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The Impact of the National Minimum Wage on Industry-Level Wage Bargaining in France
No full textThis paper examines empirically how industry-level wage floors are set in French industry-level wage agreements and how the national minimum wage (NMW) interacts with industry-level wage bargaining. For this, we use a unique dataset containing about 48,000 occupation-specific wage floors, in more than 340 French industries over the period 2006-2014. We find that the NMW has a significant impact on the seasonality and on the timing of the wage bargaining process. Inflation, past sectoral wage increases and real NMW increases are the main drivers of wage floor adjustments; elasticities of wage floors with respect to these macro variables are 0.6, 0.3 and 0.25 respectively. Wage floor elasticities to inflation and to the NMW both decrease along the wage floor distribution but are still positive for all levels of wage floors
Stochastic precession of the polarization in a polariton laser
No full textInternational audienceMicrocavity polaritons in the lasing regime undergo a spontaneous symmetry-breaking transition resulting in coherent emission with a well-defined polarization. The order parameter is thus a vector describing both the laser global phase and its polarization. Using an ultrafast single-shot detection technique, we show that polariton lasing in GaAs-based microcavities presents a high degree of second-order coherence [g(2)(τ=0)≈1] above threshold, and that the initial polarization is stochastic, taking any possible direction in the Poincaré sphere (linear, elliptical, or circular). Once the polarization direction is established, subsequent oscillations of the emission probability witness the presence of an intrinsic polarization splitting. These results show the intricate polarization dynamics in the onset of polariton lasers
Vacuum laser acceleration of relativistic electrons using plasma mirror injectors
No full textInternational audienceAccelerating particles to relativistic energies over very short distances using lasers has been a long-standing goal in physics. Among the various schemes proposed for electrons, vacuum laser acceleration has attracted considerable interest and has been extensively studied theoretically because of its appealing simplicity: electrons interact with an intense laser field in vacuum and can be continuously accelerated, provided they remain at a given phase of the field until they escape the laser beam. But demonstrating this effect experimentally has proved extremely challenging, as it imposes stringent requirements on the conditions of injection of electrons in the laser field. Here, we solve this long-standing experimental problem by using a plasma mirror to inject electrons in an ultraintense laser field, and obtain clear evidence of vacuum laser acceleration. With the advent of petawatt lasers, this scheme could provide a competitive source of very high charge (nC) and ultrashort relativistic electron beams
Probing the Mechanical Strength of an Armored Bubble and Its Implication to Particle-Stabilized Foams
No full textInternational audienceBubbles are dynamic objects that grow and rise or shrink and disappear, often on the scale of seconds. This conflicts with their uses in foams where they serve to modify the properties of the material in which they are embedded. Coating the bubble surface with solid particles has been demonstrated to strongly enhance the foam stability, although the mechanisms for such stabilization remain mysterious. In this paper, we reduce the problem of foam stability to the study of the behavior of a single spherical bubble coated with a monolayer of solid particles. The behavior of this armored bubble is monitored while the ambient pressure around it is varied, in order to simulate the dissolution stress resulting from the surrounding foam. We find that above a critical stress, localized dislocations appear on the armor and lead to a global loss of the mechanical stability. Once these dislocations appear, the armor is unable to prevent the dissolution of the gas into the surrounding liquid, which translates into a continued reduction of the bubble volume, even for a fixed overpressure. The observed route to the armor failure therefore begins from localized dislocations that lead to large-scale deformations of the shell until the bubble completely dissolves. The critical value of the ambient pressure that leads to the failure depends on the bubble radius, with a scaling of ΔPcollapse∝R−1, but does not depend on the particle diameter. These results disagree with the generally used elastic models to describe particle-covered interfaces. Instead, the experimental measurements are accounted for by an original theoretical description that equilibrates the energy gained from the gas dissolution with the capillary energy cost of displacing the individual particles. The model recovers the short-wavelength instability, the scaling of the collapse pressure with bubble radius, and the insensitivity to particle diameter. Finally, we use this new microscopic understanding to predict the aging of particle-stabilized foams, by applying classical Ostwald ripening models. We find that the smallest armored bubbles should fail, as the dissolution stress on these bubbles increases more rapidly than the armor strength. Both the experimental and theoretical results can readily be generalized to more complex particle interactions and shell structures
Kummer: efficient hyperelliptic signatures and key exchange on microcontrollers
No full textInternational audienceWe describe the design and implementation of efficient signature and key-exchange schemes for the AVR ATmega and ARM Cortex M0 microcontrollers, targeting the 128-bit security level. Our algorithms are based on an efficient Montgomery ladder scalar multiplication on the Kummer surface of Gaudry and Schost's genus-2 hyperelliptic curve, combined with the Jacobian point recovery technique of Costello, Chung, and Smith. Our results are the first to show the feasibility of software-only hyperelliptic cryptography on constrained platforms, and represent a significant improvement on the elliptic-curve state-of-the-art for both key exchange and signatures on these architectures. Notably, our key-exchange scalar-multiplication software runs in under 9740k cycles on the ATmega, and under 2650k cycles on the Cortex M0
Gender Quota inside the Boardroom: Female Directors as New Key Players?
