15771 research outputs found
Sort by
Rate of convergence of the Nanbu particle system for hard potentials and Maxwell molecules
No full textWe consider the (numerically motivated) Nanbu stochastic particle system associated to the spatially homogeneous Boltzmann equation for true hard potentials. We establish a rate of propagation of chaos of the particle system to the unique solution of the Boltzmann equation. More precisely, we estimate the expectation of the squared Wasserstein distance with quadratic cost between the empirical measure of the particle system and the solution. The rate we obtain is almost optimal as a function of the number of particles but is not uniform in time.nonnonouirechercheInternationa
Biobjective planning of an active debris removal mission
No full textThe growth of the orbital debris population has been a concern to the international space community for several years. Recent studies have shown that the debris environment in Low Earth Orbit (LEO, defined as the region up to 2000 km altitude) has reached a point where the debris population will continue to increase even if all future launches are suspended. As the orbits of these objects often overlap the trajectories of satellites, debris create a potential collision risk. However, several studies show that about 5 objects per year should be removed in order to keep the future LEO environment stable. In this article, we propose a biobjective time dependent traveling salesman problem (BiTDTSP) model for the problem of optimally removing debris and use a branch and bound approach to deal with it.nonouirechercheInternationa
A bicriteria two-machine flow-shop serial-batching scheduling problem with bounded batch size
No full textWe consider the two-machine flow-shop serial-batching scheduling problem where the machines have a limited capacity in terms of the number of jobs. Two criteria are considered here. The first criterion is the number of batches to be minimized. This criterion reflects situations where processing of any batch induces a fixed cost, which leads to a total cost proportional to the number of batches. The second criterion is the makespan. This model is relevant in different production contexts, especially when considering joint production and inbound delivery scheduling. We study the complexity of the problem and propose two polynomial-time approximation algorithms with a guaranteed performance. The effectiveness of these algorithms is evaluated using numerical experiments. Exact polynomial-time algorithms are also provided for some particular cases.nonouirechercheInternationa
Lasso and probabilistic inequalities for multivariate point processes
No full textDue to its low computational cost, Lasso is an attractive regularization method for high-dimensional statistical settings. In this paper, we consider multivariate counting processes depending on an unknown function to be estimated by linear combinations of a fixed dictionary. To select coefficients, we propose an adaptive -penalization methodology, where data-driven weights of the penalty are derived from new Bernstein type inequalities for martingales. Oracle inequalities are established under assumptions on the Gram matrix of the dictionary. Non-asymptotic probabilistic results for multivariate Hawkes processes are proven, which allows us to check these assumptions by considering general dictionaries based on histograms, Fourier or wavelet bases. Motivated by problems of neuronal activities inference, we finally lead a simulation study for multivariate Hawkes processes and compare our methodology with the {\it adaptive Lasso procedure} proposed by Zou in \cite{Zou}. We observe an excellent behavior of our procedure with respect to the problem of supports recovery. We rely on theoretical aspects for the essential question of tuning our methodology. Unlike adaptive Lasso of \cite{Zou}, our tuning procedure is proven to be robust with respect to all the parameters of the problem, revealing its potential for concrete purposes, in particular in neuroscience.ouinonouirechercheInternationa
Cost Effectiveness of Intermittent Preventive Treatment of Malaria in Infants in Ghana
No full textAim: In order to integrate malaria Intermittent Preventive Treatment in infants (IPTi) into the Ghana national immunization programme, there was the need to evaluate the feasibility of IPTi by assessing the intervention operational issues including its implementation costs, and its cost effectiveness. Study Design: Cross-sectional study. Place and Duration of Study: Upper East Region, Ghana, between July 2007 and July 2009 Methods: We calculated the costs of administrating IPTi during vaccination sessions; the costs of programme implementation during the first year of implementation (start-up costs) and in routine years (recurrent costs). For the purposes of cost-effectiveness analysis, all economic costs (including financial and opportunity costs) and the net cost were estimated. To estimate the cost effectiveness ratios of IPTi, the aggregate cost of providing the intervention for a reference target population of 1,000 infants was divided by its health outcome. Sensitivity analyses were carried out to understand the results robustness. Results: IPTi gross costs in start up and in routine years were estimated at 70.66 cents and 29.72 cents per dose, or 0.87 per infant, respectively. The gross cost per DALY saved was estimated at -3,416.38 in the routine years rending IPTi a highly cost saving intervention. Sensitivity analyses showed that the cost per DALY saved never went up more than $4.50 maintaining the intervention still highly cost effective. Conclusion: IPTi in Ghana is a highly and robust cost effective intervention. The intervention is cost-saving and should be scaled up nationally to save children’s health and economic capital.nonouirechercheInternationa
Formation en entreprise et débauchage de main d'oeuvre aux Etats-Unis : un modèle dynamique d'action collective
