Reaction pathway and phase transitions in Al–Ti–Si system during differential thermal analysis

The present paper mainly studied the phase formation and reaction pathway of the Al–Ti–Si system in detail by thermal analysis combined with XRD and SEM observations. The phase formation sequence in Al–Ti–Si system from starting mixtures to final products with increasing temperature can be described as following: Al_(l) + Ti_(s) + Si_(s) → (Al–Si)_(l) + Ti_(s) + Si_(s) → Ti(Al,Si)_3(s) + Si_(s)Ti₅(Si,Al)₃ + Al_(l). More importantly, the solubility of Si in Ti(Al,Si)₃ decreased gradually while that of Al in Ti₅(Si,Al)₃ increased with temperature increasing, suggesting the transportation of Si atoms from intermediate aluminides Ti(Al,Si)₃ to final stable silicides Ti₅(Si,Al)₃ and hence further confirming the formation of Ti₅(Si,Al)₃ at the expense of Ti(Al,Si)₃.     

重构多信道光纤光栅的改进离散层析算法

对重构多信道光纤光栅的离散层析算法进行了优化.在各信道加入相移的基础上,运用非线性最小二乘法对耦合系数进行高斯曲线拟合,降低了折射率调制深度的最大值且可以将剧烈变化的折射率调制深度平滑化.仿真表明,较之改进前的折射率调制最大值(0.001 3),利用新算法在折射率调制最大值为0.000 5时成功设计了一个8信道光纤光栅...     

芴二聚体三重激发态能量转移的理论研究

利用电子结构计算和电子转移速率理论,研究了芴二聚体的三重激发态能量转移过程. 应用限制性密度泛函理论构造得到非绝热态后,计算了控制能量转移的两个重要参数{电子耦合强度和重组能. 电子耦合强度的波动利用电子动力学模拟计算. 通过对上述参数相关函数的计算,成功得到了体系哈密顿量的对角元和非对角元波动,并应用微扰理论和波包扩散方法得到了能量转移速率. 结果表明,静态和动态的波动都明显地增加了能量转移速率,但是动态波动导致的速度增加却小于静态波动.     

Capacity for non-Kolmogorov turbulent optical links with beam wander and pointing errors

The performance of optical wireless communication links depends strongly on the atmospheric conditions and the parameters of the link such as the propagation distance, the operation wavelength, jitter variance, attenuation coefficient and effective beam spot radius at the receiver. The analytical expression for the evaluation of the average capacity of optical wireless communication systems is derived, using the gamma-gamma distribution in the non-Kolmogorov atmosphere turbulence. The impact of atmospheric attenuation, beam wander and pointing errors on the average of the optical wireless communication link is investigated. It is shown that the capacity has a fluctuation curve, when power law α increases, and the power law α of minimum point in fluctuation curve is bigger as the non-Kolmogorov turbulence strength is stronger.     

Mott transition in modulated lattices and parent insulator of (K,Tl)(y)Fe(x)Se(2) superconductors

The degree of electron correlations remains a central issue in the iron-based superconductors. The parent iron pnictides are antiferromagnetic, and their bad-metal behavior has been interpreted in terms of proximity to a Mott transition. We study such a transition in multiorbital models on modulated lattices containing an ordered pattern of iron vacancies, using a slave-rotor method. We show that the ordered vacancies lead to a band narrowing, which pushes the system to the Mott insulator side. This effect is proposed to underlie the insulating behavior observed in the parent compounds of the newly discovered (K,Tl)(y)Fe(x)Se(2) superconductors.     

Progress in improving thermodynamics and kinetics of new hydrogen storage materials

Hydrogen storage material has been much developed recently because of its potential for proton exchange membrane (PEM) fuel cell applications. A successful solid-state reversible storage material should meet the requirements of high storage capacity, suitable thermodynamic properties, and fast adsorption and desorption kinetics. Complex hydrides, including boron hydride and alanate, ammonia borane, metal organic frameworks (MOFs), covalent organic frameworks (COFs) and zeolitic imidazolate frameworks (ZIFs), are remarkable hydrogen storage materials because of their advantages of high energy density and safety. This feature article focuses mainly on the thermodynamics and kinetics of these hydrogen storage materials in the past few years.     

基于随机矩阵理论的城市人群移动行为分析

移动通信应用为人类移动规律的研究提供了独特的数据来源. 本文通过城市手机用户的分布数据,研究城市移动人群的整体动力学行为. 借助随机矩阵理论的方法,通过比较移动人群数据与随机数据在互相关矩阵谱分布上的差异,发现移动人群数据互相关矩阵的相关系数均值、最大本征值及其对应的本征向量明显偏离于随机互相关矩阵的分布,指出这种差异体现了城市移动人群的整体行为特性,且这种差异在不同时间段也会有所不同. 研究结果体现出相关系数的均值和最大本征值的波动趋势,并指出本征向量成员权重的时空模式与城市移动人群整体行为特征的波动过 关键词： 随机矩阵理论 移动人群 宏观行为     

Frabicating hydroxyapatite nanorods using a biomacromolecule template

Rod-like hydroxyapatite (HAp) nanoparticles with various aspect ratios are synthesized by means of low-temperature hydrothermal method in the presence of a N-[(2-hydroxy-3-trimethylammonium) propyl]chitosan chloride (HTCC) template. The synthesized HAps were examined by X-ray diffraction (XRD), Fourier transform infrared spectrophotometer (FTIR) and transmission electron microscopy (TEM) techniques. The results reveal that HAps are rod-like monocrystals, where the size and morphology can be tailored by varying synthesis conditions, such as pH, hydrothermal synthesis temperature and the ratio of PO₄³⁻ to the quaternary ammonium in HTCC. The mechanism of HTCC template on HAp nanorod preparation is analyzed.     

光纤激光阵列目标在回路自适应光学系统的数值模拟

研究了光纤激光阵列目标在回路自适应光学系统在实际大气环境中的传输.从光纤激光阵列、激光在大气中的传输、目标和优化算法四个方面,建立了光纤激光阵列目标在回路自适应光学系统的理论模型.在不同强度大气湍流下,对系统补偿大气湍流影响的效果进行了研究,并对系统控制参数优化进行了简单探讨.结果表明,目标在回路闭环控制结构能够有效补...     

半线性椭圆问题Petrov-Galerkin逼近及亏量迭代

本文考虑了二阶半线性椭圆问题的Petrov-Galerkin逼近格式,用双二次多项式空间作为形函数空间,用双线性多项式空间作为试探函数空间,证明了此逼近格式与标准的二次有限元逼近格式有同样的收敛阶.并且根据插值算子的逼近性质,进一步证明了半线性有限元解的亏量迭代序列收敛到Petrov-Galerkin解.