Ground pressure and overlying strata structure for a repeated mining face of residual coal after room and pillar mining

To investigate the abnormal ground pressures and roof control problem in fully mechanized repeated mining of residual coal after room and pillar mining, the roof fracture structural model and mechanical model were developed using numerical simulation and theoretical analysis. The roof fracture characteristics of a repeated mining face were revealed and the ground pressure law and roof supporting condi- tions of the repeated mining face were obtained. The results indicate that when the repeated mining face passes the residual pillars, the sudden instability causes fracturing in the main roof above the old goal and forms an extra-large rock block above the mining face. A relatively stable ＂Voussoir beam＂ structure is formed after the advance fracturing of the main roof. When the repeated mining face passes the old goaf, as the large rock block revolves and touches gangue, the rock block will break secondarily under overburden rock loads. An example calculation was performed involving an integrated mine in Shanxi province, results showed that minimum working resistance values of support determined to be reason- able were respectively 11,412 kN and 10,743 kN when repeated mining face passed through residual pillar and goaf. On-site ground pressure monitoring results indicated that the mechanical model and support resistance calculation were reasonable.

The Effect of Repeat Cardiopulmonary bypass on Epicardial Microflow and Graft Flow during Intraoperative Heart Failure

Objective\ The relationship between graft blood flow, epicardial microflow, mean arterial pressure and hemorheologic changes was studied during intraoperative heart failure. Methods\ These parameters were done to evaluate the use of repeated cardiopulmonary bypass support for the intraoperative heart failure following aorto coronary bypass surgery. Included in this study were 10 patients with a mean age of 70 and unstable angina undergoing coronary bypass grafting and suffering from intraoperative heart failure. The epicardiai microflow, graft flow, mean arterial pressure and blood cell filterability were measured. Resluts\ During heart failure, the mean arterial pressure fell by 41%(P<0.01), graft flow by 67%(P<0.01) and epicardialmicroflow by 64%(P<0.01). After 15 to 56 min of assisted cardiopulmonary bypass support, the epicardial microflow and graft flow were partially restored, while red cell and white cell filterability was reduced by 31% and 64% respectively (P<0.01). There were significant correlations between graft flow, epicardial microflow, blood cell filterability and cardiopulmonary bypass time. All patients recovered and were discharged from the hospital.Conclusion\ It is concluded that the use of temporary assisted CPB support to treat intrapoperative heart failure allows the recovery of the myocardium and thereby restores the mean arterial pressure. The recovery of graft flow and epicardial flow occurred to a lesser extent. The CPB support seemed to be suitable for about 60 min probably because of increasing disturbance to the blood cell filterability, graft flow and the epicardial microcirculation.\;