6,017 research outputs found
Measurements of surface impedance of superconductors as a function of frequency in microwave range
We report measurements of the complex resistivity in YBCO and MgB thin
films over a continuous frequency spectrum in the microwave range, making use
of a Corbino disk geometry. The paper mainly focuses on the extraction of the
resistivity from raw data, displaying data analysis procedure and its limits of
validity. We obtain and show resistivity curves as a function of frequency and
temperature denoting a frequency dependent widening of the superconducting
transition.Comment: 12 pages, 7 figures. Extended and revised version of cond-mat/0307143
(2003
New aspects of microwave properties of Nb in the mixed state
We present a study of the frequency dependence of the vortex dynamics in a
conventional superconductor. We have employed a swept-frequency, Corbino-disk
technique to investigate the temperature (3.6K-Tc) and high-field (from Hc2/2
to Hc2) microwave complex resistivity in Nb thin (20-40 nm) films as a function
of the frequency (1-20 GHz). We have found several previously unnoticed
features: (i) a field-dependent depinning frequency in the GHz range; (ii)
deviations from the accepted frequency dependence, that can be ascribed to some
kind of vortex creep; (iii) the presence of switching phenomena, reminiscent of
vortex instabilities. We discuss the possible origin of the features here
reported.Comment: 5 pages, 3 figures, presented at VORTEX VI Conference, to appear on
Physica
Vortex state microwave response in superconducting cuprates and MgB
We investigate the physics of the microwave response in
YBaCuO, SmBaCuO and MgB
in the vortex state. We first recall the theoretical basics of vortex-state
microwave response in the London limit. We then present a wide set of
measurements of the field, temperature, and frequency dependences of the vortex
state microwave complex resistivity in superconducting thin films, measured by
a resonant cavity and by swept-frequency Corbino disk. The combination of these
techniques allows for a comprehensive description of the microwave response in
the vortex state in these innovative superconductors. In all materials
investigated we show that flux motion alone cannot take into account all the
observed experimental features, neither in the frequency nor in the field
dependence. The discrepancy can be resolved by considering the (usually
neglected) contribution of quasiparticles to the response in the vortex state.
The peculiar, albeit different, physics of the superconducting materials here
considered, namely two-band superconductivity in MgB and superconducting
gap with lines of nodes in cuprates, give rise to a substantially increased
contribution of quasiparticles to the field-dependent microwave response. With
careful combined analysis of the data it is possible to extract or infer many
interesting quantities related to the vortex state, such as the
temperature-dependent characteristic vortex frequency and vortex viscosity, the
field dependence of the quasiparticle density, the temperature dependence of
the -band superfluid density in MgBComment: 51 pages, 27 figures, to appear as a book chapter (Nova Science
Surface impedance of superconductive thin films as a function of frequency in microwave range
We report measurements of the complex resistivity in and thin
films over a continuous frequency spectrum in the microwave range, making use
of a Corbino disk geometry. The paper mainly focuses on the extraction of the
resistivity from raw data, displaying data analisys procedure and its limits of
validity. We obtain and show resistivity curves as a function of frequency and
temperature denoting a frequency dependent widening of the superconductive
transition.Comment: 8 pages, Latex, 5 figure
Microwave properties of Nb/PdNi/Nb trilayers. Observation of flux flow in excess of Bardeen-Stephen theory
We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2
GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers,
grown by UHV dc magnetron sputtering, composed by Nb layers of nominal
thickness =15 nm, and a ferromagnetic PdNi layer of thickness = 1, 2,
8 and 9 nm. We focus on the vortex state. Magnetic fields up to were
applied. The microwave resistivity at fixed increases with ,
eventually exceeding the Bardeen Stephen flux flow value.Comment: 6 pages. Submitted to Journal of Superconductivity and Novel
Magnetis
Mixed-state microwave response in superconducting cuprates
We report measurements of the magnetic-field induced microwave complex
resistivity in REBaCuO thin films, with RE = Y, Sm.
Measurements are performed at 48 GHz by means of a resonant cavity in the
end-wall-replacement configuration. The magnetic field dependence is
investigated by applying a moderate (0.8 T) magnetic field along the c-axis.
