晶粒间界相对纳米Nd_2Fe_(14)B各向异性和矫顽力的影响

本文采用立方晶粒结构模型研究了晶粒间界相对纳米硬磁材料各向异性和矫顽力的影响.结果表明:晶粒间界相减弱了交换耦合作用.当晶粒尺寸D为定值时,随着晶粒间界相厚度d的增加,晶粒平均各向异性单调增加,而材料的有效各向异性Keff、矫顽力单调减小.我们计算的矫顽力随晶粒尺寸的变化与相关理论和实验结果基本一致.     

钢铁材料中形变诱导相变超细化机理研究

通过计算机编程建立奥氏体相中12[1 1 0]刃位错、奥氏体相中非形变区和形变区奥氏体/铁 素体相界模型.用实空间的连分数方法计算了非形变区和形变区奥氏体/铁素体相界界面能， 计算了碳、氮及微合金元素在完整晶体及位错区引起的环境敏感镶嵌能，进而讨论形变过程 中铁素体形核的难易程度，碳、氮及合金元素在位错区的偏聚及析出与铁素体细化的关系. 计算结果表明：α-Fe易于在高密度位错区（形变带、亚晶界、晶界）形核，在奥氏体形变 过程中，就会大大提高α-Fe形核率，细化铁素体晶粒；碳、氮和微合金元素易于单独或共 同 关键词： 奥氏体/铁素体相界 刃位错 形变 晶粒细化     

强多途环境下水听器阵列位置近场有源校正方法

针对水听器阵列近场强多途环境下的校正需求, 提出了一种高精度的多辅助源阵列位置校正方法.综合近场点源非平面波模型和泰勒近似原理, 构建了近场阵元位置二维误差模型, 进而获得信号特征向量与阵元位置误差的线性映射关系.推导并计算了校正模型的克拉美罗界(CRB).研究了多途对阵元位置校正的影响, 将多途干扰视为位置已知的相干源, 提出了多途补偿策略.理论及仿真结果表明, 近场多辅助源阵列位置校正方法具有较高的精度, 在低信噪比时接近CRB, 对于辅助源位置等误差具有一定的容忍度, 且适用于强多途环境.湖试验证了方法结论的正确性.     

Pb(Zr0.52Ti0.48)O3陶瓷畴界粘滞运动的介电损耗模拟

对不同频率下（１ —１０ ｋ Ｈｚ） Ｐｂ（ Ｚｒ０５２ Ｔｉ０４８） Ｏ３ 多晶陶瓷的介电性能的测量表明：在接近铁电相变温度 Ｔｃ 以下存在一介电损耗峰,该峰具有弛豫特征但不满足 Ａｒｒｈｅｎｉｕｓ 关系．这一损耗峰被认为是由于畴界与晶格、缺陷钉扎的互作用引起的．用畴界粘滞运动的动力学方程,考虑陶瓷样品中 Ｔｃ 离散分布的情况,模拟了该介电损耗峰在不同频率下的行为,得到了与实验数据一致的结果．并由拟合参数计算了畴界运动的粘滞系数和缺陷钉扎引起的回复力常量．     

铸造锌铝合金稀土变质机理的电子理论研究

根据分子动力学理论建立了液态锌铝合金ZA27的模型，结合计算机编程构造出了ZA27合金α 相与液相共存时的原子结构模型，利用递归方法计算了稀土固溶于晶粒内和富集于结晶前沿 时的电子结构.由此得出：稀土处于相界区比在晶内更稳定，从而解释了稀土在α相内溶解 度很小，结晶时富集于结晶前沿液体中的事实；稀土处于液态和晶态的结构能差相对于铝较 大解释了稀土在相界前的富集使α晶枝产生熔断、游离、增殖的观点.原子间的键级积分计 算也表明，稀土处于结晶前沿液体中与铝相比不容易结晶到晶体表面，起到阻碍晶粒长大， 细化晶粒的作用，这就从电子层次解释了稀土的变质机理. 关键词： 电子结构 液固相界原子结构模型 稀土变质机理     

非结构多面体二阶局部保界全局重映算法

提出一种三维非结构多面体二阶保界全局重映算法.在旧网格上选取模板利用最小二乘构造插值多项式,采用凸包算法计算多面体相交部分,最后使用局部保界修正技术修补重映后的越界量.多项数值实验表明这种格式同时具有高精度、高分辨率和高效率的特点.     

