199 research outputs found
A survey of risk behaviour for contracting HIV among adult psychiatric patients. A South African study - Part 1
OBJECTIVE: Various studies have reported increased prevalence of HIV infection among psychiatric patients. Psychiatric patients are under-evaluated in terms of their HIV risk behaviour. The study sought to establish the prevalence of HIV risk behaviour and determine the association between risk behaviour and demographic and clinical variables. METHOD: Participants were 113 consenting adult in-patients. A structured interview was conducted with each participant. A total risk behaviour score was calculated. From the risk score, three risk behaviour categories were identified: 0 = no risk; 1 to 3 = medium risk; 4 to 9 = high risk. Associations between HIV risk behaviour and demographic and clinical variables were analysed. RESULTS: Of the 113 participants, 68% were men and 32% women. The mean age was 38. Forty-five per cent were sexually active and 48% fell into the âno-risk groupâ, 29% in the âmedium-riskâ group, and 23% in the âhigh-riskâ group. Female patients with a history of treatment for sexually transmitted disease and a diagnosis of personality disorder were associated with being sexually abused. Having multiple sex partners was associated with diagnoses of substance-related disorders and cognitive disorders. Sex with someone known for less than 24 hours was associated with long-term hospitalisation and diagnoses of cognitive and personality disorders. CONCLUSION: The study confirmed that mentally ill patients are vulnerable and may be victimised. The study also suggests that mental illness may impair appreciation of consequences and lead to high-risk behaviour for contracting HIV. Special care should be taken to protect female patients in psychiatric institutions.http://www.journals.co.za/ej/ejour_medjda.htm
A survey of HIV-related knowledge among adult psychiatric patients. A South African Study - Part 2
OBJECTIVE: Studies have reported an increased prevalence of HIV infection among psychiatric patients. Inaccurate HIV knowledge is included as a factor in the increased risk of HIV infection in the mentally ill, but few studies have looked specifically at this factor. The aims of the study were to determine the knowledge of HIV and its transmission among adult psychiatric patients at Weskoppies Hospital and to determine the relationship between HIV knowledge and HIV risk behaviour. METHOD: Structured interviews were conducted with 113 consenting adult patients at Weskoppies Hospital. They were divided into three groups according to their length of hospital stay. The structured interview included questions about demographic data, the diagnoses and the AIDS Risk Behaviour Knowledge Test (AIDS-KT). Scores of 13 out of 13 represented accurate knowledge of HIV (level I); scores of 10-12 represented good knowledge (level II); scores of â€9 represented poor knowledge (level III). RESULTS: A total of 104 patients (92%) demonstrated excellent knowledge of HIV and its transmission (levels I and II). There was no significant linear association between HIV knowledge and risk-behaviour scores (Pearsonâs correlation coefficient r=-0.11). CONCLUSION: The presence of high-risk behaviours despite good HIV-related knowledge in this group of patients, leads us to think that knowledge alone will not limit HIV risk behaviours. For this reason, educational programmes should not be limited to interventions that simply increase knowledge about HIV infection but should extend to clinical factors, including patientsâ motivation and readiness to change their behaviour.http://www.journals.co.za/ej/ejour_medjda.htm
Branch and bound based coordinate search filter algorithm for nonsmooth nonconvex mixed-integer nonlinear programming problems
Publicado em "Computational science and its applications â ICCSA 2014...", ISBN 978-3-319-09128-0. Series "Lecture notes in computer science", ISSN 0302-9743, vol. 8580.A mixed-integer nonlinear programming problem (MINLP) is a problem with continuous and integer variables and at least, one nonlinear function. This kind of problem appears in a wide range of real applications and is very difficult to solve. The difficulties are due to the nonlinearities of the functions in the problem and the integrality restrictions on some variables. When they are nonconvex then they are the most difficult to solve above all. We present a methodology to solve nonsmooth nonconvex MINLP problems based on a branch and bound paradigm and a stochastic strategy. To solve the relaxed subproblems at each node of the branch and bound tree search, an algorithm based on a multistart strategy with a coordinate search filter methodology is implemented. The produced numerical results show the robustness of the proposed methodology.This work has been supported by FCT (Fundação para a CiĂȘncia e aTecnologia) in the scope of the projects: PEst-OE/MAT/UI0013/2014 and PEst-OE/EEI/UI0319/2014
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
75th Anniversary of âExistence of Electromagnetic-Hydrodynamic Wavesâ
We have recently passed the 75th anniversary of one of the most important
results in solar and space physics: Hannes Alfv\'en's discovery of Alfv\'en
waves and the Alfv\'en speed. To celebrate the anniversary, this article
recounts some major episodes in the history of MHD waves. Following an
initially cool reception, Alfv\'en's ideas were propelled into the spotlight by
Fermi's work on cosmic rays, the new mystery of coronal heating and, as
scientific perception of interplanetary space shifted dramatically and the
space race started, detection of Alfv\'en waves in the solar wind. From then
on, interest in MHD waves boomed, laying the foundations for modern remote
observations of MHD waves in the Sun, coronal seismology and some of today's
leading theories of coronal heating and solar wind acceleration. In 1970,
Alfv\'en received the Nobel Prize for his work in MHD, including these
discoveries. The article concludes with some reflection about what the history
implies about the way we do science, especially the advantages and pitfalls of
idealised mathematical models.Comment: 10 pages, accepted by Solar Physic
A Revisit of the Masuda Flare
We revisit the flare on 1992 January 13, which is now universally termed the
"Masuda flare". The revisit is motivated not only by its uniqueness despite
accumulating observations of \hxr coronal emission, but also by the improvement
of Yohkoh hard X-ray imaging, which was achieved after the intensive
investigations on this celebrated event. Through an uncertainty analysis, we
show that the hard X-ray coronal source is located much closer to the soft
X-ray loop in the re-calibrated HXT images than in the original ones.
