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Analysis of some splitting schemes for the stochastic Allen-Cahn equation
No full textInternational audienceWe introduce and analyze an explicit time discretization scheme for the one-dimensional stochastic Allen-Cahn, driven by space-time white noise. The scheme is based on a splitting strategy, and uses the exact solution for the nonlinear term contribution. We first prove boundedness of moments of the numerical solution. We then prove strong convergence results: first, L^2 (Ω)-convergence of order almost 1/4, localized on an event of arbitrarily large probability, then convergence in probability of order almost 1/4. The theoretical analysis is supported by numerical experiments, concerning strong and weak orders of convergence
Parametric identification of stochastic interaction networks
No full textInternational audienceThis article addresses issues from applied stochastic analysis for solving parameter identification problems in interaction networks. Purely discontinuous Markov processes are the most appropriate choice for modelling these systems and it is of paramount importance to estimate the unknown characteristics of the model given the measured data. The model induces a Fokker–Planck–Kolmogorov equation along with moment equations, and achieving parametric identification based on direct solutions of these equations has remained elusive. We propose a novel approach which utilizes stochastic analysis of continuous-time Markov processes to lift the curse of dimensionality in parametric identification. We illustrate through a case study from ecological engineering
Is there a trade-off between simplicity and robustness? Illustration on a lattice-gas model of swarming
No full textInternational audienceWe re-examine a cellular automaton model of swarm formation. The local rule is stochastic and defined simply as a force that aligns particles with their neighbours. This lattice-gas cellular automaton was proposed by Deutsch to mimic the self-organisation process observed in various natural systems (birds, fishes, bacteria, etc.). We explore the various patterns the self-organisation process may adopt. We observe that, according to the values of the two parameters that define the model, the alignment sensitivity and density of particles, the system may display a great variety of patterns. We analyse this surprising diversity of patterns with numerical simulations. We ask where this richness comes from. Is it an intrinsic characteristic of the model or a mere effect of the modelling simplifications
"You see yourself like in a mirror”: The effects of internet-mediated personal networks on body image and eating disorders
No full textPublished online on 6 July 2017International audienceBody image issues associated with eating disorders involve attitudinal and perceptual components: individuals’ dissatisfaction with body shape or weight, and inability to assess body size correctly. While prior research has mainly explored social pressures produced by the media, fashion, and advertising industries, this paper focuses on the effects of personal networks on body image, particularly in the context of internet communities. We use data collected on a sample of participants to websites on eating disorders, and map their personal networks. We specify and estimate a model for the joint distribution of attitudinal and perceptual components of body image as a function of network-related characteristics and attributional factors. Supported by information gathered through in-depth interviews, the empirical estimates provide evidence that personal networks can be conducive to positive body image development, and that the influence of personal networks varies significantly by body size. We situate our discussion in current debates about the effects of computer-mediated and face-to-face communication networks on eating disorders and related behaviors
Detectability of junctions of underground electrical cables with a ground penetrating radar: Electromagnetic simulation and experimental measurements
No full textInternational audienceFor electricity distribution companies, being able to accurately detect the position of buried power cables using nondestructive methods is a crucial issue. The most important issue is the localization of the junction part linking the cables to each other where most maintenance operations are carried out. In this work we have conducted a feasibility study to confirm the relevance of high frequency Ground Penetrating Radar (GPR) to detect these buried junctions in their environment despite the clutter. The cables are buried in an inhomogeneous Earth medium at about one meter deep. Consequently, we have optimized a folded bowtie antenna to fit the frequency band [0.5 GHz–3 GHz]. Then a rigorous model of the cable is considered in the numerical study using the optimized antenna in a bi-static configuration. A full wave electromagnetic simulation software (CST MWS) has been used to study the detectability of the junction within dry and wet homogeneous sands then a classical Kirchhoff migration technique has been used to process the data and localize the junction. Finally, our analysis has been validated by measurements at a test site (real environment) to show the efficiency of the proposed analysis. The measured data are also post-processed using a digital filtering technique for clutter reduction and visibility enhancement of the buried cable
Barriers to entry in frequency-regulation services markets: Review of the status quo and options for improvements
No full textInternational audienceAs the share of intermittent renewable energy sources increases, it will be necessary to increase the volume of frequency-regulation reserves. New sources of reserves can be found in distributed energy resources: controllable loads, Electric Vehicles (EVs), distributed generation units. However, it is necessary to adapt the frequency-regulation reserve market design to allow these new resources to participate through new market players known as “aggregators”. The aim of this paper is to provide a modular framework to analyze frequency regulation markets or mechanisms in order i) to identify barriers to entry for aggregators and ii) to identify some options to overcome these barriers. A case study of the situation in 2016 of four major European frequency regulation markets is performed to show how this framework could be used by aggregators or policy-makers
A full-reference Image Quality Assessment metric for 3D Synthesized Views
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Fast Inference of Individual Admixture Coefficients Using Geographic Data
No full textInternational audienceAccurately evaluating the distribution of genetic ancestry across geographic space is one of the main questions addressed by evolutionary biologists. This question has been commonly addressed through the application of Bayesian estimation programs allowing their users to estimate individual admixture proportions and allele frequencies among putative ancestral populations. Following the explosion of high-throughput sequencing technologies, several algorithms have been proposed to cope with computational burden generated by the massive data in those studies. In this context, incorporating geographic proximity in ancestry estimation algorithms is an open statistical and computational challenge. In this study, we introduce new algorithms that use geographic information to estimate ancestry proportions and ancestral genotype frequencies from population genetic data. Our algorithms combine matrix factorization methods and spatial statistics to provide estimates of ancestry matrices based on least-squares approximation. We demonstrate the benefit of using spatial algorithms through extensive computer simulations, and we provide an example of application of our new algorithms to a set of spatially referenced samples for the plant species Arabidopsis thaliana. Without loss of statistical accuracy, the new algorithms exhibit runtimes that are much shorter than those observed for previously developed spatial methods. Our algorithms are implemented in the R package, tess3r
A new approach to modelling Kelvin probe force microscopy of hetero-structures in the dark and under illumination
No full textPart of the topical collections: "2017 Numerical Simulation of Optoelectronic Devices, NUSOD'17"International audienceA numerical method is proposed to model Kelvin probe force microscopy of hetero-structures in the dark and under illumination. It is applied to FTO/TiO2 and FTO/TiO2/MAPbI3 structures. The presence of surface states on the top of the TiO2 layers are revealed by combining theoretical computation and experimental results. Basic features of Kelvin probe force microscopy under illumination, namely surface photovoltage, are simulated as well. The method paves the way toward further investigations of more complicated optoelectronic devices