等离子体二维密度重建的影响因素

利用超强超短激光脉冲产生的高能质子束的库仑能量损失可以重建稠密等离子体的二维密度分布，使用同时迭代重建算法（SIRT算法）研究等离子体二维密度重建的影响因素.研究等离子体密度梯度、密度量级和质子束入射能量对重建误差的影响，分析质子束成像探测等离子体密度之前获得等离子体大概方位的重要性，通过数据拟合确定了能量噪声和重建误差之间的解析关系式.     

修正屏蔽库仑势下二维尘埃等离子体的动力学和结构特性

本文考虑等离子体密度分布变化, 得到了修正屏蔽库仑势的解析解. 数值分析以及分子动力学模拟表明, 在常见实验室参数情况下, 等离子体密度分布变化引起的屏蔽库仑势修正对二维尘埃等离 子体系统的动力学和结构特性影响很小. 在极限参数情况下, 本模型的计算结果表明二维尘埃等离子体系统的扩散能力明显降低, 并且系统组态呈圆形分布. 此外, 本文还研究了实验室常见大小磁场对二维尘埃等离子体系统的影响. 关键词： 修正屏蔽库仑势 二维尘埃等离子体 分子动力学模拟     

双频容性耦合等离子体密度径向均匀性研究

利用自主研制的全悬浮双探针, 对影响双频容性耦合等离子体径向均匀性的因素进行了研究. 发现低频功率、放电气压和放电间距对径向均匀性有明显影响. 合适的低频功率、放电气压及较大的极板间距可以得到更均匀的等离子体. 采用与实验相同的放电参数, 利用改进的二维流体模型进行理论模拟, 得到了不同极板间距下径向离子密度分布, 并和实验测量结果进行了比较, 两者的变化趋势基本符合. 关键词： 双频容性耦合等离子体 径向均匀性 全悬浮双探针 二维流体模型     

基于发射光谱法锡等离子体特征参数的求解研究

利用调QNd:YAG 1064 nm激光器诱导产生锡等离子体,基于9条锡发射谱线,构建二维玻尔兹曼图,得到锡等离子体电子温度5063 K,利用洛伦兹函数拟合锡发射谱线Sn(I) 228.66 nm,得到锡等离子体电子密度3.8×10¹⁷ cm^-3,结果证实激光诱导的锡等离子体处于热力学平衡状态.     

二维材料解理技术新进展及展望

自从2004年首次制备出石墨烯以来,机械解理技术被广泛用于制备过渡金属二硫族化合物、黑磷等各种二维材料.在多种二维材料制备技术中,机械解理技术具有制备方法简单、普适性好等优点,最重要的是解理得到的晶体质量高,是研究很多新奇物性的理想选择.本文介绍了机械解理技术的产生背景,总结了常规机械解理技术在二维材料研究过程中的瓶颈.为了解决常规机械解理技术制备效率低、样品尺寸小的问题,一些新型机械解理技术近年来不断发展起来,如氧气等离子体辅助法和金膜辅助法等.作为自上而下的二维材料制备方法,新的解理技术在未来二维材料基础研究和应用中仍然充满生机.未来解理技术将朝更大尺寸,更高质量方向发展.     

二维等离子体填充金属光子晶体腔体特性

设计了等离子体填充的二维金属光子晶体特殊开放腔体结构,并采用粒子模拟技术(PIC)建立了基于等离子体填充腔体结构物理模型,分析了等离子体填充下二维腔体的各模式场分布特性,以及等离子体的引入对腔体内各模式工作频率、电场幅值的影响。结果表明:腔体内各模式的电场强度随等离子体密度的增加而减弱,模式频率随背景等离子体归一化频率的提高而增加,工作模式的产生与激励方式密切相关。     

单一金纳米棒的光学及折射率传感特性研究

基于贵金属纳米粒子在折射率传感及探测中的应用,本文运用离散偶极近似,模拟计算了单一金纳米棒的远场消光光谱,研究了其偶极局域表面等离子体共振波长的可调性及折射率的传感特性。研究表明,通过调控金纳米棒的长径比,纳米棒的局域表面等离子体共振波长在可见至近红外波长范围内广泛可调;在可见与近红外波长范围内,该共振波长及对应的折射率灵敏度对纳米棒长径比的响应皆分别呈现出二次与线性的分段特征。此外,利用金介电函数虚部随入射光波长的变化关系,揭示了金纳米棒表面等离子体所对应的半高宽随该共振波长的变化规律;并利用长径比对金纳米棒的品质因子进行了优化,得到了优化的长径比。本文的研究结果对未来设计和制造性能优异的基于局域表面等离子体共振的传感/探测基底和元器件具有重要的理论指导意义。     

基于自相似模型的二维X射线激光等离子体流体力学

从自相似方法出发,建立了简化的二维X射线激光等离子体流体动力学模型. 利用该模型研究了平板靶X射线激光的二维流体力学行为. 研究表明,当激光作用结束后,经过一段时间的演化电子密度和温度沿线聚焦方向逐渐达到平衡,该结果对X射线激光的优化设计具有重要意义. 关键词： X射线激光 二维流体力学计算 自相似方法     

