occur in the region between Mars and Jupiter. Collisions among the bodies in the asteroid belt and adjacent planets displace fragments and place them on a collision course with Earth. The asteroid belt is thought to be the source of most meteorites.

More information can be found at Asteroids data sheet (SPACE.com, USA).
Calculating the threat of tsunami

asteroid. A small Solar System body that orbits the sun. Most asteroids are thought to be the result of debris left over from the formation of the solar system and occur in the region between Mars and Jupiter. Collisions among the bodies in the asteroid belt and adjacent planets displace fragments and place them on a collision course with Earth. The asteroid belt is thought to be the source of most meteorites.
Life on Mars?

atmospheric pressure. The force exerted on the surface of the Earth by the weight of the atmosphere above it. Barometers are used to measure this force.
El Niño – riding the climate roller coaster

atom. The fundamental unit of all matter consisting of a nucleus of protons and neutrons surrounded by orbiting electrons (or in the case of hydrogen, just one electron). For more information see Back to Basics: Atoms and molecules (Australian Academy of Science).
Prospect or suspect – uranium mining in Australia
The picture becomes clear for magnetic resonance imaging
Synchrotrons – making the light fantastic
Nanoscience – working small, thinking big
Nanotechnology – taking it to the people
Probing past and future materials with neutrons

atomic clock.  An extremely accurate clock that is based on the vibrations of an atom or molecule. For more information see How atomic clocks work (How Stuff Works, USA), The most accurate clocks in the world (Miami University, USA) and Atomic clocks (Science Museum, UK).
GPS and never having to say: 'Where am I?'

attenuated vaccines. Vaccines are designed to stimulate antibody production without causing serious disease. To make an attenuated vaccine, a disease-causing microorganism is first isolated and then attenuated (made less virulent) by ageing it or altering its growth conditions (such as by depriving it of an essential nutrient). The vaccines for measles, mumps, and rubella are prepared in this way. Because this vaccine is actually a living microbe, it multiplies within your body and therefore causes a strong stimulation of the immune system.
Immunisation – protecting our children from disease
Kissing the Epstein-Barr virus goodbye?

atoll. Circular shaped coral islands that either partly or completely surround a central lagoon.  Atolls form around submerged volcanic islands. They are typically low lying, so their human populations are susceptible to rising sea levels due to climate change.
Science for sustainable reefs

Australian Electoral Commission. The independent organisation that is responsible for conducting federal elections and referendums. It also maintains the Commonwealth electoral roll. For more information see Australian Electoral Commission.
Can we count on your vote?

automatic dependent surveillance. A computer on board the plane uses the Global Positioning System to determine its position. It then sends this information regularly via satellite or a VHF (very high frequency) radio link to the Australian Advanced Air Traffic System, which then plots the aircraft's position on the controller's screen. This surveillance is used when an aircraft is out of radar range. Not all aircraft currently have this facility, but it seems likely that it will be installed on most international passenger aircraft.
The ups and downs of Australian air traffic control

autonomic nervous system. The part of our nervous system that regulates essential functions such as heartbeat and breathing, functions that occur without conscious involvement. It is sometimes called the involuntary nervous system. For more information see The autonomic nervous system (Neuroscience for Kids, University of Washington, USA) and Autonomic nervous system (National Dysautonomia Research Foundation, USA).
Bitumen battles – the phenomenon of road rage
Driver fatigue – an accident waiting to happen

auxetic materials. Grow fatter when stretched and thinner when compressed – the opposite of a rubber band. Auxetic materials are resistant to impact, so they have possible uses as car bumpers, gaskets in engines, soundproofing and in bullet-proof vests. For more information see Background (Auxetic Materials Network, UK) and Auxetic materials – applications (Azom.com).
It’s an advanced material world

axon. An extension of a nerve cell that transmits nerve impulses to other cells.
Getting our heads around the brain
Alcohol and cars – a volatile mix

B

babassu. A palm tree that grows naturally in Brazil and produces a seed similar to the coconut that is rich in oil. The oil of the babassu seed can be used for cooking, cosmetics and fuel production.
Flying beyond our means – air travel and the environment

bacteriocin. A small, naturally occurring protein produced by one species of bacterium that effectively protects it from competing organisms. Different bacteria produce different bacteriocins.
When bugs have you on the run

bacterium (plural bacteria). A single-celled, microscopic organism without a distinct nucleus.
More food, cleaner food – gene technology and plants
Immunisation – protecting our children from disease
Cancer immunotherapy – redefining vaccines

base (in DNA). Any one of four nitrogenous (nitrogen-containing) bases (adenine, thymine, guanine and cytosine). The sequence of the bases in DNA determines the sequence of amino acids in all proteins found in living things.
The Human Genome Project – discovering the human blueprint
More food, cleaner food – gene technology and plants
Conservation genetics – molecular detectives at work
Epigenetics – beyond genes

base pairs. Two bases held together by weak chemical bonds. The double helix shape of DNA is dependent on its two strands being held together by the bonds between the base pairs. In DNA, the bases that pair are adenine with thymine and guanine with cytosine.
The Human Genome Project – discovering the human blueprint
Epigenetics – beyond genes

battery. A source of electric current. Batteries consist of two electrodes immersed in an electrolyte. The electrolyte reacts chemically with the electrodes generating an electric current. More information about batteries can be found at How batteries work (How Stuff Works, USA)
Fuelling the 21st century

bauxite. A naturally occurring rock with one or more minerals containing aluminium, oxygen and hydrogen. Globally, most bauxite is used to produce alumina, which is used to produce aluminium. For more information see Aluminium (Geoscience Australia).
Making light of metals

BCE. Before the Common Era. There are different ways of designating dates. BCE is one way of indicating dates on the Gregorian calendar that occurred before the date traditionally regarded as the year 1.

The numbering of the Gregorian calendar was instituted by Dionysius Exiguus in 532. He investigated the date of the birth of Jesus Christ and set that as the start of the year 1. Thus, the year 1999 is referred to as 1999 CE (Common Era) or 1999 AD (anno Domini – ‘in the year of our Lord’). Years before the birth of Christ are designated as BCE – ‘before the Common Era’, or BC – ‘before Christ’.

Dates can also be designated as the number of years before the present (BP).
Calendars – keeping track of time

B-cell (B-lymphocyte). A type of white blood cell that originates and develops in the bone marrow. B-cells can be stimulated to produce antibodies.
Malaria – a growing threat
Cancer immunotherapy – redefining vaccines

bedrock. Solid rock that has been unaffected by the processes of weathering.
Looking for clues to our mineral wealth

binary code. A digital coding system that uses a sequence of only two types of symbols (eg, 0 and 1) to represent data. The two symbols are called bits (an abreviation for binary digits). For more information see How bits and bytes work (How Stuff Works, USA).
Communicating with light – fibre optics
Wireless but not clueless

biocapacity (biological capacity). The capacity of an area or ecosystem to generate an ongoing supply of resources and to absorb its wastes. Unsustainability occurs if the ecological footprint (demand on the system) exceeds biocapacity.
Making our mark – ecological footprints

biodegradable. Able to be broken down into simpler substances by the activities of living organisms and therefore unlikely to persist in the environment.
Making packaging greener – biodegradable plastics

biodiversity. A measure of the variety of life. It is usually calculated from the number of species of organisms – although genera, families, classes and phyla can all be counted too.
Australia's threatened species
Feeding the future – sustainable agriculture
Impact of global warming on biodiversity
Weeds – the real alien invaders
Science for sustainable reefs

biofiltration. Technique which uses natural living material to capture and filter out pollutants.
Stormwater – helping to tackle Australia's water crisis

biofuel. Biofuels are fuels such as bioethanol or biodiesel made from plant or (less commonly) animal material and food waste. They are promoted as a renewable energy source without the environmental impacts of fossil fuels. But using annual land-based crops such as sugar cane and corn for biofuel production can be relatively energy inefficient and also competes with food production. Algae have been suggested as an alternative source of biomass which could overcome these problems. For more information see Biomass – the growing energy resource (Nova: Science in the news).
Flying beyond our means – air travel and the environment

biofumigation. The suppression of soil-borne pests and pathogens by the use of plants that contain inhibitory chemicals. The plants can be harvested as rotation crops or ploughed back into the soil as green manure.
Feeding the future – sustainable agriculture

biological control. A strategy for the control of pests or disease-causing organisms that relies on the use of other living organisms rather than chemical pesticides.
A plague on the pest – rabbit calicivirus disease and biological control
Feeding the future – sustainable agriculture
Weeds – the real alien invaders

biomass. Plant or animal matter (including agricultural waste) used as a fuel or energy source. Alternatively, the total mass of living matter within a given environmental area.
The quest to make hydrogen the fuel of the future
Making our mark – ecological footprints

biomass. A general term for material from living things such as plants, animals, fungi, bacteria and food waste. Taken together, the Earth's biomass represents an enormous store of energy. Since biomass can be regrown, it is a potentially renewable resource. For more information see Biomass – the growing energy resource (Nova: Science in the news).
Flying beyond our means – air travel and the environment

biomaterial. A synthetic material used to replace part of a living system or to function in living tissue. A biomaterial is different from a biological material in that it is engineered rather than being naturally produced by a biological system.
It’s an advanced material world

biometrics. The application of statistical methods to biological observations and phenomena.
Putting a finger on it – the loops and whorls of biometrics

biomimetics. The study of the structure and function of biological systems as models for the design and engineering of materials. Biomimetics is of special interest to researchers in nanotechnology, robotics, artificial intelligence, the medical industry, and the military. Biomimetics is also useful for testing the validity of theories of animal function, such as locomotion, flight and navigation.
The buzz about insect robotics

biosphere. The region of Earth and its atmosphere that is inhabited by living organisms.
Making our mark – ecological footprints

bit. Binary digit. The smallest unit of information in a digital system. A bit can be 0 or 1. For more information see How bits and bytes work (How Stuff Works, USA).
Communicating with light – fibre optics

bivalve. A mollusc with the shell in two parts hinged together as in mussels, scallops or clams. Bivalves are bilaterally symmetrical, have a reduced head and large gills that are used for gas exchange and filter feeding.
Science for sustainable reefs

black hole. An astronomical object with a gravitational field that is so strong nothing can escape from it (including light). Because light cannot be emitted or reflected by black holes, they are invisible. Most black holes are thought to form from the collapse of massive stars. Nuclear fusion in stars normally causes an outward pressure from the heat produced. When the fuel for fusion runs out in massive stars, the force of gravity causes the star to collapse to form a black hole. Supermassive black holes are believed to lie at the centre of large galaxies and to have formed from matter in the early universe.
Simply astronomical – the Square Kilometre Array

black spot. A term used to refer to a section of road that is regarded as a high-risk location for car crashes. Black spot programs are designed to reduce the crash risk in these areas by improving the physical conditions or management (eg, building roundabouts, improving lighting). For more information see Black spot program (Department of Transport and Regional Services, Australia).
The shocking truth about road trauma

blood alcohol concentration (BAC). The concentration of ethanol in the blood, which is a key measure in determining the effect of ethanol on the body. It is measured in grams of ethanol per 100 millilitres of blood. For example, people with a BAC of 0.05 grams per 100 millilitres – the legal limit for most drivers – have 0.05 grams of alcohol in their body for every 100 millilitres of their blood.
Driver fatigue – an accident waiting to happen
The dope on drug-impaired driving

blood type. Refers to any one of the various types (or groups) into which our blood is classified. Blood types are based on differences in molecules (proteins and carbohydrates) on the surface of red blood cells. For transfusions, the blood type of the donor and the recipient must match. For more information see Blood types – what are they? (Australian Red Cross), and Blood groups, blood typing and blood transfusions (Nobelprize.org, Sweden).
The shocking truth about road trauma

bloom. A rapid temporary increase in the population of aquatic photosynthetic microorganisms (eg, phytoplankton or cyanobacteria) to the extent that the water becomes discoloured and, if the microorganisms are toxin-producers, unfit for drinking.
Toxic algal blooms – a sign of rivers under stress

bond. See What are bonds? (The Bond Market Association) and Bonds – Basics (The Investment FAQ, USA).
Stock markets – putting your money where your math is

bone marrow. The hard outer region of long bones (eg, the femur of the thigh) is mineralised connective tissue. The interior is bone marrow. Blood cells are manufactured from stem cells in the bone marrow near the ends of long bones.
Singing the praises of colony stimulating factors

brainstem. The brain is like two large mushrooms side by side with a single stalk. The stalk of the 'mushrooms' is called the brainstem, and it controls many vital functions such as blood pressure and breathing. In addition, all sensory information reaching the cerebral cortex of the brain (the 'mushrooms') gets there through the brainstem.

Sound signals pass from the cochlea along the auditory nerve to the brainstem, where they activate other nerve cells that transmit the message higher up the brain. If deafness is caused by damage to the cochlea or the auditory nerve, it may be possible to restore some perception of sound by carefully stimulating the correct region of the brainstem.
Cochlear implants – wiring for sound

break even. The point where the power input of a controlled nuclear fusion reaction (supplied by either external sources or the products of reaction) is equal to the power output. Three conditions need to be met for a sustained fusion reaction to occur. They are:

• plasma temperature of 100-200 million Kelvin;
• plasma density of one thousandth of a gram per cubic metre; and
• energy confinement time of 1 to 2 seconds.

The confinement time is a measure of the rate at which a system loses energy to its environment.
Thinking ahead – fusion energy for the 21st century?

broadband. A type of data transmission in which a single wire can carry several channels of data at once. Broadband transmission provides a high rate of data transfer, defined as more than 200 kilobits per second.
Wireless but not clueless

bronchodilators. (Also called 'relievers'.)These are a group of drugs that relax the smooth muscle in the airway walls and hence widen (dilate) the airways. Used to relieve the symptoms of an asthma attack.
The rise and rise of asthma

brown dwarf. An object in space, intermediate in mass between a small star and a large planet. Brown dwarfs are very difficult to detect because they are very faint; as they age and cool, they become even fainter. The radiation they emit is primarily in the near infrared. For more information see Brown dwarfs (Chandra X-ray Laboratory, USA).
Astronomy in the deep freeze

Brownian motion. The constant, erratic motion of small particles when they are suspended in water or floating in air. The motion is the result of the particles being knocked about by the movement of molecules in the water or air. The phenomenon is named after Robert Brown (1773-1858), the Scotsman who first described it.
Sodicity – a dirty word in Australia

C

Cactoblastis cactorum. A moth whose larval stage (caterpillars) feed on prickly pear.
A plague on the pest – rabbit calicivirus disease and biological control

calicivirus. A family of very small viruses, different species of which cause diseases in several animal species. One species causes haemorrhagic diseases in rabbits (called rabbit calicivirus disease or rabbit haemorrhagic disease). This disease rapidly kills mature but not young rabbits, but affects no other animal species.
A plague on the pest – rabbit calicivirus disease and biological control

cancer. One of the defining features of most cancer cells is that they grow when they should not. Ignoring signals from the rest of the body, they tend to multiply regardless, encouraging blood vessels to supply them with food and oxygen at the expense of normal tissue nearby. Once a mass of cancer cells (a tumour) has grown large enough, it will often invade other tissues. It will eventually push through the wall of a lymph vessel or blood vessel and clumps of cancer cells will break off and travel around the body. The cancer can then be very hard to cure. The clumps (called metastases) can settle almost anywhere and start to grow as a tumour. The whole body is soon seeded with tumours of the original cancer cell type. Usually, it is then only a matter of time before vital functions are interfered with and the patient dies.
Sun and skin – a dangerous combination

capacitor. A device for storing electrical energy. For more information see How capacitors work (How Stuff Works, USA).
Putting a finger on it – the loops and whorls of biometrics
Quantum computers – why would you want one?

carbon dating. A method of measuring the age of an object that contains carbon. Since living things stop taking up carbon when they die, and carbon-14 decays with a half life of 5,700 years, the amount of carbon-14 remaining in the sample can be used to determine its age.
Excuse me! The problem with methane gas

carbon dioxide fertilisation effect. Increased concentrations of carbon dioxide stimulate the growth of many different types of plant. A doubling of atmospheric carbon dioxide has been shown to stimulate leaf photosynthesis rate by up to 50 per cent depending on temperature. Experiments show that the fertilisation effect of increasing concentrations of carbon dioxide eventually reaches a saturation point. This means that other vital ingredients such as water and nutrients become limiting.
Impact of global warming on biodiversity

carbon emission reduction scheme. A method such as a carbon tax or carbon trading scheme that reduces emissions of carbon (and often other greenhouse gases). A carbon tax is a tax imposed on the production or use of fossil fuels based on the carbon content of those fossil fuels. Trading schemes set a limit to the amount of greenhouse gases that can be released. Permits are then allocated to organisations for their carbon emissions; those reducing emissions below their quota can trade the excess to other organisations. For more information see Carbon currency – the credits and debits of carbon emissions trading (Nova: Science in the news).
Rocking on with hot rocks geothermal energy

carbon-fixing organisms. Organisms that remove and store carbon dioxide from the atmosphere during photosynthesis.
Capturing the greenhouse gang

carbon monoxide. Carbon monoxide (CO) is a colourless, odourless, very poisonous gas. It is produced by the incomplete combustion of carbon-containing fuels. For example, it is a product of combustion of petrol in car engines.

It is a fast-acting poison for all animals (including humans) that use the red pigment haemoglobin to carry oxygen within the body. The gas attaches to haemoglobin, which then is unable to function. Thus, carbon monoxide stops the blood from carrying oxygen efficiently. Even at concentrations as low as 10 parts per million (0.001 per cent) CO can cause headaches, tiredness and slow reflexes, as a small proportion of the haemoglobin molecules are put out of action. Daily exposure to low levels of CO is linked with lack of fitness, a tendency to form blood clots, and disease of the heart, arteries and lungs. At concentrations above 200 ppm, exposure to CO for more than a few minutes is fatal.

The maximum acceptable level for CO in air is usually set at 30 ppm. Australian suburbs in general seldom exceed this, but busy city centres with many vehicles (such as during rush hour) and with poor air circulation may sometimes suffer a build-up of CO, sufficient to cause the first symptoms of poisoning in some individuals. Garages and road tunnels are places where CO can increase to more dangerous proportions.
Local air pollution begins at home

carbonation. The reaction between a substance and carbon dioxide to form a carbonate. For example, naturally occurring mineral silicates react with carbon dioxide to form a stable mineral carbonate.
Capturing the greenhouse gang

carbon-neutral. A state whereby emissions of carbon-containing gases are balanced by the amount being stored; for example, balancing carbon dioxide emissions by growing plants which take in carbon dioxide.
Making our mark – ecological footprints

carbon offset. An investment in an activity that reduces greenhouse gas emissions or removes them from the atmosphere. Carbon offsets are used to compensate for greenhouse gas emissions from your own activities.
Making our mark – ecological footprints

carbon offset. A means of reducing the impact of greenhouse gas emissions. Individuals and companies can purchase offsets to counteract their emissions from transport, electricity use etc. For example, many airlines allow customers to purchase carbon offsets to compensate for the emissions from their plane trip. The offset money is invested in projects that reduce greenhouse gas emissions such as renewable energy, tree planting or energy efficiency projects.
Flying beyond our means – air travel and the environment

carbon trading. The trading of greenhouse gas emission rights. Participants in carbon trading buy and sell certificates that represent specified amounts of emissions or credits for reductions in emissions. Placing a cost on carbon emissions encourages organisations to reduce them eg. through renewable energy, improved energy efficiency or carbon offsets.
Making our mark – ecological footprints

carcinogen. A substance that is known to cause cancer.
Putting on a good face – the chemistry of cosmetics

carrier. Is a person who is infected with an agent that causes a disease who shows no sign of illness. Asymptomatic carriers shed the causative agent, such as a virus or bacteria, and so can pass the disease on to others. The most famous asymptomatic carrier was Mary Mallon, or Typhoid Mary. Bird flu – the pandemic clock is ticking

carrying capacity. The maximum number of individuals of a species that can be supported in an area. Carrying capacity is usually limited by components of the environment (eg, food, nesting sites, resources)
Population and environment – what's the connection?

catalyst. A substance that increases the rate of a chemical reaction without actually undergoing any change itself.
Buckyballs – a new sphere of science
Which way ahead for hydrogen cars?
Nanoscience – working small, thinking big
Nanotechnology – taking it to the people

cataracts. Cloudiness in the lens of the eye, or the covering capsule of the lens, dimming the eyesight, producing distorted images, and eventually causing blindness. Cataracts can have several causes, one of which is prolonged exposure to too much sunlight.
Sun and skin – a dangerous combination

catchment. The area from which a river, stream, lake or other body of water receives its water.
Predicting natural events
Making every drop count

cathode. The positive electrode in an electrochemical cell. Electrons flow back into a fuel cell through the cathode.
Fuelling the 21st century

cation. A positively charged atom or group of atoms. Cations have more protons (positively charged) than electrons (negatively charged) which gives them a net positive charge.
Cleaner production – a solution to pollution?

cast. Describes a metal (or other material) that has been poured as a liquid into a mould and allowed to solidify. For example, cast iron is often used to make manhole covers.
Making light of metals

centre of gravity. The point around which a body's weight is equally balanced in all directions. The total weight of the object is concentrated at this point.
Bogged down in the four-wheel drive debate?

ceramics. Are inorganic, non-metallic solids processed or used at high temperatures. A ceramic is made by combining metallic and non-metallic elements. Traditional ceramic products such as clay pots and chinaware are hard, porous and brittle. Modern ceramics are used to create bones and teeth, cutting tools or to conduct electricity. For more information see Advanced ceramics (Azom.com) and About ceramics (The American Ceramic Society).
It’s an advanced material world
Probing past and future materials with neutrons

cerebral malaria. A type of malaria in which the red blood cells obstruct the blood vessels in the brain. Other vital organs can also be damaged. Cerebral malaria often leads to the death of the patient.
Malaria – a growing threat

channel. A band of radio frequencies assigned for a particular purpose.
Mobile phones – communications on the go

chat room. An internet site where two or more people can exchange messages in real time. People chat by typing messages, which are displayed almost instantly on the screens of others who are in the chat room
Virtual reality bytes – military uses of VR

chemical bonds. The attractions that hold atoms together to form molecules.
Biomass – the growing energy resource

chemotherapy. Treatment of disease by using chemical compounds. Cancers are commonly treated by administering chemicals that are toxic to malignant cells.
Singing the praises of colony stimulating factors
Cancer immunotherapy – redefining vaccines

chlorofluorocarbons (CFCs). Organic compounds made up of atoms of chlorine, fluorine and carbon. They were commonly used as refrigerants in refrigerators and air conditioners, as blowing agents in foam plastics, and as cleaners for computer circuit boards. CFCs do not occur naturally – their increase in the atmosphere is entirely the result of human activity. Beginning in the 1940s there was a rapid increase in the rate of manufacture, and hence the escape, of CFCs.
Earth's sunscreen – the ozone layer
Enhanced greenhouse effect – a hot international topic

chloroplasts. Small organelles found in plant cells. They contain the green pigment chlorophyll which captures solar energy from the sun and is essential for photosynthesis in plants.
Biomass – the growing energy resource

chromosome. A long DNA molecule that contains the genes of the organism. Chromosomes are visible in cells during cell division.
The Human Genome Project
More food, cleaner food – gene technology and plants
Epigenetics – beyond genes

chronic. Used to describe a medical condition that continues for a long time, often with little change. A chronic disease, such as asthma, may have acute episodes, when the situation worsens for short periods of time.
The rise and rise of asthma

clathrate. A compound that is formed by the trapping of molecules inside a substance rather than by forming chemical bonds between the two substances. Methane clathrates (also called methane hydrates) consist of methane molecules trapped inside a ‘cage’ of ice crystals. Methane hydrates form under conditions of low temperature and high pressure in deep oceanic sediments, where methane is produced by anaerobic microorganisms.
Excuse me! The problem with methane gas

clone. A group of organisms, cells or DNA sequences derived from the same ancestor.
More food, cleaner food – gene technology and plants

Code Division Multiple Access (CDMA). This technology converts analogue signals into digital which are then transmitted over a network. CDMA enables multiple phone calls to be carried on the same frequency by using a voice-coding system. For more information see How cell phones work – cellular access technologies (How Stuff Works, USA).
Mobile phones – communications on the go

coefficient of friction. The ratio of the force that is necessary to move an object and the weight of the object. It is a measure of the amount of friction that exists between two materials as one slides over the other. The coefficient of friction is zero if there is no friction, and it is infinite if no motion is possible. For more information see How Brakes Work: Friction (How Stuff Works, USA).
Death-defying designs for car safety
Bogged down in the four-wheel drive debate?

colloids. Particles dispersed in a different phase, so that they do not easily filter or settle. The simplest case of particles dispersed in water is known as a colloidal dispersion. Examples of colloids include smoke (fine liquid droplets or solid particles in a gas), homogenised milk (fine droplets of fat in an aqueous phase) and paint (fine solid particles in a liquid).
Probing past and future materials with neutrons

colony. A group of identical cells (clones) resulting from repeated divisions of a single cell. The identical cells form a cluster that lies on the surface of a food source such as a nutrient agar plate.
Singing the praises of colony stimulating factors

complementary. Describes the specific matching of base pairs. This matching occurs because the structure of one base precisely fits with, and bonds to, another specific base. In DNA adenine and thymine are complementary and form a base pair, as do cytosine and guanine. When pairing occurs between DNA and RNA, adenine and uracil are complementary, and cytosine and guanine are complementary.
More food, cleaner food – gene technology and plants
Conservation genetics – molecular detectives at work

complex hydrides. Complex hydrides combine hydrogen with metals and other substances; they typically contain more than one type of metal or metalloid (eg. sodium aluminium hydride).
The quest to make hydrogen the fuel of the future

complex system. A complex system is one in which there are multiple interactions between many components. The properties of a complex system are not completely explained by an understanding of its component parts.
Predicting natural events

composites. Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). For more information see our Nova topic Putting it together – the science and technology of composite materials.
Nanotechnology – taking it to the people
It's an advanced material world
Probing past and future materials with neutrons

composting. Breaking down aerobically plant and animal material using microorganisms. For successful composting there must be sufficient water and air to allow the microoganisms to break down the material.

