《从零学相对论》连载

正§9.2虫洞9.2.1史瓦西虫洞再次观察图9-6.在"线轴"上半部分选定某个圆周(其实是球面,其r值比2M略大),例如Q点所在的圆周,则"线轴"的下半部分必有一个r值相同的圆周,介于这两个圆周之间的"线轴"部分就称为一个虫洞(wormhole),这两个球面则称为两个洞口(mouth).洞口的选法有一定的任意性[你也可选r值比rQ略大(或小)的圆周为洞口],所以"洞口"的     

稀疏孔径双圆周阵列的成像性能研究

针对传统稀疏孔径均匀圆周阵列的调制传递甬数在截止频率区域内易出现零值而影响成像质量的问题,提出一种由两个均匀圆周阵列嵌套构成的无冗余的双圆周稀疏孔径结构.给出该阵列的光瞳函数以及调制传递函数的解析表达式.以5-3结构的双圆周阵列为例,以实际空间截止频率为像质评价准则,从子孔径直径、内环圆周半径以及内环旋转角度等几个方面详细分析了双圆周阵列的成像特性,给出不同情况下的实际截止频率值,并对双圆周阵列稀疏孔径系统进行模拟成像和图像复原.将该结构与均匀圆周阵列.Comwell优化圆周阵列进行比较.结果表明,相同条件下,该阵列具有更大的实际空间截止频率,并且成像质量随着填充因子的减小而逐渐下降.     

基于实际空间截止频率的稀疏孔径双圆周阵列的优化

提出了一种新的稀疏孔径光瞳结构-两个圆周阵内外嵌套而成的双圆周结构,并研究了该结构的调制传递函数.该结构以实际空间截止频率作为约束条件,保证调制传递函数在最小截止频率以内无零频,以阵列的u-v覆盖点间距最大化及最小冗余度来设计目标函数,并采用这种优化方法对3-3、5-3以及6-3双圆周阵列进行了优化排列.将优化结果与相同子孔径数目的均匀圆周阵以及Golay结构进行仿真实验和比较.结果表明,优化后的双圆周阵列,具有最大的实际空间截止频率和实际等效口径.     

质点在动态多边形顶点的相遇问题

想象有两个运动质点位于一线段的两端,做相对运动,无疑两质点会相遇.再设想大量质点位于一个圆周上,一个质点接一个质点运动,结果运动沿圆周循环运动,永不相遇,这是多边形两种极限情况,那么对于其间n边形情况如何呢?下面我们作具体的分析.     

基于实际空间截止频率的稀疏孔径双圆周阵列的优化

提出了一种新的稀疏孔径光瞳结构—两个圆周阵内外嵌套而成的双圆周结构,并研究了该结构的调制传递函数.该结构以实际空间截止频率作为约束条件,保证调制传递函数在最小截止频率以内无零频,以阵列的u－v覆盖点间距最大化及最小冗余度来设计目标函数,并采用这种优化方法对3-3、5-3以及6-3双圆周阵列进行了优化排列.将优化结果与相同子孔径数目的均匀圆周阵以及Golay结构进行仿真实验和比较.结果表明,优化后的双圆周阵列,具有最大的实际空间截止频率和实际等效口径.     

扭转对称光束的产生及其变换过程中的轨道角动量传递

研究了采用扭转柱面镜光学系统将厄米-高斯光束变换成为具有轨道角动量的拉盖尔-高斯扭转对称光束. 采用本征模式分解的方法分析了扭转柱面镜光学变换系统实现光束变换的原理.利用光束传输矩阵和二阶矩理论分析计算了光束经过扭转柱面透镜变换过程中的轨道角动量传递过程，证明光束与透镜系统的轨道角动量交换发生在第一个柱面透镜处，光束经过第一个柱面透镜后，具有的轨道角动量保持不变. 关键词： 轨道角动量 光束变换 扭转对称光束 轨道角动量传递     

分子构型对分子器件伏-安特性的影响

本文选取4,4′-二巯基联苯分子通过终端S原子化学吸附于两Au原子团簇形成分子结,利用从头计算方法和弹性散射格林函数理论研究了该分子两苯环之间不同位置取向对分子能级结构以及该分子结伏安特性的影响.计算结果表明苯环扭转角增加会使分子能级发生不同程度的移动,从而引起最高占据轨道(HOMO)与最低未占据轨道(LUMO)的间距增大.扭转角增大也会导致分子轨道的扩展性变差,从而使体系的导电性能降低.当扭转角为90度时,体系的导电性能最差.该工作有利于未来分子电子学器件的设计.     

