复合材料加筋板的动力分析

本文构造了九自由度三角形拟协调罚函数复合材料板单元与六自由度复合材料梁单元,考虑了剪切变形与转动惯量的影响。用这两种单元对复合材料加筋板的自由振动、阻尼特性和瞬态响应问题进行了研究,给出一些有益结果。      

有限宽度和椭圆孔形状对缺口层合板强度预测的影响

本文采用有限元方法对正交各向异性材料含有不同椭圆孔形状的有限宽度板作了分析,给出了有限宽度和椭圆孔形状对应力集中因子K₁和孔边应力分布σ_y(x,0)的影响公式。数值结果表明:正交各向异性板的有限宽度和椭圆孔形状对K_r和σ_y(x,0)的影响均与各向同性材料不同,所以有限宽度和椭圆孔形状将对缺口层合板强度的预测产生影响。      

层状材料的高阶连续统模型

本文研究了由两种各向同性线性弹性材料组成的层状复合材料。同时利用位移在上下层面处的值及各阶导数对层内位移展开,并引用层面处应力矢量为参变量,使得层面处的应力和位移连续条件自动满足。然后利用Hamilton原理,按无约束条件变分,得到界面上的Euler方程,由此得到高阶连续统模型的场方程。考虑了场方程的长波近似和短波近似,所得结果和现存理论符合得很好。      

让七十多年前的影片《迷途的羔羊》重返银幕

中国电影资料馆珍藏着大量早期影片,其中许多具有珍贵的保存价值.1936年由蔡楚生编导、任光谱曲的<迷途的羔羊>是我国第一部以流浪儿童为题材的影片,也是我国儿童影片中的第一部有声片.此片在思想和艺术上都取得了突破,尤其是以童谣形式演唱的主题歌<月光光歌>感人至深,充分发挥了音乐的魅力,增强了整部影片的感染力.影片公映后,深受广大观众的欢迎和电影工作者的赞扬.七十多年过去了,当我们准备再次让它同观众见面时,却发现能够最真实、最原始记录影音效果的原底、声底片却出现了许多问题,给复制工作带来了空前的难度,这是我们从事资料影片复制工作三十多年来从未遇到过的难题.主要有以下几方面问题:     

热力公司锅炉附属仪表使用及检定情况

目前在新疆的供热公司大多存在着麻痹思想,对锅炉的附属仪表均不够重视,因此导致的安全隐患几乎都没有意识到.     

世界著名帐篷露营地

<正>住在帐篷露营地被认为是最经济实惠的旅行住宿方式,特别是在欧美国家,帐篷营地的费用通常比附近价格最为低廉的旅店还要便宜。如今,帐篷营地已经成为一项产业并且发展得非常成熟,大多数都配有能够满足生活需要的基础设施,比如厕所、淋浴间、洗衣房等,很多还配有丰富的活动场所和设备。除此之外,     

地震吓不倒档案人

2008年5月12日下午,一场史无前例的特大地震突袭四川,造成了巨大的生命财产损失.东方电气集团东方电机有限公司位于德阳市旌阳区,离震中的直线距离不到80公里,地震烈度达到7度,许多房屋损坏,属于重灾区.灾害发生后,由于组织及时,措施得力,档案部门全体职工在几分钟内有序地撤离到安全地带,无一伤亡.     

加拿大国家档案馆珍藏概览(5)——镜头中的加拿大

1989年是照片诞生后的第150周年.自从第一次将光影与化学结合起来用于从大自然中获得永恒的图片后,自然风光摄影就倍受争议.不管怎样,无论艺术还是科学,技艺还是职业,摄影都是产生于客观性与选择性之间,创造性与现实性之上的一种档案媒介.在最新的一次统计后,国家档案馆现今保存有1500万以上的照片档案.不管是百年前拍摄的还是上个星期刚刚拍摄的,照片所要传递出的要素通常是些非常独特的信息.无论照片、底片和幻灯片,是黑白的还是彩色的,无论旧与新,不管是退色了的还是色彩艳丽的,单独的还是成集合的,最为关键的是它们都见证了加拿大历史与社会的发展与兴衰.     

DCI为什么要求数字影院放映系统的分辨率为4K或2K

上世纪90年代初,美国电影电视工程师学会"数字影像层级结构"特别工作小组对成像系统的空间分辨率要求进行了研究.该小组从分辨率的角度将显示器分为低分辨率、常规分辨率、高分辨率和超高分辨率等四个层级.该小组基于以下几个基本概念,提出了空间分辨率层级的设计理念:--基于常用的数字处理和存储体系结构的一种层级整数递进;--支持基于影像贴片(image tile)的各种宽高比和空间分辨率;--能够利用适宜分辨率的贴片,针对任何应用要求来构建显示器.通过使用贴片和仅仅四个分辨率层级,便有可能构建出适用于任何用途的新显示器,而且这种显示器还可以用于显示来自任何其它层级的影像.美国数字电影倡导组织(DCI)要求数字影院放映系统的分辨率为4K或2K,属超高分辨率或高分辨率的级别.     

Mixed-dimensional van der Waals heterojunction-enhanced Raman scattering

Van der Waals heterojunctions(vdWHs)provide an excellent material system for the research of heterojunction-enhanced Raman scattering(HERS)due to their complexity and diversity.However,the traditional two-dimensional vdWHs are not conducive to the full utilization of near-field light due to the limitation of single dimension.Herein,we fabricate T-shaped mixed-dimensional SnSe₂/ReS₂ vdWHs via chemical vapor deposition and wetting transfer method,and demonstrate that the mixed-dimensional vdWHs can be used as ultrasensitive HERS chips based on the effective photo-induced charge transfer.Besides,the radiative energy transfer effect enhanced by near-field light further magnifies the HERS signals,improving the detection limit of rhodamine 6G(R6G)to femtomolar level.Furthermore,we demonstrate that the ultrasensitive screening of crystal violet in multicomponent solutions adsorbed on SnSe₂/ReS₂ vdWHs can be achieved by adjusting the laser wavelength,which has not been achieved by noble metal materials.This work provides new insights into the mixed-dimensional vdWHs and demonstrates the great application potential of T-shaped heterojunctions.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.