ABSTRACT
To study the mesoscopic damage and permeability evolution characteristics of rock under freeze-thaw (F-T) cycles, freeze-thaw cycle experiments were carried out of shale under different F-T temperatures and numbers of cycles, and nuclear magnetic resonance (NMR) and permeability experiments of shale were conducted thereafter. On the basis of these experiments, the pores and permeability of the F-T shale were analyzed, and the existing permeability model is modified and improved; Therefore, the mesoscopic damage evolution characteristics and permeability evolution law of the F-T shale are obtained. It was found that with increasing number of cycles, the pore structure of the rock samples changed as the pore size expanded and the number of pores increased, and the average porosity also increased correspondingly. The influence of the F-T cycle temperature on the shale permeability was not as notable as that of the number of F-T cycles. Based on the SDR-REV permeability model, the spectral area ratio parameters of large pores and fractures in the T2 spectrum were considered for correction, and a direct relationship between the permeability, F-T temperature and number of cycles was obtained via regression analysis. Compared to the experimental results, it was found that the modified model achieved a good applicability. The damage and permeability characteristics of shale under different F-T conditions were analysed from a microscopic perspective, which could yield an important reference for engineering construction in frozen soil areas.
ABSTRACT
To study the creep characteristics of mudstone under disturbed load, creep rock triaxial compression disturbance tests under different disturbance amplitudes and frequencies are conducted using a self-made triaxial disturbed creep test bench for rock. The influence of different factors on the creep deformation law of each stage is analyzed. The results show that the disturbance effect has a significant impact on the creep properties of mudstone, and various factors have different effects on the creep stages. The instantaneous deformation variable, creep decay time, and steady creep rate change exponentially with the increase in axial pressure, and increase linearly with the increase in disturbance amplitude and disturbance frequency. The disturbance amplitude has a more significant effect on the instantaneous deformation, steady-state creep rate, and accelerated creep. According to the analysis of the test results, a nonlinear disturbance creep damage model based on Burger's model is established. The model is identified and calculated by the improved least squares method based on pattern search. The influence of different disturbance factors on the creep parameters is analyzed. The model fitting results and experimental results are compared to demonstrate that the model is used to simulate different disturbances. It was observed that rock creep under certain conditions exhibits certain adaptability. It is of great significance to carry out rock disturbance creep experiments and study the theory of disturbance creep to ensure the long-term stability of deep rock mass in complex environment.
ABSTRACT
Ethylene-response factors, which are a subfamily of the AP2/ERF family, play an important role in ethylene signal transduction, plant growth and plant resistant. In this study, a full-length cDNA of the AsERF1 gene was cloned from Aquilaria sinensis. Sequence analysis, prokaryotic expression and purification, subcellular localization, tissue-specific analysis and expression analysis under different abiotic stresses was performed. The open reading frame (ORF) of the AsERF1 gene was 691 bp, encoding a protein of 229 amino acids with a predicted molecular mass of 25.36 kD. The AsERF1 protein contained the conserved AP2 sequence of ERF protein. A phylogenetic analysis indicated that the AsERF1 protein showed greatest sequence similarity with ERF2 from Populus trichocarpa. The recombinant AsERF1 protein was expressed in Escherichia coli BL21(DE3) cells using the prokaryotic expression vector pET28a-AsERF1 and the recombinant AsERF1 protein was purified. Agrobacterium-mediated protein expression experiments demonstrated that AsERF1 mainly localized to the nucleus. Expression analysis indicated that AsERF1 was primarily observed in leaves. The AsERF1 expression level was induced by salt, drought, low temperature and CdCl2 treatment, while the abundance of AsERF1 was most significantly induced by drought stress. These results provide valuable insights into the role of AsERF1 in plant defense and the mechanism of agarwood formation.
