1,199 research outputs found
Recommended from our members
The connection between galaxy environment and the luminosity function slopes of star-forming regions
We present the first study of GALEX far ultra-violet (FUV) luminosity
functions of individual star-forming regions within a sample of 258 nearby
galaxies spanning a large range in total stellar mass and star formation
properties. We identify ~65,000 star-forming regions (i.e., FUV sources),
measure each galaxy's luminosity function, and characterize the relationships
between the luminosity function slope (alpha) and several global galaxy
properties. A final sample of 82 galaxies with reliable luminosity functions
are used to define these relationships and represent the largest sample of
galaxies with the largest range of galaxy properties used to study the
connection between luminosity function properties and galaxy environment. We
find that alpha correlates with global star formation properties, where
galaxies with higher star formation rates and star formation rate densities
(Sigma_SFR) tend to have flatter luminosity function slopes. In addition, we
find that neither stochastic sampling of the luminosity function in galaxies
with low-number statistics nor the effects of blending due to distance can
fully account for these trends. We hypothesize that the flatter slopes in high
Sigma_SFR galaxies is due to higher gas densities and higher star formation
efficiencies which result in proportionally greater numbers of bright
star-forming regions. Finally, we create a composite luminosity function
composed of star-forming regions from many galaxies and find a break in the
luminosity function at brighter luminosities. However, we find that this break
is an artifact of varying detection limits for galaxies at different distances.Science and Technology Facilities CouncilThis is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw169
O espectro das falências ovarianas ligadas ao cromossomo X
Clinically ovarian failure is presented by primary or secondary amenorrhea and high levels of pituitary gonadotropins mainly FSH. Monossomy or X-chromosome rearrangements are among a variable number of suggested etiopathogenic factors of ovarian failure in young women. Besides in Turner syndrome (X-monossomy or mosaicism), where the short stature and sexual infantilism point to the diagnosis, X-chromosome long arm (Xq) rearrangements, or genetic mutations of genes mapped at this segment are related with ovarian failure presented in prepubertal girls and in young women without other clinical signal. The present revision focuses these chromosomal abnormalities, some of them disclosed by conventional cytogenetic methods and other only disclosed by means of molecular biological toolsA falência ovariana manifesta-se clinicamente por amenorréia primária ou secundária, e do ponto de vista hormonal caracteriza-se pelos níveis elevados de gonadotrofinas hipofisárias, principalmente FSH, cuja etiologia pode ser atribuída a varias causas, como redução numérica ou rearranjos do cromossomo X, entre outras. Além da síndrome de Turner (monossomia do cromossomo X, com ou sem mosaicismo cromossômico), cujo principal estigma - a baixa estatura - e o infantilismo sexual apontam o diagnóstico, rearranjos do braço longo de X (Xq), ou mutações instaladas em genes mapeados neste cromossomo estão relacionados com a falência ovariana em meninas pré-púberes e em mulheres adultas jovens, sem outros sinais clínicos. Neste cromossomo, nos segmentos da falência ovariana precoce (FOP1 e FOP2) situam-se genes já relacionados à insuficiência ovariana de instalação precoce. Esta revisão trata destas alterações, algumas detectadas pelas técnicas citogenéticas convencionais, outras somente por meio de recursos de biologia molecularUniversidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Disciplina de Endocrinologia e MetabologiaUniversidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Departamento de GinecologiaUNIFESP, EPM, Disciplina de Endocrinologia e MetabologiaUNIFESP, EPM, Depto. de GinecologiaSciEL
Pentoxifylline decreases tumor necrosis factor and interleukin-1 during high tidal volume
