Commande variant dans le temps pour le contrôle d'attitude de satellites

Cette thèse porte sur la commande variant dans le temps avec comme fil directeur l application au contrôle d attitude de satellites. Nous avons étudié trois types de commande: une commande à commutation, une commande LPV et une commande adaptative directe. Pour cette dernière nous avons proposé des résultats théoriques nouveaux portant sur la structuration du gain et de l adaptation. Les résultats ont été validés en simulation et sont testés à bord d un satellite. En partant de la loi à commutation actuellement utilisée sur les satellites Myriade, une première partie de nos travaux est dédiée à la commande LPV. Notre approche, basée sur la spécification des objectifs de commande à travers un modèle de référence LPV, permet d'obtenir de nouveaux algorithmes exprimés dans ce formalisme. Testées en simulation, ces lois de commande répondent à la problématique de notre application. Toutefois, le choix du modèle de référence LPV s'avère délicat. Cette difficulté a été levée en utilisant la commande adaptative. Dans cette approche, les spécifications sur le comportement temps-variant sont traduites par des contraintes au niveau des lois d'adaptation des gains de commande. Nous introduisons ainsi une nouvelle méthode de synthèse de lois adaptatives structurées. Les preuves de stabilité établies s'appuient sur des outils de la théorie de Lyapunov. Les résultats obtenus sur un simulateur complet montrent l'intérêt de tels algorithmes adaptatifs. Ils permettent en particulier de modifier la dynamique du satellite selon les capacités disponibles des actionneurs. Sur la base de ces résultats, une campagne d essai en vol sur le satellite PICARD est actuellement en cours.This manuscript considers time varying control, with a strong emphasis on a satellite attitude control application. Three types of control structures have been studied: a switch-based approach, LPV control and direct adaptive control. In this last field we have introduced new theoretical results which allow structuring the gain and the adaptation law. The results have been validated in simulation and are currently tested on board a satellite. Starting from the switch-based control law currently implemented on the Myriade satellites, a first part of our work isdedicated to LPV control. Based on the specification of the control objectives by using of an LPV reference model, our approach allows obtaining new control algorithms expressed within this framework. The simulations carried out with theLPV algorithms obtained by using this method show that they meet the needs of our application. Nonetheless, the choice of a reference model proves to be difficult. This obstacle has been surpassed by using direct adaptive control. In this approach, specifications regarding the timevarying behaviour are added through constraints on the laws defining the control gains adaptation. We thus introduce anew synthesis method, based on which structured adaptive control laws are obtained. Stability proofs are established based on tools of the Lyapunov theory.The results obtained on a complete simulator show the interest of using such adaptive algorithms, which allow in particular to modify the satellite dynamics depending on the available capacity of the actuators. Based on these positive results, a fight-test campaign on the PICARD satellite is underway.TOULOUSE-ISAE (315552318) / SudocSudocFranceF

Ancient DNA reveals interstadials as a driver of common vole population dynamics during the last glacial period

Aim Many species experienced population turnover and local extinction during the Late Pleistocene. In the case of megafauna, it remains challenging to disentangle climate change and the activities of Palaeolithic hunter-gatherers as the main cause. In contrast, the impact of humans on rodent populations is likely to be negligible. This study investigated which climatic and/or environmental factors affect the population dynamics of the common vole. This temperate rodent is widespread across Europe and was one of the most abundant small mammal species throughout the Late Pleistocene. Location Europe. Taxon Common vole (Microtus arvalis). Methods We generated a dataset comprised of 4.2 kb long fragment of mitochondrial DNA (mtDNA) from 148 ancient and 51 modern specimens sampled from multiple localities across Europe and covering the last 60 thousand years (ka). We used Bayesian inference to reconstruct their phylogenetic relationships and to estimate the age of the specimens that were not directly dated. Results We estimated the time to the most recent common ancestor of all last glacial and extant common vole lineages to be 90 ka ago and the divergence of the main mtDNA lineages present in extant populations to between 55 and 40 ka ago, which is earlier than most previous estimates. We detected several lineage turnovers in Europe during the period of high climate variability at the end of Marine Isotope Stage 3 (MIS 3; 57-29 ka ago) in addition to those found previously around the Pleistocene/Holocene transition. In contrast, data from the Western Carpathians suggest continuity throughout the Last Glacial Maximum (LGM) even at high latitudes. Main Conclusions The main factor affecting the common vole populations during the last glacial period was the decrease in open habitat during the interstadials, whereas climate deterioration during the LGM had little impact on population dynamics. This suggests that the rapid environmental change rather than other factors was the major force shaping the histories of the Late Pleistocene faunas.info:eu-repo/semantics/publishedVersio

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Time varying satellite attitude control

Cette thèse porte sur la commande variant dans le temps avec comme fil directeur l’application au contrôle d’attitude de satellites. Nous avons étudié trois types de commande: une commande à commutation, une commande LPV et une commande adaptative directe. Pour cette dernière nous avons proposé des résultats théoriques nouveaux portant sur la structuration du gain et de l’adaptation. Les résultats ont été validés en simulation et sont testés à bord d’un satellite. En partant de la loi à commutation actuellement utilisée sur les satellites Myriade, une première partie de nos travaux est dédiée à la commande LPV. Notre approche, basée sur la spécification des objectifs de commande à travers un modèle de référence LPV, permet d'obtenir de nouveaux algorithmes exprimés dans ce formalisme. Testées en simulation, ces lois de commande répondent à la problématique de notre application. Toutefois, le choix du modèle de référence LPV s'avère délicat. Cette difficulté a été levée en utilisant la commande adaptative. Dans cette approche, les spécifications sur le comportement temps-variant sont traduites par des contraintes au niveau des lois d'adaptation des gains de commande. Nous introduisons ainsi une nouvelle méthode de synthèse de lois adaptatives structurées. Les preuves de stabilité établies s'appuient sur des outils de la théorie de Lyapunov. Les résultats obtenus sur un simulateur complet montrent l'intérêt de tels algorithmes adaptatifs. Ils permettent en particulier de modifier la dynamique du satellite selon les capacités disponibles des actionneurs. Sur la base de ces résultats, une campagne d’essai en vol sur le satellite PICARD est actuellement en cours.This manuscript considers time varying control, with a strong emphasis on a satellite attitude control application. Three types of control structures have been studied: a switch-based approach, LPV control and direct adaptive control. In this last field we have introduced new theoretical results which allow structuring the gain and the adaptation law. The results have been validated in simulation and are currently tested on board a satellite. Starting from the switch-based control law currently implemented on the Myriade satellites, a first part of our work isdedicated to LPV control. Based on the specification of the control objectives by using of an LPV reference model, our approach allows obtaining new control algorithms expressed within this framework. The simulations carried out with theLPV algorithms obtained by using this method show that they meet the needs of our application. Nonetheless, the choice of a reference model proves to be difficult. This obstacle has been surpassed by using direct adaptive control. In this approach, specifications regarding the timevarying behaviour are added through constraints on the laws defining the control gains adaptation. We thus introduce anew synthesis method, based on which structured adaptive control laws are obtained. Stability proofs are established based on tools of the Lyapunov theory.The results obtained on a complete simulator show the interest of using such adaptive algorithms, which allow in particular to modify the satellite dynamics depending on the available capacity of the actuators. Based on these positive results, a fight-test campaign on the PICARD satellite is underway

