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Search Results: 1 - 10 of 36846 matches for " Stéphane Thomas "
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Discrete limit and monotonicity properties of the Floquet eigenvalue in an age structured cell division cycle model
Stéphane Gaubert,Thomas Lepoutre
Mathematics , 2013,
Abstract: We consider a cell population described by an age-structured partial differential equation with time periodic coefficients. We assume that division only occurs after a minimal age (majority) and within certain time intervals. We study the asymptotic behavior of the dominant Floquet eigenvalue, or Perron-Frobenius eigenvalue, representing the growth rate, as a function of the majority age, when the division rate tends to infinity (divisions become instantaneous). We show that the dominant Floquet eigenvalue converges to a staircase function with an infinite number of steps, determined by a discrete dynamical system. As an intermediate result, we give a structural condition which guarantees that the dominant Floquet eigenvalue is a nondecreasing function of the division rate. We also give a counter example showing that the latter monotonicity property does not hold in general.
Tail index estimation, concentration and adaptivity
Stéphane Boucheron,Maud Thomas
Statistics , 2015,
Abstract: This paper presents an adaptive version of the Hill estimator based on Lespki's model selection method. This simple data-driven index selection method is shown to satisfy an oracle inequality and is checked to achieve the lower bound recently derived by Carpentier and Kim. In order to establish the oracle inequality, we derive non-asymptotic variance bounds and concentration inequalities for Hill estimators. These concentration inequalities are derived from Talagrand's concentration inequality for smooth functions of independent exponentially distributed random variables combined with three tools of Extreme Value Theory: the quantile transform, Karamata's representation of slowly varying functions, and R\'enyi's characterisation of the order statistics of exponential samples. The performance of this computationally and conceptually simple method is illustrated using Monte-Carlo simulations.
Comparison of Perron and Floquet eigenvalues in age structured cell division cycle models
Jean Clairambault,Stéphane Gaubert,Thomas Lepoutre
Mathematics , 2008, DOI: 10.1051/mmnp/20094308
Abstract: We study the growth rate of a cell population that follows an age-structured PDE with time-periodic coefficients. Our motivation comes from the comparison between experimental tumor growth curves in mice endowed with intact or disrupted circadian clocks, known to exert their influence on the cell division cycle. We compare the growth rate of the model controlled by a time-periodic control on its coefficients with the growth rate of stationary models of the same nature, but with averaged coefficients. We firstly derive a delay differential equation which allows us to prove several inequalities and equalities on the growth rates. We also discuss about the necessity to take into account the structure of the cell division cycle for chronotherapy modeling. Numerical simulations illustrate the results.
Hypergraphs and City Street Networks
Thomas Courtat,Catherine Gloaguen,Stéphane Douady
Computer Science , 2011,
Abstract: The map of a city's streets constitutes a particular case of spatial complex network. However a city is not limited to its topology: it is above all a geometrical object whose particularity is to organize into short and long axes called streets. In this article we present and discuss two algorithms aiming at recovering the notion of street from a graph representation of a city. Then we show that the length of the so-called streets scales logarithmically. This phenomenon leads to assume that a city is shaped into a logic of extension and division of space.
Las Dinámicas colectivas en dos cuencas lecheras Mexicanas: Tlaxco, Tlaxcala y Tizayuca, Hidalgo
Poméon,Thomas; Boucher,Fran?ois; Cervantes,Fernando; Fournier,Stéphane;
Agroalimentaria , 2006,
Abstract: this article is the result of the research in two mexican milk basins, carried out with the localized food and agriculture system (lfas) view. parting from the diagnosis of the production chains and the territories, an analysis of the collective dynamics is proposed. in this view, the history of the territory and of the activity is an indicator of great importance. despite the fact the basins show profound structural differences and in operation, pointing out some tendencies is possible. the horizontal convergence of these strategies is constructed around the production of the same product and is materialized, or not, in collective organizations. however, in these basins, strong and stable collective actions are not developed reason for which horizontal cooperation is based more of family and friendly relations while in the vertical relations opportunism dominates. the non specification of the quality of products accentuates this phenomenon. in terms of proximity and trust, developing a strong professional proximity based on a clear definition of the rules of the game and of penalties is needed. the absence is in part, responsible for coordination problems. the low level of social capital worsens the situation. moreover, the role of the state has not always been the most appropriate. to break the vicious circle of the non cooperation, reopening dialogue spaces and collective development projects leading towards strong motivation is necessary.
