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A scalable algebraic method to infer quadratic invariants of switched systems
No full textInternational audienceWe present a new numerical abstract domain based on ellip-soids designed for the formal verification of switched linearsystems. Unlike the existing approaches, this domain doesnot rely on a user-given template. We overcome the diffi-culty that ellipsoids do not have a lattice structure by ex-hibiting a canonical operator over-approximating the union.This operator is the only one which permits to perform anal-yses that are invariant with respect to a linear transforma-tion of state variables. Moreover, we show that this operatorcan be computed efficiently using basic algebraic operationson positive semidefinite matrices. We finally develop a fastnon-linear power-type algorithm, which allows one to de-termine sound quadratic invariants on switched systems ina tractable way, by solving fixed point problems over thespace of ellipsoids. We test our approach on several bench-marks, and compare it with the standard techniques basedon linear matrix inequalities, showing an important speedupon typical instances
Three-Dimensional Modelling of Venus Photochemistry
No full textInternational audienceWe have developed a new code of the Venus atmospheric chemistry based on our photochemical model already in use for Mars (e.g., Lefèvre et al., J. Geophys. Res., 2004). For Venus, the code also includes a parameterized treatment of cloud microphysics that computes the composition of sulphuric acid droplets and their number density based on a given droplet size distribution in altitude and latitude. We coupled this photochemical-microphysical package to the LMD general circulation model of Venus (Lebonnois et al., J. Geophys. Res., 2010) with a sedimentation module that takes into account the parametrized droplet size distribution. We will describe the results obtained with this first three-dimensional model of the Venus photochemistry. The space and time distribution of key chemical species as well as the modelled clouds characteristics will be detailed and compared to observations performed from Venus Express and from the Earth (e.g. Knollenberg and Hunten, J. Geophys. Res., 1980 ; Wilquet et al., J. Geophys. Res., 2009 ; Sandor et al., Icarus, 2012 ; Mahieux et al., PSS, 2014 ; Marcq et al., 2015, PSS)
From Distinguishers to Key Recovery: Improved Related-Key Attacks on Even-Mansour
No full textInternational audienceWe show that a distinguishing attack in the related key model on an Even-Mansour block cipher can readily be converted into an extremely efficient key recovery attack. Concerned ciphers include in particular all iterated Even-Mansour schemes with independent keys. We apply this observation to the Caesar candidate Prøst-OTR and are able to recover the whole key with a number of requests linear in its size. This improves on recent forgery attacks in a similar setting
The INDC counter, aggregation of national contributrions and 2°C trajectories
No full textRapport du groupe interdisciplinaire sur les contributions nationalesConsidering that limiting global warming to below 2°C implies a CO2 budget not to be exceeded and near-zero emissions by 21OO (IPCC), we can assess global 2030 greenhouse gas emissions implied by INDCs in comparison to long-term trajectories. Ahead of the COP21, we estimate that submitted INDCs would bring global greenhouse gas emissions in the range of 55 to 64 GtC02eq in 2030.Under this assumption,global emissions in 2030 are thus higher than the level of 51GtC0 2eq for the year 2012. However, this is not in contradiction with a peaking of global emissions that can only be expected after 2020, given in particular the projected dynamics of emissions in China and other developing countries.The published INDCs represent a significant step towards trajectories compatible with the 2°C goal,but remain insufficient to join trajectories presenting a reasonable probability of success.ln order to increase the chance of meeting the 2°C objective, the ambition of the short-term contributions needs to be strengthened in future negotiations.ln order to sustain a high pace in emissions reductions after 2030,structural measures are also needed, which, in order to have a rapi impact, should be prepared as early as possible. Continued efforts are needed to accelerate the development of low carbon solutions on the one hand,and demonstrate the feasibility of negative emissions on the other hand
Properties modulation of organic semi-conductors based on a donor-spiro-acceptor (D-spiro-A) molecular design: new host materials for efficient sky-blue PhOLEDs
No full textInternational audienceFour high triplet org. semi-conductors based on the donor-spiro-acceptor design (D-spiro-A) have been synthesized. Their physicochem. and photophys. properties have been studied, compared and discussed in light of the nature of their resp. donor/acceptor units. The four compds. have been used as host materials in efficient sky-blue (EQE \textgreater 10% at 10 mA cm-2) phosphorescent org. light emitting diodes
Realisability semantics of abstract focussing, formalised
No full textInternational audienceWe present a sequent calculus for abstract focussing, equipped with proof-terms: in the tradition of Zeilberger's work, logical connectives and their introduction rules are left as a parameter of the system, which collapses the synchronous and asynchronous phases of focussing as macro rules. We go further by leaving as a parameter the operation that extends a context of hypotheses with new ones, which allows us to capture both classical and intuitionistic focussed sequent calculi. We then define the realisability semantics of (the proofs of) the system, on the en basis of Munch-Maccagnoni's orthogonality models for the classical focussed sequent calculus, but now operating at the higher level of abstraction mentioned above. We prove, at that level, the Adequacy Lemma, namely that if a term is of type A, then in the model its denotation is in the (set-theoretic) interpretation of A. This exhibits the fact that the universal quantification involved when taking the orthogonal of a set, reflects in the semantics Zeilberger's universal quantification in the macro rule for the asynchronous phase. The system and its semantics are all formalised in Coq
