Radar, without tears

A brief introduction to radar: principles, Doppler effect, antennas, waveforms, power budget - and future radars. [13 pages

Dynamic permeability in soft magnetic composite materials

International audienceThis article reports on an isotropic model of the magnetic susceptibility based on an average field theory and proposes to predict the dynamic behaviors of powder magnetic materials. It was essentially built around a so-called effective demagnetizing factor capable of taking the particle shapes into account. So, for a population of randomly distributed particles of anisotropic shapes like, for instance, needles or flakes, we show that the effective demagnetizing factor of this population of particles can be significantly lowered with regard to the well known value of 1/3 classically used to represent the isotropy state. This phenomenon is interpreted as the natural tendency of particles to form clusters to which a moving demagnetizing factor must be assigned. Taking then the aggregation process of particles into account, the ability of the model to predict the dynamic properties of many composite magnetic materials is successfully demonstrated. Our development is illustrated by experimental results concerning a nickel-zinc ferrimagnetic (Ni0.7Zn0.3Fe2O4) powder

Ferromagnetic resonance of isotropic heterogeneous magnetic materials: theory and experiments

International audienceExperimental variations of the ferromagnetic resonance (FMR) recorded on soft composite bodies are presented and their interpretation is undertaken. A successful application is performed for the Kittel expression of the FMR, initially written for an ellipsoid placed in vacuum, to a magnetic inclusion of the composite. This model includes the demagnetizing effects due to the magnetic inclusions

Propriétés hyperfréquences de matériaux composites à base de poudres de ferrites doux

Nous présentons un modèle capable de prédire l'évolution statique et dynamique de la susceptibilité magnétique des matériaux composites isotropes en fonction de la concentration. Ce modèle simple s'appuie sur deux paramètres scalaires. Le premier est la susceptibilité intrinsèque i qui ne dépend que de la composition chimique de la poudre utilisée et dont la valeur se rapproche de celle de la susceptibilité rotationnelle. Le second est le coefficient effectif de forme N, rendant compte de l'aspect hétérogène de la matière et des effets démagnétisants; sa valeur est inférieure à 1/3 et dépend de la concentration en matière magnétique

Bayesian Sparse Fourier Representation of Off-Grid Targets

We consider the problem of estimating a finite sum of cisoids via the use of a sparsifying Fourier dictionary (problem that may be of use in many radar applications). Numerous signal sparse representation (SSR) techniques can be found in the literature regarding this problem. However, they are usually very sensitive to grid mismatch. In this paper, we present a new Bayesian model robust towards grid mismatch. Synthetic and experimental radar data are used to assess the ability of the proposed approach to robustify the SSR towards grid mismatch

Bayesian sparse Fourier representation of off-grid targets with application to experimental radar data

The problem considered is the estimation of a finite number of cisoids embedded in white noise, using a sparse signal representation (SSR) approach, a problem which is relevant in many radar applications. Many SSR algorithms have been developed in order to solve this problem, but they usually are sensitive to grid mismatch. In this paper, two Bayesian algorithms are presented, which are robust towards grid mismatch: a first method uses a Fourier dictionary directly parametrized by the grid mismatch while the second one employs a first-order Taylor approximation to relate linearly the grid mismatch and the sparse vector. The main strength of these algorithms lies in the use of a mixed-type distribution which decorrelates sparsity level and target power. Besides, both methods are implemented through a Monte-Carlo Markov chain algorithm. They are successfully evaluated on synthetic and experimental radar data, and compared to a benchmark algorith

Simulation and Visualisation of Functional Landscapes: Effects of the Water Resource Competition between Plants

A-07-30International audienceVegetation ecosystem simulation and visualisation are challenging topics involving multidisciplinary aspects. In this paper, we present a new generic frame for the simulation of natural phenomena through manageable and interacting models. It focuses on the functional growth of large vegetal ecosystems, showing coherence for scales ranging from the individual plant to communities and with a particular attention to the effects of water resource competition between plants. The proposed approach is based on a model of plant growth in interaction with the environmental conditions. These are deduced from the climatic data (light, temperature, rainfall) and a model of soil hydrological budget. A set of layers is used to store the water resources and to build the interfaces between the environmental data and landscape components: temperature, rain, light, altitude, lakes, plant positions, biomass, cycles, etc. At the plant level, the simulation is performed for each individual by a structural-functional growth model, interacting with the plant's environment. Temperature is spatialised, changing according to altitude, and thus locally controls plant growth speed. The competition for water is based on a soil hydrological model taking into account rainfalls, water runoff, absorption, diffusion, percolation in soil. So far, the incoming light radiation is not studied in detail and is supposed constant. However, competition for light between plants is directly taken into account in the plant growth model. In our implementation, we propose a simple architecture for such a simulator and a simulation scheme to synchronise the water resource updating (on a temporal basis) and the plant growth cycles (determined by the sum of daily temperatures). The visualisation techniques are based on sets of layers, allowing both morphological and functional landscape views and providing interesting tools for ecosystem management. The implementation of the proposed frame leads to encouraging results that are presented and illustrate simple academic cases

La Pierre philosophale

L’enjeu d’une édition critique du canevas de La Pierre philosophale, de Thomas Corneille et Donneau de Visé, publiée et représentée en 1681, est triple : d’abord, c’est un des plus longs canevas imprimés en langue française de cette période ; ensuite, la minutie de sa transcription présente un intérêt dramaturgique indéniable ; enfin, c’est un point de cristallisation non seulement dans l’histoire des formes du théâtre du merveilleux, autrement dit du théâtre machinique à effets, par son caractère hybride, mais encore dans l’histoire des mentalités et en particulier, du rapport au merveilleux, par son caractère syncrétique. Comédie de la déconstruction métathéâtrale de l’illusion, du démontage systématique de toute forme de mystification et de croyance, la pièce procède dans le même temps à un curieux réenchantement du monde, par une sorte de retour du refoulé qui passe par la réappropriation du pouvoir fantasmatique, imaginaire et symbolique de la question alchimique. L’introduction et l’édition du canevas de la pièce proposent un certain nombre de pistes dramaturgiques et de clefs herméneutiques pour mesurer les implications politiques du merveilleux théâtral, et pour entrer dans ce qu’on pourrait appeler une « alchimie dramaturgique », c’est-à-dire une esthétique combinatoire et métamorphique.La Pierre philosophale: Re-enchanting the World in the 17th Century Theatrical Wonderland (followed by an edition of the Play’s Summary). This critical edition of the summary of La Pierre philosophale (The Philosophical Stone), a play by Thomas Corneille and Donneau de Visé published and staged in 1681, will be of interest to scholars for at least three reasons: first, it is one of the longest plot summaries printed in French during this period; second, the details of the transcription reveal a lot about the dramaturgy of the time; third, this text crystallizes a unique moment both in the history of stage machinery and in the history of the “merveilleux”. Through its meta-theatrical unveiling of illusions, this comedy systematically deconstructs all forms of beliefs and mystifications, while it simultaneously re-enchants the world by staging the imaginary and symbolic powers of the alchemic fantasy. The introduction and the edition to the plot summary provide a number of clues designed to help the reader measure the political implications of the theatrical “merveilleux” and enter into the metamorphic esthetics of the dramaturgic alchemy