4,511 research outputs found
Be stars in and around young clusters in the Magellanic Clouds
We present the results of a search for Be stars in six fields centered on the young clusters NGC 330 and NGC 346 in the SMC, and NGC 1818, NGC 1948, NGC 2004 and NGC 2100 in the LMC. Be stars were identified by differencing R band and narrow-band H CCD images. Our comparatively large images provide substantial Be star populations both within the clusters and in their surrounding fields. Magnitudes, positions and finding charts are given for the 224 Be stars found. The fraction of Be stars to normal B stars within each cluster is found to vary significantly although the average ratio is similar to the average Be to B star ratio found in the Galaxy. In some clusters, the Be star population is weighted to magnitudes near the main sequence turn-off. The Be stars are redder in $
Transcriptomics modeling of the late-gestation fetal pituitary response to transient hypoxia
Background The late-gestation fetal sheep responds to hypoxia with physiological, neuroendocrine, and cellular responses that aid in fetal survival. The response of the fetus to hypoxia represents a coordinated effort to maximize oxygen transfer from the mother and minimize wasteful oxygen consumption by the fetus. While there have been many studies aimed at investigating the coordinated physiological and endocrine responses to hypoxia, and while immunohistochemical or in situ hybridization studies have revealed pathways supporting the endocrine function of the pituitary, there is little known about the coordinated cellular response of the pituitary to the hypoxia. Results Thirty min hypoxia (from 17.0±1.7 to 8.0±0.8 mm Hg, followed by 30 min normoxia) upregulated 595 and downregulated 790 genes in fetal pituitary (123-132 days' gestation; term = 147 days). Network inference of up- and down- regulated genes revealed a high degree of functional relatedness amongst the gene sets. Gene ontology analysis revealed upregulation of cellular metabolic processes (e.g., RNA synthesis, response to estrogens) and downregulation Conclusions The multiple analytical approaches used in this study suggests that the acute response to 30 min of transient hypoxia in the late-gestation fetus results in reduced cellular metabolism and a pattern of gene expression that is consistent with cellular oxygen and ATP starvation. In this early time point, we see a vigorous gene response. But, like the hypothalamus, the transcriptomic response is not consistent with mediation by HIF-1. If HIF-1 is a significant controller of gene expression in the fetal pituitary after hypoxia, it must be at a later time.Fil: Wood, Charles E.. University of Florida; Estados UnidosFil: Chang, Eileen I.. University of Florida; Estados UnidosFil: Richards, Elaine M.. University of Florida; Estados UnidosFil: Rabaglino, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Keller Wood, Maureen. University of Florida; Estados Unido
Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers
We present experimental results on a model system for studying wave
propagation in a complex medium exhibiting low frequency resonances. These
experiments enable us to investigate a fundamental question that is relevant
for many materials, such as metamaterials, where low-frequency scattering
resonances strongly influence the effective medium properties. This question
concerns the effect of correlations in the positions of the scatterers on the
coupling between their resonances, and hence on wave transport through the
medium. To examine this question experimentally, we measure the effective
medium wave number of acoustic waves in a sample made of bubbles embedded in an
elastic matrix over a frequency range that includes the resonance frequency of
the bubbles. The effective medium is highly dispersive, showing peaks in the
attenuation and the phase velocity as functions of the frequency, which cannot
be accurately described using the Independent Scattering Approximation (ISA).
This discrepancy may be explained by the effects of the positional correlations
of the scatterers, which we show to be dependent on the size of the scatterers.
