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Consistent Price Systems under Model Uncertainty
No full textInternational audienceWe develop a version of the fundamental theorem of asset pricing for discrete-time markets with proportional transaction costs and model uncertainty. A robust notion of no-arbitrage of the second kind is defined and shown to be equivalent to the existence of a collection of strictly consistent price systems
Geometric pumping in autophoretic channels
No full textInternational audienceMany microfluidic devices use macroscopic pressure differentials to overcome viscous friction and generate flows in microchannels. In this work, we investigate how the chemical and geometric properties of the channel walls can drive a net flow by exploiting the autophoretic slip flows induced along active walls by local concentration gradients of a solute species. We show that chemical patterning of the wall is not required to generate and control a net flux within the channel, rather channel geometry alone is sufficient. Using numerical simulations, we determine how geometric characteristics of the wall influence channel flow rate, and confirm our results analytically in the asymptotic limit of lubrication theory
A Convergent Radical Based Route to Trifluoromethyl Ketones and to α,β-Unsaturated Trifluoromethyl Ketones
No full textInternational audienceA convergent synthesis of trifluoromethyl ketones and alpha beta-unsaturated trifluoromethyl ketones is described, starting with aliphatic iodides and dithiocarbonates (xanthates) and exploiting both the alpha- and beta-fragmentations of a sulfonyl radical. The transformation initially furnishes the ketones in a masked enol carbonate form, from which they can be easily regenerated
Characteristics of stratospheric warming events during Northern Winter
No full textInternational audiencethe polar mid-stratosphere is characterized by the setting up of westerly winds around the pole during the wintertime; the so-called polar vortex. the polar vortex is one of the most variable features of the zonal-mean circulation of the earth atmosphere, due to a highly non linear interaction between planetary-scale rossby waves and the zonal flow. Indeed, the interaction between the upward tropospheric propagating waves and the polar vortex leads to a zonal flow weakening, implying a large day-to-day vortex variability. in the most dramatic cases, the polar vortex breaks down, the stratospheric polar flow can reverse its direction and the temperatures can rise locally by more than 50K in a span of a few days. such phenomena are known as major sudden stratospheric Warmings (SSWs) and constitute, since their discovery in 1952 (scherhag,1952) the most impressive dynamical events in the physical climate system. On the contrary, situations where the temperature increase is not associated to a polar vortex breakdown are known as minor SSWs.There is actually a renewed interest about SSWs since Baldwin and Dunkerton (2001) have shown that the major SSWs can influence weather in the troposphere. This stratospheric-tropospheric linkage has been statistically highlighted but no physical explanation has been proposed. also, other studies, that incorporate both major and minor SSWs, show that events in the stratospheric zonal flow associated with SSWs present downward- propagating anomalies that can reach the troposphere (Limpasuvan et al 2004), implying that minor SSWs have to be also considered in the study of the stratospheric- tropospheric dynamical coupling.in this study, we propose a global characterization of stratospheric warmings situations based on a temperature threshold in the 50-10hpa layer between 70n-90n, in order to better assess the properties of daily stratospheric temperature variability during the northern winter. the originality of this approach consists in evaluating the wintertime positive temperature anomalies in terms of intensity and duration without distinction between minor and major SSWs. We will show that there is a wide spectrum of warming types, where major SSWs are the most extreme, but other events – the minor SSWs – share some common properties with them. they can even have a surface signature if one look the stratospheric wave reflection on the polar vortex.
