Portail HAL Nantes Université
Not a member yet
120169 research outputs found
Sort by
A physics-compliant diagonal representation for wireless channels parametrized by beyond-diagonal reconfigurable intelligent surfaces
No full textInternational audienceThe parametrization of wireless channels by so-called “beyond-diagonal reconfigurable intelligent surfaces” (BD-RIS) is mathematically characterized by a matrix whose off-diagonal entries are partially or fully populated. Physically, this corresponds to tunable coupling mechanisms between the RIS elements that originate from the RIS control circuit. Here, we derive a physics-compliant diagonal representation for BD-RIS-parametrized channels. We recognize that any RIS control circuit can always be separated into its static parts (SLC) and a set of tunable individual loads (IL). Therefore, a BD-RIS-parametrized channel results from the chain cascade of three systems: i) radio environment (RE), ii) SLC, and iii) IL. RE and SLC are static non-diagonal systems whose cascade K is terminated by the tunable diagonal system IL. This physics-compliant representation in terms of K and IL is directly analogous to that for conventional (“diagonal”) RIS (D-RIS). Therefore, scenarios with BD-RIS can also readily be captured by the physics-compliant coupled-dipole model PhysFad, as we show. In addition, physics-compliant algorithms for system-level optimization with D-RIS can be directly applied to scenarios with BD-RIS. We demonstrate this important implication of our conceptual finding in a case study on end-to-end channel estimation and optimization in a BD-RIS-parametrized rich-scattering environment. Our case study is the first experimentally grounded system-level optimization for BD-RIS: We obtain the characteristics of RE and IL from experimental measurements and a commercial PIN diode, respectively. Altogether, our physics-compliant diagonal representation for BD-RIS enables a paradigm shift in how practitioners in wireless communications and signal processing implement system-level optimizations for BD-RIS because it enables them to directly apply existing physics-compliant D-RIS algorithms
L’ensablement du Scorff (Massif armoricain) : Facteurs, dynamiques spatiales et effets sur les habitats de reproduction de la lamproie marine (Petromyzon marinus)
No full textInternational audienceThe Scorff, a coastal river in the southwestern Armorican Massif, is suspected of becoming over-sanded in recent decades, similar to many other rivers with granitic watersheds. This project, funded and co-led by the MIAME cluster (OFB-INRAE-Institut Agro-UPPA) and LETG, first analyzes spatial relationships between the potential sand production from various sub-watersheds and the rate of sand coverage on flow facies along the river that are suitable for colonization by the sea lamprey. The evolution of these parameters over the past two decades is also examined. Finally, the project explores the potential effects of excessive sandy sediment deposits on sea lamprey spawning grounds. The distribution of sand was found to be primarily influenced by slope and the presence of numerous transverse structures, with localized exacerbation due to complex factors. For example, the Kerustang sub-basin is highly susceptible to sand erosion, and after the opening of the Pont-Calleck dam (13th century) in 2011, it has contributed a substantial sand load. Observations of spawning ground locations over the past decade suggest that, for now, these sand deposits have not reduced the availability of favorable habitats.Le Scorff, fleuve côtier du sud-ouest du Massif Armoricain est, comme de nombreux autres cours d’eau au bassin versant granitique, suspecté de subir un sur-ensablement ces dernières décennies. Financé et co-piloté par le pôle pour la gestion des migrateurs amphihalins dans leur environnement (pôle MIAME, OFB-INRAE-Institut Agro-UPPA) et le LETG, ce travail s’attache d’abord à analyser les relations spatiales entre les potentiels de production sableuse des différents sous-bassins versants et le taux de recouvrement sableux des faciès d’écoulement sur le linéaire colonisable par la lamproie marine. L’évolution de ces paramètres depuis deux décennies est également étudiée. Enfin, les effets potentiels de ces apports excessifs de sédiments sableux sur les frayères de lamproie marine sont explorés. La répartition du sable s’est révélée majoritairement contrôlée par la pente et la présence des nombreux ouvrages transversaux, et localement aggravée par des facteurs complexes. Par exemple, le sous-bassin du Kerustang, très sensible à l’érosion sableuse et au sein duquel le barrage de Pont-Calleck (XIIIe siècle) a été ouvert en 2011, a depuis apporté une charge sableuse conséquente. Au regard de l’évolution de la position des frayères au cours de la dernière décennie, ce sur-ensablement ne semble pour le moment pas réduire la disponibilité en habitats favorables
A new automatic AHP tool to assess the forest vulnerability to wind damage
