Numerical hydrodynamic and mass transport modelling accross a pyrochlore surface using OpenFOAM

The study and understanding of material dissolution plays and important role in environmental sciences, e.g. in the study of pipeline corrosion, reservoir development or nuclear waste storage. Commonly laboratory based experiments or meso-scale numerical simulations are carried out to verify the resistivity of a material with regard to dissolution. However, it is challenging to directly determine the interaction between fluid movement and mass transport on the microscale. In order to overcome this difficulty we use a 3D numerical hydrodynamic continuum model by which the fluid flow and the mass transport over a pyrochlore surface are simulated. Using the finite volume method implemented in the open-source software package OpenFOAM, we investigated the hydrodynamic flow over three pyrochlore surfaces of varying surface roughness under steady-state conditions. The steady-state flow field is further used to derive the influence on the mass transport at the microscale. The results of the hydrodynamic simulations show the horizontal stratification of the laminar flow. We observe the development of cavity flows in the surface depressions. Likewise the transport simulation show the influenve of the cavity flows, which are trapping saturated fluid close to the surface. We see a preferred transport across the surface, with little mixing into the surface depressions and the development of a diffusion boundary layer. These effects become more pronounced with increasing surface roughness

Investigation of the influence of fluid flow on the mass transport of dissolved calcite ions on the microscale using 3D numerical simulation

The study and understanding of material dissolution plays an important role in environmental sciences, e.g. in the study of pipeline corrosion, reservoir development or nuclear waste storage. Commonly laboratory based experiments or numerical simulations in the meter scale are carried out to verify the resistivity of a material with regard to corrosion. However, it is challenging to directly determine the influence of the fluid movement on the relation of advective and diffusive mass transport on the µm scale. In order to overcome this difficulty we use a 3D numerical hydrodynamic continuum model by which the fluid flow and the mass transport over a pyrochlore surface are simulated. Using the finite volume method implemented in the open-source software CFD-package OpenFOAM, we investigated the hydrodynamic flow over three pyrochlore surfaces of varying surface roughness under steady-state flow conditions. The mass transport over the surfaced was further computed using the steady-state flow field. As may be expected the diffusive transport appeared to become lower with increasing flow velocity, but interestingly also as the surface roughness increased. Apart from that, we observed typical fluid dynamical features like the development of cavity flows in the surface depressions. Although the transport simulations show no influence of these hydrodynamic features, the mass transport changes with the flow velocity and surface roughness, with a higher release of dissolved calcite ions being observed at lower velocities and a lower surface roughness. Comment: The data in these archives contains case file for numerical studies in OpenFOAM to investigate the scope described above. Archives are split between three different surface topographies. The fourth archive contains data from post-processing

Opposing microRNA families regulate self-renewal in mouse embryonic stem cells

When embryonic stem cells (ESCs) differentiate, they must both silence the ESC self-renewal program as well as activate new tissue specific programs. In the absence of DGCR8 (Dgcr8 -/-), a protein required for microRNA (miRNA) biogenesis, mouse ESCs are unable to silence self-renewal. Here, we find that the introduction of let-7 miRNAs, a family of miRNAs highly expressed in somatic cells, can suppress self-renewal in Dgcr8 -/-, but not wild-type ESCs. Introduction of ESC cell cycle regulating (ESCC) miRNAs into the Dgcr8 -/- ESCs, blocks the capacity of let-7 to suppress self-renewal. Profiling and bioinformatic analyses show that let-7 inhibits while ESCC miRNAs indirectly activate numerous self-renewal genes. Furthermore, inhibition of the let-7 family promotes de-differentiation of somatic cells to induced pluripotent stem (iPS) cells. Together, these findings show how the ESCC and let-7 miRNAs act through common pathways to alternatively stabilize the self-renewing versus differentiated cell fates

The Significance of Shift Work: Current Status and Future Directions

Family life, Mental health, Physical health, Shift work,