A Numerical Investigation of the Stress Relief Zones Around a Longwall Face in the Lower Seam for Gas Drainage Considerations

Extraction of a protective coal seam (PVCS)-below or above a coal seam to be mined with the potential of coal andgas outburst risk-plays an important role not only in decreasing the stress field in the surrounding rock mass but alsoin increasing the gas desorption capacity and gas flow permeability in the protected coal seam (PTCS). The PVCSis mined to guarantee the safe mining of the PTCS. This study has numerically evaluated the stress redistributioneffects using FLAC3D model for a longwall face in Shanxi Province. The effects of mining depth, mining height andinter-burden rock mass properties were evaluated using the stress relief angle and stress relief coefficient. Verticalstress distribution, stress relief angle and stress relief coefficient in the PTCS were analyzed as the face advancedin the PVCS. The results showed that the stress relief achieved in different locations of the PTCS varied as the faceadvanced. Sensitivity analyses on the pertinent variables indicate that the stress relief in the PTCS is affected mostby the mining depth followed by the inter-burden lithology and the mining height. Furthermore, the elastic moduliof different layers within the inter-burden rock mass are more important than their uniaxial compressive strength(UCS) and Poisson’s ratio. These observations can guide gas drainage borehole design to minimize the accidentsof coal and gas outbursts.

Evaluation and Comparison of Marine Sci-tech Innovation Ability of 11 Coastal Provinces in China: A Case Study of Guangdong

Through building an indicator system for evaluating the marine sci-tech innovation ability of China's coastal provinces,this paper made a comparative analysis on marine sci-tech innovation ability of 11 coastal provinces in 2011-2013 by the principal components analysis( PCA) method. It found these coastal regions can be divided into three levels. Guangdong Province belongs to the first level because its marine sci-tech innovation ability is relatively high. On this basis,it analyzed changes in marine sci-tech innovation ability of 11 coastal provinces with the aid of DEA's Malmquist productivity index model. Results indicate that the overall marine sci-tech innovation ability of 11 coastal provinces is rising,but there is significant difference between provinces and the influence of regional economic development level is not considerable.Technical progress is main driver for promoting marine sci-tech innovation ability of Guangdong Province and major factor influencing ranking of total factor productivity.

突出大学自主办学目标,强化外语教学校本特色——中国人民大学大学英语教学方案

《大学英语教学指南(送审稿)》强调高校大学英语教学要反映各校的校本教学特色,要与学校办学定位和办学目标一致。本文从中国人民大学办学目标和定位出发,从大学英语能力标准制定、教学目标、教学体系、课程设置、评价体系和教学管理六个方面探讨了教学方案的形成及实施过程。文章结论认为,在国家教学指南框架下设计出符合学校发展目标且具有特色的校本大学英语课程体系与评价体系是切实可行的。