Creep constitutive modeling of the shear strength of the permafrost-concrete interface considering the stress level at -1°C.

The shear creep characteristics of the contact surface between the permafrost and the structure play an important role in the study of the law of deformation and the measures for the prevention and control of pile foundations. In order to study the creep law and the development tendency of the contact surface between permafrost and concrete, it is necessary to establish an accurate creep model. In this study, based on the Nishihara model, a nonlinear element and damage factor D were introduced to establish an intrinsic model of permafrost-concrete contact surfaces considering the effect of shear stress. Creep tests with graded loading of concrete and frozen silt with different roughness at -1°C were conducted using a large stress-controlled shear apparatus. The adequacy of the model was checked using the test data and the regularity of the parameters of the model was investigated. The results show that the creep curves of the contact surface obtained with the improved Nishihara model agree well with the test results and can better describe the whole process of creep of the contact surface of frozen concrete. The analysis of the experimental data shows that: the roughness of the concrete has an inhibiting effect on the creep deformation of the contact surface, When the roughness R varies from 0 mm to 1.225 mm, the specimen corresponds to a long-term strength of 32.84 kPa to 34.57 kPa. For the same roughness and creep time, the creep deformation of the contact surface is more significant with the increasing shear stress τ. The results of the study can provide a theoretical basis for the design and numerical simulation of pile foundations in permafrost regions.

Preparation of astrocytes by directed differentiation of pluripotent stem cells and somatic cell transdifferentiation.

Astrocytes (ACs) are the most widely distributed cells in the mammalian central nervous system, which are essential for the function and homeostasis of nervous system. Increasing evidence indicates that ACs also participate in the development of many neurological diseases and repair after nerve injury. ACs cultured in vitro provide a cellular model for studying astrocytic development, function, and the pathogenesis of associated diseases. The preparation of primary ACs (pACs) faces many limitations, so it is important to obtain high-quality ACs by the differentiation of pluripotent stem cell (PSC) or somatic cell transdifferentiation. Initially, researchers mainly tried to induce embryonic stem cells to differentiate into ACs via embryoid body (EB) and then turned to employ induced PSCs as seed cells to explore more simple and efficient directed differentiation strategies, and serum-free culture was delved to improve the quality of induced ACs. While exploring the induction of ACs by the overexpression of AC-specific transcription factors, researchers also began to investigate small molecule-mediated somatic cell transdifferentiation. Here, we provide an updated review on the research progresses in this field.