丝阵Z箍缩早期消融等离子体动力学的二维数值模拟研究

采用理想磁流体力学模型,给出合理的二维(r, θ)质量注入边界条件,对丝阵Z箍缩早期消融等离子体的动力学过程进行了二维(r, θ)数值模拟研究,得到消融等离子体各参量以及磁场的二维时空分布.模拟结果表明,消融等离子体的运动包括四个主要阶段:首先向轴漂移,然后在轴线处滞止并形成先驱等离子体柱,随后先驱等离子体柱被压缩,最后缓慢膨胀.计算了不同丝阵半径和丝间距情况下消融等离子体到轴速度以及消融质量占丝阵总质量的份额,它们的变化规律与实验结果基本符合.通过 关键词： 丝阵Z箍缩 理想磁流体 消融等离子体     

高超声速模型尾迹电子密度二维分布反演方法

弹道靶利用二级轻气炮将模型加速到高超声速状态,模型在靶室内超高速飞行时形成等离子体尾迹.为实现高超声速模型尾迹电子密度径向二维分布诊断,利用七通道微波干涉仪测量系统获得了高超声速模型尾迹截面不同位置处平均电子密度.该系统采用一发七收的方式,实现平面波照射等离子体及平面波接收,天线波束可完全覆盖尾迹径向范围.多通道微波干涉仪数据处理过程常将等离子体视为分层介质,考虑到分层界面上折射效应的影响,本研究利用射线追踪方式建立电磁传播模型,结合测量数据建立目标函数,通过遗传算法优化来反演高超声速模型尾迹电子密度径向二维分布.该数据处理方法的电子密度反演结果与相同来流条件下的数值模拟结果对比吻合较好,初步验证了该方法的有效性.分析了分层模型对电子密度分布特性的影响,结果表明利用七层模型对尾迹建模效果最佳,且适用于不同厚度尾迹,最大化利用接收通道数,确保了计算精度.利用该方法实现弹道靶高超声速球模型尾迹电子密度二维分布诊断,并给出了给定实验状态下模型尾迹电子密度二维分布的一些规律.     

An experimental and statistical study of the behavior of the vibration field in two coupled lightweight wooden joist floors

The aim of this study was to evaluate the vibration level attenuation of a common wooden floor structure and to present the results together with the statistical precision of the evaluation. Linear regression was used to determine the attenuation rate in the two main directions of the floor structure. The probability for the attenuation rate to be zero was calculated. The attenuation rate was found to be high in the direction perpendicular to the beams with a probability to be zero lower than 0.001. In the direction parallel to the beams the attenuation rate was found to be close to zero.     

Numbers,scale and symbols: the public understanding of nanotechnology

Nanotechnology will be an increasing part of the everyday lives of most people in the world. There is a general recognition that few people understand the implications of the technology, the technology itself or even the definition of the word. This lack of understanding stems from a lack of knowledge about science in general but more specifically difficulty in grasping the size scale and symbolism of nanotechnology. A potential key to informing the general public is establishing the ability to comprehend the scale of nanotechnology. Transitioning from the macro to the nanoscale seems to require an ability to comprehend scales of one-billion. Scaling is a skill not common in most individuals and tests of their ability to extrapolate size based upon scaling a common object demonstrates that most individuals cannot scale to the extent needed to make the transition to nanoscale. Symbolism is another important vehicle to providing the general public with a basis to understand the concepts of nanotechnology. With increasing age, individuals are able to draw representations of atomic scale objects, but these tend to be iconic and the different representations not easily translated. Ball and stick models are most recognized by the public, which provides an opportunity to present not only useful symbolism but also a reference point for the atomic scale.     

光纤传感实验设计

提出了一种适用于教学的光纤传感器实验研究系统。在实验过程中首先测定了LED光源的I-P特性曲线,接着对光纤的纤端光场分布进行测试,并通过实验得到的数据绘出光纤的纤端光场光强曲线,然后利用光纤传感实验仪对微位移用两种方式进行测量。根据现有的实验条件设计出适合于学生进行的基本实验。     

Deflagration to detonation transition in fast flames and tracking with chemical explosive mode analysis

In the context of vapour cloud explosion, the flame acceleration process can lead to conditions promoting deflagration to detonation transition (DDT), potentially leading to increased damages in accidental scenarios. This study focuses on this phenomenon by performing simulations of detonation reinitiation for fast flames in the Chapman–Jouguet deflagration regime. It is obtained experimentally by the attenuation of an incident detonation by an array of obstacles. A primary objective of the paper is to demonstrate the ability of the numerical model to reproduce the major experimental trends, namely the variation of the reinitiation propensity for different initial pressures and blockage ratios (BRs). Chemical explosive mode analysis (CEMA) is also adapted to the context of this study, in order to identify locally the propagation regime and to provide insights on the reinitiation mechanism. An a priori validation of the CEMA methodology is first performed on relevant canonical one-dimensional configurations. Subsequently, ensembles of five realizations are computed at different initial pressures and BRs and compared to experimental data. They are shown to reproduce the major observed trends in terms of detonation reinitiation length with respect to the operating conditions, with significant variability from one realization to another. In addition, the reinitiation mechanism is also found to be consistent with experimental observations and a previous numerical study of the same configuration. The CEMA methodology adapted to this context is able to identify locally the different propagation regimes, and to track the highly reactive zones that coherently couple with transverse pressure perturbations, leading to the formation of a strongly reacting kernel which eventually triggers the detonation reinitiation.     