No full textInternational audienceThis study performs an analytical hierarchy process (AHP) approach in conjunction with spatial data to map the vulnerability of forests to wind damage. Forest management can be crucial in enhancing the resilience of forests to wind disturbances. However, to support decision-making processes to effectively manage forests, it is relevant to determine the most influential forest tree destruction drivers and calculate their weights. The criteria considered are wind speed, wind direction, the proportion of Norway spruce Picea abies, edaphic factors and tree age in the stand. However, a major obstacle to the application of decision-making aid is the inconsistency of the judgment of experts, thus the judgment matrices need to be adjusted. Here, An efficient readjusting AHP technique (Re-AHP) was developed to improve the consistency ratio. To do this, the pairwise comparison matrix in AHP method had to be adjusted to address the issue of inconsistent ratios, while retaining the original judgment intention. A user-friendly Re-AHP Matlab App Designer was designed to readjust the comparison matrix for each expert, using the case of susceptibility to wind damage as an illustration. The wind damage vulnerability map showed that over 80% of the area is at medium and high vulnerability levels. The validation proved that the selected method is the most efficient. The new tool was used to develop a speedy method for the forest context. While the study focused on a specific site, the developed methodology is universally applicable and can be adapted to various forest sites worldwide
A New Potential Energy Surface of the PO-H<sub>2</sub> Complex and Intermolecular Rovibrational State Calculations
No full textInternational audienceThe recent detection of the phosphorus monoxide cation (PO) in the interstellar medium (ISM) has generated considerable interest in its collisional excitation and reactivity in such environments. Due to the difficulties in conducting laboratory experiments in these extreme environments, theoretical calculations have become essential to model the excitation and reactivity of PO. In this context, several theoretical studies have been conducted to better understand its abundance and impact on interstellar chemical processes. An important aspect of these studies is the accurate characterization of their electronic interaction with the surrounding gas constituents. We present here a new four-dimensional potential energy surface (PES) for the interaction between the PO cation and the H2 molecule, the dominant species in the cold ISM, using the explicitly correlated coupled cluster method with single, double, and perturbative triple excitations [CCSD(T)-F12a]. The rigid rotor PES provides a global representation of the PO-H2 interaction, and presents a unique global minimum with a well depth of 1252.88 cm–1. We subsequently characterized the rovibrational states of the PO-H2 complex, up to a total angular momentum J of 3, by solving the nuclear Schrödinger equation with the block-induced relaxation procedure implemented in the Heidelberg Multi-Configuration Time Dependent Hartree (MCTDH) package. We obtained zero-point energies of 422.201 cm–1 for PO+-para-H2 and 487.805 cm–1 for the PO-ortho-H2 complex. This corresponds to dissociation energies (D0) of 830.679 and 765.075 cm–1for PO-para-H2 and of 487.805 cm–1 for the PO-ortho-H2 complex. We hope that the present theoretical results will stimulate experimental studies of the PO-H2 complex in order to validate the predictions reported in this work
Erasmus+ Project SLS4TEENS: 24 Teachers from 4 Countries Gather for Training Under the Sunny Skies of Nantes
No full textAs part of the European University Alliance EUGREEN and the Erasmus+ project SLS4TEENS (Second Language Learning at School for All Teenagers), led by Delphine Guedat-Bittighoffer from the University of Angers, Marie-Ange Dat from Nantes Université co-organized a workshop that brought together experts from three partner institutions: the universities of Magdeburg (Germany), Mérida (Spain), and Parma (Italy). The event aimed to unite all the experimental classes involved in the project, with over 20 teachers receiving training in an innovative methodology focused primarily on oral language acquisition.The workshop opened with a plenary session led by Delphine Guedat-Bittighoffer. Before handing the floor to the two workshop facilitators, David Macfarlane and Virginie Clavreul, Nadège Souchereau, Director of the Europe and International Office at Nantes Université, alongside Claire Dutertre, Erasmus+ Project Manager, presented the office’s key initiatives and highlighted several major European projects coordinated by the university.Over the course of the two-day workshop, language teachers participated in plenary sessions as well as small group discussions that brought together educators from across the participating countries. The training sessions were designed to foster meaningful exchanges of pedagogical practices and classroom experiences—an essential component for the success of SLS4TEENS. The project is built on two core pillars: the psycho-emotional security of language learners and their ability to speak spontaneously in a foreign or second language.In addition to the training sessions, the organization of the workshop allowed participants to enjoy guided visits exploring the rich historical heritage of Nantes and to savor the region’s renowned gastronomy—made even more enjoyable by the beautiful weather
En quête de lecteurs (et lectrices) philosophes : peut-on construire et susciter une expérience philosophique par la lecture d’albums ?
