Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines,a criterion of rock burst induced by roof breakage(RBRB) was proposed and the model was built.Through the model.a method calculating the varied stresses induced by roof breakage in support objects and coal body was proposed and a unified formula was derived for the calculation of stress increment on support objects and coal body under different breaking forms of roof.Whilst the formula for calculating dynamic load was derived by introducing dynamic index Kd.The formula was verified in Huating Mine by stress measurement.According to the formula for stress increment calculating,the sensitivities of dynamic load parameters were further studied.The results show that the thickness and breaking depth of roof,width of support object are the sensitive factors.Based on the discussion of the model,six associated effective methods for rock burst prevention are obtained.
To investigate the feasibility of implanting the biocomposite of calcium phosphate cement(CPC)/polylactic acid-polyglycolic acid(PLGA) into animals for bone defects repairing,the biocomposite of CPC/PLGA was prepared and its setting time,compressive strength,elastic modulus,pH values,phase composition of the samples,degradability and biocompatibility in vitro were tested.The above-mentioned composite implanted with bone marrow stromal cells was used to repair defects of the radius in rabbits.Osteogenesis was histomorphologically observed by using an electron-microscope.The results show that compared with the CPC,the physical and chemical properties of CPC/PLGA composite have some differences in which CPC/PLGA composite has better biological properties.The CPC/PLGA composite combined with seed cells is superior to the control in terms of the amount of new bones formed after CPC/PLGA composite is implanted into the rabbits,as well as the speed of repairing bone defects.The results suggest that the constructed CPC/PLGA composite basically meets the requirements of tissue engineering scaffold materials and that the CPC/PLGA composite implanted with bone marrow stromal cells may be a new artificial bone material for repairing bone defects because it can promote the growth of bone tissues.