高温超导GdBa2Cu3O7-δ薄膜双晶晶界结特性研究

在晶界夹角为24°的YSZ人工双晶基片上,采用原位直流磁控溅射法制备了高温超导双晶GdBa₂Cu₃O_7-δ超导薄膜。采用光刻技术在晶界上刻出了尺寸5×5μm²的双晶晶界结。在77K下观测了结的直流I-V特性和在10GHz微波辐射下结的Shapiro台阶。这表明我们的人工双晶晶界结具有约瑟夫森弱连接行为。对结的特性进行了初步的理论分析和在实验基础上的数值模拟,模拟结果与RSJ理论符合较好,表明我们的双晶晶界结基本符合RSJ模型。     

参数失配的受迫振动系统有误差界的同步判据

基于李雅普诺夫直接法和Sylvester准则,推导出外激励参数失配的受迫振动系统达到有误差界的同步的几种代数判据. 根据代数不等式,求得同步误差界的估计值. 通过控制同步误差界估计值,可以把实际的同步误差界值控制到小于预先给定的同步精确度. Duffing-Van der Pol受迫振动系统作为数值算例进一步验证了该方法是有效的. 关键词： 受迫振动系统 参数失配 同步误差界 代数判据     

非对称倾侧亚晶界的晶体相场法研究

采用晶体相场法研究非对称倾侧亚晶界结构及其在应力作用下的微观运动机制.分别从温度、倾斜度角以及应力施加方向等方面对其结构及迁移过程进行分析和讨论.结果表明,非对称倾侧亚晶界由符号相同的一排刃型位错等距排列,部分出现由两个相互垂直排列的刃型位错构成的位错组;在应力作用下,非对称倾侧亚晶界迁移的微观机制包括位错的滑移和攀移、位错组分解、单个位错与位错组反应、单个位错分解以及位错湮灭;温度降低和倾斜度增大都会阻碍亚晶界的迁移过程;应力方向改变导致位错运动方向改变,从而改变晶界迁移形式.     

锯齿型石墨烯纳米带的能带研究

运用π电子紧束缚模型,具体研究了锯齿型石墨烯纳米带(ZGNRs)的边界结构对能带,特别是费米面附近的导带和价带电子的影响.计算了七种不同边界结构的ZGNRs的能带色散关系及费米面附近价带电子在原胞中各原子上的分布情况.计算结果表明:两边界都无悬挂原子的NN-ZGNRs,只有一边界有悬挂原子的DN-ZGNRs,两边界都有五边形环的SPP-ZGNRs和ASPP-ZGNRs为金属性.两边界都有悬挂原子的DD-ZGNRs,一边界为五边形环另一边界无悬挂原子的PN-ZGNRs和一边界为五边形环另一边界有悬挂原子的P 关键词： 锯齿型石墨烯纳米带 紧束缚模型 电子密度分布 缺陷结构     

Intrinsic stochasticity with many degrees of freedom

We study a simple model equation describing a system with an infinity of degrees of freedom which displays an intrinsically chaotic behavior. Some concepts of fully developed turbulence are discussed in relation to this model. We also develop an approach based on Lyapunov exponent measurements. Numerical results on the distribution of Lyapunov numbers and the power spectrum of the associated Lyapunov vectors are presented and briefly discussed.     

Reducing slab track vibration into bridge using elastic materials in high speed railway

In this paper, the problem of vibration transmission from slab track structures into bridge is studied by theoretical analysis. A vehicle-track-bridge coupling system dynamics model is established based on a multibody dynamics theory and a finite element method. The system model consists of vehicle model, track-bridge model and wheel/rail interaction model. The vehicle model is established based on the multibody dynamics theory, and the tack-bridge model is established by the finite element method. The vehicle model and track-bridge model are coupled through wheel/rail interaction model, and the track irregularities are included. The system dynamic responses are calculated, and the effectiveness of elastic materials in vibration reducing is discussed. The results demonstrate that elastic materials like slab mat layer inserted between slab track and bridge can reduce vibration transmitted from track into the bridge. Some suggestions for the design and application of slab mat are provided in the end of the paper.     

