Intrinsic switching field distribution of arrays of Ni80Fe20 nanowires probed by in situ\mathit{in\, situ} magnetic force microscopy

The progress of magnetization reversal of weakly packed ferromagnetic Ni80Fe20 nanowire arrays of different diameters (40, 50, 70 and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighbouring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays.Comment: 4 pages, 5 figures. To appear in Journal of Superconductivity and Novel Magnetis

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.Comment: 7 pages, 5 figure

Evaluation du developpement territorial comme processus d'innovation et d'institutionnalisation: le cas du Territoire du Alto Sertão do Piauí e Pernambuco au Nordeste du Brésil.

Du fait de leur transversalité et de leur objet, l'évaluation des politiques de développement territorial ne peut pas s'appuyer su les outils utilisés pour évaluer les politiques sectorielles

Free and smooth boundaries in 2-D finite-difference schemes for transient elastic waves

A method is proposed for accurately describing arbitrary-shaped free boundaries in single-grid finite-difference schemes for elastodynamics, in a time-domain velocity-stress framework. The basic idea is as follows: fictitious values of the solution are built in vacuum, and injected into the numerical integration scheme near boundaries. The most original feature of this method is the way in which these fictitious values are calculated. They are based on boundary conditions and compatibility conditions satisfied by the successive spatial derivatives of the solution, up to a given order that depends on the spatial accuracy of the integration scheme adopted. Since the work is mostly done during the preprocessing step, the extra computational cost is negligible. Stress-free conditions can be designed at any arbitrary order without any numerical instability, as numerically checked. Using 10 grid nodes per minimal S-wavelength with a propagation distance of 50 wavelengths yields highly accurate results. With 5 grid nodes per minimal S-wavelength, the solution is less accurate but still acceptable. A subcell resolution of the boundary inside the Cartesian meshing is obtained, and the spurious diffractions induced by staircase descriptions of boundaries are avoided. Contrary to what occurs with the vacuum method, the quality of the numerical solution obtained with this method is almost independent of the angle between the free boundary and the Cartesian meshing.Comment: accepted and to be published in Geophys. J. In

Le consortium intermunicipal : un dispositif efficace de gouvernance territoriale?: le cas d'une expérience dans le Nordeste du Brésil.

Contexto territorial de quatro município do estado de Pernambuco e Piauí; Mobilização e Conscientização: um território em construção; Projeto territorial

Current-voltage characteristics of quasi-one-dimensional superconductors: An S-curve in the constant voltage regime

Applying a constant voltage to superconducting nanowires we find that its IV-characteristic exhibits an unusual S-behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j_{c2} at which the pure superconducting state becomes unstable and j_{c1}<j_{c2} at which the phase slip state is realized in the system.Comment: 4 pages, 5 figures, replaced with minor change

Qualité microbiologique des fromages artisanaux fabriqués au lait cru en Région wallonne

Microbiological quality of craft raw milk cheeses produced in Wallonia. The main objective of this study was to evaluatethe bacteriological quality of raw milk cheeses produced in the southern part of Belgium (Wallonia) and to compare withsamples coming from other European countries. Results from bacteriological analyses of 153 cheese samples have beencompared with regard to food microbial standards (92/46 EC Directive). It can be concluded from this work that 69% of thesamples may be considered as acceptable, while 31% showed coliforms and Staplylococcus aureus counts exceeding thestandard values. As far as pathogens were concerned, 0.7% and 7.2% of the samples have were found unsatifactory with thecriteria related to Salmonella and Listeria monocytogenes, respectively. Enterobacteriaceae contamination has also beenevaluated and demonstrated an average log count of about 3.78 cfu/g. Cheeses produced from ewe milk showed anoutstanding microbiological quality since all samples turned out to be acceptable regarding the S. aureus counts and devoidof Salmonella and L. monocytogenes contamination. Although no seasonal effect on the bacteriological quality could beobserved, the microbial quality decreased after the production stage, i.e. mainly during the storage and the distribution.Cheese made by small producers seems to be better than those originating from industrial enterprises. By comparing theseresults with those obtained on cheese samples produced in some other European countries, it appears that the mean qualitylevel of Walloon raw milk cheeses is quite satifactory

Le développement territorial durable : le cas d'une expérience dans le Nordeste du Brésil.

Cette communication traite d'une expérience de recherche-action de développement territorial durable au niveau du territoire du Alto Sertão du Oiaui et du Pernambuco dans le Nordeste du Brésil

Mechanisms of spin-polarized current-driven magnetization switching

The mechanisms of the magnetization switching of magnetic multilayers driven by a current are studied by including exchange interaction between local moments and spin accumulation of conduction electrons. It is found that this exchange interaction leads to two additional terms in the Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both terms are proportional to the transverse spin accumulation and have comparable magnitudes

Magnetic force microscopy study of the switching field distribution of low density arrays of single domain magnetic nanowires

In the present work, we report on the in situ magnetic force microscopy (MFM) study of the magnetization reversal in two-dimensional arrays of ferromagnetic Ni80Fe20 and Co55Fe45 nanowires(NW) with different diameters (40, 50, 70 and 100 nm) deposited inside low porosity (P<1%) nanoporous polycarbonate membranes. In such arrays, the nanowires are sufficiently isolated from each other so that long range dipolar interactions can be neglected. The MFM experiments performed for different magnetization states at the same spot of the samples are analysed to determine the switching field distribution (SFD). The magnetization curves obtained from the MFM images are relatively square shaped. The SFD widths are narrower compared to those obtained for high density arrays. The weak broadening of the curves may be ascribed to the NW intrinsic SFD. The influence of diameter and composition of the ferromagnetic NW is also investigated.Comment: 6 pages, 4 figures, To appear in Journal of Applied Physic