112 research outputs found
Architecture of Environmental Risk Modelling: for a faster and more robust response to natural disasters
Demands on the disaster response capacity of the European Union are likely to
increase, as the impacts of disasters continue to grow both in size and
frequency. This has resulted in intensive research on issues concerning
spatially-explicit information and modelling and their multiple sources of
uncertainty. Geospatial support is one of the forms of assistance frequently
required by emergency response centres along with hazard forecast and event
management assessment. Robust modelling of natural hazards requires dynamic
simulations under an array of multiple inputs from different sources.
Uncertainty is associated with meteorological forecast and calibration of the
model parameters. Software uncertainty also derives from the data
transformation models (D-TM) needed for predicting hazard behaviour and its
consequences. On the other hand, social contributions have recently been
recognized as valuable in raw-data collection and mapping efforts traditionally
dominated by professional organizations. Here an architecture overview is
proposed for adaptive and robust modelling of natural hazards, following the
Semantic Array Programming paradigm to also include the distributed array of
social contributors called Citizen Sensor in a semantically-enhanced strategy
for D-TM modelling. The modelling architecture proposes a multicriteria
approach for assessing the array of potential impacts with qualitative rapid
assessment methods based on a Partial Open Loop Feedback Control (POLFC) schema
and complementing more traditional and accurate a-posteriori assessment. We
discuss the computational aspect of environmental risk modelling using
array-based parallel paradigms on High Performance Computing (HPC) platforms,
in order for the implications of urgency to be introduced into the systems
(Urgent-HPC).Comment: 12 pages, 1 figure, 1 text box, presented at the 3rd Conference of
Computational Interdisciplinary Sciences (CCIS 2014), Asuncion, Paragua
Understanding a Version of Multivariate Symmetric Uncertainty to assist in Feature Selection
In this paper, we analyze the behavior of the multivariate symmetric
uncertainty (MSU) measure through the use of statistical simulation techniques
under various mixes of informative and non-informative randomly generated
features. Experiments show how the number of attributes, their cardinalities,
and the sample size affect the MSU. We discovered a condition that preserves
good quality in the MSU under different combinations of these three factors,
providing a new useful criterion to help drive the process of dimension
reduction
Breve reflexión sobre el Año Internacional de la Astronomía: motivación para las matemáticas y las ciencias
El presente trabajo presenta una breve descripción del Año Internacional de la Astronomía 2009 y su connotación en el Paraguay. Año decretado como de interés educativo, cultural y científico; y se constituyó en un motor para la articulación de eventos seminales de iniciación, restructuración y motivación a la ciencia. También, presentamos una breve descripción de las Olimpiadas Latinoamericanas de Astronomía y Astronáutica que surgió como un mecanismo de comunicación e integración regional. En lo que respecta al Paraguay, la Olimpiada Paraguaya de Astronomía y Astronáutica - OPAA y varios otros eventos del AIA2009, se han enmarcado en la estructura organizacional y han seguido los delineamientos de las Olimpiadas Matemáticas. Presentamos algunas lecciones aprendidas a lo largo de este año. Este texto es de carácter por sobre todo divulgativo
Feature Selection: A perspective on inter-attribute cooperation
High-dimensional datasets depict a challenge for learning tasks in data
mining and machine learning. Feature selection is an effective technique in
dealing with dimensionality reduction. It is often an essential data processing
step prior to applying a learning algorithm. Over the decades, filter feature
selection methods have evolved from simple univariate relevance ranking
algorithms to more sophisticated relevance-redundancy trade-offs and to
multivariate dependencies-based approaches in recent years. This tendency to
capture multivariate dependence aims at obtaining unique information about the
class from the intercooperation among features. This paper presents a
comprehensive survey of the state-of-the-art work on filter feature selection
methods assisted by feature intercooperation, and summarizes the contributions
of different approaches found in the literature. Furthermore, current issues
and challenges are introduced to identify promising future research and
development.Comment: 17 pages, 2 figure
Modelling and control of Mendelian and maternal inheritance for biological control of dengue vectors
International audienceMosquitoes are vectors of viral diseases with epidemic potential in many regions of the world, and in absence of vaccines or therapies, their control is the main alternative. Chemical control through insecticides has been one of the conventional strategies, but induces insecticide resistance, which may affect other insects and cause ecological damage. Biological control, through the release of mosquitoes infected by the maternally inherited bacterium Wolbachia, which inhibits their vector competence, has been proposed as an alternative. The effects of both techniques may be intermingled in practice: prior insecticide spraying may debilitate wild population, so facilitating subsequent invasion by the bacterium; but the latter may also be hindered by the release of susceptible mosquitoes in an environment where the wild population became resistant, as a result of preexisting undesired exposition to insecticide. To tackle such situations, we propose here a unifying model allowing to account for the cross effects of both control techniques, and based on the latter, design release strategies able to infect a wild population. The latter are feedback laws, whose stabilizing properties are studied
