R



radar (also see high resolution x-band radar)

Radar (radio detection and ranging) systems use pulses of radio waves to measure distance and track moving objects. Pulses of radio waves are sent out from an emitter and they are reflected from an object back to a receiver. By knowing the time taken for the pulse to go from emitter to receiver the position of the object can be found.

Amongst other things, radar is routinely used to track weather systems and in air traffic control.



radioactive

Unstable elements emit radiation in a bid to become more stable – they are radioactive. The radiation is given out in three forms: alpha, beta or gamma. Alpha and beta are small high-energy particles ejected from the core of the atom. They quickly collide into nearby substances, causing damage. Gamma radiation is energy released in the form of an electromagnetic wave, similar to radio or light waves, but of much higher energy. Because gamma radiation interacts less with other substances it travels much further from the radioactive material than the alpha and beta particles, but it causes less intense damage.



Reformation

The Reformation was the religious revolution that took place in the 16th century in the Western Christian Church. Reformers believed that the Church in Rome had become too rich and corrupt, indulging in political and financial scheming that robbed it of spiritual authority.

The Reformation focused on going back to the scriptures for guidance. The authoritative word of God was found in the Bible, rather than in decrees delivered by the Pope. People were saved from sin not by their works – observing correct ritual, going on pilgrimage, giving to charity – but by their faith. If a person believed and trusted in the promises of God and Christ, God granted them the grace that resulted in salvation.



regression

In statistics, regression is a way of modelling the relationship between the expected value of a random variable and the values of any other variables that may be related to it. It can be used to predict the value of one of the variables if the other values are known.

Regression is also used in biology to describe the tendency to return from an extreme to an average condition. For example, the children of very tall parents can be of average height.



Renaissance

The Renaissance was a period of intellectual and economic revival that occurred in Europe throughout the 14th, 15th and 16th centuries AD. Cities and the middle classes grew, while the power of the Roman Catholic Church and the old feudal states declined. Art, literature and thought all underwent renewal as they became influenced by classical ideas.

In the realms of science and maths, renaissance scholars obtained and translated Greek texts that had been lost to Europe for centuries. These rediscovered ideas freed them from the old ways of thinking and allowed the formation of the modern scientific method.



rinderpest

Rinderpest is a highly infectious viral disease which causes high fever, discharge from the eyes, nose and mouth and severe diarrhoea. It is spread by direct or close indirect contact with infected animals and by drinking water contaminated by the dung of infected animals. Cattle, sheep, goats and pigs as well as some wild animals are susceptible to infection.

There is no treatment for rinderpest and infected animals and those in close contact are normally slaughtered to prevent the spread of infection. A vaccine is available.



robotics

Robotics is the design and use of robots. Robots are mechanical and electronic machines which are capable of doing various tasks. Their flexibility makes them different from the automated machines, found in many factories, which are designed for only one task.

S



salmonella

Salmonella is a family of over 2000 different types of bacteria, but Salmonella enteritidis and Salmonella typhimurium are responsible for about half of all human Salmonella infections.

Salmonella infection is usually contracted by eating foods containing the bacteria. It can be prevented by proper food handling practices and cooking food thoroughly. The symptoms of infection include diarrhoea, abdominal cramps, vomiting and fever and can last up to seven days.



scientific revolution, The

'The scientific revolution' is the name commonly given to the profound changes in scientific thinking that occurred in the 16th and 17th centuries. However, many science historians now think of the period as more of an 'evolution' rather than a revolution.

Medieval science had followed the teachings of the ancient Greek philosophers. Their explanation of how nature worked was based on a desire to understand the reason why a particular object behaved the way it did, rather than a mechanical understanding of how it actually happened. The new approach emphasised rigorous, repeatable experiments and observations that provided testable theories open to modification or even replacement, as new observations were made.

The scientific revolution is generally thought of as starting in the 1540s with the theories of Copernicus, who proposed that the Earth was not at the centre of the Universe. By the 1680s, Isaac Newton had cemented the changes by showing that much of nature, from the orbits of the planets to the motion of objects on the Earth, could be explained by the same simple mathematical laws.



serotonin (5-hydroxy-tryptamine, 5-HT)

Serotonin is an amine neurotransmitter made from the amino acid tryptophan. It acts as a neurotransmitter in the central nervous system, where it's involved in producing uplifting feelings.

Serotonin also plays a role in regulating sleep - the hormone melatonin, which regulates the body clock, is manufactured from it.



sleeping sickness

Sleeping sickness is the common name for trypanosomiasis, a disease caused by the parasite Trypanosoma cruzi and spread to humans by the bite of tsetse fly. The parasite that causes sleeping sickness exists only in Africa.

The first signs of infection are a sore appearing on the site of the bite followed by redness, pain and swelling. As the infection progresses, sufferers experience fever, headache, itching, mental confusion and long periods of sleep. If untreated, sleeping sickness can be fatal.

