Search

Stress concentration of coal and rock mass is the intrinsic cause of rock burst, the dynamic evolution law of coal seam stress and roof rock stress during the advancing process of mining face is obtained by using the coal seam stress monitoring system and the developed surrounding rock stress monitoring system, In this paper, the stress variation law of coal and rock mass during mining and the correlation between them are analyzed in detail. In order to reduce the danger of rock burst caused by stress concentration, hydraulic fracturing measures of roof strata were adopted in the field, and the stress changes of coal and rock mass before and after hydraulic fracturing were compared and analyzed. The results of the inspection show: The vertical stress gradient is linearly correlated with the trend of coal seam stress. The influence of mining on the stress of rock seam is earlier than that of coal seam, but the influence of mining disturbance on the stress of coal seam is higher than that of rock seam; The increase amplitude of vertical normal stress of roof strata under mining disturbance is obviously higher than that of two horizontal stresses; the stress value of coal and rock strata decreases after hydraulic fracturing, and the decrease amplitude of stress in coal seam is larger than that of rock strata after hydraulic fracturing. The peak stress of coal seam moves toward stopping line than that before hydraulic fracturing. Field application shows that the stress evolution information of coal seam can provide the corresponding basis for anti-scouring measures and ensure the safe and efficient production of working face.

Slow light technology will play a key role in future all-optical communication. The slow-light technology based on stimulated Brillouin scattering has become a research highlight because of its additional advantages, such as compatibility of the devices with existing telecommunication systems, room-temperature operation, and tunable at arbitrary wavelengths. According to the propagation of a cw pulse through a Brillouin fiber amplifier, whose frequency is near the Stokes resonance, via three-wave coupling equations, both pump depletion and fiber losses taken into consideration, the principle of how slow-light effect based on stimulated Brillouin scattering produced and the mathematical expression of time delay are strictly deduced. A delay of 8 ns is obtained when the input Stokes pulse is 200ns and the SBS (stimulated Brillouin scattering) gain G is ~18 in our designed experiment of SBS slow-light system. Then the extent of transformation from pump waves to Stokes waves is measured using MATLAB numerical simulation according to the experiment dates, based on the relation between output pump light power and input pump light power and also the relation between output Stokes light power and input pump light power. And the relation between the input light power and propagation distance is discussed as well. Finally the relation between slow light pulse delay and SBS gain is also obtained.