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Moment of truth
The fastest man-made object that ever leave the Earth is the New Horizon spacecraft, launched in January 2006, and attained a speed of more than 36000 mph.

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Geiger-Muller tube Phys.
Also called Geiger-Muller detector, it is used to detect the amount of radiation and also counting of alpha and beta particles. It consists of a thin wire (anode) enclosed in a metal cylinder container (cathode). The cylinder is filled with a low pressure gas mixture. To use the tube, an electrical potential (several hundred volts) is applied accross the electrodes. A particle that enters the tube ionizes the gas mixture. The ionized gas particles in turn produce a cascade of charged gas particles which are collected at the anode and a current pulse is registered. After each cascade, a pause of about 0.5 ms is required to allow the gas mixture to de-ionized.

geiger counter

gel filtration chromatography Biochem.
A type of size exclusion chromatography technique in which particles are separated based on their size. An aqueous solution containing a mixture of sample is passed down a column containing a gel. Small molecules in the mixture can enter pores in the gel and move slowly down the column. Large molecules, which cannot enter the pores, move more quickly. Thus, the mixture can be separated. The technique is used for separating proteins, cell nuclei, viruses and polysaccharides. The gel medium is usually polyacrylamide, dextran or agarose and under low pressure.

The technique was invented in 1955 by G.H. Lathe and C. R. Ruthven while working at Queen Charlotte's Hosipital, London. See also gel permeation chromatography.

gel permeation chromatography Chem.
A type of size exclusion chromatography. It is a technique in which samples are seprated based on their size. The separating process is similar to gel filtration chromatography. However, an organic solvent is used, instead of water, and the technique is used to analyse the molecular weight disribution of organic-soluble polymer samples. The gel medium in the chromatography typically consists of either a silica or crosslinked polystyrene and the sample is filtered under high pressure. See also gel filtration chromatography.

gelatin(e) Chem.
A colorless, tasteless and odorless glue substance, obtained from bones, cartilage, tendons and other albuminous sunstances. It is a water-soluble protein that swells when water is added. It sets to a gel when dissolves in hot water and allows it to cool. It is used in jellies and other foodstuffs, photographic emulsions and adhesives.

gem molecule Chem.
Referring to a molecule in which two functional groups are attached to the same atom in a molecule. For instance, chloral hydrate, CCl3-CH-(OH)2, is a gem diol in which both hydroxyl (OH) groups are on the same carbon atom.

gene expression Biol.
The process by which protein are selectively made from the instructions encoded in DNA. Each cell contains a blueprint to produce whole range of protein that builds the whole body. However, gene expression provides control that allow to produce only certain specific types of proteins in cell.

genome Biol.
All information for an organism. For all kinds of cellular organisms (from bacteria to animals) genome is composed of double-stranded DNA sequences while genomes of viruses contain either single- or double-stranded DNA or RNA.

genotype Biol.
The genetic constitution, coded (genetic code) and inheritable found within almost all cells. The genetic information is used for building and maintaining a living creature via cell division or reproduction and the information is passed from one generation to the next (inheritable). It also contains information for cell to produce phenotype of the organism.

geochemistry Chem., Geol.
The scientific study of the chemical composition of the Earth. For instance, the abundance, distributions, interactions and cyclisation of minerals and elements in the environments and atmosphere. This also includes biosphere and hydrosphere.

geodesic Math.
It is the straightest possible path constrained to lie on the surface. Every straight line is a geodesic. For the surface of a sphere, there are always two geodesics between any two points: the shortest and the longest.

geometric mean Math.
Of a given n positive numbers, ar; the nth root of their product:

geometric mean

It indicates a measure of central tendency of a series of samples and is useful for highly skewed data that changes in a relative fashion.

German silver Eng.
Also called nickel silver. It is an alloy of copper, zinc and nickel. It resembles silver in appearance and is often used in jewellery as a cheaper alternative to silver, as a base metal for silver plating and tableware. It is quite corrosion resistance, ductile and malleable.

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