1,105 research outputs found
A Hybrid Godunov Method for Radiation Hydrodynamics
From a mathematical perspective, radiation hydrodynamics can be thought of as
a system of hyperbolic balance laws with dual multiscale behavior (multiscale
behavior associated with the hyperbolic wave speeds as well as multiscale
behavior associated with source term relaxation). With this outlook in mind,
this paper presents a hybrid Godunov method for one-dimensional radiation
hydrodynamics that is uniformly well behaved from the photon free streaming
(hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and
to the strong equilibrium diffusion (hyperbolic) limit. Moreover, one finds
that the technique preserves certain asymptotic limits. The method incorporates
a backward Euler upwinding scheme for the radiation energy density and flux as
well as a modified Godunov scheme for the material density, momentum density,
and energy density. The backward Euler upwinding scheme is first-order accurate
and uses an implicit HLLE flux function to temporally advance the radiation
components according to the material flow scale. The modified Godunov scheme is
second-order accurate and directly couples stiff source term effects to the
hyperbolic structure of the system of balance laws. This Godunov technique is
composed of a predictor step that is based on Duhamel's principle and a
corrector step that is based on Picard iteration. The Godunov scheme is
explicit on the material flow scale but is unsplit and fully couples matter and
radiation without invoking a diffusion-type approximation for radiation
hydrodynamics. This technique derives from earlier work by Miniati & Colella
2007. Numerical tests demonstrate that the method is stable, robust, and
accurate across various parameter regimes.Comment: accepted for publication in Journal of Computational Physics; 61
pages, 15 figures, 11 table
Imaging sub-milliarcsecond stellar features with intensity interferometry using air Cherenkov telescope arrays
Recent proposals have been advanced to apply imaging air Cherenkov telescope
arrays to stellar intensity interferometry (SII). Of particular interest is the
possibility of model-independent image recovery afforded by the good (u,
v)-plane coverage of these arrays, as well as recent developments in phase
retrieval techniques. The capabilities of these instruments used as SII
receivers have already been explored for simple stellar objects, and here the
focus is on reconstructing stellar images with non-uniform radiance
distributions. We find that hot stars (T > 6000 K) containing hot and/or cool
localized regions (T \sim 500 K) as small as \sim 0.1 mas can be imaged at
short wavelengths ({\lambda} = 400 nm).Comment: Accepted for publication in MNRAS. 6 pages, 10 figure
Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream
The X-ray binary system GX301-2 consists of a neutron star in an eccentric
orbit accreting from the massive early-type star WRAY 977. It has previously
been shown that the X-ray orbital light curve is consistent with existence of a
gas stream flowing out from Wray 977 in addition to its strong stellar wind.
Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer (RXTE)/
All-Sky-Monitor (ASM) and pointed observations by the RXTE/ Proportional
Counter Array (PCA) over the past decade are analyzed. We analyze both the flux
and column density dependence on orbital phase. The wind and stream dynamics
are calculated for various system inclinations, companion rotation rates and
wind velocities, as well as parametrized by the stream width and density. These
calculations are used as inputs to determine both the expected accretion
luminosity and the column density along the line-of-sight to the neutron star.
The model luminosity and column density are compared to observed flux and
column density vs. orbital phase, to constrain the properties of the stellar
wind and the gas stream. We find that the change between bright and medium
intensity levels is primarily due to decreased mass loss in the stellar wind,
but the change between medium and dim intensity levels is primarily due to
decreased stream density. The mass-loss rate in the stream exceeds that in the
stellar wind by a factor of 2.5. The quality of the model fits is significantly
better for lower inclinations, favoring a mass for WRAY 977 of 53 to 62 Msun.Comment: 19 pages, 6 figure
Connective tissue activation. xxxvi. the origin, variety, distribution, and biologic fate of connective tissue activating peptide–iii isoforms: characteristics in patients with rheumatic, renal, and arterial disease
Objective. To determine the origin, distribution, and biologic fate of platelet-derived connective tissue activating peptide–III (CTAP-III), to define the relative amounts of the antigen forms (CTAP-III, betathromboglobulin [Β-TG], neutrophil activating peptide–2 [NAP-2]) in plasma of normal persons and those with rheumatic or end-stage renal disease, and to define the isoforms of CTAP-III in platelets, plasma, transudates, and tissue deposits. Methods. CTAP-III in plasma was measured by enzyme-linked immunosorbent assay, and growth promoting activity of CTAP-III isoforms was tested in synovial and peritoneal cell cultures by measuring increased synthesis of 14 C-glycosaminoglycan ( 14 C-GAG) and 3 H-DNA. Isolated CTAP-III was characterized by Western blotting, microsequencing, and mass spectrometry. Results. CTAP-III was the primary isoform of this antigen family in normal platelets and platelet-rich plasma; Β-TG and NAP-2 accounted for 90%), and Β-TG was the most rare (0–1%). Deposition of CTAP-III in tissues, such as synovium, spleen, and kidney, is associated with partial processing to NAP-2–like isoforms and the potential to induce neutrophil and fibroblast activation in patients with rheumatic or end-stage renal disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37798/1/1780360816_ftp.pd
