6,406 research outputs found
Extraction of cylinders and cones from minimal point sets
We propose new algebraic methods for extracting cylinders and cones from
minimal point sets, including oriented points. More precisely, we are
interested in computing efficiently cylinders through a set of three points,
one of them being oriented, or through a set of five simple points. We are also
interested in computing efficiently cones through a set of two oriented points,
through a set of four points, one of them being oriented, or through a set of
six points. For these different interpolation problems, we give optimal bounds
on the number of solutions. Moreover, we describe algebraic methods targeted to
solve these problems efficiently
BEAT: An Open-Source Web-Based Open-Science Platform
With the increased interest in computational sciences, machine learning (ML),
pattern recognition (PR) and big data, governmental agencies, academia and
manufacturers are overwhelmed by the constant influx of new algorithms and
techniques promising improved performance, generalization and robustness.
Sadly, result reproducibility is often an overlooked feature accompanying
original research publications, competitions and benchmark evaluations. The
main reasons behind such a gap arise from natural complications in research and
development in this area: the distribution of data may be a sensitive issue;
software frameworks are difficult to install and maintain; Test protocols may
involve a potentially large set of intricate steps which are difficult to
handle. Given the raising complexity of research challenges and the constant
increase in data volume, the conditions for achieving reproducible research in
the domain are also increasingly difficult to meet.
To bridge this gap, we built an open platform for research in computational
sciences related to pattern recognition and machine learning, to help on the
development, reproducibility and certification of results obtained in the
field. By making use of such a system, academic, governmental or industrial
organizations enable users to easily and socially develop processing
toolchains, re-use data, algorithms, workflows and compare results from
distinct algorithms and/or parameterizations with minimal effort. This article
presents such a platform and discusses some of its key features, uses and
limitations. We overview a currently operational prototype and provide design
insights.Comment: References to papers published on the platform incorporate
Excentricité et forme des sections transversales de bois. Définitions, méthodologie, exemples sur l'épicéa commun (Picea abies Karst.)
Cette note fait le point sur plusieurs définitions importantes lorsqu'il s'agit de caractériser l'asymétrie de la croissance du bois en section transversale. Lorsque le contour des rondelles est discrétisé par intersection avec un certain nombre de rayons pairs (2n) équirépartis en direction sur [0.2pi) et originaires de la moelle, il est possible de définir le centre de gravité des points, de la surface et du contour. Ces points sont généralement distincts et sensibles au nombre de rayons utilisés ainsi qu'à leurs orientations. Pour calculer l'excentricité (position de la moelle par rapport au centre de gravité de la surface de la rondelle), ou le méplat (rapport entre le plus grand diamÚtre de la rondelle et son perpendiculaire, passants tous deux par le centre de la rondelle) l'utilisation de I'un ou l'autre de ces points donne des résultats trÚs différents. Les applications sont réalisées pour des figures géométriques simples (cercle. ellipse) et pour 168 rondelles d'épicéa commu
The Jungle Universe
In this paper, we exploit the fact that the dynamics of homogeneous and
isotropic Friedmann-Lemaitre universes is a special case of generalized
Lotka-Volterra system where the competitive species are the barotropic fluids
filling the Universe. Without coupling between those fluids, Lotka-Volterra
formulation offers a pedagogical and simple way to interpret usual
Friedmann-Lemaitre cosmological dynamics. A natural and physical coupling
between cosmological fluids is proposed which preserve the structure of the
dynamical equations. Using the standard tools of Lotka-Volterra dynamics, we
obtain the general Lyapunov function of the system when one of the fluids is
coupled to dark energy. This provides in a rigorous form a generic asymptotic
behavior for cosmic expansion in presence of coupled species, beyond the
standard de Sitter, Einstein-de Sitter and Milne cosmologies. Finally, we
conjecture that chaos can appear for at least four interacting fluids.Comment: 26 pages, 4 figure
Optical Quantum Random Number Generator
A physical random number generator based on the intrinsic randomness of
quantum mechanics is described. The random events are realized by the choice of
single photons between the two outputs of a beamsplitter. We present a simple
device, which minimizes the impact of the photon counters' noise, dead-time and
after pulses.Comment: 3 pages + 1 figur
Parametric Schedulability Analysis of Fixed Priority Real-Time Distributed Systems
Parametric analysis is a powerful tool for designing modern embedded systems,
because it permits to explore the space of design parameters, and to check the
robustness of the system with respect to variations of some uncontrollable
variable. In this paper, we address the problem of parametric schedulability
analysis of distributed real-time systems scheduled by fixed priority. In
particular, we propose two different approaches to parametric analysis: the
first one is a novel technique based on classical schedulability analysis,
whereas the second approach is based on model checking of Parametric Timed
Automata (PTA).