No full textInternational audienc
L'approche neurolinguistique, la perspective actionnelle, et les émotions d'accomplissement ressenties par des élèves de 6ème en cours d'anglais
No full textInternational audienceThis quantitative study examines 174 11-year-old middle schoolers’ re-sponses to the Achievement Emotions Questionnaire- English (AEQ-E, Starkey-Perret et al., 2017). We first compare their answers depending on whether the teachers use the neurolinguistic approach (NLA) (n= 94) or a generally task-based perspective (n=80). This enabled us to determine which approach has a more positive impact on the students’ achievement emotions, which in turn has an impact on student engagement in their Eng-lish class activities. We then study the results of each of the 6 teachers’ groups in order to measure teacher effect. The results show a significantly positive impact of using the NLA to reduce anxiety throughout the school year. They also show significantly higher levels of enjoyment and pride and lower levels of anger and boredom from the start of the school year for the groups in which the teachers use the NLA. However, a teacher ef-fect was detected, especially in the evolution of the emotions from the be-ginning of the school year to the end. Triangulating quantitative and quali-tative studies could give us a more robust understanding of the dynamic nature of students' achievement emotions
A Theoretical Study of the Bonding Properties of R4Sb3 Compounds
No full textInternational audienceThis study investigates the electronic structure and bonding properties of rare-earth antimonide compounds, specifically Yb₄Sb₃ and La₄Sb₃, utilizing density functional theory calculations. The analysis reveals that Yb₄Sb₃ exhibits a predominantly ionic character whereas La4Sb3 displays a greater degree of covalent bonding. Moreover, the presence of divalent ytterbium leads to p-type conduction at high temperatures in Yb4Sb3. Conversely, La₄Sb₃ displays n-type conduction because of a larger electronic transfer from the rare-earth metal towards antimony. These findings provide valuable insights into the structural and electronic properties that govern the performance of R₄Sb₃ compounds, contributing to the development of advanced materials for thermoelectric energy conversion.</div
« Du haut du musée, on va le suicider […] on va se séparer de lui pour engager le jeu … »
No full textInternational audienceDe 1985 à 1987, à l'initiative de son conservateur en chef Ousmane Sow Huchard, le Musée dynamique accueille sur son parvis trois évènements du Laboratoire Agit'Art. L’invitation tient au fait qu’Huchard est membre du collectif, et le choix d’agir à l’extérieur des murs du musée n’est pas anodin. Les titres de ces actes – théâtraux ou performatifs – donnent des indices sur leur charge critique et sur leur volonté d’interpeller la société sénégalaise. Ce texte cherche à mieux appréhender ces propositions du Laboratoire Agit’Art qui ont été peu analysées et qui, pourtant, témoignent de la philosophie et de la posture politique de ce mouvement en cette décennie 1980 difficile pour le Sénégal