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Linear Rank-Metric Intersecting Codes
No full textIn this paper we introduce and investigate rank-metric intersecting codes, a new class of linear codes in the rank-metric context, inspired by the well-studied notion of intersecting codes in the Hamming metric. A rank-metric code is said to be intersecting if any two nonzero codewords have supports intersecting non trivially. We explore this class from both a coding-theoretic and geometric perspective, highlighting its relationship with minimal codes, MRD codes, and Hammingmetric intersecting codes. We derive structural properties, sufficient conditions based on minimum distance, and geometric characterizations in terms of 2-spannable q-systems. We establish upper and lower bounds on code parameters and show some constructions, which leave a range of unexplored parameters. Finally, we connect rank-intersecting codes to other combinatorial structures such as (2, 1)-separating systems and frameproof codes
Spatio-temporal equilibrium thermodynamics of guided optical waves at positive and negative temperatures
No full textOptical thermalization has been recently studied theoretically and experimentally in the 2D spatial evolution of (quasi-)monochromatic light waves propagating in multimode fibers. In this work, we investigate the spatio-temporal equilibrium properties of incoherent multimode optical waves through the analysis of the (2+1)D Bose-Einstein thermal distribution and the corresponding classical Rayleigh-Jeans approximation. In the anomalous dispersion regime, the spatio-temporal equilibrium is characterized by positive temperatures. In this regime, we show that as the number of modes of the waveguide increases, the fundamental spatial mode becomes macroscopically populated, while its temporal spectrum undergoes significant narrowing, ultimately leading to complete (2+1)D spatio-temporal condensation in the thermodynamic limit. In the normal dispersion regime, the spatio-temporal equilibrium is characterized by negative temperature states that exhibit a hybrid character: the spatial equilibrium displays an inverted modal population, whereas the temporal spectrum remains peaked around the fundamental (carrier) optical frequency. In this regime, we predict that spatio-temporal light waves exhibit a phase transition to Bose-Einstein condensation at negative temperatures, which occurs by increasing the temperature above a negative critical value. Our work opens new avenues for future research, including the possibility for a dual spatio-temporal beam cleaning through full spatio-temporal light condensation, and lay the groundwork for the development of spatio-temporal optical thermodynamics
Stiffening cells with light
No full textInternational audienceAbstract Fluorescence microscopy is widely used to observe structures and dynamic processes in living cells and organisms and is often used as if it were purely innocuous to the cells or structures of interest. However, it can lead to phototoxicity, which can affect the cellular behavior and lead to erroneous interpretations of the observations. The major cause of cell damage through phototoxicity is the production of reactive oxygen species (ROS), which can form crosslinks between intracellular molecules, including proteins and nucleic acids. By using profile microindentation and atomic force microscopy, we demonstrate that the excitation of various fluorescent probes leads to a large increase in the stiffness of several cell types within seconds of illumination. The stiffening exhibits a dose-dependent response, where longer exposure times to exciting light are correlated with larger stiffening. This photostiffening effect explains why T cells loaded with the Fluo-4 Calcium probe stop emitting a protrusion within seconds after the excitation light is turned on. We observed photostiffening in different cell types and fluorophores. We showed that repeated cell indentation alone led to cell stiffening as well as excitation with blue or UV light in the absence of a fluoroph ore. However, in the latter case, the stiffening was much smaller than that when the fluorophore was excited. We used both sharp and blunt indenters to show that stiffening occurred not only at the cell cortex level but also deeper in the cell interior and that photostiffening is independent of actin cytoskeleton organization. We correlated the increase in cell stiffness with the production of intracellular reactive oxygen species and reproduced cell stiffening by incubating cells with a ROS inducer, H 2 O 2 . The excitation of the photosensitizer Pheophorbide a , which induces a specific type of reactive oxygen species, namely singlet oxygen, also led to cell stiffening. This study reminds the experimentalists that it is crucial to perform controls when using fluorescence. It further allows us to propose exploiting photostiffening as a new method for rapidly quantifying phototoxicity. Significance This study reveals a direct relationship between fluorescence excitation and cell mechanical properties. The generality of th is phenomenon across diverse fluorophores and cell types highlights the importance of controlling phototoxicity in fluorescence experiments, in particular in complex, quantitative cell biology and biophysical experiments, but also reveals an unexpected rol e of intracellular reactive oxygen species production and identifies cell stiffness as a proxy for assessing the efficacy of photodynamic therapy