Material derived from the aerobic breakdown of plant or animal material by microorganisms.
Making packaging greener – biodegradable plastics

compressive strength and tensile strength. Strength is determined by how much weight a material can support or how much stress it can withstand. Compressive strength is the maximum stress that a material will bear when it is subjected to a load that pushes it together. Tensile strength is the maximum stress a material will bear when it is subjected to a stretching load.
Putting it together – the science and technology of composite materials

computer memory. Computer memory is measured in bytes.

• 1 byte is equivalent to 8 bits. The information in a byte is equivalent to a letter in a word.
• 1 kilobyte is roughly 1000 (2¹⁰ or 1024) bytes or characters, approximately equal to one page of double-spaced text.
• 1 megabyte is roughly 1,000,000 (2²⁰ or 1,048,576) bytes, approximately equal to one novel.
• 1 gigabyte is about 1,000,000,000 (2³⁰ or 1,073,741,824) bytes, approximately equal to 1000 novels.
• 1 terabyte is about 1,000,000,000,000 (2⁴⁰ or 1,099,511,627,776) bytes, approximately equal to 1,000,000 novels.

For more information see How bytes and bits work (How Stuff Works, USA).
Good prospects ahead for data mining

Conference of the Parties (COP). Comprises all countries that have ratified the United Nations Framework Convention on Climate Change. COP is responsible for implementing the objectives of the Convention and has been meeting regularly since 1995. More information on outcomes from Conference of the Parties (COP) meetings is available at the United Nations Framework Convention on Climate Change.
Carbon currency – the credits and debits of carbon emissions trading

conjunction. The situation when two or more planets, or other celestial bodies, are temporarily close together in the sky. For more information see Astronomy answers: Conjunction (Utrecht University, Netherlands).
Ethnomathematics – a rich cultural diversity

contagious. A contagious disease is easily spread from one person to another by contact with the infectious agent that causes the disease. The agent may be in droplets of aerosols made by coughing or sneezing, contaminated food utensils, water or food.
Bird flu – the pandemic clock is ticking

continental drift. The very slow movement of the continents on their underlying plates. See also plate tectonics and Plate tectonics (Nova: Science in the news, Australian Academy of Science).
Looking for clues to our mineral wealth
Fixing the cracks in disaster mitigation
Discovering Australia's evolutionary past

convergent evolution. The development of similar functions and structures in unrelated or distantly-related organisms.
Discovering Australia's evolutionary past

coral bleaching. Loss of colour of corals due to an environmental stress such as increased water temperature, pollution or sedimentation. Environmental stress can cause corals to expel microscopic algae from their tissues. These symbiotic algae provide up to 90 per cent of the coral’s energy needs. Loss of these algae results in the bleached appearance of corals as they provide most of the coral’s colour. Bleached corals often starve then die if the stress persists.
A sense of things to come – smart sensors and the environment
Science for sustainable reefs

coral disease. Coral diseases can have a range of causes including bacteria, fungi and algae. Coral disease has had a significant effect on reefs in the Caribbean and the incidence in some areas of the Great Barrier Reef has increased in recent years. The coral disease White Syndrome has been linked to increasing sea temperatures on the Great Barrier Reef.
A sense of things to come – smart sensors and the environment

coral reef. A marine ridge or mound that has been built up over thousands of years from limestone (calcium carbonate) deposited in the skeletons of coral polyps. The term coral reef is often used to refer to the entire ecosystem – the coral, the substrate built by the coral and the organisms that live in, on and around the reef. The geographical shape of a reef can also be part of the definition – fringing reefs, barrier reefs and atolls. For more information see How does a coral reef form? (CRC Reef Research Centre, Australia).
Coral bleaching – will global warming kill the reefs?

corporate social responsibility. A concept whereby organisations take responsibility for their impact on society and the environment.
Cleaner production – a solution to pollution?

correlation. The closeness of the relationship between two variables. The correlation is positive if an increase in one variable implies an increase in the other, and negative if an increase in one implies a decrease in the other. Variables having no relationship at all are said to be uncorrelated.
When the numbers just don't add up

creatine. A naturally occurring compound produced by the body, which combines with phosphate to form creatine phosphate. The combination of creatine and phosphate stores energy that can then be used for muscle contraction.
055 – Drugs in sport

CrimTrac. Australia's major national policing initiative. CrimTrac includes the National Automated Fingerprint Identification System, and a National Criminal Investigation DNA Database. For more information see About us (CrimTrac, Australia)
Putting a finger on it – the loops and whorls of biometrics

criteria of fairness. See Fairness criteria (The Center for Teaching and Learning, University of Alabama, USA).
Can we count on your vote?

cryogenic. Relating to very low temperatures.
The quest to make hydrogen the fuel of the future

cryptographic. For more information see Cryptography (Webopedia, USA).
Wireless but not clueless

cryptography. The science or study of encoding and decoding messages. For more information see Cryptography (Webopedia, USA).
Quantum computers – why would you want one?

culture. To grow microorganisms such as bacteria and fungi in a laboratory under controlled conditions.
Making packaging greener – biodegradable plastics

CT scans. A series of X-ray images of the body. The body is X-rayed from many directions and the results are analysed by a computer. The computer generates images of cross-sections (slices) of the body. CT scans show details of the shape and location of soft tissues, as well as bones and blood. Other names for this technique are computerised tomography, CAT scan and computerised axial tomography. For more information see CAT scans (University of Colorado at Boulder, USA).
The shocking truth about road trauma

cytokine. A hormone-like molecule, produced by one cell, that has an effect on another cell. Some types of cytokines are normally produced in low concentration by the immune system as part of the body's defence mechanism. Some cytokines are toxic at high concentrations and cause disease symptoms such as fever.
Bird flu – the pandemic clock is ticking

D

dark energy. A form of energy believed to make up 73 per cent of the universe. Dark energy has been proposed to account for the accelerating expansion of the universe. It is unknown whether it is constant throughout the universe or whether it varies in space and time. The properties of dark energy are investigated by observing its effects on the universe.
Simply astronomical – the Square Kilometre Array

dark matter. Matter that is not visible but makes up around 22 per cent of the universe (normal matter only makes up 5 per cent). The observable matter in clusters of galaxies is not enough to create a gravitational field that would hold them together. Hence it is believed unseen dark matter accounts for the remaining mass.
Simply astronomical – the Square Kilometre Array

dB(A) or A-weighted decibels. Decibels with the sound pressure scale adjusted to conform with the frequency response of the human ear. A sound level meter that measures A-weighted decibels has an electrical circuit that allows the meter to have the same sensitivity to sound at different frequencies as the average human ear. There are also B-weighted and C-weighted scales, but the A-weighted scale is the one most commonly used for measuring loud noise.
Quiet please! Fighting noise pollution

deafness, types of: conductive and sensori-neural. Conductive deafness occurs when something prevents the sound vibrations from reaching the inner ear. This could merely be wax in the ear canal, but it could also occur if infection has caused the ear drum to become perforated so that it does not resonate normally with the vibration. Alternatively, the ossicles might become stiff so that they lose their 'lever' action. With conductive deafness, the hearing organ is basically normal, and the problem lies in getting sound to the cochlea.

In sensori-neural deafness, the defect lies in either the cochlea or the transmission of the sound signals to the brain once they have left the cochlea. This form of deafness tends to occur with age, and is accelerated by exposure to loud sounds, perhaps at a disco, perhaps from a ghetto blaster, but also from construction projects. This is why workers on noisy building sites wear ear muffs. So, too, do sporting-rifle shooters and army personnel on a rifle range.
Cochlear implants – wiring for sound

deafness. There are two types of deafness: sensori-neural and conductive.  In sensori-neural deafness, the defect lies in either the cochlea (the organ that converts vibrations to nerve impulses) or in the transmission of the sound signals to the brain once they have left the cochlea. This form of deafness tends to occur with age, and is accelerated by exposure to loud sounds (eg, at a disco, from a ghetto blaster, from a portable radio used with earphones, from construction projects). Workers on noisy building sites wear ear protectors, as do sporting rifle shooters and army personnel on a rifle range.

Conductive deafness occurs when something prevents the sound vibrations from reaching the inner ear. This could merely be wax in the ear canal, but it could also occur if infection has caused the ear drum to become perforated so that it does not move normally under the influence of sound pressure. Alternatively, the ossicles (the tiny bones connecting the ear drum to the cochlea) might become stiff so that they lose their 'lever' action. With conductive deafness, the hearing organ is basically normal, and the problem lies in getting sound to the cochlea.
Quiet please! Fighting noise pollution

decibel (dB). A logarithmic scale used to denote the intensity, or pressure level, of a sound relative to the threshold of human hearing. A step of 10 dB is a ten-fold increase in intensity or sound energy and actually sounds a little more than twice as loud.

The quietest sound we can hear is 0 dB; a soft whisper has about 100 times more sound energy and so is about 20 dB. A power lawn-mower has a factor of 10⁹ more sound energy and is about 90 dB. A rock band may be as high as 110 dB. Above 120 dB the sound produces discomfort and even pain. The scale is often adjusted to take account of the reduced sensitivity of human hearing to high and low frequencies and is then specified as dB(A). On this adjusted scale (the A-weighted scale), the range of human hearing is about 3 to 140 dB(A).

For more information see What is a decibel? (How Stuff Works, USA); What is a decibel? (University of New South Wales, Australia); and Intensity and the decibel scale (The Physics Classroom, USA).
The picture becomes clear for magnetic resonance imaging
Quiet please! Fighting noise pollution

decibels (dB). One tenth of a bel. A unit used to measure sound intensity or power. One decibel is around the smallest change in sound that the ear can detect. Two power levels P₁ and P₂ differ by n decibels when:

n =10 log₁₀P₂/P₁
Flying beyond our means – air travel and the environment

decision tree. A hierarchy of rules within a computer program, represented by a tree-like structure, that enables a set of data to be classified. A series of selection criteria classify the data into smaller and smaller categories.
Good prospects ahead for data mining

decomposer organism. An organism, usually a bacterium or a fungus, that breaks down organic material into simple chemical components, thereby returning nutrients to the physical environment.
Making packaging greener – biodegradable plastics

definitive host and intermediate host. Some parasites have two hosts in their life cycle. The host in which a parasite reaches sexual maturity and reproduces is called the definitive host. The other host is called the intermediate host. In the case of the hydatid tapeworm, dogs are the usual definitive hosts and sheep are the usual intermediate hosts.
Hydatids – when a dog is not man's best friend

demographic transition. The change in a population of an industrialised country that occurs when declines in death rates are followed by declines in birth rates. (A characteristic of non-industrial societies is high birth and death rates.)
Population and environment – what's the connection?

dendritic cell. A cell that is involved in regulation of the immune system. Dendritic cells act by consuming and presenting antigen to lymphocytes. This activates the lymphocytes to fight infection or disease.
Cancer immunotherapy – redefining vaccines

dendrogram. A diagram which shows the interrelationships between a group of organisms, as well as estimates of when the organisms evolved and separated into different species.
Discovering Australia's evolutionary past

depressant. A substance that slows down the functions of the central nervous system. More information about this type of drug can be found at About drugs (Australian Drug Foundation)
The dope on drug-impaired driving

derivatives. See Derivatives – Basics (The Investment FAQ, USA) and A Nobel formula (The Mathematical Association of America).
Stock markets – putting your money where your math is

desalination. The removal of salts from water or soil. For more information see Desalination (Ask an Expert, Australian Broadcasting Corporation).
The water down under
Making light of metals

diatom. Microscopic, single-celled algae that have a silica-based skeleton. Diatoms are found in a range of aquatic environments including freshwater, marine and moist soils.
Science for sustainable reefs

diatoms. A common type of phytoplankton which have cell walls made of silica.
Acid test for the seas

dicotyledon. One of the two classes of flowering plants. Characterised by: two seed leaves in the embryo; usually net-like veins in the leaves; flower parts in multiples of four or five.
More food, cleaner food – gene technology and plants

digital codes (digital system of codes). Information that is represented as a series of discrete digits (numbers).
Communicating with light – fibre optics

digitise. To transcribe data into a digital form (represented as a series of numerical values) so that it can be directly processed by a computer.
Putting a finger on it – the loops and whorls of biometrics

disinfection. Physical or chemical treatment to destroy harmful microorganisms. The disinfecting properties of sunlight are due to ultraviolet light.
Making every drop count

distortion. An undesired change in the shape of an electrical wave or signal. Distortion results in the loss of clarity in reception or reproduction, or even the loss of information in a digital system.
Communicating with light – fibre optics

dividend. A sum of money paid to shareholders by a company as a reward for investing. It comes out of the company’s net profit.
Stock markets – putting your money where your math is

DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts.
Prions – morphing agents of disease
Earth's sunscreen – the ozone layer
The Human Genome Project – discovering the human blueprint
Sun and skin – a dangerous combination
More food, cleaner food – gene technology and plants
The mammal copiers – advances in cloning
Conservation genetics – molecular detectives at work
Driver fatigue – an accident waiting to happen
Epigenetics – beyond genes
Discovering Australia's evolutionary past
Probing past and future materials with neutrons

DNA cloning. When a sequence of bases that constitutes a particular gene has been isolated, it can be cloned by inserting it into a bacterial plasmid. In ideal conditions bacteria reproduce very rapidly. As they reproduce, millions of copies of the modified plasmids are formed, and the original gene is cloned.
More food, cleaner food – gene technology and plants

DNA fingerprinting. Identification of the DNA of different individuals based on variation that exists between them in the sequence of bases in the DNA.
More food, cleaner food – gene technology and plants

DNA repair genes. Encode proteins that correct mistakes in DNA caused by incorrect copying during replication and environmental factors such as by-products of metabolism, exposure to ultraviolet light or mutagens. The DNA repair process must operate constantly to correct any damage to the DNA as soon as it occurs. For more information about the role of DNA repair genes in cancer see Genetics of cancer (Learner.org, USA).
Epigenetics – beyond genes

dopamine. A brain neurotransmitter (a chemical that carries messages between brain cells). In people with Parkinson's disease, their dopamine-producing cells degenerate causing loss of normal muscle function.
Stem cells – gateway to 21st centurymedicine

Döppler shift. The change in the perceived frequency of waves (electromagnetic or sound) when the source of the waves moves in relation to the receiver.

The phenomenon is named for Christian Döppler, who realised that the pitch of a sound emanating from a moving source varies for a stationary observer, depending on the speed of the source and the direction in which it is moving. Imagine you are on a train in a station and you can hear the signals ringing at a rail crossing just down the track. Since both you and the signals are stationary, the signals sound normal. They continue to ring at the same rate as the train starts to move, but now because you are travelling towards them they seem to get faster.

In effect, the time between arrival of pulses of sound is being compressed (or shortened) and the apparent frequency is increasing. The result is that the signals sound higher-pitched. This change in frequency is called a 'Döppler shift'.

For more information see Introduction to the Döppler effect for sound (Fear of Physics, USA) and How radar works (How Stuff Works, USA).
GPS and never having to say: 'Where am I?'

Dow Jones Industrial Average. See What is the Dow Jones Industrial Average? (How Stuff Works, USA) and Stocks – The Dow Jones Industrial Average (The Investment FAQ, USA).
Stock markets – putting your money where your math is

dryland salinity and irrigation salinity. There are two kinds of soil salinity resulting from human activities: dryland salinity (occurring on land not subject to irrigation) and irrigated-land salinity. Both occur when rising watertables dissolve natural salts in the soil and bring them to the surface.
Salinity – the awakening monster from the deep

dual energy X-ray absorptiometry. A technique for measuring bone density. X-rays at two wavelengths are transmitted through a patient. A detector system determines which wavelengths are absorbed by the body and, based on this, a computer calculates the bone calcium content.
Pointing the bone at osteoporosis

ductile. Describes the ability of a material (mostly metals) to be drawn out into a wire without cracking or breaking.
Making light of metals

E

ecological footprint. The amount of biologically productive land and water that is needed to supply resources and absorb wastes. Ecological footprints are usually expressed in units of global hectares.
Making our mark – ecological footprints

ecological footprint. A measure of how much land and sea is required to support human demands and to absorb any wastes. The ecological footprint can be used as a measure of sustainability by comparing it to the biocapacity of the land (the amount available). Ecological footprints are usually expressed in units of global hectares.
Flying beyond our means – air travel and the environment

ecosystem. A term used to encompass all the organisms in a community together with the associated physical environmental factors with which they interact (eg, a rockpool ecosystem, a forest ecosystem).
Toxic algal blooms – a sign of rivers under stress
A quiet revolution – the science of complex systems
Weeds – the real alien invaders
The water down under

effluent. Liquid waste. Usually refers to discharge from industrial processes or from sewage treatment plants.
Cleaner production – a solution to pollution?

electorate. The total number of all qualified voters within specified boundaries. The boundaries of an electorate can be changed.
Can we count on your vote?

electrical conductivity. When a voltage is applied across a substance, an electric current will only flow if the substance conducts electricity. When salts dissolve in water, ions are formed and the solution (the electrolyte) will conduct electricity. As a general rule, the higher the concentration of ions in solution (ie, the higher the salt concentration) the better the solution conducts electricity; in other words, its electrical conductivity increases. Electrical conductivity is often expressed in units such as deciSeimens per metre (dS/m). Rain water, for example, has a conductivity of 0.02-0.05 dS/m, while sea water has a conductivity of 50-60 dS/m.
Monitoring the white death – soil salinity
Sodicity – a dirty word in Australia
Nanotechnology – taking it to the people

electrical conductivity (EC) units. The measure of a solution's ability to conduct electricity. EC units are used to express salinity levels in soil and water. When salt is dissolved in water the conductivity increases, so the more salt, the higher the EC value. Another salinity measurement is the total dissolved solids (TDS).  For more information see Measuring the salinity of water (Department of Primary Industries, Victoria).
Salinity – the awakening monster from the deep

electrode. An electrical conductor. Electrochemical reactions occur on the surface of an electrode.

An electrode can be used to deliver electricity to the body or to receive electricity from it. Delivering electricity to the body is used to stimulate; receiving electricity from the body can be used to detect and record signals. In either case the term refers to the contact formed by the stimulating or recording device within the body.
Fuelling the 21st century
Getting our heads around the brain

electrode. An electrical conductor. Electrochemical reactions occur on the surface of an electrode.

An electrode can be used to deliver electricity to the body or to receive electricity from it. (Delivering electricity to the body is used to stimulate; receiving electricity from the body can be used to detect and record signals.) In either case the term refers to the contact formed by the stimulating or recording device within the body.

With the multi-channel cochlear implant, the electrodes are used to stimulate the cochlea by delivering electricity to it. There are 22 electrodes at different positions along the implant so that it is possible to stimulate at many different sites. When the implant is inserted into the cochlea, the 22 electrodes allow auditory nerve fibres at different sites from the base of the cochlea to its apex to be stimulated selectively, thus enhancing the ability of the patient to distinguish different frequencies of sound.
Cochlear implants – wiring for sound

electrolysis. Chemical reactions brought about by passing electricity through a solution. The following equation illustrates the process of the electrolysis of water (H₂O).

Generating new ideas for meeting future energy needs
The quest to make hydrogen the fuel of the future
Making light of metals

electrolyte. A substance that produces ions (particles with an electric charge) when dissolved in water. The resulting solution (which can also be referred to as an electrolyte) conducts electricity.
Fuelling the 21st century
Sodicity – a dirty word in Australia
Generating new ideas for meeting future energy needs
A fair cop! Accurate breath analysis and speed detection

electromagnet. A device that produces a magnetic field using an electric current flowing through a coil of wire, generally wound on a soft iron core. Electromagnets are temporary magnets – when the current is turned off, the magnetism is gone.
Looking down the track at very fast trains
Thinking ahead – fusion energy for the 21st century?

electromagnetic force. One of the four forces – gravity, strong force, electromagnetic force, weak force – that act on particles. Electromagnetic force acts on charged particles and is made up of electric and magnetic forces (eg, moving magnets produce electric forces and moving electric charges produce magnetic forces).

