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1.
弄清酸雨入渗膨胀土所产生的水土化学作用,对获取酸雨区浅表层膨胀土基本性能劣化机理及分析边坡的稳定性非常重要。为此,取广西酸雨重灾区的百色原状膨胀土,研制循环饱水试验装置并模拟不同pH值的雨水入渗环境,开展酸雨入渗膨胀土水土化学试验;运用多种微观测试技术,探究膨胀土的矿物与化学成分演变规律;采用地球化学模拟软件(PHREEQC)及水土化学理论,分析膨胀土与酸雨间水土化学作用机理。结果表明:相比静态水饱和状态,降雨入渗动态水饱和环境能促进膨胀土中矿物质的溶蚀与淋滤,加速土体结构的破坏;酸雨入渗后膨胀土中CaO、Fe2O3、K2O明显大于Si O2、Al2O3等氧化物的溶蚀与淋滤量;雨水的pH值越小,膨胀土片状微结构间溶蚀的方解石及游离氧化物等胶结物越多,离子交换作用增强;酸雨与土中矿物的相互作用加剧,部分伊利石脱钾转变为蒙脱石黏土矿物,导致伊利石含量减小,蒙脱石含量增加,土的亲水性增强而结构不稳定性变大,不利于膨胀土边坡的稳定。 相似文献
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气候变化和城镇化发展使得极端暴雨发生频率增加,实验室降雨试验可为极端暴雨灾害的研究提供数据支撑。通过开展不同情景下的实验室降雨试验与数值模拟,研究了风对落地雨强分布的影响,分析了风导致试验区域平均落地雨强减小的原因。结果表明:(1)风会使试验区域的实际平均落地雨强减小,主要原因是降雨中不同粒径雨滴在风场作用下漂移距离的不同,导致了地面受雨面积扩张。(2)受雨范围内落地雨强的均匀性受风速影响,落地雨强均匀性随风速增加而下降。为提高试验数据的准确性,在进行降雨模拟试验时需要考虑风速的影响,结合实验室实际条件合理确定试验范围。 相似文献
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针对目前集成电路版图分析与设计课程存在教学方法老化、教学模式形式化等问题,本文以OBE-CDIO教育理念为指导,对”集成电路版图分析与设计”课程的课程教学模式、课程设计、项目式教学方式和课程考核方式等方面的改革进行有益的探索与实践。将工程教学认证中对学生的专业毕业要求作为制定教学目标的依据,将BB网络平台、ISO9001等现代化教学资源和质量标准融入课堂教学,采用OBE-CDIO能力教学理念指导课程设计,实现教学环节与考核环节的科学化与多元化,通过引入课程思政激发学生学习热情,树立社会主义核心价值观,全面地培养学生的综合版图分析与设计能力和素养。 相似文献
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暴雨雨型直接影响着洪峰流量的大小及洪水过程,研究暴雨雨型可为防洪排涝、山洪灾害防治提供科学依据。根据陕西省宝鸡气象站1981~2017年自记降雨资料,采用Ward聚类分析法对120场暴雨做了分类研究,从多角度分析了雨型的发生规律,初步探讨了雨型与山洪内涝的关系。结果表明,聚类分析法在雨型分类中具有较好的适用性;宝鸡气象站120场暴雨分为5种类型,分别为单峰靠前的Ⅰ型,雨峰位于第一时段且中间雨量少的Ⅱ型,近乎均匀分配、中部略高的Ⅲ型,雨峰位于最后一时段且中间雨量少的Ⅳ型及单峰靠后的Ⅴ型;场次暴雨雨型以Ⅰ、Ⅲ型为主,不同历时Ⅰ、Ⅲ型暴雨出现的场次相当,Ⅱ、Ⅳ、Ⅴ型随着场次暴雨历时的增加发生几率减小;独立短历时场次暴雨中Ⅰ、Ⅲ型更易引发山洪内涝。 相似文献
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University students spend most of their time in classrooms, mostly in a sitting position. Prolonged sitting on ill-fitted furniture and the resulting bad posture is making students suffer from different musculoskeletal disorders (MSDs). This study evaluates the potential mismatch between furniture dimensions and anthropometric measurements. To determine potential mismatch, 13 anthropometric measurements of 550 students and 11 dimensions of two types of classroom furniture (mounted-desktop and chair-with-table) were measured and then compared. Additionally, chi-square test was performed to compare the relation between anthropometry and relevant furniture dimensions. Results showed that a significant number of mismatches emerged between anthropometric measurements and furniture dimensions. For both types of furniture, seat height was too high and seat depth was too deep. Moreover, for mounted desktop, desk height is almost appropriate for all students whereas for chair and table, it was too high for the males. These circumstances may lead to increase discomfort and increase MSDs problems among all students. It can be concluded that the dimensions of both types of classroom furniture were not appropriate for users according to anthropometric measurements. This analysis recommends the measurements of furniture dimensions based on participants’ anthropometric measurements to avoid or minimise discomfort and MSDs problems. 相似文献
8.
