6,105 research outputs found
Spectral sequences of Type Ia supernovae. I. Connecting normal and sub-luminous SN Ia and the presence of unburned carbon
Type Ia supernovae are generally agreed to arise from thermonuclear
explosions of carbon-oxygen white dwarfs. The actual path to explosion,
however, remains elusive, with numerous plausible parent systems and explosion
mechanisms suggested. Observationally, type Ia supernovae have multiple
subclasses, distinguished by their lightcurves and spectra. This raises the
question whether these reflect that multiple mechanisms occur in nature, or
instead that explosions have a large but continuous range of physical
properties. We revisit the idea that normal and 91bg-like supernovae can be
understood as part of a spectral sequence, in which changes in temperature
dominate. Specifically, we find that a single ejecta structure is sufficient to
provide reasonable fits of both the normal type Ia supernova SN~2011fe and the
91bg-like SN~2005bl, provided that the luminosity and thus temperature of the
ejecta are adjusted appropriately. This suggests that the outer layers of the
ejecta are similar, thus providing some support of a common explosion
mechanism. Our spectral sequence also helps to shed light on the conditions
under which carbon can be detected in pre-maximum SN~Ia spectra -- we find that
emission from iron can "fill in" the carbon trough in cool SN~Ia. This may
indicate that the outer layers of the ejecta of events in which carbon is
detected are relatively metal poor compared to events where carbon is not
detected
Multiparticle Interference, GHZ Entanglement, and Full Counting Statistics
We investigate the quantum transport in a generalized N-particle Hanbury
Brown--Twiss setup enclosing magnetic flux, and demonstrate that the Nth-order
cumulant of current cross correlations exhibits Aharonov-Bohm oscillations,
while there is no such oscillation in all the lower-order cumulants. The
multiparticle interference results from the orbital Greenberger-Horne-Zeilinger
entanglement of N indistinguishable particles. For sufficiently strong
Aharonov-Bohm oscillations the generalized Bell inequalities may be violated,
proving the N-particle quantum nonlocality.Comment: 4 pages, 1 figure, published versio
Spectral modeling of type II supernovae. I. Dilution factors
We present substantial extensions to the Monte Carlo radiative transfer code
TARDIS to perform spectral synthesis for type II supernovae. By incorporating a
non-LTE ionization and excitation treatment for hydrogen, a full account of
free-free and bound-free processes, a self-consistent determination of the
thermal state and by improving the handling of relativistic effects, the
improved code version includes the necessary physics to perform spectral
synthesis for type II supernovae to high precision as required for the reliable
inference of supernova properties. We demonstrate the capabilities of the
extended version of TARDIS by calculating synthetic spectra for the
prototypical type II supernova SN1999em and by deriving a new and independent
set of dilution factors for the expanding photosphere method. We have
investigated in detail the dependence of the dilution factors on photospheric
properties and, for the first time, on changes in metallicity. We also compare
our results with two previously published sets of dilution factors by Eastman
et al. (1996) and by Dessart & Hillier (2005), and discuss the potential
sources of the discrepancies between studies.Comment: 16 pages, 12 figures, 2 tables, accepted for publication in A&
A Web/Grid Services Approach for Integration of Virtual Clinical & Research Environments
Clinicans have responsibilities for audit and research, often participating in projects with basic scientist colleagues. Our work in a regional teaching hospital setting involves collaboration with the medical school computer services and builds upon work developed in computer science department as part of the Collaborative Orthopaedic Research Environment (CORE) project[1]. This has established a pilot study for proof of concept work. Users are mapped to a personal profile implemented using XML and a service oriented architecture (SOA)[2,3]. This bridges the e-Health and e-Science domains, addressing some of the basic questions of security and uptake
Electron Pair Resonance in the Coulomb Blockade
We study many-body corrections to the cotunneling current via a localized
state with energy at large bias voltages . We show that the
transfer of {\em electron pairs}, enabled by the Coulomb repulsion in the
localized level, results in ionization resonance peaks in the third derivative
of the current with respect to , centered at . Our
results predict the existence of previously unnoticed structure within
Coulomb-blockade diamonds.Comment: 5 pages, 4 figure
Spectral Sequences of Type Ia Supernovae. I. Connecting Normal and Subluminous SNe Ia and the Presence of Unburned Carbon
On the gamma-ray emission of Type Ia Supernovae
A multi-dimension, time-dependent Monte Carlo code is used to compute sample
gamma-ray spectra to explore whether unambiguous constraints could be obtained
from gamma-ray observations of Type Ia supernovae. Both spherical and
aspherical geometries are considered and it is shown that moderate departures
from sphericity can produce viewing-angle effects that are at least as
significant as those caused by the variation of key parameters in
one-dimensional models. Thus gamma-ray data could in principle carry some
geometrical information, and caution should be applied when discussing the
value of gamma-ray data based only on one-dimensional explosion models. In
light of the limited sensitivity of current gamma-ray observatories, the
computed theoretical spectra are studied to revisit the issue of whether useful
constraints could be obtained for moderately nearby objects. The most useful
gamma-ray measurements are likely to be of the light curve and time-dependent
hardness ratios, but sensitivity higher than currently available, particularly
at relatively hard energies (~2-3 MeV), is desirable.Comment: 10 pages, 8 figures. Accepted by MNRAS. Minor changes to clarify
discussion in Section
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