HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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3D multiparametric ultrasound of spontaneous murine tumors for non-invasive tumor characterization
No full textInternational audienceObjective. Non-invasive tumor diagnosis and characterization is limited today by the cost and availability of state of the art imaging techniques. Thanks to recent developments, ultrasound (US) imaging can now provide quantitative volumetric maps of different tissue characteristics. This study applied the first fully concurrent 3D ultrasound imaging set-up including B-mode imaging, shear wave elastography (SWE), tissue structure imaging with backscatter tensor imaging (BTI), vascular mapping with ultrasensitive Doppler (uDoppler) and ultrasound localization microscopy (ULM) in-vivo . Subsequent analysis aimed to evaluate its benefits for non-invasive tumor diagnosis. Approach. A total of 26 PyMT-MMTV transgenic mice and 6 control mice were imaged weekly during tumor growth. First-order statistics and radiomic features were extracted from the quantitative maps obtained, and used to build predictive models differentiating healthy from cancerous mammary pads. Imaging features were also compared to histology obtained the last week of imaging. Main results. High quality co-registered quantitative maps were obtained, for which SWE speed, BTI tissue organization, ULM blood vessel count and uDoppler blood vessel density were correlated with histopathology. Significant changes in uDoppler sensitivity and BTI tissue structure were measured during tumor evolution. Predictive models inferring the cancerous state from the multiparametric imaging reached 99% accuracy, and focused mainly on radiomics measures of the BTI maps. Significance. This work indicates the relevance of a multiparametric characterization of lesions, and highlights the strong predictive power of BTI-derived parameters for differentiating tumors from healthy tissue, both before and after the tumor can be detected by palpation
Valorisation du limonène par activation C-H
No full textInternational audienceA cause du réchauffement climatique et en particulier de l’excès de dioxyde de carbone produit par les activités humaines, il devient urgent de trouver des solutions de remplacement des ressources fossiles pour la synthèse organique. Cet article traite de l’utilisation d’hydrocarbures biosourcés, les terpènes, comme source de carbone renouvelable. Il y est question du développement d’une réaction d’activation C–H et plus particulièrement d’un couplage croisé déshydrogénant entre un terpène et un alcène pauvre en électrons par catalyse au palladium. Une étude mécanistique et une application de cette transformation en catalyse micellaire est ensuite dévoilée
Adaptive Optics Rolling Slit Ophthalmoscope: High Resolution Camera-based Multimodal Retinal Imaging, Blood Flow Visualization and Neurovascular Coupling
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La manipulation de l'énergie à l'état excité permet aux diodes électroluminescentes blanches monocouches de simuler le spectre solaire
No full textInternational audienceWhite light-emitting diodes (WLEDs) have been widely researched and applied for their characteristics of energy-saving and environmentally friendly. However, the spectrum of WLEDs is quite different from that of natural sunlight, and long-term use can have an impact on both physiological and psychological health. Three strategies have been designed to address the issue of spectral defects by revealing the exciton energy transfer and distribution behavior between multiple excited states. Here, single emitting layer (SEL)-WLEDs are designed to simulate solar spectrum, which exhibits excellent spectral stability at different operating voltages, demonstrating that exciton distribution can maintain dynamic balance. In addition, these devices can accurately replicate the sunlight during different time periods, with a high color rendering index (CRI ~ 90) and a nearly 90% coverage in the human comfort region. Meanwhile, the ultraviolet, deep blue and near-infrared regions were reduced by 100%, 80%, and 90%, respectively. These results indicate that the strategies are expected to be used to promote the physical and mental health of those who work in environments far from natural light for a long time
Sources de lumière infrarouge à base de dispositifs de matériaux 2D et nano-antennes plasmoniques uniques.
