Formation of β-distonic oxonium ions: Study of ROCH2CH2OR′ radical cations

Radical cations derived from the ethers ROCH₂CH₂OR′ (R, R′ = H, CH₃, C₂₅) were studied, since β-distonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,5-transfer of an α-hydrogen to oxygen of a terminal alkoxy group leading to a δ-distonic oxonium ion. This step is thermo-neutral and reversible in the ROCH₂CH₂OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R,′ these δ-distonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a β-distonic oxonium ion ˙CH₂CH₂O(H)⁺R and a 1,4-H migration between carbon atoms. Competition between these processes is discussed.     

Passive control of the flow around a square cylinder using porous media

The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd.     

Ein allgemeiner Satz über die Integrirbarkeit von Functionen integrirbarer Functionen

Ohne ZusammenfassungAbgedruckt aus den Sitzungsberichten der math.-phys. Classe der k. b. Akadem. d. Wiss. zu München.     

Voltammetric determination of mesotrione at hanging mercury drop electrode

A study of the electrochemical reduction of the mesotrione pesticide on a hanging mercury drop electrode (HMDE) was performed as a basis for the development of a sensitive analytical method for natural samples. The electrochemical characteristics of herbicide mesotrione dissolved in a phosphate buffer (pH 7.0) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) over a wide range of pH from 2.0 to 10.0. The experimental parameters, such as electrolyte type and its pH, pulse amplitude, and scan rate were optimized. The method was applied to the determination of the pesticide in a spiked soil samples. Using this method, a linear calibration curve for mesotrione was obtained up to the 0.1 μM range in pH 7 phosphate buffer solution with a detection limit (S/N = 3) of 50 nM. The method can be applied successfully to the determination of mesotrione in soils. The text was submitted by the authors in English.     

氘代聚合物膜靶制备技术与性能研究

 氘代聚合物膜是快点火基础物理实验的一种重要靶型。通过氘代苯乙烯单体的本体自由基聚合反应制备氘代聚苯乙烯，并利用流延法和浇铸法制备出厚度从几十nm到数百μm的膜靶。溶剂挥发过程中的随机扰动对膜厚均匀性造成影响，采用清洁的基片和在涂沫基片或模具外加防护罩可以降低这种影响。采用PVA作脱膜剂有利于获得较薄的聚合物薄膜。DSC分析表明薄膜的玻璃化转变温度与热处理过程有关，缓慢退火有利于提高Ｔ-g和储能模量。     

GM(1,1)改进模型及其应用

根据 GM( 1 ,1 )灰色模型的指数特性 ,通过在区间上求积分给出了关于背景值的一个比较确切的计算公式 ,讨论了由此建立的 GM( 1 ,1 )改进模型的适用范围和预测精度 .结果表明改进模型比原 GM( 1 ,1 )模型适用性要强、模拟和预测精度要高 ,不仅适用于低增长序列、也适用于高增长序列 ,不仅适用于短期预测 ,同样也适用于中、长期预测     

On Improvements to the Analytic Center Cutting Plane Method

In this paper, we explore a weakness of a specific implementation of the analytic center cutting plane method applied to convex optimization problems, which may lead to weaker results than Kelley's cutting plane method. Improvements to the analytic center cutting plane method are suggested, and tested on some example problems.