Continuing Studies of Plasma Erosion Switches for Power Conditioning on Multiterawatt Pulsed Power Accelerators

Recent PITHON experiments with plasma erosion switches (PES) have extended the range of operation of the switches by about 50 percent, in terms of closed time and charge passing through the switch. The quantity of charge passed through the switch has been increased to as much as 35 mC. Currents as large as 1 MA and voltages as great as 1.8 MV have been switched off to be diverted to a downstream load. The impedance of the erosion switch can be described as having three stages: 1) essentially zero impedance, 2) a transitional opening phase, and 3) an impedance which is very large (greater than 5 ?) in comparson with the subohm downstream load. Current diagnostics, consisting of Rogowski coils and segmented shunts, have been successfully developed to monitor the current which propagates to the load region. These monitors have measured rise times as short as 38 ns and slew rates as great as 1014 A/s at the load. With wire array loads, the pulse conditioning of the switch has been observed to reduce the magnitude of the current losses in the feed which are present when no switch is used. Correlations have been made between the switch closed time, voltage, current, and power with the feed inductance and the generator power injected into the magnetic insulated transmission line (MITL).     

High power, fast, microwave components based on beam generatedplasmas

It is shown that the agile mirror plasma, under development as a device to simply and cheaply give electronic steering to microwave beams, also has application as a fast, electronically controlled, high power reflector, or phase shifter. In a radar system, this can lead to such applications as pulse to pulse polarization agility and electronic control of antenna gain, as well as to innovative approaches to high power millimeter wave circulators. The basic theory of the enhanced glow plasma is also developed     

Multivariate analysis of dynamical processes

The analysis of multi-dimensional biomedical systems requires analysis techniques, which are able to deal with multivariate data consisting of both time series as well as point processes. Univariate and bivariate analysis techniques in the frequency domain for time series and point processes are established and investigated, although the number of investigations is strongly biased towards time series. Actual multivariate techniques for time series or hybrids of time series and point processes are scarcely addressed. Here, we present spectral analysis techniques which are able to analyse point processes as well as time series. Thereby, univariate, bivariate as well as multivariate techniques are discussed. Applications to simulated as well as real-world data reveal the abilities of the proposed techniques.     

Exact solution of finite size Mean Field Percolation and application to nuclear fragmentation

Random Graphs and Mean Field Percolation are two names given to the most general mathematical model of systems composed of a set of connected entities. It has many applications in the study of real life networks as well as physical systems. The model shows a precisely described phase transition, but its solution for finite systems was yet unresolved. However, atomic nuclei, as well as other mesoscopic objects (e.g. molecules, nano-structures), cannot be considered as infinite and their fragmentation does not necessarily occur close to the transition point. Here, we derive for the first time the exact solution of Mean Field Percolation for systems of any size, as well as provide important information on the internal structure of Random Graphs. We show how these equations can be used as a basis to select non-trivial correlations in systems and thus to provide evidence for physical phenomena.     

Thermal modelling of laser welding and related processes: a literature review

The main emphasis of this review is on thermal modelling and prediction of laser welding in metals. However as similar techniques are employed to model conventional welding processes such as arc, resistance and friction, as well as related processes such as alloying, cladding and surface hardening, part of this review is given over to the modelling of these processes where appropriate. The time frame of the review is up to the year 2002.     

A new 4π geometry optimized for focusing on an atom with a dipole-like radiation pattern

Focusing electromagnetic radiation efficiently onto an atom requires an open geometry, which is as close to the full solid angle as possible. Additionally, the radiant intensity should be as close as possible to a dipole radiation in order to have a similar field distribution as in the emission process. Here, we propose to make use of a novel combination of a parabolic mirror and a diffractive optical element.     

空间声的研究与应用——历史、发展与现状

空间声的目的是通过电声的手段重放声音空间信息,给聆听者再现特定的空间听觉感知。它在文化生活、通信、多媒体和虚拟现实等方面以及航空、航天等领域都有重要的应用。国内对空间声的研究起步于1958年,五十多年来进行了大量的基础研究工作,是和国际上的发展前沿相接轨的。本文在回顾空间声的基本原理与分类、国际上空间声发展历史的基础上,侧重评述了国内空间声研究和应用的历史、发展与现状,并展望了今后的发展前景。     

Design of a Compact Millimeter-Wave Microstrip Antenna with Wide Bandwidth and Broad Beamwidth

Design of a novel compact millimeter-wave microstrip antenna with wide bandwidth and broad beamwidth is presented. In the structure, multiple layers and a parasitic element as well as a coupling aperture are used to achieve wideband, while a conducting cylinder and the coupling aperture are used to obtain broad beamwidth. Finally, phased array with eight present elements has been designed as an example. Compared to traditional microstrip antennas and arrays, present antenna and array are of smaller dimension and broader beamwidth as well as wider bandwidth.     

