4,253 research outputs found
First orbital solution for the non-thermal emitter Cyg OB2 #9
After the first detection of its binary nature, the spectroscopic monitoring
of the non-thermal radio emitter Cyg OB2 #9 (P=2.4yrs) has continued, doubling
the number of available spectra of the star. Since the discovery paper of 2008,
a second periastron passage has occurred in February 2009. Using a variety of
techniques, the radial velocities could be estimated and a first, preliminary
orbital solution was derived from the HeI5876 line. The mass ratio appears
close to unity and the eccentricity is large, 0.7--0.75. X-ray data from 2004
and 2007 are also analyzed in quest of peculiarities linked to binarity. The
observations reveal no large overluminosity nor strong hardness, but it must be
noted that the high-energy data were taken after the periastron passage, at a
time where colliding wind emission may be low. Some unusual X-ray variability
is however detected, with a 10% flux decrease between 2004 and 2007. To clarify
their origin and find a more obvious signature of the wind-wind collision,
additional data, taken at periastron and close to it, are needed.Comment: 15 pages, 4 figures, accepted by Ap
A Model to Evaluate Buying and Selling Policies for Growing Lambs on Pasture
In pastoral sheep finishing systems, farmers aim to maximize profitability by deciding on when and how many animals to buy and/or sell, while taking into account feed availability and current prices. This paper describes a stochastic lamb growth simulation model with a set of heuristic rules, which has been developed to financially evaluate different management strategies for growing lambs on pasture
Sensitivity Analysis of a Growth Simulation for Finishing Lambs
A stochastic lamb growth simulation model with a set of heuristic rules has been developed to evaluate management strategies for a solely pastoral grazing system in New Zealand (Morel et al., 2005). In the present paper the results of a sensitivity analysis for this model are presented
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
Proposal for Topologically Unquenched QCD
A proposal is presented for simulating an improvement on quenched QCD with
dynamical fermions which interact with the gluon configuration only via the
topological index of the latter. Strengths and shortcomings of the method are
discussed and it is argued that the approximation - though being crude - shares
some qualitative aspects of full QCD which relate to the issue of chiral
symmetry breaking.Comment: latex, 13pp, material rearranged and better focused, final version to
appear in Phys. Rev.
Chiral perturbation theory at O(a^2) for lattice QCD
We construct the chiral effective Lagrangian for two lattice theories: one
with Wilson fermions and the other with Wilson sea fermions and Ginsparg-Wilson
valence fermions. For each of these theories we construct the Symanzik action
through order . The chiral Lagrangian is then derived, including terms of
order , which have not been calculated before. We find that there are only
few new terms at this order. Corrections to existing coefficients in the
continuum chiral Lagrangian are proportional to , and appear in the
Lagrangian at order or higher. Similarly, O(4) symmetry breaking
terms enter the Symanzik action at order , but contribute to the chiral
Lagrangian at order or higher. We calculate the light meson masses in
chiral perturbation theory for both lattice theories. At next-to-leading order,
we find that there are no order corrections to the valence-valence meson
mass in the mixed theory due to the enhanced chiral symmetry of the valence
sector.Comment: 25 pages, LaTeX2e; references adde
The Structure of Stellar Coronae in Active Binary Systems
A survey of 28 stars using EUV spectra has been conducted to establish the
structure of stellar coronae in active binary systems from the EMD, electron
densities, and scale sizes. Observations obtained by the EUVE during 9 years of
operation are included for the stars in the sample. EUVE data allow a
continuous EMD to be constructed in the range log T~5.6-7.4, using iron
emission lines. These data are complemented with IUE observations to model the
lower temperature range. Inspection of the EMD shows an outstanding narrow
enhancement, or ``bump'' peaking around log T~6.9 in 25 of the stars, defining
a fundamental coronal structure. The emission measure per unit stellar area
decreases with increasing orbital (or photometric) periods of the target stars;
stars in binaries generally have more material at coronal temperatures than
slowly rotating single stars. High electron densities (Ne>10^12 cm^-3) are
derived at ~10 MK for some targets, implying small emitting volumes. The
observations suggest the magnetic stellar coronae of these stars are consistent
with two basic classes of magnetic loops: solar-like loops with maximum
temperature around log T~6.3 and lower electron densities (Ne>10^9-10.5), and
hotter loops peaking around log T~6.9 with higher electron densities
(Ne>10^12). For the most active stars, material exists at much higher
temperatures (log T>6.9) as well. However, current ab initio stellar loop
models cannot reproduce such a configuration. Analysis of the light curves of
these systems reveals signatures of rotation of coronal material, as well as
apparent seasonal changes in the activity levels.Comment: 45 pages, 9 figures (with 20 eps files). Accepted for its publication
in ApJ
Near and mid-infrared colours of star-forming galaxies in ELAIS fields
We present J and K-band near-infrared photometry of a sample of mid-infrared
sources detected by the Infrared Space Observatory (ISO) as part of the
European Large Area ISO-Survey (ELAIS) and study their classification and
star-forming properties. We have used the Preliminary ELAIS Catalogue for the
6.7 micron (LW2) and 15 micron (LW3) fluxes. All of the high-reliability LW2
sources and 80 per cent of the LW3 sources are identified in the near-IR survey
reaching K = 17.5 mag. The near- to mid-IR flux ratios can effectively be used
to separate stars from galaxies in mid-IR surveys. The stars detected in our
survey region are used to derive a new accurate calibration for the ELAIS
ISOCAM data in both the LW2 and LW3 filters. We show that near to mid-IR
colour-colour diagrams can be used to further classify galaxies, as well as
study star-formation. The ISOCAM ELAIS survey is found to mostly detect
strongly star-forming late-type galaxies, possibly starburst powered galaxies,
and it also picks out obscured AGN. The ELAIS galaxies yield an average mid-IR
flux ratio LW2/LW3 = 0.67 +/- 0.27. We discuss this [6.7/15] ratio as a star
formation tracer using ISO and IRAS data of a local comparison sample. We find
that the [K/15] ratio is also agood indicator of activity level in galaxies and
conclude that the drop in the [6.7/15] ratio seen in strongly star-forming
galaxies is a result of both an increase of 15 mic emission and an apparent
depletion of 6.7 mic emission. Near-IR data together with the mid-IR give the
possibility to estimate the relative amount of interstellar matter in the
galaxies.Comment: 18 pages, 15 figures; accepted for publication in MNRA
Effect of high temperature on the production of 2n pollen grains in diploid roses and obtaining tetraploids via unilateral polyploidization
To integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high-temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest
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