412 research outputs found
Constraints on gamma-ray burst and supernova progenitors through circumstellar absorption lines. (II): Post-LBV Wolf-Rayet stars
Van Marle et al. (2005) showed that circumstellar absorption lines in early
Type Ib/c supernova and gamma-ray burst afterglow spectra may reveal the
progenitor evolution of the exploding Wolf-Rayet star. While the quoted paper
deals with Wolf-Rayet stars which evolved through a red supergiant stage, we
investigate here the initially more massive Wolf-Rayet stars which are thought
to evolve through a Luminous Blue Variable (LBV) stage. We perform hydrodynamic
simulations of the evolution of the circumstellar medium around a 60 Msol star,
from the main sequence through the LBV and Wolf-Rayet stages, up to core
collapse. We then compute the column density of the circumstellar matter as a
function of radial velocity, time and angle. This allows a comparison with the
number and blue-shifts, of absorption components in the spectra of LBVs,
Wolf-Rayet stars, Type Ib/c supernovae and gamma-ray burst afterglows. Our
simulation for the post-LBV stage shows the formation of various absorption
components, which are, however, rather short lived; they dissipate on time
scales shorter than 50,000yr. As the LBV stage is thought to occur at the
beginning of core helium burning, the remaining Wolf-Rayet life time is
expected to be one order of magnitude larger. When interpreting the absorption
components in the afterglow spectrum of GRB-021004 as circumstellar, it can be
concluded that the progenitor of this source did most likely not evolve through
an LBV stage. However, a close binary with late common-envelope phase (Case C)
may produce a circumstellar medium that closely resembles the LBV to Wolf-Rayet
evolution, but with a much shorter Wolf-Rayet period.Comment: accepted for publication by A&
Forming a constant density medium close to long gamma-ray bursts
The progenitor stars of long Gamma-Ray Bursts (GRBs) are thought to be
Wolf-Rayet stars, which generate a massive and energetic wind. Nevertheless,
about 25 percent of all GRB afterglows light curves indicate a constant density
medium close to the exploding star. We explore various ways to produce this, by
creating situations where the wind termination shock arrives very close to the
star, as the shocked wind material has a nearly constant density. Typically,
the distance between a Wolf-Rayet star and the wind termination shock is too
large to allow afterglow formation in the shocked wind material. Here, we
investigate possible causes allowing for a smaller distance: A high density or
a high pressure in the surrounding interstellar medium (ISM), a weak Wolf-Rayet
star wind, the presence of a binary companion, and fast motion of the
Wolf-Rayet star relative to the ISM. We find that all four scenarios are
possible in a limited parameter space, but that none of them is by itself
likely to explain the large fraction of constant density afterglows. A low GRB
progenitor metallicity, and a high GRB energy make the occurrence of a GRB
afterglow in a constant density medium more likely. This may be consistent with
constant densities beingpreferentially found for energetic, high redshift GRBs.Comment: 13 pages, 13 figures, new version: as accepted by Astronomy &
Astrophysic
The origin of blue-shifted absorption lines in a gamma-ray burst afterglow
The afterglow spectrum of GRB 021004 shows a system of blueshifted absorption lines, indicating the presence of matter moving towards us at discrete velocities in the range from 0 to more than 2000 km/s. We propose that
these lines are the result of absorption by circumstellar matter, which was ejected by gamma-ray burst progenitor (a massive star) during its evolution. We have simulated the evolution of the circumstellar medium around such a star and find that the evolutionary sequence: main-sequence, Red Supergiant, Wolf-Rayet star can qualitatively reproduce the various absorption lines systems
Vascular disease in HIV/AIDS patients
Objectives. An ongoing prospective clinical survey to determine the spectrum of vascular disease in HIV/AIDS patients and the risk factors affecting clinical outcome in order to formulate a management protocol for future use.
Methods. Comprehensive screening for risk factors for vascular disease as well as HIV/AIDS-related conditions. Disease pattern and presentation are noted and patients treated accordingly. Vascular emergencies are managed regardless of HIV status because this information is usually not available at the time of presentation. Elective management is based on immune status and risk stratification.
Results. 42 patients tested positive for HIV. The majority of patients presented with occlusive disease (57%), followed by anearysms (21%) and vascular trauma (19%). A variety of vascular surgical procedures were performed on 36 patients. There was no surgical mortality and 10 patients developed complications, including 2 amputations and 7 cases of minor wound sepsis. The 3 patients who received preoperative antiretroviral therapy showed a marked reduction in viral count and a significant improvement in CD4 T-cell count.
