Composite is a material composed of reinforcing material such as carbon or glass fibre embedded in a matriz of a bulk material such as a metal or plastic. Composite has a better components. Weakness of one component is overcome by the strength of the other component. Wood, which is composed of cellulose fibres as reinforcement in a lignin matrix, is a naturally occurring composive.
In a composite the reinforcement, which could be a gas, particle or fibre, gives strength and stiffness whereas the matrix, which could be any polymeric material such as resin or a metal of ceramic, holds the reinforcement and maintains even distribution of the applied load within the composite. Composites are finding wide applications in our everyday life. They are being widely used in aerospace industry as they provide an ideal combination of strength and light weight.
Computer virus is a tiny bit of computer code which can attach itself to a piece of normal software known as its "Trojan horse". It reproduces by copying itself on other programmes stored in the same computer. The virus can alter other programmes or destroy data. It normally lies dormant until at a predetermined, programmed time it activates itself. It then seizes control of the computer and does the damage. A single computer virus can spread to any number of compatible computer systems if provided with a pathway for infection. The virus infects a system through sharing of infected diskette of through communication links, like local area networks or program transmitted from distant system. Viruses can be malignant or benign, they destroy or merely irritate. Some of the betterknown viruses are Pakistani Brain, Gotcha, Cookie, Friday the 13th, Christmas, Bloody and Scores.
Cryogenic engineering is a branch of engineering, specialising in the technical operations at very low temperatures. Cryogenic engineering combines competence in the techniques of low-temperature physics and chemistry with capability in conventional branches of engineering such as mechanical, chemical, electrical and nuclear.
An important military application of cryogenics has been the development of extensive pretreatment because their source is most often a gas mixture- the components must first be separated, then purified. Both these processes involve cryogenics. Although still in the development stage, the application of superconductivity and associated cryogenic systems to electric power generation and transmission appears promising.
Development of superconducting magnets to provide the magnetic field needed for the generation of electric power, magnetohydrodynamic (MHD) has been undertaken. Superconducting magnets will also be needed for the magnetic confinement of plasma in the thermonuclear (nuclear fusion) power generation. Cryogenic engineering applied to several hydrogen fuels appears promising for the propulsion of jet aircraft and has also been investigated for use as a fuel in both rail and automotive transportation. Several elementary superconducting circuits have been developed to produce binary memory elements, switching devices and multivibrations for high speed computers. Low temperatures are finding increasing uses in basic biological studies as well as in practical medical procedures. Large quantities of liquid nitrogen are employed in the preservation of food by rapid freezing.
It is an acronym for Dichloro Dipheny1 Trichloroethane. It is a common insecticide insoluble in water, easily soluble in ethanol and acetone. It is a colourless, odourless insecticide used against agricultural pests, flies, lice and mosquitoes. Widespread use of DDT has resulted in pollution of crop lands and a large number of pests have become resistant to it. When it enters the food chain DDT accumulates in the fatty tissues of animals.
Dialysis is a method of separating small molecules (eg salts, urea) from large molecules (eg proteins, polysaccharides) of a solution by using a semipermeable membrane which allows only small molecules to pass (diffuse) through. Substances such as cell walls and cellophane act as semipermeable membrane. The principle of dialysis is used in the design of artificial kidneys which work by renal dialysis.
Deoxyribo Nuclei Acid. It is a biological self-replicating macromolecule which plays a vital role in heredity. It is the chief material in chromosomes, the cellular component that governs the heredity of an animal and plant.
Dry ice refers to solid carbon dioxide, which is a dense snow like substance that turns into vapour at(-) 78.50C. It is used as refrigerant, especially during shipping of perishable products like meat or ice cream. It has a temperature of (-) 700C.
It is an acronym for Dext Top Publishing, which is a computerised publishing system using an ordinary personal computer linked to a laser printer. DTP can perform all operations including editing, proofing, page make-up, designing and formatting of pages. The desired output is obtained from a laser printer on paper which is directly converted into photographic film from which plates are made for printing.
Electro Cardiogram. It is a record of the electric potential that govern the rhythmic contraction of heart muscles and is recorded as a moving curve on a strip of paper.
It is used as a diagnostic tool for recognising heart diseases and the instrument used to make an ECG is called electrocardiograph.
