共查询到19条相似文献,搜索用时 437 毫秒
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电子在晶格周期性势场影响下的运动遵循布洛赫定理. 布洛赫电子除了具有电荷和自旋两个内禀自由度外, 还有其他内禀自由度. 能带色散曲线上的某些极值点作为谷自由度, 具有独特的电子结构和运动规律. 本文从布洛赫电子的谷自由度出发, 简单介绍传统半导体的谷电子性质研究现状, 并重点介绍新型二维材料体系, 如石墨烯、硅烯、硫族化合物等材料中谷相关的物理特性. 有效利用谷自由度的新奇输运特性, 将其作为信息的载体可以制作出新颖的纳米光电子器件, 并有望造就下一代纳电子器件的新领域, 即谷电子学(valleytronics). 相似文献
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用成象自由度评价光学系统的信息量 总被引:1,自引:1,他引:0
本文探讨了一般光学系统的成象自由度传递及信息量问题,计算了不同信噪比σ0/σn下一维相干光和非相干光照明的衍射受限系统的有效自由度数Noff,并与经典分辨率理论的象素数作了比较。 相似文献
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使用有效理论方法分别讨论了自由落体、微振动和中心势场中粒子运动等问题.基于每个问题所表现出的对称性,完整理论中部分自由度可实现退耦,并给出相应的有效拉格朗日量(或有效哈密顿量).这些例子体现了有效理论方法处理经典力学的优越性. 相似文献
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量子信息处理中许多任务都要求量子通道必须是最大纠缠态,但最大纠缠态不可避免地要受到环境噪声等因素的影响,变成部分纠缠态或混合态,因此纠缠纯化至关重要。早期人们基于交叉克尔非线性主要针对单个自由度进行纯化,或者用超纠缠的一个自由度去纯化另一个自由度,很少有方案涉及到超纠缠纯化。提出了一种基于交叉克尔非线性的超纠缠纯化方案,几乎确定性地实现了空间自由度和偏振自由度两个自由度的纯化。该方案只需要线性光学元件、弱的克尔非线性、强的相干光场和零差探测。 相似文献
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多自由度超声电机是将两种以上的超声振动模式按照一定的方式组合,通过在定子的表面产生椭圆运动来实现转子的多自由度转动.文中综述了近年来发展起来的几种多自由度超声电机的结构、工作原理和特征,并就多自由度超声电机的工程应用和未来发展方向进行了展望. 相似文献
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声在多原子分子气体中传播所引起的弛豫过程是探索气体特性的重要方面. 本文通过研究气体声弛豫过程中振动自由度与平动自由度(V-T)以及振动自由度之间(V-V)的分子能量转移模型, 给出了有效比热容与弛豫时间的分解对应关系及其通用获得方法. 该分解模型与现有的声弛豫模型相比, 反映了分解后的V-T 和V-V弛豫过程中振动比热容与弛豫时间的对应关系, 并发现了较高能级是引起对应声弛豫过程的决定因素. 将基于该分解模型获得的气体声弛豫衰减谱经碰撞直径微调改进后, 比现有理论更接近实验数据, 其结果证明了该分解对应关系的正确性和合理性. 相似文献
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We study resonances of multidimensional chaotic map dynamics. We use the calculus of variations to determine the additive
forcing function that induces the largest response, that is, the greatest deviation from the unperturbed dynamics. We include
the additional constraint that only select degrees of freedom be forced, corresponding to a very general class of problems
in which not all of the degrees of freedom in an experimental system are accessible to forcing. We find that certain Lagrange
multipliers take on a fundamental physical role as the efficiency of the forcing function and the effective forcing experienced
by the degrees of freedom which are not forced directly. Furthermore, we find that the product of the displacement of nearby
trajectories and the effective total forcing function is a conserved quantity. We demonstrate the efficacy of this methodology
with several examples. 相似文献
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Merced Montesinos 《General Relativity and Gravitation》2001,33(1):1-28
We study the classical and quantum dynamics of generally covariant theories with vanishing Hamiltonian and with a finite number of degrees of freedom. In particular, the geometric meaning of the full solution of the relational evolution of the degrees of freedom is displayed, which means the determination of the total number of evolving constants of motion required. Also a method to find evolving constants is proposed. The generalized Heisenberg picture needs M time variables, as opposed to the Heisenberg picture of standard quantum mechanics where one time variable t is enough. As an application, we study the parametrized harmonic oscillator and the SL(2, R) model with one physical degree of freedom that mimics the constraint structure of general relativity where a Schrödinger equation emerges in its quantum dynamics. 相似文献
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Starting from and only using classical Hamiltonian dynamics, we prove the maximum work principle in a system where macroscopic
dynamical degrees of freedom are intrinsically coupled to microscopic degrees of freedom. Unlike in many of the standard and
