熔渗压力对制备硅颗粒增强铝基复合材料的影响

采用压力浸渗法制备硅颗粒增强铝基复合材料,与传统的粉末冶金法相比,具有成本低,工艺简单的优点,同时也很好的解决了铝与硅浸润性差的问题.通过理论计算与实验相结合,确定了制备工艺的参数.所制备的复合材料组织均匀,基体中的共晶组织可依附在颗粒表面形核生长,通过SEM和XRD分析没有检测到氧化物以及金属间化合物的存在,这说明采用压渗法即使在没有气氛保护的情况下,也可以获得增强相分布均匀、界面结合良好的材料.     

一种适用于干旱半干旱地区的产流模型

文内研究了干旱半干旱地区的产流特性，抓住流域产流的主要环节，以影响产流的主要因素──下渗为重点研究对象，提出了开始积水时间流域分配曲线．模型在河北省尚义流域应用，其合格率达８０％以上．使用表明，该模型适合在干旱半干旱地区应用，为该区的水库优化调度、水文预报提供了可靠的水文信息．     

In Situ Partial Exfiltration of Rainfall Runoff. II: Particle Separation

Metal elements or other constituents transported in urban and transportation land use rainfall runoff are often adsorbed on or incorporated with entrained particles that are ubiquitous in such runoff. Infiltration–exfiltration can be an effective in situ particle separation and quantity control structural best management practices or low impact development practices allowing runoff to return to soil after passive physical-chemical treatment. The in situ partial exfiltration reactor (PER), which combined the surface straining of the cementitious porous pavement (CPP) layer with filtration of oxide coated sand media beneath, provided control of water quantity and quality. Particle analyses were carried out for both influent and effluent to examine filter efficiency as a function of particle size and hydrology. Influent dm/dp ratios suggest that the dominant PER particle separation mechanisms were unsaturated physical–chemical filtration with the CPP layer functioning as a straining surface. Particle size distributions were modeled based on a two-parameter cumulative power-law function. The performance of the PER as a filter is shown to be a function of the unsteady site hydrology. Temporal variation in the filter coefficient and the volumetric particle fraction remaining were directly related to the unsteady influent loading rate. Particle removal efficiency by the PER based on concentration ranged from 71 to 96% on a mass-based concentration and 92–99% on a number based concentration. Results suggest that a properly designed PER can provide effective in situ control for particles and could be combined with or function separately from source control (i.e., pavement cleaning or a mass trading framework).     

Simulation Model for Level Furrows. I: Analysis of Field Experiments

The level-furrow irrigation system consists of furrowing a level basin. In level furrows, irrigation proceeds just like in level basins: the field is flooded from one point and water spreads to irrigate each furrow. Several writers have reported that this irrigation system has the potential to conserve water as compared to level-basin irrigation. However, no comparative studies on the performance of both irrigation systems are available, and the simulation of level furrows has not been attempted. In this work, two field experiments are reported. Both of them were performed in the same soil and in the same conditions. In the first experiment, infiltration was estimated for a series of furrow irrigation discharges and for a level basin. In the second experiment, a level furrow irrigation event was evaluated. A simulated level basin irrigation event in the level furrow experimental field required six times more time and water to complete advance. Infiltration equations including the irrigation discharge or the wetted perimeter as independent variables were proposed for the experimental furrow conditions. Application of a furrow simulation model to the level–furrow experiment resulted in an underestimation of the time of advance. To overcome this problem, a simulation model for level furrows was developed and is presented in a companion paper. The reported field experiments were used to validate the model, which was applied (in a companion paper) to explore adequate conditions for level furrow irrigation performance.     

Using Compost to Increase Infiltration and Improve the Revegetation of a Decomposed Granite Roadcut

Decomposed granite (DG) soils are very erosive and, when disturbed, are difficult to revegetate. Sediment eroding from DG roadcuts can severely impact nearby drainage basins. Two ways of reducing surface erosion are to increase the surface saturated hydraulic conductivity (Ksat) of the soil and to stabilize the surface with vegetation. This study examined the ability of unscreened yard waste compost to increase the Ksat of these soils and facilitate revegetation. A compost application rate of 24% by volume increased postconstruction Ksat of a DG roadcut to levels comparable to a revegetated reference site. The establishment of vegetation was important to maintain the initial increase in Ksat associated with tillage and compost amendment. By the second year, above-ground biomass significantly increased with increasing compost amendment rate. There was also a significant increase in soil Ksat in the 12 and 24% compost treatments in the second year compared to the first year, indicating the strong influence of plant growth on soil surface hydrology.     