The electric charge that is the source of electromagnetic force can either be positive or negative. Because there are two types of charge, the electromagnetic force can be either attractive or repulsive. Opposite charges attract, like charges repel. Physics theory explains that electromagnetic force is carried by photons (packets of electromagnetic radiation). For more information see Force and motion (Southern Nevada RPDP, USA).
Synchrotrons – making the light fantastic
Thinking ahead – fusion energy for the 21st century?

electromagnetic induction. The production of electrical current in a conductor due to a changing magnetic field (moving magnet) or to the movement of a conductor through a magnetic field. For more information see Faraday's magnetic field induction experiment (Florida State University, USA).
Rocking on with hot rocks geothermal energy

electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
Earth's sunscreen – the ozone layer
Sun and skin – a dangerous combination
Mobile phones – communications on the go
Monitoring the white death – soil salinity
The ups and downs of Australian air traffic control
A fair cop! Accurate breath analysis and speed detection
Astronomy in the deep freeze
Synchrotrons – making the light fantastic
The shocking truth about road trauma
Salinity – the awakening monster from the deep
Coral bleaching – will global warming kill the reefs?
Probing past and future materials with neutrons

electromagnetic radiation.  Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We can imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. The highest frequencies in the spectrum of electromagnetic radiation are gamma-rays; the lowest frequencies are radio waves.

For more information see Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA) and Measuring the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA).
GPS and never having to say: 'Where am I?'

electromagnetic radiation. Energy that travels through space in the form of waves. The highest frequencies are gamma-rays; the lowest frequencies are radio waves (microwaves are a type of radio wave). All electromagnetic radiation travels at light speed – 300 000 kilometres per second in a vacuum. Shorter wavelength radiation (eg, ultraviolet) carries more energy and is likely to be more harmful to living tissue.
Life on Mars?

electromagnetic spectrum. The complete range of frequencies (or wavelengths) of electromagnetic radiation. For more information on electromagnetic radiation and the electromagnetic spectrum see Measuring the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA) and More about the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA).
Astronomy in the deep freeze

electron. A negatively charged particle that is a constituent of an atom. Electrons can move from atom to atom. When they do, they produce an electric current.
Fuelling the 21st century
Buckyballs – a new sphere of science
A fair cop! Accurate breath analysis and speed detection
Synchrotrons – making the light fantastic Probing past and future materials with neutrons

electronic quartz timing system. In these timing devices, a quartz crystal vibrates (oscillates) because of an electric current. The oscillations of the crystal control the movement of the hands or the display of numbers. Quartz timing devices are very accurate and are almost unaffected by changes in temperature or position. (Quartz is crystalline silicon dioxide.)
Measurement in sport – the long and the short of it

electron microscope. An instrument that uses electrons, instead of light, to produce a magnified image of an object. The magnification that can be achieved is about one thousand times that of a light microscope.
Life on Mars?

electronvolts (eV). A measure of energy used for convenience in atomic systems. It is the amount of kinetic energy gained by an electron when it passes through an electrostatic potential difference of one volt. It is equal to one volt (1 volt = 1 joule per coulomb) multiplied by the charge of a single electron (in coulombs). One electronvolt is equal to 1.602×10^-19 joule.
Thinking ahead – fusion energy for the 21st century?

element. A substance made up of only one type of atom. For more information see our Back to basics topic, Atoms and molecules.
The picture becomes clear for magnetic resonance imaging
Which way ahead for hydrogen cars?

elementary particle. A particle that cannot be subdivided into component parts. These particles are also referred to as fundamental particles. For more information see Theory – fundamental particles (Stanford Linear Accelerator Center, USA).
Synchrotrons – making the light fantastic

El Niño-Southern Oscillation (ENSO). A sporadic climatic phenomenon that occurs because of changes in the usual atmospheric pressure patterns and in the sea surface temperature in parts of the Pacific Ocean. The results include the substantial reduction of the normal upwelling off the Peruvian coast, failure of the anchovy fishery in the same area, excessive rain in western South America, and droughts in Australia, parts of Asia and southern Africa.
Enhanced greenhouse effect – a hot international topic
Science for sustainable reefs

emblematic species. Species that are closely associated by the public with a particular region, nation or continent, or that seem to 'sum up' the region in question. For example, kangaroos for Australia, pandas for China, or kiwis in New Zealand.
Australia's threatened species

E=mc². E stands for the energy released, m stands for the mass that is converted into energy, and c is the speed of light (300,000 kilometres per second).
Prospect or suspect – uranium mining in Australia
Thinking ahead – fusion energy for the 21st century?

emissions trading. A means of controlling greenhouse gas emissions from organisations and companies. Commonly the government places a limit on the total amount of carbon or greenhouse gases that can be released. It then provides a number of carbon 'permits' equal to the set limit. Companies then compete against each other to buy these permits. For some companies it is cheaper to develop cleaner production technologies (or reduce emissions) than to buy the permits.
Flying beyond our means – air travel and the environment

emulsions. Small droplets of oil dispersed in water or small droplets of water dispersed in oil. Since oil and water don't mix, emulsifiers are added to produce the small droplets and to prevent the oil and water phases from separating. Emulsifiers work by changing the surface tension between the water and the oil, thus producing a homogeneous product with an even texture. Examples of emulsions include butter and mayonnaise.
Probing past and future materials with neutrons

endangered. Used to refer to species (or higher levels of classification) that are likely to become extinct unless the various threats and pressures affecting them cease.
Australia's threatened species

endemic. Describes a species (or other unit of classification) that occurs in one particular region in all months of the year, and in all years. For example, the platypus is endemic to southeast Australia, and malaria is endemic to parts of Africa.
Australia's threatened species
Warmer and sicker? Global warming and human health
Impact of global warming on biodiversity

enhanced greenhouse effect. An increase in the natural process of the greenhouse effect, brought about by human activities, whereby greenhouse gases such as carbon dioxide, methane, chlorofluorocarbons and nitrous oxide are being released into the atmosphere at a far greater rate than would occur through natural processes and thus their concentrations are increasing. Also called anthropogenic greenhouse effect or climate change.
Enhanced greenhouse effect – a hot international topic
Wind power gathers speed
Biomass – the growing energy resource
Carbon currency – the credits and debits of carbon emissions trading
Capturing the greenhouse gang

enteric fermentation. Fermentation that occurs in the digestive system of ruminants such as sheep and cattle. As microbes in the ruminant gut break down food, methane is released. This methane is then released into the atmosphere by the animal, mostly through exhaling or burping.
Excuse me! The problem with methane gas

enzyme. A protein that acts as a catalyst. Every chemical reaction in living organisms is facilitated by an enzyme.
More food, cleaner food – gene technology and plants
Singing the praises of colony stimulating factors
The bitter-sweet taste of toxic substances
Conservation genetics – molecular detectives at work
Bird flu – the pandemic clock is ticking
Epigenetics – beyond genes

eosinophil. A white blood cell that increases in number as a result of certain parasite infections and allergic diseases.
The rise and rise of asthma

epidemiology. The study of diseases or conditions in human populations and the factors that influence their incidence and prevalence.
Bird flu – the pandemic clock is ticking

epidemiologists. Researchers who study diseases or conditions in human populations and the factors that influence their incidence and prevalence.
A quiet revolution – the science of complex systems

epigenetics. Is the study of heritable changes in gene activity that occur without a change in the sequence of the genetic material. Epigenetics literally means ‘in addition to genetics’.
Epigenetics – beyond genes

equilibrium. When a reaction and its reverse occur at equal rates, they effectively cancel one another, so there is no net change.
A quiet revolution – the science of complex systems

equinox. The times of the year when the sun crosses the celestial equator (the projection of the Earth's equator onto the sky) making the length of day and night nearly equal at all latitudes. There are two equinoxes each year, one in March, known in the northern hemisphere as the 'vernal' equinox, and one in September, known in the northern hemisphere as the 'autumnal' equinox.

The dates of the equinoxes do not occur precisely when the lengths of the day and night are equal, but are out of step by a few days. This discrepancy is because of the finite size of the sun and the bending of sunlight by the atmosphere.

More information can be found at FAQ–Equinoxes (US Naval Observatory).
025 – Calendars

erosion. A term that can be applied to soil or rock. Soil erosion is the gradual loss of any type of soil from the soil surface, usually caused by water and wind. Rock is eroded when it is slowly made smoother or worn down, again by wind or water.
Predicting natural events

ester. An organic compound formed when an acid (often a carboxylic acid) and an alcohol react, releasing water. They have low melting points and often have a pleasant smell.
Clean speed ahead with catalysts

eukaryotic. Describes those cells that have their genetic material (chromosomes) contained within a nucleus.
Life on Mars?

eutrophication. An increase in the nutrient content of a body of water, occurring either naturally or as a result of human activities. It often leads to a rapid increase (bloom) in growth of algae. The death and eventual decomposition of the algae results in a lowering of the oxygen level until the water cannot support organisms that require oxygen.
Toxic algal blooms – a sign of rivers under stress

exchangeable sodium percentage (ESP). Calculated by dividing the concentration of sodium ions clay particles by the concentration of divalent ions on clay particles, then multiplying by 100. A high ESP is an indication of a sodic soil.
Sodicity – a dirty word in Australia

extinct. Occurring no more. The word is usually used for species but can apply to any level of classification. Recent extinctions are hard to prove, and an ‘official’ limit of 50 years with no recorded sightings of the species is now used.
Australia's threatened species
Conservation genetics – molecular detectives at work
Weeds – the real alien invaders

extrinsic. External or a cause coming from outside. In this type of asthma, the cause of an attack is normally the inhalation of an allergen. Extrinsic asthma is more likely than intrinsic to start in childhood, and often the trigger(s) can be identified and dealt with. In extrinsic asthma, the reaction of the airways is like an allergic reaction, and is similar to hayfever and other allergies.
The rise and rise of asthma

F

factorisation. Resolution of an object (a number, a polynomial or a matrix) into factors, which when multiplied together give the original object.
Quantum computers – why would you want one?

phase-shift. A shift from one type of ecosystem to another. Each has a distinctive set of species, and each can be highly persistent. A common example is a shift from ecosystems dominated by corals to degraded systems that are characterized by large amounts of seaweeds or other weedy species. Overfishing and pollution undermine the resilience of coral-dominated ecosystems, making phase-shifts more likely to occur.
Science for sustainable reefs

feedback. The process whereby the output of a system affects the input. Positive feedback reinforces or increases something; negative feedback acts to keep a process within certain limits. Positive feedback can work in systems by amplifying a very small effect, changing the previous equilibrium.
Getting into hot water – global warming and rising sea levels
A quiet revolution – the science of complex systems

fermentation. The breakdown of organic molecules into simpler substances in the absence of oxygen. The process of fermentation can give rise to acids producing a lower pH.
When bugs have you on the run

fermentation. The chemical conversion of carbohydrates into alcohols or acids by microorganisms. Often fermentation refers to the conversion of sugar to ethanol and carbon dioxide by yeast according to the following equation:

This type of anaerobic fermentation is used for production of ethanol for beverages and fuels as well as to produce carbon dioxide as a raising agent in cooking.
Flying beyond our means – air travel and the environment

fibreglass. A composite material made of fine glass fibres woven into a cloth then bonded together with a synthetic plastic or resin.
Putting it together – the science and technology of composite materials

fibre optics (fibre optic communications). The transmission of information by the passage of light through flexible, glass fibres. Electrical impulses are converted into light which is then transmitted through the optical fibre. The light is then re-converted into electrical impulses at its destination.
Communicating with light – fibre optics

Fisher-Tropsch process. A process that can be used to convert coal, natural gas, and low-value refinery products into fuel. Fischer-Tropsch fuel is colourless, odourless, low in toxicity and has fewer emissions than conventional diesel. The Fischer-Tropsch reaction converts carbon monoxide and hydrogen, in the presence of a catalyst, to high molecular weight hydrocarbons.
Flying beyond our means – air travel and the environment

flight data processing. This plots an aircraft's expected position as calculated by computer from the aircraft flight plan (stored electronically by the Australian Advanced Air Traffic System).
The ups and downs of Australian air traffic control

fluorescent pigment. A pigment that absorbs light (electromagnetic radiation) at one wavelength and emits it at a different wavelength. Usually the emitted light has a lower energy than the light absorbed by the pigment.
Coral bleaching – will global warming kill the reefs?

fly ash. Fine particles of ash produced from the burning of fuels, particularly from power stations.
Making light of metals

Focused Abdominal Sonography for Trauma (FAST). An ultrasound examination of the abdomen to determine if there is fluid present in body cavities. FAST can detect haemorrhaging and helps medical staff to decide what further procedures are necessary. (Some experts use FAST to stand for Focused Assessment Sonography for Trauma.)
The shocking truth about road trauma

food chain. A sequence of organisms including plants, herbivores (plant-eating animals) and carnivores (meat-eating animals), through which energy and materials move within an ecosystem.
The bitter-sweet taste of toxic substances

fossil fuels. Carbon or hydrocarbon fuels, derived from what was living material, and found underground or beneath the sea. The most common forms are coal, oil and natural gas. They take millions of years to form. Their energy is only released upon burning, when the carbon and hydrogen within them combine with the oxygen in air to form carbon dioxide (CO₂ ), or carbon monoxide (CO) and water (H₂O). Other elements within the fuels (such as sulfur or nitrogen) are also released into the air after combining with oxygen, causing further pollution with SO₂ and nitrogen oxide gases. In the case of coal, ash particles are also a problem.
Harnessing direct solar energy – a progress report
Biomass – the growing energy resource

free radical. A molecule that is unstable and highly reactive because it contains at least one unpaired electron. Free radicals combine with molecules to generate further unpaired electrons, thereby starting off chain reactions. Free radicals can damage cell membranes and DNA, eventually causing cancer and other diseases.
Buckyballs – a new sphere of science

frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).
Mobile phones – communications on the go
The ups and downs of Australian air traffic control
A fair cop! Accurate breath analysis and speed detection
GPS and never having to say: 'Where am I?'
Quiet please! Fighting noise pollution
Wireless but not clueless

frequency. A measure of how frequently a wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).
Fixing the cracks in disaster mitigation

frictional resistance. Friction is a force that impedes the slipping or sliding of two surfaces in contact. The frictional resistance depends on the roughness of the surfaces involved. When a car is skidding, the surface of the tyres and the surface of the road both affect the resistance provided by friction.
Fatal impact – the physics of speeding cars

fuel cell. A device that converts energy from chemical reactions directly into electrical energy. The simplest fuel cell 'burns' hydrogen in a flameless chemical reaction to produce electricity. In order to 'burn' the hydrogen a fuel cell needs a source of oxygen and this is usually obtained from air. The only by-product from this type of fuel cell is water.

For more information about fuel cells see our Nova topic Fuelling the 21st century.
Generating new ideas for meeting future energy needs
A fair cop! Accurate breath analysis and speed detection
Which way ahead for hydrogen cars?
Nanotechnology – taking it to the people

fuel cell. A cell that converts energy from chemical reactions directly into electrical energy. A simple fuel cell 'burns' hydrogen in a flameless chemical reaction with oxygen to produce electricity. For more information see Fuelling the 21st century (Nova: Science in the news).
Flying beyond our means – air travel and the environment

futures. See Derivatives – Futures (The Investment FAQ, USA).
Stock markets – putting your money where your math is

G

galaxy. Huge regions of space that contain hundreds of billions of stars, together with planets, glowing nebulae, gas and dust.
Astronomy in the deep freeze

Galileo. A satellite radio navigation system initiated by the European Union and developed for non-military applications. The final system will be based on a collection of 30 satellites. For more information see What is Galileo? (European Space Agency) and Galileo: European satellite navigation system (Europa, European Union).
GPS and never having to say: 'Where am I?'

gamma rays. The shortest wavelength of electromagnetic radiation. For more information see Gamma rays (NASA,USA).
When bugs have you on the run
Salinity – the awakening monster from the deep

gamete. A cell, such as a sperm or an egg, that is specialised for fertilisation. Gametes have a single set of chromosomes.
Malaria – a growing threat

gametocyte. A cell that can develop into a gamete.
Malaria – a growing threat

gasification. A process that exposes a solid fuel to heat in the presence of limited oxygen to produce a gaseous fuel. This fuel contains hydrogen but also other gases such as carbon monoxide, carbon dioxide, nitrogen, and methane. Under suitable circumstances, gasification can produce synthesis gas, a mixture of just hydrogen and carbon monoxide.
Generating new ideas for meeting future energy needs

gasification. The conversion of a substance into a gas. The conversion of coal, petroleum or biomass into a gas mixture containing carbon dioxide, carbon monoxide and hydrogen in the presence of oxygen. The gas mixture produced (syngas) can then be treated with steam to produce more hydrogen. Gasification occurs through chemical reactions at high temperature and often at high pressure.
The quest to make hydrogen the fuel of the future

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.
Prions – morphing agents of disease
The Human Genome Project – discovering the human blueprint
Sun and skin – a dangerous combination
More food, cleaner food – gene technology and plants
Malaria – a growing threat
Singing the praises of colony stimulating factors
Integrated pest management – the good, the bad and the genetically modified
Conservation genetics – molecular detectives at work
Making packaging greener – biodegradable plastics
Driver fatigue – an accident waiting to happen
Biology meets industry - genomics, proteomics, phenomics
Bird flu – the pandemic clock is ticking Epigenetics – beyond genes

gene cloning. The process of producing identical copies (clones) of a gene.
Singing the praises of colony stimulating factors

gene probe. A specific sequence of single-stranded DNA or RNA, usually labelled with a radioactive atom. A probe is designed to bind to, and therefore single out, a particular segment of DNA to which it is complementary.
More food, cleaner food – gene technology and plants

generator. A machine that converts mechanical energy into electrical energy. In a normal generator, a shaft spins a magnetic rotor. The moving magnet produces an alternating current. (It is the reverse of an electric motor.) Generators are extremely efficient in converting mechanical energy to electrical energy.
Wind power gathers speed

gene technology. The techniques used in the manipulation of DNA to alter the genetic make-up of organisms.
More food, cleaner food – gene technology and plants

genetic conditions. Those conditions or diseases that result from abnormalities in chromosomes or DNA, and are inherited.
Epigenetics – beyond genes

genetic diseases. Those diseases (malfunctions) that result from abnormalities in chromosomes or DNA, and are inherited.
The Human Genome Project – discovering the human blueprint

genetic diversity. The variety of different types of genes in a species or population. Genetic diversity is really a form of biodiversity.
Australia's threatened species
Malaria – a growing threat
Conservation genetics – molecular detectives at work

genetic engineering. A set of procedures whereby a specific piece of DNA can be excised from a chromosome and inserted into the DNA of a chromosome of a different organism.
Prions – morphing agents of disease
Integrated pest management – the good, the bad and the genetically modified
The mammal copiers – advances in cloning
Generating new ideas for meeting future energy needs

genetic map (linkage map). A map showing the sequence of genes on chromosomes.
The Human Genome Project – discovering the human blueprint

genetically modified organism. An organism with genetic material that has been altered using gene technology.
More food, cleaner food – gene technology and plants

genetic mutation. A change in the genetic material (DNA, or RNA in the case of some viruses) resulting in new or rearranged hereditary determinants. Mutations are rare, random events in which the base sequence of the nucleic acid molecule is changed. The frequency of mutations may be increased by chemicals or radiation.
Bird flu – the pandemic clock is ticking

genetics. The study of heredity and variation in organisms. It can also refer to the genetic features of an organism.
More food, cleaner food – gene technology and plants

genome. The total genetic material of an individual or species.
The Human Genome Project – discovering the human blueprint
More food, cleaner food – gene technology and plants
Epigenetics – beyond genes

genotype. The particular set of genes carried by an individual organism.
Biology meets industry - genomics, proteomics, phenomics

genus. A group of organisms which may contain one or more species that exhibit similar characteristics.
Discovering Australia's evolutionary past

geosequestration. Involves the capture and long-term underground storage of carbon dioxide. Carbon dioxide produced by coal-fired electricity stations and other industrial sources is compressed to form a liquid and injected into deep underground geological formations Possible storage sites include saline aquifers, coal seams, and used oil and gas reservoirs. For more information about geosequestration see What is geosequestration? (CO₂ Cooperative Research Centre for Greenhouse Gas Technologies).
Carbon currency – the credits and debits of carbon emissions trading

geothermal. Related to the heat emitted from the Earth; for example, hot springs are heated by geothermal sources. Geothermal energy is generated from natural steam, hot water, hot rocks or lava in the Earth's crust.
The quest to make hydrogen the fuel of the future

geothermal gradient. The rate of increase in temperature per unit depth in the Earth. For more information see Geothermal gradient (Absolute astronomy, USA).
Rocking on with hot rocks geothermal energy

gigajoule. The joule (J) is a unit for measuring energy.  A gigajoule is one thousand million (10⁹) joules. It is defined as the work done, or energy expended, by a force of one newton moving one metre in the direction of the force.
The quest to make hydrogen the fuel of the future

gigalitre. A gigalitre is one thousand million (1,000,000,000 or 10⁹) litres.
The water down under
Stormwater – helping to tackle Australia's water crisis

gigawatt. The unit of energy is the joule (J) and the unit of power is the watt (W), which is the power involved in doing 1 joule of work (or using 1 joule of energy) each second. This is a very small amount of power and in most mechanical applications, we count power in kilowatts (1 kilowatt = 1000 watts). A kilowatt is about equal to the heat energy put out by a single bar radiator, and is also about equal to the power expended by a person running up stairs. A car engine typically produces 50 to 100 kilowatts. When we consider power generation we use larger units. The megawatt is a 1,000,000 watts or 1000 kilowatts. A typical coal-burning power station produces about 1000 megawatts of power and this is the same as 1 gigawatt.
Wind power gathers speed

global hectares (gha). Unit for measuring our demands on the Earth (ecological footprint) and the ability of the Earth to supply our demands (biocapacity). A global hectare is one hectare of land or water with world-average productivity. Measurements in global hectares are adjusted according to the productivity of land or water in a given year. A land type of high productivity (eg. cropland) will have more global hectares than less productive land (eg. pasture) of an equivalent size.
Making our mark – ecological footprints

Global Positioning System. The Global Positioning System (GPS) is a collection of 24 earth-orbiting satellites which allows any person who owns a GPS receiver to determine their location on the planet. More information on the Global Positioning System can be found How a GPS receiver works (How Stuff Works, USA) and The Global Positioning System: The role of atomic clocks (Beyond Discovery, National Academy of Sciences, USA).
The ups and downs of Australian air traffic control

