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Monte Carlo methods for linear and non-linear Poisson-Boltzmann equation
No full textInternational audienceThe electrostatic potential in the neighborhood of a biomolecule can be computed thanks to the non-linear divergence-form elliptic Poisson-Boltzmann PDE. Dedicated Monte-Carlo methods have been developed to solve its linearized version (see e.g.Bossy et al 2009, Mascagni & Simonov 2004}). These algorithms combine walk on spheres techniques and appropriate replacements at the boundary of the molecule. In the first part of this article we compare recent replacement methods for this linearized equation on real size biomolecules, that also require efficient computational geometry algorithms. We compare our results with the deterministic solver APBS. In the second part, we prove a new probabilistic interpretation of the nonlinear Poisson-Boltzmann PDE. A Monte Carlo algorithm is also derived and tested on a simple test case
Concevoir mécanismes pour la confidentialité géographique avec flexibilité dans le temps et l'espace.
No full textWith the increasing popularity of GPS-enabled handheld devices, location based services (LBS) have access to accurate location information, raising serious privacy concerns for end users. Trying to address these issues, the notion of geo-indistinguishability was recently introduced, protecting privacy by reporting to the LBS only a noisy version of the user's location.Standard geo-indistinguishability works well in the case of a sporadic use, however, under repeated use over time, constantly applying noise leads to a quick loss of privacy.In the first part of this thesis we show that correlation in the trace can be in fact exploited through a prediction function that tries to guess the new location reducing the number of sanitized positions.Another drawback of geo-indistinguishability is that it treats space in a uniform way, imposing the addition of the same amount of noise everywhere on the map.In the second part of this thesis we propose a novel elastic mechanism that adapts the level of noise to the different degrees of density of each area.Avec la popularité des dispositifs équipés de GPS, les applications basées sur la géolocalisation ont accès à des informations précises sur la position des utilisateurs, posant des risques pour leur vie privée.Pour faire face à ce problème, la notion de géo-indiscernabilité a été introduite récemment, qui ajoute du bruit à la position de l'utilisateur.La géo-indiscernabilité est efficace dans le cas d'un usage sporadique dans le temps, par contre, l'application indépendante de bruit amène à une perte rapide de protection.Dans la première partie de cette thèse on montre que la corrélation présente dans les traces peut, en fait, être exploitée à travers une fonction de prédiction, qui essaie à deviner la prochaine position pour réduire la quantité des positions rapportées.Un autre problème de la géo-indiscernabilité est son traitement uniforme de l'espace, exigeant la même quantité de bruit dans les différentes zones géographiques.Dans la deuxième partie de cette thèse on propose un nouveau mécanisme élastique qui adapte le bruit aux différents degrés de densité de chaque zone
Backward Lasing of Femtosecond Plasma Filaments
No full textInternational audienceStimulated emissions in both backward and forward directions from a plasma filament in ambient air or pure nitrogen have been observed in recent years. In this article, we present our recent experimental results concerning the backward stimulated emission. We first demonstrate that backward stimulated emission from neutral N2 molecules can be effectively generated with a circularly polarized 800 nm femtosecond laser pulse in pure nitrogen. Then, we show that the presence of oxygen is detrimental to the laser gain. To further confirm the presence of population inversion, we send a counter-propagating seeding pulse into the plasma filament. This leads to an amplification of the seeding pulse by two orders of magnitude. The crucial role of pump laser polarization indicates that the inelastic collisions between the energetic electrons and the neutral N2 molecules are at the origin of population inversion between the relevant states
No complete linear term rewriting system for propositional logic
No full textInternational audienceRecently it has been observed that the set of all sound linear inference rules in propositional logic is already coNP-complete, i.e. that every Boolean tautology can be written as a (left-and right-) linear rewrite rule. This raises the question of whether there is a rewriting system on linear terms of propositional logic that is sound and complete for the set of all such rewrite rules. We show in this paper that, as long as reduction steps are polynomial-time decidable, such a rewriting system does not exist unless coNP = NP. We draw tools and concepts from term rewriting, Boolean function theory and graph theory in order to access the required intermediate results. At the same time we make several connections between these areas that, to our knowledge, have not yet been presented and constitute a rich theoretical framework for reasoning about linear TRSs for propositional logic. 1998 ACM Subject Classification F.4 Mathematical Logic and Formal Language
Approximate Consensus in Highly Dynamic Networks: The Role of Averaging Algorithms
