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951.
952.
Manuel Gutié rrez Francisco J. Palomo Alfonso Romero 《Transactions of the American Mathematical Society》2002,354(11):4505-4523
We give a Lorentzian metric on the null congruence associated with a timelike conformal vector field. A Liouville type theorem is proved and a boundedness for the volume of the null congruence, analogous to a well-known Berger-Green theorem in the Riemannian case, will be derived by studying conjugate points along null geodesics. As a consequence, several classification results on certain compact Lorentzian manifolds without conjugate points on its null geodesics are obtained. Finally, several properties of null geodesics of a natural Lorentzian metric on each odd-dimensional sphere have been found.
953.
LIUYi-Min LIXiao-Zhu YANWen-Hong BAOCheng-Guang 《理论物理通讯》2003,40(1):117-119
The methods for the few-body system are introduced to investigate the states of the barrier Li quantum dots (QDs) in an arbitrary strength of magnetic field. The configuration, which consists of a positive ion located on the z-axis at a distaneed from the two-dimensional QD plane (the x-y plane) and three electrons in the dot plane bound by the positive ion, is called a barrier Li center. The system, which consists of three electrons in the dot plane bound by the ion,is called a barrier Li QD. The dependence of energy of the state of the barrier Li QD on an external magnetic field B and the distance d is obtained. The angular momentum L of the ground states is found to jump not only with the variation orB but also with d. 相似文献
954.
955.
Cayley树上随机场的马尔可夫逼近与一类小偏差定理 总被引：2，自引：0，他引：2
通过引进样本相对熵率作为Cayley树上任意随机场与马尔可夫链场之间的偏差的一种度量, 建立了关于状态序偶频率的一类小偏差定理. 证明中应用了研究马尔可夫链强极限定理的一种新的分析方法. 相似文献
956.
Patrick Simonetta 《Proceedings of the American Mathematical Society》2003,131(12):3913-3917
In 1996 D. Macpherson and C. Steinhorn introduced -minimality as an analogue, for valued fields and some groups with a definable chain of normal subgroups with trivial intersection, of the notion of o-minimality. One of the open questions of that paper was the existence of a non abelian-by-finite -minimal group. We give here the first example of such a group.
957.
Peter Fleischmann Markus Chr. Holder Peter Roelse. 《Mathematics of Computation》2003,72(244):1887-1899
The most time-consuming part of the Niederreiter algorithm for factoring univariate polynomials over finite fields is the computation of elements of the nullspace of a certain matrix. This paper describes the so-called ``black-box' Niederreiter algorithm, in which these elements are found by using a method developed by Wiedemann. The main advantages over an approach based on Gaussian elimination are that the matrix does not have to be stored in memory and that the computational complexity of this approach is lower. The black-box Niederreiter algorithm for factoring polynomials over the binary field was implemented in the C programming language, and benchmarks for factoring high-degree polynomials over this field are presented. These benchmarks include timings for both a sequential implementation and a parallel implementation running on a small cluster of workstations. In addition, the Wan algorithm, which was recently introduced, is described, and connections between (implementation aspects of) Wan's and Niederreiter's algorithm are given.
958.
In this paper we consider two coupled scalar fields during the inflation as a dynamical system. With the Poincaré section method, we investigate the evolution of the coupled scalar fields system. We find that the evolution of the system changes from a regular motion into a chaotic motion when the energy density and the coupling constant of the system increase. 相似文献
959.
对34GHz基波回旋管双阳极磁控注入枪的优化做了详细的研究和计算,数值模拟了阳极电压、注电流、枪体尺寸加工误差、外加直流磁场等因素对电子枪的影响。模拟结果表明：增大阳极电压不但可以提高速度比,而且可以降低横向速度零散。磁场压缩比减小,使电子注具有最小速度零散的电流值增大;同时,电子注的速度比降低,最小横向速度零散值也增大。必须慎重选择阳极形状,以提高电子枪的性能并保证电子注的稳定性;同时,还发现由于阳极结构的变化导致阴极电场分布的变化,使电子注的注电流在各因子变化过程中出现了微小的扰动。减小Bc可以增大电子注的速度比,还可以减小电子注的横向速度零散,但是当电子注的速度比增大到一定值时,电子注的性能就会变得不太稳定。 相似文献
960.