Conclusion. Surgery can be safe and effective in HIV-positive patients provided the necessary precautions are taken to reduce surgical morbidity.
(South African Medical Journal: 2002 92(12): 974-977
A randomized controlled trial of the efficacy and cost-effectiveness of a brief intensified cognitive behavioral therapy and/or pharmacotherapy for mood and anxiety disorders: Design and methods
Background: Anxiety and mood disorders involve a high disease burden and are associated with high economic costs. A stepped-care approach intervention and abbreviated diagnostic method are assumed to increase effectiveness and efficiency of the mental healthcare and are expected to reduce economic costs. Methods: Presented are the rationale, design, and methods of a two-armed randomized controlled trial comparing \u27treatment as usual\u27 (TAU) with a brief intensified cognitive behavioral therapy (CBT) and/or pharmacotherapy. Eligible participants (N =500) of five Dutch outpatient Mental Healthcare Centers are randomly assigned to either TAU or to the experimental condition (brief CBT and/or pharmacotherapy). Data on patients\u27 progress and clinical effectiveness of treatment are assessed at baseline, post-treatment (3. months after baseline), and at 6 and 12. months post-treatment by Routine Outcome Monitoring (ROM). Cost analysis is performed on the obtained data. Discussion: Since few studies have investigated both the clinical and cost effectiveness of a stepped-care approach intervention and a shortened diagnostic ROM method in both anxiety and/or mood disorders within secondary mental health care, the results of this study might contribute to the improvement of (cost)-effective treatment options and diagnostic methods for these disorders
Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?
The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors
of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose
angular momentum due to their intense stellar winds. We investigate whether the
tidal interaction of a Wolf-Rayet star with a compact object in a binary system
can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the
evolution of close Wolf-Rayet binaries, including tidal angular momentum
exchange, differential rotation of the Wolf-Rayet star, internal magnetic
fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is
approximated as a point mass. We then employ a population synthesis code to
infer the occurrence rates of the various relevant binary evolution channels.
We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally
spun up and producing a collapsar -- does not occur at solar metallicity and
may only occur with low probability at low metallicity. It is limited by the
widening of the binary orbit induced by the strong Wolf-Rayet wind or by the
radius evolution of the Wolf-Rayet star that most often leads to a binary
merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with
black holes such that it becomes comparable to the occurrence rate of long
gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&
(Cost-)effectiveness of an individualised risk prediction tool (PERSARC) on patient’s knowledge and decisional conflict among soft-tissue sarcomas patients:protocol for a parallel cluster randomised trial (the VALUE-PERSARC study)
Introduction Current treatment decision-making in high-grade soft-tissue sarcoma (STS) care is not informed by individualised risks for different treatment options and patients’ preferences. Risk prediction tools may provide patients and professionals insight in personalised risks and benefits for different treatment options and thereby potentially increase patients’ knowledge and reduce decisional conflict. The VALUE-PERSARC study aims to assess the (cost-)effectiveness of a personalised risk assessment tool (PERSARC) to increase patients’ knowledge about risks and benefits of treatment options and to reduce decisional conflict in comparison with usual care in high-grade extremity STS patients. Methods The VALUE-PERSARC study is a parallel cluster randomised control trial that aims to include at least 120 primarily diagnosed high-grade extremity STS patients in 6 Dutch hospitals. Eligible patients (≥18 years) are those without a treatment plan and treated with curative intent. Patients with sarcoma subtypes or treatment options not mentioned in PERSARC are unable to participate. Hospitals will be randomised between usual care (control) or care with the use of PERSARC (intervention). In the intervention condition, PERSARC will be used by STS professionals in multidisciplinary tumour boards to guide treatment advice and in patient consultations, where the oncological/ orthopaedic surgeon informs the patient about his/her diagnosis and discusses benefits and harms of all relevant treatment options. The primary outcomes are patients’ knowledge about risks and benefits of treatment options and decisional conflict (Decisional Conflict Scale) 1 week after the treatment decision has been made. Secondary outcomes will be evaluated using questionnaires, 1 week and 3, 6 and 12 months after the treatment decision. Data will be analysed following an intention-to-treat approach using a linear mixed model and taking into account clustering of patients within hospitals. Ethics and dissemination The Medical Ethical Committee Leiden-Den Haag-Delft (METC-LDD) approved this protocol (NL76563.058.21). The results of this study will be reported in a peer-review journal.</p
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