Racemic Mixture [chapter]

Jeffrey Bada
2015 Encyclopedia of Astrobiology  
Synonyms 50:50 enantiomeric mixture Definition A racemic mixture is a mixture containing equal amounts (50:50) of both enantiomers of a chiral chemical compound (e.g., of L-and D-alanine). By definition the enantiomeric excess of a racemic mixture is equal to zero. A racemic mixture will induce no rotation of the plane of polarization of polarized light. The term racemic should not be confused with the term achiral, which refers to compounds which are not chiral. Keywords Planetesimals;
more » ... netary disk Definition Radial drift is a process in a ▶ protoplanetary disk where the semimajor axes of the orbits of solid particles/bodies are modified as a result of gas-solid interactions (e.g., gas drag). Radial drift is directed toward regions of pressure maxima (generally toward the star). Definition Radial-velocity planets are those detected indirectly by observing the orbital motion of their host stars in response to the gravitational pull of the planets. The stellar motion is measured from the ▶ Doppler effect on the stellar spectral lines. Radial-Velocity Planets Radial-Velocity Planets Butler RP et al (1999) Evidence for multiple companions to Upsilon Andromedae. Astrophys J 526:916-927 Campbell B, Walker GAH, Yang S (1988a) A search for planetary mass companions to nearby stars. In: Bioastronomy -the next steps; Proceedings of the ninety-ninth IAU Colloquium, Balaton, Hungary, 22-27 June 1987 (A88-55201 24-88). Kluwer, Dordrecht, pp 83-90 Campbell B, Walker GAH, Yang S (1988b) A search for substellar companions to solar-type stars. Astrophys J 331:902-921 Delfosse X, Forveille T, Mayor M, Perrier C, Naef D, Queloz D (1998) The closest extrasolar planet. A giant planet around the M4 dwarf GL 876. Astron Astrophys 338:L67-L70 Haghighipour N (2010) Planets in binary star systems. Astrophysics and Space Science Library, vol 366. Springer. ISBN 978-90-481-8686-0 Hatzes AP, Cochran WD, Endl M, McArthur B, Paulson DB, Walker GAH, Campbell B, Yang S (2003) A planetary companion to gamma Cephei A. Astrophys J 599:1383-1394 Howard A et al (2010) The occurrence and mass distribution of close-in Super-Earths, Neptunes, and Jupiters. Science 330:653 Latham DW et al (1989) The unseen companion of HD 114762 -a probable brown dwarf. Nature 339:38-40 Marcy GW, Butler RP, Vogt SS, Fischer D, Lissauer JJ (1998) A planetary companion to a nearby M4 dwarf, Gliese 876. Astrophys J 505:L147-L149 Marcy GW, Butler RP, Fischer D, Vogt SS, Lissauer JJ, Rivera EJ (2001) A pair of resonant planets orbiting GJ 876. Astrophys J 556:296-301 Mayor M (2009) The HARPS search for southern extrasolar planets. XIII. A planetary system with 3 superearths (4.2, 6.9, and 9.2 M E ). Astron Astrophys 493:639-644 Mayor M, Queloz D (1995) A Jupiter-mass companion to a solar-type star. Nature 378:355-359 Rivera E et al (2005) A $7.5M L planet orbiting the nearby star, GJ 876. Astrophys J 634:625-640 Radiation ▶ X-Rays (Stellar) Synonyms Radiation interactions with living matter Definition Radiation biology is an interdisciplinary subject that describes the biological effects of ionizing radiations. It is based on studies in physics, chemistry, biology, and medicine. History The history of radiation biology started shortly after the discovery of X-rays in 1895 by Wilhelm Radiation Biology 2113 R ▶ Linear Energy Transfer ▶ Radiation Biology ▶ Space Environment
doi:10.1007/978-3-662-44185-5_1329 fatcat:xge7qo2lpbb4ziijjpp5pn7fre