251 research outputs found
Sensitivity of PDR Calculations to Microphysical Details
Our understanding of physical processes in Photodissociation regions or
Photon Dominated Regions (PDRs) largely depends on the ability of spectral
synthesis codes to reproduce the observed infrared emission-line spectrum. In
this paper, we explore the sensitivity of a single PDR model to microphysical
details. Our calculations use the Cloudy spectral synthesis code, recently
modified to include a wealth of PDR physical processes. We show how the
chemical/thermal structure of a PDR, along with the calculated spectrum,
changes when the treatment of physical processes such as grain physics and
atomic/molecular rates are varied. We find a significant variation in the
intensities of PDR emission lines, depending on different treatments of the
grain physics. We also show how different combinations of the cosmic-ray
ionization rate, inclusion of grain-atom/ion charge transfer, and the grain
size distribution can lead to very similar results for the chemical structure.
Additionally, our results show the utility of Cloudy for the spectral modeling
of molecular environments.Comment: 36 pages, 17 figures, accepted for publication in Ap
On the Dynamic Stability of Cool Supergiant Atmospheres
We have developed a new formalism to compute the thermodynamic coefficient
Gamma1 in the theory of stellar and atmospheric stability. We generalize the
classical derivation of the first adiabatic index, which is based on the
assumption of thermal ionization and equilibrium between gas and radiation
temperature, towards an expression which incorporates photo-ionization due to
radiation with a temperature T_rad different from the local kinetic gas
temperature.Our formalism considers the important non-LTE conditions in the
extended atmospheres of supergiant stars. An application to the Kurucz grid of
cool supergiant atmospheres demonstrates that models with T_rad =~ T_eff
between 6500 K and 7500 K become most unstable against dynamic perturbations,
according to Ledoux' stability integral . This results from Gamma1 and
acquiring very low values, below 4/3, throughout the entire stellar
atmosphere, which causes very high gas compression ratios around these
effective temperatures. Based on detailed NLTE-calculations, we discuss
atmospheric instability of pulsating massive yellow supergiants, like the
hypergiant rho Cas (Ia+), which exist in the extension of the Cepheid
instability strip, near the Eddington luminosity limit.Comment: 54 pages including figures and the Appendix, 7 figures, Accepted for
The Astrophysical Journal, Main Journal, 558, Sept. 200
Generalized Regularization Techniques With Constraints For The Analysis Of Solar Bremsstrahlung X-Ray Spectra
Hard X-ray spectra in solar flares provide knowledge of the electron spectrum
that results from acceleration and propagation in the solar atmosphere.
However, the inference of the electron spectra from solar X-ray spectra is an
ill-posed inverse problem. Here we develop and apply an enhanced regularization
algorithm for this process making use of physical constraints on the form of
the electron spectrum. The algorithm incorporates various features not
heretofore employed in the solar flare context: Generalized Singular Value
Decomposition (GSVD) to deal with different orders of constraints; rectangular
form of the cross-section matrix to extend the solution energy range;
regularization with various forms of the smoothing operator; and
"preconditioning" of the problem. We show by simulations that this technique
yields electron spectra with considerably more information and higher quality
than previous algorithms.Comment: 21 pages, 8 fugures, accepted to Solar Physic
X-Ray Polarization of Solar Flares Measured with Rhessi
The degree of linear polarization in solar flares has not yet been precisely
determined despite multiple attempts to measure it with different missions. The
high energy range in particular has very rarely been explored, due to its
greater instrumental difficulties. We approached the subject using the Reuven
Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study 6 X-class
and 1 M-class flares in the energy range between 100 keV and 350 keV. Using
RHESSI as a polarimeter requires the application of strict cuts to the event
list in order to extract those photons that are Compton scattered between two
detectors. Our measurements show polarization values between 2% and 54%, with
errors ranging from 10% to 26% in 1 sigma level. In view of the large
uncertainties in both the magnitude and direction of the polarization vector,
the results can only reject source models with extreme properties.Comment: 26 pages, 11 figures, accepted for publication by Solar Physic
Widowhood and Mortality: A Meta-Analysis
While the "widowhood effect" is well known, there is substantial heterogeneity in the magnitude of effects reported in different studies. We conducted a meta-analysis of widowhood and mortality, focusing on longitudinal studies with follow-up from the time of bereavement.A random-effects meta-analysis was conducted to calculate the overall relative risk (RR) for subsequent mortality among 2,263,888 subjects from 15 prospective cohort studies. We found a statistically significant positive association between widowhood and mortality, but the widowhood effect was stronger in the period earlier than six months since bereavement (overall RR = 1.41, 95% CI: 1.26, 1.57) compared to the effect after six months (overall RR = 1.14, 95% CI: 1.10, 1.18). Meta-regression showed that the widowhood effect was not different for those aged younger than 65 years compared to those older than 65 (P = 0.25). There was, however, a difference in the magnitude of the widowhood effect by gender; for women the RR was not statistically significantly different from the null (overall RR = 1.04, 95% CI: 1.00, 1.08), while it was for men (overall RR = 1.23, 95% CI: 1.18, 1.28).The results suggest that further studies should focus more on the mechanisms that generate this association especially among men
