| velocity constants | Proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); e.g., in the reaction A → B + C, the rate of the reaction equals -d[A]/dt = k1[A]. The rate constant k1 is a unimolecular rate constant since there is only one molecular species reacting and has units of reciprocal time (e.g., sec-1). For the reverse reaction, B + C → A, the rate equals -d[B]/dt = d[A]/dt = k2[B][C]. The rate constant k2 is a bimolecular rate constant and has units of reciprocal concentration-time (e.g., m-1 sec-1). Synonym: velocity constants. (05 Mar 2000) |
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| velocity space | <radiobiology> Mathematical space where each point corresponds not to a certain location in reality, but to a certain velocity. Distribution functions typically involve mixes of both position and velocity spaces. (See distribution function.) Contrast with position space where each point corresponds to a given location. (09 Oct 1997) |
| velocity space instability | <radiobiology> A class of instabilities driven by particle distributions (in velocity space) which are not in thermal equilibrium. (09 Oct 1997) |
| maximum velocity | The maximum rate of an enzyme-catalyzed reaction that can be achieved by progressively increasing the substrate concentration at a given enzyme concentration; in cases of substrate inhibition, Vmax is an extrapolated value in the absence of such inhibition; Cf.: Michaelis-Menten equation. The maximum initial rate of shortening of a myocardial fibre that can be obtained under zero load; used to evaluate the contractility of the fibre. (05 Mar 2000) |
| group velocity | <radiobiology> This is derived from the dispersion relation as Vgroup = dw/dk, the group velocity is the rate at which modulations or information within a wave travel through a given medium. (09 Oct 1997) |
| critical velocity | <biology> The maximum speed a device or organism can sustain over a specified distance or length of time, or the maximum velocity against which device or organism can sustain a position over a specified length of time. <marine biology> Velocity through which a fish will not swim, creating a velocity barrier. (09 Oct 1997) |
| sedimentation velocity | The rate of movement of a substance, typically a macromolecule, in centrifugation; these centrifugation studies provide data on the structure of the macromolecule. (05 Mar 2000) |
| steady-state velocity | The velocity of an enzyme-catalyzed reaction in which, over the time course of the study, the concentration of any enzyme species is constant (i.e., for an enzyme-substrate binary complex, ES, d[ES]/dt&apprxeq;00; for this to hold true, the total enzyme concentration must be much less than the initial substrate concentration. Synonym: steady-state rate. (05 Mar 2000) |
| nerve conduction velocity | The rate of impulse conduction in a peripheral nerve or its various component fibres, generally expressed in meters per second. (05 Mar 2000) |
| drift velocity | <radiobiology> Characteristic velocity at which the centre of a particle's orbit (guiding centre) drifts when drift motion (see above) occurs. (09 Oct 1997) |
| initial velocity | The rate of a reaction, e.g., an enzyme-catalyzed reaction, at the early stages of the reaction such that the product(s) concentrations have not risen to a level to significantly affect the observable rate; typically, initial velocities are observed when less than 10% of the reaction's approach toward equilibrium has occurred. Synonym: initial rate. (05 Mar 2000) |
| thermal velocity | <radiobiology> Average speed (magnitude of velocity) of a particle at a given temperature (in a Maxwellian velocity distribution). (09 Oct 1997) |
| electron velocity | <physics> The rate of motion of an electron. (05 Aug 1998) |
| fish velocity | The velocity at the location occupied by a fish, measured at the fish's snout. (09 Oct 1997) |
| force-velocity curve | The relationship between isotonic velocity of shortening and afterload for a contracting muscle. (05 Mar 2000) |