经典洛伦兹磁力和广义洛伦兹磁力解释电子感应加速器的本质

介绍了虚构的法拉第定律与电子感应加速器不合理,用完整洛伦兹磁力解释电子感应加速器合理有效。     

Adaptive digital twins of combustion systems using sparse sensing strategies

This work proposes to implement a sparse sensing framework to build a hybrid numerical-experimental Digital Twin of a practical combustion system. The goal is to find the optimal sensor placement that minimizes the prediction error, and to predict the distribution of reacting scalars using few measurements. Three-dimensional CFD simulations with detailed chemistry were used to build the design space by varying the fuel composition (from pure methane to pure hydrogen), the equivalence ratio (from 0.7 to 1) and the air velocity. The Proper Orthogonal Decomposition (POD) was applied to the numerical data to find a tailored basis for dimensionality reduction. Then, the QR decomposition with column pivoting was applied to the tailored basis to find the optimal sensor placement. Finally, the model was employed to predict the three-dimensional temperature distribution in the unexplored part of the design space, using the experimental samples as input. The optimal placement of the sensors provides valuable information on the key locations and features, which can then be used in the design of reactor network models, for example. Also, the results show that the hybrid Digital Twin could predict an adjusted temperature distribution which reduces the error with the experimental measurements, when compared to the original CFD temperature distribution.     

Simulating coupled dynamics of a rigid-flexible multibody system and compressible fluid

As a subsequent work of previous studies of authors, a new parallel computation approach is proposed to simulate the coupled dynamics of a rigid-flexible multibody system and compressible fluid. In this approach, the smoothed particle hydrodynamics (SPH) method is used to model the compressible fluid, the natural coordinate formulation (NCF) and absolute nodal coordinate formulation (ANCF) are used to model the rigid and flexible bodies, respectively. In order to model the compressible fluid properly and efficiently via SPH method, three measures are taken as follows. The first is to use the Riemann solver to cope with the fluid compressibility, the second is to define virtual particles of SPH to model the dynamic interaction between the fluid and the multibody system, and the third is to impose the boundary conditions of periodical inflow and outflow to reduce the number of SPH particles involved in the computation process. Afterwards, a parallel computation strategy is proposed based on the graphics processing unit (GPU) to detect the neighboring SPH particles and to solve the dynamic equations of SPH particles in order to improve the computation efficiency. Meanwhile, the generalized-alpha algorithm is used to solve the dynamic equations of the multibody system. Finally, four case studies are given to validate the proposed parallel computation approach.     

Gravitational critical phenomena in the realm of the galaxies and Ising magnets

In the non-relativistic and quasi-static limit, it is possible to map exactly the system of galaxies in the observable universe onto an Ising magnet. Techniques from the theory of critical phenomena as applied to magnets can then be employed to calculate rigorously the galaxy-to-galaxy correlation function, whose critical exponent is predicted to be between 1.530 to 1.862, to be compared to the empirical/observational value of 1.6 to 1.8.This essay received the fifth award from the Gravity Research Foundation, 1996—Ed.     

Lattice dynamics of solid xenon under pressure

We use density-functional perturbation theory to obtain the phonon spectrum of fcc xenon under pressure. Thermodynamic properties obtained within the quasiharmonic approximation are in fair to good agreement with experiment at zero pressure. The transition pressure from the fcc to hcp phase is predicted to occur at 5 GPa. The fcc structure is found to be dynamically stable up to a pressure of 100 GPa, beyond which the phonon modes at the X and L symmetry points soften. We attribute the observed sluggish kinetics of the fcc-hcp transition to the small energy difference between the phases as well as to the high dynamical stability of the fcc phase.     

浅谈光电实验室的教学管理改革

实验教学是帮助学生将理论知识转化为实践技能的重要途径。因此在重视理论教学的同时,必须加强实验环节。针对光电实验室的现状,有必要进行教学方法和管理制度的改革。强化实验室仪器管理,创造好的硬件条件为实验教学服务;改革创新教学方法,使实验效果在传统实验教学的基础上更上一层楼;因材施教,满足各层次学生的不同需求;全方位展开改革实践,建立适合科技发展的教学新体系,培养理论知识扎实,实践技能过硬的复合型人才,以适应社会的发展。