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Gaussian mixtures closest to a given measure via optimal transport
No full textInternational audienceGiven a determinate (multivariate) probability measure , we characterize Gaussian mixtures which minimize the Wasserstein distance to when the mixing probability measure on the parameters (\m,\Sigma) of the Gaussians is supported on a compact set .(i) We first show that such mixtures are optimal solutions of a particular optimal transport (OT) problem where the marginal of the OT problem is also unknown via the mixing measure variable . Next (ii) by using a well-known specific property of Gaussian measures, this optimal transport is then viewed as a Generalized Moment Problem (GMP) and if the set of mixture parameters (\m,\Sigma) is a basic compact semi-algebraic set, we provide a ``mesh-free" numerical scheme to approximate as closely as desired the optimal distance by solving a hierarchy of semidefinite relaxations of increasing size. In particular, we neither assume that the mixing measure is finitely supported nor that the variance is the same for all components. If the original measure is not a Gaussian mixture with parameters (\m,\Sigma)\in S, then a strictly positive distance is detected at a finite step of the hierarchy. If the original measure is a Gaussian mixture with parameters (\m,\Sigma)\in S, then all semidefinite relaxations of the hierarchy have same zero optimal value. Moreover if the mixing measure is atomic with finite support, its components can sometimes be extracted from an optimal solution at some semidefinite relaxation of the hierarchy when Curto \& Fialkow's flatness condition holds for some moment matrix
Superior Ignition and Combustion Performance of TiB2 Integrated Al/CuO Nanothermites
No full textNational audienceNanothermites, composed of a fuel and an oxidizer, belong to a class of energetic materials that release energy as a result of a redox reaction. Reactivemultilayer films, also referred to as nanolaminates, have been widely utilized as a prevalent technology in this field. Al stands out as a prominent fuel choice due to its cost-effectiveness, abundance and high energy density. Constrained by its high ignition point, there has been a strong interest in modifying Al-based thermites through chemical alterations. This work explored the influence of nano-TiB2 addition to CuO/Al and examined the effects on the overall energetic properties
State of the art of research towards sustainable power electronics
No full textInternational audienceSustainability in Power Electronics is a recent research topic. It takes place among current actions to grasp design choices that enables eco-design and circular economy in the domain. This article shows the result and analysis of a literature review at the intersection of power electronics and sustainability without considering reliability study of the power electronics systems. The first part explains the scope of the study. The second part shows a bibliometric analysis of the collected publications that underlines a pioneering position at the European level. The third part details the state of the art and its analysis over four investigation topics which are: tools and methods, indicators, circularity, materials and sectors and communities. This article and the work behind are the result of a collaboration at French national level, as part of the workgroup CEPPS (Convertisseurs Electronique de Puissance Plus Soutenables – More Sustainable Power Electronics Converters) supported by the CNRS (Centre National de la Recherche Scientifique – French National Centre for Scientific Research) research group SEEDS (Systèmes d’énergie électrique dans leurs dimensions sociétales - Societal dimensions of electrical energy systems)
Critical analysis of optimized energy harvesting at small-scale by thermally coupled photovoltaic-thermoelectric systems
No full textInternational audienceThe prospect of combining, at small-scale, a photovoltaic cell and a thermoelectric generator has emerged as a promising approach to enhance the non-recovered and unexploited heat from a photovoltaic cell. The increase of efficiency compared to standalone photovoltaic systems has varied, in some cases, up to 30% compared to the measured base efficiency. With the potential of improving the electrical energy generation capabilities of solar photovoltaic cells, it is no surprise innovative research regarding these hybrid photovoltaic-thermoelectric (PV-TE) systems has substantially increased over the last few years. In this analysis, electrical aspects of thermally coupled photovoltaic-thermoelectric energy harvesting systems observed in research are discussed and their main properties and specificities are reviewed and analyzed. A particular focus is made on the possible electrical connection between the photovoltaic cell and the thermoelectric generator within the hybrid system. The control mechanism for maximum power point tracking (MPPT) to achieve optimized power extraction, based on studies, is also addressed. Additionally, limitations and possible improvements are discussed regarding power extraction due to their specific needs for an electronic interface. Highlights • Impact of series, parallel, electrically isolated connections on PV-TE hybridization • Review of control and MPPT techniques applied to hybrid PV-TE systems • How concepts used in large-scale systems can be relevant to small-scale systems • Analysis of the gaps of knowledge regarding the hybridization of PV-TE device
Towards H2 production from water and ethanol interactions on hydrated TiO2(101): Insights from ReaxFF molecular dynamics
No full textInternational audienceReaxFF molecular dynamics is employed to investigate interactions between water, ethanol, their mixture, and hydrated TiO2(101) surfaces. Water maintains hydration, while exchanging both hydrogen and oxygen atoms with the surface. Ethanol dissociates, leading to the formation of ethoxy radicals (CH3CH2O) permanently attached to the surface, water molecules, and acetic acid (CH3CO2) species. Ethoxy reduces the number of hydroxyl groups and hinders hydrogen migration across the surface. The mixture of water, ethanol, and TiO2(101) results in a reduction of ethoxy coverage, inhibits CH3CO2 formation, and increases hydroxyl coverage, indicating the dominant role of water. Potential of mean force analysis shows that hydroxyl formation follows exothermic paths, with activation energy lower than 0.45 eV. A narrower pathway for ethanol access to its adsorbed site is a key factor in the dominance of water. The formation of H2 molecules exhibits a prohibitive energy barrier (4 eV), suggesting that catalytic pathways, rather than purely surface reactions, could be favored
Co-designing versatile quadruped robots for dynamic and energy-efficient motions
