Corrigendum to Simplified Two-Group Two-Fluid Model for Three-Dimensional Two-Phase Flow Computational Fluid Dynamics for Vertical Upward Flow [Prog. Nucl. Energy 108 (2018) 503-516]

According to Corrigendum to A correlation for interfacial area concentration in high void fraction flows in large diameter channels [Chem. Eng. Sci. 190 (2018) 86-88], one of the equations in this paper was incorrect, Eq. (68). The corrected equation, Eq. (68), should be: [Formula presented

Simplified Two-Group Two-Fluid Model for Three-Dimensional Two-Phase Flow Computational Fluid Dynamics for Vertical Upward Flow

Recent progress in nuclear thermal-hydraulics simulations has been largely focused on coupling with other computational packages, improved closure models for subcooled boiling and for bubbly flows, and the development of higher-fidelity simulation capabilities (Kulesza et al., 2016). While high-fidelity 3D simulation is important for model validation, scientific understanding, and some design calculations, it can be prohibitively expensive for system design applications or applications involving large geometries. Thus, there is also a need for practical, simplified approaches for those applications. The two-fluid model strikes a balance between detail and computational resources, but requires the accurate specification of several key constitutive models. These include (1) interfacial forces, (2) interfacial area concentration, (3) two-phase turbulence, and (4) wall and bulk boiling and condensation. In many modern CFD packages, uncertainties in the local interfacial area concentration can have strong effects on the ability to predict the other key parameters. This paper demonstrates that the drag force in 3D CFD can be formulated in much the same way as in 1D system analysis codes and that this approach can be used to formulate a model for interfacial area concentration. The method is also applied to two-group approaches to consider the difference in transport properties for different bubble size classes. This approach may open a method to calculate the interfacial forces without the need for interfacial area transport equations. This reduces the number of differential equations and avoids the modeling challenges associated with bubble breakup and coalescence kernels and the need to specify the inlet interfacial area concentration a priori. The new method is expected to decouple the effects of interfacial area uncertainty and calibrated coefficients, and should provide reasonable local bubble diameters for both group-1 and group-2 bubbles. The approaches proposed in this study are applicable to two-phase flow simulations in rather simple geometries such as upward two-phase flow in vertical channels. In view of many applications for upward two-phase flow in vertical channels, including nuclear reactor systems, the proposed methods are considered useful

Translational Control of Sox9 RNA by mTORC1 Contributes to Skeletogenesis

Summary: The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) regulates cellular function in various cell types. Although the role of mTORC1 in skeletogenesis has been investigated previously, here we show a critical role of mTORC1/4E-BPs/SOX9 axis in regulating skeletogenesis through its expression in undifferentiated mesenchymal cells. Inactivation of Raptor, a component of mTORC1, in limb buds before mesenchymal condensations resulted in a marked loss of both cartilage and bone. Mechanistically, we demonstrated that mTORC1 selectively controls the RNA translation of Sox9, which harbors a 5′ terminal oligopyrimidine tract motif, via inhibition of the 4E-BPs. Indeed, introduction of Sox9 or a knockdown of 4E-BP1/2 in undifferentiated mesenchymal cells markedly rescued the deficiency of the condensation observed in Raptor-deficient mice. Furthermore, introduction of the Sox9 transgene rescued phenotypes of deficient skeletal growth in Raptor-deficient mice. These findings highlight a critical role of mTORC1 in mammalian skeletogenesis, at least in part, through translational control of Sox9 RNA. : Iezaki et al. demonstrated that the mTORC1/SOX9 axis has essential roles in skeletal development through its expression in undifferentiated mesenchymal cells in vivo. Moreover, they identified that mTORC1/4E-BPs cascade regulates the translation of Sox9 RNA in undifferentiated mesenchymal cells, highlighting a critical role of mTORC1/4E-BPs/SOX9 axis in regulating mammalian skeletogenesis. Keywords: mTORC1, translation, Sox9, undifferentiated mesenchymal cell