外延铁电薄膜相变温度的尺寸效应

考虑外延钙钛矿型铁电薄膜内的等效应力、表面晶格变化和表面电荷引起的退极化效应等机电耦合边界条件,利用铁电薄膜系统的动态金茨堡-朗道方程(DGL),系统分析和讨论了外延铁电薄膜相变温度与临界相变厚度的尺寸效应.结果表明,铁电薄膜相变温度与临界相变厚度完全依赖于各种与薄膜厚度相关的力电耦合边界条件.也给出了BaTiO₃外延铁电薄膜相变温度在各种边界条件下随厚度的变化,从结果看出,本文的分析与结论更符合实验数据. 关键词： 尺寸效应 外延铁电薄膜 相变温度 力电耦合边界     

用超声方法研究PSZT铁电陶瓷在高压下的相变

 用超声脉冲回波重合方法研究了具有垂直铁电（F），反铁电（AF）相界的PSZT三元系材料在高压下的相变。发现此种材料在较低压力下都有一级相变发生，并且是可逆相变。伴随着相变的发生，声速和声衰减都有较大的变化。本文对实验结果进行了初步的讨论。     

ABO3型钙钛矿的相变和晶格动力学研究

本文研究和评述了ＡＢＯ３型钙钛矿氧化物钛酸钡，钛酸铅，钛酸锶等的结构相变和晶格动力学。研究了它们的归变归属，相变序以及与相变特性有关的尺寸效应和界面效应，这有助于弄清铁电性起源。     

晶粒尺寸对Bi0.2Ca0.8MnO3电荷有序的影响

利用溶胶-凝胶法制备了平均晶粒尺寸在38—1500 nm的系列Bi_0.2Ca_0.8MnO₃多晶样品,研究了它们的结构、电输运性质和磁性.研究结果表明,随着晶粒尺寸的减小,电荷有序逐渐消失、最后被完全压制,导致低温下出现自旋玻璃态.利用马氏体相变图像和表面效应解释了相关现象. 关键词： 钙钛矿锰氧化物 电荷有序 马氏体相变 自旋玻璃     

具有形状记忆效应的反铁电材料的制备及其相变行为的研究

研究表明，铁电与反铁电材料在形状记忆方面与合金具有相似的性质，用变温Ｘ射线衍射来研究Ｐｂ０．９７Ｌａ０．０２（Ｚｒｏ０．６５Ｔｉ０．１０Ｓｎ０．２５）Ｏ３在升温过程中的相变并测得在相变的同时晶面间距ｄ有明显的跳变。还用相变潜热测量（ＤＳＣ）与电滞回线测量证实了在各个温区的相     

有电畴的铁电薄膜中的相变

本文用朗道自由能展开研究了有电畴的铁电薄膜的相变特性。畴壁的存在使自发极化和居里温度降低,使临界尺寸增大。随着温度升高,反转长度离开表面。随着厚度减小,膜将成为单畴。 关键词：     

哈斯勒合金Ni-Mn-Ga的马氏体相变和磁增强双向形状记忆效应

通过研究铁磁性金属间化合物Ni_2+xMn_1-xGa(x=-0.1,0,0.08,0.13,0.18,0.2)和Ni_2-xMn_1+x/2Ga_1+x/2(x=-0.1,0,0.04,0.06,0.1)两个系列多晶样品的交流磁化率随温度的变化行为,得到了化合物在不同组分下的马氏体相变温度TM和居里温度T_C.发现随着Ni成分的增加,前者的马氏体相变温度T_m增加,而居里温度T_C降低,后者的马氏体相变温度T_m和居里温度T_C均是先增大后减小.报道了T_m在室温附近的单晶样品Ni₅₂Mn₂₄Ga₂₄的磁场增强双向形状记忆效应.发现伴随着马氏体相变,样品在[001]方向可产生1.2%的收缩.如果在该方向施加1.2T的偏磁场可以使该应变值增大到4.0%.而垂直于[001]方向施加1.2T的偏磁场时,在[001]方向产生1.6%的膨胀.阐明了产生大应变的原因并非相界移动,而是单晶的杂散内应力小和外加磁场通过孪晶界移动使马氏体变体重组的共同结果. 关键词： 形状记忆效应 马氏体相变 2MnGa')" href="#">Ni₂MnGa     

