3,045 research outputs found
Stellar and Dust Properties of Local Elliptical Galaxies: Clues to the Onset of Nuclear Activity
We study the stellar and dust properties of a well-defined sample of local
elliptical galaxies to investigate the relationship between host galaxy
properties and nuclear activity. We select a complete sample of 45 ellipticals
from the Palomar spectroscopic survey of nearby galaxies, which includes 20
low-luminosity active galactic nuclei classified as LINERs and 25 inactive
galaxies. Using a stellar population synthesis method, we compare the derived
stellar population properties of the LINER versus the inactive subsamples. We
also study the dust and stellar surface brightness distributions of the central
regions of these galaxies using high-resolution images obtained with the {\it
Hubble Space Telescope}. Relative to the inactive subsample, ellipticals
hosting LINERs share similar total optical and near-infrared luminosity,
central stellar velocity dispersions, and nuclear stellar populations as judged
from their luminosity-weighted ages and metallicities. LINERs, on the other
hand, have a larger fraction of core-type central surface brightness profiles
and a much higher frequency of circumnuclear dust structures. Our results
support the suggestion that LINERs are powered by low-luminosity AGNs rather
than by young or intermediate-age stars. Nuclear activity in nearby elliptical
galaxies seems to occur preferentially in those systems where sufficient cold
interstellar material has managed to accumulate, perhaps via cooling
condensations from hot gas.Comment: 8 pages, accepted by A&
Cathelicidin suppresses lipid accumulation and hepatic steatosis by inhibition of the CD36 receptor.
Background and objectivesObesity is a global epidemic which increases the risk of the metabolic syndrome. Cathelicidin (LL-37 and mCRAMP) is an antimicrobial peptide with an unknown role in obesity. We hypothesize that cathelicidin expression correlates with obesity and modulates fat mass and hepatic steatosis.Materials and methodsMale C57BL/6 J mice were fed a high-fat diet. Streptozotocin was injected into mice to induce diabetes. Experimental groups were injected with cathelicidin and CD36 overexpressing lentiviruses. Human mesenteric fat adipocytes, mouse 3T3-L1 differentiated adipocytes and human HepG2 hepatocytes were used in the in vitro experiments. Cathelicidin levels in non-diabetic, prediabetic and type II diabetic patients were measured by enzyme-linked immunosorbent assay.ResultsLentiviral cathelicidin overexpression reduced hepatic steatosis and decreased the fat mass of high-fat diet-treated diabetic mice. Cathelicidin overexpression reduced mesenteric fat and hepatic fatty acid translocase (CD36) expression that was reversed by lentiviral CD36 overexpression. Exposure of adipocytes and hepatocytes to cathelicidin significantly inhibited CD36 expression and reduced lipid accumulation. Serum cathelicidin protein levels were significantly increased in non-diabetic and prediabetic patients with obesity, compared with non-diabetic patients with normal body mass index (BMI) values. Prediabetic patients had lower serum cathelicidin protein levels than non-diabetic subjects.ConclusionsCathelicidin inhibits the CD36 fat receptor and lipid accumulation in adipocytes and hepatocytes, leading to a reduction of fat mass and hepatic steatosis in vivo. Circulating cathelicidin levels are associated with increased BMI. Our results demonstrate that cathelicidin modulates the development of obesity
The role of tank-treading motions in the transverse migration of a spheroidal vesicle in a shear flow
The behavior of a spheroidal vesicle, in a plane shear flow bounded from one
side by a wall, is analysed when the distance from the wall is much larger than
the spheroid radius. It is found that tank treading motions produce a
transverse drift away from the wall, proportional to the spheroid eccentricity
and the inverse square of the distance from the wall. This drift is independent
of inertia, and is completely determined by the characteristics of the vesicle
membrane. The relative strength of the contribution to drift from tank-treading
motions and from the presence of inertial corrections, is discussed.Comment: 16 pages, 1 figure, Latex. To appear on J. Phys. A (Math. Gen.
Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides
Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is 1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. (c) (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use onl
Entangled quantum tunneling of two-component Bose-Einstein condensates
We examine the quantum tunneling process in Bose condensates of two
interacting species trapped in a double well configuration. We discover the
condition under which particles of different species can tunnel as pairs
through the potential barrier between two wells in opposition directions. This
novel form of tunneling is due to the interspecies interaction that eliminates
the self- trapping effect. The correlated motion of tunneling atoms leads to
the generation of quantum entanglement between two macroscopically coherent
systems.Comment: 4 pages, 3 figure
Infrared Spectral Energy Distributions of Seyfert Galaxies: Spitzer Space Telescope Observations of the 12 micron Sample of Active Galaxies
The mid-far-infrared spectral energy distributions (SEDs) of 83 active
galaxies, mostly Seyfert galaxies, selected from the extended 12 micron sample
are presented. The data were collected using all three instruments, IRAC, IRS,
and MIPS, aboard the Spitzer Space Telescope. The IRS data were obtained in
spectral mapping mode, and the photometric data from IRAC and IRS were
extracted from matched, 20 arcsec diameter circular apertures. The MIPS data
were obtained in SED mode, providing very low resolution spectroscopy (R ~ 20)
between ~ 55 and 90 microns in a larger, 20 by 30 arcsec synthetic aperture. We
further present the data from a spectral decomposition of the SEDs, including
equivalent widths and fluxes of key emission lines; silicate 10 and 18 micron
emission and absorption strengths; IRAC magnitudes; and mid-far infrared
spectral indices. Finally, we examine the SEDs averaged within optical
classifications of activity. We find that the infrared SEDs of Seyfert 1s and
Seyfert 2s with hidden broad line regions (HBLR, as revealed by
spectropolarimetry or other technique) are qualitatively similar, except that
Seyfert 1s show silicate emission and HBLR Seyfert 2s show silicate absorption.
The infrared SEDs of other classes with the 12 micron sample, including Seyfert
1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1 nucleus), LINER and
HII galaxies, appear to be dominated by star-formation, as evidenced by blue
IRAC colors, strong PAH emission, and strong far-infrared continuum emission,
measured relative to mid-infrared continuum emission.Comment: 78 pages, 13 figure
The Herschel Reference Survey: Dust in Early-Type Galaxies and Across the Hubble Sequence
We present Herschel observations of 62 Early-Type Galaxies (ETGs), including
39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as
ellipticals using SPIRE at 250, 350 and 500 microns (and PACS 100 and 160
microns for 19 sources) as part of the volume-limited Herschel Reference
Survey. We detect dust emission in 24% of the ellipticals and 62% of the S0s.
The mean temperature of the dust is 23.9+/-0.8 K, warmer than that found for
late-type galaxies in the Virgo Cluster. Including the non-detections, the mean
dust mass is log(Mdust) = 5.9+/-0.1 and 5.2+/-0.1 Msun for the S0s and
elliptical galaxies respectively. The mean dust-to-stellar mass is
log(Mdust/Mstar) = -4.4+/-0.1 (S0s) and -5.8+/-0.1 (ellipticals). Virtually all
the galaxies lie close to the red sequence yet the large number of detections
of cool dust, the gas-to-dust ratios and the ratios of far-infrared to radio
emission all suggest that many ETGs contain a cool interstellar medium similar
to that in late-type galaxies. The mean dust-to-stellar mass ratio for S0s is
approximatly a factor of ten less than for early-type spirals and the sizes of
the dust sources in the S0s are also much smaller. We show that the difference
cannot be explained by either the different bulge-to-disk ratios or
environmental effects such as ram-pressure stripping. The wide range in the
dust-to-stellar mass ratio for ETGs and the lack of a correlation between dust
mass and optical luminosity suggest that much of the dust in the ETGs detected
by Herschel has been acquired as the result of gravitational interactions;
these interactions are unlikely to have had a major effect on the stellar
masses of the ETGs. The Herschel observations tentatively suggest that in the
most massive ETGs, the mass of the interstellar medium is unconnected to the
evolution of the stellar populations.Comment: 28 Pages, 12 Figures. Submitted to ApJ December 2011; accepted
January 201
String theory duals of Lifshitz-Chern-Simons gauge theories
We propose candidate gravity duals for a class of non-Abelian z=2 Lifshitz
Chern-Simons (LCS) gauge theories studied by Mulligan, Kachru and Nayak. These
are nonrelativistic gauge theories in 2+1 dimensions in which parity and
time-reversal symmetries are explicitly broken by the presence of a
Chern-Simons term. We show that these field theories can be realized as
deformations of DLCQ N=4 super Yang-Mills theory. Using the holographic
dictionary, we identify the bulk fields that are dual to these deformations.
