| ABC | absolute basophil count; absolute bone conduction; acalculous biliary colic; acid balance control; a... |
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| FFE | fast field echo; fecal fat excretion |
| B0 | constant magnetic field in nuclear magnetic resonance |
| Bo | constant magnetic field in a magnetic resonance scanner |
| CEF | centrifugation extractable fluid; chick embryo fibroblast; constant electric field |
| 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) |
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| 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) |
| constant coupling | Where several premature beats are seen, the interval between each of them and the preceding normal beat is constant. Synonym: constant coupling. Variable coupling, where several extrasystoles are seen, the interval between each of them and the preceding sinus beat varies. (05 Mar 2000) |
| constant infusion pump | An electrically driven device for delivery from a reservoir of a constant, often very small, volume of solution over a prolonged period of time. (05 Mar 2000) |
| constant region | The stem and forking part of the Y-shaped antibody protein, consisting of amino acid chains, that is exactly the same in all antibody molecules within the same individual. (The ends of the Y-shaped molecule will vary widely between different antibodies). (09 Oct 1997) |
| haemoglobin Constant Spring | An abnormal haemoglobin having an extended polypeptide chain (31 additional amino acid residues) on the a chain (thus, the a chain is 172 amino acids long); approximately 20% of the individuals with Hb H disease also have this defect. (05 Mar 2000) |
| Hill constant | A measure of cooperativity in a binding process. A Hill coefficient of 1 indicates independent binding, a value of greater than 1 shows positive cooperativity binding of one ligand facilitates binding of subsequent ligands at other sites on the multimeric receptor complex. Worked out originally for the binding of oxygen to haemoglobin (Hill coefficient of 2.8). (18 Nov 1997) |