The measured vortex state complex resistivity in
YBaCuO and SmBaCuO is
analyzed within the well-known models for vortex dynamics. It is shown that
attributing the observed response to vortex motion alone leads to
inconsistencies in the as-determined vortex parameters (such as the vortex
viscosity and the pinning constant). By contrast, attributing the entire
response to field-induced pair breaking leads to a nearly quantitative
description of the data.Comment: 6 pages, 4 figures, to be published in J. Supercond. as proceedings
of 8th HTSHFF (May 26th-29th, 2004, Begur, Spain
Modeling mass transport in dense polymer membranes: cooperative synergy among multiple scale approaches
The modeling description of basic transport phenomena of either liquid, gas or vapor molecules in dense polymeric membranes is of tremendous impact for the separation industry, which relies on solid models for the design of optimal process conditions, for the selection of the most suitable membrane materials as well as for the development of novel ones. Such models need to deal with several physical aspects and phenomena, spanning over broad time and length scales, thus requiring multiple approaches. The solid frameworks now available mainly rely on the solution–diffusion theory, in which equation of state models and free volume theories are applied for the description of thermodynamic and kinetic properties, to be coupled in appropriate transport schemes
Violence and Gender: Marked Victims
Objectives: This paper aims to raise questions about the institutional assistance to violence within the health field, particularly on the topic sexual violence
Actividad antifúngica de extractos crudos de bacillus subtilis contra fitopatógenos de soja (Glycine max) y efecto de su coinoculación con bradyrhizobium japonicum
373-383Fungal species Fusarium solani and Pythium sp. are among the microorganisms causing diseases in pre and post harvest crop soybean (Glycine max). Four strains of the genus Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticated) were tested to evaluate the inhibitory response of them on the phytopathogenic fungi previously mentioned. The inoculation treatments were 1) seeds inoculated with Bradyrhizobium japonicum, and 2) seeds coinoculated with B. japonicum and B. subtilis. Plants were grown in a thermostated culture chamber at 30 more or less 1°C, 60 percent relative humidity and 16/8 light-dark photoperiod for 35 d. Data were analyzed by ANOVA and means were compared by applying the Tukey test (p less or equal to 0.05). The in vitro assays of the strain B. subtilis ATCC6633 reduced the mycelial growth of Fusarium solani (50 percent) and Pythium sp. (47 percent) compared to controls. The coinoculation of B. japonicum and B. subtilis stimulated the growth of the whole plant by 125 percent, 100 percent aerial part, 235 percent root, 20 percent number of leaves, and 88 percent nodule number compared to control. The strain B. subtilis ATCC6633 synthesized metabolites of proteinaceous nature and others with biosurfactant capacity. When the bacteria were grown in minimal saline medium, glycerol 1 percent and concentrations of L-glutamic acid between 40 and 55 mM, the highest concentration of proteinaceous metabolites (35 ug protein mL-1) was obtained and increased biofilm formation. Biofilm formation, the presence of biosurfactants and the release of antifungal metabolites positioned this bacterium in a situation competitively advantageous compared to the rest of the microbiota of the rhizosphere in the soybean plant. Entre los microorganismos causantes de enfermedades pre y post cosecha en los cultivos de soja (Glycine max) están las especies fúngicas Fusarium solani y Pythium sp. Cuatro cepas del género Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticado) se probaron para evaluar su respuesta inhibitoria en los hongos fitopatógenos mencionados. Los tratamientos de inoculación fueron: 1) semillas inoculadas con Bradyrhizobium japonicum y 2) semillas coinoculadas con B. japonicum y B. subtilis. Las plantas crecieron en cámara de cultivo termostatizada a 30 más o menos 1°C, humedad relativa 60 porciento y fotoperÃodo 16/8 luz-oscuridad durante 35 d. Los datos se analizaron mediante ANDEVA y las medias se compararon con la prueba de Tukey (p menor o igual a 0.05). Las pruebas in vitro de la cepa B. subtilis ATCC6633 redujeron el crecimiento micelial de Fusarium solani (50 porciento) y Pythium sp. (47 porciento) respecto a los testigos. La coinoculación de B. japonicum y B. subtilis estimuló el crecimiento de la planta completa en 125 porciento, parte aérea 100 porciento, raÃz 235 porciento, número de hojas 20 porciento y número de nódulos 88 porciento respecto al testigo. La cepa de B. subtilis ATCC6633 sintetizó metabolitos de naturaleza proteÃnica y otros con capacidad biosurfactante. Cuando la bacteria se cultivó en medio mÃnimo salino, glicerol 1 porciento y concentraciones de ácido L-glutámico entre 40 y 55 mM, se obtuvo la concentración mayor de metabolitos de naturaleza proteÃnica (35 mg proteÃna mL-1) y la mayor formación de biopelÃcula. La formación de la biopelÃcula, la presencia de biosurfactantes y la liberación de metabolitos antifúngicos, posicionan a esta bacteria en una situación competitivamente ventajosa en relación al resto de la microbiota de la rizósfera en la planta de soja
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