First Fundamental Axisymmetric Problem of Thermoelasticity for a Compressed Spheroid with a Concentric Spherical Cavity

An axisymmetric boundaryvalue problem of thermoelasticity for a compressed spheroid with a concentric spherical cavity is studied by the generalized Fourier method. The problem is reduced to an infinite system of linear algebraic equations with the Fredholm operator under the condition that the boundary surfaces are not crossed. Results of a numerical analysis of stresses in the case of loadfree boundary surfaces in the presence of a temperature field caused by a constant temperature distribution on the boundary surfaces are presented.     

Utilization of waste tire rubber in hybrid plywood composite panel

The aim of this work was to use waste tire rubber (WTR) in the middle layer of hybrid plywood materials. The effects of four variable parameters, namely, WTR contents (430 and 720 g), resin contents (120 and 160 g/m²), hot pressing (single‐stage and two‐stage), and arrangements of veneer layers on the mechanical, physical, and acoustical properties, were studied. Beech (Fagus orientalis) and alder (Alnus glutinosa) veneers having 1.8‐mm thickness were used in the production of hybrid plywood panels. Rubber layers of 3‐ and 5‐mm thickness were used in the middle layer of plywood samples. To produce plywood panels, single‐stage and two‐stage hot‐pressing processes were used. Bonding of wood layers was performed using 120 and 160 g/m² urea‐formaldehyde resins, and to form the rubber layers and bond them to wood layers, methylene diisocyanate resin (150 g/m²) was used. Overall trend showed that with the increase in rubber content, the physical properties (water absorption, thickness swelling, and sound absorption) of the manufactured panels were improved, while the mechanical properties (modulus of rapture, modulus of elasticity, and impact strength) of the panels were reduced. Both physical and mechanical performances of plywood panels were improved with increase in resin content. An increase in the WTR content in plywood improved the composite's acoustical property. The production process of the wood/rubber plywood did not significantly affect their properties. The order of improvement in the physical properties of the panels is rubber content > resin content > arrangement of layers > pressing process. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions

To design highly efficient catalysts, new concepts for optimizing the metal–support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni‐based nanocatalyst. The Ni nanoparticles are not only confined in Al₂O₃ nanotubes, but also embedded in the cavities of Al₂O₃ interior wall. The cavities create more Ni–Al₂O₃ interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni‐based catalyst supported on the outer surface of Al₂O₃ nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD‐assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.     

定时截尾数据缺失场合下指数分布的似然函数的近似

给出了当寿命分布为指数分布时,定时截尾寿命试验数据缺失场合下样本的似然函数的近似,从而可以简化平均寿命的Bayes估计。     

Ionic Liquids as Performance Ingredients in Space Lubricants

Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.     

On Invertibility of Elastic Single-Layer Potential Operator

The question of unique solvability of the boundary integral equation of the first kind given by the single-layer potential operator is studied in the case of plane isotropic elasticity. First, a sufficient condition of the positivity, and hence invertibility, of this operator is presented. Then, considering a scale transformation of the domain boundary, the well known formula for scaling the Robin constant in potential theory is generalized to elasticity. Subsequently, an explicit equation for evaluation of critical scales for a given boundary, when the single-layer operator fails to be invertible, is deduced. It is proved that there are either two simple critical scales or one double critical scale for any domain boundary. Numerical results, obtained applying a symmetric Galerkin boundary element code, confirm the propositions of the theory developed for both single and multi-contour boundaries.     

三维分区算法在复杂多连域湍流问题中的应用

提出并实现了一种适合于任意曲线坐标系下非交错网格系统的流体力学数值模拟的三维分区算法 ,通过三维立方块绕流问题对其进行了考证和优化工作 ,证明有良好、稳定的工作性能。在此基础上 ,将该算法有效地应用到了具有典型多连域特征的涉及内外流耦合作用的串列双空气冷却塔定常绕流流动问题 ,揭示了横向风对其运行性能产生不利影响的主要原因     

Two-Dimensional Electroelastic Problem for a Multiply Connected Piezoelectric Body

In this paper, we present the basic relationships for the complex potentials of a two-dimensional electroelastic problem, their general representations for a multiply connected domain, expressions for stress, displacement, electrostatic field intensity and induction, and potential. A closed solution is found for a body with one elliptic cavity or one elliptic crack under the action at infinity of a constant electroelastic field or concentrated forces and charges