摩擦力矩对高速旋转体升起运动的简易实验演示及理论分析

摩擦力矩对高速旋转体升起运动的简易实验演示及理论分析梁法库（黑龙江省克山师专物理系１６１６０１）在理论力学的欧勒动力学方程教学中，发现学生对这部分知识感到难于理解，特别是摩擦力矩对旋转体的影响，如图１所示的几种常见．图１为了引导学生观察身边的力学现象...     

浅谈摩擦现象

在众多的物理现象中，摩擦现象是最常见。最简单不过的现象之一，正因为如此，不少学生在学习物理的过程中对摩擦现象的认识存在着一定的误区，而且一旦形成就很难纠正过来，所以教师必须认真对待，让学生正确认识和理解摩擦现象．     

基于自适应算法的光电跟踪转台摩擦补偿方法研究

为了解决低速状态下跟踪转台在摩擦力矩作用下出现低速爬行现象,以某光电跟踪转台为研究对象,根据Lyapunov稳定性理论和自适应控制理论,提出了自适应摩擦补偿方法。通过在经典伺服控制回路中增加摩擦补偿器,以达到抑制低速爬行现象,提高设备低速平稳性能。对比补偿前后转台的输出速度仿真曲线,表明该方法能够有效地抑制低速爬行现象的产生,提高转台的稳定跟踪性能,适合于工程应用。     

摩擦因数探析

在日常的生产和生活中，人们时刻都离不开摩擦，摩擦现象是物理学中最古老、最有趣的问题之一．摩擦的机制颇耐人寻味．摩擦学方面的专著屡见不鲜，摩擦问题的复杂性可见一斑，本文谨在中学范围内对摩擦现象及摩擦因数作一点浅显的探讨．     

摩擦振子行为的建模与探究

一般认为滑动摩擦力正比于接触面之间的正压力，而摩擦系数只和接触面材料有关，与摩擦副之间的相对运动速度大小无关。在对IYPT2020第13课题“摩擦振子”的研究中，我们搭建了适用的实验设备，得到摩擦振子振幅先随时间增大，然后受摩擦轮转速限制而稳定在一定值的实验结果。由理论分析可知，振幅随时间增大的现象是摩擦系数随摩擦副之间的相对速度增大而减小决定的。摩擦系数随速度变化的定量测量证明了这一依赖关系。     

宝光的理论

国外从本世纪４０年代开始对宝光进行理论研究，先后提出了几种解释宝光现象的理论，从而对宝光问题作出了相当深刻的解释，本文简要介绍和评述了这些研究成果，主要包括米氏散射理论、范德赫尔斯特的表面波理论和努森兹维格的复角动量理论．显然，经典的几何光学和一般的衍射理论都不能或难以解释宝光现象．     

基于滑动势能面的二维材料原子尺度摩擦行为的量化计算

近年来,二维材料优异的摩擦特性成为人们关注的焦点,然而目前缺乏理论上对其摩擦力进行快速、有效、精确的计算预测方法.本文提出采用密度泛函理论计算真实体系的滑动势能面,利用得到的"数值型势能面"替代传统的解析势函数,并结合Prandtl-Tomlinson模型,量化求解具有复杂形状势能面的真实二维材料体系的摩擦行为.基于该方法,揭示了原子力显微镜实验中观察到的石墨烯Moire纹超晶格结构的双周期"黏-滑"摩擦现象;理论预测了二维材料异质结构的层间超低摩擦现象,相对于同质材料,其静摩擦力和滑动摩擦力均成数量级降低,发现势能面起伏和驱动弹簧刚度均会影响层间相对滑动路径,进而对层间的摩擦行为产生影响.该方法同样可拓展到其他van der Waals作用主导的界面摩擦体系.     