Commande variante dans le temps pour le contrôle d'attitude de satellites

This manuscript considers time varying control, with a strong emphasis on a satellite application. Three types of control structures are studied : a switch-based approach, LPV control and direct adaptive control. In this last field we introduce new theoretical results which allow structuring the gain and the adaptation law. The results are validated in simulation and are currently tested on board a satellite. The application we consider is satellite attitude control using reaction wheels. Taking into account the inherent limitations of these actuators, we first point out the need to implement control laws that vary according to the operating conditions. In particular, one seeks controllers that guarantee a fast response when the pointing error is small, whilst limiting the control effort when the satellite is far from its reference position. Starting from the preliminary results concerning the switch-based control law currently implemented on the Myriade satellites, a first part of our work is dedicated to LPV control. A synthesis method is developed, which allows obtaining new control algorithms expressed within this framework. The proposed approach is based on the specification of the control objectives through an LPV reference model, describing the ideal closed-loop behaviour. The simulations carried out with LPV algorithms obtained by using this method show that they meet the needs of our application. Nonetheless, the choice of a reference model proves to be difficult. This obstacle has been surpassed by using direct adaptive control. In this approach, specifications regarding the behaviour at small and large pointing errors can be added through constraints on the laws defining the control gains adaptation. We thus introduce a new synthesis method, based on which structured adaptive control laws are obtained. The closed loop stability proofs are based on tools of the Lyapunov theory, specific to adaptive and robust control. This combination allows us to establish stability proofs for structured adaptive laws containing, for instance, the sigma-modification. Several laws obtained in this way have been tested on a complete simulator, based on a non-linear model of a satellite in its orbital environment. The results show the interest of such adaptive algorithms, which allow in particular to modify the satellite dynamics depending on the available capacity of the actuators. Based on these positive results, a fight-test campaign on the Picard satellite is underway.Cette thèse porte sur la commande variant dans le temps avec comme fil directeur une application satellite. Nous avons étudié trois types de commande: une commande à commutation, une commande LPV et une commande adaptative directe. Pour cette dernière nous avons proposé des résultats théoriques nouveaux portant sur la structuration du gain et de l'adaptation. Les résultats ont été validés en simulation et sont testés à bord d'un satellite. L'application que nous considérons au cours de cette étude est la commande d'attitude des satellites par roues à réaction. A partir des limitations de ces actionneurs, nous exposons dans un premier temps le besoin de mettre en place des lois de commande qui varient selon les conditions de fonctionnement. En particulier, on cherche des correcteurs assurant une réponse rapide lorsque l'erreur d'attitude est faible, tout en limitant l'effort de commande lorsque le satellite se trouve loin de sa position de consigne. En partant des résultats préliminaires portant sur la commande à commutation, actuellement utilisée sur les satellites Myriade, une première partie de nos travaux est dédiée à la commande LPV. Une méthode de synthèse est développée, permettant d'obtenir de nouveaux algorithmes exprimés dans ce formalisme. L'approche que nous proposons se base sur la spécification des objectifs de commande à travers un modèle de référence LPV qui décrit le comportement idéal en boucle fermée. Testées en simulation, les lois de commande LPV obtenues répondent à la problématique de notre application. Toutefois, le choix du modèle de référence LPV s'avère délicat. Cette difficulté a été levée en utilisant la commande adaptative. Dans cette approche, les spécifications concernant les comportements aux dépointages faibles et forts sont traduites par des contraintes au niveau des lois d'adaptation des gains de commande. Nous introduisons ainsi une nouvelle méthode de synthèse permettant d'obtenir des lois adaptatives structurées. Les preuves de stabilité en boucle fermée se basent sur des outils de la théorie de Lyapunov, spécifiques à la commande adaptative, mais également à la commande robuste. Cette combinaison permet d'établir des preuves de stabilité asymptotique pour des lois d'adaptation structurées faisant apparaitre, entre autre, la sigma-modification. Plusieurs lois ainsi obtenues ont été testées sur un simulateur complet du un modèle non-linéaire d'un satellite dans son environnement orbital. Les résultats montrent l'intérêt de l'utilisation de tels algorithmes adaptatifs, qui permettent en particulier de modifier la dynamique du satellite en fonction des capacités disponibles des actionneurs. Sur la base de ces résultats positifs, une campagne d'essais en vol sur le satellite Picard est actuellement en cours

Structured adaptive attitude control applied on a Myriade simulation benchmark

This paper considers the problem of reaction-wheel attitude control inside the mission mode of the Myriade satellites. A structured adaptive algorithm, allowing to extend the operating domain of a static proportional- derivative controller is presented and conditions for designing a stabilizing, continuous-time adaptive law are given. In view of implementation, a discrete-time adaptive algorithm is derived and tested on a benchmark of the DEMETER satellite, which was part of the Myriade program. Simulation results show that the structured adaptation and the use of the sigma-modification allow the adaptive closed-loop to follow attitude step references of up to 20 degrees without saturating the reaction wheels. This allows the adaptive law to cover the whole mission mode and replace the currently-implemented switched-based control strategy, thus potentially simplifying the verification and validation process