Takashi Tsuchida Takeo Moriwaki Shinji Nakai A.M.R.G. Athapaththu 《Soils and Foundations》2019,59(4):1085-1102
This study was intended to examine the mechanism of multiple slope failures and debris flows that occurred in the outskirts of Hiroshima on 20th August 2014. A field survey of the mountain stream where large-scale damage was incurred was carried out and the characteristics of debris flows which made serious damages were investigated. There were five findings of this study. (1) The initiation of debris flows was not limited to thin and planar shallow failures, but also showed V or U shapes, where the eroded sediments seemed to be pushed out by artesian water, and the eroded depth exceeded several meters at many locations. (2) There were areas with high permeability, such as faults, fracture zones, and joints in Mt. Abusan. It is inferred that the constantly present groundwater in these areas became artesian water because of a large amount of rainfall in upstream locations. This quickly destabilized the slopes on a large scale. (3) There were at least three estimated debris flows at the mountain stream above Midorigaoka prefectural apartments in Yagi 3-Chome, where the worst damage occurred. The mountain stream near Abu-no-Sato housing complex also had multiple debris flows. Here, the secondary debris flow changed its flow path because of the presence of sediments from an earlier debris flow. (4) The actual volumes of flowed mass were much larger than that predicted at 11 of the 18 mountain streams in Midori-i and Yagi districts. The volume of the mass of five of these mountain streams was more than twice the estimated volume. It is necessary to modify the method of calculating the volume of unstable sediments in the mountain stream. (5) It was found that the devastating damage of buildings and human lives took place in the areas well beyond the special restricted zones. The present method to designate the special restricted zone must be revised considering such problems as the underestimation of the volume of unstable sediments, the assumptions of a single debris flow and on the direction of debris flow, and the effect of the difference on rock and soil types. 相似文献
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Effect of raindrop size distribution and rain rate inhomogeneity on the relationship between attenuation and depolarization 下载免费PDF全文
Peeramed Chodkaveekityada Hajime Fukuchi 《International Journal of Satellite Communications and Networking》2018,36(1):134-145
In addition to attenuation, depolarization due to rain is another factor that degrades satellite propagation signals, especially in the higher frequency bands and in places that have high rates of rainfall. A formula to predict cross‐polarization as a function of attenuation has been proposed, and it is derived by a theoretical calculation using frequency, the forward scattering amplitude of raindrops, rainfall rates, the raindrop size distribution (DSD), and various other propagation parameters. In this paper, a formula for predicting cross‐polarization is derived on the basis of the assumption of a gamma‐type DSD up to 100 GHz. These results are compared with conventional exponential‐type DSDs, such as the Marshall‐and‐Palmer DSD. Moreover, for a more realistic propagation situation, we consider the effect on the aforementioned relationship of rainfall rate inhomogeneity along the propagation path. It is shown that, for practical purposes, this inhomogeneity does not have a significant effect on satellite propagation. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献