The proposed analytic method extends existing sensitivity analysis for single
processors to the case of a distributed system, supporting preemptive and
non-preemptive scheduling, jitters and unconstrained deadlines. Parametric
Timed Automata are used to model all possible behaviours of a distributed
system, and therefore it is a necessary and sufficient analysis. Both
techniques have been implemented in two software tools, and they have been
compared with classical holistic analysis on two meaningful test cases. The
results show that the analytic method provides results similar to classical
holistic analysis in a very efficient way, whereas the PTA approach is slower
but covers the entire space of solutions.Comment: Submitted to ECRTS 2013 (http://ecrts.eit.uni-kl.de/ecrts13
Fe(II)âFe(III)-Bearing Phases As a Mineralogical Control on the Heterogeneity of Arsenic in Southeast Asian Groundwater
International audienceAlthough groundwater arsenic constitutes a major hazard to the health of the people of Southeast Asia, the exact mineralogical origin of the arsenic in these fluvial aquifers is still under debate. Fe(III) oxides are the dominant hosts of mobilizable arsenic in the sediments, with the role of secondary Fe(II)-bearing phases like mackinawite, siderite, vivianite, magnetite, and carbonate green rust (fougerite) still unclear. Based on published field data from Chakdaha (India), the importance of the phases for arsenic mobility is evaluated quantitatively using models of growing complexity. Arsenic heterogeneity can be explained by the presence of two contrasted redox zones in the aquifers, with Fe(III) oxides being the dominant sorbent for arsenic in the less reduced zones and Fe(II) sulfides and/or Fe(II) carbonates being the solid-phase hosts for arsenic under more reduced conditions below impermeable soils or close to rivers where sulfate is reduced. A 1D reactive transport model which simulates the transition between the two environments has been developed and compared to field data. The results show that microbial sulfate reduction followed by abiotic and/or biotic reduction of As(III)-bearing iron oxides accounts for the spatial heterogeneity of arsenic in such reduced aquifers
On the cut-off phenomenon for the transitivity of randomly generated subgroups
38 pagesInternational audienceConsider independent copies of the random walk on the symmetric group starting from the identity and generated by the products of either independent uniform transpositions or independent uniform neighbor transpositions. At any time n\in\NN, let be the subgroup of generated by the positions of the chains. In the uniform transposition model, we prove that there is a cut-off phenomenon at time for the non-existence of fixed point of and for the transitivity of , thus showing that these properties occur before the chains have reached equilibrium. In the uniform neighbor transposition model, a transition for the non-existence of a fixed point of appears at time of order (at least for ), but there is no cut-off phenomenon. In the latter model, we recover a cut-off phenomenon for the non-existence of a fixed point at a time proportional to by allowing the number to be proportional to . The main tools of the proofs are spectral analysis and coupling techniques
RĂ©seaux dâinformation des PME en milieu non mĂ©tropolitain
L'article analyse les réseaux d'information des PME situées au Québec en milieu non métropolitain. Le recours aux réseaux est analysé en fonction de l'internationalisation et de leur localisation en site rural ou urbain. Il appert qu'il n'y a pas de différences significatives entre les PME exportatrices et non exportatrices quant aux recours aux ressources externes, à l'exception des associations sectorielles et des organismes gouvernementaux davantage utilisés par les entreprises exportatrices. Contrairement à l'opinion largement répandue, l'implantation en milieu rural des PME a peu d'effet sur le caractÚre novateur des entreprises. En fait, l'inconvénient le plus important sur le plan de l'information est leur accessibilité aux centres de recherches privés. Bref, l'écart entre les zones urbaines et rurales en matiÚre de réseaux d'information, d'innovation et d'exportation s'est amenuisé pour les PME en milieu non métropolitain.This paper refers to Québec non-metropolitan SME information networks. The latter are analyzed with respect to globalization taking into account an urban as well as a rural localization. With regard to external resources, this study shows an absence of difference between exporting and non-exporting SME with the exception of sectorial organizations and governmental agencies whose resources are more utilized by exporting SME. Contrary to what it is generally thought, a rural localization has no negative effect on innovation. Actually, the main disadvantage these enterprises have to cope with is the isolation from research centres. We can conclude that for the non-metropolitan SME, the differential between rural and urban areas, concerning information networks and their impact on innovation and exportations, has decreased very significantly in recent years
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