Topological phase transition in a ladder of the dimerized Kitaev superconductor chains

We investigate the topological properties of a ladder model of the dimerized Kitaev superconductor chains.The topological class of the system is determined by the relative phase θ between the inter-and intra-chain superconducting pairing.One topological class is the class BDI characterized by the Z index,and the other is the class D characterized by the Z_2 index.For the two different topological classes,the topological phase diagrams of the system are presented by calculating two different topological numbers,i.e.,the Z index winding number W and the Z_2 index Majorana number M,respectively.In the case of θ=0,the topological class belongs to the class BDI,multiple topological phase transitions accompanying the variation of the number of Majorana zero modes are observed.In the case of θ = π/2 it belongs to the class D.Our results show that for the given value of dimerization,the topologically nontrivial and trivial phases alternate with the variation of chemical potential.     

Finite size effects on the helical edge states on the Lieb lattice

For a two-dimensional Lieb lattice,that is,a line-centered square lattice,the inclusion of the intrinsic spin–orbit(ISO)coupling opens a topologically nontrivial gap,and gives rise to the quantum spin Hall(QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap.Generally,due to the finite size effect in QSH systems,the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum.In this paper,we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions,i.e.,the straight,bearded and asymmetry edges.The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice.For a strip Lieb lattice with two straight edges,the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum.Moreover,it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice,and no gap is opened in the edge band.It is concluded that the finite size effect of QSH states is absent in the case with the straight edges.However,in the other two cases with the bearded and asymmetry edges,the energy gap induced by the finite size effect is still opened with decreasing the width of the strip.It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms.     

热-电应力下Cu/Ni/SnAg_(1.8)/Cu倒装铜柱凸点界面行为及失效机理

微互连铜柱凸点因其密度高、导电性好、噪声小被广泛应用于存储芯片、高性能计算芯片等封装领域,研究铜柱凸点界面行为对明确其失效机理和组织演变规律、提升倒装封装可靠性具有重要意义.采用热电应力实验、在线电学监测、红外热像测试和微观组织分析等方法,研究Cu/Ni/SnAg_1.8/Cu微互连倒装铜凸点在温度100—150℃、电流密度2×10~4—3×10~4 A/cm~2热电应力下的互连界面行为、寿命分布、失效机理及其影响因素.铜柱凸点在热电应力下的界面行为可分为Cu_6Sn_5生长和Sn焊料消耗、Cu_6Sn_5转化成Cu_3Sn、空洞形成及裂纹扩展3个阶段,Cu_6Sn_5转化为Cu_3Sn的速率与电流密度正相关.热电应力下,铜凸点互连存在Cu焊盘消耗、焊料完全合金化成Cu_3Sn、阴极镍镀层侵蚀和层状空洞4种失效模式.基板侧Cu焊盘和铜柱侧Ni镀层的溶解消耗具有极性效应,当Cu焊盘位于阴极时,电迁移方向与热迁移方向相同,加速Cu焊盘的溶解以及Cu_3Sn生长,当Ni层为阴极时,电迁移促进Ni层的消耗,在150℃,2.5×10~4 A/cm~2下经历2.5h后,Ni阻挡层出现溃口,导致Ni层一侧的铜柱基材迅速转化成(Cu_x,Ni_y)_6Sn_5和Cu_3Sn合金.铜柱凸点互连寿命较好地服从2参数威布尔分布,形状参数为7.78,为典型的累积耗损失效特征.研究结果表明:相比单一高温应力,热电综合应力显著加速并改变了铜柱互连界面金属间化合物的生长行为和失效机制.     

基于高光谱技术的农作物常见病害监测研究

农作物病害是制约产量的重要因素之一,目前农作物病害的早期监测主要依靠植保人员田间取样判断危害等级的传统方式,存在主观性强、效率低、滞后性等弊端,也有些病害采用提前施药来进行预防,但此方法有农药过量的风险,从而影响到水稻生长的生态环境。近年来随着信息技术的快速发展,高光谱技术以数据量丰富、灵敏、可靠的特点迅速应用于农业生产中,成为主要检测农作物病害的有效技术手段之一。文章阐述了植物在病害胁迫下光谱响应机制,从粮食作物、经济作物、蔬菜作物、果类和其他农作物五个方面梳理和总结了近七年国内外高光谱技术在农作物病害的研究进展,在此基础上提出目前该技术在农作物监测应用领域的不足以及对未来的展望。为农作物的病害监测提供参考。     

物理学人才多元化协同培养模式的研究与实践

针对社会对人才培养的新要求和当前高等教育改革的实际, 提出了一种“ 以人为本, 因材施教, 分流培 养”的物理学专业多元化人才协同培养模式, 阐述了该教学模式的设计思路、 人才培养方案、 课程体系、 教学方式和 教学方法, 并简要分析了教学成效     

捷联惯导系统尺寸效应误差及其补偿算法

在捷联惯导系统中,陀螺和加速度计直接感测载体的角运动、线运动和干扰运动,由于载体角运动的影响,当三个加速度计测量质心与载体质心不重合时,将引起加速度计的测量误差(即尺寸效应误差)。对于中高精度的捷联惯导系统,当载体处于高动态情况下,尺寸效应误差已不能忽略,需要对其进行误差补偿。首先对加速度计组件在一般安装关系下的尺寸效应误差模型进行推导,然后提出一种新的利用陀螺输出角度增量信息和尺寸效应参数来计算加速度计尺寸效应误差的积分表达式,将其从加速度计输出速度增量中去除,即可完成尺寸效应误差补偿。最后通过仿真证明,新补偿算法产生的导航系统定位误差的舒拉周期振荡幅值明显减小,定位精度比补偿前提高了5-6倍左右。     

用太阳光谱测量空气中NO2浓度的方法研究

根据Noxon方法 ,利用NO2 在 430— 45 0nm范围内的吸收特性 ,测量空气中NO2 的浓度 .介绍了一种利用光学差分吸收原理 ,以太阳光为光源 ,二极管阵列为探测器 ,黄山光明顶上的太阳光谱为参考光谱测量大气中NO2 浓度的新光学方法 .     

氧化铁气凝胶的制备及其表征

气凝胶是由纳米量级超细微粒或高聚物分子构成的多孔性固态材料^[1,2],其杨氏模量、声传播速率、折射率、热导率和电导率等均与其宏观密度成标度关系.它拥有反常输运特性、动力学性质和低温热学性质.     

L-(-)-肉碱的合成

探讨了以手性环氧氯丙烷为原料,对中间体进行重结晶提高光学纯度的方法合成了L-(-)-肉碱,其质量指标符合美国药典USP(24)版的要求：     

巧解等腰三角形的“第三顶点”问题

给出一条已知线段,以它作为等腰三角形的一条边,在另外的已知一条(或者几条)线上找出它的第三顶点,在中考数学试题中常见.这样的问题学生都能动笔做一做,但总是在寻找"第三顶点"时感觉很乱且花费较多的时间,解答的结果往往不能够完整,下面我们一起来探究此类问题的解题方法.