Imaging small-amplitude magnetization dynamics in a longitudinally magnetized microwire

Copyright © 2008 The American Physical SocietyWe have used time-resolved scanning Kerr microscopy to study spin waves in a magnetic microwire subjected to a bias magnetic field applied parallel to its long axis. The spin-wave spectra obtained from different points near one end of the wire reveal several normal modes. We found that modes of a higher frequency occupied regions located further from the end of the wire. This was interpreted in terms of the confinement of the spin-wave modes by a nonuniform demagnetizing field. Furthermore, at a particular distance from the end of the wire, two or more modes occupying different regions along the width of the wire were observed. This was interpreted in terms of the confinement of the spin-wave modes due to an asymmetric variation in the local angle between the static magnetization and the effective direction of the wave vector of the confined modes. Images of the dynamic magnetization that are acquired at fixed pump-probe time delays revealed stripes lying perpendicular to the long axis of the wire and, hence, to the applied magnetic field. We interpret the stripe pattern in terms of a collective mode of the quasiperiodic system of ripple domains existing within the polycrystalline sample. Cur results give an additional insight into the connection between the nonuniform static magnetic state in small magnetic elements and their precessional dynamics, which is fundamentally important for the design of future high-speed switching and spin-wave logic devices of magnonics

The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy

The CAT (Cherenkov Array at Themis) imaging telescope, equipped with a very-high-definition camera (546 fast phototubes with 0.12 degrees spacing surrounded by 54 larger tubes in two guard rings) started operation in Autumn 1996 on the site of the former solar plant Themis (France). Using the atmospheric Cherenkov technique, it detects and identifies very high energy gamma-rays in the range 250 GeV to a few tens of TeV. The instrument, which has detected three sources (Crab nebula, Mrk 421 and Mrk 501), is described in detail.Comment: 24 pages, 15 figures. submitted to Elsevier Preprin

Le modèle de texture sous-déterminé de March-Dollase influence-t-il la détermination structurale ?

International audienceFor a very long time, structural determination on powders has been carried out using the March-Dollase model [1,2] to compensate for poor intensity representations due to the existence of crystallographic texture. Although this model is integrated in most structural refinement software using the Rietveld method, and is in fact limited to the representation of particular textures (single or multi-component fibre textures in some software), to our knowledge the influence of its use on the atomic positions has not yet been conducted. The main objective of this study is to compare the structural results obtained from Bragg-Brentano powder diffraction measurements on the one hand and from full crystallographic texture measurements [3] on the other hand, on a standard NIST Corundum sample [4]. The first measurement is performed on a Bruker D8 Advance 2-circle high resolution diffractometer (Figure 1), and the second on an Inel-Thermofisher 4-circle diffractometer measuring complete patterns for each sample orientation (Figure 2). The first analysis consists of releasing the MD factor during structural refinement, the second of simultaneously refining the ODF to account for the actual texture of the sample. This study highlights a difference in free atomic positions between the two refinement methods and points to the need to take texture into account in a real way (i.e. to measure it completely).Depuis très longtemps la détermination structurale sur poudres s’opère en utilisant le modèle de March-Dollase [1,2] pour compenser les mauvaises représentations d’intensités dues à l’existence de texture cristallographique. Bien que ce modèle soit intégré à la plupart des logiciels d’affinement structural utilisant la méthode de Rietveld, et qu’il est de fait limité à la représentation de textures particulières (textures de fibres simples ou à plusieurs composantes de fibre dans certains logiciels), à notre connaissance l’influence de son utilisation sur les positions atomiques n’a pas encore été menée. L’objectif principal de cette étude est de comparer les résultats structuraux obtenus d’une part à partir de mesures de diffraction des rayons X sur poudre en mode Bragg-Brentano et d’autre part sur mesures complètes de textures cristallographiques [3], sur un échantillon standard de Corindon du NIST [4]. La première mesure est opérée sur un diffractomètre Bruker D8 Advance 2-cercles haute résolution (Figure 1), et la deuxième sur un diffractomètre Inel-Thermofisher 4-cercles mesurant les diagrammes complets pour chaque orientation d’échantillon (Figure 2). La première analyse consiste à libérer le facteur MD lors de l’affinement structural, la deuxième à affiner simultanément l’ODF afin de tenir compte de la texture réelle de l’échantillon. Cette étude permet de mettre en évidence une différence de positions atomiques libres entre les deux méthodes d’affinement et de pointer du doigt la nécessité de prendre la texture en compte de manière réelle (donc de la mesurer complètement)

Le modèle de texture sous-déterminé de March-Dollase influence-t-il la détermination structurale ?