Cooperation between scientists and the government in the US: benefits and problems

This paper discusses the importance of maintaining close working relations between scientists and their government. Several examples of this cooperation in the U.S. are presented to illustrate the benefits, as well as problems, that result from such cooperation, or lack thereof. These examples include government support of scientific research, as well as contributions by science to help governments understand both the possibilities and the limitations of science as they formulate national policy.     

牙齿龋齿损伤可见-近红外光谱偏振检测研究

针对不同龋齿损伤程度有效表征问题,探究一种光谱偏振无损低耗的检测方法,作为对常规检测方法如化学分析法、表面轮廓测定法、显微放射照相术的有益补充。牙齿龋齿损伤由脱矿溶解牙釉质与牙本质的钙与磷酸盐造成,牙齿组织表面微观结构发生了不同程度的变化,结构的变化导致其对光波散射特性与相位改变呈现不同程度的差异。基于偏振光谱对观测样本表面微观结构敏感的特征,不同龋齿损伤样本其表面微观结构变化与偏振信息强烈关联,提出一种光谱偏振有效表征牙齿龋齿损伤度的方法。分别选取450,550,670和860 nm四个不同观测光谱研究波段,选择六个不同龋坏程度的实验样本,选取偏振度参量描述不同牙齿样本的光谱偏振特性。实验结果表明,同一观测光谱波段随着牙齿龋坏程度的加深其偏振度表征参量呈现增加趋势,同时,对于同一观测样本450 nm光谱波段的偏振特性强于其他波段,呈现观测光谱波段与其偏振特性负相关关系。为进一步定量刻画偏振光谱与牙齿龋坏损伤等级的表征关系,构建光谱偏振特征参量与不同损伤等级牙齿样本的指数关联数学模型,通过数学模型解译其内在耦合关联。为有效验证构建模型的稳健性,对模型仿真预测结果与实测数据进行定量化验证,选取和方差（SSE）、模型确定系数（R-square）、均方根（RMSE）等评价因子对构建的模型进行定量评判。结果表明,四个不同光谱波段的模型确定系数均接近于1,和方差与均方根数值均较小,且450nm观测光谱波段接近于0,定量评价结果验证了构建模型的稳健性与有效性,构建模型可有效解译不同龋齿样本与光谱偏振特征的耦合关联。该研究内容有效扩展了牙齿龋齿检测方式,揭示了光谱偏振可有效表征龋齿损伤,发展了一种无损低耗的新型偏振光谱检测技术手段。     

Computational performance of Free Mesh Method applied to continuum mechanics problems

The free mesh method (FMM) is a kind of the meshless methods intended for particle-like finite element analysis of problems that are difficult to handle using global mesh generation, or a node-based finite element method that employs a local mesh generation technique and a node-by-node algorithm. The aim of the present paper is to review some unique numerical solutions of fluid and solid mechanics by employing FMM as well as the Enriched Free Mesh Method (EFMM), which is a new version of FMM, including compressible flow and sounding mechanism in air-reed instruments as applications to fluid mechanics, and automatic remeshing for slow crack growth, dynamic behavior of solid as well as large-scale Eigen-frequency of engine block as applications to solid mechanics.     

Simulating feedback and reversibility in substrate-enzyme reactions

We extend discrete event models (DEM) of substrate-enzyme reactions to include regulatory feedback and reversible reactions. Steady state as well as transient systems are modeled and validated against ordinary differential equation (ODE) models. The approach is exemplified in a model of the first steps of glycolysis with the most common regulatory mechanisms. We find that in glycolysis, feedback and reversibility together act as a significant damper on the stochastic variations of the intermediate products as well as for the stochastic variation of the transit times. This suggests that these feedbacks have evolved to control both the overall rate of, as well as stochastic fluctuations in, glycolysis.     

Evidence for a role of glutamate as an efferent transmitter in taste buds

Background  

Glutamate has been proposed as a transmitter in the peripheral taste system in addition to its well-documented role as an umami taste stimulus. Evidence for a role as a transmitter includes the presence of ionotropic glutamate receptors in nerve fibers and taste cells, as well as the expression of the glutamate transporter GLAST in Type I taste cells. However, the source and targets of glutamate in lingual tissue are unclear. In the present study, we used molecular, physiological and immunohistochemical methods to investigate the origin of glutamate as well as the targeted receptors in taste buds.     

