类岩石材料中表面裂纹扩展模式的实验研究

采用粘贴式轴拉方法实现了类岩石材料的直接拉伸实验,通过在类岩石材料试件中预制表面裂纹研究了类岩石材料中表面裂纹的扩展模式.研究发现,粘贴式轴拉方法可以满足一般类岩石材料的直接拉伸实验;类岩石材料中表面裂纹首先从试件正面开始扩展;表面裂纹的存在极大地影响着材料的破坏模式,类岩石材料在试件的正面上会表现出明显的二维穿透性裂纹的扩展形态,但是受其影响裂纹在厚度方向扩展会发生偏转,从而使得试件背面的最终贯通方向没有与加载方向垂直,而是呈一倾角,并且和表面裂纹的倾角和深度有关.     

有限元后验误差估计方法的研究进展

有限元后验误差估计主要有两大类,即,残余型和后处理型．本文详细介绍了后验误差估计的二大类方法的起源、发展过程以及最新的研究进展．着重介绍了ＺＺ误差估计方法的基本原理及其最新的研究进展,并对各种误差估计方法的优缺点进行评述．对有限元后验误差估计方法今后的研究方向提出了看法．     

一种基于雪崩二极管电容特性提取通讯波段单光子信号的方法

InGaAs/InP雪崩二极管(APD)可用于探测光通讯波段的单光子.APD工作于门模盖革模式时,单个光子引起的雪崩电流信号通常淹没在电容瞬时充放电脉冲中,光电流信号提取困难.本文通过调整实验参数和APD的寄生电容,使雪崩信号与放电脉冲在时域上有效叠加,并由高速比较器将光电流信号直接甄别出来.本文设计的基于InGaAs/InP APD的单光子探测系统,运行稳定,方法简单可靠,说明这种利用APD的电容特性提取单光子信号是一种有效的方法.     

基于微分几何理论的参数失配系统时空同步研究

本文采用状态反馈精确线性化方法,实现了参数失配系统的时空同步控制. 引入微分几何理论,首先采用李导数判定了参数失配系统的仿射模型是否满足状态精确线性化的充要条件,通过非线性坐标变换得到了其线性解耦系统,并结合线性最优控制理论确定了同步控制律,数值仿真证实了该控制方法的有效性,从非线性控制角度探索了混沌系统时空同步的新方法. 关键词： 时空同步 微分几何 精确线性化 参数失配     

一种确保激光陀螺低温启动的辅助启辉方法

激光陀螺在低温下启辉电压过高,严重影响了其工程应用。为了确保低温下陀螺可靠启动,借鉴激光器领域内的预电离技术,提出一种激光陀螺辅助启辉方法。在陀螺谐振腔阴极附近放置一个辅助启辉发光装置,发射高能量光束照射陀螺谐振腔阴极内表面,增加阴极的次级电子发射能力,可以有效降低陀螺辉光放电电压。分别利用紫外气体发光管和紫外波段半导体发光二极管作为光源进行了陀螺启辉电压对比试验,结果表明:低温下两种光源均可有效降低陀螺启辉电压,但两者降低启辉电压的效率有差异,紫外灯效率在5%～30%之间,紫外波段的半导体发光二极管的效率在12%～28%之间,前者降低电压离散性较大,后者较为均匀,综合看,后者效果更为显著。     

冷冻/解冻制备的聚乙烯醇水凝胶的结构和流变性研究

研究了冷冻/解冻法制备的不同浓度(5wt%～25wt%)聚乙烯醇(PVA)水凝胶的结构和流变行为之间的关系.由XRD确定了凝胶中PVA的结晶度和晶粒尺寸.用应力流变仪研究了凝胶的流变行为,包括动态模量和蠕变等.在频率为1Hz和低应力的条件下,测量了凝胶的储能模量和损耗模量.在该试验条件下,PVA水凝胶的形变是完全可以回复的.低频率区和低应变区的储能模量随浓度增加而变大,但当浓度超过20wt%时,储能模量增加速率明显降低.由PVA水凝胶在1Hz时的储能模量和结晶度的数据,理论分析得到了形成PVA水凝胶的最低PVA浓度和最小结晶度.当PVA浓度低于15wt%时,储能模量主要由PVA的微晶控制,分子链间的氢键影响很小.通过低应变区储能模量的数值计算出了凝胶网孔尺寸的结构参数.同时对不同温度下PVA水凝胶的储能模量数据进行了标度分析.PVA水凝胶的蠕变行为显示,随浓度提高,凝胶的蠕变黏弹性由线性向非线性转变.     

聚焦中考中的中心投影

中心投影问题源于生活实际,具有趣味性、直观性和一定的操作性,它不仅能考查对图形抽象概括能力,还能考查对动态图形观察、分析能力,体现一定的综合性,在几何题中别具一格,现从中考题中选取几类试题,供大家欣赏.1.单个投影中心下投影图形的边长或面积例1(2011荆州)如图1,位似     

Loss of time-delay signature in a ring of three unidirectionally coupled semiconductor lasers

A ring of three unidirectionally coupled semiconductor lasers(RTUC-SLs) is used to generate broadband chaos with no pronounced time-delay(TD) signature. Using the autocorrelation function and permutation entropy as the TD measures, we demonstrate that under suitable coupling strength, the loss of the TD signature of the lasers in the RTUC-SL configuration is achieved both for the intensity and the phase. These findings should prove valuable for developing high-quality optical chaos for potential applications, such as chaos-based communications and random number generation.     

Study of neutron activation yields in spallation reaction of 400 MeV/u carbon on a thick lead target

The spallation-neutron yield was studied experimentally by bombarding a thick lead target with 400 MeV/u carbon beam. The data were obtained with the activation analysis method using foils of Au, Mn, Al, Fe and In. The yields of produced isotopes were deduced by analyzing the measured γ spectra of the irradiated foils. According to the isotopes yields, the spatial and energy distributions of the neutron field were discussed. The experimental results were compared with Monte Carlo simulations performed by the GEANT4+FLUKA code.     

Optimization of the lattice function in the planar undulator applied for terahertz FEL oscillators

Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser (FEL), optimization of the undulator lattice becomes important. In this paper, the transfer matrix of the planar undulator is obtained from differential equations of the electron motion. Based on this, the lattice function of the planar undulator in a terahertz FEL oscillator proposed by Huazhong University of Science and Technology (HUST-FEL) is optimized and the expressions of the average beta function are derived. The accuracy of the optimization result was confirmed well by the numerical method. The application range of this analytical method is given as well. At last, the emittance growth in the horizontal direction due to the attenuation of the magnetic field is discussed.