International audienceFor a very long time, structural determination on powders has been carried out using the March-Dollase model [1,2] to compensate for poor intensity representations due to the existence of crystallographic texture. Although this model is integrated in most structural refinement software using the Rietveld method, and is in fact limited to the representation of particular textures (single or multi-component fibre textures in some software), to our knowledge the influence of its use on the atomic positions has not yet been conducted. The main objective of this study is to compare the structural results obtained from Bragg-Brentano powder diffraction measurements on the one hand and from full crystallographic texture measurements [3] on the other hand, on a standard NIST Corundum sample [4]. The first measurement is performed on a Bruker D8 Advance 2-circle high resolution diffractometer (Figure 1), and the second on an Inel-Thermofisher 4-circle diffractometer measuring complete patterns for each sample orientation (Figure 2). The first analysis consists of releasing the MD factor during structural refinement, the second of simultaneously refining the ODF to account for the actual texture of the sample. This study highlights a difference in free atomic positions between the two refinement methods and points to the need to take texture into account in a real way (i.e. to measure it completely).Depuis très longtemps la détermination structurale sur poudres s’opère en utilisant le modèle de March-Dollase [1,2] pour compenser les mauvaises représentations d’intensités dues à l’existence de texture cristallographique. Bien que ce modèle soit intégré à la plupart des logiciels d’affinement structural utilisant la méthode de Rietveld, et qu’il est de fait limité à la représentation de textures particulières (textures de fibres simples ou à plusieurs composantes de fibre dans certains logiciels), à notre connaissance l’influence de son utilisation sur les positions atomiques n’a pas encore été menée. L’objectif principal de cette étude est de comparer les résultats structuraux obtenus d’une part à partir de mesures de diffraction des rayons X sur poudre en mode Bragg-Brentano et d’autre part sur mesures complètes de textures cristallographiques [3], sur un échantillon standard de Corindon du NIST [4]. La première mesure est opérée sur un diffractomètre Bruker D8 Advance 2-cercles haute résolution (Figure 1), et la deuxième sur un diffractomètre Inel-Thermofisher 4-cercles mesurant les diagrammes complets pour chaque orientation d’échantillon (Figure 2). La première analyse consiste à libérer le facteur MD lors de l’affinement structural, la deuxième à affiner simultanément l’ODF afin de tenir compte de la texture réelle de l’échantillon. Cette étude permet de mettre en évidence une différence de positions atomiques libres entre les deux méthodes d’affinement et de pointer du doigt la nécessité de prendre la texture en compte de manière réelle (donc de la mesurer complètement)

Analyse combinée FluoX-caméra RVB et FluoX-DRX des gisements de latérite nickélifère de Nouvelle-Calédonie : nouvelle approche méthodique

International audienceAs part of the European SOLSA project, BRGM and CRISMAT are participating in the development of a multi-sensor expertise bench (SOLSA ID2A-ID2B). The major challenge of SOLSA is to understand the approach of a field geologist to samples in order to enable the retranscription of his knowledge in the form of intelligent algorithms. In this context, a sample prepared in three forms (powder, thin slide and raw sample) was selected in this study. It is a serpentinised harzburgite. The sample was first characterised in the laboratory (X-ray fluorescence, ICP-AES, and X-ray diffraction) and then analysed under these different preparations on SOLSA ID2B. This study showed that the field approach allows similar results to those obtained in the laboratory but with a higher profitability. By comparing the results obtained on the three types of preparation, it was shown that the influence of the sample preparation is minor on the combined FluoX-DRX results. Finally, by creating an algorithm allowing the superposition of RGB images and the spatial distribution of chemical elements (Fig 1), it was possible to improve the knowledge of substitutions within the phases present, the location of certain elements in preferential zones and the element/element and phase/element correlations.Dans le cadre du projet européen SOLSA, le BRGM et le CRISMAT, participent au développement d’un banc d’expertise multi-capteurs (SOLSA ID2A-ID2B). L’enjeu majeur de SOLSA, est d’appréhender l’approche d’un géologue de terrain sur des échantillons afin de permettre une retranscription de son savoir sous forme d’algorithmes intelligents. Dans ce contexte, un échantillon préparé sous trois formes (poudre, lame mince et échantillon brut) a été sélectionné dans cette étude. Il s’agit d’une harzburgite serpentinisée. L’échantillon a d’abord été caractérisé en laboratoire (fluorescence X, ICP-AES, et diffraction des rayons X) puis analysé sous ces différentes préparations sur SOLSA ID2B. Cette étude a permis de montrer que l’approche de terrain admet des résultats similaires aux résultats obtenus en laboratoire mais avec une rentabilité plus élevée. En comparant les résultats obtenus sur les trois types de préparation, il a été démontré que l’influence de la préparation de l’échantillon est mineure sur les résultats combinés FluoX-DRX. Enfin, par la création d’algorithme permettant la superposition d’image RVB et la distribution spatiale des éléments chimiques (Fig 1), il a été possible d’améliorer la connaissance des substitutions au sein des phases présentes, la localisation de certains éléments dans des zones préférentielles et les corrélations éléments/éléments et phases/éléments