扭转应变下的YBCO超导带材临界电流特性研究

为了推动YBCO带材应用于大电流导体及高场磁体,有必要研究YBCO带材在扭转状态下的特性.本文自制了一个高温超导带材扭转测试装置,研究了上海超导的YBCO带材在液氮自场下临界电流与扭转角度的变化关系.在扭转状态下,带材的临界电流会发生衰退行为,当扭转角大于720°时,临界电流快速下降,带材n值的变化与临界电流的变化大体相似.研究发现沿带材纵向上的临界电流退化行为较为均匀,表明带材上的扭转形变比较一致.当扭转角度达720°时,临界电流有97%的衰退,撤去扭转时发现临界电流并未恢复到初始状态,并且此后的临界电流都不可恢复,说明此时的扭转应力对带材造成了永久损害.以95%Ico为临界扭转标准,带材的临界扭转角为750°,相应的临界扭距为136.8mm,极限扭转剪切应变为0.46%.     

光学耦合CT系统几何位姿参数标定方法

利用光学耦合CT系统对样品进行高分辨清晰成像的前提是准确求取系统的几何位姿参数.为求取系统几何位姿参数,针对光学耦合CT系统,提出一种数学参数定标模型.该模型利用由两个微球组成的双微球模体,通过对模体进行圆周扫描成像,获取双微球投影构成的椭圆轨迹,建立椭圆方程与几何位姿参数之间的数学关系,从而求解几何位姿参数.实验结果...     

贯流风机内部旋涡非定常演化的数值模拟

本文采用非定常三维Navier-Stokes方程、κ-ε两方程模型分析了贯流风机内部旋涡产生、发展、耗散、消失的演化过程。数值模拟显示:偏心涡产生于进气侧,随后横穿叶轮内部朝出气侧移动,最后位于出气侧叶片内圆周上。叶轮外圆周脱落的旋涡是不稳定的,它们互相融合,最后被吸入叶轮内部。数值模拟的结果显示偏心涡先于贯流而产生,是由于偏心涡的存在导致了贯流的产生,并非贯流形成了偏心涡。本文证实了ECK的旋涡理论和文献[3]的实验结果。     

Microobject manipulations using laser beams with nonzero orbital angular momentum

Microobject manipulation with a laser is investigated. The functional capabilities of the laser manipulators can be significantly enhanced using beams with predetermined distributions of intensity and angular momentum. Beams with nonzero angular momentum are generated using phase and amplitude-phase masks. Such beams make it possible to rotate weakly absorbing particles and to move them along a given trajectory. Experimental results on the microobject motion along various trajectories (circle, triangle contour, self-intersecting curve, and Archimedes spiral) are presented.     

A dynamical mother body in a Hele-Shaw problem

It is well-known that in the framework of the internal Hele-Shaw problem the fluid cannot be fully removed through a single point sink because of a cusp formation occurring prior to the moving boundary reaching the sink unless the initial domain is a circle with a sink located in its center. We give a definition of a dynamical mother body and use it for developing an algorithm of complete removal of a fluid droplet having an algebraic boundary. To illustrate our theory we consider examples where fluid can be completely removed through the sinks distributed along arcs of curves and/or points.     

Concentric piecewise azimuthally polarized beam by a pure phase plate

Focusing properties of the azimuthally polarized beam induced by a pure phase plate are investigated theoretically. The pure phase plate consists of two concentric portions, one center circle portion and one outer annular portion, through which the azimuthally polarized beam passed evolves into concentric piecewise azimuthally polarized beam. When the phase shift of the center portion is π, one ring focus may evolve into novel focal patterns with increasing radius of the center circle portion, such as cylindrical crust focus, two-ring focus, and three-ring focus. And if the geometrical parameters are unchanged, focal patterns also changes considerably with tunable phase of the center portion. Ring focus shifts along the optical axis on the increasing phase. Some optical gradient force distributions and dependence of focal shift on phase shift are also illustrated. This kind of concentric piecewise azimuthally polarized beam can be used in optical manipulation technology.     

利用扫描透射X射线显微镜观测磁涡旋结构

利用上海光源软X射线谱学显微光束线站(STXM)并结合X射线的磁圆二色效应, 我们对方形、圆形和三角形的Ni₈₀Fe₂₀薄膜微结构中的磁涡旋结构进行了定量实验观测, 并利用同步辐射光源的元素分辨特性, 分别在Fe和Ni的L₃吸收边对涡旋磁结构进行了观测. 我们还对磁涡旋中磁矩的分布进行了定量分析, 发现实验结果与微磁学模拟结果完全符合.     

