A linking invariant for algebraic curves

We construct a topological invariant of algebraic plane curves, which is in some sense an adaptation of the linking number of knot theory. This invariant is shown to be a generalisation of the I-invariant of line arrangements developed by the first author with Artal and Florens. We give a practical tool for computing this invariant, using a modification of the usual braid monodromy. As an application, we show that this invariant distinguishes a new Zariski pair of curves, i.e. a pair of curves having same combinatorics, yet different topology. These curves are composed of a smooth cubic with 5 tangent lines at its inflexion points. As in the historical example of Zariski, this pair can be geometrically characterized by the mutual position of their singular points

An electronic instability in bismuth far beyond the quantum limit

We present a transport study of semi-metallic bismuth in presence of a magnetic field applied along the trigonal axis extended to 55 T for electric conductivity and to 45 T for thermoelectric response. The results uncover a new field scale at about 40 T in addition to the previously detected ones. Large anomalies in all transport properties point to an intriguing electronic instability deep in the ultraquantum regime. Unexpectedly, both the sheer magnitude of conductivity and its metallic temperature dependence are enhanced by this instability.Comment: 5 pages, 4 figure

Masses of the components of SB2 binaries observed with Gaia. I. Selection of the sample and mass ratios of 20 new SB2s discovered with Sophie

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries is being observed since 2010 with the Sophie spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1% when the astrometric measurements of Gaia are taken into account. Simultaneously, the luminosities of the components in the Gaia photometric band G will also be obtained. Our observation program started with 200 SBs, including 152 systems that were only known as single-lined. Thanks to the high efficiency of the Sophie spectrograph, an additional component was found for 25 SBs. After rejection of 5 multiple systems, 20 new SB2s were retained, including 8 binaries with evolved primary, and their mass ratios were derived. Our final sample contains 68 SB2s, including 2 late-type giants and 10 other evolved stars.Comment: 8 pages, 3 figures, accepted for publication in MNRA

The polarisation fluctuation length scale shaping the superconducting dome of SrTiO3_3

Superconducting domes, ubiquitous across a variety of quantum materials, are often understood as a window favorite for pairing opened by the fluctuations of competing orders. Yet, a quantitative understanding of how such a window closes is missing. Here, we show that inelastic neutron scattering, by quantifying a length scale associated with polar fluctuations, $\ell_0$, addresses this issue. We find that the superconducting dome of strontium titanate definitely ends when $\ell_0$ vanishes. Moreover, the product of $\ell_0$ and the Fermi wavevector peaks close to the maximum critical temperature. Thus, this superconducting dome stems from the competition between the increase of the density of states and the unavoidable collapse of the quantum paraelectric phase, both induced by doping. The successful quantitative account of both the peak and the end of the superconducting dome implies a central role in the pairing mechanism played by the soft ferro-electric mode and its hybridisation with the acoustic branch. Such a scenario may also be at work in other quantum paraelectric materials, either bulk or interfaces.Comment: SM on reques

Gestion optimale d'un réservoir hydraulique multiusages et changement climatique. Modèles, projections et incertitudes (Application à la réserve de Serre-Ponçon)

Pouvoir évaluer l'impact du changement climatique sur la ressource en eau, et les systèmes de gestion qui lui sont associés, est une préoccupation majeure de nos sociétés. Une telle évaluation nécessite la mise en place d'une chaîne de simulation qui permet, sur la base d'expériences climatiques futures, i) d'estimer à l'échelle régionale l'évolution possible de la ressource et de sa variabilité, ii) de simuler le comportement des systèmes utilisés pour leur gestion pour iii) estimer les éventuelles modifications de performance. Cette thèse vise à tester la possibilité de mettre en place une chaîne de simulation de ce type pour un système de gestion réel et à identifier quelles sont les composantes à considérer dans ce cas. Pour ce faire, nous chercherons en particulier à apporter des éléments de réponse aux questions suivantes: - Quelles représentations peut-on faire d'un système de gestion opérationnel pour une application en climat modifié ? - Quels éléments d'évaluation peuvent permettre d'estimer l'impact du changement climatique sur ce système de gestion ? - Quelles sont les sources d'incertitudes influençant cette évaluation ? Quelles sont les contributions relatives à l'incertitude totale des différentes méthodes et modèles utilisés ? Nous considérerons plus précisément le système de gestion du barrage de Serre-Ponçon, alimenté par le haut bassin versant de la Durance. Ce barrage, géré par EDF, est l'un des plus grands barrages artificiels européens. Il est multi-usages (irrigation, soutien d'étiage, production d'hydroélectricité, tourisme). Dans un premier temps, nous présenterons le contexte du système de gestion actuel. Nous mettrons ensuite en place un modèle de gestion du barrage visant à reproduire de façon réaliste du point de vue du gestionnaire actuel (EDF), mais simplifiée pour pouvoir être appliqué sous scénarios futurs - la gestion actuelle du barrage. Nous développerons pour cela i) des modèles permettant d'estimer les différentes demandes en eau et ii) un modèle d'optimisation de la gestion sous contraintes. Ce modèle permettra de simuler la gestion du système au pas de temps journalier sur plusieurs décennies du climat récent, ou de climats futurs modifiés. Nous proposerons ensuite un ensemble d'indicateurs qui permettent de fournir une estimation de la performance d'un tel système à partir des sorties du modèle de gestion obtenues par simulation pour différentes périodes de 30 ans. Nous explorerons la façon dont la performance estimée dépend du modèle choisi pour la représentation du système de gestion actuel, et plus précisément de la façon dont la stratégie utilisée pour l'optimisation de la gestion est élaborée. A ce titre, nous proposerons trois modèles de gestion basés sur trois types de stratégies, obtenues pour des degrés différents de prévisibilité des apports et sollicitations futurs à la retenue. Pour ces simulations, les modèles d'impacts nécessitent des scénarios de forçages météorologiques à l'échelle de bassin versant (e.g. modèle hydrologique, modèle d'usages de l'eau, modèle de gestion de la ressource). Ces scénarios peuvent être obtenus par des méthodes de descente d'échelle statistique (MDES), sur la base des simulations grande échelle des modèles climatiques globaux. Enfin, nous évaluerons les incertitudes liées aux deux types de modèles et estimerons leurs contributions relatives à l'incertitude globale. Nous utiliserons pour cela les scénarios issus de différentes chaines de simulation GCM/MDES produits sur la période 1860-2011 dans le cadre du projet RIWER2030. Nous montrerons que ces deux sources d'incertitudes sont du même ordre de grandeur sur l'estimation des modifications de performance.Assess the impact of climate change on water resources and management systems associated, is a major concern of our society. This requires the establishment of a simulation chain which allows, on the basis of future climate experiments i) to estimate the possible changes in regional resource and its variability, ii) to simulate the behavior of the systems used to manage them in order to iii) estimate the possible changes in performance. This thesis aims to test the feasibility of establishing a chain simulation of such a management system to identify what are the real components to consider in this case. To do this, we have to provide answers to the following questions: - How can we represent an operational management system in a climate change context? - What elements of evaluation can be used to estimate the impact of climate change on the management system? - What are the sources of uncertainty influencing this assessment? What are the relative contributions to the total uncertainty of these different methods and models used? We consider the system of management of the reservoir of Serre-Ponçon, built on the high basin of the Durance. This dam, operated by EDF, is one of the largest artificial dams Europe. It is multi-purpose (irrigation, low-flow support, hydropower, tourism). As a first step, we will present the context of the current management system. Then, we will establish a management model to reproduce - in a realistic way from the point of view of the current manager (EDF), but simplified to be applied in future scenarios - the current management of the Serre-Ponçon reserve. We will develop for this, i) different models to estimate different water demands and ii) an optimization model with constraints management. This model will simulate the management system in daily time step on several decades of recent climate or future climate change. We then propose a set of indicators to provide an estimate of the performance of such a system from the outputs of the management model obtained by simulation for different periods of 30 years. We will explore how the estimated performance depends on the model chosen to represent the current management system, and more specifically how the strategy used to optimize the management is developed. To this end, we will propose three management models based on three types of strategies, obtained for different degrees of predictability of future inflows and constraints. For these simulations, the impact models require meteorological forcing scenarios at watershed scale (eg hydrological model, model of water use model of resource management). These scenarios can be obtained by statistical downscaling methods (SDM), on the basis of large-scale simulations of global climate models. Finally, we will evaluate the uncertainties associated with the two types of models and will estimate their relative contributions to the overall uncertainty. We have used this scenario from different GCM/SDM simulations over the period 1860-2100 obtained within the RIWER2030 project. We show that these two sources of uncertainty are of the same order of magnitude estimate of changes in performance.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

