A model of the thermal processing of particles in solar nebula shocks: Application to the cooling rates of chondrules
摘要:
Abstract— We present a model for the thermal processing of particles in shock waves typical of the solar nebula. This shock model improves on existing models in that the dissociation and recombination of H2 and the evaporation of particles are accounted for in their effects on the mass, momentum and energy fluxes. Also, besides thermal exchange with the gas and gas‐drag heating, particles can be heated by absorbing the thermal radiation emitted by other particles. The flow of radiation is calculated using the equations of radiative transfer in a slab geometry. We compute the thermal histories of particles as they encounter and pass through the shock.We apply this shock model to the melting and cooling of chondrules in the solar nebula. We constrain the combinations of shock speed and gas density needed for chondrules to reach melting temperatures, and show that these are consistent with shock waves generated by gravitational instabilities in the protoplanetary disk. After their melting, cooling rates of chondrules in the range 10–1000 K h−1 are naturally reproduced by the shock model. Chondrules are kept warm by the reservoir of hot shocked gas, which cools only as fast as the dust grains and chondrules themselves can radiate away the gas's energy. We predict a positive correlation between the concentration of chondrules in a region and the cooling rates of chondrules in that region. This correlation is supported by the unusually high frequency of (rapidly cooled) barred chondrules among compound chondrules, which must have collided preferentially in regions of high chondrule density. We discuss these and other compelling consistencies between the meteoritic record and the shock wave model of chondrule formation.
The preparation of 13-methylgon-4-enes and novel 13-polycarbonalkylgon-4-enes by a new total synthesis is described. 13-Alkylgon-4-enes having progestational, anabolic and androgenic activities are prepared by forming a tetracylic gonane structure unsaturated in the 1,3,5(10),9(11) and 14-positions, selectively reducing in the B- and C-rings, and converting the aromatic A-ring compounds so-produced to gon-4-enes by Birch reduction and hydrolysis.
1. A therapeutic composition having progestational activity comprising as active ingredient a 17-aliphatic carboxylic acid ester of 17.alpha.-ethynyl-18-methyl-19-nortestosterone and a pharmaceutical carrier for said compound.
Substitution des halogéno-1 alcynes-1 par les dérivés organométalliques du cuivre. accès à une nouvelle classe de synthons: application à
作者:A. Commerçon、J.F. Normant、J. Villieras
DOI:10.1016/0040-4020(80)87021-9
日期:1980.1
1-Bromo- and 1-iodo-1-alkynes are alkylated by organocopper(I) compounds. Alkenylcopper(I) derivatives undergo substitution with retention of configuration leading to conjugated and functional enynes, from which conjugated dienes can be obtained.
Novel 17α-bromoethynyl, 17α-chloroethynyl, 17-αiodoethynyl, 17-αtrifluoropropynyl, 17α-vinyl and 17α-triflourovinyl-17β-hydroxy (and/or 17β-alkoxy)-steroids have been prepared for biological examination.
Darstellung und schwingungsspektren der verbindungen (CH3)3SiCCCl, (CH3)3GeCCCl, (CH3)3SnCCCl und (CH3)3PbCCCl
作者:Wolfgang Steingross、Werner Zeil
DOI:10.1016/s0022-328x(00)93645-3
日期:1966.8
The following compounds: (CH3)3SiCCCl, (CH3)3GeCCCl, (CH3)3SnCCCl and (CH3)3PbCCCl, have been synthesised. The IR and Raman spectra of these compounds have been investigated and the IR and Raman frequencies are interpreted in terms of the normal vibrations.