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Recent changes in north-west Greenland climate documented by NEEM shallow ice core data and simulations, and implications for past-temperature reconstructions
No full textInternational audienceCombined records of snow accumulation rate, δ 18 O and deuterium excess were produced from several shallow ice cores and snow pits at NEEM (North Greenland Eemian Ice Drilling), covering the period from 1724 to 2007. They are used to investigate recent climate variability and characterise the isotope–temperature relationship. We find that NEEM records are only weakly affected by inter-annual changes in the North Atlantic Oscillation. Decadal δ 18 O and accumulation variability is related to North Atlantic sea surface temperature and is enhanced at the beginning of the 19th century. No long-term trend is observed in the accumulation record. By contrast, NEEM δ 18 O shows multidecadal increasing trends in the late 19th century and since the 1980s. The strongest annual positive δ 18 O values are recorded at NEEM in 1928 and 2010, while maximum accumulation occurs in 1933. The last decade is the most enriched in δ 18 O (warmest), while the 11-year periods with the strongest depletion (coldest) are depicted at NEEM in 1815–1825 and 1836–1846, which are also the driest 11-year periods. The NEEM accumulation and δ 18 O records are strongly correlated with outputs from atmospheric models, nudged to atmospheric reanalyses. Best performance is observed for ERA reanalyses. Gridded temperature reconstructions, instrumental data and model outputs at NEEM are used to estimate the multidecadal accumulation–temperature and δ 18 O– temperature relationships for the strong warming period in 1979–2007. The accumulation sensitivity to temperature is estimated at 11 ± 2 % • C −1 and the δ 18 O–temperature slope at 1.1 ± 0.2 ‰ • C −1 , about twice as large as previously used to estimate last interglacial temperature change from the bottom part of the NEEM deep ice core. Published by Copernicus Publications on behalf of the European Geosciences Union. 1482 V. Masson-Delmotte et al.: Recent changes in northwest Greenland climate Figure 1. Map of Greenland showing the position of ice core records (red) and meteorological stations (green) used to establish a SW Greenland instrumental temperature record. The grey/white shading indicates elevation (source: NOAA/GLOBE, http://www. ngdc.noaa.gov/mgg/topo/globe.html)
A Declarative View of Signaling Pathways
No full textInternational audienceDue to the inherent limitations of wet-lab techniques, the experimental data regarding cellular signaling pathways often consider single pathways or a small subset of them. We propose a methodology for composing signaling pathways data in a coherent framework. Our method consists in specifying the signaling pathway as a computationally executable model. We rely on the timed concurrent constraint language ntcc to represent the system in hand as a set of stoichiometric-like equations resembling the essential features of molecular interactions. The main advantages of our approach stem from the use of constraints (formulas in logic) and from modeling of discrete time clocks in ntcc. We can deal with partial information, representing the fact that several features of the biological system may be undetermined. We can explicitly represent the time needed for a reaction to occur. We model and simulate some well known cross-talking networks, such as the TNFα, the EGF and the insulin signaling pathways as well as their interactions
GOUVERNANCE ET PERFORMANCE D'ENTREPRISE: QUELLE EQUATION DE DURABILITE ?
No full textIn order to achieve a sustainable growth and to respond to external pressures (regulation, society), firms take more and more frequently into account their social and environmental externalities in the decision-making process, through the development of their Corporate Social Responsibility policy (CSR). Corporate governance appears here as a way to integrate shareholders’ and stakeholders’ objectives. Is corporate governance a strategic mediator between CSR objectives and firm performance? Is corporate governance a key stone of CSR firm commitment?This dissertation provides both theoretical and empirical evidences in the French case where corporate governance is defined as a hybrid model between the shareholder and stakeholder models. After introducing the dissertation, chapters 2 and 3 investigate the link between firm objectives and performance. From an INSEE national survey on sustainable development, Chapter 2 shows how firm motivations (defensive, pro-social or strategic) is a key determinant of their social, societal and environmental CSR awareness. In particular, firms implementing strategic CSR commit more to the issues related to their strategic stakeholders. CSR motivations may therefore mediate the relationship between CSR commitment and financial performance. Integrating firm objectives, the decision-making process at the top is driven by the board of directors. Chapter 3 theoretically demonstrates how board composition may affect firm outcomes. In particular, the model determines the optimal board functioning (monitoring or advising) depending on the relative cost and benefit of board expertise and independence. After highlighting that board composition is a key determinant of governance effectiveness, the three last chapters explore how corporate governance, and in particular board composition, may achieve some CSR demands from shareholders, stakeholders and society and affect firm outcomes. These chapters rely on empirical studies based on listed companies (SBF120) over the 2006-2014 period. Chapter 4 studies the link between independent directors and operating performance in order to evaluate their efficiency. The independence of directors is indeed usually considered as an answer to shareholders’ demands to reduce the conflict of interest with management. We show that in France, independents directors are better selected than affiliated directors in terms of intrinsic ability but suffer from an informational gap. However, this gap may be shortened by industry expertise and/or social connections. Chapter 5 investigates from the shareholder and stakeholder perspectives how board composition is related to CSR commitment. We show that CSR engagement is driven by the reduction of conflicts with stakeholders rather than the creation of private benefit for managers. Stakeholder representation inside the boardroom may therefore affect investment in the different CSR issues. Chapter 6 analyzes how firms comply with the French gender quota of women inside the boardroom in 2014. The quota has indeed broken the glass-ceiling experienced by female managers and increased the number of women in the director labor market. However, female directors earn 6% less in fees than their male counterparts, one third due to their characteristics (age, expertise, tenure..) and two thirds due to their positions (committees) inside the boardroom. Female directors have then experienced an inner glass-ceiling which may jeopardize the positive expected effects of board diversity on firm policy and performances. In conclusion, the discussion provides the main new prospects and research avenues opened up by this dissertation. It focuses attention on the role of corporate governance in the development of CSR and the possible applications in terms of public policy and regulation.Afin de participer à une croissance durable de la société, les entreprises développent leur Responsabilité Sociale et Environnementale (RSE). La gouvernance d’entreprise, et en particulier le conseil d’administration, jouent un rôle central en intégrant les objectifs environnementaux et sociaux dans la prise de décisions. La gouvernance est-elle un médiateur stratégique entre objectifs RSE et performances des entreprises ? Est-elle la clé de voûte de l’engagement RSE ? Cette thèse présente des arguments théoriques et empiriques dans le cas français défini comme un modèle hybride (actionnarial-partenarial) de gouvernance. Après un chapitre introduction, les chapitres 2 et 3 analysent le lien entre objectifs et performances des entreprises. A partir d’une enquête INSEE sur le développement durable, le chapitre 2 montre que la motivation RSE (défensive, pro-sociale ou stratégique) détermine le niveau de prise en compte des enjeux sociaux et environnementaux. En particulier, les entreprises mettant en place une RSE stratégique investissent davantage dans les enjeux liés à leurs parties prenantes. Ces résultats suggèrent que la motivation RSE pourrait être un médiateur de la relation RSE-performance. Intégrant les objectifs de l’entreprise, le processus de décision au sommet de l’entreprise est contrôlé par le conseil