Approximation of an Eigenvalue Problem Associated with the Stokes Problem by the Stream Function-Vorticity-Pressure Method

By means of eigenvalue error expansion and integral expansion techniques, we propose and analyze the stream function-vorticity-pressure method for the eigenvalue problem associated with the Stokes equations on the unit square. We obtain an optimal order of convergence for eigenvalues and eigenfuctions. Furthermore, for the bilinear finite element space, we derive asymptotic expansions of the eigenvalue error, an efficient extrapolation and an a posteriori error estimate for the eigenvalue. Finally, numerical experiments are reported. The first author was supported by China Postdoctoral Sciences Foundation.     

Determination of tributyltin in sediments by hydride generation /GC/QFAAS

All steps involved in the determination of tributyltin in sediments by anhydrous acetic acid extraction, hydride generation, cold trapping, gas chromatographic separation and quartz furnace atomic absorption spectrometry are critically examined. Detection limits (1.8 ng Sn.g^–1) and reproducibility at representative concentration levels (6–12%) are satisfying for practical purposes.     

Investigation of Plasma Parameters in a Magnetoplasma Compressor

The article presents the results of experimental investigations that were carried out at the Center for Science and Technology Development in Belgrade (Yugoslavia) and pertained to the plasma streams generated by a gasdischarge magnetoplasma compressor (MPC). The integral characteristics of the discharge, the dynamic parameters of a compression flux, and the concentration of the plasma electrons in the magnetoplasma compressor have been determined. The distinguishing features of the discharge afterglow from the volume of a vacuum chamber for a long time after the termination of the discharge current have been investigated.     

Register Synthesis for Algebraic Feedback Shift Registers Based on Non-Primes

In this paper, we describe a solution to the register synthesis problem for a class of sequence generators known as algebraic feedback shift registers (AFSRs). These registers are based on the algebra of -adic numbers, where is an element in a ring R, and produce sequences of elements in R/(). We give several cases where the register synthesis problem can be solved by an efficient algorithm. Consequently, any keystreams over R/() used in stream ciphers must be unable to be generated by a small register in these classes. This paper extends the analyses of feedback with carry shift registers and algebraic feedback shift registers by Goresky, Klapper, and Xu.     

Determination of the parameters of a three-dimensional heat release region in a supersonic stream from pressure measurements

Three-dimensional steady-state supersonic flow with weak heat release is analyzed. Two conjugate problems are considered: determination of the forces exerted on surfaces surrounding a given heat source and determination of the release region and the amount of heat released from pressure measurements in the surrounding space. Features of the three-dimensional flow are found. The characteristic properties of the three-dimensional flow are illustrated with reference to a spherical Gaussian source.     

DVB传输流捕获系统的实现

研究了DVB传输流实时捕获系统的结构及其实现方法．该系统的硬件利用复杂可编程逻辑器件和总线接口芯片,实现了传输流与PcI总线之间的接口,软件利用设备驱动程序将硬件采集的数据流传入计算机．同时保证了高速的数据交换速率,可以对捕获的数据流进行实时的处理,该系统在DvB的分析、测试、存储、编辑和复用中都有着广阔的应用前景．     

Isotopengeochemische Charakterisierung kohlenwasserstoffbildender organischer Substanzen

Within the framework of a larger research project on contributions of isotope investigations to natural gas and crude oil exploration, the following publication is a first part of research reports from the author's laboratory.

The isotopic composition of carbon in fossil organic matter is primarily determined by the type of biological precursors. The main constituents forming organic matter in sediments are higher plants and microorganisms (algae, bacteria). These precursors contain a great number of organic compounds with corresponding isotope signatures. Hydrocarbons and lignin e.g., are enriched in carbon 13, while lipids in most cases are depleted.

Semi-empirical calculations on a thermodynamic basis are used to precalculate isotopic compositions of components or single compounds, applying the so-called β-factor method. The results are compared with numerous data from references about isotopic compositions of higher plants, algae and plant components. Also environmental conditions of plant growing-including paleoenvironment-have been taken into consideration.

The δ¹³C values of more than 150 types of organic substances in sediments of several geological formations have been measured in our isotope geochemical department.

The results allow a characterization and classification of organic matter: humic and sapropelitic organic substances can in many cases be distinguished by their isotopic signatures taking into account exceptions of e.g., regional origins. Influences of maturity (characterized by vitrinite reflectance) and especially of macerale composition of organic matter on it's isotope values and on the formation of hydrocarbons including their isotopic compositions are elucidated. The interpretation concept is also assured using special examples of drilling sites in Germany. The obtained results and proposed interpretation concept can contribute to further development in the understanding of hydrocarbon formation and natural gas exploration.     

Leaching Behaviour and Solid Phase Fractionation of Selected Metals as Affected by Thermal Treatment of a Polluted Sediment

Abstract

A contaminated dredged sediment was subjected to a thermal treatment at temperatures ranging from 120 to 450°C. The leaching behaviour of selected metals (Cd, Cu, Pb, Zn, Fe, Mn) was studied using NH₄OAc-EDTA extraction. In addition, solid phase fractionation was carried out by means of a sequential extraction procedure.

The NH₄OAc-EDTA extraction showed a sharp increase in metal leachability from sediments treated at intermediate temperatures (120–350°C). The metal fractionation of the solid phases at the different temperatures did not reveal relevant shifts except for Cu. The decrease of the oxidizable Cu fraction was highly correlated (P < 0.001) with the disappearance of organic matter at higher treatment temperatures. It is suggested that binding energy changes within the fractions rather than shifts between chemical forms account for the observed leaching behaviour.     

A locally conservative,discontinuous least‐squares finite element method for the Stokes equations

Conventional least‐squares finite element methods (LSFEMs) for incompressible flows conserve mass only approximately. For some problems, mass loss levels are large and result in unphysical solutions. In this paper we formulate a new, locally conservative LSFEM for the Stokes equations wherein a discrete velocity field is computed that is point‐wise divergence free on each element. The central idea is to allow discontinuous velocity approximations and then to define the velocity field on each element using a local stream‐function. The effect of the new LSFEM approach on improved local and global mass conservation is compared with a conventional LSFEM for the Stokes equations employing standard C⁰ Lagrangian elements. Copyright © 2011 John Wiley & Sons, Ltd.