依据扬声器的力学性质拓展其低频响应的电路原理初探

本文阐述了在低频段闭箱上扬声器轴向远场声压频平坦时，分别作用于扬声器阻尼，质量和弹性三元件上的力，以及这三个力与频率的关系以及这三个力间的相位关系，根据这些关系，提出了一种处理声频信号电压的电路原理，该电路将声频信号电压处理为分别上述作用于三元件上的力相对应的三个信号电压，这三信号电压相加后，再馈于扬声器，可拓展其低频响应。     

二维Bloch电子在电场和磁场作用下输运的突变现象及非线性理论分析

磁场作用下二维Bloch电子，在非极低温情况下，电子Bloch能带的磁致裂隙对电子运动的影响将不重要，这时在准经典近似下分析霍耳漂移速率．通过数值求解，得到不同磁感应强度下波矢空间的稳定唯一周期解或稳定焦点不动解，并通过大量数值计算找出了参数空间中周期解与不动解的参数划分；进一步给出了霍耳漂移速率随磁感应强度变化过程中的突变现象．数值解的性质与Poincaré-Bendixson定理相一致 关键词：     

非线性k－ε模型的力学实质探讨

本文运用非线性连续介质力学的变形与本构理论及湍流建模准则作为依据，对非线性ｋ－ε模型的Ｒｅｙｎｏｌｄｓ应力计算表达式进行详尽的分析与探讨，得出针对本构关系而涉及二阶变形率及其Ｏｌｄｒｏｙｄ导数的非线性项是改善涡粘模型又反映脉动结构的各向异性的有效途径，建立各向异性模型应该采用客观物理量，现实性的考虑可以保证附加应力无迹来实现。     

等离子体在高频调制场作用下形成自生磁场的机制

研究了等离子体在高频调制场作用下,形成自生磁场的机制.通过求解双时标双流体方程,可以得到一组相互耦合的非线性方程。这组方程可以用来描述自生磁场的形成和演化.数值计算的结果显示,在高频调制场作用下,可以有自生磁场形成.计算得到的磁场强度和特征长度,与太阳日冕内的观测值符合得很好.随着时间的增加,自生磁场可以产生塌缩现象,导致磁场强度在很小的范围内有很大的值. 关键词： 自生磁场 双流体方程 高频调制场     

楔环连接结构非线性力学行为的实验和有限元数值模拟

楔环连接用于连接两个简体，在一些武器结构上已实际应用。研究和认识楔环连接结构的静、动力学行为，不仅有助于提高人们对该种结构的设计水平，也可以加强人们对诸如此类复杂结构中各种力学规律的认识，促进学科发展。     

超强激光功率密度对等离子体中自生磁场和电子热传导的影响

应用多光子非线性康普顿散射模型、3维粒子模拟模型和数值计算方法,研究了超强激光与等离子体作用中自生磁场产生和电子热传导过程,提出了将非线性康普顿散射光作为改变等离子体自生磁场和电子热传导的新机制,给出了自生磁场最大饱和值和超热电子热传导的修正方程和数值计算结果。研究发现在时间为100~160范围内,自生磁场能量随入射激光功率密度增大而迅速增大,之后处于较高饱和阶段。增大的初始时刻较散射前提前了20,增大阶段的时间延长了30,饱和阶段增幅为40。入射激光功率密度为1019~1020W/cm2时,自生磁场强度最大模拟值为1.47104~3.75104T,单电子能谱峰值出现在3.3MeV和6.6MeV附近,能谱曲线在4~15 MeV和11~14.3MeV范围迅速衰减,在6.7MeV和13.2MeV以上时,超热电子有效温度为2.6MeV和4.5MeV,比无散射的理论值和拟合值均有一定增大。随入射激光强度增大,热流随激光脉冲一起向等离子体内流动的时间缩短,自生磁场限制热流的时间延长。并对所得结果给出了初步物理解释。     

超强激光功率密度对等离子体中自生磁场和电子热传导的影响

应用多光子非线性康普顿散射模型、3维粒子模拟模型和数值计算方法,研究了超强激光与等离子体作用中自生磁场产生和电子热传导过程,提出了将非线性康普顿散射光作为改变等离子体自生磁场和电子热传导的新机制,给出了自生磁场最大饱和值和超热电子热传导的修正方程和数值计算结果。研究发现在时间为100~160范围内,自生磁场能量随入射激光功率密度增大而迅速增大,之后处于较高饱和阶段。增大的初始时刻较散射前提前了20,增大阶段的时间延长了30,饱和阶段增幅为40。入射激光功率密度为1019~1020W/cm2时,自生磁场强度最大模拟值为1.47104~3.75104T,单电子能谱峰值出现在3.3MeV和6.6MeV附近,能谱曲线在4~15 MeV和11~14.3MeV范围迅速衰减,在6.7MeV和13.2MeV以上时,超热电子有效温度为2.6MeV和4.5MeV,比无散射的理论值和拟合值均有一定增大。随入射激光强度增大,热流随激光脉冲一起向等离子体内流动的时间缩短,自生磁场限制热流的时间延长。并对所得结果给出了初步物理解释。     

