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Moment of truth
The word 'nanotechnology' is first coined by University of Tokyo researcher Norio Taniguchi back in 1974.

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acanthoma Med.
A tumor of epidermal cells. For example, clear cell acanthoma, a reddish plague, usually seen on the thigh and legs.

acceleration Phys.
The rate of change of velocity. The acceleration of a body occurs when a force is acting on it. However, deceleration occurs when a force is acting in the opposite direction to the direction of a body's motion. The standard expression is in meters per second square (ms-2). It is a vector quantity and has both magnitude (speed) and direction.

accretion disk Astron.
A flat disk of gas and dust that surrounds a black hole, a new born star or other enormous object that is growing by attracting matter to it with its gravitional field.

achondrite Space
A stoney meteorite that does not have chondrules. It consists of crystallized portions of various minerals such as hypersthene, plagioclase, diopside and also nickel-iron. It belongs to the main meteoritic group, aerolites.

acid anhydride Chem.
A chemical substance that reacts with water to give an acid. These are usually non-metallic oxide compounds. For example, sulfur dioxide is an acid anhydride that reacts with water to give sulfurous acid.

sulfurous acid

Another example is acetic anhydride, an organic chemical substance that reacts with water to give ethanoic (acetic) acid.

acetic acid

An acid anhydride is therefore relate to the corresponding acid by the loss of water.

actinobiology Biol.
The study of effects of radiation upon living organisms.

Actinomycetes Biol.
A group of bacteria that produce mycelia and sometimes arthrospores and conidia and forming radiating colonie. For example, streptomyces which are responsible to impart fresh, healthy soil its 'earthy' smell, while many also produce antibiotics (streptomycin).

actinotherapy Med.
Treatment by means of ultraviolet, infrared and luminous radiations. The therapy was introduced by Dr. N. R. Finsen from Copenhagen in 1896. Can be used to treat certain skin diseases, disorders. The physiological effects include decreases pain and facilitates tissue healing etc.

activated aluminium Chem.
Heated form of hydrated aluminium hydroxide (Al(H2O)3(OH)3) which consists of a mixture of a reduced number of hydroxyl group and comes in a range of porosity and particle size. It is used as a desiccant, catalyst support, and chromatography.

activated carbon Chem.
It is a carbon made by steaming or heating vegetable matter in the absence of air, or in vacuum. Different pore sizes, which can be as small as 2 nm to greater than 50 nm, are created to give large internal surface area. It has the property of adsorbing large quantities of gas and is useful for purifying purposes. Its use can be as wide ranging as from decolorisation of sugar, drinking water treatment to production of pharmaceuticals.

activation energy Chem.
The minimum energy require for a chemical reaction to occur. During a chemical reaction, reactant molecules approach one another close enough and chemical bonds are broken. Energy is required for this process to occur. and subsequently proceeds to a maximum. However, energy is decreased (released) when new bonds form to make new molecules (products). The difference between the maximum energy and minimum energy is the activation energy.

active galactic nuclei Astron.
Abbreviated as AGN, it is a region that produces enormous amount of energy, at all wavelengths of the electromagnetic spectrum. Loosely referred to the bright central region of a galaxy which outshines the stars in the galaxy. AGN is though to consist of a supermassive blackhole attracting materials from the surrounding galaxy. Distant quasars are thought to be an AGN.

active site Chem., Biochem.
A molecular site on a catalyst or enzyme where catalytic activity is taken place. In the case of molecular enzyme, the arrangement of amino acid residues give a three dimensional polypeptide structure which governs the nature of interactions at the active site. Such an arrangement is also often to exclude certain molecules from entering into the active site.

acute angle Math.
An angle of less than 90.

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