On Spectrum Congestion and Capacity of Radio Links

This paper addresses the operation of radio links under mutual interference conditions, an important problem in spectrum management and radio link design. It introduces the capacity loss and isolation index as measures of effective use of radio links and radio frequency spectrum resources.     

Interactive vortex shedding from a pair of circular cylinders in a transverse arrangement

Interactive vortex shedding in the multiply connected domain formed by a pair of circular cylinders is analysed by the FEM–FDM blending technique. The vorticity–streamfunction formulation is used to solve the incompressible Navier–Stokes equations at Re = 100, with the time-dependent wall streamfunctions determined from the pressure constraint condition and the far-field streamfunctions from the integral series formula developed earlier by the authors. The standard Galerkin finite element method is used in the relatively small FEM subdomain and the finite difference method based on the general co-ordinate system in the rest of the flow domain. Symmetric, antisymmetric and asymmetric wake patterns are obtained confirming the earlier experimental findings. The bistable nature of the asymmetric vortex shedding as well as the intermittent drifting from one status to the other between symmetric and antisymmetric wake patterns are reported.     

Thermal Analysis of the High-Energetic Material HNF

In a search for new storable high performance propellants for the European Space Agency (ESA), the solid oxidiser hydrazinium nitroformate (HNF) has been identified as a very promising ingredient for a new storable composite propellant. The purity and stability of HNF after production are very important indicators for the quality of HNF. In order to characterise HNF,many thermal analysis techniques as DSC and TG/DTA were performed to obtain more information about its stability and its (in)compatibility with other materials. Also some less familiar techniques such as the vacuum stability test and microcalorimetry have been performed. In relation to the safety, a relation between the friction and impact sensitivity and the physical-chemical properties is made. This revised version was published online in July 2006 with corrections to the Cover Date.     

A simple approach toward low‐dielectric polyimide nanocomposites: Blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane

This article describes a new and simple method for preparing polyimide nanocomposites that have very low dielectric constants and good thermal properties: simply through blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane derivative, octakis(dimethylsiloxyhexafluoropropyl) silsesquioxane (OF). The low polarizability of OF is compatible with polyimide matrices, such that it can improve the dispersion and free volume of the resulting composites. Together, the higher free volume and lower polarizability of OF are responsible for the lower dielectric constants of the PI‐OF nanocomposites. This simple method for enhancing the properties of polyimides might have potential applicability in the electronics industry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6296–6304, 2008     

Preparation and characterization of cellulose and konjac glucomannan blend film from ionic liquid

Blend films from cellulose and konjac glucomannan (KGM) in room temperature ionic liquid 1‐allyl‐3‐methylimidazolium chloride were satisfactorily prepared by coagulating with water. The composition of the blend films was gravimetrically analyzed, and the compatibility of the two natural polymers was characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction. The results indicate good compatibility and strong interactions between cellulose and KGM, resulting in almost no loss of the water‐soluble KGM from the blend films even after the water coagulating and washing. However, microstructure analyses portrayed phase separations in the blend films, namely, egg‐like new phase particles were embedded in a continuous matrix base (MB). Phase diagram analysis and differential scanning calorimetry of the phase inversion coagulation process suggest that relative low molecular mass part of both cellulose and KGM formed the continuous MB, whereas the egg‐like new phase particles were super patterns of relative high molecular mass of both polymers, which played an important role in strengthening the blend material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1686–1694, 2009     

平均值组合评价方法的优良性研究

综合评价方法广泛应用于教育、管理等很多领域.在一定程度上可以说综合评价的结果是决策的基础.因此选用好的综合评价方法非常重要.提出了一种新的综合评价方法:平均值组合评价方法.这种方法在一定程度上克服了单一综合评价方法的片面性.研究结果还表明所提的平均值组合评价方法在平方损失函数和兼容度两种标准下具有优良性.     

Complementary energy principle for large elastic deformation

Using the “base forces” as the fundamental unknowns to determine the state of an elastic system, the complementary energy principle for large elastic deformation is constructed for the conjugate quantities being displacement gradients, which possesses exactly the same form as that of classical linear elasticity. It is revealed that the complementary energy contains deformation part and rotation part.     

羟乙基壳聚糖的合成及其与聚乳酸的相容性

本文以异丙醇为溶剂,碱化壳聚糖与2-氯乙醇反应制备了羟乙基壳聚糖,对产物的结构与性能进行了分析表征;然后以二甲基亚砜为溶剂,采用溶液共混法制备了一系列不同组成的壳聚糖/聚乳酸和羟乙基壳聚糖/聚乳酸复合膜,对两组分间的相容性进行了研究。结果表明,羟乙基化反应在-OH和-NH2上均有发生,壳聚糖单元糖环上的羟乙基取代度为2.46;改性后,壳聚糖结晶性能和起始热分解温度下降,溶解性能得到改善。复合膜的电镜结果显示,在壳聚糖/聚乳酸复合膜中,相分离现象显著存在,壳聚糖在聚乳酸基体中的分散不均匀,有团聚现象,随着壳聚糖含量增加,两组分间的相分离程度增大,团聚现象更为严重,当壳聚糖含量达到50%时,已难以制备完整的复合膜;与之相反,羟乙基壳聚糖/聚乳酸复合膜中两种组分之间的相容性有所改善,相分离现象不明显,并且,当羟乙基壳聚糖含量从10%增加到50%,复合膜中两种组分之间的相容性变化不大。     

羟基磷灰石/聚乳酸微粒复合生物支架的体外细胞相容性评价

利用溶液共混法以及溶剂挥发法制备了羟基磷灰石(Nano-HA)/聚乳酸(PLA)微粒,再粘结微粒加工成三维多孔Nano-HA/PLA微粒复合生物支架。借助相差显微镜、扫描电子显微镜和MTT法检测了鼠骨髓基质细胞(BMSCs)在该支架材料上的生长情况,通过细胞形态学观察和细胞增殖情况评价了该复合生物支架材料的生物相容性。结果表明,SEM观察到支架材料上培养细胞4d后,细胞主要附着、铺展在支架的低洼处或孔洞处表面,并向孔洞深部沿壁生长;在支架材料上培养细胞8d后,细胞多为梭形形态,并有许多生长角,直接贴附于支架的微粒表面,开始连片生长,有明显的增值,各组没有变形、坏死现象。支架材料上培养细胞2,3,4,5,6和8d的MTT检测表明,各实验组RGR均达到100%以上,细胞毒性为0级;细胞在支架材料上的生长曲线显示,实验组细胞活力比对照组高26%。因此,该Nano-HA/PLA微粒复合生物支架没有细胞毒性,并对细胞有良好的粘附和增殖能力,为较具潜力的骨修复材料。