309 research outputs found
GRB 090510: a short burst from a massive star ?
GRB afterglow 090510 is (so far) the best-monitored afterglow in the optical,
X-ray, and above 100 MeV, measurements covering 2-3 decades in time at each
frequency. Owing to its power-law temporal decay and power-law spectrum, it
seems very likely that the highest energy emission is from the forward-shock
energizing the ambient medium (the standard blast-wave model for GRB
afterglows), the GeV flux and its decay rate being consistent with that model's
expectations. However, the synchrotron emission from a collimated outflow (the
standard jet model) has difficulties in accounting for the lower-energy
afterglow emission, where a simultaneous break occurs at 2 ks in the optical
and X-ray light-curves, but with the optical flux decay (before and after the
break) being much slower than in the X-rays (at same time). The measured X-ray
and GeV fluxes are incompatible with the higher-energy afterglow emission being
from same spectral component as the lower-energy afterglow emission, which
suggests a synchrotron self-Compton model for this afterglow. Cessation of
energy injection in the blast-wave and an ambient medium with a wind-like n ~
r^{-2} density can explain all features of the optical and X-ray light-curves
of GRB afterglow 090510. Such an ambient medium radial structure is
incompatible with this short-GRB originating from the merger of two compact
stars.Comment: 12 pages, to appear in MNRA
Commentary: Unravelling the mechanisms linking climate change, agriculture and avian population declines
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Stochastic multiple mapping conditioning for a piloted, turbulent jet diffusion flame
A stochastic implementation of the multiple mapping conditioning (MMC) approach has been applied to a turbulent jet diffusion flame (Sandia Flame D). This implementation combines the advantages of the basic concepts of a mapping closure methodology with a probability density approach. A single reference variable has been chosen. Its evolution is described by a Markov process and then mapped to the mixture fraction space. Scalar micro-mixing is modelled by a modified “interaction by exchange with the mean” (IEM) mixing model where the particles mix with their -in reference space- conditionally averaged means. The formulation of the closure leads to localness of mixing in mixture fraction space and consequently improved localness in composition space. Results for mixture fraction and reactive species are in good agreement with the experimental data. The MMC methodology allows for the introduction of an additional “minor dissipation time scale” that controls the fluctuations around the conditional mean. A sensitivity analysis based on the conditional temperature fluctuations as a function of this time scale does not endorse earlier estimates for its modelling, but only relatively large dissipation time scales of the order of the integral turbulence time scale yield acceptable levels of conditional fluctuations that agree with experiments. With the choice of a suitable dissipation time scale, MMC-IEM thus provides a simple mixing model that is capable of capturing extinction phenomena, and it gives improved predictions over conventional PDF predictions using simple IEM mixing models
Physiotherapists demonstrate weight stigma: a cross-sectional survey of Australian physiotherapists
Question: Do physiotherapists demonstrate explicit and implicit weight stigma? Design: Cross-sectional survey with partial blinding of participants. Participants responded to the Anti-Fat Attitudes questionnaire and physiotherapy case studies with body mass index (BMI) manipulated (normal or overweight/obese). The Anti-Fat Attitudes questionnaire included 13 items scored on a Likert-type scale from 0 to 8. Any score greater than zero indicated explicit weight stigma. Implicit weight stigma was determined by comparing responses to case studies with people of different BMI categories (where responses were quantitative) and by thematic and count analysis for free-text responses. Participants: Australian physiotherapists (n = 265) recruited via industry networks. Results: The mean item score for the Anti-Fat Attitudes questionnaire was 3.2 (SD 1.1), which indicated explicit weight stigma. The Dislike (2.1, SD 1.2) subscale had a lower mean item score than the Fear (3.9, SD 1.8) and Willpower (4.9, SD 1.5) subscales. There was minimal indication from the case studies that people who are overweight receive different treatment from physiotherapists in clinical parameters such as length of treatment time (p = 0.73) or amount of hands-on treatment (p = 0.88). However, there were indications of implicit weight stigma in the way participants discussed weight in free-text responses about patient management. Conclusion: Physiotherapists demonstrate weight stigma. This finding is likely to affect the way they communicate with patients about their weight, which may negatively impact their patients. It is recommended that physiotherapists reflect on their own attitudes towards people who are overweight and whether weight stigma influences treatment focus
Ferromagnetic behavior of ultrathin manganese nanosheets
Ferromagnetic behaviour has been observed experimentally for the first time
in nanostructured Manganese. Ultrathin ( 0.6 nm) Manganese nanosheets
have been synthesized inside the two dimensional channels of sol-gel derived
Na-4 mica. The magnetic properties of the confined system are measured within
2K-300K temperature range. The confined structure is found to show a
ferromagnetic behaviour with a nonzero coercivity value. The coercivity value
remains positive throughout the entire temperature range of measurement. The
experimental variation of susceptibility as a function of temperature has been
satisfactorily explained on the basis of a two dimensional system with a
Heisenberg Hamiltonian involving direct exchange interaction.Comment: 13 pages, 9 figure