No full textInternational audienceWe investigate the approximate consensus problem in highly dynamic networks in which topology may change continually and unpredictably. We prove that in both synchronous and partially synchronous networks, approximate consensus is solvable if and only if the communication graph in each round has a rooted spanning tree. Interestingly, the class of averaging algorithms, which have the benefit of being memory- less and requiring no process identifiers, entirely captures the solvability issue of approximate consensus in that the problem is solvable if and only if it can be solved using any averaging algorithm. We develop a proof strategy which for each positive result consists in a reduction to the nonsplit networks. It dramatically improves the best known upper bound on the decision times of averaging algorithms and yields a quadratic time non-averaging algorithm for approximate consensus in non-anonymous networks. We also prove that a general upper bound on the decision times of averaging algorithms have to be exponential, shedding light on the price of anonymity. Finally we apply our results to networked systems with a fixed topology and benign fault models to show that with n processes, up to 2n−3 of link faults per round can be tolerated for approximate consensus, increasingby a factor 2 the bound of Santoro and Widmayer for exact consensus
Probing GPDs in photoproduction processes at hadron colliders
No full textInternational audienceGeneralized parton distributions (GPDs) enter QCD factorization theorems for hard exclusive reactions. They encode rich information about hadron partonic structure. We explore a possibility to constrain GPDs in experiments at LHC considering two different exclusive processes: the timelike Compton scattering and the photoproduction of heavy vector mesons
Modélisation du comportement viscoélastique d'un élastomère fortement chargé sous sollicitations multiaxiales
No full textClassify amongst the family of highly filled elastomer, solid propellant is used in the solid propulsion media. In order to guarantee the integrity of the structure, the behavior of solid propellant must be highlighted. Solid propellant behavior is viscoelastic, but present several non-linearities due to his high volume fraction of filler. This study focuses on the impact of the prestrain on the viscoelastic properties. The objective here is to characterize this impact, model it, implement it into a numerical code and investigate this influence on the response of a complete motor under dynamic solicitations.To do this, the work is divided in several parts. First, the microstructure of the propellant is studied in order to determine the microscopic causes of the macroscopic non-linearities. Then viscoelastic properties are characterized, both into the time or frequency domain, using uni axial and bi axial solicitations. To perform bi axial tests, a bi axial traction device is developed. A base on the experimental results, a continuous model is identified to describe the viscoelastic properties as a function of the prestrain. This model is discretized, in order to be implemented into a constitutive law, which permits to give a relation between strain and stress into the material. The constitutive law is traduced into a finite element code, in order to perform computation. Simulations are done on a numerical model of a solid propulsion motor. The properties of the propellant are alternatively modeled by a linear viscoelastic and non-linear viscoelastic (developed in this study) model. The two responses of the complete structure under dynamic solicitations are then compared, to prove it is important to take into account the non-linear influence of the prestrain, and the necessity to exactly model the propellant behavior. In a similar way, future works could investigate the non-linearity induced by the dynamic part of the strain on the viscoelastic properties.Le propergol composite est un élastomère fortement chargé utilisé dans les moteurs à propulsion solide. Garantir la fiabilité d’un tel moteur repose sur la bonne connaissance des propriétés mécaniques de ses constituants. Malgré son fort taux de charge, le comportement du propergol est viscoélastique, mais présente de nombreuses non linéarités. L’étude menée ici se concentre sur l’influence de la déformation statique sur les propriétés visqueuses du composite. L’objectif est de caractériser cette non linéarité, la modéliser, l’implémenter dans un outil de simulation numérique et déterminer son influence sur la réponse générale d’un moteur à propulsion solide soumis à une sollicitation dynamique.Afin d’atteindre cet objectif, les travaux se divisent en plusieurs étapes. La première consiste à déterminer à l’échelle microscopique les causes des phénomènes non linéaires observables à l’échelle macroscopique. Puis les propriétés viscoélastiques sont caractérisées, en fonction de la déformation statique. Cette étape expérimentale est réalisée à la fois dans le domaine temporel et dans le domaine fréquentiel, et ce sous des sollicitations uni axiales et bi axiales. Pour ce faire, une machine de traction dynamique bi axiale est développée. Puis un modèle non linéaire continu est identifié sur l’ensemble des résultats obtenus, permettant de reproduire à la fois les effets du temps mais également les effets de la déformation statique sur les propriétés mécanique. Ce modèle continu est discrétisé en vue d’être implémenté dans une loi de comportement viscoélastique non linéaire, permettant de donner une relation entre la déformation appliquée dans un matériau et la contrainte générée. Ce modèle est introduit dans un code éléments finis. Pour déterminer l’influence de la non linéarité engendrée par la déformation statique, une simulation est réalisée sur un modèle de moteur à propulsion solide. Les propriétés du propergol le constituant sont successivement modélisées par un comportement linéaire et non linéaire (développé dans ces travaux). Les deux réponses sont comparées et indiquent l’importance de ne pas négliger l’impact de l’effet engendré par la déformation statique, ainsi que la nécessité de modéliser finement le comportement du propergol. De manière analogue, un travail de modélisation pourrait être poursuivit en essayer de prendre en compte cette fois ci la partie dynamique de la déformation sur les propriétés du composite
