M. Le Floc'h

The MUSE second-generation VLT instrument

Summary: The Multi Unit Spectroscopic Explorer (MUSE) is a second-generation VLT panoramic integral-field spectrograph currently in manufacturing, assembly and integration phase. MUSE has a field of 1x1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by the VLT ground layer adaptive optics ESO facility using four laser guide stars. The instrument is a large assembly of 24 identical high performance integral field units, each one composed of an advanced image slicer, a spectrograph and a 4kx4k detector. In this paper we review the progress of the manufacturing and report the performance achieved with the first integral field unit.

Extension of the effective medium approximation for determination of the permeability tensor of unsaturated polycrystalline ferrites

This paper presents a physical model of the properties of polycrystalline ferrites below magnetic saturation, a common condition in many applications of ferrites in microwave devices. The properties are mainly characterized through the elements of the effective permeability tensor as functions of magnetization state, anisotropy field, and frequency. Partially magnetized states are characterized by a suitable distribution of magnetic domains over orientations. The magnetic domain shapes studied were cylinders and spheres. Homogeneity of the medium is obtained in the effective medium approximation, which allows us to treat heterogeneous magnetic materials as a function of the volume fraction of nonmagnetic matter present in the material. The model gives all the components of the permeability tensor in a single calculation phase. The paper presents results for different partially magnetized states at remanence (with no external field applied) and compares them with empirical formulations of permeability tensor components, in their domain of validity.

A physical model for heterogeneous magnetic materials

Abstract A macroscopic transposition of the composite state (a mixture of magnetic and non-magnetic millimetre-sized balls) is proposed to interpret and anticipate the properties of the heterogeneous magnetic materials. The model is supported by a simple theory leading to a useful relationship connecting the effective susceptibility to the basic properties of the material.

Theoretical and experimental determination of the permeability tensor components of magnetized ferrites at microwave frequencies

We compare the diagonal /spl mu/ and off-diagonal /spl kappa/ permeability tensor components of magnetized polycrystalline ferrites given by the theoretical model of Gelin and Berthou with experimental ones at microwave frequencies. We used a broad-band and noniterative measurement technique recently developed within our research group. Whatever the ferrite magnetization state is, simulated and measured /spl mu/ and /spl kappa/ points agree well. This study provides an experimental validation of the Gelin-Berthou model. Moreover, by using this characterization method, we show how the measurement of the magnetic properties can be affected by the size of the ferrite sample under test.

Effect of pressure on soft magnetic materials

After a review of previous work, the authors show their results obtained in the study of the effect of pressure on the magnetization mechanisms of polycrystalline soft ferrites up to 1.5 kbar and in a temperature range from 263°K to 573°K. Three kinds of pressures were applied : hydrostatic pressure, lateral pressure inducing stresses along the director circles of toroids and pressure perpendicular to the plane surfaces of toroids. All the results concerning reversible and irreversible magnetization mechanisms under hydrostatic pressure are explained from an unique idea: the change in the topography of domain walls in the grains due to random stresses from the hydrostatic pressure because of compressibility anisotropy. That was confirmed by the effect of directional stresses and by a pressure induced hysteresis. The origin of the compressibility anisotropy was found in the closed porosity.

Effect of the magnetic fraction on the complex susceptibility of soft magnetic composite materials

Abstract A model for the description of soft magnetic composite materials has been developed and tested in frequency through two basic behaviours: the relaxation-type mechanism and the resonance process described by the Gilbert modification of the Landau-Lifshitz equation. Prediction and comparison with experimental data have been found to be very good.

Static and magic angle spinning 31P NMR spectroscopy of two natural plasma membranes

Static and magic angle spinning 31P NMR spectroscopy was used for the first time in natural plasma membranes from erythrocytes and skeletal muscle to study phospholipid arrangement and composition. Typical static powder‐like spectra were obtained showing that phospholipids were in a bilayer arrangement. Magic angle spinning narrowed spectra into two components. The first one corresponded to phosphatidylcholine and the second one to the other phospholipids with intensities in agreement with the known phospholipid composition. These findings show that NMR data previously acquired using model membranes can be transposed to studies on phospholipids in their natural environment.

Theoretical and experimental modelling of composites with oriented soft magnetic particles

Abstract We present susceptibility measurements for systems of macroscopic soft magnetic particles (short rods, cylinders, oblate ellipsoids of millimetric size) embedded in a non-magnetic matrix and oriented along the field. Assumption of the effective medium theory allows the association of a critical fraction of magnetic matter with the component of a tensorial demagnetizing factor which is associated with the applied field direction.

Study of transverse susceptibility in polycrystalline soft magnetic materials

The transverse susceptibility was measured in polycrystalline soft ferrimagnetic ring samples. It is shown that the very peculiar shape of the transverse susceptibility curve comes form the combination of two magnetization processes: the 180 degrees domain-wall motions which give rise to the initial susceptibility, and the sudden rotation of domains magnetized perpendicular to the applied field when a certain threshold of the biasing field is reached. The temperature dependence of this threshold has been investigated and has shown a close connection with the effective anisotropy field. >

Controlled potential oxidation of some arylhydrazides

Electrochemical oxidation of arylhydrazides ArCONHNHR does not lead to the expected benzaldehydes. For R = H, benzoic acids and eventually diaroylhydrazines are obtained; in the special case of o-nitrobenzoylhydrazine, unexpected formation of o-nitrosobenzoic acid is observed. For R = Ph, oxidation is a two-electron process leading to unstable 1-aroyl-2-phenyl-diimides; the latter can be trapped with p-toluenesulfinic acid when electrolysis is carried out in a water-acetonitrile mixture.