diamond
each can be scratched by any of the minerals higher up the scale, and other minerals can be assigned numbers in the same scale, according to which minerals will scratch them.
mole : a gram molecular mass (also called gram molecular weight) of a substance; the molecular mass of a substance in grams. One mole contains Avogadro's number of particles (6.026 x 1023).
molecular oxygen : a molecule that is composed of two oxygen atoms, O2, and has no colour, odor, or taste. It is present in both the atmosphere and dissolved in the oceans and freshwater sources exposed to the atmosphere. Solar radiation with wavelengths less then 242 nm can break it back into oxygen atoms, O2 ---> O + O. One of these oxygen radicals in turn can combine with O2 to form ozone, O2 + O ---> O3.
mollusc : A group of animals, including slugs and snails.
Monera : The kingdom that includes all those organisms that lack nuclei in their cells; the Monera are all prokaryotes.
monocotyledon : Any plant having only one cotyledon.
monocytes : One of three types of leucocytes; large highly mobile cells whose main function is phagocytosis.
monsoon : heavy winds characterized by a pronounced seasonal change in direction. Winds usually blow from land to sea in the winter, while in the summer, the flow reverses and precipitation is more common. Monsoons are most typical in India and southern Asia.
Montreal Protocol : A international environmental agreement (one of the first) to prevent the use of substances that are harmful to ozone, such as chlorofluorocarbons and halons, in order to protect the ozone layer in a global manner. It was agreed upon in 1987 and has been amended repeatedly since that time.
Moon (Astronomy) : The Earth's only natural satellite, having an average distance from the Earth is 238,328 miles and a diameter of 2155 miles. It has no magnetic field and only 1/6th of the Earth's gravity. It's origin is still a mystery with four widely accepted theories; it formed near Earth as a separate body; it was torn from Earth; it formed somewhere else and was captured by our planet's gravity, or it was the result of a collision between Earth and an asteroid about the size of Mars. The last theory has some good support but is far from certain.
morphine : A narcotic analgesic drug obtained from opium and used in medicine. Its depressant effect on the brain accounts for the pain killing properties. In high doses it also inhibits he breathing and cough centres. Other side effects include constipation, nausea and vomiting. Morphine is an addictive drug and readily leads to severe physical dependence.
morphogenetic movement : All movements (migrations) that change the shape of differentiating tissues in an embryo.
mosaic theory : An embryological idea which holds that certain regions of the egg are designated to become specific parts of the organism.
MTBE : the compound methyl tertiary butyl ether (MTBE) was blended in gasoline originally in 1979 to serve as an oxygenate. This would theoretically cause the combustion process in internally combustion engines to be more complete. This effort to improve air quality by producing a fuel that was more readily oxidized and decrease the resulting troposheric ozone production was somewhat effective. A problem arises, however, in the fact that MTBE moves extremely well in water (it may actually move upstream because of its high affinity for water molecules), causes fish kills due to its toxicity to fish, and even at low concentrations, it can render large surface or groundwater sources to be useless. Its use has since been banned in California.
mu ( M, m ) :
Mullein ducts : Tubules that develop in the mammalian embryo just lateral to the Wolffian ducts and are precursors of the Fallopian tubes, uterus, and part of the vagina.
multiple alleles : Sets of alleles that contain more than two contrasting members for a given locus.
muon : A negatively charged unstable elementary particle (lifetime 2x10-6 seconds; mass 207 times that of the electron) that decays into an electron and two neutrinos. It has a corresponding antiparticle. It was originally thought to be a meson(and was called the mu-meson) but is now classified as a lepton.
Murphy's law :
mutagen :
A chemical or physical agent that can cause a change (mutation) in the genetic material of a living cell.
mutation : An inherited structural or functional variation of an offspring in relation to its parents. Mutations are due to a change in the chemical structure of DNA, the molecule bearing hereditary information. Once a mutation has occurred it is transmitted to future generations.
mutualism : A relationship between two species of organisms in which both derive benefits from the other. It is more commonly referred to as symbiosis.
"n" : the photometric parameter generated when calculating a comet's absolute magnitude. It indicates the comet's rate of brightening and fading as it approaches or recedes from the sun, respectively.
Nacreous Clouds : Clouds that occur in the stratosphere at altitudes above 20 km and are usually iridescent and luminous in color. They may also be called mother of pearl clouds.
nadir : The pint diametrically opposite to the zenith.
nalorphine : A specific antidote to morphine overdose.
nano (n) : 10-9
naphthalene : a naturally occurring volatile organic compound, is a component of petroleum and coal and is released by the burning of wood or tobacco. It is also used in moth repellants, dyes and pharmaceuticals. Like other nonmethane hydrocarbons, it reacts with NO in the atmosphere to produce NO2. The NO2 is photolized to produce NO and O. The O then reacts with O2 to produce ozone.
narcotics :
National Ambient Air Quality Standards (NAAQS) : Sets the levels of air quality for the United States, in the Code of Federal Regulations (40 CFR §50.2), to protect the populationís health. These are the minimum and might be more stringent from state to state.
National Center for Atmospheric Research (NCAR) : A non-profit organization dedicated to furthering understanding of the Earth's atmosphere. Located in Boulder, Co., NCAR is operated by the University Corporation for Atmospheric Research (UCAR) and sponsored by the National Science Foundation (NSF).
National Oceanic and Atmospheric Administration (NOAA) : A United States Government agency created in 1970 as part of the United States Department of Commerce to determine how our oceans and atmosphere should be developed, regulated, analyzed, formed, and mined. NOAA tries to achieve these goals with the help of eight major federal services, The National Oceanic Survey, The National Weather Service, The National Fisheries Service, The Environmental Research Laboratories, The Environmental Data Service, The Environmental Satellite Service, The Office of Sea Grant, and The Office of Coastal Zone Management. NOAA has been threatened with extinction in the spring of 1995 with the possible dissolution of the Department of Commerce under the guise of "necessary" budget cuts.
nebula : A cloud of interstellar gas and dust that becomes visible for one of three reasons. In an emission nebula the gas is ionised by ultraviolet radiation, generally from a hot star within the cloud; the ions interact with free electrons in he cloud, and light (predominantly red and green) is emitted. In a reflection nebula light from a nearby star is reflected in all directions by dust in the cloud, thus illuminating the cloud. The dust in a dark nebula reduces quite considerably the amount of light passing through it (by absorption and scattering) and a dark region is seen against a brighter background.
nectary : A group of cells secreting nectar.
negative acceleration phase : The period of decreasing growth rate in a population, following the exponential increase that occurs during the logarithmic phase.
negative feedback : A mechanism of self regulation where by a change in a system in one direction is converted into a command for a chance in the opposite direction. A means of helping maintain a biological system in dynamic equilibrium.
Neptune (Astronomy) : The smallest of the gas planets it is the eighth planet from the Sun which it orbits at a distance of 30.06 astronomical units, in an almost circular orbit.. With an equatorial diameter of about 49,400 kilometres (30,700 miles), once every 164.79 years. Neptune is only slightly smaller than Uranus, to which it is a twin planet. One day on Neptune is 16 hours and 7 minutes. The gravity on Neptune is 1.15 of Earth's gravity. It was discovered in 1846 on the basis of predictions made by John Adams and Urbain Le Verrier, but may have been sketched by Galileo in 1613, without him realising it was a planet.
neural crest : During mammalian embryogenesis, cells that become detached from the forming neural tube, move laterally, and then move dorsally between the closed tube and the overlying ectoderm. The spinal and cranial nerve ganglia are developed from neural crest cells.
neural tube : In vertebrate embryos the tube formed along the dorsal surface, produced by he infolding of a large mass of ectodermal tissue. The neural tube develops into the entire central nervous system and parts of the peripheral system as well.
neutrinos : A group of three elementary particles and their antiparticles. They are classified as leptons, have no charge, and are probably massless. One type of neutrino is associated with the electron, one with the muon, and one with the tau particle.
neutron : An elementary particle that is constituent of all atomic nuclei except 1H. It has no electric charge and its mass is slightly greater than that of the proton. Inside the nucleus the neutron is stable but when free it decays by the weak interaction to a proton, an electron and an antineutrino. It's mean life is about 12 minutes.
neutron star : A star that has undergone gravitational collapse to the extent that most of the protons making up its constituent atoms have coalesced into neutrons. The density is extremely high (about 1017 kg m-3) and all the pressure exerted by the densely packed neutrons can support the star against further contraction. Neutron stars are thought to form when the mass of the stellar core remaining after a supernova, exceeds about 1.4 sun masses.
Newton : The SI unit of force defined as the force required to give a mass of one kilogram an acceleration of one metre per second per second.
nicotine : The only alkaloid (apart from coniie) which is not solid at normal temperatures. Pure nicotine is a pale yellowish oil, but it discolours brown in light. It is present in minute quantities in cigarettes and to a greater extent in horticultural preparations where it is used as an insecticide. Less than one grain can induce a fatal paralysis of the respiratory system, and in addition nicotine can be absorbed through the skin. Large doses produce a burning sensation in the mouth, down through the oesophagus and in the stomach. Vomiting and diarrhoea follow, then mental confusion and giddiness. If the subject is not yet dead then muscular twitching becomes spasmic, and convulsions will be succeeded by unconsciousness and death. Death can occur within a few minutes (Only hydrocyanic acid acts more rapidly).
niche : The ecological position of an organism - the organisms "occupation" within the biological community.
nimbo- : indicates a precipitating cloud.
nimbostratus clouds : Cloud formation consisting of dark-gray layers of clouds and occurring at altitudes which produce prolonged rain and snow.
nimbus clouds : used to describe a cloud that is precipitating.
ninhydrin : A substance that reacts with amino acids to produce strongly coloured compounds that can be easily detected.
nitric acid - HNO3 : this is a corrosive, non-volatile, and inorganic acid. It is a strong acid (dissociates completely in aqueous solution) and is also an oxidizer. In the atmosphere it is formed by the conversion of nitrogen monoxide into nitrogen dioxide, and ultimately into nitric acid:
2NO + O2 --> 2NO2
3NO2 + H2O --> 2HNO3 + NO
Nitrogen monoxide in this process most often come from (fossil fuel-based) combustion processes that use atmospheric air (containing 78.1% N2) which combines with atmospheric oxygen in those high temperature combustion process (see nitrogen monoxide and nitrogen dioxide entries below). Nitric acid is highly water soluble. This solubility with water allows easy removal of nitric acid from the troposphere by atmospheric precipitation. Commonly, this is referred to as acid rain or snow. Nitric acid has a relatively low concentration in the atmosphere but provides an important role in the production of sulfuric acid. It acts as a catalyst in the conversion of sulfur dioxide to sulfuric acid. Sulfuric acid is usually formed within cloud droplets by oxidation of dissolved sulfur dioxide again most foten released by fossil fuel combustion.
nitrification : The conversion of nitrogen organic compounds to inorganic compounds of nitrogen. This conversion is accomplished, in the main, by bacteria.
nitrobenzene :
nitrogen fixing bacteria : Bacterial organisms that are capable of drawing nitrogen from the atmosphere and converting it into soluble nitrates. These nitrates can then be used by plants.
nitrogen (N2): a colorless, tasteless, odorless gas which makes up 78.1% of the atmosphere. Atmospheric nitrogen is converted by nitrogen fixation and nitrification into compounds used by plants and animals. In the far upper atmosphere, N2 is broken down when large numbers of energetic secondary electrons are produced and available to react with the N2. This leads to the eventual production of NO in that part of the atmosphere and is not--by definition--anthropogenic in nature.
nitrogen dioxide (NO2) : is the lesser of the two emitted NOx gases from high temperature combustion in air. It is an important species in the atmosphere. Since it absorbs in the visible wavelength region, creating the Brown Cloud see over Denver, LA, Mexico City, Beijing, etc. and can be photolyzed and yield oxygen atoms that can react with molecular oxygen to create ozone, NO2 and the NO/NO2 ratio is important in tropospheric chemistry.
nitrogen monoxide (nitric oxide) (NO) : is the principal emitted NOx gas from high temperature combustion in air. This gas can acts a catalyst in the reactions that cause the destruction of ozone. Reacting with ozone and tropospheric radicals, NO is inextricably linked with the polluted urban atmospheric production of NO2, ozone, and other secondary pollutants such as peroxyacetyl nitrate.
nitrogen oxides (NOx) : produced from high temperature combustion in air. They are nitrogen oxide and nitrogen dioxide.
nitroglycerine (C3H5(NO3)3) : A yellow oily highly explosive liquid. It is used as an explosive either alone or as dynamite or gelignite.
nitrous oxide (N2O) : this is a by-product of biological activity of a symbiotic bacteria living in leguminous plant roots. It is a principal greenhouse gas that absorbs in the infrared wavelength region and unfortunately falls in an IR "window" between IR absorbing features of water and carbon dioxide (a characteristic of all the "trace" greenhouse gases with significant radiative forcing). It is also laughing gas used in medicine as a gentle general anesthetic.
noble gases : The elements forming group 0 of the periodic table. All are odourless, colourless, tasteless gases which are slightly soluble in water. They are virtually inert chemicals owing to their filled outer electron shells ;
The electronic structures of the noble gasses :
| Inert gas |
Electronic structure (Bohr model) |
Electronic structure (s,p,d,f notation) |
| He | 2 | 1s2 |
| Ne | 2.8 | [He] 2s2 2p6 |
| Ar | 2.8.8 | [Ne] 3s2 3p6 |
| Kr | 2.8.18.8 | [Ar] 3d10 4s2 4p6 |
| Xe | 2.8.18.18.8 | [Kr] 4d10 5s2 5p6 |
| Rn |
2.8.18.32.18.8 |
[Xe] 4f14 5d10 6s2 6p6 |
noble metals : Metals, such as gold, silver and platinum that do not rust or tarnish in air or water and are not easily attacked by acids.
noctulucent clouds : Relatively unusual wavy, thin, bluish-white clouds that form at altitudes of about 80 to 90 km.
node (botany) : The point where the leaf is attached to a stem.
"nodoc" : see anticodon.
nodules : Swellings on the roots of certain leguminous plants where nitrogen-fixing bacteria reside in a symbiotic relationship with the plant.
nondisjunction : The failure of a pair of chromatids to separate at metaphase, creating an abnormality of chromosome number in both daughter cells. Nondisjunction usually leads to deformed offspring.
nonmethane hydrocarbons (NMHCs) : These are hydrocarbons such as ethylene, butane, hexane, propane and, by definition, exclude the first member of that analogous series, CH4. Large quantities of NMHCs are emitted from vegetation, the vast majority as isoprene, C5H8. The natural emission of isoprene is significant compared to that of anthropogenic NMHC.
normal phase HPLC : chromatography in which the stationary phase is polar and the mobile phase is non polar.
notochord : A rod shaped body located dorsally and serving as an internal skeleton in the embryos of all chordates and in adults of some; replaced by a vertebral column in vertebrates.
nu ( N, n ) :
nuclear fission : A process whereby the nucleus divides into two main fragments of nearly comparable mass.
nuclear membranes : The unit membrane that separates the nuclear material from the surrounding cytoplasm in a cell. The nuclear membrane is not continuous, but rather is broken at different intervals by nuclear pores that provide a physical passage between the nuclear and surrounding cytoplasm.
nuclear winter : In the event of a significant nuclear war, researchers (Paul Crutzen and John Birks initially) predicted that a barrier of smoke (from incinerated urban centers and forests) would fill tropospheric skies, and eventually surround the earth, reducing the tropospheric temperature and causing damage to ecosystems and atmospheric components such as stratospheric ozone.
nucleation : A process in which water condenses on a small atmospheric particle. Nucleation aides in the process of condensation (see methanesulfonic acid).
nucleation scavenging : Term for water vapor that removes particulate matter from the atmosphere.
nucleic acid : A polymer composed of ribose sugar rings and phosphate groups, with organic bases of thymine, guamine, cytosine, adenine, and/or uracil. Both DNA and RNA are nucleic acids.
nuclease : An enzyme that hydrolyses nucleic acids by breaking phosphodiester bonds.
nucleon : A collective name for a proton or neutron.
nucleolus :
nucleoplasm : The living material within the nucleus.
nucleotide : The molecule formed from the combinations of a purine or pyramidine, an appropriate sugar (ribose or deoxyribose), and a phosphate residue. Nucleotides are the basic units of nucleic acid structure.
nucleus (atomic): The dense area in the central part of an atom where all the protons and neutrons are located.
nucleus (cellular): A body found in nearly all cells which contains the hereditary information of the cell and acts as the control centre of the cell function.
nucleus (astronomical): The actual solid body of a comet. The nucleus is rarely visible when the comet is in the inner solar system because of the coma. It has been referred to as a "dirty snowball" because it is believed to be composed of about 75 percent of various ices and about 25 percent of various dusts. A photo of the nucleus of Halley's comet by the Giotto probe revealed the nucleus as an asteroidal-looking body. Most comet's have a nucleus that measures only a few kilometers across.
number base : A real number x can be represented using any integer number b as a base (sometimes also called a radix or scale). The choice of a base yields to a representation of numbers known as a number system. In base b, the digits 0, 1, ..., are used (where, by convention, for bases larger than 10, the symbols A, B, C, ...are generally used as symbols representing the decimal numbers 10, 11, 12, ...).
oblique lighting :
Occupational Exposure Standard (UK) :
The concentration of an airborne substance (averaged over a reference period) at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees if they are exposed by inhalation, day after day. (Specified by HSC in Guidance Note EH40).
ocean : The oceans cover approximately 70% of the Earth's surface and are apparently unique in the solar system (although keep an eye on some of the giant planets' moons...). The oceans are important for the regulation of tropospheric heat and the storage and production of oxygen and carbon dioxide.
odour threshold :
The minimum concentration of a substance at which the majority of test subjects can detect and identify the substance’s characteristic odor.
