Portail HAL de l'Université du Littoral Côte d'Opale
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Offline Bayesian Change Point Detection for Carrier-Phase in GNSS-Reflectometry
No full textInternational audienceChange detection techniques are essential for identifying and quantifying variations in data over time, with applications in remote sensing, signal processing, and environmental monitoring. The ability of GNSS-Reflectometry (GNSS-R), a bistatic radar technique that utilizes navigation satellite signals as signals of opportunity, to analyze surface characteristics has recently been explored by studying the coherence of reflected GNSS signal phases. However, detecting changes in the carrier phase of multiple reflections GNSS signals remains unexplored in the literature, as conventional change detection methods are designed for linear data, whereas phase data is inherently circular. In this work, we adapt an offline Bayesian Change-Point Detection approach, assuming the phase noise follows a Von Mises distribution, to detect changes in the reflected GNSS signal by estimating change points through minimizing a contrast function. The method is evaluated using both synthetic and real GNSS-R measurements, demonstrating superior performance compared to a conventional spectral change detection technique. Results highlight the method's accuracy in detecting surface variations in real GNSS-R observations
Les jeunes. Une géographie différenciée selon le cycle de vieillissement
No full textNational audienceYouth can either refer to the period when an individual is dependent on their parents or the period of emancipation. The present analysis distinguishes between 0-14 year olds, i.e. dependent minors, and 15-29 year olds, a more heterogeneous group. Both groups’ share and recent trends are mapped at the level of counties or cities ("cantons-ou-villes"). The spatial distribution of the former, particularly their over-representation in the peri-urban areas of metropolitan areas, can be explained by the location of families and recent fertility patterns. The second category includes minors, students and some workers. Their share is growing in metropolitan areas. At a more refined level, dynamics vary according to ageing, housing construction, university locations and processes of gentrification or social diversity.La jeunesse peut renvoyer à la période où un individu est dépendant de ses parents et à celle de l’émancipation. Elle est ici analysée en distinguant les 0-14 ans, mineurs dépendants, et les 15-29 ans, groupe plus hétérogène. Leur part et son évolution récente sont cartographiées au niveau des cantons-ou-villes. La distribution spatiale des premiers, notamment leur surreprésentation dans les zones périurbaines des métropoles, s’explique par la localisation des familles et la géographie récente de la fécondité. La deuxième catégorie comprend à la fois des mineurs, des étudiants et une partie d’actifs. Leur part est en augmentation dans les métropoles. À des échelles plus fines, les dynamiques varient selon le vieillissement, la construction de logements, les implantations universitaires et les processus de gentrification ou de mixité sociale
A Memory-Enhanced Greedy Randomized Adaptive Search Procedure for the Multi-Pickup and Delivery Problem with Time Windows
No full textThis study investigates the Multi-Pickup and Delivery Problem with Time Win-dows (MPDPTW), an advanced variant of the traditional Pickup and DeliveryProblem (PDP), where each delivery is associated with multiple pickup loca-tions. This problem commonly arises in real-life scenarios such as urban lo-gistics, retail distribution, and e-commerce, where multiple pickups must beconsolidated into single deliveries, requiring efficient routing and scheduling so-lutions. The MPDPTW introduces additional complexities, including the needto respect time window constraints and precedence relations between multiplepickups and their corresponding delivery.To address this problem, we propose an optimization framework that com-bines adaptive constructive search, long-term memory, and route recombinationstrategies within an integrated architecture. The constructive phase is basedon a Greedy Randomized Adaptive Search Procedure designed to explore thesearch space effectively. Its performance is reinforced by a long-term memorythat stores feasible routes and infeasible subsets, reducing redundant evalua-tions. Finally, a post-optimization stage strategically recombines routes fromhigh-quality solutions to further minimize the total travel cost and enhance thebest-found solutions.A series of computational experiments was conducted on standard bench-mark instances to evaluate the performance of our approach. The analysisconfirms that our method retains all the best-known solutions reported in theliterature. Furthermore, it achieves an improvement of 0.41% over the best-known solutions, highlighting its potential to enhance both solution quality andcomputational efficiency
IDLA with sources in a hyperplane of
No full textInternational audienceWe consider a random growth model based on the IDLA protocol with sourcesin a hyperplane of . We provide a stabilization result and a shape theoremgeneralizing [7] in any dimension by introducing new techniques leading to a roughglobal upper bound
A robust determination of the effective thermal conductivity of a multilayer Si3N4/SiO2 stack using multiple heater geometries in the 3-omega method
