Improved nanopatterning for YBCO nanowires approaching the depairing current

An improved nanopatterning procedure has been developed to obtain YBCO nanowires with cross sections as small as 50x50 nm^2, protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 10^8 A/cm^2 have been achieved at T=4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to Tc, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with same nanowires, without the Au capping layer.Comment: ASC 2012 conference contributio

Critérios e indicadores para avaliação da sustentabilidade de empresa florestal em Tailândia, Pará, na Amazônia brasileira.

O objetivo deste trabalho foi gerar fundamentos de um grupo de critérios e indicadores (C&I) adequados para serem utilizados em monitoramento empresarial e em auditagem de sustentabilidade das atividades de indústria madeireira na Amazônia oriental brasileira. O estudo se baseia na suposição de que C&I práticos e viáveis dependem das considerações dos interesses, visões e valores dos principais grupos de atores envolvidos no sistema de uso florestal. A ideia central do estudo foi identificar diferenças entre quatro grupos de atores (atores locais, governo, grupo operacional e pesquisadores) na avaliação de um conjunto de C&I definidos por pesquisadores internacionais em um Workshop, e usar as diferenças detectadas para elaborar, em forma participativa, os critérios adequados para monitoramento e auditagem. Um elemento metodológico importante foi a avaliação da sustentabilidade das atividades de uma empresa florestal pela aplicação pratica de C&I. O estudo confirmou o grande potencial desses critérios para avaliação da sustentabilidade das atividades de avaliação entre os diversos grupos. Pode-se afirmar que para os usuários potenciais, a praticidade e a simplicidade dos C&I são muito importantes, como também a relação entre custos e benefícios da aplicação dos mesmos. Conclui-se que o resultado da avaliação da sustentabilidade através dos C&I depende muito dos métodos utilizados para levantar informações. Para facilitar a aplicação de C&I em ferramentas de monitoramento e auditagem, os esforços futuros devem dimensionar-se na busca de verificadores inquestionáveis, de métodos de avaliação e definição de recomendações especificas introduzidas de resultados de avaliação.bitstream/item/63186/1/Oriental-Doc34.pd

Comparison of Josephson vortex flow transistors with different gate line configurations

We performed numerical simulations and experiments on Josephson vortex flow transistors based on parallel arrays of YBa2Cu3O(7-x) grain boundary junctions with a cross gate-line allowing to operate the same devices in two different modes named Josephson fluxon transistor (JFT) and Josephson fluxon-antifluxon transistor (JFAT). The simulations yield a general expression for the current gain vs. number of junctions and normalized loop inductance and predict higher current gain for the JFAT. The experiments are in good agreement with simulations and show improved coupling between gate line and junctions for the JFAT as compared to the JFT.Comment: 3 pages, 6 figures, accept. for publication in Appl. Phys. Let

Are Scattering Properties of Graphs Uniquely Connected to Their Shapes?

The famous question of Mark Kac "Can one hear the shape of a drum?" addressing the unique connection between the shape of a planar region and the spectrum of the corresponding Laplace operator can be legitimately extended to scattering systems. In the modified version one asks whether the geometry of a vibrating system can be determined by scattering experiments. We present the first experimental approach to this problem in the case of microwave graphs (networks) simulating quantum graphs. Our experimental results strongly indicate a negative answer. To demonstrate this we consider scattering from a pair of isospectral microwave networks consisting of vertices connected by microwave coaxial cables and extended to scattering systems by connecting leads to infinity to form isoscattering networks. We show that the amplitudes and phases of the determinants of the scattering matrices of such networks are the same within the experimental uncertainties. Furthermore, we demonstrate that the scattering matrices of the networks are conjugated by the, so called, transplantation relation.Comment: 3 figures; Physical Review Letters, 201

Andreev Bound States in High Temperature Superconductors

Andreev bound states (ABS) at the surface of superconductors are expected for any pair potential showing a sign change in different k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report on the observation of ABS in HTS employing tunneling spectroscopy on bicrystal grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic field. The tunneling spectra of GBJ formed by YBCO, BSCCO, and LSCO show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS NCCO no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev bound states are discussed and experimental evidence for anomalous Meissner currents is presented.Comment: 17 pages, 10 figures, to appear in Eur. Phys. J.

Balances of bioelements in useful tropical plants.

The productivity of different useful tropical plants is compared with respect to their biomass production. Furthermore, analyses of nutrient contents serve to explain the interrelationship between nutrient supply and primary production. The biomass and nutrient contents from three to six month old plants from Bertholletia excelsia H.B.K. (castanha-do-Brasil), Cedrela odorata L. (cedro vermelho), Dipteryx alata (cumaru), Theobroma grandiflorum (Spreng.) K. Schum. (cupuacu), Elaeis guineensis Jacq. (dende), Swietenia macrophylla King (mahogany), Sclerobium paniculatum Vogel (taxi branco) and Bixa orellana L. (urucum) within the different plant fraction were determined. The elements Ca, Mg, K, Na, Fe, Al, Zn, Cu, and P were analysed with the inductively coupled argon plasma with optical-emission-spectrometry (ICP-OES) method. Compared to plants of temperate regions, the mineral content is distinctly higher than that for tropical plants, but most values still lie within the range of existing data. Extremely high values were found for aluminium and iron

Biomass production and mineral element supply of selected useful tropical plants.

This current investigation is part of a cooperative project of CPAA-Manaus and Hamburg University entitled "Recultivation of degraded and abandoned monocultures instable mixed cultures with special reference to soil biological factors". In this study the biomass product and the mineral element supply of selected useful tropical plants will be determined. Parallel to it the availability of nutrient element in the soil will be analyzed. These experiments may allow an evaluation, in which way a sustainable growth of the suggested plant system under the prevailing site conditions is possible.Poster 11

One-dimensional quantum chaos: Explicitly solvable cases

We present quantum graphs with remarkably regular spectral characteristics. We call them {\it regular quantum graphs}. Although regular quantum graphs are strongly chaotic in the classical limit, their quantum spectra are explicitly solvable in terms of periodic orbits. We present analytical solutions for the spectrum of regular quantum graphs in the form of explicit and exact periodic orbit expansions for each individual energy level.Comment: 9 pages and 4 figure