Analyse combinée FluoX-caméra RVB et FluoX-DRX des gisements de latérite nickélifère de Nouvelle-Calédonie : nouvelle approche méthodique

International audienceAs part of the European SOLSA project, BRGM and CRISMAT are participating in the development of a multi-sensor expertise bench (SOLSA ID2A-ID2B). The major challenge of SOLSA is to understand the approach of a field geologist to samples in order to enable the retranscription of his knowledge in the form of intelligent algorithms. In this context, a sample prepared in three forms (powder, thin slide and raw sample) was selected in this study. It is a serpentinised harzburgite. The sample was first characterised in the laboratory (X-ray fluorescence, ICP-AES, and X-ray diffraction) and then analysed under these different preparations on SOLSA ID2B. This study showed that the field approach allows similar results to those obtained in the laboratory but with a higher profitability. By comparing the results obtained on the three types of preparation, it was shown that the influence of the sample preparation is minor on the combined FluoX-DRX results. Finally, by creating an algorithm allowing the superposition of RGB images and the spatial distribution of chemical elements (Fig 1), it was possible to improve the knowledge of substitutions within the phases present, the location of certain elements in preferential zones and the element/element and phase/element correlations.Dans le cadre du projet européen SOLSA, le BRGM et le CRISMAT, participent au développement d’un banc d’expertise multi-capteurs (SOLSA ID2A-ID2B). L’enjeu majeur de SOLSA, est d’appréhender l’approche d’un géologue de terrain sur des échantillons afin de permettre une retranscription de son savoir sous forme d’algorithmes intelligents. Dans ce contexte, un échantillon préparé sous trois formes (poudre, lame mince et échantillon brut) a été sélectionné dans cette étude. Il s’agit d’une harzburgite serpentinisée. L’échantillon a d’abord été caractérisé en laboratoire (fluorescence X, ICP-AES, et diffraction des rayons X) puis analysé sous ces différentes préparations sur SOLSA ID2B. Cette étude a permis de montrer que l’approche de terrain admet des résultats similaires aux résultats obtenus en laboratoire mais avec une rentabilité plus élevée. En comparant les résultats obtenus sur les trois types de préparation, il a été démontré que l’influence de la préparation de l’échantillon est mineure sur les résultats combinés FluoX-DRX. Enfin, par la création d’algorithme permettant la superposition d’image RVB et la distribution spatiale des éléments chimiques (Fig 1), il a été possible d’améliorer la connaissance des substitutions au sein des phases présentes, la localisation de certains éléments dans des zones préférentielles et les corrélations éléments/éléments et phases/éléments

Increasing exploration efficiency with SOLSA Expert System

SOLSA is the first automated expert system for on-site cores analysis. The scope is to provide a prototype to be an innovative and necessary tool for geo-metallurgy, in order to optimize the valorization of the ore. The Expert System consists in the combination of an integrated drilling rig providing cores of high quality, an automated scanner and phase identification software, developed for nickel laterites and bauxites but usable as well in other sectors. SOLSA combines non-destructive sensors and the whole system is driven by an innovative, user-friendly and intelligent software. SOLSA provides more complete information while optimizing the exploration stage, with a significant reduction of costs and return time. Such objective involves, in the first place, to fast, cheaper and systematic acquisition of the data needed for optimizing the process. The adding value takes place first at the exploration or grade control stage, furnishing systematic characterization and regionalization of the different types of ore. Then such information can be used for improving the ore scheduling at the mining and processing stages, toward improving the recovery and efficiency of the processin

Spectrum of TeV gamma-rays from the Crab Nebula by the CAT Cherenkov Imaging Telescope

For an anthropology of communication What do we mean by “anthropology of communication”? The term is used for the ethnographic analysis of human communication as well as for behavioural changes due to the application of new information technologies. We put forward an introduction (below), to be followed by seven texts: three reflections on “anthropology”, three on “communication” and one concerned with the overlap between these two concepts. Starting with December 2004, these papers will be accessible at the rate of one paper a month. Our intention is to search for all terms associated with “anthropology” and “communication”, to create an inventory of representative semantic fields for them, to indicate current overlaps established by colleagues carrying out communications and information research as well as possible overlaps in the future

Spectrum of TeV gamma-rays from the Crab Nebula by the CAT Cherenkov Imaging Telescope

For an anthropology of communication What do we mean by “anthropology of communication”? The term is used for the ethnographic analysis of human communication as well as for behavioural changes due to the application of new information technologies. We put forward an introduction (below), to be followed by seven texts: three reflections on “anthropology”, three on “communication” and one concerned with the overlap between these two concepts. Starting with December 2004, these papers will be accessible at the rate of one paper a month. Our intention is to search for all terms associated with “anthropology” and “communication”, to create an inventory of representative semantic fields for them, to indicate current overlaps established by colleagues carrying out communications and information research as well as possible overlaps in the future