Characterizing France's Plausible Future Droughts: A Multi-Perspective Spatiotemporal Framework
No full textInternational audienceDroughts have severely impacted France across multiple socio-economic sectors (agriculture, energy, forestry), with climate change projected to aggravate these events. To construct tangible assessments of future drought risks, we develop a comprehensive framework analyzing meteorological, soil moisture, and hydrological droughts across short-term and long-term timescales using standardized drought indices. Our analysis benefits from a recent ensemble of high-resolution hydro-climate simulations (1960-2100) and treats droughts as contiguous spatiotemporal events. Three historical events (1976, 1989, 2015) serve as references for quantifying the projected changes. We analyze drought evolution by focusing on three characteristics: duration, spatial extent and intensity. We examine whether these characteristics exhibit significant trends for the RCP8.5 scenario, how their distributions for different global warming levels (+1.5°C, +2°C, +3°C) evolve, and detail the drought evolution in two contrasted hydro-climate simulations (storylines). All drought types present a significant intensity increase under climate change, with current benchmark intensities becoming more frequent even under +1.5°C warming. At +3°C warming, 8-17% of soil moisture and hydrological drought events exceed the exceptional duration of the 1989 event. Notably, even the wettest storyline does not significantly reduce drought intensity, duration, and spatial extent, while the driest one generates unprecedented drought conditions. As a result, adaptation planning should take into account the increased frequency of historical benchmarks, but also drought conditions exceeding them. Our analysis also highlights the sensitivity of future drought projections to how well models represent key driving factors: evolving aerosol concentrations and vegetation physiological responses to increasing CO2
Nanoscale imaging of reduced forward bias at V-defects in green-emitting nitride LEDs
No full textRecord wall-plug efficiencies in long-wavelength, III-nitride light-emitting diodes (LEDs) have recently been achieved through improvements in electrical efficiency in devices containing V-defects. Numerical modeling suggests this may be due to reduced barrier heights for charge injection in thinned, low-Indium quantum wells parallel to semi-polar V-defect facets. To test this proposition, a novel approach in which the tip of a scanning tunneling luminescence microscope as a local hole injector, is used to map the optoelectronic properties of commercial, green-emitting LED heterostructures around V-defects with nanoscale spatial resolution. A 1 V reduction in the forward bias necessary for current injection at V-defect rims is observed. This, combined with the observation of small (≈ 10 meV) blue shifts in the locally emitted electroluminescence, unambiguously confirms the charge injection mechanism
Analyse de premiers principes du transport des porteurs et des propriétés vibrationnelles dans les chalcogénures de métaux de transition structurés en pyrite
No full textThis thesis presents a detailed first-principles study of the thermoelectric transport properties of selected transition metal chalcogenides crystallizing in the pyrite structure.These materials are of significant interest due to their earth-abundance, chemical stability, and promising potential for application in energy conversion and storage technologies, suchas thermoelectrics, photovoltaics, catalysis, and batteries.Chapters 1 and 2 lay the groundwork by introducing the fundamental concepts of thermoelectricity, providing an overview of pyrite-structure based materials, and describing the computa-tional methods employed. This foundation supports the detailed analysis of electronic and transport properties in the subsequent chapters.Chapter 3 investigates the evolution of the electronic structurein Co1−xFexS2 with increasing Fe content. Despite variationsacross exchange-correlation functionals, a consistent trend ofbroadening in the lowest-lying minority-spin conduction bandsand a reduction in exchange-splitting is observed as the com-position approaches stoichiometric FeS2. These results, alongwith photoemission spectroscopic evidence showing occupied minority-spin states at the Fermi level in pure CoS2, confirm thepresence of minority-spin states throughout the series, contra-dicting earlier theoretical predictions.Chapter 4, motivated by discrepancies in reported room-temperature thermopower in self- and Co-doped FeS2, analyzes electron-doped FeS2 using explicit Co-substitution, jellium doping, and Fermi level shift within the rigid band approximation. Chapter 5 extends this analysis to hole doping, incorporating electron-phonon scattering. In both cases, the predicted thermoelectric performance indicates that doped FeS2 