International Professional University of Technology in Nagoya Repository
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KNN perovskite thin films grown by PLD for tunable microwave devices: influence of the deposition parameters
No full textInternational audienc
Millimeter-Wave Fresnel Zone Plate Lens with new technological process
No full textInternational audienceFresnel Zone Plate lens (FZPL) antennas working in the V and W band are reported in this paper with half and quarter phase correction respectively. A low cost and straightforward technological process is used to manufacture the dielectric lenses using only one foam material where the dielectric constant is controlled. Simulation and measurement results are in good agreement that confirms the viability of such a process to fabricate inhomogeneous structures. Good loss efficiency of 73 and 55% are obtained at 60 and 85 GHz respectively with the two different FZPL designs. © 2016 Cambridge University Press and the European Microwave Association
MOSFET et IGBT : circuits de commande, sécurisation et protection du composant à semi-conducteur
No full textNational audienceThis article deals with advanced gate drivers for MOSFET and IGBT power electronics components.It details with a pragmatic approach close to the application, methods used for power componentssecuring and protection. It consists in four main parts which are the transmission of switchingcommands, structures of gate driving circuits, structures for over-current monitoring, soft shut downpower components protection and Active Clamping.Cet article s'intéresse aux circuits de commande évolués pour les composants de type MOSFET ouIGBT utilisés en électronique de puissance. Il aborde en détail, par une approche très pragmatique etproche de l'application, les méthodes de sécurisation et de protection des composants de puissance àsemi-conducteur. Il est construit autour de quatre parties principales qui sont la transmission desordres de commande, les structures des étages de pilotage de la grille, les méthodes de détection ducourant de court-circuit, le mécanisme de protection par le blocage en douceur du composant depuissance et/ou par sa remise en conduction partielle
Construction of a stochastic model of track geometry irregularities and validation through experimental measurements of dynamic loading
No full textInternational audienceThis paper describes the construction of a stochastic model of urban railway track geometry irregularities, based on experimental data. The considered irregularities are track gauge, su-perelevation, horizontal and vertical curvatures. They are modelled as random fields whose statistical properties are extracted from a large set of on-track measurements of the geometry of an urban railway network. About 300 to 1000 terms are used in the Karhunen-Lò eve/Polynomial Chaos expansions to represent the random fields with appropriate accuracy. The construction of the random fields is then validated by comparing on-track measurements of the contact forces and numerical dynamics simulations for different operational conditions (train velocity and car load) and horizontal layouts (alignment, curve). The dynamics simulations are performed both with and without randomly generated geometrical irregularities for the track. The power spectrum densities obtained from the dynamics simulations with the model of geometrical irregularities compare extremely well with those obtained from the experimental contact forces. Without irregularities, the spectrum is 10 to 50 dB too low
Modélisation par la méthode Lattice Boltzmann de la diffusion de chaleur et d’humidité dans des matériaux biosourcés à partir de leur morphologie 3D
No full textAs thermal performance of buildings is increasing, the simulation codes used during design require more accurate construction material data. Moreover, the use of bio-based materials which are hygroscopic (their moisture content balances with the ambient moist air) is booming. Their thermal conductivity and mass diffusivity must therefore be accurately characterized. A key factor affecting these properties is the microstructure of the materials. This work is dedicated to the prediction of macroscopic properties of spruce and fibreboards (heterogeneous and anisotropic materials) from their real 3D morphology. This is obtained by synchrotron X-ray microtomography, a powerful and nondestructive technique to characterize the internal structure of materials. Image processing allows the segmentation of the solid and gaseous phases. To model heat and mass diffusion, we choose the Lattice Boltzmann method because of its simple numerical development, suitability for parallel computing and easy processing of complex morphologies. The equivalent thermal conductivity and mass diffusivity are calculated in three orthogonal directions for each material. The results highlight the influence of the internal structure and the strong anisotropy of the materials studied (ratio of 2 between tangential and longitudinal directions of wood for heat diffusion and of 30 for mass diffusion). The transverse thermal conductivity of the lightweight board is about 0,04 W m−1 K−1.Avec la performance thermique croissante des bâtiments, les codes de simulation utilisés en conception requièrent des données de plus en plus précises sur les matériaux de construction. De plus, l’utilisation de matériaux biosourcés qui sont hygroscopiques (leur teneur en eau s’équilibre avec l’air humide ambiant) est en pleine expansion. Leur conductivité thermique et leur diffusivité massique doivent ainsi être caractérisées précisément. Un facteur essentiel affectant ces propriétés est la microstructure des matériaux. Ce travail de thèse propose de prédire les propriétés macroscopiques d’épicéa et de panneaux de fibres de bois (matériaux hétérogènes et anisotropes) à partir de leur morphologie réelle 3D. Celle-ci est obtenue par micro-tomographie synchrotron aux rayons X, outil très performant pour caractériser la structure interne d’un matériau de façon non destructive. Un traitement d’images permet de segmenter les phases solide et gazeuse. La méthode numérique choisie pour modéliser la diffusion de chaleur et de masse est la méthode Lattice Boltzmann car elle est simple à implémenter et à paralléliser et qu’elle peut facilement traiter des morphologies complexes. Les conductivités thermiques et diffusivités massiques équivalentes sont calculées dans trois directions orthogonales pour chaque matériau. Les résultats mettent en évidence l’influence de la structure interne et la forte anisotropie des matériaux étudiés (rapport 2 entre les directions tangentielle et longitudinale du bois en thermique et 30 en massique). La conductivité thermique transversale du panneau léger est de 0,04 W m−1 K−1
