number

1. A symbol expressive of a certain value or of a specific quantity determined by count. 2. The place of any unit in a series.

- atomic n. (Z) the n. of protons in the nucleus of an atom; it indicates the position of the element in the periodic system.

- Avogadro n. (Λ, N_A) the n. of molecules in 1 gram-molecular weight (1 mol) of any compound; defined as the n. of atoms in 0.0120 kg of pure carbon-12; equivalent to 6.0221367 × 10²³. SYN: Avogadro constant.

- Brinell hardness n. (BHN) a n. related to the size of the permanent impression made by a ball indenter of specified size (usually 10 mm in diameter) pressed into the surface of the material under a specified load : where P = applied load in kg, D = diameter of the ball in mm, and d = diameter of the impression in mm.

- CT n. a normalized value of the calculated x-ray absorption coefficient of a pixel (picture element) in a computed tomogram, expressed in Hounsfield units, where the CT n. of air is −1000 and that of water is 0. SYN: Hounsfield n..

- electronic n. the n. of electrons in the outermost orbit (valence shell) of an element.

- gold n. SYN: gold equivalent.

- Hehner n. the weight or percentage of the nonvolatile fatty acid s yielded by 5 g of a saponified fat or oil. SYN: Hehner value.

- Hogben n. unique personal identifying n. constructed by using a sequence of digits for birth date, sex, birthplace, and other identifiers; invented by and named for Lancelot Hogben, British mathematician; Hogben numbers are the basis for identification numbers in many primary care facilities and are used in many record linkage systems.

- Hounsfield n. SYN: CT n..

- hydrogen n. the quantity of hydrogen that 1 g of fat will absorb; it is a measurement of the amount of unsaturated fatty acid s in the fat. SEE ALSO: iodine n..

- iodine n. an indication of the quantity of unsaturated fatty acid s present in a fat; it represents the n. of grams of iodine absorbed by each 100 g of fat. SEE ALSO: hydrogen n.. SYN: iodine value.

- Kestenbaum n. the difference between the two pupil diameters when each eye is measured in bright light with the other eye tightly covered; an indicator of the relative afferent pupillary defect in patients with two normally innervated irises.

- Knoop hardness n. (KHN) a n. obtained by dividing the load in kg applied to a pyramid-shaped diamond of specific size divided by the projected area of the impression : KHN = L/A, where A= the projected area of the impression in mm² and L = the load in kg; used for measurements of hardness of any materials, especially very hard and brittle substances such as tooth dentin and enamel.

- Koettstorfer n. SYN: saponification n..

- linking n. (L) a property of a long biopolymer (such as duplex DNA) equal to the n. of twists (related to the frequency of turns around the central axis of the helix) plus the writhing n..

- Loschmidt n. (n₀) the n. of molecules in 1 cm³ of ideal gas at 0°C and 1 atm of pressure; Avogadro n. divided by 22,414 ( i.e., 2.6868 × 10¹⁹ cm⁻³).

- Mach n. a n. representing the ratio between the speed of an object moving through a fluid medium, such as air, and the speed of sound in the same medium.

- mass n. the mass of the atom of a particular isotope relative to hydrogen-1 (or to 112 the mass of carbon-12), generally very close to the whole n. represented by the sum of the protons and neutrons in the atomic nucleus of the isotope (indicated in the name or symbol of the isotope; e.g., oxygen-16, ¹⁶O); not to be confused with the atomic weight of an element, which may include a n. of isotopes in natural proportion.

- MIM n. the catalog assignment for a mendelian trait in the MIM system. If the initial digit is 1, the trait is deemed autosomal dominant; if 2, autosomal recessive; if 3, X-linked. Wherever a trait defined in this dictionary has a MIM n., the n. from the 12th edition of MIM, is given in square brackets with or without an asterisk (asterisks indicate that the mode of inheritance is known; a n. symbol (#) before an entry n. means that the phenotype can be caused by mutation in any of 2 or more genes) as appropriate e.g., Pelizaeus-Merzbacher disease [MIM*169500] is a well-established, autosomal, dominant, mendelian disorder.

- Polenské n. the n. of milliliters of 0.1 n KOH required to neutralize the nonvolatile fatty acid s obtained from 5 g of a saponified fat or oil.

- Reichert-Meissl n. an index of the volatile acid content of a fat; the n. of milliliters of 0.1 n KOH required to neutralize the soluble volatile fatty acid s in 5 g of fat that has been saponified, acidified to liberate the fatty acid s, and then steam-distilled. SYN: volatile fatty acid n..

- Reynolds n. a dimensionless n. that describes the tendency for a flowing fluid, such as blood, to change from laminar flow to turbulent flow or vice versa.

- saponification n. the n. of milligrams of KOH required to saponify 1 g of fat; an approximate measure of the average molecular weight of a fat, with which it varies inversely. SYN: Koettstorfer n..

- stoichiometric n. (ν) the n. associated with a reactant or product participating in a defined chemical reaction; usually an integer.

- thiocyanogen n. the n. of grams of thiocyanogen taken up by 100 g of fat; analogous to the iodine n., except that thiocyanogen will not add to all the double bonds in polyunsaturated fatty acid s, as will iodine. SYN: thiocyanogen value.

- transport n. the fraction of the total current carried through a solution by a particular type of ion present in that solution.

- turnover n. (k_cat) the n. of substrate molecules converted into product in an enzyme-catalyzed reaction under saturating conditions per unit time per unit quantity of enzyme; e.g., k_cat = V_max/[E_total].

- volatile fatty acid n. SYN: Reichert-Meissl n..

- wave n. the n. of waves (of any waveform such as light or sound) per unit length.

- writhing n. the n. of times a DNA duplex axis crosses over itself in space.

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num·ber (numґbər) [Fr. nombre, from L. numerus] a symbol, as a figure or word, expressive of a certain value or of a specified quantity determined by count.