Mammalian mesenchymal stem cells (MSCs) have been shown to be strongly immunosuppressive in both animal disease models and human clinical trials. We have reported that the key molecule mediating immunosuppression by MSCs is species dependent: indoleamine 2,3-dioxygenase (IDO) in human and inducible nitric oxide synthase (iNOS) in mouse. In the present study, we isolated MSCs from several mammalian species, each of a different genus, and investigated the involvement of IDO and iNOS during MSC-mediated immunosuppression. The characterization of MSCs from different species was by adherence to tissue culture plastic, morphology, specific marker expression, and differentiation potential. On the basis of the inducibility of IDO and iNOS by inflammatory cytokines in MSCs, the tested mammalian species fall into two distinct groups: IDO utilizers and iNOS utilizers. MSCs from monkey, pig, and human employ IDO to suppress immune responses, whereas MSCs from mouse, rat, rabbit, and hamster utilize iNOS. Interestingly, based on the limited number of species tested, the iNOS-utilizing species all belong to the phylogenetic clade, Glires. Although the evolutionary significance of this divergence is not known, we believe that this study provides critical guidance for choosing appropriate animal models for preclinical studies of MSCs.
The global optimization of sensor locations for structural health monitoring systems is studied in this paper. First, the performance function based on damage detection is presented. Then, genetic algorithms (GAs) are adopted to search for the optimal locations of sensors. However, the simple GAs can result in infeasible solutions to the problem. Some improved strategies are presented in this paper, such as crossover based on identification code, mutation based on two gene bits, and improved convergence. The analytical results from the improved genetic algorithm are compared with the penalty function method and the forced mutation method. It is concluded that the convergence speed with the proposed improved genetic algorithm is faster than that with the penalty function method and the forced mutation method, and the result of placement optimization is better.
A nanostructured surface layer with thickness of about 20 µm was formed on commercially pure zirconium using surface mechanical attrition treatment (SMAT). The microstructural features of the surface layer were systematically investigated using optical microscopy (OM), x-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), respectively. Based on the results obtained, a grain refinement mechanism induced by plastic deformation during SMAT of Zr is proposed. At the initial stage of SMAT, twinning dominates the plastic deformation of Zr and divides the coarse grains of Zr into finer twin plates. With increasing strain, intersection of twins occurs, and dislocation slips are activated, becoming the predominant deformation mode instead of twinning. As a result of the dislocation slips, high-density dislocation arrays are formed, which further subdivide the twin plates into subgrains of size about 200-400 nm. With a further increase of strain, the dislocations accumulate and rearrange to minimize the energy state of the high-strain-energy subgrains, the dense dislocation walls convert to grain boundaries, and the submicronic grains are subdivided, leading to the formation of nanosized grains at the top of the treated surface.
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