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This study introduced gas control technology in goaf using adjacent roadway large-diameter (550 mm) boreholes to control gas accumulation in the upper corner of a fully mechanized working face in high-gas coal seams. The gas control process in the upper corner and gas interception in goaf by large-diameter boreholes was analyzed using the CFD model of the gas flow in goaf. The latter considered the control equation of gas flow, the established permeability model of goaf, and the gas emission law in goaf. Using the 2-105 working face of the Tenghui Coal Mine, Shanxi Province, China, as a case study, the distribution patterns of gas concentration and flow field in the goaf for various extraction flow parameters and different positions of boreholes were numerically simulated. The dependences between various locations, drainage flows, and the gas concentration in the upper corner were determined and fitted by engineering equations. The evolution pattern of the spontaneous combustion zone in the goaf under the drainage conditions was also analyzed. The optimal borehole configuration parameters ensuring the extraction flow rate exceeding 3 m·s−1 and the effective gas control in the upper corner of the working face at a distance of 5 m–15 m behind the working face were identified. The engineering practice proved the feasibility of gas control in the goaf using the adjacent roadway large-diameter borehole. The gas concentrations in the return airflow and the upper corner of the working face were kept below 0.65 and 0.8%, respectively, to ensure production safety and improve the gas utilization efficiency.

In underground coalmines, the porosity of the goaf area is a significant indicator for evaluating the working face stability and subsidence of the ground surface. However, porosity is difficult to measure directly in a closed goaf. To overcome this, we investigated seismic wave attenuation and elastic velocity changes through porous rock by laboratory measurements using compressed porous rock and coal samples consisting of crushed coal and rock particles. The attenuation of seismic waves through porous rock is strongly influenced by porosity. However, for equal porosity, compressed porous media comprising large particles shows lower seismic attenuation than media with smaller particles. To evaluate seismic attenuation and elastic velocity changes in rock/coal with different porosities, we investigated the effect of particle size (D) and seismic wavelength (λ). We developed a new seismic attenuation model (the Revision model) based on the multi-fractured rock attenuation model by Boadu and Long (Geophysical Journal International 127(1):86–110, 1996). The Revision model accounts for (i) greater attenuation through fragmented rock due to increased contact points between the particles, and (ii) decreased attenuation caused by network propagating through the porous media. The Revision model was applied to the laboratory measurement results of ultrasonic wave attenuation using compressed porous rock and coal samples, and good agreement was found for various porosities, particle sizes and wavelength. Thus, the Revision model may be a useful tool for estimating the porosity in a goaf based on measurements of seismic attenuation and velocity change.

To study the adsorption characteristics of CO, CO2, N2, O2, and their binary-components in lignite coal, reveal the influence of CO2 or N2 injection and air leakage on the desorption of CO in goafs, a lignite model (C206H206N2O44) was established, and the supercell structure was optimized under temperatures of 288.15–318.15 K for molecular simulation. Based on molecular dynamics, the Grand Canonical Monte Carlo method was used to simulate the adsorption characteristics and the Langmuir equation was used to fit the adsorption isotherms of gases. The results show that for single-components, the order of adsorption capacity is CO2 > CO > O2 > N2. For binary-components, the competitive adsorption capacities of CO2 and CO are approximate. In the low-pressure zone, the competitive adsorption capacity of CO2 is stronger than that of CO, and the CO is stronger than N2 or O2. From the simulation, it can be seen that CO2, N2 or O2 will occupy adsorption sites, causing CO desorption. Therefore, to prevent the desorption of the original CO in the goaf, it is not suitable to use CO2 or N2 injection for fire prevention, and the air leakage at the working faces need to be controlled.

