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Tribofilm thickness measurement using scanning white light interferometry combined to a thin metallic reflective layer: Method, reliability and limitations
No full textInternational audienc
Enhancing Morphological and Optoelectronic Properties of Silicon Clathrate Films through Thermal Press Annealing and SF 6 Treatment
No full textInternational audienceAlthough silicon clathrates were discovered about 60 years ago, there has been little research on diverse applications of such materials beyond thermoelectrics. With a direct bandgap of about 1.7 eV and given the advantages of the silicon element such as abundance, nontoxicity and stability, silicon clathrates hold potential for use in photovoltaics and optoelectronics. Additionally, due to their unique cage structure that can store and release sodium atoms with minimal lattice parameter changes, they are promising for battery applications. However, issues like nonhomogeneity, defects, and poor density in clathrate films have hindered such applications. We provide in this work substantial pathways to mitigate such issues with the use of SF6 etching and thermal press annealing, enabling an improvement of the optoelectronic properties, by a factor of 7 as observed by the surface photovoltage technique. The photovoltage response of above 200 mV at 0.2 sun being above key photovoltaic thin film absorbers such as CIGS and rivaling III–V semiconductors such as GaAs
Shallow brambles
No full text12 pagesInternational audienceA graph class has polynomial expansion if there is a polynomial function such that for every graph , each of the depth- minors of has average degree at most . In this note, we study bounded-radius variants of some classical graph parameters such as bramble number, linkedness and well-linkedness, and we show that they are pairwise polynomially related. Furthermore, in a monotone graph class with polynomial expansion they are all uniformly bounded by a polynomial in
Cartan motion groups: regularity of K-finite matrix coefficients
No full textIf is a connected semisimple Lie group with finite center and is a maximal compact subgroup of G, then the Lie algebra of admits a Cartan decomposition . This allows us to define the Cartan motion group . In this paper, we study the regularity of -finite matrix coefficients of unitary representations of . We prove that the optimal exponent for which all such coefficients are -H\"older continuous coincides with the optimal regularity of all -finite coefficients of the group itself. Our approach relies on stationary phase techniques that were previously employed by the author to study regularity in the setting of . Furthermore, we provide a general framework to reduce the question of regularity from -finite coefficients to -bi-invariant coefficients
Panel Method for 3D Inviscid Flow Simulation of Low-Pressure Compressor Rotors with Tip-Leakage Flow
No full textInternational audienceThis paper presents a low-order three-dimensional approach for predicting the inviscid flow around low-pressure compressors. The method is suitable for early design stages and allows a broad exploration of design possibilities at minimal cost. It combines the vortex lattice method with the panel method by using a mixed boundary condition. In addition, it models the tip-leakage flow using an iterative algorithm. First, the verification of the approach is carried out on a low-pressure compressor configuration. The wake length is a decisive parameter for ensuring correct flow deflection in ducted applications. A periodicity condition is introduced and validated, which reduces the computational and memory requirements. On average, the calculations take less than one minute in real time. The approach is validated on the same low-pressure compressor configuration. A good agreement is obtained with RANS concerning the mean flow and the tip-leakage flow characteristics. Sensitivity to the mass flow rate is also fairly well predicted, although discrepancies develop at lower mass flow rates
Adaptive Class Aware Memory Selection and Contrastive Representation Learning for Robust Online Continual Learning in both Balanced and Imbalanced Data Environments
