柠檬酸对Ca(NO3)2-P2O5体系合成羟基磷灰石粉体的影响

采用Ca(NO3)2·4H2O和P2O5为主要原料,柠檬酸为螯合剂,利用溶胶-凝胶法合成了纳米羟基磷灰石粉体.通过DSC,XRD和SEM等手段,分析了纳米HA粉体的形成历程,系统地研究了柠檬酸对粉体形成过程、产物杂质相及粉体粒度的影响,并对其影响机理进行了初步探讨.结果表明:柠檬酸的加入提高了胶体的稳定性,通过螯合作用...     

鳌合剂对溶胶凝胶制备纳米羟基磷灰石的影响

采用硝酸钙(Ca(NO3)2.4H2O)、磷酸三甲酯(PO(CH3O)3,简称TMP)作为钙与磷的先驱体,用溶胶凝胶法合成纳米羟基磷灰石粉体.探讨了工艺过程中添加乙二醇、柠檬酸、甘氨酸三种鳌合剂对粉体制备及其特性的影响.实验结果表明,在合适配比下,鳌合剂的加入影响干凝胶的形态,并促使碳酸钙晶相出现.柠檬酸和甘氨酸会改变体系pH值,影响酯的水解反应,同时通过鳌合作用及表面电荷作用影响粉体粒径.研究表明甘氨酸是低温下制备纳米羟基磷灰石粉体合适的鳌合剂.     

锂离子电池正极材料——Li3 V2 (PO4)3 的合成及其性能研究

以LiOH·H2O,NH4H2PO4和V2O5为原料,加入导电碳,用高温固相法合成Li3V2(PO4)3;以LiOH·H2O,NH4H2PO4,NH4VO3为原料,柠檬酸作为还原剂和碳源,用溶胶凝胶法合成Li3V2(PO4)3,并对材料的化学电化学性能进行了研究.     

柱状纳米羟基磷灰石的制备和结构表征

以P2O5,Ca(NO3)2.4H2O为原料,无水乙醇为溶剂,通过调节pH值控制凝胶的形成,利用溶胶-凝胶/水热法制备柱状纳米羟基磷灰石(HAP).通过XRD、FTIR、电镜(TEM、SEM)等检测手段,对凝胶燃烧产物和经水热处理后的粉体相组成、形貌进行分析,探讨HAP晶体形成的原因.结果表明,利用溶胶-凝胶经低温燃烧后形成主晶相为纳米级的HAP,形状以柱状为主,经水热处理后,可得高纯度的HAP柱状晶体(100 nm×1800 nm),杂以少量粒状纳米粒子(30 nm×60 nm).     

燃烧合成超细ITO粉体

以In粒和Sn粒为原料,尿素为燃料,柠檬酸为添加剂,燃烧合成ITO(掺锡氧化铟)粉体,利用粉末X射线衍射、扫描电子显微镜对产品进行表征,并研究柠檬酸(C6H8O7)对燃烧产物的影响.结果表明,以尿素为燃料燃烧合成是制备ITO粉体的有效途径,添加剂柠檬酸能有效抑制粉体的团聚,使颗粒分散性变好,得到颗粒细小均匀的ITO粉体...     

纳米(CeO_2)_(0.86)(Sm_2O_3)_(0.14)的形貌控制与表征

以Ce(NO3)3·6H2O和(NH4)2CO3为沉淀源,搀杂稀土氧化物Sm2O2,利用柠檬酸作为络合剂和分散剂,制备出纳米(CeO2)0.86(Sm2O3)0.14.并采用TEM、XRD等方法对其热分解所得纳米(CeO2)0.86(Sm2O3)0.14的形貌及结晶性等进行了表征.结果表明:随着柠檬酸加入量的增加,焙烧生成的纳米(CeO2)0.86 (Sm2O3)0.14颗粒的形貌从纳米线向类球形颗粒变化,所得(CeO2)0.86(Sm2O3)0.14为立方萤石结构,且随焙烧温度的提高,晶化程度增大.     

Al_2O_3/ZrO_2复合粉体的制备及表征

以Al(NO3)3.9H2O和ZrOCl2.8H2O为前躯体,NH3.H2O为沉淀剂,用共沉淀法制备出了Al∶Zr不同摩尔比的复合粉体,在不同温度下煅烧,利用TG-DSC、XRD、SEM分别对粉体进行表征,并由谢乐公式算出粉体粒度.结果表明相同煅烧温度下复合粉体的粒度随氧化锆含量的增加而增长,复合粉体中t-ZrO2的存在不仅受煅烧温度的影响而且受Al∶Zr摩尔比的制约.     

不同摩尔配比Al2O3-ZrO2复合粉体的物相

用Al(NO3)3·9H2O和ZrOCl2·8H2O为原料,氨水做沉淀剂,采用共沉淀法分别制备了不同摩尔比的Al2O3-ZrO2复合粉体,利用XRD、TEM对所得粉体进行了分析表征.结果表明,相同热处理温度(1 200 ℃)下,ZrO2均以四方相存在且粒径逐渐减小;相同摩尔配比条件下,随着煅烧温度的升高,m-ZrO2的体积分数逐渐增加.表明在复合粉体中Al2O3的存在抑制了ZrO2的t→m相变和晶粒长大,ZrO2对Al2O3的长大也有一定的阻碍作用.     

羟基磷灰石的制备及其热稳定性研究

以C a(NO3)2.4H2O和(NH4)2HPO4为前驱物,采用微波法制备纳米羟基磷灰石(HAP)粉末,研究了微波辐射时间、微波功率、低温煅烧对HAP粉体热稳定性的影响.研究结果表明:①HAP的热稳定性与微波辐射时间密切相关,最佳微波辐射时间是1 h;②以一个适中的微波功率(约470 W)辐射处理的反应溶液制得的HAP热稳定性最好;③微波法比传统沉淀法制得的HAP结晶度好,热稳定性更高;④低温预烧可以提高HAP的热稳定性.     

燃烧法制备纳米ZnFe_2O_4及其性能研究

以Fe(NO3)3·9H2O和Zn(CH3COO)2·2H2O为原料,以柠檬酸为还原剂,采用燃烧法制备ZnFe2O4纳米粉体,用X-射线粉末衍射仪(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)等手段对样品进行表征.结果表明,样品为尖晶石型铁酸锌纳米粉体,其粒径在30～50nm之间,且具有超顺磁性.同时研究了ZnFe2O4纳米粉体的光催化性能.     

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.     

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     

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.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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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。