Investigating low-permeability sandstone based on physical experiments and predictive modeling

An innovative method is proposed for preparing low-permeability sandstone with different moisture saturation.The permeability of the prepared low-permeability sandstone sample is measured under different confinement and seepage pressures.Based on the experimental results,10 types of different machine-learning models combined with optimization algorithms are established to predict the permeability of low-permeability sandstone.A comprehensive evaluation and comparison of the 10 types of machine-learning models are conducted to identify the machine-learning model with the best performance.Next,a sensitivity analysis is conducted on the factors influencing the permeability of low-permeability sandstone to elucidate the internal mechanism according to the established machinelearning model.The following conclusions are drawn.With an increase in the confinement pressure,the permeability of lowpermeability sandstone with different moisture-saturation levels decreases,and the permeability of low-permeability sandstone decreases with an increase in the moisture saturation.The hybrid particle swarm optimization algorithm-backpropagation artificial neural network(PSO-BPANN)model provides the best results for predicting the permeability of low-permeability sandstone.The established PSOBPANN model is also reliable for predicting the permeability of low-permeability sandstone from other engineering sites.Among the influencing factors,moisture saturation has the largest effect on the permeability of low-permeability sandstone,followed by the confinement pressure.

Surgical Treatment of Left Atrial Dissection and Severe Mitral Valve Obstruction

Left atrial dissection is a rare complication of mitral valve replacement surgery.Here,a case of left atrial dissection followed by mitral valvular obstruction was presented.It is suspected that the dissection was caused by trematodiases infection.Cardiac surgery was finally performed,which not only confirmed the diagnosis but also acted as an effective treatment.Especially,surgery is of essential value to confirm the perforation locating at the basal posterior wall of the left ventricle,to repair the atrial dissection,and to relieve the mitral valvular obstruction.