isunlikely to serve as an efficient thermoelectric material.Finally, Chapter 6 presents a comparative thermal transportstudy of two isoelectronic pyrites, FeS2 and RuS2. RuS2 ex-hibits lower room-temperature lattice thermal conductivity, attributed to reduced phonon velocities due to the heavier Ruatoms and increased anharmonic phonon scattering. Thesefindings underscore the influence of atomic mass and anhar-monicity in governing thermal transport in pyrite systems.Cette thèse présente une étude détaillée des premiers principes des propriétés de transport thermoélectrique de chalcogénures de métaux de transition sélectionnes cristallisant dans la structure de la pyrite. Ces matériaux sont d’un grand intérêt en raison de leur abondance sur terre, de leur stabilité chimique et de leur potentiel prometteur d’appli-cation dans les technologies de conversion et de stockage de l’énergie, telles que la thermoélectricité, la photovoltaïque, la catalyse et les batteries.Les chapitres 1 et 2 posent les bases en introduisant les concepts fondamentaux de la thermoélectricité, en donnant un aperçu des matériaux à base de structure pyriteuse et en décrivant les méthodes de calcul utilisées. Cette base soutient l’analyse détaillée des propriétés électroniques et de transport dans les chapitres suivants. Le chapitre 3 étudie l’évolution de la structure électronique du Co1−xFexS2 avec l’augmentation de la teneur en Fe. Malgré des variations entre les fonctionnelles d’échange-corrélation, une tendance cohérente à l’élargissement des bandes de conduction à spins minoritaires les plus basses et une réduction de l’échange-séparation sont observées à me-sure que la composition s’approche du FeS2 stœchiométrique. Ces résultats, ainsi que les preuves spectroscopiques de photo émission montrant des états de spins minoritaires occupes au niveau de Fermi dans le CoS2 pur, confirment la présence d’états de spins minoritaires dans toute la série, ce qui contredit les prédictions théoriques antérieures. Le chapitre 4, motivé par des divergences dans la puissance thermique à température ambiante rapportée dans le FeS2auto-dopé et dopé au Co, analyse le FeS2 dopé aux électrons en utilisant la substitution explicite du Co, le dopage jellium et le décalage du niveau de Fermi dans l’approximation de la bande rigide. Le chapitre 5 étend cette analyse au dopage par trous, en incorporant la diffusion électron-phonon. Dans les deux cas, les performances thermoélectriques prévues indiquent qu’il est peu probable que le FeS2 dope serve de matériau thermoélectrique efficace.Enfin, le chapitre 6 présente une étude comparative du transport thermique de deux pyrites isoélectriques, FeS2 etRuS2. RuS2 présente une conductivité thermique du réseau à température ambiante plus faible, attribuée à des vitesses de phonon réduites dues à des atomes de Ru plus lourds et à une diffusion de phonon anharmonique plus importante. Ces résultats soulignent l’influence de la masse atomique et de l'harmonicité sur le transport thermique dans les systèmes de pyrite
Étude de la dynamique de réplication de l'archée polyploïde Haloferax volcanii à l'échelle nanométrique
No full textDNA replication is an essential process for the proliferation of all living beings, ensuring the maintenance of genetic information for cell descendants. The replication mechanism is broadly conserved across all three domains of life, although the composition of the replisome differs greatly between bacteria and eukaryotes. Archaea have a replisome that resembles the eukaryotic machinery, making them particularly interesting organisms for the study of replication.We have therefore investigated DNA replication in Haloferax volcanii, a model organism of the Haloarchaeota. H. volcanii has interesting features regarding replication: a circular chromosome, but with 4 replication origins, and a high and heterogeneous copy number. To study replication in such a complex population, the team was able to observe the essential replication protein Rpa2, which binds to single-stranded DNA at the lagging strand. This first study showed that the protein localized as foci, whose wide distribution seems to reflect the heterogeneity of the population.I therefore implemented directSTORM imaging of the Rpa2 protein in fixed H. volcanii cells, together with a robust image analysis pipeline for the detection of foci, enabling us to take full advantage of the higher level of information available. Our results suggest that during exponential phase, H. volcanii is always replicating DNA. The replication dynamics we observed appear to be closely linked to cell size and DNA content, in an almost linear fashion~: the largest cells are also those with the most DNA and the greatest number of replication foci. This original profile has led us to hypothesize a regulation of replication that resembles a uniform probability of initiation per origin of replication.