d’administration. Le chapitre 3 démontre théoriquement comment la composition du conseil affecte les performances de l’entreprise. Le modèle prédit le fonctionnement optimal du conseil (surveillant ou conseillant) en fonction des coûts et bénéfices relatifs de l’expertise par rapport à l’indépendance. Après avoir mis en exergue la composition du conseil d’administration comme facteur déterminant de l’efficience de la gouvernance, les trois chapitres suivants analysent comment la composition du conseil d’administration peut répondre aux demandes RSE de la part des actionnaires, des parties prenantes et de la société, et affecter les performances de l’entreprise. Ces trois chapitres reposent sur des analyses empiriques fondées sur les entreprises cotées françaises (SBF120) sur la période 2006-2014. Le chapitre 4 évalue l’efficience des administrateurs indépendants. En effet, ce type d’administrateurs est une réponse aux pressions des actionnaires pour réduire les conflits d’intérêts avec le management. En France, les administrateurs indépendants sont mieux sélectionnés que les administrateurs affiliés mais ils souffrent d’un déficit informationnel. Ce déficit peut être réduit par de l’expertise et des relations sociales. Le chapitre 5 étudie le lien entre la composition du conseil et l’engagement RSE des entreprises. Les résultats montrent que cet engagement est davantage motivé par l’objectif de réduire les conflits avec les parties prenantes que de constituer des bénéfices privés pour le management. La représentation des parties prenantes au sein du conseil peut donc affecter l’engagement RSE des entreprises. Le chapitre 6 analyse comment les entreprises se mettent en conformité avec le quota de genre au sein des conseils d’administration en 2014. Le quota a cassé le plafond de verre en accroissant le nombre de femmes sur le marché des administrateurs. Cependant, elles gagnent 6% de moins que les hommes. Ce différentiel est dû pour un tiers aux caractéristiques (âge, ancienneté,…) des administratrices et pour deux tiers aux positions qu’elles occupent au sein du conseil (comités). Les administratrices se heurtent donc à un plafond de verre interne, ce qui peut annihiler les bénéfices attendus de l’accroissement de la diversité au sein des conseils sur les choix stratégiques et les performances de l’entreprise.En conclusion, la discussion décrit les nouvelles perspectives de recherche s’ouvrant à la suite de cette thèse. Elle met l’accent sur le rôle de la gouvernance dans le développement de la RSE et les potentiels enseignements en termes de politiques publiques et de régulations
Équation aux dérivées partielles dépendante de la trajectoire: théorie et appliquations
No full textIn the previous works, Ekren, Keller, Touzi & Zhang [35] and Ekren, Touzi & Zhang [37, 38], the new notion of viscosity solutions to path dependent PDEs is introduced, and a wellposedness theory is proved by a ‘path-frozen’ argument. This new notion generalizes that of viscosity solutions to PDEs developed intensively in the years of 80’s and 90’s, and can be used to characterize the value function of non-Markovian stochastic control problem. In this thesis, we report the recent development of the new theory. We improve the argument for the comparison result, and provide a PDE-style Perron’s method for proving the existence of viscosity solutions to semi- linear path dependent PDEs. As in the seminar work of Barles and Souganidis [4] in the context of PDEs, we show that a family of numerical schemes satisfying the so- called monotonicity condition provides numerical solutions converging to viscosity solutions of fully nonlinear path dependent PDEs. Further, we develop a notion of elliptic path dependent PDEs, and provide a wellposedness theory by following the lines of arguments in [38]. This thesis also includes some interesting applications of path dependent PDEs. One of them is on the large deviations of non-Markovian dif- fusion. As Fleming used the stability of viscosity solutions of PDEs to establish the large deviation principle in Markovian case (see [51]), we use the theory of backward stochastic differential equations and that of path dependent PDEs to generalize his result for non-Markovian diffusions. Moreover, the large deviation result is applied to investigate the short maturity asymptotics of the implied volatility surface in financial mathematics. Finally, a study of dual algorithm for stochastic control pro- blems is presented. As Monte-Carlo simulations for the stochastic control problems provide low-biased estimate, a dual algorithm offer upper bounds of the true values. The idea of ‘path-frozen’ is exploited to give a dual representation of non-Markovian stochastic control problems.Dans les travaux précédents, Ekren, Keller, Touzi & Zhang [35] et Ekren, Touzi & Zhang [37, 38], les auteurs ont introduit une notion de solutions de viscosité des EDPs dépendantes de la trajectoire (EDP-P) et ils ont montré des résultats d’unicité et d’existence par un argument appelé ‘trajectoire gelée’. Les solutions de viscosité des EDP-Ps généralisent les solutions de viscosité des EDPs, en particu- lier, elles peuvent être utilisées pour caractériser les fonctions valeur des problèmes de contrôle stochastique non-markovien. Dans cette thèse, nous présentons le dé- veloppement récent de la nouvelle théorie. Au cas des EDP-Ps semi-linéaires, nous améliorons l’argument pour le résultat de la comparaison et nous proposons une méthode de Perron pour prouver l’existence de solution de viscosité. En outre, comme dans le travail de Barles et Souganidis [4] dans le contexte d’EDP, nous montrons qu’une famille de schémas numériques satisfaisant les conditions de mo- notonie fournit les solutions numériques convergeant vers les solutions de viscosité des EDP-P’s. De plus, nous essayons de développer la notion des EDP-Ps elliptiques et nous arrivons à montrer les résultats d’unicité et d’existence en suivant les ar- guments dans [38]. Cette thèse contient aussi certaines applications intéressantes des EDP-Ps. L’une des application concerne les grandes déviations des diffusions non-markoviennes. Comme Fleming a utilisé la stabilité des solutions de viscosité des EDPs pour montrer le principe de grandes déviations dans le cas markovien (voir [51]), nous utilisons les équations différentielles stochastiques rétrogrades et les EDP-Ps pour généraliser son résultat au cas non-markovien. En plus, on ap- plique ce résultat de grandes déviations à l’étude du comportement asymptotique de la surface de volatilité implicite en mathématiques financières. Enfin, nous pré- sentons un algorithme dual pour des problèmes de contrôle stochastique. Lorsque les simulations de Monte Carlo des problèmes de contrôle stochastique fournissent des estimations biaisées inférieurement, l’algorithme dual donne des bornes supé- rieures des fonctions valeur. L’idée de ‘trajectoire gelée’ est utilisée pour donner des représentations duales des problèmes de contrôle stochastique non-markovien
Long and Winding Central Paths
No full textMinisymposia "Complexity Issues in Control Computation and Max-Plus Methods"International audienceWe disprove a continuous analog of the Hirsch conjecture proposed by Deza, Terlaky and Zinchenko, by constructing a family of linear programs with 3r+4 inequalities in dimension 2r+2 where the central path has a total curvature in Ω(2^r/r). Our method is to tropicalize the central path in linear programming. The tropical central path is the piecewise-linear limit of the central paths of parameterized families of linear programs viewed through logarithmic glasses
ϕ meson production in d+Au collisions at √sNN=200GeV
No full textInternational audienceThe PHENIX Collaboration has measured ϕ meson production in d+Au collisions at sNN−−−√=200 GeV using the dimuon and dielectron decay channels. The ϕ meson is measured in the forward (backward) d-going (Au-going) direction, 1.2<y<2.2 (−2.2<y<−1.2) in the transverse-momentum (pT) range from 1–7 GeV/c and at midrapidity |y|<0.35 in the pT range below 7 GeV/c. The ϕ meson invariant yields and nuclear-modification factors as a function of pT, rapidity, and centrality are reported. An enhancement of ϕ meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p+p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects
MOVPE growth of InGaN alloys with high In content on ZnO template substrates
No full textInternational audienc
Nanoselective area growth of high quality thick InGaN/GaN on sacrificial ZnO templates
No full textInternational audienc
Optimizing Urban Freight Deliveries: From Designing and Testing a Prototype System to Addressing Real Life Challenges
No full text9th International Conference on City Logistics, Tenerife, ESPAGNE, 17-/06/2015 - 19/06/2015In this article, we present efforts towards building a city-wide freight delivery rounds optimization system aimed at leveraging city traffic information to optimize professional vehicle rounds. This project, called SmartDeliveries, has been developed as part of the OptimodLyon project. We present the system's architecture and general objective. Then we present early evaluations which have led us to identify three main technical challenges to address, but also to quantify the potential productivity gains for its users: 18% in distance savings and 11% in time. This could lead, if the system were to be generalized at the scale of the city, to a reduction in as much as 5% in traffic, and to corresponding savings in emissions, which are the primary motivation of the project leaders. Finally we discuss the remaining challenges to address, from a technical as well as an organizational standpoint, to introduce real life implementation of the system
Supertropical SLn
No full textAlso arXiv:1508.04483Extending earlier work on supertropical adjoints and applying symmetrization, we provide a symmetrized supertropical version SLn of the special linear group, which we partition into submonoids, based on " quasi-identity " matrices, and we display maximal sub-semigroups of SLn. We also study the monoid generated by SLn. Several illustrative examples are given of unexpected behavior. We describe the action of elementary matrices on SLn, which enables one to connect different matrices in SLn, but in a weaker sense than the classical situation