Molecular dynamics simulations on interaction between dislocation and Y2O3 nanocluster in FE

For a new insight on the mechanical properties of oxide dispersion strengthened (ODS) steels from atomistic viewpoints, we have implemented molecular dynamics simulations on the interaction between Y2O3 nanocluster and dislocation in bcc Fe. There is so far no all-round interatomic potential function that can represent all the bonding state, i.e. metal, ion and covalent systems, so that we have adopted rough approximation. That is, each atom in Y2O3 is not discriminated but treated as “monatomic” pseudo-atom; and its motion is represented with the simple pairwise potential function as same as Johnson potential for Fe. The potential parameters are fitted to the energy change in the hcp infinite crystal, by using the ab-initio density functional theory(DFT) calculation for explicitly discriminated Y and O. We have set edge/screw dislocation in the centre of periodic slab cell, and approached it to the “YO” monatomic nano-cluster coherently precipitated in bcc-Fe matrix. The dislocation behavior is discussed by changing the size and periodic distance of the nano-cluster. Among the many useful results, we have obtained a conclusion that the edge dislocation is strongly trapped by YO sphere larger than the diameter of d =0 .9nm, while the screw dislocation shows various behavior, e.g. it cuts through the precipiate without remarkable resistance if the dislocation line tension is high, or it changes the slip plane leaving jogs at the position anterior to the precipiate with loose line tensio

Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells. We propose that stem cell homeostasis is achieved through competition for a limited supply of FGFs. We show that the quantitative dependence of stem cell density on FGF dosage, the biased localization of stem cells toward FGF sources, and stem cell dynamics during regeneration following injury can all be predicted and explained within the framework of a minimal theoretical model based on “mitogen competition.” We propose that this model provides a generic and robust mechanism to support stem cell homeostasis in open, or facultative, niche environments

Molecular dynamics simulations on interaction between dislocation and Y2O3 nanocluster in FE

For a new insight on the mechanical properties of oxide dispersion strengthened (ODS) steels from atomistic viewpoints, we have implemented molecular dynamics simulations on the interaction between Y2O3 nanocluster and dislocation in bcc Fe. There is so far no all-round interatomic potential function that can represent all the bonding state, i.e. metal, ion and covalent systems, so that we have adopted rough approximation. That is, each atom in Y2O3 is not discriminated but treated as “monatomic” pseudo-atom; and its motion is represented with the simple pairwise potential function as same as Johnson potential for Fe. The potential parameters are fitted to the energy change in the hcp infinite crystal, by using the ab-initio density functional theory(DFT) calculation for explicitly discriminated Y and O. We have set edge/screw dislocation in the centre of periodic slab cell, and approached it to the “YO” monatomic nano-cluster coherently precipitated in bcc-Fe matrix. The dislocation behavior is discussed by changing the size and periodic distance of the nano-cluster. Among the many useful results, we have obtained a conclusion that the edge dislocation is strongly trapped by YO sphere larger than the diameter of d =0 .9nm, while the screw dislocation shows various behavior, e.g. it cuts through the precipiate without remarkable resistance if the dislocation line tension is high, or it changes the slip plane leaving jogs at the position anterior to the precipiate with loose line tensio

Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche.

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells. We propose that stem cell homeostasis is achieved through competition for a limited supply of FGFs. We show that the quantitative dependence of stem cell density on FGF dosage, the biased localization of stem cells toward FGF sources, and stem cell dynamics during regeneration following injury can all be predicted and explained within the framework of a minimal theoretical model based on "mitogen competition." We propose that this model provides a generic and robust mechanism to support stem cell homeostasis in open, or facultative, niche environments.Wellcome Trus