HAL-INSA Toulouse
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Positive to negative photoconductance switching in plasmonic gold nanoparticle networks
No full textInternational audienceThe elaboration of versatile materials in which electrical conduction is tuned by light irradiation is of paramount relevance to such diverse applications as photodetectors, photodiodes, solar cells or light sensors. Although positive photoconductance is increasingly common, systems with negative photoconductance are scarcely reported. In this work, a switching from positive to negative photoconductance is observed upon simple annealing of well-organized networks of gold nanoparticles stabilized by dodecanethiols. The photoconductance properties are investigated experimentally using impedance spectroscopy. The measured Nyquist plots and resonance curves of the impedance are analyzed in terms of equivalent electrical circuits consisting in parallel resistance, capacitance and photoconductance. The positive and negative photo-current conversion efficiencies of the nanoparticles network are estimated k PPC = 389 ± 40 nS.W -1 .cm 2 and k NPC = -241 ± 40 nS.W -1 .cm 2 , respectively. With the aid of density functional theory calculations, the origin of the photoconductance is discussed, at the nanoscale level, in terms of changes of molecular conformation. Such molecular effects assist charge carrier tunneling between first neighbor nanoparticles, and favor the formation of traps introduced by the annealing of the sample. The present work contributes to the understanding of plasmo-electronic properties of hybrid molecule-nanoparticle self-assembled nano-structures
Heat transfer modelling of radiant flux from a halogen lamp for enhancing Infrared thermography simulation
No full textInternational audienceInfraRed Thermography (IRT) is widely used in Non-Destructive Evaluation (NDE) for its ability to provide real-time, two-dimensional, non-contact measurements of heat distribution. Enhancing the analysis of thermal results requires a comprehensive understanding of the entire measurement chain from the heat source, through propagation, to detection, signal processing and data interpretation, which demands an effective combination of simulation and experimental approaches. This study presents the modelling of heat transfer, with particular emphasis on accurately characterising the radiant heat flux emitted by a halogen lamp. A fluxmeter sensor was employed to measure the radiant heat flux at different distances and spatial locations. Subsequently, 3D heat transfer models incorporating these heat sources were established and applied to an Acrylonitrile Butadiene Styrene plate to investigate thermal behaviour and the influence of factors within the measurement chain. Critical parameters were also considered, including thermal conductivity, convective heat transfer coefficients, fluxmeter sensor sensitivity, heat flux characteristics and measurement methods. Simulation results were validated against experimental data using both an infrared camera and a pyrometer and demonstrated strong agreement. Relative errors were below 4.2 % for pyrometer measurements, whereas slightly higher errors, up to 5.9 % for IRT method, which is mainly attributed the influence of environmental factors on this technique. These findings confirm the accuracy and reliability of the calibrated heat source and modelling parameters. Integrating experimental data into the thermal simulation enhances both accuracy and consistency, thereby establishing a more robust framework for the application of numerical methods throughout the IRT measurement chain in NDE applications
On L¹ and time-optimal state transitions in piecewise linear models of gene-regulatory networks
No full textInternational audienceIn this paper, we investigate optimal state transfers for a generic class of piecewise-linear models widely used to qualitatively describe gene-regulatory networks. Motivated by the main practical drawbacks of artificially regulating gene expression through chemical inducers, the optimality of the transitions is defined as the convex combination of the total time and the L¹ cost of the control. Solutions are studied through a Hybrid Pontryagin's Maximum Principle approach, which allows to characterize the optimal trajectories and control for the general formulation of the problem. Then, we focus on two practical examples of two-dimensional regulatory networks: the bistable switch, for which the objective is to induce optimal transitions between its two stable steady states, and the damped genetic oscillator, where the goal is to induce sustained oscillatory behaviors. The resulting optimal control strategies can be expressed in state feedback form, involving both bang arcs and inactive control periods, and are shown to slide over certain separatrices of the uncontrolled system that characterize the boundaries of the admissibility set
Front-surface cooling of infrared thermophotovoltaic cells
No full textInternational audienceThis paper proposes a front-surface cooling method for thermophotovoltaic (TPV) cells utilizing microfluidic channels for efficient heat dissipation. Unlike conventional back-surface cooling, front-surface cooling minimizes thermal resistance by directly cooling the top surface of the cell. The microfluidic channel layer also functions as an antireflection layer through the gradual change in the refractive index. The proposed cooling method was evaluated using a thermo-fluid analysis, considering factors such as the emitter temperature, cell reflectance, thermal resistance, and fluid optical properties. We examined liquids with ideal absorption characteristics and actual liquids whose absorption coefficients were measured. The results showed that front-surface cooling significantly outperformed back-surface cooling in terms of the net power density. This method is particularly advantageous for high emitter temperatures or in cases where the thermal resistance between the cell and backsurface liquid is high. Moreover, this study highlights the potential application of the cooling method in bifacial TPV cells, which can generate electricity from thermal radiation incident on both sides. Bifacial cells offer higher power generation per unit area but face cooling challenges. The proposed cooling technique addresses these challenges, paving the way for innovative TPV system configurations and improved performance
