Knudsen layer lâye-ye Knudsen Fr.: couche de Knudsen The thin layer of → vapor immediately adjacent to an irradiated surface. The thickness of the Knudsen layer is generally recognized to be in the order of a few → mean free paths from the surface. Named after Danish physicist Martin Knudsen (1871-1949); → layer. |
Kochab (β Ursae Minoris) Kowkab (#) Fr.: Kochab The second brightest star in the constellation → Ursa Minor. It is a reddish, evolved → giant of → spectral type K4 with a visual magnitude of 2.1. It is almost 500 times more luminous than the Sun and lies at a distance of 126 light years. Also called Kocab, Kochah. Kochab, from Ar. al-Kaukab ( |
Kolmogorov constant pâyâ-ye Kolmogorov (#) Fr.: constante de Kolmogorov The proportionality constant C in Kolmogorov's mathematical analysis of → turbulence which states that the spectral energy E(k) in the range of turbulent scales is E(k) =C ε^{2/3} k^{-5/3}, where k represents the → wave number (inversely proportional to the wavelength or → eddy size), and ε is the average energy dissipation per unit mass in the fluid. Experimental measurements give C close to 1.5. Andrei Nikolaevich Kolmogorov (1903-1987), a prominent Soviet mathematician, who made major advances in different scientific fields, mainly probability theory, topology, turbulence, classical mechanics, and computational complexity; → constant. |
Kolmogorov scale marpel-e Kolmogorov Fr.: échelle de Kolmogorov Length scale of → turbulent flow below which the effects of molecular → viscosity are non-negligible. → Kolmogorov constant; → scale. |
Kolmogorov spectrum binâb-e Kolmogorove Fr.: spectre de Kolmogorov The distribution of energy over different scales in a → turbulent flow where → energy cascade occurs. Let E be the energy per unit → wave number (k) and ε the energy → dissipation parameter, E = E(k,ε). → Dimensional analysis yields: E = Cε^{2/3}k^{-5/3}, where C is the → Kolmogorov constant. A. N. Kolmogorov, 1941, Local structure of turbulence in an incompressible fluid for very large Reynolds numbers, Doklady Acad Sci. USSR 31, 301; → spectrum. |
Kozai-Lidov mechanism sâzokâr-e Kozai-Lidov Fr.: mécanisme de Kozai-Lidov In the → three-body problem, the → perturbation of the orbit of a → secondary body by the garvity of a third body located at a distance much larger than the separation between the → primary body and the secondary. The secondary's orbit oscillates about a constant value involving a periodic exchange between the extreme values of its → inclination and orbital → eccentricity. The Kozai-Lidov mechanism results from the conservation of the quantity (1 - e^{2})^{1/2}.cos i for each component, where e is eccentricity and i is inclination. The total → angular momentum of the system remains constant while the angular momentum is exchanged betwwen the components. It has been suggested that the Kozai mechanism is responsible for the high eccentricities observed in the orbits of → extrasolar planets. If the parent star has a massive yet unseen substellar companion, orbiting at a great distance, and in an orbit highly inclined to the plane of the planets' orbits, the mechanism should induce high eccentricities into the orbits of the planets. Similarly, this mechanism may be responsible for the high eccentricities observed in the orbits of many → Kuiper Belt Objects such as 2003 UB313. Named for the japanese Yoshihide Kozai (1962, Astronomical J. 67, 591), and the Russian Michael Lidov (1962, Planetary & Space Science 9, 719). |
Kramers' law qânun-e Kramers (#) Fr.: loi de Kramers An approximate expression for deriving the → opacity that depends upon temperature with a power law: κ ∝ ρT^{-3.5}, where ρ represents the density. In → partial ionization zones, a part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. As the temperature of the compressed layer has not substantially increased, the increase in density produces a corresponding increase in the opacity of the layer. Likewise, during the expansion phase, the temperature does not decrease significantly since the ions release energy when they recombine with electrons. Derived in 1923 by the Dutch physicist Henrik Kramers (1894-1952); → law. |
Kramers' opacity law qânun-e kederi-ye Kramers (#) Fr.: loi de l'opacité de Kramers Same as → Kramers' law. Named after Henrik Kramers (1894-1952); → law. |
Kronecker delta deltâ-ye Kronecker (#) Fr.: delta de Kronecker The function δ^{i}_{k} of two variables i and j defined by δ^{i}_{k} = 1 if i = j, and δ^{i}_{k} = 0 if i ≠ j. Leopold Kronecker (1823-1891), a German mathematician; delta, Gk. letter of alphabet. |
Kruskal diagram nemudâr-e Kruskal Fr.: diagramme de Kruskal A diagram used to plot trajectories in → space-time near a → black hole. The vertical and horizontal axes are two complicated functions of time and distance from the black hole. Lines of constant time radiate from the origin of the diagram, with steeper slopes corresponding to later times. Lines of constant distance are hyperbolas, lines of constant time pass through the origin; photons always travel along diagonal lines at ±45° to the vertical. The trajectory of an object falling into the black hole is shown as a curving line moving upward on the diagram at less than 45° to the vertical. Named after the American physicist Martin David Kruskal (1925-2006); → diagram. |
krypton kripton (#) Fr.: krypton A colorless, odorless, highly un-reactive gaseous chemical element and a member of the inert gas family. Symbol Kr; atomic number 36; atomic weight 83.80; melting point -156.6°C; boiling point -152.3°C. Krypton, from Gk. kryptos "concealed, hidden". It was discovered in liquefied atmospheric air by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898. |
Kuiper belt kamarband-e Kuiper (#) Fr.: ceinture de Kuiper A region of the → Solar System extending roughly from the orbit of → Neptune, or 30 → astronomical units (AU), to 50 AU from the Sun that contains many small icy bodies. The Kuiper belt is now considered to be the source of the → short-period comets. Named after Gerard Peter Kuiper (1905-1973), a Dutch-born American astronomer, who predicted the belt in 1951. He is also considered the father of modern planetary science for his contributions to the study of our solar system; → belt. |
Kuiper belt object (KBO) barâxt-e kamarband-e Kuiper Fr.: objet de la ceinture de Kuiper A → Solar System object belonging to the → Kuiper belt. The largest known objects of this type are → Pluto and its moon → Charon, → Quaoar, → Sedna, and → Orcus. See also → trans-Neptunian object. → Kuiper belt; → object. |
kurtosis afrâštegi (#) Fr.: aplatissement The measure of "peakedness" of the curve describing a frequency distribution in the region about its mode. The kurtosis of the normal distribution is 0. From Gk. kurtosis "bulging, curvature," from kurtos "convex," kirkos "a ring;" cf. Av. skarəna- "round;" L. circus "circle, ring;" PIE base *sker- "to turn, bend." Afrâštegi condition, state adj. of afrâšté "elevated, erect, upright," p.p. of afrâštan "to raise, exalt, extole," from Mid.Pers. abrâstan, abrâz- "to lift, raise," from ab-, from O.Pers./Av. abiy-/aiwi- "to, upon, against;" cf. Skt. abhi-, Gk. amphi- + râst "straight, direct, true;" from O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right; PIE base *reg- "move in a straight line," hence, "to direct, rule." |