Echo is the effect produced when sound or other radiation is reflected or thrown back on meeting a solid obstacle or a reflecting medium. If the reflecting object is stationary there is no change in the frequency of reflected wave. The reflected sound wave is of sufficient magnitude and time delay is to be perceived as a sound wave distinct from that directly transmitted. The minimum distance required between the source of sound or radiation and the solid barrier which produces an echo has to be more than 10 m.
Echo location refers to the location of an object, both stationary as well as moving, by determining the direction of echo reflected from it, or by time taken for the echo to return. Certain animals such as bats and dolphins emit high pitched sounds often beyond the range of human hearing. These are reflected back off the object (obstacles ahead of prey) and detected by sensory receptor. Other examples of echo location are radar and sonar.
Electro Encephalo Gram. It is a graphic recording of the electric discharges of the cerebral cortex of brain as detected by electrodes placed on the scalp surface. It is used to study certain clinical conditions of brain. Cessation of brain activity as reflected in an EEG is taken as brain death. The equipment used to make an EEG is called electron
Electroplating is the deposition of a layer of metal by electrolysis. Copper is often plated with nickel to protect it from corrosion and jewellery is plated with gold and silver to make them more attractive.
Endoscopy is a diagnostic method used for detecting diseases of any hollow organs of the body such as throat, stomach or intestine by peeping directly into the affected organ using a device called endoscope. Endoscope is a hollow metallic tube fitted with a light source and a viewing system. It uses flexible bundles of optical fibres both for transmitting light to the affected organ and transmitting the image of it to the eyepiece outside for viewing.
Modern endoscopes are having surgical attachments also to carry out minor operations or biopsy.
Fallout is the deposition of radioactive substances upon the surface of the earth after the explosion of a nuclear weapon or mishap at a nuclear reactor. The radioactive debris deposited on vegetation and water surface can enter the human body through the food chain.
Fax or facsimile refers to transmission or communication of a written document, photograph, map or other graphic material electronically over a long distance within minutes. The information or document to be sent is placed in the facsimile or fax machine which scans it and converts it into electronic signals that are then entered into the transmission system which may be wire or radio. At the receiving end a facsimile receiver reconverts the signals into a copy of the original material.
Fine glass fibres are usually less than a quarter of a micrometre in diameter. When used as such they are called glass wool. The fibres are widely used for glass reinforced plastic composites, which in common parlance are called fibre glass. It has high tensile strength and corrosion resistance.
Flying saucers are disc like mysterious aircraft which have been in almost every part of the world on different occasions, possessing a speed of about 1000 miles per hour. No clue has yet been discovered about their identity. It is said to be a supermachine but nobody knows who control them and what their exact origin is. There are different theories about its origin- some believe they come from Mars and others believe they come from the USSR.
It stands for Frequency Modulation. It is a type of radio transmission system in which the frequency of a carrier wave is modulated rather than its amplitude (as in amplitude modulation). It provides a method of transmission free from static interference.
Fraternal twins are nonidentical twins that develop from two different reproductive cells or ova that are fertilised by two different sperms at the same time. They are also called heteroxygons twins.
Freons is the trade name for type of fluorocarbon used as refrigerant and solvent.
Fullerene, the third allotropic form of carbon, quite distinct in structure and properties from the two earlier known allotropes- graphite and diamond- was discovered in 1985 by Harry Kroto of the University of Sussex, UK and Richard Smalley of Rice University, USA. Comprising of 60 carbon atoms, the new allotrope of carbon was christened Buckminister Fullerene, or 'bucky ball' in short, after Buckminster Fuller, an architect who had earned much name and fame due to his invention of geodesic domes.
Graphite has a plane layer of six membered carbon rings and diamond has a three dimensional network of tetrahedrally bonded carbons, whereas fullernes have spherical cage-like structure such as the famous geodesic domes invented by Buckminster Fuller.
Fullerenes have diverse applications. By doping it with potassium atoms, a new super, conducting material (they conduct electricity without any loss) is produced which has a critical temperature of 19.3 K. Fullerene, being spherical and very tough, are used as effective lubricant and can also act as molecular ball bearings. It can also act as a semiconductor and as a catalyst in some chemical reactions.
