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Derniers dépôts dans PRUNEL

On the performance of greedy algorithms for energy minimization

We revisit the well-known greedy algorithm for scheduling independent jobs on parallel processors, with the objective of energy minimization. We assess the performance of the online version, as well as the performance of the offine version, which sorts the jobs by non-increasing size before execution. We derive new approximation factors, as well as examples that show that these factors cannot be improved, thereby completely characterizing the performance of the algorithms. Lien vers le documentStatistical distributions in the folding of elastic structures

The behaviour of elastic structures undergoing large deformations is the result of the competition between confining conditions, self-avoidance and elasticity. This combination of multiple phenomena creates a geometrical frustration that leads to complex fold patterns. By studying the case of a rod confined isotropically into a disk, we show that the emergence of the complexity is associated with a well defined underlying statistical measure that determines the energy distribution of sub-elements,``branches'', of the rod. This result suggests that branches act as the ``microscopic'' degrees of freedom laying the foundations for a statistical mechanical theory of this athermal and amorphous system. Lien vers le documentFluctuations of the extreme eigenvalues of finite rank deformations of random matrices

Consider a deterministic self-adjoint matrix X_n with spectral measure converging to a compactly supported probability measure, the largest and smallest eigenvalues converging to the edges of the limiting measure. We perturb this matrix by adding a random finite rank matrix with delocalized eigenvectors and study the extreme eigenvalues of the deformed model. We show that the eigenvalues converging out of the bulk exhibit Gaussian fluctuations, whereas under additional hypotheses, the eigenvalues sticking to the edges are very close to the eigenvalues of the non-perturbed model and fluctuate in the same scale. We can also generalise these results to the case when X_n is random and get similar behaviour when we deform some classical models such as Wigner or Wishart matrices with rather general entries or the so-called matrix models. Lien vers le documentLarge deviations of the extreme eigenvalues of random deformations of matrices

Consider a real diagonal deterministic matrix $X_n$ of size $n$ with spectral measure converging to a compactly supported probability measure. We perturb this matrix by adding a random finite rank matrix of a certain form, with delocalized eigenvectors. We show that the joint law of the extreme eigenvalues of the perturbed model satisfies a large deviation principle, in the scale n with a good rate function given by a variational formula. We tackle both cases when the extreme eigenvalues of X_n converge to the edges of the support of the limiting measure and when we allow some eigenvalues of X_n, that we call outliers, to converge out of the bulk. We can also generalise our results to the case when X_n is random, with law proportional to e^{- Trace V(X)}d X, for V growing fast enough at infinity and any perturbation of finite rank with orthonormal eigenvectors. Lien vers le documentOrbit Equivalence and Measured Group Theory

We give a survey of various recent developments in orbit equivalence and measured group theory. This subject aims at studying infinite countable groups through their measure preserving actions. Lien vers le documentReconstructing Social Interactions Using an unreliable Wireless Sensor Network

In the very active field of complex networks, research advances have largely been stimulated by the availability of empirical data and the increase in computational power needed for their analysis. These works have led to the identification of similarities in the structures of such networks arising in very different fields, and to the development of a body of knowledge, tools and methods for their study. While many interesting questions remain open on the subject of static networks, challenging issues arise from the study of dynamic networks. In particular, the measurement, analysis and modeling of social interactions are first class concerns. In this article, we address the challenges of capturing physical proximity and social interaction by means of a wireless network. In particular, as a concrete case study, we exhibit the deployment of a wireless sensor network applied to the measurement of Health Care Workers' exposure to tuberculosis infected patients in a service unit of the Bichat-Claude Bernard hospital in Paris, France. This network has continuously monitored the presence of all HCWs in all rooms of the service during a 3 month period. We both describe the measurement system that was deployed and some early analysis on the measured data. We highlight the bias introduced by the measurement system reliability and provide a reconstruction method which not only leads to a significantly more coherent and realistic dataset but also evidences phe- nomena a priori hidden in the raw data. By this analysis, we suggest that a processing step is required prior to any adequate exploitation of data gathered thanks to a non-fully reliable measurement architecture. Lien vers le documentEnabling Connectors in Hierarchical Component Models

The continual growth of computing and storage capabilities enables scientific numerical applications to integrate more and more phenomena in their computations at the price of increased complexity. Hierarchical component models appear as an interesting approach to handle such complexity. However defining and implementing efficient interactions between hierarchical components is a difficult task, especially in the case of parallel and distributed applications. Connectors originating from Architecture Description Languages (ADL) offer a promising solution to this problem. There are however some cases where a simple combination of hierarchy and connectors in a single component model forces users to choose between an efficient implementation of components and their black box behavior. This paper describes HLCM, a model with connectors and hierarchy that provides /open connections/ as a mechanism to describe component interface that enhances encapsulation and eases component implementation replacement while supporting efficient interactions. Complex interactions such as data sharing and parallel method calls are successfully supported by HLCM. An implementation, based on model transformation and on CCM, illustrates its feasibility and benefits. Lien vers le documentDu gène à la fleur

Au-delà de l'expérimentation in vitro, l'expérimentation sur ordinateur devrait permettre de mieux comprendre les conditions de croissance des plantes. Lien vers le documentInspections ab initio des hystérèses magnétiques et rédox

Les systèmes bistables connaissent un intérêt croissant motivé, entre autres, par la perspective d'applications en électronique moléculaire. Parmi ces systèmes certains possèdent la capacité d'exister sous deux états électroniques dans les mêmes conditions, i.e. présentant une hystérèse. Deux propriétés sont couramment associées à l'hystérèse, le magnétisme et l'activité rédox. Si ces phénomènes sont connus de longues dates, des zones d'ombre demeurent dans leur mécanisme. Par l'application de calculs ab initio basés sur la fonction d'onde, l'objet de ce travail est de dégager les phénomènes physiques sous-jacents à l'ouverture de boucle d'hystérésis dans les composés à transition de spin (bistabilité magnétique) et dans des complexes de porphyrine (bistabilité rédox). Les ingrédients microscopiques ainsi récoltés sont utilisés pour remonter au comportement macroscopique des matériaux par le biais de modèles thermodynamiques ou de hamiltoniens modèles. Lien vers le documentN=6 Superspace Constraints, SUSY Enhancement and Monopole Operators

We present a systematic analysis of the N=6 superspace constraints in three space-time dimensions. The general coupling between vector and scalar supermultiplets is encoded in an SU(4) tensor $W^i_j$ which is a function of the matter fields and subject to a set of algebraic and super-differential relations. We give a genuine N=6 classification for superconformal models with polynomial interactions and find the known ABJM and ABJ models. We further study the issue of supersymmetry enhancement to N=8 and the role of monopole operators in this scenario. To this end we assume the existence of a composite monopole operator superfield which we use to formulate the additional supersymmetries as internal symmetries of the N=6 superspace constraints. From the invariance conditions of these constraints we derive a system of superspace constraints for the proposed monopole operator superfield. This constraint system defines the composite monopole operator superfield analogously to the original N=6 superspace constraints defining the dynamics of the elementary fields. Lien vers le document

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