235 research outputs found
Solar hybrid road: from concept to modeling and lab scale mock-up experiments
International audience; We present in this paper the concept of solar hybrid road and the numerical model studied and develop to compute its thermal state at any time step. The aim of these new structures is to collect part of the solar radiation during the summer period, to prevent from icing at the surface during the winter period. As it is reversible, it will help also to prevent from a too high structure temperature (in particular closed to the surface) in summer season. Two types of modifications, compared to traditional structures are presented. The first one concerns the insertion of a porous layer allowing a heat fluid to exchange thermal energy. The second one concerns the use of a semi-transparent material at pavement surface allowing the solar radiation to penetrate deeper in the structure. The numerical model of this multi-physics problem develop with the finite element method is presented and discussed. A validation on two test cases is proposed. First results on energy harvesting evaluation for few locations (i.e. climatic conditions) in France are presented and discussed. Finally, conclusion and perspectives are proposed.
Document type: Conference objec
Two distinct halo populations in the solar neighborhood. IV. Lithium abundances
We investigate if there is a difference in the lithium abundances of stars
belonging to two halo populations of F and G main-sequence stars previously
found to differ in [alpha/Fe] for the metallicity range -1.4 < [Fe/H] < -0.7.
Li abundances are derived from the LiI 6707.8 A line measured in
high-resolution spectra using MARCS model atmospheres. Furthermore, masses of
the stars are determined from the logTeff - logg diagram by interpolating
between Yonsei-Yale evolutionary tracks. There is no significant systematic
difference in the lithium abundances of high- and low-alpha halo stars. For the
large majority of stars with masses 0.7 < M/M_sun < 0.9 and heavy-element mass
fractions 0.001 < Z < 0.006, the Li abundance is well fitted by a relation
A(Li) = a0 + a1 M + a2 Z + a3 M Z, where a0, a1, a2, and a3 are constants.
Extrapolating this relation to Z = 0 leads to a Li abundance close to the
primordial value predicted from standard Big Bang nucleosynthesis calculations
and the WMAP baryon density. The relation, however, does not apply to stars
with [Fe/H] < -1.5. We suggest that metal-rich halo stars were formed with a Li
abundance close to the primordial value, and that lithium in their atmospheres
has been depleted in time with an approximately linear dependence on stellar
mass and Z. The lack of a systematic difference in the Li abundances of high-
and low-alpha stars indicates that an environmental effect is not important for
the destruction of lithium.Comment: 10 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Lithium in the Upper Centaurus Lupus and Lower Centaurus Crux Subgroups of Scorpius-Centaurus
We utilize spectroscopically derived model atmosphere parameters and the
\ion{Li}{1} subordinate line and the doublet to
derive lithium abundances for 12 members of the Upper-Centaurus Lupus (UCL) and
Lower-Centaurus Crux (LCC) subgroups of the Scorpius Centaurus OB Association.
The results indicate any intrinsic Li scatter in our 0.9-1.4 stars
is limited to dex, consistent with the lack of dispersion in
stars in the 100 Myr Pleiades and 30-50 Myr IC 2391 and
2602 clusters. Both ab initio uncertainty estimates and the derived abundances
themselves indicate that the 6104 line yields abundances with
equivalent or less scatter than is found from the 6708 doublet as a
result of lower uncertainties for the subordinate feature, a result of low
sensitivity to broadening in the subordinate feature. Because NLTE corrections
are less susceptible to changes in surface gravity and/or metallicity for the
6104 {\AA} line, the subordinate Li feature is preferred for deriving lithium
abundances in young Li-rich stellar association stars with K.Comment: Accepted for publication in Astronomical Journal (abstract shortened
for astro-ph submission
Magneto-Convection and Lithium Age Estimates of the \beta Pictoris Moving Group
Although the means of the ages of stars in young groups determined from Li
depletion often agree with mean ages determined from Hertzsprung - Russell
diagram isochrones, there are often statistically significant differences in
the ages of individual stars determined by the two methods. We find that
inclusion of the effects of inhibition of convection due to the presence of
magnetic fields leads to consistent ages for the individual stars. We
illustrate how age consistency arises by applying our results to the \beta
Pictoris moving group. We find that, although magnetic inhibition of convection
leads to increased ages from the Hertzsprung - Russell diagram isochrones for
all stars, Li ages are decreased for fully convective M stars and increased for
stars with radiative cores. Our consistent age determination for the \beta
Pictoris moving group of 40 Myr is larger than previous determinations by a
factor of about two.Comment: Submitted to the Astrophysical Journal; 16 pages including 8 figure
Taxonomy of Iberian Hoplia (Col., Scarabaeoidea, Hopliinae) based on mtDNA analysis