基础油在热处理、超声和磁场作用下的太赫兹频段分子动力学

利用太赫兹时域光谱技术研究了基础油在热处理、超声和磁场作用下的动力学过程及相互作用机制.由于超声处理过程中声空化作用引起高温高压,而样品在热处理中的作用能量较低,基础油在超声处理后的折射率变化大于其在热处理和磁场作用下的变化.样品在1.7 THz和2.3 THz处有较明显的吸收峰,该吸收来源为分子间的相互作用,以这两处...     

偏振模色散和非线性效应对光纤传输特性的综合影响

本文采用变分法,研究多色色散、偏振模色散(PMD)以及非线性效应对单模光纤中光脉冲传输的综合影响.模拟分析结果表明,非线性对偏振模色散具有一定的抑制作用;但它们的综合作用所导致的脉冲展宽比PMD或非线性单独作用时要大.     

Controlling self-Kerr nonlinearity with an external magnetic field in a degenerate two-level inhomogeneously broadened medium

The magnitude and sign of self-Kerr nonlinear coefficient in a degenerate two-level inhomogeneously broadened medium are simply controlled by an external magnetic field. By changing the external magnetic field we can switch a negative peak of Kerr nonlinear coefficient into a positive peak and vice versa, and transform a zero value of Kerr nonlinear coefficient into a positive or negative peak in resonant region. Such a controllable Kerr nonlinear coefficient can be used to manipulate the working characteristics of photonic devices such as optical switches and bistable elements.     

磁约束等离子体推进器磁体系统的电磁力和机械应力分析

根据磁约束等离子体推进器磁体系统的设计参数,通过ANSYS有限元分析软件在电磁-结构耦合场方面的计算,得到磁体系统的轴向电磁力和机械应力的分布。计算超导磁体在通电情况下,磁体中平面上所有节点所受的轴向电磁压缩力以及磁体间的相互作用力;计算出磁体外层用不锈钢钢丝加固前后机械应力分布情况的变化。     

Effects of excessive grain growth on the magnetic and mechanical properties of hot-deformed NdFeB magnets

The magnetic and mechanical properties of rare-earth magnets hot-deformed at temperature range 750-950 °C have been investigated. The grains tended to grow excessively from dozens of nanometers to several microns at the temperatures above 850 °C. The alignment of grains was disrupted by the hot deformation at the high temperatures. The Nd-rich phase was extruded at the temperatures which are higher than 850 °C. The Nd-rich phase extrusion resulted in the reduction of density by 1% and the reduction of remanence from 1.42 to 0.72 T. The reduction of grain boundaries caused by flat platelet-shaped grains changing to spherical grains and the weak binding strength among large grains of Nd₂Fe₁₄B phase may be the main reasons for the low mechanical strength of hot-deformed magnets.     

Synthesis of copper-nickel nanoparticles prepared by mechanical milling for use in magnetic hyperthermia

Mechanical alloying of a mixture of copper and nickel powders has been applied for the preparation of copper-nickel alloy particles in the nanometer range. The particles were designed to be used for controlled magnetic hyperthermia applications. The milling conditions were optimized using the desired alloy composition. Utilizing a ball-to-powder mass ratio of 20, we could obtain a nanocrystalline Cu_27.5Ni_72.5 (at%) alloy with a crystallite size of around 10 nm and a Curie temperature of 45 °C.Thermal demagnetization in the vicinity of the Curie temperature of the nanoparticles was determined by thermomagnetic measurements using an adapted TGA-SDTA apparatus. The size and morphology of the particles were determined by XRD measurements and TEM analyses. The magnetic properties were also examined with a VSM. The magnetic heating effects were measured for the powdered material.     

The similarity of interactions between （3＋1）D spatiotemporal optical solitons in both the dispersive medium with cubic-quintic nonlinearity and the saturable medium

By making use of the split-step Fourier method, this paper numerically simulates dynamical behaviors, including repulsion, fusion, scattering and spiraling of colliding (3+1)D spatiotemporal solitons in both the dispersive medium with cubic-quintic and the saturable medium. Careful comparison of the colliding behaviors in these two media is presented. Although the origin of the nonlinearities is different in these two media, the obtained results show that the dynamical behaviors are very similar. This presents additional evidence to support the supposition of universality of interactions between solitons.     

