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1.
Depending on various assumptions on the energy scale of inflation and assuming a primordial power spectrum of a step‐like structure, we explore new possibilities for Primordial Black Holes (PBH) and Planck relics to contribute substantially to Cold Dark Matter in the Universe. A recently proposed possibility to produce Planck relics in four‐dimensional string gravity is considered in this framework. Possible experimental detection of PBHs through gravitational waves is also explored. We stress that inflation with a low energy scale, and also possibly when Planck relics are produced, leads unavoidably to relics originating from PBHs that are not effectively classical during their formation, rendering the usual formalism inadequate for them. 相似文献
2.
The γ-hydroxymetal hydrides OH (M = Si, Ge, Sn) were synthesized by reduction of γ-acetoxychloro- or γ-hydroxychloro-silanes, -germanes and -stannanes. These derivatives with MH bonds lead, by cyclisation at room- or higher temperatures, with or without catalyst, depending on the nature of the metal, to various oxametallacyclopentanes. The cyclisation proceeds by intramolecular dehydrocondensation between MH and OH bonds. These dehydrocondensation reactions are analysed and discussed according to the polarity of the MH bonds. Intramolecular addition of the MH bond into the unsaturated carboncarbon bonds of the corresponding non-cyclic compounds is also an excellent way of preparing the same heterocycles.The IR and NMR analyses of all new compounds are given. 相似文献
3.
Jacques Barrau Marsan Bouchaut Hlne Lavayssiere Gabriel Dousse Jacques Satg 《Helvetica chimica acta》1979,62(1):152-154
Complexed dialkylgermylenes R2GeNR3 or R2GePy react with oxiranes or thiirane and lead to dialkylgermanone and germathione via germaoxetanes or germathiacyclobutane. The formation of germadioxolanes or germadithiolane finally observed arises from condensation of dialkylgermanone (or germathione) on oxiranes (or thiirane). 相似文献
4.
Jacques Barrau Ghassoub Rima Tajani El Amraoui 《Journal of organometallic chemistry》1998,570(2):8645
The reactions of the divalent species (ArO)2M (Ar=2,4,6-[(CH3)2NCH2]3C6H2; M=Ge, Sn) with either Me3SiN3, elemental S8, Se or transition metal complexes M′(CO)n+1 (M′=Fe, n=4; M′=Cr, W; n=5) (Ph3P)2Pt·C2H4 have resulted in the isolation of either the new stable formal metallanimines (ArO)2M=N–SiMe3, germanethione, -selone (ArO)2Ge=E (E=S, Se) (the expected formations of the stannanethione and -selone were not observed), or the (ArO)2M=M′(CO)n, (ArO)2M=Pt(PPh3)2 complexes, respectively. The direct oxidation of the (ArO)2M species with various oxidizing agents led to the formation of the corresponding metalloxanes [(ArO)2M–O–]2. All of the chalcogenido- and transition metal–metal 14 complexes have been physicochemically and chemically characterized. The reactions of the (ArO)2Ge=E (E=S, Se) compounds with 3,5-di-tert-butyl-1,2-benzoquinone produced, by extrusion of sulfur or selenium, the dioxametalloles corresponding to the formal addition of the divalent species (ArO)2M to the benzoquinone. A substitution reaction of chalcogen (S/Se) has been observed permitting to go from germaneselone to germanethione. 相似文献
5.
Jacques Barrau 《Heteroatom Chemistry》1991,2(6):601-611
The present review describes recent work on the synthesis, spectroscopic analysis, and investigation of the chemical behaviors of new polynuclear heterocyclic complexes 1–7 having M–M′–M catenation. Various CO substitution, cleavage, expansion, and adducts decomposition reactions are described. 相似文献
6.
Amand T. Robart D. Marie X. Baylac B. Barrau J. Brousseau M. Planel R. 《Il Nuovo Cimento D》1995,17(11):1339-1342
Il Nuovo Cimento D - Fast initial decays of both the luminescence intensity and the circular luminescence polarization at high exciton densities, under resonant excitation, are reported for the... 相似文献
7.
J. Barrau J.C. Brabant M. Brousseau J. Collet M. Heckmann H. Maareff 《Solid State Communications》1975,16(9):1079-1082
The microwave absorption technique was used to measure the transient free carrier density following an electric injection in silicon at 4°K. The experiment agrees with the idea that droplets are obtained by free carrier condensation directly, without a preliminary formation of free excitons.1 An Auger recombination process in droplets explains the observed kinetics; parameters are measured. 相似文献
8.
We report here the observation of the hysteresis effect of the drop luminescence in silicon at the temperature of 6.6 K. Hysteresis ratios up to 2.1 have been registered. The surface energy σ of drops is deduced from the measurement of the energy shift of the drops luminescence at low pumping level. The results yield: σ = (125±60) × 10?4ergcm?2. 相似文献
9.
J. Barrau M. Heckmann J. Collet M. Brousseau 《Journal of Physics and Chemistry of Solids》1973,34(9):1567-1577
A free electron and a free hole in a crystal may be bound together due to the attractive coulomb field: in semiconductors such an electron-hole pair is similar to the Wannier-Mott exciton. The probability of binding into the fundamental state has been calculated by Lipnik[1]. Lipnik's model does not predict our recent low temperature measurements[2]. Actually the binding probabilities of excited states of excitons must be considered. This is the purpose of the present paper: a quantum model, (adequate in the low temperature limit) and a semi-classical model (adequate when the temperature rises) are presented. 相似文献
10.
X. Marie F. Lephay T. Amand J. Barrau F. Voillot M. Brousseau 《Superlattices and Microstructures》1991,10(4)
We report experimental and theoretical results on picosecond time resolved photoluminescence spectroscopy of 2D-excitons in multiquantum well structures. A theoretical model is formulated which includes the cooling of the free exciton gas by acoustical phonon emission and the localization of excitons due to interface defects. The cooling rate of 2D excitons is shown to be enhanced with respect to the 3D case. 相似文献