| universal tube | A straight, cylindrical glass vial that holds about 25 millilitres and istopped with a screw-on cap. (09 Oct 1997) |
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| acid dissociation constant | <chemistry> This is the equilibrium constant for the breaking apart of a weak acid into its hydrogen and conjugate base in a water solution. (09 Oct 1997) |
| Ambard's constant | <physiology> Obsolete law's for output of urea: 1. With the urinary urea concentration constant, urea output varies directly as the square of the concentration of the blood urea. 2. With the blood urea concentration constant, urea output varies inversely as the square root of its urinary concentration. (05 Mar 2000) |
| association constant | <chemistry> Reciprocal of dissociation constant. A measure of the extent of a reversible association between two molecular species at equilibrium. (18 Nov 1997) |
| Avogadro's constant | <physics> The number of molecules in a mole (gram molecular weight) of a substance, equals 6.02 x 1023 molecules. (09 Oct 1997) |
| base dissociation constant | <chemistry> This is the equilibrium constant for the reaction in which a weak base breaks apart in water to form its conjugate acid and hydroxide ion. (09 Oct 1997) |
| binding constant | <chemistry> Reciprocal of dissociation constant. A measure of the extent of a reversible association between two molecular species at equilibrium. (18 Nov 1997) |
| boltzmann constant | <radiobiology> K = 1.38 x 10^-16 erg/degree. This is the ratio of the universal gas constant to Avogadro's number. It is also used to relate temperatures (Kelvin) to energies (ergs or Joules) via E = (constant of order unity) kT. (09 Oct 1997) |
| radioactive constant | <physics, radiobiology> The fraction of the amount of a radionuclide that undergoes transition per unit time. Formally: Lamda=dP/dt Where dP is the probability of a given nucleus undergoing spontaneous nuclear transition in the time interval dt. (16 Dec 1997) |
| gas constant | R (symbol for the constant) = 8.314 × 107 ergs per degree Celsius per mole = 8.314 J K-1 mol-1 (joules per kelvin mole). (05 Mar 2000) |
| permeability constant | A measure of the ease with which an ion can cross a unit area of membrane driven by a 1.0 m difference in concentration; usually expressed in centimeters per second. Compare: permeability coefficient. (05 Mar 2000) |
| Michaelis constant | <chemistry> The true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolised by Ks), the concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved (when velocities are measured under initial rate and steady state conditions). The ratio of rate constants (k2 + k3)/k1 in the single-substrate enzyme-catalyzed reaction: E + S &dblarr; ES &dblarr; E + products where E represents the free enzyme, S is the substrate, and ES is the central binary complex. The expression for the Michaelis constant will be more complex for multisubstrate reactions. An apparent Michaelis constant is a constant determined either under conditions that are not strictly steady state and initial rate or one that varies with the concentration of one or more cosubstrates. See: Michaelis-Menten equation. Synonym: Michaelis-Menten constant. (05 Mar 2000) |
| Michaelis-Menten constant | <chemistry> The true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolised by Ks), the concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved (when velocities are measured under initial rate and steady state conditions). The ratio of rate constants (k2 + k3)/k1 in the single-substrate enzyme-catalyzed reaction: E + S &dblarr; ES &dblarr; E + products where E represents the free enzyme, S is the substrate, and ES is the central binary complex. The expression for the Michaelis constant will be more complex for multisubstrate reactions. An apparent Michaelis constant is a constant determined either under conditions that are not strictly steady state and initial rate or one that varies with the concentration of one or more cosubstrates. See: Michaelis-Menten equation. Synonym: Michaelis-Menten constant. (05 Mar 2000) |
| Planck's constant | A constant, 6.6260755 × 10-34 J - s (joule-seconds) or 6.6260755 × 10-27 erg-seconds = 6.6260755 × 10-34 J Hz-1 (joule per hertz). (05 Mar 2000) |
| constant | A quantity that, under stated conditions, does not vary with changes in the environment. (05 Mar 2000) |