High permeability and low power loss of Ti and Zn substitution lithium ferrite in high frequency range

The effect of Zn and Ti on the magnetic, power loss and structural properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in step of 0.05)+0.5 wt% Bi₂O_3, prepared by standard ceramic technique, has been investigated. Complex permeability (μ*=μ′−jμ″) has been analyzed at room temperature in frequency range from 1 to 10³ MHz. It was found an enhancement in permeability with Ti and Zn concentration in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ and exhibits the maximum value 106 for x=0.20 sample. Complex permeability of these ferrites exhibits stable frequency response up to 7 MHz beyond which the real part decreases sharply and imaginary part increases to have a peak at the relaxation frequency. Power loss measurements have been carried out in induction condition (B=10 mT) in frequency range of 50 kHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti and Zn in lithium ferrite.     

低损耗宽带近零色散高非线性光子晶体光纤设计

提出了一种兼具低损耗、宽带近零色散和高非线性的光子晶体光纤结构,该结构光纤包层空气孔直径从纤芯向外层方向渐进增加;应用多极法,通过改变包层空气孔间距Λ、各层空气孔直径和空气孔层数N_r,对光子晶体光纤色散、损耗和非线性特性进行分析,获得了各特性随包层结构参数变化的规律,并最终设计出最佳结构参数。计算结果表明,该结构光纤存在3个零色散点,在1.25～1.55 μm较宽的波长范围内,色散值波动小于0.27 ps·nm⁻¹·km⁻¹,色散斜率小于0.008 ps·km⁻¹·nm⁻²,1.55 μm波长处损耗为0.021 dB/km,在常用的飞秒激光泵浦波长0.8,1.06,1.55 μm处非线性系数分别达到78.6,60.4,38.2 W⁻¹·km⁻¹。     

Effect of hot deformation temperature on the magnetic and mechanical properties of Nd-Fe-B magnets prepared by spark plasma sintering

The magnetic and mechanical properties of Nd-Fe-B magnets at different hot deformation temperatures have been investigated. The results showed that the optimum magnetic and mechanical properties and the highest crystallographic alignment of Nd-Fe-B magnets were obtained at 700 °C, and the possible reasons were analyzed. The microstructures show that abnormal grain growth is not observed at 650 °C; there exist many small spherical grains, and these small grains do not align during die upsetting. The average size of the grains and the volume fraction of coarse grains increase with increase in deformation temperature. The coarse grains do not align during die upsetting, and the non-alignment regions enlarge with increase in deformation temperature.     

Infrared thermography based defect detection in ferromagnetic specimens using a low frequency alternating magnetic field

A new active infrared thermography based technique is proposed for defect detection in ferromagnetic specimens using a low frequency alternating magnetic field induced heating. The test specimens (four mild steel specimens with artificial rectangular slots of 8.0, 5.0, 3.3 and 3.0 mm depths) are magnetized using a low frequency alternating magnetic field and by using an infrared camera, the surface temperature is remotely monitored in real time. An alternating magnetic field induces an eddy current in the specimen which increases the specimen temperature due to the Joule’s heating. The experimental results show a thermal contrast in the defective region that decays exponentially with the defect depth. The observed thermal contrast is attributed to the reduction in induction heating due to the leakage of magnetic flux caused by magnetic permeability gradient in the defective region. The proposed technique is suitable for rapid non-contact wide area inspection of ferromagnetic materials and offers several advantages over the conventional active thermography techniques like fast direct heating, no frequency optimization, no dependence on the surface absorption coefficient and penetration depth.     

Localization in the model of contacting media with specific nonlinearity and interface interaction

In this paper, we consider the new model of nonlinear contacting media based on nonlinear Schrodinger equation with point potential and term, which is depended stepwise on field amplitude. Such a model theoretically describes a change in properties of the boundary regions along the interface between a Kerr-type crystal with cubic nonlinearity and a nonlinear medium characterized by abruptly change in dielectric constant depending on field amplitude. The short-range local interaction between wave and interface is taken into account by point potential in nonlinear Schrodinger equation. We obtain two new types of localized states characterized by composite structure consisting of three parts of the field distributions. We find exact and approximate solutions of dispersion equations. We described new properties of the spectrum of localized states arising as a result of the interaction of the wave with the interface and the presence of threshold field of the switching between the medium constants. All results are obtained in an analytical form. The proposed theory can be used to describe the propagation features of intense light beams localized along media interfaces in nonlinear optics, and to describe Bose-Einstein condensates with cubic nonlinearity.