聚合物介电弛豫的温度特性

运用极限的概率模型和Ngai的耦合概念,导出了聚合物介电弛豫的KohlrauschWilliamsWatts(KWW)方程(t)=exp[-(tτ)β],证明了弛豫的能量势垒为Ngai的活化能量E.由β的温度关系推出了适用于聚合物的WilliamsLandelFerry方程和过冷液体的VogelTammannFulcher方程,特别是提出了由聚合物的β(T)可导出弛豫时间的温度函数.认为KWW行为由单个衰减单元产生,幂律行为由局部区域内多个衰减单元的协同衰减造成.将活化能量E引入热刺激电流公式,得到了可通过改变升温速率测量β(T)的公式. 关键词： 介电弛豫 聚合物 极限概率模型 KWW方程     

有矩形脉冲内热源的平板中非傅里叶导热研究

 对矩形激光短脉冲能量以内热源形式在有限厚绝热平板内释放所导致的非傅里叶导热过程进行了理论研究，利用格林函数与有限积分变换方法求得了绝热平板内温度分布的解析解,分析了平板内热波传播与反射行为以及温度场的特征。研究结果表明，温度波动频率取决于平板厚度和材料的热弛豫时间，而其幅值则与内热源释放区域的大小和脉冲宽度的长短有关。     

Evolution of microstructure and dielectric properties of (LiCe)-doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

Aurivillius type (NaBi)_0.5?x(LiCe)_xBi₂Nb₂O₉ ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce⁴⁺ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb⁵⁺ ions by the Ce⁴⁺ ions.     

晶界滞弹性弛豫理论的现代进展

上世纪中期,人们通过扭摆试验测量内耗,发现晶界滞弹性弛豫峰．后来尽管很多学者提出了各种理论模型,但晶界滞弹性弛豫的微观机理仍然是不清楚的．最近,Xu根据弹性应力引起晶界溶质偏聚或贫化实验结果,提出了晶界滞弹性弛豫的微观机理是晶界吸收或发射空位,建立了晶界滞弹性弛豫的平衡方程和动力学方程,解析地表述了晶界滞弹性弛豫过程,并成功地阐明了普遍存在于金属中的中温脆性峰温度移动现象．本文将综述晶界滞弹性弛豫理论的这一现代发展．     

On the two-dimensional stochastic Ising model in the phase coexistence region near the critical point

We consider the two-dimensional stochastic Ising model in finite square with free boundary conditions, at inverse temperature >₀ and zero external field. Using duality and recent results of Ioffe on the Wulff construction close to the critical temperature, we extend some of the results obtained by Martinelli in the low-temperature regime to any temperature below the critical one. In particular we show that the gap in the spectrum of the generator of the dynamics goes to zero in the thermodynamic limit as an exponential of the side length of , with a rate constant determined by the surface tension along one of the coordinate axes. We also extend to the same range of temperatures the result due to Shlosman on the equilibrium large deviations of the magnetization with free boundary conditions.     

取代基对卟啉三阶光学非线性及弛豫过程的影响

研究了取代基对卟啉三阶光学非线性和激发态弛豫过程的影响，发现在同一取代位置，推电子基团取代使得卟啉三阶光学非线性极化纱数Ｘ值相对影响，而吸电子基团取代使得卟啉Ｘ值相对减少，对同一取代基在不同取代装置，发现推电子基团在邻位取代的Ｘ值大于其在对位取代卟啉的Ｘ值，而吸电子基团在邻位取代的Ｘ值小于其在对位取代卟啉的Ｘ值，另外，还发现推电子基团取代的卟啉弛豫过程比吸电子基团取代的卟啉弛豫过程快７倍。     

Minimalist landscape model of glass relaxation

The relaxation behavior of glass is of great scientific and technological importance. However, prediction of glass relaxation behavior using direct first principles techniques is currently infeasible for realistic laboratory time scales. The enthalpy landscape approach has proven to be successful in overcoming this time scale constraint and providing insights into the fundamental physics governing glass transition and relaxation behavior. However, it is still too computationally intensive to calculate representative enthalpy landscapes for multicomponent glasses of industrial interest. It is thus interesting to consider a simplified enthalpy landscape that captures the essential features of glass relaxation and can be solved analytically. Here, we present the analytical solution for such a “minimalist landscape” model that is complicated enough to capture both primary (α$\alpha$) and secondary (β$\beta$) relaxation processes, yet simple enough to offer a closed-form solution. Using this minimalist landscape, we perform model calculations to illustrate the relative impact of activation barriers and entropy on glass relaxation behavior. The results of our model show that α$\alpha$ and β$\beta$ relaxation processes are largely decoupled, in agreement with recently published experimental results.     

Spin relaxation in nanowires by hyperfine coupling

Hyperfine interactions establish limits on spin dynamics and relaxation rates in ensembles of semiconductor quantum dots. It is the confinement of electrons which determines nonzero hyperfine coupling and leads to the spin relaxation. As a result, in nanowires one would expect the vanishing of this effect due to extended electron states. However, even for relatively clean wires, disorder plays a crucial role and makes electron localization sufficient to cause spin relaxation on the time scale of the order of 10 ns. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Response of thermal source in a transversely isotropic thermoelastic half-space with mass diffusion by finite element method

The two-dimensional problem of generalized thermoelastic diffusion material with thermal and diffusion relaxation times is investigated in the context of Lord-Shulman theory. As an application of the problem, a particular type of thermal source is considered and the problem is solved numerically by using a finite element method. The components of displacement, stress, temperature distribution, chemical potential, and mass concentration are obtained. The resulting quantities are depicted graphically for a special model. Appreciable effect of relaxation times is observed on various resulting quantities.     

气体声弛豫过程中有效比热容与弛豫时间的分解对应关系

声在多原子分子气体中传播所引起的弛豫过程是探索气体特性的重要方面. 本文通过研究气体声弛豫过程中振动自由度与平动自由度(V-T)以及振动自由度之间(V-V)的分子能量转移模型, 给出了有效比热容与弛豫时间的分解对应关系及其通用获得方法. 该分解模型与现有的声弛豫模型相比, 反映了分解后的V-T 和V-V弛豫过程中振动比热容与弛豫时间的对应关系, 并发现了较高能级是引起对应声弛豫过程的决定因素. 将基于该分解模型获得的气体声弛豫衰减谱经碰撞直径微调改进后, 比现有理论更接近实验数据, 其结果证明了该分解对应关系的正确性和合理性.