Ogliocene epoch : The third epoch of the Teriary period lasting from about 38 to 24.6 million years ago.
ohm (W) : Unit of electrical resistance, transmitting a current of one ampere when subjected to a potential difference of one volt.
oligopeptide : A small number of nucleotides joined by phosphodiester bonds.
oligotropic (lake) : Lacking in biological productivity; not yielding much biomass.
omega ( W, w ) :
omicron ( O, o ) :
one dimensional model : An atmospheric modelling technique in which a concentration or another unknown can be calculated relative to certain parameters, such as altitude or temperature.
oogenesis : The process by which haploid female gametes are produced.
opacity : A measure of light blocking by atmospheric particles.
operon, a genetic unit consisting of genes that function co-ordinately under the joint control of an operator and a repressor.
opium : The dried juice obtained from the seed capsule of the opium poppy. A narcotic drug also used in medicine for pain relief. The main uses today include the extraction of it's active ingredients, morphine, codeine, etc.
order : A group of genera, all of which agree in some striking particular.
Ordovocian period : A geological period of the Lower Palaeozoic era. It lasted from about 5.15 to 4.45 x 108 years ago. It is divided into the Upper and Lower Ordovician, based on the graphite fossils that are abundant in the deepwater deposits.
organ : A unit composed of various types of tissues grouped together to perform a necessary function. The liver and a plant leaf are examples of organs.
organelle : A small body appearing within the cell cytoplasm, with a characteristic structure and a definite, though perhaps not always clearly defined function. Cytoplasmic organelles include mitochondria, ribosomes, the Golgi complex, and the endoplasmic reticulum.
orogenesis : The process of mountain building, including folding, faulting and thrusting, resulting from the collision of two continents, which compresses the sediment between them into mountain chains.
orthochromatic :
orthogenesis : An erroneous conception, originating in the 19th century, that evolution progresses in a given straight line direction.
osmium (Os) :
osmosis : The passage of a solvent from a region of greater concentration to a region of lesser concentration through a semi-permeable membrane.
ostium : The upper end of the fallopian tubes, where eggs released from the ovaries enter for transport to the uterus.
outgassing : The release of "young" gases into the earth's atmosphere by volcanic activity.
ovary : In plants, the basal portion of the pistil which encloses the ovules. The ovules in turn, contain the female sex cell. After fertilisation, the ovary becomes the fleshy part of the fruit and the ovules become the seeds. In animals the organ (usually paired) of the female which produces the ovum, or egg.
oviparous : Term applied to organisms that lay eggs in which the embryo continues to develop for some period of time, deriving nourishment from the yolk.
ovoviviparous : Term applied to organisms whose young develop within the body of the mother but derive most or all of their nourishment from the egg yolk.
ovulation : The release of an unfertilised egg from the ovary. In human beings ovulation involves the discharge of a mature ovum from a Graffian follicle of the ovary.
ovum : The female reproductive cell containing the haploid number of chromosomes, derived by meiosis from a diploid germ cell. The ovum is fertilised by the sperm, producing the zygote.
oxalic acid :
oxidation : A type of chemical reaction involving the loss of electrons. Frequently but by no means necessarily, the element oxygen is involved.
oxidants : Chemical species that readily accept electrons. The electron accepting species is reduced in a chemical reaction.
oxidation : a process that results in a species having a higher oxidation state, that is, the net loss of electrons from an atom. Quite often oxygen is involved in the oxidation of another atom therefore it is an oxidant.
oxidative phosphorylation : The process whereby electrons removed from substrate molecules are passed through the electron transport chain (cytochromes), in such a way that their potential energy is coupled to the formation of ATP (from ADP and inorganic phosphate).
oxygen (O2) : found on Earth as a gas and constitutes about 20.8% of the air we breathe. Elemental molecular oxygen consists of two oxygen atoms bonded together. A photochemical reaction of oxygen is (ultimately) responsible for the production of ozone in the stratosphere. Oxygen concentrations found in ice core samples (using isotopic 16O/18O rations) have been used to determine past atmospheric levels of oxygen and have helped in determining past climates.
oxygen debt : The amount of oxygen required to oxidise the excess lactic acid accumulated in muscle cells during strenuous exercise.
Oxygen Deficiency :
Depletion of oxygen content in an atmosphere to below the normal 21%. Exposure to <18% must not be permitted.
oxygen enrichment :
Increase in oxygen content of air to above the normal 21%. Enrichment within a room to >25% can promote or accelerate combustion.
oxytocin : A hormone produced in the hypothalmus and secreted by the pituitary gland, regulating uterine contractions.
ozone (O3) : is a molecule that consists of three oxygen atoms bonded together. The ozone layer in the stratosphere absorbs UV radiation and creates a warm layer of air in the stratosphere and is therefore responsible for the thermal structure of the stratosphere. Ozone that is present in the troposphere is mostly a result of anthropogenic pollution and therefore higher concentrations are found in urban areas. Ozone is involved with NOx in the photochemical production of many of the constituents of pollution environments (see nitrogen oxides and hydroxyl radicals.)
ozone depletion potential(ODP) : The is the ratio of a particular ozone depleting compound environmental effect compared to the depleting ability of a standard compound, CFC-11, which arbitrarily defined as 1.0. An example would be the ODP of of halon-1301 which is about 13.
ozone destruction : In addition to photolytic destruction by infrared light (wavelengths of 1140 nanometers or less), stratospheric ozone is destroyed by interaction with a variety of chemical substances in the stratosphere. Some of these chemicals, such as the chlorine free radical, liberated by the photolysis of chlorofluorocarbons, are not normally produced there in nature at such high concentrations. This leads to the conclusion that human activities, and not natural chemical cycles, are responsible for the current rate of stratospheric ozone destruction. Ozone destruction is most noticeable (alarmingly!) over the South Pole, where seasonal plummeting in stratospheric ozone concentrations have been measured since the 1970s and are apparently still increasing (1999). That said, estimates based on declining CFC use (because of the Montreal Protocol) suggest that the damage to the global ozone layer will max out soon in the 21st century and that that ozone damage will decrease within the next 75 to 100 years.
ozone distribution : Nearly all of the planet's natural ozone in the atmosphere is found in the stratosphere. The thickness and distribution of this stratospheric ozone vary seasonally and by location. Ozone also occurs in the troposphere as a pollutant, often in photochemical smog.
ozone hole : The ozone hole refers to the total amount of ozone in the atmosphere over Antarctica that was discovered to be decreasing at an alarming rate over an observation site in Antarctica. The hole was discovered by J.C. Farman, B.G. Gardiner and J.D. Shanklin.
ozone formation : Molecular oxygen in the stratosphere is broken into a pair of oxygen radicals by light with a wavelength of 240 nanometers or less. If one of these O radicals encounters an oxygen molecule, it can bond to produce ozone. This reaction is only stable if another molecule is present to absorb the excess energy released as the oxygen radical and molecule bond. This is a called a three body reaction, and the third body exhibits its removal of the excess energy by whizzing off at a higher energy and thereby increasing the temperature of the atmosphere where this reaction occurs.
Palaeocene epoch : First epoch of the Tertiary period. It lasted from about 65 to 54.9 million years ago. The sudden diversification of the mammals is a noticeable feature of this epoch.
Palaeozoic era : The era of geological time lasting from about 5.9 to 2.4 x 108 years ago. It is divided into the Upper Palaeozoic which contains the Cambrian, Ordovician, and Silurian periods and the Lower Palaeozoic, containing the Devonian, Carboniferous, and Permian. It is the first era of Phanerozoic time. The Caledonian and Variscan orogenies both occurred in this era.
panchromatic :
panicle : Term used when the pedicel are branched, supporting two or more flowers in a loose cluster.
Pangea : A huge protocontinent thought to have existed 200 million years ago and from which all present continents are thought to have formed.
paraldehyde :
parasite : An organism that derives its food from another species by living in or on the host organism, usually to the detriment of the host.
parasitism : A type of heterotrophic nutrition found among both plants and animals. An organism engaging parasitism lives in or on the body of a living plant or animal (host) and attains nourishment from it.
parsec : A unit of distance, used in astronomy, corresponding to a parallax of one second of arc. 1 parsec = 3.26 light years or 3.08 x 1016 metres.
parthenogenesis : The development of an egg, without fertilisation , into a new individual. Parthenogenesis occurs naturally in some organisms (such as aphids, rotifers, bees and ants) but can be induced artificially in higher forms (such as frogs) by chemical or physical stimulus to the egg.
partial pressure : The pressure exerted by a given component gas in a mixture of gasses,
partial pressure of gas = Volume of gas / total volume
partial specific volume : The volume increment per gram of solute.
particle physics : The study of elementary particles and their interactions. Until the discovery of the electron the atom had been thought of as a minute, indivisible "billiard ball". The existence of the electron and the discovery of the proton made it clear that the atom had an internal structure. When the neutron was discovered it appeared that the whole of the universe was constructed of just these three particles. The outstanding problem was the nature of the force that held the neutrons and protons together in the atomic nucleus. The only two fundamental forces known at the time were gravitational force and he electromagnetic force(em);, the gravitational force was too weak to account for the great stability of the nucleus and the em force had no effect on the electrically charged neutron.
The concept of exchange forces (the meson) and the subsequent discovery of short lived particles led to intensive research into particle physics throughout the world. By the 1960's some 200 elementary particles had been identified and it became clear that there were four basic types of force, in addition to gravitational and em forces there were strong interactions (100 times more powerful than em forces) and weak interactions (1010 times weaker than em forces). It also became evident that some elementary particles were more elemental than others. In general, there are now believed to be two classes, leptons (the electron, muon, tau particle and neutrinos), which interact by the em or weak forces and have no apparent internal structure, and haydrons (including the proton, neutron, pion, etc.), which interact by the strong interaction and do appear to have an internal structure.
During the past twenty years the main preoccupation of particle physicists has been the elucidation of hadron structure. The current model is concerned with the quark. In this model, haydrons themselves are divided into two classes: baryons, which decay into protons, and mesons, which decay into leptons and photons or into proton pairs. Baryons consist of three quarks and mesons consist of a quark-antiquark pair. Thus all the matter in the universe is now seen as being made of leptons and quarks.
Quark theory is fairly elaborate; quarks have fractional electronic charges (+2/3 or -1/3 of the electronic charge) and come inn six "flavours" called up (u; +2/3 ), down (d; -1/3 ), charmed (c; +2/3 ), strange (s; -1/3 ), top (t; +2/3 )and bottom (b; -1/3). For each flavour there is an equivalent antiquark (u, d, etc.). The proton consists of uud (2/3 + 2/3 -1/3 = 1) and the neutron consists of udd (2/3 -1/3 -1/3 = 0).
In this limited form quark theory conflicted with the Pauli exclusion principle and it therefore became necessary to introduce the concept of "colour". Thus each quark can have one of the three colours red, yellow or blue, with the antiquarks having the corresponding anticolours. "Colours" in this sense has no connection with visual colour but the analogy is useful . All haydrons are regarded as white and baryons must consist of a red a blue and a yellow (since these visual colours produce white), mesons consist of a quark of any colour and it's corresponding anticolour. This aspect of particle physics is known as quantum chromodynamics by analogy with quantum electrodynamics.
Parts Per Million (ppm) and Parts Per Billion (ppb) : These terms give scientists a way to describe how much of a substance is contained in a sample: parts of analyte per million parts of sample, for instance. In atmospheric chemistry these become volume parts of analyte per volume parts of atmosphere: ppmv, ppbv, etc. At low analyte gas phase concentrations the analyte is assumed to act as an ideal gas. For instance, a 1 ppmv concentration of formaldehyde would represent 1 liter of formaldehyde per every 1,000,000 liters of air; also equivalent to 1 microliter of H2CO per 1 L air. In gas phase concentrations these units are also called gas phase mixing ratios. The reason is because they are just that, ratios of analyte volume to sample volume; the volume of the sample doesn't matter.
pascal (Pa) : Unit of pressure equivalent to one Newton per square metre.
pathology : The branch of medicine concerned with the study of disease and disease processes in order to understand their causes and nature. The speciality originated in the mid 19th century when Virchow demonstrated that changes in the structure of cells and tissues were related to specific diseases.
Pauli exclusion principle : In any atomic system no two electrons can have identical wave functions.
PCV Systems : A PCV system is an air pollution control device in automobile engines. PCV stands for positive crankcase ventilation. Automobile makers began installing PCV systems in all new cars in 1963. It helps to recycle hydrocarbon contaminated gases inside the engine (blowby) back into the engine's combustion process.
"pecking order" : The establishment of social hierarchies, first noted in domestic chickens.
pedicel : A flower stalk supporting several flowers without footstalks.
Pedosphere : This is the area of the Earth comprised of the solid plates of the continental crust, loose rocks and soil.
penumbra : A partly shaded region round the shadow of an opaque body.
peptide bond : The bond, formed by dehydration synthesis (elimination of water), which links together two amino acids.
perennial : Rootstocks that increase and expand yearly.
perianths : Flowers showing no distinction between calyx and corolla.
Percutaneous Absorption :
Absorption via the skin, e.g. due to local contamination or a splash of chemical.
Perihelion Date (T) :
The date an object reaches its closest distance from the sun.
Perihelion Distance (q) :
The point in an orbit when an object is closest to the sun. The value is usually given in astronomical units.
Period (astronomical):
The amount of time, usually given in years, that it takes an object to orbit the sun.
periodic table : A tabular arrangement of the elements in order of the atomic numbers, which also brings together those elements who's atoms have a similar pattern of orbiting electrons. Chemically related elements consequently tend to appear in the same column or row of the table. Go to table.
perithecium : bottle-shaped ascocarp with a pore at the top through which individual asci are discharged.
Permafrost : Soil, silt and rock located in perpetually cold areas which remains frozen year-round. Though a thin layer may thaw during summer months, the majority of the permafrost in a given location will remain frozen until the local climate dramatically changes, as from continental drift toward the equator or global warming.
permeability : The ability of a material to permit a substance to pass through it. From an actual quantitative level, it is the amount of a substance which passes through the material under given conditions.
Permian period : The last geological period of the Palaeozoic era, occurring about 3.7 to 2.8 x 108 years ago. Widespread continental conditions prevailed, which continued into the Triassic, and the two periods are often linked together as the Permo-Triassic, during which the New Red Sandstone was laid down.
Permit-To-Work :
A document needed when safeguards provided in normal production are unavailable and the manner in which a job is done is critical to safety. Identifies conditions required for safe operation.
peroxisome : A cytoplasmic cell organelle containing enzymes for the production and decomposition of hydrogen peroxide.
Peroxyacetylnitrate (PANs) : A class of chemical substances found as a pollutant in the troposphere, formed by photolysis from natural and manufactured organic chemicals. These chemicals act as irritants and mutagens in mammals and are toxic to many plants.
persistent train :
train luminosity that lasts more than a second.
perturbation : a disturbance; often develops into a low pressure system.
peta (P) : 1015
pH : Symbol for the logarithmic scale, running from 0 to 14, representing the concentration of hydrogen ions or protons (usually hydronium ions) per litre solution. On the pH scale 7 represents neutrality, the lower numbers acidity (acids) and the higher numbers alkalinity (bases).
pH : The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that ranges from about 0 to 14. pH 7 is neutral; <7 is acidic; and >7 is alkaline.
phagocyte : A cell in the body capable of engulfing cytoplasm for enzymatic breakdown (phagocytosis). Phagocytes are found in large numbers lining the walls of lymph node sinuses; they destroy bacteria that have entered the body and been picked up by the lymphatic system. Leucocytes and macrophages are examples of phagocytes in man.
phagocytosis : The engulfing of micro-organisms, other cells, or foreign particles by a cell. For example, phagocytosis occurs when an amoeba engulfs its prey or when a white blood cell engulfs a bacterium.
pharmacology : The study of the action of drugs on living organisms. Pharmacologists examine the uptake of drugs after administration, the routes by which they reach their site of actin, their subsequent effects, how drugs are destroyed by the body, their unwanted side effects, and the interaction between different drugs. Clinical pharmacology (therapeutics) studies the effects of drugs in treating disease.
