HAL Portal UPHF (Université Polytechnique Hauts-de-France)
Not a member yet
28473 research outputs found
Sort by
Investigating the orientation dependence on functional properties in Bi0.5Na0.5TiO3-BaTiO3 films
No full textInternational audienceThe morphotropic phase boundary (MPB) composition in lead free (1-x) Bi0.5 Na0.5TiO3 – x BaTiO3 (BNTBT) solid solution has attracted extensive research due to its significant potential for piezoelectric and high-power energy storage applications. Here, epitaxial (001) and (111) BNTBT films with composition around the MPB are investigated. A complex domain pattern is evidenced for both film orientation, due to the coexistence of a weak polar phase and a strong polar ferroelectric phase. An electric field induced phase switching is shown in both (001) and (111) oriented film, as well as a weakening of the polar state in the (111) BNTBT film. The enhanced ergodic relaxor state in the (111) BNTBT film gives rise to a reduced piezoelectric response and improved energy storage performances. The epitaxial symmetry engineering is shown to provide a complementary approach to the composition strategy to improve the functional properties in BNTBT films
A feasibility study of leveraging intermuscular coherence in EMG-driven neuromusculoskeletal modeling to improve muscle moment estimation
No full textInternational audienceCurrent musculoskeletal models often oversimplify the neural strategies underlying muscle activation, potentially leading to unsatisfactory estimates of muscle forces. Numerous studies in motor control have established that the central nervous system synchronizes muscle activation by sending a common drive to synergistic muscles, measurable through intermuscular coherencethe frequency correlation between two EMG signals. As interest grows in understanding how muscles synchronize during movement coordination, leveraging intermuscular coherence into musculoskeletal models represents an innovative approach. This could enhance the accuracy of muscle effort estimation and introduce a physiologically meaningful component of motor control. In this study, we introduce a new method that decomposes EMG signals into common and independent components, informed by intermuscular coherence, and integrates them into an EMG-driven model to estimate muscle moments. Using data from twenty-four healthy subjects performing horizontal upper limb extensions, we estimated moments of the four main muscles actuating the elbow and compared these estimations with those from a traditional EMG-driven model informed by full-wave rectified signal envelopes. Our results demonstrate that incorporating intermuscular coherence significantly enhanced kinetic data tracking and improved the robustness of muscle moment estimations against variations in model parameters, addressing a major limitation of traditional EMG-driven models. Furthermore, antagonist muscle moments were more accurately represented, resulting in more realistic co-contraction index values. By integrating neural control strategies via intermuscular coherence into musculoskeletal models, the proposed approach offers a more accurate representation of muscle coordination. We recommend that future neuromusculoskeletal models incorporate intermuscular coherence to improve physiological realism of muscle effort estimations
Exploring Quantum Analogies: Superradiance, Bipartite Correlations, and static Bell Tests in Pilot-Wave Hydrodynamics
No full textInternational audienceSince its discovery in 2005, the hydrodynamic pilot-wave system has provided a macroscopic realization of wave-particle duality, reproducing an increasing number of quantum-like effects. A key question is how closely particle-particle correlations in this classical system can mimic those at the quantum scale. Here, we introduce a numerical model of cooperative tunneling in a bipartite pilot-wave system as a new platform for exploring this question.We first establish bipartite hydrodynamic analogs of superradiance, both numerically and experimentally, demonstrating a sinusoidal modulation of the excited-to-ground state transition rate as a function of the separation between the two subsystems. Additionally, we conduct a static Bell test, where the system’s geometry remains fixed while the two subsystems are coupled through the intervening wave field. This wave-mediated coupling does not conform to the assumptions underlying Bell’s theorem, providing a rationale for the observed violations. However, these violations are elusive, emerging only within a narrow region of parameter space
Point-of-Care Applicability of Graphene-Based Field Effect Transistors upon Modification with a Pyrene-Tagged Antifouling Copolymer: Application for cTnI Sensing in Blood