The geometries describing the groundstates of the non-Abelian LCS gauge
theories realized here exhibit a mass gap.Comment: 25+14 pages, 3 figures; v2: significant corrections regarding IR
geometry, resulting in new section 5; journal versio
Reflection in Seyfert Galaxies and the Unified Model of AGN
We present a deep study of the average hard X-ray spectra of Seyfert
galaxies. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the
165 Seyfert galaxies detected at z<0.2. Our final sample consists of 44 Seyfert
1's, 29 Seyfert 1.5's, 78 Seyfert 2's, and 14 Narrow Line Seyfert 1's. We
derived the average hard X-ray spectrum of each subsample in the 17-250keV
energy range. All classes of Seyfert galaxies show on average the same nuclear
continuum, as foreseen by the zeroth order unified model, with a cut-off energy
of Ec>200keV, and a photon index of Gamma ~1.8. Compton-thin Seyfert 2's show a
reflection component stronger than Seyfert 1's and Seyfert 1.5's. Most of this
reflection is due to mildly obscured (10^23 cm^-2 < NH < 10^24 cm^-2) Seyfert
2's, which have a significantly stronger reflection component
(R=2.2^{+4.5}_{-1.1}) than Seyfert 1's (R<=0.4), Seyfert 1.5's (R<= 0.4) and
lightly obscured (NH < 10^23 cm^-2) Seyfert 2's (R<=0.5). This cannot be
explained easily by the unified model. The absorber/reflector in mildly
obscured Seyfert 2's might cover a large fraction of the X-ray source, and have
clumps of Compton-thick material. The large reflection found in the spectrum of
mildly obscured Seyfert 2's reduces the amount of Compton-thick objects needed
to explain the peak of the cosmic X-ray background. Our results are consistent
with the fraction of Compton-thick sources being ~10%. The spectra of Seyfert
2's with and without polarized broad lines do not show significant differences,
the only difference between the two samples being the higher hard X-ray and
bolometric luminosity of Seyfert 2's with polarized broad lines. The average
hard X-ray spectrum of Narrow line Seyfert 1's is steeper than those of Seyfert
1's and Seyfert 1.5's, probably due to a lower energy of the cutoff.Comment: 19 pages, accepted for publication in Astronomy and Astrophysics,
final versio
The impact of albendazole treatment on the incidence of viral- and bacterial-induced diarrhea in school children in southern Vietnam: study protocol for a randomized controlled trial
Anthelmintics are one of the more commonly available classes of drugs to treat infections by parasitic helminths (especially nematodes) in the human intestinal tract. As a result of their cost-effectiveness, mass school-based deworming programs are becoming routine practice in developing countries. However, experimental and clinical evidence suggests that anthelmintic treatments may increase susceptibility to other gastrointestinal infections caused by bacteria, viruses, or protozoa. Hypothesizing that anthelmintics may increase diarrheal infections in treated children, we aim to evaluate the impact of anthelmintics on the incidence of diarrheal disease caused by viral and bacterial pathogens in school children in southern Vietnam.This is a randomized, double-blinded, placebo-controlled trial to investigate the effects of albendazole treatment versus placebo on the incidence of viral- and bacterial-induced diarrhea in 350 helminth-infected and 350 helminth-uninfected Vietnamese school children aged 6-15 years. Four hundred milligrams of albendazole, or placebo treatment will be administered once every 3 months for 12 months. At the end of 12 months, all participants will receive albendazole treatment. The primary endpoint of this study is the incidence of diarrheal disease assessed by 12 months of weekly active and passive case surveillance. Secondary endpoints include the prevalence and intensities of helminth, viral, and bacterial infections, alterations in host immunity and the gut microbiota with helminth and pathogen clearance, changes in mean z scores of body weight indices over time, and the number and severity of adverse events.In order to reduce helminth burdens, anthelmintics are being routinely administered to children in developing countries. However, the effects of anthelmintic treatment on susceptibility to other diseases, including diarrheal pathogens, remain unknown. It is important to monitor for unintended consequences of drug treatments in co-infected populations. In this trial, we will examine how anthelmintic treatment impacts host susceptibility to diarrheal infections, with the aim of informing deworming programs of any indirect effects of mass anthelmintic administrations on co-infecting enteric pathogens.ClinicalTrials.gov: NCT02597556 . Registered on 3 November 2015
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