431 research outputs found
Recrutement électromyographique des ischio-jambiers selon 30 exercices de rééducation sollicitant le genou
Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure
Context. DG Tau is a low-mass pre-main sequence star, whose strongly
accreting protoplanetary disk exhibits a so-far enigmatic behavior: its
mid-infrared thermal emission is strongly time-variable, even turning the 10
m silicate feature from emission to absorption temporarily. Aims. We look
for the reason for the spectral variability at high spatial resolution and at
multiple epochs. Methods. We study the temporal variability of the mid-infrared
interferometric signal, observed with the VLTI/MIDI instrument at six epochs
between 2011 and 2014. We fit a geometric disk model to the observed
interferometric signal to obtain spatial information about the disk. We also
model the mid-infrared spectra by template fitting to characterize the profile
and time dependence of the silicate emission. We use physically motivated
radiative transfer modeling to interpret the mid-infrared interferometric
spectra. Results. The inner disk (r<1-3 au) spectra exhibit a 10 m
absorption feature related to amorphous silicate grains. The outer disk (r>1-3
au) spectra show a crystalline silicate feature in emission, similar to the
spectra of comet Hale-Bopp. The striking difference between the inner and outer
disk spectral feature is highly unusual among T Tauri stars. The mid-infrared
variability is dominated by the outer disk. The strength of the silicate
feature changed by more than a factor of two. Between 2011 and 2014 the
half-light radius of the mid-infrared-emitting region decreased from 1.15 to
0.7 au. Conclusions. For the origin of the absorption we discuss four possible
explanations: a cold obscuring envelope, an accretion heated inner disk, a
temperature inversion on the disk surface and a misaligned inner geometry. The
silicate emission in the outer disk can be explained by dusty material high
above the disk plane, whose mass can change with time, possibly due to
turbulence in the disk.Comment: 16 pages, 13 figure
ER stress activates the NLRP3 inflammasome via an UPR-independent pathway
Uncontrolled endoplasmic reticulum (ER) stress responses are proposed to contribute to the pathology of chronic inflammatory diseases such as type 2 diabetes or atherosclerosis. However, the connection between ER stress and inflammation remains largely unexplored. Here, we show that ER stress causes activation of the NLRP3 inflammasome, with subsequent release of the pro-inflammatory cytokine interleukin-1β. This ER-triggered proinflammatory signal shares the same requirement for reactive oxygen species production and potassium efflux compared with other known NLRP3 inflammasome activators, but is independent of the classical unfolded protein response (UPR). We thus propose that the NLRP3 inflammasome senses and responds to ER stress downstream of a previously uncharacterized ER stress response signaling pathway distinct from the UPR, thus providing mechanistic insight to the link between ER stress and chronic inflammatory diseases
The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
The predicted orbital period histogram of an sdB population is bimodal with a
peak at short ( 250 days) periods. Observationally, there
are many short-period sdB systems known, but only very few long-period sdB
binaries are identified. As these predictions are based on poorly understood
binary interaction processes, it is of prime importance to confront the
predictions to observational data. In this contribution we aim to determine the
absolute dimensions of the long-period sdB+MS binary system PG1104+243.
High-resolution spectroscopy time-series were obtained with HERMES at the
Mercator telescope at La Palma, and analyzed to obtain radial velocities of
both components. Photometry from the literature was used to construct the
spectral energy distribution (SED) of the binary. Atmosphere models were used
to fit this SED and determine the surface gravity and temperature of both
components. The gravitational redshift provided an independent confirmation of
the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a
mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB
component has an effective temperature of Teff = 33500 +- 1200 K and a surface
gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a
G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a
canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07
Msun, and its Teff corresponds to what is expected for a terminal age
main-sequence star with sub-solar metalicity. PG1104+243 is the first
long-period sdB binary in which accurate physical parameters of both components
could be determined, and the first sdB binary in which the gravitational
redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that
shows consistent evidence for being formed through stable Roche-lobe overflow.Comment: Accepted by A&A on 05-10-201
Towards truly simultaneous PIXE and RBS analysis of layered objects in cultural heritage
For a long time, RBS and PIXE techniques have been used in the field of
cultural heritage. Although the complementarity of both techniques has long
been acknowledged, its full potential has not been yet developed due to the
lack of general purpose software tools for analysing the data from both
techniques in a coherent way. In this work we provide an example of how the
recent addition of PIXE to the set of techniques supported by the DataFurnace
code can significantly change this situation. We present a case in which a non
homogeneous sample (an oxidized metal from a photographic plate -heliography-
made by Niepce in 1827) is analysed using RBS and PIXE in a straightforward and
powerful way that can only be performed with a code that treats both techniques
simultaneously as a part of one single and coherent analysis. The optimization
capabilities of DataFurnace, allowed us to obtain the composition profiles for
these samples in a very simple way.Comment: 9 pages, 3 figure
Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae
We report on the discovery of an infrared emission band in the Spitzer
spectrum of the S-type AGB star NP Aurigae that is caused by TiO molecules in
the circumstellar environment. We modelled the observed emission to derive the
temperature of the TiO molecules (\approx 600 K), an upper limit on the column
density (\approx 10^17.25 cm^{-2}) and a lower limit on the spatial extent of
the layer that contains these molecules. (\approx 4.6 stellar radii). This is
the first time that this TiO emission band is observed. A search for similar
emission features in the sample of S-type stars yielded two additional
candidates. However, owing to the additional dust emission, the identification
is less stringent. By comparing the stellar characteristics of NP Aur to those
of the other stars in our sample, we find that all stars with TiO emission show
large-amplitude pulsations, s-process enrichment, and a low C/O ratio. These
characteristics might be necessary requirements for a star to show TiO in
emission, but they are not sufficient.Comment: 4 pages, 4 figures, letter to the edito
Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex
A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous
silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica
nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen
VLTI/MIDI atlas of disks around low- and intermediate-mass young stellar objects
Context. Protoplanetary disks show large diversity regarding their morphology
and dust composition. With mid-infrared interferometry the thermal emission of
disks can be spatially resolved, and the distribution and properties of the
dust within can be studied. Aims. Our aim is to perform a statistical analysis
on a large sample of 82 disks around low- and intermediate-mass young stars,
based on mid-infrared interferometric observations. We intend to study the
distribution of disk sizes, variability, and the silicate dust mineralogy.
Methods. Archival mid-infrared interferometric data from the MIDI instrument on
the VLTI are homogeneously reduced and calibrated. Geometric disk models are
used to fit the observations to get spatial information about the disks. An
automatic spectral decomposition pipeline is applied to analyze the shape of
the silicate feature. Results. We present the resulting data products in the
form of an atlas, containing N band correlated and total spectra, visibilities,
and differential phases. The majority of our data can be well fitted with a
continuous disk model, except for a few objects, where a gapped model gives a
better match. From the mid-infrared size--luminosity relation we find that
disks around T Tauri stars are generally colder and more extended with respect
to the stellar luminosity than disks around Herbig Ae stars. We find that in
the innermost part of the disks (~au) the silicate feature is
generally weaker than in the outer parts, suggesting that in the inner parts
the dust is substantially more processed. We analyze stellar multiplicity and
find that in two systems (AB Aur and HD 72106) data suggest a new companion or
asymmetric inner disk structure. We make predictions for the observability of
our objects with the upcoming MATISSE instrument, supporting the practical
preparations of future MATISSE observations of T Tauri stars.Comment: 54 pages, 14 figures, 6 tables, accepted for publication in A&
- …