Heating process in the pre-Breakdown regime of the Quantum Hall Efect : a size dependent effect

Our study presents experimental measurements of the contact and longitudinal voltage drops in Hall bars, as a function of the current amplitude. We are interested in the heating phenomenon which takes place before the breakdown of the quantum Hall effect, i.e. the pre-breakdown regime. Two types of samples has been investigated, at low temperature (4.2 and 1.5K) and high magnetic field (up to 13 T). The Hall bars have several different widths, and our observations clearly demonstrate that the size of the sample influences the heating phenomenon. By measuring the critical currents of both contact and longitudinal voltages, as a function of the filling factor (around $i=2$), we highlight the presence of a high electric field domain near the source contact, which is observable only in samples whose width is smaller than 400 microns.Comment: 4 pages, 5 igures, 7th International Symposium of Research in High Magnetic Fields, to be published in physica

Magnetic nanowires as permanent magnet materials

We present the fabrication of metallic magnetic nanowires using a low temperature chemical process. We show that pressed powders and magnetically oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe at 300 K). We discuss the magnetic properties of these metamaterials and show that they have the suitable properties to realize "high temperature magnets" competitive with AlNiCo or SmCo permanent magnets. They could also be used as recording media for high density magnetic recording.Comment: 5 pages, 5 figure

Nouveaux arrivants et enseignement en milieu franco-manitobain : défis et dynamiques

Les écoles francophones du Manitoba connaissent depuis quelques années une augmentation notable du nombre d’immigrants dans leur population scolaire. Ces nouveaux arrivants viennent de divers pays et de divers contextes de migration, qui font varier le profil des élèves, du point de vue tant ethnoculturel que sociolinguistique. Par ailleurs, un regard plus appuyé sur le paysage scolaire montre une tendance migratoire majoritairement africaine et relevant de la catégorie d’immigration dite «humanitaire». La recherche présentée dans cet article est axée autour des deux aspects suivants: connaître les perspectives des enseignants de la communauté francophone de Winnipeg par rapport à l’inclusion des nouveaux arrivants en milieu scolaire; comprendre les expériences qu’ils ont vécues, les défis auxquels ils sont confrontés dans le développement de pratiques pédagogiques inclusives et les divers ordres de facteurs qui caractérisent leurs comportements. En ce qui concerne les facteurs personnels, un sentiment d’accomplissement peut être dégagé; par contre, les enseignants, confrontés à de nombreux défis, avouent ressentir un sentiment d’insuffisance. En ce qui concerne les facteurs contextuels, les enseignants dans leur quasi-totalité décrivent le cadre idéologique et politique relatif à l’inclusion des nouveaux arrivants comme étant un facteur positif; par contre, ils se questionnent quant à la faisabilité d’une intégration scolaire réussie et sont préoccupés par l’isolement social, voire la marginalisation, qu’éprouvent certains jeunes nouveaux arrivants. Les enjeux de leur inclusion sont en effet multidimensionnels, dans la mesure où les discontinuités touchent au social, à l’identitaire, au langage, à l’affectif et au pédagogique. L’article, qui montre que les enseignants ne sont pas, à l’évidence, indifférents en ce qui concerne l’intégration scolaire des nouveaux arrivants, se termine par quelques implications, qui touchent, entre autres, à la mise en oeuvre de la politique d’inclusion, à la formation initiale et continue au personnel enseignant, aux pratiques pédagogiques exemplaires et à la mise sur pied au Manitoba d’un forum sur l’intégration scolaire des élèves immigrants.In recent years, francophone schools in Manitoba have seen a marked increase in the number of immigrants in their student population. These newcomers come from a variety of countries and a variety of migration contexts. This translates into a diversity of student profiles from an ethno-cultural perspective as well as from a socio-linguistic point of view. Moreover, a closer look at the scholastic landscape reveals a migratory trend that is made up of a majority of Africans and immigrants admitted as immigrants on a “humanitarian“ basis. The research presented in this article aims 1) to hear the perspective of teachers from the francophone community in Winnipeg in regard to the inclusion of newcomers in the scholastic setting, and 2) to learn about the experiences that they have had, the challenges that they have faced in developing inclusive pedagogical practices, and the various factors that characterize their behaviour. On a personal level, teachers may feel a sense of accomplishment as a result of their dealings with a diverse immigrant population; however, teachers, faced with numerous challenges, admit having feelings of inadequacy. As for contextual factors, teachers, almost without exception, describe the ideological and political framework in regard to inclusion of these newcomers as being a positive factor. However, they question the feasibility of a successful integration into the school system and are concerned about the social isolation or even exclusion experienced by some young newcomers. What is at stake in regard to their inclusion is in fact multifaceted, and the discontinuities experienced have an effect on socialization, identity, language, emotional issues and pedagogy. The article, which shows that teachers are clearly not indifferent to the issue of the integration of new arrivals into schools, ends by addressing a few implications of this situation, which touch on such matters as implementation of the inclusion policy, initial and ongoing training for teaching staff, exemplary pedagogical practices, and establishment in Manitoba of a forum for discussion of scholastic integration of immigrant students

The quantum metrology triangle and the re-definition of the SI ampere and kilogram; Analysis of a reduced set of observational equations

We have developed a set of seven observational equations that include all of the physics necessary to relate the most important of the fundamental constants to the definitions of the SI kilogram and ampere. We have used these to determine the influence of alternative definitions being considered for the SI kilogram and ampere on the uncertainty of three of the fundamental constants (h, e and mu). We have also reviewed the experimental evidence for the exactness of the quantum metrology triangle resulting from experiments combining the quantum Hall effect, the Josephson effects and single-electron tunnelling.Comment: 16 pages, 3 figures & 5 table

Double beta decay experiments

The present status of double beta decay experiments are reviewed. The results of the most sensitive experiments, NEMO-3 and CUORICINO, are discussed. Proposals for future double beta decay experiments are considered. In these experiments sensitivity for the effective neutrino mass will be on the level of (0.1-0.01) eV.Comment: 20 pages, 7 fugures; talk at 12-th Lomonosov Conference on Elementary Particle Physics (Moscow, August 25-31, 2005

Exchange bias in Co/CoO core-shell nanowires: Role of the antiferromagnetic superparamagnetic fluctuations

The magnetic properties of Co (=15 nm, =130nm) nanowires are reported. In oxidized wires, we measure large exchange bias fields of the order of 0.1 T below T ~ 100 K. The onset of the exchange bias, between the ferromagnetic core and the anti-ferromagnetic CoO shell, is accompanied by a coercivity drop of 0.2 T which leads to a minimum in coercivity at $\sim100$ K. Magnetization relaxation measurements show a temperature dependence of the magnetic viscosity S which is consistent with a volume distribution of the CoO grains at the surface. We propose that the superparamagnetic fluctuations of the anti-ferromagnetic CoO shell play a key role in the flipping of the nanowire magnetization and explain the coercivity drop. This is supported by micromagnetic simulations. This behavior is specific to the geometry of a 1D system which possesses a large shape anisotropy and was not previously observed in 0D (spheres) or 2D (thin films) systems which have a high degree of symmetry and low coercivities. This study underlines the importance of the AFM super-paramagnetic fluctuations in the exchange bias mechanism.Comment: 10 pages, 10 figures, submitted to Phys. Rev.