利用数字万用表实现放电法测电容

利用数字万用表自动定时记录数据的功能,提出了一种测量电容值的实验方法.     

用光纤光栅传感器研究压电陶瓷的特性

提出了一种利用光纤光栅传感器研究压电陶瓷特性的新方法.该方法采用非平衡Michelson扫描干涉仪对光纤光栅传感信号进行相位解调,通过观测波长漂移引起的相移,从而获得压电陶瓷的位移量与所加电压间的关系.实验分析了迟滞特性和蠕变现象,得到了压电陶瓷的电压-位移特性曲线以及蠕变特性曲线.实验表明,光源功率的波动对压电陶瓷迟滞特性不能造成影响且压电陶瓷的蠕变特性与电压方向无关.     

基于压电陶瓷迟滞特性模型的原子力显微镜仿真平台研究

将基于双二次拉格朗日插值方法的压电陶瓷迟滞非线性Preisach模型,加到原子力显微镜(AFM)仿真平台中,实现在任意加压情况下由于迟滞效应所产生的图像畸变的仿真,更准确地反映原子力显微镜的扫描结果,使得学生在仿真实验中能更好地掌握AFM实验的真实情况.为了校正样品图像的畸变,提出搜索求逆算法,并利用此算法对Preisach模型进行精确求逆,通过改变输入电压抵消了压电陶瓷迟滞效应带来的非线性特性.仿真结果表明,该方法有效地校正了样品图像的畸变.     

应用于高速转子系统的金属橡胶阻尼环动力特性分析

针对金属橡胶构件的非线性特性及结构不同时弹性阻尼力学性能不同的特点, 利用实验和理论相结合的方法建立了金属橡胶构件迟滞回线边界变形过程力学模型, 推导了不同相对密度金属橡胶构件非线性迟滞恢复力表达式. 分析了简谐激励载荷作用下金属橡胶阻尼环动力学特性, 对该阻尼环进行了实验研究, 研究了存在预变形情况下阻尼环的弹性阻尼性能, 实验和理论分析结果基本一致, 为该种阻尼环的实际应用奠定了理论基础. 关键词： 金属橡胶构件 力学模型 非线性迟滞恢复力     

金属橡胶迟滞特性本构模型研究

金属橡胶作为一种新型阻尼材料, 其原材料及加工工艺具有一定特殊性. 基于材料的细观结构特征, 选取了金属丝螺旋卷作为金属橡胶的基本微元体结构, 并以圆柱压缩螺旋弹簧理论为基础, 分别建立了横向和纵向排列微元体结构的刚度. 鉴于库仑摩擦模型, 分别建立三种接触状态螺旋卷接触对的力学模型. 考虑整个加工工艺流程的特点, 分析了不同接触状态数目变化规律, 建立了金属橡胶迟滞特性本构模型. 从理论上解释了金属橡胶迟滞特性的特点, 以及刚度和阻尼非线性的产生机理. 最后, 通过对比不同相对密度金属橡胶试件的理论和试验结果, 验证了理论模型的适用性. 本模型从螺旋卷微元体结构上描述了金属橡胶迟滞特性, 为工程上预测和分析金属橡胶的刚度、阻尼特性和设计金属橡胶产品提供了有效的理论基础.     

基于迟滞非线性补偿系统的光学元件形貌检测

为了减少相移干涉仪中压电陶瓷致动器进行相移时,其迟滞非线性对相移算法中的相位计算带来的误差,设计了一套压电陶瓷致动器的控制系统.利用高精度电阻应变传感器和基于锁相放大原理的信号调理电路检测压电陶瓷致动器位移,建立多项式数学模型描述迟滞非线性,然后提出了一种前馈开环控制方法补偿其迟滞非线性.最后,基于所提出的方案对压电陶瓷致动器进行了期望轨迹的跟踪控制实验,同时将补偿控制系统与干涉仪相结合检测光学元件表面形貌.实验结果表明:补偿后,压电陶瓷致动器的跟踪误差在-0.156μm与+0.078μm之间,迟滞非线性度由10.4%降到2.4%,且干涉仪所测得的光学元件表面面形起伏高度均方根和峰谷分别改变了0.795nm和3.937nm.该系统对于高精度的光学元件形貌检测具有重要的意义.     

