287,970 research outputs found
PopStar Evolutionary Synthesis Models II: Optical emission-line spectra from Giant H{\sc ii} regions
This is the second paper of a series reporting the results from the PopStar
evolutionary synthesis models. Here we present synthetic emission line spectra
of H{\sc ii} regions photoionized by young star clusters, for seven values of
cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing Spectral
Energy Distributions (SEDs) are those obtained by the PopStar code
\citep*{mgb09} for six different metallicities, with a very low metallicity
set, Z=0.0001, not included in previous similar works. We assume that the
radius of the H{\sc ii} region is the distance at which the ionized gas is
deposited by the action of the mechanical energy of the winds and supernovae
from the central ionizing young cluster. In this way the ionization parameter
is eliminated as free argument, since now its value is obtained from the
cluster physical properties (mass, age and metallicity) and from the gaseous
medium characteristics (density and abundances). We discuss our results and
compare them with those from previous models and also with a large and data set
of giant H{\sc ii} regions for which abundances have been derived in a
homogeneous manner. The values of the [OIII] lines (at 4363,
4959, 5007\AA) in the lowest metallicity nebulae are found to be very weak and
similar to those coming from very high metallicity regions (solar or
over-solar). Thus, the sole use of the oxygen lines is not enough to
distinguish between very low and very high metallicity regions. In these cases
we emphasize the need of the additional support of alternative metallicity
tracers, like the [SIII] lines in the near-\textit{IR}.Comment: 20 pages, 26 figures, accepted for publication in MNRAS Main Journa
An African Christian perspective of death
Death is the end or absence of life; it also refers to the end of a thing or an event It is a common phenomenon, which is unavoidable. Africans, like other people are interested in it, and they view and treat it from their cultural perspectives. However, those Africans who are converted to Christianity face a sort of dilemma in that Christianity came with its own views and teachings on death, along with a mixture of the cultures and backgrounds of the missionaries who brought it, whereas the Africans already had their own views. This paper attempts to examine death both from the Christian and African perspectives with particular emphasis on the Efik people of Nigeria, then it attempts to synthesize both positions in an attempt to formulate an African Christian Theology on Death which is avoid of foreign cultural influence and is not contrary to the Bible. In order to achieve this, constant references are made to the Bible and African views on various aspects of death such as its meaning, causes, types, purposes, and the Afterlife
Children and young peopleâs experiences and perceptions of self-management of type 1 diabetes: A qualitative meta-synthesis
The aim of this review was to conduct a meta-synthesis of the experiences and perceptions of self-management of type 1 diabetes of children and young people living with type 1 diabetes (CYPDs). Six databases were systematically searched for studies with qualitative findings relevant to CYPDsâ (aged 8â18âyears) experiences of self-management. A thematic synthesis approach was used to combine articles and identify analytical themes. Forty articles met the inclusion criteria. Two analytical themes important to CYPDsâ experiences and perceptions of self-management were identified: (1) negotiating independence and (2) feeling in control. The synthesis contributes to knowledge on contextual factors underpinning self-management and what facilitates or impedes transition towards autonomous self-management for CYPDs
Energy Feedback from X-ray Binaries in the Early Universe
X-ray photons, because of their long mean-free paths, can easily escape the
galactic environments where they are produced, and interact at long distances
with the inter-galactic medium, potentially having a significant contribution
to the heating and reionization of the early Universe. The two most important
sources of X-ray photons in the Universe are active galactic nuclei (AGN) and
X-ray binaries (XRBs). In this Letter we use results from detailed, large scale
population synthesis simulations to study the energy feedback of XRBs, from the
first galaxies (z~ 20) until today. We estimate that X-ray emission from XRBs
dominates over AGN at z>6-8. The shape of the spectral energy distribution of
the emission from XRBs shows little change with redshift, in contrast to its
normalization which evolves by ~4 orders of magnitude, primarily due to the
evolution of the cosmic star-formation rate. However, the metallicity and the
mean stellar age of a given XRB population affect significantly its X-ray
output. Specifically, the X-ray luminosity from high-mass XRBs per unit of
star-formation rate varies an order of magnitude going from solar metallicity
to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of
stellar mass peaks at an age of ~300 Myr and then decreases gradually at later
times, showing little variation for mean stellar ages > 3 Gyr. Finally, we
provide analytical and tabulated prescriptions for the energy output of XRBs,
that can be directly incorporated in cosmological simulations.Comment: Accepted for publication to ApJ Letters, 6 pages, 2 figures, 2 table.
