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991.
B. Dorner D. Visser U. Steigenberger K. Kakurai M. Steiner 《Zeitschrift für Physik B Condensed Matter》1988,72(4):487-496
We have measured the magnetic excitations in CsFeBr3 along the chain direction (z-axis) and perpendicular to it by inelastic neutron scattering. The measured dispersion curves can be reproduced by the formula $$\omega ^2 (q) = A^2 - 8A[J\cos (\pi q_c ) + J'\gamma (2\pi q_ \bot )]R(T)$$ which is very different from dispersion relations for usual 1 D antiferromagnets, because of the singlet groundstate of this system. The large value of the anisotropy energyA/k=29.8±0.5 K, which is independent of temperature, causes the singlet groundstate. The intra-and inter-chain exchange parameters areJ/k=?3.2±0.15K andJ'/k=?0.32±0.02 K determined atT=1.4 K. At 1.4 K the renormalisation factor is taken to beR(T)=1. AtT=30 K the value forR(T) was found to be 0.5±0.1 keepingJ andJ' unchanged. The excitations at (1/3 1/31) show soft mode behaviour but no phase transition. The observed intensities are interpreted by a heuristic model for the eigenvectors in the excited state including antiferro-as well as ferromagnetic configurations of the fluctuations. 相似文献
992.
F. N. Gygax B. Hitti E. Lippelt A. Schenck S. Barth 《Zeitschrift für Physik B Condensed Matter》1988,71(4):473-490
Using a high purity Bi single crystal the temperature and orientation dependence of the zero and transverse field muon spin relaxation rate has been studied in detail. The results imply that the + occupies one of the two possible interstitial sites in the distorted rhombohedral crystal structure of Bi below 10 K and the other site above 80 K. At both sites the nearest neighbor Bi atoms are found to be shifted towards the + by 10% of their nominal distance, implying a large local lattice contraction. In concomitance extremely strong electric field gradients are manifest at the nn Bi nuclei. An almost temperature independent reduced relaxation rate in the temperature range from 20 K to 60 K is interpreted in terms of short range diffusion along a limited chain of alternating types of sites. Above 100 K both long range and short range diffusion are indicated. 相似文献
993.
E. Braun G. Jackel B. Roden J. G. Sereni D. Wohlleben 《Zeitschrift für Physik B Condensed Matter》1988,72(2):169-173
We have measured the specific heat, the electrical resistance and the magnetic susceptibility of YBa2Cu3O7–x in a superconducting (sc) and in a non-superconducting (nsc) version. The latter was obtained by inducing a small loss of oxygen. In the sc sample we find a jump of the specific heat with C=3.6 J mole–1 K–1. Below the maximum nearT
c
the specific heat of the sc version drops too fast for an electronic effect alone: there is a cross-over from excess to deficiency already at 0.9T
c
. The specific heat of the nsc version shows a change of slope in the temperature range between 70 and 80 K, which indicates the existence of a second specific heat anomaly, which apparently exists independently of that due to the onset of superconductivity and explains at least partially the premature crossover.Alexander von Humboldt fellow. On leave in absence from Centro Atomico Bariloche—CNEA Argentina 相似文献
994.
A method has been developed for the determination of gaseous nitric acid in air based on its separation from particulate nitrate aerosol using diffusion denuder tubes. An integrated value of nitric acid concentration in air is obtained. The experimentally derived absorption efficiencies of the diffusion denuder tubes ranged from 87.6 to 96.9%. The standard deviation of the method was calculated as 0.10 mug/m(3) for nitric acid concentrations in the range 0.54-1.72 mug/m(3). A correction procedure, using two diffusion denuders in series, should be applied if measurements are made in the presence of high levels of nitrogen oxides. 相似文献
995.
A conformational analysis has been made by the method of molecular mechanics of the -apienes — natural sesquiterpenes isolated from plants of the Apiaceae family. The results of the mathematical method with the inclusion of those x-ray structural studies have shown that in the molecules under consideration it is possible to expect the predominant realization of four conformations of the 11-membered ring:14A
8
7
,14A
7
8
,14A
7
8
, and14A
8
7
. These four conformations of unsubstituted -apiene and its natural derivatives have been characterized energetically, and the barriers to their interconversions have been evaluated.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 197–202, March–April, 1992. 相似文献
996.