基于LVQ神经网络的目标识别技术

通过对目标特征的分析比较,选取不变矩作为识别特征.为了达到很好的识别效果,对不变矩做了优化处理.采用LVQ神经网络技术建立了识别模型,提高了识别速度.运用有限的样本对目标识别技术进行了测试,结果表明采用此技术后的识别成功率较高,平均约为98%,识别速度快,每幅二值目标图像的识别时间约为16 ms.     

低本底液闪中子探测器的材料测试研究

为测量中国锦屏地下实验室（China JinPing underground Laboratory,CJPL）极低通量的中子本底,需要建造大型快中子液体闪烁体探测器。建造探测器需要选用低放射性本底材料,并且化学性质稳定,不与液体闪烁体发生反应而影响液体闪烁体（EJ-335）的性能。为此,建造了小型液闪探测器,在其中分别放入聚四氟乙烯、无氧铜、氟橡胶、全氟醚橡胶这4种材料进行长期浸泡,并分别进行了如下测试:液闪长时间浸泡各种材料前后液闪的吸收光谱测试;用60Co γ源检测小型液闪探测器光产额随时间的变化情况;用Am-Be中子源检验探测器在浸泡前后的n-γ甄别性能。最终实验结果表明,聚四氟乙烯和全氟醚这2种材料与液闪有很好的兼容性,可作为大型快中子液闪探测器的容器和密封圈的备选材料。In order to measure the flux and spectrum of neutron background which is extremely low in China JinPing underground Laboratory (CJPL), liquid scintillator detector with large scale used to detect fast neutron need to be fabricated. Surrounding materials used in detector require the excellent performance, such as low radioactivity as well as stable chemical properties, which do not react with liquid scintillator, so as to avoid affecting the performance of detector. Polytetrafluoroethylene(PTFE), highly purified no-oxygen copper, fluororubber and perfluoroelastomer had been put in a small detector and soaked for a long time. The change of absorption spectrum and light yield along with time as well as the performance of n-γ discrimination after soaked were tested. The results show that PTFE and Perfluoroelastomer are compatible with liquid scintillator, which offers a reference for the selection of material used in container and seal of liquid scintillator detector used to detect fast neutron.     

Interdigitated electrode design and optimization for dielectrophoresis cell separation actuators

Among all particle separation approaches, dielectrophoresis actuators which use electric properties difference between particles, have turned into strong separating tools. This way, the particles in the fluid within non-uniform electric field experience the dielectrophoresis force. The amount and direction of this force depend on the fluid and particle polarization, particle size and electric field gradient. In this paper after presenting governing equations concerning the dielectrophoresis phenomenon, a microfluidic actuator introduced in which an interdigitated electrode pattern is applied in. Voltage, pitch, and width to pitch ratio of electrode as well as channel height are of the most important geometrical parameters of this actuator whose individual effect on particles separation was investigated using finite element analysis (FEM). The simulation results showed that if the actuator is intended to work in the efficient conditions, channel height and electrodes pitch should be near to each other, height needs to be as minimum as possible while voltage as maximum as possible in order to reach to the least time duration and the highest quantity for particles separation. Then, using theoretical equations and simulation results, a flowchart is introduced to design and optimize dielectrophoresis separation actuators. Finally, experimental results for k562 cell separation, as a biological particle, from Polystyrene, as a standard particle, is presented. In the fabricated actuator recovery and purity efficiency are 93% and about 100% respectively.     

基于层次分析法的屋顶绿化智慧管理系统

快速的城市化进程使得当前城市普遍面临绿地面积减少、抗自然灾害能力下降等问题。针对城市资源与需求的矛盾,对现有屋顶绿化自动管理系统进行了研究,设计了一种基于无线传感器网络的屋顶绿化智慧管理系统。通过实时获取光照强度等植物生长环境参数；使用层次分析法对植物生长环境进行评估与分析,提出了量化环境适宜度指标,通过反馈控制系统,实现屋顶绿化植物的智慧管理。实验结果表明,与传统屋顶绿化方法相比较,系统可以提高24%的植物存活率,同时可实现屋顶降温20%的目标。系统具有成本低、自适应管理等优点,可以广泛应用于当前我国的城市屋顶绿化中,也可以为学界和业界的相关研究提供参考。