1,172 research outputs found
Vortex Redistribution below the First-Order Transition Temperature in the \beta-Pyrochlore Superconductor KOs_2O_6
A miniature Hall sensor array was used to detect magnetic induction locally
in the vortex states of the -pyrochlore superconductor KOsO.
Below the first-order transition at K, which is associated
with a change in the rattling motion of K ions, the lower critical field and
the remanent magnetization both show a distinct decrease, suggesting that the
electron-phonon coupling is weakened below the transition. At high magnetic
fields, the local induction shows an unexpectedly large jump at
whose sign changes with position inside the sample. Our results demonstrate a
novel redistribution of vortices whose energy is reduced abruptly below the
first-order transition at .Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let
Defect-unbinding and the Bose-glass transition in layered superconductors
The low-field Bose-glass transition temperature in heavy-ion irradiated
Bi_2Sr_2CaCu_2O_8+d increases progressively with increasing density of
irradiation-induced columnar defects, but saturates for densities in excess of
1.5 x10^9 cm^-2. The maximum Bose-glass temperature corresponds to that above
which diffusion of two-dimensional pancake vortices between different vortex
lines becomes possible, and above which the ``line-like'' character of vortices
is lost. We develop a description of the Bose-glass line that is in excellent
quantitative agreement with the experimental line obtained for widely different
values of track density and material parameters.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Thermodynamics of a Heavy Ion-Irradiated Superconductor: the Zero-Field Transition
Specific heat measurements show that the introduction of amorphous columnar
defects considerably affects the transition from the normal to the
superconducting state in zero magnetic field. Experimental results are compared
to numerical simulations of the 3D XY model for both the pure system and the
system containing random columnar disorder. The numerics reproduce the salient
features of experiment, showing in particular that the specific heat peak
changes from cusp-like to smoothly rounded when columnar defects are added. By
considering the specific heat critical exponent alpha, we argue that such
behavior is consistent with recent numerical work [Vestergren et al., PRB 70,
054508 (2004)] showing that the introduction of columnar defects changes the
universality class of the transition.Comment: 4 pages, 2 figure
Genetic variation among parthenogenetic Meloidogyne species revealed by AFLPs and 2D-protein electrophoresis contrasted to morphology
Des isolats appartenant aux espèces parthénogénétiques améiotiques #Meloidogyne arenaria, #M. hapla race B, #M. incognita, #M. javanica et parthénogénéiques méiotiques #M. chitwoodi, #M. fallax, #M. hapla race A, #M. naasi ont été comparés quant à leurs protéines totales solubles - par électrophorèse sur gel en deux dimensions (2-DGE) -, leur ADN génomique total - par AFLP - et leurs caractères morphologiques - par mensurations directes et données provenant de la littérature. Ces données ont été transformées en coefficients de similarité en utilisant le coefficient Dice basé sur plus de 100 spots protéiniques, 192 fragments d'AFLP et 21 caractères morphologiques. Les dendogrammes, établis suivant la méthode UPGMA basés sur les données fournies par les protéines et l'ADN sont congruents. Le groupement des races A et B de #M. hapla montre une similarité élevée, les trois espèces tropicales #M. incognita, M. javanica et #M. arenaria forment un autre groupe et les espèces spécialisées envers les graminées, #M. naasi, #M. chitwoodi; #M. fallax, sont distantes des autres, les deux dernières montrant une similarité élevée. Le dendogramme basé sur les données morphologiques diffère de ceux basés sur les données moléculaires, notamment pour #M. incognita et #M. naasi$. Il est discuté de cette non correspondance entre données provenant des protéines et de l'ADN, d'une part, et données morphologiques, d'autre part. (Résumé d'auteur
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