1,147 research outputs found
Conservative formulations of general relativistic kinetic theory
Experience with core-collapse supernova simulations shows that accurate
accounting of total particle number and 4-momentum can be a challenge for
computational radiative transfer. This accurate accounting would be facilitated
by the use of particle number and 4-momentum transport equations that allow
transparent conversion between volume and surface integrals in both
configuration and momentum space. Such conservative formulations of general
relativistic kinetic theory in multiple spatial dimensions are presented in
this paper, and their relevance to core-collapse supernova simulations is
described.Comment: 48 page
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. xxxv. detection of connective tissue activating peptide–iii isoforms in synovium from osteoarthritis and rheumatoid arthritis patients: patterns of interaction with other synovial cytokines in cell culture
Objective. To determine whether extracts of unincubated osteoarthritis (OA) and rheumatoid arthritis (RA) synovial tissue contain connective tissue activating peptide–III (CTAP-III) isoforms and prostaglandin E 2 (PGE 2 ), and whether such extracts have growth-promoting activity, and to determine whether binary combinations of CTAP-III with other cytokines reported to be present in synovial tissue lead to synergistic, additive, or inhibitory effects on growth. Methods. Acid–ethanol extracts of human synovium were examined for growth-promoting activity by measuring formation of 14 C-glycosaminoglycan ( 14 CGAG) and 3 H-DNA in synovial cell cultures; PGE 2 was measured by enzyme immunoassay, and CTAP-III isoforms were identified by Western blotting of extracted proteins separated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Growth-promoting activity of CTAP-III and other cytokines was tested in synovial cultures treated with the agonists singly and in binary combination, by measuring changes in synthesis of 14 C-GAG and 3 H-DNA. Results. Platelet-derived CTAP-III and a cleavage isoform with the electrophoretic mobility of CTAP-III–des 1–15/neutrophil-activating peptide–2 (NAP-2) and PGE 2 were found in biologically active extracts of synovial samples from patients with RA and OA. Five growth factors (recombinant epidermal growth factor [rEGF], recombinant interleukin-1Β [rIL-1Β], basic fibroblast growth factor [bFGF], PGE 1 , and PGE 2 ) in binary combination with CTAP-III showed synergism in stimulating GAG synthesis; two (recombinant platelet-derived growth factor type BB [rPDGF-BB] and recombinant transforming growth factor Β [rTGFΒ]) had an additive effect. In combination with CTAP-III, rEGF and rPDGF-BB had a synergistic effect in promoting DNA synthesis, rTGFΒ and rbFGF had an additive effect, and rIL-1Β, PGE 1 , and PGE 2 were antagonistic. Conclusions. The results suggest that, in addition to endogenous factors, CTAP-III and other plateletderived cytokines may play roles in regulating synovial cell metabolism in RA and OA, and that combinations of growth factors may be more significant than single agents in amplification or suppression of important cell functions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37793/1/1780350712_ftp.pd
Cáncer de la vesĂcula biliar: limitaciones diagnĂłsticas y terapĂ©uticas
Antecedentes: El cáncer de la vesĂcula biliar tienebaja frecuencia en SudamĂ©rica, excepto en Chile;por lo general es diagnosticado y tratado en etapasavanzadas.Objetivo: Estudiar la frecuencia, el perfil demográfico,el cuadro clĂnico, el diagnĂłstico y los resultadosde la cirugĂa en pacientes con cáncer vesicularMaterial y mĂ©todo: estudio descriptivo y retrospectivobasado en pacientes sometidos a colecistectomĂapor litiasis en el periodo 1992-2002. Fueronseleccionados los casos comprobados de cáncervesicular; se evalĂşan: frecuencia, perfil demográfico,cuadro clĂnico, aportes de los medios de diagnĂłsticoy resultados inmediatos del tratamiento.Resultados: Fueron hallados 16 casos de cáncervesicular sobre 3239 colecistectomĂas (0.5%); 