No full textInternational audienceMultilayer dielectric thin films are fundamental components in modern microelectronic and photonic devices where thermal management is critical. This work presents a robust methodological framework for accurately determining the cross-plane effective thermal conductivity (κeff,⊥) of such complex systems using the 3-omega method. We use a five-layer Si3N4/SiO2 stack fabricated by plasma-enhanced chemical vapor deposition as a case study. The analysis combines experimental data from multiple heater geometries with a 3D finite element method based inverse analysis. We first demonstrate, through a frequency-dependent sensitivity analysis, that a direct multi-parameter fit for intrinsic layer properties is an ill-posed problem. This analysis provides a clear, quantitative justification for adopting a simpler and more robust effective medium model (EMA). The validity and application boundaries of the EMA are then rigorously established through a numerical study on a series of “virtual samples.” Finally, applying this validated framework to our experimental data, the thermal conductivity of a fused silica substrate was determined to be 1.287 ± 0.030 W/(m K), and the effective thermal conductivity of the 1288 nm thick stack was reliably determined to be 0.621 ± 0.008 W/(m K). This work provides not only a key thermophysical property for Si3N4/SiO2 multilayers but also a comprehensive and validated workflow for reliably characterizing complex thin film systems where standard analytical solutions fail
Environmental Variables Influence on Spatial Distribution of Bacterial Communities Across the English Channel in Two Main Productive Seasons
No full textInternational audienceThe English Channel features a wide range of ecological habitats that host numerous biodiversity resources and are submitted to natural and/or anthropogenic pressures. During the ‘EcoPel’ oceanographic campaigns (spring and summer 2018) in French waters of the English Channel and North Sea, a variety of coastal pelagic habitats were sampled for analysing environmental variables and bacterial communities. Results of PCA suggest that main environmental variables were SPM, POM, PIM, salinity and NO 2 − /NO 3 + in spring and salinity, SPM, Si and Chl‐ a in summer. The Shannon index suggested summer alpha diversity had higher richness and equitability compared to spring. A clear seasonality in the bacterial community structure was also revealed by hierarchical cluster analysis. Most of the spring communities had a higher proportion of Bacteroidetes while most of the summer communities had a higher proportion of Proteobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes. Based on distance correlations and statistical significance, the spring taxonomic composition was correlated with Chl‐ a , PO 4 , POM, SPM and PIM, while the summer composition was correlated with salinity. According to hierarchical cluster analyses, both environmental variables and bacterial communities seem to be clustered in parallel with the coast, evidencing the main influence of coastal‐offshore gradients and implying possible links with river inputs and phytoplankton/algae dynamics
How can food-webs models be relevant to assess the direct and indirect impacts of human activities on marine mammals
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Challenges of dipeptide identification for a better characterization of nutritional quality of food and derivatives
No full textInternational audienceBioactive peptides (2 to 20 amino acids (AAs)) from food sources are typically inactive within the sequence of the parent protein but, after being released through enzymatic proteolysis, can exert a range of physiological functions. Bioactive peptides derived from agri-food industry products or byproducts exhibit a wide range of biological activities, such as antihypertensive, antioxidative, antibacterial... BIOPEP is one of the most comprehensive databases of bioactive peptides, referencing more than 5,000 peptides. Nearly 45% of these latter are ultra-short- peptides (USPs, composed of 2 to 5 AAs)—comprising 581 dipeptides, 754 tripeptides, 385 tetrapeptides, and 511 pentapeptides, totaling 2,231 USPs. However, while analytical methods are efficient for larger peptides, USPs still present characterization challenges due to their “metabolomic” nature.First, 209 molecular descriptors were computed from the SMILES of all 400 L-dipeptides and used for principal component analysis (PCA) and heatmap visualization to select 25 representative dipeptides based on their descriptor-based heterogeneity. Each AA appears at least once in this model dipeptide set. Second, dipeptide analyses were performed using both C18 and HILIC HPLC columns, coupled with an ESI-QTOF-MS.This work illustrates the bioinformatic strategy employed for dipeptide selection and highlights the importance of chromatographic phase orthogonality. Furthermore, we present the strategy envisioned for annotating USPs, leveraging the maximum amount of information extracted from MS/MS data. Although manual identification of dipeptides in a standard mixture is feasible under the described peptidomic conditions, current metabolomics- and peptidomics-dedicated software lacks the capability for accurate and automated dipeptide annotation. Optimizing HPLC conditions (e.g., column type, temperature) or leveraging amino acid-specific fragment ions could enhance dipeptide identification
Les litiges du mesurage de l’assiduité au travail
No full textInternational audienceCombating absenteeism requires (for the employer) to begin by objectifying it, by observing it. The problem is that several methods of monitoring attendance are illegal. Because they infringe on individual freedoms. Moreover, even identifying workers considering strike action seems questionable. On the other hand, attendance can be certified by the workers themselves. This leads to fraud on their part. Indeed, some attendances turn out to be fictitious, and others ineffective, meaning they are of no interest to the employer.La lutte contre l’absentéisme suppose (pour l’employeur) de commencer par l’objectiver, par le constater. Le problème est plusieurs modalités de contrôles de l’assiduité sont illégales. Car elles portent atteintes aux libertés individuelles. D’ailleurs, même l’identification des travailleurs envisageant de faire grève semble critiquable. D’un autre côté, les présences peuvent être attestées par les travailleurs eux-mêmes. Alors, des fraudes surviennent de leur part. En effet, quelques présences se révèlent fictives, et d’autres ineffectives, c’est-à-dire sans intérêt pour l’employeur