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Bone defect (BD) caused by trauma, infection, congenital defects, or neoplasia is a major cause of physical limitation. Distraction osteogenesis (DO) is a highly effective procedure for bone regeneration, while the concrete mechanism remains unknown. In this study, canine DO and BD models of the mandible were established. The results of micro–computed tomography and histological staining revealed that DO led to an increased mineralized volume fraction and robust new bone formation; in contrast, BD demonstrated incomplete bone union. Mesenchymal stem cells (MSCs) from DO and BD calluses were isolated and identified. Compared with BD-MSCs, DO-MSCs were found to have a stronger osteogenic capability. Single-cell RNA sequencing analysis was further performed to comprehensively define cell differences between mandibular DO and BD calluses. Twenty-six clusters of cells representing 6 major cell populations were identified, including paired related homeobox 1–expressing MSCs (PRRX1 +MSCs), endothelial cells (ECs), T cells, B cells, neutrophils, and macrophages. Interestingly, 2 subpopulations in PRRX1 +MSCs in the DO group were found to express the marker of neural crest cells (NCCs) and were associated with the process of epithelial–mesenchymal transition. The immunofluorescence assay was performed to further corroborate these results in vivo and in vitro, experimentally validating that continuous distraction maintained the PRRX1 +MSCs in an embryonic-like state. Finally, we used CRISPR/Cas9 to knock out (KO) PRRX1 in the context of DO, which significantly blunted the capability of jawbone regeneration, resulting in a diminished NCC-like program and reduction of new bone volume. In addition, the ability of osteogenesis, cell migration, and proliferation in cultured PRRX1 KO MSCs was inhibited. Taken together, this study provides a novel, comprehensive atlas of the cell fates in the context of DO regeneration, and PRRX1 +MSCs act essential roles. [ABSTRACT FROM AUTHOR]

To mine coal resources trapped under embankment dams safely and efficiently while, at the same time, disposing of waste rock, solid backfill mining has been proposed as a solution. The extreme value of dam deformation was obtained by analysing geological conditions in the area and structural characteristics of the dam. It was determined that the filling ratio of the working face and the equivalent mining height were the two key factors that control dam deformation. In addition, the extreme values of these two key factors varied with the distance between the working face and the embankment dam in a regular pattern. When mining was completed at the first working face in the pilot area, the maximum sink value of the dam was 42 mm, and the maximum horizontal strain was 0-16 mm m-1. Field demonstrations have shown that solid backfill mining is effective in controlling strata movement and surface deformation. [ABSTRACT FROM AUTHOR]

Direct chill (DC) semicontinuous casting process has been successfully used to produce sound Mg-3·0Nd-0·4Zn-0·4Zr (NZ30K) billets. The influence of process parameters such as casting speed, casting temperature on the microstructure and macrosegregation was studied. The results show that the casting speed affects the macrosegregation greatly while it has a slight influence on the grain size of the billet; the casting temperature has a slight influence on macrosegregation of the billet while the grain size of the billet increases as the casting temperature increases. The optimal process parameters have been experimentally determined as follows: casting temperature 700°C and casting speed 90 mm min−1. The ultimate tensile strength, yield strength and elongation of billets cast at the optimal casting parameters are 196 MPa, 125 MPa and 16·5% respectively. [ABSTRACT FROM AUTHOR]

A phase field model is developed to simulate γ' rafting in single crystal Ni-Al under the influence of external stress. Lattice and modulus mismatch between the γ and γ' phases and γ channel plasticity are considered simultaneously in the model. To increase the computational efficiency, an average plastic strain is introduced to describe the channel plasticity based on experimental observation of dislocation density. With the elastic moduli of both phases and their lattice misfit at the aging temperature from direct experimental measurement, and thermodynamic and mobility data from available databases as inputs, the simulation results show that the type of rafting is determined by channel plasticity while modulus mismatch between the precipitate and the matrix affects only the kinetics of the rafting process. The model can be used to quickly estimate the type of rafting and, more importantly, the time when rafts fully develop. [ABSTRACT FROM AUTHOR]

A study was carried out of the characteristics of electrode degradation in resistance spot welding of aluminium, and its influence on weld quality. Based on analysis of electrode life test results, an imaging approach was developed to determine quantitatively the status of electrode degradation, in which three parameters were defined to represent the tip surface characteristics, namely, relative radius, edge concentration, and eccentricity. This image analysis revealed a clear relationship between these defined electrode surface features and the weld quality, based on which a reasonable understanding was achieved of the causes of weld quality deterioration in electrode life tests. [ABSTRACT FROM AUTHOR]