Reconstructing aspects of human embryogenesis with pluripotent stem cells

Understanding human development is of fundamental biological and clinical importance. Despite its significance, mechanisms behind human embryogenesis remain largely unknown. Here, we attempt to model human early embryo development with expanded pluripotent stem cells (EPSCs) in 3-dimensions. We define a protocol that allows us to generate self-organizing cystic structures from human EPSCs that display some hallmarks of human early embryogenesis. These structures mimic polarization and cavitation characteristic of pre-implantation development leading to blastocyst morphology formation and the transition to post-implantation-like organization upon extended culture. Single-cell RNA sequencing of these structures reveals subsets of cells bearing some resemblance to epiblast, hypoblast and trophectoderm lineages. Nevertheless, significant divergences from natural blastocysts persist in some key markers, and signalling pathways point towards ways in which morphology and transcriptional-level cell identities may diverge in stem cell models of the embryo. Thus, this stem cell platform provides insights into the design of stem cell models of embryogenesis.

Research on the Effect of Impeller Reflux Balance Holes on Pressure and Axial Force of Centrifugal Pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5m3/h, H=60m, n=2950r/min was selected to be designed with eight axial reflux balance holes 4.5mm in diameter. The simulated Q-H curve and NPSH were in good agreement with experimental data, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic to that with traditional reflux balance holes; however, it appeared little difference in head and efficiency. Compared with experiment results, the error of pressure at monitoring points in rear pump chamber was within permission. The pressure in rear pump chamber at 0.6 times rated flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rated flow and 28.33% at 1.4 times rated flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreased as flow rate increased. Radical reflux balance holes chosen to be 5.2mm and 5.9mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics of reflux holes with different diameters was conducted based on momentum equations and standard turbulence model (κ-ε). It is found that axial force of pump with radical reflux balance holes 5.2mm and 5.9mm in diameter is significantly less than that with radical reflux balance holes 4.5mm in diameter, so are the head and efficiency. Better effect of axial force balance can be obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.

A thermodynamic cavitation model applicable to high temperature flow

Cavitation is not only related with pressure, but also affected by temperature. Under high temperature, temperature depression of liquids is caused by latent heat of vaporization. The cavitation characteristics under such condition are different from those under room temperature. The paper focuses on thermodynamic cavitation based on the Rayleigh-Plesset equation and modifies the mass transfer equation with fully consideration of the thermodynamic effects and physical properties. To validate the modified model, the external and internal flow fields, such as hydrofoil NACA0015 and nozzle, are calculated, respectively. The hydro-foil NACA0015?s cavitation characteristic is calculated by the modified model at different temperatures. The pressure coefficient is found in accordance with the experimental data. The nozzle cavitation under the thermodynamic condition is calculated and compared with the experiment.