Stability mechanism and control of the pumpable supports in longwall recovery room

The load-bearing performance(LBP)of pumpable supports(PPS)is crucial for the stability of longwall pre-driven recovery room(PRR)surrounding rock.However,the unbalanced bearing coefficient(UBC)of the PPS(undertaking unequal load along the mining direction)has not been investigated.A mechanical model of the PRR was established,considering the main roof cantilever beam structure,to derive an assessment formula for the load,the failure criteria,and the UBC of the PPS.Subsequently,the generation mechanisms,and influencing factors of the UBC were revealed.Global sensitivity analysis shows that the main roof hanging length(l_(2))and the spacing between the PPS(r)significantly impact the UBC.A novel design of the PPS and the coupling control technology were proposed and applied to reduce the UBC of the PPS in the adjacent longwall PRR.Monitor results showed no failure of the PPS at the test site,with the UBC(ζ)reduced to 1.1 consistent with the design value(1.15)basically,fully utilizing the collaborative LBP of the PPS.Finally,the maximum roof-to-floor convergence of the PRR was 234 mm,effectively controlling the stability of the surrounding rock of the PRR and ensuring the mining equipment recovery.

Motor Imagery did not Improve Strength of Biceps Brachii

Numerous studies have confirmed that motor imagery may result in plastic change in motor system as actual physical activity. However, whether motor imagery can improve muscle strength of the trained persons remains unclear. The aim of this study is to investigate the effect of motor imagery on muscle strength. Totally 12 healthy college students were involved in 4 weeks of mental rehearsal of right upper limb movements (flexion and extension of elbow) during 30 min supervision session three times a week. Electromyogram (EMG) and peak torque of biceps brachii, reaction time of subjects were analyzed. Results showed that no significant change in EMG of biceps brachii was observed during motor imagery. After motor rehearsal for 4 weeks, statistically significant difference in EMG, peak torque and reactivity were not observed (P > 0.05) when compared with the baseline data. Therefore, motor imagery could not enhance muscle strength of subjects. Whether mental practice is a valid rehabilitation technique needs to be investigated further.

Emergence and prevalence of naturally occurring lower virulent African swine fever viruses in domestic pigs in China in 2020

African swine fever virus(ASFV)has been circulating in China for more than two years,and it is not clear whether the biological properties of the virus have changed.Here,we report on our surveillance of ASFVs in seven provinces of China,from June to December,2020.A total of 22 viruses were isolated and characterized as genotype II ASFVs,with mutations,deletions,insertions,or short-fragment replacement occurring in all isolates compared with Pig/HLJ/2018(HLJ/18),the earliest isolate in China.Eleven isolates had four different types of natural mutations or deletion in the EP402R gene and displayed a nonhemadsorbing(non-HAD)phenotype.Four isolates were tested for virulence in pigs;two were found to be as highly lethal as HLJ/18.However,two non-HAD isolates showed lower virulence but were highly transmissible;infection with 106 TCID50 dose was partially lethal and caused acute or sub-acute disease,whereas 103 TCID50 dose caused non-lethal,sub-acute or chronic disease,and persistent infection.The emergence of lower virulent natural mutants brings greater difficulty to the early diagnosis of ASF and creates new challenges for ASFV control.