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Active disturbance rejection control for four-wire inverters in standalone renewable resources-based microgrid -islanded microgrids ADRC-based control-
No full textInternational audienceThis paper presents an active disturbance rejection control (ADRC) approach for three-phase four-legs voltage source inverters (FL-VSIs) in a standalone renewable energy resources (RES)-based islanded microgrid. The key purpose of the proposed approach is to improve the control robustness against load-side disturbances, power supply parameters uncertainties, and faulty operating conditions. Indeed, a notable benefit of ADRC is its ability to operate effectively without the need for precise knowledge of disturbance characteristics or accurate modeling and FL-VSI parameters. As compared with conventional PI controllers, this advanced control strategy allows improving the voltage waveforms quality and conforming to existing power quality standards and metrics while using only output voltage sensors. Extensive simulations on Matlab/Simulink software have been conducted to assess the effectiveness of the proposed approach
Constant Payoff Property in Zero-Sum Stochastic Games with a Finite Horizon
No full textInternational audienceThis paper examines finite zero-sum stochastic games and demonstrates that when the game's duration is sufficiently long, there exists a pair of approximately optimal strategies such that the expected average payoff at any point in the game remains close to the value. This property, known as the constant payoff property, was previously established only for absorbing games and discounted stochastic games
Modelling-assisted geometrical optimization of colloidal quantum color convertor based pixels fabricated by dielectrophoretic directed assembly
No full textInternational audienceHypothesis: Building competitive color conversion pixels for microdisplays made of semiconductor nanocrystals requires reaching a deposition thickness high enough to absorb all the blue light from the backlight unit. In the case of dielectrophoretic directed assembly of such nanocrystals, modeling and simulations may help understand what the intrinsic limitations of the process are, and may be used to propose new assembly routes.Experiments: A theoretical model of dielectrophoretic interactions between polarizable nano-spheres and an electrostatically patterned substrate has been developed. Monte Carlo simulations have been run using this model to rationalize the effects of parameters driving the dielectrophoretic directed assembly and to find optimal deposition conditions for reaching a maximal thickness of nanocrystal pixels. Experiments with CdSe quantum plates and with alumina spheres embedding quantum plates (micro-pearls) have been carried out and compared to the model. Findings: Modeling and simulations reveal that the directed assembly of semiconductor nanocrystals is limited essentially by the small object size, which sets the maximum dielectrophoretic force they can undergo. They indicate that using larger objects should allow reaching unprecedented assembly heights, but will induce lateral extension of the assembly. This trade-off has been illustrated with diagrams in the parameter space and confirmed experimentally with micro-pearls
Shifting sands of hardware and software in exascale quantum mechanical simulations
No full textInternational audienceThe era of exascale computing presents both exciting opportunities and unique challenges for quantum mechanical simulations. While the transition from petaflops to exascale computing has been marked by a steady increase in computational power, the shift towards heterogeneous architectures, particularly the dominant role of graphical processing units (GPUs), demands a fundamental shift in software development strategies. This review examines the changing landscape of hardware and software for exascale computing, highlighting the limitations of traditional algorithms and software implementations in light of the increasing use of heterogeneous architectures in high-end systems. We discuss the challenges of adapting quantum chemistry software to these new architectures, including the fragmentation of the software stack, the need for more efficient algorithms (including reduced precision versions) tailored for GPUs, and the importance of developing standardized libraries and programming models
In-plane and out-of-plane compressive properties of regular and graded cellular cores of sandwich panels fabricated by additive manufacturing
