On the design of multiple key hashing files for concurrent orthogonal range retrieval between two disks

This paper concerns the following problem: given a set of multi-attribute records, a fixed number of buckets and a two-disk system, arrange the records into the buckets and then store the buckets between the disks in such a way that, over all possible orthogonal range queries (ORQs), the disk access concurrency is maximized. We shall adopt the multiple key hashing (MKH) method for arranging records into buckets and use the disk modulo (DM) allocation method for storing buckets onto disks. Since the DM allocation method has been shown to be superior to any other allocation methods for allocating an MKH file onto a two-disk system for answering ORQs, the real issue is knowing how to determine an optimal way for organizing the records into buckets based upon the MKH concept.

A performance formula that can be used to evaluate the average response time, over all possible ORQs, of an MKH file in a two-disk system using the DM allocation method is first presented. Based upon this formula, it is shown that our design problem is related to a notoriously difficult problem, namely the Prime Number Problem. Then a performance lower bound and an efficient algorithm for designing optimal MKH files in certain cases are presented. It is pointed out that in some cases the optimal MKH file for ORQs in a two-disk system using the DM allocation method is identical to the optimal MKH file for ORQs in a single-disk system and the optimal average response time in a two-disk system is slightly greater than one half of that in a single-disk system.     

1960年前黄河下游河槽淤积物粒径组成分析

利用1999年汛前深层钻孔取样资料和历年淤积实测大断面资料分析出1960年前无三门峡水库影响的“自然”水沙情况下,下游河道主槽淤积物中d≥0.1 mm以上泥沙占50.7%,比1960-1999年大30个百分点,这种泥沙在下游的淤积比高达83.1%,比0.05 mm以上泥沙的淤积比高39个百分点。指出应在黄河中游寻找出0.1 mm以上的粗泥沙集中来源区作为近期水土保持的重点区域。     

醋酸纤维素—纤维素增强膜的结构特征和分离性能

本文描述了醋酸纤维素－纤维素大孔增强超滤膜的结构特征一分离性能之间的关系。详细论述了膜材料含量和粘连剂含量及其分子量对膜结构和性能的影响。论述了不同配方铸膜液的膜，其孔径，水通量和截留率随操作压力的变化规律。实验证明这种高强度的ＣＡＣ膜经多次重复使用后，其结构性能保持完好。     

Microstructure evolution during metal forming processes

Recrystallization and grain growth evolutions during metal forming processes are considered. Coupling between the thermo-mechanical and microstructure processes is realized. Die forging of a rear-axle flange is simulated numerically on the base of the finite element method. Material parameters of the models are obtained experimentally. The influence of interpass and holding times on grain size distributions in the end product is shown.     

基于改进PSO算法的结构损伤检测

结构的损伤检测常转化为求解约束优化问题,针对粒子群算法容易出现早熟问题,增大算法后期的粒子位置的改变量,从而增加粒子位置的差异,因而能够增强其在求解约束优化问题时抵抗局部极小的能力。两层刚架单损伤和多损伤识别的数值结果和收敛曲线表明了改进后的粒子群算法优于传统的带惯性因子的粒子群算法。三层框架结构的4种损伤工况的试验研究进一步说明了该算法应用于结构损伤检测领域的有效性。     

工艺过程中假废品的研究

对机械零件加工过程中出现的假废品现象进行了分析和研究,并提出了判别的方法.     

Role of Specimen Geometry in the Effect of Fiber Orientation on the Thermal Conductivity of a Uniaxial Carbon-Fiber-Reinforced Aluminoborosilicate Glass-Matrix Composite

A study concerning the effect of fiber orientation on the thermal conductivity of a uniaxial carbon-fiber-reinforced borosilicate glass was conducted. For thin specimens, and thick specimens with specimen sides cut parallel to the fiber direction, the dependence of thermal conductivity on fiber orientation showed excellent agreement with theoretical behavior predicted for a composite infinite in extent. In contrast, the thermal conductivity data for rectangular thick specimens fell well below the data for the thin and angled specimens. For fiber orientation of 45° and higher, at which the heat was directed toward the side of the specimen rather than across, the thermal conductivity values showed excellent agreement with theoretical behavior predicted for a finite composite strip with insulated sides.     

现金流量与公司投资决策--从公司规模角度的实证研究

根据现代公司金融理论，将融资因素引进公司的投资模型，研究不同规模的公司投资与现金流量的关系，并探寻不同规模公司投资决策行为差异的背后动机。实证研究发现：大规模公司投资对现金流量的敏感性要高于小规模公司，动因检验的结果表明大规模公司投资依赖于现金流量源于信息不对称理论，小规模公司源于自由现金流量的代理成本理论，这为我国完善资本市场、制定合理政策提供了借鉴的依据。     

埕岛油田东部斜坡带东下段沉积特征及油藏类型研究

埕岛油田东部斜坡带下第三系油藏以三角洲、浊积扇砂体隐蔽油气藏为主，储层埋藏深、厚度变化大，油气成藏复杂。通过对该带的沉积特征、沉积体系和沉积物源的研究，指出其东下段砂体的分布主要受物源和沉积相带两方面控制，砂体只有在有效圈闭情况下才能成藏，并且从构造上总结了三种油藏类型。最后指出该带下一步勘探重点是沿主物源方向展布的、成藏条件良好的各种砂体。