截卵形头部平台直径对初始侵彻弹道偏转的影响

针对截卵形头部弹体斜侵彻靶标时弹道发生初始偏转的问题,建立了分析截卵平台直径对初始弹道偏转影响的理论和数值仿真计算模型,计算了相同侵彻条件下不同截卵平台直径时,头部侵彻产生的偏转函数和偏转角速度。结果表明:截卵平台头部侵彻产生的偏转力矩会减小弹轴与靶标法线之间的夹角,且随着截卵平台直径的增大,偏转力矩增大,偏转角速度增大,当截卵平台直径增大到1.5倍时,偏转力矩增大到约1.2倍,当截卵平台直径增大到2.0倍时,偏转力矩增大到约2倍;相同截卵平台直径下,随着头部形状系数的减小,偏转力矩和偏转角速度增大。     

磁电式交流电压表的测量原理

磁电式表头是一只灵敏电流表，矩形线圈通入直流电后，在磁感线辐向匀称分布的磁场中受到磁力矩肘．的作用而绕固定转动轴转动，使固定在转动轴上的指针发生偏转．在线圈转动过程中，因其平面总与磁感线平行，则磁力矩M1=NBSI=k1I将不随偏转角而改变．     

阴极射线偏转演示实验释疑

在“磁场对电流的作用力”和“磁场对运动电荷的作用力”教学中，阴极射线偏转演示实验起着承上启下的作用．在学生已知磁场对电流有作用力后，自然地提出磁场力是否直接作用于运动电荷？将阴极射线管放在马蹄形磁铁的两极间，从荧光屏上可以观察到：电子束的运动径迹发生弯曲．证明了我们的推想：运动电荷确实受到磁场力的作用．同时可以推论，不载电流的物体是不会使电子束发生偏转的．但是，当我们把一只手靠近射线管时，出乎意料的是电子束也发生了偏转！它偏离了手的方向．而用书本代替手做同样的实验时，却没有明显的偏离现象．为什么…     

杆摆中的内力、内力矩及其功

讨论了杆摆运动中的切向内力及其力矩、法向内力及其力矩;计算了内力及内力矩所作的功,这对进一步理解“质点”、“刚体”等概念有一定的参考价值．     

两种不同方法测量材料剪切模量

当一线圈悬挂于铜丝下,会因受到铜丝的扭转力矩而作简谐振动,测量简谐振动周期可以计算出铜丝的剪切模量.线圈通电后,因处于地磁场中而受到地磁力矩,利用光杠杆放大原理,只要测量出线圈通电前后的微小偏转角度,也可计算出铜丝的剪切模量.为了减少测量时间,只要将捕捉到的线圈通电前后的简谐振动图像进行图像数值分析,便可在非常短的时间内测量出线圈偏转角度,达到即时测量铜丝的剪切模量.利用运动学、力学、光学、电磁学原理及图像分析技术综合方法测量材料的剪切模量,既提高了测量精度,又降低了测量成本,易于操作,非常适合在大学物理教学中推广.     

利用激光光热技术研究钛酸钡材料的导热性能

利用激光光热偏转技术测量了钛酸钡材料的热扩散率。根据所测量材料的光热光偏转信号,通过最小二乘法中的非线性拟合,直接拟合出了材料的热扩散率,克服了光热偏转技术中“Mirage effect”步骤多、计算复杂、误差大的缺点。测量了在不同成型压力和不同烧结温度下钛酸钡材料的热扩散率,得到了热扩散率随成型压力和烧结温度的变化规律。对实验结果进行了分析和讨论。     

“平行板电容器的电容”演示实验探讨

分析了“平行板电容器的电容”演示实验中与静电计指针偏转变化量有关的因素。     

气动负载虚拟加载系统设计

飞行器在飞行过程中,舵机将承受到空气动力的力矩载荷,气动负载虚拟负载模拟器是用于模拟空气力矩载荷变化规律的地面半实验设备。针对在地面试验过程中,传统负载模拟器与承载系统因机械结构耦合而产生的“多余力矩”问题,以磁粉离合器和力矩传感器为核心,构建虚拟负载模拟器,利用系统输出转矩的大小和方向分别只与励磁电流的大小和速度滑差的方向有关的特性,较彻底地解决“多余力矩”的问题,提高力矩加载试验设备的性能,从而进一步提高飞行器虚拟试验的水平。     

高斯光束孤波演化过程中的自偏转

研究了无耗晶体的扩散效应对高斯光束在光伏光折变晶体中孤波演化特性的影响。结果表明，对于给定的与晶体参量匹配的高斯光束，晶体的扩散效应将造成高斯光束孤波演化的自偏转，而且其自偏转过程与同参量的屏蔽光伏明孤子的自偏转过程具有极其类似的特征。同时发现，高斯光束的波形即光束的横截面对其孤波演化的自偏转影响最大。比较了高斯光束孤波演化的自偏转与明孤波自偏转的理论曲线，结果表明，对于匹配的高斯光束，其自偏转程度与解析计算结果非常接近。     

LiNbO3电光偏转器的研究

从电光效应出发，对ＬｉＮｂＯ３电光偏转器的基本品质因子进行研究，导出了偏转器的设计公式，用有限差分法计算了四柱面电极电光偏转器的电场分布，对不同结构参数，给出了梯度线性度和结构因子。     

Perpendicular spin torques in magnetic tunnel junctions

We quantitatively determine a perpendicular spin torque in magnetic tunnel junctions by measuring the room-temperature critical switching current at various magnetic fields and current pulse widths. We find that the magnitude of the torque is proportional to the product of the current density and the bias voltage, and the direction of the torque reverses as the polarity of the voltage changes. By taking into account the energy-dependent inelastic scattering of tunnel electrons, we formulate the bias dependence of the perpendicular spin torque which is in qualitative agreement with the experimental results.     