%I was able to extend this study to the localization of Rpa2 in a mutant deleted for all four replication origins. The mutant shows an organization very similar to that of the wild-type strain under optimal conditions, but partially lost at lower temperatures. These results underline the complexity of replication regulation in this organism, and the need to better understand how replication initiation is regulated in the presence and absence of replication origins.La réplication de l'ADN est un processus essentiel pour la prolifération de tous les êtres vivants, en assurant le maintien de l'information génétique à la descendance cellulaire. Le mécanisme de réplication est largement conservé dans les trois domaines du vivant, bien que la composition du réplisome diffère grandement entre bactéries et eucaryotes. Les archées ont un réplisome qui se rapproche de celui de la machinerie eucaryote, faisant d'elles des organismes particulièrement intéressant pour l'étude de la réplication.Nous nous sommes ainsi intéressé à la réplication de l'ADN chez Haloferax volcanii, espèce modèle des Haloarchaeota. H. volcanii est un organisme au profil particulier concernant la réplication : un chromosome circulaire, mais avec 4 origines de réplication, et un nombre de copies élevé et hétérogène. Pour étudier la réplication dans une population aussi complexe, l'équipe a pu observer la protéine de réplication essentielle Rpa2, qui se lie à l'ADN simple brin au niveau du brin retardé. Cette première étude a montré que la protéine localisait sous la forme de foyers, dont la distribution large semble être le reflet de l'hétérogénéité de la population. Face au faible nombre de foyers détectés en comparaison du nombre de fourches potentielle, le passage à des méthodes de super-résolution est nécessaire pour comprendre plus finement la résolution.J'ai donc implémenté l'imagerie en directSTORM de la protéine Rpa2 dans les cellules h. volcanii fixées, ainsi qu'un dispositif d'analyse d'image robuste pour la détection des foyers, permettant de tirer pleinement parti du plus haut niveau d'informations disponibles. Nos résultats suggèrent qu'en prolifération exponentielle H. volcanii réplique son ADN en permanence. La dynamique de réplication observée apparaît étroitement liée à la taille des cellules et à leur quantité d'ADN, de manière quasiment linéaire : les cellules les plus grandes sont aussi celles qui ont le plus d'ADN et le plus grand nombre de foyers de réplication. Ce profil original nous a conduits à supposer une régulation de la réplication de la réplication qui s'apparente à une probabilité uniforme d'initiation par origine de réplication.J'ai pu étendre cette étude à la localisation de Rpa2 dans un mutant délété des quatre origines de réplication. Le mutant présente une organisation très similaire à celle de la souche sauvage dans des conditions optimales, mais moins conservée à plus basse température. Ces premiers résultats soulignent la complexité de la régulation de la réplication chez cet organisme, et la nécessité de mieux comprendre comment est régulée l’initiation de la réplication en présence comme en absence d’origines de réplication
Time Delay Distribution and Laser Stability in Arbitrary Detuning Asynchronous Optical Sampling
No full textInternational audienceArbitrary Detuning ASynchronous OPtical Sampling (ADA-SOPS) is an emerging technique for extending standard pump−probeexperiments performed with two femtosecond lasers to multitimescale experiments, which are of great interest for the study of complex systems.Although no specific requirements are needed for laser repetition rates, their ratio determines the achievable delay distribution and therefore is strongly related to the temporal resolution of the technique. We report a detailed theoretical analysis of measurement performances with respect to laser repetition rates, and we validate our model with experimental data. In the case of amplified laser systems, we demonstrate that achieved delays are inherently correlated to the time interval between amplified pulses, which affects the pulse energy and can generate artifacts. Nevertheless, a deep understanding of the origin of such artifacts allows to suggest several compensation strategies, either during data analysis or at the conception of the experimental setup. Finally we present a new algorithm integrated into the ADASOPS device: by selecting pairs of probe pulses having the same elapsed time with respect to the previous pulse, it automatically compensates any effect of energy fluctuation
Twisted orientifold planes and S-duality without supersymmetry
No full textInternational audienceWe show that the coupling of a massive spin-2 field to undeformed N = 1 supergravity in four dimensions is unique, leading to a specific non-minimal coupling to the Riemann tensor. The massive spin-2 coupling reproduces the one of an oscillator mode in open string theory, while the massive spin-1 coupling includes a higher-derivative term that is expected to violate causality in the background of a gravitational shock wave. We argue that the resolution of causality and the unitarity bound in the Regge limit require the introduction of infinitely many higher-spin fields similar to the Regge trajectories in string theory, therefore providing an argument in favour of the string lamppost principle with minimal supersymmetry in four dimensions. To obtain this result, we construct the general stress-energy tensor multiplet for the massive spin-2 multiplet with N = 1 supersymmetry
