Numerical experiments of preconditioned Krylov subspace methods solving the dense non-symmetric systems arising from BEM

Discretization of boundary integral equations leads, in general, to fully populated non-symmetric linear systems of equations. An inherent drawback of boundary element method (BEM) is that, the non-symmetric dense linear systems must be solved. For large-scale problems, the direct methods require expensive computational cost and therefore the iterative methods are perhaps more preferable. This paper studies the comparative performances of preconditioned Krylov subspace solvers as bi-conjugate gradient (Bi-CG), generalized minimal residual (GMRES), conjugate gradient squared (CGS), quasi-minimal residual (QMR) and bi-conjugate gradient stabilized (Bi-CGStab) for the solution of dense non-symmetric systems. Several general preconditioners are also considered and assessed. The results of numerical experiments suggest that the preconditioned Krylov subspace methods are effective approaches solving the large-scale dense non-symmetric linear systems arising from BEM.     

Survey of nitrate and nitrite contents of vegetables grown in Korea.

A scientific basis for the evaluation of the risk to public health arising from excessive dietary intake of nitrate in Korea is provided. The nitrate () and nitrite () contents of various vegetables (Chinese cabbage, radish, lettuce, spinach, soybean sprouts, onion, pumpkin, green onion, cucumber, potato, carrot, garlic, green pepper, cabbage and Allium tuberosum Roth known as Crown daisy) are reported. Six hundred samples of 15 vegetables cultivated during different seasons were analysed for nitrate and nitrite by ion chromatography and ultraviolet spectrophotometry, respectively. No significant variance in nitrate levels was found for most vegetables cultivated during the summer and winter harvests. The mean nitrates level was higher in A. tuberosum Roth (5150 mg kg(-1)) and spinach (4259 mg kg(-1)), intermediate in radish (1878 mg kg(-1)) and Chinese cabbage (1740 mg kg(-1)), and lower in onion (23 mg kg(-1)), soybean sprouts (56 mg kg(-1)) and green pepper (76 mg kg(-1)) compared with those in other vegetables. The average nitrite contents in various vegetables were about 0.6 mg kg(-1), and the values were not significantly different among most vegetables. It was observed that nitrate contents in vegetables varied depending on the type of vegetables and were similar to those in vegetables grown in other countries. From the results of our studies and other information from foreign sources, it can be concluded that it is not necessary to establish limits of nitrates contents of vegetables cultivated in Korea due to the co-presence of beneficial elements such as ascorbic acid and alpha-tocopherol which are known to inhibit the formation of nitrosamine.     

带肋钢筋套筒挤压连接的质量控制

针对太原可口可乐综合厂房主筋采用φ28、φ32三级钢存在的可焊性差的问题，提出了在施工中采用套筒挤压连接的方式，并对该方法的操作要点及质量控制措施进行了总结。     

Effects of alloying elements on fracture toughness in the transition temperature region of base metals and simulated heat-affected zones of Mn-Mo-Ni low-alloy steels

This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment, and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and increased Mo and Ni content, the number of fine M₂C carbides was greatly increased and the number of coarse M₃C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to precipitate fine M₂C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base metals.     

基于资源流分析的企业生态补偿机制研究

循环经济作为一种新型的经济范式,成为理论界和实业界共同关注的焦点问题.在循环经济模式下引入了投入产出的资源流管理模型,该模型反映各个过程中资源流的流向和流量,为建立生态补偿机制提供了详细的基础数据,并利用外部环境的完善,推动生态补偿机制在微观领域的实施,从而达到改善企业环境绩效,减少环境污染的目的.     

Design of the ECRH/ECCD Launcher System for HL-2A Tokamak

An ECRH/ECCD system with two 68GHz/500kW/1S gyrotrons will be built up in HL-2A tokamak. The location of the Gaussian beam waist is 580 mm away from the center of the plasmas and the beam radius is 37 mm at the center of the plasmas. Compared to the minor plasma radius （420 mm）, it is small enough for localized control. The launcher system covers a wide toroidal and poloidal steering range by the two steering plane mirrors. Therefore it is possible to explore the on- and off-axis heating over half of the plasma minor cross section and the co-current drive.     

光纤光栅视觉系统

利用光学衍射原理，研制成了光纤光栅衍射屏，并与计算机神经网络相结合，开发了了一种识别立体形状的视觉系统。本文介绍了光纤光栅的设计原理及计算方法，给出了系统的总体结构及工作原理，完成了三棱 柱，三棱锥、四棱柱，四棱锥和球等立体形状学习与识别，并讨论了实验结果。     

Toughening mechanisms and properties of mullite matrix composites reinforced by the addition of SiC particles and Y-TZP

Mullite matrix composites reinforced by SiC particles and Y-TZP, were fabricated by hot-pressing. The effects of adding SiC particles and Y-TZP to mullite or mullite-based materials on properties and toughening mechanisms in the composites were investigated. Crack deflection is proposed as the principal toughening mechanism, produced by the addition of SiC particles. Transformation and microcrack toughening are the two main toughening mechanisms caused by Y-TZP addition. However, the magnitude of their contribution varied with increasing Y-TZP addition. With low Y-TZP addition, the transformation toughening dominated, while at a higher Y-TZP content, the microcrack toughening was dominant. The simultaneous addition of SiC particles and Y-TZP to mullite resulted in higher increases in both flexural strength and fracture toughness, than the simple sum of those obtained by the separate processes. It appears that the two toughening processes were coupled, thereby leading to synergistic toughening and strengthening effects in the mullite composites.