No full textThe subject of light-matter interactions in the mid- and far-infrared ranges is of particular significance due to its association with enhanced energy management, a necessity that is particularly pressing in the present age. The comprehension, control and enhancement of phenomena associated with these technologies present both opportunities and challenges, ranging from radiative cooling to the improvement of photovoltaic panel performance. The objective of this study is to broaden our understanding of light emission by small-scale, sub-wavelength devices or devices based on 2D materials. Due to the equivalence between the absorption and emission properties of bodies, this work is situated at the intersection of two fields: the design of new infrared sources and the advancement of knowledge pertaining to the absorption of radiation by objects.The primary objective of this study is to enhance our comprehension of the behaviour exhibited by infrared meta-surfaces, which are typically arranged in a network configuration, through the analysis of the properties exhibited by a single particle. In order to accomplish this objective, we are utilising two highly sensitive signal detection methodologies, thus empowering us to measure the thermal emission of a solitary sub-wavelength object while it is embedded within the ambient infrared thermal radiation (spatially-modulated infrared spectroscopy, IR-SMS), or to probe its response on a very sub-wavelength scale (scanning near-field optical microscopy, SNOM). The present study underscores the significance of the near-field coupling that transpires between a cylindrical gold antenna deposited on a polar substrate. This coupling significantly alters the spectral emission characteristics of the antenna or substrate when considered separately, resulting in the assembly becoming a temporally coherent thermal emitter. This phenomenon can be attributed to the presence of surface electromagnetic waves confined to the interface between polar materials, such as silicon carbide or quartz, and air. In the spectral band in which such waves exist, gold antennae have been observed to exhibit a negative effective extinction cross-section. This phenomenon has not been reported in experimental studies to our knowledge.Secondly, this work describes the observations made on high-quality graphene field-effect transistors (HGFETs). We demonstrate the appearance of an electroluminescent infrared emission regime linked to the pumping of graphene electrons into a highly non-equilibrium state, thanks in particular to the Zener-Klein tunneling effect. This electroluminescence regime is manifested by the excitation of electromagnetic modes in the material encapsulating the graphene of transistors, hexagonal boron nitride, where they are confined, making their detection in the far field inaccessible. However, the IR-SMS experiment enabled us to detect and characterise these waves following their scattering by discontinuities in the structure, enabling us to experimentally confirm their electroluminescent nature. We then show that these modes represent a tiny fraction of the energy emitted by graphene, and that they are accompanied by a very efficient transfer of energy to the substrate, exceeding by several orders of magnitude the cooling capacities of conventional electroluminescent devices such as LEDs.Les interactions lumière-matière dans les gammes infrarouges moyenne et lointaine représentent un défi d'ampleur de par leurs liens avec une meilleure gestion de l’énergie, plus que nécessaire de nos jours. Du refroidissement radiatif à l’amélioration des performances des panneaux photovoltaïques, la compréhension, la maîtrise et l’optimisation des phénomènes relatifs à ces technologies offrent autant d’opportunités que d’interrogations. Ce travail vise ainsi à approfondir les connaissances sur l’émission de lumière par des dispositifs à petite échelle, sub-longueur d’onde ou à base de matériaux 2D. De par l’équivalence entre les propriétés d’absorption et d’émission des corps, ce travail se situe donc à l’intersection entre la conception de nouvelles sources infrarouges, et l’approfondissement de notre maîtrise de l’absorption de rayonnement par les objets.Dans un premier temps, nous cherchons à parfaire la compréhension du comportement des méta-surfaces infrarouges, généralement organisées en réseau, en étudiant les propriétés d’une particule unique. Pour cela, nous utilisons des méthodes de détection de signal extrêmement sensible, nous permettant de mesurer l’émission thermique d’un seul objet sub-longueur d’onde alors même qu’il est noyé dans le rayonnement thermique infrarouge ambiant (spectroscopie infrarouge par modulation spatiale, IR-SMS), ou encore de sonder leur réponse à une échelle fortement sub-longueur d’onde (microscopie optique de champ proche à balayage, SNOM). Nos travaux font émerger l’importance du couplage en champ proche se produisant entre une antenne cylindrique en or déposée sur un substrat polaire. En particulier, ce couplage vient modifier drastiquement les caractéristiques spectrales d’émission de l’antenne ou du substrat considérés séparément, faisant de l’ensemble un émetteur thermique temporellement cohérent, ce qui s’explique par l’existence d’ondes électromagnétiques de surface confinées à l’interface entre les matériaux polaires comme le carbure de silicium ou le quartz, et l’air. En dehors de la bande spectrale d’existence de telles ondes, les antennes d’or présentent une section efficace d’extinction négative, ce qui n’a jamais été rapporté expérimentalement à notre connaissance.Dans