地轴进动演示与定量测量实验仪

论述了地轴进动演示与定量测量实验仪的结构、各部位名称及物理含义;介绍了演示的自然现象,以及定量测量原理与测量公式推导;讨论了采用该实验仪进行定量测量思路、实验内容和创新知识点。     

亚洲的暴风雨与地球的旋转

地球自身的旋转轴经受着多种旋转力的作用，例如二分点（即旋转轴处于春分、秋分点时）的进动等．最近发现有两个重要的旋转运动不被人注意地相互间抵消了．比利时的地球物理学家S．Lambert博士精确地测量到了这类在常规下是很难探测到的微弱晃动．这两个晃动分别是现在还不太明白其起因的钱德勒章动（Chandler wobble），这个章动的周期是433天．另一个是起源于地球上气候变化引起的晃动．这两个运动的综合后果应该导致地轴发生大于10米的移动．但由于这两个晃动的相互抵消作用，从2005年12月到2006年2月这段时间，地轴的移动却降低到了1米以下．     

进动的数值分析

介绍了大学物理及力学教材中对飞轮进动的描述及进动角速度计算公式的局限性,根据欧拉运动学方程对飞轮的定点转动进行了理论分析及数值计算,给出了飞轮的章动、进动及自旋的一般规律,有利于对进动的全面理解.     

基于解析结果的拉格朗日陀螺运动特性分析

本文建立拉格朗日陀螺运动方程的解析方法.导出拉格朗日陀螺做规则进动的条件,用级数展开技术得到规则进动附近的小角度章动和进动的解析解.给出陀螺自转轴运动的简明图像,即重力引起绕竖直轴的规则进动和无重力的自由进动的叠加.利用解析结果对陀螺不倒之谜给出解释.     

Sen时空中的陀螺进动效应

采用Frenet-Serret形式研究了Sen时空中的陀螺进动效应,得出了沿圆轨迹以任意常数角速 度运动的轨道陀螺进动的一般公式,当陀螺在赤道平面上沿短程线运动时,由一般公式出发 可得到精确的轨道周期进动角公式.作为特例,研究了静态dilaton时空中的陀螺进动效应. 将所得结果分别与Kerr-Newman和Reissner-Nordstrm时空中的情形相比较,发现dilaton 耦合使陀螺进动速率减慢,轨道周期进动角减小. 关键词： Sen时空 Frenet-Serret标架 Fermi-Walker移动     

一种新的角动量守恒演示实验仪

介绍了新研制成功的一种物理演示实验仪,它是以进动过程中突然除去进动的原因而使进动中止的方式来演示角动量守恒的．实验仪结构简单,操作方便,反映的物理原理深刻．     

电磁控制陀螺转子进动角速度的计算

分析了现代激光制导武器中陀螺稳定光学系统式位标器的两种进动控制方式———受控磁环轴向充磁与控制线圈径向布置和受控磁饼径向充磁与控制线圈轴向布置。由现代电磁场理论 ,磁体在磁场中的受力及进动理论 ,分别推导出了它们的进动角速度的计算公式 ,并进行了第一种进动控制方式的计算机模拟计算 ,结果与实际相符     

杠杆式回转仪定量演示方法研究

在对杠杆式回转仪运动现象进行理论分析的基础上,通过测量出圆轮自转角速度,旋转轴进动角速度、进动角度的参数,定量研究了力矩与进动速度间关系、角速度与进动速度间关系、角动量定理的实验验证,最后将测量值与理论计算值进行了比较。将杠杆式回转仪运动状态的定量分析引入大学物理实验,培养了学生实际动手能力,加深了学生对角动量定理,力...     

陀螺进动中的“角动量不守恒”问题

一些力学教科书中对回转效应的讲解就是直接利用重力力矩导致陀螺角动量变化得到均匀进动角速度,但是这会导致竖直方向出现进动角动量而无法解释的问题,即看似角动量不守恒。本文从基本的力学原理出发,分析了陀螺水平释放后从开始到稳定过程中的进动和章动,并对结果进行了数值模拟,证明忽略进动阻尼时稳定进动角动量与陀螺下倾导致的自转角动量竖直分量大小相等、方向相反,保证了系统竖直方向角动量恒为零。     

进动演示实验的改进

讲解进动一般用进动陀螺演示,但仪器太小,在大班上看不清,讲解时不好比着仪器讲。以后我们改用车轮,用绳将车轮轴的一端吊在架子上。这样作也不好,车轮产生进动后不断将绳扭紧而     

Observing Lense-Thirring precession in tidal disruption flares

When a star is tidally disrupted by a supermassive black hole (SMBH), the streams of liberated gas form an accretion disk after their return to pericenter. We demonstrate that Lense-Thirring precession in the spacetime around a rotating SMBH can produce significant time evolution of the disk angular momentum vector, due to both the periodic precession of the disk and the nonperiodic, differential precession of the bound debris streams. Jet precession and periodic modulation of disk luminosity are possible consequences. The persistence of the jetted x-ray emission in the Swift J164449.3+573451 flare suggests that the jet axis was aligned with the spin axis of the SMBH during this event.     

Experimental observation of the tilting mode of an array of vortices in a dilute Bose-Einstein condensate

We have measured the precession frequency of a vortex lattice in a Bose-Einstein condensate of Rb87 atoms. The observed mode corresponds to a collective motion in which all the vortices in the array are tilted by a small angle with respect to the z axis (the symmetry axis of the trapping potential) and synchronously rotate about this axis. This motion corresponds to excitation of a Kelvin wave along the core of each vortex and we have verified that it has the handedness expected for such helical waves, i.e., precession in the opposite sense to the rotational flow around the vortices.     