High Temperature Operation and Spectral Stability of InGaN/GaN Ring Microlasers on Silicon
No full textInternational audienceIII-N ring microlasers on a silicon substrate with InGaN/GaN active layers emitting near 420 nm were investigated. The growth conditions and fabrication steps were optimized to realize stable lasing under optical pumping in cavities with a diameter of 6- 10 μ m. Chemically sensitive transmission electron microscopy images indicate that InGaN layers present in form of isolated islands. Between these InGaN islands, large areas of GaN are visible, forming barriers to lateral transport of free charge carriers in the active region and preventing their nonradiative surface recombination. For the first time, temperature stability of InGaN/GaN microring lasers characteristics are studied and lasing up to 100 degrees Celsius is demonstrated with the wavelength shift less than 1 nm. At room temperature, the threshold pump power is as low as 220 kW/cm 2 . The obtained results significantly expand the potential areas of application of III-N microlasers
From colloidal nanoparticles in non-polar solvents to 3D microstructures: a new paradigm in Convective Self-Assembly
No full textInternational audienceColloidal nanoparticles (NPs) exhibit unique and tunable physical properties, making them highly attractive for advanced applications in sensing, photonics, flexible electronics, and beyond. Harnessing these properties in functional devices often requires assembling NPs into three-dimensional (3D) microstructures that combine substantial thickness to enhance their functional response, micrometer-scale resolution for precise pattern definition, and high selectivity to minimize material loss. Directed assembly techniques aim to meet these stringent requirements but face significant challenges when NPs are dispersed in non-polar solvents, commonly used for their role in synthesis and colloidal stabilization. Indeed, such solvents hinder NP assembly because of their high wettability and volatility. These limitations are particularly pronounced in Convective Self-Assembly (CSA), which performs efficiently with aqueous dispersions but struggles with non-polar media.In this study, we investigate how the properties of non-polar solvents influence CSA on topographically patterned substrates. To overcome these issues, we propose an upgraded CSA method that combines solvent selection, surface functionalization, and controlled evaporation. This approach enables reproducible and precise assembly of NPs into micrometer-scale 3D structures. The method is versatile, compatible with various nanoparticle types and patterns, and allows sequential co-assembly on a single substrate, offering a scalable route for high-resolution nanomanufacturing of complex multifunctional architectures
Orchestrating on-board sensors for global hybrid robust stabilization of unicycles
No full textWe consider mobile robots described through unicycle dynamics equipped with on-board range sensors and cameras, one facing forward and one facing backward, providing measurements of the distance and misalignment to a target. We propose a hybrid control law combining the two on-board measurements and discuss stability results for the closed-loop expressed in the on-board camerabased coordinates, using Lyapunov-based arguments. We prove robustness of the stability properties to uncertainties affecting the sensors and external perturbations acting on the robot. The results are illustrated via simulations
Numerical analysis of the impact of water temperature setpoint and energy strategies on indoor pool performance
No full textInternational audienceIndoor swimming pools (ISPs) consume significant amounts of electrical and thermal energy to ensure the heating of water and air, ventilation, and maintaining adequate humidity levels. This is measured in GWh per year for large installations, such as Olympic swimming pools (SPs). In this paper, the problem is initially addressed using a phenomenological approach at steady state of the air-water coupling, based on a real case study. The aim is to identify the key phenomena and the constraints that are the most sensitive, including those related to water and air quality management. A key action lever is found in evaporation, and more specifically, water temperature and the indoor dewpoint temperature, which act as its precursors. In a second step, two different strategies were tested to reduce energy consumption for water heating. It was determined that a strategy which incorporates night setback in conjunction with a precise restart time yields a maximum gain of 4%. The second strategy aims to enhance the energy recovery of thermal solar panels by enabling slight overheating of the pool. Its large volume provides effective energy storage, with estimated energy savings of up to 17% for a 1◦ C overheating. This strategy appears to be a viable option, as it is straightforward to implement. However, the impact of water overheating on the energy consumption of AHU still needs to be analyzed and managed