HernioplastÃa Inguinal Electiva
Antecedentes: La hernioplastÃa es la técnica más utilizada para reparar la hernia inguinal.Objetivos: determinar las caracterÃsticas demográficas, tipos de hernia, clasificación y resultados de la cirugÃa.Pacientes y Método: Serie de 229 pacientes sometidos a hernioplastia inguinal electiva en la Primera Cátedra de ClÃnica Quirúrgica en el periodo 2005–2009; estudio descriptivo retrospectivo longitudinal con las siguientes variables: caracterÃsticas demográficas, co-morbilidad, tipo de hernia, clasificación de Gilbert, modalidad de reparación y resultados inmediatos.Resultados: La edad media fue de 46 años y 90 % eran varones; la hernia era indirecta en 84%, directa en 7% y mixtas en 5%. En 112 casos la hernia se situaba a la derecha, en 99 a la izquierda y en 18 bilateral. Se encontró hipertensión arterial en 46 pacientes, cardiopatÃa hipertensiva en 8, cardiopatÃa isquémica en 2, tabaquismo 5 y diabetes mellitus en 2 ; 10 pacientes tenÃan hipertrofia prostática, 5 asma o alergia a medicamentos y 5 trastornos psiquiátricos ; 18% correspondÃan al tipo I de Gilbert, 45% al tipo II, 18% al III, 4% al IV, 8% al V y el restante tipo VI y VII. Se empleó la técnica del Plugstein en 207 pacientes y la técnica de Lichtenstein en 22. Las complicaciones fueron: hematoma en 3 y seroma en 2. Un paciente desarrolló infección del sitio quirúrgico. Una recidiva precoz fue comprobada en 3 pacientes (1.3%).Conclusiones: la hernia inguinal es más frecuente en la 5a década y en el sexo masculino. La variedad más frecuente es la indirecta y la mayorÃa son de tipo II de Gilbert. La hernioplastia electiva permite obtener resultados inmediatos satisfactorios, con escasa recidiva
A dynamical magnetosphere model for periodic Halpha emission from the slowly rotating magnetic O star HD191612
The magnetic O-star HD191612 exhibits strongly variable, cyclic Balmer line
emission on a 538-day period. We show here that its variable Halpha emission
can be well reproduced by the rotational phase variation of synthetic spectra
computed directly from full radiation magneto-hydrodynamical simulations of a
magnetically confined wind. In slow rotators such as HD191612, wind material on
closed magnetic field loops falls back to the star, but the transient
suspension of material within the loops leads to a statistically overdense, low
velocity region around the magnetic equator, causing the spectral variations.
We contrast such "dynamical magnetospheres" (DMs) with the more steady-state
"centrifugal magnetospheres" of stars with rapid rotation, and discuss the
prospects of using this DM paradigm to explain periodic line emission from also
other non-rapidly rotating magnetic massive stars.Comment: 5 pages, 5 figures, accepted for publication in MNRAS letter
A hydrodynamic scheme for two-component winds from hot stars
We have developed a time-dependent two-component hydrodynamics code to
simulate radiatively-driven stellar winds from hot stars. We use a
time-explicit van Leer scheme to solve the hydrodynamic equations of a
two-component stellar wind. Dynamical friction due to Coulomb collisions
between the passive bulk plasma and the line-scattering ions is treated by a
time-implicit, semi-analytic method using a polynomial fit to the Chandrasekhar
function. This gives stable results despite the stiffness of the problem. This
method was applied to model stars with winds that are both poorly and
well-coupled. While for the former case we reproduce the mCAK solution, for the
latter case our solution leads to wind decoupling.Comment: accepted to Astronomy and Astrophysic
Numerical simulations of super-luminous supernovae of type IIn
We present numerical simulations that include 1-D Eulerian multi-group
radiation-hydrodynamics, 1-D non-LTE radiative transfer, and 2-D polarised
radiative transfer for super-luminous interacting supernovae (SNe). Our
reference model is a ~10Msun inner shell with 10^51erg ramming into a ~3Msun
cold outer shell (the circumstellar-medium, or CSM) that extends from 10^15cm
to 2x10^16cm and moves at 100km/s. We discuss the light curve evolution, which
cannot be captured adequately with a grey approach. In these interactions, the
shock-crossing time through the optically-thick CSM is much longer than the
photon diffusion time. Radiation is thus continuously leaking from the shock
through the CSM, in disagreement with the shell-shocked model that is often
invoked. Our spectra redden with time, with a peak distribution in the near-UV
during the first month gradually shifting to the optical range over the
following year. Initially Balmer lines exhibit a narrow line core and the broad
line wings that are characteristic of electron scattering in the SNe IIn
atmospheres (CSM). At later times they also exhibit a broad blue shifted
component which arises from the cold dense shell. Our model results are broadly
consistent with the bolometric light curve and spectral evolution observed for
SN2010jl. Invoking a prolate pole-to-equator density ratio in the CSM, we can
also reproduce the ~2% continuum polarisation, and line depolarisation,
observed in SN2010jl. By varying the inner shell kinetic energy and the mass
and extent of the outer shell, a large range of peak luminosities and
durations, broadly compatible with super-luminous SNe IIn like 2010jl or
2006gy, can be produced.Comment: paper accepted to MNRA
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