Accessing European Strong-Motion Data : An Update on ORFEUS Coordinated Services

Strong ground motion records and free open access to strong‐motion data repositories are fundamental inputs to seismology, engineering seismology, soil dynamics, and earthquake engineering science and practice. This article presents the current status and outlook of the Observatories and Research Facilities for European Seismology (ORFEUS) coordinated strong‐motion seismology services, namely the rapid raw strong‐motion (RRSM) and the engineering strong‐motion (ESM) databases and associated web interfaces and webservices. We compare and discuss the role and use of these two systems using the Mw 6.5 Norcia (Central Italy) earthquake that occurred on 30 October 2016 as an example of a well‐recorded earthquake that triggered major interest in the seismological and earthquake engineering communities. The RRSM is a fully automated system for rapid dissemination of earthquake shaking information, whereas the ESM provides quality‐checked, manually processed waveforms and reviewed earthquake information. The RRSM uses only data from the European Integrated Waveform Data Archive, whereas the ESM also includes offline data from other sources, such as the ITalian ACcelerometric Archive (ITACA). Advanced software tools are also included in the ESM to allow users to process strong‐motion data and to select ground‐motion waveform sets for seismic structural analyses. The RRSM and ESM are complementary services designed for a variety of possible stakeholders, ranging from scientists to the educated general public. The RRSM and ESM are developed, organized, and reviewed by selected members of the seismological community in Europe, including strong‐motion data providers and expert users. Global access and usage of the data is encouraged. The ESM is presently the reference database for harmonized seismic hazard and risk studies in Europe. ORFEUS strong‐motion data are open, “Findable, Accessible, Interoperable, and Reusable,” and accompanied by licensing information. The users are encouraged to properly cite the data providers, using the digital object identifiers of the seismic networks. © 2021 Seismological Society of AmericaISSN:0895-0695ISSN:1938-205

Ancient DNA reveals interstadials as a driver of the common vole population dynamics during the last glacial period

The common vole is a temperate rodent widespread across Europe. It was also one of the most abundant small mammal species throughout the Late Pleistocene. Phylogeographic studies of its extant populations suggested the Last Glacial Maximum (LGM, 26.5–19 ka ago) as one of the main drivers of the species’ population dynamics. However, analyses based solely on extant genetic diversity may not recover the full complexity of past population history. The main aim of this study was to investigate the evolutionary history and identify the main drivers of the common vole population dynamics during the Late Pleistocene in Europe. We generated a dataset comprising 4.2 kb-long fragment of mitochondrial DNA from 148 63 ancient and 51 modern specimens sampled from multiple localities across Europe and covering the last 60 thousand years (ka). We used Bayesian inference to reconstruct their phylogenetic relationships and to estimate the age of specimens that were not directly dated. We estimate the time to the most recent common ancestor of all Last Glacial and extant common vole lineages to 90 ka ago and the divergence of the main mtDNA lineages present in extantpopulations to between 55 and 40 ka ago, earlier than previous estimates. We find multiple lineage turnovers in Europe in the period of high climate variability at the end of Marine Isotope Stage 3 (MIS 3; 57–29 ka ago) in addition to those found previously around the Pleistocene/Holocene transition. Conversely, data from the Western Carpathians suggest continuity throughout the LGM even at high latitudes. Our results suggest that the main factor affecting the common vole populations during the last glacial period was the reduction of open habitats during the interstadial periods while the climate deterioration during the LGM had little impact on species’ population dynamics

Measurement of the W±ZW^{\pm}Z boson pair-production cross section in pppp collisions at s=13\sqrt{s}=13 TeV with the ATLAS Detector

The production of $W^{\pm}Z$ events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb$^{-1}$. The $W^{\pm}Z$ candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu \ell \ell}^{\textrm{fid.}} = 63.2 \pm 3.2$ (stat.) $\pm 2.6$ (sys.) $\pm 1.5$ (lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is $53.4^{+3.6}_{-2.8}$ fb. The extrapolation of the measurement from the fiducial to the total phase space yields $\sigma_{W^{\pm}Z}^{\textrm{tot.}} = 50.6 \pm 2.6$ (stat.) $\pm 2.0$ (sys.) $\pm 0.9$ (th.) $\pm 1.2$ (lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of $48.2^{+1.1}_{-1.0}$ pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent $W^+Z$ and $W^-Z$ cross sections and their ratio

Search for direct top squark pair production in final states with two leptons in s=13\sqrt{s} = 13 TeV pppp collisions with the ATLAS detector

International audienceThe results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using $36.1~\hbox {fb}^{-1}$ of integrated luminosity from proton–proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi }_{1}^{\pm }$ into a b-quark and the lightest chargino with $\tilde{\chi }_{1}^{\pm } \rightarrow W \tilde{\chi }_{1}^{0}$ , the decay $\tilde{t} \rightarrow t \tilde{\chi }_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi }_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi }_{1}^{0}$ . No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the $\tilde{t}$ and $\tilde{\chi }_{1}^{0}$ masses. The results exclude at 95% confidence level $\tilde{t}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches