坚硬顶板综采工作面推进速度对矿压规律影响研究

以顾桥煤矿坚硬顶板综采工作面工程地质条件为背景,运用理论分析、数值模拟和现场实测手段,分析了开采速度对工作面覆岩运动、围岩破坏、应力分布和液压支架承载特性的影响。研究结果表明:1个周期来压内工作面落煤引起的岩梁刚性回转下沉量是一定的,工作面作业循环时间引起的岩梁蠕变下沉量与岩梁刚性回转下沉量呈正比,加快工作面推进速度仅减少围岩体蠕变引起的岩梁下沉部分。工作面开采速度增加,覆岩塑性区发育范围减小,煤壁应力集中位置变浅、应力集中系数变小。工作面快速推进时,液压支架承载多为2次増阻和3次増阻,支架工作阻力较小;缓慢推进时,液压支架承载多为1次急增阻,载荷近似呈线性增长,支架工作阻力较大。     

Aftermath of natural disasters: Coping through residential mobility

Most studies of population movement have concentrated on the more developed nations and on trends that have not been influenced by man-made or natural disasters. The experience of developing countries in the Caribbean basin, as studied after the Guatemalan earthquake of 1976 and the impact of Hurricane David in the Dominican Republic of 1979, highlights the importance of socio-economic factors in the decision to make permanent migrations after a disaster, regardless of whether the migrant had personally suffered losses. In many cases the opportunities for personal betterment created by the disaster acted as a catalyst and accelerated a previously-existing trend of migration.     

UNCERTAINTIES IN ESTIMATING THE WATER BALANCE OF LAKES1

ABSTRACT: Evaluation of hydrologic methodology used in a number of water balance studies of lakes in the United States shows that most of these studies calculate one or more terms of the budget as the residual. A literature review was made of studies in which the primary purpose was error analysis of hydrologic measurement and interpretation. Estimates of precipitation can have a wide range of error, depending on the gage placement, gage spacing, and areal averaging technique. Errors in measurement of individual storms can be as high as 75 percent. Errors in short term averages are commonly in the 15-30 percent range, but decrease to about 5 percent or less for annual estimates. Errors in estimates of evaporation can also vary widely depending on instrumentation and methodology. The energy budget is the most accurate method of calculating evaporation; errors are in the 10–15 percent range. If pans are used that are located a distance from the lake of interest, errors can be considerable. Annual pan-to-lake coefficients should not be used for monthly estimates of evaporation because they differ from the commonly used coefficient of 0.7 by more than 100 percent. Errors in estimates of stream discharge are often considered to be within 5 percent. If the measuring section, type of flow profile, and other considerations, such as stage discharge relationship, are less than ideal errors in estimates of stream discharge can be considerably greater than 5 percent. Errors in estimating overland (nonchannelized) flow have not been evaluated, and in most lake studies this component is not mentioned. Comparison of several lake water balances in which the risdual consists solely of errors in measurement, shows that such a residual, if interpreted as ground water, can differ from an independent estimate of ground water by more than 100 percent.     

LOCAL FLOW ACCELERATIONS IN RIVERS1

The geometry and formation of and the energy dissipation in flow accelerations in short steep reaches have been assessed, the latter as to its contribution to the energy expenditure in a long channel reach. An analysis of river gradients, aerial photos and additional field surveys has shown that flow accelerations can (1) originate naturally and sequentially from bars across a channel and nonsequentially from channel abandonment and channelside deposits and (2) be induced by a bankside groyne.     

The rise and fall of the nature conservation movement in Japan in relation to some cultural values

The Japanese are traditionally regarded as nature-loving people, living in “harmony” with nature. However, this assumption is difficult to accept when observing the environmental problems in Japan. How can one explain the incongruities? Has the Japanese people's attitude toward nature changed as Japan has modernized? Is the concept of the nature-loving Japanese merely a myth? Is there another reason to explain this contradiction? This study shows political and economic origins of the paradox. The origin of the Japanese traditional idea of nature is fear and reverence of nature based on a primitive religion that developed in a rural subsistence living situation. Aesthetic and spiritual values of nature for cultural, educational, and intellectual entertainment were developed by the ruling class in the seventh century. Japan's first nature conservation movement, imported from the West, developed among the intellectual community and was advocated and promoted by the elite in the Meiji period (1868–1911). However, because deep commitment was lacking, the movement was abused by the military government before World War II. In the early 1970s the nature conservation movement seemed to be on the ascendancy, mainly because it was combined with the antipollution movement claiming the basic rights of survival. The Japanese nature conservation movement is still in the embryonic stage; in the future, the blending of some traditional resource management with the scientific philosophy of nature conservation may help promote the new wave of nature conservation in Japan.     

Seeding agroecology through new farmer training in Canada: knowledge,practice, and relational identities

As a concept, agroecology emphasises the interweaving of scientific and traditional ecological knowledge and is evolving in conjunction with farmer-led social movements from around the world addressing the health, equity and ecological sustainability of food systems. In Canada, many new agroecological farmers come from non-farming backgrounds and are finding limited training opportunities and support structures. While there is a growing literature on the evolution of agroecology, there is limited research on the existence and impact of training programmes on the subject-formation of new farmers. In this paper, we consider the subject-formation of new agroecological farmers through a case study of the Everdale Community Learning Centre, one of Canada’s only agroecological farm schools. In particular, we explore how the knowledge, practice, and relational identities of participating graduates are informed by and build on the science, practice, and movement of agroecology. Drawing on a survey and interviews with past participants, we found that Everdale’s education programme contributes to an agroecological subject-formation by promoting the co-creation of place-based agricultural knowledge; teaching the complexities of agroecology practice through both experiential and theoretical training; and, building a supportive community of peers. We conclude with reflections on ways to encourage a greater diversity of new farmer entrants and opportunities to support training programme graduates in establishing successful farms. These findings provide insight into developing new agroecological farmers and supporting the growing agroecological movement in Canada.     

尾矿坝溃决泥浆运动机制及其预测模型研究

以尾矿溃坝砂流下游演进动力学过程为研究重点,综合运用水文学及水动力学等运动理论和数值计算方法,建立描述尾矿坝溃决泥浆运动的数学模型,采用VOF模型对溃坝后的砂流运动过程进行数值模拟。以某溃决尾矿坝为例,对溃坝后下泄砂流演进过程进行模拟,模拟得到的最终影响范围及泥深均与该溃决尾矿坝溃后的现场观测结果相吻合,证明了模拟的有效性和正确性。     

煤壁应力峰值动态移动诱发封孔漏气机理研究

基于有效应力原理分析了煤体吸附瓦斯对煤体强度的影响,提出应用煤体单轴抗压强度衰减比k_σ表征瓦斯压力变化对煤体强度的影响;应用数值分析方法研究了煤体瓦斯抽采前后煤壁前方煤体应力、屈服破坏范围的变化。结果表明,抽采期间,煤壁前方煤体应力峰值处于"动态移动"状态,致使煤壁前方的屈服破坏区间同时发生移动,水泥封孔段由受压转为应力卸载状态而发生膨胀破坏,在封孔段水泥与煤壁之间形成松动漏气通道,孔外空气将沿该漏气通道进入孔内,使抽采浓度降低。为提高带压封孔方法的封孔效果,应科学判定抽采前期煤体应力峰值区间,并考虑抽采期间煤体"应力峰值移动"的影响,在应力峰值区间适当向两侧延伸封孔段长度,注重封孔器材和封孔材料的研制和选择。     

高层建筑管道井内烟气运动大涡模拟

采用火灾过程的场模拟理论,以大涡模拟为基础,分析了火灾烟气流动过程的动力学特征;为了验证大涡模拟数值方法的准确性,针对Mercier和Jaluria竖井内的实验工况进行了模拟研究,其模拟结果与试验结果吻合较好,表明大涡模拟可以较好地预测竖井内烟气流动情况;通过设定不同的火灾场景,对不同火源功率和不同几何尺寸条件下管道井内烟气的流动过程进行了数值模拟,其结果给出了不同的几何尺寸和火源功率对管道井内所形成“烟囱效应”的影响情况。笔者的模拟和研究表明:大涡模拟可较准确地预测高层建筑管道井内烟气的流动状态,对高层建筑的防火设计具有指导性作用。