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V V Borovkov J M Lintuluoto Y Inoue 《Journal of the American Chemical Society》2001,123(13):2979-2989
The achiral syn folded (face-to-face conformation) host molecule of the ethane-bridged bis(zinc porphyrin) transforms into the corresponding chiral extended anti bis-ligated species in the presence of enantiopure amine guests. The mechanism of the supramolecular chirogenesis is based upon the screw formation in bis(zinc porphyrin), arising from steric interactions between the largest substituent at the ligand's asymmetric carbon and peripheral alkyl groups of the neighboring porphyrin ring pointing toward the covalent bridge. The screw direction is determined by the guest's (amines) absolute configuration resulting in a positive chirality induced by (S)-enantiomers due to formation of the right-handed screw, and a negative chirality produced by the left-handed screw of (R)-enantiomers. The screw magnitude is strongly dependent upon the structure of the chiral guests. The amines with bulkier substituents result in stronger CD signals and larger (1)H NMR resonance splittings of enantiotopic protons. This system possesses a high degree of chiroptical activity, which allows the differentiation of one of the smallest homologous elements of organic chemistry, that is, the methyl and ethyl groups attached to the asymmetric carbon, and additionally, which senses a remote chiral center at a position beta to the amine binding group. 相似文献
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O. I. Kotov A. V. Khlybov L. B. Liokumovich S. I. Markov A. V. Medvedev V. A. Rukavishnikov A. I. Borovkov D. V. Shevchenko 《Technical Physics》2006,51(11):1494-1499
It is shown that a lateral pressure applied to a circular single-mode optical waveguide changes the phase difference between two orthogonally polarized modes and thereby modulates the polarization state of light (elastooptic effect). The efficiency of polarization modulation is characterized by a strain-to-phase difference conversion factor as applied to polarization modes of the fiber. An expression relating the phase difference between the modes and the displacement of squeezing plates is obtained and checked in real experiments and numerically. The efficiency of conversion of lateral pressure to phase difference between the polarization modes is shown to be fairly high, on the order of 104 rad/(μm m). 相似文献
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A. A. Belyanin V. V. Kocharovsky VI. V. Kocharovsky 《Radiophysics and Quantum Electronics》1996,41(1):22-27
It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the
near future since the expected photon flux, consisting mainly of photons with energies ≳ GeV, is too low. Contrary to this
point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 103 s) can be liberated as a burst of soft γ-ray emission of duration 10−1–103 s and luminosity 1028–1031 erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard
Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow
from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than
half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with
energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and
estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with
evaporating black holes.
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh
Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 36–45, January, 1998. 相似文献
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L. Rosenthaler P. Krumholz J. Vasquez Sanchez F. Feigl A. S. Komarowsky N. S. Poluektoff J. V. Dubský J. Trtilek A. Oká G. Hellsing K. Heumann F. Emich Olga S. Fedorova Georges Glomaud J. Trtílek VI. Stanék T. Nemes Carl Urbach R. Baril und J. H. Yoe 《Fresenius' Journal of Analytical Chemistry》1935,102(7-8):280-289
Ohne Zusammenfassung 相似文献
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