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Computation of invariant sets for discrete‐time uncertain systems
No full textInternational audienceAbstract This article proposes novel methods for the computation of state and output bounding sets for discrete‐time uncertain systems. The systems under consideration are formed from the interconnection of a nominal linear time‐invariant system and an uncertainty operator that is known to lie within a prespecified set. The set of allowable uncertainties is described by a pointwise integral quadratic constraint (IQC), that is, a quadratic constraint that holds for all time‐steps. Examples of pointwise IQCs characterizing common uncertainty sets are provided. The exogenous input to the system is assumed to lie in a given polytope or ellipsoid for all time‐steps. The proposed methods are illustrated via an example
Computing optimal trajectories for light soaring aircraft using Fast Marching Tree Star
No full textIn the last couple of years, performances of light soaring aircraft (para gliders, hang gliders, or light sailplanes) have increased significantly, allowing pilots to fly great distances using only the convective energy of the atmosphere. This activity, called "Cross-Country flying" or "soaring", requires topological and aerological knowledge and a lot of pre-flight preparation in order to make the right decisions, thus maximizing the flying distance or minimizing the flying time in a race. To optimize these flights, a pre-tactical decision support tool has been developed. This tool results from the adaptation of the Fast Marching Tree Star algorithm. It is extended in such a way it can deal with differential constraints associated with light soaring aircraft, operating in a convective atmosphere, in a field of wind, and close to reliefs. The method has been tested and validated on a real competition light soaring aircraft
Absolute Environmental Sustainability Assessment of aviation transition scenarios
No full textInternational audienceThe aviation sector is currently responsible for 2-3% of annual anthropogenic CO2 emissions and for 5-6% of the climate impact ([1] Référentiel ISAE-SUPAERO Aviation et Climat, 2021). In order to assess its climate footprint over time, the sector and its various stakeholders have developed numerous prospective scenarios (e.g. [2] Dray et al. 2022 and [3] Bergero et al. 2023) incorporating different assumptions about traffic growth, fleet renewal, the introduction of new technologies, and the use of alternative fuels. These scenarios are primarily used to evaluate their potential for decarbonization by comparing them to a "business-as-usual" reference scenario. To evaluate the climate impact in an absolute rather than relative manner, some publications compare the cumulative emissions of the sector generated by a prospective scenario to a given carbon budget (e.g. compliance with the Paris Agreement).However, the various solutions proposed are only assessed through the prism of climate. The primary decarbonization lever being considered is the introduction of alternative fuels. In the event of a significant increase in traffic flow, the primary energy requirement could be multiplied by a factor of 3 or 4. If we take the example of fuel produced from biomass, the increasing resource demand could give rise to issues pertaining to land-system change, water use, and the application of nitrogen or phosphorus-based fertilizers. Alternative fuel sources, particularly liquid hydrogen and electrofuels, which rely on electricity as their primary energy source, may also cause environmental displacement issues.The Planetary Boundaries framework ([4] Steffen et al. 2015) provides a reference for absolute environmental sustainability at the global scale. After identifying the nine key processes that govern the equilibrium of the Earth system, the researchers behind the concept associated them with control variables and thresholds that should not be exceeded in order to remain within a Safe Operating Space for humanity. By reducing the scale from global to sectoral, this framework can therefore be used to perform an Absolute Environmental Sustainability Assessment (AESA) of contrasted prospective scenarios for the aviation sector.The literature surrounding the operationalization of Planetary Boundaries at smaller scales has undergone significant development in recent times. In this study, we will present an application of the PB-LCIA methodology (Life Cycle Impact Assessment) ([5] Ryberg et al. 2018) to the aviation sector, as well as discuss certain methodological questions that have been raised, such as non-CO2 effects, high-altitude emissions, and the relative usefulness of aviation, among others. Following this, we will present some preliminary results regarding the current situation and some prospective scenarios, which may highlight the possibility of problem displacement, such as the disruption of the phosphorus cycle in the case of biofuels .References:[1] doi: 10.34849/76rd-c592 [2] doi: 10.1038/s41558-022-01485-4 [3] doi: 10.1038/s41893-022-01046-9 [4] doi: 10.1126/science.1259855 [5] doi: 10.1016/j.ecolind.2017.12.06
Floating to Fixed-Point Conversion of Deep Neural Networks with Guaranteed Error Bounds1