Genome dedoubling by DCJ and reversal
Thomas Antoine,Varré Jean-Stéphane,Ouangraoua A?da
BMC Bioinformatics , 2011, DOI: 10.1186/1471-2105-12-s9-s20
Abstract: Background Segmental duplications in genomes have been studied for many years. Recently, several studies have highlighted a biological phenomenon called breakpoint-duplication that apparently associates a significant proportion of segmental duplications in Mammals, and the Drosophila species group, to breakpoints in rearrangement events. Results In this paper, we introduce and study a combinatorial problem, inspired from the breakpoint-duplication phenomenon, called the Genome Dedoubling Problem. It consists of finding a minimum length rearrangement scenario required to transform a genome with duplicated segments into a non-duplicated genome such that duplications are caused by rearrangement breakpoints. We show that the problem, in the Double-Cut-and-Join (DCJ) and the reversal rearrangement models, can be reduced to an APX-complete problem, and we provide algorithms for the Genome Dedoubling Problem with 2-approximable parts. We apply the methods for the reconstruction of a non-duplicated ancestor of Drosophila yakuba. Conclusions We present the Genome Dedoubling Problem, and describe two algorithms solving the problem in the DCJ model, and the reversal model. The usefulness of the problems and the methods are showed through an application to real Drosophila data.
Genome Halving by Block Interchange
Antoine Thomas,A?da Ouangraoua,Jean-Stéphane Varré
Computer Science , 2011,
Abstract: We address the problem of finding the minimal number of block interchanges (exchange of two intervals) required to transform a duplicated linear genome into a tandem duplicated linear genome. We provide a formula for the distance as well as a polynomial time algorithm for the sorting problem.
Tandem halving problems by DCJ
Antoine Thomas,A?da Ouangraoua,Jean-Stéphane Varré
Computer Science , 2012,
Abstract: This paper has been withdrawn by the author.
A packing problem approach to energy-aware load distribution in Clouds
Thomas Carli,Stéphane Henriot,Johanne Cohen,Joanna Tomasik
Computer Science , 2014,
Abstract: The Cloud Computing paradigm consists in providing customers with virtual services of the quality which meets customers' requirements. A cloud service operator is interested in using his infrastructure in the most efficient way while serving customers. The efficiency of infrastructure exploitation may be expressed, amongst others, by the electrical energy consumption of computing centers. We propose to model the energy consumption of private Clouds, which provides virtual computation services, by a variant of the Bin Packing problem. This novel generalization is obtained by introducing such constraints as: variable bin size, cost of packing and the possibility of splitting items. We analyze the packing problem generalization from a theoretical point of view. We advance on-line and off-line approximation algorithms to solve our problem to balance the load either on-the-fly or on the planning stage. In addition to the computation of the approximation factors of these two algorithms, we evaluate experimentally their performance. The quality of the results is encouraging. This conclusion makes a packing approach a serious candidate to model energy-aware load balancing in Cloud Computing.
Pricing and Hedging in Stochastic Volatility Regime Switching Models  [PDF]
Stéphane Goutte
Journal of Mathematical Finance (JMF) , 2013, DOI: 10.4236/jmf.2013.31006

We consider general regime switching stochastic volatility models where both the asset and the volatility dynamics depend on the values of a Markov jump process. Due to the stochastic volatility and the Markov regime switching, this financial market is thus incomplete and perfect pricing and hedging of options are not possible. Thus, we are interested in finding formulae to solve the problem of pricing and hedging options in this framework. For this, we use the local risk minimization approach to obtain pricing and hedging formulae based on solving a system of partial differential equations. Then we get also formulae to price volatility and variance swap options on these general regime switching stochastic volatility models.


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