神经元网络螺旋波诱发机理研究

实验研究发现大脑皮层电活动和信号传播有类似螺旋波的特征.本文利用包含离子通道效应的Hodgkin-Huxley神经元构造规则网络来研究螺旋波的形成机理,利用缺陷阻挡行波的方法在神经元网络中诱导到不同周期的螺旋波,分析了螺旋波产生条件和耦合强度对螺旋波的影响.同时,对脑皮层中螺旋波形成的机理进行了讨论.     

小通道气液两相流电容测量方法研究

本文设计了一套用于小通道气液两相流的电容测量系统,并对内径为1.6 mm、2.5 mm和3.6 mm的玻璃管气液两相流进行了实验研究.文中首先对电容方法在小通道下的应用做了探索性尝试,设计了用于小通道气液两相流的电容传感器;然后利用所设计的电容传感器对小通道气液两相流弹状流电容动态数据进行采集、处理和分析;最后利用相关原理对气弹速度的测量进行了研究.研究结果表明所提出的电容方法可用于小通道气液两相流的分析研究中,是一种有效的小通道气液两相流参数检测手段,并为小通道两相流检测的研究提供了一定的借鉴.     

用电容充电法测量普朗克常量

提出一种利用光电管产生的光电流给电容充电来准确测量光电管截止电压的方法,从而得到普朗克常量.实验中采用了6种颜色的LED器件做光源直接照射光电管上,并通过具有高输入阻抗的数据采集卡实时测量电容两端的电压.实验测得的普朗克常量值与公认值的误差小于3％.     

"电感和电容对交变电流的影响"演示实验的改进

"电感和电容对交变电流的影响"演示实验的操作难度大且现象不明显,为此介绍了2种演示该实验的方法,一是通过将电灯分别与电感(电容)和电阻串联对比进行实验来演示电感和电容对交变电流的影响;二是通过信号发生器和示波器来研究交流电对电感(电容)的影响.2种方法演示效果均较好.     

Realizing reliable logic and memory function with noise-assisted Schmitt trigger circuits

Schmitt trigger is a comparator circuit with hysteresis, implemented by applying positive feedback to a noninverting input. Recently, it has been verified that noise under certain condition can help nonlinear circuit to realize reliable logical stochastic resonance (LSR). In this letter, we demonstrate that, without any modifications, Schmitt trigger can operate flexibly both as logic operation and latch operation in an optimal noise range. In traditional Schmitt trigger, the hysteresis is designed for resisting noise. In the new design, the hysteresis tends to enhance the LSR effect in Schmitt trigger with the help of noise and helps the system to perform better at higher noise levels. Thus, our results extend the application scope and generality of the traditional Schmitt trigger.     

Asymmetric magnetization reversal behavior and noncollinear anisotropies in exchange-bias system

The effect of noncollinearity between unidirectional and uniaxial anisotropies on asymmetric magnetization reversal of ferromagnet/antiferromagnet (FM/AFM) bilayer has been investigated. The results show the emergence of noncollinear anisotropies comes from the competition among applied magnetic field, magnetic anisotropy and exchange coupling in FM/AFM interface. The noncollinearity can lead to the asymmetry of hysteresis loop of FM/AFM bilayer. However, when the magnetic field is applied along the uniaxial anisotropy axis of FM layer, the hysteresis loop of FM/AFM bilayer is always symmetry independence of the noncollinear angle. Our results indicate that the asymmetry not only originates from the noncollinearity but also depends on the applied magnetic field orientation. Moreover, the asymmetry of hysteresis loop is always along with the appearance of unequivalence for magnetization reversal of FM/AFM bilayer, and there is a periodicity of π with orientation of applied field for its periodicity independence of the angle of the noncollinearity between the uniaxial and unidirectional anisotropies. The results can help us to open additional avenues to tailor the future advance magnetic device.     

Optical bistability in GaInAsP/InP coupled-circular resonator microlasers

Optical bistability is realized in GaInAsP/InP coupled-circular resonator microlasers, which are fabricated by planar technology. For a coupled-circular resonator microlaser with the radius of 20?μm and a 2?μm-wide bus waveguide, hysteresis loops are observed for the output power coupling into an optical fiber versus the cw injection current at room temperature. The laser output spectra of the upper and lower states of the hysteresis loop indicate that the bistability is related to mode competitions. The optical bistability can be explained as the mode competition between the symmetry and antisymmetry coupled modes relative to the bus waveguide.     

