Pore pressure fluctuations of overlying aquifer during residual coal mining and water-soil stress coupling analysis

Three test models and a simulation model were constructed based on the prevailing conditions of the Taiping coalmine in order to analyze pore pressure fluctuations of an overlying aquifer during residual coal mining. As well, the relation between pore pressure and soil stress was evaluated. The model tests show the vibrations of pore pressure and soil stress as a result of mining activities. The simulation model tells of the response characteristics of pore pressure after mining and its distribution in the sand aquifer. The comparative analysis reveals that pore pressure and soil stress vibration are activated by unexpected events occurring in mines, such as collapsing roofs. An increased pore pressure zone always lies above the wall in front or behind the working face of a mine. Both pore pressure and vertical stress result in increasing and decreasing processes during movements of the working face of a mine. The vibration of pore pressure always precedes soil stress in the same area and ends with a sharp decline. Changes in pore pressure of sand aquifer are limited to the area of stress changes. Obvious changes are largely located in a very small frame over the mining face.

企业与市场:相关关系及其性质——一个基于回归古典的解析框架

通过对科斯替代逻辑的反思 ,重新考察了企业与市场的相关关系。认为交易费用的提出虽然打开了新古典企业的“黑箱” ,但是由此来解释企业的性质 ,其结论与现实相悖。本文提出了一个趋于古典的分析框架 ,发现企业与市场是分别建立在两种不同但有紧密相关性的分工基础上的 ,因而 ,它们各自的性质及其相互关系源于一般分工与个别分工各自的性质及其相关关系———企业是要素所有者为分享“合作剩余”而达成的合约 ,而市场则是商品所有者交换比较优势的制度安排。两者互补而不相互替代。这一结论较好地解释了实体经济中不论是企业规模 ,还是企业数量都在不断扩张 ,同时市场范围随之不断扩展 ,两方面相互促进、正相关推进发展的现实。