A faint optical flash in dust-obscured GRB 080603A - implications for GRB prompt emission mechanisms
We report the detection of a faint optical flash by the 2-m Faulkes Telescope
North simultaneously with the second of two prompt gamma-ray pulses in INTEGRAL
gamma-ray burst (GRB) 080603A, beginning at t_rest = 37 s after the onset of
the GRB. This optical flash appears to be distinct from the subsequent emerging
afterglow emission, for which we present comprehensive broadband radio to X-ray
light curves to 13 days post-burst and rigorously test the standard fireball
model. The intrinsic extinction toward GRB 080603A is high (A_V,z = 0.8 mag),
and the well-sampled X-ray-to-near-infrared spectral energy distribution is
interesting in requiring an LMC2 extinction profile, in contrast to the
majority of GRBs. Comparison of the gamma-ray and extinction-corrected optical
flux densities of the flash rules out an inverse-Compton origin for the prompt
gamma-rays; instead, we suggest that the optical flash could originate from the
inhomogeneity of the relativistic flow. In this scenario, a large velocity
irregularity in the flow produces the prompt gamma-rays, followed by a milder
internal shock at a larger radius that would cause the optical flash. Flat
gamma-ray spectra, roughly F propto nu^-0.1, are observed in many GRBs. If the
flat spectrum extends down to the optical band in GRB 080603A, the optical
flare could be explained as the low-energy tail of the gamma-ray emission. If
this is indeed the case, it provides an important clue to understanding the
nature of the emission process in the prompt phase of GRBs and highlights the
importance of deep (R> 20 mag), rapid follow-up observations capable of
detecting faint, prompt optical emission.Comment: 22 pages, 11 figures, accepted to MNRA
Progenitors of Type Ia Supernovae: Binary Stars with White Dwarf Companions
Type Ia SNe (SNe Ia) are thought to come from carbon-oxygen white dwarfs that
accrete mass from binary companions until they approach the Chandrasekhar
limit, ignite carbon, and undergo complete thermonuclear disruption. A survey
of the observed types of binaries that contain white dwarfs is presented. We
propose that certain systems that seem most promising as SN Ia progenitors
should be more intensively observed and modeled, to determine whether the white
dwarfs in these systems will be able to reach the Chandrasekhar limit. In view
of the number of promising single-degenerate systems and the dearth of
promising double-degenerate systems, we suspect that single-degenerates produce
most or perhaps all SNe Ia, while double-degenerates produce some or perhaps
none.Comment: 34 pages, to appear in New Astronomy Review
Gamma Ray Bursts Flares detected and observed by the Swift Satellite
The detection of flares with the Swift satellite triggered a lot of
bservational and theoretical interest in these phenomena. As a consequence a
large analysis effort started within the community to characterize the
phenomenon and at the same time a variety of theoretical speculations have been
proposed to explain it. In this presentation we discuss part of the results we
obtained analyzing a first statistical sample of GRBs observed with Swift. The
first goal of this research is very simple: derive those observational
properties that could distinguish between internal and external shock and
between an ever active central engine and delayed shocks (refreshing) related
to a very small initial Lorentz bulk factor. We discuss first the method of
analysis and the morphology evidencing the similarities such flares have with
the prompt emission pulses. We conclude that GRB flares are due to internal
shocks and leave still open the question of whether or not the central engine
is active for a time of the order of 105 seconds after the prompt emission.Comment: Proceedings of the Beijing COSPAR Assembly 2006; submitted Nov 2,
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Informing the development of an online self-management program for men living with HIV: a needs assessment
Background: The aim of this mixed methods study was to conduct a multifaceted needs assessment to inform the development of an online self-management program for men living with HIV. The objectives were to describe the health-related quality of life for men living with HIV, the impact of living with HIV, and the perceived problem areas and service and support needs of these men. The needs assessment was conducted in accordance with the PRECEDE model for health promotion program planning.Methods: A survey assessing the quality of life of men living with HIV (n = 72) was conducted and results were compared to Australian normative data. Focus groups were also undertaken with men living with HIV (n = 11) and a multidisciplinary team of service providers working in the area of HIV (n = 11). Focus groups enabled an in-depth description of the impact of HIV on quality of life and perceived problem areas in daily life.Results: HIV-positive men experience significantly lower quality of life when compared with Australian normative data, particularly in those domains concerned with social and emotional aspects of quality of life. Qualitative focus groups yielded an overarching theme ‘The psychosocial impact of HIV’ which contained three sub-themes; (1) Life before and after HIV – a changed identity and its repercussions; (2) Resilience and the importance of social support; (3) Negotiating the practicalities – intimate relationships and disclosure.Conclusions: The findings from this needs assessment highlight the need to target socio-emotional contexts of HIV positive men’s daily lives to improve quality of life and well-being. Intervention priorities for the proposed online self-management program include: (1) managing the emotional impact of HIV; (2) disclosing HIV status to family and friends; (3) maintaining social connectedness; (4) managing HIV within intimate relationships; and (5) disclosure of HIV status to intimate partners
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