23,201 research outputs found
Hydrodynamical instabilities induced by atomic diffusion in A stars and their consequences
Aims. Atomic diffusion, including the effect of radiative accelerations on
individual elements, leads to important variations of the chemical composition
inside the stars. The accumulation in specific layers of the elements, which
are the main contributors of the local opacity, leads to hydrodynamical
instabilities that modify the internal stellar structure and surface
abundances. Our aim is to study these effects and compare the resulting surface
abundances with spectroscopic observations Methods. We computed the detailed
structure of A-type stars including these effects. We used the Toulouse-Geneva
Evolution Code (TGEC), where radiative accelerations are computed using the
Single Valued Parameter (SVP) method, and we added double-diffusive convection
with mixing coefficients deduced from three-dimensional (3D) simulations.
Results. We show that the modification of the initial chemical composition has
important effects on the internal stellar mixing and leads to different surface
abundances of the elements. The results fit the observed surface chemical
composition well if the layers, which are individually mixed by
double-diffusive convection, are connected.Comment: 7 pages, 7 figures, accepted in A&
Lithium abundances in exoplanet host stars as test of planetary formation scenarii
Following the observations of Israelian et al. 2004, we compare different
evolutionary models in order to study the lithium destruction processes and the
planetary formation scenarii.Comment: 4 pages, 5 figures, proceeding of the meeting "Element Stratification
in stars : 40 years of atomic diffusion", Mons 6-11 Juin 200
Abundance anomalies in pre-main-sequence stars: Stellar evolution models with mass loss
The effects of atomic diffusion on internal and surface abundances of A and F
pre-main-sequence stars with mass loss are studied in order to determine at
what age the effects materialize, as well as to further understand the
processes at play in HAeBe and young ApBp stars. Self-consistent stellar
evolution models of 1.5 to 2.8Msun with atomic diffusion (including radiative
accelerations) for all species within the OPAL opacity database were computed
and compared to observations of HAeBe stars. Atomic diffusion in the presence
of weak mass loss can explain the observed abundance anomalies of
pre-main-sequence stars, as well as the presence of binary systems with metal
rich primaries and chemically normal secondaries such as V380 Ori and HD72106.
This is in contrast to turbulence models which do not allow for abundance
anomalies to develop on the pre-main-sequence. The age at which anomalies can
appear depends on stellar mass. For A and F stars, the effects of atomic
diffusion can modify both the internal and surface abundances before the onset
of the MS. The appearance of important surface abundance anomalies on the
pre-main-sequence does not require mass loss, though the mass loss rate affects
their amplitude. Observational tests are suggested to decipher the effects of
mass loss from those of turbulent mixing. If abundance anomalies are confirmed
in pre-main-sequence stars they would severely limit the role of turbulence in
these stars.Comment: 9 pages, 6 figures, accepeted for publicatio
The relevance of positivity in spin physics
Positivity reduces substantially the allowed domain for spin observables. We
briefly recall some methods used to determine these domains and give some
typical examples for exclusive and inclusive spin-dependent reactions.Comment: 7 pages, 3 figures, Talk presented at CIPANP 2009, San Diego
California, USA, May 26-31, 2009 To be published in AIP Conference
Proceeding
Distinct metabolic programs induced by TGF-β1 and BMP2 in human articular chondrocytes with osteoarthritis
Objectives: Cellular energy metabolism is important for the function of all tissues, including cartilage. Recent studies indicate that superficial and deep subpopulations of articular chondrocytes (ACs) have distinct metabolic profiles. At the cellular and molecular level, osteoarthritis (OA) is characterised by alteration from a healthy homoeostatic state towards a catabolic state. Several molecular pathways, including transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signalling, have been identified as critical players in the pathogenesis and progression of OA. However, the manner in which these factors influence cellular energy metabolism in ACs is not well understood. This study investigates the effect of TGF-β or BMP signalling on energy metabolism in human articular chondrocytes (hACs).
Methods: ACs were isolated from residual macroscopically full thickness and intact cartilage from the femoral condyle of human samples obtained from patients with OA. ACs were treated with Vehicle (control), TGF-β1 or BMP2 for 48–72 hours. Metabolic assays were performed to determine glucose consumption, lactate production and adenosine triphosphate (ATP) production, whereas the mitochondrial stress test was performed to determine oxygen consumption rate. Protein was isolated to assess translational activity and was evaluated using Western blot.