Treatment for sleeping sickness is available, but avoiding contact with tsetse flies is preferable since most of the treatments have severe side effects.


space shuttle

Until the recent Columbia disaster, there were actually four space shuttles – Columbia, Discovery, Atlantis and Endeavour. They are designed to be launched like conventional rockets but return to Earth like planes, making them reusable – and therefore more cost effective.

The shuttles have three main components: the orbiter which carries the crew and cargo, the fuel tank and the booster rockets. The fuel tank and booster rockets are discarded shortly after blast off whilst the orbiter carries on up into space.



sperm

Sperm are the sex cells produced by males. They contain half the full complement of chromosomes and will ultimately combine with an egg at fertilisation. Males tend to produce vast quantities of sperm at any one time. Sperm are tiny, each one requires only a small amount of resources to produce.



spore

Spores are dormant seed-like reproductive bodies produced by some plants, bacteria and fungi. They have tough outer envelopes and are difficult to destroy. They can develop into a new organism once they become embedded in the right environment.



stem cells

Stem cells are cells that have yet to take on a specific form and function – they have the potential to become any kind of specialised cell (eg skin, bone, hair) other than a sex cell. The obvious place to find stem cells is in the developing embryo, but they are also found in the bone marrow of adults.



sub-atomic

although atoms were once thought to be indivisible particles [see atoms], there are further layers of structure and particles below the level of the atom. Atoms consist of a core of protons and neutrons surrounded by a cloud of electrons arranged in sets of shells and subshells.

Below this layer of order lies further organisation. Protons and neutrons, at least, are made up of smaller particles called quarks. Like a series of Russian Dolls stacked inside each other, no-one knows how many series of particles there are.



supply module

Supply modules were unmanned spacecraft that took food, water and equipment to Mir and removed rubbish, allowing the Russian space station to remain habitable.

T



tissue cultures (also see culture collections and American Type Culture Collection)

A tissue culture is the growth of a single type of specialised cell (eg skin cells) outside of a living organism. The cells are grown by placing them in a suitable mixture of salts and nutrients called a medium. The cells that form the tissue can then be used for research or, for example, as skin grafts to treat burns victims.



TNT

TNT (trinitrotoluene) is an unstable chemical that is used as an explosive. Explosives work by rapidly producing a huge volume of gas which expands out in a damaging shockwave.

In weaker explosives, such as gunpowder, various chemicals have to be ground together so that they can react and cause an explosion. TNT contains all the explosive requirements within itself, so it can react more quickly, producing a devastating shockwave.



transformer

A transformer consists of two sets of wires coiled around iron cores and placed side by side. It uses electromagnetic induction to change the voltage and current of a current-carrying wire. A changing current in one of the coils creates a changing magnetic field around both this wire and the second coil. This changing magnetic field creates a changing current in the second wire. The size of the second current can be controlled by the number of coils in each wire.

Electricity from a power station has a high current and a low voltage, so lots of energy would be lost as heat in the power cables. A transformer reduces the current and increases the voltage before the electricity reaches the power cable. At the other end a second transformer increases the current and reduces the voltage again, making it safe for use in homes.



transmute

Transmutation is the changing one thing into another using alchemy. 'Impure' forms and substances were transmuted to a state of perfection. These transformations were not simply of materials, but also of the body (from sick to healthy, from old to young), or even of the soul (from an Earthly existence to an eternal one).

Alchemists believed that substances could be transmuted by undergoing various procedures such as heating, mixing with other substances, and distilling. Some believed in an elixir, or philosopher's stone, that would transmute things quickly and easily, and possibly even grant eternal life.



tularaemia

Tularaemia is caused by the bacterium Francisella tularensis. Many small animals, such as rats, harbour the disease which can then be spread to humans through flea bites, contaminated food and water or by inhaling infected airborne particles.

The symptoms of tularaemia include fever, headaches, vomiting and extreme weakness. In some cases blisters appear that quickly fill with pus and then open to form ulcers. If the lungs are affected, pneumonia can develop.

Tularaemia can be treated with antibiotics and an effective vaccine is available.



typhus

Typhus is the general name for several infectious diseases caused by the micro-organism Rickettsia. The symptoms of typhus include severe headache, sustained high fever, depression, delirium and the eruption of red rashes on the skin.

Rickettsia normally live in ticks, mites, fleas and lice and can be spread to humans by the bites or faeces of these creatures.

Typhus can be treated with antibiotics and can be prevented by vaccines.

