A model study for the steady state error of numerical approximations of inviscid flow equations on Cartesian grid

The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. In this paper we consider the influence of the refined interfaces on the steady state errors for second‐order three‐point difference approximations of flow equations. Since the various characteristic components of the Euler equations should behave similarly on such grids with regard to refinement‐induced errors, it is sufficient enough to conduct the analysis on a scalar model problem. The error we consider is a global error, different to local truncation error, and reflects the interaction between multiple interfaces. The steady state error will be compared to the errors on smooth refinement grids and on uniform grids. The conclusion seems to support the numerical findings of Yamaleev and Carpenter (J. Comput. Phys. 2002; 181: 280–316) that refinement does not necessarily reduce the numerical error. Copyright © 2005 John Wiley & Sons, Ltd.     

方位伺服系统扭转振动固有频率的分析

本文阐述了伺服系统结构设计中估算系统固有频率的必要性,介绍了一种分析和计算经纬仪方位伺服系统扭转振动固有频率的方法。     

DIELS-ALDER REACTIONS OF FURAN WITH DIENOPHILES CATALYZED BY YbCl3

The yield and stereoselectivity of the Diels-Alder reactions between furan(or 2-methylfuran)and different dienophiles are markedly enhanced by the catalysis of anhydrous YbCl₃.     

Representing workloads in GI/G/1 queues through the preemptive-resume LIFO queue discipline

We give in this paper a detailed sample-average analysis of GI/G/1 queues with the preemptive-resume LIFO (last-in-first-out) queue discipline: we study the long-run state behavior of the system by averaging over arrival epochs, departure epochs, as well as time, and obtain relations that express the resulting averages in terms of basic characteristics within busy cycles. These relations, together with the fact that the preemptive-resume LIFO queue discipline is work-conserving, imply new representations for both actual and virtual delays in standard GI/G/1 queues with the FIFO (first-in-first-out) queue discipline. The arguments by which our results are obtained unveil the underlying structural explanations for many classical and somewhat mysterious results relating to queue lengths and/or delays in standard GI/G/1 queues, including the well-known Bene's formula for the delay distribution in M/G/l. We also discuss how to extend our results to settings more general than GI/G/1.     

沈阳市健康人血清中Mg、Zn、Cu、Se、Cr含量及其相关关系探讨

报告了143例沈阳市健康人血清中Mg、Zn、Cu、Se、Cr含量及Cu／Zn值，并指出健康人血清中Mg与Cu量正相关，Mg与Cr呈负相关，Mg与Cu／Zn值呈正相关.Zn与Cr呈正相关.Zn与Cu/Zn呈负相关.Cu与Cr呈负相关。Cu与Cu／Zn值呈负相关.Cr与Cu／Zn值呈负相关.     

双甘肽稀土配合物溶液结构的13C和1H NMR研究

~(13)C and ~1H NMR technique was used to study the interaction of Gly-Gly with heavy lanthanide cations Dy~(3+), Ho~(3+), Er~(3+), Tm~(3+) and Yb~(3+) in aqueous solution. The stability constants for the 1:1 and 1:2 complexes of Gly-Gly with Ho~(3+) and Yb~(3+) were determined from the titration curves of chemical shift versus concentration ratio of lanthanide to Gly-Gly. The solution structure of the Ln-Gly-Gly complex was analyzed based upon the ~(13)C and ~1H lanthanide-induced shifts and the results show that in the complex Gly-Gly is coordinated to the lanthanide ion through the carboxyl oxygens with the backbone of the ligand in an extended state.     

酶分子在试管内的定向进化及其在手性有机物合成中的应用

本文扼要介绍了当今改进酶分子性能的有效手段———分子定向进化技术的基本方法如易错PCR和DNA洗牌,以及派生的一些新技术的原理与进展,并列举了在手性有机物合成中一些成功的实例,为该领域的研究与应用提供了一些新的信息。