6,013 research outputs found
Condensation and Metastability in the 2D Potts Model
For the first order transition of the Ising model below , Isakov has
proven that the free energy possesses an essential singularity in the applied
field. Such a singularity in the control parameter, anticipated by condensation
theory, is believed to be a generic feature of first order transitions, but too
weak to be observable. We study these issues for the temperature driven
transition of the states 2D Potts model at . Adapting the droplet
model to this case, we relate its parameters to the critical properties at
and confront the free energy to the many informations brought by previous
works. The essential singularity predicted at the transition temperature leads
to observable effects in numerical data. On a finite lattice, a metastability
domain of temperatures is identified, which shrinks to zero in the
thermodynamical limit. ~Comment: 32 pages, 6 figures, Late
Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite
We aim to determine the fundamental parameters of a sample of B stars with
apparent visual magnitudes below 8 in the field-of-view of the CoRoT space
mission, from high-resolution spectroscopy. We developed an automatic procedure
for the spectroscopic analysis of B-type stars with winds, based on an
extensive grid of FASTWIND model atmospheres. We use the equivalent widths
and/or the line profile shapes of continuum normalized hydrogen, helium and
silicon line profiles to determine the fundamental properties of these stars in
an automated way. After thorough tests, both on synthetic datasets and on very
high-quality, high-resolution spectra of B stars for which we already had
accurate values of their physical properties from alternative analyses, we
applied our method to 66 B-type stars contained in the ground-based archive of
the CoRoT space mission. We discuss the statistical properties of the sample
and compare them with those predicted by evolutionary models of B stars. Our
spectroscopic results provide a valuable starting point for any future seismic
modelling of the stars, should they be observed by CoRoT.Comment: 31 pages (including 14 pages online material), 32 figure
Power calculation for gravitational radiation: oversimplification and the importance of time scale
A simplified formula for gravitational-radiation power is examined. It is
shown to give completely erroneous answers in three situations, making it
useless even for rough estimates. It is emphasized that short timescales, as
well as fast speeds, make classical approximations to relativistic calculations
untenable.Comment: Three pages, no figures, accepted for publication in Astronomische
Nachrichte
Fracture characterization of wood under Mode I loading using the SEN-TPB Test
Mode I fracture characterization was induced in wood (Picea abies L.) using the single-edge-notched beamloaded in three-point-bending. A developed data reduction scheme based on the equivalent linear elasticfracture mechanics was used to evaluate the Resistance-curve instead of classical methods. The method isfound on beam theory and crack equivalent concept taking into account the triangular stress relief regionthat develops in the crack vicinity. The method dispenses crack length monitoring in the course of theloading process, providing a complete Resistance-curve which is essential for a clear identification of thefracture energy. The validation of the procedure has been performed numerically using a bilinear cohesivedamage model, thus allowing the simulation of both damage initiation and growth. The numerical modelalso provided the critical specimen dimensions that permit the attainment of accurate evaluation of thefracture toughness in wood
A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapour and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system
A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour profiles and cirrus cloud using a preliminary Raman channels setup on an existing Rayleigh lidar above La Reunion over the period 2002–2005. With this instrument, we performed a first measurement campaign of 350 independent water vapour profiles. A statistical study of the distribution of water vapour profiles is presented and some investigations concerning the calibration are discussed. Analysis regarding the cirrus clouds is presented and a classification has been performed showing 3 distinct classes. Based on these results, the characteristics and the design of a future lidar system, to be implemented at the new Reunion Island altitude observatory (2200 m) for long-term monitoring, is presented and numerical simulations of system performance have been realised to compare both instruments
Light signaling and plant responses to blue and UV radiations – Perspectives for applications in horticulture
Ultra-violet (UV) and blue radiations are perceived by plants through several photoreceptors. They regulate a large range of processes throughout plant life. Along with red radiations, they are involved in diverse photomorphogenic responses, e.g., seedling development, branching or flowering. In this paper, we present an overview of UV- and blue-radiations signaling pathways in some key physiological processes and describe effects of plant exposure to these wavelengths on phenotype as well as on contents in useful metabolites and resistance to bio aggressors. Taking these knowledge into account, we finally discuss possible applications of the use of such radiations to improve plant production in horticulture