三维动态Ising模型中的非平衡相变:三临界点的存在

用Monte Carlo方法模拟了三维动态Ising模型中的非平衡相变,用统计的观点研究了序参量的大小和分布以描述该相变过程.保持温度和外场频率不变,改变外场大小使之由小到大变化,序参量由非零值变成零值.在低温阶段,序参量呈非连续变化,为典型的非连续相变,在高温阶段,序参量呈连续变化,为典型的连续相变.本文确定了界定非平衡转变的相界,并进一步确定了相界上区分非连续连续相变的三临界点.外场频率ω减小时,三临界点温度T_TCP向高温部分移动,并满足T_TCP=1.33× 关键词： 动态相变 Ising模型 三临界点     

低熔点合金相变换热特性实验研究

本文针对熔点为70°的Bi-Cd-Pb-Sn低熔点合金的相变换热特性开展了实验研究,讨论了冷却水流量对冷却速率及相界面移动速率的影响。结果表明:低熔点合金在冷却过程中出现明显的相变带,相变潜热释放完后合金温度出现陡降;冷却水流量越大相界面的移动速率越快,当Q80 L·h~(-1)时流量对固液相界面的移动速率影响减小,相同流量下固液相界面的移动速率随热阻的增加逐渐减小。     

基于焓法的固-液相变格子Boltzmann模型

潜热储能系统中的相变材料固液相变问题是一个重要的多相流动问题.本文研究了在具有不同类型源项下的焓法格子Boltzmann相变模型在还原温度场分布上的特性.为了消除外力项对温度场的额外影响,本文对源项进行了修正,并通过求解单区域相变问题和自然对流相变问题,验证了由Chapman-Enskog展开得到的焓守恒方程中源项的影响.结果 表明,在单区域相变问题中,改进模型的温度分布更加准确.另外,在有相变的自然对流问题中,没有潜热附加项的改进模型的熔化过程比其他模型略慢,同一时刻的最大液相率与最小液相率之差小于0.01.     

Sharp interface tracking using the phase-field equation

A general interface tracking method based on the phase-field equation is presented. The zero phase-field contour is used to implicitly track the sharp interface on a fixed grid. The phase-field propagation equation is derived from an interface advection equation by expressing the interface normal and curvature in terms of a hyperbolic tangent phase-field profile across the interface. In addition to normal interface motion driven by a given interface speed or by interface curvature, interface advection by an arbitrary external velocity field is also considered. In the absence of curvature-driven interface motion, a previously developed counter term is used in the phase-field equation to cancel out such motion. Various modifications of the phase-field equation, including nonlinear preconditioning, are also investigated. The accuracy of the present method is demonstrated in several numerical examples for a variety of interface motions and shapes that include singularities, such as sharp corners and topology changes. Good convergence with respect to the grid spacing is obtained. Mass conservation is achieved without the use of separate re-initialization schemes or Lagrangian marker particles. Similarities with and differences to other interface tracking approaches are emphasized.     

Diffusive fluxes associated with interfacial defeet motion and interaction

The diffusional flux associated with the motion of interfacial defects is described by an equation expressed in terms of the topological parameters which characterise defects, namely their Burgers vectors and step heights, the defect velocity and the concentration of each atomic species in the two adjacent crystals. This expression demonstrates that glide/climb behaviour of grain boundary defects is analogous to motion of dislocations in single crystals; climb motion results if a component of b is perpendicular to the interface plane. However, the situation is more complex in the case of interphase interface defects, but the present approach, which considers the step and dislocation portions of defects separately, enables a straightforward analysis. Several examples are illustrated to show the various possibilities, such as climb motion even when b is parallel to the interface, and glide motion when b is not. The latter case arises in martensitic transformation where the existence of an invariant-plane-strain relation at the interface leads to equal and opposite fluxes to the step and dislocation portions of transformation defects so that overall the motion is diffusionless.Interfacial processes involve the motion and interaction of defects. The present analysis facilitates the consideration of diffusive fluxes associated with defect interaction since the step and dislocation portions can be treated independently. A general expression is derived for the total flux arising, and a particular case, the interaction of transformation dislocations with crystal dislocations which have reached the interface during lattice-invariant deformation in martensite formation, is considered.     