A Unique Voltage Sensor Sensitizes the Potassium Channel AKT2 to Phosphoregulation

Among all voltage-gated K+ channels from the model plant Arabidopsis thaliana, the weakly rectifying K+ channel (Kweak channel) AKT2 displays unique gating properties. AKT2 is exceptionally regulated by phosphorylation: when nonphosphorylated AKT2 behaves as an inward-rectifying potassium channel; phosphorylation of AKT2 abolishes inward rectification by shifting its activation threshold far positive (>200 mV) so that it closes only at voltages positive of +100 mV. In its phosphorylated form, AKT2 is thus locked in the open state in the entire physiological voltage range. To understand the molecular grounds of this unique gating behavior, we generated chimeras between AKT2 and the conventional inward-rectifying channel KAT1. The transfer of the pore from KAT1 to AKT2 altered the permeation properties of the channel. However, the gating properties were unaffected, suggesting that the pore region of AKT2 is not responsible for the unique Kweak gating. Instead, a lysine residue in S4, highly conserved among all Kweak channels but absent from other plant K+ channels, was pinpointed in a site-directed mutagenesis approach. Substitution of the lysine by serine or aspartate abolished the “open-lock” characteristic and converted AKT2 into an inward-rectifying channel. Interestingly, phosphoregulation of the mutant AKT2-K197S appeared to be similar to that of the Kin channel KAT1: as suggested by mimicking the phosphorylated and dephosphorylated states, phosphorylation induced a shift of the activation threshold of AKT2-K197S by about +50 mV. We conclude that the lysine residue K197 sensitizes AKT2 to phosphoregulation. The phosphorylation-induced reduction of the activation energy in AKT2 is ∼6 kT larger than in the K197S mutant. It is discussed that this hypersensitive response of AKT2 to phosphorylation equips a cell with the versatility to establish a potassium gradient and to make efficient use of it

Toucheo: Multitouch and Stereo Combined in a Seamless Workspace.

International audienceWe propose a new system that efficiently combines direct multitouch interaction with co-located 3D stereoscopic visualization. In our approach, users benefit from well-known 2D metaphors and widgets displayed on a monoscopic touchscreen, while visualizing occlusion-free 3D objects floating above the surface at an optically correct distance. Technically, a horizontal semi-transparent mirror is used to reflect 3D images produced by a stereoscopic screen, while the user's hand as well as a multitouch screen located below this mirror remain visible. By registering the 3D virtual space and the physical space, we produce a rich and unified workspace where users benefit simultaneously from the advantages of both direct and indirect interaction, and from 2D and 3D visualizations. A pilot usability study shows that this combination of technology provides a good user experience

Contracts for Systems Design: Theory

Aircrafts, trains, cars, plants, distributed telecommunication military or health care systems,and more, involve systems design as a critical step. Complexity has caused system design times and coststo go severely over budget so as to threaten the health of entire industrial sectors. Heuristic methods andstandard practices do not seem to scale with complexity so that novel design methods and tools based on astrong theoretical foundation are sorely needed. Model-based design as well as other methodologies suchas layered and compositional design have been used recently but a unified intellectual framework with acomplete design flow supported by formal tools is still lacking.Recently an “orthogonal” approach has been proposed that can be applied to all methodologies introducedthus far to provide a rigorous scaffolding for verification, analysis and abstraction/refinement: contractbaseddesign. Several results have been obtained in this domain but a unified treatment of the topic that canhelp in putting contract-based design in perspective is missing. This paper intends to provide such treatmentwhere contracts are precisely defined and characterized so that they can be used in design methodologiessuch as the ones mentioned above with no ambiguity. In addition, the paper provides an important linkbetween interface and contract theories to show similarities and correspondences.This paper is complemented by a companion paper where contract based design is illustrated throughuse cases