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排序方式: 共有159条查询结果,搜索用时 15 毫秒
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N. S. Kopelev V. Chechersky A. Nath B. -H. O M. I. Larkin J. T. Markert J. -L. Peng R. L. Greene 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(2):391-400
The as-prepared electron-doped system Nd2–xCexCuO4 (where x0.16) is not superconducting. It becomes superconducting only after removal of a minuscule amount of extraneous oxygen (0.02 of O per unit formula). Mössbauer effect studies were carried out for oxygenated and deoxygenated Nd2–xCexCu(57Co)O4 with x=0.14, 0.16, and 0.18. The spectra show evidence of oxygen anions attaching to the probe57Co in apical positions, to form 5- and 6-coordinated species. A conventional procedure for deoxygenation brings about little change in the Mössbauer spectra both above and below the optimal superconducting concentration; however, for x=0.16, a dramatic change is observed—a major fraction of the magnetically split five-coordinated species manifests itself as a paramagnetically relaxed doublet upon deoxygenation, which costitutes a microscopic measure of the superconducting volume fraction. This apparently anomalous behavior at x0.16, where the extraneous oxygen is more readily desorbed, may be related to an electronic and/or local structural change in the CuO2 plane. 相似文献
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T Mizuochi M W Spellman M Larkin J Solomon L J Basa T Feizi 《Biomedical chromatography : BMC》1988,2(6):260-270
This report together with the paper by T. Mizuochi, M. W. Spellman, M. Larkin, J. Solomon, L. J. Basa and T. Feizi (1988) Biochem. J. 254, 599-603 describes the structural elucidation of the N-linked oligosaccharides of the HIV envelope glycoprotein, gp120 (cloned from the HTLV-III B isolate and expressed as a secreted fusion protein after transfection of Chinese hamster ovary cells), which is known to bind with high affinity to human T4 lymphocytes. Oligosaccharides were released from peptide by hydrazinolysis, fractionated by paper electrophoresis, high performance lectin affinity chromatography and Bio-Gel P-4 column chromatography, and their structures determined by sequential exoglycosidase digestions in conjunction with methylation analysis. The glycoprotein was found to be unique in its diversity of oligosaccharide structures. These include high-mannose type and hybrid type, as well as four categories of complex type chains: mono-, bi-, tri- and tetra-antennary, with or without N-acetyllactosamine repeats, and with or without a core region fucose residue. Among the sialidase-treated oligosaccharides no less than 29 structures were identified as follows: (formula; see text) where G = galactose; GN = N-acetylglucosamine; M = mannose; F = fucose; +/- = residues present in a proportion of chains. The actual number of oligosaccharide structures is much greater since before desialylation there was evidence that among the hybrid and complex type chains all but 6% contained sialic acid at the C-3 position of terminal galactose residues, and partially sialylated forms of the bi- and multiantennary chains were present. 相似文献
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Larkin JD Fossey JS James TD Brooks BR Bock CW 《The journal of physical chemistry. A》2010,114(47):12531-12539
o-(N,N-Dialkylaminomethyl)arylboronate systems are an important class of compounds in diol-sensor development. We report results from a computational investigation of fourteen o-(N,N-dialkylaminomethyl)arylboronates using second-order M?ller-Plesset (MP2) perturbation theory. Geometry optimizations were performed at the MP2/cc-pVDZ level and followed by single-point calculations at the MP2/aug-cc-pVDZ(cc-pVTZ) levels. These results are compared to those from density functional theory (DFT) at the PBE1PBE(PBE1PBE-D)/6-311++G(d,p)(aug-cc-pVDZ) levels, as well as to experiment. Results from continuum PCM and CPCM solvation models were employed to assess the effects of a bulk aqueous environment. Although the behavior of o-(N,N-dialkylaminomethyl) free acid and ester proved to be complicated, we were able to extract some important trends from our calculations: (1) for the free acids the intramolecular hydrogen-bonded B-O-H···N seven-membered ring conformers 12 and 16 are found to be slightly lower in energy than the dative-bonded N→B five-membered ring conformers 10 and 14 while conformers 13 and 17, with no direct boron-nitrogen interaction, are significantly higher in energy than 12 and 16; (2) for the esters where no intramolecular B-O-H···N bonded form is possible, the N→B conformers 18 and 21 are significantly lower in energy than the no-interaction forms 20 and 23; (3) H(2)O insertion reactions into the N→B structures 10, 14, 18, and 21 leading to the seven-membered intermolecular hydrogen-bonded B···OH(2)···N ring structures 11, 15, 19, and 22 are all energetically favorable. 相似文献
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R.V. Ryabova Yu.A. Bykovsky V.A. Elkhov A.I. Larkin V.L. Potapov L.N. Gnatiuk M.L. Gurari S.N. Marchenko 《Optics Communications》1976,18(3):406-409
New photographic materials for recording the radiation of injection lasers (λ=840 nm) with a sensitivity of ?10-4 J/sm2 and a resolution of 4300 lines/mm, and photographic materials for recording the radiation in the region of 1060 nm with a sensitivity of ?10-4 J/sm2 and a resolution of 1000 lines/mm are described. 相似文献
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Structural Chemistry - Boronic acids, R–B(OH)2, play an important role in synthetic, biological, medicinal, and materials chemistry. Borinic acids, R–BH(OH), find relevance in similar... 相似文献