We propose a self-consistent approach for taking this "polydisperse
correlation" into account and show that our model better describes the
experimental results than the ISA
Ketamine decreases inflammatory and immune pathways after transient hypoxia in late gestation fetal cerebral cortex
Transient hypoxia in pregnancy stimulates a physiological reflex response that redistributes blood flow and defends oxygen delivery to the fetal brain. We designed the present experiment to test the hypotheses that transient hypoxia produces damage of the cerebral cortex and that ketamine, an antagonist of NMDA receptors and a known anti-inflammatory agent, reduces the damage. Late gestation, chronically catheterized fetal sheep were subjected to a 30-min period of ventilatory hypoxia that decreased fetal PaO2 from 17 ± 1 to 10 ± 1 mmHg, or normoxia (PaO2 17 ± 1 mmHg), with or without pretreatment (10 min before hypoxia/normoxia) with ketamine (3 mg/kg, i.v.). One day (24 h) after hypoxia/normoxia, fetal cerebral cortex was removed and mRNA extracted for transcriptomics and systems biology analysis (n = 3-5 per group). Hypoxia stimulated a transcriptomic response consistent with a reduction in cellular metabolism and an increase in inflammation. Ketamine pretreatment reduced both of these responses. The inflammation response modeled with transcriptomic systems biology was validated by immunohistochemistry and showed increased abundance of microglia/macrophages after hypoxia in the cerebral cortical tissue that ketamine significantly reduced. We conclude that transient hypoxia produces inflammation of the fetal cerebral cortex and that ketamine, in a standard clinical dose, reduces the inflammation response.Fil: Chang, Eileen I.. University of Florida; Estados UnidosFil: Zárate, Miguel A.. University of Florida; Estados UnidosFil: Rabaglino, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Provincia de Córdoba. Ministerio de Ciencia y Técnica. Centro de Excelencia en Productos y Procesos de Córdoba; ArgentinaFil: Richards, Elaine M.. University of Florida; Estados UnidosFil: Arndt, Thomas J.. University of Florida; Estados UnidosFil: Keller Wood, Maureen. University of Florida; Estados UnidosFil: Wood, Charles E.. University of Florida; Estados Unido
Ketamine reduces inflammation pathways in the hypothalamus and hippocampus following transient hypoxia in the late-gestation fetal sheep
The physiological response to hypoxia in the fetus has been extensively studied with regard to redistribution of fetal combined ventricular output and sparing of oxygen delivery to fetal brain and heart. Previously, we have shown that the fetal brain is capable of mounting changes in gene expression that are consistent with tissue inflammation. The present study was designed to use transcriptomics and systems biology modeling to test the hypothesis that ketamine reduces or prevents the upregulation of inflammation-related pathways in hypothalamus and hippocampus after transient hypoxic hypoxia. Chronically catheterized fetal sheep (122 ± 5 days gestation) were subjected to 30 min hypoxia (relative reduction in PaO2∼50%) caused by infusion of nitrogen into the inspired gas of the pregnant ewe. RNA was isolated from fetal hypothalamus and hippocampus collected 24 h after hypoxia, and was analyzed for gene expression using the Agilent 15.5 k ovine microarray. Ketamine, injected 10 min prior to hypoxia, reduced the cerebral immune response activation to the hypoxia in both brain regions. Genes both upregulated by hypoxia and downregulated by ketamine after hypoxia were significantly associated with gene ontology terms and KEGG pathways that are, themselves, associated with the tissue response to exposure to bacteria. We conclude that the results are consistent with interruption of the cellular response to bacteria by ketamine.Fil: Chang, Eileen I.. University of Florida; Estados UnidosFil: Zarate, Miguel A.. University of Florida; Estados UnidosFil: Arndt, Thomas J.. University of Florida; Estados UnidosFil: Richards, Elaine M.. University of Florida; Estados UnidosFil: Rabaglino, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Ciencias de la Salud. Universidad Nacional de Córdoba. Instituto de Investigaciones en Ciencias de la Salud; ArgentinaFil: Keller Wood, Maureen. University of Florida; Estados UnidosFil: Wood, Charles E.. University of Florida; Estados Unido
Long Period Variables in the Magellanic Clouds: OGLE + 2MASS + DENIS
(abridged) The 68000 I-band light curves of variable stars detected by the
OGLE survey in the Large and Small Magellanic Clouds (MCs) are fitted by
Fourier series, and also correlated with the DENIS and 2MASS databases and with
lists of spectroscopically confirmed M-, S- and C-stars. Lightcurves and the
results of the lightcurve fitting (periods and amplitudes) and DENIS and 2MASS
magnitudes are presented for 2277 M-,S-,C-stars in the MCs. The following
aspects are discussed: the K-band period-luminosity relations for the
spectroscopically confirmed AGB stars, period changes over a timespan of about
17 years in a subset of about 400 LPVs, and candidate obscured AGB stars.Comment: Astronomy and Astrophysics, accepte
Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
High dispersion near-infrared spectra have been taken of seven
highly-evolved, variable, intermediate-mass (4-6 Msun) AGB stars in the LMC and
SMC in order to look for C, N and O variations that are expected to arise from
third dredge-up and hot-bottom burning. The pulsation of the objects has been
modelled, yielding stellar masses, and spectral synthesis calculations have
been performed in order to derive abundances from the observed spectra. For two
