5,809 research outputs found
A Systematic Search for Corotating Interaction Regions in Apparently Single Galactic Wolf-Rayet Stars. II. A Global View of the Wind Variability
This study is the second part of a survey searching for large-scale
spectroscopic variability in apparently single Wolf-Rayet (WR) stars. In a
previous paper (Paper I), we described and characterized the spectroscopic
variability level of 25 WR stars observable from the northern hemisphere and
found 3 new candidates presenting large-scale wind variability, potentially
originating from large-scale structures named Co-rotating Interaction Regions
(CIRs). In this second paper, we discuss an additional 39 stars observable from
the southern hemisphere. For each star in our sample, we obtained 4-5
high-resolution spectra with a signal-to-noise ratio of ~100 and determined its
variability level using the approach described in Paper I. In total, 10 new
stars are found to show large-scale spectral variability of which 7 present
CIR-type changes (WR 8, WR 44, WR 55, WR 58, WR 61, WR 63, WR 100). Of the
remaining stars, 20 were found to show small-amplitude changes and 9 were found
to show no spectral variability as far as can be concluded from the data in
hand. Also, we discuss the spectroscopic variability level of all single
galactic WR stars that are brighter than v~12.5, and some WR stars with 12.5 <
v <= 13.5; i.e. all the stars presented in our two papers and 4 more stars for
which spectra have already been published in the literature. We find that 23/68
stars (33.8 %) present large-scale variability, but only 12/54 stars (~22.1 %)
are potentially of CIR-type. Also, we find 31/68 stars (45.6 %) that only show
small-scale variability, most likely due to clumping in the wind. Finally, no
spectral variability is detected based on the data in hand for 14/68 (20.6 %)
stars. Interestingly, the variability with the highest amplitude also have the
widest mean velocity dispersion.Comment: 14 pages, 24 figures, 2 tables, Accepted in Ap
Revealing frame dynamics through comparing associative fields in diachrony
The article shows that the changes of an associative field in diachrony can somewhat schematically, but quite accurately reflect the dynamics of the corresponding frame over time. The undertaken comparative analysis of associative fields of stimuli ‘napitok’ (drink) and ‘pit’yo’ (drink(ing)) - as of 1988-1997 (the data of “Russian associative dictionary”) and 2013-2014 (the results of the author experiment) - helps to develop the model of the frame “drink” - to the extent of slots actualized through associative reactions - and reveals some changes in its structure. Ascertained dynamics implies variation in the relevancy of almost all slots. The revealed trends also reflect some harmonization of this frame with its Western analoguesye
Partially Quenched QCD with Non-Degenerate Dynamical Quarks
We discuss the importance of using partially quenched theories with three
degenerate quarks for extrapolating to QCD, and present some relevant results
from chiral perturbation theory.Comment: LATTICE99 talk. 3 pages, 2 figures. Uses epsf and espcrc2.st
An Investigation of the Large-scale Variability of the Apparently Single Wolf-Rayet Star WR 1
In recent years, much studies have focused on determining the origin of the
large-scale line-profile and/or photometric patterns of variability displayed
by some apparently single Wolf-Rayet stars, with the existence of an unseen
(collapsed?) companion or of spatially extended wind structures as potential
candidates. We present observations of WR 1 which highlight the unusual
character of the variations in this object. Our narrowband photometric
observations reveal a gradual increase of the stellar continuum flux amounting
to Delta v = 0.09 mag followed by a decline on about the same timescale (3-4
days). Only marginal evidence for variability is found during the 11 following
nights.
Strong, daily line-profile variations are also observed but they cannot be
easily linked to the photometric variations.