No full textNous proposons, dans cet article, un modèle dynamique d'action collective permettant d'étudier les conditions d'émergence d'un système de formation en entreprise dans l'économie américaine. Ce type de formation comporte certaines des caractéristiques d'un bien collectif et sa production soulève, de ce fait, un problème de coordination de type dilemme du prisonnier à n joueurs. Nous modélisons celui-ci à l'aide d'un formalisme emprunté à la mécanique statistique et en supposant les entreprises fortement hétérogènes. Nous montrons qu'un équilibre à haut niveau de formation en entreprise peut en théorie émerger spontanément. Cela s'avère cependant impossible pour des valeurs des paramètres caractéristiques de l'économie américaine.Training and labor poaching in the U.S : a dynamical model of collective action This article presents a dynamical model of collective action which provides a framework for studying whether the American economy may ever spontaneously shift towards a high-training equilibrium in the absence of any institutional intervention. In-firm training has some of the characteristics of a collective good and its production thus raises a problem of coordination, very close to a n-player prisoner's dilemma. We modelize this problem, borrowing from statistical physics and assuming that firms are heterogeneous. We show that, in theory, a high-training equilibrium may eventually emerge, in the long run. However, this proves impossible in the United-States given the values of the parameters for the American economy.nonouirecherchenationa
Croissance et formation : le rôle de la politique éducative
No full textCroissance et formation : le rôle de la politique éducative, par Eve Caroli. Nous proposons, dans cet article, une première approche de la relation entre croissance et politique de formation. Nous reprenons et étendons, pour ce faire, le modèle élaboré par R. Lucas en 1988 qui constitue l'une des premières tentatives d'endogénéisation du capital humain dans un modèle de croissance. Notre hypothèse est que la productivité du temps moyen par individu consacré à la formation - en termes de taux de croissance du capital humain - n'est pas indépendante des caractéristiques du système éducatif. Nous supposons qu'il s'agit d'une fonction croissante mais saturante du taux d'encadrement qui constitue ici la variable exogène de politique éducative. Corrélativement, l'expression de la fonction de production tient compte du fait que les formateurs sont autant d'actifs en moins dans le secteur de la production finale. La résolution du modèle met en évidence le fait que le long du sentier de croissance équilibrée, le taux de croissance de l'économie est une fonction croissante puis décroissante du taux d'encadrement. Cela signifie qu'au-delà d'un certain seuil, l'augmentation du taux d'encadrement est contre-productive en termes de croissance. Il existe donc une politique de formation optimale. Celle-ci varie de plus selon l'efficacité des enseignants et l'on conclut que plus la qualité du personnel enseignant est faible et/ou plus les conditions d'enseignement sont mauvaises, et plus le taux de croissance maximal que l'économie peut atteindre est faible.Growth and Training: The Role of Education Policies, by Eve Caroli. This paper proposes a preliminary approach to the relation between growth and training policies. We use an extended version of the 1988 R. Lucas model, which was one of the first attempts at making human capital endogenous in a growth model. Our hypothesis is that the productivity of average per-capita training time - in terms of human capital growth rates - is not independent of the characteristics of the education system. We posit that it is an increasing, yet saturating, function of the training rate, which here is the exogenous variable in the education policy. Correlatively, the production function expression takes account of the fact that trainers represent so many staff less in the final production sector. The solving of the model shows that the economy's growth rate is an increasing and then decreasing function of the training rate all the way down the balanced growth path. This means that beyond a certain threshold, the increase in the training rate is counterproductive for growth. There thus exists an optimal training policy. This policy varies with the efficiency of the teachers. It is concluded that the lower the quality of the training staff and/or the poorer the teaching conditions, the lower the maximum growth rate able to be attained by the economy.nonouirecherchenationa
Operators in Food Processing Industries: Coping with Increasing Pressure
No full textnonouirechercheinternationa
Weak transport inequalities and applications to exponential and oracle inequalities
No full textWe extend the dimension free Talagrand inequalities for convex distance using an extension of Marton’s weak transport to other metrics than the Hamming distance. We study the dual form of these weak transport inequalities for the euclidian norm and prove that it implies sub-gaussianity and convex Poincaré inequality. We obtain new weak transport inequalities for non products measures extending the results of Samson. Many examples are provided to show that the euclidian norm is an appropriate metric for classical time series. Our approach, based on trajectories coupling, is more efficient to obtain dimension free concentration than existing contractive assumptions. Expressing the concentration properties of the ordinary least square estimator as a conditional weak transport problem, we derive new oracle inequalities with fast rates of convergence in dependent settings.nonnonouirechercheInternationa
Interactive Search for Compromise Solutions in Multicriteria Graph Problems
No full textIn this paper, the purpose is to adapt classical interactive methods to multicriteria combinatorial problems in order to explore the non-dominated solutions set. We propose an interactive procedure alternating a calculation stage determining the current best compromise solution and a dialogue stage allowing decision maker to specify his/her preferences. For the calculation stage, we propose an efficient procedure which relies on algorithms providing k-best solutions of a scalarized version of the problem. Moreover, we show how to exploit previous iterations to speed-up the interactive process. We provide numerical experiments of our method on multicriteria shortest path and spanning tree problems.ouinonouirechercheInternationa