U



uranium235

Uranium235 contains a total of 235 protons and neutrons: 92 protons and 143 neutrons. The large number of neutrons makes uranium235 unstable and by radioactive decay it transforms through a series of other elements until it reaches a stable form of lead. This process is very slow – the time taken for half a given amount of uranium235 to decay is one billion years.



uranium238

Uranium238 contains a total of 238 protons and neutrons: 92 protons and 146 neutrons. The large number of neutrons makes uranium238 unstable and by radioactive decay it transforms through a series of other elements until it reaches a stable form of lead. This process is very slow – the time taken for half a given amount of uranium238 to decay is 4.5 billion years.



utopia

A utopia is a place of perfection, where social conditions, laws and government in particular are ideal. It is also a place that doesn't exist. 'Utopia' is often used as a derogatory description of schemes for impractical social improvements. The opposite of a utopia is a dystopia

V



variant CJD

Variant CJD (vCJD) is so called because it is a relatively recently identified version of the condition Creutzfeld-Jakob Disease (CJD). CJD is a degenerative and fatal condition that produces muscle spasms and progressive dementia in people over the age of 50. CJD can be inherited or it can be sporadic, occurring for no known reason.

Variant CJD has the same symptoms as inherited or sporadic CJD, but it can occur in much younger people (the youngest sufferer contracted vCJD at 12) and has been linked to BSE or 'mad cow disease'. It is thought that people could have contracted vCJD after eating meat contaminated with BSE.

All versions of CJD and BSE are thought to be caused by prions, a type of protein found on the surface of cells in the nervous system.



Vesalius, Andre

Andre Vesalius (1514-1564) was a Flemish physician who revolutionised the study of human anatomy.

Until the 16th century the standard anatomy text used by surgeons was written by the Greco-Roman physician Galen, and dated back to the 2nd century AD. Galen had based most of his work on non-human animals, whose anatomy can be quite different to ours.

Vesalius brought a new thoroughness to human dissection, and gave demonstrations of his methods to students. He critically evaluated the ancient texts, demonstrating that they were not infallible. Working with the best artists of the day he produced the Fabrica – a more accurate textbook on human anatomy that was also a masterpiece of design and illustration.



virulent

A virulent organism is one that is harmful or deadly.

A highly virulent organism is capable of causing disease that is likely to lead to death in those infected.



virus

A virus is a disease-causing micro-organism much smaller than a bacterium. Viruses can only grow and multiply once inside the cell of another living thing as they don't contain any of the internal 'machinery' necessary for reproduction. They are parasites.



vitamins

Vitamins are substances that are needed by the body in relatively small amounts but are necessary for the body to function properly. A lack of a particular vitamin in the diet leads to a deficiency disease eg scurvy is caused by a lack of vitamin C and beri-beri is caused by a lack of vitamin B1.

There are basically two sorts of vitamins – water soluble and fat soluble. Vitamins A, D, E and K are classed as fat soluble, vitamins C and the B vitamins (there is a whole group of B vitamins – B6, B12 etc) are water soluble.

W



warhead

The warhead is the part of a missile that is designed to do the damage. Warheads are often described in terms of the 'charge' they are carrying. So, amongst others, there are nuclear warheads, chemical warheads, explosive warheads and incendiary warheads.



wheat rust

Wheat rust is a common name for several fungal infections that affect wheat. The disease causes huge reductions in yield and can destroy whole crops.

Wheat rust is identifiable by the formation of rust coloured, oval lesions on the plant.

X



x-ray

X-rays are electromagnetic waves with short wavelengths of less than one billionth of a metre (visible light is also electromagnetic waves but with wavelengths 1000 times longer). X-rays are very penetrating and can pass through flesh but they don't have enough energy to pass through bone. This means that they can be used to produce 'x-rays', ie shadowy images of bone.



X-ray crystallography

X-ray crystallography is a method of determining the structure and arrangement of molecules. Molecules are made up of atoms strung together in a particular order, like beads threaded on a chain or net. Determining the exact arrangement of atoms can be very difficult, particularly with large molecules like proteins or DNA.

A crystal contains many molecules stacked together in a regular, repeating pattern. When X-rays are beamed through a crystal, they are scattered off the atoms in a regular pattern, allowing the exact arrangement of atoms in the molecule to be deduced.



X-ray and ultraviolet telescopes

Stars and galaxies don't only give out light which our eyes can see. Different parts of the same object can emit different wavelengths of electromagnetic radiation such as radio, infrared, ultraviolet and X-rays. So to get the whole picture, it is important to look at an object at all wavelengths. X-ray and ultraviolet telescopes are sensitive to the higher energy ultraviolet and X-ray parts of the electromagnetic spectrum rather than visible light. This means they can be used to look at the more energetic or hotter parts of a star or galaxy.

Z



zinc cadmium sulphide

Zinc cadmium sulphide is a chemical that fluoresces – it produces light for a short period of time. This property means that it has been used as a meteorological air tracer.

There are now some claims that zinc cadmium sulphide may be potentially carcinogenic although it was considered safe at the time.