Vorticity and vortex-core states

The origin of the vortex-core states in s-wave and d_{x^2-y^2}-wave superconductors is investigated by means of some selected numerical experiments. By relaxing the self-consistency condition in the Bogoliubov-de Gennes equations and tuning the order parameter in the core region, it is shown that the suppression of the superfluid density in the core is not a necessary condition for the core states to form. This excludes ``potential well'' types of interpretations for the core states. The topological defect in the phase of the order parameter, however, plays a crucial role. This observation is explained by considering the effect of the vortex supercurrent on the Bogoliubov quasiparticles, and illustrated by comparing conventional vortices with multiply-quantized vortices and vortex-antivortex pairs. The core states are also found to be extremely robust against random phase disorder.Comment: REVTeX 4, 11 pages, 8 EPS figure

Interplay of the pseudogap and the BCS gap for heteropairs in 40^{40}K-6^6Li mixture

The description of heteropairs like $^{40}$K-$^6$Li near and in the superconducting state requires a fully selfconsistent theory [see Hanai and Ohashi, Phys. Rev. A 90, 043622 (2014)]. We derive analytic pseudogap Green's functions for the "normal" and superconducting states from the Luttinger-Ward theory with the T-matrix in the static separable approximation. The self-consistency in the closing loop of self-energy has two pronounced effects on the single-particle spectrum. First, the single-particle excitations decay before the asymptotic quasiparticle propagation is established, therefore the normal state is not a Fermi liquid. Second, the pseudogap has a V shape even for s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere resulting in slope breaks of the gap walls and the in-gap states in the density of states. Various consequences of an incomplete self-consistency are demonstrated.Comment: Published versio

Gorkov equations for a pseudo-gapped high temperature superconductor

A theory of superconductivity based on the two-body Cooperon propagator is presented. This theory takes the form of a modified Gorkov equation for the Green's function and allows one to model the effect of local superconducting correlations and long range phase fluctuations on the spectral properties of high temperature superconductors, both above and below Tc. A model is proposed for the Cooperon propagator, which provides a simple physical picture of the pseudo-gap phenomenon, as well as new insights into the doping dependence of the spectral properties. Numerical calculations of the density of states and spectral functions based on this model are also presented, and compared with the experimental STM and ARPES data. It is found, in particular, that the sharpness of the peaks in the density of states is related to the strength and the range of the superconducting correlations and that the apparent pseudo-gap in STM and ARPES can be different, although the underlying model is the same.Comment: REVTEX 3.1, 8 pages, 5 EPS figures, submitted to Phys. Rev.

Effets de facteurs pédoclimatiques sur la composition et l’anatomie du bois de cinq cultivars de saule destinés aux biocarburants

En 2011, cinq (5) cultivars de saules ont été sélectionnés pour leur rendement en biomasse. Ils ont été plantés sur quatre sites de la province du Québec et ont été maintenus selon le protocole de la culture intensive sur courtes rotations (CICR) afin de déterminer leur potentiel pour la bioénergie dans des environnements contrastés. La composition et l’anatomie du bois de ces cultivars ont été caractérisées et comparés en fonction des conditions environnementales caractéristiques de chaque site. La hauteur et le diamètre à la base des plantes diffèrent selon les sites. Ainsi, les cultivars répondent de façon spécifique aux conditions pédoclimatiques dans lesquelles ils sont cultivés. L’effet de l’environnement n’a pas été mis en évidence sur la teneur en lignine des cultivars. Cependant, un effet génotypique a pu être constaté soulignant l’importance de la sélectivité des cultivars. La densité du bois a étonnamment conservé la même hiérarchie génotypique entre les sites. À l’opposé, l’anatomie du bois présente des différences notamment au niveau des caractéristiques des fibres et des vaisseaux. Une forte teneur en polyphénols ainsi que des fibres moins larges et des vaisseaux plus nombreux ont été observés sur le site dont le bois est le plus dense supposant l’effet probable d’un stress abiotique. De plus, deux fois plus de fibres gélatineuses, fibres riches en cellulose, ont été identifiées sur ce site montrant un intérêt pour la production de bioéthanol.In 2011, five (5) willow cultivars were selected for biomass yield. They were planted according to SRC (Short Rotation Coppice) protocol on four sites in Quebec (Canada) to determine their bioenergy potential in contrasting environments. Wood composition and anatomical traits were characterized and compared between both genotypes and environmental growing conditions. Tree height and stem diameter differed between sites, and pedoclimatic conditions more favorable for willow growth were identified. However, each cultivar showed a specific response to its environment. While no significant variation in lignin content was observed between sites, a clonal effect confirms the importance of cultivar selection. Surprisingly, the pattern of genotype variability in stem density was the same on all sites. Wood anatomy differed on fiber and vessel traits between high and low wood density sites, which suggests a probable effect of an abiotic stress. Furthermore, twice as many cellulose-rich G fibers were also found at the most dense site, evidence of potential for use in bioethanol production

A theory of the strain-dependent critical field in Nb3Sn, based on anharmonic phonon generation

We propose a theory to explain the strain dependence of the critical properties in A15 superconductors. Starting from the strong-coupling formula for the critical temperature, and assuming that the strain sensitivity stems mostly from the electron-phonon alpha^2F function, we link the strain dependence of the critical properties to a widening of alpha^2F. This widening is attributed to the nonlinear generation of phonons, which takes place in the anharmonic deformation potential induced by the strain. Based on the theory of sum- and difference-frequency wave generation in nonlinear media, we obtain an explicit connection between the widening of alpha^2F and the anharmonic energy. The resulting model is fit to experimental datasets for Nb3Sn, and the anharmonic energy extracted from the fits is compared with first-principles calculations.Comment: 10 pages, 3 figure

Home Sweet Home: pratiques d'animation en EMS, Valais romand

Ce travail, réalisé dans le cadre de l’obtention du diplôme Bachelor of Art in Travail Social, orientation animation socioculturelle, vise à comprendre et à promouvoir les besoins de la population âgée qui vit en institution. La recherche qui suit débute par un apport théorique à propos des notions de vieillesse, de besoins humains, d’établissement médico-social (EMS) et d’animation. Ensuite, l’enquête sur le terrain s’effectuera avec la collaboration de six EMS du Valais romand. Suivra une analyse des données recueillies qui mettra en lumière les points de vue des professionnels et des bénéficiaires. Le bilan final relèvera les conclusions de la recherche et les perspectives qui en découlent. Les annexes contiennent la mise en place de l’enquête ainsi qu’une synthèse des résultats des entretiens menés. La fonction de ce travail est d’éclairer les différents enjeux de l’animation socioculturelle auprès des personnes âgées, et également de promouvoir l’aspect réflexif de la profession sociale