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Managing lifestyle change to reduce coronary risk: a synthesis of qualitative research on peoplesâ experiences
Background
Coronary heart disease is an incurable condition. The only approach known to slow its progression is healthy lifestyle change and concordance with cardio-protective medicines. Few people fully succeed in these daily activities so potential health improvements are not fully realised. Little is known about peoplesâ experiences of managing lifestyle change. The aim of this study was to synthesise qualitative research to explain how participants make lifestyle change after a cardiac event and explore this within the wider illness experience.
Methods
A qualitative synthesis was conducted drawing upon the principles of meta-ethnography. Qualitative studies were identified through a systematic search of 7 databases using explicit criteria. Key concepts were identified and translated across studies. Findings were discussed and diagrammed during a series of audiotaped meetings.
Results
The final synthesis is grounded in findings from 27 studies, with over 500 participants (56% male) across 8 countries. All participants experienced a change in their self-identity from what was âfamiliarâ to âunfamiliarâ. The transition process involved âfinding new limits and a life worth livingââ, âfinding support for selfâ and âfinding a new normalâ. Analyses of these concepts led to the generation of a third order construct, namely an ongoing process of âreassessing past, present and future livesâ as participants considered their changed identity. Participants experienced a strong urge to get back to ânormalâ. Support from family and friends could enable or constrain life change and lifestyle changes. Lifestyle change was but one small part of a wider âlifeâ change that occurred.
Conclusions
The final synthesis presents an interpretation, not evident in the primary studies, of a person-centred model to explain how lifestyle change is situated within âwiderâ life changes. The magnitude of individual responses to a changed health status varied. Participants experienced distress as their notion of self identity shifted and emotions that reflected the various stages of the grief process were evident in participantsâ accounts. The process of self-managing lifestyle took place through experiential learning; the level of engagement with lifestyle change reflected an individualâs unique view of the balance needed to manage ârealistic changeâ whilst leading to a life that was perceived as âworth livingâ. Findings highlight the importance of providing person centred care that aligns with both psychological and physical dimensions of recovery which are inextricably linked
Predicted gamma-ray line emission from the Cygnus complex
The Cygnus region harbours a huge complex of massive stars at a distance of
1.0-2.0kpc from us. About 170 O stars are distributed over several OB
associations, among which the Cyg OB2 cluster is by far the most important with
about 100-120 O stars. These massive stars inject large quantities of
radioactive nuclei into the interstellar medium, such as 26Al and 60Fe, and
their gamma-ray line decay signals can provide insight into the physics of
massive stars and core-collapse supernovae. Past studies of the nucleosynthesis
activity of Cygnus have concluded that the level of 26Al decay emission as
deduced from CGRO/COMPTEL observations was a factor 2-3 above the predictions
based on the theoretical yields available at that time and on the observed
stellar content of the Cygnus region. We reevaluate the situation from new
measurements of the gamma-ray decay fluxes with INTEGRAL/SPI and new
predictions based on recently improved stellar models including some of the
effects of stellar rotation for the higher mass stars and a coherent estimate
of the contribution from SNIb/c. We developed a population synthesis code to
predict the nucleosynthesis activity and corresponding decay fluxes of a given
stellar population of massive stars. The observed decay fluxes from the Cygnus
complex are found to be consistent with the values predicted by population
synthesis at solar metallicity. The observed extent of the 1809keV emission
from Cygnus is found to be consistent with the result of a numerical simulation
of the diffusion of 26Al inside the superbubble blown by Cyg OB2. Our work
indicates that the past dilemma regarding the gamma-ray line emission from
Cygnus resulted from an overestimate of the 1809keV flux of the Cygnus complex,
combined with an underestimate of the nucleosynthesis yields.Comment: 13 pages, 9 figures, accepted for publication in A&
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