Phenol :
1) A corrosive poisonous crystalline acidic compound present in coal tar and wood tar that in dilute solutions is used as a disinfectant and
2) any of various acidic compounds analogous to phenols and regarded as hydroxyl derivatives of aromatic hydrocarbons. When coal and wood are burned for energy, phenols are released into the atmosphere.
phenotype (genetics): The outward appearance of an organism, as contrasted with its genetic make up (genotype).
Phi ( F, f ) :
Protoplasm : The name given to the material of a biological cell.
phlogiston theory : The theory that held that the substance phlogiston was contained in all combustible bodies and was released from these bodies upon their burning (producing phlogisticated air). It remained popular until the advent of the oxygen theory of combustion.
phon : A unit used for measuring the loudness of sound equal to the intensity in decibels of a sound of a frequency 1000 hertz which appears to the ear to be as loud as the sound to be measured.
phosphoglyceric acid (PGA) : An intermediate product in carbohydrate metabolism, composed of a 3-carbon backbone with a phosphate group attached to one (usually position 3) of the carbons.
phospholipids : An important structural part of the cellular membrane, containing phosphorus, fatty acids, glycerine, and nitrogenous base.
phosphorylation : The addition of a phosphate group ( such as H2PO3) to a compound, as in oxidative of ADP (producing ATP) during respiration.
Photic Zone : In the ocean (or in lakes) this is the area near the surface with enough light to support photosynthesis. In this zone, both the chemical and biological activity can be enhanced by penetrating solar radiation. This zone is about 20 meters in depth in the ocean. In the upper surface of this zone, the marine photochemistry is most vigorous. Changes in the ultraviolet light content penetrating this region because of changes in the UV-blocking ability of the ozone layer may create unexpected biological results there.
Photochemical Smog : Natural and artificially emitted hydrocarbons in the presence of oxides of nitrogen undergo photochemical reactions which produce a cloud of toxic chemicals including ozone and a variety of caustic agents. This process is powered by sunlight and some of the products, such as ozone, reach a peak soon after photon flux from the sun reaches a maximum, around midday. The thermal inversions often associated with some cities can lead to a dangerous buildup of smog in urban areas. Human deaths have been attributed to photochemical smog since the Industrial Revolution in cities such as London and New York.
photoconductivity : The increase in the conductivity of certain semi-conductors, such as selenium, when exposed to light. It occurs when photons excite electrons in the material form the valence band into the conduction band.
Photodissociation : This is a specific type of photolysis reaction, in which the destruction of a molecule is initiated strictly by solar energy.
photoelectric effects : A number of effects in which electromagnetic radiation interacts with matter, frequently with the emission of electrons. These effects include photo conductivity, he photovoltaic effect ad the Compton effect and the Augur effect. The frequency of the radiation (f) has to be such that the energy of the photon , hf (where h is Planck's constant) is sufficient to liberate the electron.
For solids the minimum energy required is called the work function: for free atoms or molecules it is equal to the first ionisation potential, the effect then being known as photoionization. For most substances, an ultraviolet frequency is needed to eject an electron, but for some metals, such as caesium, visible light is sufficient.
photoionization : The ionization of an atom when it is bombarded with electromagnetic radiation. The frequency of the radiation has to be such that the energy of its photons exceeds the first ionization potential of the atom.
Photolysis : The destruction of a molecule by electromagnetic radiation, which provides the energy required for a constituent atom to break the chemical bonds between it and the other atoms comprising the molecule.
photon : The quantum of electromagnetic radiation, having an energy of hf where h is Planck's constant and f is the frequency of the radiation. It may be regarded as an elementary particle with spin 1 and zero mass that travels at the speed, of light.
Photostationary State : This describes a condition in which there is equilibrium in a photochemical reaction. For this condition to take place the rate of dissociation of the reactants has to be equal to the rate of their recombination.
Photosynthesis : a biological process which plays a vital role in cycling the atmosphere's carbon dioxide, while simultaneously producing oxygen and other complex substances. Green plants, with chlorophyll, utilize the sun's energy to convert carbon dioxide and water into the plant biomass while oxygen that is released into the atmosphere.
photovoltaic effect : The production of a voltage when light falls on certain materials coated with another substance. The effect can be detected by connecting the two materials through an external circuit to generate a current. It occurs in copper (I) oxide on copper and in selenium on iron.
phrenology :
phyletic speciation : The process of evolutionary change in which one population gives rise, over time, to another single population genetically different from the original.
phylogenetic chart : A diagram showing the evolutionary relationships among a group of species, or with a single species. The so called family tree is an example of a phylogenetic chart.
phylogeny : The study of the evolutionary history of a species.
physical environment : All of the elements surrounding an organism but excluding other living organisms.
physostigmine (ersine) : Extracted by some tribes from the calabar bean and used in ceremonies as an "ordeal" poison. The effects of ingestion are mental excitement and hallucination; an overdose of the drug causes vomiting, epigastric pains, and in severe cases interferes with the function of the heart causing death.
physiology :
phytol : The alcohol constituent of chlorophyll.
Pi ( P, p ) : In mathematics the value (approx. 3.142 or 22/7 ) that is equivalent to the circumference of a circle divided by it's diameter.
pico (p) : 10-12
pilo carpine : an alkaloid extracted from the dried leaves of the jaborandi and used medicinally in eyedrops to constrict the pupil and treat glaucoma.
Pinhole Camera :
pinocytosis : The process by which materials can be taken into the interior of a cell without passing through the plasma membrane.
pion : A group of three elementary particles classified as mesons(p), the charged pions (p+ and p-) and have a mass of 139.6 MeV, the neutral pion (po) a mass of 136MeV. The strong interaction can be represented by the exchange of virtual pions between particles.
Pirani gauge : A pressure gauge used for measuring low gas pressures. It consists of an electrically heated wire placed into the gas. The rate at which the gas conducts heat away from the wire depends upon it's pressure; the pressure is measured by observing the resistance of the wire at fixed voltage or observing the voltage at a fixed resistance.
pistil : The seed bearing organ of a flower, consisting of an ovary, style and stigma.
pistol : A short range small arm that can be used with one hand. There are two classes, the revolver and the automatic.
placenta : A structure created by the fusion of the chlorion from the young embryo with the wall of the uterus. Respiratory, excretory , and nutritional functions of the foetus are carried on by exchanges across this structure. The placenta also secretes hormones regulating certain aspects of foetal development. Presence of a placenta is characteristic of all mammals, except the marsupials, and monotremes.
Planck's constant (h): A fundamental constant that relates the quantum of energy (E) of a photon to the frequency (f) of the corresponding electromagnetic radiation by the equation E=hf. It's value is 6.626196 x 10-34 joule second.
Planck's radiation law : Electromagnetic radiation is emitted from and absorbed by matter in discrete amounts (quanta) known as photons. The energy (E) of a photon is related to the frequency (f) of the radiation by the equation E = hf where h is known as Planck's constant.
Planck's Law : This is a derived formula, from the German physicist Max Planck, that portrays the amount of radiation emitted by a blackbody as theoretically determined by its temperature. It is an equation that produces a curve, termed Planck's blackbody radiation curve, which illustrates that the warmer a body is, the greater is its blackbody emission at each wavelength and the shorter is the wavelength at which emissions peak.
planetary motion, laws of :
The first law states that the planets move around the sun in elliptical paths.
The second law states that the speed of a planet changes with its distance from the sun.
The third law states that the sidereal period is related to the cube of the planets distance from the sun.
Plankton : forms of marine, organic life that gather vital energy for life through photosynthesis. Since they are very low on the food chain, they are vital to all marine life. They are also vital to the atmosphere in that they consume large amounts of carbon dioxide, which contribute to enhanced global warming when excess amounts are present. Plankton are considered to be one of the more important contributors of oxygen to the atmosphere.
plasma (biology) : A protein containing fluid, the liquid portion of blood.
plasma (physics) : A gas, the atoms of which have been completely ionised. Sometimes called the fourth state of matter, plasmas occur at enormously high temperatures, such as those in the Sun. Plasmas are also created in thermonuclear reactors.
plasmagene : A term applied to a gene of cytoplasmic, rather than nuclear origin.
plasma membrane : A lipoprotein of a definite structure which surrounds and contains the living matter within a cell. The membrane has three layers: two outer protein surfaces surrounding an inner core of lipid. The polar part of each lipid molecule is associated with protein on the surface, while the non polar portions into the middle of the "sandwich". The average plasma membrane has a diameter of 75 angstroms.
plastic : any synthetic organic polymer that is liquid at some stage in its manufacture. Plastics are classified by their behaviour on heating. Thermoplastics soften on heating and harden as they cool, for example polystyrene and polyvinyl chloride. Thermosetting plastics remain rigid in their final shape and do not soften on heating, for example resins, melamine, polyester, Bakelite.
During manufacture plastics are moulded and shaped while they are in the heat softening stage and then cooled for thermoplastics, or heated further for thermosetting plastics to yield the final product. The processing of plastics can produce a wide variety of materials from rigid and inflexible to soft and bendy. They can be extruded to make pipes and rods. Plastics can be strengthened by the addition of carbon fibres for use in aircraft or engineering.
Due to the difficulties in disposal of plastics a number of biodegradable plastics are now in use, including polyhydroxybutrate (PHB), which is made from sugar and digested by micro-organisms in the soil.
plastic (adj.) : describing a material or process in which the material is deformed by a force and does not return to its original shape once the forced is removed.
plastids : Small bodies occurring in the cytoplasmic portion of plant cells. They are classified according to colour.
Plate Tectonics : The process of planetary surface plate formation, movement, interaction, and destruction. The consequence of this process is that many regions of the planet are situated near interacting--and slowly moving--plates. The process causes earthquakes such as those along the West Coast of the United States.
plate tectonics : The theory developed mainly in the 1960's that the Earth's crust is divided up into rigid plates (oceanic, continental, or a combination of both), which move about the Earth's surface at rates between 10 and 90 mm per annum. The edges of the plates are called margins. At constructive plate margins new oceanic crust is created where two plates are moving apart and magma rises to fill the gap; this occurs at mid ocean ridges. At destructive plate margins two plates collide and one dips beneath the other, producing deep sea trenches and the associated volcanic land arcs. Where two continental plates collide, mountain chains are formed. All the major structural features of the Earth's surface and almost all seismic and volcanic activity can be ascribed to plate movements.
platinum (Pt) : a very unreactive metal used to make inactive electrodes for electrolysis. It also acts as a catalyst in a wide range of reactions.
at. # relative at. mass m. p. b. p. relative density
78 195.1 1 772 oC 3 800oC 21.3
platonic solid : any of the five regular polyhedrons - the cube, dodecahedron, icosahedron, octahedron, tetrahedron.
Pleistocene : The period of geological time that lasted from about 1.8million to 100,000 years ago. It is often called the Ice Age because during this time the earth experienced great fluctuations in temperature: cold glacial periods, when the ice margins advanced towards the equator, separated by warmer interglacials, when temperatures at times were higher than today. Four main ice advances are recognised in the Pleistocene. Fossils from the Pleistocene include horses pigs and elephants.
Pleistocene : An epoch in Earth history from about 2-5 million years to 10,000 years ago. Also refers to the rocks and sediment deposited in that epoch.
Pliocene epoch : The final epoch of the Tertiary period lasting from about 5.1 to 2 million years ago. I t was a time when world temperatures were falling and many species of mammals that had flourished earlier in the Tertiary were becoming extinct.
Plume : a visible smoke-like structure, which may contain pollutants emitted from an exhaust or smoke stack and released into the atmosphere. This elongated band of smoke has changing characteristics that vary with its local environmental conditions. These conditions may include the physical and chemical nature of the pollutant, weather conditions and downwind topography.
Pluto (Astronomy) : The ninth planet from the Sun and the smallest of the known planets, orbiting at an average of 39.44 astronomical units every 248 years. The orbit is highly elliptical, the distance varies between about 30 and 50 AU at different parts of its orbit, which takes it inside the orbit of Neptune for approximately 20 years. It has a diameter of 2,170 miles and a surface gravity equivalent to 0.05 of Earth's gravity The surface temperature is -369o F. One day on Pluto equals 6 Earth days, 9 hours, and 18 minutes. Pluto's orbit is also highly inclined, tilted 17 degrees to the orbital plane of the other planets.
It has been suggested by some that the irregular orbit of Pluto is due to another planet in our system that has not yet been discovered.
pnicogens : The group five elements.
Point Source : Pollutants which are put into the atmosphere by stationary objects, such as refineries, power plants, mills, and the like. In Texas any source that emits more than one ton in a calendar year is considered a point source.
polar body : The small daughter cells produced during meiotic divisions of the oocyte. From the first division one polar body is produced; form the second three polar bodies are produced. A single primary oocyte thus gives rise to one large mature ovum and three polar bodies. The polar bodies contain the extra sets of chromosomes produced by meiosis. They contain very little cytoplasm however, since most of this is reserved for inclusion in the single ovum.
polarisation : The term applied to the unequal distribution (separation) of charged ions, producing an electric potential. Cell membranes are said to be in a state of polarisation when they have a greater concentration of positive ions on the outside than on the inside, or vice versa.
Polaroid Camera :
Historically used by the Police when image sharpness is not important. As these provide an instant print there is no chain of custody.
Polar Stratospheric Clouds (PSCs) : stratospheric clouds.
Polar Vortex : This is a phenomenon that occurs during the polar winter in which stratospheric air moves in a circular motion, with an area of relatively still air in its center. The temperature in the vortex is approximately -130oF (-80oC), which assists in the formation of polar stratospheric clouds. Though usually more prolonged and colder over Antarctica, the Arctic polar vortex does form to a degree, and when the temperatures there are coldest and the vortex persists, Arctic stratospheric ozone destruction on Arctic polar stratospheric clouds has also been observed.
Pollutants : any substance, usually an unwanted by-product or waste, that is released into the environment as a result of (human) activities that alter the chemical, physical and biological characteristics of the environment. These substances may be found in any of the solid, liquid or gas phases. Their long-term effects are difficult to predict and depend upon future human or cultural judgments.
polydactyly : Supernumerary fingers which, although normally existing as merely an ill-formed appendage to the thumb or little finger, can occasionally manifest as six or more fully formed fingers.
polygenic character : A quantitatively variable phenotypic trait determined by interaction of numerous genes.
polymorphism : The existence within a single species of members showing many different, but distinct and recurring forms; for example, the drone, queen and workers, occurring in the honeybee.
Polynuclear Aromatic Hydrocarbons (PAHs) : These compounds are large ring aromatic hydrocarbons that are molecules containing carbon and hydrogen. It could also be any large ring that consists of five or more cyclic compounds of carbons and any elements that may be bonded to the ring. They usually exist in nature in low amounts. Many times these hydrocarbons exist within the atmosphere in the aerosol phase from combustion processes.
polyribosome : A cluster of connected ribosomes, usually arranged along a strand of mRNA.
polysaccharides : Complex carbohydrate molecules built up from simpler sugar units (such as glucose) into long chain polymers. Polysaccharides are the major constituents of the cell walls and capsules of various micro-organisms.
polysome : A cluster of connected ribosomes, usually arranged along a strand of mRNA.
polyspermy : The fertilisation of an egg by more than one sperm at a time.
population genetics : The application of genetic principles to a large number of breeding organisms.
Position Angle (PA) :
An angular measurement indicating which side of the comet nucleus something is located. A "PA" of 0 degrees indicates an object is located north of the nucleus, while 90 degrees indicates east, 180 degrees is south, and 270 degrees is west. It is most commonly used to indicate the direction the tail is pointing. On occasion, when a comet's nucleus has broke up, the position angle is used to indicate which direction the nuclear fragments are located from the primary nucleus.
positive acceleration phase : The first section of a sigmoid growth curve for a population, where the system described is just beginning to increase.
positive feedback (biology) : An abnormal state in which a change in a systemin one direction serves as a command for continued change in that same direction. This can create a severe physiological imbalance leading to the death of an organism.
positron : The antiparticle of the electron, having the same mass and spin as the electron but opposite electric charge. A positron and an electron annihilate each other on collision, producing two gamma - ray photons.
potential energy : Energy capable of doing work.
