4,551 research outputs found
Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. III. Abundances and Velocities for a Sample of 14 Clusters
We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters
in the region of the CaII lines with FORS2 on the Very Large Telescope (VLT).
We determined the mean metallicity and radial velocity with mean errors of 0.05
dex and 2.6 km/s, respectively, from a mean of 6.5 members per cluster. One
cluster (B113) was too young for a reliable metallicity determination and was
excluded from the sample. We combined the sample studied here with 15 clusters
previously studied by us using the same technique, and with 7 clusters whose
metallicities determined by other authors are on a scale similar to ours. This
compilation of 36 clusters is the largest SMC cluster sample currently
available with accurate and homogeneously determined metallicities. We found a
high probability that the metallicity distribution is bimodal, with potential
peaks at -1.1 and -0.8 dex. Our data show no strong evidence of a metallicity
gradient in the SMC clusters, somewhat at odds with recent evidence from CaT
spectra of a large sample of field stars Dobbie et al. (2014). This may be
revealing possible differences in the chemical history of clusters and field
stars. Our clusters show a significant dispersion of metallicities, whatever
age is considered, which could be reflecting the lack of a unique AMR in this
galaxy. None of the chemical evolution models currently available in the
literature satisfactorily represents the global chemical enrichment processes
of SMC clusters.Comment: 49 pages, 15 figures. Accepted for publication in A
Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold
Controlling and confining light by exciting plasmons in resonant metallic
nanostructures is an essential aspect of many new emerging optical
technologies. Here we explore the possibility of controllably reconfiguring the
intrinsic optical properties of semi-continuous gold films, by inducing
permanent morphological changes with a femtosecond (fs)-pulsed laser above a
critical power. Optical transmission spectroscopy measurements show a
correlation between the spectra of the morphologically modified films and the
wavelength, polarization, and the intensity of the laser used for alteration.
In order to understand the modifications induced by the laser writing, we
explore the near-field properties of these films with electron energy-loss
spectroscopy (EELS). A comparison between our experimental data and full-wave
simulations on the exact film morphologies hints toward a restructuring of the
intrinsic plasmonic eigenmodes of the metallic film by photothermal effects. We
explain these optical changes with a simple model and demonstrate
experimentally that laser writing can be used to controllably modify the
optical properties of these semi-continuous films. These metal films offer an
easy-to-fabricate and scalable platform for technological applications such as
molecular sensing and ultra-dense data storage.Comment: Supplementary materials available upon request ([email protected]
Tidal dwarfs in the M81 group: the second generation?
We derive quantitative star formation histories of the four suspected tidal
dwarf galaxies in the M81 group, HolmbergIX, BK3N, Arp-loop (A0952+69), and
Garland, using Hubble Space Telescope/Wide Field Planetary Camera2 images in
F606W and F814W obtained as part of a Snapshot survey of dwarf galaxies in the
Local Universe. We consider the spatial distribution and ages of resolved
stellar populations in these dwarf irregular galaxies. We use synthetic
color-magnitude diagrams to derive the ages of the major star formation
episodes, star formation rates, and approximate metallicity ranges. All the
galaxies show evidence of continuous star formation between about 20 and 200
Myr ago with star formation rates in the range 7.5*10^(-3)- 7.6*10^(-4)
M(sun)/yr. The metallicity of the detected stars spans a wide range, and have
lower than solar abundance. A possible scenario is that all four dwarf galaxies
were formed from material in the metal-poor outer part of the giant spiral
galaxy M81 after the tidal interaction between M81, M82, and NGC3077 about 200
Myr ago. While we do not directly detect pronounced old stellar populations,
the photometric limits of our data are such that the presence of such a
population is not entirely ruled out
Quantum Hall Effect on the Hofstadter Butterfly
Motivated by recent experimental attempts to detect the Hofstadter butterfly,
we numerically calculate the Hall conductivity in a modulated two-dimensional
electron system with disorder in the quantum Hall regime. We identify the
critical energies where the states are extended for each of butterfly subbands,
and obtain the trajectory as a function of the disorder. Remarkably, we find
that when the modulation becomes anisotropic, the critical energy branches
accompanying a change of the Hall conductivity.Comment: 4 pages, 6 figure
Drosophila Parkin requires PINK1 for mitochondrial translocation and ubiquitinates Mitofusin
Loss of the E3 ubiquitin ligase Parkin causes early onset Parkinson's disease, a neurodegenerative disorder of unknown etiology. Parkin has been linked to multiple cellular processes including protein degradation, mitochondrial homeostasis, and autophagy; however, its precise role in pathogenesis is unclear. Recent evidence suggests that Parkin is recruited to damaged mitochondria, possibly affecting mitochondrial fission and/or fusion, to mediate their autophagic turnover. The precise mechanism of recruitment and the ubiquitination target are unclear. Here we show in Drosophila cells that PINK1 is required to recruit Parkin to dysfunctional mitochondria and promote their degradation. Furthermore, PINK1 and Parkin mediate the ubiquitination of the profusion factor Mfn on the outer surface of mitochondria. Loss of Drosophila PINK1 or parkin causes an increase in Mfn abundance in vivo and concomitant elongation of mitochondria. These findings provide a molecular mechanism by which the PINK1/Parkin pathway affects mitochondrial fission/fusion as suggested by previous genetic interaction studies. We hypothesize that Mfn ubiquitination may provide a mechanism by which terminally damaged mitochondria are labeled and sequestered for degradation by autophagy
Modeling of mouse experiments suggests that optimal anti-hormonal treatment for breast cancer is diet-dependent
Estrogen receptor positive breast cancer is frequently treated with
anti-hormonal treatment such as aromatase inhibitors (AI). Interestingly, a
high body mass index has been shown to have a negative impact on AI efficacy,
most likely due to disturbances in steroid metabolism and adipokine production.
