标准样件的材料热膨胀系数

材料热膨胀系数的精确获得具有重要的理论研究与应用价值.选用方体、圆柱体和球体三种典型形体试件,对样件形体特征参数在材料热膨胀系数中的影响进行了实验测定和分析,表明了样件形体尺寸对材料热膨胀系数的影响是不容忽视的.经过分析比较,指出球体作为标准样件具有较好的稳定性,有利于获得稳定的材料热膨胀系数值.该方面的发现对材料热物性理论及生产实践具有重要的理论研究与实用价值.     

烧成曲线对合成堇青石热膨胀系数的影响

研究了不同烧成曲线对合成堇青石材料热膨胀系数的影响,提出了一种降低堇青石材料热膨胀系数的新途径。结果表明,采用成核-生长曲线法烧成时,试样的热膨胀系数为1.6-1.8×10-6/℃左右,比采用直接升温法时的热膨胀系数(2.0-2.4×10-6/℃)的值降低0.3-0.5×10-6/℃左右。     

烧成曲线对合成堇青石热膨胀系数的影响

研究了不同烧成曲线对合成堇青石材料热膨胀系数的影响,提出了一种降低堇青石材料热膨胀系数的新途径.结果表明,采用成核-生长曲线法烧成时,试样的热膨胀系数为1.6～1.8×10-6/℃左右,比采用直接升温法时的热膨胀系数(2.0～2.4×10-6/℃)的值降低0.3～0.5×10-6/℃左右.     

低维材料热膨胀系数测量装置

准确测量不同材料的热膨胀系数，是航天和超导等领域中大型工程项目进行材料选择和结构设计的前提．对于具有一定厚度的三维结构材料，目前有多种测量热膨胀系数的方法．其中应变片法是一种较为简单且常用的方法．但由于低维材料(一维线材和二维带材)自身强度低和不能承压，目前只有测量薄膜厚度方向热膨胀系数的方法，     

硬化水泥砂浆热膨胀系数影响因素

热膨胀性能是影响水泥基材料温度变形和开裂的重要指标.通过对硬化砂浆不同龄期热膨胀系数的测定,研究了水胶比、胶集比、矿物掺合料种类、粉煤灰掺量和细集料种类对砂浆热膨胀系数的影响规律.结果表明,硬化砂浆的热膨胀系数随水胶比和胶集比的增加而增大,其本质区别是用水量和水泥用量增加导致的水泥石热膨胀系数变化.矿粉能够增加砂浆的热膨胀系数,而粉煤灰则起抑制作用,热膨胀系数随着粉煤灰掺量的增加而降低.在对砂浆热膨胀系数的降低效果方面,大理岩砂玄武岩砂砂岩砂天然砂.     

ZrO2/β-ZrWMoO8可控热膨胀复合材料的制备

采用共沉淀法成功制备了纯度较高的各向同性的负热膨胀材料β-ZrWMoO8.将ZrO2与β-ZrWMoO8按一定比例机械混合,在1 020 ℃烧结2 h制备了热膨胀系数可控的ZrO2/β-ZrWMoO8复合材料.以X射线衍射和扫描电子显微镜对所得材料结构及形貌进行表征,以热膨胀仪测定复合材料热膨胀系数.研究结果表明:在30～600 ℃温度区间内,所得ZrO2/β-ZrWMoO8复合材料的热膨胀系数皆线性一致,并且可以通过改变β-ZrWMoO8的质量分数,将复合材料的热膨胀系数控制为正、负或0.当β-ZrWMoO8的质量分数为50%时,复合材料的热膨胀系数接近0.     

基于均匀化理论的复合材料热膨胀系数预测方法

建立了基于均匀化理论的复合材料热膨胀系数预测方法。给出了预测热膨胀系数的细观均匀化问题的形式及其有限元求解过程。利用该方法预测了空心材料和单向纤维复合材料的热膨胀系数。所得结果与理论分析结果和实验值吻合较好，说明该方法是可靠的。     

薄膜线膨胀系数的一种精确测量方法

热膨胀系数(α)是衡量材料性能优劣的一个重要参数,但目前对薄膜试样热膨胀系数测量方法的文献报道较少.具体介绍一种采用热机械分析仪测量薄膜试样热膨胀系数的方法.在此基础上分析引起测量误差的原因,并通过参比铜箔对仪器进行了校正,获得仪器的修正参数.结果表明,通过校正消减了仪器自身热膨胀,能精确求出薄膜的热膨胀系数.     

材料热膨胀系数非一致性的原因

在精密测量和精密工程技术领域，影响精度的众多因素中，温度变化引起的热变形误差所占的比重越来越大，因此对热误差修正的好坏直接影响着精度。各种手册或工具书中提供的材料热膨胀系数一致性较差，给正确引用带来了困难。为此，系统地分析了造成这种非一致性的主要原因，指出热膨胀系数定义的差异，测量方法的差异，试样化学成分、加工方法和形体尺寸的差异是造成各种手册或工具书上热膨胀系数非一致性的主要原因。该研究为在工程实际中选用恰当的材料热膨胀系数提供了依据。     

高硅铝合金材料高温充氧氧化工艺

针对应用广泛的高硅铝合金电子封装材料,采用高温充氧氧化工艺,对已挤压成形的Al-30Si及Al-40Si高硅铝合金材料进行后续处理,通过扫描电镜、金相显微镜、热物性测试仪及电子万能拉伸试验机等,对材料显微组织、密度、气密性、热膨胀系数、热导率及抗压强度进行了分析比较。研究结果表明:高温充氧氧化后材料晶粒长大,Si含量高的材料长大更为明显,并存在Si颗粒偏聚现象;高温氧化后材料致密度增加,气密性提高;氧化后Al-30Si材料热膨胀系数略有增加,而充氧氧化对Al-40Si材料的热膨胀系数的影响不明显,但可提高材料热导率,Al-30Si与Al-40Si材料热导率分别提高16.4%和23.5%;高温氧化工艺显著降低材料抗压强度,Al-30Si与Al-40Si材料经氧化后抗压强度分别下降26.8%和20.5%。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

Features of Women''s language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme