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Ultraviolet behavior of 6D supersymmetric Yang-Mills theories and harmonic superspace
No full text55 pagesInternational audienceWe revisit the issue of higher-dimensional counterterms for the N=(1,1) supersymmetric Yang-Mills (SYM) theory in six dimensions using the off-shell N=(1,0) and on-shell N=(1,1) harmonic superspace approaches. The second approach is developed in full generality and used to solve, for the first time, the N=(1,1) SYM constraints in terms of N=(1,0) superfields. This provides a convenient tool to write explicit expressions for the candidate counterterms and other N=(1,1) invariants and may be conducive to proving non-renormalization theorems needed to explain the absence of certain logarithmic divergences in higher-loop contributions to scattering amplitudes in N=(1,1) SYM
A model for porous single crystals with cylindrical voids of elliptical cross-section
No full textInternational audienceThis work presents a rate-dependent constitutive model for porous single crystals with arbitrary number of slip systems and orientations. The single crystal comprises cylindrical voids with elliptical cross-section at arbitrary orientations and is subjected to general plane-strain loadings. 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. The MVAR model is validated by periodic finite element simulations for a large number of parameters including general in-plane crystal anisotropy, general in-plane void shapes and orientations, various creep exponents (i.e., nonlinearity) and general plane strain loading conditions. The MVAR model, which at the present state involves no calibration parameters, is found to be in good agreement with the finite element results for all cases considered in this work. 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
Minimax estimation of linear and quadratic functionals on sparsity classes
No full textFor the Gaussian sequence model, we obtain non-asymp-totic minimax rates of estimation of the linear, quadratic and the 2-norm functionals on classes of sparse vectors and construct optimal estimators that attain these rates. The main object of interest is the class B 0 (s) of s-sparse vectors θ = (θ 1 ,. .. , θ d), for which we also provide completely adaptive estimators (independent of s and of the noise variance σ) having logarithmically slower rates than the minimax ones. Furthermore, we obtain the minimax rates on the q-balls B q (r) = {θ ∈ R d : q ≤ r} where 0 < q ≤ 2, and q = d i=1 |θ i | q 1/q. This analysis shows that there are, in general, three zones in the rates of convergence that we call the sparse zone, the dense zone and the degenerate zone, while a fourth zone appears for estimation of the quadratic functional. We show that, as opposed to estimation of θ, the correct logarithmic terms in the optimal rates for the sparse zone scale as log(d/s 2) and not as log(d/s). For the class B 0 (s), the rates of estimation of the linear functional and of the 2-norm have a simple elbow at s = √ d (boundary between the sparse and the dense zones) and exhibit similar performances, whereas the estimation of the quadratic functional Q(θ) reveals more complex effects: the minimax risk on B 0 (s) is infinite and the sparseness assumption needs to be combined with a bound on the 2-norm. Finally, we apply our results on estimation of the 2-norm to the problem of testing against sparse alternatives. In particular, we obtain a non-asymptotic analog of the Ingster-Donoho-Jin theory revealing some effects that were not captured by the previous asymptotic analysis
Edge flutter of long beams under follower loads
No full textInternational audienceThe linear instability of a beam tensioned by its own weight is considered. It is shown that for long beams, in the sense of an adequate dimensionless parameter, the characteristics of the instability caused by a follower force do not depend on the length. The asymptotic regime significantly differs from that of short beams: flutter prevails for all types of follower loads, and flutter is localized at the edge of the beam. An approximate solution using matched assymptotic expansion is proposed for the case of a semi-infinite beam. Using a local criterion based on the stability of waves, the characteristics of this regime as well as its range of application can be well predicted. These results are finally discussed in relation with cases of flow-induced instabilities of slender structures
Comment une idée abstraite peut devenir un dispositif de gestion : le cas du développement durable