Global System for Mobile Telecommunications (GSM). Digital systems of mobile phones convert voices into a series of on-or-off electrical pulses which are then relayed in short bursts as packages of data. GSM is efficient because in the intervals between bursts, other phones can also send packets of data: in this way, this digital technology enables up to eight conversations to be held on the same channel virtually simultaneously. More information on analogue and digital systems can be found at Sound into pulses: The benefits of digital transmission (Telstra Learning Centre, Australia) and What is the difference between analog and digital cell phones? (How Stuff Works, USA).
Mobile phones – communications on the go

global warming. An increase in the average temperature of the Earth's surface. Global warming is one of the consequences of the enhanced greenhouse effect and will cause worldwide changes to climate patterns.
Enhanced greenhouse effect – a hot international topic
Warmer and sicker? Global warming and human health
Predicting natural events
Impact of global warming on biodiversity
Weeds – the real alien invaders
Making every drop count

global warming potential. The global warming strength of one kilogram of a greenhouse gas relative to one kilogram of carbon dioxide over a chosen time period. Global warming potential takes into account the variation in the time that different gases remain in the atmosphere and the ability to absorb radiation.
Excuse me! The problem with methane gas

GLONASS. Global Navigation Satellite System, operated by the Russian Federation Ministry of Defence. When completed, it will have a constellation of 24 satellites, and is intended to service maritime and aviation users throughout the world. For more information see GLONASS – summary (Andrews Space and Technology, USA).
GPS and never having to say: 'Where am I?'

gnomon. A column that can indicate the time of day by the shadow that it casts on a marked surface. On a sundial, the pin or vertical triangular plate that casts the shadow is called a gnomon. More information can be found at Design of the Richard D. Swensen sundial (University of Wisconsin-River Falls, USA)
025 – Calendars

greenhouse effect. The trapping and build-up of heat in the lower atmosphere near a planet's surface. Some of the heat flowing back towards space from the Earth's surface is absorbed by water vapour, carbon dioxide, methane and other gases in the atmosphere. If the atmospheric concentration of these gases rises, then theory predicts that the average temperature of the lower atmosphere will gradually increase. The greenhouse effect in part explains the temperature differences of Mars, Venus and Earth.
Enhanced greenhouse effect – a hot international topic
Carbon currency – the credits and debits of carbon emissions trading

greenhouse gas. A gas that is transparent to incoming solar radiation and absorbs some of the longer wavelength infrared radiation (heat) that the Earth radiates back. The result is that some of the heat given off by the planet accumulates, making the surface and the lower atmosphere warmer. For more information see The greenhouse effect (CSIRO Atmospheric Research, Australia).
Earth's sunscreen – the ozone layer
Fuelling the 21st century
Generating new ideas for meeting future energy needs
Making packaging greener – biodegradable plastics
Bogged down in the four-wheel drive debate?
Warmer and sicker? Global warming and human health
Getting into hot water – global warming and rising sea levels
Impact of global warming on biodiversity
Making our mark – ecological footprints

groundwater. Water stored naturally below the land surface in a saturated zone of the soil. The top of this groundwater is called the watertable. For more information see What is groundwater? (Connected Waters, University of New South Wales, Australia).
Salinity – the awakening monster from the deep
Impact of global warming on biodiversity
Making every drop count

groundwater dependent ecosystem (GDE). Ecosystems that require a supply of groundwater to maintain their current structure (special composition) and function (for example, rates of carbon fixation). Some GDEs need a continual supply of groundwater, others require intermittent supply.
The water down under

granite. A hard, coarse grained, rock that is often used in building materials. Granite is an intrusive, igneous rock ie. it forms from magma underground. Like most other rocks, granite contains low levels of radioactive elements.
Rocking on with hot rocks geothermal energy

grey matter. The tissue of the nervous system that appears greyish because of the relatively high proportion of nerve cell nuclei that occur there. This is in contrast to white matter which consists mainly of axons. It appears whitish because of the insulating lipid-protein sheath around axons. Photomicrographs of grey matter and white matter can be found at a site from the Department of Anatomy and Cell Biology at the University of Kansas, USA. Getting our heads around the brain

H

habitat. 1. The place normally occupied by a particular organism or population. 2. The sum of all the factors that determine the existence of a community (eg, the freshwater habitat).
A plague on the pest – rabbit calicivirus disease and biological control
Australia's threatened species
Weeds – the real alien invaders

haemagglutinin. A protein which forms a rod-shaped spike on the surface of influenza virus. The name haemagglutinin is given because the spikes are capable of adhering to red blood cells, causing them to be agglutinated (clumped).
Bird flu – the pandemic clock is ticking

half-life. The time it takes for half the atoms in a sample of radioactive material to break down into a non-radioactive element. Half-lives vary significantly, from a few days for some elements to millions of years for others. Half-life measurement is important when considering the long-term storage or disposal of radioactive waste.
The water down under

hallucinogen. A substance that alters perception and can induce delusions or hallucinations. More information can be found at Hallucinogens (New South Wales Department of Health, Australia).
The dope on drug-impaired driving

halocarbons. Compounds of carbon combined with one or more of the elements called halogens (fluorine, chlorine, bromine, iodine, and astatine). Halocarbons containing fluorine, chlorine and bromine contribute to ozone depletion and to the enhanced greenhouse effect.
Enhanced greenhouse effect – a hot international topic

herbicide. A chemical used to kill plants or inhibit their growth. Herbicides can be selective (kills some plants but not others) or non-selective. They can affect the whole plant, or only part of a plant, at particular stages of development.
Weeds – the real alien invaders

heat pump. By circulating water underground, a geothermal heat pump uses the relatively constant heat of the earth to alter the temperature of the circulated water. This water can then be used to heat or cool buildings. Heat pumps can extract heat from the earth for heating buildings in winter and deliver heat from buildings to the earth in summer.
Rocking on with hot rocks geothermal energy

hieroglyphics. A form of writing in which pictures and symbols are used to represent objects, concepts or sounds.
Ethnomathematics – a rich cultural diversity

histones. Proteins found associated with DNA in eukaryotic cells that play a role in gene regulation. The DNA winds around the histone protein to form chromatin. For more information about the role of histones see The nucleus (Kimball’s Biology Pages, USA).
Epigenetics – beyond genes

hormone. A substance produced in one part of the body and carried by the blood to another part of the body where it causes a response (eg, insulin, produced by the pancreas, that promotes the uptake of glucose by body cells). For more information see The hormones of the human (Kimball's Biology Pages, USA) and The hormones (Center for Bioenvironmental Research, Tulane and Xavier Universities, USA).
Prions – morphing agents of disease
Singing the praises of colony stimulating factors
Pointing the bone at osteoporosis
Who will win the drugs race?
Bitumen battles – the phenomenon of road rage
Driver fatigue – an accident waiting to happen

host. An organism on or in which a parasite lives.
A plague on the pest – rabbit calicivirus disease and biological control
Bird flu – the pandemic clock is ticking

house dust mites. Tiny mites (about one-third of a millimetre long) that feed off human skin flakes and bodily secretions. They colonise houses, especially in warm, humid areas. They tend to live in carpets, mattresses, pillows and soft furnishings. Although quite harmless, their droppings contain substances that are allergens. Exposure to the droppings (invisible to the eye) can cause sneezing, itchy, red eyes or asthma attacks.
The rise and rise of asthma

humectant. A substance that can absorb water from moist surroundings.
Putting on a good face – the chemistry of cosmetics

hydration. A chemical reaction involving the addition of water to a compound.
Clean speed ahead with catalysts

hydrocarbon. Compound containing only the two elements, carbon and hydrogen.
Local air pollution begins at home
Biomass – the growing energy resource
Generating new ideas for meeting future energy needs

hydrochlorofluorocarbons (HCFCs). Organic compounds like CFCs but with extra hydrogen atoms, and a lower ozone-destroying potential. They have similar properties to CFCs and are being used as temporary substitutes for them.
Earth's sunscreen – the ozone layer

hydrology. The study of water, its properties and movement through the Earth’s land and atmosphere. Hydrology includes the study of the distribution of water, the accumulation of water – in lakes, oceans and underground – and the effects of water on the earth's surface.
Predicting natural events

hydrophilic. Describes a substance that absorbs, dissolves in or is attracted to water.
Putting on a good face – the chemistry of cosmetics

hydrothermal. Describes geothermal systems with naturally occurring groundwater that has been heated by either heat-producing rocks or nearby volcanic activity.
Rocking on with hot rocks geothermal energy

hypothalamus. A part of the brain that is connected to, and controls activity in, the pituitary gland. It also controls various aspects of homeostasis such as regulation of body temperature and appetite. There are regions of the hypothalamus that are associated with aggressive behaviour.
Bitumen battles – the phenomenon of road rage
Driver fatigue – an accident waiting to happen

I

ice cores. Cylinders of ice drilled from glaciers and icesheets that are used to provide information about the earth's climate history.
Discovering Australia's evolutionary past

ice sheet. A very large body of land-based ice. Ice sheets are found in Greenland and Antarctica and are also known as continental glaciers.
Getting into hot water – global warming and rising sea levels

immune rejection. Can occur as a result of a transplant when the donor type of cell or organ is not a close enough match to the recipient type. Drugs to suppress the patient's immune system help reduce this problem. For more information see Transplant rejection (Medline Plus Medical Encyclopedia, US National Library of Medicine and the National Institutes of Health).
Stem cells – gateway to 21st centurymedicine

immune system. The cells, tissues and organs that assist the body to resist infection and disease by producing antibodies and/or altered cells that inhibit the multiplication of the infectious agent.
Malaria – a growing threat
Immunisation – protecting our children from disease
The mammal copiers – advances in cloning
Bird flu – the pandemic clock is ticking
It's an advanced material world

immune system. The cells, tissues and organs that assist the body to resist infection and disease by producing antibodies and/or altered cells that inhibit the multiplication of the infectious agent and provide resistance to disease.
Cancer immunotherapy – redefining vaccines

immunisation. The process by which the body develops the capacity to combat a specific infection. Immunisation can be induced by introducing vaccines into the body. This is more correctly called vaccination or inoculation, but the word immunisation is used to mean the same thing.
Immunisation – protecting our children from disease

immunity. A body's reaction to the introduction of foreign substances, through the production of defensive substances such as antibodies.
A plague on the pest – rabbit calicivirus disease and biological control
Kissing the Epstein-Barr virus goodbye?

immunoassay. A laboratory test that uses antibodies to identify and quantify substances. Often the antibody is linked to a marker such as a fluorescent molecule, a radioactive molecule, or an enzyme.
The dope on drug-impaired driving

immunotherapy. The use of the immune system to treat existing disease. This can be either through active immunotherapy, in which the patient's own immune system is trained to recognise diseased cells to be destroyed, or through the passive immunotherapy in which diseased cells are destroyed by antibodies created outside the body.
Cancer immunotherapy – redefining vaccines

impermeable. A substance that cannot be penetrated. A rock or material that stops the movement of water or other liquids through it.
Capturing the greenhouse gang
Rocking on with hot rocks geothermal energy

inflamed/inflammation. Inflammation is the process that makes living tissue swell, become painful and turn red. Inflamed tissue contains damaged cells and has a higher than normal blood flow through it – which is why it’s red and warm. It is usually ‘infiltrated’ by many cells of the immune system. Compounds released from damaged cells cause fluid and more inflammatory cells to leak out of the blood vessels in the area; this fluid accumulates and may make the tissue swell or block tubes. Inflammation is often associated with infection but it can also be caused by allergic reactions. One of the major inflammatory cells in asthma is the eosinophil, which can damage the airway lining. This can ultimately lead to permanent damage in the airways. Inflammation of the lining of the nose, for example, causes the blocked nose characteristic of colds or of hayfever. Inflammation of the airways occurs in asthma, but is not unique to it.
The rise and rise of asthma

infrared. The part of the electromagnetic spectrum between visible light and microwaves. The wavelength of infrared light is between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.)
A fair cop! Accurate breath analysis and speed detection
Astronomy in the deep freeze

infrared light. A form of electromagnetic radiation with wavelengths between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.) Infrared light is primarily thermal radiation, and we can think of this as being heat.
Synchrotrons – making the light fantastic

infrared telescope. A telescope designed to observe in the infrared section of the electromagnetic spectrum. Infrared telescopes look like optical reflecting telescopes and operate in a similar way. The infrared radiation is collected and focused by mirrors onto detectors sensitive to infrared.

One problem with infrared telescopes is that the telescope itself is a source of unwanted infrared radiation, but this is minimised by cooling the components of the telescope with liquid nitrogen for near infrared observations and with liquid helium for the far infrared.
Astronomy in the deep freeze

insulin. A hormone produced by special cells in the pancreas. Insulin allows glucose to enter the body's cells, where it is used as an energy source. In type 1 diabetes (insulin-dependent diabetes) the body does not produce insulin, causing glucose to build up in the blood, giving high blood sugar levels. Type 1 diabetics can't make their own insulin so they must inject it every day. For more information see Type 1 diabetes (Medline Plus Medical Encyclopedia, US National Library of Medicine and the National Institutes of Health).
Stem cells – gateway to 21st centurymedicine
Biology meets industry - genomics, proteomics, phenomics

intelligent sensor. A sensor that has an inbuilt ability to sense information (eg, light, temperature, salinity), process the information and send selected information to an external receiver (including to other sensors). Also called a smart sensor, mote or smart dust. Intelligent sensors are able to detect particular conditions such as abnormal temperature and react according to programmed instructions (eg, by increasing the sampling rate).
A sense of things to come – smart sensors and the environment

intensity. Measures the strength of shaking produced by an earthquake at a certain location. Intensity is determined from the effects on paople and structures. Intensity isusually measured in the Modified Mercalli intensity scale (Association of Bay Area Governments, USA).
Fixing the cracks in disaster mitigation

interface device. A tool that allows a person to interact with a computer. For example, a mouse is an interface device that allows you to put information into a computer. Virtual reality includes interface devices such as head-mounted displays that transmit sensations of the artificial world, as well as transmitting information into the computer.
Virtual reality bytes – military uses of VR

Intergovernmental Panel on Climate Change (IPCC). An organisation established in 1988 by the World Meteorological Organization and the United Nations Environment Programme to provide the most widely accepted information available about climate change. The IPCC does not conduct new research or monitor climate-related data, its mandate is to assess existing data and to produce balanced and objective reports. For more information see Intergovernmental Panel on Climate Change (Switzerland).
Getting into hot water – global warming and rising sea levels
Warmer and sicker? Global warming and human health
Impact of global warming on biodiversity

interleukin. A chemical messenger secreted by cells of the immune system. They act by affecting the behaviour of the rest of the immune system. For example, they may attract immune system cells to an area of the body or they may stimulate the development of some cells of the immune system.
The rise and rise of asthma

International System of Units (abbreviated to SI). SI is based on the seven units shown in the table; all other units are derived from them. These measurements are based on reproducible, agreed standards which allow accurate comparisons to be made anywhere in the world. CSIRO Division of Applied Physics maintains Australia's physical standards of measurement.

The seven SI base units of measurement

Quantity	Base unit	Symbol
Mass Length Time Temperature Amount of substance Electric current Luminous intensity	kilogram metre second kelvin mole ampere candela	kg m s K mol A cd

Measurement in sport – the long and the short of it

intrinsic. Instrinsic asthma has no clear connection with allergy. It can start at any age. The triggers are usually infection, polluted air, exercise, or cold temperatures, but some attacks occur without any obvious trigger.
The rise and rise of asthma

inverse square law of radiation. If you halve the distance from a radiation source (such as a light, a fire, or a radio transmitter) you multiply by four the intensity of the radiation. This means that if you hold your hand one metre away from a light, then move your hand half way towards the light (so it is just 50 cms away) – there will be not double but four times as much light reaching your hand. It you halve the distance again to just 25 cms there will be sixteen times as much light reaching you hand compared to when it was a metre away. The same things happens with radiated heat – which is why if you sit with your feet pointing at a camp fire, your feet can feel very hot while your chest is cool. Or, why a heat source strong enough to make metal glow red, may feel just pleasantly warm a short distance away.
Communicating with light – fibre optics

invertebrates. Usually defined as animals without backbones, invertebrates make up the vast majority of all animal species. Only fish, amphibians, reptiles, birds and mammals are not invertebrates. Insects, spiders, worms, slaters and many marine creatures such as corals, sponges and jellyfish are examples of invertebrates.
Australia's threatened species
The water down under

ion. A positively or negatively charged atom or group of atoms.
Simply astronomical – the Square Kilometre Array
Making light of metals

ion, anion, cation, and divalent ion. An ion is an electrically charged atom or group of atoms. The charge is the result of the loss (positive ion) or gain (negative ion) of one or more electrons.

The gain of one or more electrons produces an ion with a negative charge (anion). The loss of one or more electrons produces an ion with a positive charge (cation). Ions that have gained or lost two electrons are called divalent ions.
Cleaner production – a solution to pollution?
Sodicity – a dirty word in Australia
The bitter-sweet taste of toxic substances

ion channel. A protein-coated pore in a cell membrane that selectively regulates the diffusion of ions into and out of the cell. An ion channel switches between open and closed when the protein undergoes a conformational change. For more information see Ions cannot cross membranes (University of Washington, USA).
Nanoscience – working small, thinking big

ion implantation. Process by which the ions of a material are placed on the surface of a solid. The process modifies the physical properties of the solid.
Quantum computers – why would you want one?

ionising radiation. Any form of radiation that has sufficient energy to remove electrons from atoms, so producing charged particles called ions. It can consist of high energy particles (electrons, protons or alpha particles) or short wavelength electromagnetic radiation (ultraviolet, X-rays and gamma rays).
Prospect or suspect – uranium mining in Australia
Thinking ahead – fusion energy for the 21st century?

isotope. One of the different kinds of an atom of the same element. All atoms of an element have the same chemical properties, but the different isotopes have different weights. The different weights are because the isotopes have a different number of neutrons. For more information, see Isotopes (Carlton Comprehensive High School, Canada)
Who will win the drugs race?
The water down under
Thinking ahead – fusion energy for the 21st century?

J

Jatropha. A group of plants, shrubs and trees that can grow in dry, less productive land. Jatropha curcas seeds contain up to 40 per cent oil which can be used for biofuel. Because Jatropha grows on land of lower productivity, it is sometimes considered to be a biofuel that does not compete with food growing land and resources. However, commercially viable production of Jatropha can still use productive land, water and fertilisers. Jatropha curcas is considered a potential weed in Australia.
Flying beyond our means – air travel and the environment

K

Kevlar. Kevlar is a synthetic polymer fibre and is used when reduced weight, increased strength and long wear life are required. The tensile strength of Kevlar is more than three times greater than that of steel, and its density is less by a factor five, so it is ideal for making very strong, light, flexible structures. It has become a household name, being used for yacht sails, bullet-proof vests and in the aerospace industry.
It's an advanced material world

kilowatt, megawatt, gigawatt. The basic unit of power (the rate at which energy is used) in the metric system is the watt (W); a kilowatt is 1000 watts. A watt is a very small amount of power and in most mechanical applications we count power in kilowatts. A kilowatt is about equal to the heat energy put out by a single bar radiator, and is also about equal to the power expended by a person running up stairs. A car engine typically produces 50 to 100 kilowatts.

When we consider power generation, we use larger units. A megawatt is 1,000,000 watts or 1000 kilowatts. A typical coal-burning power station produces about 1 gigawatt (1000 megawatts) of power.
Biomass – the growing energy resource
Generating new ideas for meeting future energy needs
Thinking ahead – fusion energy for the 21st century?

kilowatt hour. A unit of energy that is normally used to measure the consumption of domestic electricity. The joule (1 watt per second) could be used but the numbers become very large and it is common to use the kilowatt hour (1 kilowatt hour = 3,600,000 joules or 3.6 megajoules).
Wind power gathers speed
Thinking ahead – fusion energy for the 21st century?

kinetic energy. Kinetic energy is the energy associated with a moving object (energy of motion). For more information see Energy basics (Box 3 of Nova: Science in the news topic, Wind power gathers speed).
Fatal impact – the physics of speeding cars
Death-defying designs for car safety

Kroll process. The process used to produce titanium (or zirconium) from its ore. The ore is converted first to titanium tetrachloride, and then reduced to produce titanium, usually by reacting it with magnesium. For more information see Titanium (Chemguide, UK).
Making light of metals

Kyoto Protocol. The third session of the Conference of the Parties to the UN Framework Convention on Climate Change took place in Kyoto, Japan in December 1997, resulting in the Kyoto Protocol. This working agreement of the signatories commits developed countries to reduce their collective emissions of six greenhouse gases by at least 5 per cent of 1990 levels by 2012. The Kyoto agreement became legally binding on 16 February 2005 when 132 signatory countries agreed to strive to decrease carbon dioxide emissions. More information can be found at the official The Kyoto Protocol site.
Enhanced greenhouse effect – a hot international topic
Carbon currency – the credits and debits of carbon emissions trading

Kyoto Protocol. This working agreement of participating countries commits developed countries to reduce their emissions of six greenhouse gases by at least 5 per cent of 1990 levels by 2012. The Kyoto agreement became legally binding on 16 February 2005 when 132 signatory countries agreed to strive to decrease carbon dioxide emissions. More information can be found at the official The Kyoto Protocol site.
Flying beyond our means – air travel and the environment

L

larva (plural, larvae ). The immature stage of an animal. The larva does not have the same structure as the adult form. For example, tadpoles are frog larvae and caterpillars are butterfly larvae.
Hydatids – when a dog is not man's best friend

laser. Light amplification by stimulated emission of radiation. A device that produces a high-intensity, directional, monochromatic beam of light.
Communicating with light – fibre optics
Thinking ahead – fusion energy for the 21st century?

