Thermal conductivity of open‐cell polyolefin foams

The thermal conductivity and the cellular structure of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene‐vinyl acetate copolymer (EVA) and a low‐density polyethylene (LDPE) have been studied in the temperature range between 24 and 50 °C. The experimental results have shown that the cellular structure of the analyzed materials has interconnected cells because of the presence of large and small holes in the cell walls, this structure being clearly different to the typical structure of open‐cell polyurethane foams. It has been found that at low temperatures the materials have a slightly higher thermal conductivity than closed‐cell polyolefin foams of similar densities. The different mechanisms of heat flow, conduction, convection, and radiation have been analyzed by using experimental measurements and a theoretical model. It has been proved that, in spite of having an open‐cell structure, the convention mechanism is negligible, being the radiation mechanism the one which made different the conductivity of materials with varying cellular structures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 212–221, 2008     

β-Na（Y_（1.5-x-y）Na_（0.5））F_6：Yb_xTm_y纳米颗粒的合成及其上转换发光性质

本文采用水热合成法制备了β-Na（Y1.5-x-yNa0.5）F6：YbxTmy（x=0.2~1.0,y=0.001~0.008）纳米颗粒,并利用X射线粉末衍射仪、透射电子显微镜和F-4600荧光分光光度计表征了其样品的物相、形貌和发光性质.结果表明样品物相为六角相,颗粒平均直径约22nm,并探讨了Yb3＋和Tm3＋掺杂浓度对样品的上转换发光性质的影响,结果表明敏化剂Yb3＋的最佳掺杂浓度为60%,而激活剂Tm3＋的最佳掺杂浓度为0.6%.     

Absolutely isolated singularities of a differential equation

In this paper we solve the problemof desingularization of an absolutely isolatedsingularity of a differential equation, including thedicritical case. As an application, we prove thefiniteness of the number of dicritical points in theblowing up tree of an absolutely isolated singularity.     

Decarboxylative Cyclization of Allylic Cyclic Carbamates: Mechanism Studies and Applications to the Synthesis of Natural Products

The mechanism of decarboxylative cyclization of allylic cyclic carbamates 1 leading to 2-substituted △~3-piperidines and-pyrrolidines, as well as its applications to the total synthesis of (--)codonopsine, are described.     

藏药"西藏猫乳"的色谱指纹谱研究

用75%乙醇回流法提取出藏药"西藏猫乳(生等)"的有效成分并浓缩精制后,采用HPLC梯度洗脱法,在选定的色谱条件{DuPont ZORBAX ODS C18色谱柱(4.6 mm×25 cm),用甲醇(A)-甲酸铵水溶液(pH=3.5,1.0 mL·min-1,B)进行梯度洗脱(甲醇浓度0～10 min,20%～25%;10～20 min,25%～40%;20～55 min,40%～55%;55～75 min,55%～75%;75～85 min,75%～90%),检测波长为290 am}下,对藏药"生等"的提取液进行了有效的分离与检测,并建立了"生等"药材的数字化色谱指纹谱(DFPS).所建立的方法能对藏药的产地归属进行有效的分辨.     

Relaxation Limit for Aw-Rascle System

We study the relaxation limit for the Aw-Rascle system of traffic flow. For this we apply the theory of invariant regions and the compensated compactness method to get global existence of Cauchy problem for a particular Aw-Rascle system with source, where the source is the relaxation term, and we show the convergence of this solutions to the equilibrium state.     

Yb3+/Er3+共掺(MLaFn)x(M=0,K;n=3,4;x=1,1.5)纳米材料的控制合成及其上转换发光性质

采用水热与溶剂热结合的方法,在乙二醇-正己醇体系中,通过调节KF与RE(RE=La,Yb,Er)的量比、反应温度和反应时间实现了由LaF_3(六角相)到KLaF_4(立方相、六角相)晶型的控制合成。借助透射电子显微镜(TEM)和X射线粉末衍射(XRD)对样品的结构和微观形貌进行表征。结果表明,当KF/RE比例为2. 25时,制备的样品为片状的六角相LaF_3纳米颗粒;当KF/RE比例为3. 00时,得到具有近似球形的立方相KLaF_4纳米颗粒;当KF/RE比例为4. 25时,得到了六角相(KLaF_4)_(1. 5)纳米颗粒。上转换发射光谱显示:所有的样品在近红外光(980 nm)激发下,均有3个明显的发射峰,在522 nm、544 nm处分别对应于Er~(3+)的~4S_(3/2),~2H_(11/2)→~4I_(15/2)能级跃迁,655 nm处属于Er~(3+)的~4F_(9/2)→~4I_(15/2)能级跃迁。     

The Numerical Solution of Laplace's Equation on a Wedge

Laplace's equation is considered on regions in the plane, withthe boundary having corners; and the double-layer potentialis used to derive a solution. The essential difficulties, boththeoretically and numerically, are reduced to the case in whichthe boundary is a simple open wedge. The theoretical behaviourof the double layer integral equation is studied explicitly,and then piecewise linear and piecewise quadratic collocationmethods are applied to the numerical solution of the equation.The major question of interest is the stability of the inversesof the approximating equations. The behaviour of the numericalmethods is somewhat surprising, and it is much better than pastanalyses would have led one to expect.     

拟桶式空间的强对偶空间值的向量测度

证明了在某种紧性条件下拟桶式空间的强对偶空间值的向量测度的唯一存在性。