| personal equation | A slight error in judgment, perceptual response, or action peculiar to the individual and so constant that it is usually possible to allow for it in accepting the person's statements or conclusions, thus arriving at approximate exactness; observed in persons whose work involves readings of events in time, such as navigators and air traffic controllers. (05 Mar 2000) |
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| Michaelis-Menten equation | <chemistry> Equation derived from a simple kinetic model for a single-substrate non-cooperative enzyme-catalyzed reaction that successfully accounts for the hyperbolic adsorption isotherm) relationship between substrate concentration and reaction rate. V = Vmax x S/(S + Km), where V is the initial velocity of the reaction, Km is the Michaelis constant, Vmax is the maximum rate approached by very high substrate concentrations and S is the initial substrate concentration. Similar equations can be derived for conditions in which the product is present and for multisubstrate enzymes. Synonym: Victor-Michaelis-Menten equation. (12 Jul 2000) |
| constant field equation | An equation derived to predict membrane potentials in terms of the membrane's permeability to ions and their concentrations on either side. Synonym: constant field equation, Goldman-Hodgkin-Katz equation, GHK equation. (05 Mar 2000) |
| Henderson-Hasselbalch equation | <chemistry> The Henderson-Hasselbalch equation is the equation: PH = pK + log ([A-]/[HA]) Where pH is the acidity or alkalinity of the buffer solution, pK is the negative logarithm of the equilibrium constant (Kd) for the ionisation of the acid form (A-) of the compound used to buffer the solution for the reaction HA = H+ +A-, [A-] is the molar concentration of the ionised form of the buffer compound, and [HA] is the molar concentration of the nonionised form of the buffer compound. (09 Oct 1997) |
| Hill's equation | The equation,y(1-y) = [S]n/Kd, where y is the fractional degree of saturation, [S] is the binding ligand concentration, n is the Hill coefficient, and Kd is the dissociation constant for the ligand. The Hill coefficient is a measure of the cooperativity of the protein; the larger the value, the higher the cooperativity. This coefficient cannot be higher than the number of binding sites. For the oxygen binding curve of haemoglobin, an association constant, Ka, is used and the equation becomes y/(1-y) = Ka[S]n. For human blood, n equals 2.5. Compare: Hill plot. (05 Mar 2000) |
| Nernst equation | <physics> A basic equation of biophysics that describes the relationship between the equilibrium potential difference across a semipermeable membrane and the equilibrium distribution of the ionic permeant species. It is described by: E = (RT/zF).ln[C1/C2 Where E is the potential on side 2 relative to side 1 in volts), R is the gas constant (8.314 J Kexp 1 molexp 1), T is the absolute temperature, z is the charge on the permeant ion, f is the Faraday constant (96500 C molexp 1) and C1 and C2 are the concentrations (more correctly activities) of the ions on sides 1 and 2 of the membrane. It can be seen that this equation is a solution of the more general equation of electrochemical potential, for the special case of equilibrium. The equation described the voltage generated by ion selective electrodes, like the laboratory pH electrode and approximates the behaviour of the resting plasma membrane (see resting potential). (13 Nov 1997) |
| Nernst's equation | The equation relating the equilibrium potential of electrodes to ion concentrations; the equation relating the electrical potential and concentration gradient of an ion across a permeable membrane at equilibrium: E = [RT / nF Origin: Ln (C1/C 2)], where E = potential, R = absolute gas constant, T = absolute temperature, n = valence, F = the Faraday, ln = the natural logarithm, and C1 and C2 are the ion concentrations on the two sides; in nonideal solutions, concentration should be replaced by activity. See: Nernst's theory, activity. (05 Mar 2000) |
| Svedberg equation | See: sedimentation constant. (05 Mar 2000) |
| difference equation | <epidemiology> The mathematical formulation corresponding to a discrete time model. (05 Dec 1998) |
| differential equation | <epidemiology> The mathematical formulation corresponding to a continuous model; an equation involving derivatives. (05 Dec 1998) |
| Einthoven's equation | In the electrocardiogram the potential of any wave or complex in lead II is equal to the sum of the potentials of leads I and III. Synonym: Einthoven's equation. (05 Mar 2000) |
| equation | 1. A making equal; equal division; equality; equilibrium. "Again the golden day resumed its right, And ruled in just equation with the night." (Rowe) 2. <mathematics> An expression of the condition of equality between two algebraic quantities or sets of quantities, the sign = being placed between them; as, a binomial equation; a quadratic equation; an algebraic equation; a transcendental equation; an exponential equation; a logarithmic equation; a differential equation, etc. 3. <astronomy> A quantity to be applied in computing the mean place or other element of a celestial body; that is, any one of the several quantities to be added to, or taken from, its position as calculated on the hypothesis of a mean uniform motion, in order to find its true position as resulting from its actual and unequal motion. 4. Equation box, or Equational box, a system of differential gearing used in spinning machines for regulating the twist of the yarn. It resembles gearing used in equation clocks for showing apparent time. 5. <astronomy> Equation of the center, the difference between the place of a planet as supposed to move uniformly in a circle, and its place as moving in an ellipse. Origin: L. Aequatio an equalizing: cf. F. Equation equation. See Equate. Source: Websters Dictionary (01 Mar 1998) |
| Fokker-Planck equation | <radiobiology> An equation that describes the time rate of change of a particle's velocity as a result of small-angle collisional deflections. Applicable when the cumulative effect of many small-angle collisions is greater than the effect of rarer large-angle deflections. (09 Oct 1997) |
| Lineweaver-Burk equation | A rearrangement of the Michaelis-Menten equation, 1/v = 1/Vmax + (Km/Vmax)(1/[S]). Compare: double-reciprocal plot. (05 Mar 2000) |