684 research outputs found
Satisfiability of General Intruder Constraints with and without a Set Constructor
Many decision problems on security protocols can be reduced to solving
so-called intruder constraints in Dolev Yao model. Most constraint solving
procedures for protocol security rely on two properties of constraint systems
called monotonicity and variable origination. In this work we relax these
restrictions by giving a decision procedure for solving general intruder
constraints (that do not have these properties) that stays in NP. Our result
extends a first work by L. Mazar\'e in several directions: we allow non-atomic
keys, and an associative, commutative and idempotent symbol (for modeling
sets). We also discuss several new applications of the results.Comment: Submitted to the Special issue of Information and Computation on
Security and Rewriting Techniques (SecReT), 2011. 59 page
Pt-modified Ni aluminides, MCrAlY-base multilayer coatings and TBC systems fabricated by Spark Plasma Sintering for the protection of Ni-base superalloys
Pt-modified Ni aluminides and MCrAlY coatings (where M=Ni and/or Co) are widely used on turbine blades and vanes for protection against oxidation and corrosion and as bond coatings in thermal barrier coating (TBC) systems. The present work shows the ability of a new fabrication technique, the Spark Plasma Sintering, to develop rapidly new coating compositions and microstructures. This technique allows combining powders and metallic foils on a superalloy substrate in order to obtain multilayered coatings in a single short experiment. Fabrication of MCrAlY overlays with local Pt and/or Al enrichment is shown, as well as fabrication of coatings made of ζ-PtAl2, Δ-PtAl, α-AlNiPt2, martensitic ÎČ- (Ni,Pt)Al or Pt-rich Îł/ÎłâČ phases. The realization of a complete TBC system with a porous and adherent Yttria Stabilized Zirconia (YSZ) layer on a Îł/ÎłâČ low mass bond coating is also demonstrated. Difficulties of fabrication are reviewed and discussed, such as Y segregation, risks of carburization, local overheating, or difficulty to coat complex shape parts. Finally, some first results of cyclic oxidation are given
Intruder deducibility constraints with negation. Decidability and application to secured service compositions
The problem of finding a mediator to compose secured services has been
reduced in our former work to the problem of solving deducibility constraints
similar to those employed for cryptographic protocol analysis. We extend in
this paper the mediator synthesis procedure by a construction for expressing
that some data is not accessible to the mediator. Then we give a decision
procedure for verifying that a mediator satisfying this non-disclosure policy
can be effectively synthesized. This procedure has been implemented in CL-AtSe,
our protocol analysis tool. The procedure extends constraint solving for
cryptographic protocol analysis in a significative way as it is able to handle
negative deducibility constraints without restriction. In particular it applies
to all subterm convergent theories and therefore covers several interesting
theories in formal security analysis including encryption, hashing, signature
and pairing.Comment: (2012
The Effects of Reduced Social Security Contributions on Employment: an Evaluation of the 2003 French Reform
In 2003, the French government decided to reform the system managing the different minimum wage regulations and the targeted reductions to employers' social security contributions. The main objective of the reform was to simplify the complex regulations that were created by the progressive introduction of the 35-hour week. The reform incidentally created large variations in labour costs, depending on the type of firm and the wage level within the firm. This paper presents an evaluation of the impact of this reform on employment using a balanced panel of firms with more than five employees, drawn from a matching between several administrative data sources from 2000 to 2005. In both types of firm, significant employment elasticities can be found with respect to labour costs that have the expected signs: a rise of 1% in average labour costs reduces employment by 0.4%. As the majority of firms that remained on the 39-hour week received greater reductions, the Fillon reform allowed them to raise their level of employment. Firms that adopted the 35-hour week experienced the opposite: the reform led to a fall in employment. Ultimately, the Fillon reform has had no clear effect on aggregate employment, measured either in job numbers or full-time equivalents (FTE)
