Mechanism of strength deterioration of red sandstone on reservoir bank slopes under the action of dry-wet cycles.

To investigate the micro-scale mechanism of strength deterioration under different times of dry-wet cycles, laboratory tests of physical properties, triaxial compression, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on red sandstone on reservoir bank slopes. The research results showed that when the 5th dry-wet cycle ended, the dry mass and peak strength started to rapidly decline, while the porosity and saturated mass increased rapidly. In general, all of these behaviours become relatively stable when the number of cycles increased. Similarly, cohesion and internal friction angle changed most significantly from 0 to 10 cycles and then became stable. In addition, the physical expansion of the adsorbed water film and the dissolution and expansion of mineral particles increased the number of internal microcracks and pores and the porosity and saturated mass of the sample. In addition, the pore fluid effect and fracture flow effect made the microcracks in the red sandstone grow and connect; thus, the peak strength of the sample decreased. Moreover, during the dry-wet cycles, the change in the relative content of mineral particles and the pore fluid effect weakened the clay cementation, and then the dry mass and cohesion of the samples decreased. The research reported in this paper will play a very significant role in the scientific analysis of slope stability in the Three Gorges Reservoir area.

Experimental Study on Mechanical Properties of Root-Soil Composite Reinforced by MICP.

Mechanical properties of undisturbed root-soil composites were investigated through direct shear tests under different cementation concentrations by microbially induced carbonate precipitation (MICP). The results show that MICP has a significant strengthening effect on the undisturbed root-soil composite, and the maximum shear strength increases by about 160% after grouting. The shear strength of root-soil composites increases with the increase in calcium chloride concentration, and the shear strength increases the most when the concentration is 0.75M. Calcium carbonate formed by MICP treatment has cementitious properties, which increases the cohesion and internal friction angle of the root-soil composite by about 400% and 120%, respectively. The results show that it is feasible to solidify slope and control soil erosion together with microbial and vegetation roots. The research results can serve as a scientific basis and reference for the application of MICP technology in vegetation slope protection engineering.

[Rho/ROCK signaling pathway and anti-cryodamage ability of human sperm].

OBJECTIVE: To investigate the influence of the Rho/ROCK signaling pathway on the anti-cryodamage ability of human sperm and provide some theoretical evidence for the development of high-efficiency semen cryoprotectants. METHODS: We collected semen samples from 25 healthy males, each divided into a fresh, a normal cryopreservation control and an Rho-inhibition group. Before and after freezing, we detected sperm motility, viability, membrane integrity, morphology, DNA fragmentation index (DFI), acrosomal enzyme activity (AEA) and mitochondrial membrane potential (MMP) and determined the expressions of RhoA and ROCK proteins in the sperm by immunofluorescence staining. RESULTS: Compared with the normal cryopreservation control, the frozen-thawed sperm of the Rho-inhibition group showed significantly increased sperm motility （ ï¼»51.20 ± 7.70ï¼½% vs ï¼»57.50 ± 6.83ï¼½%, P = 0.002), survival rate ( ï¼»52.87 ± 5.07ï¼½% vs ï¼»60.24 ± 5.53ï¼½%, P = 0.001), membrane integrity (ï¼»59.78±5.56ï¼½% vs ï¼»67.10 ± 4.43ï¼½%, P = 0.001), percentage of morphologically normal sperm (ï¼»4.83 ± 1.11ï¼½% vs ï¼»7.46 ± 1.28ï¼½, P = 0.001) and MMP (56.30 ± 4.28 vs 63.11 ± 2.97, P = 0.001), but decreased DFI (ï¼»27.64 ± 6.64ï¼½% vs ï¼»18.87 ± 4.07ï¼½%, P = 0.001). There was no statistically significant difference in the AEA of the frozen-thawed sperm between the control and Rho-inhibition groups (97.65 ± 9.31 vs 98.30 ± 11.33, P > 0.05). Immunofluorescence staining revealed extensive expressions of RhoA and ROCK proteins in the head and neck of the sperm. CONCLUSIONS: The Rho/ROCK signaling pathway plays a role in the cryodamage to human sperm, and inhibiting the activity of Rho/ROCK can significantly improve the ability of sperm to resist cryodamage.

[Construction of a mouse model of spermatogonial stem cell transplant recipient by high-temperature heat stress].

OBJECTIVE: To investigate the feasibility of constructing a mouse model of spermatogonial stem cell (SSC) transplant recipient by high-temperature heat stress. METHODS: Four-week-old C57BL/6 male mice and B6(Cg)-Tyrc-2J/J coat color gene homozygous mutant male mice were heat-treated at 43 ℃ for an hour in the incubator. The best transplantation time was determined by HE staining, immunohistochemistry and TUNEL and the SSCs were transplanted into the seminiferous tubules of the mice followed by regular observation of the proliferation, differentiation and spermiogenesis of the SSCs in the testis of the recipient mice. Then the recipients were mated with age-matched normal female mice and the epigenetic features of their offspring were observed. RESULTS: After 3－5 days of high-temperature heat stress, the spermatogenic cells in the testicular seminiferous tubules of the recipient mice showed obviously decreased layers, disordered and loose arrangement, massive deletion, significant apoptosis, reduced mesenchymal cells and increased autophagy, which were basically recovered in about 12 days. At 8 weeks after transplantation, the isolated and purified SSCs were differentiated into spermatogenic cells and sperm with genetic function in the testicular seminiferous tubules of the recipient mice, and normal offspring were reproduced after natural mating. CONCLUSIONS: High-temperature heat stress can be used as an efficient method for rapid construction of the mouse model of spermatogonial stem cell transplantation recipient.

Experimental investigation and constitutive model for lime mudstone.

In order to investigate the mechanical properties of lime mudstone, conventional triaxial compression tests under different confining pressures (0, 5, 15 and 20 MPa) are performed on lime mudstone samples. The test results show that, from the overall perspective of variation law, the axial peak stress, axial peak strain and elastic modulus of lime mudstone tend to gradually increase with increasing confining pressure. In the range of tested confining pressure, the variations in axial peak stress and elastic modulus with confining pressure can be described with linear functions; while the variation in axial peak strain with confining pressure can be reflected with a power function. To describe the axial stress-strain behavior in failure process of lime mudstone, a new constitutive model is proposed, with the model characteristics analyzed and the parameter determination method put forward. Compared with Wang' model, only one parameter n is added to the new model. The comparison of predicted curves from the model and test data indicates that the new model can preferably simulate the strain softening property of lime mudstone and the axial stress-strain response in rock failure process.