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We present Hall effect measurements on highly oriented pyrolytic graphite that indicate the occurrence of the integer quantum-Hall-effect. The evidence is given by the observation of regular plateau-like structures in the field dependence of the transverse conductivity obtained in van der Pauw configuration. Measurements with the Corbino-disk configuration support this result and indicate that the quasi-linear and non-saturating longitudinal magnetoresistance in graphite is governed by the Hall effect in agreement with a recent theoretical model for disordered semiconductors. 相似文献
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V. M. Kopelevich L. N. Bulanova Yu. V. Belousova A. V. Lysenkova V. F. Pozdnev V. I. Gunar 《Chemistry of Natural Compounds》1988,23(4):493-495
The synthesis has been performed of dephosphocoenzyme A, 4,4-di-0-(2,3-9-isopropylideneadenosineuronyl)pantethine, and of 4,4-di(2,3-isopropylideneadenosineuronylamino)-4,4-dideoxypantethine from 2,3-0-isopropylidene adenosineuronic acid, using as condensing agents the tert-butyl dicarbonatepyridine and the N,N-dicyclohexylcarbodiimide-N-hydroxysuccinimide systems, respectively.Vitaminy Scientific-Production Amalgamation, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 587–590, July–August, 1987. 相似文献
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The synthesis of - and -N-(4-amino-3, 3-dimethyl-2-hydroxybutyryl)- β-alanine () is described. Compound is an analog of pantothenic acid in which the 4′-hyroxy group is replaced by amino group. The synthetic sequence leading to involved the synthesis L-4-amino-3,3-dimethyl-2-hydroxybutyric acid and its resolution. Coupling of N-benzyloxycarbonyl N-hydroxysuccinimide ester () with β-alanine and followed by removal of the protecting group gave . 相似文献
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Urbano RR Pagliuso PG Rettori C Kopelevich Y Moreno NO Sarrao JL 《Physical review letters》2002,89(8):087602
We report the first observation of the field distribution and flux-line lattice (FLL) depinning in the vortex-state (VS) of a type-II superconductor probed by conduction electron spin resonance (CESR). CESR was performed in MgB (2) (T(c) approximately 39 K) at 4.1 GHz (1455 Oe) and 9.5 GHz (3390 Oe). The field distribution, n(H), and a standard deviation of sigma approximately 14 Oe (at 28 K/4.1 GHz and at 7 K/9.5 GHz) were inferred, respectively, from the distortion and broadening of the CESR in the VS. For both frequencies, the FLL depinning temperature was determined. 相似文献
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A. G. Rabinkov V. F. Pozdnev S. V. Amontov V. M. Kopelevich V. I. Gunar 《Chemistry of Natural Compounds》1989,25(3):350-353
The synthesis has been effected of the pentafluorophenyl ester of D-biotin by the reaction of D-biotin with bispentafluorophenyl carbonate or pentafluorophenyl trifluoroacetate. The possibility has been shown of using the ester obtained for the biotinylization of amino acids and NH2-containing macromolecules, and D-biotinyl--aminocaproic acid and -[14C]glycine have been synthesized. It is proposed to use the biotinyl-[14C]glycine for measuring the activity of avidin.Institute of Molecular Biology, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 404–408, May–June, 1989. 相似文献
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The quantum de Haas-van Alphen (dHvA) and Shubnikov-de Haas oscillations measured in graphite were decomposed by pass-band filtering onto contributions from three different groups of carriers. Generalizing the theory of dHvA oscillations for 2D carriers with an arbitrary spectrum and by detecting the oscillation frequencies using a method of two-dimensional phase-frequency analysis which we developed, we identified these carriers as (i) minority holes having a 2D parabolic massive spectrum p(2)(perpendicular)/2m(perpendicular), (ii) massive majority electrons with a 3D spectrum and (iii) majority holes with a 2D Dirac-like spectrum +/-vp(perpendicular) which seems to be responsible for the unusual strongly-correlated electronic phenomena in graphite. 相似文献
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We report magnetization measurements performed on graphite-sulfur composites which demonstrate a clear superconducting behavior below the critical temperature T(c0) = 35 K. The Meissner-Ochsenfeld effect, screening supercurrents, and magnetization hysteresis loops characteristic of type-II superconductors were measured. The results indicate that the superconductivity occurs in a small sample fraction, possibly related to the sample surface. 相似文献
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A review is given of the latest advances on the chemical synthesis and isolation of natural pantothenic acid, including bioprecursors of CoA. The value of the individual sections of the CoA molecule for the manifestation of coenzyme activity is discussed.Vitaminy Scientific-Industrial Association, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 477–492, July–August, 1988. 相似文献