708 research outputs found
The X-ray variability and the near-IR to X-ray spectral energy distribution of four low luminosity Seyfert 1 galaxies
We present the results from a study of the X-ray variability and the near-IR
to X-ray spectral energy distribution of four low-luminosity, Seyfert 1
galaxies. We compared their variability amplitude and broad band spectrum with
those of more luminous AGN in order to investigate whether accretion in
low-luminosity AGN operates as in their luminous counterparts. We used archival
XMM-Newton and, in two cases, ASCA data to estimate their X-ray variability
amplitude and determine their X-ray spectral shape and luminosity. We also used
archival HST data to measure their optical nuclear luminosity, and near-IR
measurements from the literature, in order to construct their near-IR to X-ray
spectra. The X-ray variability amplitude of the four Seyferts is what one would
expect, given their black hole masses. Their near-IR to X-ray spectrum has the
same shape as the spectrum of quasars which are 10^2-10^5 times more luminous.
The objects in our sample are optically classified as Seyfert 1-1.5. This
implies that they host a relatively unobscured AGN-like nucleus. They are also
of low luminosity and accrete at a low rate. They are therefore good candidates
to detect radiation from an inefficient accretion process. However, our results
suggest that they are similar to AGN which are 10^2-10^5 times more luminous.
The combination of a "radiative efficient accretion disc plus an X-ray
producing hot corona" may persist at low accretion rates as well.Comment: 11 pages, 8 figures, accepted for publication in A&
Jahn-Teller effect and stability of the charge-ordered state in La1-xCaxMnO3 (0.5<x<0.9) manganites
The longitudinal ultrasonic sound velocity and attenuation, the resistivity,
and lattice parameters were studied as a function of temperature from 30 K to
300 K in La1-xCaxMnO3 (0.5<x<0.9). For all the samples, a dramatic stiffening
of the sound velocity below the charge ordering transition temperature TCO was
directly driven by distinct changes of the lattice parameters due to the
formation of long range ordering of Jahn-Teller distorted MnO6 octahedra. The
relative change of the sound velocity (DeltaV/V) below TCO depends on the Ca
concentration x and reaches the maximum at x=0.75, implying that the effective
strength of electron-lattice interaction with the Jahn-Teller distortion is the
strongest at x=0.75 and hence the charge ordered state is mostly stabilized
near x=0.75 and insensitive to the application of a magnetic field, which is
supported by the charge transport properties under high magnetic fields up to
14T.Comment: 16 pages, 5 figures, PD
Semi-Supervised Deep Learning for Multi-Tissue Segmentation from Multi-Contrast MRI
Segmentation of thigh tissues (muscle, fat, inter-muscular adipose tissue
(IMAT), bone, and bone marrow) from magnetic resonance imaging (MRI) scans is
useful for clinical and research investigations in various conditions such as
aging, diabetes mellitus, obesity, metabolic syndrome, and their associated
comorbidities. Towards a fully automated, robust, and precise quantification of
thigh tissues, herein we designed a novel semi-supervised segmentation
algorithm based on deep network architectures. Built upon Tiramisu segmentation
engine, our proposed deep networks use variational and specially designed
targeted dropouts for faster and robust convergence, and utilize multi-contrast
MRI scans as input data. In our experiments, we have used 150 scans from 50
distinct subjects from the Baltimore Longitudinal Study of Aging (BLSA). The
proposed system made use of both labeled and unlabeled data with high efficacy
for training, and outperformed the current state-of-the-art methods with dice
scores of 97.52%, 94.61%, 80.14%, 95.93%, and 96.83% for muscle, fat, IMAT,
bone, and bone marrow tissues, respectively. Our results indicate that the
proposed system can be useful for clinical research studies where volumetric
and distributional tissue quantification is pivotal and labeling is a
significant issue. To the best of our knowledge, the proposed system is the
first attempt at multi-tissue segmentation using a single end-to-end
semi-supervised deep learning framework for multi-contrast thigh MRI scans.Comment: 20 pages, 9 figures, Journal of Signal Processing System
The Hellenic type of nondeletional hereditary persistence of fetal hemoglobin results from a novel mutation (g.-109G>T) in the HBG2 gene promoter
Nondeletional hereditary persistence of fetal hemoglobin (nd-HPFH), a rare hereditary condition resulting in elevated levels of fetal hemoglobin (Hb F) in adults, is associated with promoter mutations in the human fetal globin (HBG1 and HBG2) genes. In this paper, we report a novel type of nd-HPFH due to a HBG2 gene promoter mutation (HBG2:g.-109G>T). This mutation, located at the 3′ end of the HBG2 distal CCAAT box, was initially identified in an adult female subject of Central Greek origin and results in elevated Hb F levels (4.1%) and significantly increased Gγ-globin chain production (79.2%). Family studies and DNA analysis revealed that the HBG2:g.-109G>T mutation is also found in the family members in compound heterozygosity with the HBG2:g.-158C>T single nucleotide polymorphism or the silent HBB:g.-101C>T β-thalassemia mutation, resulting in the latter case in significantly elevated Hb F levels (14.3%). Electrophoretic mobility shift analysis revealed that the HBG2:g.-109G>T mutation abolishes a transcription factor binding site, consistent with previous observations using DNA footprinting analysis, suggesting that guanine at position HBG2/1:g.-109 is critical for NF-E3 binding. These data suggest that the HBG2:g-109G>T mutation has a functional role in increasing HBG2 transcription and is responsible for the HPFH phenotype observed in our index cases
Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Her
We present the results of a multi-site photometric campaign carried out in
2004-2008 for the Algol-type eclipsing binary system CT Her, the primary
component of which shows Delta Scuti-type oscillations. Our data consist of
differential light curves collected in the filters B and V which have been
analysed using the method of Wilson-Devinney (PHOEBE). After identification of
an adequate binary model and removal of the best-matching light curve solution,
we performed a Fourier analysis of the residual B and V light curves to
investigate the pulsational behaviour. We confirm the presence of rapid
pulsations with a main period of 27.2 min. Up to eight significant frequencies
with semi-amplitudes in the range 3 to 1 mmag were detected, all of which
surprisingly lie in the frequency range 43.5-53.5 c\d. This result is
independent from the choice of the primary's effective temperature (8200 or
8700 K) since the light curve models for the binary are very similar in both
cases. This is yet another case of a complex frequency spectrum observed for an
accreting Delta Scuti-type star (after Y Cam). In addition, we demonstrate that
the amplitudes of several of these pulsation frequencies show evidence of
variability on time scales as short as 1-2 years, perhaps even less. Moreover,
our analysis takes into account some recently acquired spectra, from which we
obtained the corresponding radial velocities for the years 2007-2009.
Investigation of the O-C diagram shows that further monitoring of the epochs of
eclipse minima of CT Her will cast a new light on the evolution of its orbital
period.Comment: 13 pages, 13 encapsulated Postscript figures. Tables~3, 4, 9 and 12
will be available in electronic form only. Astronomy and Astrophysics, in
process (2011). Replaced the abstract with its final versio
Tensor Analyzing Powers for Quasi-Elastic Electron Scattering from Deuterium
We report on a first measurement of tensor analyzing powers in quasi-elastic
electron-deuteron scattering at an average three-momentum transfer of 1.7
fm. Data sensitive to the spin-dependent nucleon density in the deuteron
were obtained for missing momenta up to 150 MeV/ with a tensor polarized
H target internal to an electron storage ring. The data are well described
by a calculation that includes the effects of final-state interaction,
meson-exchange and isobar currents, and leading-order relativistic
contributions.Comment: 4 pages, 3 figure
Universal scaling, beta function, and metal-insulator transitions
We demonstrate a universal scaling form of longitudinal resistance in the
quantum critical region of metal-insulator transitions, based on numerical
results of three-dimensional Anderson transitions (with and without magnetic
field), two-dimensional quantum Hall plateau to insulator transition, as well
as experimental data of the recently discovered two-dimensional metal-insulator
transition. The associated reflection symmetry and a peculiar logarithmic form
of the beta function exist over a wide range in which the resistance can change
by more than one order of magnitude. Interesting implications for the
two-dimensional metal-insulator transition are discussed.Comment: 4 pages, REVTEX, 4 embedded figures; minor corrections to figures and
tex
Dual Vortex Theory of Strongly Interacting Electrons: Non-Fermi Liquid to the (Hard) Core
As discovered in the quantum Hall effect, a very effective way for
strongly-repulsive electrons to minimize their potential energy is to aquire
non-zero relative angular momentum. We pursue this mechanism for interacting
two-dimensional electrons in zero magnetic field, by employing a representation
of the electrons as composite bosons interacting with a Chern-Simons gauge
field. This enables us to construct a dual description in which the fundamental
constituents are vortices in the auxiliary boson fields. The resulting
formalism embraces a cornucopia of possible phases. Remarkably,
superconductivity is a generic feature, while the Fermi liquid is not --
prompting us to conjecture that such a state may not be possible when the
interactions are sufficiently strong. Many aspects of our earlier discussions
of the nodal liquid and spin-charge separation find surprising incarnations in
this new framework.Comment: Modified dicussion of the hard-core model, correcting several
mistake
A Comprehensive Spectral and Variability Study of Narrow-Line Seyfert 1 Galaxies Observed by ASCA: I. Observations and Time Series Analysis
(Abridged) I present a comprehensive and uniform analysis of 25 {\it ASCA}
observations from 23 Narrow-line Seyfert 1 galaxies. The time series analysis
is presented in this paper, Part 1, and the spectral analysis and correlations
are presented in the companion paper, Part 2.Comment: 51 pages, 32 figures, accepted for publication in ApJS. Report also
available also at http://www.astro.columbia.edu/~leighly/research.htm
- …