Dynamic Formation of Metastable Intermediate State Patterns in Type-I Superconductors

Structure of the intermediate state in type-I superconducting lead (Pb) is shown to be very sensitive to the ramp rate of an applied magnetic field. The configurations of resulting static patterns depend sensitively on the shape of the specimen. In particular, geometric barrier, present in the samples with rectangular cross-section, plays an important role in determining the sharp boundary between the phases of different topology. We propose that seemingly laminar (stripe) pattern obtained as a result of the fast field ramp is simply an imprint left behind by the fast-moving flux tubes. Our results confirm that flux tube phase is topologically favorable.Comment: to be presented at LT-25 (Amsterdam, 2008

Enhancement of power system transient stability using superconducting fault current limiters

Transient stability investigations consist of studying the rotor oscillations of generators (electro-mechanic oscillations, 0.1-2 Hz) after the occurrence of a fault of large amplitude, e.g. short circuit. The goal is to indicate if the generators are capable to stay synchronous after a fault has occurred. The fault duration is one of the most important factors to be determined. In fact, the shorter the fault, the more the maintaining of synchronisation can be guaranteed. Now in case of a fault, a fault current limiter has an extremely fast current transition in comparison to electro-mechanic time constants. This implies a quasi-instantaneous elimination of the fault through a limitation of the current and consequently a better ability to maintain the synchronisation of the system. We recall that in a classic system, the elimination of a fault, by opening a circuit breaker, is carried out in two or three cycles in the best case. We have here studied a simple, radial electric network configuration with a machine and an infinite network. The study covers simulations of a fault that can occur in a network and the consequences of the recovery time of the fault current limiter

Parametrised Preisach Modelling of Hysteresis in High Temperature Superconductors

We present a parametrised Preisach-type model that describes the hysteresis exhibited by the high temperature superconductors (HTSC); hysteresis is the main cause for losses in the subcritical domain. The parametrised model, in combination with electrical measurements, is independent of geometry, number of filaments and other physical measures, and is identified by a novel method that uses electrical lock-in (loss) measurement technique, which greatly enhances the signal to noise ratio. Identification results from measurements on Bi-2223 multi-filamentary tapes are presented. We have further derived exact models for the hysteretic losses in strip and elliptic geometry strips, where the energy losses were calculated by Norris. The paper contains analysis of the Preisach Model, of its losses and of the suggested parametrisation

Bi(2223) Ag sheathed tape Ic and exponent n characterisation and modelling under DC applied magnetic field

We use a dual channel digital lock-in to perform electrical measurement of AC losses at power frequencies. A DC magnetic field between 2 and 400 mT is applied with a varying angle from parallel to perpendicular to the tape surface, thus having a complete view of the loss behavior under DC applied field. Furthermore, the same experimental layout is used to acquire time series of current and voltage across the sample. Using a triangular input current, we measure and average the voltage, which then is fitted to a power law (I/Ic)^n. The measurements are repeated for the mentioned magnetic field and angle domain to give the dependencies of Ic and n with magnetic field and angle. For device modeling purposes, we can then express a phenomenological law giving Ic and n as a function of the applied magnetic field's intensity and direction

MRI in multiple myeloma : a pictorial review of diagnostic and post-treatment findings

Magnetic resonance imaging (MRI) is increasingly being used in the diagnostic work-up of patients with multiple myeloma. Since 2014, MRI findings are included in the new diagnostic criteria proposed by the International Myeloma Working Group. Patients with smouldering myeloma presenting with more than one unequivocal focal lesion in the bone marrow on MRI are considered having symptomatic myeloma requiring treatment, regardless of the presence of lytic bone lesions. However, bone marrow evaluation with MRI offers more than only morphological information regarding the detection of focal lesions in patients with MM. The overall performance of MRI is enhanced by applying dynamic contrast-enhanced MRI and diffusion weighted imaging sequences, providing additional functional information on bone marrow vascularization and cellularity. This pictorial review provides an overview of the most important imaging findings in patients with monoclonal gammopathy of undetermined significance, smouldering myeloma and multiple myeloma, by performing a 'total' MRI investigation with implications for the diagnosis, staging and response assessment. Main message aEuro cent Conventional MRI diagnoses multiple myeloma by assessing the infiltration pattern. aEuro cent Dynamic contrast-enhanced MRI diagnoses multiple myeloma by assessing vascularization and perfusion. aEuro cent Diffusion weighted imaging evaluates bone marrow composition and cellularity in multiple myeloma. aEuro cent Combined morphological and functional MRI provides optimal bone marrow assessment for staging. aEuro cent Combined morphological and functional MRI is of considerable value in treatment follow-up

Classification d'expressions vocales passives versus actives

Six expressions sont généralement considérées pour caractériser les états émotifs humains : Sourire, Surprise, Colère, Tristesse, dégoût et Neutre. Différentes mesures peuvent être extraites à partir du signal de parole pour caractériser ces expressions, à savoir la fréquence fondamentale, l'énergie, le SPI (rapport des énergies des HF et des BF dans le signal) et le débit de parole. Une classification automatique des cinq expressions basées sur ces caractéristiques présente des conflits entre la Colère, la Surprise et le Sourire d'une part et le Neutre et la Tristesse d'autre part. Ce conflit entre classes d'expressions est également retrouvé chez le classifieur humain. Nous proposons donc de définir deux classes d'expressions: Active regroupant le Sourire, la Surprise et la Colère et Passive regroupant le Neutre et la Tristesse. Une telle classification est également plus réaliste et plus appropriée pour l'intégration d'information de parole dans un système de classification multimodale combinant la parole et la vidéo, ce qui est à long terme le but de notre travail. Dans ce papier, différentes méthodes de classification sont testées: un classifieur Bayésien, une Analyse Discriminante Linéaire (ADL), le classifieur au K plus proches vosins(KNN) et un classifieur à Machine à Vecteur de Support (SVM) avec une fonction de base gaussienne. Pour les deux classes considérées, les meilleurs taux de classification sont obtenus avec le classificateur SVM avec un taux de reconnaissance de 89.74% pour l'état Actif et de 86.54 % pour l'état Passif