660 research outputs found
An embedded formulation with conforming
Use of strong discontinuities with satisfaction of compatibilit
A Continuous-Discontinuous Approach to Simulate Heat Transfer in Fractured Media
A macroscopic framework to model heat transfer in materials and composites, subjected to physical degradation, is proposed. The framework employs the partition of unity concept and captures the change from conduction-dominated transfer in the initial continuum state to convection and radiation-dominated transfer in the damaged state. The underlying model can be directly linked to a mechanical cohesive zone model, governing the initiation and subsequent growth and coalescence of micro-cracks. The methodology proved to be applicable for quasi-static, periodic, and transient problem
Objective multiscale analysis of random heterogeneous materials
The multiscale framework presented in [1, 2] is assessed in this contribution for a study of random heterogeneous materials. Results are compared to direct numerical simulations (DNS) and the sensitivity to user-defined parameters such as the domain decomposition type and initial coarse scale resolution is reported. The parallel performance of the implementation is studied for different domain decompositions
Population synthesis of classical low-mass X-ray binaries in the Galactic Bulge
Aims. We model the present-day population of 'classical' low-mass X-ray
binaries (LMXBs) with neutron star accretors, which have hydrogen-rich donor
stars. Their population is compared with that of hydrogen-deficient LMXBs,
known as ultracompact X-ray binaries (UCXBs). We model the observable LMXB
population and compare it to observations. Methods. We combine the binary
population synthesis code SeBa with detailed LMXB evolutionary tracks to model
the size and properties of the present-day LMXB population in the Galactic
Bulge. Whether sources are persistent or transient, and what their
instantaneous X-ray luminosities are, is predicted using the thermal-viscous
disk instability model. Results. We find a population of ~2.1 x 10^3 LMXBs with
neutron star accretors. Of these about 15 - 40 are expected to be persistent
(depending on model assumptions), with luminosities higher than 10^35 erg s^-1.
About 7 - 20 transient sources are expected to be in outburst at any given
time. Within a factor of two these numbers are consistent with the observed
population of bright LMXBs in the Bulge. This gives credence to our prediction
of the existence of a population of ~1.6 x 10^3 LMXBs with low donor masses
that have gone through the period minimum, and have present-day mass transfer
rates below 10^-11 Msun yr^-1. Conclusions. Even though the observed population
of hydrogen-rich LMXBs in the Bulge is larger than the observed population of
(hydrogen-deficient) UCXBs, the latter have a higher formation rate. While
UCXBs may dominate the total LMXB population at the present, the majority would
be very faint, or may have become detached and produced millisecond radio
pulsars. In that case UCXBs would contribute significantly more to the
formation of millisecond radio pulsars than hydrogen-rich LMXBs. [abridged]Comment: 8 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysics. v2: minor language correction
The dynamics of the nebula M1-67 around the run-away Wolf-Rayet star WR 124
A new point of view on the dynamics of the circumstellar nebula M1-67 around the run-away Wolf-Rayet (WR) star WR 124 is presented. We found that it has been interacting with the surrounding ISM and has formed a bow shock due to its high velocity of about 180 km/s relative to the local ISM. The star is about 1.3 parsec away from the front of this bow shock. The outbursts that are responsible for the nebula are assumed to be discrete outbursts that occurred inside this bow shock. The ejecta collide with this bow shock shortly after the outburst. After the collision, they are dragged away by the pressure of the ISM, along the surface of the bow shock. The bow shock is oriented in such way that we are looking from the rear into this paraboloid, almost along the main axis. Evidence for this is given firstly by the fact that the far hemisphere is much brighter than the near hemisphere, secondly by the fact that there is hardly any emission found with radial velocities higher than the star's radial velocity, thirdly by the fact that the star looks to be in the centre of the nebula, as seen from Earth, and finally by the asymmetric overall velocity distribution of the nebula, which indicates higher radial velocities in the centre of the nebula, and lower velocities near the edges. We find evidence for at least two discrete outbursts that occurred inside this bow shock. For these outbursts, we find expansion velocities of about 150 km/s and dynamical timescales of about 8 and 20 kyr, which are typical values for LBV outbursts. We therefore conclude that M1-67 originates from several outbursts that occurred inside the bow shock around WR 124, during an LBV phase that preceded the current WR phase of the star
Coulomb Distortion Effects for (e,e'p) Reactions at High Electron Energy
We report a significant improvement of an approximate method of including
electron Coulomb distortion in electron induced reactions at momentum transfers
greater than the inverse of the size of the target nucleus. In particular, we
have found a new parametrization for the elastic electron scattering phase
shifts that works well at all electron energies greater than 300 . As an
illustration, we apply the improved approximation to the reaction
from medium and heavy nuclei. We use a relativistic ``single particle'' model
for as as applied to and to recently measured data
at CEBAF on to investigate Coulomb distortion effects while
examining the physics of the reaction.Comment: 14 pages, 3 figures, PRC submitte
On gradient-enhanced damage and plasticity models for failure in quasi-brittle and frictional materials
Exploring short gamma-ray bursts as gravitational-wave standard sirens
Recent observations support the hypothesis that a large fraction of
"short-hard" gamma-ray bursts (SHBs) are associated with compact binary
inspiral. Since gravitational-wave (GW) measurements of well-localized
inspiraling binaries can measure absolute source distances, simultaneous
observation of a binary's GWs and SHB would allow us to independently determine
both its luminosity distance and redshift. Such a "standard siren" (the GW
analog of a standard candle) would provide an excellent probe of the relatively
nearby universe's expansion, complementing other standard candles. In this
paper, we examine binary measurement using a Markov Chain Monte Carlo technique
to build the probability distributions describing measured parameters. We
assume that each SHB observation gives both sky position and the time of
coalescence, and we take both binary neutron stars and black hole-neutron star
coalescences as plausible SHB progenitors. We examine how well parameters
particularly distance) can be measured from GW observations of SHBs by a range
of ground-based detector networks. We find that earlier estimates overstate how
well distances can be measured, even at fairly large signal-to-noise ratio. The
fundamental limitation to determining distance proves to be a degeneracy
between distance and source inclination. Overcoming this limitation requires
that we either break this degeneracy, or measure enough sources to broadly
sample the inclination distribution. (Abridged)Comment: 19 pages, 10 figures. Accepted for publication in ApJ; this version
incorporates referee's comments and criticism
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