Practicable :
Capable of being done in the light of current knowledge and invention.
praseodymium (Pr) :
Pre-Cambrian : Geological time from the formation of the Earth's crust, about 45 to about 5.9 years x 108 years ago when the Palaeozoic era began. Pre-Cambrian rocks lie below the Cambrian system and fossils are rare and often obscure. The rocks have been subjected to much alteration because of their great age. Most are metamorphosed and have undergone one or more Pre-Cambrian mountain building periods as well as later ones. The largest areas of exposed Pre-Cambrian rocks are the shield areas. Correlation of successive strata is done, where possible by radioactive dating.
Precambrian : All geologic time from the beginning of Earth history to 570 million years ago. Also refers to the rocks that formed in that epoch.
precipitate : An insoluble product of a chemical reaction in a solution.
Precipitation : What often occurs when clouds form upon reaching 100% relative humidity. If condensation nuclei are present, liquid or solid particles of water will form. When this material becomes heavy enough to fall towards the ground, it is known as the common phenomenon snow, rain, sleet, or hail
precision : the scatter of repeated measurements, i.e. if measurements on the same sample are close to each other then the method is said to give precise results.
predation : The process by which one species uses another species for food.
preformation : The idea that an already formed, miniature individual exists within the egg and merely increases in size during embryological development.
primary feathers, The main flight feathers, on the outer part of the wings.
primary germ layers, The first distinguishable areas within the developing embryo, namely the ectoderm, mesoderm, and endoderm. These areas give rise to the tissues and the organs of the mature organism.
Primary Pollutant : This refers to the types of pollutants that are either found in the atmosphere or on the ground and are emitted directly from some sources such as automobile tailpipes or smoke stacks. This is contrasted with secondary pollutants which in and of themselves are not directly emitted from a source. Instead they are created from chemical and photochemical reactions of primary pollutants. Nitrogen monoxide is an example of a primary pollutant and ozone is an example of a secondary pollutant.
primary spermatocyte : The cells in the testes that derive from spermatagonia and ultimately undergo meiosis to produce haploid sperm.
primary standard : A substance that is used to make a primary standard by dissolving in deionised water. They must be
i. chemically stable in the solid and aqueous states,
ii. pure (at least 95%), and
iii. soluble in water.
primitive streak : A longitudinal groove that develops on the surface of the embryo of fishes, reptiles, birds and mammals. Formation of the streak is a consequence of the movement of cells and
Pulmonary Oedema :
Production of watery fluid in the lungs.
Pyrophoric Substance :
A material that undergoes such vigorous oxidation or hydrolysis (often with evolution of highly flammable gases) when exposed to atmospheric oxygen or to water, that it rapidly ignites without an external source of ignition. This is a special case of spontaneous combustion.
Q-fever : An infection with the organism Coxiella burnetti. It affects mainly cattle and sheep but can be transmitted to humans through contaminated milk. The incubation period is two to four weeks and the disease usually takes the form of a viral pneumonia. Treatment is with tetrcycline antibiotics.
Qualitative data : That which can be placed in categories or with respect to attributes.
quantasome : One of the individual membranous structures arranged in columns within a granum. Molecules of chlorophyll are aligned on the quantasomes.
quantitative : That which can be measured or described in some definite and precise (generally numerical) form.
quantum : A tiny energy packet in which light travels.
quantum number : An integral or half integral number that gives the possible values of a property of a system according to the quantum theory. For example, in Bohr's atomic theory the angular momentum of an electron moving around an atomic nucleus can only have the values nh/2p, where n is a quantum number specifying these values and h is Planck's constant. Bohr's theory has now been replaced by the more versatile theory of wave mechanics, but the concept of quantum numbers is useful in some contexts. It is also used to quantify the properties of elementary particles. For example spin is characterised by the quantum numbers +1/2 or -1/2 for an electron, depending on whether it is parallel or anti-parallel to a specific direction. Parity, electric charge, strangeness, charm, isotropic spin, etc. are other properties of elementary particles expressed by quantum numbers.
quantum theory : The model which holds that light is composed of tiny energy packets (quanta, or photons) which are given off by any light emitter and travel intact through space.
quarantine : The period during which a person or animal suspected of carrying a n infectious disease is kept in isolation. The term was originally applied to a 40 day period but is now slightly longer than the incubation period of the disease.
quark : Any of a group of hypothetical components. Quarks are held to carry a charge one third or two thirds of that of the proton.
quark theory, The recapitulation, at a deeper level, of efforts earlier in the century to explain all atomic properties in terms of electrons, protons and neutrons.
quasar : A class of celestial objects lying beyond our Galaxy. They appear as star-like points of light, each emitting more energy than several hundred giant galaxies. Quasar redshifts are extremely large, indicating that they are the most distant and the youngest extragalactic objects known. They must be highly luminous to be visible at such distances. Of the 3500 quasars known, the most distant is 73x1027 miles away. They appear to be about 0.01 x the size of the stars of the Milky way but which radiate between 50 and 150 times as much energy.
Quasi-Biennial Oscillation : Periodic variation in the direction, either easterly or westerly, of tropical lower stratospheric winds. The direction changes every 26 months.
Quaternary : The period of Earth's history from about 2 million years ago to the present; also, the rocks and deposits of that age.
Quaternary period : The most recent period of geological time which includes the Pleistocene (Ice age) and Holocene epochs. It is the period in which man became the dominant terrestrial species. Some authorities consider the Quaternary to be a division of the Tertiary.
quinine : A bitter drug obtained from the bark of the cinchona tree, used to reduce fever and as a tonic. It was the first drug used to treat Malaria but has now been largely replaced by other drugs which have fewer side affects and which are less toxic.
quinidine : A quinine like compound used to treat abnormal heart rhythms.
quinone (O:C6H4:O): An aromatic compound with two hydrogen atoms in the benzene ring replaced by two oxygen atoms. Quinones are used in photography and dye manufacture and are found in plants.
quotient : The result of a division sum.
r- strategists :
raceme : Flowers arranged like a spike, but with footstalks.
rad : The unit of absorbed dose on ionising radiation equivalent to an energy absorption of 100 ergs per gram of irradiated material.
radial velocity : The velocity of a star etc. along the line of sight, i.e. towards or away from the earth. It is calculated from the Doppler shift on the lines of the stars spectrum.
radian : The SI unit of plane angle equal to the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle, i.e. 1 rad = q(p/180).
Radiant : The point from which a meteor appears to emanate.
Radiant Drift : The movement of a meteor shower's radiant against the star background. This characteristic is common to all meteor showers and is caused by Earth's passage through a meteor stream.
Radiation Flux : This is defined as the way heat from the sun is absorbed, scattered, returned, or deposited around the earth and can be expressed as some radiation arrival rate per the unit of area of the surface. The radiation flux can be the total amount of radiation that the earth collects, emits, and disperses.
Radiative Forcing : Reduction of radiation reflecting from earth per units of increase of a chemical component that causes this change in the atmosphere. The result is often used to compare the relative effect of greenhouse gases which can alter climate on earth. This means that components that are present in the atmosphere at low concentrations (e.g. methane at 1.7 ppmv) but with high radiative forcing have a greater effect on global warming than higher concentration components with a lower radiative forcing.
Radical (free radical) : A highly reactive molecule or atom with an unpaired electron. The species is often represented by a formula with a single dot as the unpaired electron.
Radical Chain Reaction : Free radicals are molecules that, through photolysis or chemical reaction, have an unpaired electron in their outer valance shell. These radicals are very reactive and thus have a short life. When a free radical reacts with a more stable molecule, the radical often pulls an atom from it and becomes a stable molecule itself. The original molecule then becomes a free radical and will react with other species of atoms and molecules in a long series (or chain) of reactions until the process reaches the termination phase. In this phase two free radicals combine, sharing the pair of electrons and breaking the chain.
Radical Propagation : Free radicals react with molecules, atoms, other radicals in long series of chain reactions. A radical is formed in the atmosphere through photolysis or chemical reaction. Radicals are very reactive and will pull atoms or electrons from other molecules to fill their outer valance shell. New radicals may formed from the original molecule which then react with another molecule, etc. This reaction propagates from one species to another until a termination reaction occurs. The termination reaction usually involves the reaction of two free radicals to form a stable product.
Radioactive Decay - The spontaneous breakdown of certain kinds of atomic nuclei into one or more nuclei of different elements, involving the release of energy and subatomic particles.
radioactive decay : The decrease in mass of certain unstable elements by emission of elementary particles, continuing until a stable isotopic form has been reached.
Radiocarbon Dating : Establishing the relative age of various materials with the use of carbon -14. This involves measuring the amount of 14C and of 12C and comparing the measured ratio to the one established by the production of 14C in the upper atmosphere by cosmic rays. When an organism is alive the 14C : 12C ratio in its biomass is constant (because of constant atmospheric 14C production, difussion to the lower atmsophere, absorption by organisms, and because of constant 14C radioactive decay) but when the organism dies the ratio begins to change, at a very predictable rate. Therefore knowing the carbon -14 : carbon -12 ratio now in some artifact gives a very good measure of how long the carbon has been "dead." The object however must obviously have organic material either in it or on it for this method to work. Also the lenth of time one can "look back" is limited because the amount of carbon -14 must be detected with some certainty for the age to be known with confidence, and the longer the sample has been dead the less 14C is present because it is continually decaying.
radio galaxy : A radio source that lies beyond our Galaxy, is identified with an optical galaxy, and the radio-power output of which greatly exceeds that of a normal galaxy. The size can be immense. A massive black hole at the galaxy centre has been postulated as a possible energy source.
radiography : The technique of examining the internal structure by passing X-rays or gamma radiation through it to produce an image on a photographic plate or fluorescent screen. Radiography is used in medicine and in industry to find structural defects.
radiosonde : a light-weight instrument package carried aloft by a weather balloon; radios to earth upper atmosphere data.
Rainout : One item necessary for a rain drop to form is called a condensation nucleus. Pollutants in the air such as nitric acid and sulfuric acid form nucleation sites (particles) where water vapor often condenses and forms a droplet. As these droplets grow they collect more moisture and may ultimately fall out as precipitation. This accounts for some of the acid rain deposition on the planet's surface.
random errors : these result in repeat measurements on the same sample to vary in a number of tests.
rangefinder : a camera in which the subject is viewed through a separate view finder. There will always be the problem that what you see may not be what is taken, the classic examples being close ups of blurred fingers, and lens caps left on.
Raoult's law : The partial vapour pressure of any volatile component, A, of an ideal solution is equal to he vapour pressure of pure A multiplied by the mole fraction of A in the solution.
Rayleigh Scattering : The scattering of light by a body with a particle diameter (Dp) less than 0.03 micrometers is termed Rayleigh Scattering. The wavelength of light scattered is dependent on the Dp, and the amount of light scattered is dependent on the number of particles present per unit volume. Shorter visible wavelengths, such as blue, are scattered by smaller particles than are the longer wavelengths like red.
Reaction Rate : The speed of chemical reactions is expressed as a rate of change in the concentration of a participating species with respect to time.
Reasonably Practicable :
The implication that the quantum of risk is balanced against the sacrifice or cost in terms of money, time and trouble necessary to avert that risk. If the risk overweighs the sacrifice or cost, additional precautions are necessary.
recessive (genetics) : referring to the relative lack of phenotypic effect of a gene in the presence of its dominant allele. Thus the gene for the blue eyes is said to be recessive for that for brown in the human population, because when one allele for blue eyes and one for brown eyes are present in an individual, the blue condition is masked and the individual has brown eyes.
recombination (genetics), The formation of new genotypes (a combination of genes not present in either of the parents) in offspring due to independent assortment of genes and chromosomes during gamete formation.
red giant : A greatly distended cool but very luminous giant star, often variable in nature. It is one of the final evolutionary stages of a normal star, attained when its central hydrogen has been converted to helium. Hydrogen burning in a shell surrounding the inert helium core causes a rapid expansion and cooling of the outer atmosphere of the star.
red shift : An overall displacement towards larger wavelengths of the spectral lines of a celestial object. Its astronomical significance, suggested by Hubbell, is connected with it's use as the basis of the theory that the universe is expanding. A red shift usually arises from the Doppler effect, that is from recession of a celestial object. It increases as the objects radial velocity increases and for an extragalactic body can be used as a measure of distance. A gravitational redshift occurs whenever radiation is emitted by a body: it is generally negligible except when the gravitational field is very strong.
reduction (chemistry) : A reaction involving the gain of electrons.
reduction division : A cell division, during which the number of chromosomes in each daughter cell is reduced to one half of that found in the parent cell. This is accomplished by nuclear division without previous chromosomal division.
refraction : The bending of a beam of radiation as it passes from one medium to another. For a light ray the amount by which it is bent depends on the angle of the incident ray and on the refractive indices of the two media, the exact dependence being given by Snell's law. Refraction is caused by the difference in the velocity of the radiation of the two media. The ratio of the velocity of light in the media is known as the refractive index. If the first medium is a vacuum, the ratio is known as the absolute refractive index.
regeneration : The development process by which a lost part of an organism (such as an organ, part of an organ, or tissue) is replaced after damage. Repair of wounds and the regrowth of a salamanders amputated arm are examples of regeneration.
relative density (specific gravity): The density of a substance divided by the density of water at 4oC. This value is numerically one thousandth of the density.
Relative Humidity : This is the ratio between the actual water vapor content of the atmosphere and the maximum water vapor content possible at that given temperature. If the temperature of a given parcel of air rises, the amount of moisture it can hold increases and as such its relative humidity decreases. If there is no change in temperature but the moisture content decreases then the relative humidity will again decrease because the ratio of actual water vapor present is less than the maximum amount the air could hold. Conversely, if the water content does not change but the temperature falls, the relative humidity increases until saturation and possible precipitation occurs.
relative humidity : a ratio of the amount of water vapour that the air is holding to the amount of water vapour the air can hold, which depends on temperature.
relative velocity : The velocity of one body relative to another.
Reportable Disease (UK) :
A disease which must be reported to the authorities when linked to specified types of work. (The Reporting of Injuries Disease and Dangerous Occurrences Regulations 1985).
Respirable Dust :
That fraction of total inhalable dust which penetrates to the gas exchange region of the lung.
respiratory assembly : A series of complex molecules (including cytochromes), found on the inner membranes of mitochondria, and capable of oxidation and reduction. Such assemblies accept electrons from reduced acceptors during the citric acid cycle and pass them along to the final acceptor, oxygen. The enzymes for oxidative phosphorylation are also components of the respiratory assembly.
Respiratory Sensitizer :
A substance that may cause sensitization on inhalation, causing, e.g., asthma, rhinitis or extrinsic allergic alveolitis.
response : A change in behaviour on the part of an organism (or tissue) as a result of some chemical or physical change in the environment.
restriction fragment length polymorphism : a technique, also known as DNA fingerprinting, that allows familial relationships to be established by comparing the characteristic polymorphic patterns that are obtained when certain regions of genomic DNA are amplified (typically by PCR) and cut with certain restriction enzymes. In principle, an individual can be identified unambiguously by RFLP (hence the use of RFLP in forensic analysis of blood, hair or semen). Similarly, if a polymorphism can be identified close to the locus of a genetic defect, it provides a valuable marker for tracing the inheritance of the defect.
Return Stroke : A short-lived, high amplitude discharge of electricity that accompanies a cloud-to-ground lightning event. The bright lightning flash that is visible to the human eye is actually composed of extremely rapid electric discharges called strokes. The return stoke follows a downward extending leader, or conductive path of ionized air. The electrons in the cloud flow down this conductive pathway toward the surface of the earth. As electrons continually migrate down the path, electrons remaining higher up on the path in the cloud begin to consecutively move down the channel to the surface. Since the path of electron flow is progressively lengthened upward, the discharge of the elevated electrons high in the cloud to a lower place in the cloud and then down the pathway to the ground is called the return stroke.
reverse phase HPLC : chromatography in which the stationary phase is non-polar and the mobile phase is polar.
reversible reaction : A reaction system where reactants and products are inter convertible. If left to themselves , reversible chemical reactions reach an equilibrium point where just as much reactant is being converted into product as product into reactant at any time. Nearly all chemical reactions are to some extent reversible.
revolver : A short range small arm having a revolving cylinder containing the rounds behind the barrel. In single action types pressing the trigger cocks the weapon and simultaneously rotates the cylinder; further pressure fires it. Double action types perform these functions automatically but their stiffer mechanism impairs accuracy. Calibre's range from .21 inches to .455 inches.
