263 research outputs found
Trefoil peptides as proangiogenic factors in vivo and in vitro: implication of cyclooxygenase-2 and EGF receptor signaling
Improving the Care of Patients with Cirrhosis at MMC
Purpose: Improve the rate and timeliness of paracenteses for patients with decompensated cirrhosis.https://knowledgeconnection.mainehealth.org/lambrew-retreat-2021/1021/thumbnail.jp
Terahertz oscillations in an In<sub>0.53</sub>Ga<sub>0.47</sub>As submicron planar gunn diode
The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode – the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600nm and 700nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In<sub>0.53</sub>Ga<sub>0.47</sub>A on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 µW was obtained from a 600 nm long ×120 µm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible – the Monte Carlo model used predicts power output at frequencies over 300 GHz
Dynamical mass of a star cluster in M83: a test of fibre-fed multi-object spectroscopy
(Abridged) Aims: We obtained VLT/FLAMES+UVES high-resolution, fibre-fed
spectroscopy (FFS) of five young massive clusters in M83 (NGC 5236). This forms
the basis of a pilot study testing the feasibility of using FFS to measure the
velocity dispersions of several clusters simultaneously, in order to determine
their dynamical masses; Methods: We adopted two methods for determining the
velocity dispersion of the star clusters: cross-correlating the cluster
spectrum with the template spectra and minimising a chi^2 value between the
cluster spectrum and the broadened template spectra. Cluster 805 in M83 was
chosen as a control to test the reliability of the method, through a comparison
with the results obtained from a standard echelle VLT/UVES spectrum obtained by
Larsen & Richtler; Results: We find no dependence of the velocity dispersions
measured for a cluster on the choice of red giant versus red supergiant
templates, nor on the method adopted. We measure a velocity dispersion of
sigma_los = 10.2+/-1.1 km/s for cluster 805 from our FFS. Our FLAMES+UVES
velocity dispersion measurement gives M_vir = (6.6+/-1.7)e5 M_sun, consistent
with previous results. This is a factor of ~3 greater than the cluster's
photometric mass, indicating a lack of virial equilibrium. However, based on
its effective star formation efficiency, the cluster is likely to virialise,
and may survive for a Hubble time, in the absence of external disruptive
forces; Conclusions: We find that reliable velocity dispersions can be
determined from FFS. The advantages of observing several clusters
simultaneously outweighs the difficulty of accurate galaxy background
subtraction, providing that the targets are chosen to provide sufficient S/N
ratios, and are much brighter than the galaxy background.Comment: 10 pages, 4 figures, accepted by A&
The volume densities of giant molecular clouds in M83
Using observed GALEX far-ultraviolet (FUV) fluxes and VLA images of the 21-cm
HI column densities, along with estimates of the local dust abundances, we
measure the volume densities of a sample of actively star-forming giant
molecular clouds (GMCs) in the nearby spiral galaxy M83 on a typical resolution
scale of 170 pc. Our approach is based on an equilibrium model for the cycle of
molecular hydrogen formation on dust grains and photodissociation under the
influence of the FUV radiation on the cloud surfaces of GMCs. We find a range
of total volume densities on the surface of GMCs in M83, namely 0.1 - 400 cm-3
inside R25, 0.5 - 50 cm-3 outside R25 . Our data include a number of GMCs in
the HI ring surrounding this galaxy. Finally, we discuss the effects of
observational selection, which may bias our results.Comment: 9 pages, 11 figure
A Study of Cepheids in M81 with the Large Binocular Telescope (Efficiently Calibrated with HST)
We identify and phase a sample of 107 Cepheids with 10<P/days<100 in M81
using the LBT and calibrate their BVI mean magnitudes with archival HST data.