Specifically, the centroid of the M1-band (23--33 keV) coronal source is above
the brightest pixel of the SXT loop by ~5000+/-1000 km (~9600 km in the
original data); and above the apex of the 30% brightness contour of the SXT
loop by ~2000+/-1000 km (~7000 km in the original data). We suggest that this
change may naturally account for the fact that the spectrum of the coronal
emission was reported to be extremely hard below ~20 keV in the pre-calibration
investigations, whereas it has been considerably softer in the literature since
Sato's re-calibration circa 1999. Still, the coronal spectrum is flatter at
lower energies than at higher energies, owing to the lack of a similar source
in the L-band (14--23 keV), which remains a puzzle
Flux-rope twist in eruptive flares and CMEs : due to zipper and main-phase reconnection
Funding: UK Science and Technology Facilities CouncilThe nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered. The reconnection has two phases: first of all, 3D âzipper reconnectionâ propagates along the initial coronal arcade, parallel to the polarity inversion line (PIL); then subsequent quasi-2D âmain phase reconnectionâ in the low corona around a flux rope during its eruption produces coronal loops and chromospheric ribbons that propagate away from the PIL in a direction normal to it. One scenario starts with a sheared arcade: the zipper reconnection creates a twisted flux rope of roughly one turn (2Ï radians of twist), and then main phase reconnection builds up the bulk of the erupting flux rope with a relatively uniform twist of a few turns. A second scenario starts with a pre-existing flux rope under the arcade. Here the zipper phase can create a core with many turns that depend on the ratio of the magnetic fluxes in the newly formed flare ribbons and the new flux rope. Main phase reconnection then adds a layer of roughly uniform twist to the twisted central core. Both phases and scenarios are modeled in a simple way that assumes the initial magnetic flux is fragmented along the PIL. The model uses conservation of magnetic helicity and flux, together with equipartition of magnetic helicity, to deduce the twist of the erupting flux rope in terms the geometry of the initial configuration. Interplanetary observations show some flux ropes have a fairly uniform twist, which could be produced when the zipper phase and any pre-existing flux rope possess small or moderate twist (up to one or two turns). Other interplanetary flux ropes have highly twisted cores (up to five turns), which could be produced when there is a pre-existing flux rope and an active zipper phase that creates substantial extra twist.PostprintPublisher PDFPeer reviewe
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Physical Processes in Star Formation
© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00693-8.Star formation is a complex multi-scale phenomenon that is of significant importance for astrophysics in general. Stars and star formation are key pillars in observational astronomy from local star forming regions in the Milky Way up to high-redshift galaxies. From a theoretical perspective, star formation and feedback processes (radiation, winds, and supernovae) play a pivotal role in advancing our understanding of the physical processes at work, both individually and of their interactions. In this review we will give an overview of the main processes that are important for the understanding of star formation. We start with an observationally motivated view on star formation from a global perspective and outline the general paradigm of the life-cycle of molecular clouds, in which star formation is the key process to close the cycle. After that we focus on the thermal and chemical aspects in star forming regions, discuss turbulence and magnetic fields as well as gravitational forces. Finally, we review the most important stellar feedback mechanisms.Peer reviewedFinal Accepted Versio
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