Background The ongoing coronavirus disease 19 (COVID‐19) is posing a threat to the public health globally. Serological test for SARS‐CoV‐2 antibody can improve early diagnosis of COVID‐19 and serves as a valuable supplement to RNA detection. Method A SARS‐CoV‐2 IgG/IgM combined antibody test strip based on colloidal gold immunochromatography assay was developed, with both spike protein and nucleocapsid protein of SARS‐CoV‐2 antigen used for antibody detection. From 3 medical institutions across China, serum or plasma of 170 patients with confirmed COVID‐19 diagnosis and 300 normal controls were collected and tested with the strip. Sensitivity, specificity, kappa coefficient, receiver operating characteristic (ROC) curve, and area under the curve (AUC) were analyzed. Positive rates in different medical centers, age group, gender, and different disease course were compared. Results 158 out 170 samples from confirmed COVID‐19 patients had positive results from the test, and 296 out of 300 samples from normal controls had negative results. The kit was 92.9% sensitive and 98.7% specific. The positive rate was 77.3% during the first week after disease onset, but reached 100% since day 9. AUC and kappa coefficient were 0.958 and 0.926, respectively, which showed the consistency of the test results with the standard diagnosis. Age or gender caused little variations in the kit sensitivity. Conclusion The rapid, easy‐to‐use SARS‐CoV‐2 IgG/IgM combined antibody test kit has a superior performance, which can help with accurate diagnosis and thus timely treatment and isolation of COVID‐19 patients, that contributes to the better control of the global pandemic., A SARS‐CoV‐2 IgG/IgM combined antibody test strip based on immunochromatography assay was developed with both spike protein and nucleocapsid protein used for detection. With clinical assessment from 3 medical centers from across China, the kit was 92.9% sensitive and 98.7% specific. The positive rate was 77.3% during the first week after disease onset and reached 100% since day 9.

As an index gas of spontaneous combustion, C2H4 has been used in several coal mines, but its adsorption on residual coal during the process from generation to sampling has an impact on evaluation. The molecular structure models of lignite and anthracite were constructed through molecular mechanics and dynamics, and the Grand Canonical Monte Carlo systems were used to simulate the adsorption of C2H4 and other common gases on lignite and anthracite at temperatures of 288.15–318.15 K. The order of adsorption capacity was CO2 > C2H4 > O2 > N2 in the lignite and anthracite molecular models within the low-pressure zone. When the pressure increases, the adsorption capacity of O2 and N2 exceeded that of C2H4. The C2H4 and CO2 have similar and concentrated adsorption sites, and it is easier to reach the limit adsorption capacity; O2 and N2 have similar adsorption sites, the number of sites is much more than that of C2H4 and CO2, and their limit adsorption capacities are larger than those of C2H4 and CO2. When C2H4 is monitored in a goaf, its concentration is not quite accurate because of the adsorption of residual coal, which is different from the detected temperature of the C2H4 concentration obtained from the experiment. This is of great significance to further experiments and more on-site data statistics to fix the problem for coal mines.

This study was conducted to analyze the influence of outburst power from coal and gas on mine ventilation systems in order to avoid damage from secondary disasters to mine ventilation systems. Through the outburst dynamic experiment of a simple ventilation network system, the unsteady movement characteristics of mine air flow under the combined action of gas outburst source flow and fan ventilation are studied. In this study, the “11.8” coal and gas outburst accident that occurred in the Qunli Coal Mine was simulated numerically. The TF1M simulation program was used to analyze the entire process of the diffuse flow of the countercurrent and outburst gas in the mine ventilation system as well as the dynamic change process of the natural wind pressure in each stage. The results indicate that the power of the outburst source causes the ventilation system to run against the current, the gas in the air intake system of the mine exceeds the limit, and the airflow disturbance of the mine ventilation system is influenced by natural gas pressure and fan pressure. The air pressure of the fan cannot change the rate of air flow but can reduce the time of air flow disorder and promote the gas discharge in the ventilation system. In a word, the research achievements do have important theoretical and practical significance for disaster prevention and aid in outburst mine as well as effectively preventing the occurrence of secondary disasters.

Aiming at the problems of long time-consuming auxiliary operation, low excavation efficiency, high labor intensity and poor production safety in mechanized excavation construction of coal roadway, a temporary support for rapid excavation of top coal in thick coal seam is developed. The support is composed of inner frame assembly, outer frame assembly, inner and outer outrigger oil cylinders, walking oil cylinder, deviation rectification oil cylinder, auxiliary frame, hydraulic pipeline and hydraulic system. Through the design of the hydraulic system of the temporary support for the fast excavation of top coal in thick coal seam, the working pressure of the hydraulic system is determined, the composition and working principle of the hydraulic control system are analyzed and designed, and the hydraulic cylinder of inner frame outrigger, the hydraulic cylinder of outer frame outrigger, the hydraulic cylinder of auxiliary frame, the horizontal hydraulic cylinder and the adjustable spring hydraulic cylinder of the temporary support for the fast excavation of top coal in thick coal seam are designed and verified. The temporary support for fast excavation of top coal in thick coal seam can timely support the new exposed roof cut by roadheader, protect the safety of personnel and equipment in the working space, shorten the working time of support, improve the working efficiency of excavation support, reduce the labor intensity of workers, improve the production safety, accelerate the excavation speed of heading face, and improve the economic and social benefits of enterprises.