12,511 research outputs found
Spectral Models for Low-luminosity Active Galactic Nuclei in LINERs: The Role of Advection-dominated Accretion and Jets
We perform an exploratory study of the physical properties of accretion flows
and jets in low-luminosity active galactic nuclei (LLAGNs) by modeling the
spectral energy distributions (SEDs) of 12 LLAGNs in low-ionization nuclear
emission-line regions (LINERs). These SEDs we constructed from high-resolution
radio, X-ray and optical/UV observations of the immediate vicinity of the black
hole. We adopt a coupled accretion-jet model comprising an inner
advection-dominated accretion flow (ADAF) and an outer standard thin disk. We
present best-fit models in which either the ADAF or the jet dominate the X-ray
emission. Six sources in our sample display an optical-UV excess with respect
to ADAF and jet models; this excess can be explained as emission from the
truncated disk with transition radii 30-225 Rs in four of them. In almost all
sources the optical emission can also be attributed to unresolved, old stellar
clusters with masses ~1E7-1E8 Msun. We find evidence for a correlation between
the accretion rate and jet power and an anti-correlation between the
radio-loudness and the accretion rate. We confirm previous findings that the
radio emission is severely underpredicted by ADAF models and explained by the
relativistic jet. We find evidence for a nonlinear relation between the X-ray
and bolometric luminosities and a slight IR excess in the average model SED
compared to that of quasars. We suggest that the hardness of the X-ray spectrum
can be used to identify the X-ray emission mechanism and discuss directions for
progress in understanding the origin of the X-rays.Comment: Accepted for publication in MNRAS. 27 pages, 22 figures. arXiv admin
note: substantial text overlap with arXiv:1112.464
2D stellar population and gas kinematics of the inner kiloparsec of the post-starburst quasar SDSS J0330-0532
We have used optical Integral Field Spectroscopy in order to map the star
formation history of the inner kiloparsec of the Post-Starburst Quasar (PSQ)
J0330--0532 and to map its gas and stellar kinematics as well as the gas
excitation. PSQs are hypothesized to represent a stage in the evolution of
galaxies in which the star formation has been recently quenched due to the
feedback of the nuclear activity, as suggested by the presence of the
post-starburst population at the nucleus. We have found that the old stellar
population (age 2.5 Gyr) dominates the flux at 5100 \AA\ in the inner
0.26 kpc, while both the post-starburst (100 Myr age 2.5 Gyr) and
starburst (age 100 Myr) components dominate the flux in a circumnuclear
ring at 0.5 kpc from the nucleus. With our spatially resolved study we
do not have found any post-starburst stellar population in the inner 0.26\,kpc.
On the other hand, we do see the signature of AGN feedback in this region,
which does not reach the circumnuclear ring where the post-starburst population
is observed. We thus do not support the quenching scenario for the J0330-0532.
In addition, we have concluded that the strong signature of the post-starburst
population in larger aperture spectra (e.g. from Sloan Digital Sky Survey) is
partially due to the combination of the young and old age components. Based on
the M relationship and the stellar kinematics we
have estimated a mass for the supermassive black hole of 1.48 0.66
10 M.Comment: 16 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1210.120
Fibroblast growth factor receptor 4 single nucleotide polymorphism Gly388Arg in head and neck carcinomas
BACKGROUND Head and neck squamous cell carcinoma (HNSCC) is considered to be a progressive disease resulting from alterations in multiple genes regulating cell proliferation and differentiation like receptor tyrosine kinases (RTKs) and members of the fibroblast growth factor receptors (FGFR)-family. Single-nucleotide polymorphism (SNP) Arg388 of the FGFR4 is associated with a reduced overall survival in patients with cancers of various types. We speculate that FGFR4 expression and SNP is associated with worse survival in patients with HSNCC. AIM To investigate the potential clinical significance of FGFR4 Arg388 in the context of tumors arising in HNSCC, a comprehensive analysis of FGFR4 receptor expression and genotype in tumor tissues and correlated results with patients' clinical data in a large cohort of patients with HNSCC was conducted. METHODS Surgical specimens from 284 patients with HNSCC were retrieved from the Institute of Pathology at the Ludwig-Maximilian-University in Germany. Specimens were analyzed using immunohistochemistry and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The expression of FGFR4 was analyzed in 284 surgical specimens of HNSCC using immunohistochemstry. FGFR4 polymorphism was detected by PCR-RFLP. Patients' clinical data with a minimum follow-up of 5 syears were statistically evaluated with a special emphasis on survival analysis employing Kaplan-Meier estimator and Cox regression analysis. RESULTS Concerning the invasive tumor areas the intensity of the FGFR4 expression was evaluated in a four-grade system: no expression, low expression, intermediate and high expression. FGFR4 expression was scored as "high" (+++) in 74 (26%), "intermediate" (++) in 103 (36.3%), and "low" (+) in 107 (36.7%) cases. Analyzing the FGFR4 mutation it was found in 96 tumors (33.8%), 84 of them (29.6%) having a heterozygous and 12 (4.2%) homozygous mutated Arg388 allele. The overall frequency concerning the mutant alleles demonstrated 65% vs 34% mutated alleles in general. FGFR4 Arg388 was significantly associated with advanced tumor stage (P < 0.004), local metastasis (P < 0.0001) and reduced disease-free survival (P < 0.01). Furthermore, increased expression of FGFR4 correlated significantly with worse overall survival (P < 0.003). CONCLUSION In conclusion, the FGFR4 Arg388 genotype and protein expression of FGFR4 impacts tumor progression in patients with HNSCC and may present a useful target within a multimodal therapeutic intervention
New design of electrostatic mirror actuators for application in high-precision interferometry
We describe a new geometry for electrostatic actuators to be used in sensitive laser interferometers, suited for prototype and table top experiments related to gravitational wave detection with mirrors of 100 g or less. The arrangement consists of two plates at the sides of the mirror (test mass), and therefore does not reduce its clear aperture as a conventional electrostatic drive (ESD) would do. Using the sample case of the AEI-10 m prototype interferometer, we investigate the actuation range and the influence of the relative misalignment of the ESD plates with respect to the test mass. We find that in the case of the AEI-10 m prototype interferometer, this new kind of ESD could provide a range of 0.28 μm when operated at a voltage of 1 kV. In addition, the geometry presented is shown to provide a reduction factor of about 100 in the magnitude of the actuator motion coupling to the test mass displacement. We show that therefore in the specific case of the AEI-10 m interferometer, it is possible to mount the ESD actuators directly on the optical table without spoiling the seismic isolation performance of the triple stage suspension of the main test masses
Short timescale variations of the H{\alpha} double-peaked profile of the nucleus of NGC 1097
The broad (FWHM ~ 10,000 km/s) double-peaked H{\alpha} profile from the
LINER/Seyfert 1 nucleus of NGC 1097 was discovered in 1991, and monitored for
the following 11 years. The profile showed variations attributed to the
rotation of gas in a non-axisymmetric Keplerian accretion disk, ionized by a
varying radiatively inefficient accretion flow (RIAF) located in the inner
parts of the disk. We present and model 11 new spectroscopic observations of
the double-peaked profile taken between 2010 March and 2011 March. This series
of observations was motivated by the finding that in 2010 March the flux in the
double-peaked line was again strong, becoming, in 2010 December, even stronger
than in the observations of a decade ago. We also discovered shorter timescale
variations than in the previous observations: (1) the first, of ~7 days, is
interpreted as due to "reverberation" of the variation of the ionizing source
luminosity, and the timescale of 7 days as the light crossing time between the
source and the accretion disk; this new timescale and its interpretation
provides a distance between the emitting gas and the supermassive black hole
and as such introduces a new constraint on its mass; (2) the second, of
approximately 5 months, was attributed to the rotation of a spiral arm in the
disk, which was found to occur on the dynamical timescale. We use two accretion
disk models to fit theoretical profiles to the new data, both having
non-axisymmetric emissivities produced by the presence of an one-armed spiral.
Our modeling constrains the rotation period for the spiral to be approximately
18 months. This work supports our previous conclusion that the broad
double-peaked Balmer emission lines in NGC 1097, and probably also in other
low-luminosity active nuclei, originate from an accretion disk ionized by a
central RIAF.Comment: Published in ApJ (2012 March). 13 pages, 11 figure
Robustness of Transcriptional Regulation in Yeast-like Model Boolean Networks
We investigate the dynamical properties of the transcriptional regulation of
gene expression in the yeast Saccharomyces Cerevisiae within the framework of a
synchronously and deterministically updated Boolean network model. By means of
a dynamically determinant subnetwork, we explore the robustness of
transcriptional regulation as a function of the type of Boolean functions used
in the model that mimic the influence of regulating agents on the transcription
level of a gene. We compare the results obtained for the actual yeast network
with those from two different model networks, one with similar in-degree
distribution as the yeast and random otherwise, and another due to Balcan et
al., where the global topology of the yeast network is reproduced faithfully.
We, surprisingly, find that the first set of model networks better reproduce
the results found with the actual yeast network, even though the Balcan et al.
model networks are structurally more similar to that of yeast.Comment: 7 pages, 4 figures, To appear in Int. J. Bifurcation and Chaos, typos
were corrected and 2 references were adde
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