基于数据仓库的OLAP中的索引技术研究

数据仓库建立好后,需要对其充分高效地利用,OLAP联机分析处理就是一个很好的数据分析展现工具。人们对速度的追求是永无止境的,建立索引可以更快捷地响应用户的查询。索引的种类很多,相关研究表明位图索引既能节省空间,又能利用其进行的位运算而提高相应的查询速度,然而位图索引对字段基数较低的字段有比较好的效果,当遇到字段基数较高的字段时也会占据大量的空间,其效果不及B‐T ree索引,论文针对这种情况对位图索引进行了扩展,引入了标识符索引,并对其进行了比较讨论,最后提出可以根据维的各自特征建立不同的索引。     

Properties of concrete pavements prepared with ferrochromium slag as concrete aggregate

This paper presents the results of investigation related to both the properties of the ferrochromium slag and the standard physical and mechanical properties of Portland cement concrete pavements (PCCP) made with this slag as aggregate, according to the relevant Croatian standards. Slag is formed as a liquid at 1700 °C in the manufacture of the high-carbon ferrochromium metal and, by slow cooling in the air, the slag crystallizes to give a stable CaO–MgO–Al₂O₃–silicate product with mechanical properties similar to basalt. With a proper selection of slag as an artificial aggregate, concrete pavements with compressive strengths, wear resistance and specific weight higher than in those from natural (limestone) aggregate in commercial Portland cement, type CEM II/B-S 42.5 (EN 197), can be made. The 28-day compressive strength of the concretes made with original unfractioned slag and with standard limestone as aggregates (w/c=0.64 and 350 kg/m³) reached the values of 57.00 MPa and 36.70 MPa, respectively. Volume stability, high volume mass, good abrasion resistance to wear and crushability make this reinforced slag concrete suitable for wearing courses of concrete pavements for traffic load classes 1 and 2 where carbonate stone material (limestone) mainly does not meet the Standard Technical Requirements for cement concrete slab pavements according to the relevant Croatian standard.     

Film model for coated cement concrete

The performance of a polymer concrete coated cement concrete under sulfuric acid environment was studied for 3 years. Both dry and wet concrete specimens were used in this study. The mass transfer coefficient ratio of cement concrete to polymer concrete was over 12. Coated cement concrete cylinders with pinholes were used to study the chemical resistance of the coated concrete under sulfuric acid environments to represent the worst sewer condition. Effects of pinhole sizes on the performance of coated concrete were studied, and changes in weight of the coated concrete specimens were measured regularly. The weight change in coated cement concrete was modeled using a film model and the effect of the pinhole sizes on the performance of the coated concrete was quantified.     

Aspects of moisture kinetics of coal bottom ash in concrete

The moisture kinetics aspects of composite granular material samples composed of natural sand and bottom ash (BA) from thermoelectric power stations and the use of this material in the production of durable concretes, in relation to water transport, are here discussed. The evaluations of the phenomenon of water absorption by capillarity and the loss of water through air drying until hygroscopic equilibrium, were carried out in accordance with classic procedures found in the literature and also newly developed procedures. The results showed that due to the high porosity of BA, the water absorption by capillarity along with the absorption velocity were higher in the compositions with greater BA content. The values for moisture equilibrium from air drying, absorption from capillarity and sorptivity obtained in the hygroscopic equilibrium tests, carried out on the same samples after absorption, were also higher in the samples with BA. These samples also requited a longer drying time.     

Multiply subtractive Kramers-Kronig relations for impedance function of concrete

The impedance function of concrete is considered and multiply subtractive Kramers-Kronig relations and sum rules are given for the impedance function. It is proposed that multiply subtractive Kramers-Kronig relations provide better convergence, and thus increase the reliability of numerical analysis of impedance of concrete than the conventional Kramers-Kronig relations.     

Properties of lightweight expanded polystyrene concrete reinforced with steel fiber

Expanded polystyrene (EPS) concrete is a lightweight, low strength material with good energy-absorbing characteristics. However, due to the light weight of EPS beads and their hydrophobic surface, EPS concrete is prone to segregation during casting, which results in poor workability and lower strength. In this study, a premix method similar to the ‘sand-wrapping’ technique was utilized to make EPS concrete. Its mechanical properties were investigated as well. The research showed that EPS concrete with a density of 800-1800 kg/m³ and a compressive strength of 10-25 MPa can be made by partially replacing coarse and fine aggregate by EPS beads. Fine silica fume greatly improved the bond between the EPS beads and cement paste and increased the compressive strength of EPS concrete. In addition, adding steel fiber significantly improved the drying shrinkage.     

Modeling bond strength of corroded reinforcement without stirrups

Deterioration of bond strength between concrete and reinforcement is of great importance in studying the strength of structural members with corroded reinforcements. A simple analytical model is proposed to demonstrate the effect of corrosion of reinforcing bar on reduction of bond strength. The corrosion pressure due to expansive action of corrosion products before and after corrosion cracking is firstly estimated. Then, reduction of bar confinement caused by cover cracking, change of friction coefficient between the steel and the concrete, and reduction of the friction force on the bearing face as well as deterioration of the ribs of the deformed bars due to steel corrosion are considered in calculating the mechanical interactions between reinforcing bar and concrete. As a result, the bond strength of corroded bars is calculated. The theoretical results are compared with the experimental results and agree with those results well.     

陕西地区男性老年人体型研究

利用接触式人体测量技术采集了190名60～75岁的陕西地区老年男性人体数据,应用SPSS软件对这些数据进行主成分分析及因子分析及相关分析等一系列的研究．提取了能够全面反映该群体上体体型特征的长度因子、宽度因子等6大因子,胸围、腰围、腹围、身高、背长、前腰节长、肩斜角、肩宽、后腰节长、颈围10个特征指标及AX、BX、CY、BY等4种体型．为男性老年上装结构设计提供了合理可行的人体部位数据参考信息．     

无卤阻燃橡胶的研制

研究无卤阻燃橡胶,其配方是在丁腈橡胶中添加氢氧化镁和氢氧化铝,使橡胶不失其力学性能,又具有一定的阻燃功能.实验结果表明,老化前,当氢氧化镁和氢氧化铝为40份时,力学性能最好.随氢氧化镁和氢氧化铝份数的增加,试样的力学性能逐渐减小.老化后,随氢氧化镁和氢氧化铝份数的增加,试样的力学性能逐渐减小.当填料的用量为70份时,阻燃性能最好.同样质量条件下氢氧化镁的O I（氧指数）大于氢氧化铝,表示氢氧化镁的阻燃性比氢氧化铝的阻燃性好.     

Resistance of concrete protected by fabric to projectile impact

This paper reports on impact behavior of concrete panels protected by Polypropylene and Zylon fabric, respectively. Concrete panels were cast with different thickness and subjected to impact by a steel projectile. The initial and residual velocities were measured experimentally and the energy absorbed by the different concrete panels with and without fabric was calculated. All concrete panels were able to absorb almost all the kinetic energy of the projectiles. For concrete panels protected by fabric scabbing of concrete from the back face was considerably reduced and the debris contained by the fabric. Upper and lower bounds are proposed for energy absorbed per unit thickness and penetration results are compared with the available empirical formulas. It is shown that current penetration equations do not accurately predict impact parameters for concrete protected by fabric.