Tumor necrosis factor-alpha (TNF-alpha) is one of the most important proinflammatory cytokines which plays a central role in host defense and in the acute inflammatory response related to tissue injury. The major source of TNF-alpha are immune cells such as neutrophils and macrophages. We tested the hypothesis that pentoxifylline, a methylxanthine derivative, down-regulates proinflammatory cytokine expression during acute lung injury in rats. Male Wistar rats weighing 250 to 450 g were anesthetized ip with 50 mg/kg sodium thiopental and randomly divided into three groups: group 1 (N = 7): tidal volume (V T) = 7 ml/kg, respiratory rate (RR) = 50 breaths/min and normal saline infusion; group 2 (N = 7): V T = 42 ml/kg, RR = 9 breaths/min and normal saline infusion; group 3 (N = 7): V T = 42 ml/kg, RR = 9 breaths/min and pentoxifylline infusion. The animals were ventilated with an inspired oxygen fraction of 1.0, a positive end-expiratory pressure of 3 cmH2O, and normal saline or pentoxifylline injected into the left femoral vein. The mRNA of TNF-alpha rapidly increased in the lung tissue within 180 min of ventilation with a higher V T with normal saline infusion. The concentrations of inflammatory mediators were decreased in plasma and bronchoalveolar lavage (BAL) in the presence of higher V T with pentoxifylline infusion (TNF-alpha: plasma, 102.2 ± 90.9 and BAL, 118.2 ± 82.1; IL-1ß: plasma, 45.2 ± 42.7 and BAL, 50.2 ± 34.9, P < 0.05). We conclude that TNF-alpha produced by neutrophil influx may function as an alert signal in host defense to induce production of other inflammatory mediators.Universidade Federal de São Paulo (UNIFESP) Departamento de Doenças Infecciosas e Parasitárias Disciplina de PneumologiaUniversidade Federal de São Paulo (UNIFESP) Departamento de Doenças Infecciosas e Parasitárias Laboratório de Ginecologia MolecularUniversidade Federal de São Paulo (UNIFESP) Departamento de Doenças Infecciosas e Parasitárias Laboratório de ImunologiaUniversidade Estadual de Campinas Departamento de Clínica Médica Disciplina e Laboratório de Imunologia ClínicaUNIFESP, Depto. de Doenças Infecciosas e Parasitárias Disciplina de PneumologiaUNIFESP, Depto. de Doenças Infecciosas e Parasitárias Laboratório de Ginecologia MolecularUNIFESP, Depto. de Doenças Infecciosas e Parasitárias Laboratório de ImunologiaSciEL
Localizing Sagittarius A* and M87 on Microarcsecond Scales with Millimeter VLBI
With the advent of the Event Horizon Telescope (EHT), a
millimeter/sub-millimeter very-long baseline interferometer (VLBI), it has
become possible to image a handful of black holes with sub-horizon resolutions.
However, these images do not translate into microarcsecond absolute positions
due to the lack of absolute phase information when an external phase reference
is not used. Due to the short atmospheric coherence time at these wavelengths,
nodding between the source and phase reference is impractical. However, here we
suggest an alternative scheme which makes use of the fact that many of the VLBI
stations within the EHT are arrays in their own right. With this we show that
it should be possible to absolutely position the supermassive black holes at
the centers of the Milky Way (Sgr A*) and M87 relative to nearby objects with
precisions of roughly 1 microarcsecond. This is sufficient to detect the
perturbations to Sgr A*'s position resulting from interactions with the stars
and stellar-mass black holes in the Galactic cusp on year timescales, and
severely constrain the astrophysically relevant parameter space for an orbiting
intermediate mass black hole, implicated in some mechanisms for producing the
young massive stars in the Galactic center. For M87, it allows the registering
of millimeter images, in which the black hole may be identified by its
silhouette against nearby emission, and existing larger scale radio images,
eliminating present ambiguities in the nature of the radio core and
inclination, opening angle, and source of the radio jet.Comment: 18 pages, 4 figures, Accepted for publication in Ap
The S-Star Cluster at the Center of the Milky Way: On the nature of diffuse NIR emission in the inner tenth of a parsec
Sagittarius A*, the super-massive black hole at the center of the Milky Way,
is surrounded by a small cluster of high velocity stars, known as the S-stars.
We aim to constrain the amount and nature of stellar and dark mass associated
with the cluster in the immediate vicinity of Sagittarius A*. We use
near-infrared imaging to determine the -band luminosity function
of the S-star cluster members, and the distribution of the diffuse background
emission and the stellar number density counts around the central black hole.
