Effective Swarm Parameters And Transport Coefficients In CO2 Laser Mixtures

A pulsed electron swarm technique has been used to obtain effective attachment and ionization cross-sections as well as electron drift velocities in mixtures of CO2 laser interest. In binary CO2:N 2 mixtures, below a reduced electric field of E/N=60*10 -17 V cm2, attachment was the principal ion production process. (N is the total gas number density.) The reduced attachment coefficients measured were small and in excellent agreement with numerical predictions. In ternary mixtures of He:CO2:N2, positive ion formation described by Townsend\u27s first ionisation coefficient played a more important role over the same range of E/N. The reduced coefficient for total ion formation was measured and found to be in good agreement with numerical calculations. Electron drift velocities in both the binary and ternary mixtures were determined using a time-of-flight technique. Overall agreement with previous experimental and numerical results was good

Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films

We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.Comment: 14 pages, 3 figures. Submitted to AP

Processing of YBCO/IBAD YSZ coated conductors on flexible substrates

Continuous coaters capable of producing 1.1 m long x 1 cm wide tapes of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) on biaxially oriented yttria-stabilized zirconia (YSZ) on flexible Ni-alloy substrates have been developed at this laboratory. Using a 1 {micro}V/cm criterion, the authors have achieved transport critical current (I{sub c}) values of 29 A (75 K, self field) between voltage taps spaced 1 m apart. The corresponding critical current density (J{sub c}) value for this tape is 290 kA/cm{sup 2}. For shorter tapes, (12 cm voltage tap separation) they have attained J{sub c} values of 0.67 MA/cm{sup 2}. Individual 1 x 1 cm sections within these shorter tapes have attained J{sub c} values of 1 MA/cm{sup 2}

Strongly Enhanced Current Densities in Superconducting Coated Conductors of YBa2Cu3O7-x + BaZrO3

There are numerous potential applications for superconducting tapes, based on YBa2Cu3O7-x (YBCO) films coated onto metallic substrates. A long established goal of more than 15 years has been to understand the magnetic flux pinning mechanisms which allow films to maintain high current densities out to high magnetic fields. In fact, films carry 1-2 orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialisation of conductors is much closer, for both better performance and lower fabrication costs, an important goal is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route which yields a 1.5 to 5-fold improvement in the in-field current densities of already-high-quality conductors

High-temperature change of the creep rate in YBa 2Cu 3O 7-δ films with different pinning landscapes

Magnetic relaxation measurements in YBa 2Cu 3O 7-δ (YBCO) films at intermediate and high temperatures show that the collective vortex creep based on the elastic motion of the vortex lattice has a crossover to fast creep that significantly reduces the superconducting critical current density (J c). This crossover occurs at temperatures much lower than the irreversibility field line. We study the influence of different kinds of crystalline defects, such as nanorods, twin boundaries, and nanoparticles, on the high-temperature vortex phase diagram of YBCO films. We found that the magnetization relaxation data is a fundamental tool to understand the pinning at high temperatures. The results indicate that high J c values are directly associated with small creep rates. Based on the analysis of the depinning temperature in films with columnar defects, our results indicate that the size of the defects is the relevant parameter that determines thermal depinning at high temperatures. Also, the extension of the collective creep regime depends on the density of the pinning centers.Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Miura, M.. No especifíca;Fil: Baca, J.. No especifíca;Fil: Maiorov, B.. No especifíca;Fil: Usov, I.. No especifíca;Fil: Dowden, P.. No especifíca;Fil: Foltyn, S. R.. No especifíca;Fil: Holesinger, T. G.. No especifíca;Fil: Willis, J. O.. No especifíca;Fil: Marken, K. R.. No especifíca;Fil: Izumi, T.. No especifíca;Fil: Shiohara, Y.. No especifíca;Fil: Civale, L.. No especifíca

Magneto-optical imaging and current distributions in high-{Tc} superconductors

Recent studies on the magneto-optical (MO) imaging of the magnetic flux and current distributions in polycrystalline high-{Tc} superconductors are summarized. The authors studied a wide spectrum of high-{Tc} materials, from single grain boundaries in YBCO bicrystals, to polycrystalline YBCO thick films deposited on an IBAD-buffer layer grown on a polycrystalline Hastelloy substrate, to Bi-2223 tapes. In all cases they found that structural defects (e.g., high-angle grain boundaries, second phase precipitates, microcrack networks, etc.) significantly limit the current-carrying capability. These defects make the magnetic flux distribution highly inhomogeneous, in turn producing granular and percolative current flow. By inverting the Biot-Savart law for thin film and slab geometries, they were able to reconstruct the local current flow patterns around defects and thus identify the current-carrying percolative paths and map the distribution of local critical currents J{sub c}(r). Such studies show that, even in high-J{sub c} materials, the local J{sub c}(r) can vary by a factor 2--10 due to defects. Since the maximum local J{sub c}(r) values can significantly exceed the numbers obtained by transport measurements, it is clear that there are still significant opportunities for raising the J{sub c} of polycrystalline HTS conductors

Measurement properties of the Minimal Insomnia Symptom Scale (MISS) in an elderly population in Sweden

<p>Abstract</p> <p>Background</p> <p>Insomnia is common among elderly people and associated with poor health. The Minimal Insomnia Symptom Scale (MISS) is a three item screening instrument that has been found to be psychometrically sound and capable of identifying insomnia in the general population (20-64 years). However, its measurement properties have not been studied in an elderly population. Our aim was to test the measurement properties of the MISS among people aged 65 + in Sweden, by replicating the original study in an elderly sample.</p> <p>Methods</p> <p>Data from a cross-sectional survey of 548 elderly individuals were analysed in terms of assumptions of summation of items, floor/ceiling effects, reliability and optimal cut-off score by means of ROC-curve analysis and compared with self-reported insomnia criteria.</p> <p>Results</p> <p>Corrected item-total correlations ranged between 0.64-0.70, floor/ceiling effects were 6.6/0.6% and reliability was 0.81. ROC analysis identified the optimal cut-off score as ≥7 (sensitivity, 0.93; specificity, 0.84; positive/negative predictive values, 0.256/0.995). Using this cut-off score, the prevalence of insomnia in the study sample was 21.7% and most frequent among women and the oldest old.</p> <p>Conclusions</p> <p>Data support the measurement properties of the MISS as a possible insomnia screening instrument for elderly persons. This study make evident that the MISS is useful for identifying elderly people with insomnia-like sleep problems. Further studies are needed to assess its usefulness in identifying clinically defined insomnia.</p