Specific features in precession dynamics of magnetization of a uniaxial magnetic film

The precession dynamics of the magnetization of a film with in-plane uniaxial anisotropy in the case of its biasing along the hard magnetization axis has been analyzed by numerically solving the Landau-Lifshitz equations. It has been revealed that the ferromagnetic resonance spectrum near the magnetic anisotropy field exhibits an additional peak, which is associated with the angular bistability due to the presence of two symmetric angular equilibrium positions. The trajectories of precession motion during biasing along the hard magnetization axis differ substantially from the trajectories corresponding to the biasing along the easy axis.     

Precession of an electron-magnetohydrodynamic field-reversed configuration

A field-reversed configuration is generated in a large laboratory plasma in the parameter regime of electron magnetohydrodynamics. During its free relaxation, the magnetic moment is observed to precess when tilted from its original axis. The precession velocity is the electron drift velocity in the toroidal current layer. The precession is a manifestation of frozen-in field lines in a moving electron fluid.     

Relativistic precession of a gyroscope. I. Circular orbits

The relativistic precession of the rotation axis of a spherical gyroscope is treated in the framework of monadic specification of the frame of reference. It is found that the precession in the comoving frame compensates the rotation of the frame of reference itself. An exact expression is derived for the angular velocity of precession for motion of a gyroscope in circular epiequatorial orbits in the Kerr field. The results are compared with the approximate expression obtained by Schiff. Numerical examples are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 64–68, March, 1981.     

2H-ZnS单晶层错几率的旋进法测定中影响因素的研究

作者首次使用X光旋进照相法测定了2H-ZnS单晶rp的层错组态和层错几率.并对测定方法中的符种影响因素进行了研究:比较了两种“定向”方法(定向照相法和锥轴照相法),指出了它们各自的适用条件;分析了倒易点阵面“定向”偏差对衍射强度分布的影响;研究了反射时问对衍射强度分布的影响,征明罗伦兹-偏振修正的必要性.同时对测定方法中其他应注意的问题也进行了讨论.     

Ultrafast optical study of magnons in the ferromagnetic semiconductor GaMnAs

Coherent oscillations of the magnetization were observed in magneto-optical Kerr measurements in thin films of the ferromagnetic semiconductor GaMnAs. For magnetic fields oriented in the film plane, two precession modes were observed. Their frequencies increase with the field when it is along the [100] axis, whereas they behave non-monotonically when the field is oriented along the in-plane hard axis [110]. Spectra are also presented for fields applied normal to the film plane. From the measured field-dependence of the magnon frequency, the spin stiffness and magnetic anisotropy constants were obtained.     

Biased quasiballistic spin torque magnetization reversal

We explore the ultrafast limit of spin torque magnetization reversal time. Spin torque precession during a spin torque current pulse and free magnetization ringing after the pulse is detected by time-resolved magnetotransport. Adapting the duration of the pulse to the precession period allows coherent control of the final orientation of the magnetization. In the presence of a hard axis bias field, we find optimum quasiballistic spin torque magnetization reversal by a single precessional turn directly from the initial to the reversed equilibrium state.     

弱磁场中质子的自由进动和一个野外测磁场的实验

本文报导了我们在弱场中进行的核矩预极化和核矩自由进动的实验和分析。主要研究了极化磁场衰减过程中核矩的运动、讯号的绝对强度,并观察到探头转动对讯号频率的影响,指出了这是测核磁矩正负号的最直接的方法。此外,弱磁场中质子自由进动现象在高空磁场测量、地质探矿、石油开采等方面都有重要的实际应用,本文的结果对解决这些应用中的具体问题是有帮助的。为了检验全套仪器在野外工作时的性能,以及观察周围大体积的磁性物质对讯号频率的影响,我们在野外进行了一系列的测磁实验,获得了肯定的结果。测磁的相对精密度达到1×10^-5。     

Two-magnon relaxation reversal in ferrite spheres

The reversal of two-magnon relaxation associated with linear scattering of oscillations of uniform magnetization precession from sample nonuniformities is studied theoretically and experimentally in ferrite spheres of yttrium iron garnet (YIG). Relaxation reversal is performed by parametric phase conjugation of dipole-exchange spin waves formed as a result of scattering of uniform precession from inhomogeneities. As a result of two-magnon backward scattering of dipole-exchange spin waves with a certain time delay, magnetization oscillations are renewed with an amplitude that could exceed the initial amplitude of uniform precession. The relaxation reversal is due to crystallographic anisotropy of the sample and is manifested most strongly when a YIG sphere is magnetized along the intermediate axis [110]. Experiments were carried out on YIG spheres of diameter 0.65–1.05 mm for a parallel pumping frequency ω _p /2π ≈ 9.4 GHz, which is about twice the uniform precession frequency. The maximal delay time for the restored signal of uniform precession was about 2 μs, while the maximal amplitude exceeded the initial uniform precession amplitude by a factor of about 5. The “latent” relaxation parameters of ferrites, e.g., the natural ferromagnetic resonance linewidth associated with many-particle processes and the linewidth associated with two-magnon scattering at bulk nonuniformities, are determined experimentally.