String Cosmological Models with Magnetic Field

A new class of string cosmological models withand without magnetic field in the context of aspace-time with G₃ symmetry has beenpresented. In order to study the effects of magneticfield, the standard energy-momentum tensor is modified byincorporating additional term due to magnetic field. Thephysical and kinematical behaviours of the stringcosmological models have been discussed.     

Finding Collineations of Kimura Metrics

Kimura investigated static spherically symmetric metrics and found several to have quadratic first integrals. We use REDUCE and the package Dimsym to seek collineations for these metrics. For one metric we find that three proper projective collineations exist, two of which are associated with the two irreducible quadratic first integrals found by Kimura. The third projective collineation is found to have a reducible quadratic first integral. We also find that this metric admits two conformal motions and that the resulting reducible conformal Killing tensors also lead to Kimura's quadratic integrals. We demonstrate that when a Killing tensor is known for a metric we can seek an associated collineation by solving first order equations that give the Killing tensor in terms of the collineation rather than the second order determining equations for collineations. We report less interesting results for other Kimura metrics.     

Hypersurface-Orthogonal Generators of an Orthogonally Transitive G2I, Topological Identifications, and Axially and Cylindrically Symmetric Spacetimes

A criterion given by Castejón-Amenedo and MacCallum for the existence of (locally) hypersurface-orthogonal generators of an orthogonallytransitive two-parameter Abelian group of motions (a G₂I) in spacetime is re-expressed as a test for linear dependence with constant coefficients between the three components of the metric in the orbits in canonical coordinates. In general, it is shown that such a relation implies that the metric is locally diagonalizable in canonical coordinates, or has a null Killing vector, or can locally be written in a generalized form of the windmill solutions characterized by McIntosh. If the orbits of the G₂I have cylindrical or toroidal topology and a periodic coordinate is used, these metric forms cannot in general be realized globally as they would conflict with the topological identification. The geometry then has additional essential parameters, which specify the topological identification. The physical significance of these parameters is shown by their appearance in global holonomy and by examples of exterior solutions where they have been related to characteristics of physical sources. These results lead to some remarks about the definition of cylindrical symmetry.     

不同溶剂对硝酸钕盐冠醚配合物振子强度的影响

本文通过Judd-Ofelt理论测定并计算了硝酸钕冠醚配合物吸收光谱的振子强度, 讨论了不同溶剂对配合物振子强度及其对称性的影响。     

The Dynamical Instability of Static, Spherically Symmetric Solutions in Nonsymmetric Gravitational Theories

We consider the dynamical stability of a class of static, spherically symmetric solutions of the nonsymmetric gravitational theory. We numerically reproduce the Wyman solution and generate new solutions for the case where the theory has a nontrivial fundamental length scale ^-1. By considering spherically symmetric perturbations of these solutions we show that the Wyman solutions are generically unstable.     

叠氮酸桥联双核铜配合物磁偶合的密度泛函研究

在密度泛函理论的框架下,采用对称性破损态方法,对EE,EO两种连接方式叠氮酸桥联双核铜模型配合物进行计算,结果表明,EE方式连接为反铁磁偶合;EO方式则为铁磁偶合,但只发生在θ＝91°～107°区间,与实验值96°～104°基本一致,研究揭示了其磁偶合构效关系的本质在于SOMOb1g轨道中Nμ的Px轨道与Cu的dxy轨道间的d-p-d三中心σ反键作用,在θ＝91°～110°区间具有最大的反键重叠,因而铁磁偶合最大,同时发现J值随Cu与配位叠氮酸酸N原子间距离的增大而减小,但叠氮酸偏离平面的角度对J值影响不大。