A semi-analytic boundary element method for parabolic problems

A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems.     

复射线展开法分析圆柱面对平面波散射的精度问题

讨论了用复射线展开法计算圆柱面对入射平面波散射时的计算误差特性，提出了控制其计算精度的复射线展开参数选择方法，证实了通过恰当选择展开参数可以有效地提升计算精度、实现误差控制。     

Thermal Expansion Behavior of La1—xSrxMn1—yCoyO3—δ Perovskites

The thermal expansion behavior of La1-xSrxMn1-yCoyO3-δ (x=0.2-0.4, y=0.1-0.3) perovskites in air has been investigated. The average linear thermal expansion coefficients increased with increasing Sr content up to 40 mole fraction or Co content up to 30 mole fraction. The expansion is generally attributed to an increase in the average cation radius as some of the cations in the perovskite are reduced in valence when oxygen ions are removed from the structure.     

The problem of definition expansion and contraction

This article is the fourth of a series of articles discussing various open research problems in automated reasoning. The problem proposed for research focuses on finding criteria that would enable an automated reasoning program to expand or contract definitions wisely. For evaluating a proposed solution to this research problem, we include suggestions concerning possible test problems.This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38.     

纤维复合材料的热膨胀系数

提出了一种利用压电光声技术测量材料热膨胀系数的实验方法,并测试了单向复合材料C/C、C/Al的横向、纵向的热膨胀系数。根据已有的理论计算方法与实验结果对该方法的测试结果进行验证,证明了该检测方法的可靠性,进而又测量了C/C、C/Al材料在任一方向上的热膨胀系数。这种方法克服了理论计算过程复杂以及常规手段无法测量任一方向上热膨胀系数的缺陷。     

Ensuring primary realization of pressure unit in the vacuum range without typically utilized static expansion system

After the break-up of Czechoslovakia in 1993 the primary metrological standards authority almost fully remained in Slovakia. So we had to build our primary vacuum metrology anew. But we could do it using uptodate techniques that are more effective and they enable us to fulfil our task more effectively and in a shorter time.The steady demand to widen the lower pressure range and a steady demand for maximal accuracy collide with the financial possibilities open to a small country. So it is impossible to follow the classical pattern for the vacuum standards: liquid columns, static expansion system and dynamic expansion system. But it is possible to utilize contemporary progress in construction of piston manometers. This enables us to discard liquid column and static expansion techniques in favour of piston technique [Tesar J, Prazak D. Vacuum 2002; 67: 311, Tesar J, Prazak D, Krajicek Z. In:Proceedings of international symposium on Pressure and Vacuum, 2003. p. 169, Tesar J, Repa P, Prazak D, Krajicek Z, Peksa L. Vacuum 2004; 76: 491.]. Such system fulfils all the needs of a little industrial country and is economically acceptable.     

Strategic appraisal of energy models for Mozambique

The needs that an energy supply system must meet are constantly changing, due to technological, social and political reasons. Effective energy planning is a dynamic process that is repeated periodically and adjusts to changing conditions. Energy decision makers and planners are no longer able to rely on inductive decision making since they have to investigate the effect of various decision parameters and possible future changes. To help in this process, models have been developed where estimates of future load growth, candidate power plants, fuels and other key factors can be introduced, from which the planners can evaluate decision parameters and the available alternatives. The paper presents the different methodologies and practices that are used by 11 energy models for energy demand forecasting, supply side management and generation expansion planning, demand side management and integrated resource planning. The paper concludes to the presentation of a strategic appraisal of the examined energy models appropriate for energy planning in Mozambique. Three models are proposed for conducting demand forecasting, generation expansion planning and demand side management. Copyright © 2002 John Wiley & Sons, Ltd.     

Influence of Ni Interlayers on the Mechanical Properties of Ti6Al4V/(WC-Co) Friction Welds

Ni interlayers were introduced prior to dissimilar friction welding of Ti6Al4V base material to three cemented carbide substrates. The fracture strength of Ti6Al4V/(WC-6 wt% Co) welds were poor and were markedly improved when 20-µm thick Ni interlayers were introduced prior to dissimilar friction welding. These results were only produced when the (WC-6 wt% Co) cermet was electroplated prior to friction welding. When the Ti6Al4V alloy was electroplated prior to friction welding, fractured WC particles and cracking were observed in the (WC-Co) carbide substrate. The fracture strengths of Ti6Al4V/(WC-11 wt% Co) and Ti6Al4V/(WC-24 wt% Co) welds were not improved when 20-µm thick Ni interlayers were introduced prior to friction welding. During mechanical testing, the Ni layer retained at the dissimilar joint interface created a region of weakness.     

山西铝厂锅炉水冷壁膨胀异常原因分析及对策

针对山西铝厂160t／h锅炉在实际运行中膨胀异常的问题，对不同的施工方法下，水冷壁膨胀量是否正常这一问题进行分析，找出了水冷壁膨胀异常的原因，并提出了解决对策。     

An analysis of the electrical conductivity in BaSO4-added Ag2SO4 solid electrolyte system

The compositions (1 −x)Ag₂SO₄−(x)BaSO₄, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba²⁺ in Ag₂SO₄ was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained using a detailed impedance analysis. The partial substitution of Ba²⁺ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model based on lattice distortion (expansion) due to partial substitution of Ag⁺ by the bigger Ba²⁺ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO₄-dispersed Ag₂SO₄ conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO₄ dispersed Ag₂SO₄ is due to percolation threshold.