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排序方式: 共有595条查询结果,搜索用时 265 毫秒
41.
J. M. Aguirregabiria Ll. Bel J. Martín A. Molina E. Ruiz 《General Relativity and Gravitation》2001,33(10):1809-1837
To compare two space-times on large domains, and in particular the global structure of their manifolds, requires using identical frames of reference and associated coordinate conditions. In this paper we use and compare two classes of time-like congruences and corresponding adapted coordinates: the harmonic and quo-harmonic classes. Besides the intrinsic definition and some of their intrinsic properties and differences we consider with some detail their differences at the level of the linearized approximation of the field equations. The hard part of this paper is an explicit and general determination of the harmonic and quo-harmonic coordinates adapted to the stationary character of three well-know metrics, Schwarzschild's, Curzon's and Kerr's, to order five of their asymptotic expansions. It also contains some relevant remarks on such problems as defining the multipoles of vacuum solutions or matching interior and exterior solutions. 相似文献
42.
Belén Altava Dalgi S. Barbosa M. Isabel Burguete Jorge Escorihuela Santiago V. Luis 《Tetrahedron: Asymmetry》2009,20(9):999-1003
A family of new imidazolium salts derived from natural amino acids has been synthesized and tested for NMR enantiodiscrimination, as chiral shift reagents, of carboxylic acids. These imidazolium receptors contain different structural modifications and the splitting of the signals of the acids, after addition of the corresponding CSRs, depends on these structural variables. Compound 8b exhibited the strongest chiral solvating properties for racemic Mosher acid and was recognized as a suitable CSR for the determination of its enantiomeric composition. 相似文献
43.
Jimena Scoccia M. Julia Castro M. Belén Faraoni Cecilia Bouzat Víctor S. Martín Darío C. Gerbino 《Tetrahedron》2017,73(20):2913-2922
A novel and efficient synthesis of dibenzo[b,e]oxepin-11(6H)-ones by direct intramolecular ortho-acylation from readily available 2-(phenoxymethyl)benzoic acids was developed. The method takes advantage of a newly developed cooperative system consisting of sustainable FeCl2 and Cl2CHOCH3 as the key components. This methodology is compatible with a wide variety of functional groups in good to excellent yields and high regioselectivity. The synthetic application of new protocol was extended to the synthesis of known tricyclic drug doxepin as well as a small library of oxepin based derivatives. For the first time, the obtained dibenzo[b,e]oxepinone derivatives were evaluated for their biological activities on the free-living nematode Caenorhabditis elegans as an effective and cost-efficient model system for anthelmintic discovery. 相似文献
44.
O. B. Bel’skaya O. V. Maevskaya A. B. Arbuzov T. V. Kireeva V. K. Duplyakin V. A. Likholobov 《Kinetics and Catalysis》2010,51(1):98-104
The interaction of platinum(IV) and palladium(II) chloro complexes with the γ-Al2O3 surface in a wide range of surface metal concentrations is reported. Varying the concentration of the adsorbed metal complex
on the alumina surface causes changes both in the proportions of weakly and strongly bound desorbable platinum species and
in the proportions of desorbable (ion-exchanged) and nondesorbable (coordinatively bound) complexes. The adsorbed palladium
complexes are more uniform in chemical composition and binding strength and consist largely of desorbable species removable
from the surface by competitive sorption of anions. The absolute amount of coordinatively bound platinum and palladium species
increases as the total metal content of the sample is raised to 1.0% and remains almost invariable at higher metal contents. 相似文献
45.
Georgopoulou AN Adam R Raptopoulou CP Psycharis V Ballesteros R Abarca B Boudalis AK 《Dalton transactions (Cambridge, England : 2003)》2010,39(20):5020-5027
Complexes [M(II)Gd(III){pyCO(OEt)pyC(OH)(OEt)py}?](ClO?)?·EtOH [M(II) = Cu(II) (1), Mn(II) (2), Ni(II) (3), Co(II) (4) and Zn(II) (5)] crystallize in the monoclinic Cc space group and contain one hexacoordinate M(II) ion and one enneacoordinate Gd(III) ion, bridged by three {pyCO(OEt)pyC(OH)(OEt)py}? ligands. Magnetic susceptibility measurements indicate a ferromagnetic interaction for 1 and antiferromagnetic interactions for 2-4. Using the ? = -J?(Gd(III))?(M(II)) spin Hamiltonian formalism, fits to the magnetic susceptibility data yielded J values of +0.32 cm?1 for 1, -1.7 cm?1 for 2, and -0.22 cm?1 for 3. In complex 4, the orbital contributions of Co(II) precluded the determination of the magnetic coupling. The complex follows the Curie-Weiss law with θ = -2.07 K (-1.44 cm?1). 相似文献
46.
Peltier P Beláňová M Dianišková P Zhou R Zheng RB Pearcey JA Joe M Brennan PJ Nugier-Chauvin C Ferrières V Lowary TL Daniellou R Mikušová K 《Chemistry & biology》2010,17(12):1356-1366
UDP-galactofuranose (UDP-Galf) is a substrate for two types of enzymes, UDP-galactopyranose mutase and galactofuranosyltransferases, which are present in many pathogenic organisms but absent from mammals. In particular, these enzymes are involved in the biosynthesis of cell wall galactan, a polymer essential for the survival of the causative agent of tuberculosis, Mycobacterium tuberculosis. We describe here the synthesis of derivatives of UDP-Galf modified at C-5 and C-6 using a chemoenzymatic route. In cell-free assays, these compounds prevented the formation of mycobacterial galactan, via the production of short "dead-end" intermediates resulting from their incorporation into the growing oligosaccharide chain. Modified UDP-furanoses thus constitute novel probes for the study of the two classes of enzymes involved in mycobacterial galactan assembly, and studies with these compounds may ultimately facilitate the future development of new therapeutic agents against tuberculosis. 相似文献
47.
48.
L. L. Tolstikova A. V. Bel’skikh B. A. Shainyan 《Russian Journal of General Chemistry》2011,81(3):474-480
Protonation (alkylation) of triphenylphosphine, triethylphosphite, triphenylphosphine oxide, triethylphosphate, hexamethylphosporamide, and dimethylphosphite with trifluoromethanesulfonic acid, its bisimide, and methyl ester was studied and the corresponding 1H, 13C, 19F, 31P NMR spectra were analyzed. 相似文献
49.
High-frequency whistles of beluga whales are analyzed. The signals are recorded in a belgua summer assemblage off Solovetskii
Island in the White Sea. The high-frequency whistles are narrowband signals with a continuous waveform and a fundamental frequency
above 5 kHz. On the average, they make up 7.7% of the total vocal production of the animals. Based on the shape of the fundamental
frequency contour and its time-frequency parameters, the high-frequency whistles are classed into 12 types. The HF whistles
have a mean fundamental frequency of 9.7 kHz, an average bandwidth of 3.3 kHz, and an average duration of 1.0 s. The number
of inflection points per signal ranges from 0 to 56 with a mean of 2.3. The predominant types are flat (50%), rising (23%),
and wavy (7%) high-frequency whistles. Presumably, beluga whales can use some of the whistle types for short-range communication
and other types for long-range communication.
Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 2, pp. 156–164.
The article was translated by the authors. 相似文献
50.
E. A. Doisy R. D. Bel W. C. Ball und E. Tschopp 《Fresenius' Journal of Analytical Chemistry》1926,69(1-2):63-67
Ohne Zusammenfassung 相似文献