I. B. Plećaš A. D. Perić S. D. Glodić A. M. Kostadinović 《Journal of Radioanalytical and Nuclear Chemistry》1992,166(5):373-381
Results are presented of a series of experimental tests performed to determine the influence of matrix characteristics on the leaching mechanism of copper aluminium oxychloride immobilized into cement matrices. The objective of this research was to investigate the leaching mechanism of copper as a constituent of copper aluminium oxychloride (CAOX). 相似文献
997.
Patricia M. G. Paiva Luana C. B. B. Coelho 《Applied biochemistry and biotechnology》1992,36(2):113-118
Two additional electrophoretically distinct molecular forms, isoforms (iso) 2 and 3, with lectin properties were isolated
fromCratylia mollis Mart, seeds (FABACEAE), by extraction with 0.15M NaCl and ammonium sulfate fractionation, followed by chromatography on Sephadex
G-75 and Bio-Gel P-200 (iso 2), as well as CM-Cellulose and Sephadex G-75 (iso 3). Both isoforms were human group nonspecific
and showed distinct specificity. Polyacrylamide gel electrophoresis resolved iso 2 and 3 in polypeptides of apparent mol wts
60 and 31 kDa, respectively; a distinct isoelectric focusing pattern was obtained for iso 2 and 3, under denaturing and reducing
conditions. 相似文献
998.
The classical Harary-Read numbers for catafusenes (catacondensed simply connected polyhexes) are reproduced without using generating functions. A complete (mathematical) solution is given for the distribution of these numbers over the different symmetry groups to which the catafusenes belong. 相似文献
999.
R. Bacaud M. Besson D. Brodzki P. Bussière H. Charcosset G. Diega-Mariadassou M. Oberson B. K. Sharma 《Hyperfine Interactions》1989,46(1-4):583-589
Mössbauer Spectroscopy, X-Ray Diffraction and Electron Microscopy were applied to the study of solid residues of coal hydroliquefaction, for which tin-based catalysts were used. In the general case hydroliquefaction runs were performed in the presence of added sulphur and of finely dispersed SnO2 as a catalyst precursor. The only observed tin species were SnO2 and SnS, the former with percentages higher than expected from XRD, due to its large f factor, the latter as a symmetric doublet, which suggests that any asymmetry should be ascribed to small particle sizes rather than to structure. When the S content was only that of coal and the catalyst precursor β-Sn, FeSn2 occurred together with Sn sulfides and oxides, while no β-Sn was detected. The main catalytic role is ascribed to SnS. 相似文献
1000.
S. I. Dolinsky V. P. Druzhinin M. S. Dubrovin V. B. Golubev V. N. Ivanchenko A. P. Lysenko A. A. Mikhailichenko E. V. Pakhtusova A. N. Peryshkin S. I. Serednyakov Yu. M. Shatunov V. A. Sidorov 《Zeitschrift fur Physik C Particles and Fields》1989,42(4):511-518
The results of the measurements of radiative decays of ρ and ω mesons with the Neutral Detector at thee + e ? collider VEPP-2M are presented. The branching ratio of the decay ω→π 0γ was measured with higher than in previous experiments accuracy: $${\rm B}(\omega \to \pi ^0 \gamma ) = 0.0888 \pm 0.0062$$ . The ρ0→π 0 γ branching ratio was measured for the first time: $$B(\rho ^0 \to \pi ^0 \gamma ) = (7.9 \pm 2.0) \cdot 10^{ - 4} $$ . The decays ρ, ω→ηγ were studied. Their branching ratios with the assumption of constructive ρ?ω interference are: $$\begin{gathered} B(\omega \to \eta \gamma ) = (7.3 \pm 2.9) \cdot 10^{ - 4} , \hfill \\ B(\rho \to \eta \gamma ) = (4.0 \pm 1.1) \cdot 10^{ - 4} \hfill \\ \end{gathered} $$ . The branching ratios of ρ, ω→ηγ and ω→e + e ? decays were also measured: $$\begin{gathered} B(\omega \to \pi ^ + \pi ^ - \pi ^0 ) = 0.8942 \pm 0.0062, \hfill \\ B(\omega \to e^ + e^ - ) = (7.14 \pm 0.36) \cdot 10^{ - 5} \hfill \\ \end{gathered} $$ . The upper limit for the ω→π 0 π 0 γ branching ratio was placed: B(ω→π 0 π 0 γ)<4·10?4 at 90% confidence level. 相似文献