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Rock burst is a major disaster in deep mining, where bursting liability is an important indicator of rock burst risk. This study therefore intends to explore the impact of microwave thermal shock on rocks with strong bursting liability by testing the microwave thermal shock and uniaxial compression of typical hard brittle sandstone and analyzing their physical and mechanical properties and the response of bursting liability indicators after microwave thermal shock. The research results show that: (1) After microwaving, the surface temperature of the sandstone continues to rise with the increase of thermal shock time, until it breaks at 150 s; (2) Microwave thermal shock has a significant effect on the structural damage of sandstone. After 120 s of microwaving, the longitudinal wave velocity and elastic modulus decrease by 15.12 % and 8 % respectively. The AE signal density increases at each stage of uniaxial compression, and the maximum absolute energy at the final destruction of sandstone decreases by 42.3 %; The dynamic failure time of rock increases by 259 %, the impact energy index decreases by 95 %, and the elastic energy index decreases by 92 %. This research offer references for efficient rock breaking in deep earth engineering and prevention and control of rock burst in resource mining.

This study aims to tackle the problem of frequent coal-rock dynamic events caused by local stress concentration in deep mining working face under high static stress environment. Specifically, by taking the deep working face of Hongqinghe Mine located in Xinjie Mining Area as an example for analysisthis paper investigates the geological conditions of No. 3-1coal seam that are affected by the mining method and the coal rock dynamic disaster events occurred during mining; utilizes numerical simulation to simulate the mining stress field and energy field of the stope; analyzes the potential coal burst instability area and mechanism of coal burst gestation and catastrophe in the stope during the mining of the No. 3-1103 working face; probes into the sources of catastrophic stress and influencing factors of coal-rock disasters in dangerous areas, puts forward targeted prevention and control measures. Results show that: ① the roof strata structure, goaf and coal pillar are the key factors influencing coal burst in the stope during the mining of the No. 3-1103 working face; ② the simulation results indicatethe location and characteristics of the coal burst instability area in the stope of the No. 3-1103 working faces, as well as the simulation outlines 5 strong coal burst areas and 11 medium coal burst areas presented in the stope; ③ Measures are proposed for coal burst during mining from the perspective of cutting off the dynamic load source, reducing static load stress concentration, and blocking the transmission of high concentration stress. Detailed measures include implementing multi-source prevention and control in areas with high static or high static+dynamic loads, implement pre-pressure off-load measures prior to mining, and local risk relief and coal burst prevention and reduction treatments during mining.

Making clear the vibration response law of buildings(structures)due to blasting is of great significance both engineeringly and the economically. By conducting blasting experiment at subway station entrance A, the vibration signal of building NO.2 was analyzed through Hilbert-Huang transform. Results indicate that as height increases, the three-vector peak vibration velocity attenuate sharply, and then shows a wave-shaped change in the middle and amplify on the top floor, which was divided into attenuation area(0~26.15 m], fluctuation area(26.15~71.75 m]and amplification area(71.75~94.55 m]. The shape of the Hilbert spectrum gradually changes from three-peak to single-peak, the dominant frequency band attenuates from 75~125 Hz to 10~40 Hz and the energy amplitude decreases. This demonstrates that the lower vibration frequency of the floor in the amplification area could easily cause resonance. Based on the composition of the top-level energy spectrum fitted by the ground measuring points, it is verified that the essence of the top-level amplification effect is to selectively amplify the energy close to the natural frequency of the building in the blasting seismic wave.

In order to improve the pointing accuracy of roll-pitch semi-strapdown photo-electricity stabilized platform, a method for error modeling and parameter calibration of stabilized platform is proposed. Based on the mechanical structure characteristics of the roll-pitch seeker, the main error sources of the stabilized platform are analyzed. Established the linear error model of the misalignment angle by using the coordinate transformation method and Taylor formula, and designed a method to improve the line-of-sight measurement accuracy of the stable platform by compensating the misalignment angle error. The least square method is used to design the calibration method of error parameters. The simulation results show that the error parameter calibration method can effectively calibrate the error parameters, and the method of compensating the misalignment angle error through the misalignment angle linear error model can significantly improve the line of sight pointing measurement accuracy of the stabilized platform.

Objective To investigate the effect of bone morphogenetic protein 4 (BMP4) overexpression in MLO-Y4 osteocytes on osteogenic differentiation of bone marrow stromal ST2 cells through Notch signaling. Methods Ad-GFP or Ad-BMP4 infected MLO-Y4 cells were co-cultured with ST2 cells, and designated as GFP and BMP4 group respectively. Western blotting was used to detect the BMP4 protein level in MLO-Y4 cells. Real-time fluorescence quantitative analysis (qPCR) was applied to determine the mRNA expression of BMP4 and Notch ligands genes as well as osteoblast genes in the MLO-Y4 cells, and Notch target genes and angiogenesis factors in the co-cultured systems. The activity of alkaline phosphatase (ALP) was determined by ALP staining and biochemical quantification. Notch signal inhibitor DAPT was added to the co-culture system to detect the above indexes again. Results Overexpression of BMP4 upregulated the expression of Notch ligands Jag1, Jag2 and Dll4 in MLO-Y4 cells. ALP staining and biochemical quantitative results demonstrated that there was no significant difference in ALP activity at day 1 between the GFP and BMP4 groups, and stronger ALP activity was seen in the latter group at day 3 and 5 (P < 0.05). In the BMP4 group, at day 1 among the osteoblast genes, only runt-related transcription factor 2 (Runx2) was obviously expressed (P < 0.05), and the levels of Alp, Runx2, osteocalcin (Ocn), and collagen Ⅰ were all highly expressed in the BMP4 group (P < 0.05). At day 3, Notch signaling target genes Hey1 and Hey2, angiogenesis factors vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1 (HIF1α) were also highly expressed in the BMP4 group compared with the control group (P < 0.05). After addition of DAPT to inhibit Notch signaling, the activity of ALP and expression of osteoblast genes and angiogenesis genes were all decreased (P < 0.05). Conclusion Overexpression of BMP4 in MLO-Y4 cells promotes osteogenic differentiation of ST2 cells, which may be related to the enhancement of Notch signaling.

The height of overburden fissure zone is an important index to study the deformation and failure of overburden, but the existing single index can not reflect the fracture degree of surrounding rock in different space parts of stope. Based on 81505 working face of Baode Mine with typical shallow burial conditions in Shendong, the unification of coal sample damage degree and index RFD (Rock Failure Degree) is completed by laboratory experiments, and a similar model and a numerical model are constructed. Based on the index RFD, the maximum destructive depth in numerical simulation is extracted, and the law of development height of overburden mining fissure zone and its variation with mining height are studied by comparing similar simulation results. The results show that the index RFD can well assess the development characteristics of mining fissure zone under typical shallow burial conditions in Shendong. And the development height of fissure zone continuously with the increase of mining height but the growth rate decreases gradually. The research in this paper provides theoretical support and technical basis for distribution and destruction characteristics of fractured zones, occurrence of rock pressure and safe mining.

Acoustic emission and infrared radiation measurements were carried out on medium sandstone, fine sandstone and siltstone in the coal measures of the Ordos Basin under uniaxial compression, the stress, the acoustic energy and the average infrared radiation temperature (AIRT) versus time evolution of characteristics were analyzed, the acoustic and the thermal effects characteristics of different granular sandstones during the rupture process were studied.The results show that the AIRT in the different areas of the same sandstone has the same trend in the compaction and elasticity phase,but the tendency is different in the plasticity and damage stages.It generally shows a wave downward trend; and the temperature in the middle is higher than that in the upper and lower parts.The temperature changes in different sandstones are related to energy accumulation and dissipation,and the overall trend of AIRT on the sandstone surface shows a wave downward trend, acoustic emission (AE) is not obvious at the beginning ,but it raise rapidly during the later stage of plasticity, there are still a large number of AE events after the peak; the precursor of infrared radiation priority to the acoustic emission warning, the average infrared warning time of middle sandstone is 20.533s, fine sandstone is 6.516s ahead, and siltstone is 6.4s, but the sensitivity of the acoustic emission is higher than that of the infrared radiation.The acoustic and the thermal effects of sandstone is closely related to the particle size,the larger the particles, the more pronounced the acoustic thermal effects.The sensitivity of the acoustic thermal effect is in the order of medium sandstone, fine sandstone and siltstone.

The coupling characteristics of coal seam stress,fracture and seepage directly affect the migration characteristics of pressure relief gas during the protective seam mining.In this paper,combined with cubic law,the method for the selection of the fluid solid coupling parameters of elastic joints and persistent fracture was proposed based on the experimental data of the elastic and persistent fracture coal samples.Meanwhile,the simulation modeling of fluid solid coupling for triaxial flow test of coal samples was built.On the basis of this simulation method,the coupling characteristics of the coal sample stress,fracture and flow were simulated and analyzed during uniaxial and triaxial loading.The simulation results show that the permeability of coal samples changes as S type with the increase of axial strain.The permeability of coal sample decreases gradually with the increase of axial pressure before the fracture of coal sample development.The permeability of the coal samples increases with the development of the fractures,and the faster the fracture expansion rate is,the higher the permeability increases.The increase of confining pressure resulted in the decrease of internal fracture generation and propagation,and the permeability reduction stage was extended.The initial permeability and yielding permeability of the coal samples decreased gradually.

The effects of axial pressures and penetrative pressures on the permeability of broken rocks were investigated by using the system of deformation-seepage of broken rocks to study the seepage of broken rocks under five axial pressures and eight penetrative pressures.The results found that the permeability of broken rocks were reduced with the increase of axial pressures and penetrative pressures.The effect of penetrative pressures on permeability was higher than axial pressures.With the increase of axial pressures, the responsive degree of the permeability of broken rocks to axial pressures was increasing, decreasing and increasing under the same penetrative pressures.With the increase of penetrative pressures, the responsive degree of the permeability of broken rocks to penetrative pressures was decreasing monotonously under the same axial pressures.In order to predict the permeability more accurately, the functional relationship between the permeability of broken rocks and the axial pressures, the penetrative pressures was derived.

This paper focuses on the differences in crowding perception among different types of passengers in trains, aiming to optimize passenger experience and improve the level of service of urban rail transit. Based on data from a passenger survey on the Beijing subway, this paper introduces the concept of Crowding Perception Threshold (CPT) and analyzes the principle of passenger spatiotemporal crowding. Considering factors such as gender, age, travel purpose, and standing density of passengers, the paper constructs a quantitative model of crowding perception using the ordered logit model and proposes a method for classifying the level of service accordingly. The study results indicate that the CPTs for all types of passengers range from 91.8% to 101.6%, with the females, elderly individuals, and noncommuters showing greater sensitivity to crowding. In the temporal dimension, all types of passengers have higher CPTs during peak hours than during off-peak hours, influenced by passengers' crowding expectations. In the spatial dimension, the level of service for most types of passengers is considered crowded at standing densities of 6-7pax/m[sup.2] during peak hours, while the level of service for all types of passengers is deemed to be very crowded at 8pax/m[sup.2], at which point additional passengers are not recommended., Author(s): Xia Lu [1]; Baohua Mao (corresponding author) [1]; Min Wang (corresponding author) [2,3]; Yixin Zhao [1]; Peining Tian [1] 1. Introduction In some cities in China, the issue of [...]