推动人类文明与进步的物理学：量子理论（一）

量子理论是关于微观客体的理论。它基于物质的波粒二象性。在量子力学的基础上建立了原子物理理论、原子核理论和凝聚态物理理论。它统一解释了原子和分子的各种光谱，统一解释了元素周期表，统一解释了各种分子键，统一解释了各种物性、现象，它推动了物理，化学甚至生物学的统一进程。但是它不能处理粒子的产生、湮没等现象。     

划时代的发现--法拉第电磁感应现象

法拉第是19世纪自学成才的伟大的物理学家，他发现的电磁感应定律揭示了电现象和磁现象之间的联系，是电磁理论发展的重要基础，本文简要地介绍了法拉第电磁感应现象发现和探索研究的历程。     

石墨烯层间纳米摩擦性质的第一性原理研究

基于密度泛函理论的第一性原理计算方法研究了纳米尺度下石墨烯层间摩擦现象, 探讨了对称和非对称两种情况下双层石墨烯层间沿不同方向的摩擦性质. 研究发现对于对称的双层石墨烯, 层间摩擦沿不同方向同性; 摩擦因数依赖于正压力, 随正压力增大, 摩擦因数的变化曲线分为三个阶段, 在较小以及较大压力下, 摩擦因数遵循Amonton法则不随压力变化而变化; 而在中间3-6 nN阶段, 摩擦因数随压力增加线性增加. 整个研究压力范围内摩擦因数在0.05-0.25之间. 对于非对称性双层石墨烯层间摩擦, 不同压力下摩擦因数在0.006上下波动, 摩擦因数较两层对称性石墨烯大大降低. 上述研究结果与实验一致.     

On correct nonlocal generalized theories of elasticity

The paper discusses nonlocal elasticity theories among which are models of media with defect fields, gradient elasticity theories, and hybrid nonlocal elasticity theories. Gradient theories are analyzed, and their correctness properties are examined. Applied theories that satisfy the correctness conditions are developed, and known applied gradient theories are verified for the correctness properties. A new nonlocal generalized theory has been developed for which the operator of balance equations is represented as the product of the equilibrium operator of classical elasticity theory and the Helmholtz operator. It is shown that this theory is one-parameter and is the only representative of hybrid models constructed by a complete system of equations for forces and moments. Unlike classical elasticity that is free from scale parameters characterizing the internal material structure, nonlocal elasticity theories naturally incorporate these parameters. That is why they are suitable for the modeling of scale effects and find application in the solution of numerous applied problems for heterogeneous structures with developed phase interfaces where the degree of influence of scale effects depends on the density of phase boundaries. Nonlocal continuum models are especially attractive for modeling the properties of various micro/nanostructures, elastic properties of composites and structured materials with submicron- and nanosized internal structures in which effective properties are to a great extent defined by the scale effects (short-range interaction effects of cohesion and adhesion). Generalized elasticity theories even for isotropic materials contain many additional physical constants that are difficult or impossible to determine experimentally. Applied models with a small number of additional physical parameters are therefore of great interest. However, the reduction of nonlocal theories aimed at reducing the number of additional parameters is a nontrivial task and may lead to incorrect theories. The goal of this paper is to study the symmetry properties in gradient theories, to analyze the correctness of gradient theories, and to develop applied one-parameter elasticity theories.     

Holomorphic Chern-Simons-Witten theory: From 2D to 4D conformal field theories

It is well known that rational 2D conformal field theories are connected with Chern-Simons theories defined on 3D real manifolds. We consider holomorphic analogues of Chern-Simons theories defined on 3D complex manifolds (six real dimensions) and describe 4D conformal field theories connected with them. All these models are integrable. We describe analogues of the Virasoro and affine Lie algebras, the local action of which on fields of holomorphic analogues of Chern-Simons theories becomes non-local after pushing down to the action on fields of integrable 4D conformal field theories. Quantization of integrable 4D conformal field theories and relations to string theories are briefly discussed.     

Purely transmitting defect field theories

We define an infinite class of integrable theories with a defect which are formulated as chiral defect perturbations of a conformal field theory. Such theories are massless in the bulk and are purely transmitting through the defect. The integrability of these theories requires the introduction of defect degrees of freedom. Such degrees of freedom lead to a novel set of Yang-Baxter equations. The defect degrees of freedom are identified through folding the chiral defect theories onto massless boundary field theories. The examples of the sine-Gordon theory and Ising model are worked out in some detail.     