The use of a ground-based telescope to identify and phase the Cepheids and HST
only for the final calibration reduces the demand on HST by nearly an order of
magnitude and yields Period-Luminosity (PL) relations with dispersions
comparable to the best LMC samples. We fit the sample using the OGLE-II LMC PL
relations and are unable to find a self-consistent distance for different band
combinations or radial locations within M81. We can do so after adding a radial
dependence to the PL zero point that corresponds to a luminosity dependence on
metallicity of g_mu=-0.56+/-0.36 mag/dex. We find marginal evidence for a shift
in color as a function of metallicity, distinguishable from the effects of
extinction, of g_2=+0.07+/-0.03 mag/dex. We find a distance modulus for M81,
relative to the LMC, of mu(M81-LMC)=9.39+/-0.14 mag, including uncertainties
due to the metallicity corrections. This corresponds to a distance to M81 of
3.6+/-0.2 Mpc, assuming a LMC distance modulus of 18.41 mag. We carry out a
joint analysis of M81 and NGC4258 Cepheids and simultaneously solve for the
distance of M81 relative to NGC4258 and the metallicity corrections. Given the
current data, the uncertainties of such joint fits are dominated by the
relative metallicities and the abundance gradients rather than by measurement
errors of the Cepheid magnitudes or colors. We find mu(M81-LMC)=9.40
(-0.11/+0.15) mag, mu(N4258-LMC)=11.08 (-0.17/+0.21) mag and
mu(N4258-M81)=1.68+/-0.08 mag and joint metallicity corrections of g_mu=-0.62
(-0.35/+0.31) mag/dex and g_2=0.01+/-0.01 mag/dex. Quantitative analyses of
Cepheid distances must take into account both the metallicity dependencies of
the Cepheids and the uncertainties in the abundance estimates. (ABRIDGED)Comment: 45 pages, 14 figures, 4 tables, appeared in The Astrophysical Journa
Novel insights into the cardio-protective effects of FGF21 in lean and obese rat hearts
Aims: Fibroblast growth factor 21 (FGF21) is a hepatic metabolic regulator with pleotropic actions. Its plasma concentrations are increased in obesity and diabetes; states associated with an increased incidence of cardiovascular disease. We therefore investigated the direct effect of FGF21 on cardio-protection in obese and lean hearts in response to ischemia.
Methods and Results: FGF21, FGF21-receptor 1 (FGFR1) and beta-Klotho (βKlotho) were expressed in rodent, human hearts and primary rat cardiomyocytes. Cardiac FGF21 was expressed and secreted (real time RT-PCR/western blot and ELISA) in an autocrine-paracrine manner, in response to obesity and hypoxia, involving FGFR1-βKlotho components. Cardiac-FGF21 expression and secretion were increased in response to global ischemia. In contrast βKlotho was reduced in obese hearts. In isolated adult rat cardiomyocytes, FGF21 activated PI3K/Akt (phosphatidylinositol 3-kinase/Akt), ERK1/2(extracellular signal-regulated kinase) and AMPK (AMP-activated protein kinase) pathways. In Langendorff perfused rat [adult male wild-type wistar] hearts, FGF21 administration induced significant cardio-protection and restoration of function following global ischemia. Inhibition of PI3K/Akt, AMPK, ERK1/2 and ROR-α (retinoic-acid receptor alpha) pathway led to significant decrease of FGF21 induced cardio-protection and restoration of cardiac function in response to global ischemia. More importantly, this cardio-protective response induced by FGF21 was reduced in obesity, although the cardiac expression profiles and circulating FGF21 levels were increased.