No full textInternational audienceThis paper presents a bi-level optimization framework to concurrently optimize a quadruped hardware and control policies for achieving dynamic cyclic behaviors. The longterm vision to drive the design of dynamic and efficient robots by means of computational techniques is applied to improve the development of a new quadruped prototype. The scale of the robot and its actuators are optimized for energy efficiency considering a complete model of the motor, that includes friction, torque, and bandwidth limitations. This model is used to optimize the power consumption during bounding and backflip tasks and is validated by tracking the output trajectories on the first prototype iteration. The co-design results show an improvement of up to 87% for a single task optimization. It appears that, for jumping forward, robots with longer thighs perform better, while for backflips, longer shanks are better suited. To understand the trade-off between these different choices, a Pareto set is constructed to guide the design of the next prototype
Robust decision trees for the multi-mode project scheduling problem with a resource investment objective and uncertain activity duration
No full textInternational audienceIn this paper, we advocate the use of robust decision trees for the problem of assembly line scheduling problem, which is modeled as a multi-mode resource constrained project scheduling Problem, with uncertainty about activity duration and a resource investment objective. The idea of a robust decision tree is that at each node, the decision maker has access to some information about the ongoing scenario. Depending on the different information they could obtain, a partial solution is proposed. Considering that the level of uncertainty is lowered, the new partial solution is less conservative and improve the robustness guarantee. However, since all accessible information may not be relevant, we turned the information selection part into an optimization problem. We first introduce the industrial context and the problem at stake. Then we propose algorithms to solve the information selection problem, using constraint programming, and then to build such robust decision trees. Finally we provide experimental results for benchmarks instances and industrial instances
Three-dimensional imaging of acoustic pressure by tomography applied to optical feedback interferometry
No full textInternational audienceThis paper presents a novel experimental technique for three-dimensional imaging of acoustic pressure waves by means of an optical feedback interferometer associated to standard Radon transformation algorithm for tomography. The imaging system is based on the sensing of the optical refractive index changes induced by the pressure variation in the medium where the acoustic wave propagates. Thanks to the compactness allowed by the laser optical feedback interferometer, this technique allows to image in three dimensions the variations of pressure of any acoustic source without any displacement of the source
How Future Defence Strategies are Driving Technological Advancements from Devices to Systems ?
No full textInternational audienceRF technologies are integral to the development of robust defense, space, and security systems, providing essential capabilities for communication, surveillance, navigation, electronic warfare, and cybersecurity in an increasingly complex and dynamic global security environment. These evolving technologies have a significant impact on society and are developed for a more secure world by strengthening the different domains of communication, navigation and positioning, surveillance and reconnaissance, space operations and cybersecurity. Along the same lines, we must also consider the domain of electronic warfare. These new systems and standards rely heavily on the development of emerging technologies, such as cognitive radio and software-defined networks. They provide increased flexibility, efficiency and security in military communications and networks, enabling adaptive and resilient defense systems. Space communication, navigation and surveillance, supporting satellite networks for civil and military applications, including remote sensing and global positioning, require ever-increasing technological capabilities in performance, power consumption and integration. Based on this, the developed RF sensors and systems are essential for surveillance and reconnaissance activities, as they provide real-time intelligence on enemy movements, threats and potential targets. One of the most critical aspects for RF technologies concerns Electronic Warfare, including jamming enemy communications, intercepting signals, and detecting and countering hostile radar and missile systems. Thus, even regarding cybersecurity, RF wireless communication channels are vulnerable to interception and hacking: ensuring the security of RF communications is essential for safeguarding sensitive military information and preventing unauthorized access. Finally, reliable communication between military personnel, vehicles and command centers, facilitating coordination and decision-making in defense operations, are also crucial aspects for which RF technologies play a crucial role. Radio frequency-based navigation systems, such as GPS or Galileo, are essential for guiding military assets with precision, ensuring accurate targeting, navigation and situational awareness in various operational environments. All these points will be addressed through a set of conferences sessions given by experts in the field, covering a structure ranging from military needs, systems development and instrumentation, and devices technology. The round table will be the highlight of this day and will allow listeners to interact with the different speakers of this Forum 2024 on Defence, Security and Space
Virtual Link Resource Allocation in Federated Multi-Administrative Networks
No full textInternational audienceA federated network can be seen as a collection of network domains, typically under different authorities, who collaborate and share network resources to enable the provision of end-to-end multi-domain services with possibly performance guarantees. To provide these services, domains need to disclose a compact portrayal of their topology. The interconnection of all exposed abstracted topologies serves as input to compute the appropriate paths that are needed to support an end-to-end service. Domains basically resort to a topology abstraction that reduces to a mesh of abstract links that connect to their border nodes. Such an abstraction voluntarily limits the information disclosed to other domains, but, on the other hand, leads to inefficient resource usage. In order to enable effective collaborations between domains, in this paper, we propose to enrich the topology aggregation exposed by domains by including additional abstract topology constructs, e.g. abstract non-border nodes, domain-level slices, etc. We then revisit the virtual link embedding problem to include the proposed aggregation. Our evaluations on real and random topologies show significant gains in terms of admission ratios and resource usage