5,928 research outputs found
The Glass Transition and the Jarzynski Equality
A simple model featuring a double well potential is used to represent a
liquid that is quenched from an ergodic state into a history dependent glassy
state. Issues surrounding the application of the Jarzynski Equality to glass
formation are investigated. We demonstrate that the Jarzynski Equality gives
the free energy difference between the initial state and the state we would
obtain if the glass relaxed to true thermodynamic equilibrium. We derive new
variations of the Jarzynski Equality which are relevant to the history
dependent glassy state rather than the underlying equilibrium state. It is
shown how to compute the free energy differences for the nonequilibrium history
dependent glassy state such that it remains consistent with the standard
expression for the entropy and with the second law inequality.Comment: 16 pages, 5 figure
Dust in a Type Ia Supernova Progenitor: Spitzer Spectroscopy of Kepler's Supernova Remnant
Characterization of the relatively poorly-understood progenitor systems of
Type Ia supernovae is of great importance in astrophysics, particularly given
the important cosmological role that these supernovae play. Kepler's Supernova
Remnant, the result of a Type Ia supernova, shows evidence for an interaction
with a dense circumstellar medium (CSM), suggesting a single-degenerate
progenitor system. We present 7.5-38 m infrared (IR) spectra of the
remnant, obtained with the {\it Spitzer Space Telescope}, dominated by emission
from warm dust. Broad spectral features at 10 and 18 m, consistent with
various silicate particles, are seen throughout. These silicates were likely
formed in the stellar outflow from the progenitor system during the AGB stage
of evolution, and imply an oxygen-rich chemistry. In addition to silicate dust,
a second component, possibly carbonaceous dust, is necessary to account for the
short-wavelength IRS and IRAC data. This could imply a mixed chemistry in the
atmosphere of the progenitor system. However, non-spherical metallic iron
inclusions within silicate grains provide an alternative solution. Models of
collisionally-heated dust emission from fast shocks ( 1000 km s)
propagating into the CSM can reproduce the majority of the emission associated
with non-radiative filaments, where dust temperatures are K, but
fail to account for the highest temperatures detected, in excess of 150 K. We
find that slower shocks (a few hundred km s) into moderate density
material ( cm) are the only viable source of heating
for this hottest dust. We confirm the finding of an overall density gradient,
with densities in the north being an order of magnitude greater than those in
the south.Comment: Accepted by ApJ. 11 pages, 5 figures, 1 table. Produced using
emulateapj forma
Identification of structure in condensed matter with the topological cluster classification
We describe the topological cluster classification (TCC) algorithm. The TCC
detects local structures with bond topologies similar to isolated clusters
which minimise the potential energy for a number of monatomic and binary simple
liquids with particles. We detail a modified Voronoi bond detection
method that optimizes the cluster detection. The method to identify each
cluster is outlined, and a test example of Lennard-Jones liquid and crystal
phases is considered and critically examined.Comment: 28 pages, 28 figure
Magnetic-Field Amplification in the Thin X-ray Rims of SN1006
Several young supernova remnants (SNRs), including SN1006, emit synchrotron
X-rays in narrow filaments, hereafter thin rims, along their periphery. The
widths of these rims imply 50 to 100 G fields in the region immediately
behind the shock, far larger than expected for the interstellar medium
compressed by unmodified shocks, assuming electron radiative losses limit rim
widths. However, magnetic-field damping could also produce thin rims. Here we
review the literature on rim width calculations, summarizing the case for
magnetic-field amplification. We extend these calculations to include an
arbitrary power-law dependence of the diffusion coefficient on energy, . Loss-limited rim widths should shrink with increasing photon
energy, while magnetic-damping models predict widths almost independent of
photon energy. We use these results to analyze Chandra observations of SN 1006,
in particular the southwest limb. We parameterize the full widths at half
maximum (FWHM) in terms of energy as FWHM . Filament
widths in SN1006 decrease with energy; to , implying
magnetic field amplification by factors of 10 to 50, above the factor of 4
expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules
out magnetic damping models. It also favors short mean free paths (small
diffusion coefficients) and strong dependence of on energy ().Comment: Accepted by ApJ, 49 pages, 10 figure
The First Reported Infrared Emission from the SN 1006 Remnant
We report results of infrared imaging and spectroscopic observations of the
SN 1006 remnant, carried out with the Spitzer Space Telescope. The 24 micron
image from MIPS clearly shows faint filamentary emission along the northwest
rim of the remnant shell, nearly coincident with the Balmer filaments that
delineate the present position of the expanding shock. The 24 micron emission
traces the Balmer filaments almost perfectly, but lies a few arcsec within,
indicating an origin in interstellar dust heated by the shock. Subsequent
decline in the IR behind the shock is presumably due largely to grain
destruction through sputtering. The emission drops far more rapidly than
current models predict, however, even for a higher proportion of small grains
than would be found closer to the Galactic plane. The rapid drop may result in
part from a grain density that has always been lower -- a relic effect from an
earlier epoch when the shock was encountering a lower density -- but higher
grain destruction rates still seem to be required. Spectra from three positions
along the NW filament from the IRS instrument all show only a featureless
continuum, consistent with thermal emission from warm dust. The dust-to-gas
mass ratio in the pre-shock interstellar medium is lower than that expected for
the Galactic ISM -- as has also been observed in the analysis of IR emission
from other SNRs but whose cause remains unclear. As with other SN Ia remnants,
SN 1006 shows no evidence for dust grain formation in the supernova ejecta.Comment: 24 pages, 6 figure
Chandra and Hubble Study of a New Transient X-ray Source in M31
We present X-ray and optical observations of a new transient X-ray source in
M31 first detected 23-May-2004 at R.A.=00:43:09.940 +/- 0.65'',
Dec.=41:23:32.49 +/- 0.66''. The X-ray lightcurve shows two peaks separated by
several months, reminiscent of many Galactic X-ray novae. The location and
X-ray spectrum of the source suggest it is a low mass X-ray binary (LMXB).
Follow-up HST ACS observations of the location both during and after the
outburst provide a high-confidence detection of variability for one star within
the X-ray position error ellipse. This star has B ~ 1 mag, and there is
only a ~1% chance of finding such a variable in the error ellipse. We consider
this star a good candidate for the optical counterpart of the X-ray source. The
luminosity of this candidate provides a prediction for the orbital period of
the system of 2.3 days.Comment: 17 pages, 3 figures, 4 tables, accepted for publication in Ap
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