24,227 research outputs found
Stellar Photometric Structures of the Host Galaxies of Nearby Type 1 Active Galactic Nuclei
We present detailed image analysis of rest-frame optical images of 235
low-redshift ( 0.35) type 1 active galactic nuclei (AGNs) observed with
the Hubble Space Telescope. The high-resolution images enable us to perform
rigorous two-dimensional image modeling to decouple the luminous central point
source from the host galaxy, which, when warranted, is further decomposed into
its principal structural components (bulge, bar, and disk). In many cases, care
must be taken to account for structural complexities such as spiral arms, tidal
features, and overlapping or interacting companion galaxies. We employ Fourier
modes to characterize the degree of asymmetry of the light distribution of the
stars, as a quantitative measure of morphological distortion due to
interactions or mergers. We examine the dependence of the physical parameters
of the host galaxies on the properties of the AGNs, namely radio-loudness and
the width of the broad emission lines. In accordance with previous studies,
narrow-line (H FWHM km~s) type 1 AGNs, in contrast to
their broad-line (H FWHM km~s) counterparts, are
preferentially hosted in later type, lower luminosity galaxies, which have a
higher incidence of pseudo-bulges, are more frequently barred, and are less
morphologically disturbed. This suggests narrow-line type 1 AGNs experienced a
more quiescent evolutionary history driven primarily by internal secular
evolution instead of external dynamical perturbations. The fraction of AGN
hosts showing merger signatures is larger for more luminous sources. Radio-loud
AGNs generally preferentially live in earlier type (bulge-dominated), more
massive hosts, although a minority of them appears to contain a significant
disk component. We do not find convincing evidence for enhanced merger
signatures in the radio-loud population.Comment: Published in ApJ
Simulation of aromatic SOA formation using the lumping model integrated with explicit gas-phase kinetic mechanisms and aerosol-phase reactions
The Unified Partitioning-Aerosol phase Reaction (UNIPAR) model has been
developed to predict the secondary organic aerosol (SOA) formation through
multiphase reactions. The model was evaluated with aromatic SOA data produced
from the photooxidation of toluene and 1,3,5-trimethylbenzene (135-TMB) under
various concentrations of NO<sub>x</sub> and SO<sub>2</sub> using an outdoor
reactor (University of Florida Atmospheric PHotochemical Outdoor Reactor
(UF-APHOR) chamber). When inorganic species (sulfate, ammonium and water)
are present in aerosol, the prediction of both toluene SOA and 135-TMB SOA,
in which the oxygen-to-carbon (O : C) ratio is lower than 0.62, are approached
under the assumption of a complete organic/electrolyte-phase separation below
a certain relative humidity. An explicit gas-kinetic model was employed to
express gas-phase oxidation of aromatic hydrocarbons. Gas-phase products are
grouped based on their volatility (6 levels) and reactivity (5 levels) and
exploited to construct the stoichiometric coefficient (α<sub>i,j</sub>)
matrix, the set of parameters used to describe the concentrations of organic
compounds in multiphase. Weighting of the α<sub>i,j</sub> matrix as a function
of NO<sub>x</sub> improved the evaluation of NO<sub>x</sub> effects on aromatic
SOA. The total amount of organic matter (OM<sub>T</sub>) is predicted by two modules
in the UNIPAR model: OM<sub>P</sub> by a partitioning process and OM<sub>AR</sub> by
aerosol-phase reactions. The OM<sub>AR</sub> module predicts multiphase reactions of
organic compounds, such as oligomerization, acid-catalyzed reactions, and
organosulfate (OS) formation. The model reasonably simulates SOA formation
under various aerosol acidities, NO<sub>x</sub> concentrations, humidities and
temperatures. Furthermore, the OS fractions in the SOA predicted by the model
were in good agreement with the experimentally measured OS fractions
Mechanisms and biomarkers of airway epithelial cell damage in asthma: a review
Bronchial asthma is a heterogeneous disease with complex pathological mechanisms representing different phenotypes, including severe asthma. The airway epithelium is a major site of complex pathological changes in severe asthma due, in part, to activation of inflammatory and immune mechanisms in response to noxious agents. Current imaging procedures are unable to accurately measure epithelial and airway remodeling. Damage of airway epithelial cells occurs is linked to specific phenotypes and endotypes which provides an opportunity for the identification of biomarkers reflecting epithelial, and airway, remodeling. Identification of patients with more severe epithelial disruption using biomarkers may also provide personalized therapeutic opportunities and/or markers of successful therapeutic intervention. Here, we review the evidence for ongoing epithelial cell dysregulation in the pathogenesis of asthma, the sentinel role of the airway epithelium and how understanding these molecular mechanisms provides the basis for the identification of candidate biomarkers for asthma prediction, prevention, diagnosis, treatment and monitoring
Infrared spectroscopy under multi-extreme conditions: Direct observation of pseudo gap formation and collapse in CeSb
Infrared reflectivity measurements of CeSb under multi-extreme conditions
(low temperatures, high pressures and high magnetic fields) were performed. A
pseudo gap structure, which originates from the magnetic band folding effect,
responsible for the large enhancement in the electrical resistivity in the
single-layered antiferromagnetic structure (AF-1 phase) was found at a pressure
of 4 GPa and at temperatures of 35 - 50 K. The optical spectrum of the pseudo
gap changes to that of a metallic structure with increasing magnetic field
strength and increasing temperature. This change is the result of the magnetic
phase transition from the AF-1 phase to other phases as a function of the
magnetic field strength and temperature. This result is the first optical
observation of the formation and collapse of a pseudo gap under multi-extreme
conditions.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
Detection of mechanical resonance of a single-electron transistor by direct current
We have suspended an Al based single-electron transistor whose island can
resonate freely between the source and drain leads forming the clamps. In
addition to the regular side gate, a bottom gate with a larger capacitance to
the SET island is placed underneath to increase the SET coupling to mechanical
motion. The device can be considered as a doubly clamped Al beam that can
transduce mechanical vibrations into variations of the SET current. Our
simulations based on the orthodox model, with the SET parameters estimated from
the experiment, reproduce the observed transport characteristics in detail.Comment: 4 pages, 3 figure
Langerin-expressing dendritic cells in pulmonary immune-related diseases
Dendritic cells (DCs) are "frontline" immune cells dedicated to antigen presentation. They serve as an important bridge connecting innate and adaptive immunity, and express various receptors for antigen capture. DCs are divided into various subclasses according to their differential expression of cell surface receptors and different subclasses of DCs exhibit specific immunological characteristics. Exploring the common features of each sub-category has became the focus of many studies. There are certain amounts of DCs expressing langerin in airways and peripheral lungs while the precise mechanism by which langerin+ DCs drive pulmonary disease is unclear. Langerin-expressing DCs can be further subdivided into numerous subtypes based on the co-expressed receptors, but here, we identify commonalities across these subtypes that point to the major role of langerin. Better understanding is required to clarify key disease pathways and determine potential new therapeutic approaches
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