Practical Free-Start Collision Attacks on 76-step SHA-1
No full textInternational audienceIn this paper we analyze the security of the compression function of SHA-1 against collision attacks, or equivalently free-start collisions on the hash function. While a lot of work has been dedicated to the analysis of SHA-1 in the past decade, this is the first time that free-start collisions have been considered for this function. We exploit the additional freedom provided by this model by using a new start-from-the-middle approach in combination with improvements on the cryptanalysis tools that have been developed for SHA-1 in the recent years. This results in particular in better differential paths than the ones used for hash function collisions so far. Overall, our attack requires about evaluations of the compression function in order to compute a one-block free-start collision for a 76-step reduced version, which is so far the highest number of steps reached for a collision on the SHA-1 compression function. We have developed an efficient GPU framework for the highly branching code typical of a cryptanalytic collision attack and used it in an optimized implementation of our attack on recent GTX-970 GPUs. We report that a single cheap US$350 GTX-970 is sufficient to find the collision in less than 5 days. This showcases how recent mainstream GPUs seem to be a good platform for expensive and even highly-branching cryptanalysis computations. Finally, our work should be taken as a reminder that cryptanalysis on SHA-1 continues to improve. This is yet another proof that the industry should quickly move away from using this function
Problèmes de commande optimale sur des domaines structurés et lois de commandes en boucles fermées stratifiées
No full textThe aim of this dissertation is to study some issues in Control Theory of ordinary differential equations. Optimal control problems with tame state-constraints and feedback controls with stratified discontinuities are of special interest. The techniques employed along the manuscript have been chiefly taken from control theory, nonsmooth analysis, variational analysis, tame geometry, convex analysis and differential inclusions theory.The first part of the thesis is devoted to provide general results and definitions required for a good understanding of the entire manuscript. In particular, a strong invariance criterion adapted to manifolds is presented. Moreover, a short insight into manifolds and stratifications is done. The notions of relatively wedged sets is introduced and in addition, some of its properties are stated. The second part is concerned with the characterization of the Value Function of an optimal control problem with state-constraints. Three cases have been taken into account. The first one treats stratifiable state-constraints, that is, sets that can be decomposed into manifolds of different dimensions. The second case is focused on linear systems with convex state-constraints, and the last one considers convex state-constraints as well, but from a penalization point of view. In the latter situation, the dynamics are nonlinear and verify an absorbing property at the boundary.The third part is about discontinuous feedbacks laws whose singularities form a stratified set on the state-space. This type of controls yields to consider stratified discontinuous ordinary differential equations, which motivates an analysis of existence of solutions and robustness with respect to external perturbation for these equations. The construction of a suboptimal continuous feedback from an optimal one is also addressed in this part.The fourth part is dedicated to investigate optimal control problems on networks. The main feature of this contribution is that no controllability assumption around the junctions is imposed. The results can also be extended to generalized notions of networks, where the junction is not a single point but a manifold.Cette thèse porte sur la théorie de la commande optimale. Les problèmes de contrôle optimale sous contraintes d'état bien structurées et les lois de feedback stratifiées sont considérés. Les techniques utilisées dans ce manuscrit concernent principalement la théorie de la commande, l'analyse non lisse, l'analyse variationnelle, la géométrie modérée, l'analyse convexe et les inclusions différentielles.La première partie de la thèse est consacrée à donner des résultats et définitions généraux mais nécessaires pour mieux comprendre les parties suivantes de la thèse. En particulier, un critère d'invariance forte est présenté. De plus, un bref aperçu sur les variétés lisses et les ensembles stratifiés est exposé. La notion d'ensemble relativement wedged est introduite et de plus, quelques de ses propriétés sont aussi analysées.La deuxième partie est concernée à caractériser la Fonction Valeur d'un problème de contrôle optimal sous contraintes d'état. Trois situations ont été considérées. Le premier cas traite les contraintes d'état qui sont également des ensembles stratifiés, c'est-à-dire ceux qui peuvent être décomposé en une collection de variétés de différents dimensions. La deuxième situation se concentre sur les systèmes linéaires sous contraintes d'état convexes. Le dernier cas considère aussi les contraintes d'état qui sont ensembles convexes mais avec une technique de pénalisation. Dans cette dernière situation, les dynamiques sont non linéaires et absorbants sur la frontière de l'ensemble de contraintes.La troisième partie se focalise sur les lois de feedback discontinues dont les ensembles de points singuliers ont une structure stratifiée par rapport à l'espace d'état. Ces contrôles produisent des équations différentielles ordinaires stratifiées, ce qui motive une étude sur l'existence des solutions et sur la robustesse par rapport aux perturbations externes de ses équations. La construction de lois de feedback continues mais sous-optimaux à partir de l'information fourni par les contrôles optimaux est aussi traitée dans cette partie.La quatrième partie est dédiée à l'étude des problèmes de contrôle optimale sur des réseaux. La principale contribution de cette étude est qu'il n'y a pas de hypothèse de contrôlabilité autour des jonctions. Les résultats sont étendus aux réseaux généralisés dont les jonctions ne sont plus de points isolés mais de variétés
Angular analysis of the decay B0 to K*0 mu mu from pp collisions at sqrt(s) = 8 TeV
No full textsee paper for full list of authorsInternational audienceThe angular distributions and the differential branching fraction of the decay B0 to K*0(892) mu mu are studied using data corresponding to an integrated luminosity of 20.5 inverse femtobarns collected with the CMS detector at the LHC in pp collisions at sqrt(s) = 8 TeV. From 1430 signal decays, the forward-backward asymmetry of the muons, the K*0(892) longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared. The measurements are among the most precise to date and are in good agreement with standard model predictions
INSTITUTIONALIZATION OF IMPACT INVESTING THROUGH SOCIETAL MANAGEMENT PRESSURES: AN ACTION RESEARCH INQUIRY
No full textImpact investments are emerging as a new asset class of social finance. These investments intend to create positive societal impact beyond a financial return through the development of social enterprises. Scholars have highlighted the conflicting institutional logics that these later hybrid organizations must face when combining social welfare and profitability. Yet we lack in-depth, systemic insight into how impact investing funds areresponding to similar pressures and specifically to the pressure to conform to societal performance management. This paper builds on a three year action-research program conducted with Schneider Electric, a multinational enterprise specialized in energy management. The company initiated and sponsored an impact investing fund targeting energy access ventures in Sub-Saharan Africa, alongside four Development Finance Institutions. The article is grounded in neo-institutional and resource dependence theories to analyze the perceptions of the fund’s managers’ regarding emerging societal performance management procedures they were urged to adopt. The findings suggest a pattern of responses from the fund’s managers starting with passive conformity to external pressures and eventually turning to more resistive compromise with their own investors through interorganizational arrangements. The paper further asserts the establishment of impact investing as an institution in the making with potentially conflicting but not incompatible logics
Mercury-T: A new code to study tidally evolving multi-planet systems. Applications to Kepler-62
No full textInternational audienceA large proportion of observed planetary systems contain several planets in a compact orbital configuration, and often harbor at least one close-in object. These systems are then most likely tidally evolving. We investigate how the effects of planet-planet interactions influence the tidal evolution of planets. We introduce for that purpose a new open-source addition to the Mercury N-body code, Mercury-T, which takes into account tides, general relativity and the effect of rotation-induced flattening in order to simulate the dynamical and tidal evolution of multi-planet systems. It uses a standard equilibrium tidal model, the constant time lag model. Besides, the evolution of the radius of several host bodies has been implemented (brown dwarfs, M-dwarfs of mass , Sun-like stars, Jupiter). We validate the new code by comparing its output for one-planet systems to the secular equations results. We find that this code does respect the conservation of total angular momentum. We applied this new tool to the planetary system Kepler-62. We find that tides influence the stability of the system in some cases. We also show that while the four inner planets of the systems are likely to have slow rotation rates and small obliquities, the fifth planet could have a fast rotation rate and a high obliquity. This means that the two habitable zone planets of this system, Kepler-62e ad f are likely to have very different climate features, and this of course would influence their potential at hosting surface liquid water
Inverse scattering without phase information
No full textInternational audienceWe report on nonuniqueness, uniqueness and reconstruction results in quantum mechanical and acoustic inverse scattering without phase information. We are motivated by recent and very essential progress in this domain. This paper is an extended version of the talk given at Séminaire Laurent Schwartz on March 31, 2015