Entropy generation through hexagonal cross‐sectional duct for constant wall temperature in laminar flow

Second law analysis of heat transfer in laminar flow for hexagonal cross‐section duct was analysed analytically. Geometrical effect of hexagonal duct was considered. The variation of total entropy generation was studied along the duct length. As a working fluid water and unused engine oil were used to compare the effect of fluid in the duct. Results were compared with circular cross‐section duct. It is found that the non‐dimensional entropy generation in a hexagonal cross‐section duct can be as high as a factor of four than that for a circular duct. Further, the unused engine oil gives up to about ten times lower non‐dimensional entropy generation values than that of water but needs about ten times more pumping power to heat transfer ratio. Copyright © 2004 John Wiley & Sons, Ltd.     

氮化硼薄膜的脉冲激光沉积

用Ｑ开关ＹＡＧ激光器的１．０６μｍ的脉冲激光在硅及玻璃衬底上沉积了氮化硼薄膜。做了ＳＥＭ，ＸＲＤ，红外透射谱和紫外一可见透射谱等测试。确认为六方氮化硼（ｈ－ＢＮ）薄膜．并测出其禁带宽度、晶格常数等。     

Discrete topology and contour definition

For all kinds of stationary plane grids only the 6-neighborhood is consistent. It admits the definition of a digital curve, in particular a contour, as a set of pixel pairs. Thus curves become objects of zero thickness and may be coded with one bit per grid step.     

Interlamellar failure at transcrystalline interfaces in glass/polypropylene composites

Transcrystalline microstructures are normally not observed at the interface between E-glass fibers and an isotactic polypropylene matrix, unless mechanical translation is applied to the fiber while it is in the supercooled polymer melt. We demonstrate here that transcrystallinity can form at the surface of E-glass fibers if appropriate nucleating agents are used to coat the fibers. These agents can nucleate either the (monoclinic) or β (hexagonal) crystal forms of polypropylene. Single-fiber composite experiments were performed to assess the effect of transcrystallinity on matrix deformation. The preliminary results presented here reveal the occurrence of a previously unreported damage mechanism by which interlamellar fractures form preferentially at the interface well before any bulk matrix damage occurs. The density of this damage zone is higher in transcrystallinity of the β crystal form than of the form, although it was found that in the form the damage can propagate into the matrix. The occurrence of this damage mechanism suggests that toughness increases may potentially be obtained by careful design of the interfacial transcrystalline region in E-glass/polypropylene composites.     

Internal friction in hexagonal metalś

An overview of the studies of internal friction in hexagonal metals and alloys is presented. An outline of the experimental techniques of measurement and the atomistic mechanisms causing internal friction is also given.     

铜银改性六方介孔硅材料的结构及抗菌性能

采用溶胶-凝胶法,合成了铜银改性的六方介孔二氢化硅(hexagonal mesoporous silica,HMS)无机抗菌材料,通过X射线衍射、顺磁共振、紫 外漫反射、Fourier红外、热重-差热分析、环境扫描电镜、电子能谱及N2的吸附-脱附技术对材料结构进行了表征,并以大肠杆菌、金黄色葡萄球菌、枯草杆菌及芽孢杆菌为实验对象考察了材料的抗菌性能.结果表明:铜、银已引入HMS载体的骨架,材料的介孔结构、孔径、粒子形貌等也发生了明显变化,脱模的热化学过程大大缩短,对紫外-可见光吸收明显增强;抗菌实验显示材料抗菌惟能良好.对枯草杆菌及芽孢杆菌的抗菌效果最佳,铜银原位改性HMS的用量为1.00g/L,12h后即可将两者彻底杀灭.     

碳酸化分解法合成板状氢氧化铝的研究

介绍了一种制备板状氢氧化铝粉体的新方法。从晶体生长行为和反应机理出发,研究碳酸化分解法不同工艺条件:原料液偏铝酸钠浓度、反应气体CO2通气速率、碳分终点pH值、干燥条件等因素对氢氧化铝粉体板状结构的影响。同时,也考察了不同晶型向导剂和分散剂对粉体形貌的影响。得到的产品采用扫描电镜(SEM)、X射线衍射(XRD)和BET比表面积等检测手段进行表征。实验结果表明,当偏铝酸钠溶液的浓度为2.0~2.5 mol/L,CO2气体通气速率为100~200 L/h,反应终点控制为pH=12,添加一定量的A lF3和三乙醇胺作为晶型向导剂和分散剂时,可以得到六角板状氢氧化铝,其平均粒径为16.520μm,径厚比为30~60,比表面积351.350 3 m2/g。     

Bridging a Culture: The Design of Museo Soumaya

Fernando Romero and Armando Ramos of Fernando Romero EnterprisE (FREE) describe how the firm's design for an iconic museum in Mexico City, which adopted complex computational techniques, required them to develop an integrated and highly collaborative approach to design; with a central digital 3-D model being applied throughout the construction phase.     

新型六角芯光子晶体光纤的色散补偿特性研究

文章利用多极法对新型六角芯光子晶体光纤的色散特性进行了数值模拟与分析,研究发现,通过改变第一包层空气孔直径和空气孔间距,可以灵活地设计波长在1.55μm附近具有高色散值、大的负色散斜率和能在短波长内单模传输的色散补偿型光纤.数值模拟和分析表明,该光子晶体光纤在色散补偿型光纤方面具有广泛的应用前景.     

基于六边形网格结构的针织物三维建模

为方便快捷地构造出接近针织物真实线圈的三维几何模型,提出一种基于六边形网格结构理论的方法。首先根据针织线圈穿套时形成的交织点,构建出六边形网格结构,由此确定每个线圈单元的8个特殊型值点,并根据纱线线密度和织物厚度通过三角函数关系求得型值点的具体坐标。其次将型值点插入非均匀有理B样条曲线,利用反算法推算出控制顶点及确认最终纱线路径,并进行扫面操作形成单个纱线线圈。最后通过阵列方法依次重复排列,得到特定组织循环的针织三维模型,并且对单元模型进行导热分析。结果表明,最终模拟计算结果与实际测量值的误差在4%以内,所建模型具有较好的实用性和合理性。