Influencing factors analysis of hard limestone reformation and strength weakening under acidic effect

Roof disaster has always been an important factor restricting coal mine safety production.Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics,which is an effective way to control the hard limestone roof.In this study,the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed.The results show that the acid with stronger hydrogen production capacity after ionization(pK_(a)<0)has more prominent damage to the mineral grains of limestone.When pKa increases from−8.00 to 15.70,uniaxial compressive strength and elastic modulus of limestone increase by 117.22%and 75.98%.The influence of acid concentration is manifested in the dissolution behavior of mineral crystals,the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength,and the strength after 15%concentration reformation can be reduced by 59.42%.The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage(within 60 min).The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system.Based on the analytic hierarchy process method,the influence weights of acid type,acid concentration and acidification time on strength are 24.30%,59.54% and 16.16%,respectively.The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.

技术冲击与企业网络演化的时机和方向——激光光盘行业的案例

以1995~2008年激光光盘行业的战略联盟网络为对象,采用纵向案例研究方法,从企业网络演化的时机和方向考察网络演化过程。以行业关键事件作为分析企业网络演化时机的＂时间窗口＂,通过结构强化效应和结构弱化效应来分析企业网络演化方向。我们认为,企业网络演化是企业网络对行业中发生的关键事件作出的反应,这些事件可能会强化网络结构或者弱化网络结构。通过分析行业关键事件的特征,可以事先识别出这些事件对网络结构的影响,从而使管理者能够采取适当的战略行为塑造网络结构,为企业获取竞争优势创造有利的外部环境。