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Towards Accurate Gait Instability Assessment: Identifying a Fixed Pelvis Point that Best Matches the Whole-Body Center of Mass
No full textInternational audienc
Study of temperature-dependent breakdown in AlGaN/GaN normally-off HEMT under drain step-stress
No full text#45 Final article depositen collaboration avec le LAAS-CNRS, l'université de Toulouse, le CNES Toulouse et l'ADERA.International audienceThis paper investigates the temperature-dependent breakdown of commercially available GaN-on-Si power transistorsduring off-state drain step-stress. This setup allows us to obtain novel results on commercially available 650V p-GaN HEMTsubjected to step-stress under various conditions of temperature and gate voltage. Previously observed breakdown mechanismsare compared with the one observed on the current structure and a physical interpretation is proposed to explain thephenomenon. Activation energy, Weibull parameters and failure analysis are explored to provide understanding on the failuremechanisms
Effect of top metallic contacts on energy conversion performances for near-field thermophotovoltaics
No full textInternational audienceThe design of metallic contact grids on the front side of thermophotovoltaic cells is critical since it can cause significant optical and electrical resistive losses, particularly in the near field. However, from the theoretical point of view, this effect has been either discarded or studied by means of extremely simplified models like the shadowing methods, that consist in simply ignoring the fraction of the semiconductor surface covered by metal. Our study, based on a rigorous three-body theoretical framework and implemented using the scattering matrix approach with the Fourier modal method augmented with adaptive spatial resolution, provides deeper insight into the influence of the front metal contact grid. This approach allows direct access to the radiative power absorbed by the semiconductor, enabling the proposal of an alternative definition for the thermophotovoltaic cell efficiency. By modeling this grid as a metallic grating, we demonstrate its significant impact on the net radiative power absorbed by the cell and, consequently, on the generated electrical power. Our analysis reveals behaviors differing substantially from those predicted by previous simplistic approaches
Detecting Destabilizing Nonlinearities in Absolute Stability Analysis of Discrete-Time Feedback Systems
No full text8 pages, 5 figuresInternational audienceThis paper is concerned with the absolute stability analysis of discrete-time feedback systems with slope-restricted nonlinearities. By employing static O'Shea-Zames-Falb multipliers in the framework of integral quadratic constraints, we can obtain a certificate for the absolute stability in the form of a linear matrix inequality (LMI). However, since this LMI certificate is only a sufficient condition, we cannot draw any definite conclusion if the LMI turns out to be infeasible. To address this issue, we focus on the dual LMI that is feasible if and only if the original (primal) LMI is infeasible. As the main result, if the dual solution satisfies a certain rank condition, we prove that we can detect a destabilizing nonlinearity within the assumed class of slope-restricted nonlinearities as well as a non-zero equilibrium point of the resulting feedback system, thereby we can conclude that the system of interest is never absolutely stable. The effectiveness of the technical results is demonstrated through numerical examples
Why bumblebees have become model species in apidology: A brief history and perspectives
No full textInternational audienceIn recent years, bumblebees have increasingly been used to study various aspects of bee biology, ecology and evolution. They are now broadly accepted as tractable model species, complementary to the domestic honey bees, for fundamental and applied apidology. Here, we provide a brief history of how bumblebee research developed since their domestication and commercialisation for crop pollination in the 1990s. Bumblebees are large social bees that can be kept and trained in the lab year-round. They are easy to manipulate and track individually in their small colonies. These practical advantages have offered new possibilities for experimental bee research, leading to major breakthroughs in different fields such as cognition, navigation, nutrition, host-parasite interactions, and insect declines. Many of these findings have later been confirmed in honey bees and other pollinators. We discuss some exciting directions for future apidology research based on bumblebees
Exploring the subject heterogeneity of scientific research projects funding-example of the Chinese natural science foundation
No full textIn the increasingly competitive landscape of science and technology funding, understanding the heterogeneous factors and outcomes in funding allocation is crucial. This study proposes a research framework of subject heterogeneity to explore how the individual and combined characteristics of scholars and research topics impact funding acquisition, intensity, and performance. We use the case of the National Natural Science Foundation of China (NSFC) funding for artificial intelligence projects from 2009 to 2018 to empirically validate our framework. The findings reveal that scholars affiliated with high-level institutions, who focus on specialized areas and produce high-quality representative work, are more likely to secure funding. Unexpectedly, funding incentives did not significantly alter scholars' enthusiasm for pursuing popular topics. Moreover, the results indicate that funding has a more substantial impact on cultivating scholars than on advancing new research topics, particularly in the short term. Expanding the scope of funding proves to be more effective in enhancing research performance than merely increasing funding intensity. These insights provide valuable guidance for researchers in topic selection and submission strategies, as well as for policymakers aiming to optimize the management of competitive scientific projects.</div
Critical function placement based on service chains in multi-administrative federated networks
No full textInternational audienceAlthough the Service Function Chains (SFCs) embedding problem is broadly investigated in the literature, few works address it in a sliced multi-administrative network federation. In this work, we provide several insights into the problem. First, we describe a new federated-level topology abstraction. Second, we introduce a novel optimization model and heuristic (for large scale), which solve SFC embedding. Third, we conduct experiments on various multi-domain topologies and compare the algorithms regarding resource allocation efficiency and runtime. We analyze the trade-off between slice deployment costs and link utilization. Finally, we emulate two security scenarios on Containernet, Docker, and Open vSwitch architecture
Leveraging Christoffel-Darboux Kernels to Strengthen Moment-SOS Relaxations
No full text25 pages, 4 algorithms, 5 figures, 5 tablesInternational audienceThe classical Moment-Sum Of Squares hierarchy allows to approximate a global minimum of a polynomial optimization problem through semidefinite relaxations of increasing size. However, for many optimization instances, solving higher order relaxations becomes impractical or even impossible due to the substantial computational demands they impose. To address this, existing methods often exploit intrinsic problem properties, such as symmetries or sparsity. Here, we present a complementary approach, which enhances the accuracy of computationally more efficient low-order relaxations by leveraging Christoffel-Darboux kernels. Such strengthened relaxations often yield significantly improved bounds or even facilitate minimizer extraction. We illustrate the efficiency of our approach on several classes of important quadratically constrained quadratic Programs
Memguard-RW: Improved Real-Time Memory Bandwidth Regulation Within a Hypervisor
No full textInternational audienceMemory bandwidth is a critical factor in the performance of DRAM-based computing architectures, particularly in memory-intensive computations. Modern multi-core processors share critical resources, such as main memory and cache, which impact the predictability of real-time systems due to resource contention. Techniques like memory access regulation, cache partitioning, and static hypervisors aim to mitigate this contention.This paper presents an improvement of a memory control mechanism based on MemGuard, named MemGuard-RW, designed and implemented within a hypervisor. MemGuard-RW uses two performance counters for measuring the memory accesses, one for memory readings and another one for writings, thus decreasing the pessimism on the original memory access budget from MemGuard. Additionally, we extend the MemGuard schedulability analysis considering the two-counter approach. To evaluate the effectiveness of the implementation and analysis, we deployed FreeRTOS as a guest alongside three stress-generating guests, measuring the interference experienced by the FreeRTOS instance and comparing the analysis with two counters with the original analysis with one counter, using modern benchmarks. The results demonstrate that the proposed mechanism successfully regulates memory accesses, showing its potential for enhancing the predictability and performance of real-time systems in multi-core environments. Our proposed analysis with two counters reduces the upper bound of around 20% for tasks having medium and high memory usage
Multifunctional Diffractive Optical Element for Microcavity Mode Control
No full textInternational audienceThe work introduces a multifunctional diffractive optical element (DOE) designed to achieve precise mode control in photonic microcavities, specifically Cavity Resonator Integrated Grating Filters (CRIGFs). Traditional mode-selective excitation often relies on bulky, costly phase-only spatial light modulators (SLMs), which hinder integration into compact systems.The proposed DOE is a binary phase mask that simultaneously handles phase modulation, effective amplitude shaping (via duty-cycle), and focusing within a single compact device. Its design combines gradient-based numerical optimization with physics-based rules, balancing mode selectivity against scattering losses. Fabricated through standard single-level photolithography, the DOE is compatible with established semiconductor manufacturing. Experimental results demonstrate selective excitation of higher-order CRIGF modes, confirmed by transmission spectra with clear resonance dips. Compared with SLM-based systems, the DOE reduces complexity, size, and cost while retaining flexibility. Future applications include few-mode fiber systems for data multiplexing and integration into collimators or coupling optics, paving the way for highly compact, multifunctional photonic devices.Ce travail présente un élément optique diffractif multifonctionnel (DOE) conçu pour assurer un contrôle précis des modes dans des microcavités photoniques, en particulier les filtres à réseau intégrés résonants de cavité (CRIGF). Les méthodes classiques d’excitation sélective de modes reposent souvent sur des modulateurs spatiaux de phase (SLM) encombrants et coûteux, qui limitent leur intégration dans des systèmes compacts.Le DOE proposé est un masque binaire de phase qui assure simultanément la modulation de phase, le façonnage effectif de l’amplitude (via le rapport cyclique) et la focalisation dans un composant unique et compact. Sa conception combine une optimisation numérique par gradient avec des règles physiques, conciliant sélectivité des modes et pertes par diffusion. Fabriqué par photolithographie standard à un seul niveau, le DOE est compatible avec les procédés de fabrication semi-conducteurs établis.Les résultats expérimentaux démontrent l’excitation sélective de modes d’ordre supérieur dans le CRIGF, confirmée par des spectres de transmission présentant des résonances marquées. Comparé aux systèmes basés sur SLM, le DOE réduit la complexité, la taille et le coût tout en conservant une grande flexibilité. Parmi les perspectives d’application figurent les systèmes à fibres à quelques modes pour le multiplexage de données et l’intégration dans des collimateurs ou des optiques de couplage, ouvrant la voie à des dispositifs photoniques multifonctionnels et très compacts