波束域下利用角度散布特征抑制宽带混响

通过研究宽带信号的信源空间展宽特征,提出了一种宽带波束域的混响抑制方法。在有效观测角度范围内,进行密集的波束形成,将数据从阵元域转换至波束域,通过与蒙特卡洛积分得到的参考值比较,得到角度散布指数ADI。信混比越大,ADI越小。因此,设定合适的ADI阈值,去除高ADI值的成分,目标回波能够从混响背景下分离出来。该滤波器兼容于声呐现有的波束形成和信号检测流程,并且计算复杂度低。通过仿真分析了ADI与频率、带宽、信混比的关系。湖海试数据的处理结果表明了该方法能够抑制混响,并且ADI滤波器阈值选取具有容错性。     

Quantum phase transition and von Neumann entropy of quasiperiodic Hubbard chains

The half-filled Hubbard chains with the Fibonacci and Harper modulating site potentials are studied in a selfconsistent mean-field approximation. A new order parameter is introduced to describe a charge density order. We also calculate the von Neumann entropy of the ground state. The results show that the von Neumann entropy can identify a CDW/SDW （charge density wave/spin density wave） transition for quasiperiodic models.     

三个不同时间尺度的电耦合模型的组合簇放电

胰岛中间隙连接的胰腺β细胞的簇放电行为对胰岛素分泌起着重要的作用. 本文利用了最小的phantom 簇放电模型, 研究两个电耦合胰腺β细胞具有簇同步的组合簇放电, 其膜电位表现出一个长簇和几个短簇组成的放电簇集和振幅先减小后增大的小振幅阈下振荡的相互转迁. 在两个慢变量和快的膜电位的三维空间中, 分别考虑了中慢变量和慢慢变量作为分岔参数的多层次的快慢动力学分析, 研究这两个时间尺度不同的慢变量如何共同或单独地控制着这种组合簇放电的复杂动力学行为. 特别地, 探讨了耦合强度引起的组合簇放电的每个簇集中短簇个数变化的内在机理. 关键词： 电耦合 具有不同时间尺度的慢变量 组合簇放电 快慢动力学分析     

聚酰亚胺/铜纳米颗粒复合物的分子动力学模拟研究

通过分子动力学模拟对聚酰亚胺/铜纳米颗粒复合物的形态结构、 热力学性质、力学特性进行计算, 分析其随模拟温度和纳米颗粒尺寸的变化规律. 模拟结果表明, 聚酰亚胺/铜纳米颗粒复合物为各向同性的无定形态结构, 铜纳米颗粒与聚酰亚胺基体之间通过较强的范德华作用结合在一起使结构更加稳定, 铜纳米颗粒表面多个原子层呈现无定形状态, 在铜颗粒和聚酰亚胺基体之间形成界面层, 界面区域随颗粒尺寸和温度的增加分别减小和增加. 聚酰亚胺/铜纳米颗粒复合物的等容热容随着颗粒尺寸增大而明显增高, 随温度变化比聚酰亚胺体系更为缓慢, 在较低温度下较小颗粒尺寸复合物的热容比聚酰亚胺体系更低. 聚酰亚胺/铜纳米颗粒复合物的热压力系数随颗粒尺寸增加而显著增大, 比聚酰亚胺体系的热压力系数更小, 且随温度升高而减小的程度要小得多. 聚酰亚胺/铜纳米颗粒复合物的热力学性质表现出明显的尺度效应, 温度稳定性明显高于聚酰亚胺体系. 聚酰亚胺/铜纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量, 具有比聚酰亚胺体系更低的杨氏模量和泊松比, 随温度升高分别减小和增大, 与聚酰亚胺体系随温度的变化趋势相反, 且杨氏模量的温度稳定性显著提高, 同时泊松比随纳米颗粒尺寸增大而减小, 具有明显的尺度效应. 加入铜纳米颗粒形成复合物可获得与聚酰亚胺体系显著不同的力学新特性. 关键词： 分子动力学模拟 聚合物纳米复合物 聚酰亚胺 纳米颗粒     

A novel method to calibrate LiNbO_3-based polarization controllers

A fast and reliable method to calibrate LiNbO3-based polarization controllers （PCs） presented theoretically and experimentally. Particle swarm optimization （PSO） algorithm is used as an adaptive searching algorithm. Experimental results show that PSO algorithm is powerful in calibrating LiNbO3-based multistage PCs. Only less than one minute is spent for all stages of the PC to be calibrated thoroughly.     