A class of fast-slow models for adaptive resistance evolution
International audienceResistance to insecticide is considered nowadays one of the major threats to insect control, as its occurrence reduces drastically the efficiency of chemical control campaigns, and may also perturb the application of other control methods, like biological and genetic control. In order to account for the emergence and spread of such phenomenon as an effect of exposition to larvicide and/or adulticide, we develop in this paper a general time-continuous population model with two life phases, subsequently simplified through slow manifold theory. The derived models present density-dependent recruitment and mortality rates in a non-conventional way. We show that in absence of selection, they evolve in compliance with Hardy-Weinberg law; while in presence of selection and in the dominant or codominant cases, convergence to the fittest genotype occurs. The proposed mathematical models should allow for the study of several issues of importance related to the use of insecticides and other adaptive phenomena
The Lyman alpha Reference Sample: Extended Lyman alpha Halos Produced at Low Dust Content
We report on new imaging observations of the Lyman alpha emission line (Lya),
performed with the Hubble Space Telescope, that comprise the backbone of the
Lyman alpha Reference Sample (LARS). We present images of 14 starburst galaxies
at redshifts 0.028 < z < 0.18 in continuum-subtracted Lya, Halpha, and the far
ultraviolet continuum. We show that Lya is emitted on scales that
systematically exceed those of the massive stellar population and recombination
nebulae: as measured by the Petrosian 20 percent radius, RP20, Lya radii are
larger than those of Halpha by factors ranging from 1 to 3.6, with an average
of 2.4. The average ratio of Lya-to-FUV radii is 2.9. This suggests that much
of the Lya light is pushed to large radii by resonance scattering. Defining the
"Relative Petrosian Extension" of Lya compared to Halpha, \xi_ext = RP20_Lya /
RP20_Ha, we find \xi_ext to be uncorrelated with total Lya luminosity. However
\xi_ext is strongly correlated with quantities that scale with dust content, in
the sense that a low dust abundance is a necessary requirement (although not
the only one) in order to spread Lya photons throughout the interstellar medium
and drive a large extended Lya halo.Comment: Published in ApJ Letters ~~ 6 pages using emulateapj, 4 figures ~~
Higher-resolution, larger, nicer jpeg versions of Figures 1 and 2 can be
found here: http://xayes.org/pub/press_lars.htm
The Lyman Alpha Reference Sample: V. The impact of neutral ISM kinematics and geometry on Lyman Alpha escape
We present high-resolution far-UV spectroscopy of the 14 galaxies of the
Lyman Alpha Reference Sample; a sample of strongly star-forming galaxies at low
redshifts (). We compare the derived properties to global
properties derived from multi band imaging and 21 cm HI interferometry and
single dish observations, as well as archival optical SDSS spectra. Besides the
Lyman line, the spectra contain a number of metal absorption features
allowing us to probe the kinematics of the neutral ISM and evaluate the optical
depth and and covering fraction of the neutral medium as a function of
line-of-sight velocity. Furthermore, we show how this, in combination with
precise determination of systemic velocity and good Ly spectra, can be
used to distinguish a model in which separate clumps together fully cover the
background source, from the "picket fence" model named by Heckman et al.
(2011). We find that no one single effect dominates in governing Ly
radiative transfer and escape. Ly escape in our sample coincides with a
maximum velocity-binned covering fraction of and bulk outflow
velocities of km s, although a number of galaxies show
these characteristics and yet little or no Ly escape. We find that
Ly peak velocities, where available, are not consistent with a strong
backscattered component, but rather with a simpler model of an intrinsic
emission line overlaid by a blueshifted absorption profile from the outflowing
wind. Finally, we find a strong anticorrelation between H equivalent
width and maximum velocity-binned covering factor, and propose a heuristic
explanatory model.Comment: 28 pages, 19 figures, 5 table
The Lyman Alpha Reference Sample: III. Properties of the Neutral ISM from GBT and VLA Observations
We present new H I imaging and spectroscopy of the 14 UV-selected
star-forming galaxies in the Lyman Alpha Reference Sample (LARS), aimed for a
detailed study of the processes governing the production, propagation, and
escape of Ly photons. New H I spectroscopy, obtained with the 100m
Green Bank Telescope (GBT), robustly detects the H I spectral line in 11 of the
14 observed LARS galaxies (although the profiles of two of the galaxies are
likely confused by other sources within the GBT beam); the three highest
redshift galaxies are not detected at our current sensitivity limits. The GBT
profiles are used to derive fundamental H I line properties of the LARS
galaxies. We also present new pilot H I spectral line imaging of 5 of the LARS
galaxies obtained with the Karl G. Jansky Very Large Array (VLA). This imaging
localizes the H I gas and provides a measurement of the total H I mass in each
galaxy. In one system, LARS 03 (UGC 8335 or Arp 238), VLA observations reveal
an enormous tidal structure that extends over 160 kpc from the main interacting
systems and that contains 10 M of H I. We compare various H I
properties with global Ly quantities derived from HST measurements. The
measurements of the Ly escape fraction are coupled with the new direct
measurements of H I mass and significantly disturbed H I velocities. Our
robustly detected sample reveals that both total H I mass and linewidth are
tentatively correlated with key Ly tracers. Further, on global scales,
these data support a complex coupling between Ly propagation and the H
I properties of the surrounding medium.Comment: Preprint form, 16 figures, accepted in Ap
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