LD₅₀ . The amount of a substance that is lethal to 50 per cent of the experimental animals exposed to it. LD₅₀ is usually expressed as the weight of the substance per unit of body weight of the animal in order to account for weight difference among animals. More information about LD₅₀ and other measures of exposure to toxic substances can be found at Dose-response relationships in toxicology (Extension Toxicology Network, USA)
The bitter-sweet taste of toxic substances

lead carbonate. A naturally occurring white amorphous powder with a chemical formula of PbCO₃. Used in exterior paints, ceramics, cements, processing of parchment and as a laboratory reagent.
Putting on a good face – the chemistry of cosmetics

legal limit of 0.05. The legal limit of 0.05 refers to the blood alcohol concentration (BAC) and is measured in grams of ethanol per 100 millilitres of blood. For example, men and women with a BAC of 0.05 grams per 100 millilitres have 0.05 grams of alcohol in their body for every 100 millilitres of their blood. The legal limit is lower for certain road user groups (eg, those who hold learner or provisional licences). Depending on the state or territory, this lower limit is either zero or 0.02.
A fair cop! Accurate breath analysis and speed detection

leukaemia. Form of cancer resulting in an overproduction of abnormal white blood cells. This overproduction suppresses normal red blood cell and platelet production.
Singing the praises of colony stimulating factors

Life Cycle Assessment (LCA). An assessment of the impact of a product on the environment throughout its life. Measures what is needed during production and what is produced from 'cradle to grave'. This includes energy and materials used for obtaining the raw materials for the product, product manufacture and assembly, transport of the product, its use and disposal. Wastes produced during the product's life are also accounted for.
Making our mark – ecological footprints

light-sensitive cell. A device having a photoelectric property such as the ability to generate a current or change its electrical resistance when exposed to light.
Communicating with light – fibre optics

lignotuber. A woody swelling on underground or partly underground stems or roots containing buds and food reserves. Plant species which possess lignotubers are mostly fire tolerant. Species that do not possess lignotubers usually survive fires through massive seed regeneration.
Bushfires spark extensive search for answers

limbic system. Interconnecting parts of the brain that are associated with the control of emotions and memory. For more information see Limbic system (Universal Health Services Neurobehavioral Systems, USA) and The emotional nervous system – the limbic system (Shippensburg University, USA).
Bitumen battles – the phenomenon of road rage

linear discriminant analysis. A method of classification that uses a weighted sum. For each object that is to be classified, linear discriminant analysis takes a weighted sum of values of the variables that determine the classification. The value of the weighted sum is then used to determine the classification. For example, a bank may wish to classify loan customers into those at risk of defaulting and those not at risk, based on salary and financial commitments. In the plot of financial commitments against salary, a linear discriminant function appears as a line. The high-risk customers will have a low salary and high financial commitments and lie above the line, while those with a high salary and low financial commitment will have low risk and lie below the line.
Good prospects ahead for data mining

linked. The association of traits that occurs when the genes coding for them are on the same chromosome.
The Human Genome Project – discovering the human blueprint

lipophilic. Describes a substance that dissolves in or is attracted to fats, oils or other lipids. Lipophilic functional groups or molecules prefer to be in an environment where there is no water.
Putting on a good face – the chemistry of cosmetics

'living' soil. A healthy soil that contains living organisms. These organisms (biota) are important to the health of soil, and a gram of healthy agricultural soil can contain several million micro-organisms. Productive soil is made up of mineral particles; organic matter in the form of decaying parts of plants and animals and the waste products of living things; and hundreds of millions of micro-organisms and other living things (eg, nematodes, arthropods, worms). For more information see The living soil (Sun Prairie Organic, Canada).
Feeding the future – sustainable agriculture

locus (plural loci). The position on a chromosome of a gene or other chromosome marker.
The Human Genome Project – discovering the human blueprint

logarithmic scale. A scale of measurement in which an increase or decrease of one unit represents a ten-fold change in the quantity measured.
Acid test for the seas

lustre. The way that light interacts with the surface of a material, its sheen or gloss. Lustre is used to describe minerals eg, metallic lustre, greasy lustre.
Making light of metals

M

macropod. Literally meaning ‘big foot’, the word is used to describe kangaroos, wallabies and rat kangaroos.
Australia's threatened species

magnetic fields. Are created by electric currents in wires or electrons moving in orbit around a nucleus. Sources of magnetic fields have a north and south magnetic pole. The SI unit for magnetic field is the Tesla (T). For more information see Magnetism (School for Champions).
Thinking ahead – fusion energy for the 21st century?

magnesite. A mineral ore containing magnesium carbonate and used as a source of magnesium. For more information see Magnesium (Geoscience Australia).
Making light of metals

magnitude. The severity of an earthquake is determined by its magnitude and intensity. The magnitude of an earthquake is a measure of the amount of energy released by the seismic event that caused it. Its intensity is its capacity to cause damage at a given point on the earth's surface. Thus, there is usually one value for an earthquake's magnitude but many measures of its intensity – depending on factors such as the distance of a given point from the earthquake's hypocentre.
Fixing the cracks in disaster mitigation

malleable. The ability of metals to be shaped or hammered when cold without breaking. For example, aluminium can be hammered or rolled into sheets (aluminium foil).
Making light of metals

map. A plan of the linear sequence of chromosomes.
The Human Genome Project – discovering the human blueprint

mapping. Constructing a plan (or map) of the linear sequence of chromosomes.
The Human Genome Project – discovering the human blueprint

marker gene. An easily identified gene that is inserted into the organism, along with the desired gene. The presence of the marker gene tells researchers that the transformation was successful.
More food, cleaner food – gene technology and plants

mass. The amount of matter in an object.
Bogged down in the four-wheel drive debate?

mass spectrometry. A method of determining the types, and relative amounts, of ions in a sample. In a mass spectrometer, atoms or molecules in a sample are ionised by an electric beam. The ions are accelerated by an electric field and then deflected by a powerful magnet. Different ions are deflected to different degrees, so the composition of the sample can be determined. More information can be found at An introduction to mass spectrometry (University of Leeds, UK).
Who will win the drugs race?

megajoule. The unit of energy is the joule (J). It is defined as the work done, or energy expended, by a force of one newton moving one metre in the direction of the force. When we consider power generation, we use larger units. A megajoule is 1,000,000 joules.
Rocking on with hot rocks geothermal energy

megalitre. A megalitre is one million (1,000,000 or 10⁶) litres.
The water down under

megatonne (Mt). A megatonne is one million (1,000,000 or 10⁶) tonnes.
Excuse me! The problem with methane gas

meiosis. A division of the nucleus that involves the separation of pairs of chromosomes into different cells. Meiosis takes place in the reproductive organs of sexually reproducing organisms. Meiosis involves two nuclear divisions, both of which may take place before division of the cell itself is complete. The eventual result is four cells, each with half the number of chromosomes present in the original cell. Crossing over of chromosomes during meiosis creates new combinations of genes in the progeny that were not present in either adult. For more information see How cells divide: Mitosis versus meiosis (Public Broadcasting Service, USA).
Malaria – a growing threat
Epigenetics – beyond genes

melanin. A dark pigment produced by cells called melanocytes in the skin. It absorbs ultraviolet radiation and is thus a natural sunscreen. Exposure to ultraviolet radiation stimulates more melanin production, resulting in a tan. However, getting a tan entails the risk of skin damage. Dark-skinned people naturally produce much more melanin than fair-skinned types and so are less liable to experience sunburn or skin cancer.
Sun and skin – a dangerous combination

melatonin. A hormone that can influence the hypothalamus and pituitary gland and may affect appetite and sleep. It is derived from the amino acid, tryptophan.
Driver fatigue – an accident waiting to happen

membrane. A thin, pliable sheet or layer. Biological membranes consist of a double layer of lipids – organic molecules that are not soluble in water – and associated proteins. Biological membranes are selectively permeable – not all molecules can pass through the membrane. For more information see Structure of plasma membranes (British Broadcasting Corporation, UK) and Cell membranes (Kimball's Biology Pages, USA).
Nanoscience – working small, thinking big
Making every drop count
Probing past and future materials with neutrons

merozoite. A cell formed by asexual reproduction in the life cycle of plasmodium. Merozoites disperse and infect additional red blood cells within the host.
Malaria – a growing threat

mesenchymal stem cell. A type of adult stem cell found in bone marrow that gives rise to a number of different kinds of cells (eg, bone cells and fat cells). They are also known as bone marrow stromal cells. For more information see The latest research on bone marrow stem cells (Stem Cells Information Center, American Federation for Aging Research).
Stem cells – gateway to 21st centurymedicine

messenger RNA. RNA molecule that is transcribed from DNA and is used to direct the synthesis of a protein.
Biology meets industry – genomics, proteomics, phenomics
Epigenetics – beyond genes

metabolic pathways. A group or series of chemical reactions occurring within a cell, catalysed by enzymes. Pathways can breakdown compounds to yield energy, or involve the step by step modification of an initial compound to create a new product.
A quiet revolution – the science of complex systems

metal alloys. Metal mixtures with greater strength, hardness or malleability than their component metals. The ratio of each component determines the properties of the alloy. Modern alloys may be created by adding just a few per cent of another metal.
It's an advanced material world

metal hydrides. Compounds in which hydrogen is bonded chemically to a metal or metalloid (eg. boron or silicon).
The quest to make hydrogen the fuel of the future

metal-organic frameworks (MOFs). Compounds consisting of metal ions associated with organic (carbon-containing) molecules that form three dimensional porous structures. The pores allow storage of gases such as hydrogen by adsorption.
The quest to make hydrogen the fuel of the future

metastasis. The movement of cancer cells from one location to another part of the body, usually via the blood or lymphatic system.
Cancer immunotherapy – redefining vaccines

metathesis. A chemical reaction between two compounds in which parts of each are interchanged to form two new compounds (AB+CD→AD+CB). In organic chemistry metathesis can involve the breaking and making of double bonds between carbon atoms in such a way that groups from two molecules can change place. A catalyst is used to break the double bonds.
Clean speed ahead with catalysts

meteorite. A fragment of an asteroid or a planet that has been broken off by a collision and eventually falls on the Earth. It consists of solid matter which survives the descent and lands on the Earth's surface.
Calculating the threat of tsunami
Life on Mars?

methane hydrate. (also called methane clathrate). A substance in which methane is trapped inside a ‘cage’ of ice crystals. Methane hydrates form under conditions of low temperature and high pressure in deep oceanic sediments, where methane is produced by anaerobic microorganisms.
Excuse me! The problem with methane gas

methanogens. Anaerobic microorganisms that use simple organic compounds for energy, producing methane as a by-product. They occur in a range of anaerobic environments including the digestive systems of animals (particularly ruminants and termites) as well as in wetlands, marine sediments and hot springs.
Excuse me! The problem with methane gas

methanotrophs. Microorganisms that use methane for carbon and energy (and so remove methane from the environment). Methanotrophs occur in both aerobic and anaerobic conditions. They are mostly found in soils but also occur in a range of environments associated with methane such as landfill, marshes, rice paddies and the ocean.
Excuse me! The problem with methane gas

microchip. This is a very small computer in the form of a silicon chip. It is normally put together with other items to produce a finished piece of equipment. For more information see Jack St. Clair Kilby – inventor of the microchip (Massachusetts Institute of Technology, USA).
Putting a finger on it – the loops and whorls of biometrics

microfiltration. A membrane filtration process which removes contaminants from a liquid by passage through a microporous membrane. The pore size of a typical microfiltration membrane ranges from 0.1 to 10 micrometres. Microfiltration can remove many pathogens from water including Giardia, Cryptosporidium and large bacteria.
Making every drop count

micronutrient. A chemical element that is essential for plants to grow and reproduce but is only needed in very small amounts. There are seven micronutrients: iron, chlorine, copper, manganese, zinc, molybdenum, and boron.
The Southern Ocean and global climate

microserver. A self-contained computer system that can be integrated into a remote network with limited support. A micro-server can receive, process and forward information (eg, from sensor nodes).
A sense of things to come – smart sensors and the environment

microwaves. The highest frequency radio waves, with wavelengths between about 1 millimetre and 30 centimetres and frequencies between about 300 gigahertz and 300 megahertz. Microwaves are a type of electromagnetic radiation.
Synchrotrons – making the light fantastic
Thinking ahead – fusion energy for the 21st century?

mineral. A naturally occurring, inorganic substance. It can be in the form of a chemical element or a compound which has a distinctive chemical composition and therefore predictable chemical properties. Examples of minerals are bauxite, diamond, gold, tin, and salt.
Looking for clues to our mineral wealth

model. Solving complex problems associated with real situations is often made easier by setting up a model of the situation – a mathematical description of the problem. To set up a model, a problem is simplified and only those aspects that can be represented mathematically are included.

After the problem is solved mathematically, tentative solutions are translated back to the real situation, as possible real solutions. At this stage the inadequacy of the simple model may be revealed, and some parts of the process may need to be changed. More information on models and modelling can be found at What is modelling? (Australian Academy of Science).
When the numbers just don't add up
Predicting natural events
A quiet revolution – the science of complex systems

modem. Modulator/demodulator. A device connected between a computer and a telephone line. It consists of a modulator that converts digital computer signals into audio signals for transmission over the telephone line and a corresponding demodulator to convert the incoming audio signals into digital form.
Communicating with light – fibre optics

molecular phylogenetics. The study of molecular structures to establish the evolutionary relationships of organisms.
Discovering Australia's evolutionary past

molecule. The smallest unit of a chemical compound that can exist. It consists of two or more atoms held together by chemical bonds. Molecules can vary greatly in size and complexity.
Nanoscience – working small, thinking big
Nanotechnology – taking it to the people

moles. Areas of pigmentation, darker than the surrounding skin, and often raised. Harmless moles are usually less than about 5 millimetres across and have well-defined edges. A change to a mole or the appearance of a new one could indicate cancer. The number of moles on a person seems to be an indication of their exposure to the sun.
Sun and skin – a dangerous combination

monoclonal antibodies (mAbs). Artificially created, identical antibodies that can be used to treat disease. mAbs will only bind to one antigen. They are created by fusing antibody-producing B-lymphocytes with immortal cancer cells.
Cancer immunotherapy – redefining vaccines

monocotyledon. One of the two classes of flowering plants. Characterised by: a single seed leaf in the embryo; usually parallel veins in the leaves; flower parts in multiples of three.
More food, cleaner food – gene technology and plants

monoculture. The cultivation of a single crop, usually on a large area of land and on a commercial trading basis.
Feeding the future – sustainable agriculture

monomer. A molecule that can join with other molecules to form a large molecule called a polymer. A monomer is the smallest repeating unit in a polymer chain.
Making packaging greener – biodegradable plastics
083 – Chemicals in cosmetics

Montreal Protocol. An intergovernmental document signed by many countries in 1987 (and regularly revised) which established restrictions for the manufacture and use of ozone-depleting substances in an international effort to reduce ozone depletion. The text of the Protocol with the 1990 and 1992 amendments is available.
Earth's sunscreen – the ozone layer
Enhanced greenhouse effect – a hot international topic

Moore's Law. Refers to the advance in computing power per unit cost. Moore's law is based on the observation that the number of transistors on a computer chip, which is a rough measure of computer processing power, doubles every 18 months. A graph plotting the number of transistors on a chip versus time on a log scale is a straight line. The graph plotting transistor size versus time is also a straight line.
Thinking ahead – fusion energy for the 21st century?

moving averages. See Moving averages (Chart School, StockCharts.com, USA).
Stock markets – putting your money where your math is

morphology. A branch of biology that deals with the shape and form of organisms.
Discovering Australia's evolutionary past

mutagen. Any agent (such as a chemical substance or radiation) that induces mutations by permanently altering the genes or chromosomes.
Earth's sunscreen – the ozone layer
Sun and skin – a dangerous combination

mutation. A change in the DNA sequence of a gene that may be harmful or beneficial. It is the only process that actually leads to new forms of a gene, and it is the ultimate source of all variation.
Epigenetics – beyond genes
Cancer immunotherapy – redefining vaccines

myxomatosis. A disease in rabbits caused by the myxoma virus, transmitted by mosquitoes and fleas.
A plague on the pest – rabbit calicivirus disease and biological control

myxoma virus. (Also referred to as myxomatosis virus.) The virus that causes myxomatosis in rabbits.
A plague on the pest – rabbit calicivirus disease and biological control

N

nano-engineered. Constructed at the atomic or molecular level, generally at 100 nanometres or smaller. One nanometre is equal to one-billionth of a metre.
A sense of things to come – smart sensors and the environment

nanometre (nm). One-millionth of a millimetre (or one-billionth of a metre). This is the scale at which we measure atoms and the molecules they make. For example, ten hydrogen atoms laid side by side measure a nanometre across and a pin head is around a million nanometres wide. The 'machines' inside our cells and the molecular constructions they put together are measured in nanometres.
Nanotechnology – taking it to the people

nanopowders. Nano-sized particles exhibit a range of physical, chemical and biological properties that are quite different to bulk materials of the same substance. Industry is now making use of these changed properties to enhance the functionality of many products.
Nanotechnology – taking it to the people

nanotubes. Extremely small tubes made from pure carbon. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland).
Buckyballs – a new sphere of science
Which way ahead for hydrogen cars?
Nanoscience – working small, thinking big
Nanotechnology – taking it to the people

nanotubes. Extremely small tubes that can be made from pure carbon. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland).
The quest to make hydrogen the fuel of the future

national measurement system. Australia's national measurement system is coordinated by The National Measurement Institute. The NMI commenced on 1 July 2004 and is responsible for establishing and maintaining Australia's units and standards of measurement. NMI has been formed from the National Measurement Laboratory (CSIRO) the National Standards Commission and the Australian Government Analytical Laboratories.
A fair cop! Accurate breath analysis and speed detection

near, mid and far infrared. Infrared radiation is often subdivided into three regions – near, mid and far. Near infrared includes shorter wavelengths of infrared radiation, closer to visible light; far infrared includes longer wavelengths of infrared radiation, closer to microwave radiation. For more information see Near, mid and far infrared (Infrared Processing and Analysis Center, USA)
Astronomy in the deep freeze

neoprene. The DuPont name for a synthetic rubber fabric made from polymers of chloroprene. While it can only stretch a little, it is very strong. Because of its durability, neoprene is used for many industrial and commercial applications.
It's an advanced material world

neural network. A statistical analysis procedure based on models of nervous system learning in animals. Neural networks have the ability to ‘learn’ from a collection of examples to discover patterns and trends. These data-mining techniques can be used in forecasting or predicting. For more information see An introduction to neural networks (University of Stirling, UK).
Good prospects ahead for data mining

neuraminidase. An enzyme which forms a mushroom-shaped projection on the surface of an influenza virus particle. The enzyme assists in the release of newly-formed virus particles from the surface of an infected cell.
Bird flu – the pandemic clock is ticking

neurotransmitter. A chemical substance, given off by the terminals of a nerve cell or nerve fibre, which affects the next nerve cell or fibre in the chain, thus allowing a message to be passed between different links in the chain. It is the arrival of the electrical impulse at the end of the nerve fibre that causes the release of a neurotransmitter into the small gap (called the synapse) between nerve cells. The neurotransmitter travels across the synapse and excites or inhibits the next nerve cell in the chain.
Cochlear implants – wiring for sound
Getting our heads around the brain
Alcohol and cars – a volatile mix
Bitumen battles – the phenomenon of road rage

neutron. A particle having no charge that is a constituent of an atom. It has a mass similar to a proton.
Synchrotrons – making the light fantastic
Thinking ahead – fusion energy for the 21st century?
Probing past and future materials with neutrons

neutron star. A middle-sized star that has used up its nuclear fuel so no longer has an energy source. This causes the star to undergo gravitational collapse. Neutron stars have an extremely high density; a teaspoon of their matter would weigh several million tonnes. Pulsars are believed to be neutron stars.
Simply astronomical – the Square Kilometre Array

newton. The SI unit of force. One newton gives an acceleration of 1 metre per second per second to a mass of 1 kilogram. The weight you feel when you hold an average size apple in your hand is about one newton (mass is about 0.1 kilogram and gravitational acceleration of about 10 metres per second per second). It is named after Sir Isaac Newton.
Measurement in sport – the long and the short of it
Fatal impact – the physics of speeding cars

nitrogen cycle. The continuous natural cycle by which nitrogen passes from the atmosphere to soil to organisms and back to the atmosphere.
Feeding the future – sustainable agriculture

nitrogen fixation. The process of producing nitrogen compounds by combining nitrogen from the air with other substances. The only organisms that can use nitrogen gas to make organic molecules are a few kinds of bacteria. Most nitrogen-fixing bacteria live in the soil or water, but some species live in nodules on the roots of legumes such as lucerne, peas, beans and clovers.
Feeding the future – sustainable agriculture

nitrogen oxides. Chemical formula NO_x. This covers the gases nitric oxide (chemical formula NO) and nitrogen dioxide (chemical formula NO₂). Both can be toxic but nitrogen dioxide is considered to be of most concern for asthmatics. The main source of the gases in urban areas are motor vehicle exhaust and gas cookers and kerosene heaters indoors. The brown haze sometimes seen over cities is mainly nitrogen oxides. These gases are also partly responsible for the generation of ozone, when acted upon by sunlight in the presence of other chemicals. Although air pollution can cause irritating symptoms and increased asthma symptoms in some people, it is unlikely to be an important cause of asthma in Australia.
The rise and rise of asthma
Local air pollution begins at home

node. In computing a node is a network junction or connection point. In intelligent sensor networks each sensor can therefore be considered as a node in the network.
A sense of things to come – smart sensors and the environment

non-linear. For non-linear systems, a small perturbation may cause a large effect, a proportional effect, or even no effect at all – the behaviour of the system is not simply the sum of its parts. In linear systems, effect is directly proportional to the cause. Many systems are best represented by non-linear equations that are difficult to solve, but can give rise to interesting phenomena.
A quiet revolution – the science of complex systems

non-renewable energy. Used to describe energy sources that exist in a limited amount on Earth. Thus all available material could eventually be completely used up. Coal, oil and gas (see fossil fuels) are considered as non-renewable energy sources because the rate of their formation is so slow on human timescales that they we are using them without them being replaced. Uranium (used in nuclear power) is also non-renewable, although its reserves are very large compared to its rate of use. Compare renewable energy.
Harnessing direct solar energy – a progress report

normal prion protein. Special proteins that can change shape and be stable in the new form. Most proteins fold into a particular shape that allows them to perform their function, and if they don't fold into the correct shape they get degraded and the body gets rid of them.
Prions – morphing agents of disease

nuclear fission. Also referred to as atomic fission. The process by which large nuclei are split into two parts, by bombarding them with neutrons, in order to release large amounts of energy.
Prospect or suspect – uranium mining in Australia
Thinking ahead – fusion energy for the 21st century?
Probing past and future materials with neutrons

nuclear magnetic resonance (NMR) spectroscopy. Nuclear magnetic resonance (NMR) spectroscopy provides information on the position of specific atoms within a molecule by using the magnetic properties of nuclei. For more information see Nuclear Magnetic Resonance Spectroscopy (University of Calgary, Canada).
Nanoscience – working small, thinking big

nucleic acid. A large molecule made up of a sequence of phosphorylated nitrogen-containing bases. DNA and RNA are both nucleic acids.
Kissing the Epstein-Barr virus goodbye?
Bird flu – the pandemic clock is ticking

nutrient agar plate. A sterile, enclosed dish with a layer of a jelly-like substance containing complete food requirements for growth of bacteria, other small organisms or cells. If the bacteria are well-spaced when they are introduced to the plate, each bacterium will produce a colony of bacteria.
More food, cleaner food – gene technology and plants
Singing the praises of colony stimulating factors

O

occlusion. The act of closing, shutting or stopping up. In cosmetics this usually refers to a shield or film that is spread onto the skin to slow or prevent moisture evaporation. This shield or film is usually made up of materials, such as oils and waxes that cannot be penetrated by water.
Putting on a good face – the chemistry of cosmetics

ocean acidification. The lowering of the pH of oceans due to increasing levels of carbon dioxide. Ocean acidification affects the growth, structure and health of certain types of microscopic algae (phytoplankton), corals and other marine organisms with calcium carbonate skeletal structures. For more information see Acid test for the seas (Nova: Science in the news).
Science for sustainable reefs

occupational sensitisers. Chemicals or compounds that causes airway inflammation leading to asthma. These sensitisers occur in particular occupations such as carpentry (eg, western red cedar wood dust is a sensitiser) and commercial spray painting (some duco paints are sensitisers).
The rise and rise of asthma

OECD. Organisation for Economic Co-operation and Development.
Stormwater – helping to tackle Australia's water crisis

oestrogen. A female sex hormone secreted by the ovaries.
Pointing the bone at osteoporosis

on balance volume. See On Balance Volume (OBV) (Chart School, StockCharts.com, USA)
Stock markets – putting your money where your math is

oncogenes. Mutated forms of genes which produce protein products that normally enhance cell division or inhibit normal cell death. For more information see Genetics of cancer (Learner.org, USA).
Epigenetics – beyond genes

optical fibre. A glass thread that acts as a guide for lightwaves. Fibres used in telecommunications usually have a cladding of glass of a lower refractive index. In a communication system, several fibres are made up into a cable.
Communicating with light – fibre optics
Wireless but not clueless

optical telescope and radio telescope. Telescopes are instruments that are used to observe radiation from a distant object. They can produce an image of the object or enable the radiation to be analysed.