Investigation of elastic moduli and constants of zinc-blende Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>Ga<Subscript>1-<Emphasis Type="Italic">y</Emphasis></Subscript>As alloy by statistical moment method

The elastic moduli and elastic constants of the ternary semiconductor alloy Al _y Ga_1-yAs at finite temperature have been investigated using the statistical moment method. The Young, shear, bulk moduli and elastic constants C₁₁, C₁₂, C₄₄ of the zinc-blende Al _y Ga_1?yAs crystal are calculated as functions of Al composition and temperature. Numerical calculations have been performed and compared with those of the experimental and other theoretical results showing the reasonable agreements. Our study shows that elastic moduli and C₁₁, C₁₂ constants of zinc-blende Al _y Ga_1?yAs alloy are decreasing functions of the temperature and Al composition; C₄₄ constant is a decreasing function of the Al composition.     

First-principles calculations of the stibnite at the level of modified Becke–Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb₂S₃), a chalcogenide binary material is considerably investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, theoretical calculations of the structural, electronic and optical properties of stibnite (Sb₂S₃) crystal structure are presented using the full potential (FP) linearized augmented plane wave (LAPW) framed within density functional theory (DFT). To incorporate the exchange-correlation part in the total energy functional, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA), Perdew–Burke–Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew–Burke–Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA) are used for the calculations of the structural parameters, where the Trans-Blaha approach of the modified Becke–Johnson (TB-mBJ) potential is used to get more reliable results for the fundamental band gap energy value. These calculations are performed by involving spin-orbit coupling (SOC) contribution. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity, absorption coefficient, refractive index, reflectivity, and electron energy loss function are analyzed. Our first-principles calculations show that Wu-Cohen GGA (WC-GGA) reproduces results for lattice parameters comparable to the experimental measurements. The obtained results of the band gap energy and optical properties with TB-mBJ potential are also closer to the experimental data and, endorse its potentiality for the photovoltaics applications.     

Influence of disorder and deformation on the optical properties of two-dimensional photonic crystal waveguide

We investigate the effect of disorder and mechanical deformation on two- dimensional photonic crystal waveguide. The dispersion characteristics and transmittance of the waveguide are studied by using the finite element method. Results show that the geometric change of the dielectric material perpendicular to the light propagation direction has a larger influence on the waveguide characteristics than that parallel to the light propagation direction. Mechanical deformation has an obvious influence on the performance of the waveguide. In particular, longitudinal deformed structure exhibits distinct optical characteristics from the ideal one. Studies on this work will provide useful guideline to the fabrications and practical applications based on photonic crystal waveguides.     

量子相干态的二维电子光谱测量的原理、应用和发展

二维电子光谱是一种同时具有高的时间分辨率和光谱分辨率的非线性光谱学方法.它不仅可以对凝聚相分子复杂动力学过程进行直接测量,还可以测量不同电子态、电子态-振动态之间的量子相干过程.2007年,Flemming课题组利用二维电子光谱于低温77 K的条件下在捕光天线蛋白Fenna-Matthews-Olson中发现了能量传递过程存在量子相干现象.尽管后续的实验研究表明,该体系中实验观测到的量子相干现象不可能是由单纯的电子态相干引起的,然而这一实验现象的报道极大地激发了人们对天然或人工模拟光合系统中存在量子相干传能途径的探索,目前还是一个相当活跃的研究领域.本文旨在通过介绍二维电子光谱学原理、装置及其在光合作用体系能量传递中量子相干现象的应用,使二维电子光谱这种实验方法能够在更多的研究领域得以普及与推广.     

通过测量~(137)Cs的β衰变和内转换电子能谱研究其衰变特性

本研究用Si(Li)漂移探测器测量了~(137)Cs的β衰变能谱和内转电子能谱,对β衰变能谱进行了居里描绘和从内转电子能谱取得了内转换系数.得到β衰变的最大能量为(513.11±1.76)ke V,与参考值误差为0.17%;得到内转换系数K/L=5.712±0.217和M/L=0.264±0.018,与参考值的误差分别为0.92%和1.54%;并确定了~(137)Cs在β和γ衰变中的跃迁级次,给出了~(137)Cs及其衰变子核137Ba各能级的自旋和宇称,绘制出了~(137)Cs的衰变纲图.说明该实验方法是可靠的,可用于实验方面的教学和原子核结构的研究,并为其提供必要的实验数据.