No full textInternational audienceSustainable development is an abstract idea. Through which mechanisms can such an idea affect firms’ management, and thus, at the most operational level? This article first describes the arrangement of mechanisms at play, with a focus on the role of meta-organizations. It then investigates the resulting organizational complexity.Le développement durable est une idée abstraite. Par quel enchaînement de mécanismes une telle idée peut-elle avoir un effet sur la gestion de firmes, et ce, au niveau le plus opérationnel ? Cet article décrira tout d’abord cet ensemble de dispositifs en mettant notamment l’accent sur le rôle des méta-organisations. Il s’interrogera ensuite sur la complexité organisationnelle qui en découle
Estimating Gender Differences in Access to Jobs
No full textInternational audienceThis paper proposes a new measure of gender differences in access to jobs based on a job assignment model. This measure is the probability ratio of getting a job for a female and a male at each rank of the wage ladder. We derive a nonparametric estimator of this access measure and estimate it for French full-time executives aged 40–45 in the private sector. Our results show that the gender difference in the probability of getting a job increases along the wage ladder from 9% to 50%. Females thus have a significantly lower access to high-paid jobs than to low-paid jobs
Effects de l'anisotropie solide-solide sur les microstructures de solidification directionnelle
No full textThe microstructures arising from the solidification processing possess various types of boundaries: solid(S)-liquid(L) interfaces, grain boundaries (GB), interphase boundaries (IB). Whereas solid-liquid interface has been investigated extensively, relatively little attention has been paid to the S-S boundaries (GB and IB). Recently, it has been found that S-S boundary anisotropy can also have a significant influence, particularly on the overall orientation selection of the growing patterns. The present thesis investigates the effects of GB and IB anisotropy through simulations of solidification morphologies. We use a recent multi-phase field model for this study. In essence, we work with a grand-canonical functional combining the interfacial and bulk free energies of the system and then minimising it with respect to the field variables to obtain the equations of motion for the phase fields and the composition fields. We use this code to study three problems stemming from the directional solidification of lamellar eutectics and polycrystals with a particular focus on the effects of the solid-solid boundary anisotropy. During thin-film directional solidification experiments on lamellar eutectics, it has been observed that in response to the IB anisotropy, lamellae grow at an angle with the growth axis. We characterize this drift angle using our numerical simulations and then compare it successfully with a recent theoretical prediction. Then, we exploit this IB anisotropy in bulk lamellar eutectics to understand the emergence of certain minimum energy directions in the system leading to preferred orientations in the microstructure. Then, we repeat our thin-film eutectic study for polycrystals with grain boundaries, motivated by the fact that anisotropic low-angle grain boundaries or sub-boundaries grow at an angle with respect to the growth axis. We quantify this tilt angle and compare it successfully with a recent analytical prediction. In this way, we establish the influence of the solid-solid boundary anisotropy on the directionally solidified microstructures.Les microstructures qui se forment lors de la solidification d'alliagescontiennent différent types d'interfaces: des interfaces solide-liquid (SL),des joints de grain (grain boundaries, GB) et des joints interphase(interphase boundaries, IB). Tandis que les interfaces solide-liquideont beaucoup été étudiés, les interfaces solide-solide (GB et IB) ontreçu peu d'attention. Récemment, il a été démontré que l'anisotropie deces interfaces solide-solide peut aussi avoir une influence marquée, enparticulier sur la texture et les orientations des motifs sélectionnés.Dans cette thèse, la relation entre anisotropie solide-solide et sélectionmorphologique est étudiée à l'aide de simulations numériques de microstructuresde solidification.Nous utilisons un modèle multi-champ-de-phase récemment développé. Cemodèle est basé sur une fonctionnelle grand-canonique qui combine lesénergies libres de volume et de