No full textInternational audienceField-effect transistors (FETs) are an integrated part of various electronic products and play an irreplaceable role in modern-day bioelectronics and biosensors. The electronic performance of FET-based sensors is intrinsically correlated with the choice of the sensing layer, with graphene being one of the most widely employed active semiconductor materials through which charge carriers (i.e., electrons or holes) propagate upon bioreceptor–analyte interactions. One of the challenges remaining before widespread practical applications of graphene-based FET (gFET) is linked to its direct operation in blood, as the complex protein environment matrix causes significant issues. Here, we propose a sensitive and rapid detection of cardiac troponin I (cTnI) in unprocessed blood samples by integrating pyrene-tagged antifouling copolymer thin films onto the graphene channel. By leveraging the unique properties of the zwitterionic copolymer composed of N-(2-hydroxypropyl) methacrylamide (HPMAA) and carboxy betaine methacrylamide (CBMAA) in the form of a pyrene-tagged poly[HPMAA-co-CBMAA], we demonstrate excellent signal stability in whole blood, along with the potential for sensitive cTnI sensing in high ionic strength media (1× PBS) upon immobilization of DNA aptamers onto the copolymer network. With a limit of detection of 0.6 ± 0.1 pg mL–1 and a limit of quantification of 1.8 ± 0.3 pg mL–1, the sensor operates well within the clinically relevant cTnI range, demonstrating a significant step forward for cardiovascular biomarker monitoring in physiologically relevant conditions
Les massacres coloniaux français en Afrique après la Seconde Guerre mondiale : défis historiographiques et pédagogiques
No full textThis thesis offers an in-depth study of the colonial massacres perpetrated by France in Africa after the Second World War, focusing on analyzing their various implications: historical, historiographical, memorial, didactic, and pedagogical. In the aftermath of the Second World War, in a context of weakening colonial authority, France embarked on a policy of reconquest, or at least reaffirmation of its presence, in several African territories where colonial control had partially disintegrated. This effort to restore the imperial order was accompanied, between 1944 and 1950, by a series of massacres, including those in Thiaroye (1944), Sétif, Guelma, and Khérata (1945), and Madagascar (1947). Long overlooked or downplayed in official narratives and dominant historiography, these "violences" have been the subject of critical reexamination since the beginning of the 21 st century, at the intersection of colonial history, memory studies, and postcolonial issues. This work focuses, on the one hand, on the historiographical challenges associated with the reconstruction and analysis of these events: limited access to archives, conflicting interpretations, the questioning of the "national narrative", but also the emergence of counter-narratives put forward by African historians, activists, or descendants of victims. It also examines recent efforts at institutional recognition and the public debates they have sparked, balancing the "duty to remember" with political resistance. Furthermore, this thesis addresses the didactic and pedagogical issues raised by the teaching of the "colonial fact", particularly in the French school context, where colonial massacres are rarely discussed. How are these events integrated into school curricula and history textbooks? What obstacles do teachers encounter in transmitting this complex memory? These questions invite us to reflect on the current limitations of teaching colonial history and the need for an approach capable of accounting for the complexity of the violence that still surrounds these.Ce mémoire propose une étude approfondie des massacres coloniaux perpétrés par la France en Afrique après la Seconde Guerre mondiale, en s’attachant à en analyser les implications diverses : historique, historiographique, mémorielle, didactique et pédagogique.Aux lendemains de la Seconde Guerre mondiale, dans un contexte de fragilisation de l’autorité coloniale, la France s’engage dans une politique de reconquête ou, du moins, de réaffirmation de sa présence dans plusieurs territoires africains où l’encadrement colonial s’était partiellement désagrégé. Cette entreprise de restauration de l’ordre impérial s’accompagne, entre 1944 et 1950, d’une série de massacres parmi lesquels ceux de Thiaroye (1944), de Sétif, Guelma et Khérata (1945), ainsi que celui de Madagascar (1947). Longtemps passées sous silence ou