15fueron mujeres. La edad media fue 63 años (r 53-77).El dolor fue el principal motivo de consulta. El 75%presentĂł ictericia + coluria + acolia. La ecografĂacomprobĂł engrosamiento de la pared vesicular en 6casos y vesĂcula escleroatrĂłfica en uno.La colecistectomĂa simple fue efectuada en 2 casos;ella se asociĂł a drenaje biliar externo en 3, biopsiahepática en 2 y a derivaciĂłn biliodigestiva en 1.Una derivaciĂłn biliodigestiva, dos drenajes biliaresexternos, 4 biopsias y una prĂłtesis endoscĂłpica completanla serie.Uno de los pacientes presentĂł una fĂstula biliodigestiva.Cinco pacientes fallecieron (31%): 4 porcomplicaciones infecciosas con falla orgánica mĂşltipley 1 por tromboembolismo pulmonar.ConclusiĂłn: El cáncer vesicular es raro, predominaen el sexo femenino y se acompaña con frecuenciade obstrucciĂłn biliar. La orientaciĂłn diagnĂłstica escasi nula por ecografĂa; sĂłlo en engrosamiento localizadocoexistente con la litiasis vesicular parecesignificativo y obliga a realizar una biopsia extemporánea
Testing Hydrodynamic Models of LMC X-4 with UV and X-ray Spectra
We compare the predictions of hydrodynamic models of the LMC X-4 X-ray binary
system with observations of UV P Cygni lines with the GHRS and STIS
spectrographs on the Hubble Space Telescope. The hydrodynamic model determines
density and velocity fields of the stellar wind, wind-compressed disk,
accretion stream, Keplerian accretion disk, and accretion disk wind. We use a
Monte Carlo code to determine the UV P Cygni line profiles by simulating the
radiative transfer of UV photons that originate on the star and are scattered
in the wind. The qualitative orbital variation predicted is similar to that
observed, although the model fails to reproduce the strong orbital asymmetry
(the observed absorption is strongest for phi>0.5). The model predicts a
mid-eclipse X-ray spectrum, due almost entirely to Compton scattering, with a
factor 4 less flux than observed with ASCA. We discuss how the model may need
to be altered to explain the spectral variability of the system.Comment: 11 figures, accepted by Ap
Aspherical Explosion Models for SN 1998bw/GRB 980425
The recent discovery of the unusual supernova SN1998bw and its apparent
correlation with the gamma-ray burst GRB 980425 has raised new issues
concerning both the GRB and supernovae. Although the spectra resemble those of
TypeIc supernovae, there are distinct differences at early times and SN1998bw
appeared to be unusually bright and red at maximum light. The apparent
expansion velocities inferred by the Doppler shift of (unidentified) absorption
features appeared to be high, making SN1998bw a possible candidate for a
"hypernova" with explosion energies between 20 and 50E51 erg and ejecta masses
in excess of 6 - 15 M_o. Based on light curve calculations for aspherical
explosions and guided by the polarization observations of "normal" SNIc and
related events, we present an alternative picture that allows SN1998bw to have
an explosion energy and ejecta mass consistent with core collapse supernovae
(although at the 'bright' end). We show that the LC of SN1998bw can be
understood as result of an aspherical explosion along the rotational axis of a
basically spherical, non-degenerate C/O core of massive star with an explosion
energy of 2foe and a total ejecta mass of 2 M_o if it is seen from high
inclinations with respect to the plane of symmetry. In this model, the high
expansion velocities are a direct consequence of an aspherical explosion which,
in turn, produces oblate iso-density contours. It suggests that the fundamental
core-collapse explosion process itself is strongly asymmetric.Comment: 12 pages, 8 figures, latex, aas2pp4.sty, submitted to Ap
The Evolution of Relativistic Binary Progenitor Systems
Relativistic binary pulsars, such as B1534+12 and B1913+16 are characterized
by having close orbits with a binary separation of ~ 3 R_\sun. The progenitor
of such a system is a neutron star, helium star binary. The helium star, with a
strong stellar wind, is able to spin up its compact companion via accretion.