Similarly to the continuum flux variations, coherent time-dependent changes
are observed in 1996 in the centroid, equivalent width, and skewness of He II
4686. Despite the generally coherent nature of the variations, we do not find
evidence in our data for the periods claimed in previous studies. While the
issue of a cyclical pattern of variability in WR 1 is still controversial, it
is clear that this object might constitute in the future a cornerstone for our
understanding of the mechanisms leading to the formation of largely anisotropic
outflows in Wolf-Rayet stars.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Optimal fabrication processes for unidirectional metal-matrix composites: A computational simulation
A method is proposed for optimizing the fabrication process of unidirectional metal matrix composites. The temperature and pressure histories are optimized such that the residual microstresses of the composite at the end of the fabrication process are minimized and the material integrity throughout the process is ensured. The response of the composite during the fabrication is simulated based on a nonlinear micromechanics theory. The optimal fabrication problem is formulated and solved with non-linear programming. Application cases regarding the optimization of the fabrication cool-down phases of unidirectional ultra-high modulus graphite/copper and silicon carbide/titanium composites are presented
Evolution of Exoplanets and their Parent Stars
Studying exoplanets with their parent stars is crucial to understand their
population, formation and history. We review some of the key questions
regarding their evolution with particular emphasis on giant gaseous exoplanets
orbiting close to solar-type stars. For masses above that of Saturn, transiting
exoplanets have large radii indicative of the presence of a massive
hydrogen-helium envelope. Theoretical models show that this envelope
progressively cools and contracts with a rate of energy loss inversely
proportional to the planetary age. The combined measurement of planetary mass,
radius and a constraint on the (stellar) age enables a global determination of
the amount of heavy elements present in the planet interior. The comparison
with stellar metallicity shows a correlation between the two, indicating that
accretion played a crucial role in the formation of planets. The dynamical
evolution of exoplanets also depends on the properties of the central star. We
show that the lack of massive giant planets and brown dwarfs in close orbit
around G-dwarfs and their presence around F-dwarfs are probably tied to the
different properties of dissipation in the stellar interiors. Both the
evolution and the composition of stars and planets are intimately linked.Comment: appears in The age of stars - 23rd Evry Schatzman School on Stellar
Astrophysics, Roscoff : France (2013
Light elements in massive single and binary stars
We highlight the role of the light elements (Li, Be, B) in the evolution of
massive single and binary stars, which is largely restricted to a diagnostic
value, and foremost so for the element boron. However, we show that the boron
surface abundance in massive early type stars contains key information about
their foregoing evolution which is not obtainable otherwise. In particular, it
allows to constrain internal mixing processes and potential previous mass
transfer event for binary stars (even if the companion has disappeared). It may
also help solving the mystery of the slowly rotating nitrogen-rich massive main
sequence stars.Comment: 10 pages, 8 figures, to appear in proc. IAU-Symp. 268. C. Charbonnel
et al., eds
Methods for heat transfer and temperature field analysis of the insulated diesel phase 2 progress report
This report describes work done during Phase 2 of a 3 year program aimed at developing a comprehensive heat transfer and thermal analysis methodology for design analysis of insulated diesel engines. The overall program addresses all the key heat transfer issues: (1) spatially and time-resolved convective and radiative in-cylinder heat transfer, (2) steady-state conduction in the overall structure, and (3) cyclical and load/speed temperature transients in the engine structure. During Phase 2, radiation heat transfer model was developed, which accounts for soot formation and burn up. A methodology was developed for carrying out the multi-dimensional finite-element heat conduction calculations within the framework of thermodynamic cycle codes. Studies were carried out using the integrated methodology to address key issues in low heat rejection engines. A wide ranging design analysis matrix was covered, including a variety of insulation strategies, recovery devices and base engine configurations. A single cylinder Cummins engine was installed at Purdue University, and it was brought to a full operational status. The development of instrumentation was continued, concentrating on radiation heat flux detector, total heat flux probe, and accurate pressure-crank angle data acquisition
Metal Matrix Laminate Tailoring (MMLT) code: User's manual
The User's Manual for the Metal Matrix Laminate Tailoring (MMLT) program is presented. The code is capable of tailoring the fabrication process, constituent characteristics, and laminate parameters (individually or concurrently) for a wide variety of metal matrix composite (MMC) materials, to improve the performance and identify trends or behavior of MMC's under different thermo-mechanical loading conditions. This document is meant to serve as a guide in the use of the MMLT code. Detailed explanations of the composite mechanics and tailoring analysis are beyond the scope of this document, and may be found in the references. MMLT was developed by the Structural Mechanics Branch at NASA Lewis Research Center (LeRC)
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