No full textThis paper examines whether women’s situation within French boards has improved following theadoption of a board-level gender quota in 2011. To do so, we focus on the individual role of femaledirectors as proxied by their fees. Our sample includes the listed companies belonging to the SBF120index over the 2006-2014 period. We first show that the quota has succeeded in opening the doors ofboardrooms to new, unseasoned female directors (not present on the director labor market before theregulation). These unseasoned female directors have distinctive characteristics (in terms of independence,experience, age, nationality, etc.) as compared to other board members. More importantly, weshow that women, whether unseasoned or seasoned, experience an inner glass ceiling, with “positional”gender segregation within French boards. In particular, companies have failed so far to open the accessof the most important board committees (namely monitoring committees: audit, compensation andnomination) to women. It results in a within-firm gender fees gap of 5%. Overall, the quota has ratheramplified this segregation process, with an increase in the average within-firm gender fees gap
Measurement of the t-tbar production cross section in the e-mu channel in proton-proton collisions at sqrt(s) = 7 and 8 TeV
No full textSubmitted to J. High Energy Phys ; see paper for full list of authorsInternational audienceThe inclusive cross section for top quark pair production is measured in proton-proton collisions at sqrt(s) = 7 and 8 TeV, corresponding to 5.0 and 19.7 invers-femtobarns, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributions related to identified b quark jets and other jets in the event. The measured cross section values are 173.6 +/- 2.1 (stat) +4.5-4.0 (syst) +/- 3.8 (lumi) pb at sqrt(s) = 7 TeV, and 244.9 +/- 1.4 (stat) +6.3-5.5 (syst) +/- 6.4 (lumi) pb at sqrt(s) = 8 TeV, in good agreement with QCD calculations at next-to-next-to-leading-order accuracy. The ratio of the cross sections measured at 7 and 8 TeV is determined, as well as cross sections in the fiducial regions defined by the acceptance requirements on the two charged leptons in the final state. The cross section results are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, giving a best result of 173.8 +1.7-1.8 GeV. The data at sqrt(s) = 8 TeV are also used to set limits, for two neutralino mass values, on the pair production of supersymmetric top squarks with masses close to the top quark mass
Laser-initiated primary and secondary nuclear reactions in Boron-Nitride
No full textInternational audienceNuclear reactions initiated by laser-accelerated particle beams are a promising new approach to many applications, from medical radioisotopes to aneutronic energy production. We present results demonstrating the occurrence of secondary nuclear reactions, initiated by the primary nuclear reaction products, using multicomponent targets composed of either natural boron (B) or natural boron nitride (BN). The primary proton-boron reaction (p + 11B → 3 α + 8.7 MeV), is one of the most attractive aneutronic fusion reaction. We report radioactive decay signatures in targets irradiated at the Elfie laser facility by laser-accelerated particle beams which we interpret as due to secondary reactions induced by alpha (α) particles produced in the primary reactions. Use of a second nanosecond laser beam, adequately synchronized with the short laser pulse to produce a plasma target, further enhanced the reaction rates. High rates and chains of reactions are essential for most applications
Gradient damage modeling of brittle fracture in an explicit dynamics context
No full textInternational audienceIn this contribution we propose a dynamic gradient damage model as a phase-field approach for studying brutal fracture phenomena in quasi-brittle materials under impact-type loading conditions. Several existing approaches to account for the tension-compression asymmetry of fracture behavior of materials are reviewed. A better understanding of these models is provided through a uniaxial traction experiment. We then give an efficient numerical implementation of the model in an explicit dynamics context. Simulations results obtained with parallel computing are discussed both from a computational and physical point of view. Different damage constitutive laws and tension-compression asymmetry formulations are compared with respect to their aptitude to approximate brittle fracture
Linear lambda terms as invariants of rooted trivalent maps
No full textInternational audienceThe main aim of the paper is to give a simple and conceptual account for the correspondence (originally described by Bodini, Gardy, and Jacquot) between α-equivalence classes of closed linear lambda terms and isomorphism classes of rooted trivalent maps on compact-oriented surfaces without boundary, as an instance of a more general correspondence between linear lambda terms with a context of free variables and rooted trivalent maps with a boundary of free edges. We begin by recalling a familiar diagrammatic representation for linear lambda terms, while at the same time explaining how such diagrams may be read formally as a notation for endomorphisms of a reflexive object in a symmetric monoidal closed (bi)category. From there, the “easy” direction of the correspondence is a simple forgetful operation which erases annotations on the diagram of a linear lambda term to produce a rooted trivalent map. The other direction views linear lambda terms as complete invariants of their underlying rooted trivalent maps, reconstructing the missing information through a Tutte-style topological recurrence on maps with free edges. As an application in combinatorics, we use this analysis to enumerate bridgeless rooted trivalent maps as linear lambda terms containing no closed proper subterms, and conclude by giving a natural reformulation of the Four Color Theorem as a statement about typing in lambda calculus