un second temps, ce travail décrit les observations faites sur des transistors à effet de champ à base graphène haute qualité (HGFET). Nous mettons en évidence l’apparition d’un régime d’émission infrarouge électroluminescente lié au pompage des électrons du graphène dans un état fortement hors-équilibre grâce notamment à l’effet tunnel de Zener-Klein. Ce régime d’électroluminescence se manifeste par l’excitation de modes électromagnétiques dans le matériau encapsulant le graphène des transistors, le nitrure de bore hexagonal, où ils sont confinés, rendant leur détection en champ lointain inaccessible. L’expérience IR-SMS permet toutefois de détecter et caractériser ces ondes suite à leur diffusion par des discontinuités dans la structure, permettant de confirmer expérimentalement leur caractère électroluminescent. Nous montrons ensuite que ces modes représentent une infime partie de l’énergie émise par le graphène, et qu’ils s’accompagnent d’un transfert très efficace d’énergie vers le substrat, dépassant de plusieurs ordres de grandeurs les capacités de refroidissement des dispositifs électroluminescents usuels, comme les LED
Modeler la lumière en milieux complexes résonants
No full textThis work presents a theoretical and numerical study of the propagation of light waves through disordered media composed of resonant point-like scatterers. It falls within the framework of the recent development of wavefront shaping techniques, which open up new perspectives for controlling light transport in complex environments.First, we investigate the statistical properties of the transmission matrix as well as those of the dwell time operator of light within a resonant complex medium. The study is conducted in a two-dimensional waveguide under a scalar approximation (TM polarization). We show that the introduction of resonators enables the exploration of different transport regimes — ballistic, diffusive, and localized — by tuning only the frequency of the incident light. The study of the eigenvalue distribution of the transmission matrix across these regimes reveals that it is entirely governed by a mesoscopic parameter, the mean free path, in addition to the system's geometric characteristics. The open and closed channels observed in the diffusive regime are similar to those found in non-resonant media. In the localized regime, the channels of maximal transmission adopt a "necklace" structure, optimizing transmission through the coupling of exponentially localized eigenmodes. Regarding the dwell time operator, whose eigenvalues reflect dynamic aspects of transport, its distribution highlights the impact of the reduced energy propagation speed due to the presence of resonators, thus revealing a phenomenon of light trapping. We further demonstrate that the use of optimized wavefronts significantly enhances both transmission and dwell time.In a second part, we show that the total electromagnetic energy stored in a disordered set of resonators decomposes into two contributions: one associated with radiation, the other with matter. For resonators with high quality factors, the matter energy largely dominates, and their ratio tends toward a universal value in the thermodynamic limit. Using multiple scattering theory, we establish that, in this limit, the energy transport velocity is entirely determined by the ratio between the matter and radiation energies. Finally, the potential for energy deposition modulation is explored via wavefront shaping, an approach that allows manipulation of the dynamic degrees of freedom of the scattered wave by acting solely on its spatial components.As an exploratory study, the case of vector waves is considered to assess the influence of polarization on the transport properties in disordered media.Ce travail présente une étude numérique et théorique de la propagation des ondes lumineuses dans des milieux désordonnés constitués d'obstacles ponctuels résonants. Il s'inscrit dans le cadre du développement récent des techniques de façonnage de fronts d'onde, qui ouvrent de nouvelles perspectives pour le contrôle du transport lumineux dans des environnements complexes.Dans un premier temps, nous étudions les propriétés statistiques de la matrice de transmission ainsi que celles de l'opérateur de temps de séjour de la lumière au sein d'un milieu complexe résonant. L'analyse est réalisée dans un guide d'onde bidimensionnel, en régime scalaire (polarisation TM). Nous montrons que l'introduction de résonateurs permet d'explorer les différents régimes de transport — balistique, diffus et localisé — en modulant uniquement la fréquence de la lumière incidente. L'étude de la distribution des valeurs propres de la matrice de transmission à travers ces régimes révèle qu'elle est entièrement gouvernée par un paramètre mésoscopique, le libre parcours moyen, en plus des caractéristiques géométriques du système. Les canaux ouverts et fermés observés dans le régime diffus sont similaires à ceux des milieux non résonants. En régime localisé, les canaux de transmission maximale adoptent une structure en collier de perles, optimisant la transmission par couplage de modes propres localisés de manière exponentielle. Concernant l'opérateur de temps de séjour, dont les valeurs propres traduisent des aspects dynamiques du transport, sa distribution révèle l'impact de la réduction de la vitesse de propagation de l'énergie due aux résonateurs, mettant ainsi en évidence un phénomène de piégeage lumineux. Nous démontrons finalement que l'utilisation de fronts d'onde optimisés permet d'accroître significativement à la fois la transmission et le