Acoustic properties of micro-perforated panel absorber having arbitrary cross-sectional perforations

Micro-perforated panel absorber is used in many noise control applications as a next-generation absorbing material. Perforation shapes of micro-perforated panel studied are usually circular in the past. However, in practice, the perforations are often non-circular or irregular shape due to manufacturing techniques. Sound absorption coefficient and absorption bandwidth of the micro-perforated panel absorber may be further improved, when the perforations in shape are changed. In view of the existing exact solutions of sound propagation in tubes, the simple formulas of specific acoustic impedances of the tubes for triangle and square cross-sectional perforations are derived. Mass reactance end correction of the micro-perforated panel is obtained based on the sound radiation of a shaped piston. The specific acoustic impedance ratio of the micro-perforated panel absorber is calculated and analyzed, which can predict its sound absorption bandwidth. Finally, for closed perforations, the influences of the perforations in shape (including triangle, circle, square and irregular circle) on sound absorption of the MPP absorber are discussed in collaboration with FE simulations.     

三角形钠原子团簇中的表面等离激元

运用含时密度泛函理论研究等边三角形钠原子团簇中的表面等离激元激发.发现:在团簇尺寸较大时,沿三角形底边和底边中垂线方向激发的共振模式不同,然而沿两方向的吸收光谱线形一样,主要吸收峰的共振能量也相同.低能聚集共振在空间引起电场增强的极大值主要分布在三角形的端点附近.     

内部带特征约束的任意平面域的三角形网格生成方法

基于Ｄｅｌａｕｎａｙ三角化方法 ,给出了内部带有任意复杂特征约束的任意平面域的三角形网格生成方法。区域内部特征约束可以是点、直线、圆、圆弧、平面样条曲线以及由它们组合构成的封闭环或者不封闭环。     

An Analysis of the Trigonal Center Structure of Yb3+ Ion in CsCaF3

The crystal field parameters determined from interpretation of optical spectra are used to analyze distortions of a crystal lattice in the vicinity of an impurity ion and vacancy at a Cs⁺ site compensating the excess positive charge in the trigonal centers of Yb³⁺ ions in CsCaF₃ crystal. Interactions of the impurity ion with the nearest neighbors (an octahedron of F^? ions) and the next nearest neighbors (a cube of Cs⁺ ions) are considered within the superposition model. It is established that, at formation of the trigonal center, three F^? ions of the nearest octahedron, placed symmetrically along the threefold axis on the side of the vacancy, move away from the impurity ion a little and significantly deviate from this axis. The second triangle of F^? ions, on the contrary, comes nearer to the impurity ion and nestles on the axis of the center a little. The three Cs⁺ ions, the second neighbors on the side of the vacancy, slightly come nearer to Yb³⁺ ion and considerably nestle on the center axis. The second triangle of Cs⁺ ions, from the opposite side of vacancy, also comes nearer to the paramagnetic ion and also nestles on the center axis a little. The Cs⁺ ion, lying on the center axis, comes considerably nearer to the impurity ion.     

Analog Metal-Oxide-Semiconductor Integrated Circuit Implementation of Approach Detection with Simple-Shape Recognition Based on Visual Systems of Lower Animals

We proposed an analog network for motion detection of an approaching object with simple-shape recognition based on the visual systems of lower animals. Locusts can detect an approaching object by performing a simple process in a descending contralateral motion detector (DCMD) existing in their brain, which senses the increase in size and expansion velocity of the image projected on a retina just before collision. The responses correspond to the approaching velocity and direction. Frogs can recognize a simple shape by performing a simple process in a tectum and thalamus existing in their brain based on retinal information; this is called the Ewert von Seelen model. The proposed network was constructed with simple analog metal-oxide-semiconductor (MOS) circuits. Simulation results with a simulation program with integrated circuit emphasis (SPICE) showed that the network was able to detect the approaching velocity and direction, and also recognized simple shapes such as a circle, square, triangle and rectangle.     

On whether azimuthal isotropy and alongshelf translational invariance are present in low-frequency acoustic propagation along the New Jersey shelfbreak

To understand the issues associated with the presence (or lack) of azimuthal isotropy and horizontal (along isobath) invariance of low-frequency (center frequencies of 600 Hz and 900 Hz) acoustic propagation in a shelfbreak environment, a series of experiments were conducted under the Autonomous Wide-Aperture Cluster for Surveillance component of the Shallow Water 2006 experiment. Transmission loss data reported here were from two mobile acoustic sources executing (nearly) circular tracks transmitting to sonobuoy receivers in the circle centers, and from one 12.5 km alongshelf acoustic track. The circle radii were 7.5 km. Data are from September 8, 2006. Details of the acoustic and environmental measurements are presented. Simple analytic and computer models are used to assess the variability expected due to the ocean and seabed conditions encountered. A comparison of model results and data is made, which shows preliminary consistency between the data and the models, but also points towards further work that should be undertaken specifically in enlarging the range and frequency parameter space, and in looking at integrated transmission loss.