No full textInternational audienceIn this article, we introduce a tool, Popinns, to implement Deep Neural Networks (DNNs) on fixed point architectures. Popinns takes as input the Tensorflow model of a DNN whose coefficients are floating-point numbers and generates a C code in fixed-point arithmetic. The approach implemented in Popinns is based on a formal semantics describing the propagation of the errors through the computations performed by the network. From this semantics, we deduce a system of constraints made of inequalities between linear expressions among integers and of min and max operations. The solution of this system, computed by an optimizing SMT solver, gives the optimal formats of the fixed-point numbers at each point of the DNN. As a result, we synthesize a fixed-point C code that satisfies an error bound set by the user with respect to the initial Tensorflow model. The present article describes Popinns architecture, its features as well as the intermediary and final results computed by the tool
Novel Metamaterial Lined Probe for High Precision Planar Near-Field Measurements
No full textInternational audienceFor planar near field (PNF) antenna measurements, the size of the probe is a critical parameter since the multiple reflections with the device under test (DUT) affect the overall measurement uncertainty. In this communication, the modal expansion theory (MET) is used to design an open-ended waveguide (OEW) with reduced cross section, using a metamaterial lining of the inner walls of the probe. The performance of this novel design is compared in a measurement experiment to a standard metallic probe covering the same nominal bandwidth
Triple-Band Dielectric Resonator Antenna Based on Anisotropic and Heterogeneous Ceramics
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: Animal and Human Movement : Biomechanics, Biorobotics, BiomimetismGDR 2088 Biomimetism Bioinspiration
No full textInternational audienceThe "Movement, Displacement, Biomechanics, and Biorobotics" axis of GDR Biomim 2088 focuses on the study of movement and displacement, which are observable in organized behavior from perception and translate action, and even intention. Research in this area is dedicated to understanding the mechanisms that enable migration, evasion, concealment, pursuit, capture, and the ability to move either alone or in perfectly coordinated groups of individuals. These skills have provided those who possess them with a survival capacity, and the effectiveness of biological models can be demonstrated at various scales, in different contexts, and environments. They inspire the modeling and prototyping of sensors, actuators, poly-articulated systems, and "hard or soft" robots, which, in addition to assisting humans in their tasks, contribute to advancing our understanding of life by testing hypotheses derived from biology, neuroscience, physics, and mechanics.L'axe "Mouvement, Déplacement, Biomécanique Biorobotique" du GDR Biomim 2088 est centré sur l’étude du déplacement et du mouvement, observables du comportement organisé depuis la perception et traduisant l’action voire l’intention. Les recherches s’intéressent ici à la compréhension de ces mécanismes qui permettent de migrer, de fuir et de se dissimuler ou de poursuivre et attraper, enfin de se déplacer seul ou en groupe d’individus parfaitement coordonnés. Ces habiletés ont assuré à qui les a acquises une capacité de survie et l’efficacité des modèles biologiques peut être démontrée à différentes échelles, dans différents contextes et environnements. Ils inspirent des modélisations et prototypes de capteurs, d’actionneurs, de systèmes poly-articulés et de robots « durs ou mous », qui, en plus de suppléer l’homme dans ses tâches, permettent d’avancer sur la compréhension du vivant en testant des hypothèses issues de la biologie, des neurosciences, de la physique et de la mécanique
Impact des répéteurs GNSS sur les récepteurs d'avion en phase d'approche
No full textInternational audienceThis paper develops a classification to quantify the impact of a meaconer on an aircraft GNSS receiver, from the trackingloops up to the position estimation, during an SBAS-guided LPV-200 approach. Depending on the scenario, the impact of themeaconer on the estimated position can be catalogued for each GNSS signal at a given epoch into one of the four followingsituations - nominal, jamming, multipath or spoofing. In the nominal situation, the meaconer has no appreciable impact onthe aircraft position. In the jamming situation, the meaconer induces higher noise levels resulting in greater errors in theposition estimation than in the nominal situation. In the multipath situation, the meaconer effect on the position is similar to aGNSS multipath error. In the spoofing situation, the meaconer adds a deterministic bias on a subset of PRNs that can lead tosignificantly erroneous position estimations. Extensive simulations demonstrate that a meaconer with a high power and close tothe aircraft trajectory can degrade the GNSS receiver performance and provoke faulty estimations of the aircraft position, whichare not compliant with the civil aviation standards
Network Robustness Improvement based on Alternative Paths Consideration
No full textMany services have a complex network infrastructure (transport, Internet, etc.). Disruptions caused by accidents or weather conditions can paralyze traffic for a long time. But how to improve the robustness of networks? This robustness improvement would reduce the time of exposure to disruptions and their impact on overall traffic. Lots of studies have been done on identifying critical links and nodes but not so many analyze the paths. In this paper, we propose a new method to measure network robustness based on alternative paths. Beyond improving the French low-cost flight network robustness by 15%, the method attempts to show the relevance of analyzing network vulnerability from a path-based approach