Sealing Anticorrosion Pastes for Resistant Spot Welding of Aluminum Alloys

This article investigates the application of PSP-2M and KSP-2AK pastes modified by Laproxid 603 for protection of the internal cavity of welding overlap of aluminum alloys. It has been demonstrated that, upon resistant spot welding of 1913 and 1370 aluminum alloys over such modified coatings, the weld joints are characterized by superior mechanic and corrosion properties.     

有机杂化硫代碲酸盐化合物(H_2en)TeS_3和[Ni(en)_3]TeS_3的溶剂热合成与表征

用低温溶剂热法合成了2种分立结构的有机杂化硫代碲(Ⅳ)酸盐化合物(H2en)TeS3(1)和[Ni(en)3]TeS3(2)(en=乙二胺),通过X-射线单晶衍射,红外光谱,元素分析等手段对它们的结构进行了表征。晶体结构解析结果表明:2个化合物均属单斜晶系,空间群分别为P21和P21/c。化合物1和2具有孤立三角锥[TeS3]2-阴离子,化合物1的平衡阳离子为双质子化乙二胺[H2en]2+,阴离子基团[TeS3]2-和阳离子基团[H2en]2+之间通过N-H…S氢键连接。化合物2的阳离子基团为过渡金属Ni与乙二胺的配合物[Ni(en)3]2+。另外,对该2种晶体进行了紫外-可见漫反射光谱测试和热重分析。     

羧基膦酸改性氧化锆固定相的制备及其色谱性能

用十二胺-N乙酸-N亚甲基膦酸（DAPA）改性氧化锆制备了一种新的锆基质色谱固定相（DAPAZ），研究发现，DAPA在氧化锆表面有两种结合方式：红外光谱中1611cm^-1处的特征吸收表明羧基主要与胺基形成偶极离子，以羧酸根离子形式存在，大部分的DAPA分子通过膦酸基团与氧化锆结合；而与钼酸的显色反应则表明有少量DAPA以羧居与氧化锆结合，另外，对固定相的屏蔽效应、碱性条件（pH9．5）下的稳定性等色谱性能的研究也证实这两种吸附方式同时存在，但以膦酸基结合为主。     

Broadband radio-absorbing materials based on porous composites with carbon nanotubes

The reflection coefficient of an electromagnetic wave has been theoretically studied as a function of the thickness of a material and its dielectric properties. Samples based on spheroplastics with noncovalently modified carbon nanotubes have been obtained. The radio-engineering and electrophysical properties of these composites are discussed as well. The prospects for applying porous nanocomposites with carbon nanotubes in the fabrication of radio-absorbing materials are also shown.     

Influence of the difference in the density of solid and liquid phases on the dynamics of an alloy solidification front at crystallization of a finite volume with a moving boundary $$\sqrt t $$

In this paper we obtain the exact analytical solution for a finite solidifying alloy with the upper boundary moving with the time as k _t√ . Thus, a three-phase problem including solid, solid-liquid, and liquid phases is analytically solved. Linearization of the heat conduction equation for an alloy is based on the method proposed in paper [1]. Unlike the paper indicated, this paper considers the case of different densities in solid ρ_s and liquid ρ_l phases. The exact analytical solution presented is an important test example for analysis of the numerical schemes used for systems with moving boundaries, e.g., for programs simulating vacuum arc remelting. As an example, we consider the dependences of the local solidification time, the velocity of the liquidus isotherm, the width of the mush zone, and the temperature gradient in the liquid phase on the liquidus isotherm on the parameters k _t and μ = ρ_l/ρ_s.     

Experimental and Theoretical Study of an Intramolecular CF3‐Group Shift in the Reactions of α‐Bromoenones with 1,2‐Diamines

The reactions of trifluoromethylated 2‐bromoenones and N,N′‐dialkyl‐1,2‐diamines have been studied. Depending on the structures of the starting compounds, the formation of 2‐trifluoroacetylpiperazine or 3‐trifluoromethylpiperazine‐2‐ones was observed. The mechanism of the reaction is discussed in terms of multistep processes involving sequential substitution of bromine in the starting α‐bromoenones and intramolecular cyclization of the captodative aminoenones as key intermediates to form the target heterocycles. The results of theoretical calculations are in perfect agreement with the experimental data. The unique role of the trifluoromethyl group in this reaction is demonstrated.     

Effect of carbon nanotubes dispersed in binder on properties of epoxy nanocomposite

Effect of quality parameters of starting raw materials, native carbon nanotubes (degree of defectiveness, thermal stability, morphology) on the properties of carboxylated and amidated nanotubes produced from these raw materials and on the homogeneity of a dispersion of amidated nanotubes in an epoxy oligomer was studied. The physicomechanical properties of epoxy nanocomposites produced from these dispersions were examined. It was found experimentally that an increase in the defectiveness of native nanotubes leads to a rise in the size of numerous aggregates in dispersions composed of an epoxy resin and amidated carbon nanotubes and, as a result, to deterioration of the physicomechanical characteristics of epoxy nanocomposites based on these dispersions.     

INDUCED OSCILLATIONS GENERATED BY PROTECTIVE THRESHOLD POLICIES IN THE MANAGEMENT OF EXPLOITED POPULATIONS

Abstract Management and conservation of exploited populations have been a central issue in theoretical and empirical studies. In this work, it is shown that threshold policies can induce cyclic behavior in an otherwise exploited stable population as a consequence of the combination of harvest pressure and excessively protective threshold densities. Moreover, the dynamical outcomes generated by these extremely protective policies may vary according to the initial densities. These results may be of significant concern in conservation as well as in management of exploited population.