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AlN film thickness effect on photoluminescence properties of AlN/carbon nanotubes shell/core nanostructures for deep ultra-violet optoelectronic devices
No full textInternational audienceAluminum nitride (AlN) nanostructures are very attractive in various optoelectronic applications such as deep ultraviolet light emitting devices. The fabrication of these AlN nanostructures with good crystalline quality and compatibility in line with other micro-fabrication processes has significant importance for practical applications. AlN films of different thickness values were deposited via DC reactive magnetron sputtering over vertically aligned multiwalled carbon nanotube (CNTs) arrays to obtAln AlN/CNTs vertically-aligned shell/core nanostructure assembly. Such hybrid nanostructures were characterized using scanning electron microscope, transmission electron microscope, X-ray diffraction, Raman spectroscopy and time-resolved photoluminescence spectroscope (TR-PL) techniques. The results indicated that AlN/CNTs have a nanorods structure morphology with good AlN crystalline quality. The PL measurements revealed a maximum increase in the luminescent intensity of the exciton band in case of AlN/CNTs with 600 nm thick AlN layer, which is many orders of magnitude higher than that of AlN film produced over silicon substrate. It is anticipated that synergistic effects of CNTs and AlN through an increase in the specific surface area and oxygen-induced defects cause enhancement in the photoluminescence properties, making these hybrid nanostructures a promising candidate for optoelectronic applications
Self-Triggered Control for Sampled-data Systems using Reachability Analysis
No full textInternational audienceIn this work, we design the sampling policy in sampled-data systems. It is known that implementing such systems using variable sampling periods, instead of a constant period, is more efficient in terms of performance and resource utilization. Thus, after rewriting the system in the framework of impulsive linear systems, a self-triggered control strategy obtained using reachability analysis is proposed in order to define the sampling period as a function of the state
Upwind-downwind asymmetry of the sea backscattering normalized Radar cross section versus the skewness function
No full textInternational audienceFrom the first-order small slope approximation, thispaper presents a closed-form expression of the sea backscatteringNRCS (normalized radar cross section) versus the skewnessfunction to predict the upwind-downwind asymmetry. This effectis produced by the fact that the surface height distributionslightly deviates from a Gaussian one. Introducing the azimuthalproperty of the sea height autocorrelation and skewness (spatial)functions, the integration over the azimuthal direction can bedone analytically, whereas the integration over the radial distancecan be done by using the property that the skewness correlationdistance is much smaller than that of the gravity waves. Then,the backscattering NRCS is expressed from the sea skewnessspectrum at a wave number different of the Bragg wave number.In addition, a simple inversion algorithm is proposed to performthe parameters of the skewness function from experimental datain C and Ku bands
Learning Collaborative Foraging in a Swarm of Robots using Embodied Evolution
No full textInternational audienceIn this paper, we study how a swarm of robots adapts over time to solve a collaborative task using a distributed Embodied Evolutionary approach , where each robot runs an evolutionary algorithm and they locally exchange genomes and fitness values. Particularly, we study a collabo-rative foraging task, where the robots are rewarded for collecting food items that are too heavy to be collected individually and need at least two robots to be collected. Further, the robots also need to display a signal matching the color of the item with an additional effector. Our experiments show that the distributed algorithm is able to evolve swarm behavior to collect items cooperatively. The experiments also reveal that effective cooperation is evolved due mostly to the ability of robots to jointly reach food items, while learning to display the right color that matches the item is done suboptimally. However, a closer analysis shows that, without a mechanism to avoid neglecting any kind of item, robots collect all of them, which means that there is some degree of learning to choose the right value for the color effector depending on the situation
Switched beam patch array antenna using SPDT GaN HEMT switches
No full textInternational audienceIn this article, a single-fed 4-panel 4 x 1 patch array antenna operating at 2.43 GHz with switched beam capability is proposed. The design allows the beam to be switched between 4 discrete directions giving 360 degrees coverage. The antenna beam is switched over the azimuth plane for phi=0 degrees, phi=90 degrees, phi=180 degrees, and phi=270 degrees. The beam control is achieved using GaN-based HEMT SPDT switches. Only 3 SPDT switches are integrated directly into the structure, allowing its nature to be electrically controlled over the desired 4 directions. Simulated and measured reflection coefficients and radiation patterns for the 4 cases are presented and discussed, showing good agreement. The antenna gain is around 3.8 dB including switches losses at 2.43 GHz
Limits of DC bus behavior on photovoltaic systems in distributed architecture
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Reduction of Power Transformer Core Noise Generation due to Magnetostriction Induced Deformations using Fully Coupled Finite Element Modeling Optimization Procedures
No full textInternational audienceThis work focuses on the development of an algorithm for the prediction of transformer core deformation, using a fully coupled magneto-mechanical approach. An imposed magnetic flux method coupled with finite element modeling is employed for the magnetic resolution. The constitutive law of the material is considered with a simplified multi-scale model (SMSM) describing both magnetic and magnetostrictive anisotropies. Magnetostriction is introduced as an input free strain of a mechanical problem to get the deformation and displacement fields. A 3D estimation of acoustic power is carried out to evaluate the global core deformation and acoustic noise level. The numerical process is applied to a three-phase transformer made of Grain Oriented (GO) FeSi core, leading to a set of noise estimation for different flux excitations and core geometries
Visible and near-infrared photo-detector combining Polysilicon TFT and PbS quantum dots Semiconductor Technology for Ultra Large Scale Integrated Circuits and Thin Film Transistors VI
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Formal verification of protocols based on short authenticated strings
No full textInternational audienceModern security protocols may involve humans in order to compare or copy short strings between different devices. Multi-factor authentication protocols, such as Google 2-factor or 3D-secure are typical examples of such protocols. However, such short strings may be subject to brute force attacks. In this paper we propose a symbolic model which includes attacker capabilities for both guessing short strings, and producing collisions when short strings result from an application of weak hash functions. We propose a new decision procedure for analysing (a bounded number of sessions of) protocols that rely on short strings. The procedure has been integrated in the AKISS tool and tested on protocols from the ISO/IEC 9798-6:2010 standard