No full textOnline Continual Learning (OCL) is a framework where models learn continuously from a stream of data without revisiting previously seen data. This is crucial for many reallife applications, e.g., autonomous driving, healthcare monitoring, and robotics, where data evolves over time. However, current state-of-the-art continuous learning methods struggle with dynamic and unbalanced data, often failing to adapt and leading to severe performance degradation. In this paper, we introduce Memory Selection with Contrastive Learning (MSCL), an advanced approach to Continual Learning (CL) designed to tackle these challenges. MSCL integrates Feature-Distance Based Sample Selection (FDBS) for effective memory adaptation, emphasizing inter-class similarities and intra-class diversity, with a novel contrastive learning loss (SCL) for evolving data representation consolidation. Our extensive evaluations on datasets including CIFAR-100, Mini-ImageNet, PACS, and DomainNet demonstrate that MSCL not only surpasses existing memorybased CL methods on data balanced scenarios, but also excels particularly in imbalanced scenarios, thereby establishing a novel state of the art in both balanced and imbalanced learning contexts. Additionally, we carefully conduct ablation studies to highlight the contribution of each component, i.e., FDBS and SCL, and analyze the impact of the key hyperparameter, i.e., memory size, on the performance of the proposed MSCL method.</div
Coupling hydrodynamics of several Facilitated Exclusion Processes with closed boundaries
No full text22 pagesIn this paper, we prove the hydrodynamic limit for the ergodic dynamics of Facilitated Exclusion Process with closed boundaries in the symmetric, asymmetric and weakly asymmetric regimes. For this, we couple it with a Simple Exclusion Process by constructing a mapping that transforms the facilitated dynamics into the simple one. As the hydrodynamic behaviour of simple exclusion process has been extensively studied, we can deduce the corresponding hydrodynamics for the facilitated exclusion process
Active voltage balancing by turn‐off delays regulation for multiple series‐connected SiC MOSFETs
No full textInternational audienceAbstract SiC MOSFETs are currently the most appropriate solution for high‐efficiency conversions at low kilovolts (). For higher voltages, the series connection of SiC MOSFETs shows great promise. However, voltage sharing remains a significant technical challenge. This article proposes an active voltage balancing approach for a stack of N SiC MOSFETs, achieved through precise adjustment of turn‐off delays based on real‐time voltage feedback. Using an analytical model tailored to describe voltage sharing, a control method is designed, configured, and evaluated. Control behavior is experimentally validated on hard switching converters
Characterization of local energy transfer in large-scale intermittent stratified geophysical flows via space filtering
No full textInternational audienceRecent studies based on simulations of the Boussinesq equations indicate that stratified turbulent flows can develop large-scale intermittency in the velocity and temperature fields, as detected in the atmosphere and in the oceans. In particular, emerging powerful vertical drafts were found to generate local turbulence, proving necessary for stratified flows to dissipate the energy as efficiently as homogeneous isotropic turbulent flows. The existence of regions characterized by enhanced turbulence and dissipation, as observed, for instance, in the ocean, requires appropriate tools to assess how energy is transferred across the scales and at the same time locally in the physical space. After refining a classical space-filtering procedure, here we investigate the feedback of extreme vertical velocity drafts on energy transfer and exchanges in subdomains of simulations of stably stratified flows of geophysical interest. Our analysis shows that vertical drafts are indeed able to trigger upscale and downscale energy transfers, strengthening the coupling between kinetic and potential energies at certain scales, depending on the intensity of the local vertical velocity
Complexity of Maker-Breaker Games on Edge Sets of Graphs
No full textInternational audienceWe initiate the study of the algorithmic complexity of Maker-Breaker games played on edge sets of graphs for general graphs. We mainly consider three of the big four such games: the connectivity game, perfect matching game, and H-game. Maker wins if she claims the edges of a spanning tree in the first, a perfect matching in the second, and a copy of a fixed graph H in the third. We prove that deciding who wins the perfect matching game and the H-game is PSPACE-complete, even for the latter in graphs of small diameter if H is a tree. Seeking to find the smallest graph H such that the H-game is PSPACE-complete, we also prove that there exists such an H of order 51 and size 57. On the positive side, we show that the connectivity game and arboricity-k game are polynomial-time solvable. We then give several positive results for the H-game, first giving a structural characterization for Breaker to win the P 4-game, which gives a linear-time algorithm for the P 4-game. We provide a structural characterization for Maker to win the K 1,ℓ-game in trees, which implies a linear-time algorithm for the K 1,ℓ-game in trees. Lastly, we prove that the K 1,ℓ-game in any graph, and the H-game in trees are both FPT parameterized by the length of the game. We leave the complexity of the last of the big four games, the Hamiltonicity game, as an open question