Bismut(II)-chalkogenometallate(III) Bi2M4X8, Verbindungen mit Bi24+-Hanteln (M = Al,Ga; X = S,Se)

Bismuth(II) Chalcogenometallates(III) Bi₂M₄X₈, Compounds with Bi₂⁴⁺ Dumbbells (M = Al, Ga and X = S, Se) The ternary bismuth(II) chalcogenometallates(III) Bi₂M₄X₈ (with M = Al, Ga and X = S, Se) were synthesized from the binary chalcogenides M₂X₃ and Bi₂X₃ and elementary bismuth. All compounds are diamagnetic semiconductors with E_g (opt.) = 1.8–2.7 eV. The phases (except Bi₂Al₄Se₈) are thermodynamically stable and decompose peritectically above 965–1020 K. Bi₂Al₄Se₈ is metastable below 825 K and is obtained only by rapid quenching from T > 825 K. The isotypic compounds crystallize in a new tetragonal tP28 structure type (P4/nnc). The characteristic unit is the hitherto unknown clustercation Bi₂⁴⁺, with the mean bond length d(Bi–Bi) = 314.2 pm, the Raman frequency 102 cm^–1 ≤ ν_s ≤ 108 cm^–1, and the mean force constant of f = 0.68 N · cm^–1. The Electron Localization Function, ELF, shows the covalent Bi–Bi bond, the lone electron pairs of the ψ-octahedrally coordinated Bi(II) cations, and the polar character of the Bi–X bonds.     

The Enrichment of Stale Tailings of Bom-gorhon Tungsten Ore Deposits

The results of mineralogical studies of technogenic tungsten raw material (stale tailings of Bom-Gorhon deposit) are represented. Its particle size distribution as well as tungsten and accompanying element distribution among the fractions were determined. The necessity of grinding the heaps down to 0.2-0.25 mm in size was established. It allows increasing the recovery rate of two or more times in comparison with the traditional pattern of tailing processing.     

Preparation and characterization of Fully stoichiometric SrCoO3 by electrochemical oxidation

A nearly stoichiometric SrCoO₃ phase had been prepared up to now only using high oxygen pressure. A new method for preparing fully stoichiometric SrCoO₃ has been proposed using electrochemical oxidation. Brownmillerite-type SrCoO_2.50 is oxidized into a completely stoichiometric perovskite at a potential of 500 mV for 180 hours at room temperature in alkaline media (1 M KOH). The oxidized phase has a cubic unit cell (a=383.5 pm). It is metallic and, at temperatures below T=280 K, it shows ferromagnetic behavior. The magnetic moment at 0 K is 2.1 μ_B. The physical properties of SrCoO_3.00 have been explained in terms of partial occupancy of a σ*e band.     

我国上市公司资本结构影响因素实证分析

本文选取了可能影响企业资本结构的多个指标变量进行分析 ,利用主成分分析提供的方法将变量综合成彼此互不相关的少数几个主成分。再用主成分 (作为回归自变量 )对企业的 5种资本负债比 (作为回归因变量 )进行多元回归分析 ,得出了影响企业资本结构的主要因素 ,以及这些因素与企业资本结构之间的关系 ,为企业确定资本结构提供参考依据 ,为企业财务决策提供支持。     

浅谈成人教育物理实验课操作性考试的科学实施

研究在自学考试中设立物理实验课操作性考试的目的 ,报告考试的设计、组织实施的情况 ,总结经验。     

Viscoelastic properties of phosphoric and oxalic acid-based chitosan hydrogels

In a previous work, we have shown that chitosan true physical gelation occurs in some organic and inorganic acids (Hamdine et al. 2004). Two systems presenting similar gelation mechanisms were characterized furthermore in order to investigate the sol–gel transition: the chitosan–phosphoric acid and the chitosan–oxalic acid systems. By performing rheological measurements in the framework of linear viscoelasticity, we have investigated the effect of time, temperature, and polymer concentration on the gelation evolution. For both acid-based systems, gelation occurred above a critical polymer concentration around 5% w/v (g/100 ml) of chitosan. Isothermal time sweep experiments showed that the gelation occurs in three stages: (i) incubation; (ii) rapid increase of G′; and (iii) a last stage where G′ slowly reached its equilibrium value due to slow molecular diffusion. At the gel point, G′ and G′′ scaled with ω ⁿ , with n=0.55 for both acid-based systems and a fractal dimension d _f of 1.9. Cooling–heating cycles revealed that the gels showed thermoreversibility after one sequence, but became permanent during subsequent cycles.This revised version was published online in October 2005 with corrections to the author's name.     

结构粘弹性分析的线法

本文将以现代常微分方程求解器为支撑软件的线法推广应用于含时间变量的粘弹性力学问题。基基本思想是先用拦普拉斯积分变换把问题的控制偏微分方程组和定解条件进行交换,得到拉氏变换空间中的定常问题,然后用传统的线法借助于常微分方程求解器得到该变换空间中的数值解,再应用拉氏数值逆变换求得原时空域中的数值解。文中还给出方法的基本原理和实施过程。算例表明,采用拉普拉斯积分变换于线法分析结构粘弹性力学等含时间变量的