397 research outputs found
Rotating massive O stars with non-spherical 2D winds
We present solutions for the velocity field and mass-loss rates for 2D
axisymmetric outflows, as well as for the case of mass accretion through the
use of the Lambert W-function. For the case of a rotating radiation-driven wind
the velocity field is obtained analytically using a parameterised description
of the line acceleration that only depends on radius r at any given latitude
. The line acceleration g(r) is obtained from Monte-Carlo multi-line
radiative transfer calculations. The critical/sonic point of our equation of
motion varies with latitude . Furthermore, an approximate analytical
solution for the supersonic flow of a rotating wind is derived, which is found
to closely resemble the exact solution. For the simultaneous solution of the
mass-loss rate and velocity field, we use the iterative method of our 1D method
extended to the non-spherical 2D case. We apply the new theoretical expressions
with our iterative method to the stellar wind from a differentially rotating 40
O5-V main sequence star as well as to a 60 O-giant star,
and we compare our results to previous studies that are extensions of the
Castor et al. (1975, ApJ, 195, 157) CAK formalism. Next, we account for the
effects of oblateness and gravity darkening. Our numerical results predict an
equatorial decrease of the mass-loss rate, which would imply that
(surface-averaged) total mass-loss rates are lower than for the spherical 1D
case, in contradiction to the Maeder & Meynet (2000, A&A, 361, 159) formalism
that is oftentimes employed in stellar evolution calculations for rotating
massive stars. To clarify the situation in nature we discuss observational
tests to constrain the shapes of large-scale 2D stellar winds.Comment: 20 pages, 4 figures, 7 tables, accepted for publication in A&A, (one
corrected sentence in sect. 4.1.), a generalization of arXiv paper:
arXiv:0810.190
The Role of Diffusive Shock Acceleration on Nonequilibrium Ionization in Supernova Remnant Shocks II: Emitted Spectra
We present a grid of nonequilibrium ionization models for the X-ray spectra
from supernova remnants undergoing efficient diffusive shock acceleration. The
calculation follows the hydrodynamics of the blast wave as well as the
time-dependent ionization of the plasma behind the shock. The ionization state
is passed to a plasma emissivity code to compute the thermal X-ray emission,
which is combined with the emission from nonthermal synchrotron emission to
produce a self-consistent model for the thermal and nonthermal emission from
cosmic-ray dominated shocks. We show how plasma diagnostics such as the
G'-ratio of He-like ions, defined as the ratio of the sum of the
intercombination, forbidden, and satellite lines to the resonance line, can
vary with acceleration efficiency, and discuss how the thermal X-ray emission,
when the time-dependent ionization is not calculated self-consistently with the
hydrodynamics, can differ from the thermal X-ray emission from models which do
account for the hydrodynamics. Finally we compare the thermal X-ray emission
from models which show moderate acceleration (~ 35%) to the thermal X-ray
emission from test-particle models.Comment: 17 pages, 12 figures. accepted for publication in the Astrophysical
Journa
Quark propagator from an improved staggered action in Laplacian and Landau gauges
Studies of gauge dependent quantities are afflicted with Gribov copies, but
Laplacian gauge fixing provides one possible solution to this problem. We
present results for the lattice quark propagator in both Landau and Laplacian
gauges using standard and improved staggered quark actions. The standard
Kogut-Susskind action has errors of \oa{2} while the improved ``Asqtad'' action
has \oa{4}, \oag{2}{2} errors and this improvement is seen in the quark
propagator. We demonstrate the application of tree-level corrections to these
actions and see that Landau and Laplacian gauges produce very similar results.
In addition, we test an ansatz for the quark mass function, with promising
results. In the chiral limit, the infrared quark mass, is found to
be MeV.Comment: 5 pages, 8 figs., Talk given at LHP workshop, Cairn
Particle Acceleration in Supernova Remnants and the Production of Thermal and Nonthermal Radiation
If highly efficient, cosmic ray production can have a significant effect on
the X-ray emission from SNRs as well as their dynamical evolution. Using
hydrodynamical simulations including diffusive shock acceleration, we produce
spectra for both the thermal and nonthermal forward shock emission. For a given
ambient density and explosion energy, we find that the position of the forward
shock at a given age is a strong function of the acceleration efficiency,
providing a signature of cosmic-ray production. Using an approximate treatment
for the ionization state of the plasma, we investigate the effects of slow vs.
