以SiHCl3为工作介质生产高丰度28Si

为了获得高丰度的28S i同位素,生产高纯度的单晶硅,利用气体离心机对硅同位素进行离心分离。通过对S iH-C l3中组成元素的不同同位素丰度的分析,计算了天然S iH-C l3中不同相对分子质量的分子组成。分析结果表明:虽然氯有两种同位素,但也可以将S iHC l3作为分离28S i同位素的工作介质。通过4台离心级联的分离实验,得到了28S i丰度达到99%的S iHC l3样品。离心分离得到的高丰度S iHC l3不用经过化学转化就可以直接用于单晶硅的生产。实验结果表明,采用离心法分离S iHC l3可以得到高丰度28S i。     

离心级联基本全分离因子的计算与分析

离心级联分离多组分稳定同位素可以用一组含有单位相对分子质量差下的基本全分离系数的方程表示。通过对不同形式的离心级联进行丰度计算,得到任意两种组分间的全分离因子与它们的相对分子质量之差成指数关系。对矩形级联中各种参数,如级联分流比、供料丰度、以及单机的基本全分离因子等,对于级联的基本全分离因子的影响进行了详细的讨论,得到了级联基本全分离因子同各种参数的关系曲线,确定了基本全分离因子为影响级联分离性能的重要参数之一。     

充气量和供料对脉冲级联稳态丰度分布的影响

脉冲级联是新提出的同位素分离级联的概念,了解脉冲稳态丰度分布是开发脉冲级联应用中的一个重要方面。为了明白稳态丰度分布的影响因素并加以利用,以提高脉冲级联的分离性能,利用一种结合了Q迭代法的时间推进方法求解脉冲级联的稳态丰度分布,并将分离效果用平均分离系数来整体描述。通过对矩形脉冲级联分离钨同位素的讨论,分析了充气量和供料对稳态丰度分布的影响。结果表明:级联的平均分离系数不随级联各级离心机充气量的变化而变化,但随着管道充气量与供料量之比的增加而增大;在级联中部存在一个最佳供料位置,使得平均分离系数最大。     

激光分离同位素

一、引言稳定同位素(包括铀同位素)的分离在原子能科学技术、国防工业中具有极为重要的意义。然而,分离同位素、特别是分离铀同位素却是非常困难的。例如目前国外分离U~(235)-U~(238)的方法是用气体扩散法或超离心法。但是气体扩散法的分离系数很小,仅为1.0043,故需要上千级以上的级联装置,同时需要大量的压缩机,故耗电量多、成本昂贵。超离心法虽然分离系数可达1.05,但需要每分钟数万转的超高速离心机,因此对离心机材料和结构要求很高、制造困难、寿命较短,招致很高的运行和维修费用。所以国外还一直致力研究过其它的各种方法,但至今均未见有很大成效。     

离心级联全分离因子的实验数据分析

在离心级联分离多组分稳定同位素过程中,找出组分间的全分离因子同它们的相对分子质量差之间存在的确定性关系,有利于级联的分离计算和实验研究。建立了实验数据可靠性分析原则,确定了符合实验条件的数据;得到在定常态下短离心级联中,任意组分间的全分离因子与其组分间的相对分子质量之差存在指数关系。应用所建立的级联全分离因子关系式,对文献中发表的离心级联分离稳定同位素的实验数据进行了分析研究和补全工作。     

硅同位素的应用及分离研究进展

介绍了同位素纯硅材料的应用研究进展,综述了低温精馏法、激光法、气体离心法、化学交换法等方法在硅同位素分离领域的研究进展,分析了目前工业化过程分离硅同位素存在的问题,指出化学交换法将是实现硅同位素工业化分离的最优路径.     

分离级联中出现峰值组分的质量与平均质量的关系

为了获得所需丰度的同位素，需要将多个分离单元联结成级联。因而必须对多元同位素混合物在级联中的分离情况进行深入研究。假定分离系数小，从多组分级联输运方程出发，利用全分离系数与不同组分质量差的关系，导出了在级联中某组分丰度出现峰值处该组分质量与平均质量的关系。并对级联中分离单元的分离情况进行了分析。得出以下结论：在级联分离多组分同位素混合物的过程中，当某一组分的丰度在级联中出现峰值，其质量等于此处平均质量（略有偏移），以上结论是在小分离系数的条件下得到的，对于大分离系数的情况也有参考价值     

考虑轻杂质时离心级联中组分分布的数值模拟

为了清楚地了解离心机级联中轻杂质的传播与分布,对利用离心法获取同位素过程中存在的轻杂质问题进行了数值模拟。根据实际的物理过程,建立了新的质量损失模型及轻杂质(HF)产生模型。数值模拟中将反映物质守恒的微分方程进行差分处理,以W F6为工作介质,考虑腐蚀损耗、供料中的轻杂质及离心机级联系统漏率,求解差分方程组,得到了离心级联中各组分的丰度分布,并与旧的模型进行了比较。数值计算结果显示新模型得到的轻杂质丰度在精料端的积累量远高于旧模型,理论上该模型能够更准确地反映离心级联中轻杂质传播与分布情况。     

多元分离矩形级联最佳供料位置的确定

多元同位素分离理论是稳定同位素分离的理论基础。矩形级联具有机器种类少，连接简单等特点，适合分离种类多，小规模生产的稳定同位素。用矩形级联分离多元同位素，在外界参数不变的情况下，改变供料位置，目标同位素的产品丰度有较大差别，这就要求选择最佳供料位置使产品丰度最高。从推导二元小分离系数短矩形级联的最佳供料位置出发，分析了当分离系数增大及级联加长时供料位置的变化趋势，并通过求解非定常态多元分离级联丰度非线性方程组，得出多元分离的最佳供料位置的变化趋势及最佳供料级入口丰度和供料丰度之间的关系     

多组分气体离心分离级联的解析优化

为降低级联的建设和运行成本,使设计总流量较小,提出了一种多组分分离级联的一维解析优化方法。应用匹配丰度级联理论的基本原理,计算了不同关键相对分子质量下的级联,分析了级联参数的变化。在匹配丰度级联中,关键相对分子质量是两个关键组分相对分子质量的平均值。得到一种通过调整关键相对分子质量和级联的级数以得到总流量较小级联的解析计算方法。用这种方法,设计了一个分离28S i的级联,并将此结果和文献中的结果进行了比较。该方法得到的级联总流量接近最小值,计算量很小,可以用于多组分分离的优化设计。     

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.     

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     

WIMAX与WI-FI技术分析及联合组网

介绍了WiMAX与Wi-Fi两种无线宽带接入技术,并对两者之间的关系及相互之间的影响做了对比及分析,并对WiMAX的关键技术进行了详细说明,最后对两者的联合组网方式做了简单的探讨。