Description of the unsteady flow pattern from peak efficiency to near surge in subsonic centrifugal compressor stage
This paper aims to describe the flow structure modifications when the operating point moves from peak efficiency to near stall condition in a moderate pressure ratio centrifugal compressor stage consisted of a splittered unshrouded impeller and a vaned diffuser. The investigations are based on three-dimensional U-RANS simulation results. The flow is described in the impeller and in the vaned diffuser through time-averaged flow quantities and unsteady fluctuations. Results show that at low mass flow rate, the effects of secondary flow in the impeller are more pronounced, inducing both, high time-averaged values and temporal fluctuations of the flow angle near the shroud at the diffuser inlet, leading to vane suction side boundary layer separation. Pressure waves due to impeller diffuser interaction spread through the vaned diffuser generating unsteadiness which intensifies at near surge condition
Les effets des aides publiques aux HÎtels Cafés Restaurants et leurs interactions
La Mission Animation de la Recherche DARES du MinistĂšre du Travail, de l'Emploi et de la SantĂ© (MAR-DARES) a lancĂ© au cours de l'Ă©tĂ© 2009 un appel d'offre intitulĂ© " Evaluation des effets de l'aide financiĂšre aux employeurs du secteur des HĂŽtels-cafĂ©s-restaurants dans le cadre de la loi du 9 aoĂ»t 2004 " dans le but de quantifier l'impact sur l'emploi et les salaires d'une politique sectorielle originale. L'Ă©quipe du Centre d'Etude de l'Emploi a Ă©tĂ© retenue pour Ă©valuer les effets de cette politique sur les entreprises des diffĂ©rents secteurs des HĂŽtels-cafĂ©s-restaurants. L'objet de ce rapport est des prĂ©senter les rĂ©sultats de ce travail d'Ă©valuation.Ăvaluation politique publique, aide Ă l'emploi sectorielle, HĂŽtel-cafĂ©-restaurant
Metal enrichment in a semi-analytical model, fundamental scaling relations, and the case of Milky Way galaxies
Gas flows play a fundamental role in galaxy formation and evolution,
providing the fuel for the star formation process. These mechanisms leave an
imprint in the amount of heavy elements. Thus, the analysis of this metallicity
signature provides additional constraint on the galaxy formation scenario. We
aim to discriminate between four different galaxy formation models based on two
accretion scenarios and two different star formation recipes. We address the
impact of a bimodal accretion scenario and a strongly regulated star formation
recipe. We present a new extension of the eGalICS model, which allows us to
track the metal enrichment process. Our new chemodynamical model is applicable
for situations ranging from metal-free primordial accretion to very enriched
interstellar gas contents. We use this new tool to predict the metallicity
evolution of both the stellar populations and gas phase. We also address the
evolution of the gas metallicity with the star formation rate (SFR). We then
focus on a sub-sample of Milky Way-like galaxies. We compare both the cosmic
stellar mass assembly and the metal enrichment process of such galaxies with
observations and detailed chemical evolution models. Our models, based on a
strong star formation regulation, allow us to reproduce well the stellar mass
to gas-phase metallicity relation observed in the local universe. However, we
observe a systematic shift towards high masses. Our $Mstar-Zg-SFR relation is
in good agreement with recent measurements: our best model predicts a clear
dependence with the SFR. Both SFR and metal enrichment histories of our Milky
Way-like galaxies are consistent with observational measurements and detailed
chemical evolution models. We finally show that Milky Way progenitors start
their evolution below the observed main sequence and progressively reach this
observed relation at z = 0.Comment: 22 pages, 11 figure