Evaluation of Currents Induced in Human Body by Plane Wave Exposure At 1-90 MHz
No full textInternational audienceIn existing exposure standards and guidelines the relationship between dosimetric quantities at a given frequency is not always consistent as some simultaneously applied limits are more restrictive than others, e.g. limits on induced currents compared to those on external electric field or specific absorption rate (SAR). To evaluate the current induced in the human body in 1 – 90 MHz range, we propose an equivalent circuit composed of two elements: the first one provides the voltage at human body mid-height and the second one describes the equivalent human body impedance. Then, assuming that the human body is equivalent to an antenna between 1 and 90 MHz, we calculate induced currents at the human body height. Using the relationship between external electric field and voltage at the body mid-height, we calculate the current along the body and suggest updated limits on induced currents more consistent with the external electric field limits
Information-Estimation relationship in mismatched Gaussian channels
No full textInternational audienceIn this paper, we investigated the connection between information and estimation measures for mismatched Gaussian models. In addition to the input prior mismatch we take into account the noise mismatch and establish a new relation between relative entropy and excess mean square error. The derived formula shows that the input prior mismatch may be cancelled by the noise mismatch. Finally, an example illustrates the impact of model mismatches on estimation accuracy
The HiPEAC Vision 2017
No full textInternational audienceInformation technology is one of the cornerstones of modern society and it is evolving rapidly: while the main challenges identified in the HiPEAC Vision 2015 remain valid and have even increased in importance, new challenges are ahead of us.Computers are disappearing from view. They are taking on new forms, such as cars, smart meters, thermostats, and so on. They communicate with their users using voice, sound, pictures and video, closely resembling human interaction. We are entering the Artificial Intelligence era. This will not only change how we interact with machines, but it will also redefine how we instruct a machine what to do: less programming and more learning.The function of the computer is shifting from carrying out computational tasks to provide answers to numerical problems, to working together with humans (what we call the beginning of the Centaur Era), augmenting reality to assist us, or even creating virtual worlds for us to explore: the cyber-physical entanglement between the physical and virtual world.Computers will increasingly interact with the physical world, leading to a expansion from security into safety. Humans need to trust both the machines and the information that they keep about us, and therefore enforcement of security and privacy is of paramount importance.For compute-intensive tasks, we will continue to use the cloud and supercomputers (HPC); this means that connectivity is crucial, yet local processing is becoming increasingly important. The increasing computational requirements are making computer system architects look for accelerators for specialized tasks, diverting in many cases from the traditional Von Neumann architecture.Energy efficiency of computing systems remains a major challenge for the coming years.As the cost per transistor is no longer decreasing, we might see diversified paths for using silicon technology: many designs will not use the latest technology node, but the more mature (and cheaper) one. It is also the right time to revisit the basic assumptions in order to open new tracks and approaches and to eventually reinvent computing.With the flood of new systems and new system architectures, increasing attention must be paid to composability and interoperability between systems. The complexity of the new systems will be so high that human designers will only be able to master it with the help of computers using AI-based techniques. Innovative approaches will be required to ensure that the systems will do what they are supposed to do, both at the functional and at the non-functional level (e.g. timing requirement or reliability). We need to develop design techniques that go beyond predictability by design and allow the building of reliable systems from unreliable parts.Finally, holistic approaches, implying multi-disciplinary techniques, will be needed in order to meet all the requirements of trustability, efficiency and cost
X-ray Computed Tomography using a sparsity enforcing prior model based on Haar transformation in a Bayesian framework
No full textInternational audienceX-ray Computed Tomography (CT) has become a hot topic in both medical and industrial applications in recent decades. Reconstruction by using a limited number of projections is a significant research domain. In this paper, we propose to solve the X-ray CT reconstruction problem by using the Bayesian approach with a hierarchical structured prior model basing on the multilevel Haar transformation. In the proposed model, the multilevel Haar transformation is used as the sparse representation of a piecewise continuous image, and a generalized Student-t distribution is used to enforce its sparsity. The simulation results compare the performance of the proposed method with some state-of-the-art methods