Front Propagation for Reaction–Diffusion Equations in Composite Structures

We consider asymptotic problems concerning the motion of interface separating the regions of large and small values of the solution of a reaction–diffusion equation in the media consisting of domains with different characteristics (composites). Under certain conditions, the motion can be described by the Huygens principle in the appropriate Finsler (e.g., Riemannian) metric. In general, the motion of the interface has, in a sense, non-local nature. In particular, the interface may move by jumps. We are mostly concerned with the nonlinear term that is of KPP type. The results are based on limit theorems for large deviations.     

Non-brownian microrheology of a fluid-gel interface

We use stroboscopic video microscopy to study the motion of a sheared fluid-gel interface. Mechanical noise plays a role analogous to temperature, but with a low-frequency breakdown of linear response consistent with an underlying instability. We relate the fast motion of the interface to the rheological properties of the gel, laying the foundation for a non-Brownian optical microrheology.     

Thermocapillary motion of a drop near a plane interface between liquids

The thermocapillary motion of a liquid drop immersed into another liquid near an infinite plane interface between two liquids is theoretically analyzed. The motion is considered under the conditions of a constant temperature gradient normal to the interface at infinity and small Reynolds and Peclet numbers. The problem is solved in bispherical coordinates. The analysis takes into consideration the thermal conductivity of the liquids and the thermocapillary motion of the liquids due to a nonuniform temperature distribution over the plane interface.     

运动界面上反射超声散斑空间运动的研究

在Kirchhoff 衍射理论的基础上，应用随机信号相关原理，推导了作刚体运动的界面上反射超声散斑在空间运动时，保持其复振幅相关的必要条件.由此得到超声散斑的空间运动公式.界面、超声散斑和超声接收探头之间的相对运动，导致界面孔径的改变.分析表明，在保持界面孔径相关的条件下，界面所允许的最大平移量和转角值，与声源位置、接收用聚焦探头的数值孔径、超声入射角以及观察角有关.应用数字相关技术和三维扫描信号采集系统，根据散斑场子集相关系数的单峰性质，对超声散斑空间运动公式进行了实验验证.实验结果表明，理论分析所得的 关键词： 超声散斑 相关原理 空间运动     

可变摆长的单摆运动的MATLAB仿真

文章对可变摆长的单摆运动进行了详细的理论分析和推导,并根据不同的摆长将运动分成八种情况。     

空气/水界面水分子的取向和运动

对四种不同的实验构型下空气／水界面自由O-H键在3700cm~(-1)的和频振动光谱的分析表明,水分子在空气／水界面的取向运动只可能是在平衡位置附近有限角度之内的受限转动。界面水分子的自由O-H键取向距界面法线约33°,而取向分布或运动的宽度不超过15°。这一图像显著地不同于Wei等人(Phys. Rev. Lett.86,4799(2001))只通过单一的SFG实验构型所得出结论,即：空气／水界面的水分子在超快的振动弛豫时间内在很大的角度范围内运动。     

Migration and shape of cells on different interfaces

Impacts of microenvironments on cell migration have been reported in various interaction modes. A rapid tumor metastasis occurs along topological interfaces in vivo, such as the interface between the blood vessels and nerves. In this work, we culture MDA-MB231 cells at dish-liquid, dish-hydrogel, and hydrogel-liquid interfaces, respectively, to study how these different interfaces influence cell dynamics and morphology. Our results show that the migration mode of cells changes from an amoeboid motion to a mesenchymal motion but their speed do not change obviously if the interface changes from hydrogel-liquid to dish-liquid. In contrast, the migration mode of cells at a dish-hydrogel interface maintains as a mesenchymal motion, whereas their speed increases significantly.     

Conserved dynamics and interface roughening in spontaneous imbibition: A phase field model

The propagation and roughening of a fluid-gas interface through a disordered medium in the case of capillary driven spontaneous imbibition is considered. The system is described by a conserved (model B) phase-field model, with the structure of the disordered medium appearing as a quenched random field . The flow of liquid into the medium is obtained by imposing a non-equilibrium boundary condition on the chemical potential, which reproduces Washburn's equation for the slowing down motion of the average interface position H. The interface is found to be superrough, with global roughness exponent , indicating anomalous scaling. The spatial extent of the roughness is determined by a length scale arising from the conservation law. The interface advances by avalanche motion, which causes temporal multiscaling and qualitatively reproduces the experimental results of Horv'ath and Stanley (Phys. Rev. E 52, 5166 (1995)) on the temporal scaling of the interface. Received 24 November 1999