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排序方式: 共有468条查询结果,搜索用时 46 毫秒
1.
Hiroshi Maruyama Tadao Ishii Naruhiko Bamba Hironobu Maeda Akihisa Koizumi Yuzo Yoshikawa Hitoshi Yamazaki 《Physica C: Superconductivity and its Applications》1989,160(5-6):524-532
The temperature dependence of the extended X-ray absorption fine structure (EXAFS) is studied in the high Tc superconductors, YBa2Cu3O7−δ. The measurements were done at the Cu K-edge for samples of two orthorhombic phases (Tc≈90 K and ≈58 K, respectively) and a nonsuperconducting tetragonal phase. Interatomic distances and mean square relative displacements σ2 for Cu-O bonds are determined by the least squares refinement. The results indicate that values of σ2 increase near Tc for both the orthorhombic samples. It is concluded that this anomalous behavior related to Tc is caused by an anomalous vibration of oxygen atoms in the Ba-O layer. Changes in the Cu-O distances from 300 to 20 K are not found. 相似文献
2.
Tadao Nozawa Fumio MorimotoRikio Harazono Norimoto Nouchi 《Journal of magnetism and magnetic materials》2006
Evaporative deposition at oblique incidence is shown to enhance the magnetic anisotropy of an Fe20Ni80 magnetic film and induce magnetic anisotropy in an overlying, strongly isotropic Fe70Co30 film. This deposition method for the formation of an underlayer of several lattice parameters in thickness and semi-hard overlayer of a few thousands Angstroms in thickness achieves a significant change in the magnetization process and strong suppression of the coercive forces of Fe70Co30 in the hard magnetization direction. Soft magnetization of the Fe70Co30 overlayer is not achieved when one of the layers is deposited at oblique incidence. It is anticipated that shape magnetic anisotropy is responsible in part for the magnetic anisotropy induced in both in Fe20Ni80 under- and Fe70Co30 overlayer by oblique incidence evaporation. 相似文献
3.
Maria Carmelita Kasuya 《Journal of fluorine chemistry》2007,128(5):562-565
A series of fluorinated galactosides, dodecyl 2-deoxy-2-fluoro-β-d-galactopyranoside (2F Gal), dodecyl 4-deoxy-4-fluoro-β-d-galactopyranoside (4F Gal) and dodecyl 6-deoxy-6-fluoro-β-d-galactopyranoside (6F Gal), was chemically synthesized and introduced to B16 cells to serve as scaffolds for cellular enzyme glycosylation. Results showed that the presence of fluorine exercised significant effects on cell viability. Among the fluorinated galactosides used, 2F Gal was glycosylated to afford a GM4 analogue. 相似文献
4.
5.
Tadao Seguchi Naoyuki Tamura 《Journal of polymer science. Part A, Polymer chemistry》1974,12(9):1953-1964
The regions trapping allyl radicals in irradiated polyethylene and the reactivity of the radicals with various monomers have been studied by electron spin resonance. Most of the allyl radicals are trapped in defects or surfaces of the crystallite, and only 10% of the radicals are trapped inside the crystallites. Since the reactivity of the allyl radicals depends on whether they come in contact with reactive monomers, the rate of reaction is related to the concentration of the monomers. When grafting reactions are initiated by allyl radicals, the rate of initiation is rapid and the rate of termination at the initial stage is also very fast. Consequently the yield of grafting increases at the initial stage but soon levels off, which is in contrast to the grafting behavior with alkyl radicals. 相似文献
6.
A cyclic oligosaccharide derivative was synthesized by cationic ring-opening polymerization of an anhydrodisaccharide derivative under high vacuum in dichloromethane with 20 mol% of PF5 as initiator. Analysis of the spectral results showed that the oligomer chain is composed of only 3 glucose units connected by -1,6 linkages with a glucopyranosyl branching unit at C-4 of each sugar residue in the main chain. 相似文献
7.
A capillary gas chromatographic-mass spectrometric method for the simultaneous determination of cortisol, cortisone, prednisolone and prednisone in human plasma is described. [1,1,19,19,19-2H5]Cortisol, [1,1,19,19,19-2H5]cortisone, [1,19,19,19-2H4]prednisolone and [1,19,19,19-2H4]prednisone were used as internal standards. Formation of the bismethylenedioxy-3-heptafluoro-n-butyryl (BMD-HFB) derivatives made possible the separation of the four corticosteroids with good gas chromatographic behaviour. The new double derivatization has been demonstrated to be of value for sensitive and selective quantification by this technique. Detection was performed by monitoring the molecular ion (M+) of the BMD-HFB derivatives for cortisone and prednisolone, the [M - 18]+ ion for cortisol, and the [M - 30]+ ion for prednisone. The method requires no complex corrections for contributions and provides good accuracy and precision. 相似文献
8.
Polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs) are two classes of dioxin precursors formed in municipal solid waste incinerators (MSWIs); they produce negative health effects similar to those of dioxins. Reducing the analytical time required for determining the concentrations of these compounds in MSWIs is important for quickly evaluating their importance and assessing associated health risks. In the present study, water is used as a safe and environmentally friendly solvent in microwave-assisted extraction (MAE) for PCB and CBz analyses. MAE is compared with traditional Soxhlet extraction (SE) to determine the extraction efficiencies. The evaluation of extraction efficiencies shows that MAE has a high extraction efficiency compared with that of SE when water content is lower than 60%. Furthermore, the extraction time and organic solvent consumption are reduced with MAE compared with SE. 相似文献
9.
Flow injection spectrofluorimetry with in-line Winklers procedure was developed for the dissolved oxygen (DO) determination. 2-Thionaphthol reacted with iodine produced by Winkler’s method to form fluorescence inactive disulfide compound. To automate the process completely, a 5-channel flow system with a newly designed 16-way valve was assembled. The system consisted of a dispersion coil (DC), a precipitate formation coil (PFC), a precipitate dissolving coil (PDC), and extraction coil (EC). A calibration can be constructed by using a standard iodine solution for dissolved oxygen. The calibration graph was linear over the range 1.2×10−4∼6.0×10−4 mol l−1 iodine (1.96∼9.80 mg O l−1)). The relative standard deviation (n=6) was below 0.3% for the 4×10−4 mol l−1 iodine (6.27 mg O l−1) determination. The sample throughput was 12/h. 相似文献
10.
Tomonari Wakabayashi Daisuke Kasuya Haruo Shiromaru Shinzo Suzuki Koichi Kikuchi Yohji Achiba 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):414-417
Systematic fractional change in the yield of various isomers of fullerenes was revealed to strongly depend on temperature of a buffer gas. A new kinetic consideration is proposed for understanding the observed temperature- and pressure-dependence of yield of fullerenes. The model consists of three competitive reactions in consideration of plausible behaviors of a precursor, (1) decomposition into smaller fragments, (2) isomerization leading to formation of a stable fullerene cage, and (3) growth into a larger carbon cluster. Arrhenius activation energy of formation of stable fullerenes was determined to be 0.8 eV for both C60 and C70, while a higher energy of 2.0?3.3 eV for seven different isomers of higher fullerenes ranging from C76 to C84. Correlation in the activation energy is noted for a series of higher fullerenes with different sizes, suggesting the existence of a specific precursor in their formation processes. 相似文献