recent works on the second law, the macroscopic dynamics is not governed by an external action but undergoes the back reaction
of the microscopic degrees of freedom. Our theorems cover such physical situations as impact between macroscopic bodies, thermodynamic
machines, and molecular motors. Our work identifies and quantifies the physical limitations on the applicability of the second
law for small systems.
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Barak Kol 《General Relativity and Gravitation》2008,40(10):2061-2068
Identifying the fundamental degrees of freedom of a black hole poses a long-standing puzzle. Recently Goldberger and Rothstein
forwarded a theory of the low frequency degrees of freedom within the effective field theory approach, where they are relevancy
ordered but of unclear physical origin. Here these degrees of freedom are identified with near-horizon but non-compact gravitational
perturbations which are decomposed into delocalized multipoles. Their world-line (kinetic) action is determined within the
classical effective field theory (CLEFT) approach and their interactions are discussed. The case of the long-wavelength scattering
of a scalar wave off a Schwarzschild black hole is treated in some detail, interpreting within the CLEFT approach the equality
of the leading absorption cross section with the horizon area.
Fifth Award in the 2008 Essay Competition of the Gravity Research Foundation. 相似文献
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A Monte Carlo procedure is constructed for lattice gauge theories with fermions by replacing integration over fermion degrees of freedom in the path integral by conventional integration over effective boson degrees of freedom. The method is applied to gauge theories over two discrete subgroups of SU(2). 相似文献
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Wolfram Just Katrin Gelfert Nilüfer Baba Anja Riegert Holger Kantz 《Journal of statistical physics》2003,112(1-2):277-292
We apply standard projection operator techniques known from nonequilibrium statistical mechanics to eliminate fast chaotic degrees of freedom in a low-dimensional dynamical system. Through the usual perturbative approach we end up in second order with a stochastic system where the fast chaotic degrees of freedom are modelled by Gaussian white noise. The accuracy of the perturbation expansion is analysed in detail by the discussion of an exactly solvable model. 相似文献
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The adiabatic effective baryon-baryou interactions and dibaryon candidates are studied systematically with three constituent quark models based on different effective degrees of freedom:Glozman-Riska-Brown Goldstone boson exchange model based on constituent quark and Goldstone boson coupling;Fujiwara model based on constituent quark gluon coupling and Nijmegen one-boson exchange;QDCSM based on constituent quark and gluon coupling with quark delocalization and color screening.We find that the three models predicted the similar effective baryon-baryon interactions for roughly two thirds among the 64 states consisted of octet and decuplet baryons.The differences among three models and their separate characteristics are also studied. 相似文献
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Barry R. Holstein 《Foundations of Physics》2000,30(3):413-437
The use of effective field theory, in situations wherein the energy-momentum of light particles is much lower than the rest mass of heavy degrees of freedom, has become an important one in contemporary physics. Herein we examine various means by which this effective action can be evaluated, using the effective photon–photon interaction—the Euler–Heisenberg Lagrangian—as a pedagogical example. 相似文献
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