Dynamical density functional theory for orientable colloids including inertia and hydrodynamic interactions

Over the last few decades, classical density-functional theory (DFT) and its dynamic extensions (DDFTs) have become powerful tools in the study of colloidal fluids. Recently, previous DDFTs for spherically-symmetric particles have been generalised to take into account both inertia and hydrodynamic interactions, two effects which strongly influence non-equilibrium properties. The present work further generalises this framework to systems of anisotropic particles. Starting from the Liouville equation and utilising Zwanzig's projection-operator techniques, we derive the kinetic equation for the Brownian particle distribution function, and by averaging over all but one particle, a DDFT equation is obtained. Whilst this equation has some similarities with DDFTs for spherically-symmetric colloids, it involves a translational-rotational coupling which affects the diffusivity of the (asymmetric) particles. We further show that, in the overdamped (high friction) limit, the DDFT is considerably simplified and is in agreement with a previous DDFT for colloids with arbitrary shape particles.Comment: dynamical density functional theory ; colloidal fluids ; arbitrary-shape particles ; orientable colloid

Potential for Fuel Bubble Collapse in Sodium Pool

When assessing the radiological source term for LMFBR site evaluation, a hypothetical accident involving vaporization of part of the core is often postulated. It is generally perceived that the potential for plutonium release in an LMFBR assident would significantly increase with fuel vaporization. However, no quantitative evaluation of the plutonium source term associated with fuel vaporization has yet been made, mainly because of a number of phenomenological uncertainties involved. Among the important uncertainties is the dynamic behavior of a fuel vapor bubble formed in the sodium pool. This paper discusses the potential for fuel bubble collapse in the sodium pool, based on a scoping analysis of the quenching behavior of a single fuel bubble formed in the sodium pool

Argonne National Laboratory Reports

A treatment is formulated for surface-to-surface radiative heat exchange between fuel pins and between pins and duct wall of a nuclear reactor subassembly voided of coolant. Specific attention is given to the case of equal power generation in each pin with uniform duct-wall temperature. Detailed temperature profiles and heat flux values are reported for hexagonal-ring subassemblies ranging in size from one to nine rings. It is found that a duct wall at 1153 degrees K can cool by radiation even a nine-ring voided subassembly operating at a power of up to 0.54 kW/ft per pin or 5.4% of full power without fuel slumping or melting, or that a seven-pin assembly can be cooled by radiation up to a power of 7.3 kw/ft

Microenvironmental Sensing by Fibroblasts Controls Macrophage Population Size

AbstractAnimal tissues are comprised of diverse cell types. However, the mechanisms controlling the number of each cell type within tissue compartments remain poorly understood. Here, we report that different cell types utilize distinct strategies to control population numbers. Proliferation of fibroblasts, stromal cells important for tissue integrity, is limited by space availability. In contrast, proliferation of macrophages, innate immune cells involved in defense, repair, and homeostasis, is constrained by growth factor availability. Examination of density-dependent gene expression in fibroblasts revealed that Hippo and TGF-β target genes are both regulated by cell density. We found YAP1, the transcriptional co-activator of the Hippo signaling pathway, directly regulates expression of Csf1, the lineage-specific growth factor for macrophages, through an enhancer of Csf1 that is specifically active in fibroblasts. Activation of YAP1 in fibroblasts elevates Csf1 expression and is sufficient to increase the number of macrophages at steady state. Our data also suggest that expression programs in fibroblasts that change with density may result from sensing of mechanical force through actin-dependent mechanisms. Altogether, we demonstrate that two different modes of population control are connected and coordinated to regulate cell numbers of distinct cell types. Sensing of the tissue environment may serve as a general strategy to control tissue composition.Significance StatementCollections of distinct cell types constitute animal tissues. To perform their unique functions, each cell type must exist in the correct number and proportion in a given tissue compartment. However, many of the mechanisms regulating and coordinating cell population sizes remain enigmatic. Our study characterizes two different modes of population size control, utilized by two ubiquitous cell types, macrophages and fibroblasts. Macrophage populations are more sensitive to the presence of growth factors in the environment and fibroblasts are more sensitive to space limitations. Intriguingly, space-sensing mechanisms in fibroblasts directly control the production of growth factor for macrophages and thus macrophage numbers. This link suggests a mechanism by which macrophage compartment size is controlled by stromal cells according to the microenvironment.</jats:sec