56,203 research outputs found
Massive star evolution in close binaries:conditions for homogeneous chemical evolution
We investigate the impact of tidal interactions, before any mass transfer, on
various properties of the stellar models. We study the conditions for obtaining
homogeneous evolution triggered by tidal interactions, and for avoiding any
Roche lobe overflow during the Main-Sequence phase. We consider the case of
rotating stars computed with a strong coupling mediated by an interior magnetic
field. In models without any tidal interaction (single stars and wide
binaries), homogeneous evolution in solid body rotating models is obtained when
two conditions are realized: the initial rotation must be high enough, the loss
of angular momentum by stellar winds should be modest. This last point favors
metal-poor fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is high enough
(typically a time-averaged surface velocities during the Main-Sequence phase
above 250 km s), whatever the mass losses. In close binaries, mixing is
stronger at higher than at lower metallicities. Homogeneous evolution is thus
favored at higher metallicities. Roche lobe overflow avoidance is favored at
lower metallicities due to the fact that stars with less metals remain more
compact. We study also the impact of different processes for the angular
momentum transport on the surface abundances and velocities in single and close
binaries. In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in binary or
single star models. In contrast, models computed with mild coupling may produce
strong surface enrichments associated to low surface velocities. Close binary
models may be of interest for explaining homogeneous massive stars, fast
rotating Wolf-Rayet stars, and progenitors of long soft gamma ray bursts, even
at high metallicities.Comment: 21 pages, 13 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Geometric stabilization of extended S=2 vortices in two-dimensional photonic lattices: theoretical analysis, numerical computation and experimental results
In this work, we focus our studies on the subject of nonlinear discrete
self-trapping of S=2 (doubly-charged) vortices in two-dimensional photonic
lattices, including theoretical analysis, numerical computation and
experimental demonstration. We revisit earlier findings about S=2 vortices with
a discrete model, and find that S=2 vortices extended over eight lattice sites
can indeed be stable (or only weakly unstable) under certain conditions, not
only for the cubic nonlinearity previously used, but also for a saturable
nonlinearity more relevant to our experiment with a biased photorefractive
nonlinear crystal. We then use the discrete analysis as a guide towards
numerically identifying stable (and unstable) vortex solutions in a more
realistic continuum model with a periodic potential. Finally, we present our
experimental observation of such geometrically extended S=2 vortex solitons in
optically induced lattices under both self-focusing and self-defocusing
nonlinearities, and show clearly that the S=2 vortex singularities are
preserved during nonlinear propagation
Quantum Dynamical - Matrix with Spectral Parameter from Fusion
A quantum dynamical -matrix with spectral parameter is constructed
by fusion procedure. This spin-1 -matrix is connected with Lie
algebra and does not satisfy the condition of translation invariance.Comment: 6 pages, LaTeX, no figure
VISHNU hybrid model for viscous QCD matter at RHIC and LHC energies
In this proceeding, we briefly describe the viscous hydrodynamics + hadron
cascade hybrid model VISHNU for relativistic heavy ion collisions and report
the current status on extracting the QGP viscosity from elliptic flow data.Comment: 4 pages, 1 figure, the proceedings of 7th International Workshop on
Critical Point and Onset of Deconfinement, Wuhan, China, Nov. 7-11, 201
Theoretical Study on Rotational Bands and Shape Coexistence of {Tl} in the Particle Triaxial-Rotor Model
By taking the particle triaxial-rotor model with variable moment of inertia,
we investigate the energy spectra, the deformations and the single particle
configurations of the nuclei Tl systemically. The calculated
energy spectra agree with experimental data quite well. The obtained results
indicate that the aligned bands observed in Tl originate from
the , , proton
configuration coupled to a prolate deformed core, respectively. Whereas, the
negative parity bands built upon the isomeric states in
Tl are formed by a proton with the
configuration coupled to a core with triaxial oblate deformation, and the
positive parity band on the isomeric state in Tl is
generated by a proton with configuration coupled to a
triaxial oblate core.Comment: 16 pages, 5 figures. To appear in Physical Review
Influence of Primary Cosmic Radiation Mass Composition on the Estimation of Eas Energy
At the Yakutsk EAS array E_em is determined by using measurements of EAS
Cherenkov light flux and charged particle flux. It is known from calculations
that these characteristics depend on a sort of primary particle and, therefore,
the estimation of E_em depends on a primary particle mass. In the work the
dependence of the E_em/E_0 ratio on the energy is given and experimental data
are compared with calculations by the QGSJET model. The calculations have been
carried out for the primary proton and iron nucleus. The average calculated
meaning of the value of E_em/E_0 ratio (between the proton and iron nucleus)
within experimental errors is in agreement with experimental data that doesnt
contradict to the mixed mass composition of primary cosmic radiation.Comment: 19th European Cosmic Ray Symposium. Aug 30 - Sep 3 2004, Florence,
Italy. 3 pages, 1 figure. Subbmitted for publication in International Journal
of Modern Physics
Very Long Baseline Array observations of the Intraday Variable source J1128+592
Short time-scale flux density variations of flat spectrum radio sources are
often explained by the scattering of radio waves in the turbulent, ionized
Interstellar Matter of the Milky Way. One of the most convincing observational
arguments in favor of this is the annual modulation of the variability
time-scale caused by the Earth orbital motion around the Sun. J1128+592 is an
IDV source with a possible annual modulation in its variability time-scale. We
observed the source in 6 epochs with the VLBA at 5, 8 and 15 GHz in total
intensity and polarization. The VLBA observations revealed an east-west
oriented core-jet structure. Its position angle agrees with the angle of
anisotropy derived from the annual modulation model. No significant long-term
structural changes were observed with VLBI on mas-scales, however, compared to
archival data, the VLBI core size is expanded. This expansion offers a possible
explanation to the observed decrease of the strength of IDV. VLBI polarimetry
revealed significant changes in the electric vector position angle and Rotation
Measure of the core and jet. Part of the observed RM variability could be
attributed to a scattering screen (37 pc distance), which covers the source
(core and jet) and which may be responsible for the IDV. Superposition of
polarized sub-components below the angular resolution limit may affect the
observed RM as well.Comment: accepted for A&A (11 pages, 11 figures
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