minimisées dans les récits officiels et l’historiographie dominante, ces « violences » font l’objet d’un réexamen critique depuis le début du XXIe siècle, à la croisée de l’histoire coloniale, des études mémorielles et des enjeux postcoloniaux. Ce travail s’attache d’une part à interroger les défis historiographiques liés à la reconstitution et à l’analyse de ces événements : accès limité aux archives, conflits d’interprétation, mise en cause du « roman national », mais aussi émergence de contre-récits portés par des historiens africains, des militants ou des descendants de victimes. Il examine également les efforts récents de reconnaissance institutionnelle et les débats publics qu’ils suscitent, entre « devoir de mémoire » et résistances politiques. D’autre part, ce mémoire aborde les enjeux didactiques et pédagogiques soulevés par l’enseignement du « fait colonial », en particulier dans le contexte scolaire français où les massacres coloniaux sont peu présents. Comment ces événements sont-ils intégrés aux programmes scolaires et aux manuels d’histoire ? Quels obstacles rencontrent les enseignants dans la transmission de cette mémoire complexe ? Ces questionnements invitent à réfléchir aux limites actuelles de l’enseignement de l’histoire coloniale et à la nécessité d’une approche capable de rendre compte de la complexité de la violence qui entourent encore ces événements
New photodiodes ready to bridge optical and sub-THz communications
No full textInternational audienceSimultaneous high-bandwidth and high-optoelectronic conversion efficiency in photodiodes is difficult to achieve. Now, researchers have demonstrated waveguide-integrated photodiodes with over 200 GHz bandwidth, 0.81 A/W responsivity and a bandwidth–efficiency product of 133.5 GHz, thus enabling amplifier-free 120 Gbps wireless transmission over 54 m
Effets thermiques dans les phénomènes de fracture et de décohésion : modèles multi-échelles basés sur la Mécanique Statistique
No full textFracture and decohesion phenomena in soft materials result from homogenized effects of complex phenomena of bond breaking and reforming at the molecular scale. Despite their diversity, several material responses in artificial and biological systems are governed by analogous complex transition phenomena, such as protein folding–unfolding processes, martensitic transformations in metallic alloys, and crack propagation in engineering structures. These transitions are of fundamental interest for the design and engineering of innovative materials, nanotechnology, and soft matter, including rubber-like substances and biomaterials. These systems share common features with the fracture and decohesion phenomena of interest in this thesis: (i) the presence of multi-basin energy landscapes, where changes in boundary conditions can trigger transitions between a multiplicity of metastable states; (ii) the emergence of macroscopic responses from intricate interactions occurring at smaller scales, such as microcracking leading to material failure; and (iii) a pronounced sensitivity to temperature and rate effects, as exemplified by the reduction of the required force for DNA denaturation or for thin-film delamination with increasing temperature and the rate of loading effects.Building on these unifying aspects, this thesis develops and investigates multiscale models that explicitly account for temperature effects in a range of transition phenomena, including crack propagation, adhesion and de-adhesion processes, and the stiffness variation of entropic springs in mechanically interlocked polymers (MIPs). The analysis spans applications from classical mechanical sciences (e.g., fracture mechanics) to emerging fields such as biomaterials (e.g., cell adhesion and de-adhesion, DNA denaturation), artificial cytoskeletons, synthetic cells, and nano-mechanical logic gates.Methodologically, the multiscale framework is here implemented through the concurrent formulation of discrete and continuum limit models. The discrete models incorporate temperature effects through classical statistical mechanics, capturing molecular- and nano-scale fluctuations, thus allowing a rigorous derivation of the entropic and thermal effects on fracture and decohesion behavior. The continuum limit models describe elasticity and fracture propagation mechanisms at mesoscopic scales. All results are derived in closed analytical form, thereby providing a rigorous characterization of the fundamental underlying physical mechanisms.From a methodological point of view, fracture and decohesion are analyzed using an energetic approach based on the Griffith energy criterion. A key contribution of this thesis is the extension of