Abstract The morphology of some Hoplia species (Scarabaeoidea: Hopliinae) is so variable that parapatric populations have often been considered different species or subspecies. In this study we analyze the nucleotide sequences of a fragment of mitochondrial gene cytochrome c oxidase subunit I (COI) of six species and two subspecies of Palaearctic Hoplia to reexamine the species limits. Based on the analysis of sequences from COI and morphological and ecological observations, we consider Hoplia freyi Baraud to be a junior synonym of Hoplia chlorophana Erichson and H. philanthus ramburi Heyden to be a junior synonym of H. philanthus philanthus (Fuessly). However, complete resolution of relationships among H. philanthus subspecies requires the addition of sequences from genes evolving faster than COI. Phylogenetic relationships among the species studied are discussed
Fundamental Properties of Stars using Asteroseismology from Kepler & CoRoT and Interferometry from the CHARA Array
We present results of a long-baseline interferometry campaign using the PAVO
beam combiner at the CHARA Array to measure the angular sizes of five
main-sequence stars, one subgiant and four red giant stars for which solar-like
oscillations have been detected by either Kepler or CoRoT. By combining
interferometric angular diameters, Hipparcos parallaxes, asteroseismic
densities, bolometric fluxes and high-resolution spectroscopy we derive a full
set of near model-independent fundamental properties for the sample. We first
use these properties to test asteroseismic scaling relations for the frequency
of maximum power (nu_max) and the large frequency separation (Delta_nu). We
find excellent agreement within the observational uncertainties, and
empirically show that simple estimates of asteroseismic radii for main-sequence
stars are accurate to <~4%. We furthermore find good agreement of our measured
effective temperatures with spectroscopic and photometric estimates with mean
deviations for stars between T_eff = 4600-6200 K of -22+/-32 K (with a scatter
of 97K) and -58+/-31 K (with a scatter of 93 K), respectively. Finally we
present a first comparison with evolutionary models, and find differences
between observed and theoretical properties for the metal-rich main-sequence
star HD173701. We conclude that the constraints presented in this study will
have strong potential for testing stellar model physics, in particular when
combined with detailed modelling of individual oscillation frequencies.Comment: 18 pages, 12 figures, 7 tables; accepted for publication in Ap
Thermographic monitoring of asphalt concrete surface with phase change materials inclusions for icing delays purposes
International audienceIf de-icers still are the main solution to avoid black ice occurrence and snow accumulation on pavements, some alternatives based on transportation infrastructure modifications have been tested over the past years. They aim at the reduction of environmental impacts and at coping with budgets constraints and cuts, including in winter maintenance. Among existing ones, the implementation of phase changes materials (PCM) into the infrastructure was evaluated to delay the occurrence of water in its solid phase on the surface. Additional results were obtained with an asphalt concrete in simulated winter conditions, indicating a tenuous thermal effect at the surface
The solar-like CoRoT target HD 170987: spectroscopic and seismic observations
The CoRoT mission is in its third year of observation and the data from the
second long run in the galactic centre direction are being analysed. The
solar-like oscillating stars that have been observed up to now have given some
interesting results, specially concerning the amplitudes that are lower than
predicted. We present here the results from the analysis of the star HD
170987.The goal of this research work is to characterise the global parameters
of HD 170987. We look for global seismic parameters such as the mean large
separation, maximum amplitude of the modes, and surface rotation because the
signal-to-noise ratio in the observations do not allow us to measure individual
modes. We also want to retrieve the stellar parameters of the star and its
chemical composition.We have studied the chemical composition of the star using
ground-based observations performed with the NARVAL spectrograph. We have used
several methods to calculate the global parameters from the acoustic
oscillations based on CoRoT data. The light curve of the star has been
interpolated using inpainting algorithms to reduce the effect of data gaps. We
find power excess related to p modes in the range [400 - 1200]muHz with a mean
large separation of 55.2+-0.8muHz with a probability above 95% that increases
to 55.9 +-0.2muHz in a higher frequency range [500 - 1250] muHz and a rejection
level of 1%. A hint of the variation of this quantity with frequency is also
found. The rotation period of the star is estimated to be around 4.3 days with
an inclination axis of i=50 deg +20/-13. We measure a bolometric amplitude per
radial mode in a range [2.4 - 2.9] ppm around 1000 muHz. Finally, using a grid
of models, we estimate the stellar mass, M=1.43+-0.05 Msun, the radius,
R=1.96+-0.046 Rsun, and the age ~2.4 Gyr.Comment: 12 pages, 15 figures, accepted for publication in A&
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