Phase diagrams of a transverse Ising nanowire

Phase diagrams of a cylindrical nanowire described by the transverse Ising model are investigated by the use of two theoretical frameworks, namely the mean field theory and the effective field theory with correlations. The phase diagram of the system is strongly affected by the surface situations. Some characteristic phenomena are found in the phase diagram, depending on the ratio of the physical parameters in the surface shell and the core.     

Properties of Hydrated Alkali Metals Aimed at the Ion Channel Selectivity

The hydration structure properties of different alkali metal ions with eight water molecules and potassium ions with different numbers of water molecules are studied using the mixed density functional theory, B3LYP, with 6-3110 basis set. The hydration structures are obtained from structure optimization and the optimum numbers of water molecules in the innermost hydration shell for the alkali metal ions are found. Some useful information about the ion channel selectivity is presented.     

Ground-state magnetic properties of the spin-2 transverse Ising model

The ground-state magnetic properties of the spin-2 transverse Ising model with a longitudinal crystal field are studied within the framework of mean-field theory (MFT) and effective-field theory (EFT), respectively. The phase diagrams and magnetization curves are examined in detail. It is found that the system exhibits a tricritical behavior in the ground-state phase diagrams. Some interesting phenomena have been found, especially the first-order phase transition from one ordered phase to the other ordered phase, which is due to the high spin. The spin correlation has important effect on the magnetic properties of the system. We also find that the ground-state phase diagrams of the spin-2 transverse Ising model are very different from those of the spin-3/2 transverse Ising model.     

A Cosmological Model with Negative Constant Deceleration Parameter in Brans-Dicke Theory

Bermann (1983) [Nuovo Cimento B, 74, 182] obtained a cosmological model with the help of special law of variation for Hubble's parameter that yields constant deceleration parameter models of the universe. Here, we present Bianchi-I model with negative constant deceleration parameter in Brans-Dicke (1961) [Phys. Rev., 124, 925] theory in the presence of perfect fluid source with disordered radiation. Some physical properties of the model are also discussed. PACS numbers: 98-90.     

分布式冷热电三联供系统的单耗分析模型研究

基于"单耗分析"理论,建立了针对燃料为天然气的分布式冷、热、电三联产系统的常见运行模式下的多热源、多冷源的燃料单耗模型和成本单耗模型.利用该模型进行了案例计算,结果清楚地表明了系统各个环节燃料附加单耗的分布.通过对计算结果的分析,得出了一些有益的结论.     

Rb原子磁光阱中囚禁原子数目与实验参数的依赖关系

研究表明，Rb原子磁光阱中所囚禁的原子数目对囚禁光的光强和失谐量，回泵光的强度以及磁场梯度有很大的依赖关系.用二能级系统模型对囚禁原子数目随囚禁光的光强和失谐量的变化关系进行了预估，理论预测的结果与实验结果定性符合.实验结果也展示了囚禁原子数目随回泵光的强度和磁场梯度的变化关系，要定量解释这些实验结果则需要更复杂的理论模型.通过囚禁原子数目对实验参数依赖关系的研究，得到特定的实验参数，来获得最大数目的冷原子. 关键词： 磁光阱 冷原子     

Some characteristic properties of initial susceptibility in a Ising nanotube

Initial susceptibility and magnetization of a cylindrical nanotube described by the Ising model are investigated by the use of the effective field theory with correlations (EFT), since the phase diagrams of the system have been examined in the previous work of Kaneyoshi (2010) [8] using the two theoretical frameworks of the mean field theory and the EFT. The effects of the two exchange couplings at the surface shell and in the core to the initial susceptibility are clarified. Some characteristic phenomena are found in the thermal variations, depending on the ratios of the physical parameters in the surface shell and the core. It is also discussed whether the Neel hyperbola in the paramagnetic region is valid for a nano-scaled ferrimagnetic system.