this classical criterion to explicitly incorporate the influence of thermal fluctuations.The main innovation, compared with classical energetic approaches to fracture mechanics, is the minimisation of the system's total free energy, with entropic contributions added to the classical elastic and dissipative fracture terms.Analytical results are obtained for the dependence of fracture and decohesion energy terms, as well as for the corresponding limit stresses and strains, including dissipative contributions arising from temperature. These results show quantitative agreement with various benchmark experiments considered in the thesis. The proposed theoretical framework highlights significant temperature effects, with the critical load decreasing monotonically as temperature increases. Remarkably, a critical temperature is identified at which the system undergoes a phase transition, leading to fracture or decohesion even in the absence of any applied mechanical load. These findings provide new insights into the interplay between temperature and fracture phenomena within a multiscale mechanics framework, offering perspectives for the rational design of advanced materials and systems across diverse disciplines.Les phénomènes de fracture et de décohésion dans les matériaux mous résultent de la rupture et du reformage de liaisons à l’échelle moléculaire. Malgré leur diversité, plusieurs réponses des systèmes artificiels et biologiques suivent des transitions analogues, comme le repliement-dépliement des protéines, les transformations martensitiques dans les alliages métalliques ou la propagation des fissures dans les structures d’ingénierie. Ces transitions sont fondamentales pour la conception de matériaux innovants, la nanotechnologie et la matière molle, incluant biomatériaux et substances de type caoutchouc. Ces systèmes partagent des caractéristiques avec la fracture et la décohésion qui font l'objet de cette thèse: (i) la présence de paysages énergétiques à bassins multiples, où des changements dans les conditions limites peuvent déclencher des transitions entre une multiplicité d'états métastables; (ii) l’émergence de réponses macroscopiques à partir d’interactions à petite échelle, comme la micro-fissuration conduisant à la défaillance des matériaux; et (iii) une sensibilité prononcée aux effets de température et de vitesse, comme la réduction de la force nécessaire pour la dénaturation de l’ADN ou pour la délamination de films minces avec l’augmentation de la température et de la vitesse de chargement. En s’appuyant sur ces aspects unificateurs, cette thèse développe et étudie des modèles multi-échelles qui prennent explicitement en compte les effets de la température dans une gamme de phénomènes de transition, incluant la propagation des fissures, les processus d’adhésion et de désadhésion, ainsi que la variation de rigidité des ressorts entropiques dans les polymères mécaniquement entrelacés (mechanically interlocked polymers, MIPs). Les applications vont de la mécanique classique à l’étude de biomatériaux, cytosquelettes artificiels, cellules synthétiques et portes logiques nano-mécaniques. Méthodologiquement, le cadre multi-échelles est ici mis en œuvre à travers la formulation concurrente de modèles discrets et de modèles en limite continue. Les modèles discrets intègrent les effets de la température via la mécanique statistique classique, capturant les fluctuations à l’échelle moléculaire et nanométrique, ce qui permet une dérivation rigoureuse des effets entropiques et thermiques sur le comportement en fracture et décohésion. Les modèles en limite continue décrivent les mécanismes d’élasticité et de propagation de fissure à l’échelle mésoscopique. Tous les résultats sont obtenus sous forme analytique fermée, fournissant ainsi une caractérisation rigoureuse des mécanismes physiques fondamentaux sous-jacents. Du point de vue méthodologique, la fracture et la décohésion sont analysées à l’aide d’une approche énergétique basée sur le critère d’énergie de Griffith. Une contribution clé de cette thèse est l’extension de ce critère classique pour incorporer explicitement l’influence des fluctuations thermiques. L’innovation principale réside dans la minimisation de l’énergie libre totale du système, avec des contributions entropiques ajoutées aux termes classiques de fracture. Des résultats analytiques sont obtenus pour la dépendance des termes d'énergie de rupture et de décohésion, ainsi que pour les contraintes et déformations limites correspondantes, y compris les contributions résultant de la température. Le cadre théorique proposé met en évidence des effets significatifs de la température, la charge critique diminuant avec l’augmentation de la température. Fait remarquable, une température critique est identifiée à laquelle le système subit une transition de phase, conduisant à la fracture ou à la décohésion même en l’absence de toute charge mécanique appliquée. Ces résultats offrent de nouvelles perspectives sur l’interaction entre température et phénomènes de fracture dans un cadre de mécanique multi-échelles, ouvrant des perspectives pour la conception rationnelle de matériaux et systèmes avancés dans divers domaines
