A novel approach to accelerate the reaction between Ti and Al

Pure Ti foils and SiCp/Al composite foils were employed to investigate the parabolic growth kinetics of TiAl₃ at 660 °C. Compared with pure Al foils, the introduction of SiC particles significantly refined TiAl₃ grain size by the solid solution of silicon. Corresponding refinement mechanisms were concluded from the perspective of the nucleation of TiAl₃. Micromechanics analysis shows that the fine TiAl₃ grains own a small viscous resistance, and subsequently an improvement in the reaction rate could be achieved. This meaningful law also applies extensively to Ni/Al and Fe/Al systems.     

Davidson类方法本质的研究及一个新算法

本文利用有关矩阵扰动理论,从分析Davidson类方法中子空间的扩充向量入手,对Davidson方法的本质作了较为深入的研究,分析结果较为合理地解释了有关文献中的一些数值试验现象,本文利用文献[2]所提出的精化策略对D avidson类方法进行改造,得到了一个新的算法。数值试验表明,新算法是非常有效的,同时也验证了本文对Davidson类方法的本质的研究结论。     

Al2O3/TiB2/AlN/TiN复合陶瓷材料的力学性能及显微结构

将金属Al、Al3Ti和TiB2以AlTiB中间合金的形式引入Al2O3基体材料中,采用热压原位反应生成法制备了Al2O3/TiB2/AlN/TiN复合陶瓷材料.复合材料在烧结过程处于过渡液相烧结,并有新相AlN和TiN生成;对热压烧结后材料的硬度、断裂韧性和抗弯强度进行了测试和分析;分析了复合材料力学性能随AlTiB体积百分含量的变化规律;探讨了复合材料断面断裂方式的变化对其力学性能的影响;并对AlTiB中间合金的细化特性进行了分析.     

Adaptive strategy of the supersonic turbulent flow over a backward‐facing step

An adaptive strategy incorporating mesh remeshing and refining is developed to study the supersonic turbulent flow over a backward‐facing step on a mixed quadrilateral–triangular mesh. In the Cartesian co‐ordinate system, the unsteady Favre‐averaged Navier–Stokes equations with a low‐Reynolds‐number k–εturbulence model are solved using a locally implicit scheme with an anisotropic dissipation model. In the present adaptive strategy, two error indicators for both mesh remeshing and refining, respectively, are presented. The remeshing error indicator incorporates unified magnitude of substantial derivative of pressure and that of vorticity magnitude, whereas the refining error indicator incorporates unified magnitude of substantial derivative of pressure and that of weighted vorticity magnitude. To assess the present approach, the transonic turbulent flow around an NACA 0012 airfoil is performed. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. According to the high‐resolutional result on the adaptive mesh, the structure of backstep corner vortex, expansion wave and oblique shock wave is distinctly captured. Copyright © 2004 John Wiley & Sons, Ltd.     

微量Al-RE对Zn-2%Ni合金的组织细化研究

研究了RE，Al及Al-RE合金对Zn-2％（质量分数，下同）Ni合金组织中Zn-Ni合金相粒子的细化作用，利用扫描电镜（SEM）及能谱分析（EDS）等方法分析了合金凝固组织特点。结果表明：在Zn-2％Ni合金中，加入0．02％～1％RE会产生新的Zn—RE—Ni合金相粒子，对Zn-Ni合金相粒子没有明显的细化作用；加入0．02％～1％Al，虽然对Zn-Ni合金粒子有细化作用，但此合金组织不适宜在热镀锌中运用。在铝浓度较低（〈0．1％）时。凝固组织中的合金相粒子尺寸不均匀；当铝浓度较高（〉0．2％）时，高熔点、低密度β-NiAl相核心长大，合金相粒子易上浮，出现比重偏析；加入0．02％～0．2％Al-RE时，能形成细小弥散而均匀分布的异质晶核β-NiAl相，促进了γ-Ni2Zn5相的生成，获得细小且均匀分布的γ-Ni2Zn5相。Al-RE合金细化效果明显优于RE和Al，其最佳加入浓度为0．05％～0．1％。     

The effect of Trichoderma reesei cellulases and hemicellulases on the paper technical properties of never-dried bleached kraft pulp

