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排序方式: 共有799条查询结果,搜索用时 31 毫秒
91.
D. D. Pawar S. W. Bhaware A. G. Deshmukh 《International Journal of Theoretical Physics》2008,47(3):599-605
In this paper we have investigated bulk viscous fluid plane symmetric dust magnetized string cosmological model. To get a
deterministic model, it is assumed that ε=λ, and a relation between metric potential B=RA
n
. The behaviour of the model in the presence and absence of magnetic field together with physical and geometrical aspects
of the model are also discussed. 相似文献
92.
Raj Bali Anirudh Pradhan Hassan Amirhashchi 《International Journal of Theoretical Physics》2008,47(10):2594-2604
A model of a cloud formed by massive strings is studied in the context of the usual general relativity. This model is used
as a source of Bianchi type VI
0 massive with magnetic field and bulk viscosity. To get a determinate model, we assume that the expansion (θ) in the model is proportional to the shear (σ) and also the fluid obeys the barotropic equation of state. The behaviour of the models from physical and geometrical aspects
in presence and absence of magnetic field and bulk viscosity is discussed. 相似文献
93.
Møller’s energy-momentum complex is employed in order to determine the energy and momentum distributions for a spacetime described by a “generalized Schwarzschild” geometry in (3+1)-dimensions on a noncommutative curved D3-brane in an effective, open bosonic string theory. The geometry considered is obtained by an effective theory of gravity coupled with a nonlinear electromagnetic field and depends only on the generalized (effective) mass and charge which incorporate corrections of first order in the noncommutativity parameter. 相似文献
94.
The haploid–diploid cycle where, under unfavorable conditions the population becomes diploid, is modeled by a Monte-Carlo method in the framework of the Jan–Stauffer–Moseley hypothesis. Diploidy and sex may have first arisen as a way to escape death, when a simple unicellular individual is threatened by too many deleterious mutations. Using a bit string model, we find that in a system where competition is present (through the Verhulst factor), diploids dominate. In this case the transition from haploid to essentially diploid population takes place in a short time interval reminiscent of phase transitions in physical systems. 相似文献
95.
96.
基于一阶非线性梁理论和物理中面概念,导出了纵横向载荷作用下功能梯度材料(FGM)梁非线性弯曲和过屈曲问题的控制方程,并获得了该问题的精确解;据此解研究了梯度材料性质、外载荷、横向剪切变形以及边界条件等因素对功能梯度材料梁非线性力学行为的影响,分析中假设功能梯度材料性质只沿梁厚度方向,并按成分含量的幂指数函数形式变化。结果表明:纵横载荷共同作用下,功能梯度梁的弯曲构形将有无限多个;随着梯度指数的增大,梁的变形减小,临界载荷升高;随着长高比的增大,横向剪切变形的影响减小。 相似文献
97.
海洋油气资源钻探中隔水管的弯曲对钻柱振动以及钻进特性有特别的影响。为得到隔水管弯曲对钻柱振动的影响规律,对南海已钻深水井使用非线性有限元软件建立全井钻井数值计算模型,研究获得了不同垂深时隔水管弯曲对钻柱振动特性的影响规律。研究表明:隔水管弯曲会加剧钻柱的振动,钻柱振动加剧会导致钻井能耗上升、钻头切削能力下降并且会加快钻柱疲劳;当隔水管的弯曲达到某临界值,钻柱与隔水管间的接触力会陡增;井口的钩载越大,隔水管弯曲带来的井口钩载波动量越大;井越深,隔水管弯曲对全井钻柱最大弯矩和钻头切削能力的影响越小。 相似文献
98.
Atropoenantioselective Redox‐Neutral Amination of Biaryl Compounds through Borrowing Hydrogen and Dynamic Kinetic Resolution 下载免费PDF全文
Dr. Jianwei Zhang Prof. Dr. Jian Wang 《Angewandte Chemie (International ed. in English)》2018,57(2):465-469
We report herein a novel atropoenantioselective redox‐neutral amination of biaryl compounds triggered by a cascade of borrowing hydrogen and dynamic kinetic resolution under the cooperative catalysis of a chiral iridium complex and an achiral Brønsted acid. This protocol features broad substrate scope and good functional‐group tolerance, and allows the rapid assembly of axially chiral biaryl compounds in good to high yields and with high to excellent enantioselectivity. 相似文献
99.
Zeta-nonlocal scalar fields 总被引:1,自引:0,他引:1
B. Dragovich 《Theoretical and Mathematical Physics》2008,157(3):1671-1677
We consider some nonlocal and nonpolynomial scalar field models originating from p-adic string theory. An infinite number
of space-time derivatives is determined by the operator-valued Riemann zeta function through the d’Alembertian □ in its argument.
The construction of the corresponding Lagrangians L starts with the exact Lagrangian for the effective field of the p-adic tachyon string, which is generalized by replacing p with an arbitrary natural number
n and then summing over all n. We obtain several basic classical properties of these fields. In particular, we study some solutions of the equations
of motion and their tachyon spectra. The field theory with Riemann zeta-function dynamics is also interesting in itself.
Dedicated to Vasilii Sergeevich Vladimirov on his 85th birthday
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 157, No. 3, pp. 364–372, December, 2008. 相似文献
100.
We study a relativistic quantum particle in cosmic string spacetime in the presence of a magnetic field and a Coulomb-type scalar potential. It is shown that the radial part of this problem possesses the su(1,1) symmetry. We obtain the energy spectrum and eigenfunctions of this problem by using two algebraic methods: the Schrödinger factorization and the tilting transformation. Finally, we give the explicit form of the relativistic coherent states for this problem. 相似文献