A HYPERBOLIC SYSTEM OF CONSERVATION LAWS FOR FLUID FLOWS THROUGH COMPLIANT AXISYMMETRIC VESSELS

We are concerned with the derivation and analysis of one-dimensional hyperbolic systems of conservation laws modelling fluid flows such as the blood flow through compliant axisymmetric vessels.Early models derived are nonconservative and/or nonhomogeneous with measure source terms,which are endowed with infinitely many Riemann solutions for some Riemann data.In this paper,we derive a one-dimensional hyperbolic system that is conservative and homogeneous.Moreover,there exists a unique global Riemann solution for the Riemann problem for two vessels with arbitrarily large Riemann data,under a natural stability entropy criterion.The Riemann solutions may consist of four waves for some cases.The system can also be written as a 3×3 system for which strict hyperbolicity fails and the standing waves can be regarded as the contact discontinuities corresponding to the second family with zero eigenvalue.     

Asymptotically exact a posteriori estimators for the pointwise gradient error on each element in irregular meshes. Part II: The piecewise linear case

We extend results from Part I about estimating gradient errors elementwise a posteriori, given there for quadratic and higher elements, to the piecewise linear case. The key to our new result is to consider certain technical estimates for differences in the error, , rather than for itself. We also give a posteriori estimators for second derivatives on each element.

     

Maximum-norm estimates for resolvents of elliptic finite element operators

Let be a convex domain with smooth boundary in . It has been shown recently that the semigroup generated by the discrete Laplacian for quasi-uniform families of piecewise linear finite element spaces on is analytic with respect to the maximum-norm, uniformly in the mesh-width. This implies a resolvent estimate of standard form in the maximum-norm outside some sector in the right halfplane, and conversely. Here we show directly that such a resolvent estimate holds outside any sector around the positive real axis, with arbitrarily small angle. This is useful in the study of fully discrete approximations based on -stable rational functions, with small.

     

亚胺膦R_3PNH(R =CH_3,Cl)的极性及P-N键性质的理论研究

用从头算方法在B3LYP/ 6 31G 水平上对亚胺膦R3PNH(R =CH3,Cl)进行了理论计算研究。结果表明这两种亚胺膦的极性 ,P -N键性质及分子轨道存在明显差异 ,亚胺膦 (CH3) 3P =NH及其P -N键的极性很强 ,而Cl3P =NH的极性则较弱。与Cl3P =NH相比 (CH3) 3P =NH可能是较好的类Wittig反应试剂。     

棉花植株及土壤中丙硫克百威及其代谢物残留气相色谱测定

研究超声波提取、毛细管气相色谱配氮磷检测器(NPD)检测棉花植株及土壤中丙硫克百威及其代谢物残留 ,各组分回收率83%～110 % ,线性范围0.1～100mg/L,最低检测质量分数0.01×10-6～0.02×10-6(w) ;该法具有简单、快速、节省试剂的特点     

Asymptotically exact a posteriori estimators for the pointwise gradient error on each element in irregular meshes. Part 1: A smooth problem and globally quasi-uniform meshes

A class of a posteriori estimators is studied for the error in the maximum-norm of the gradient on single elements when the finite element method is used to approximate solutions of second order elliptic problems. The meshes are unstructured and, in particular, it is not assumed that there are any known superconvergent points. The estimators are based on averaging operators which are approximate gradients, ``recovered gradients', which are then compared to the actual gradient of the approximation on each element. Conditions are given under which they are asympotically exact or equivalent estimators on each single element of the underlying meshes. Asymptotic exactness is accomplished by letting the approximate gradient operator average over domains that are large, in a controlled fashion to be detailed below, compared to the size of the elements.

     

Parabolic finite element equations in nonconvex polygonal domains

Let Ω be a bounded nonconvex polygonal domain in the plane. Consider the initial boundary value problem for the heat equation with homogeneous Dirichlet boundary conditions and semidiscrete and fully discrete approximations of its solution by piecewise linear finite elements in space. The purpose of this paper is to show that known results for the stationary, elliptic, case may be carried over to the time dependent parabolic case. A special feature in a polygonal domain is the presence of singularities in the solutions generated by the corners even when the forcing term is smooth. These cause a reduction of the convergence rate in the finite element method unless refinements are employed.     

High quality YBCO superconductive thin films fabricated by laser molecular beam epitaxy

High quality YBa₂.Cu₃O_{6 +x}(YBCO) superconductive thin films have been fabricated on the SrTiO₃(100) substrate using laser molecular beam epitaxy (laser-MBE). The active oxygen source was used, which made the necessary ambient oxygen pressure be 2–3 orders lower than that in pulsed laser deposition (PLD). T_c0 is 85–87 K, and J_c, 1.0 × 10⁶ A/cm². Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm. High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.     

花生酸-钌有机螯合物Ru(phen)_3~(2+)的单分子膜和LB膜中分子聚集行为的研究

以功能性的钌有机螯合物Ru(phen) 2 + 3 作为亚相离子 ,花生酸在亚相表面上形成稳定的单分子膜 .π A等温线和动态弹性测量表明 ,此膜因花生酸与钌螯离子发生了静电相互作用而有更大的可压缩性 ,并在固态区发生了分子聚集 .用垂直法成功地制备了嵌有Ru(phen) 2 + 3 离子的超薄有序Y 型LB膜 .光谱实验表明 ,所得LB膜是稳定、均匀的层状三明治结构 ,在层面内Ru(phen) 2 + 3 与花生酸结合成相对稳定的分子基团并形成了J 聚体