Temperature Effects on the Infiltration Rate through an Infiltration Basin BMP

Infiltration Best Management Practices (BMPs) are becoming more readily acceptable as a means of reducing postdevelopment runoff volumes and peak flow rates to pre-construction levels, while simultaneously increasing recharge. However, the design, construction, and operation of infiltration basins to this point have not been standardized due to a lack of understanding of the infiltration processes that occur in these structures. Sizing infiltration BMPs to hold and store a predetermined volume of runoff, typically called the Water Quality Volume, has become a widely accepted practice. This method of sizing BMPs does not account for the infiltration that is occurring in the BMP during the storm event; which could result in significantly oversized BMPs. The objective of this study was to develop a methodology to simulate varying infiltration rates observed from a large scale rock infiltration basin BMP. The results should aid in improved design of such structures. This methodology is required to predict the performance of these sites using single event and continuous flow models. The study site is a Pervious Concrete Infiltration Basin BMP built in 2002 in a common area at Villanova University. The system consists of three infiltration beds filled with coarse aggregate, lined with geotextile filter fabric, overlain with pervious concrete and underlain by undisturbed silty sand. The BMP is extensively instrumented to facilitate water quantity and quality research. The infiltration performance of the site is the focus of the study. Recorded data indicates a wide variation of linear infiltration rates for smaller storm events. A model was developed using the Green–Ampt formula to characterize the infiltration occurring in the basin for small storm events characterized by an accumulated depth of water in the infiltration bed of less than 10?cm. The effectiveness and accuracy of the model were measured by comparing the model outputs with observed bed water elevation data recorded from instrumentation on site. Results show that for bed depths of <10?cm, hydraulic conductivity is the most sensitive parameter, and that the storm event measured infiltration rate is substantially less then the measured saturated hydraulic conductivity of the soil. The governing factor affecting hydraulic conductivity, and subsequently, infiltration rate is temperature; with higher rates occurring during warmer periods, affecting the infiltration rate by as much as 56%.     

基于可变下渗容量模型和Palmer 干旱指数的区域干旱化评价研究

基于可变下渗容量(Variable Infiltration Capacity,VIC)模型的流域网格划分及其对径流、蒸散发和土壤含水量变化的模拟,对Palmer干旱指数各水量平衡分量的计算进行了优化,并采用分级修正的方式,改进了Palmer干旱指数中气候特征系数K的确定方法。在此基础上,建立了基于VIC模型和Palmer干旱指数的区域气候干湿变化评价系统,并采用该系统对黄土高原进行了研究。结果表明,近40年黄土高原气候正向暖干化趋势发展,1990年以后暖干化趋势尤为明显。研究区干旱发生频率在空间上呈由西北向东南递减趋势,不同季节干旱发生频率空间分布存在一定差异。该评价系统物理机制清晰,地区适应性较强,在实时监测和评估气候干湿变化及其时空分布上存在较大应用潜力。     

ZTA/YL302复合材料的组织与力学性能

对挤压铸渗法制备的ZTA/YL302复合材料进行冲击和磨粒磨损试验。利用光学显微镜和电子显微镜观察复合材料试验前后的表面形貌。结果表明,ZTA预制件的孔隙率为40%～55%,渗透的基体为YL302合金。相比YL302合金,复合材料的耐磨性能显著提高,但是冲击韧度有所下降;复合材料在铸态（F）下的冲击韧度比T6热处理后的冲击韧度略高,铸态下的耐磨性能比T6热处理后的高。     

压铸工艺生产的铝基复合材料的组织和性能

报道了压铸浸渗法生产的γ Al2 O3 长纤维、δ Al2 O3 短纤维和SiC颗粒强化铝基复合材料的组织特征和强度性能检测结果。试验结果表明 ,采用优化工艺条件 ,在工业压铸机上可以生产出高浸渗质量、可热处理的铝基复合材料。所获复合材料与 130MPa挤压浸渗生产的复合材料相仿 ,具有理想的工艺质量和组织结构 ,强度性能达到或超过混合律的预测值。     

高钨触头合金的熔浸机理探讨

对ＣｕＷ或ＡｇＷ等高钨含量电触头合金的熔浸机理探讨,有助于控制熔浸制品的质量。文中研究的“定向”熔浸工艺较好地克服了“黑心”等质量缺陷,使制品质量的合格率有所提高