Optical telescopes are used to observe wavelengths of visible light. They make distant objects distinct and visible by producing a magnified image of the object and by collecting more light than the naked eye. There are two main types of optical telescopes: refracting telescopes use lenses and reflecting telescopes use mirrors.

Radio telescopes are used to observe longer wavelengths of radiation (radio waves), with large dishes to collect and concentrate the radiation onto antennae for detection.

For more information see It takes more than one kind of telescope to see the light (Science@NASA, USA).
Astronomy in the deep freeze

optic flow. Optic flow can be thought of as the speed at which the landscape appears to move past as you make your way through it. If objects in the landscape (say, some trees) are close by, they will appear to move quickly. If the objects are far away (say, a distant mountain range), they will appear to move slowly. A flying insect such as a bee uses optic flow to avoid obstacles by continuously trying to balance the optic flow on its left and right. If, for example, it suddenly finds an object moving quickly on its left side it will veer to the right – because that object must be close by (and it doesn't want to fly into it). Bees also use optic flow to help assess the distance they've travelled, and for landing. More information can be found at What is 'optic flow'? (Centeye, USA).
The buzz about insect robotics

options. See Derivatives – Stock Option Basics (The Investment FAQ, USA) and Options 101 (Orion Futures Group, USA).
Stock markets – putting your money where your math is

ore. A natural mineral aggregate, especially one that is mined to extract minerals.
Looking for clues to our mineral wealth
Making light of metals

organ. A specialised structural unit which serves a particular function in a body. Examples of animal organs are kidneys and hearts. Different tissues are organised into organs.
The mammal copiers – advances in cloning

organism. Any living thing, whether single celled or many celled.
A plague on the pest – rabbit calicivirus disease and biological control

osmosis. The movement of water between two solutions, separated by a membrane that permits the free passage of water but prevents or slows down the passage of dissolved substances. The water moves more rapidly from the less concentrated solution to the solution of a higher concentration than in the opposite direction. Reverse osmosis is the movement of a solvent in the opposite direction from osmosis. Pressure – usually 5 MPa - 20 MPa – is applied on the high concentration side of the membrane, forcing the solvent through a membrane to a solution of lower concentration. Pure solvent is obtained on the other side. The membranes used for reverse osmosis do not have pores: rather, separation takes place in a polymer layer of microscopic thickness. For more information see How reverse osmosis works (How Stuff Works, USA).
Making every drop count

oxidation. Any chemical reaction in which a material increases in oxidation number such as when a substance combines with oxygen. A reaction involving a loss of electrons.
Clean speed ahead with catalysts

ozone. Ozone (O₃ ) is a form of oxygen. It is a colourless gas that has a very pungent odour. It exists naturally at low concentrations in the stratosphere where it absorbs ultraviolet radiation. In the troposphere it exists naturally at extremely low concentrations. But these concentrations increase when sunlight acts on various gases, coming mainly from vehicle exhausts, and ozone then becomes a pollutant in the troposphere. Ozone is a highly corrosive gas and is poisonous to most organisms. At concentrations as low as 0.00001 per cent (or 10 parts per hundred million) it can irritate the membranes lining the nose, throat and airways and can trigger or exacerbate asthma attacks.
Earth's sunscreen – the ozone layer
The rise and rise of asthma
Sun and skin – a dangerous combination
Local air pollution begins at home

ozone-depleting substances. Any substance that causes a net loss of ozone in the stratosphere. Such substances must be sufficiently stable to survive the time needed to mix into the stratosphere. Common ozone-depleting substances are the CFCs (there are more than one hundred different types), the HCFCs, carbon tetrachloride and methyl chloroform – all of which contain chlorine; as well as methyl bromide and oxides of nitrogen. Some ozone-depleting substances are naturally occurring, but by the far the greatest ozone-depleting potential comes from compounds synthesised and/or released as a result of human activity.
Earth's sunscreen – the ozone layer

ozone formation and destruction. Ozone is formed when ultraviolet radiation causes oxygen molecules (O₂ ) in the upper layers of the atmosphere to split apart. If a freed oxygen atom (O) bumps into an oxygen molecule (O₂ ), the three oxygen atoms re-form as ozone (O₃ ).

Ultraviolet radiation can cause ozone to break apart, resulting in an oxygen molecule (O₂ ), and a single oxygen atom that is highly reactive. The oxygen molecule is quickly converted back to ozone. The reactive oxygen atom can play a part in breaking down more ozone molecules if ozone-depleting substances are present.
Earth's sunscreen – the ozone layer

ozone 'hole'. The ozone 'hole' does not refer to a complete absence of ozone molecules but rather a general decrease in the number of ozone molecules scattered throughout a band of the stratosphere above certain regions of the Earth. The phenomenon is more like a carpet thinning.
Earth's sunscreen – the ozone layer

P

Pacific Rim. A region which includes countries bordering the Pacific Ocean.
Discovering Australia's evolutionary past

palaeontologists. Scientists who study prehistoric lifeforms by examining plant and animal fossils.
Discovering Australia's evolutionary past

pandemic. The worldwide outbreak of a disease.
Bird flu – the pandemic clock is ticking

parallel processing. The simultaneous processing of a task by two or more computer systems; also referred to as parallel computing.
Quantum computers – why would you want one?

parasitaemia. The presence of parasites in the blood.
Malaria – a growing threat

parasite. An organism that lives on or in an organism of a different species (the host) and gains some advantage at the host's expense.
A plague on the pest – rabbit calicivirus disease and biological control
Malaria – a growing threat
Hydatids – when a dog is not man's best friend

parasympathetic and sympathetic nervous systems. Divisions of the autonomic nervous system. When parasympathetic and sympathetic nerves innervate the same organ, they often have opposite effects. In general, the parasympathetic division acts to conserve energy (eg, stimulates digestion, slows the heart). The sympathetic division increases energy use and prepares the body for action (eg, accelerates the heart, increases metabolic rate).
Bitumen battles – the phenomenon of road rage

parent rock. The original rock from which a soil has come. For example, sandstones are often the parent rocks for sandy soils. Except where there is extensive weathering, the composition of the mineral fraction of the soil generally indicates the nature of the parent rock underneath. Layers of soil and subsoil lie on top of the bedrock.
Monitoring the white death – soil salinity
Salinity – the awakening monster from the deep

parliament. A political assembly of the representatives of a nation.
Can we count on your vote?

particles. Very small pieces of solid or liquid matter. Particles of dust, sea salt, and material from volcanic eruptions occur naturally in the atmosphere. Sulfate particles are also produced naturally from gases emitted by marine organisms. Industry and motor vehicles add significantly to the concentration of particles in the atmosphere – high concentrations are found in big cities and industrial areas. These particles remain airborne for long periods, lowering visibility. The brown haze which is often seen over large cities in autumn, winter and spring is due mainly to particles.

Particles in the air can cause breathing difficulties and worsen respiratory diseases. Some particles contain cancer-producing materials.
Local air pollution begins at home

parts per million. This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Therefore 500,000 ppm is the same as 50 per cent, because 500,000 is half of a million. The concentration of oxygen in unpolluted fresh water is about 8 ppm – only 8 parts of oxygen for every 1 million parts of other substances.

More information on parts per million can be found at the following site:

• How much is a part per million? (Extension Toxicology Network, USA)

Cleaner production – a solution to pollution?
Thinking ahead – fusion energy for the 21st century?

parts per million (ppm). This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Therefore 500,000 ppm is the same as 50 per cent, because 500,000 is half of a million.
Acid test for the seas

pascal (Pa). The SI unit of pressure equivalent to one newton acting uniformly over an area of one square metre (newton per metre squared).
Sounding out the secrets of the sea

passive solar heating. The use of the sun to heat buildings. Careful design and positioning of buildings can ensure that sunlight in the winter months will warm them by day, with much of the warmth remaining during the night. Summer sunlight is usually kept out. This does not involve the conversion or harnessing of solar energy.
Harnessing direct solar energy – a progress report

patch test. Test used to identify allergies due to chemicals coming in contact with skin. Individual chemicals are applied separately to the skin and then the skin is observed for reactions over a few days. For more information see Patch testing (dermatology.co.uk).
Putting on a good face – the chemistry of cosmetics

pathogen. An organism capable of causing a disease.
More food, cleaner food – gene technology and plants
Malaria – a growing threat
When bugs have you on the run
Integrated pest management – the good, the bad and the genetically modified
Weeds – the real alien invaders

PE ratio. See Analysis – Price-Earnings (P/E) ratio (The Investment FAQ, USA).
Stock markets – putting your money where your math is

peptide. A molecule consisting of a short chain of amino acids. Longer chains of amino acids are called proteins.
Kissing the Epstein-Barr virus goodbye?
Who will win the drugs race?

peripheral nervous system. Consists of neurons connecting the central nervous system (the brain and the spinal cord) to the rest of the body. Sensory neurons bring information to the central nervous system from sensory receptors of the body. Motor neurons carry signals from the central nervous system to organs such as muscles and glands.
Bitumen battles – the phenomenon of road rage

permafrost. Permanently frozen ground, as occurs in the polar regions.
Excuse me! The problem with methane gas

pesticide treadmill. A situation in which farmers apply a pesticide to control a pest, which then develops resistance. Pest numbers increase, so more frequent applications of pesticide are needed for control. Finally the pesticide performs so poorly that farmers introduce a new pesticide. Over time the cycle (treadmill) is repeated with the new pesticide.
Feeding the future – sustainable agriculture

pH. The pH scale is used to measure the strength of acids and bases (or alkalis). The acid strength in the human stomach is about pH 2. Alkalis such as caustic soda and basic household cleaners have a pH of about 12 to 14. Neutral is pH 7, (ie, neither acidic or alkaline). The scale is logarithmic, so pH 4 is ten times as acidic as pH 5 and pH 2 is ten times as acidic as pH 3, and so on. For more information see About soil pH (National Aeronautics and Space Administration, USA).
When bugs have you on the run
Feeding the future – sustainable agriculture
Putting on a good face – the chemistry of cosmetics

pH. The pH scale is used to measure the strength of acids and bases (or alkalis). The acid strength in the human stomach is about pH 2. Alkalis such as caustic soda and basic household cleaners have a pH of about 12 to 14. Neutral is pH 7, (ie, neither acidic or alkaline). The scale is logarithmic, so pH 4 is ten times as acidic as pH 5 and pH 2 is ten times as acidic as pH 3, and so on.
Acid test for the seas

phagocyte. A type of white blood cell that can engulf and destroy foreign organisms, cells and particles. Phagocytes are an important part of the immune system.
Malaria – a growing threat

phenotype. The observable characteristics of an individual. The expression of these characteristics results from the interaction of genetic and environmental factors.
Biology meets industry – genomics, proteomics, phenomics

photoelectrochemical cell. Light (eg. solar) cells that use semiconductors to capture light energy and convert it into electrical energy. The electrical energy is then used directly to produce hydrogen in a process similar to the electrolysis of water.
The quest to make hydrogen the fuel of the future

photon. A photon is the smallest unit of light energy.
A fair cop! Accurate breath analysis and speed detection
Quantum computers – why would you want one?

photoreceptor. A light-sensitive cell.
Communicating with light – fibre optics

photosynthesis. The biochemical process in which green plants (and some microorganisms) use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as:

CO₂ + H₂O + energy® [CH₂O] + O₂

Toxic algal blooms – a sign of rivers under stress
Biomass – the growing energy resource
Generating new ideas for meeting future energy needs
Carbon currency – the credits and debits of carbon emissions trading
Making packaging greener – biodegradable plastics
Coral bleaching – will global warming kill the reefs?
Impact of global warming on biodiversity

photosynthesis. The process in which green plants and some other organisms such as algae use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as:

CO₂ + H₂O + energy ® [CH₂O] + O₂ The quest to make hydrogen the fuel of the future

photosynthesis. The biochemical process in which some microorganisms use energy from light to synthesise carbohydrates from carbon dioxide and water. Photosynthesis can be shown as:

CO₂ + H₂O + energy® [CH₂O] + O₂
Acid test for the seas

photovoltaic (PV) cells. Also known as solar cells. A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. (Electrons are negatively charged particles that orbit the nuclei of atoms.) The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical energy.
Harnessing direct solar energy – a progress report
Generating new ideas for meeting future energy needs
Which way ahead for hydrogen cars?

physical map. A map showing the location of sites (loci) on a chromosome.
The Human Genome Project – discovering the human blueprint

phytoplankton. Plankton that possess plant-like characteristics.
Acid test for the seas
Science for sustainable reefs

phytoplankton. Microscopic, photosynthetic algae that live in water. Plant-like plankton.
Capturing the greenhouse gang

placebo. An imitation of a medical treatment. This can be an inactive substance (eg, a sugar pill) or some other form of treatment which simulates a medical treatment, but should have no physiological effect. A placebo is given to a person, often as an experimental control, to enable comparison with the effects of a real drug or treatment.
Who will win the drugs race?

placenta. A temporary organ that develops in the uterus during pregnancy. It provides nutrients for the fetus and eliminates its waste products.
Stem cells – gateway to 21st century medicine

plankton. Microscopic plants and animals that live near the surface of oceans and lakes.
Coral bleaching – will global warming kill the reefs?

plankton. Free-floating, mostly microscopic, aquatic organisms. Plankton can be divided into phytoplankton (plants) and zooplankton (animals). For more information see What is plankton? (Australian Museum Online).
Carbon currency – the credits and debits of carbon emissions trading

plasmid. A small, circular DNA molecule. Bacteria can have plasmids in addition to the DNA of the main chromosome. Foreign DNA can be added to plasmids. The modified plasmid then transports the DNA into a new cell.
More food, cleaner food – gene technology and plants
Kissing the Epstein-Barr virus goodbye?

plastics. Solid materials consisting of organic polymers. More information can be found at How is plastic made? (Plastics Resource, USA).
Putting it together – the science and technology of composite materials

plate tectonics. The theory that the Earth's surface is made up of huge plates that have moved very slowly during geological history, and continue to move, thus changing the position of continent and oceans. The plates are about 100 kilometres thick and move at a rate of about 1-12 centimetres per year. (See also continental drift.)
Looking for clues to our mineral wealth
Generating new ideas for meeting future energy needs
Discovering Australia's evolutionary past

pluripotent stem cell. A stem cell able to give rise to almost all cell types in the body. There are also two other types of stem cell: totipotent and multipotent. A totipotent cell has the ability to give rise to all cell types, while multipotent cells can only differentiate into a limited range of cell types. For more information see Saving Superman: A look into stem cell research (National Center for Case Study Teaching in Science, USA).
Stem cells – gateway to 21st century medicine

polarity. Describes a situation in which there are opposing physical properties at different points in an object or system. When this refers to magnetic poles, the two opposite poles are called ‘North’ and ‘South’; when it refers to electric charges, the two opposite properties are called positive and negative. Unlike poles (and charges) attract; like poles (and charges) repel.
Looking down the track at very fast trains

polar stratospheric clouds (PSCs). Long faint clouds which form in the stratosphere only when the temperature falls below about -80°C. They are common above the poles in winter. These clouds appear to play a role in the depletion of stratospheric ozone. The ice particles in the cloud provide surfaces on which a reaction takes place to release free chlorine. The chlorine then reacts with ozone to form chlorine monoxide and oxygen.
Earth's sunscreen – the ozone layer

pollen. The male sex cells of seed plants that carries the gametes to fertilise female eggs.
Weeds – the real alien invaders

polycyclic aromatic hydrocarbon (PAH). An organic compound containing only hydrogen and carbon. The atoms are organised into a number of stable, unsaturated ring structures, like benzene. The main sources of PAHs on Earth are vehicle exhaust and smoke from burning fossil fuels.
Life on Mars?

polyhydroxyalkanoate (PHA). A biodegradable polymer produced by bacteria that has the qualities of plastic. At one extreme, PHAs share properties with polypropylene, and at the other end of the range, they are similar to natural rubber. For more information see Material: PHAs – polyhydroxyalkanoates (Design inSite, Denmark).
Making packaging greener – biodegradable plastics

polylactide (PLA). A biodegradable polymer derived from lactic acid. Because this polymer is broken down in our bodies, it has biomedical applications (eg, sutures). For more information see Material: PLA – polyactide (Design inSite, Denmark).
Making packaging greener – biodegradable plastics

polymer. Polymers are large molecules that are made up of many units (monomers) linked together in a chain. There are naturally occurring polymers (eg, starch and DNA) and synthetic polymers (eg, nylon and silicone). More information can be found at The basics – polymer definition and properties (Plastic Resource, USA), Introduction to polymers (Case Western Reserve University, USA) and History of polymers and plastics for teachers (Hands On Plastics, American Plastics Council).
Putting it together – the science and technology of composite materials
Making packaging greener – biodegradable plastics
Putting on a good face – the chemistry of cosmetics
It's an advanced material world
Probing past and future materials with neutrons

polymer. Large molecules consisting of repeating units connected by chemical bonds. Polymers can be both natural (proteins, cellulose) and synthetic (nylon).
Clean speed ahead with catalysts

polymerase chain reaction. A technique for amplifying or making multiple copies of minute amounts of specific fragments of DNA. Polymerase chain reaction rapidly amplifies a single DNA molecule into many billions of identical molecules.
More food, cleaner food – gene technology and plants

polymers of intrinsic microporosity (PIMs). Are organic polymers that are porous to certain substances and not to others, so they can filter out target molecules. They are useful in industrial processing, medical technologies and in the laboratory, and can supply clean drinking water.
It's an advanced material world

polymorphic. Literally meaning having more than one form. In terms of genes it means that there are several variants (alleles) of a particular gene that occur simultaneously in a population.
Malaria – a growing threat

polysaccharide. A carbohydrate made up of a long chain of simple sugar molecules joined together. Starch and cellulose are examples of polysaccharides.
Putting on a good face – the chemistry of cosmetics

population. All the organisms of one species that inhabit a given area.
A plague on the pest – rabbit calicivirus disease and biological control

potable. Water that is fit for drinking purposes.
Making every drop count

potential energy andkinetic energy. Potential energy is stored or supressed energy. For example, the wound-up spring of a toy has potential energy. Kinetic energy is the energy associated with a moving object (energy of motion). In the example of the toy, potential energy is converted into kinetic energy when the toy is set running.

For more information see Energy basics (Box 3 of Nova topic, Wind power gathers speed).
Generating new ideas for meeting future energy needs

powder technology. (powder metallurgy). The production of metal as a powder which is then used to form shaped products. The powdered metal is usually placed in a mould, compacted and heated (sintered) to make the powder particles bond together.
Making light of metals

prion. A small proteinaceous infectious particle which resists inactivation by procedures that modify nucleic acid. Most researchers think that prions are the cause of several diseases including scrapie in sheep, bovine spongiform encephalopathy in cattle and kuru and Creutzfeldt-Jakob disease in humans
Prions – morphing agents of disease

prokaryotic. Describes those cells, or organisms, that do not have their genetic material enclosed within a nucleus. Bacteria and archaea are prokaryotic.
Life on Mars?

promoter. The DNA sequence adjacent to the coding sequence of a gene, which interacts with inducers or repressors and RNA polymerase to determine whether that gene is active or not.
Epigenetics – beyond genes

prophylactic. A medical procedure or practice that prevents or protects against a disease or condition (eg, vaccines, antibiotics, drugs).
Bird flu – the pandemic clock is ticking

Proteaceae. An ancient family of flowering plants found mostly in the southern hemisphere.
Discovering Australia's evolutionary past

protease inhibitors. Molecules that block the function of enzymes that degrade proteins. They are classified either by the type of protease they inhibit or by their mechanism of action. Protease inhibitors are used in the treatment of HIV, where they prevent the activity of a protease that makes the active form of an enzyme used to make more viral particles. For more information see Disarming a deadly virus: Proteases and their inhibitors (National Academy of Sciences, USA).
Probing past and future materials with neutrons

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).
Prions – morphing agents of disease
More food, cleaner food – gene technology and plants
Singing the praises of colony stimulating factors
The bitter-sweet taste of toxic substances
Integrated pest management – the good, the bad and the genetically modified
Who will win the drugs race?
Synchrotrons – making the light fantastic
Driver fatigue – an accident waiting to happen
Bird flu – the pandemic clock is ticking
It's an advanced material world
Epigenetics – beyond genes
Probing past and future materials with neutrons

proton. A particle with positive electric charge equal but with the opposite sign to an electron. Protons are present in the nucleus of all atoms. The proton is the same as a hydrogen ion or the nucleus of a hydrogen atom.
Clean speed ahead with catalysts

protons and neutrons. Small particles that form the nucleus of an atom. Protons have a small positive charge; neutrons have no charge.
The picture becomes clear for magnetic resonance imaging
Synchrotrons – making the light fantastic

protoscoleces. Tapeworm larvae. The scolex (plural, scoleces) is the headlike part of the tapeworm, with hooks and suckers that the animal uses to attach to the tissues of its host.
Hydatids – when a dog is not man's best friend

protozoan. A single-celled animal.
Malaria – a growing threat

pterygium. A small non-cancerous growth in the eye, arising from the outer layer of the eyeball. It is associated with long-term exposure to sunlight. Most pterygia are easily removed.
Sun and skin – a dangerous combination

public health. The aspect of medical activity directed towards improving the health of the whole community.
Bird flu – the pandemic clock is ticking

pulsar. A star that emits radiation at regular intervals. Believed to be neutron stars, pulsars emit radio signals as they rotate at very high speeds.
Simply astronomical – the Square Kilometre Array

pultrusion. A continuous moulding process that mechanically aligns long strands of reinforcements for a composite material then passes them through a bath of thermosetting resin. The coated strands are then assembled by a mechanical guide before the curing process. More information can be found at The pultrusion process (About Composite Materials, USA).
Putting it together – the science and technology of composite materials

pyrolysis. A process which involves heating biomass to drive off the volatile matter, leaving behind the black residue we know as charcoal. More sophisticated pyrolysis techniques have been developed recently to collect volatiles – gaseous compounds – that are otherwise lost to the system. The collected volatiles produce a gas rich in hydrogen and carbon monoxide.
Generating new ideas for meeting future energy needs

Q

quantum decoherence. The process that takes place when a quantum system interacts with its environment.
Quantum computers – why would you want one?

quantum error correction. A method used in quantum computing to minimise the impacts of quantum decoherence and other quantum noise.
Quantum computers – why would you want one?

quantum superposition. A phenomenon where an object exists in more than one state simultaneously.
Quantum computers – why would you want one?

quasar. An abbreviation for quasi-stellar due to the resemblance of quasars to stars. Quasars are extremely distant, bright objects from the early universe. They are thought to be the cores of distant galaxies.
Simply astronomical – the Square Kilometre Array

qubit. A unit of information in quantum computing.
Quantum computers – why would you want one?

quinine. A bitter-tasting drug obtained from the bark of the cinchona tree. This plant is related to coffee and gardenia. Quinine has been used in the treatment of malaria.
Malaria – a growing threat

quota. The prescribed number of votes needed to win an election. In the Australian Senate, the quota is dependent upon the number of senators being elected. For example, the quota needed when there are two senators being elected is one vote more than one-third of all votes, and the quota needed when there are twelve senators being elected is one vote more than one-thirteenth of all votes.
Can we count on your vote?