Intermittent renewable generation and network congestion: an empirical analysis of Italian Power Market
No full textThe literature demonstrates the likely reduction of wholesale electricity prices due to a larger penetration of renewable energy sources (RES). When markets are organized as two or more inter-connected sub-markets within a larger power market the final impact of increasing RES production may be less straightforward given the presence of network constraints. We tests this phenomenon by analyzing the impact of RES production on the probability of congestion and on the size of congestion cost in Italy. Using a database with hourly observations for a five year period we estimate two econometric models on five zonal pairings: a multinomial logit model for the occurrence and direction of congestion and a three stage least square model for the size of congestion costs. The analysis suggests that the effect of a larger local wind and solar supply is to decrease the probability of suffering congestion in entry and to increase the probability of causing a congestion in exit compared to no congestion case. Increasing hydroelectric production has a similar effect. These results hold for both importing and exporting regions, but importing regions are less likely to cause congestion in exit, therefore the installation of new RES capacity in these zones may have a positive effects in terms of flow balance between regions. Concerning the cost level, a larger local RES supply seems to push the congestion cost towards negative values as it decreases the marginal cost for balancing the system. This is true for all zones in the case of explicit congestion cost, but it is only verified in importing regions in the case of implicit congestion cost. This result suggests that the increase of RES production should be promoted in importing zones, but the overall growth should be controlled in order to avoid congestion in the opposite direction
SV-Bay: structural variant detection in cancer genomes using a Bayesian approach with correction for GC-content and read mappability
No full textMotivation: Whole genome sequencing of paired-end reads can be applied to characterize the landscape of large somatic rearrange-ments of cancer genomes. Several methods for detecting structural variants with whole genome sequencing data have been developed. So far, none of these methods has combined information about abnormally mapped read pairs connecting rearranged regions and associated global copy number changes. Our aim was to create a computational method that could use both types of information, i.e., normal and abnormal reads, and demonstrate that by doing so we can highly improve both sensitivity and specificity rates of structural variant prediction.Results: We developed a computational method, SV-Bay, to detect structural variants from whole genome sequencing mate-pair or paired-end data using a probabilistic Bayesian approach. This ap-proach takes into account depth of coverage by normal reads and abnormalities in read pair mappings. To estimate the model likeli-hood, SV-Bay considers GC-content and read mappability of the genome, thus making important corrections to the expected read count. For the detection of somatic variants, SV-Bay makes use of a matched normal sample when it is available. We validated SV-Bay on simulated datasets and an experimental mate-pair dataset for the CLB-GA neuroblastoma cell line. The comparison of SV-Bay with several other methods for structural variant detection demonstrated that SV-Bay has better prediction accuracy both in terms of sensitivi-ty and false positive detection rate
Training Schr\"odinger's cat: quantum optimal control
No full text31 pages; this is the starting point for a living document - we welcome feedback and discussionIt is control that turns scientific knowledge into useful technology: in physics and engineering it provides a systematic way for driving a system from a given initial state into a desired target state with minimized expenditure of energy and resources -- as famously applied in the Apollo programme. As one of the cornerstones for enabling quantum technologies, optimal quantum control keeps evolving and expanding into areas as diverse as quantum-enhanced sensing, manipulation of single spins, photons, or atoms, optical spectroscopy, photochemistry, magnetic resonance (spectroscopy as well as medical imaging), quantum information processing and quantum simulation. --- Here state-of-the-art quantum control techniques are reviewed and put into perspective by a consortium uniting expertise in optimal control theory and applications to spectroscopy, imaging, quantum dynamics of closed and open systems. We address key challenges and sketch a roadmap to future developments