Mercury-T: Tidally evolving multi-planet systems code
No full text2015ascl.soft11020B - Astrophysics Source Code Library, record ascl:1511.020Mercury-T calculates the evolution of semi-major axis, eccentricity, inclination, rotation period and obliquity of the planets as well as the rotation period evolution of the host body; it is based on the N-body code Mercury (Chambers 1999, ascl:1201.008). It is flexible, allowing computation of the tidal evolution of systems orbiting any non-evolving object (if its mass, radius, dissipation factor and rotation period are known), but also evolving brown dwarfs (BDs) of mass between 0.01 and 0.08 M⊙, an evolving M-dwarf of 0.1 M⊙, an evolving Sun-like star, and an evolving Jupiter
Internal exponential stabilization to a nonstationary solution for 1D Burgers equations with piecewise constant controls
No full textInternational audienceThe feedback stabilization of the Burgers system to a nonstationary solution using a finite number of internal piecewise constant controls is considered. Estimates for the number of needed controls are derived. In the particular case of no constraint on the support of the control a better estimate is derived, so the possibility of getting an analogous estimate for the general case is discussed.That possibility is suggested by the results of some numerical simulations
Confluence of layered rewrite systems
No full textInternational audienceWe investigate the new, Turing-complete class of layered systems, whose lefthand sides of rules can only be overlapped at a multiset of disjoint or equal positions. Layered systems define a natural notion of rank for terms: the maximal number of non-overlapping redexes along a path from the root to a leaf. Overlappings are allowed in finite or infinite trees. Rules may be non-terminating, non-left-linear, or non-right-linear. Using a novel unification technique, cyclic unification, we show that rank non-increasing layered systems are confluent provided their cyclic critical pairs have cyclic-joinable decreasing diagrams
Homogénéisation non linéaire des matériaux poreux monocristallins: Modélisation, implémentation numérique et applications au fluage et à la fatigue
No full textThis study is concerned with the development of a rate-dependent constitutive model for porous single crystals with arbitrary crystal structure containing general ellipsoidal voids. The proposed model, called modified variational model (MVAR), is based on the nonlinear variational homogenization method, which makes use of a linear comparison porous single crystal material to estimate the response of the nonlinear porous single crystal. Thus, the main objective of this work is to propose a general constitutive model that accounts for the evolution of the microstructure and hence the induced anisotropy resulting when the initially anisotropic porous single crystal is subjected to finite deformations.Furthermore, periodic finite element simulations are used in order to validate the MVAR for a large number of parameters including cubic (FCC, BCC) and hexagonal (HCP) crystal anisotropy, various creep exponents (i.e., nonlinearity), several stress triaxiality ratios, Lode angle, general void shapes and orientations and various porosity levels. The MVAR model is found to be in good agreement with the finite element results for all cases considered in this study. The model is then used in a predictive manner to investigate the complex response of porous single crystals in several cases with strong coupling between the anisotropy of the crystal and the (morphological) anisotropy induced by the shape and orientation of the voids. In addition, an innovate way of calibrating the MVAR with just two adjustable parameters is depicted in the rate-independent context so that an excellent agreement related to simulation results is obtained. Moreover, a porous Tresca model is derived by an original approach starting from the novel porous single crystal model and considering the limiting case on infinite number of slip systems which leads to the Tresca criterion.Finally, the above-mentioned results are then extended to account for the evolution of microstructure when the material is subjected to finite deformations.Ce travail de thèse porte sur le développement d'un modèle constitutif viscoplastique pour monocristaux poreux à structure cristalline arbitraire et microstructures ellipsoïdales. Le modèle proposé, appelé modèle variationel modifié (MVAR), est basé sur la méthode d'homogénéisation variationelle non linéaire, qui utilise un composite linéaire de comparaison pour estimer la réponse non linéaire du monocristal poreux. Par conséquent, l'objectif principal de cette étude est de proposer un modèle constitutif général prenant en compte l'évolution de la microstructure et l'anisotropie induite quand le monocristal poreux est sollicité en déformations finies.En outre, des simulations EF périodiques sont utilisées pour valider le MVAR pour un grand nombre de paramètres incluant l'anisotropie cristalline cubique (FCC, BCC) et hexagonale (HCP), plusieurs exposants de uage (i.e. non linéarité), différentes triaxialités, angles de Lode, formes et orientations de pores et plusieurs niveaux de porosité. Le MVAR est en bon accord avec les résultats EF pour tous les cas considérés dans cette étude. Il est ensuite utilisé pour investiguer la réponse mécanique complexe des monocristaux poreux sous differentes conditions avec notammant le très fort couplage entre l'anisotropie cristalline et l'anisotropie morphologique induite par la forme et l'orientation des pores. De plus, uneapproche nouvelle de calibration avec seulement deux paramètres ajustables est proposée de manière à obtenir un excellent accord entre modèle et simulations. Par ailleurs, un modèle de Tresca poreux est dérivé par le biais d'une approche originale se servant du modèlepour monocristaux poreux et considérant le cas limite d'un nombre infini de systèmes de glissements (qui conduit au critère de Tresca).Enfin, les différents résultats sus-mentionnés sont étendus afin de prendre en compte l'évolution de la microstructure quand le matériau est sollicité en déformations finies