R

radar. The use of reflected radio waves to determine the location of an object and its speed if it is moving. It is an acronym derived from radio detecting and ranging. For more information see How radar works (How Stuff Works, USA).
The ups and downs of Australian air traffic control
A fair cop! Accurate breath analysis and speed detection

radiative forcing. A measure of the effect of a climatic factor (eg, greenhouse gases, cirrus cloud) on the balance of incoming and outgoing energy in the Earth-atmosphere system. This can be used to assess the factor's impact on climate change. Positive forcing tends to warm Earth's surface while negative forcing has a cooling effect. Forcing values are expressed in watts per square metre (Wm^-2).
Flying beyond our means – air travel and the environment

radio frequency. This is lowest of the electromagnetic radiation frequencies. Radio frequencies, or radio waves, have wavelengths ranging from less than a centimetre to as long as 100 kilometres. (See also electromagnetic radiation).

We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM (amplitude modulation), FM (frequency modulation) and CB (citizens' band) radio, television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency - at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource. For more information see How the radio spectrum works (How Stuff Works).
The ups and downs of Australian air traffic control

radiogenic. Produced by radioactive decay, eg, the heat and isotopes produced as a result of the decay of uranium in the Earth’s crust are radiogenic.
Rocking on with hot rocks geothermal energy

radioisotope. A form of an element that spontaneously disintegrates into other substances and emits small particles (radiation or radioactivity). The presence and movement of the radioisotope in the body can be detected by monitoring the emission of the small particles.
Getting our heads around the brain

radiotherapy. The use of high energy radiation to treat cancerous cells. The radiation destroys or slows the abnormal cells.
Cancer immunotherapy – redefining vaccines

radio waves. Low frequency electromagnetic radiation. Radio waves have wavelengths ranging from less than a centimetre to as long as 100 kilometres. The hertz (Hz) is the unit of frequency and means one complete oscillation per second. Many frequencies are much higher than this so other units are used (eg, 1 megahertz (1MHz) = 1,000,000Hz).

We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM radio (amplitude modulation), FM radio (frequency modulation) and CB radio (citizens' band), television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency – at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource.

The frequency of radio waves used in magnetic resonance imaging range from 1-100 megahertz, depending on the strength of the magnetic field in the scanner. This is close to the range of frequencies used for FM radio (88-108 megahertz). For more information see How the radio spectrum works (How Stuff Works, USA).
Mobile phones – communications on the go
Cochlear implants – wiring for sound
A fair cop! Accurate breath analysis and speed detection
The picture becomes clear for magnetic resonance imaging
Wireless but not clueless

Ramsar-listed wetland. A wetland listed under the Ramsar Convention – an international treaty aimed to conserve and maintain the sustainability of wetlands.
Bushfires spark extensive search for answers

rare. Used to describe species with small populations or a very restricted distribution. Rarity may be a natural characteristic of some species, but it can also come about because of various pressures, and thus be a worrying sign about the future viability of a species. A rare species is more likely to become endangered or extinct, and so must should be treated carefully in management plans.
Australia's threatened species

resilience. The ability of an ecosystem, such as a coral reef, to cope with repeated external disturbances (such as a major warming of the ocean or a large storm) without fundamentally changing. Resilience is an aspect of ecosystem dynamics that prevents phase-shifts. Ecosystems with greater biodiversity are usually more resilient to disturbances.
Science for sustainable reefs

recharge or discharge.The recharge rate is the rate at which an aquifer is replenished or topped up with water (inflow). The other important variable for groundwater management is the discharge rate, or the rate at which water is taken out of the system (outflow). In some cases aquifers can discharge naturally to rivers and springs and so the water is not being removed from the system. The two variables determine the water balance, which is part of the larger water cycle involving the journey of water as it falls from the sky, onto land or sea or aquifer, and back again.
Salinity – the awakening monster from the deep
Impact of global warming on biodiversity
The water down under

recombinant DNA. Genetically engineered DNA that is prepared in a laboratory by cutting up DNA molecules and splicing together specific DNA fragments. Usually the DNA that is combined is from more than one species. The spliced DNA can then be used to synthesise proteins. More information can be found at Speaking the language of recombinant DNA (Access Excellence, USA).
Who will win the drugs race?
Hydatids – when a dog is not man's best friend

red dwarf. A small, very faint and cool dwarf star. It is thought that red dwarfs are the most common star in the universe. For more information see A galaxy dweller's guide to planets, stars and dwarfs (Space Telescope Science Institute, USA)
Astronomy in the deep freeze

red giant star. An old star with a very large radius and a relatively low surface temperature. The colour of a star is a guide to its surface temperature – blue-white is the hottest and red is the coolest.
Buckyballs – a new sphere of science

reduction. A reaction in which an atom gains electrons. This may involve the removal of oxygen or the addition of hydrogen.
Clean speed ahead with catalysts

reflected, refracted, diffracted. All three terms refer to a change in the direction of a wave. A wave has long crests and valleys called wavefronts. The distance between successive crests is called the wavelength. The wave always travels in a direction that is at right angles (90°) to the wavefronts. A wave is reflected when it bounces off a smooth obstacle that is long compared to the wavelength. A wave is refracted when it travels from one medium to another in which its speed is different (eg, from deep water to shallow water); and it is diffracted when it passes through a small opening in, or around the edge of, a large obstacle. A wave is scattered when it bounces off a small or rough obstacle. For more information see Behaviour of waves (The Physics Classroom, USA) and Wave behavior (Alaska Tsunami, USA).
Ethnomathematics – a rich cultural diversity

reflection, scattering, absorption. Sound waves can be reflected by hard surfaces, scattered by rough surfaces, or absorbed by soft porous surfaces, in much the same way as light waves. Because the wavelength of sound ranges from centimetres to metres, smoothness must be judged on a similar scale.

When sound meets with a large surface, the sound may be absorbed or reflected depending on the nature of the surface. Hard, glossy surfaces such as glass, bricks and ceramic tiles are efficient reflectors; porous surfaces such as carpets and curtains are good absorbers. These differences are important in the design of living rooms, recording studios and concert halls.

For more information see Behavior of sound waves – reflection, refraction and diffraction (The Physics Classroom, USA).
Quiet please! Fighting noise pollution

regression. A regression relationship allows the approximate prediction of one variable from the value of one or more other variables. For example, we might be interested in the prediction of the weight of Australian women given their height. Such a relationship is commonly expressed in the form of a mathematical equation, often a straight line equation.
Good prospects ahead for data mining

rising sea levels. Increasing height of sea levels due to global warming. A warmer world will have a higher sea level because as the land and atmosphere warm, heat is transferred into the oceans. When materials are heated they expand (thermal expansion). So the heat that is transferred causes sea water to expand, which then results in a rise in sea level. In addition, water from land-based ice such as glaciers and ice sheets may enter the ocean, thus adding to the rise. For more information see Getting into hot water – global warming and rising sea levels (Nova: Science in the news).
Science for sustainable reefs

Relenza. The commercial name for an anti-influenza drug (zanamivir) that binds to and inactivates an enzyme, preventing the formation of new viral particles. For more information see CSIRO research leads to effective treatment against the flu virus (CSIRO, Australia).
Probing past and future materials with neutrons

remote sensing. The act of obtaining information about an object from a distance. Although that distance can be small or large, remote sensing usually means gathering data from some distance above the Earth's surface (eg, aerial photography and satellite remote sensing).  For more information see About remote sensing (Australian Centre for Remote Sensing, Geoscience Australia) and An introduction to remote sensing (CSIRO Mathematical and Information Sciences, Australia).
Salinity – the awakening monster from the deep

renewable energy. Used to describe energy sources that are replenished by natural processes on a sufficiently rapid time-scale so that they can be used by humans more or less indefinitely, provided the quantity taken per unit of time is not too great. Examples are animal dung, ethanol (derived from plant sugars), wood, wind, falling water and sunlight. Compare non-renewable. For more information see Renewable energy (Australian Greenhouse Office).
Harnessing direct solar energy – a progress report

resistance (biological). The ability to withstand the effects of a disease-causing organism.
A plague on the pest – rabbit calicivirus disease and biological control
Integrated pest management – the good, the bad and the genetically modified

respiration. Cellular respiration is the process by which organisms release energy from complex organic molecules, typically sugars. All living things, including plants, respire. Most use oxygen (aerobic respiration) and release carbon dioxide. The balanced chemical equation for aerobic respiration is

C₆H₁₂O₆ + 12O₂® 6CO₂ + 6H₂O + energy (ATP) In the absence of oxygen anaerobic respiration occurs, producing lactic acid or ethanol.
Carbon currency – the credits and debits of carbon emissions trading

restriction enzyme. Restriction enzyme is a shorthand way of saying restriction endonuclease. (Nuclease = an enzyme that cuts a nucleic acid; endo = cuts in the middle, not at the ends; restriction = cutting is restricted to specific sites.) Therefore it is an enzyme that cuts the DNA molecule at specific locations along its length. Each type of restriction enzyme recognises a particular base sequence of the DNA and cuts precisely at the same point each time. (For example, the restriction enzyme EcoR1 recognises the sequence GAATTC, and cuts between the G and its adjacent A. The complementary strand of DNA has the sequence CTTAAG, and here also the enzyme cuts between the A and the G.)
More food, cleaner food – gene technology and plants

retina. The light-sensitive cell layers of the inner lining of the back of the eye.
Communicating with light – fibre optics

Richter scale. A scale for measuring the magnitude or size of an earthquake. The scale relates to the energy released by an earthquake and is determined from the logarithm of the amplitudes (heights) of the seismic waves recorded at seismograph stations on the Earth's surface. For more information see The Richter magnitude scale, The severity of an earthquake, Measuring the size of an earthquake and Magnitude/intensity comparison (United States Geological Survey).
Calculating the threat of tsunami

Richter scale. A scale for measuring the magnitude or size of an earthquake. The scale relates to the energy released by an earthquake and is determined from the logarithm of the amplitudes (heights) of the seismic waves recorded at seismograph stations on the Earth's surface. See also magnitude and intensity. For more information see The severity of an earthquake, Measuring the size of an earthquake and Magnitude intensity comparison (United States Geological Survey).

The largest recorded earthquake, measuring 9.5 on the Richter scale, occurred in Chile in 1960. Seismologists have devised several other scales of measuring the magnitude of earthquakes, although the Richter scale remains the main scale used by the media to inform the public about earthquake size. For more information about the earthquake in Chile see Great Chile earthquake of May 22, 1960 (National Geophysical Data Center, USA).
Fixing the cracks in disaster mitigation

Ring of Fire.  A region around the Pacific Ocean where volcanoes and earthquakes frequently occur, corresponding to the edge of the Pacific tectonic plate. For a map see Ring of Fire (US Geological Survey).
Rocking on with hot rocks geothermal energy

RNA (ribonucleic acid). A nucleic acid similar to DNA. There are a number of types of RNA, the major ones being messenger RNA, transfer RNA and ribosomal RNA. RNA can serve as a messenger between DNA and proteins, as a structural molecule, as an enzyme and as regulators of gene expression. In some viruses RNA is the genetic material. For more information see Introduction to RNA and its functions (University of Newfoundland, Canada).
More food, cleaner food – gene technology and plants
Epigenetics – beyond genes

root mean square. The square root of the average of the squares of a set of numbers.
Sounding out the secrets of the sea

router. A device located where two or more networks connect that determines the best path for forwarding the data packets.
Wireless but not clueless

ruminant. An animal which chews regurgitated food (cud) and usually has a stomach divided into four compartments, one of which is the rumen. Partially digested food is returned from the stomach to the mouth and chewed, allowing further digestion. Ruminants include cows, sheep, goats and deer. Their digestive system allows them to digest fibrous plant material which would be indigestible to other animals.
Excuse me! The problem with methane gas

rutile. A mineral from which titanium is extracted. Rutile is black, yellow or brownish-red in colour and contains titanium dioxide.
Making light of metals

S

salinisation. The accumulation of soluble salts in soil or water so that they become unfit for their normal uses, such as growing plants or providing drinking water. The main salt is sodium chloride (common table salt) but potassium chloride and magnesium sulfate can also accumulate.
Calculating the threat of tsunami

scale-free networks. A network pattern commonly seen in living systems that has some nodes with many links, many nodes with a few links, and the remaining nodes lying somewhere in between. In this system, known as a scale-free network, there is no clear average number of links per node. Scale-free networks are resilient structures because the random removal of any particular node is unlikely to stop the network from functioning. On the other hand, if a node with many links was targeted and removed it could create a large system-wide disturbance. For more information, see Scale-Free Networks (Computerworld, USA).

In some networks the nodes are connected randomly, in others each node has a fixed number of links to adjacent nodes, giving rise to a regular pattern. But most systems observed in nature fall somewhere between these two extremes.
A quiet revolution – the science of complex systems

scanning probe microscopy. Scanning probe microscopes (SPMs) pass a needle-like probe over the surface of a molecule and record an image of that surface. Different SPMs can not only map the topography but also determine the type of atoms and their thermal and magnetic properties. Scanning tunnelling microscopes and atomic force microscopes are types of SPMs. For more information see Scanning probe microscopy (SPM) (Missouri Botanical Garden, USA).
Nanoscience – working small, thinking big

sea-ice. The sea around Antarctica begins to freeze in March and the area covered by floating sea-ice increases until September or October when it reaches a maximum of about 19 million square kilometres. This sea-ice 'blanket' affects sea temperatures and sea currents by shielding the ocean surface from the strong winds that blow in the high latitudes. Sea-ice is also important because it is white and reflects back to space most of the sun's radiation that falls on it. The presence of more sea-ice cools the earth. For more information see Sea ice (National Snow and Ice Data Center, USA).
The Southern Ocean and global climate

sedimentary. A class of rocks that are formed from sediments eg, sandstone or from precipitation of chemicals from solution eg, limestone.
Rocking on with hot rocks geothermal energy

seismic waves. Waves that transmit the energy released from movement of the Earth's crust. Primary waves (P-waves) are longitudinal waves that shake the ground in the direction of the wave. Secondary waves (S-waves) are shear waves that shake the ground perpendicular to the direction of travel. For more information see What is seismology? (Michigan Technological University, USA).
Fixing the cracks in disaster mitigation

semiconductor. Is a material that conducts electricity at a level between an insulator and a conductor. The electrical properties of semiconductors can be controlled by adding small amounts of other atoms or impurities – called doping. Transistors made from semiconductors are used in all electronics including computers, mobile phones, calculators, CD and DVD players. Some semiconductors can also be made to emit light when exposed to an electric field, including diode lasers and light emitting diodes, or LEDs. Silicon is currently the most widely used semiconductor in computer chips and other electronic components. For more information see How semiconductors work (How Stuff Works, USA).
It's an advanced material world

semiconductor wafer. A tiny complex of electronic components and their connections, produced in or on a small slice of material (like silicon). For more information see Semiconductor manufacturing: How a chip is made (Texas Instruments, USA).
Nanoscience – working small, thinking big

sensitivity. The ability of an object to detect weak signals eg, the sensitivity of a radio telescope is its ability to detect weak radio signals.
Simply astronomical – the Square Kilometre Array

sequester. To store something so that it is no longer available. Carbon sequestration involves the removal or storage of carbon dioxide so that it can't be released into the atmosphere.
Capturing the greenhouse gang

serotonin. One of the neurotransmitters found in the brain. Studies have shown that low levels of serotonin are associated with increased levels of aggression in animals.
Bitumen battles – the phenomenon of road rage

sewage. Liquid and solid waste carried in sewers.
Making every drop count

sexual reproduction. A type of reproduction that involves the union of two cells. The offspring from this type of reproduction have a unique combination of genes.
The mammal copiers – advances in cloning

shear strength. The maximum stress a material will bear when it is twisted or otherwise deformed without stretching or compression.
Fixing the cracks in disaster mitigation

siderite. Natural iron(II) carbonate, FeCO₃.
The water down under

signal transduction pathway. A series of steps by which a signal outside the cell causes a functional change inside the cell. Signal transduction pathways are important means of regulating numerous cellular functions in response to changes in the cell's chemical or physical environment.
Biology meets industry – genomics, proteomics, phenomics

simulation. A computer model of a real phenomenon or system. The system is described by a set of mathematical formulae or models in a computer program. Running the computer program shows how the system works and, by changing variables, it is possible to make predictions about how the real system will change. When there are many variables, simulation is often the only way to reasonably predict an outcome.
Virtual reality bytes – military uses of VR

skin allergy. An allergy is a hypersensitivity to substances in the environment which do not bother most people. Allergy to cosmetics usually manifests as a rash on the skin where the product has been applied. This condition is known as allergic contact dermatitis, and is often due to fragrances and preservatives in the cosmetic product. For more information see Allergic contact dermatitis (New Zealand Dermatological Society).
Putting on a good face – the chemistry of cosmetics

smart sensor. A sensor that has an inbuilt ability to sense information (eg, light, temperature, salinity), process the information and send selected information to an external receiver (including to other sensors). Also called an intelligent sensor, mote or smart dust. Smart sensors are able to detect particular conditions such as abnormal temperature and react according to programmed instructions (eg, by increasing the sampling rate).
A sense of things to come – smart sensors and the environment

smelter. An industrial plant that uses a high-temperature process to separate out a pure metal, usually in a molten form, from an ore.
The bitter-sweet taste of toxic substances
Making light of metals

smelting. A high-temperature process that separates out a pure metal, usually in a molten form, from an ore.
Cleaner production – a solution to pollution?

smooth muscle. All airways have bronchial smooth muscles in their walls. These muscles are classed as 'smooth' muscle – which means they are not under voluntary control, like the muscles of our legs and arms, but instead respond to circulating hormones and compounds released locally by damaged or inflamed tissue. Many drugs will cause changes in smooth muscle without any effects on our voluntary muscles. Smooth muscle contraction will narrow airways and can also constrict arteries and many other tubes in the body. Smooth muscle relaxation will dilate (widen) these tubes.
The rise and rise of asthma

sodium absorption ratio (SAR). The ratio of the concentration of the sodium ion concentration in the soil solution to the square root of the total divalent ion concentration. A high SAR indicates a sodic soil.
Sodicity – a dirty word in Australia

soil profile. Where soil has been cut through vertically, such as along a roadside embankment, you may see that it has various layers of different textures and shades. This is called the soil profile. The top layer, called the A horizon, contains most of the plant roots, it is where most biological activity occurs and where organic matter accumulates. Water washes clay particles down out of this horizon.

The next layer – the B horizon – is where the clay particles and soluble substances washed down from above tend to accumulate. Below that is the C horizon, or parent rock. The type of parent rock can affect the fertility and structure of the soil that develops above it.
Monitoring the white death – soil salinity
Salinity – the awakening monster from the deep

soil salinity. This characteristic of soils relates to their salt content. These salts usually involve sodium chloride, but other salts occur in some soils. Soil salinity can be measured by determining the electrical conductivity of a solution, obtained by saturating a soil sample with water (a soil 'saturation extract'). A soil is said to be slightly saline when the electrical conductivity of a soil 'saturation extract' is 4-8 deciSeimens per metre (dS/metre), moderately saline at 8-16 dS/metre, and strongly saline at more than 16 dS/m.
Sodicity – a dirty word in Australia

soil structure. Refers to the arrangement of soil particles and the pore spaces between them.