Elastic wave propagation in diatom frustules
No full textMatériaux poreux et métamatériaux acoustiques; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-Sonore: GVB - Vibro acoustique et Contrôle du Bruit: GABE - Acoustique du Bâtiment et de l'EnvironnementNational audienceDiatoms are microscopic algae encapsulated inside a silica inorganic exoskeleton called frustule featuring a complex quasi-regular and hierarchical distribution of micro- and nano-scaled pores. The mechanical and optical behaviors of these biological systems have already been investigated in literature, demonstrating that the 3D hierarchical pore distribution is responsible for (i) enhanced mechanical strength and (ii) it confers to these micro-algae a photonic crystal behavior, used for solar protection and optimizing photosynthesis features. By contrast, their acoustic behavior remains elusive, so far. In this preliminary study, we start unveiling the effects of the complex and hierarchical architecture of diatom frustules on the propagation of elastic waves. Firstly, we observe the in-plane and cross-section distribution of pores for different diatom species by Scanning Electron Microscopy (SEM) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), respectively. Then, we reconstruct the diatom 3D architecture into a FE model, and we numerically demonstrate that the quasi- regular arrangement of pores of some diatom frustules make them behave as phononic crystals thanks to the presence of elastic bandgaps. This study could help to shed light on the comprehension of the elasto-dynamic behavior of these biological systems, largely unexplored, so far
Ultra-thin normal-shear-coupled meta-barrier for low-frequency underwater sound insulation
No full textMatériaux poreux et métamatériaux acoustiques; GABE - Acoustique du Bâtiment et de l'Environnement: GAPSUS - Acoustique Physique, Sous-Marine et Ultra-Sonore: GVB - Vibro acoustique et Contrôle du BruitNational audienceUnderwater noise pollution from anthropogenic activities, such as offshore oil and gas exploration, poses significant threats to marine life. A common mitigation strategy involves enclosing primary noise sources within physical barriers to reduce noise levels in surrounding environments. Underwater noise-mitigating barriers typically achieve sound reduction through two primary mechanisms: (i) sound absorption using locally resonant systems (e.g., foam and bubble elements, modified Helmholtz resonators) or (ii) sound reflection using structures such as air bubble curtains and double cylindrical casings. While effective, these approaches have limitations: optimal performance is usually restricted to specific frequency ranges, and transmission loss can drop to zero at other frequencies. Locally resonant systems can achieve substantial attenuation but are generally narrow-band and struggle with low frequency noise. Addressing significant low-frequency noise attenuation remains a challenge, especially for thin structures with small thickness-to-wavelength ratios that can operate over broad frequency ranges. In this work, we present a novel design for thin metamaterial-based underwater barriers that attenuate acoustic waves through anisotropic effective material properties. Using a topology optimization approach, we design a unit cell for a meta-barrier that maximizes coupling between normal stresses and shear strains (and vice versa). The resulting meta-barriers achieve remarkable performance: (i) a sub-wavelength thickness ratio (approximately 1/70) at low frequencies below 1 kHz; (ii) high sound transmission loss values at higher frequencies (above 2 kHz), depending on the number of unit cells used in the thickness direction. Additionally, we evaluate the impact of increased hydro-static pressure on the submerged structures and propose modifications to enhance their viability for real-world applications. Our results not only introduce a new metamaterial-based solution for underwater noise mitigation, but also highlight the potential of leveraging anisotropy to develop advanced acoustic insulation technologies, paving the way for innovative applications in underwater environments