Chiral Lagrangians
An overview of the field of Chiral Lagrangians is given. This includes Chiral
Perturbation Theory and resummations to extend it to higher energies,
applications to the muon anomalous magnetic moment,
and others.Comment: Invited talk at the XX International Symposium on Lepton and Photon
Interactions at High Energies 23rd-28th July 2001, Rome Italy, 15 pages, uses
ws-p10x7.cls Changes: 2 references added, numbers in g-2 hadronic changed
slightl
Bilinear softening parameters and equivalent LEFM R-curve in quasibrittle failure
For composites and adhesive joints, the determination of the cohesive zone parameters from Double Cantilever Beam specimens loaded with pure moments is now well established and documented. However, for quasibrittle materials used in Civil Engineering such as concrete or wood, the difficulty to apply a pure bending moment lies inappropriated the method used for composites. Nevertheless, the one-to-one correspondence which exists between the R-curve and the softening curve is here revisited and adapted for any kind of specimen geometry and for the bilinear approximation of the softening function, well-known to successfully describe the failure of a wide group of quasibrittle materials. It is shown that even though the connections between the cohesive parameters and the ‘equivalent LEFM’ R-curve are geometry and material dependent, their trends are preserved whatever the specimen geometry and the material are. The outline of a general estimation procedure of the cohesive zone parameters funded on the equivalent LEFM R-curve is proposed
Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
A precise characterisation of the red giants in the seismology fields of the
CoRoT satellite is a prerequisite for further in-depth seismic modelling.
High-resolution FEROS and HARPS spectra were obtained as part of the
ground-based follow-up campaigns for 19 targets holding great asteroseismic
potential. These data are used to accurately estimate their fundamental
parameters and the abundances of 16 chemical species in a self-consistent
manner. Some powerful probes of mixing are investigated (the Li and CNO
abundances, as well as the carbon isotopic ratio in a few cases). The
information provided by the spectroscopic and seismic data is combined to
provide more accurate physical parameters and abundances. The stars in our
sample follow the general abundance trends as a function of the metallicity
observed in stars of the Galactic disk. After an allowance is made for the
chemical evolution of the interstellar medium, the observational signature of
internal mixing phenomena is revealed through the detection at the stellar
surface of the products of the CN cycle. A contamination by NeNa-cycled
material in the most massive stars is also discussed. With the asteroseismic
constraints, these data will pave the way for a detailed theoretical
investigation of the physical processes responsible for the transport of
chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised
version after language editing
WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?
A 30-day contiguous photometric run with the MOST satellite on the WN5-6b
star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 +/- 0.55
days along with a number of harmonics at periods P/n, with n ~ 2,3,4,5 and 6,
and a few other possible stray periodicities and/or stochastic variability on
timescales longer than about a day. Spectroscopic RV studies fail to reveal any
plausible companion with a period in this range. Therefore, we conjecture that
the observed light-curve cusps of amplitude ~ 0.01 mag that recur at a 4.08 day
timescale may arise in the inner parts, or at the base of, a corotating
interaction region (CIR) seen in emission as it rotates around with the star at
constant angular velocity. The hard X-ray component seen in WR 110 could then
be a result of a high velocity component of the CIR shock interacting with the
ambient wind at several stellar radii. Given that most hot, luminous stars
showing CIRs have two CIR arms, it is possible that either the fundamental
period is 8.2 days or, more likely in the case of WR 110, there is indeed a
second weaker CIR arm for P = 4.08 days, that occurs ~ two thirds of a rotation
period after the main CIR. If this interpretation is correct, WR 110 therefore
joins the ranks with three other single WR stars, all WN, with confirmed CIR
rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the
lowest amplitude photometric modulation. This illustrates the power of being
able to secure intense, continuous high-precision photometry from space-based
platforms such as MOST. It also opens the door to revealing low-amplitude
photometric variations in other WN stars, where previous attempts have failed.
If all WN stars have CIRs at some level, this could be important for revealing
sources of magnetism or pulsation in addition to rotation periods.Comment: 25 pages, 8 figures, 2 tables, accepted in Ap
- …