Galaxy is giant system of stars, dust and gas held together by gravity. Galaxies are scattered throughout the universe; some galaxies are found isolated in space but most are clustered thousand to half a million light years. Large galaxies may have more than a million million (1012) stars and small galaxies may have a fewer than a thousand million. Solar system lies near the edge of a galaxy called Milky Way. Andromeda galaxy, about two million light years away, is the most distant astronomical body visible to unaided eye.
Gene is a basic unit of inheritance. It is a short length of a chromosome made of DNA which influences a particular set of characters in a particular way. Genes can be either dominant or recessive. A dominant gene always expresses itself in the physical characteristics of an organism while a recessive gene expresses itself only when the dominant gene is absent.
Genetic code is a sequence of bases along the DNA molecule. Genetic information is stored in genes as linear sequences of the nitrogenous bases adenine, cytosine, guanine and thymine in DNA.
Genetic counselling is the counselling which informs the people and makes them understand about genetic problems or defects which are or may be inherent in their families or prospective families. It utilises a wide range of information on human heredity.
It is a satellite that appears to be stationary in the sky in the geostationary orbit from the earth. The geostationary satellite orbits the earth above its equator, at a height of 36,000 km, with the same orbital speed as that of the earth's rotation (one rotation in 24 hours) and so the satellite appears to be stationary in the sky from earth. These satellites are preferred as the ground based communication antennas can, have an access to the satellite by remaining fixed pointing to the satellite and need not change the direction to follow the satellite in the sky.
Geostationary satellites have on board transponders, for communication, which receive signals from earth stations, amplify them and send them back to the satellite dish antennas on earth.
Geosynchronous Satellite Launch Vehicle, designed by ISRO and weighing 2500 kg, aims to put a two tonne payload- an INSAT-2 series communication satellite- into a geostationary orbit. It is a three-stage rocket with the last stage involving a cryogenic engine.
It is a mixture of potassium nitrate (KNO3), powdered charcoal and sulphur. When it is ignited a number of chemical reactions take place rapidly evolving gases, thus producing an explosion in confined space. The expansion of the gas inside the barrel of a gun can accelerate a bullet to great speed. Gunpowder is therefore used as a propellant in a variety of ammunition, in fireworks and in explosives designed for blasting operations.
Hail is a precipitation in the form of round or irregularly shaped lumps of ice called hailstones. Hailstones are hard, frozen balls of ice with a layered structure which comes down with thunder. They grow inside thunder clouds from tiny frozen droplets.
Half-life is the time taken for one half of the atoms in a quantity of a radioactive substance to disintergrate. Half lives very widely from isotope to isotope.
Halogen lamp is a tungsten-halogen filament lamp, in which presence of a small amount of iodine reduces the evaporation of tungsten permitting a higher operating temperature and hence brighter light. Because of the chemical effect of iodine on glass, the filament is enclosed in a quartz rather than a glass bulb. Though these lamps have white colour and longer life, they have not yet been used for general domestic lighting. They are widely used in studio lighting, light projectors and scientific equipments and also in automobile headlamp.
Hard Water & Heavy Water
Hard water contains soluble salts of calcium and magnesium which form an insoluble precipitate with soap of calcium magnesium salts of fatty acids (such as those present in soap). That is why hard water does not produce lather with soap but forms a scum. The hydrogen in nature exists mainly in three forms (isotopes), protium, deuterium and tritium. Natural water (H2O) contains hydrogen in two forms : protium (99.5%) and deuterium (0.5%). Heavy water contains deuterium and is chemically called deuterium oxide (D2O). It is used in nuclear reactors and is generally obtained from ordinary water by electrolysis.
Heatstroke Heatstroke occurs when the heat regulating mechanism of body stops working. Heatstroke generally occurs in very young and very old people as their body temperature regulating mechanisms are not very efficient. Also people who are not used to heat, overweight, heavy drinker or suffering from fever are more susceptible to heatstroke.
caused by excessive exposure to sun is called sunstroke. The main symptoms of heatstroke are : (i) Very high body temperature (more than 410 C), (ii) total absence of sweating, and (iii) nervous system problems (like disorientation, headache and irritation). Heatstroke is an extremely dangerous condition and nearly 20% of patients may die even with treatment. The immediate treatment of heatstroke is to give a cold water bath to the patient.
