| ATN | <nephrology> A kidney disorder that results in damage to the renal tubule cells leading to acute renal failure. Acute tubular necrosis can result from any condition which deprives the kidney of oxygen (ischaemia). Acute tubular necrosis may occur as a complication of shock, trauma or sepsis. Conditions such as diabetes or liver disease can predispose people to the development of acute tubular necrosis. Certain medications (for example aminoglycosides, amphotericin B, cyclosporine) are known to cause acute tubular necrosis as a toxic side effect. Radiopaque contrast dyes, used in some radiologic procedures, may also result in acute tubular necrosis as a rare complication from contrast dye use. Acronym: ATN (13 Nov 1997) |
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| atokous | <zoology> Producing only asexual individuals, as the eggs of certain annelids. Origin: Gr. Barren; priv. + offspring. Source: Websters Dictionary (01 Mar 1998) |
| atom | <chemistry, physics, radiobiology> A particle of matter indivisible by chemical means. It is the fundamental building block of the chemical elements. The elements, such as iron, lead and sulphur, differ from each other because they contain different kinds of atoms. There are about six sextillion (6 followed by 21 zeros or 6 x 1021) atoms in an ordinary drop of water. According to present day theory, an atom contains a dense inner core (the nucleus) and a much less dense outer domain consisting of electrons in motion around the nucleus. Atoms are electrically neutral. (16 Dec 1997) |
| atomic | 1. Of or pertaining to atoms. 2. Extremely minute; tiny. Atomic philosophy, or Doctrine of atoms, a system which assuming that atoms are endued with gravity and motion accounted thus for the origin and formation of all things. This philosophy was first broached by Leucippus, was developed by Democritus, and afterward improved by Epicurus, and hence is sometimes denominated the Epicurean philosophy. <chemistry> Atomic theory, or the Doctrine of definite proportions, the weight of the atom of an element as compared with the weight of the atom of hydrogen, taken as a standard. Origin: Cf. F. Atomique. Source: Websters Dictionary (01 Mar 1998) |
| atomic absorption spectrophotometry | Determination of concentration by the ability of atoms to absorb radiant energy of specific wavelengths. (05 Mar 2000) |
| atomic bomb | <physics, radiobiology> A weapon with a large explosive power due to the sudden release of energy when the nuclei of heavy atoms such as plutonium-239 or uranium-235 are split. This fission is brought about by the bombardment of the fuel with neutrons, setting off a chain reaction. The bomb releases shock, blast, heat, light, and lethal radiation. The world's first atomic bomb was successfully tested by the United States on July 16, 1945. (13 Nov 1997) |
| atomic core | The nucleus plus the nonvalence electrons. (05 Mar 2000) |
| atomic heat | The amount of heat required to raise an atom from 0 |
| atomic mass | <chemistry, physics> The mass of an atom relative to other atoms. The present-day basis of the scale of atomic weights is carbon, the most common isotope of this element has arbitrarily been assigned an atomic weight of 12. The unit of the scale is 1/12 the weight of the carbon atom or roughly the mass of one proton or one neutron. The atomic weight of any element is approximately equal to the total number of protons and neutrons in is nucleus (16 Dec 1997) |
| atomic mass unit | <chemistry> One-twelfth the mass of a neutral atom of the most abundant isotope of carbon. (16 Dec 1997) |
| atomic number | <chemistry> Symbol Z. The number of protons in the nucleus of an atom and also its characteristic atomic number. The atomic numbers of the known elements form a complete series from 1 (hydrogen) to 103 (lawrencium). (16 Dec 1997) |
| atomic theory | That chemical compounds are formed by the union of atoms in certain definite proportions; in its modern form, first advanced in 1803 by John Dalton. (05 Mar 2000) |
| atomic volume | The atomic weight of an element divided by its density in the solid state; the volume of the gram-atomic weight of a solid element. (05 Mar 2000) |
| atomic weight | <chemistry> The average weight of an atom of an element, i.e. The total mass of protons and neutrons in an atom. (09 Oct 1997) |
| atomical | 1. Of or pertaining to atoms. 2. Extremely minute; tiny. Atomic philosophy, or Doctrine of atoms, a system which assuming that atoms are endued with gravity and motion accounted thus for the origin and formation of all things. This philosophy was first broached by Leucippus, was developed by Democritus, and afterward improved by Epicurus, and hence is sometimes denominated the Epicurean philosophy. <chemistry> Atomic theory, or the Doctrine of definite proportions, the weight of the atom of an element as compared with the weight of the atom of hydrogen, taken as a standard. Origin: Cf. F. Atomique. Source: Websters Dictionary (01 Mar 1998) |