Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.     

Copper(II) complexes with pyridine-2,6-dicarboxylic acid from the oxidation of copper(I) iodide

Via an oxidation reaction of Cu(I) iodide with pyridine-2,6-dicarboxylic acid (H₂L) in DMF three copper(II) complexes, [(CH₃)₂NH₂]₂[CuL₂] (1), K₂[CuL₂]?H₂L?H₂O (2) and [Cu(L)(H₂O)]_n (3), were synthesized and characterized. The structures of 1–3 were determined by single crystal X-ray diffraction studies. In-situ DMF decomposition produces dimethylamine base under solvothermal conditions and a proton transfer reaction takes place for the complex formation of 1. 3-D networks are stabilized in 1 and 2 via hydrogen bonds. Complex 3 is a 1-D coordination polymer with Cu-O semi-coordination bonds. Thermal decomposition of the complexes results in the corresponding metal oxides. Also, the electrochemical behavior of 1 was determined to be a metal-centered and diffusion-controlled, one-electron reduction process.     

Statistical Extensions of Some Classical Tauberian Theorems for Cesàro Summability of Triple Sequences

Some growth conditions of the resolvent function of a Banach space operator are investigated using higher order Cesàro means. More precisely, Abel and Nevanlinna estimates are obtained under the condition of boundedness of some weighted Cesàro averages. Also, certains results related to the (strong or uniform) convergence of Cesàro means are mentioned.     

On the cross ratios of points and lines in Moufang planes

In this paper, first we extend the known definition of cross-ratio of collinear points to whole Moufang plane. Later we introduce the cross-ratios for lines, and we adapt the known results about the cross-ratios of points to cross-ratios of lines using the principle of duality. Finally, we give a theorem which describes the relation between the cross-ratios of points and lines. Received 2 March 2000; revised 22 November 2000.     

The new robust conic GPLM method with an application to finance: prediction of credit default

This paper contributes to classification and identification in modern finance through advanced optimization. In the last few decades, financial misalignments and, thereby, financial crises have been increasing in numbers due to the rearrangement of the financial world. In this study, as one of the most remarkable of these, countries’ debt crises, which result from illiquidity, are tried to predict with some macroeconomic variables. The methodology consists of a combination of two predictive regression models, logistic regression and robust conic multivariate adaptive regression splines (RCMARS), as linear and nonlinear parts of a generalized partial linear model. RCMARS has an advantage of coping with the noise in both input and output data and of obtaining more consistent optimization results than CMARS. An advanced version of conic generalized partial linear model which includes robustification of the data set is introduced: robust conic generalized partial linear model (RCGPLM). This new model is applied on a data set that belongs to 45 emerging markets with 1,019 observations between the years 1980 and 2005.     

Electron paramagnetic resonance and FT-IR spectroscopic studies of DL-2-aminoadipic acid and ammonium acetate powders

Exposure of powder forms of DL-2-aminoadipic acid and ammonium acetate to gamma radiation results in the formation of free radicals detected by the electron paramagnetic resonance spectroscopy at room temperature. In these compounds, the observed paramagnetic species were attributed to the HOOCCH₂CH₂CH₂CHCOOH and CH₂COONH₄ radicals, respectively. The g values and the hyperfine coupling constants of the unpaired electron with the environmental protons were determined for these two radicals. In work, the observed paramagnetic species were found to be stable at room temperature for more than two months. Also, these compounds were characterised by FT-IR and UV–VIS. Their thermal stabilities were determined by TGA and DTA measurements. Thermal analyses were shown to be unstable of the HOOCCH₂CH₂CH₂CH(NH₂)COOH and CH₃COONH₄ against thermo-oxidative decomposition.     

Three Types of Expression in Dark-Soliton Perturbation Theory Based on Squared Jost Solutions

Three types of expression in the dark-soliton perturbation theory based on squared Jost solutions are invesgigaged in ghis paper. It is shown that there are three formally different results about the effects of perturbagion on a dark soliton, and it is proved by means of a transformation between two integral variables that they are essentially equivalent.     

共面对称条件下Mg原子(e,2e)反应的三重微分截面的计算

采用修正的扭曲波玻恩近似(DWBA)方法,本文计算了共面对称几何条件下电子碰撞Mg(3s2) 原子(e,2e)反应的三重微分截面.理论方法通过引入Gamow因子来表示(e,2e)反应的后碰撞相互作用(PCI).将计算结果与实验结果及标准DWBA计算结果进行了比较,发现PCI效应起着重要的作用.     

一种紫外-可见光谱法检测水质COD的浊度影响实验研究

消除浊度影响是直接光谱法检测水质COD的关键技术问题。此源于紫外-可见光谱法检测水质参数的关键依赖于化学计量法所建立的准确的水质参数分析模型,而浊度是影响其建模的一个重要参数。为此,选取福尔马肼浊度液和邻苯二甲酸氢钾标准溶液,开展了紫外-可见吸收光谱法检测水质COD的浊度影响实验研究,获得了选定溶液在245,300,360和560 nm几个特征波长点的吸光度随浊度变化的最小二乘法拟合曲线,分析了吸光度随浊度的变化规律。研究结果表明,在240～380 nm的紫外光谱段,由于引起浊度的颗粒物对有机物产生了吸附,致使浊度对水样的紫外光谱影响较为复杂;在380～780 nm的可见光谱区域,浊度对光谱的影响则是随着波长的增大而减弱。基于此,开展了多元散射校正法对受浊度影响的水样光谱进行校正试验。对某溪水水样的紫外-可见吸收光谱进行多元散射校正,通过处理前后光谱对比表明,浊度引起各个波长点的基线偏移都得到了有效的校正,而在紫外区域特征并未减弱。接着对选取的三种液体的紫外-可见吸收光谱进行多元散射校正,实验结果表明：该方法可在不影响水样紫外-可见吸收光谱特征的前提下对其吸收曲线进行有效的校正,这不仅提高了光谱法检测水质COD的信噪比,而且还为化学计量法建立准确、有效的水质检测COD分析模型进行数据预处理提供了一种新途径。     

Conversion of carbon dioxide to cyclic carbonates using diimine Ru(II) complexes as catalysts

Cationic diimine Ru(II) complexes were synthesized and tested as catalysts for the formation of cyclic organic carbonates from CO₂ and liquid epoxides (propylene oxide, epichlorohydrine, 1,2‐epoxybutane and styrene oxide) which served as both reactant and solvent. The reaction rates not only depended on the type of ligand, but also on reaction conditions such as temperature, pressure, base, the epoxide substrates and the use of an additional solvent. Reaction rates in terms of turnover frequencies up to 4050 mol_product mol_cat.^?1 h^?1 at 99% selectivity were achieved by optimizing the diimine ligand as well as the reaction temperature and CO₂ pressure. Consistent with CV measurements, the electron donating group on the p‐position of the aryl ring accelerated the reaction rate. Copyright © 2008 John Wiley & Sons, Ltd.