Mining a coal seam below a heating goaf with a force auxiliary ventilation system at Longhua underground coal mine, China

Extraction of a coal seam which lies not far below a heating goafcan be a major safety challenge. A force auxiliary ventilation system was adopted as a control method in successful extraction and recovery of the panel 30110 of the #3-1 coal seam, which is about 30-40 rn below the heating goaf of the #2-2 seam at Longhua underground coal mine, Shanxi Province, China. Booster fans and ventilation control devices such as doors and regulators were used in the system. The results show that, provided that a force auxiliary ventilation system is properly designed to achieve a pressure balance between a panel and its overlying goat＇, the system can be used to extract a coal seam overlain by a heating goal. This paper describes the design, installation and performance of the ventilation system during the extraction and recovery phases of the oanel 30110.

Effect of Morphology and Age on the Closure Ability of Asian Box Turtles(Cuora)

The ability of box turtles to close their shell as an antipredation adaptation and the potential impact of the anterior and posterior lobes of the plastron on the closing force and closing time remain relatively unexplored.Here,keeled(Cuora mouhotii)and flowerback(C.galbinifrons)box turtles,whose shell cannot and can be completely closed,respectively,were studied.Anterior and posterior closing forces were measured using a force transducer,and the closing time was recorded.The anterior closing force in both turtle species was substantially greater than the posterior closing force,reaching approximately 4-fold in adults.Moreover,the anterior closing time in adults was significantly longer than the posterior closing time.This closing force difference can be attributed to the substantially smaller anterior plastron lobe than the posterior lobe in the two species.Additionally,the anterior and posterior closing forces in both species positively correlated with body weight and showed no relationship with the length of the bridge and hinge.Interspecies comparison showed that the anterior and posterior closing forces were significantly greater(approximately 2–4-fold)in flowerback box turtle than in keeled box turtles,regardless of age,and the closure time was significantly longer in adult flowerback box turtles than in adult keeled box turtles.Although the closing forces in both species showed negative allometry,the increase rate was significantly higher in flowerback box turtle than in keeled box turtle.The closing forces in both species were observed to be approximately 4-fold stronger in adults than in juveniles.No sexual dimorphism concerning the anterior and posterior closing forces was observed in either species.In summary,this is the first study to comparatively evaluate the anterior and posterior closing ability of box turtles,demonstrating that age,weight,plastron shape,and the degree of shell closure are important factors affecting closing ability.

INVESTIGATION OF ENERGY EQUILIBRIUM EQUATION ON CRACK FORMATION OF ELECTRICAL CONTACT SURFACE

Experiment investigations on crack propagation of silver based contact surface are carried out with various currents and contact closed forces.It is found that crack propagation of contact surface is caused by arc energy and contact closed forces.Meanwhile, the energy equilibrium equation of crack propagation of silver based contact material under arc energy and contact closed force is provided.