基于自相关函数的激光散斑统计半径的测量

为了测量激光散斑的统计半径,运用统计光学理论推导了二维近场散斑光强的归一化自相关函数,并提出了通过求解散斑图像自相关拟合函数的系数来计算激光散斑统计半径的一种测量方法,利用该测量方法编制的测量软件可以方便地计算出激光散斑的统计半径.通过对尺寸已知的模拟散斑的测量,测量结果与实际尺寸相吻合,证实了该测量方法的可行性.     

A high-pressure study of PbCO3 by XRD and Raman spectroscopy

The pressure-induced phase transitions of PbCO3 are studied using synchrotron radiation in a diamond anvil cell at room temperature. The XRD measurement indicates that PbCO3 with an initial phase of aragonite-type structure undergoes two phase transitions at ～7.8GPa and ～15.7GPa respectively. The higher-pressure phase appearing at ～ 15.7GPa is stable up to 51.8GPa. The two phase transitions are further confirmed by Raman scattering up to 23.3GPa. During the decompression process, the high-pressure phases of PbCO3 are gradually recovered to the starting aragonite-type structure, but exhibit some hysteresis. The bulk modulus B0 of the aragonite-type structure is obtained to be 63±(3) GPa by fitting the volume-pressure data to the Birch-Murnaghan equation of states with B0 fixed to 4.     

中美非物理专业大学物理教育的比较与对策

大学物理作为理工科专业学生必修的一门基础课,在培养学生的科学素质、思维方式和创新精神方面起着十分重要的作用.本文主要从教材、教学方式、教学内容、实验教学、教学研究和考核方式等方面,详细比较了中美大学的物理教育现状,找出我国目前大学物理教育存在的不足,并根据目前国内的现状给出若干改革的建议,从而提高大学物理教学的效果和提高学生的创新素质.     

共掺调剂离子Na+/Gd3+调控Eu∶ CaF2晶体的发光特性研究

采用多孔坩埚温度梯度法生长了0.6at; Eu∶ CaF2晶体和共掺0.6at; Eu,6.4at; Na∶ CaF2,0.6at; Eu,6.4at; Gd∶CaF2晶体.XRD测试表明晶体仍均表现为纯CaF2的立方相,共掺后吸收强度降低.以398 nm氙灯激发晶体材料,荧光光谱表明共掺调剂离子后可明显增加Eu2在424 nm处的发光强度,而Eu3的特征发射5 D0→7FJ(J=1,2,3,4)除了表现出半峰宽变大外,峰位和强度均无明显变化.0.6at; Eu,6.4at; Gd∶ CaF2表现出Eu3+的5 D2→7F3和5 D0→7F0特征发射峰,主要可能归因于共掺Gd3+后打破了非反演对称结构,R值(电、磁偶极跃迁比值)明显降低,提高了晶体格位结构的对称性.共掺Na+后在CIE色域坐标图上显示坐标由(0.303 7,0.142 5)可变为(0.204 3,0.062 6),对应从紫色到蓝色的色域调控.     

大学物理与高中物理衔接教育的探讨

通过对两份文件《普通高中物理课程标准(实验)》与《非物理类理工学科大学物理课程教学基本要求》的研读,分别从教学内容、教学方法、考核方式三个方面讨论了物理课程的衔接问题,提出解决问题的改革之道,促进教学的顺利交接.     

Equal compressibility structural phase transition of molybdenum at high pressure

We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction (RXRD) in a diamond anvil cell (DAC). It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa, and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred. The slope of pressure-volume curve shows continuity before and after this phase transition, when fitting the pressure-volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure. A bulk modulus of 261.3 (2.7) GPa and a first-order derivative of the bulk modulus of 4.15 (0.14) are obtained by using the nonhydrostatic compression data at the angle ψ = 54.7° between the diffracting plane normal and stress axis.     

截面为矩形的无限长载流柱面磁场的空间分布

根据面电流在空间某点的磁场公式和场强叠加原理,求出了截面为矩形的无限长载流柱面空间磁场分布的普遍表达式。     

以石墨烯为电极的有机噻吩分子整流器的设计及电输运特性研究

传统硅基半导体器件受到了量子尺寸效应的限制,发展分子电子学器件有可能解决这一难题.本文提出了由石墨烯电极和有机噻吩分子相结合构造分子器件的思想,建构了"石墨烯-噻吩分子-石墨烯"结构的分子器件,并运用非平衡态格林函数结合密度泛函理论的方法研究了其电输运特性.系统地分析了电子给体"氨基"和电子受体"硝基"两种取代基的位置对有机噻吩分子电输运的影响.计算表明,有机噻吩二聚物被"氨基"和"硝基"取代后会产生明显的负微分电阻效应和整流效应.进一步对产生这些效应的物理机制进行分析,发现氨基的位置可以调整负微分电阻的强弱,硝基的位置可以改变整流的方向.     

Structural phase transition,strength,and texture in vanadium at high pressure under nonhydrostatic compression

The structural phase transition, strength, and texture of vanadium have been studied under nonhydrostatic compression up to 70 GPa using an angle-dispersive radial x-ray diffraction technique in a 2-fold paranomic diamond anvil cell and up to 38 GPa using an angle-dispersive x-ray diffraction technique in a modified Mao–Bell diamond anvil cell at room temperature. We have confirmed a phase transition from body-centered cubic structure to rhombohedral structure at 27–32 GPa under nonhydrostatic compression. The radial x-ray diffraction data yields a bulk modulus K_0= 141(5) GPa and its pressure derivative K_0′= 5.4(7) for the bcc phase and K_0= 154(13) GPa with K_0′= 3.8(3) for the rhombohedral phase at ψ = 54.7°. The nonhydrostatic x-ray diffraction data of both bcc and rhombohedral phases yields a bulk modulus K_0= 188(5) GPa with K_0′= 2.1(3). Combined with the independent constraints on the high-pressure shear modulus, it is found that the vanadium sample can support a differential stress of ～1.6 GPa when it starts to yield with plastic deformation at ～36 GPa. A maximum differential stress as high as ～ 1.7 GPa can be supported by vanadium at the pressure of ～ 47 GPa.In addition, we have investigated the texture up to 70 GPa using the software package MAUD. It is convinced that the bodycentered cubic to rhombohedral phase transition and plastic deformation due to stress under high pressures are responsible for the development of texture.     

A Model for Extreme Ultraviolet Radiation Conversion Efficiency From Laser Produced Mass-Limited Tin-Based Droplet Target Plasmas

Simple arguments are used to construct a model to explain the extreme ultraviolet radiation conversion efficiency(EUV-CE) of a tin-based droplet target laser produced plasmas by calculating the laser absorption efficiency,radiation efficiency,and spectral efficiency.The dependence of drive laser pulse duration and laser intensity on EUV-CE is investigated.The results show that at some appropriate laser intensity,where the sum energy of the thermal conduction,out-off band radiation and plasma plume kinetic losses is at a minimum,the EUV-CE should reach a maximum.The EUV-CE predicted by the present simple model is also compared with the available experimental and simulation data and a fair agreement between them is found.