Results: We showed that TGF-β1, known to maintain chondrocyte homoeostasis, stimulated glycolysis by upregulating key glycolytic factors, such as glucose transporter 1 (Glut1) and hexokinase II, while reducing oxidative phosphorylation in hACs. In contrast, BMP2 enhanced mitochondrial metabolism and oxidative phosphorylation and had a minimal effect on key glycolytic regulators.
Conclusions: Our data revealed distinct metabolic programs induced by TGF-β1 and BMP2 in hACs, suggesting that the regulation of cellular metabolism may represent a new mechanism underlying the pathogenesis of OA.
The translational potential of this article: The findings define the regulation of energy metabolism as a potential novel therapeutic approach for the treatment of OA
Models of Metal Poor Stars with Gravitational Settling and Radiative Accelerations: I. Evolution and Abundance Anomalies
Evolutionary models have been calculated for Pop II stars of 0.5 to
1.0 from the pre-main-sequence to the lower part of the giant branch.
Rosseland opacities and radiative accelerations were calculated taking into
account the concentration variations of 28 chemical species, including all
species contributing to Rosseland opacities in the OPAL tables. The effects of
radiative accelerations, thermal diffusion and gravitational settling are
included. While models were calculated both for Z=0.00017 and 0.0017, we
concentrate on models with Z=0.00017 in this paper. These are the first Pop II
models calculated taking radiative acceleration into account. It is shown that,
at least in a 0.8 star, it is a better approximation not to let Fe
diffuse than to calculate its gravitational settling without including the
effects of . In the absence of any turbulence outside of
convection zones, the effects of atomic diffusion are large mainly for stars
more massive than 0.7. Overabundances are expected in some stars with
\teff \ge 6000K. Most chemical species heavier than CNO are affected. At 12
Gyr, overabundance factors may reach 10 in some cases (e.g. for Al or Ni) while
others are limited to 3 (e.g. for Fe). The calculated surface abundances are
compared to recent observations of abundances in globular clusters as well as
to observations of Li in halo stars. It is shown that, as in the case of Pop I
stars, additional turbulence appears to be present.Comment: 40 pages, 17 color figures, to appear in The Astrophysical Journal,
April 2002 (paper with original high resolution figures can be found at
http://www.cerca.umontreal.ca/~richer/Fichiersps/popII_1.ps
Associations between religiosity and sexuality in a representative sample of Australian adults
Many studies have examined the influence on sexual attitudes and behavior of religious belief (i.e., religious denomination) or religiosity (e.g., attendance at services, subjective importance of religion). However, few studies have examined the combined effects of religion and religiosity on sexual attitudes and behavior. This study examined such effects in a representative sample of 19,307 Australians aged 16–59 years (response rate, 73.1%). The study compared members of four religious groups (Protestant, Catholic, Buddhist, Muslim) and two levels of frequency of attendance at religious service (less than monthly, at least monthly). Religious participants were compared to their non-religious peers in analyses adjusted for potential confounding by demographic variables. The outcomes were five sexual behaviors and five corresponding measures of sexual attitudes. The study revealed inconsistent patterns of association between religion/religiosity and a range of sexual behaviors and attitudes. In general, greater attendance at religious services was associated with more conservative patterns of behavior and attitudes. However, religious people who attended services infrequently were more similar to their non-religious peers than their more religious peers. The results of this study highlight the importance of considering not only religion or religiosity, but the intersection between these two variables
High frequency and high wavenumber solar oscillations
We determine the frequencies of solar oscillations covering a wide range of
degree (100< l <4000) and frequency (1.5 <\nu<10 mHz) using the ring diagram
technique applied to power spectra obtained from MDI (Michelson Doppler Imager)
data. The f-mode ridge extends up to degree of approximately 3000, where the
line width becomes very large, implying a damping time which is comparable to
the time period. The frequencies of high degree f-modes are significantly
different from those given by the simple dispersion relation \omega^2=gk. The
f-mode peaks in power spectra are distinctly asymmetric and use of asymmetric
profile increases the fitted frequency bringing them closer to the frequencies
computed for a solar model.Comment: Revised version. 1.2 mHz features identified as artifacts of data
analysis. Accepted for publication in Ap
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