Effect of preparation pH on properties of silica gel

Silica gels were obtained by drying the silica hydrogels formed at pH values between 1 and 4 at 100°C. The bulk density of the 2–3 mm diameter fraction decreased from 0·62 g cm^?3 to 0·20 g cm^?3 as the preparation pH increased from pH 3 to pH 3·65. The apparent density of silica gels was between 1·43 and 1·95 g cm^?3. Isotherms for the adsorption of water vapour on samples prepared at different pH values showed hysteresis in all cases. Thermogravimetry analysis showed that the amount of bound water was in the range of 4·4 to 5·5% on a dry weight basis. Specific heats were determined by a differential scanning calorimetry method using a sapphire standard and were between 0·82 and 0·97 J g^?1 K¹.     

埕岛油田馆陶组上亚段油藏注水时机动态评价

馆陶组上亚段油藏是埕岛油田的主力含油层系，其探明储量占总储量的80％。运用数值模拟和动态资料验证等手段，对馆陶组上亚段油藏的注水时机进行了深入研究。研究认为馆陶组上亚段油藏的注水时机和压力保持水平应在饱和压力至0．85倍的饱和压力之间。实践证明，实施注水对改善埕岛油田油藏的开发是非常有效的。     

分布式博弈树搜索算法

本文提出了分布式博弈树搜索ＤＤＳ算法，从通信开销、存储开销、加速比等方面分析了算法性能，并与ＳＳＳ和α－β算法在搜索结点个数方面作了比较，模拟实验表明ＤＤＳ是一种高效实用的分布式搜索算法。     

黄河上中游流域泥沙优化配置研究

针对流域水土流失的灾害性、泥沙利用现状及泥沙优化配置的必要性，基于大系统分解-协调思想的流域泥沙优化配置原理与流域各子系统的泥沙多目标优化配置方法，构建了流域泥沙优化配置理论框架。进而建立了黄河上中游流域泥沙优化配置数学模型，该模型包括相互联系的各子系统、各分区和大系统三级泥沙优化配置数学模型，开展了不同水沙条件下黄河上中游流域泥沙优化配置方案计算，对计算结果进行了评价并提出了建议方案，为黄河上中游流域泥沙的科学治理提供了参考依据。     

Minorant Methods of Stochastic Global Optimization

Generalizations of the branch and bound method and of the Piyavskii method for solution of stochastic global optimization problems are considered. These methods employ the concept of a tangent minorant of an objective function as a source of global information about the function. Calculus of tangent minorants is developed.__________Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 56–70, March–April 2005.     

On computing the determinant in small parallel time using a small number of processors

The determinant, characteristic polynomial and adjoint over an arbitrary commutative ring with unity can be computed by a circuit with size O(n^3.496) and depth O(log²n). Furthermore, the circuits can be constructed uniformly (by a log space bounded Turing machine).     

磁场对GaAs/Al_xGa_(1-x)As异质结系统中束缚极化子的影响

对GaAs/AlxGa1-xAs单异质结系统引入三角势近似异质结势,同时考虑体纵光学(LO)声子和有效近似下两支界面光学(IO)声子的影响,采用变分法讨论了外界恒定磁场对束缚于近界面杂质的光学极化子结合能的影响.利用改进的Lee-Low-Pines(LLP)中间耦合方法处理电子-声子和杂质-声子的相互作用,计算了杂质态结合能随杂质位置、磁场强度、电子面密度的变化关系.结果表明,极化子结合能随磁场呈现增加的趋势,其中LO声子对结合能的负贡献受磁场影响显著,而IO声子的负贡献受磁场的影响并不明显,但当杂质靠近界面时,杂质-IO声子相互作用对磁场的影响很敏感.结果还表明,     

Safety maps in bimetallic extrusions

In this paper, the upper bound method has been applied, in combination with the minimum energy principle, to obtain a fracture condition in the hot extrusion of bimetallic tubes. The simultaneous deformation of material components with quite different plastic properties or under unfavourable geometric conditions may lead to decohesion or fracture. A criterion based on the geometric compatibility of the deformation of each material has been used here. The dependence of the fracture condition on the different extrusion parameters involved in the process is analysed, and several maps containing safety and fracture zones for each parameter are obtained. It is concluded that the yield stress ratio, the die angle and the extrusion ratio appear as the most effective factors in the failure control. The fracture condition is promoted by an increase in the yield stress ratio, in the extrusion die angle, or by decreasing the extrusion ratio. A die angle of 54° or higher, as well as a reduction of 29% or lower, implies that the extrusion operation is only possible at yield stress ratios lower than 2. This limit has many practical implications in the selection of suitable material combinations.     

汾河上游河道治理中的生物防护措施

汾河上游干流生物防护工程是汾河上游干流河道治理工程的重要措施，一方面通过生物措施保护堤防安全运行，稳定河槽中小水流路；另一方面通过生物措施改善汾河上游沿岸生态环境，促进经济发展，提高沿岸人民生活水平。