Four purified cellulases, a xylanase and mannanase from Trichoderma reesei were used to treat never-dried bleached pine kraft pulp prior to refining, and the effects on pulp properties were evaluated. The enzymatic treatments hydrolysed up to 0.8% of pulp dry weight. The results demonstrated that the individual cellulases have profoundly different modes of action in modifying pulp carbohydrates. This is especially clear when comparing their effects at the same level of hydrolysis. Pretreatment with cellobiohydrolases I (CBH I) and II (CBH II) had virtually no effect on the development of pulp properties during refining, except for a slight decrease in strength properties. On the contrary, endoglucanase I (EG I) and endoglucanase II (EG II) improved the beatability of the pulp as measured by Schopper--Riegler value, sheet density and Gurley air resistance. Of the endoglucanases, EG II was most effective in improving the beating response. The combinations of CBH I with EG I and EG II had similar effects on the pulp properties as the endoglucanases alone, although the amount of hydrolysed cellulose was increased. Pretreatments with xylanase or mannanase did not appear to modify the pulp properties. The same enzyme treatments which improved the beatability, however, slightly impaired the pulp strength, especially tear index at the enzyme dosages used. When compared at a given level of cellulose hydrolysis, the negative effect of EG II on strength properties was more pronounced compared with EG I. Thus, the exploitation of cellulases for fibre treatments requires careful optimization of both enzyme composition and dosage. Since the endoglucanases had no positive effect on the development of tensile strength, it is suggested that the explanation for the increased beating response is increased fibre breakage and formation of fines, rather than improved flexibilization. This revised version was published online in August 2006 with corrections to the Cover Date.     

准凸映照齐次展开式的精细估计

本文给出C~n中单位多圆柱上和复Banach空间中单位球上的准凸映照(含A型准凸映照和B型准凸映照)f齐次展开式的精细估计,其中x=0是f(x)-x的k 1阶零点.同时,还讨论了复Banach空间单位球上准凸映照的构造,它为准凸映照齐次展开式的精细估计提供极值映照.     

DHAC改性膨润土对炼油碱渣废液的吸附机理探讨

以有机插层剂双十八烷基二甲基氯化铵(DHAC),对新疆夏子街膨润土进行插层改性,制备DHAC改性膨润土。红外光谱(FTIR)分析表明,双烷基阳离子插层进入蒙脱石片层。X射线衍射(XRD)表明,DHAC改性膨润土片层间距为3．772 nm,为改性前的2．07倍,表明改性后蒙脱土片层间距增大。SEM分析观察, DHAC捕层改性后膨润土颗粒更加疏松,蒙脱石颗粒表面有明显的刻蚀痕迹。通过研究改性膨润土的吸附机理分析表明,DHAC改性膨润土在不同温度下的等温吸附模型符合Freundlich模型,且相关性较高。挥发酚在改性膨润土上的吸附焓值为-2．64 kJ／mol,属于物理吸附,且△Gθ<0,说明该吸附为自发的放热过程。室温下DHAC改性膨润土吸附挥发酚的动力学模型遵循Bingham和Langmuir速率方程。     

An efficient strategy based on liquid‐liquid extraction and pH‐zone‐refining counter‐current chromatography for selective enrichment,separation, and purification of alkaloids and organic Acids from natural products

This study presents an efficient strategy based on liquid‐liquid extraction and pH‐zone‐refining counter‐current chromatography for selective enrichment, separation, and purification of alkaloids and organic acids from natural products. First, an acid or base modified two‐phase solvent system with maximum or minimum partition coefficient was developed for the liquid‐liquid extraction of the crude extract. As a result, alkaloids or organic acids could be selectively enriched in the upper or lower phase. Then pH‐zone‐refining counter‐current chromatography was employed to separate and purify the selectively enriched alkaloids or organic acids efficiently. The selective enrichment and separation of five bufadienolide from toad venom of Bufo marinus was used as an example to show the advantage of this strategy. As a result, 759 mg of selectively enriched bufadienolide was obtained from 2 g of crude extract and the total content of five targets was increased from 14.64 to 83%. A total of 31 mg of marinobufagin‐3‐adipoyl‐l ‐arginine, 42 mg of telocinobufagin‐3‐pimeloyl‐l ‐arginine, 51 mg of telocinobufagin‐3‐suberoyl‐l ‐arginine, 132 mg of marinobufagin‐3‐suberoyl‐l ‐arginine, and 57 mg of bufalin‐3‐suberoyl‐l ‐arginine were all simultaneously separated from 500 mg of selectively enriched sample, with the purity of 92.4, 97.5, 90.3, 92.1, and 92.8%, respectively.     

Multiobjective Optimization of Industrial Petroleum Processing Units Using Genetic Algorithms

For many years most of refining processes were optimized using single objective approach, but practically such complex processes must be optimized with several objectives. Multiobjective optimization allows taking all of desired objectives directly and provide search of optimal solution with respect to all of them. Genetic algorithms proved themselves as a powerful and robust tool for multi-objective optimization. In this article, the review for a last decade of multi-objective optimization cases is provided. Most popular genetic algorithms and techniques are mentioned. From a practical point it is shown which objectives are usually chosen for optimization, what constraint and limitations might impose multi-objective optimization problem formulation. Different types of petroleum refining processes are considered such as catalytic and thermal.