The mineral or inorganic part of soil consists of particles of different sizes. Between the soil particles are spaces, called pores. Their number and size strongly influence soil structure. Pores are important in allowing air and water to penetrate the soil. Small pores enable the soil to hold greater amounts of water; larger ones allow for faster drainage. Good soil needs many pores, varying in size with some holding air and some water. Loss of pores changes soil structure for the worse as far as plant growth is concerned.
Sodicity – a dirty word in Australia

solar cells. Convert light energy into electrical energy. Also known as photovoltaic cells. A solar cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction (often refered to as P-N junction) which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Though most widely used solar cells are made of silicon, other materials could also be used to create P-N junctions.
Nanotechnology – taking it to the people

solar collectors. Devices for capturing the sun’s energy over a large area and focussing it on a small area, thereby concentrating it. In this way it can be made to provide extremely high temperatures, used to generate steam that will expand, or to carry out a chemical reaction to produce a portable fuel such as hydrogen. Solar collectors may be curved dishes – like satellite receiving dishes – coated with reflective material, or can consist of an array of reflectors, arranged like flower petals, focussing onto a central point. Usually the dish or the individual reflectors can be steered to follow the sun across the sky.
Harnessing direct solar energy – a progress report

solar energy. Energy derived ultimately from the sun. It can be divided into direct and indirect categories. Most energy sources on Earth are forms of indirect solar energy, although we usually don’t think of them in that way. Coal, oil and natural gas derive from ancient biological material which took its energy from the sun (via plant photosynthesis) millions of years ago. All the energy in wood and foodstuffs also comes from the sun. Movement of the wind (which causes waves at sea), and the evaporation of water to form rainfall which accumulates in rivers and lakes, are also powered by the sun. Therefore, hydroelectric power and wind and wave power are forms of indirect solar energy.
Direct solar energy is what we usually mean when we speak of solar power – it is the use of sunlight for heating or generating electricity.
Harnessing direct solar energy – a progress report

solar keratoses. (Also known as sunspots.) These are harmless areas of slightly changed pigmentation, not as distinct as freckles or moles. Although not cancerous, they are a sign of skin damage by ultraviolet radiation. Actinic keratoses are more scaly growths which may develop into cancer.
Sun and skin – a dangerous combination

solstice. The time of year when the sun is furthest from the celestial equator (the projection of the Earth's equator onto the sky). The summer solstice occurs in mid-summer and the winter solstice in mid-winter. For more information see The equinoxes and solstices (National Maritime Museum, Greenwich, UK).
Calendars – keeping track of time

solvent. A substance (usually a liquid) that dissolves other substances (solutes) in it.
Clean speed ahead with catalysts

sound pressure. The pressure deviation from the ambient pressure caused by a sound wave. Sound pressure underwater is measured using a hydrophone. The unit for sound pressure is the pascal (Pa). The reference sound pressure in air is 20 micropascals (root-mean-square). In water, the reference sound pressure is 1 micropascal (root-mean-square).
Sounding out the secrets of the sea

sound pressure level (SPL). A logarithmic measure of the root mean square pressure (force/area) of a particular noise relative to a reference noise source. It is measured in decibels.
Sounding out the secrets of the sea

sound wave. A wave that is transmitted through a solid, liquid, or gas as a result of mechanical vibrations of particles in the medium. The direction of motion of the particles is parallel to the direction of propagation of the wave.
Sounding out the secrets of the sea

sources and sinks. A source is the place or compartment from which a substance comes while a sink is the place or process that takes the substance out of circulation. For example, young growing forests are a carbon sink, while the burning of fossil fuels is a carbon source.
Carbon currency – the credits and debits of carbon emissions trading

Southern Oscillation Index (SOI). A measure for monitoring the Southern Oscillation. The index is compiled by measuring the atmospheric pressure differences between Tahiti and Darwin (monthly or seasonally) and comparing the result with the mean for that time of year. The index scale ranges between about +30 and -30. A strongly negative (more negative than -10) SOI for several months indicates an El Niño event; a strongly positive (greater than +10) SOI for several months indicates a La Niña. For more information about the SOI and how it is calculated see Southern oscillation index (Bureau of Meteorology, Australia).
El Niño – riding the climate roller coaster

species. Living things of the same kind that are potentially capable of breeding and producing fertile offspring. Theoretically, plants or animals of different species cannot interbreed. However, occasionally this does not hold true.
More food, cleaner food – gene technology and plants
Australia's threatened species
Conservation genetics – molecular detectives at work
Bird flu – the pandemic clock is ticking

spectroscopy. The technique of detecting and analysing the spectrum of an object to get information on its chemical and physical nature (eg, temperature, motion). Using a spectroscope the radiation or light from an object is dispersed into its different colours or wavelengths (like a rainbow). The position of emission and absorption lines in the spectrum provides information on what chemicals are present. For example, emission at a wavelength of 21 centimetres corresponds to hydrogen. Large telescopes have spectroscopes to measure the properties of astronomical objects.
Simply astronomical – the Square Kilometre Array

spectrum. Plural spectra. The distribution of electromagnetic radiation when it is dispersed (eg, the dispersal of visible light into a rainbow). Astronomers gain different information about astronomical objects by examining their spectra from different parts of the electromagnetic spectrum (eg, visible light, radio waves, X-rays).
Simply astronomical – the Square Kilometre Array

sphincter. A ring of muscle surrounding a tubular organ or the opening to a hollow organ such as the stomach. When a sphincter muscle contracts, the organ is closed off.
Alcohol and cars – a volatile mix

spintronics. Also known as ‘spin-based electronics’, is the science of using electrons to store data. It uses the charge on an electron as well as its ‘spin’ state to store ‘qubits’ of information. Spintronics may lead to a new way of calculating called quantum computing. For more information see Spintronics (Nanotechnology Now) and Spindoctors (PC Magazine, UK).
It's an advanced material world

sporozoite. One stage of the Plasmodium life cycle. Sporozoites are formed in the mosquito and are transferred to the host where they move to the liver cells.
Malaria – a growing threat

stem cell. An undifferentiated cell which is a precursor to a number of differentiated (specialised) cell types.
The mammal copiers – advances in cloning

stick chart. A three-dimensional map of ocean patterns that was used by Marshall Islanders to teach and preserve their navigational knowledge. Each map was created by tying together midribs of coconut-palm leaves or pieces of split bamboo in patterns that represented wave and current patterns. Shells were used to indicate the position of islands in relation to the ocean currents. For more information see Traditional Marshallese Stickchart Navigation (Dirk Spennemann, Charles Sturt University, Australia).
Ethnomathematics – a rich cultural diversity

stimulant. A substance that speed up the functions of the central nervous system. For more information see Stimulants (Missouri Department of Mental Health, USA).
The dope on drug-impaired driving

stochastic oscillator. See The stochastic oscillator (The Traders' Magazine, USA).
Stock markets – putting your money where your math is

storm surge. A rise in sea-level accompanying a hurricane or other intense storm. Storm surge height is usually measured as the difference between the observed sea-level height and the normal sea-level height. The main causes of storm surge are wind and reduction in atmospheric pressure.
Warmer and sicker? Global warming and human health

stormwater. Any rain that falls on roofs or paved areas such as footpaths or roads.
Stormwater – helping to tackle Australia's water crisis

stratosphere. The layer of atmosphere that lies about 15 to 50 kilometres above the Earth's surface. In the stratosphere, the temperature rises with increasing height, which is the opposite of the situation in the lower atmosphere. Ozone occurs in minute quantities throughout the full depth of the atmosphere, but its concentration peaks within the stratosphere at an altitude of about 35 kilometres. This is referred to as the ozone layer. There is little up-and-down air movement in the stratosphere, so the ozone layer stays in position.
Earth's sunscreen – the ozone layer

stress. Force per unit area. It is measured in the same units as pressure, namely pascals (Pa). Materials typically have strengths in the megapascal (MPa) range (1 MPa = 1,000,000 Pa).
Putting it together – the science and technology of composite materials

subsonic. Movement at less than the speed of sound. Most aircraft travel at subsonic speeds.
Flying beyond our means – air travel and the environment

sulfur dioxide. Sulfur dioxide (chemical formula SO₂) is an acrid-smelling gas that even at low concentrations irritates the membranes of the nose and respiratory system. It is thought to exacerbate many respiratory diseases, including asthma. Sulfur dioxide is produced whenever sulfur-containing compounds are burnt. Its commonest source in Australia is power-stations burning coal containing slight sulfur impurities.
The rise and rise of asthma
Local air pollution begins at home

superconducting magnet. A type of electromagnet (a temporary magnet formed when an electric current is conducted through a coil of wire). In superconducting magnets, the wire is cooled to a temperature close to absolute zero. At this temperature, there is virtually no resistance to the flow of electricity through the wire. For more information see How electromagnets work (How Stuff Works, USA).
The picture becomes clear for magnetic resonance imaging
Thinking ahead – fusion energy for the 21st century?

superconductor. A substance that has no resistance to the flow of an electric current. Superconductors currently require very low temperatures to function. They can be used for energy storage, storing and retrieving digital information, medical imaging machines and friction free transport. For more information see What is superconductivity? (How Stuff Works, USA) and Superconductor information for the beginner (Superconductors.org).
Buckyballs – a new sphere of science
It's an advanced material world
Thinking ahead – fusion energy for the 21st century?
Probing past and future materials with neutrons

supercritical fluid. A substance that when placed under a certain temperature and pressure acts like both a liquid and a gas. Carbon dioxide stored underground as a supercritical fluid diffuses like a gas with a liquid-like density.
Capturing the greenhouse gang

supersonic. Movement at greater than the speed of sound. Supersonic aircraft include military aircraft and Concorde (which ceased operation in 2003). At these fast speeds, air ahead of the plane is compressed, shock waves form and drag increases. Supersonic aircraft often fly at higher altitudes where the density of air is lower to reduce drag.
Flying beyond our means – air travel and the environment

surface coil. A device that closely fits against the surface of the part of the body being imaged. It acts like a radio antenna, receiving radio signals from the patient's body.
The picture becomes clear for magnetic resonance imaging

surface tension. A property of liquid surfaces that causes the surface layer to behave like a thin elastic 'skin'. Molecules in a liquid have attractive forces that hold them together. Molecules on the surface are attracted to molecules from all sides and below, but not from above. This results in a downward and sideways pull on molecules on the surface layer. For more information see Surface tension (Georgia State University, USA).
Putting on a good face – the chemistry of cosmetics

sustainable. An activity that is capable of being maintained at a steady level without depleting natural resources or causing excess damage to an ecosystem. A sustainable yield in fisheries is achieved when the number of fish removed does not eventually cause the fish stock to collapse.
Science for sustainable reefs

symbiotic. Describes a relationship between two species that live together, to the benefit of at least one of them. Some symbiotic species are unable to live without each other. Algae (called zooxanthellae) live within corals. The zooxanthellae gain protection, access to sunlight for photosynthesis and nutrients from the nitrogen waste that the coral produces. The coral benefits from the removal of wastes and from the sugars produced by the zooxanthellae.
Science for sustainable reefs

T

T-cell. White blood cells that are important for the body's immune response to specific antigens. Killer T-cells are like soldiers who search out and destroy invading bacteria or viruses or cancer cells.
Cancer immunotherapy – redefining vaccines

tectonic plates. The Earth's surface is made up of huge tectonic plates that have moved very slowly during geological history, and continue to move, thus changing the position of continent and oceans. The plates are about 100 kilometres thick and move at a rate of about 1-12 centimetres per year. For more information see Plate tectonics (Nova: Science in the news, Australian Academy of Science).
Calculating the threat of tsunami
Fixing the cracks in disaster mitigation
Rocking on with hot rocks geothermal energy

teflon. A polymer of fluorinated ethylene with the chemical name polytetrafluoroethylene (PTFE). It was invented in 1938 and is one of the most slippery substances ever made.
It's an advanced material world

telecommunications. The communication of information over a distance by means of radio waves, optical signals or along a transmission line.
Communicating with light – fibre optics
Wireless but not clueless

tempering. A technique used by blacksmiths and in the metal processing industry that increases the hardness of metals. The metal is first heated, then cooled quickly with water or oil to form tiny metal crystals (quenching). It is then reheated to a lower temperature. This reheating prevents the metal from becoming too brittle during the heat treatment.
Making light of metals

therapeutic cloning. Medical and scientific applications of cloning technology that do not result in the production of genetically identical fetuses or babies. For more information see Therapeutic cloning for tissue repair (Australian Academy of Science).
The mammal copiers – advances in cloning

thermal conductivity. A measure of the ability of a substance to conduct heat. A potential geothermal resource is evaluated in terms of heat flow, estimated from the geothermal gradient and thermal conductivity measurements. An overlying layer of rock of low thermal conductivity (eg, sedimentary rock) helps to maintain the heat of a geothermal resource.
Rocking on with hot rocks geothermal energy

thermal expansion. Global warming causes the water in oceans and seas to expand in volume as it warms. The IPCC projects that thermal expansion will be the main component of expected sea-level rises over the 21st century.
Impact of global warming on biodiversity

threshold. The point at which a signal can be detected or is strong enough to trigger a change.
Predicting natural events

tissue. A group of specialised cells with a common structure and function. Examples of animal tissues include nervous tissue and muscle tissue. Illustrations of different tissue types can be found at Mammalian differentiated cell types, part 1 and Mammalian differentiated cell types, part 2 (Access Excellence, USA).
The mammal copiers – advances in cloning

tokamak. For more information see Tokamaks (National Space Research Institute, Brazil).
Thinking ahead – fusion energy for the 21st century?

topography. Surface features of a region (eg, mountains, valleys).
Calculating the threat of tsunami

toxins. Substances, produced by microorganisms, which affect the functioning of another organism.
Immunisation – protecting our children from disease
Kissing the Epstein-Barr virus goodbye?
Cancer immunotherapy – redefining vaccines

traction. The amount of forward thrust that a wheel can provide before it slips. It is the product of the weight bearing down on the wheel (generally 25 per cent of the vehicle weight on a level road) and the coefficient of friction, which depends on the nature of the tyre and the surface of the road. Traction helps determine the steepest road a vehicle can climb.
Death-defying designs for car safety
Bogged down in the four-wheel drive debate?

transducer. A device that converts one form of energy into another. For example, an electric jug converts electrical energy into heat energy. A transducer connected to a starter's pistol converts sound energy into electrical energy.
Measurement in sport – the long and the short of it

transect. An imaginary line drawn through an area in order to help scientists sample and monitor organisms or conditions along the line. The results obtained from samples along the line give an indication of the organisms or conditions in the entire area.
The Southern Ocean and global climate

transesterification. A process that converts animal fats or more commonly plant oils to biodiesel. The oils (or triglycerides) are reacted with an alcohol such as ethanol in the presence of a catalyst such as sodium hydroxide. This converts the triglycerides to esters (the biodiesel) and glycerol. The biodiesel produced is used in ground transport but usually cannot be used as an aviation fuel due to its high freezing point.
Flying beyond our means – air travel and the environment

transferrin. A type of protein that acts as the vehicle for transporting iron between different sites in the body.
Who will win the drugs race?

transformer. A device consisting of two coils of wire wound on a soft iron core which is used to change the voltage of an alternating current. Transformers can either increase the voltage (a step-up transformer) or decrease the voltage (a step-down transformer). TV receivers have a step-up transformer that increases the voltage enough to operate the picture tube, and also a step-down transformer to reduce the supply voltage (240 volts) to the 5 volts needed to run transistors.
Looking down the track at very fast trains

trellis-coded modulation. A coding system used for high speed, reliable data transmission over telephone lines.
Communicating with light – fibre optics

trigger. A stimulus that causes asthma symptoms or an attack. Triggers include irritants such as fumes, cigarette smoke, allergens such as house dust mite or moulds, viral respiratory tract infections, and exercise. Not every asthmatic responds to every trigger. And not every asthmatic responds to the same trigger in the same way on each exposure. Some triggers, such as allergens, can cause worsening airway inflammation.
The rise and rise of asthma

tuber. A thickened short underground stem or branch formed by some plants (eg, potatoes) as a food storage organ. Each of the 'eyes' on a potato are buds that can grow into new roots and shoots.
Making packaging greener – biodegradable plastics

tumour suppressor gene. Genes that encode proteins that normally repress cell division or enhance cell death. For more information see Genetics of cancer (Learner.org, USA).
Epigenetics – beyond genes

turbidity. A measure of the amount of suspended solids (usually fine clay or silt particles) in water. Increased turbidity reduces the penetration of light through water, reducing the growth of aquatic plants. For more information see Water quality: Turbidity (NSW Environmental Protection Authority).
Sodicity – a dirty word in Australia
Science for sustainable reefs

turbine. A device in which a stream of water or gas turns a bladed wheel, converting the kinetic energy of the fluid flow into mechanical energy available from the turbine shaft. The earliest turbines were water wheels. Now, steam turbines are driven by jets of high-temperature steam; gas turbines are driven by burning fuel vapour; and wind turbines use the power of moving air.
Fuelling the 21st century
Wind power gathers speed
Generating new ideas for meeting future energy needs
Rocking on with hot rocks geothermal energy

Turner syndrome. A condition affecting females who have only one X chromosome instead of the usual two. Ovaries do not develop normally in females with Turner syndrome. More information can be found at Turner’s Syndrome Society of the United States.
Pointing the bone at osteoporosis

U

ultrafiltration. Is a type of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane allowing only the passage of small molecules. Ultrafiltration only differs from reverse osmosis and microfiltration in the size of the molecules it retains.
Making every drop count

ultrasound. The use of sound waves with frequencies above the range of normal hearing to examine structures inside the body. For more information see How ultrasound works (How Stuff Works, USA).
The shocking truth about road trauma

ultraviolet (UV). A form of electromagnetic radiation. UV radiation has shorter wavelengths than visible light and it therefore carries more energy. It is divided into three broad categories: A, B and C. UV-A has the longest wavelength and is the least damaging form, although sufficient exposure will cause sunburn. UV-B damages proteins in unprotected organisms and can cause cancer, while UV-C is extremely dangerous because it can cause mutations in DNA.

Ultraviolet disinfection can be used to kill microorganisms in water. For more information see FAQs about ultraviolet water disinfection (Triangular Wave Technologies, USA).
Earth's sunscreen – the ozone layer
Sun and skin – a dangerous combination
Coral bleaching – will global warming kill the reefs?
Nanotechnology – taking it to the people
Making every drop count

unsustainable. Use of resources at a rate that will eventually deplete the resources and/or cause major ecological damage. An activity that uses natural resources at a rate above the natural rate of their replacement.
Making our mark – ecological footprints

uranium. A radioactive heavy metal. The natural element is a mixture of different isotopes or atomic forms. The isotope uranium-235 is used in nuclear non-breeder reactors.
Prospect or suspect – uranium mining in Australia
Thinking ahead – fusion energy for the 21st century?
Probing past and future materials with neutrons

V

vaccine. A preparation consisting of antigens of a disease-causing organism which, when introduced into the body, stimulates the production of specific antibodies or altered cells. This produces an immunity to the disease-causing organism. The antigen in the preparation can be whole disease-causing organisms (killed or weakened) or parts of these organisms.
Malaria – a growing threat
Immunisation – protecting our children from disease
Bird flu – the pandemic clock is ticking

variable. Something that takes on different values that can be measured or counted. If one variable can be controlled exactly (such as the selling price of apples) then it is called an 'independent variable', while the remaining variable (in this case the number of apples bought) is called a 'dependent variable'.
When the numbers just don't add up

valence (valency). The number of electrons in the outermost electron shell of an atom. These are the electrons involved in chemical reactions.
Making light of metals

vector. An organism that transmits parasites, viruses or bacteria from one host to another.
A plague on the pest – rabbit calicivirus disease and biological control
Warmer and sicker? Global warming and human health

vesicle. A small sac surrounded by a membrane within the protoplasm of a cell.
Prions – morphing agents of disease

VHF (very high frequency) radio. Radios that use frequencies in the range 30 to 300 megahertz (millions of oscillations per second). The wave length of these VHF radio waves range from 1 metre to 10 metres.
The ups and downs of Australian air traffic control

virtual reality (VR). An artificial environment created by computers, in which people can immerse themselves and feel that this artificial reality really does exist. For more information see Virtual reality (Whatis.com, USA).
Communicating with light – fibre optics
Virtual reality bytes – military uses of VR

virulence. The degree to which a disease-causing organism can affect the organism it attacks.
A plague on the pest – rabbit calicivirus disease and biological control

virulent. Highly lethal; causing severe illness or death.
Bird flu – the pandemic clock is ticking

virus. A submicroscopic infectious agent consisting of a nucleic acid (DNA or RNA) molecule surrounded by a protein coat. Viruses cannot replicate outside a living cell. More information can be found at How viruses work (How Stuff Works, USA).
A plague on the pest – rabbit calicivirus disease and biological control
More food, cleaner food – gene technology and plants
Immunisation – protecting our children from disease
Bird flu – the pandemic clock is ticking
Probing past and future materials with neutrons
Cancer immunotherapy – redefining vaccines

visible light. The wavelength of visible light ranges from 400 to 700 nanometres while the wavelength of X-rays ranges from about 0.01 to 10 nanometres. The relatively long wavelength of visible light sets the limit of how small an image it can produce. For more information see Electromagnetic radiation (Back to basics, Australian Academy of Science).
Nanotechnology – taking it to the people

volatile. Volatile substances readily change from a solid or liquid form to a gaseous form. They have a low boiling point and a high vapour pressure.
Alcohol and cars – a volatile mix

volatile. A substance that easily forms a vapour, evaporating at normal temperatures and pressures.
Clean speed ahead with catalysts

vulnerable. Sometimes used synonymously with endangered, but also used to refer to species believed likely to move into the endangered category within the next 25 years if no action is taken.
Australia's threatened species

W

water (hydrological) cycle. A biogeochemical cycle through which the Earth’s fixed supply of water is collected, purified and redistributed from the environment to living organisms and back to the environment. The water cycle is powered by the sun causing evaporation into the atmosphere of water from plants and from the Earth’s surface.
Predicting natural events

water table. The top level of water in the ground that occupies spaces in rock or soil and lies above a layer of impermeable (non-porous) rock. When the water table rises about ground level a spring, lake or wetland is formed.
Looking for clues to our mineral wealth
Feeding the future – sustainable agriculture

watertable. The top surface of the groundwater.
Salinity – the awakening monster from the deep

wavelength. The distance between two adjacent wave crests. Visible light and X-rays are both electromagnetic waves and differ from each other only in the length of the wave. The wavelength of visible light ranges from 400 to 700 nanometres while the wavelength of X-rays ranges from about 0.01 to 10 nanometres. The relatively long wavelength of visible light sets the limit of how small an image it can produce. For more information see Electromagnetic radiation (Back to basics, Australian Academy of Science).
Nanoscience – working small, thinking big
Nanotechnology – taking it to the people
Simply astronomical – the Square Kilometre Array

weight. The downward force of gravity on an object.
Death-defying designs for car safety
Bogged down in the four-wheel drive debate?

weighted sound reduction index. A single-number rating of the sound reduction through a wall or other building element. Since the sound reduction may be different at different frequencies, test measurements are subjected to a standard procedure which yields a single number that is about equal to the average sound reduction in the middle of the human hearing range.
Quiet please! Fighting noise pollution

white blood cells. (Also known as leucocytes.) White blood cells are the immune system cells. They can be divided into many different categories on the basis of their function and appearance. Many are not found in the blood at all and those that are may have the ability to crawl out of blood vessels, squeezing between the cells of the vessel walls. While some produce antibodies, others produce cocktails of destructive chemicals, others kill virus-infected cells by punching holes in them, and a further class control the entire immune response. For more information see White blood cells (Puget Sound Blood Center, Washington).
The rise and rise of asthma
Singing the praises of colony stimulating factors

X

X-ray. An image produced by sending a beam of X-rays (very high energy electromagnetic radiation) through the body. Different tissues in the body have different densities and absorb and deflect the X-rays differently. A camera records on photographic film the varying levels of X-rays that have passed through the body. For more information see What are X-rays? (MCG Health System, USA) and How X-rays work (How Stuff Works, USA).
The shocking truth about road trauma

X-ray. A high energy form of electromagnetic radiation with very short wavelengths (less than 1 x 10-8 metres). For more information see How X-rays work (How Stuff Works, USA) and From X-rays to synchrotron light (ELETTRA Synchrotron Light Laboratory, Italy).
Synchrotrons – making the light fantastic
Probing past and future materials with neutrons

X-ray crystallography. X-ray crystallography involves firing X-rays through the crystal of a molecule to produce a diffraction pattern. This pattern provides information on the structure of that crystal. For example, X-ray crystallography helped scientists discover that the DNA molecule exists as a double helix. For more information see Introduction to crystallography (Matter, UK) and X-ray crystallography (The British Biophysical Society, UK).
Nanoscience – working small, thinking big
Probing past and future materials with neutrons

Z

zoonoses. Diseases that are transferable to humans from animals.
Bird flu – the pandemic clock is ticking

zooplankton. Plankton that possess animal-like characteristics.
Acid test for the seas

zooxanthellae. Symbiotic algae that live in a range of marine animals such as corals. In corals, the zooxanthellae gain protection, access to sunlight for photosynthesis and nutrients from the nitrogen waste that the coral produces. The coral benefits from the removal of wastes and from the sugars produced by the zooxanthellae, which make up over 90 per cent of the coral's food.
Science for sustainable reefs

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The Australian Foundation for Science and the Australian Government's National Innovation Awareness Strategy are supporters of Nova.

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