temps de séjour.Dans un second temps, nous montrons que l'énergie électromagnétique totale stockée dans un ensemble désordonné de résonateurs se décompose en deux contributions : l'une associée au rayonnement, l'autre à la matière. Pour des résonateurs de haut facteur de qualité, l'énergie de matière domine nettement, et leur rapport tend vers une valeur universelle dans la limite thermodynamique. À l'aide de la théorie de la diffusion multiple, nous établissons que, dans cette même limite, la vitesse de transport de l'énergie est entièrement déterminée par le rapport entre les énergies de matière et de rayonnement. Enfin, le potentiel de modulation du dépôt d'énergie est exploré via le façonnage de fronts d'onde, approche permettant d'agir sur les degrés de liberté dynamiques de l'onde diffusée en manipulant uniquement ses composantes spatiales.À titre exploratoire, le cas des ondes vectorielles est étudié afin d'évaluer l'influence de la polarisation sur les propriétés de transport dans les milieux désordonnés
Aerodynamic consequences of wing damage in dragonflies
No full textAccepted in J. Roy. Soc. InterfaceFlapping wings are the primary means by which dragonflies generate forces, but they are susceptible to damage due to their inherent fragility. The damage results in a reduction in wing area and a distortion of the original wing, which in turn leads to a decline in flight ability. Furthermore, the flows of dragonfly fore- and hindwings exhibit an interaction, thus damage to the forewing can also impact the aerodynamic performance of the ipsilateral hindwing. In this study, we examine this problem through CFD (computational fluid dynamics) simulations on a series of damaged dragonfly fore-/hindwing models according to the probability of area loss from the literature. The flow fields and aerodynamic forces for the different damaged wing cases are compared with those for the intact wings. This comparative analysis reveals how the different patterns of wing damage modify the vortex structures around the flapping wings and lead to a drop in aerodynamic force production. The causes behind the diminishing aerodynamic performance are shown to be subtler than the pure area loss and are regulated by the changes in the flow field that result from wing damage. Wing-wing interaction becomes particularly important when forewing damage occurs
Yielding and plasticity in amorphous solids
No full textInternational audienceThe physics of disordered media, from metallic glasses to colloidal suspensions, granular matter and biological tissues, offers difficult challenges because it often occurs far from equilibrium, in materials lacking symmetries and evolving through complex energy landscapes. Here, we review recent theoretical efforts to provide microscopic insights into the mechanical properties of amorphous media using approaches from statistical mechanics as unifying frameworks. We cover both the initial regime corresponding to small deformations, and the yielding transition marking a change between elastic response and plastic flow. We discuss the specific features arising for systems evolving near a jamming transition, and extend our discussion to recent studies of the rheology of dense biological and active materials
Migration and segregation of confined droplets flowing in flexible channels with a rectangular cross-section
No full textInternational audienceWe investigate the behavior of droplets flowing through flexible rectangular channels and uncover a fascinating phenomenon: pancake-shaped confined droplets migrate transversely toward the channel center. Our findings reveal that this migration is driven by a gradient in interfacial energy, created by the deformation of the channel under the flow of the carrier phase. To explain this behavior, we introduce a simple hydrodynamic model that accurately predicts the trajectories of individual droplets and their dependence on key experimental parameters, such as droplet volume and total flow rate. In concentrated emulsions, this effect results in a striking segregation phenomenon, where all droplets converge and concentrate in the central region of the channel. These insights pave the way for deeper understanding and control of droplet dynamics in confined environments
Automated Detection of Attention and Retention in Educational Videos Using Eye-Tracking, Dynamic Areas of Interest and Feature Fusion
No full textInternational audienceEducational videos are widely used in remote and blended learning. However, learners' attention often fluctuates while watching, which can hinder their retention of key information. This, in turn, may impact their overall learning outcomes. Detecting when learners lose attention or fail to memorize key elements of a video could help address these challenges-for example, by enabling adaptive support that enhances engagement and retention, bridging the gap between passive video consumption and active learning. Such automated detection could also provide valuable insights to instructors about when attention and retention drop in their videos. In this study, we explore how to detect learners' attention and retention while they watch an educational video in a blended course on green chemistry, using eye-tracking data. To achieve this, we develop machine learning classifiers that analyze eye movements, pupil dilation, eye-screen distance, and attention to dynamically tracked areas of interest (AOIs). We investigate different strategies for fusing these types of information and find that dynamic AOIs can significantly improve ML predictions, albeit with moderate performance