LES DISCRIMINATIONS A L'EMBAUCHE DANS LA SPHERE PUBLIQUE : EFFETS RESPECTIFS DE L'ADRESSE ET DE L'ORIGINE
Cette Ă©tude Ă©value la discrimination dans lâaccĂšs Ă lâemploi dans trois professions prĂ©sentes Ă la fois dans le secteur privĂ© et dans la Fonction Publique. Deux dimensions sont examinĂ©es : lâeffet de la rĂ©putation du lieu de rĂ©sidence et lâeffet de lâorigine maghrĂ©bine. Elle est rĂ©alisĂ©e sur donnĂ©es expĂ©rimentales de testing rĂ©alisĂ© dans trois professions en tension pour lesquelles la discrimination devrait a priori ĂȘtre trĂšs rĂ©duite : les responsables administratifs de catĂ©gorie A, les techniciens de maintenance de catĂ©gorie B et les aides soignantes de catĂ©gorie C. Pour chaque profession, nous avons construit 3 profils fictifs de candidats Ă lâemploi similaires en tout point Ă lâexception de la caractĂ©ristique testĂ©e (lâorigine signalĂ©e par la consonance du prĂ©nom et du nom, ou la rĂ©putation du lieu de rĂ©sidence). Entre octobre 2015 et avril 2016, nous avons envoyĂ© 3258 candidatures en rĂ©ponse Ă 1086 offres dâemploi. LâĂ©tude consiste en une exploitation statistique des rĂ©sultats de ces envois.Nous mettons en avant trois principaux rĂ©sultats, conditionnellement au fait que des donnĂ©es de testing ne fournissent quâune mesure partielle, ponctuelle et localisĂ©e des discriminations Ă lâembauche. PremiĂšrement, nous ne trouvons pas que les discriminations Ă lâembauche sont plus faibles dans la Fonction Publique que dans le secteur privĂ©. DeuxiĂšmement, nous ne sommes pas parvenus Ă mettre en Ă©vidence lâexistence de discriminations qui seraient spĂ©cifiques Ă la Fonction Publique dâEtat ; en revanche, nous fournissons plusieurs preuves de lâexistence dâune discrimination dans lâaccĂšs Ă lâemploi, selon lâorigine et le lieu de rĂ©sidence, pour les Fonctions Publiques HospitaliĂšre et Territoriale.TroisiĂšmement, le mode de recrutement par concours tel quâil est organisĂ© dans la Fonction Publique Territoriale ne permet pas de garantir un accĂšs Ă©gal Ă lâemploi public : nous trouvons des discriminations Ă la fois pour les recrutements de contractuels et pour ceux de fonctionnaires titulaires aprĂšs un concours
Estimation of relative position and coordination of mobile underwater robotic platforms through electric sensing.
International audienceIn the context of underwater robotics, positioning and coordination of mobile agents can prove a challenging problem. To address this issue, we propose the use of electric sensing, with a technique inspired by weakly electric fishes. In particular, the approach relies on one or several of the agents applying an electric field to their environment. Using electric measures, others agents are able to reconstruct their relative position with respect to the emitter, over a range that is function of the geometry of the emitting agent and of the power applied to the environment. Efficacy of the technique is illustrated using a number of numerical examples. The approach is shown to allow coordination of unmanned underwater vehicles, including that of bio-inspired swimming robotic platforms
Action-Perception Trade-Offs for Anguilliform Swimming Robotic Platforms with an Electric Sense
International audienceThe work presented addresses the combination of anguilliform swimming-based propulsion with the use of an electric sensing modality for a class of unmanned underwater vehicles, and in particular investigates the relative influence of adjustments to the swimming gait on the platform's displacement speed and on sensing performance. This influence is quantified, for a relevant range of swimming gaits, using experimental data recordings of displacement speeds, and a boundary element method-based numerical simulation tool allowing to reconstruct electric measures. Results show that swimming gaits providing greater movement speeds tend to degrade sensing performance. Conversely, gaits yielding accurate sensing tend to prove slower. To reconcile opposing tendencies, a simple action-perception cost function is designed, with the purpose of adjusting an anguilliform swimmer's gait shape, in accordance with respective importance afforded to action (i.e. movement speed) and perception
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