24,372 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
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
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
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.
Investigating the trade-off between the effectiveness and efficiency of process modeling
Despite recent efforts to improve the quality of process models, we still observe a significant dissimilarity in quality between models. This paper focuses on the syntactic condition of process models, and how it is achieved. To this end, a dataset of 121 modeling sessions was investigated. By going through each of these sessions step by step, a separate ‘revision’ phase was identified for 81 of them. Next, by cutting the modeling process off at the start of the revision phase, a partial process model was exported for these modeling sessions. Finally, each partial model was compared with its corresponding final model, in terms of time, effort, and the number of syntactic errors made or solved, in search for a possible trade-off between the effectiveness and efficiency of process modeling. Based on the findings, we give a provisional explanation for the difference in syntactic quality of process models
Understanding suicide attempts among gay men from their self-perceived causes
Gay men are at higher risk of suicidality. This paper describes the causes of suicide attempts as perceived by the men themselves and analyzes their impact on severity and recidivism. Mental health surveys conducted among gay men in Geneva, Switzerland, from two probability-based time-space samples in 2007 and 2011, were merged to yield a combined sample N = 762. Suicide ideation, plans, and attempts were assessed, and respondents who had ever attempted suicide answered open questions about perceived causes which were coded and categorized for analysis within the framework of cultural epidemiology. In all, 16.7% of the respondents reported a suicide attempt in their lifetime (59.5% of them with multiple attempts). At their latest attempt, over two thirds asserted intent to die, and half required medical assistance. There was a wide variety of perceived causes, with most individuals reporting multiple causes and many of the most common causes cited at both the first and most recent subsequent attempts. Social/inter-personal problems constitute the most prominent category. Problems with love/relationship and accepting one's homosexuality figure consistently among the top three causes. Whereas the former tend to be associated with weaker intent to die, the latter are associated with the strongest intent to die and reported at multiple attempts. Problems with family are among the most common perceived causes at first attempt but not at the most recent subsequent attempt. Nevertheless, they tend to be related to the strongest intent to die and the greatest medical severity of all the perceived causes. Ten percent of men attempting suicide cited depression as a cause. Although it tended to be associated with weaker intent to die, depression was most likely to be reported at multiple attempts. Respondent-driven assessment yielded both common and idiosyncratic causes of suicide and their distinct effects. Some of these perceived causes are not prominent in the curren literature, yet they have important implications for understanding risk and preventing suicide among gay men
The Origin of the Intrinsic Scatter in the Relation Between Black Hole Mass and Bulge Luminosity for Nearby Active Galaxies
We investigate the origin of the intrinsic scatter in the correlation between
black hole mass (MBH) and bulge luminosity [L(bulge)] in a sample of 45
massive, local (z < 0.35) type~1 active galactic nuclei (AGNs). We derive MBH
from published optical spectra assuming a spherical broad-line region, and
L(bulge) from detailed two-dimensional decomposition of archival optical Hubble
Space Telescope images. AGNs follow the MBH-L(bulge) relation of inactive
galaxies, but the zero point is shifted by an average of \Delta log MBH ~ -0.3
dex. We show that the magnitude of the zero point offset, which is responsible
for the intrinsic scatter in the MBH-L(bulge) relation, is correlated with
several AGN and host galaxy properties, all of which are ultimately related to,
or directly impact, the BH mass accretion rate. At a given bulge luminosity,
sources with higher Eddington ratios have lower MBH. The zero point offset can
be explained by a change in the normalization of the virial product used to
estimate MBH, in conjunction with modest BH growth (~ 10%--40%) during the AGN
phase. Galaxy mergers and tidal interactions appear to play an important role
in regulating AGN fueling in low-redshift AGNs.Comment: To appear in ApJ; 67 pages, 56 figures, 4 tables, version with full
resolution figures at http://users.ociw.edu/mjkim/papers/scatter.pd
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