Numerical Study of Heterogeneous Reactions in an SOFC Anode with Oxygen Addition

Previous experimental studies have shown that addition of small amounts of oxygen to a hydrocarbon fuel stream can control coking in the anode, while relatively large amounts of oxygen are present in the fuel stream in single-chamber solid oxide fuel cells (SOFCs). In order to rationally design an anode for such use, it is important to understand the coupled catalytic oxidation/reforming chemistry and diffusion within the anode under SOFC operating conditions. In this study, the heterogeneous catalytic reactions in the anode of an anode-supported SOFC running on methane fuel with added oxygen are numerically investigated using a model that accounts for catalytic chemistry, porous media transport, and electrochemistry at the anode/electrolyte interface. Using an experimentally validated heterogeneous reaction mechanism for methane partial oxidation and reforming on nickel, we identify three distinct reaction zones at different depths within the anode: a thin outer layer in which oxygen is nearly fully consumed in oxidizing methane and hydrogen, followed by a reforming region, and then a water–gas shift region deep within the anode. Both single-chamber and dual-chamber SOFC anodes are explored

Macrophages in wound healing: activation and plasticity.

Macrophages are critically involved in wound healing, from dampening inflammation to clearing cell debris and coordinating tissue repair. Within the wound, the complexity of macrophage function is increasingly recognized, with adverse outcomes when macrophages are inappropriately activated, such as in fibrosis or chronic non-healing wounds. Recent advances in in vivo and translational wound models, macrophage-specific deletions and new technologies to distinguish macrophage subsets, have uncovered the vast spectrum of macrophage activation and effector functions. Here, we summarize the main players in wound-healing macrophage activation and function, including cytokines, apoptotic cells, nucleotides and mechanical stimuli. We highlight recent studies demonstrating cooperation between these factors for optimal wound healing. Next, we describe recent technologies such as cell tracking and single-cell RNA-seq, which have uncovered remarkable plasticity and heterogeneity in blood-derived or tissue-resident macrophages and discuss the implications for wound healing. Lastly, we evaluate macrophage dysfunction in aberrant wound healing that occurs in aging, diabetes and fibrosis. A better understanding of the longevity and plasticity of wound-healing macrophages, and identification of unique macrophage subsets or specific effector molecules in wound healing, would shed light on the therapeutic potential of manipulating macrophage function for optimal wound healing

Dust-Deficient Palomar-Green Quasars and the Diversity of AGN Intrinsic IR Emission

To elucidate the intrinsic broadband infrared (IR) emission properties of active galactic nuclei (AGNs), we analyze the spectral energy distributions (SEDs) of 87 z<0.5 Palomar-Green (PG) quasars. While the Elvis AGN template with a moderate far-IR correction can reasonably match the SEDs of the AGN components in ~60% of the sample (and is superior to alternatives such as that by Assef), it fails on two quasar populations: 1) hot-dust-deficient (HDD) quasars that show very weak emission thoroughly from the near-IR to the far-IR, and 2) warm-dust-deficient (WDD) quasars that have similar hot dust emission as normal quasars but are relatively faint in the mid- and far-IR. After building composite AGN templates for these dust-deficient quasars, we successfully fit the 0.3-500 {\mu}m SEDs of the PG sample with the appropriate AGN template, an infrared template of a star-forming galaxy, and a host galaxy stellar template. 20 HDD and 12 WDD quasars are identified from the SED decomposition, including seven ambiguous cases. Compared with normal quasars, the HDD quasars have AGN with relatively low Eddington ratios and the fraction of WDD quasars increases with AGN luminosity. Moreover, both the HDD and WDD quasar populations show relatively stronger mid-IR silicate emission. Virtually identical SED properties are also found in some quasars from z = 0.5 to 6. We propose a conceptual model to demonstrate that the observed dust deficiency of quasars can result from a change of structures of the circumnuclear tori that can occur at any cosmic epoch.Comment: minor corrections to match the published versio

A Two-Dimensional Model of a Single-Chamber SOFC with Hydrocarbon Fuels

The single chamber fuel cell (SCFC) is a novel simplification of the conventional solid oxide fuel cell (SOFC) into which a premixed fuel/air mixture is introduced. It relies on the selectivity of the anode and cathode catalysts to generate a chemical potential gradient across the cell. For SCFC running on hydrocarbon fuels, the anode catalyst promotes in-situ internal reforming of the hydrocarbon and electrochemical oxidation of the syngas, while the cathode catalyst reduces oxygen simultaneously. Laboratory tests of small designs of such fuel cells have demonstrated excellent electrical performance (1, 2)

On Minimum-time Paths of Bounded Curvature with Position-dependent Constraints

We consider the problem of a particle traveling from an initial configuration to a final configuration (given by a point in the plane along with a prescribed velocity vector) in minimum time with non-homogeneous velocity and with constraints on the minimum turning radius of the particle over multiple regions of the state space. Necessary conditions for optimality of these paths are derived to characterize the nature of optimal paths, both when the particle is inside a region and when it crosses boundaries between neighboring regions. These conditions are used to characterize families of optimal and nonoptimal paths. Among the optimality conditions, we derive a "refraction" law at the boundary of the regions that generalizes the so-called Snell's law of refraction in optics to the case of paths with bounded curvature. Tools employed to deduce our results include recent principles of optimality for hybrid systems. The results are validated numerically.Comment: Expanded version of paper in Automatic

Splitting of Surface Plasmon Frequencies of Metal Particles in a Nematic Liquid Crystal

We calculate the effective dielectric function for a suspension of small metallic particles immersed in a nematic liquid crystal (NLC) host. For a random suspension of such particles in the dilute limit, we calculate the effective dielectric tensor exactly and show that the surface plasmon (SP)resonance of such particles splits into two resonances, polarized parallel and perpendicular to the NLC director. At higher concentrations, we calculate this splitting using a generalized Maxwell-Garnett approximation, which can also be applied to a small metal particle coated with NLC. To confirm the accuracy of the MGA for NLC-coated spheres, we also use the Discrete Dipole Approximation. The calculated splitting is comparable to that observed in recent experiments on NLC-coated small metal particlesComment: 11 pages, 2 figures. To be published in Appl. Phys. Let