Geometry and topology of chiral anomalies in gauge theories

Geometrical and topological aspects of chiral anomalies in gauge theories are reviewed. Geometrical and topological concepts and results for chiral anomalies in gauge theories are considered, including differential forms, Lie groups, homotopy, homology, cohomology, Riemannian manifolds, fibre bundles, characteristic classes, index theorems and spectral flow. Gauge theories and their formulation in terms of differential forms and fibre bundles are described. The quantisation of gauge theories is performed using path integrals, and the orbit space, BRST symmetries and ? vacuum are discussed. Gauge theories with fermions are formulated, including realistic models of strong and weak interactions. Chiral anomalies and related issues such as the existence of Schwinger terms, their origins in terms of differential forms, cohomology, the orbit space, BRST identities, Hamiltonian systems and relations to index theorems are analysed. Constraints on models for particle physics from chiral anomalies and theories involving spontaneously broken chiral symmetry described by effective Lagrangians are also mentioned.     

振动条件下颗粒的分离现象

介绍并分析比较了竖直振动条件下巴西坚果效应与反巴西坚果效应形成的机制和转化条件,以及水平振动下颗粒的分离现象,提出一些意见和建议.     

Brane tilings and reflexive polygons

Reflexive polygons have attracted great interest both in mathematics and in physics. This paper discusses a new aspect of the existing study in the context of quiver gauge theories. These theories are 4d supersymmetric worldvolume theories of D3 branes with toric Calabi‐Yau moduli spaces that are conveniently described with brane tilings. We find all 30 theories corresponding to the 16 reflexive polygons, some of the theories being toric (Seiberg) dual to each other. The mesonic generators of the moduli spaces are identified through the Hilbert series. It is shown that the lattice of generators is the dual reflexive polygon of the toric diagram. Thus, the duality forms pairs of quiver gauge theories with the lattice of generators being the toric diagram of the dual and vice versa.     

The Transformation Properties at the Quantum Level in Field Theories for a Gauge-Invariant System with a Higher-Order Lagrangian

Based on the configuration-space generating functional of the Green functions for the gauge-invariant system in higher-order derivatives theories, the equations of the transformation properties at the quantum level have been derived. It follows that the sufficient conditions are found which implies that there exists the conservation laws and the expressions of the quantal conserved laws are also given. Applying the results to the non-Abelian Chern-Simons higher-order derivatives theories, the quantal BRST conserved charge and other conserved charges are found, the transformation properties of the conformal transformation at the quantum level is discussed, the quantal conserved angular momentum is derived, it is pointed out that fractional spin in this system may be also preserved in quantum theories. But the connection between the symmetries and conservation laws in classical theories are not always preserved in quantum theories.     

Remarks on nonrenormalizable interactions

It is argued that certain quantum field theories, including conventional nonrenormalizable theories, do not reduce to free theories when the interaction is turned off. The limiting, “pseudo-free” theories are formally characterized and suggested as alternative “unperturbed” theories possibly suitable for a meaningful perturbation analysis.     

The confrontation between general relativity and experiment: An update

The status of experimental tests of general relativity to the end of 1983 is reviewed. The experimental support for the Einstein equivalence principle is summarized. If this principle is valid, gravitation must be described by a curved space-time, “metric” theory of gravity. General properties of metric theories are described and the parametrized post-Newtonian (PPN) formalism for treating the weak-field, slow-motion limit of such theories is set up. A zoo of selected metric theories of gravity is presented. Experimental tests of metric theories are then described, including the “classical” tests, tests of the strong equivalence principle, and others. The possibility of using gravitational-wave observations to test metric theories is discussed. A review is presented of the binary pulsar, in which the first evidence for gravitational radiation has been found. Finally cosmological tests of alternative theories are briefly described.     

Canonical quantization of interacting WZW theories

Using canonical quantization we find the Virasoro centre for a class of conformally invariant interacting Wess-Zumino-Witten theories. The theories have a group structure similar to that of Toda theories (both abelian and non-abelian) but the usual Toda constraints on the coupling constants are relaxed and the theories are not necessarily integrable. The general formula for the Virasoro centre is compared to that derived by BRST methods in the Toda case, and helps to explain the structure of the latter.