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Parallel multi-wavelength calibration algorithm for radio astronomical arrays
No full textInternational audienc
Optimal Planning of Virtual Mobile Networks
No full textInternational audienceThe explosive growth of smartphones and other portable devices, along with new traffic types generated by M2M applications, are creating huge volumes of mobile data traffic and signaling overhead, therefore requiring a radical change to the current mobile network architecture. This has promoted new virtualization paradigms, which combine diverse packet core services, and provide network functions implemented in software, rather than in dedicated hardware appliances, in order to scale capacity and introduce new services in a fast and cost-effective way. In this paper1we study the optimization and resource allocation problems taking into account the deployment of virtualization structures. Our aim is to develop a theoretical framework of resource orchestration for mobile access networks, deriving the fundamental performance limits as well as the tradeoffs among the key system parameters. We therefore study optimal, time-varying placement and chaining of network functions. With respect to existing works, our optimization framework provides a much more precise system modeling, with, among others, a separation between control and data plane functions. We perform an extensive numerical analysis using both real traffic traces provided by a mobile operator (Vodafone UK) and real positions for radio access points for the UK area, and discuss the impact of network parameters on the system performance. Numerical results show that our proposed optimization framework permits to carefully model key aspects of network virtualization and service deployment/chaining in such scenarios, thus representing a very promising framework for the design of efficient and cost-effective mobile networks
Polar Codes for Covert Communications over Asynchronous Discrete Memoryless Channels
No full textInternational audienceThis paper introduces an explicit covert communication code for binary-input asynchronous discrete memoryless channels based on binary polar codes, in which legitimate parties exploit uncertainty created by both the channel noise and the time of transmission to avoid detection by an adversary. The proposed code jointly ensures reliable communication for a legitimate receiver and low probability of detection with respect to the adversary, both observing noisy versions of the codewords. Binary polar codes are used to shape the weight distribution of codewords and ensure that the average weight decays as the block length grows. The performance of the proposed code is severely limited by the speed of polarization, which in turn controls the decay of the average codeword weight with the block length. Although the proposed construction falls largely short of achieving the performance of random codes, it inherits the low-complexity properties of polar codes
Simulation temporelle et spatiale des changements d'occupation du sol par modélisation stochastique
No full textInternational audienceThe landscape patterns are the results of the human activity that adapts the land cover and its use (LUC) to constraints or economic opportunities encountered by various actors. The temporal and spatial arrangement of LUC has a strong influence on environmental risks. Its knowledge allows to develop prospective simulation models to assess the impact of different scenarios on the evolution of the land use and land cover change (LUCC). This paper presents a methodology based on stochastic models to identify, locate and simulate the temporal LUCC of regions differentiated by their successions by means of " neutral " models. The concept of a " neutral " model has been introduced in ecology for describing the characteristics of coexisting populations in a territory. Every individual-whatever its species it belongs to in the ecosystem-undergoes the same constraints without taking precedence over another. The result is a balance that is regulated by processes whose dynamics do not vary. In the framework of spatially explicit models coupled to a geographical information system according to the categorization defined by [AGG + 00], the territory is described as an assembly of homogeneous discontinuous units-called patches-represented by a regular grid of pixels. We propose a territorial simulation method that takes into account the dynamics of temporal and spatial patterns of previous successions observed in different sub-regions. We carry out a classification of the territory in homogeneous patches with respect to their LUC. The simulation of the LUC succession is then made on these patches at the pixel level taking into account the rotations / successions that were practiced the previous two years. The differences between simulated and observed data make it possible to detect breaks in the process of developing the territory according to the constraints or opportunities for farmers. Differences are measured using the pixel recognition rate on a rasterized representation of the territory. We assess our method on data that come from surveys in the Vittel-Contrex´eville territory (East of France) which is subject to water quality issues.L'organisation d'un territoire est le reflet de l'activité humaine qui y adapte la couverture du sol et son usage en fonction des contraintes ou opportunités économiques. L'arrangement temporel et spatial des occupations du sol a une forte influence sur les risques environnementaux. Sa connaissance permet d'élaborer des modèles de simulation prospective afin d'évaluer l'impact de différents scénarios d'évolution de la couverture du sol. Cet article présente une méthodologie à base de modèles stochastiques pour identifier, localiser et simuler les occupations temporelles des régions différenciées par leurs successions de culture dans la perspective de construction d'un modèle ``neutre''. Le concept de modèle ``neutre'' a été introduit en écologie pourdécrire les caractéristiques des populations coexistant dans un territoire. Les individus -- quelquesoit leur nature -- endurent les mêmes contraintes sans qu'une espèce ne prenne le pas sur une autre. Il en résulte un équilibre qui est régulé par des processus dont la dynamique ne varie pas. Nous nous plaçons dans un cadre de définition de modèles spatialement explicites couplés à un système d'information géographique selon la catégorisation définie par Agarwal {agarwal2000}. Le territoire est décrit comme un assemblage d'unités homogènes discontinues -- appelées patchs -- lesquelles sont constituées d'une grille régulière de pixels. sous la forme d'une image raster. Nous effectuons préalablement une classification du territoire d'étude en patchs homogènes vis à vis des successions de culture qui s'y pratiquent. La simulation de la succession est ensuite faite sur ces \patchs au niveau du pixel en tenant compte des rotations / successions qui se pratiquaient les deux années précédentes. Nous proposons ainsi une méthode de simulation du territoire qui tienne compte des dynamiques temporelles et spatiales des successions précédentes observées dans différentes sous régions. L'écart entre données simulées et observées permet de déceler des ruptures dans le processus de mise en valeur du territoire en fonction des contraintes ou opportunités s'offrant aux agriculteurs. Les écarts sont mesurés à l'aide du taux de reconnaissance de pixels sur une représentation rasterisée du territoire. Les données utilisées dans cette étude proviennent d'enquêtes effectuées sur le territoire de Vittel-Contrexéville concernant la qualité des eaux souterraines
Adaptive Continous Beam Steering in Quasi-optical Antenna Solutions
No full textInternational audienceThis paper introduces a novel adaptive continuous beam steering (ACBS) solution for quasi-optical antenna technologies. The main advantages of this solution compared to discontinuous beam switching approaches are small steering angle steps (high resolution), improved beam crossing level and lower RF losses. This solution is based on a phase correcting aperture transfer function and the relation between a focal array amplitude tapering and its phase center displacement. The proposed solution is verified by comparing its results with 3D full-wave simulations. With a 2x2 focal source array illuminating a Fresnel dielectric lens, it is possible to achieve a scanning range of 1.6° with a steering angle step of 0.3° and a beam crossing level of 0.2dB. The ACBS solution can be integrated into active antennas for self-alignment purposes
SIR model with time dependent infectivity parameter : approximating the epidemic attractor and the importance of the initial phase.