rapid heating of the postshock electrons on the ratio of thermal to nonthermal
X-ray emission at the forward shock. We also investigate the effects of
magnetic field strength on the observed spectrum for efficient cosmic-ray
acceleration. The primary effect of a large field is a considerable flattening
of the nonthermal spectrum in the soft X-ray band. Spectral index measurements
from X-ray observations may thus be indicators of the postshock magnetic field
strength. The predicted gamma-ray flux from inverse-Compton (IC) scattering and
neutral pion decay is strongly affected by the ambient conditions and, for the
particular parameters used in our examples, the IC emission at E ~ 1 TeV
exceeds that from pion decay, although at both lower and higher energies this
trend is reversed for cases of high ambient density. More importantly, high
magnetic fields produce a steepening of the electron spectrum over a wide
energy range which may make it more difficult to differentiate between IC and
pion-decay emission solely by spectral shape.Comment: 30 pages, 12 figures, submitted to ApJ January 200
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Anisotropic material properties of the human uterus
The mechanical function of the uterus is crucial for the protection of the fetus during a healthy pregnancy. Early contractile activation of uterine tissue can lead to preterm labor and birth (PTB). In 2014, 9.56 percent of pregnancies ended in PTB; it is also the leading cause of death in children under five years of age. Characterizing the material properties of uterine tissue is important for understanding the mechanical failures of the uterus and the causes of PTB. In this study, a workflow of experiments and data processing techniques were employed. 78 uterine specimens were collected from consenting 28 patients who underwent hysterectomy. A four-level ramp-hold indentation test was performed. IFEA was performed to fit four material parameters to the experimental data: Young's Modulus E, Poisson’s ratio v, the fiber stiffness factor ksi, and the fiber angle concentration b. Within each uterus, significant differences in Young’s Modulus E and Poisson’s ratio n were observed at different locations and different layers, indicating the heterogeneity of the human uterine material properties. However, the fitted values for fiber stiffness x and angle concentration b exhibited a wide spread with no significant differences observed across comparison groups. There were also no obvious differences between patients with different parities, as suggested in previous studies
Lattice quark propagator in Landau and Laplacian gauges
Copyright © 2001 Published by Elsevier Science B.V. All rights reserved. Copyright © 2001. Submitted to Cornell University’s online archive www.arXiv.org in 2001 by Patrick O. Bowman. Post-print sourced from www.arxiv.org.We present results for the lattice quark propagator in both Landau and Laplacian gauges using standard and improved staggered quark actions. The standard Kogut-Susskind action has errors of \oa{2} while the improved ``Asqtad'' action has \oa{4}, \oag{2}{2} errors. This improvement is seen in the quark propagator. We demonstrate the application of tree-level corrections to these actions and see that Landau and Laplacian gauges produce very similar results.Patrick O. Bowman, Urs M. Heller and Anthony G. Williamshttp://www.elsevier.com/wps/find/journaldescription.cws_home/505717/description#descriptio
Gluon Propagator on Coarse Lattices in Laplacian Gauges
The Laplacian gauge is a nonperturbative gauge fixing that reduces to Landau
gauge in the asymptotic limit. Like Landau gauge, it respects Lorentz
invariance, but it is free of Gribov copies; the gauge fixing is unambiguous.
In this paper we study the infrared behavior of the lattice gluon propagator in
Laplacian gauge by using a variety of lattices with spacings from
to 0.35 fm, to explore finite volume and discretization effects. Three
different implementations of the Laplacian gauge are defined and compared. The
Laplacian gauge propagator has already been claimed to be insensitive to finite
volume effects and this is tested on lattices with large volumes.Comment: RevTex 4.0, 14 pages, 9 colour figures; Correction to Reference
Linking the concentrations of itraconazole and 2-hydroxypropyl-β-cyclodextrin in human intestinal fluids after oral intake of Sporanox<sup>®</sup>
In a previously performed small-scale clinical study, healthy volunteers were asked to ingest an oral solution of itraconazole (Sporanox®) containing 40% 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) (i) with or (ii) without a standardized volume of water (240 mL) after which gastrointestinal and blood samples were collected. Although omitting water during the administration of Sporanox® resulted in noticeably higher duodenal concentrations of itraconazole, systemic exposure was almost unaffected. It is assumed that this discrepancy can be explained by differences in the extent of entrapment of itraconazole in the duodenum caused by differential complexation depending on the concentration of cyclodextrins. To further substantiate this hypothesis, the quantification of HP-β-CD concentrations in the aspirated intestinal fluids was performed by LC-MS/MS. When comparing the intestinal concentrations of itraconazole and HP-β-CD for one single healthy volunteer (HV02) in both test conditions, an excellent correlation was observed (Spearman's rank coefficient of 0.96). Moreover, the data suggest that, similar to aqueous buffer media, also in human intestinal fluids a non-linear relationship exists between itraconazole solubility and HP-β-CD concentration (Ap-type profile; Spearman's rank coefficient of 0.78), indicating that higher order complexes are formed at higher concentrations of HP-β-CD. This difference in extent of entrapment in the inclusion complexes helps to understand the observed impact of water intake on precipitation and permeation behavior of itraconazole in man. Without water intake, higher HP-β-CD concentrations resulted in less precipitation and increased duodenal concentrations of itraconazole. On the other hand, the stronger interaction at higher HP-β-CD concentrations reduced the free fraction of the drug explaining that increased intraluminal concentrations of itraconazole were not translated into an enhanced uptake. In conclusion, quantifying the concentrations of the solubilizing agent HP-β-CD in human intestinal fluids appeared to be of crucial importance to interpret the intraluminal behavior of an orally administered cyclodextrin-based solution
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