Out-of-Plane Torque Influence on Magnetization Switching and Susceptibility in Magnetic Multilayers

Based on both the spin diffusion equation and the Landau-LlTshitz-Gilbert （LLG） equation, we demonstrate the influence of out-of-plane spin torque on magnetization switching and susceptibility in a magnetic multilayer system. The variation of spin accumulation and local magnetization with respect to time are studied in the magnetization reversal induced by spin torque. We also research the susceptibility subject to a microwave magnetic field, which is compared with the results obtained without out-of-plane torque.     

Ordering in Heisenberg spin glasses

For five different Heisenberg spin glass systems, torque experiments were performed in applied magnetic fields up to 4 T. The Dzyaloshinski-Moriya random anisotropy strengths, the in-field torque onset temperatures, and the torque relaxation were measured. Critical exponents were estimated independently using a standard protocol. The data are strong evidence for a true spin glass ordered state which survives under high applied magnetic fields; they can be interpreted consistently in terms of a chiral ordering model with replica symmetry breaking as proposed by Kawamura and co-workers.     

Temperature dependence of the induced torque of potassium

Sharp peaks observed in the induced torque of potassium as a function of magnetic field direction above about 4 T are temperature dependent in the range 1.1–1.9 K that was investigated. The amplitude and magnetic field direction of some of the peaks change with temperature. Induced torque amplitude at a fixed field direction and magnetic field above 4 T changes non-monotonically with temperature. The high-field peaks are independent of the presence of a four-fold torque which depends on sample conditions.     

Spin connection resonance in magnetic motors

A mechanism is proposed for rotation of magnetic assemblies by a torque consisting of the magnetic dipole moment of the assembly and a magnetic field generated from space–time in Einstein–Cartan–Evans (ECE) field theory. It is shown that when the magnetic assembly is stationary, the space–time is described by a Helmholtz wave equation in the tetrad as eigenfunction. This is a balance condition in which the Cartan torsion of the space–time is zero, but in which the tetrad and spin connection are non-zero. This balance may be broken by a driving current density produced by the magnetic assembly. The Helmholtz equation becomes an undamped oscillator equation. At resonance the torque on the magnetic assembly may be amplified sufficiently to cause the whole assembly to rotate, as observed experimentally in a repeatable and reproducible manner.     

Analysis of a non-contact magnetoelastic torque transducer

Results are presented for the performance of a magnetoelastic torque transducer that converts a torque-induced strain in a non-magnetic shaft into changes in a measurable magnetic field. The magnetic field is generated by a thin magnetostrictive layer that is coated onto the circumference of the shaft. The layer is magnetized and has an initial residual strain. The magnetization within the layer rotates in response to changes in the strain which occur when the shaft is torqued. The magnetic field produced by the layer changes with the magnetization and this can be sensed by a magnetometer to monitor the torque on the shaft. In this paper, a phenomenological theory is developed for predicting the performance of the transducer. The theory can be used to predict the magnetic field distribution of the transducer as a function of the physical properties of the magnetic coating, its residual strain, and the applied torque. It enables rapid parametric analysis of transducer performance, which is useful for the development and optimization of novel non-contact torque sensors.     

Spin transfer in magnetic tunnel junctions with hot electrons

Recent data on the bias dependence of the spin transfer effect in magnetic tunnel junctions have shown that torque remains intact at bias voltages for which the tunneling magnetoresistance has been strongly reduced. We show that the current induced excitations due to hot electrons, while reducing the magnetoresistance, enhance both the charge current and the spin transfer in magnetic tunnel junctions in such a manner that the ratio of the torque to the charge current does not significantly change.     

Thermopower, figure of merit and spin-transfer torque induced by the temperature gradient in planar tunnel junctions

The thermopower, charge and thermal conductance, and figure of merit as well as the spin-transfer torque generated by the temperature gradient in the planar tunnel junction consisting of ferromagnetic layers and the nonmagnetic tunnel barrier are investigated in the free-electron-like spin-polarized one-band model. In particular, the influence of the parameters of the junction as well as the influence of the relative orientation of magnetic moments on the studied phenomena are investigated. The thermopower can be related to the voltage drop generated by the temperature difference between electrodes under the condition that the charge current vanishes. It depends on the magnetic configuration of the junction. In junctions with high barriers the thermopower is maximal in the antiparallel configuration and it can be enhanced in junctions with strong spin-splitting of the electron bands. The component of the torque studied in the present paper is oriented in the plane formed by magnetic moments and it appears in the absence of the bias voltage. Its magnitude is insensitive to the sign of the temperature difference in contrast to the bias-induced in-plane torque which strongly depends on the polarization of the bias. The studied torque is usually smaller than the torque generated by the bias: however, it can be significant in junctions with low barriers.     

The determination of magnetic anisotropy constants from torque curves

The procedures by which magnetic anisotropy constants are evaluated from torque curves are examined with reference to some calculated torque curves for an ideal uniaxial crystal. The results are compared with some torque measurements on a crystal of cobalt.     

Dynamics of magnetization in ferromagnet with spin-transfer torque

We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out-of-plane precession, and bistable states can be realized. Th