3,464 research outputs found
Viscoelastic Behaviour Characterization of a Gap-graded Asphalt Mixture with SBS Polymer Modified Bitumen
Oscillating K giants with the WIRE satellite: determination of their asteroseismic masses
Mass estimates of K giants are generally very uncertain. Traditionally,
stellar masses of single field stars are determined by comparing their location
in the Hertzsprung-Russell diagram with stellar evolutionary models. Applying
an additional method to determine the mass is therefore of significant interest
for understanding stellar evolution. We present the time series analysis of 11
K giants recently observed with the WIRE satellite. With this comprehensive
sample, we report the first confirmation that the characteristic acoustic
frequency, nu_max, can be predicted for K giants by scaling from the solar
acoustic cut-off frequency. We are further able to utilize our measurements of
nu_max to determine an asteroseismic mass for each star with a lower
uncertainty compared to the traditional method, for most stars in our sample.
This indicates good prospects for the application of our method on the vast
amounts of data that will soon come from the COROT and Kepler space missions.Comment: 4 pages, 3 figures. Accepted for publication in ApJ
The Clusters AgeS Experiment (CASE). II. The Eclipsing Blue Straggler OGLEGC-228 in the Globular Cluster 47 Tuc
We use photometric and spectroscopic observations of the eclipsing binary
OGLEGC-228 (V228) to derive the masses, radii, and luminosities of the
component stars. Based on measured systemic velocity, proper motion and
distance, the system is a blue straggler member of the globular cluster 47 Tuc.
Our analysis shows that V228 is a semi-detached Algol. We obtain M=1.512 +/-
0.022 Msun, R=1.357 +/- 0.019 Rsun, L=7.02 +/- 0.050 Lsun for the hotter and
more luminous primary component and M=0.200 +/- 0.007 Msun, R=1.238 +/- 0.013
Rsun, L=1.57 +/- 0.09 Lsun for the Roche lobe filling secondary.Comment: 19 pages, 5 figures, AJ, in pres
Clear-air lidar dark band
Abstract. This paper illustrates measurements carried out by the
Raman lidar BASIL in the frame of the HD(CP)2 Observational Prototype
Experiment (HOPE), revealing the presence of a clear-air dark band phenomenon
(i.e. a minimum in lidar backscatter echoes) in the upper portion of the
convective boundary layer. The phenomenon is clearly distinguishable in the
lidar backscatter echoes at 532 and 1064 nm, as well as in the particle
depolarisation data. This phenomenon is attributed to the presence of lignite
aerosol particles advected from the surrounding open pit mines in the
vicinity of the measuring site. The paper provides evidence of the phenomenon
and illustrates possible interpretations for its occurrence
The Nature and Cause of Spectral Variability in LMC X-1
We present the results of a long-term observation campaign of the
extragalactic wind-accreting black-hole X-ray binary LMC X-1, using the
Proportional Counter Array on the Rossi X-Ray Timing Explorer (RXTE). The
observations show that LMC X-1's accretion disk exhibits an anomalous
temperature-luminosity relation. We use deep archival RXTE observations to show
that large movements across the temperature-luminosity space occupied by the
system can take place on time scales as short as half an hour. These changes
cannot be adequately explained by perturbations that propagate from the outer
disk on a viscous timescale. We propose instead that the apparent disk
variations reflect rapid fluctuations within the Compton up-scattering coronal
material, which occults the inner parts of the disk. The expected relationship
between the observed disk luminosity and apparent disk temperature derived from
the variable occultation model is quantitatively shown to be in good agreement
with the observations. Two other observations support this picture: an inverse
correlation between the flux in the power-law spectral component and the fitted
inner disk temperature, and a near-constant total photon flux, suggesting that
the inner disk is not ejected when a lower temperature is observed.Comment: 35 pages, 10 figures, to be published in Ap
A Study of the B-V Colour Temperature Relation
We attempt to construct a B-V colour temperature relation for stars in the
least model dependent way employing the best modern data. The fit we obtained
with the form Teff = Teff((B-V)0,[Fe/H],log g) is well constrained and a number
of tests show the consistency of the procedures for the fit. Our relation
covers from F0 to K5 stars with metallicity [Fe/H] = -1.5 to +0.3 for both
dwarfs and giants. The residual of the fit is 66 K, which is consistent with
what are expected from the quality of the present data. Metallicity and surface
gravity effects are well separated from the colour dependence. Dwarfs and
giants match well in a single family of fit, differing only in log g. The fit
also detects the Galactic extinction correction for nearby stars with the
amount E(B-V) = 0.26 +/-0.03 mag/kpc. Taking the newly obtained relation as a
reference we examine a number of B-V colour temperature relations and
atmosphere models available in the literature. We show the presence of a
systematic error in the colour temperature relation from synthetic calculations
of model atmospheres; the systematic error across K0 to K5 dwarfs is 0.04-0.05
mag in B-V, which means 0.25-0.3 mag in Mv for the K star range. We also argue
for the error in the temperature scale used in currently popular stellar
population synthesis models; synthetic colours from these models are somewhat
too blue for aged elliptical galaxies. We derive the colour index of the sun
(B-V)sun = 0.627 +/-0.018, and discuss that redder colours (e.g., 0.66-0.67)
often quoted in the literature are incompatible with the colour-temperature
relation.Comment: AASLaTeX (aaspp4.sty),36 pages (13 figures included), submitted to
Astronomical Journal, replaced (typo in author name
Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z=0.02
We present new synthetic broad-band photometric colors for late-type giants
based on synthetic spectra calculated with the PHOENIX model atmosphere code.
