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941.
目的 通过分析高龄老年(≥80岁)男性腰椎骨密度(LBMD)的独立相关因素,寻找提高高龄老年男性LBMD 的方法。方法 对1066例高龄老年男性进行LBMD测定、血液生化、骨代谢和生殖激素等指标的检测,运用多元回归分析筛选高龄老年男性LBMD 的独立相关因素。结果 高龄老年男性LBMD的独立相关因素有体重指数(β=0.018,P<0.01)、I型胶原羧基端肽β特殊序列(β=-0.226,P<0.01)、慢性阻塞性肺疾病(β=-0.047,P<0.01)、雌二醇(β=0.002,P<0.01)。结论 维持合理的体重指数和雌二醇水平,降低血清I型胶原羧基端肽β特殊序列水平,积极防治慢性阻塞性肺疾病,可能是提高高龄老年男性LBMD的重要方法。 相似文献
942.
The paramagnetic center of tetragonal symmetry formed by the Yb3+ ion in the KZnF3 crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb3+ center in KMgF3 have been established. The empirical scheme of the energy levels of the Yb3+ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb3+. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb3+ and F− ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values. 相似文献
943.
Time-dependent expectation values and correlation functions for many-body quantum systems are evaluated by means of a unified variational principle. It optimizes a generating functional depending on sources associated with the observables of interest. It is built by imposing through Lagrange multipliers constraints that account for the initial state (at equilibrium or off equilibrium) and for the backward Heisenberg evolution of the observables. The trial objects are respectively akin to a density operator and to an operator involving the observables of interest and the sources. We work out here the case where trial spaces constitute Lie groups. This choice reduces the original degrees of freedom to those of the underlying Lie algebra, consisting of simple observables; the resulting objects are labeled by the indices of a basis of this algebra. Explicit results are obtained by expanding in powers of the sources. Zeroth and first orders provide thermodynamic quantities and expectation values in the form of mean-field approximations, with dynamical equations having a classical Lie–Poisson structure. At second order, the variational expression for two-time correlation functions separates–as does its exact counterpart–the approximate dynamics of the observables from the approximate correlations in the initial state. Two building blocks are involved: (i) a commutation matrix which stems from the structure constants of the Lie algebra; and (ii) the second-derivative matrix of a free-energy function. The diagonalization of both matrices, required for practical calculations, is worked out, in a way analogous to the standard RPA. The ensuing structure of the variational formulae is the same as for a system of non-interacting bosons (or of harmonic oscillators) plus, at non-zero temperature, classical Gaussian variables. This property is explained by mapping the original Lie algebra onto a simpler Lie algebra. The results, valid for any trial Lie group, fulfill consistency properties and encompass several special cases: linear responses, static and time-dependent fluctuations, zero- and high-temperature limits, static and dynamic stability of small deviations. 相似文献
944.
945.
Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/Tc) β, effective geometry parameter αg and Vuks’ scaling factor SC. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method. 相似文献
946.
E. Vessally 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2636-2644
The molecular structures of S-phenyl-thiabenzene 1, S-phenyl-1-thianaphthalene 2, S-phenyl-2-thianaphthalene 3, and S-phenyl-9-thiaanthracene 4 are studied by ab initio calculations using HF as well as DFT methods at the 6–311+G? level of theory. The non-planar boat conformers of 1–4 with 6π electrons in the heterocyclic ring appear to be more stable than the corresponding planar conformers with 8π electrons in the ring. The activation energy for the inversion at the sulfur atom is compared for 1–4. Conformational flexibility of 1–4 is studied. 相似文献
947.
A. J. Banister 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):421-428
Abstract General methods of preparation and typical bond distances and bond angles (at sulfur and nitrogen) are reviewed for cyclic sulfur–nitrogen compounds. Correlations between sulfur-nitrogen bond distance and unstrained bond angles in SNS and NSN groups can be used to assess angular strain in 4 and 5 atom thiazene rings and the optimum ring geometries of larger thiazene cations such as S5N+ 5 and S4N2+ 4. The geometry of S3N? 3 is also discussed. 相似文献
948.
Xiao-Bo Ma Jing-Lin Zhang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):233-237
Abstract 1,3,2-Diazaphosphetidin-4-one derivatives were synthesized. Their 1H NMR signals at ambient temperature displaed a broad doublet which eventually coalesced before becoming sharp upon warming, and the 13C NMR spectra also showed that the α-and β-carbons of the dialkylamino group were non-equivalent. The phenomena were ascribed to restricted rotation about the exocyclic P—N bond. 相似文献
949.
L. Engman A. Wojtoń B. J. Oleksyn J. Śliwiński 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):285-292
The crystal structure of 2-[N,N-dimethylamino)methyl]benzenetel-lurenyl chloride (2), a compound previously formulated as bis[[2-(N,N-dimethylamino)methyl]phenyl] ditelluride bis hydrochloride (1a), was determined. In the molecule 2, tellurium is bonded to the carbon of the phenyl group [2.120(3) Å], the nitrogen of the ortho dimethylamino substituent [2.362(3) Å], and the chlorine atom [2.536(1) Å]. There also is an intermolecular interaction of the tellurium atom with the phenyl ring of a neighbouring molecule [3.655(1) Å], resulting in the formation of zigzag chains along the b axis. The noncentrosymmetric space group of the crystal can be explained by the chiral surrounding of tellurium. 相似文献
950.
Giovanna Delogu Ottorino De Lucchi Maria Paola Fois Giovanni Valle 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):417-425
Abstract Ketimines la-d derived from ortho-aminosubstituted phenylthioethers were prepared in order to determine the degree of chirality transfer from the chiral auxiliary to the sulfur atom in the formation of the sulfoxide or to the α-carbon atom in the reaction of the anion with alkyl halides or benzaldehyde. Oxidation to the sulfoxide occurred with little or no asymmetric induction. The crystalline benzyl sulfone 4c was deprotonated by alkyllithium or Grignard reagents and reacted with alkyl halides and benzaldehyde, in all cases with little to fair transfer of chirality. The major diastereoisomer from methylation of the anion of 4c with methyl iodide, was isolated, and afforded the enantiomerically pure amine 5 after removal of the chiral auxiliary. An X-ray structure determination of 4d allowed the assignment of the absolute configuration of the asymmetric carbon and revealed that the conformation of the ketimine in the crystal state is not homogeneous. 相似文献