No full textInternational audienceCellular materials with a gradient of properties become appealing as cores of the sandwich panels due to the possibility of improving strength and absorbed energy in lightweight components. 2D cellular structures designated by honeycombs have an anisotropic behaviour when loaded under in- and out-plane. Thus, when proposing new designs, it is essential to analyse how the in-plane arrangement with a gradient in cell wall thickness affects in-plane and out-of-plane mechanical properties. This work aims to study graded cellular structures in comparison with regular hexagonal honeycombs. Structures were manufactured by laser powder bed fusion using an aluminium alloy. Regular arrangements were formed with cells with the same thickness, while graded structures possessed a radial gradient of cell thickness. Three types of innovative gradients, where cell length varies radially along concentric layers, were analysed. The compressive properties of regular and graded structures were evaluated when loaded both under in-plane and out-of-plane conditions. Compression behaviour was assessed, both experimentally and by numerical modelling. Even though there is a mismatch between numerical and experimental results, they exhibit the same trends. All graded samples showed an increased mechanical performance when loaded under out-of-plane conditions in comparison with the results from tests under in-plane loading with values, for example, of stiffness four hundred times larger, absorbed energy around thirty times higher and with yield stress four times larger. The results showed that the graded samples attain higher values of strength, stiffness and absorbed energy in comparison with regular hexagonal honeycombs, for the same relative density
In Vitro Neurons on a Chip: From Fundamental Neuroscience to Applied Neurotechnology
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Scaled Vertical Transport Gate-All-Around Nanostructured Channel (Nanosheet/Nanowire) Technology for Advanced CMOS Devices
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Porohyperelastic modeling of collagen-gel responses to periodic pressure actuation shows that embedded senescent fibroblasts induce tissue softening associated with fibrous-network reorganization
No full textInternational audienceThe poroelastic properties of tissues regulate molecular transport and mechanical signaling, yet their evolution during aging remains poorly understood. In particular, senescent fibroblasts accumulate in aged tissues, contributing to extracellular matrix (ECM) remodeling, but their impact on tissue mechanics and permeability is unclear. In this study, we developed a microfluidic-based in vitro model to assess the poroelastic properties of collagen gels embedded with senescent fibroblasts over time. Our approach integrates periodic pressure actuation with real-time pressure monitoring in a sealed air cavity, enabling the detection of fluid permeation and solid matrix deformations. We analyze our data using analytical and numerical models based on a porohyperelastic framework. This framework combines compressible Neo-Hookean elasticity with the Kozeny-Carman permeability relationship. We demonstrate that senescent fibroblasts induce a progressive softening of the ECM without altering its permeability. Immunostaining reveals that this softening correlates with structural reorganization of the collagen network, characterized by increased branching and network remodeling. Our findings provide insights into the biomechanical effects of senescent fibroblasts on ECM homeostasis. We further argue that our platform offers a unique solution to investigate ECM remodeling not only in aging but also fibrosis, cancer progression, or regenerative medicine strategies
Toward Next-Generation Bioelectronic Interfaces for In Vitro Neural Network Analysis Using 3D Nanoelectrodes
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Etudes des mécanismes de perte d'expression plasmidique chez Cupriavidus necator au cours de la production hétérologue d'isopropanol : analyse à l’échelle de la cellule unique et des sous-populations.
No full textThe loss of production has long been observed in axenic bacterial bioprocesses, and is known to be related to the many numbers of generations occurring in industrial processes. This leads to population diversification through stochastic processes surrounding cell metabolism and adaptive mutations in the presence of stress. Production instability is even more pronounced in engineered strains with plasmid-based production operons. In this work we have explored the effect of burdensome expression on strain expression stability using engineered Cupriavidus necator Re2133 with a plasmid-based recombinant isopropanol operon. Through techno-economic assessment, we have uncovered that strain stability has a large impact on the economic viability of the autotrophic bioproduction of isopropanol. Our results highlight the importance of expression stability. In order to study plasmid expression instability at single cell level, flow cytometry was used with a biosensing strain co-expressing eGFP constitutively under the non-native Lac promoter (Boy et al. (2022)). This sensor has been applied in fed-batch conditions parallel with an isopropanol producing strain and an eGFP-producing strain. This comparison highlighted conflicts in interactions between the isopropanol production pathway and the fluorescent reporter system. However, the mechanisms of plasmid expression heterogeneity during isopropanol expression have yet to be uncovered. In this work we have explored possible biases for faulty interpretation of the biosensor signal in the presence of isopropanol production including the effects of photobleaching and eGFP-stability. Furthermore, through shake flaks and bioreactor cultivations we have determined that the induction of the isopropanol operon led to the loss of plasmid expression. This was not caused by feed limitation, nor the presence of isopropanol. We explored whether the population heterogeneity concerning the plasmid expression stability could be influenced. To this end, the plasmid structure was altered in two ways: the plasmid backbone was exchanged, and gene duplications were removed from the isopropanol operon. Impact was seen on expression stability. The influence of the host strain on plasmid expression stability was also seen using PHB producer and PHB producer (H16) with the deletion of a putative defence mechanism (H16 DWadjet). The impact of the bioprocess was examined through continuous addition of selective pressure through kanamycin. Although this did not halt the expression loss, it did lead to the regaining of the plasmid-expressing population. Finally, we determined the mechanisms behind the plasmid expression loss through assessment of the plasmid copy number as well as through sequencing of the bulk biomass and single-cell colonies. With this work, a better understanding has been gained in the complexities of plasmid expression loss, and C. necator's multi-facetted approach to relieve itself of burdensome expression.La perte des performances de production est un phénomène bien connu dans les bioprocédés bactériens axéniques, étroitement liée au grand nombre de générations impliquées dans les procédés industriels. Ce phénomène entraîne une diversification des populations au cours de la production, résultant de processus stochastiques associés au métabolisme cellulaire et à des mutations adaptatives en réponse à des conditions de stress. Les souches génétiquement modifiées sont particulièrement sujettes à ces instabilités. Dans ce travail, nous avons exploré l’effet de l’expression hétérologue plasmidique d’une voix de biosynthèse d’isopropanol sur la robustesse d’une souche de C. necator Re2133. A travers une évaluation technico-économique, nous avons mis en évidence que la stabilité de la souche a un impact significatif sur la viabilité économique de la bioproduction autotrophe d’isopropanol. Nos résultats soulignent ainsi l’importance de la robustesse de la souche et de la stabilité de l’expression.Pour étudier l’instabilité de l’expression plasmidique à l’échelle de la cellule unique, un biocapteur a été développé dans des travaux antérieurs (C. Boy et al. 2022). La souche biocapteur co-exprime l’eGFP sous le contrôle d’un promoteur constitutif pLac, et l’opéron de synthèse de l’isopropanol sous le contrôle d’un promoteur inductible pBAD. Des cultures en mode fed-batch ont été réalisées avec ce biocapteur et comparées à une souche productrice d’isopropanol ainsi qu’à une souche productrice d’eGFP. Cette comparaison a mis en évidence des conflits d’interaction entre la voie de production d’isopropanol et le système rapporteur fluorescent. Cependant, les mécanismes d’hétérogénéité de l’expression plasmidique durant la production d’isopropanol restent à élucider.Dans le cadre de cette thèse, les biais potentiels d’interprétation du signal du biocapteur en condition de production d’isopropanol ont été explorés, en mettant particulièrement l’accent sur les effets du photoblanchiment et de la stabilité de l’eGFP. Par la mise en œuvre de cultures en flask agitée et en bioréacteur, il a été déterminé que l’induction de l’opéron isopropanol entraînait une perte d’expression plasmidique, sans que cela soit dû à une limitation ou à la présence d’isopropanol. De plus, l’impact de la construction plasmidique sur la stabilité de la souche a été évalué. À cette fin, la structure plasmidique a été modifiée de deux manières : en remplaçant le squelette plasmidique et en supprimant les duplications géniques de l’opéron isopropanol. L’influence de la souche hôte sur la stabilité de l’expression plasmidique a également été examinée en utilisant la souche sauvage (H16) naturellement productrice de PHB, et une souche dérivée de la souche (H16) délété d’un mécanisme de défense putatif (H16 ∆Wadjet). Par ailleurs, l’impact du bioprocédé a été évalué en appliquant une pression de sélection via l’ajout de kanamycine par pulse ou de manière continue. Bien que ces approches n’aient pas stoppé la perte d’expression, cela a contribué à reconstituer la population exprimant le plasmide. Enfin, les mécanismes sous-jacents à la perte d’expression plasmidique ont été explorés en évaluant le nombre de copies du plasmide et en séquençant à partir d’échantillons issus de la biomasse totale ainsi que de colonies isolées. Ces travaux nous ont permis d’acquérir une meilleure compréhension des complexités liées à la perte plasmidique et de l’approche multidimensionnelle de C. necator pour surmonter cette expression restrictive