383 research outputs found
Nucleosynthesis imprints from different Type Ia Supernova explosion scenarios and implications for galactic chemical evolution
We analyze the nucleosynthesis yields of various Type Ia supernova explosion
simulations including pure detonations in sub- Chandrasekhar mass white dwarfs,
double detonations and pure helium detonations of sub-Chandrasekhar mass white
dwarfs with an accreted helium envelope, a violent merger model of two white
dwarfs and deflagrations as well as delayed detonations in Chandrasekhar mass
white dwarfs. We focus on the iron peak elements Mn, Zn and Cu. To this end, we
also briefly review the different burning regimes and production sites of these
elements as well as the results of abundance measurements and several galactic
chemical evolution studies. We find that super-solar values of [Mn/Fe] are not
restricted to Chandrasekhar mass explosion models. Scenarios including a helium
detonation can significantly contribute to the production of Mn, in particular
the models proposed for calcium-rich transients. Although Type Ia supernovae
are often not accounted for as production sites of Zn and Cu, our models
involving helium shell detonations can produce these elements in super-solar
ratios relative to Fe. Our results suggest a re-consideration of Type Ia
supernova yields in galactic chemical evolution models. A detailed comparison
with observations can provide new insight into the progenitor and explosion
channels of these events.Comment: 15 paged, 8 figures, accepted for publication in A&
The Infrared Continuum Sizes of Be Star Disks
We present an analysis of the near-infrared continuum emission from the
circumstellar gas disks of Be stars using a radiative transfer code for a
parametrized version of the viscous decretion disk model. This isothermal gas
model creates predicted images that we use to estimate the HWHM emission radius
along the major axis of the projected disk and the spatially integrated flux
excess at wavelengths of 1.7, 2.1, 4.8, 9, and 18 ?m. We discuss in detail the
effect of the disk base density, inclination angle, stellar effective
temperature, and other physical parameters on the derived disk sizes and color
excesses. We calculate color excess estimates relative to the stellar V -band
flux for a sample of 130 Be stars using photometry from 2MASS and the AKARI
infrared camera all-sky survey. The color excess relations from our models make
a good match of the observed color excesses of Be stars. We also present our
results on the projected size of the disk as a function of wavelength for the
classical Be star ? Tauri, and we show that the model predictions are
consistent with interferometric observations in the H, K', and 12 \mu m bands
Thermodynamic Phase Diagram of the Quantum Hall Skyrmion System
We numerically study the interacting quantum Hall skyrmion system based on
the Chern-Simons action. By noticing that the action is invariant under global
spin rotations in the spin space with respect to the magnetic field direction,
we obtain the low-energy effective action for a many skyrmion system.
Performing extensive molecular dynamics simulations, we establish the
thermodynamic phase diagram for a many skyrmion system.Comment: 4 pages, RevTex, 2 postscript figure
An atlas of 2.4 to 4.1 microns ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with the
Short Wavelength Spectrometer (SWS) during the Post-Helium program of the
Infrared Space Observatory (ISO). This program is aimed at extending the Morgan
& Keenan classification scheme into the near-infrared. Later type stars will be
discussed in a seperate publication. The observations consist of 57 SWS
Post-Helium spectra from 2.4 to 4.1 microns, supplemented with 10 spectra
acquired during the nominal mission with a similar observational setting. For
B-type stars, this sample provides ample spectral converage in terms of subtype
and luminosity class. For O-type stars,the ISO sample is coarse and therefore
is complemented with 8 UKIRT L'-band observations. In terms of the presence of
diagnostic lines, the L'-band is likely the most promising of the near-infrared
atmospheric windows for the study of the physical properties of B stars.
Specifically, this wavelength interval contains the Brackett alpha, Pfund
gamma, and other Pfund lines which are probes of spectral type, luminosity
class and mass loss. Here, we present simple empirical methods based on the
lines present in the 2.4 to 4.1 microns interval that allow the determination
of: the spectral type of B dwarfs and giants to within two subtypes; the
luminosity class of B stars to within two classes; the mass-loss rate of O
stars and B supergiants to within 0.25 dex.Comment: 19 pages, 11 Postscript figures, accepted by A&
Evaluating Adults With Idiopathic Pancreatitis for Genetic Predisposition: Higher Prevalence of Abnormal Results With Use of Complete Gene Sequencing
OBJECTIVES: In adults with unexplained pancreatitis, the yield of complete gene versus select exosome sequencing on mutation detection and distinguishing clinical characteristics associated with mutations requires clarification. We sought to (1) compare frequency of mutations identified using different techniques and (2) compare clinical characteristics between adults with and without mutations.
METHODS: This is a cohort study of adults with unexplained pancreatitis who underwent genetic testing between January 2008 and December 2012. We compare probabilities of having a positive mutation with complete gene sequencing versus alternatives and describe differences in characteristics among patients with and without mutations.
RESULTS: Of the 370 patients, 67 (18%) had a genetic mutation; 24 (6%) were of high risk. Mutations were significantly more prevalent with use of complete sequencing (42%) versus other approaches (8%, P < 0.0001). Most (44/67, 66%) with a mutation had no family history. Those with high-risk mutations were more likely to have a family history of chronic pancreatitis (21% vs 4%, P = 0.002). Patients with pancreas divisum were more likely to have mutations (27% vs 14%, P = 0.0007).
CONCLUSION: Among individuals with adult-onset pancreatic disease, the probability of finding any mutation, including high risk, is significantly higher using complete gene sequencing. The impact on patients and providers requires further investigation
Zero-temperature phase diagram of binary boson-fermion mixtures
We calculate the phase diagram for dilute mixtures of bosons and fermions at
zero temperature. The linear stability conditions are derived and related to
the effective boson-induced interaction between the fermions. We show that in
equilibrium there are three possibilities: a) a single uniform phase, b) a
purely fermionic phase coexisting with a purely bosonic one and c) a purely
fermionic phase coexisting with a mixed phase.Comment: 8 pages, revtex, 3 postscript figures; NORDITA-1999/71 C
Sliding motion of a two-dimensional Wigner crystal in a strong magnetic field
We study the sliding state of a two-dimensional Wigner crystal in a strong
magnetic field and a random impurity potential. Using a high-velocity
perturbation theory, we compute the nonlinear conductivity, various correlation
functions, and the interference effects arising in combined AC + DC electric
effects, including the Shapiro anomaly and the linear response to an AC field.
Disorder is found to induce mainly transverse distortions in the sliding state
of the lattice. The Hall resistivity retains its classical value. We find that,
within the large velocity perturbation theory, free carriers which affect the
longitudinal phonon modes of the Wigner crystal do not change the form of the
nonlinear conductivity. We compare the present sliding Wigner crystal in a
strong magnetic field to the conventional sliding charge-density wave systems.
Our result for the nonlinear conductivity agrees well with the
characteristics measured in some experiments at low temperatures or large
depinning fields, for the insulating phases near filling factor = 1/5. We
summarize the available experimental data, and point out the differences among
them.Comment: appeared in RPB vol. 50, 4600 (1994); LaTex file; 3 figures available
from [email protected]
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