stars, abundances of C, N, O, Na, Al, Ti, Sc and Fe were derived and compared
with the abundances predicted by detailed AGB models. Both stars show very
large N enhancements and C deficiencies. These results provide the first
observational confirmation of the long-predicted production of primary nitrogen
by the combination of third dredge-up and hot-bottom burning in
intermediate-mass AGB stars. It was not possible to derive abundances for the
remaining five stars: three were too cool to model, while another two had
strong shocks in their atmospheres which caused strong emission to fill the
line cores and made abundance determination impossible. The latter occurrence
allows us to predict the pulsation phase interval during which observations
should be made if successful abundance analysis is to be possible.Comment: Accepted for publication in MNRA
Dynamical Opacity-Sampling Models of Mira Variables. I: Modelling Description and Analysis of Approximations
We describe the Cool Opacity-sampling Dynamic EXtended (CODEX) atmosphere
models of Mira variable stars, and examine in detail the physical and numerical
approximations that go in to the model creation. The CODEX atmospheric models
are obtained by computing the temperature and the chemical and radiative states
of the atmospheric layers, assuming gas pressure and velocity profiles from
Mira pulsation models, which extend from near the H-burning shell to the outer
layers of the atmosphere. Although the code uses the approximation of Local
Thermodynamic Equilibrium (LTE) and a grey approximation in the dynamical
atmosphere code, many key observable quantities, such as infrared diameters and
low-resolution spectra, are predicted robustly in spite of these
approximations. We show that in visible light, radiation from Mira variables is
dominated by fluorescence scattering processes, and that the LTE approximation
likely under-predicts visible-band fluxes by a factor of two.Comment: 9 pages, 10 figures, accepted for MNRA
Photometric Calibration of the Supernova Legacy Survey Fields
We present the photometric calibration of the Supernova Legacy Survey (SNLS)
fields. The SNLS aims at measuring the distances to SNe Ia at (0.3<z<1) using
MegaCam, the 1 deg^2 imager on the Canada-France-Hawaii Telescope (CFHT). The
uncertainty affecting the photometric calibration of the survey dominates the
systematic uncertainty of the key measurement of the survey, namely the dark
energy equation of state. The photometric calibration of the SNLS requires
obtaining a uniform response across the imager, calibrating the science field
stars in each survey band (SDSS-like ugriz bands) with respect to standards
with known flux in the same bands, and binding the calibration to the UBVRI
Landolt standards used to calibrate the nearby SNe from the literature
necessary to produce cosmological constraints. The spatial non-uniformities of
the imager photometric response are mapped using dithered observations of dense
stellar fields. Photometric zero-points against Landolt standards are obtained.
The linearity of the instrument is studied. We show that the imager filters and
photometric response are not uniform and publish correction maps. We present
models of the effective passbands of the instrument as a function of the
position on the focal plane. We define a natural magnitude system for MegaCam.
We show that the systematics affecting the magnitude-to-flux relations can be
reduced if we use the spectrophotometric standard star BD +17 4708 instead of
Vega as a fundamental flux standard. We publish ugriz catalogs of tertiary
standards for all the SNLS fields.Comment: 46 pages, 23 figures. Accepted by Astronomy and Astrophysics. Online
material available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or
alternatively from: http://supernovae.in2p3.fr/snls3/regnault09_cds.tar.g
The radial distribution of dust species in young brown dwarf disks
We present a study of the radial distribution of dust species in young brown
dwarf disks. Our work is based on a compositional analysis of the 10 and 20
micron silicate emission features for brown dwarfs in the Taurus-Auriga
star-forming region. A fundamental finding of our work is that brown dwarfs
exhibit stronger signs of dust processing in the cold component of the disk,
compared to the higher mass T Tauri stars in Taurus. For nearly all of our
targets, we find a flat disk structure, which is consistent with the stronger
signs of dust processing observed in these disks. For the case of one brown
dwarf, 2M04230607, we find the forsterite mass fraction to be a factor of ~3
higher in the outer disk compared to the inner disk region. Simple large-scale
radial mixing cannot account for this gradient in the dust chemical
composition, and some local crystalline formation mechanism may be effective in
this disk. The relatively high abundance of crystalline silicates in the outer
cold regions of brown dwarf disks provides an interesting analogy to comets. In
this context, we have discussed the applicability of the various mechanisms
that have been proposed for comets on the formation and the outward transport
of high-temperature material. We also present Chandra X-ray observations for
two Taurus brown dwarfs, 2M04414825 and CFHT-BD-Tau 9. We find 2M04414825,
which has a ~12% crystalline mass fraction, to be more than an order of
magnitude brighter in X-ray than CFHT-BD-Tau 9, which has a ~35% crystalline
mass fraction. Combining with previous X-ray data, we find the inner disk
crystalline mass fractions to be anti-correlated with the X-ray strength.Comment: Accepted in MNRA
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