Ultimately exposed roof area prediction of bauxite deposit goaf based on macro joint damage

The ultimately exposed roof area(UERA)of goaf is crucial to the safety and economics of underground mining.The prediction models do not consider the mechanical weakness of rock mass and ignore the influence of the joint damage factor,causing a large predicted exposure area with a high roof falling risk.This work adopted joint damage factor to derive a new UERA prediction model.The relationships between the UERA(S)and the span ratio(m),the density(k)and the diameter of fracture(d)were analysed by the new prediction model.The results showed that the exposed area S and the span ratio m have a U-shaped curve relationship.The S decreases with the increase of m and then increases when m is beyond 2.The exposed roof area S is in an inversely proportional power-law relationship with the fracture surface density k,and the curvature of the S-k relationship curve decreases when d=0.5 and k>7,and S is close to 0.There is a negative correlation between S and the fracture surface diameter d,the curvature of the S-d curve decreases with the increase of d and k,and the variation rate increases first and then decreases with the increase of d;when k=0.5 and d>9,S is close to 0.The predicted values of the UERA prediction model are 119.3,112.8,and 114.6 m2 with different joint damage parameters,which are slightly smaller than the actual critical exposure area of a roof(S=120 m2).The case study shows that the alternative prediction model is reasonable and acceptable and provides new theoretical support for the underground mining safety of sedimentary bauxite ore.

Unexplained elevation of erythrocyte sedimentation rate in a patient recovering from COVID-19:A case report

BACKGROUND A disease caused by a novel coronavirus virus,named coronavirus disease 2019(COVID-19),broke out in Wuhan,China in December 2019,and spread around the word.As of March 4,2020,93090 confirmed cases and 2984 deaths have been reported in more than 80 countries and territories.It has triggered global public health security.However,the features and prognosis of COVID-19 are incompletely understood.CASE SUMMARY We here report that the erythrocyte sedimentation rate(ESR)increased in a confirmed COVID patient.The high level of ESR sustained for a long time even after the patient recovered from COVID-19,while all results related to tumor,tuberculosis,rheumatic diseases,anemia,etc.cannot explain the abnormal elevation of ESR presented in this case.CONCLUSION Although the increased ESR cannot be explained by all existing evidence,it possibly links the abnormal pathologic change in some COVID-19 patients and negative prognosis,and provides the clue to dissect the mechanism of illness progressing in COVID-19 and its prognosis.