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

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

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

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

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. For more information see Metals and metal alloys and Properties of metals and metal alloys (Cornell University, USA).
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

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 Southern Ocean and Antarctic Circumpolar Current (CSIRO Marine Research).
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

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

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

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

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

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 How atomic clocks work (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?

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

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

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

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

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

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

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

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

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

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 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 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

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?

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

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

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 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 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?

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?

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

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

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?

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

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

E

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

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 Electromagnetic force (Argonne National Laboratory, USA) and The four fundamental forces (ThinkQuest, USA).
Synchrotrons – making the light fantastic
Thinking ahead – fusion energy for the 21st century?

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 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

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 and parts of Indonesia.
Enhanced greenhouse effect – a hot international topic

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?

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

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

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?

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

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

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?

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

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 waves (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

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

gigalitre. A gigalitre is one thousand million (1,000,000,000 or 10⁹) litres.
The water down under

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 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

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 concentrations 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