Conclusion: In an ex vivo Langendorff system, we show that FGF21 induced cardiac protection and restoration of cardiac function involving autocrine-paracrine pathways, with reduced effect in obesity. Collectively, our findings provide novel insights into FGF21-induced cardiac effects in obesity and ischemia
The central region of M83: Massive star formation, kinematics, and the location and origin of the nucleus
We report new near-IR integral field spectroscopy of the central starburst
region of the barred spiral galaxy M83 obtained with CIRPASS on Gemini-S, which
we analyse in conjunction with GHaFaS Fabry-Perot data, an AAT IRIS2 Ks-band
image, and near- and mid-IR imaging from the Hubble and Spitzer space
telescopes. The bulk of the current star formation activity is hidden from
optical view by dust extinction, but is seen in the near- and mid-IR to the
north of the nucleus. This region is being fed by inflow of gas through the bar
of M83, traced by the prominent dust lane entering into the circumnuclear
region from the north. An analysis of stellar ages confirms that the youngest
stars are indeed in the northwest. A gradual age gradient, with older stars
further to the south, characterises the well-known star-forming arc in the
central region of M83. Detailed analyses of the Pa beta ionised gas kinematics
and near-IR imaging confirm that the kinematic centre coincides with the
photometric centre of M83, and that these are offset significantly, by about 3
arcsec or 60 pc, from the visible nucleus of the galaxy. We discuss two
possible options, the first of which postulates that the kinematic and
photometric centre traces a galaxy nucleus hidden by a substantial amount of
dust extinction, in the range A_V=3-10 mag. By combining this information with
kinematic results and using arguments from the literature, we conclude that
such a scenario is, however, unlikely, as is the existence of other "hidden"
nuclei in M83. We thus concur with recent authors and favour a second option,
in which the nucleus of the galaxy is offset from its kinematic and photometric
centre. This is presumably a result of some past interaction, possibly related
to the event which lies at the origin of the disturbance of the outer disk of
the galaxy. (Abridged)Comment: MNRAS, in press; 16 pages latex, 15 figure
X-ray emission from the extended disks of spiral galaxies
We present a study of the X-ray properties of a sample of six nearby
late-type spiral galaxies based on XMM-Newton observations. Since our primary
focus is on the linkage between X-ray emission and star formation in extended,
extranuclear galactic disks, we have selected galaxies with near face-on aspect
and sufficient angular extent so as to be readily amenable to investigation
with the moderate spatial resolution afforded by XMM-Newton. After excluding
regions in each galaxy dominated by bright point sources, we study both the
morphology and spectral properties of the residual X-ray emission, comprised of
both diffuse emission and the integrated signal of the fainter discrete source
populations. The soft X-ray morphology generally traces the inner spiral arms
and shows a strong correlation with the distribution of UV light, indicative of
a close connection between the X-ray emission and recent star formation. The
soft (0.3-2 keV) X-ray luminosity to star formation rate (SFR) ratio varies
from 1-5 x 10^39 erg/s(/Msun/yr), with an indication that the lower range of
this ratio relates to regions of lower SFR density. The X-ray spectra are well
matched by a two-temperature thermal model with derived temperatures of
typically ~0.2 keV and ~0.65 keV, in line with published results for other
normal and star-forming galaxies. The hot component contributes a higher
fraction of the soft luminosity in the galaxies with highest X-ray/SFR ratio,
suggesting a link between plasma temperature and X-ray production efficiency.
The physical properties of the gas present in the galactic disks are consistent
with a clumpy thin-disk distribution, presumably composed of diffuse structures
such as superbubbles together with the integrated emission of unresolved
discrete sources including young supernova remnants.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society. 17 pages, 6 figures, 7 table
Resolved photometry of extragalactic young massive star clusters
We present colour-magnitude diagrams (CMDs) for a sample of seven young
massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC
7793. The clusters have ages in the range 5-50 million years and masses of 10^5
-10^6 Msun. Although crowding prevents us from obtaining photometry in the
central regions of the clusters, we are still able to measure up to 30-100
supergiant stars in each of the richest clusters, along with the brighter main
sequence stars. The resulting CMDs and luminosity functions are compared with
photometry of artificially generated clusters, designed to reproduce the
photometric errors and completeness as realistically as possible. In agreement
with previous studies, our CMDs show no clear gap between the H-burning main
sequence and the He-burning supergiant stars, contrary to predictions by common
stellar isochrones. In general, the isochrones also fail to match the observed
number ratios of red-to-blue supergiant stars, although the difficulty of
separating blue supergiants from the main sequence complicates this comparison.
In several cases we observe a large spread (1-2 mag) in the luminosities of the
supergiant stars that cannot be accounted for by observational errors. This
spread can be reproduced by including an age spread of 10-30 million years in
the models. However, age spreads cannot fully account for the observed
morphology of the CMDs and other processes, such as the evolution of
interacting binary stars, may also play a role.Comment: 15 pages, 12 figures, accepted for publication in A&
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