Reynolds number :
Rhesus (Rh) factor : An antigen found in the red blood cells of certain human beings (designated Rh+). The Rh factor acts as an antigen so that individuals with this factor cannot donate blood to individuals who normally lack it (Rh- individuals). The factor derives its name as it was first discovered in the Rhesus monkey.
rho ( R, r ):
ribonuclectic acid (RNA) : A complex single stranded molecule consisting of repeating nucleotide bases; adenine, guanine, cytosine and uracil. At least three types of RNA are known, all of which are involved in transcribing the genetic code into protein.
ribosomal RNA (rRNA): A type of RNA found as part of the ribosomes. The function of rRNA is not well understood although it appears to have some role in protein synthesis.
ribosomes : Small particles found either free in the cytoplasm or attached to the outer surface of the endoplasmic reticulum in the cells of all eukaryotes and many prokaryotes. Ribosomes contain high concentrations of ribonucleic acid (RNA) and are centres of protein synthesis.
ricin poisoning :
Richter scale : A logarithmic scale (from 0-9) used to measure earthquake magnitude. It is based on seismic recordings and takes into account the distance from the epi-centre. The strongest earthquake so far recorded had a Richter scale value of 8.6
ridge : an area of high pressure. An area of anticyclonically curving winds.
rifle : A shoulder small arm with a spiral inside its long barrel to make the projectile spin during it's trajectory.
rifling marks : The marks formed on a bullet as a result of its passage along the barrel of a firearm. Revolvers and self loading pistols are divided into five "types":
| Steer type |
Used in all of the earlier self loading pistols |
| Browning type |
The most common with six broad grooves with narrow lands and a right hand twist. |
| Colt type |
Used in all Colt pistols, Bayard pistols and Spanish copies of the Colt. Six broad grooves with narrow lands and a left hand twist. |
| Webley type |
Used in all Webley revolvers. Seven broad grooves with narrow bands and a right hand twist. |
| Smith and Wesson type |
Used in all S+W revolvers, Harington and Richardson revolvers and Iver Johnson revolvers but not used in any self loaders. Five grooves and lands of equal width with a right hand twist |
Right Ascension : The celestial equivalent of Earth's longitude, beginning at a line running pole to pole and cutting through eastern Pegasus. In meteor astronomy the right ascension is handled in degrees, starting at zero degrees and advancing eastward around the sky for a full 360 degrees ending in eastern Pegasus. For the rest of astronomy, the right ascension is handled as a time measurement. Since it takes 24 hours for the Earth to rotate, the sky is divided into 24 one hour wide bands. Each hour of right ascension equals 15 degrees.
roentgen : A unit used to measure the amount of energy in X-ray (or gamma ray) beams. One roentgen is the amount of radiation which, under ideal conditions (0oC and 760Hg), liberates 2.083 x 109 ion pairs per cubic centimetre of air.
rootstock : An underground stem.
RR Lyrae stars : A class of short period pulsating variable stars that are very old giant stars found principally in globular star clusters, all with about the same mean luminosity.
rudimentary phallus : Genital folds in both male and female embryos. In males the rudimentary phallus develops into the penis. In females the phallus grows only slightly and develops into the clitoris.
Rydberg constant : 1.097 x 105 cm-1.
safe system of work :
A formal procedure resulting from systematic examination of a task to identify all the hazards. Defines safe methods to ensure that hazards are eliminated or risks controlled.
satellite : can be natural or artificial. The artificial are electronic devices placed into orbit to monitor and examine regions which we may not be able observe from earth. These are used routinely to monitor atmospheric ozone, ultraviolet radiation, and many other constituents. Satellite altimetry and radar interferometry are used to measure magnetic field intensity and track Antarctic ice flow.
saturated hydrocarbons : a hydrocarbon in which the maximum valencies of the carbon atoms are satisfied by single links.
saturation : the point at which the air cannot hold any more water vapour; the point at which condensation occurs. RH =100%. Saturation is where the amount of water condensing is equal to the amount of water evaporating.
Saturn (Astronomy): The sixth planet from the sun with an orbit of 29,48 Earth years, and a spin period of 10 hours, 39 minutes and 20 seconds. It has a diameter of 74,400 miles (the second largest of the planets) and a gravity equivalent to 1.07 that of the Earth. It has 21 moons and over a thousand rings. It is the least dense planet in the solar system and has no solid surface. A magnetic field was discovered around Saturn, aligned parallel to the planet's rotation axis.
scalar quantity : A quantity that is represented by magnitude only. Unlike a vector quantity a scalar quantity has no direction. Examples include mass, time and speed.
Schlieren photography : A method of observing differences of density in a transparent medium, such as air. Light from a spark is photographed as it passes through the medium; any differences in density present cause local variations in the refractive index, which show up as streaks in the photograph. The method is used for observing sound waves, shock waves and flaws in glass.
Schwartzchild radius (SR) : The radius of a contracting star at which nothing, including light, can escape from it. It then becomes a black hole. The Schwartzchild radius for the Sun is 3 km (actual radius 7x108 m).
sclerotium (pl. sclerotia) : firm mass of hyphae, usually without spores, which can survive dormancy and give rise to mycelia or a fruiting body. Usually visible with the unaided eye.
scopolamine :
Scott test : A three part test for cocaine. Solution A is composed of 2% cobalt thiocyanate in one part each of water and glycerine. This is added to the suspect substance which, if it contains cocaine, will turn it blue. Confirmation can be provided by solution B which is concentrated hydrochloric acid, and which will turn the blue solution pink. With the addition of solution C, chloroform, the blue colour will reappear in the chloroform layer.
sea level : This is the average level of the ocean over the entire earth. Tidal fluctuation is taken into account when determining sea level. Mean Sea Level (MSL) is used to reference the height of structures above ground level and depth below the ocean's surface. Atmospheric pressure is also referenced from sea level. At sea level, 760mm (29.92 inches) of mercury is normally displaced by the pressure of the air column above that point on the earth.
secondary spermocyte : The daughter cells produced by the first meiotic division if the primary spermocyte during spermatogenesis.
secretin : hormone secreted by the cells of the duodenum under the stimulus of hydrochloric acid from the stomach. Secretin in turn causes the pancreas to secrete certain digestive enzymes into the duodenum.
sediment : Particles carried by water or air that are deposited in other areas or elevation are called sediment. Usually associated with water flow, sediment will accumulate at the mouth of a river or stream as it empties into a larger, slower moving body of water. Sediment deposition is also effected by particle size.
sedimentary rock :
seismic belts : The narrow distinct belts on the Earth's surface that are subject to frequent earthquakes. They usually follow the line of plate boundaries, especially along mid-ocean ridges, near young orogenic belts, along island arc systems, and along major faults.
seismology :
segregation (of alleles) : The separation during gametogenesis of paired factors influencing a single condition.
selectivity : the extent to which a method suffers from interference.
seminal vesicles : the portion of the male reproductive duct in which sperm are stored prior to copulation.
seminiferous tubules : Tubules within the testes where the male sperm are produced. Each testis contains about 1000 highly coiled seminiferous tubules.
semi-permeable (differentially permeable): Term applied to a membrane that allows some substances to pass through while prohibiting the passage of others.
sensitization dermatitis :
Inflammation of the skin due to an allergic reaction to a sensitizer .
sex chromosome : The chromosomes commonly referred to as "x" and "y", whose presence in certain combinations determines the sex of an organism.
sensitivity : the ability of an instrumental method to distinguish between small differences between analyte concentrations.
sessile : Leaves or flowers connected to the stem without footstalks.
sex pilus :
shear strain : An angular measure of deformation.
short-period comets : Comets moving in orbits having periods less than 200 years.
SI multiples :
SubmultiplesMultiples
| Value | Symbol | Name | | Value | Symbol | Name
10–1| d | deci | | 101| da | deca |
10–2| c | centi | | 102 | h | hecto |
10–3| m | milli | | 103| k | kilo |
10–6| µ | micro | | 106| M | mega |
10–9| n | nano | | 109| G | giga |
10–12| p | pico | | 1012| T | tera |
10–15| f | femto | | 1015| P | peta |
10–18| a | atto | | 1018| E | exa |
10–21| z | zepto | | 1021| Z | zetta |
10–24| y | yocto | | 1024| Y | yotta | | | | | | | | | | | | | | | | | | | | | | | |
sial : The Earth's continental crust, which is composed of granite rocks rich in silicon and aluminium. It is less dense than the underlying layer of sima and much thicker.
sickle cell anaemia : A hereditary disease caused by a mutant form of haemoglobin. Under low oxygen tension in the blood, red blood cells containing sickle cell haemoglobin collapse, assuming a half moon, or sickle shape. The disease is mild in the heterozygous form but greatly shortens lifespan in the homozygous dominant form.
sidereal period : The time taken by a planet or satellite to return to the same point in it's orbit, i.e. to complete one revolution with reference to the background stars. It can be determined from the body's synodic period.
siemens (S): Unit of electrical conductance equivalent to the reciprocal of the ohm.
sigma ( S, s ):
Silurian period : A geological period lasting from about 4.45 to 4.15 x 108 years ago. Conditions were mainly marine and all the first true fish appeared. The first evidence of land plants also comes from the Silurian rocks. The Caledonian period of mountain building reached it's peak towards the end of the period.
sima : The Earth's oceanic crust, which is composed of basilic rocks rich in silica and magnesium. It is denser than the sial of the continental crust and is believed to continue below it.
simple sugar : A molecule composed of a single five or six-carbon sugar.
sine rule, any angle divided by the sine of the angle is equivalent to any other.
singularity (cosmology) : The point of infinite density at the central point of a black hole.
sink : a natural removal process for pollutants in the troposphere such as dissolution and removal via rain.
sintering : The heating, without melting, of a powdered substance, usually metal or plastic, so that it becomes a solid mass.
sleet : frozen precipitation that falls as little chucks of ice.
single lens reflex (SLR): a camera in which the photographer views exactly what will appear on the film. 
Lenses are interchangeable and close up attachments are easy to fit. They are very versatile and convenient for forensic photography. The most common type of these cameras is the 35mm. Similar in construction is the 2 ¼ inch which offers a larger film format. This will give a sharper picture than the 35mm and is therefore good for forensic photography.
small-arms : Short range, low weight firearms, originally defined as capable of being handled by one individual, they include pistols, submachine guns, rifles, grenades and shotguns. An artificial calibre ceiling of 0.6 inches, in some classification systems 20mm has had to be abandoned with the introduction of small rockets and anti-tank guided missiles.
smallpox : a severe infectious viral disease, controllable by cowpox vaccine.
smog : a term used to describe a mixture of smoke and fog. Smog occurs when high concentrations of moisture is combined with smoke (often containing oxides of sulfur and nitrogen) in the presence of high temperatures or thermal inversions and the absence of wind. These conditions cause polluted air to stagnate over industrial areas and can create a respiratory health hazard. Large coastal industrial centers with surrounding high ground are more prone to smog. There is often a diurnal (over a day) variation in the process of smog formation because one of the necessary components for its formation is sunlight.
smoke : the product of incomplete combustion and consisting mostly of carbon and small liquid and solid particles. Smoke is primarily caused by the burning of wood, coal, gasoline, or other biomass. Smoke particles are usually less than 1.0 micrometers in size. Wind intensity, particle size, air temperature, and atmospheric pressure all effect how smoke behaves in the environment.
Snell's law : When a ray of light passes from one medium to another the angle q between the refracted ray and a line normal to the interface between the media is related to the angle (i) of the incident ray, also taken to the normal, by the equation sin i/sin r = n, where n is the relative refractive index of the media.
SOCO ( Scene Of Crime Officer ) :Police Officer involved in case.
sodium dodecyl sulphate (SDS) : A detergent that disrupts most protein-protein and protein-lipid interactions.
solar longitude :This is an angular measurement that specifies the location of Earth in its orbit around the sun. More precisely, it is the longitude of the sun as given in geocentric coordinates. The evaluation of meteor data strongly relies on this figure rather than a conventional date.
solar radiation : This is electromagnetic radiation (light energy) emitted by the sun. This energy is transmitted through space in the units of electromagnetic energy called photons. The strength of the solar energy that reaches our outer atmosphere is called the solar constant and has a value of approximately 2.0 calories per minute per square centimeter. Roughly one-half (1.0 cal min-1 cm-2) of all the solar radiation that enters the upper atmosphere is available at the earth's surface. Of the fifty percent loss, approximately 32 percent is reflected back into space by either clouds, dust, or aerosols; the remaining 18 percent is absorbed by clouds, dust, water, and atmospheric gases. The short high-energy wavelengths that are absorbed by the Earth are re-radiated at longer, lower energy wavelengths mostly in the IR wavelength region. These lower-energy wavelengths are, in part, prevented from escaping into space by the greenhouse gases in the atmosphere. Solar radiation is the fuel source that provides a mechanism for all biological processes on earth. Without solar radiation, life on earth would not exist. (This statement, of course, neglects the contribution to the earth's surface temperature from radioactive decay in the earth.)
Solar system : A system comprising the sun and the astronomical bodies gravitationally bound to the sun, that is the nine major planets, heir satellites, ad the immense numbers of minor planets, comets and meteoroids. Almost all of the mass of the solar system (99.86%) resides in the Sun. The planets orbit the sun in the same direction and, with the exception of Pluto, move in paths close to the Earth's orbit (i.e. close to the ecliptic) and the suns equator. This and other information is taken as evidence of the common origin of the sun and the planets, some 4600 million years ago, following the contraction and subsequent flattening of a rotating cloud of interstellar gas and dust.
| Body |
distance from sun
(x106 m)
|
sidereal period |
spin period |
radius
(km)
|
no. of satellites |
mass (kg) |
mean density |
| Sun |
--- |
--- |
25.38d |
696000 |
9 |
1.99 x1030 |
|
| Mercury |
58 |
88 d |
59d |
2434 |
--- |
3.3 x 1023 |
5490 |
| Venus |
108 |
225 d |
244d |
6052 |
--- |
4.9 x 1024 |
5246 |
| Earth |
150 |
365 d |
1d |
6378 |
1 |
6 x 1024 |
5517 |
| Moon |
--- |
--- |
--- |
1738 |
|
7.4 x 1022 |
3342 |
| Mars |
228 |
687 d |
24h |
3395 |
2 |
6.4 x 1023 |
3937 |
| Jupiter |
778 |
11.86 y |
10h |
70866 |
12 |
1.9 x 1027 |
1363 |
| Saturn |
1430 |
29.5 y |
10h |
60016 |
9 |
5.7 x 1026 |
696 |
| Uranus |
2870 |
84 y |
10h |
25402 |
5 |
8.9 x 1025 |
1335 |
| Neptune |
4500 |
165 y |
15h |
22300 |
2 |
1 x 1026 |
1570 |
| Pluto |
5900 |
248 y |
6.4d |
3200
(2750)
|
--- |
6.6 x 1023 |
4800
(7900)
|
Solar Wind : The outflow of charged particles from the solar corona into space. Because of the high temperature of the particles of the corona (mostly protons and electrons), they are moving at speeds higher than the solar escape velocity. At the orbit of the Earth, these particles are moving at about 500 km/sec. Some of these particles are captured by the magnetic fields of the planets, forming their magnetospheres.
soluble RNA : see transfer RNA
solute : The substance that is dissolved by a solvent.
solvent : That part of the solution that is present in the largest amount, most often the part that, if pure, is normally liquid.
somatoplasm : A term used to describe all the cells of an organism except for the reproductive cells(germ plasm). In each generation the somatoplasm is derived from the germ plasm of the previous generation, but is distinct from it in that changes in somatoplasm (body cells) will not be passed on to the next generation.
somites : Paired, block like masses of mesoderm arranged in a longitudinal series along the side of the neural tube of the embryo. Each somite will form one vertebra and its associated muscles.
sorption : A class of processes by which one material is taken up by another. Absorption is refers to the process of the penetration of one material into another; adsorption to the action of one material being collected on another's surface.
sound : A disturbance propogated through a medium by longitudinal waves. Strictly the term applies only to those waves that are audible to the human ear, i.e. with frequencies between about 20 and 20,000Hertz, those with frequencies above 20,000 Hz being called ultrasound and those below 20 Hz being called infrasound. Sound is propogated by vibrations of molecules in the medium, producing fronts of compression and rarefaction. Sound waves are longitudinal as the molecules vibrate in the direction of propagation. The three basic principles of sound are it's pitch (the frequency of the wave).
sounding : a temperature profile of the atmosphere measured by a radiosonde. Also can indicate wind and dew point.
sound intensity : The rate at which sound energy is propagated through a unit area perpendicular to the direction of propagation. It is measured in watts per square metre. The intensities of two sound levels are compared by a unit called a decibel. The intensity of a sound is not the same as its loudness, the latter being the magnitude of the sensation produced by the human ear, which is dependent upon the frequency of the sound.
sound, speed of : 760 mph or 332 m-s
space time continuum : A co-ordinate system that has four dimensions, three representing physical space and the fourth time. The four dimensional space-time continuum is used in relativity to define an event. For example an event occurring on the sun would be observed at different times on Earth and on Jupiter, as the light from the Sun takes some 35 minutes longer to reach Jupiter than to reach the earth. Thus the concept of simultaneity requires a four dimensional co-ordinate system to define events without ambiguity.
spathe : The large bract that envelops certain flowers before opening.
special creation : An account of the origin of life and its diverse forms by some act of divine creation.
specialisation (of cells) : The change in cell capability from the performance of a wide variety of functions to concentrate on one activity or set of activities.
speciation : The process by which the accumulated effects of variation within a population make cross breeding between two given organisms difficult or impossible.
species : The smallest unit of taxonomic classification, referring to the most part a group of individuals capable of breeding amongst themselves. Species are defined by morphological, ecological, physiological, and biochemical criteria.
specific gravity (relative density): The density of a substance divided by the density of water at 4oC. This value is numerically one thousandth of the density.
specific heat capacity (c) : The quantity of heat needed to raise a unit mass of substance by 1oC. It is measured in joules per Kelvin per kilogram. For gasses the specific heat capacity at constant pressure (cp) exceeds that at a constant volume (cv) as heat is required to do work against the surroundings during the expansion. The rate of cp/cv (symbol: y) is 1.66 for monoatomic gases, 1.4 for diatomic gases and about 1 for other gases.
speculum : A patch of brightly coloured feathers on a ducks wing.
spectroscopy, The analysis of light by which the chemical make up of the light source can be identified by the dark lines created by individual elements within the light spectrum.
spectrum : In general the way in which a particular property of a system is distributed over it's components. The visible spectrum, for example, is observed in a rainbow, which shows the distribution of frequencies when sunlight is split up into it's components by raindrops. The visible part of the spectrum however is only a small part of the electromagnetic spectrum, which ranges from X-rays to radio waves.
spherical aberration : the tendency of a lens to focus the rays of light passing through the centre at one point while focussing rays from the outer portion at a different point.
Many photographic lenses have six or more elements that have been introduced to cancel both colour and spherical aberrations. This is especially true for special lenses such as fast ( wide aperture ) lenses.
spontaneous combustion :
Combustion that results when materials undergo atmospheric oxidation at such a rate that the heat generation exceeds heat dissipation and the heat gradually builds up to a sufficient degree to cause the mass of material to inflame.
spontaneous generation : A concept according to which living organisms develop from non-living matter.
sporodochium (pl., sporodochia) : cushion-shaped mass of hyphae covered with conidiophores.
spring equinox : In the Northern hemisphere, March 21 or 22; on these dates, the rays of the sun are striking vertically at noon at the equator (0 degrees latitude), for the earth is in such a position in its orbit that the axis is tilted neither toward nor away from the sun. For latitudes above the equator, the dates are earlier then these dates.
squamous (pavement) epithelium : Epithelium composed of flat nucleated scales of various shapes, usually polygonal and varying in size. These cells fit together by their edges, like the tiles of a mosaic pavement.
SS/Fix ( Signed Speed Fix ) : Method of sealing certain types of item packaging that could otherwise be easily tampered with, such as CJA and SSPB packaging. Uses a sticky label with the sealer’s initials and date, covered by sellotape.
stability : possessing the ability to return to its original position; suppresses convection.
standard solution : Any solution of known concentration.
star : a luminous celestial body that is composed of gas and that derives it's energy from thermonuclear reactions in it's hot dense core. The Sun is a typical star. Stellar mass usually ranges from about 0.05 to 60 times the suns mass. A star's mass determines it's luminosity, surface temperature, size, and other properties as well as it's evolutionary path and lifetime: the higher the mass, the brighter, hotter, and larger the star and the shorter it's life. During the course of their history stars evolve, a process called stellar evolution. Young stars evolve from the protostar stage when they begin to generate energy by the thermonuclear fusion of hydrogen to form helium. This continues for some 1010 years for stars of solar mass but for only a few million years for the most massive stars. When the hydrogen is exhausted, stars evolve into giant stars, those of near solar mass becoming red giants. Further thermonuclear reactions occur involving fusion of helium, and possibly the heavier elements in more massive stars. A low-mass star finally evolves into a white dwarf. More massive stars explode as super-novae, the surviving cores possibly forming neutron stars or black holes depending on mass. Stars are not distributed uniformly through the universe but are grouped into enormous assemblies, called galaxies, as a result of gravitational forces.
starch : The principle reserve carbohydrate of plants.
star cluster : A group of stars that are associated by gravitational effects and that shared a common origin. Open clusters are loosely bound asymmetrical groupings of up top a few hundred stars occupying the disc of our Galaxy. Globular clusters are compact spherical groupings containing many thousands of very old stars and occur in the galactic halo.
static equilibrium : A state of balance in which there is no activity.
statistical analysis, The use of mathematics to determine whether deviations from a pattern, as predicted by a hypothesis, are correct.
steady state theory : The model that holds that new matter is created in the spaces between the moving galaxies, so as to keep the density of the universe constant.
steam explosion :
Overpressure associated with the rapid expansion in volume on instantaneous conversion of water to steam.
steering : directing other motion. The jet stream steers surface storm systems.
Stefans constant (s) : 5.67 x 10-8Jm-2 s-1 degK-4
steradian (sr) : The SI unit of solid angle equal to a solid angle that encloses a surface on a sphere equal to the square of its radius.
stere : metric unit of volume equal to one cubic metre.
steroids : A class of compounds containing four fused hydrocarbon rings.
stibium (St): The original name given to Antimony.
stimulus : Any physical or chemical change in the environment which brings about a change in the activity on the part of an organism (or portion of an organism, such as isolated tissue).
Stoke's law : The resisting force acting on a sphere, radius r, moving through a fluid under gravity with velocity v is 6prhv, where h is the viscosity of the fluid. This law is used in the determination of viscosity.
strain (physics) : The deformation of a body when it is subjected to stress.
strangeness : A property of matter expressed as a quantum number (s), postulated to account for the unusually long lifetime of some hadrons. In the quark model strange hadrons contain the strange quark or it's antiquark. Strangeness is conserved in strong interactions and electromagnetic interactions.
stratified epithelium : Several layers of cells superimposed on top of one another and varying greatly in shape. The cells of the deepest layer normally columnar and forming a single layer. Above these are several layers of spheroidal cells, becoming more compressed up to the superficial flattened cell layer.
stratocumulus clouds : Low altitude gray colored clouds composed of water droplets that have a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen.
stratopause : The boundary between the stratosphere and the mesosphere. It occurs at a height in the atmosphere of approximately 50 kilometers; however this depends on latitude. The atmosphere is characterized by a decrease in pressure with respect to increased altitude. More importantly, regions within the atmosphere like the troposphere, stratosphere, and mesosphere are distinguishable because of distinct temperature gradients with relatively well-defined starting and ending points. The stratopause is the highest portion of the stratosphere, with a temperature of approximately 0oC; the stratopause can also be described as the warmest region between the mesosphere and the stratosphere.
stratosphere : The thermal atmospheric region of the atmosphere between the troposphere and the mesosphere. The lower boundary of the stratospheric region is marked by the tropopause and begins at approximately 13 kilometers; however, this altitude of the troposphere depends on latitude. The upper limit of the stratosphere is marked by the stratopause at approximately 50 kilometers. The stratosphere is characterized by relatively stable temperatures (between -80 and -50 degrees Celsius) in the lower regions, and begins warming near 20 kilometers, reaching its maximum temperature of approximately 0oC at the stratopause. Stratospheric chemistry is of particular interest to scientists because ozone, the principal substance that shields the earth from incoming solar ultraviolet radiation, is found in the stratosphere. It should also be noted that wind currents in the stratosphere are primarily horizontal in nature.
stratospheric clouds : These are clouds found in the stratospheric region of the atmosphere. Unlike the moisture laden troposphere, the stratosphere is almost moisture free. A lack of moisture means that cloud formation in the stratosphere is a relatively uncommon occurrence. Because of the very low temperatures, nacreous clouds, a type of stratospheric cloud, occur during winter conditions at the higher latitudes. A second type of stratospheric cloud, called a polar stratospheric cloud (PSC), occurs in the polar regions during winter and early spring. Polar stratospheric clouds are of particular interest to scientists studying the Antarctic Ozone Hole. Polar stratospheric clouds form under extremely cold conditions, whereby nitric acid, water vapor and other trace chemicals freeze to form ice crystals. PSCs provide a solid surface on which chlorine-containing reservoir compounds can gather, and on this surface the chemical reactions involved in the depletion of ozone are greatly increased.
stratospheric ozone : This is also called the ozone layer, where ozone concentrations are as high as 10 parts per million, and is a vitally important region of the atmosphere. This layer of ozone is located approximately 20-50 kilometers above the earth's surface. Stratospheric ozone is important because it prevents most of the high-energy ultraviolet solar radiation from reaching the earth's surface. Photodissociation, a photochemical process, is responsible for the formation of the protective ozone layer in the stratosphere. In the upper atmosphere, diatomic oxygen absorbs high-energy ultraviolet radiation. The absorption of radiation causes the diatomic oxygen molecule to break forming two oxygen radicals. The oxygen radical can then recombine with other diatomic oxygen molecules to form triatomic oxygen, or ozone. In the middle regions of the stratosphere, ozone is found in concentrations as high as 10 parts per million. Ozone can also form in the lower portions of the troposphere, due to anthropogenic activity and by a completely different mechanism. Without the protective stratospheric ozone layer in the upper atmosphere, life (as we know it) on earth would not be possible.
stratus cloud : In general, clouds are classified and named according to their appearance and altitude at which they occur, being either high, medium, or low. Stratus clouds are low clouds, and as the root word suggests they are layered in appearance. They occur in broad sheets across most or all of the sky. Generally their formation is due to condensation within layered air that is not subjected to strong vertical movement.
strychnine : An alkaloid poison derived from plants of the genus Strychnos. It acts upon the C.N.S., causing convulsions and ultimately death. It is still used as a poison for pests such as moles.
styrene : chemical formula C8H8, also commonly called vinyl benzene. Styrene is an aromatic hydrocarbon originating from petroleum and natural gas by-products. It is used to manufacture resilient, lightweight packaging materials and fiberglass. Styrene is extremely volatile in air and evaporates quickly; as a result, it does not remain in the atmosphere for long periods of time.
sublimation : The evaporation of a substance without melting. For any substance the liquid phase only occurs within certain limits of temperature and pressure - if the pressure is low enough, heating a solid will result in sublimation. Substances that sublime at atmospheric pressure include carbon dioxide (dry ice) and iodine.
sub-machine gun : A light short range small arm developed from the infantry light machine gun. They are more accurate than the pistol and smaller than the rifle. They almost all use 9mm ammunition, fire automatically, and depend on blow-back action (i.e. use the expanding gas of the ammunition to activate the reloading mechanism).
subsidence : sinking air.
substrate : The molecule upon which an enzyme acts during an enzyme catalysed reaction.
succession : Ecological development that begins in a habitat or area not previously occupied by the given community of a previously unoccupied area.
Secondary succession : refers to the replacement of one community by another.
sucrose : A carbohydrate consisting chemically of one molecule each of glucose and fructose linked together. It is commercially the most important of the sugars, being used as a sweetener in food and drinks. When heated to 160oC it forms barley sugar and at 200oC becomes caramel.
sulphur dioxide : This is a colorless gas consisting of a single sulfur atom and two oxygen atoms. Sulfur dioxide is a major primary pollutant in the atmosphere originating mostly from coal fired power plants and other fossil fuels combustion. In the atmosphere, sulfur dioxide is usually oxidized by ozone and hydrogen peroxide to form sulfur trioxide, a secondary pollutant. Sulfur trioxide, similar to sulfur dioxide, is extremely soluble in water. If these sulfur oxides are present in the atmosphere when condensation occurs, droplets of sulfuric acid (acid rain) are formed. Volcanic eruptions provide a natural source of sulfur dioxide in the atmosphere. However the real problem associated with the production of sulfuric acid in the atmosphere is not with the sulfur dioxide expelled by volcanoes. Anthropogenic production of sulfur dioxide, caused by the burning of fossil fuels, is largely responsible for damage caused by acid rain.
sulphuric acid : In the atmosphere sulfur oxides (see sulfur dioxide) are converted to sulfuric acid. Oxides of sulfur and nitrogen combine with atmospheric moisture to produce acid rain. Although some sulfur oxides are introduced into the atmosphere by natural means, such as volcanic eruptions, the majority of the sulfur oxides responsible for the damaging effects of acid rain come from anthropogenic sources, mainly the burning of fossil fuels. Areas in the northeastern United States, eastern Canada, and northern Europe have suffered damage due to the effects of acid rain. In many areas damage to forests, crops, lakes, and streams are so severe that they are completely devoid of any life forms. Steps are now being taken in many parts of the world to reduce the amount of sulfur dioxide introduced into the atmosphere. In 1990, amendments where made to the Clean Air Act that places restrictions on the release of sulfur dioxides by power plants. The amendment calls for the reduction of sulfur emissions from a 1990 level of nearly 20 million tons per year to approximately 10 million tons per year by January 1, 2000.
summer solstice : In the Northern Hemisphere occurs on about June 21 of each year. The summer solstice is the longest day of the year and marks the beginning of the summer season. If the earth's axis were not tilted in relation to the plane of earth's orbit around the sun (the ecliptic) there would be no seasonal changes on earth. But because the earth's axis is tilted in relationship to its plane of orbit around the sun (~23.5 degrees) and assumes a constant direction, with the North Pole pointing towards the North Star, seasons occur, and daylight hours can fluctuate in length. Each day prior to the summer solstice the sun appears farther north in the sky; but at the summer solstice, the sun reaches its most northerly position in the sky, directly above the Tropic of Cancer, 23.5 degrees north latitude. Following the summer solstice the sun moves farther south in the sky, and on about September 23 it is directly overhead at the equator (the fall equinox).
Sun : the nearest star to the Earth and the centre of our Solar system. It dwarfs the other bodies, having a diameter of 864,000 miles and representing approximately 99.86 percent of all the mass in the solar system. As a star, the Sun generates energy by the process of fusion. The temperature at it's core is 15 x 106 K, and the pressure there is 340 billion atmospheres. The surface temperature is 5,500oC. At the solar core, hydrogen can fuse into helium, producing energy. The Sun consists of three layers: the photosphere, the chromosphere, and the corona, and spins on it's axis from left to right.
sunspot cycle : This cycle, lasting an average period of 11 years, involves recurring increases and decreases in the number of sunspots that occur on the sun's surface.
sunspots : A dark area, which is strongly magnetic, that occurs in the area of the photosphere on the disk of the sun.
supercell : a large thunderstorm in which the updrafts and downdrafts are in such close balance that the storm may have a lifetime of several hours.
supercooled water, water that is below the freezing temperature but is still in liquid form.
supercooling : The reduction of a temperature of a liquid below its freezing point without it's solidification. The effect can be achieved by slow and continuous cooling with pure liquids, since any solid matter would cause the liquid to solidify around it. A super cooled liquid is in a meta-stable state and any disturbance will cause solidification.
superfluid : A fluid that exhibits a very high thermal conductivity and virtually no friction at temperatures close to absolute zero. Such a fluid will flow up the sides and out of an open container. Liquid helium becomes a superfluid at 2.19 Kelvin's, called the lambda point.
supergiant : The largest and most luminous type of star, bright enough to be visible in nearby galaxies. They evolve from very massive but more complex stars are very rare.
supernova : A cataclysmic stellar explosion, seen as a sudden increase in the e stars brightness by a million times or more. It occurs in the late evolution of stars, one type almost certainly involving a massive supergiant stars, another type, possibly disrupting white dwarfs. Most or all of the stars substance is blown off at high velocity, forming an expanding gas shell - the supernova remnant. If the stars core survives it will most probably end up as a neutron star or a black hole.
Svedberg unit : Unit used to describe in multiples of 10-13 sec. the velocity attained per unit of applied force by a particle moving though a liquid medium.
syllogism : A logical scheme or analysis of a formed argument, consisting of three propositions called respectively the major premise, minor premise and the conclusion. e.g. Every virtue is commendable, patience is a virtue, therefore patience is commendable.
symbiosis : A relationship between two species of organisms in which both derive benefits from the other.
syndactyly : Commonly called "webbed Fingers", where the digits are joined together with skin. A rarer form of this can occur when the fingers are fused together by the bone.
synodic period : The average time taken by a planet or satellite to return to the same point in its orbit, relative to the sun, as seen from earth or from the satellites primary (i.e. the body it orbits).
synoptic scale : a large scale event that is usually measured in hundreds to thousands of kilometres and days to weeks; e.g. fronts, cyclones, and anticyclones.
synthesis : The process by which larger molecules can be built up from smaller molecules or atoms.
system : An association of independent organs throughout the body for the performance of a necessary body function. Some systems in higher animals are the circulatory, digestive, muscular, skeletal, and excretory systems.
systematic errors : an error which affects all measurements equally, making all measurements either higher or lower than the true value.
systematics : A term originally used to refer to the study of different systems of classifying animals and plants. Today the term "systematics" is used more or less synonymously with the term taxonomy.
tail : the most distinctive feature of comets, especially great ones. It is typically directed away from the sun. Ancient and medieval observers frequently described a comet as a broom or sword, depending on the look of the tail. Typically, telescopic comets will exhibit either no tail or one extending a few arc minutes. Naked-eye comets can show a tail extending up to several tens of degrees. Comets can display two basic types of tails: one gaseous and the other largely composed of dust. The dust tail can be curved, spread out, and yellowish in appearance, while the gas tail is usually very straight and bluish.
tamper evident bag : type of packaging used by certain police forces for submitting items to the FSS. Method of sealing is such that the SS/Fix is not required.
tap root : A stout, elongated, primary root.
tau ( T, t ) :
tau particle : An elementary particle with a very short lifetime (5x10-12 sec.) and a mass about 3500 times that of the electron. It is classified as a lepton. It reacts by weak interaction.
tautology : A statement that is always true and therefore gives no information. For example "IT is either raining or it isn't."
taxonomy : The science of classification; in biology this refers to the classification of organisms into kingdom, phylus, class, order, family, genus and species.
tectonic activity : The process of the formation, movement, interaction, and destruction of parts of the earth's crust on a generally large scale. This can be used to explain seismicity, volcanism, and mountain building.
tectonics : The structural arrangement of rocks in any crust of a planet. Used to understand rock structures.
teleology : Assigning purpose to an action, such as saying the cell takes in Calcium ions "in order to...."
temperature inversion : The abnormal reversal of temperature in the troposphere caused by the entrapment of urban air pollution. Under normal circumstances, air in the troposphere is cold at high altitudes and warm at low altitudes, or near the earthís surface. When air pollutants, such as SO2 or NOx, in urban areas get too concentrated, smog is produced. Since cold air underlies the warmer air at high altitudes, the air does not mix well which can lead to human health disturbances in people with respiratory illnesses such as asthma.
tendon : The sinew joining muscle to a bone.
telophase : The final phase of mitosis, in which the cytoplasm of the dividing cell is cleaved and two daughter cells are formed.
tera (T) : 1012
teratogen :
a chemical or physical agent that can cause defects in a developing embryo or foetus when the pregnant female is exposed to the harmful agent.
terminal burst : The flare at the end of a meteor's path.
territoriality : The tendency of some organisms to defend a section of space surrounding them and/or their family.
termolecular reaction : A reaction containing three particles. In the atmosphere an example of a termolecular reaction is one in which a molecule acquires the excess energy released by a reaction so that the products created do not convert back to the original state of the reactants. The reaction of molecular oxygen with an oxygen atom (radical) to produce ozone is a good example of an important atmospheric termolecular reaction. In the atmosphere this third body is most often molecular nitrogen because statistically this is the most likely next collision since atmospheric N2 = 78% by volume.
terpene : A naturally occurring organic compound, of the general empirical formula, C10H16, biologically built from a naturally occurring "monomer" called isoprene, C5H8, which is found as a volatile oil in plants. A clearly important, and olifactorily obvious, example is alpha-terpinene found in lemon oil.
tertbutyl alcohol : a highly flammable, volatile, colorless liquid which has a camphor-like odor. It is miscible in esters, and aromatic and aliphatic hydrocarbons, and soluble in water. Based on its vapor pressure, tert-butyl alcohol will exist mainly in the vapor phase in the atmosphere. It is most likely to react with the hydroxyl (OH) radical at this state. The reaction products are formaldehyde and acetone.
Tertiary Period : This extended from about 65 million years ago to about 2.5 million years ago.
Tertiary period : The first geological period of the Cainozoic era lasting from about 65 to 1.8 x 106 years ago and contains the Pleistocene, Eocene, Ogliocene, Miocene, and Pliocene epochs, in ascending order. Most of the rocks of the period were laid down in shallow water. Modern invertebrates and mammals evolved and became increasingly abundant; the modern angiosperms became the dominant plants. The Alpine period of mountain formation extended through the period and reached it's peak in the Miocene. The climate began to deteriorate in the Oligocene, finally leading to the ice age of the Pleistocene.
tesla : The SI unit of magnetic flux density equal to one weber per square metre and equivalent to 10,000 gauss.
testosterone : An androgen; a hormone produced in the interstitial cells of the testes of males and responsible for the characteristic changes associated with puberty.
tetrad : In meiosis, the four part structure resulting from the duplication of each pair of homologous chromosomes.
thermacidophiles : Bacteria which grow optimally at 105oC and at pH2.
thermodynamics : That branch of physical science which deals with heat as a form of energy. It is concerned with such problems as the exchange of energy (measured always in respect to the gain or loss of heat from a system) during chemical or physical processes.
thermodynamics : The science of heat and temperature and of the laws governing the conversion of heat into mechanical, electrical, or chemical energy.
thermosphere : The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude.
theta ( Q, q ) :
thickness : the vertical distance between two levels of constant pressure. The greater the average temperature of the layer, the "thicker" it is.
threshold limit value – ceiling ( TLV-C) :
limit for the atmospheric concentration of a chemical which may not be exceeded at any time, even instantaneously in workroom air.
threshold limit value – short term exposure limit ( TLV – STEL ) :
A maximum limit on the concentration of a chemical in workroom air which may be reached, but not exceeded, on up to four occasions during a day for a maximum of 15 minutes each time with each maximum exposure separated by at least one hour.
threshold limit value – time weighted average ( TLV – TWA ) :
A limit for the atmospheric concentration of a chemical, averaged over an 8hr day, to which it is believed that most people can be exposed without harm.
thylakoid disc : Flattened pancake like sacks with double layered walls, formed from the inner membrane system of the chloroplast. The lamellae and grana inside chloroplasts are composed of thykaloid discs.
thymine :
time dilation : An effect produced by Einstein's special theory of relativity. If two observers, A and B, are moving at a velocity v, relative to each other, it will appear to a that Bs clock will show that time is running more slowly; thus a time t, measured on A's clock, will be t(1 - v2/c2)0.5 on B's clock, where c is the velocity of light.. The effect has been observed in some particles moving at high velocities which appear to have an anomalously long lifespan.
tissue : An aggregate of similar cells bound together in an ordered structure and working together to perform a common function.
TNT (trinitrotoluene, C6H2(NO2)3CH3 ) : A highly explosive pale yellow crystalline solid. It is prepared from toluene treated with concentrated sulphuric and nitric acids and is used in shells, bombs, etc., and blasting explosives.
toluene : a highly volatile and water-soluble benzene derivative that is highly toxic to most forms of life. Its estimated lifespan in air is 60 hours in the case of a photochemical reaction with hydroxyl radical and is eventually oxidized to carbon dioxide. Toluene is used in a variety of industries including the manufacture of TNT, pharmaceuticals, rubbers, and other benzene derivatives, and is also a fuel additive and a paint solvent. Toluene also reaches the atmosphere from natural sources such as coal tar, mineral oils, and forest fires.
torr : The pressure of air that supports 1mm of mercury in a barometer at sea level. 1 atm = 760 torr = 101.325 kPa.
total column ozone : The total amount of ozone that is found in a column of air above the earth from the surface to the top of the atmosphere. The majority of this amount is typically found in the stratosphere.
total inhalable dust :
The fraction of airborne dust which enters the nose and mouth during breathing and is available for deposition in the respiratory tract.
toxic air pollutants : in the atmosphere, toxic air pollutants are present in small amounts that can have adverse effects on the health of human populations and the environment. Toxic air pollutants include polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, polychlorinated biphenyls (PCBs), and heavy metals, such as, mercury, copper, lead, zinc, arsenic, and cadmium. These pollutants are carried by particulate matter and can be mixed with precipitation. The Integrated Atmosphere Deposition Network (IADN) studies the transportation of specific toxic substances located in the atmosphere.
trace gases : These are gases in the atmosphere that do not occur in large quantities but are significant to life on Earth or are important constituents of the chemical cycles in the atmosphere.
trade winds : Wind systems occupying most of the tropics, which blow from 30 degrees North and South toward the equator; winds are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.
trajectory : The flight path of a missile dependent upon the speed of the missile, the air resistance acting upon it, the forces exerted by gravity and any wind pressure pushing it laterally.
transamination : The stepwise series of reactions in which the amino groups from one amino acid type is transferred to an intermediate substance, thus producing another type of amino acid.
transduction : the transfer of genes between bacteria by bacteriophages.
transfer RNA (soluble RNA) : A type of RNA in the cytoplasm of which there are at least 20 varieties, one specific for each amino acid. tRNA unites with its specific amino acid and draws it to the ribosome during protein synthesis.
transformation : a mode of gene transfer in bacteria in which a piece of free DNA is taken up by a bacterial cell and integrated into the recipient genome.
transitional epithelium : Epithelium in which the cells , in three or four layers, are so fitted together that the appearance is not one of distinct stratification. Found in the ureters and urinary bladder of humans.
translation : An aspect of protein synthesis in which the genetic information coded on messenger RNA is used top specify the order of amino acids in a polypeptide. Translation occurs in the ribosomes, where messenger RNA, ribosomal RNA, and activated amino acids meet and peptide bonds are formed.
transmitted lighting :
transmutation : The conversion of one element into another. They were achieved eventually by bombarding elements with alpha particles or neutrons. An example is the production of oxygen 17 when nitrogen 14 is bombarded with alpha-particles.
transmutation (of species) : An older term for the idea that over a long period of time new species arise though modification of old species.
transuranic elements : Elements with a higher atomic number than uranium. Apart from traces of neptunium and plutonium, none of them has ever been detected in nature since no isotopes of sufficient half life exist: they have been created since 1940, usually in minute amounts, in nuclear reactions.
trefoil (botany) : A simple form of division.
Triassic period : A period of geological time at the beginning of the Mesozoic era, lasting from about 2.4 to 2 x 108 years ago. The rocks of the period, laid down mainly under continental conditions often considered with those of the preceding Permian period as the Permo-Triassic. The dinosaurs, ichthyosaurs and plesiosaurs appeared in the Triassic.
tribology : The study of friction and such applied topics as lubrication, abrasives, surface wear, etc.
trichloroethylene (C2HCl3) : this is an industrial solvent used primarily for vapor degreasing and cold cleaning. It is an extraction solvent for greases, oils, fats, waxes, and tars, and is used by the textile processing industry to sour cotton, wool, and other fabrics. Exposure to moderate amounts of trichloroethylene may cause various health effects such as headaches, vertigo, visual disturbance, tremors, and dizziness. Death may occur from inhalation of large amounts. People located near or downwind of sites where TCE may be in operation might be exposed to higher levels. It is a carcinogen.
trichlorofluoromethane (Freon -11) : One of the principal greenhouse gases, a gas with absorption bands in the infrared portion of the spectrum. There is extensive evidence showing that a class of synthetic compounds, the chlorofluorocarbons (CFCs), are responsible for the destruction of the ozone layer. CFCs are molecules that contain one or more atoms of both chlorine and fluorine. In September of l992, the ozone hole over Antarctica was the largest ever recorded and was almost THREE times as large as the area of the U.S. Because CFCs are so unreactive, they do not break down when released into the air in the troposphere where they are spilled. In time, air currents and diffusion carry them into the stratosphere, where, under the influence of UV radiation, they release chlorine radicals that initiate the destruction of ozone. Data collected by NASA have shown conclusively, that there is an inverse relationship between ozone concentration and the chlorine monoxide radical in the stratosphere; ClO is formed by chlorine atom attack on O3. CFCs are very useful inert, nontoxic, nonflammable compounds that had been used for years as coolants and as spray can propellants for aerosol forms of hair sprays and deodorants. They had been unsurpassed as solvents for cleaning electronic microcircuits. Commercially, the most important CFCs are the halogenated methanes, Freon-11 (trichlorofluoromethane) and Freon-12 (dichlorodifluoromethane). Over 50% of asthma inhalers contain chlorofluorocarbns as the solvent and gaseous propellent. These CFCs have relatively recently been prohibited in all products except in those medicinal inhaler dispensers for asthmatics and a few other limited exceptions. In Finland alone there are over a million medicinal dispensers that disperse freons into the atmosphere. This is equal to the freon concentration of the cooling devices in approximately l00,000 refrigerators.
Trojan group : Minor planets that lie close to either of two points in Jupiter's orbit. Each point forms an equilateral triangle with Jupiter and the Sun.
trophic level : Levels of nourishment in a food chain. A food chain is the transfer of energy from its ultimate source in plants through a series of organisms, each of which eats the preceding organism.
trophoblast : In mammals the thin walled side of a blastocyst which gives rise to the placenta and the membranes that surround the embryo.
tropopause : The area where the temperature in the troposphere no longer decreases, indicating the boundary between the troposphere and the stratosphere.
troposphere : The lowest layer of the Earth's atmosphere, ranging from the ground to the base of the stratosphere with a altitude of 10-15 kilometers depending on the latitude. This is where all weather occurs. The word troposphere is derived from the Greek words tropos, turning and spharia, sphere.
trough : an area of low pressure. Cyclonically curving winds.
tuber : The fleshy underground part of the stem of a plant.
tunnel effect :
twin lens reflex camera :
Tyndall effect : When a parallel beam of light, such as a wavelength that none is absorbed, is passed through a gas, liquid, or transparent solid, part of it is scattered in all directions so that it may be seen from the side.
UARS (Upper Atmosphere Research Satellite) : A satellite deployed by NASA to study the chemistry in the upper atmosphere of Earth.
UEL ; Upper Flammable (or Explosive) Limit :
The maximum concentration of vapor/gas in air at a given pressure and temperature in which a flame can be propagated.
ultra -centrifuge : A high speed centrifuge used to determine the size of small particles and large molecules by their rate of sedimentation.
ultra-microscope : An optical microscope used to detect particle smaller than the wavelength of light by illuminating them at an angle, so that the light scattered by the particles can be observed against a dark background.
ultraviolet : Just beyond he violet end of the physical spectrum.
ultraviolet radiation : Electromagnetic radiation, the frequency of which lies between that of the violet end of he visible spectrum and X-rays, i.e. between about 380 and 5 nanometres. Ultraviolet radiation is produced during arc discharges and by gas discharge tubes (e.g. the mercury vapour lamp). It is also produced in large quantities by the sun, although the radiation below 200nm is absorbed by he ozone layer.
umbel : A flat topped cluster of flowers, having their footstalks of pretty equal lengths and radiating like the ribs of an umbrella.
umbra : A region of complete shadow where no light reaches the surface.
unicellular : An organism consisting of just one cell.
unified field theory : The theory that encompasses he four fundamental interactions - strong, weak, electromagnetic, and gravitational - in terms of a single field, analogous to the electromagnetic or gravitational fields.
unit membrane : The model that sees cell membranes (plasma, nuclear, etc.) as consisting of a mosaic of small sandwiches; that is phospho-lipid molecules between an inner and outer layer of protein.
univalent : Having a chemical valency of one.
universal gravity law : The model that holds that every piece of matter in the universe pulls every other piece of matter in the universe towards it.
updrafts : the warm moist air that is involve din the formation of cumulonimbus clouds.
upsilon ( U, u ) :
upwelling : a rising-up of colder water.
uracil : A base found only in RNA. Abbreviated U for the free base, rU for uridine, and dU for deoxyidine.
uranium-thorium dating : An absolute dating technique which uses the properties of the radioactive half-life of Uranium-238 and Thorium-230. The half-life of uranium-238 is 4.5 billion years, that is, in that many years half of the original amount is still uranium-238 while the other half has lost nucleons to form a different element which is more stable.
Uranus :
The seventh planet from the Sun, and the first to be discovered using a telescope (by William Herschel in 1781). Uranus has an equatorial diameter of 51, 200 km and orbits the Sun once every 84 years at a distance varying between 18.3 and 20.1 astronomical units. It rotates once every 17.24 hours, and has a mass 14.5 times that of the Earth, giving it a density 1.3 times that of water. Unlike every other planet in the Solar System, Uranus lies almost on it's side in it's orbit, pointing first one pole and then the other towards the Sun as it moves around it's orbit. This may be the result of the impact of a large comet with Uranus long ago. It has at least eleven moons.
Uranus (Astronomy): The third largest planet in our solar system and the seventh from the Sun, which it orbits every 84.01 Earth years. One day on Uranus is 17 hours, 14 minutes, and 24 seconds long. The gravity of Uranus is .86 of the Earth's and the planet is 120% as dense as the Earth. It has a diameter of 32,116 miles and 15 moons.
Uranus lies tipped on its side with its north and south poles alternately facing the Sun during an 84-year swing around the solar system.
urban air pollution : pollution that occurs in cities from the burning of fossil fuels and the emissions of hydrocarbons. Urban air pollution can be in the form of ozone, smog, acid rain, carbon monoxide, particulate matter (PM-10), and nitrogen oxides.
uric acid (C5H4N4O3) : A degradation product of purine in mammals, in which the ring structure is preserved. The compound is formed during the nitrogen metabolism of animals and the chief nitrogenous excretory product of reptiles and birds. In man, raised levels of uric acid in the blood are associated with gout.
uterus : The womb; the hollow muscular organ of the female reproductive tract in which the foetus undergoes development.
UV-A : Ultraviolet light that has wavelengths of 320nm to 400nm. The wavelengths of this light are shorter than visible light and are not absorbed in the stratosphere by ozone.
UV-B : An ultraviolet wavelength of light between 280 nm and 320 nm whose intensity is increasing at the earth's surface (probably causing increases in skin cancer), This UV increase is because of decreases in statospheric ozone.
UV-C : Light that spans the spectrum with wavelengths of 10nm to 290nm. These wavelengths of ultraviolet light are extremely dangerous to human and animal tissue and is totally absorbed in the stratosphere by ozone and molecular oxygen.
UVCE ; Unconfined Vapor Cloud Explosion :
Explosion involving a large mixed vapor/air cloud in the open.
UV/Vis spectrophotometry : Ultraviolet/visible spectrophotometry is used to measure the absorption capabilities of certain compounds with reference to wavelengths of light on the ultraviolet and visible light ranges.
UV radiation : energy that is emitted in the form of electromagnetic waves with a wavelength of 1-380nm, which is composed of UV-A, UV-B, and UV-C light; UV-A light being the longest wavelength and having the smallest energy and UV-C light being the shortest wavelength and having the highest energy. All UV-C light and most UV-B light is filtered out of the atmosphere via the ozone layer. However, UV-A light travels to the surface of the earth.
vacuolar membrane : A unit membrane structure that separates the contents of vacuole from the surrounding cytoplasm.
vacuole : A bubble like structure surrounded by a membrane, occurring in the cytoplasm, and serving as a reservoir to hold food and waste products.
vacuum, A region of space that contains no matter. In practice a perfect vacuum is impossible to obtain and any region where the pressure of the gas is less than about one millimetre of mercury may be considered a vacuum. In technical work a soft (or low) vacuum goes down to a pressure of 10-4 mm Hg, a hard (or high) vacuum is between 10-4 and 10-9 mm Hg, and an ultrahigh vacuum is below 10-9 mm Hg.
Vadose zone : The unsaturated zone in a soil where chemical processes are at their most active. Its extent is determined partly by the content of the soil water, but it cannot extend beyond the water table, below which voids are completely filled with water.
valence electrons : The outermost electrons of an atom that are in the orbitals of highest principal quantum number of all electrons in the atom and don't fill that orbital completely.
valency : the combining power of an atom.
vanadium (V):
Van der Waal's equation : A modification of the ideal gas equation in which V is adjusted to (V-b) to take account of the volume occupied by the gas molecules. Assuming that forces of attraction exist between the gas molecules the pressure term is then adjusted to (p - a/V2). Both a and b are constant for a particular gas.
Van Urk test : Specific for LSD which will turn the reagent blue-purple.
vas deferens : A long tube like structure at the top and back of the testes, in which sperm are stored and through which they pass out through the penis.
veering : clockwise shifting of the winds with time or distance.
vegetal pole : The surface of an egg opposite the animal pole, on the axis running through the nucleus. The yolk density within the egg is greatest at the vegetal pole.
veins : Vessels which carry blood from the various organs to the heart.
velocity (v) : The speed of a body in a specified direction, i.e. it's rate of displacement (s) in a specified direction is given by v = ds/dt. Velocity is a vector quantity, whereas speed is a scalar quantity. In SI units velocity is measured in metres per second.
Venus : Distance from Sun 108 x 106 km, diameter 12102 km
Venus :
Second planet out from the Sun. In size Venus is almost a twin of the Earth, with 82% of the Earth's mass. It orbits the Sun once every 225 days at an average distance of just over 0.72 astronomical units, in a nearly circular orbit. It rotates backwards (retrograde) once every 243 days, relative to the fixed stars, so in a sense a 'day' on Venus is longer than a 'year'. Because of the motion of Venus in its orbit, however, if you could see the Sun from the surface of the planet, the time from noon to noon would be 116.8 of our days, so there would be just under two Venusian days in each Venusian year
The equatorial diameter of Venus is 12, 104 km. Unlike the Earth, Venus has a very thick atmosphere rich in carbon dioxide. This produces a strong greenhouse effect, which, combined with the fact that it is closer too the Sun than we are, raises the surface temperature to 730 Kelvin. The pressure of this atmosphere at the surface of Venus is 90 times the atmospheric pressure at sea level on Earth.
Venus is completely cloud covered and has a high albedo, reflecting 79% of the incoming sunlight. As a result, after the Sun and the Moon, Venus is the brightest object in the sky, seen close to the Sun as the evening star or morning star, depending on it's position in its orbit. It has no moons.
albedo, a measure of the reflectivity of an object. A perfectly reflecting surface has an albedo of 1, while a black surface that absorbs all light that falls on it has an albedo of 0.
Venus (Astronomy) : The second planet from the Sun. Whist Venus resembles the Earth in size, physical composition and density more closely than any other known planets it's rotation is retrograde and it is also closer to a perfect sphere. It has a nickel-iron core but no magnetic field. The surface temperature is 900° F with an atmospheric pressure 97 times that of the Earth's and the 0.91 of the Earth's gravity. It's orbit, which is nearly circular is 224.7 Earth days. It has a mass of 4.872 x 1027g; radius of cloud surface about 6100 Km; radius of solid surface about 6056 Km; surface temperature 737K; temperature of cloud tops 250K; cloud composition more than 75% H2SO4 and about 25% water; atmosphere (by volume) 90-95% CO2 with traces of SO2, water, CO, H2SO4, Ar, Ne, HF, HCl. Atmospheric pressure 92-95 atm.
vernal equinox : A time during the spring season when the sun is directly above the equator which results in an equal amount of time for day and night.
vertical flux : In dry deposition this refers to the rate at which a gas particle is deposited onto another surface without the aid of precipitation. Vertical flux equals concentration of the species multiplied by the deposition velocity.
vertical mixing : The movement of air in a vertical direction usually caused by differences in temperature and density.
vestigial organ : A structure in a degenerate state that remains in an organism but has little or no present function. The appendix in human beings is a vestigial organ.
video surveillance units : These are becoming increasingly cheaper and of a higher quality are widely used in locations such as shops, traffic lights, police stations. They are even available for baby alarms.
vinyl bromide : a toxic compound that was established as a federal hazardous air pollutant in 1993. Sources of vinyl bromide may include rubber substitution, flame-retarding treatment of acrylics, laminating, and/or preparing films. It is also important to point out that vinyl bromide may be the result of the atmospheric degradation of 1,2-dibromoethane. Based on a typical atmospheric gas phase reaction with a hydroxyl radical, the lifetime of vinyl bromide in the atmosphere is between 1.5 and 2.1 days resulting in the products formaldehyde and formyl bromide.
visibility : A measurement of the ability to see and identify objects at different distances.
virus : A non-cellular, sub-microscopic particle composed of a protein coat surrounding a nucleic acid core. Viruses can reproduce only inside living cells (eukaryotes or prokaryotes).
vitalism : The view that life is an expression of something above and beyond the chemical and physical interactions of a group of molecules.
vitamin : A chemical substance, required in only trace amounts, that are thought to aid enzymes in catalysing specific chemical reactions.
vitamin A : A fat soluble vitamin and an essential constituent of the visual pigments of the eyes. It also functions in the maintenance of healthy mucous membranes. Vitamin A deficiency leads to dryness of membranes lining the mouth and respiratory tract, blindness and effective growth.
vitamin B complex : A group of water soluble vitamins that are all constituents of coenzymes involved in metabolic reactions. Thiamine (B1) is important in carbohydrate metabolism. Deficiency leads to Beriberi. Riboflavin (B2) is involved in carbohydrate and amino acid metabolism. Nicotinamide (nicotinic acid or niacin) can be synthesised from the amino acid tryptophan. Vitamin. B6 (pyridoxine) is essential for amino acid metabolism. Also common in many foods are pantothetic acid, a constituent of coenzyme A; biotin, which is synthesised by intestinal bacteria; and choline, a precursor of acetylcholine (which transmits nervous impulses). Folic acid and Vitamin. B12 (cyanocobalamin) can be synthesised by intestinal bacteria; deficiency of either causes megaloblastic or pernicious anaemia.
vitamin C (ascorbic acid) : A water soluble compound that is required for several metabolic processes, especially for the maintenance of healthy connective tissue. It cannot be synthesised by man and certain animals, in whom it must for part of the diet. Deficiency leads to Scurvy.
vitamin D : A fat soluble vitamin consisting of several related compounds (sterols), principally cholecalciferol (D3) and ergocalciferol (D2). Vitamin. D is important in calcium and phosphorus metabolism, especially in the absorption of calcium from the gut and the deposition and resorbtion of bone minerals. efficiency in infants causes rickets.
vitamin E : A vitamin consisting of a group of related compounds that function as biological antioxidants, inhibiting the oxidation of unsaturated fatty acids. The most potent form of vitamin E is alphatocopherol. Deficiency, which is rare, may lead to anaemia.
vitamin K : A vitamin consisting of a group of quinone-based compounds that are necessary for the formation of prothrombin, important in blood clotting. It can be synthesised by intestinal bacteria.
viviparous : Term applied to organisms whose embryos develop within the body of the mother and derive their nourishment from their mother.
Volcanoes - Openings in the earth's crust that release molten rock, steam, reduced and oxidized compounds, and ash from within the earth's interior into the atmosphere.
volt (v) : The unit of potential, potential difference, or electromotive force equal to the potential difference between two points on a conductor carrying a steady current of one ampere when the power dissipated is one watt.
volumetric analysis, the process of reacting a solution with a solution of known concentration with one of unknown concentration, in order to determine the equivalence point.
vorticity : spin of the air indicating rotation. Positive vorticity is cyclonic flow, while negative vorticity is anticyclonic.
vulva : The external female sex organs (genitalia).
Walker Cell : a zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell.
water : a triatomic molecule(H2O)that covers three quarters of the Earth's surface, 60-70% of the world's weight, regenerates and redistributes through evaporation and other atmospheric processes. Water is involved in electrical charge separation because it has two types and positions of atoms giving it a net dipole movement. Water vapor also absorbs 17% of solar radiation in the troposphere, thus making it one of the two principal greenhouse gases. Of the solar energy absorbed by the Earth's surface a little more than half goes into latent heat, which is heat absorbed by water because of its transformation from a liquid to a gas. When these molecules condense back into a liquid, usually higher in the atmosphere, they released that energy back into the atmosphere as local warming.
water cycle : the process by which water is transpired and evaporated from the land and water, condensed in the clouds, and precipitated out onto the earth once again to replenish the water in the bodies of water on the earth.
water vapour : water present in the atmosphere in gaseous form; the source of all forms of condensation and precipitation. Water vapor, clouds, and carbon dioxide are the main atmospheric components in the exchange of terrestrial radiation in the troposphere, serving as a regulator of planetary temperatures via the greenhouse effect. Approximately 50 percent of the atmosphere's moisture lies within about 1.84 km of the earth's surface, and only a minute fraction of the total occurs above the tropopause.
watt : Unit of power, the rate of working of one joule per second, corresponding to an electric current where the electromotive force is one volt and the current one ampere.
wavelength : the distance between successive peaks or troughs of a wave. It is equal to the velocity of the wave divided by its frequency. For electromagnetic radiation it is a parameter specifying the part of the electromagnetic spectrum to which the radiation belongs.
wave number : the inverse of wavelength, i.e. the number of cycles executed by a wave in a unit length.
wave theory of light : the model that depicts light as demonstrating all the properties of wave motion, analogous to waves on the surface of water.
weak Sun paradox : referring to the fact that our sun has probably increased its luminosity during its lifetime (approximately 3.5 x 109 years). This assumption is based on astrophysical observations of many other stars. The best scientific conclusions are that when our sun was young it had a luminosity (total energy output) of 70-80% of what it is today; however, there has clearly been (based on geological records and long term evidence for the presence of liquid water) approximately the SAME long term planetary temperature on earth (about 15o C, averaged planet-wide) instead of colder earlier surface temperatures followed later by warmer surface temperatures. This paradox suggests that the planet's surface temperature may have been controlled by atmospheric gas concentrations that varied over time while keeping (via the greenhouse effect) the surface temperature relatively constant (see Gaia hypothesis).
weber (wb) : the SI unit of magnetic flux equal to the flux linking a circuit of one turn that produces an electromotive force of one volt when reduced uniformly to zero in one second.
wet bulb temperature (Tw) : an easily measurable quantity (using a sling psychrometer) which indicates the effect of evaporative cooling on temperature; used to determine relative humidity.
white dwarf : a very small faint low-mass star (less than 1.44 solar masses) that has undergone gravitational collapse following exhaustion of its nuclear fuel. Electrons are stripped from the constituent atoms and it is the pressure exerted by these densely packed electrons that eventually halts the stars contraction. The density is hen 107 - 1011 kgm -3. As they cool their colours change from white (for the brightest) through yellow and red until they become cold black objects.
wind shear : a changing of wind speed or direction with distance; vertical wind shear is changing of wind with respect to height.
whorl : Arranged in radii around an axis, especially relevant in fingerprinting.
Wolffian ducts : a pair of tubules which, in conjunction with mesonepheric ducts, form the primitive urogenital system of the male mammalian embryo. Both male and female embryos develop, though in females these ducts degenerate by the beginning of the third month.
work : An indirect measure of the energy required to move matter a given distance.
xenon (Xe) :
xi ( X, x ) : fourteenth letter of the Greek alphabet.
xylem : woody tissue at the stem of a plant that carries water and dissolved minerals upwards from the ground.
xylene : an aromatic hydrocarbon used as a common industrial solvent, also named dimethylbenzene; exists as 3 isomers: m-xylene, o-xylene, and p-xylene. Xylene is usually obtained from petroleum and natural gas distillates. It is used in paint, rubber and leather industries, and also as a cleaning agent or degreaser.
xylosyl :
X-rays : Electromagnetic radiation lying between ultraviolet radiation and gamma rays in he electromagnetic spectrum. X-rays may have wavelengths between 10-9 m and 10-11 m, the shorter wavelengths being known as hard X-rays and the longer wavelengths as soft X-rays. They are produced when heavy atoms, usually tungsten, are struck by sufficiently energetic electrons, as in an X-ray tube. The electrons in an X-ray tube are produced by a heated cathode in a n evacuated tube and accelerated to the heavy metal anode by an electric field. The collisions knock inner electrons from the atoms. X-rays cause ionisation in gasses and penetrate matter.
zenith : the point in the sky lying directly above the observer and 900 from all points on his horizon.
zenithal hourly rate (ZHR) : This is the rate a meteor shower would produce if seen by an observer with a clear, dark sky, and with the radiant at the zenith.
Zeolite : microporus silicate or aluminosilicate structured minerals that can act as an absorbing filter or sieve on a molecular level. Mainly used by the petroleum industry for the cracking of petroleum or use as a filter against various compounds.
zeta (Z, z ) :
zodiacal light : a faint glow that is visible in the western sky just after sunset and the eastern sky just before sunrise, especially in the tropics. It can be seen along the directions of the ecliptic, tapering upwards from the horizon to an altitude of up to 20o. It is the result of sunlight reflected from interplanetary dust particles.
zonal : in the west-east direction.
zonal sedimentation : An ultra-centrifugal technique in which the sediment in a solute is separated into discrete regions.
zone focus : the ability to focus to a zone rather than a single point as in cameras that have fixed focus lenses. By retaining a large depth of field it is possible to cover all subjects with just one lens position.
zoology : The study of animals.
zwitterion : A molecule that can be either positively or negatively charged, depending on the pH.
zygote : A diploid cell formed from the union of male (sperm) and female (egg) reproductive cells (gametes).
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