No full textWe consider a SIR model with birth and death terms and time-varying infectivity parameter β (t). In the particular case of a sinusoidal parameter, we show that the average Basic Reproduction Number ¯ R o , introduced in [Bacaër & Guernaoui, 2006], is not the only relevant parameter and we emphasize the rôle played by the initial phase, the amplitude and the period. For a (general) periodic infectivity parameter β (t) a periodic orbit exists, as already proved in [Katriel, 2014]. In the case of a slowly varying β (t) an approximation of such a solution is given, which is shown to be asymptotically stable under an extra assumption on the slowness of β (t). For a non necessarily periodic β (t) , all the trajectories of the system are proved to be attracted into a tubular region around a suitable curve, which is then an approximation of the underlying attractor. Numerical simulations are given
Low electrical percolation thresholds and nonlinear effects in graphene-reinforced nanocomposites: a numerical analysis
No full textInternational audienceA numerical model of graphene-reinforced nanocomposites taking into account the electric tunneling effect is employed to analyze the influence of microstructural parameters on the effective electric conductivity and the per-colation thresholds of the composite. The generation procedure for the random microstructures of graphene reinforced nanocomposites is described. Effects of the barrier height, of graphene aspect ratio and alignment of graphene sheets have been quantitatively evaluated. The results show that both higher graphene aspect ratio and lower barrier height can lead to smaller percola-tion threshold, and the alignment of graphene sheets results in anisotropic electrical behavior without affecting the percolation threshold. The numerical model also shows the importance of the tunneling effect to reproduce the nonlinear electric behavior and the low percolation thresholds reported in the literature. Finally, results are compared with available experimental data
Global optimization approach for circular and chloroplast genome assembly
No full textInternational audienceWe describe a global optimization approach for genome assembly where the steps of scaffolding, gap-filling, and scaffold extension are simultaneously solved in the framework of a common objective function. The approach is based on integer programming model for solving genome scaffolding as a problem of finding a long simple path in a specific graph that satisfies additional constraints encoding the insert-size information. The optimal solution of this problem allows one to obtain new kind of contigs that we call distance-based contig. We test the algorithm on a benchmark of chloroplasts and compare the quality of the results with recent scaffolders
Vérification de programmes OCaml fortement impératifs avec Why3
No full textNational audienceCet article présente une méthodologie pour prouver des programmes OCaml fortement impératifs avec l'outil de vérification déductive Why3. Pour un programme OCaml donné, un modèle mémoire spécifique est construit et on vérifie un programme Why3 qui le mani-pule. Une fois la preuve terminée, on utilise la capacité de Why3 à traduire ses programmes vers le langage OCaml, tout en remplaçant les opérations sur le modèle mémoire par les opérations correspondantes sur des types mutables d'OCaml. Cette méthode est mise à l'épreuve sur plusieurs exemples manipulant des listes chaînées et des graphes mutables
Results in descriptive set theory on some represented spaces
No full textDescriptive set theory was originally developed on Polish spaces. It was later extended to ω-continuous domains [Selivanov 2004] and recently to quasi-Polish spaces [de Brecht 2013]. All these spaces are countably-based. Extending descriptive set theory and its effective counterpart to general represented spaces, including non-countably-based spaces has been started in [Pauly, de Brecht 2015].We study the spaces , and the Kleene-Kreisel spaces . We show that there is a -subset of which is not Borel. We show that the open subsets of cannot be continuously indexed by elements of or even , and more generally that the open subsets of cannot be continuously indexed by elements of . We also derive effective versions of these results.These results give answers to recent open questions on the classification of spaces in terms of their base-complexity, introduced in [de Brecht, Schröder, Selivanov 2016]. In order to obtain these results, we develop general techniques which are refinements of Cantor's diagonal argument involving multi-valued fixed-point free functions and that are interesting on their own right