A hologram is an intermediate photographic record that contains the information for reproducing a 3-D image, without cameras of lenses, using laser illumination.
This method of producing hologram is called holography, which was invented by Denis Gabor in 1948. In this method a beam of coherent light from a laser is split into two by a semi-transparent mirror, so that one beam (the signal beam) can be diffracted by the object to be reproduced onto a photographic film or plate. The other beam (the reference beam) falls directly onto the film or plate.
The two beams form interference pattern on the plate thus forming the hologram. To reproduce the image the hologram is illuminated by coherent light (usually of the same wavelength as the original beam). Holography is finding wide application in industry and research, like to check flaws in aircraft wings, tyres and lenses. Hologram is being used in documents such as voter identity cards and credit cards for avoiding forgery.
Hubble space telescope
It is the largest and most sophisticated astronomical telescope placed in space in 1990 by US. Deployed from the space shuttle Discovery, the telescope is designed to see astronomical objects because of the turbulent atmosphere. These telescopes can distinguish objects only to a distance of 2000 million light years. The Hubble telescope can detect objects 50 times fainter and can produce 10 times sharper images. All the observation by the telescope is carried out by remote control. The information gathered is converted into electronic signals and transmitted by relay satellites to ground stations which are then processed by computer.
The entire genetic make-up of humans constitutes human genome. Gene is the smallest physical unit of heredity. Over a lakh genes are contained in about 3 x 109 base pairs present in every human cell. Presently an international research programme, the human genome project, launched in 1988 and expected to be completed by 2005, is underway whose objective is to map all human genes precisely to their respective positions on chromosomes and to identify their DNA sequences. Such gene maps will make easier the study of disease involving multifactorial inheritance. It will also help in finding cures for some of the hereditary diseases and ultimately will lead to a stage where any defective or disease causing gene(s) may become replaceable with other healthy gene (s) thus restoring health.
Hybrid in its widest sense, describes progeny resulting from a cross between two genetically non-identical individuals.
Hydrogen bomb, also called fusion bomb, is an explosive device that gets its power from the fusion of two isotopes of hydrogen, deuterium (2H1) and tritium (3H1), at very high temperature. It works in two main stages. First, an atomic fission bomb explodes to produce extremely high pressure and temperature required for second stage the fusion reaction. In the fission reaction, atoms are split to produce energy. In the second stage, fusion reaction occurs in which nucleus of deuterium and tritum fuse to produce a helium nucleus, a free neutron and even larger amount of energy. The explosive effect of a hydrogen bomb is comparable to the explosion of tens of megatons of TNT.
Twins produced from two genetically identical cells which are cleavage products of a single fertilised egg (called zygote) that become completely separate (failure to do so may give rise to Siamese twins). Identical twins have same sex and are genetically identical but their fingerprints are different.
Imaging is a technique by which electronic data collected by various means is converted into visual image by use of computers. It is used for imaging of objects not easily accessible, such as those inside human body or from outer space. Examples of this technique are MRI, Satellite imaging, PET scan and nuclear imaging.
It is the production of immunity in an individual by artificial means. Active immunization involves the introduction, either orally or by injection, of specially treated bacteria, viruses or their toxins to stimulate the production of antibodies. Passive immunization is induced by the injection of preformed antibodies.
Information technology (IT)
Information technology refers to all equipment and methods used to handle information. The information is collected, processed, stored and use. Modern information technology combines electronics and telecommunications so that large amounts of data can be stored and transmitted. TV. computer, satellites and telephones are just some types of equipments used in information technology.
Inheritance is the acquisition of characteristics by transmission of the genetic matter from parents to offspring.
Integrated circuit (IC)
It is a complex microelectronic circuit consisting of several transistors and capacitors incorporated into a small chip of silicon. A Large Scale Integrated Circuit (LSI) Comprises thousands of components on a chip which forms a complete system, such as a microcomputer. Another advancement is a Very Large Scale Integrated Circuit (VLSI)that contains all the electrical components and complex functioning circuits which formerly would have required dozen of LSI chips. ICs are used in transistor radio sets, television sets, computers, calculators, watches and others where small reliable electronic control circuits are required.