1,232 research outputs found
General principles for the non-equilibrium relaxation of populations in quantum materials
We examine the problem of how excited populations of electrons relax after
they have been excited by a pump. We include three of the most important
relaxation processes: (i) impurity scattering; (ii) Coulomb scattering; and
(iii) electron-phonon scattering. The relaxation of an excited population of
electrons is one of the most fundamental processes measured in pump/probe
experiments, but its interpretation remains under debate. We show how several
common assumptions about non-equilibrium relaxation that are pervasive in the
field may not hold under quite general conditions. The analysis shows that
non-equilibrium relaxation is more complex than previously thought, but it
yields to recently developed theoretical methods in non-equilibrium theory. In
this work, we show how one can use many-body theory to properly interpret and
analyze these complex systems. We focus much of the discussion on implications
of these results for experiment.Comment: 13 pages, 10 figure
A method for computing chemical-equilibrium compositions of reacting-gas mixtures by reduction to a single iteration equation
Computing equilibrium chemical composition and thermodynamic properties of reacting gas mixtures by reduction to single iterative equatio
Modelling the alumina abundance of oxygen-rich evolved stars in the Large Magellanic Cloud
In order to determine the composition of the dust in the circumstellar
envelopes of oxygen-rich asymptotic giant branch (AGB) stars we have computed a
grid of modust radiative-transfer models for a range of dust compositions,
mass-loss rates, dust shell inner radii and stellar parameters. We compare the
resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec
Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars
with a mid-infrared excess. We use these models to fit a sample of 37 O-rich
AGB stars in the LMC with optically thin circumstellar envelopes, for which
535-m Spitzer infrared spectrograph (IRS) spectra and broadband
photometry from the optical to the mid-infrared are available. From the
modelling, we find mass-loss rates in the range to
M, and we show that a grain
mixture consisting primarily of amorphous silicates, with contributions from
amorphous alumina and metallic iron provides a good fit to the observed
spectra. Furthermore, we show from dust models that the AKARI [11][15]
versus [3.2][7] colour-colour diagram, is able to determine the fractional
abundance of alumina in O-rich AGB stars.Comment: 22 pages, 17 figures, accepted MNRA
Flamingo Vol. IX N 3
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Ollapod, Cornell. Untitled. Prose. 3.
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Smith, Reed. Untitled. Cartoon. 8.
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J.C.K. You Disgraceful Being, She Said . Picture. 10.
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O\u27Dell, Dorothy. Edifying Adventures of Alice (In Wonderland) . Prose. 12.
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Smrcina, Orville. Things That Freshmen Do Know . Picture. 13
On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants
We investigate the occurrence of crystalline silicates in oxygen-rich evolved
stars across a range of metallicities and mass-loss rates. It has been
suggested that the crystalline silicate feature strength increases with
increasing mass-loss rate, implying a correlation between lattice structure and
wind density. To test this, we analyse Spitzer IRS and Infrared Space
Observatory SWS spectra of 217 oxygen-rich asymptotic giant branch stars and 98
red supergiants in the Milky Way, the Large and Small Magellanic Clouds and
Galactic globular clusters. These encompass a range of spectral morphologies
from the spectrally-rich which exhibit a wealth of crystalline and amorphous
silicate features to 'naked' (dust-free) stars. We combine spectroscopic and
photometric observations with the GRAMS grid of radiative transfer models to
derive (dust) mass-loss rates and temperature. We then measure the strength of
the crystalline silicate bands at 23, 28 and 33 microns. We detect crystalline
silicates in stars with dust mass-loss rates which span over 3 dex, down to
rates of ~10^-9 solar masses/year. Detections of crystalline silicates are more
prevalent in higher mass-loss rate objects, though the highest mass-loss rate
objects do not show the 23-micron feature, possibly due to the low temperature
of the forsterite grains or it may indicate that the 23-micron band is going
into absorption due to high column density. Furthermore, we detect a change in
the crystalline silicate mineralogy with metallicity, with enstatite seen
increasingly at low metallicity.Comment: Accepted for publication in MNRAS, 24 pages, 16 figure
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