Adaptive model-driven user interface development systems
Adaptive user interfaces (UIs) were introduced to address some of the usability problems that plague many software applications. Model-driven engineering formed the basis for most of the systems targeting the development of such UIs. An overview of these systems is presented and a set of criteria is established to evaluate the strengths and shortcomings of the state-of-the-art, which is categorized under architectures, techniques, and tools. A summary of the evaluation is presented in tables that visually illustrate the fulfillment of each criterion by each system. The evaluation identified several gaps in the existing art and highlighted the areas of promising improvement
Assessing survival in widowers, and controls -A nationwide, six- to nine-year follow-up
To access full text version of this article. Please click on the hyperlink "View/open" at the bottom of this pageThe aim of this study was to assess if widowers had an increased mortality rate during the first 6 to 9 years after the death of their wife, compared initially to an age-matched control group and also compared to the general population of Iceland. The study base was comprised of all 371 men born in 1924-1969 who were widowed in Iceland in 1999-2001 and 357 controls, married men, who were matched by age and residence.The widowers and controls were followed through the years 2002-2007 using information from Statistics Iceland. Mortality rates were compared between the groups and also with the general population. The mortality rate comparisons were: study group vs. control group, on the one hand, and study group vs. general population on the other. Causes of death were also compared between widowers and their wives. A statistically significant increase in mortality in the widowers' group, compared to controls, was observed.Lifestyle-related factors could not be excluded as contributing to cause of death in these cases. Being a widower was related to an increased risk of death for at least 9 years after the death of their wife.Landspitali - National University Hospital in Reykjavik Iceland,
Rannis, the Icelandic Centre for Research (provides assistance to Icelandic science & technology, Reykjavik, Iceland),
Utfararstofa Islands (a funeral home, Reykjavik, Iceland),
Swedish Cancer Society (Cancerfonden),
Styrktarsjodur Lifsins samtaka um liknarmedferd (Palliative Care Association, Iceland),
Utfarastofa Kirkjugardanna (a funeral home, Reykjavik, Iceland
Solar soft X-rays and solar activity
Soft solar X-rays (8 ⩽ gl ⩽ 12 Å) were observed from OSO-III. An analysis of the X-ray enhancements associated with 165 solar flares revealed that there is a tendency for a weak soft X-ray enhancement to precede the cm- λ burst and H α flare. The peak soft X-ray flux follows the cm- λ peak by about 4 min, on the average. Additionally, it was found that flare-rich active centers tend to produce flares which are stronger X-ray and cm- λ emitters than are flares which take place in flare-poor active centers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43754/1/11207_2004_Article_BF00155382.pd
Recommendations to reduce inequalities for LGBT people facing advanced illness : ACCESSCare national qualitative interview study
This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).BACKGROUND: Lesbian, gay, bisexual and/or trans (LGBT) people have higher risk of certain life-limiting illnesses and unmet needs in advanced illness and bereavement. ACCESSCare is the first national study to examine in depth the experiences of LGBT people facing advanced illness. AIM: To explore health-care experiences of LGBT people facing advanced illness to elicit views regarding sharing identity (sexual orientation/gender history), accessing services, discrimination/exclusion and best-practice examples. DESIGN: Semi-structured in-depth qualitative interviews analysed using thematic analysis. SETTING/PARTICIPANTS: In total, 40 LGBT people from across the United Kingdom facing advanced illness: cancer ( n = 21), non-cancer ( n = 16) and both a cancer and a non-cancer conditions ( n = 3). RESULTS: In total, five main themes emerged: (1) person-centred care needs that may require additional/different consideration for LGBT people (including different social support structures and additional legal concerns), (2) service level or interactional (created in the consultation) barriers/stressors (including heteronormative assumptions and homophobic/transphobic behaviours), (3) invisible barriers/stressors (including the historical context of pathology/criminalisation, fears and experiences of discrimination) and (4) service level or interactional facilitators (including acknowledging and including partners in critical discussions). These all shape (5) individuals' preferences for disclosing identity. Prior experiences of discrimination or violence, in response to disclosure, were carried into future care interactions and heightened with the frailty of advanced illness. CONCLUSION: Despite recent legislative change, experiences of discrimination and exclusion in health care persist for LGBT people. Ten recommendations, for health-care professionals and services/institutions, are made from the data. These are simple, low cost and offer potential gains in access to, and outcomes of, care for LGBT people.Peer reviewedFinal Published versio
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