1,528 research outputs found
Chemical and photometric evolution models for disk, irregular and low mass galaxies
We summarize the updated set of multiphase chemical evolution models
performed with 44 theoretical radial mass initial distributions and 10 possible
values of efficiencies to form molecular clouds and stars. We present the
results about the infall rate histories, the formation of the disk, and the
evolution of the radial distributions of diffuse and molecular gas surface
density, stellar profile, star formation rate surface density and elemental
abundances of C,N, O and Fe, finding that the radial gradients for these
elements begin very steeper, and flatten with increasing time or decreasing
redshift, although the outer disks always show a certain flattening for all
times. With the resulting star formation and enrichment histories, we calculate
the spectral energy distributions (SEDs) for each radial region by using the
ones for single stellar populations resulting from the evolutive synthesis
model {\sc popstar}. With these SEDs we may compute finally the broad band
magnitudes and colors radial distributions in the Johnson and in the SLOAN/SDSS
systems which are the main result of this work. We present the evolution of
these brightness and color profiles with the redshift.Comment: 22 pages, 18 figures, accepted in Advances in Astronom
Characterizing stellar populations in spiral disks
It is now possible to measure detailed spectral indices for stellar
populations in spiral disks. We propose to interpret these data using
evolutionary synthesis models computed from the Star Formation Histories
obtained from chemical evolutionary models. We find that this technique is a
powerful tool to discriminate between old and young stellar populations. We
show an example of the power of Integral Field spectroscopy in unveiling the
spatial distribution of populations in a barred galaxy.Comment: 5 pages, to be published in "Science Perspectives for 3D
Spectroscopy", Eds. M. Kissler-Patig, M.M. Roth and J.R. Walsh
(Springer-Verlag, ESO astrophysics symposia series
Scaling methods for categorical self-assessed health measures
The lack of a continuous health valuation is a major drawback in health analyses over broad populations. The use of categorical health variables to estimate a continuous health variable is an usual procedure in healthstudies. The most common approaches (ordered probit/logit model and interval regression model) do not admit any skewness in the distribution of health. In the present study a new procedure is suggested, that is attaching a log-normal distribution to health values. Different scaling procedures have been compared, with data obtained from the Catalan Health Survey (2006). The validity of the scaling approaches is assessed by measuring to what extent the health values derived from categorical health variables suit the actual health values. Two different health tariffs have been used for each procedure (VAS tariff and TTO tariff), so that the results are robust to the selection of a metric. In general, models under log normality outperform the other approaches.Health-Related Quality of Life, Health Measurement, Interval
Document Distance for the Automated Expansion of Relevance Judgements for Information Retrieval Evaluation
This paper reports the use of a document distance-based approach to
automatically expand the number of available relevance judgements when these
are limited and reduced to only positive judgements. This may happen, for
example, when the only available judgements are extracted from a list of
references in a published review paper. We compare the results on two document
sets: OHSUMED, based on medical research publications, and TREC-8, based on
news feeds. We show that evaluations based on these expanded relevance
judgements are more reliable than those using only the initially available
judgements, especially when the number of available judgements is very limited.Comment: SIGIR 2014 Workshop on Gathering Efficient Assessments of Relevanc
Quality of Life Lost Due to Non-Fatal Road Crashes
The objective of this paper is to evaluate the effect of a nonfatal road crash on the health-related quality of life of injured people. A new approach is suggested, based on the cardinalization of categorical Self-Assessed Health valuations. Health losses have been estimated by using different Time Tradeoff and Visual Analogue Scale tariffs, in order to assess the robustness of the results. The methodology is based on the existing literature about treatment effects. Our main contribution focuses on evaluating the loss of health up to one year after the non-fatal accident, for those who are noninstitutionalized, which aids the appropriate estimation of the aggregated health losses in quality-of-life terms.Health-related quality of life, health measurement, road crashes, scaling methods
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