surface. Sa minimisation donne leséquations de mouvement pour les champs de phase et de concentration.Ce code est utilisé pour examiner trois problèmes qui viennent dela solidification directionnelle d'alliages eutectiques et dilués,avec une attention particulière aux effets de l'anisotropiedes interfaces solide-solide.Durant la solidification d'alliages eutectiques en échantillons minces,il a été observé qu'en réponse à l'anisotropie des IB, les lamelleseutectiques croissent dans une direction qui fait un angle bien définiavec la direction de croissance principale. Nous caractérisons cetangle dans nos simulations numériques, et trouvons un bon accord avecune théorie récente de la croissance anisotrope. Ensuite, nous examinonsle lien entre l'anisotropie des IB et l'émergence d'orientations préférentiellesdans des systèmes étendus. Finalement, nous répétons notre étude d'échantillonsminces pour des polycristaux, dans lesquels des GB de faible désorientationcroissent également avec un angle défini par rapport à la direction principalede croissance. Nous déterminons cet angles de croissance et trouvons à nouveauun bon accord avec des prédictions théoriques. De cette manière, nous confirmonsl'influence de l'anisotropie solide-solide sur les microstructures desolidification directionnelle
Double-stage soft x-ray laser pumped by multiple pulses applied in grazing incidence
No full textInternational audienceIn this paper we report on results obtained with a compact double-stage molybdenum x-ray laser (XRL), operated with a total pump energy of 600 mJ. The two gain regions were pumped using the double-pulse grazing incidence pumping technique, which includes travelling wave excitation for both the seed- and the amplifier-target. In addition, the influence of an additional pre-pulse has been studied. Seeded XRL operation has been demonstrated in both schemes, resulting in XRL pulses with a divergence of 2 × 2 mrad. The peak brilliance of the amplified XRL of 4 × 10^23 photons/s/mm2/mrad2 in 5 × 10^−5 relative bandwidth was more than two orders of magnitude larger compared to the original seed pulses. The presented experimental concept provides an alternative approach to the currently more common use of high-order harmonic pulses as a seed source, well suited for applications like laser spectroscopy of highly-charged ions at a storage ring
Asymptotic expansion of the multi-orientable random tensor model
No full textInternational audienceThree-dimensional random tensor models are a natural generalization of the celebrated matrix models. The associated tensor graphs, or 3D maps, can be classified with respect to a particular integer or half-integer, the degree of the respective graph. In this paper we analyze the general term of the asymptotic expansion in N , the size of the tensor, of a particular random ten-sor model, the multi-orientable tensor model. We perform their enumeration and we establish which are the dominant configurations of a given degree
Circulating cell membrane microparticles transfer heme to endothelial cells and trigger vasoocclusions in sickle cell disease
No full textInternational audienceIntravascular hemolysis describes the relocalization of heme and hemoglobin (Hb) from erythrocytes to plasma. We investigated the concept that erythrocyte membrane microparticles (MPs) concentrate cell-free heme in human hemolytic diseases, and that hemeladen MPs have a physiopathological impact. Up to one-third of cell-free heme in plasma from 47 patients with sickle cell disease (SCD) was sequestered in circulating MPs. Erythrocyte vesiculation in vitro produced MPs loaded with heme. In silico analysis predicted that externalized phosphatidylserine (PS) in MPs may associate with and help retain heme at the cell surface. Immunohistology identified Hb-laden MPs adherent to capillary endothelium in kidney biopsies from hyperalbuminuric SCD patients. In addition, heme-laden erythrocyte MPs adhered and transferred heme to cultured endothelial cells, inducing oxidative stress and apoptosis. In transgenic SAD mice, infusion of hemeladen MPs triggered rapid vasoocclusions in kidneys and compromised microvascular dilation ex vivo. These vascular effects were largely blocked by heme-scavenging hemopexin and by the PS antagonist annexin-a5, in vitro and in vivo. Adversely remodeled MPs carrying heme may thus be a source of oxidant stress for the endothelium, linking hemolysis to vascular injury. This pathway might provide new targets for the therapeutic preservation of vascular function in SCD