This allows us to determine the stellar light and mass contribution expected
from the faint members of the cluster. We then use post-Newtonian N-body
techniques to investigate the effect of stellar perturbations on the motion of
S2, as a means of detecting the number and masses of the perturbers. We find
that the stellar mass derived from the -band luminosity
extrapolation is much smaller than the amount of mass that might be present
considering the uncertainties in the orbital motion of the star S2. Also the
amount of light from the fainter S-cluster members is below the amount of
residual light at the position of the S-star cluster after removing the bright
cluster members. If the distribution of stars and stellar remnants is strongly
enough peaked near Sagittarius A*, observed changes in the orbital elements of
S2 can be used to constrain both their masses and numbers. Based on simulations
of the cluster of high velocity stars we find that at a wavelength of 2.2
m close to the confusion level for 8 m class telescopes blend stars will
occur (preferentially near the position of Sagittarius A*) that last for
typically 3 years before they dissolve due to proper motions.Comment: 14 pages, 11 figures, minor changes to match the published version in
Astronomy & Astrophysic
Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*
Chandra has detected optically thin, thermal X-ray emission with a size of ~1
arcsec and luminosity ~10^33 erg/s from the direction of the Galactic
supermassive black hole (SMBH), Sgr A*. We suggest that a significant or even
dominant fraction of this signal may be produced by several thousand late-type
main-sequence stars that possibly hide in the central ~0.1 pc region of the
Galaxy. As a result of tidal spin-ups caused by close encounters with other
stars and stellar remnants, these stars should be rapidly rotating and hence
have hot coronae, emitting copious amounts of X-ray emission with temperatures
kT<~ a few keV. The Chandra data thus place an interesting upper limit on the
space density of (currently unobservable) low-mass main-sequence stars near Sgr
A*. This bound is close to and consistent with current constraints on the
central stellar cusp provided by infrared observations. If coronally active
stars do provide a significant fraction of the X-ray luminosity of Sgr A*, it
should be variable on hourly and daily time scales due to giant flares
occurring on different stars. Another consequence is that the quiescent X-ray
luminosity and accretion rate of the SMBH are yet lower than believed before.Comment: 18 pages, 7 figures. Accepted to MNRA
Resilience and physical and mental well-being in adults with and without HIV
Resilience has been related to improved physical and mental health, and is thought to improve with age. No studies have explored the relationship between resilience, ageing with HIV, and well-being. A cross sectional observational study performed on UK HIV positive (N = 195) and HIV negative adults (N = 130). Associations of both age and ‘time diagnosed with HIV’ with resilience (RS-14) were assessed, and the association of resilience with depression, anxiety symptoms (PHQ-9 and GAD-7), and problems with activities of daily living (ADLs) (Euroqol 5D-3L). In a multivariable model, HIV status overall was not related to resilience. However, longer time diagnosed with HIV was related to lower resilience, and older age showed a non-significant trend towards higher resilience. In adults with HIV, high resilience was related to a lower prevalence of depression, anxiety, and problems with ADLs. It may be necessary to consider resilience when exploring the well-being of adults ageing with HIV
Myeloperoxidase-dependent oxidation of etoposide in human myeloid progenitor CD34+ cells
ABSTRACT Etoposide is a widely used anticancer drug successfully utilized for treatment of many types of cancer in children and adults. Its use, however, is associated with an increased risk of development of secondary acute myelogenous leukemia (t-AML) involving MLL gene MOL #68718
Supernova kicks and dynamics of compact remnants in the Galactic Centre
The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a supermassive black hole (SMBH). Here, we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 3
7 104 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes an SN explosion and analyse the impact of SN kicks on the orbits of stars and compact remnants.We find that SN explosions scatter the lighter stars in the pair on completely different orbits, with higher eccentricity and inclination. In contrast, stellar-mass black holes (BHs) and massive stars retain memory of the orbit of their progenitor star. Our results suggest that SN kicks are not sufficient to eject BHs from the GC. We thus predict that all BHs that form in situ in the central parsec of our Galaxy remain in the GC, building up a cluster of dark remnants. In addition, the change of neutron star (NS) orbits induced by SNe may partially account for the observed dearth of NSs in the GC. About 40 per cent of remnants stay bound to the stellar companion after the kick; we expect up to 70 per cent of them might become X-ray binaries through Roche lobe filling. Finally, the eccentricity of some light stars becomes > 0.7 as an effect of the SN kick, producing orbits similar to those of the G1 and G2 dusty objects
- …