22,308 research outputs found
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
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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
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