Susceptibility and Inverted Hysteresis Loop of Prussian Blue Analogs with Orthorhombic Structure

The magnetic susceptibility of ternary metal Prussian blue analogues with orthorhombic structure is studied using Ising model. Within the frame work of effective-field theory with correlations, the roles of the mole fraction y, uniaxial magnetic anisotropy, transverse and longitudinal magnetic field are discussed in details. The temperature dependence of the magnetic susceptibility is also investigated. The interesting phenomenon of the inverted magnetic hysteresis loop has been found. The results can help to understand the experimental work of the molecule-based ferri-ferrimagnet.     

Susceptibility and Inverted Hysteresis Loop of Prussian Blue Analogs with Orthorhombic Structure

The magnetic susceptibility of ternary metal Prussian blue analogues with orthorhombic structure is studied using Ising model. Within the frame work of effective-field theory with correlations, the roles of the mole fraction y, uniaxial magnetic anisotropy, transverse and longitudinal magnetic field are discussed in details. The temperature dependence of the magnetic susceptibility is also investigated. The interesting phenomenon of the inverted magnetic hysteresis loop has been found. The results can help to understand the experimental work of the molecule-based ferriferrimagnet.     

Dynamical hysteresis and spatial synchronization in coupled non-identical chaotic oscillators

We identify a novel phenomenon in distinct (namely non-identical) coupled chaotic systems, which we term dynamical hysteresis. This behavior, which appears to be universal, is defined in terms of the system dynamics (quantified for example through the Lyapunov exponents), and arises from the presence of at least two coexisting stable attractors over a finite range of coupling, with a change of stability outside this range. Further characterization via mutual synchronization indices reveals that one attractor corresponds to spatially synchronized oscillators, while the other corresponds to desynchronized oscillators. Dynamical hysteresis may thus help to understand critical aspects of the dynamical behavior of complex biological systems, e.g. seizures in the epileptic brain can be viewed as transitions between different dynamical phases caused by time dependence in the brain’s internal coupling.     

铁磁材料磁化曲线的智能观测系统

利用单片机系统控制物理实验过程，智能地测绘起始磁化曲线和磁滞回线，从而使学生们看到完整的磁化过程，对铁磁物质的磁滞现象有个充分的认识。     

Vibrations of sessile drops

This study focuses on the effects of vertical vibrations on sessile drops deposited on hydrophobic substrates. At low amplitudes the contact line remains pinned because of contact angle hysteresis and only drop surface modes areobserved. Above a first threshold the contact line starts to move and exhibits a stick-slip behavior that presents some analogies with the solid friction on amechanical oscillator. At larger amplitudes, non-axisymmetric contour modes show up (modes m=2, 3...). They can be interpreted as a coupling between surface modes and contact line motion. These subharmonic modes are welldescribed within the framework of parametric oscillators. We also discuss here why vibrations can help to measure equilibrium contact angle.     

Bistable surface anchoring and hysteresis of pitch jumps in a planar cholesteric liquid crystal

The relationship between bistable surface anchoring and the pitch jump process is examined for a planar cholesteric liquid crystal. Introducing a high-order, azimuthal surface anchoring potential into a simple model to describe a cholesteric, we derive an expression for the director twist as the natural pitch of the liquid crystal is allowed to vary. Writing the energy in terms of the surface twist, we are able to determine the twists which minimize the total energy of the system. We demonstrate how a pitch jump is related to an energy exchange from one branch of metastable states to another. We then discuss how the co-existence of energy minima and their associated solution branches may help explain the thermal hysteresis observed experimentally in cholesterics in the neighbourhood of a pitch jump. The presence of a higher-order surface energy term can expand the range of anchoring strengths in which pitch jumps are possible. We also investigate the influence of bidirectional surface anchoring on the behaviour of the total energy. Intermediate quarter-turn pitch jumps can occur, depending on the relative strength of the high-order anchoring term, and these can have a significant effect on the system hysteresis.     

Thickness-dependent magnetic order and phase-transition dynamics in epitaxial Fe-rich FeRh thin films

The control of magnetic order and phase-transition dynamics by various means is a key towards low-power spintronics. Here, we report a control on magnetic order and phase-transition dynamics by tuning film thickness in epitaxial FeRh films. Reduction of film thicknesses from 200 nm to 5 nm results in an anti-ferromagnetic to ferromagnetic phase change, accompanied by a 0.55% lattice expansion for c-axis. The phase-transition dynamics is highly dependent on the film thickness, and involves the release and recovery of lattice strain that results in a lower transition temperature and larger thermal hysteresis in thinner films. The findings help to understand the origin of thermal hysteresis and phase-transition dynamics in ultra-thin FeRh films. Possible approaches to narrow down thermal hysteresis are proposed.