The grid covers effective temperatures T_eff=3000...5000K, gravities log
g=-0.5...+3.5, and metallicities [M/H]=+0.5...-4.0. We show that individual
broad-band photometric colors are strongly affected by model parameters such as
molecular opacities, gravity, microturbulent velocity, and stellar mass. Our
exploratory 3D modeling of a prototypical late-type giant shows that convection
has a noticeable effect on the photometric colors too, as it alters
significantly both the vertical and horizontal thermal structures in the outer
atmosphere. The differences between colors calculated with full 3D
hydrodynamical and 1D model atmospheres are significant (e.g., \Delta(V-K)~0.2
mag), translating into offsets in effective temperature of up to ~70K. For a
sample of 74 late-type giants in the Solar neighborhood, with interferometric
effective temperatures and broad-band photometry available in the literature,
we compare observed colors with a new PHOENIX grid of synthetic photometric
colors, as well as with photometric colors calculated with the MARCS and ATLAS
model atmosphere codes. (abridged)Comment: 30 pages, 21 figures, A&A in press. Table 2 can be obtained from the
CDS or directly from the author
PTP4A1 promotes TGFβ signaling and fibrosis in systemic sclerosis.
Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis of skin and internal organs. Protein tyrosine phosphatases have received little attention in the study of SSc or fibrosis. Here, we show that the tyrosine phosphatase PTP4A1 is highly expressed in fibroblasts from patients with SSc. PTP4A1 and its close homolog PTP4A2 are critical promoters of TGFβ signaling in primary dermal fibroblasts and of bleomycin-induced fibrosis in vivo. PTP4A1 promotes TGFβ signaling in human fibroblasts through enhancement of ERK activity, which stimulates SMAD3 expression and nuclear translocation. Upstream from ERK, we show that PTP4A1 directly interacts with SRC and inhibits SRC basal activation independently of its phosphatase activity. Unexpectedly, PTP4A2 minimally interacts with SRC and does not promote the SRC-ERK-SMAD3 pathway. Thus, in addition to defining PTP4A1 as a molecule of interest for TGFβ-dependent fibrosis, our study provides information regarding the functional specificity of different members of the PTP4A subclass of phosphatases
Effect of Plant Growth Promoting Bacteria on the Growth of Wheat Seedlings Subjected to Phosphate Starvation
Certain phosphorous solubilizing (PSB) and phosphorous mineralizing (PMB) bacteria may improve plant growth by improving nutrient availability. The aim of this work was to evaluate the effect of inoculation with two Bacillus spp. strains, 12A and 25A, on wheat seedlings growth. To this aim, a durum and a bread wheat genotype were grown under controlled conditions in a low P compost medium to evaluate: (i) the effect of the bacterial isolates on plant growth and root system architecture; (ii) the expression of two key genes indicative of the P-starvation response and phosphate (Pi) uptake, TaIPS1 and TaPHT1.6-B1. The results showed that 12A Bacillus sp. significantly increased root length, surface area and biomass. Furthermore, an enhanced shoot dry weight and P content were observed. This might be explained by the capacity of strain 12A to produce indole-3-acetic acid (IAA) in addition to P mineralizing and P solubilizing capability. No effect on plant growth was observed for 25A strain. The semi-quantitative gene expression analysis showed an overall lower expression of TaIPS1 in the inoculated plants and highest expression of TaPHT1.6-B1 in 12A inoculated plants. This suggests that Pi-responsive genes might be useful molecular indicators for the effectiveness of PSB and PM
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