Here, we propose a mathematical model based on a system of ordinary
differential equations to investigate the effect of high-fat diet on tumor
growth. We inform the model with data from mouse experiments, where the animals
are fed with high-fat or control (normal) diet. By incorporating AI treatment
with drug resistance into the model and by solving optimal control problems we
found differential responses for control and high-fat diet. To the best of our
knowledge, this is the first attempt to model optimal anti-hormonal treatment
for breast cancer in the presence of drug resistance. Our results underline the
importance of considering high-fat diet and obesity as factors influencing
clinical outcomes during anti-hormonal therapies in breast cancer patients.Comment: 44 pages, 21 figure
Phosphorylation of vimentin by protein kinases A and C is restricted to the head domain.
The in vitro phosphorylation of vimentin, the intermediate filament protein of mesenchymal cells, by kinases A and C is serine-specific and involves only the N-terminal head domain. In oligomeric protofilament units each kinase recognizes five sites, which have been identified by sequence analysis. Kinase C introduces 1.5 mol phosphate/mol vimentin, while kinase A treatment results in 4 mol phosphate/mol. Kinase-A-treated oligomers do not polymerize in standard assays whereas kinase C treatment has no inhibitory effect. Filaments exposed to kinase A remain stable and incorporate only 1.7 mol phosphate/mol vimentin. These phosphates are essentially restricted to two of the five kinase A sites found in protofilament units. Thus the head domain, previously related to in vitro assembly competence and filament stability, changes in accessibility between the oligomeric and polymeric state. We discuss the possibility that in vivo phosphorylation of vimentin filaments by kinase A may not necessarily be accompanied by an extensive depolymerization. It could instead involve a dynamic change of the filament surfaces, which could alter the interaction of the filaments with other cellular structures
Transient Oscillation of Currents in Quantum Hall Effect of Bloch Electrons
We consider the quantum Hall effect of two-dimensional electrons with a
periodic potential and study the time dependence of the Hall and longitudinal
currents when the electric field is applied abruptly. We find that the currents
oscillate in time with very large frequencies because of quantum fluctuation
and the oscillations eventually vanish, for their amplitudes decay as 1/t.Comment: 16 pages and 8 figure
Massive open star clusters using the VVV survey III: A young massive cluster at the far edge of the Galactic bar
Context: Young massive clusters are key to map the Milky Way's structure, and
near-IR large area sky surveys have contributed strongly to the discovery of
new obscured massive stellar clusters.
Aims: We present the third article in a series of papers focused on young and
massive clusters discovered in the VVV survey. This article is dedicated to the
physical characterization of VVV CL086, using part of its OB-stellar
population.
Methods: We physically characterized the cluster using near-infrared
photometry from ESO public survey VVV images, using the VVV-SkZ pipeline, and
near-infrared -band spectroscopy, following the methodology presented in the
first article of the series.
Results: Individual distances for two observed stars indicate that the
cluster is located at the far edge of the Galactic bar. These stars, which are
probable cluster members from the statistically field-star decontaminated CMD,
have spectral types between O9 and B0V. According to our analysis, this young
cluster ( Myr age Myr) is located at a distance of
kpc, and we estimate a lower limit for the cluster total mass of
. It is likely that the cluster
contains even earlier and more massive stars.Comment: Accepted for publication as a Letter in A&
Massive open star clusters using the VVV survey II. Discovery of six clusters with Wolf-Rayet stars
Context: The ESO Public Survey "VISTA Variables in the V\'ia L\'actea" (VVV)
provides deep multi-epoch infrared observations for an unprecedented 562 sq.
degrees of the Galactic bulge, and adjacent regions of the disk. In this survey
nearly 150 new open clusters and cluster candidates have been discovered. Aims:
This is the second in a series of papers about young, massive open clusters
observed using the VVV survey. We present the first study of six recently
discovered clusters. These clusters contain at least one newly discovered
Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first
paper of the series, wide-field, deep JHKs VVV observations, combined with new
infrared spectroscopy, are employed to constrain fundamental parameters for a
subset of clusters. Results: We affirm that the six studied stellar groups are
real young (2-7 Myr) and massive (between 0.8 and 2.2 10^3 Msol) clusters. They
are highly obscured (Av ~ 5-24 mag) and compact (1-2 pc). In addition to WR
stars, two of the six clusters also contain at least one red supergiant star.
We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission
lines which could be classified WR or OIf. Preliminary analysis provides
initial masses of ~30-50 Msol for the WR stars. Finally,we discuss the spiral
structure of the Galaxy using as tracers the six new clusters together with the
previously studied VVV clusters.Comment: 17 pages, 8 figurs, accepted in A&
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