The neutron star's magnetic field is then lowered to observed values of about
10^{10} Gauss. As the pulsar lifetime is inversely proportional to its magnetic
field, the possibility of observing such a system is, thus, enhanced by this
type of evolution. We will show that a nascent (Crab-like) pulsar in such a
system can, through accretion-braking torques (i.e. the "propeller effect") and
wind-induced spin-up rates, reach equilibrium periods that are close to
observed values. Such processes occur within the relatively short helium star
lifetimes. Additionally, we find that the final outcome of such evolutionary
scenarios depends strongly on initial parameters, particularly the initial
binary separation and helium star mass. It is, indeed, determined that the
majority of such systems end up in the pulsar "graveyard", and only a small
fraction are strongly recycled. This fact might help to reconcile theoretically
expected birth rates with limited observations of relativistic binary pulsars.Comment: 24 pages, 10 Postscript figures, Submitted to The Astrophysical
Journa
Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars
We report on neon abundances derived from {\it Spitzer} high resolution
spectral data of eight Wolf-Rayet (WR) stars using the forbidden line of
[\ion{Ne}{3}] 15.56 microns. Our targets include four WN stars of subtypes
4--7, and four WC stars of subtypes 4--7. We derive ion fraction abundances
of Ne^{2+} for the winds of each star. The ion fraction abundance is a
product of the ionization fraction in stage i and the abundance by
number of element E relative to all nuclei. Values generally
consistent with solar are obtained for the WN stars, and values in excess of
solar are obtained for the WC stars.Comment: to appear in Astrophysical Journa
Molecular line radiative transfer in protoplanetary disks: Monte Carlo simulations versus approximate methods
We analyze the line radiative transfer in protoplanetary disks using several
approximate methods and a well-tested Accelerated Monte Carlo code. A low-mass
flaring disk model with uniform as well as stratified molecular abundances is
adopted. Radiative transfer in low and high rotational lines of CO, C18O, HCO+,
DCO+, HCN, CS, and H2CO is simulated. The corresponding excitation
temperatures, synthetic spectra, and channel maps are derived and compared to
the results of the Monte Carlo calculations. A simple scheme that describes the
conditions of the line excitation for a chosen molecular transition is
elaborated. We find that the simple LTE approach can safely be applied for the
low molecular transitions only, while it significantly overestimates the
intensities of the upper lines. In contrast, the Full Escape Probability (FEP)
approximation can safely be used for the upper transitions (J_{\rm up} \ga 3)
but it is not appropriate for the lowest transitions because of the maser
effect. In general, the molecular lines in protoplanetary disks are partly
subthermally excited and require more sophisticated approximate line radiative
transfer methods. We analyze a number of approximate methods, namely, LVG, VEP
(Vertical Escape Probability) and VOR (Vertical One Ray) and discuss their
algorithms in detail. In addition, two modifications to the canonical Monte
Carlo algorithm that allow a significant speed up of the line radiative
transfer modeling in rotating configurations by a factor of 10--50 are
described.Comment: 47 pages, 12 figures, accepted for publication in Ap
Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind
We show that the orbital variation in the UV P Cygni lines of the X-ray
binary LMC X-4 results when X-rays photoionize nearly the entire region outside
of the X-ray shadow of the normal star. We fit models to HST GHRS observations
of N V and C IV P Cygni line profiles. Analytic methods assuming a spherically
symmetric wind show that the wind velocity law is well-fit by v~(1-1/r)^beta,
where beta is likely 1.4-1.6 and definitely <2.5. Escape probability models can
fit the observed P Cygni profiles, and provide measurements of the stellar wind
parameters. The fits determine Lx/Mdot=2.6+/-0.1 x10^43 erg/s/Msun yr, where Lx
is the X-ray luminosity and Mdot is the mass-loss rate of the star. Allowing an
inhomogeneous wind improves the fits. IUE spectra show greater P Cygni
absorption during the second half of the orbit than during the first. We
discuss possible causes of this effect.Comment: 56 pages, 12 figures, to be published in the Astrophysical Journa
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