1,794 research outputs found
On narrowing coated conductor film: emergence of granularity-induced field hysteresis of transport critical current
Critical current density Jc in polycrystalline or granular superconducting
material is known to be hysteretic with applied field H due to the focusing of
field within the boundary between adjacent grains. This is of concern in the
so-called coated conductors wherein superconducting film is grown on a
granular, but textured surface of a metal substrate. While previous work has
mainly been on Jc determined using induced or magnetization currents, the
present work utilizes transport current via an applied potential in strip
geometry. It is observed that the effect is not as pronounced using transport
current, probably due to a large difference in criterion voltage between the
two types of measurements. However, when the films are narrowed by patterning
into 200-, 100-, or 80-micron, the hysteresis is clearly seen, because of the
forcing of percolation across higher-angle grain boundaries. This effect is
compared for films grown on ion-beam-assisted-deposited (IBAD) YSZ substrate
and those grown on rolling-assisted-biaxially-textures substrates (RABiTS)
which have grains that are about ten times larger. The hysteresis is more
pronounced for the latter, which is more likely to have a weak grain boundary
spanning the width of the microbridge. This is also of concern to applications
in which coated conductors will be striated in order to reduce of AC losses.Comment: text-only: 10 pages, plus 5 figures on 5 page
Numerical simulations on the motion of atoms travelling through a standing-wave light field
The motion of metastable helium atoms travelling through a standing light
wave is investigated with a semi-classical numerical model. The results of a
calculation including the velocity dependence of the dipole force are compared
with those of the commonly used approach, which assumes a conservative dipole
force. The comparison is made for two atom guiding regimes that can be used for
the production of nanostructure arrays; a low power regime, where the atoms are
focused in a standing wave by the dipole force, and a higher power regime, in
which the atoms channel along the potential minima of the light field. In the
low power regime the differences between the two models are negligible and both
models show that, for lithography purposes, pattern widths of 150 nm can be
achieved. In the high power channelling regime the conservative force model,
predicting 100 nm features, is shown to break down. The model that incorporates
velocity dependence, resulting in a structure size of 40 nm, remains valid, as
demonstrated by a comparison with quantum Monte-Carlo wavefunction
calculations.Comment: 9 pages, 4 figure
Low Power Superconducting Microwave Applications and Microwave Microscopy
We briefly review some non-accelerator high-frequency applications of
superconductors. These include the use of high-Tc superconductors in front-end
band-pass filters in cellular telephone base stations, the High Temperature
Superconductor Space Experiment, and high-speed digital electronics. We also
present an overview of our work on a novel form of near-field scanning
microscopy at microwave frequencies. This form of microscopy can be used to
investigate the microwave properties of metals and dielectrics on length scales
as small as 1 mm. With this microscope we have demonstrated quantitative
imaging of sheet resistance and topography at microwave frequencies. An
examination of the local microwave response of the surface of a heat-treated
bulk Nb sample is also presented.Comment: 11 pages, including 6 figures. Presented at the Eight Workshop on RF
Superconductivity. To appear in Particle Accelerator
Superconducting Material Diagnostics using a Scanning Near-Field Microwave Microscope
We have developed scanning near-field microwave microscopes which can image
electrodynamic properties of superconducting materials on length scales down to
about 2 m. The microscopes are capable of quantitative imaging of sheet
resistance of thin films, and surface topography. We demonstrate the utility of
the microscopes through images of the sheet resistance of a YBa2Cu3O7-d thin
film wafer, images of bulk Nb surfaces, and spatially resolved measurements of
Tc of a YBa2Cu3O7-d thin film. We also discuss some of the limitations of the
microscope and conclude with a summary of its present capabilities.Comment: 6 pages with 9 figures, Proceedings of the Applied Superconductivity
Conference 199
Scanning tunneling microscopy and spectroscopy at low temperatures of the (110) surface of Te doped GaAs single crystals
We have performed voltage dependent imaging and spatially resolved
spectroscopy on the (110) surface of Te doped GaAs single crystals with a low
temperature scanning tunneling microscope (STM). A large fraction of the
observed defects are identified as Te dopant atoms which can be observed down
to the fifth subsurface layer. For negative sample voltages, the dopant atoms
are surrounded by Friedel charge density oscillations. Spatially resolved
spectroscopy above the dopant atoms and above defect free areas of the GaAs
(110) surface reveals the presence of conductance peaks inside the
semiconductor band gap. The appearance of the peaks can be linked to charges
residing on states which are localized within the tunnel junction area. We show
that these localized states can be present on the doped GaAs surface as well as
at the STM tip apex.Comment: 8 pages, 8 figures, accepted for publication in PR
The impact of an elective on disability and global health on the perception of medical students regarding persons with disabilities
Non-equilibrium Superconductivity and Quasiparticle Dynamics studied by Photo Induced Activation of Mm-Wave Absorption (PIAMA)
We present a study of non-equilibrium superconductivity in DyBa2Cu3O7-d using
photo induced activation of mm-wave absorption (PIAMA). We monitor the time
evolution of the thin film transmissivity at 5 cm-1 subject to pulsed infrared
radiation. In addition to a positive bolometric signal we observe a second,
faster, decay with a sign opposite to the bolometric signal for T>40 K. We
attribute this to the unusual properties of quasi-particles residing near the
nodes of an unconventional superconductor, resulting in a strong enhancement of
the recombination time.Comment: 4 pages, REVTeX, Submitted to Phys. Rev. Letter
The combined effect of chemoprophylaxis with single dose rifampicin and immunoprophylaxis with BCG to prevent leprosy in contacts of newly diagnosed leprosy cases: A cluster randomized controlled trial (MALTALEP study)
Background: Despite almost 30 years of effective chemotherapy with MDT, the global new case detection rate of leprosy has remained quite constant over the past years. New tools and methodologies are necessary to interrupt the transmission of M. leprae. Single-dose rifampicin (SDR) has been shown to prevent 57% of incident cases of leprosy in the first two years, when given to contacts of newly diagnosed cases. Immunization of contacts with BCG has been less well documented, but appears to have a preventive effect lasting up to 9 years. However, one major disadvantage is the occurrence of excess cases within the first year after immunization. The objective of this study is to examine the effect of chemoprophylaxis with SDR and immunoprophylaxis with BCG on the clinical outcome as well as on host immune responses and gene expression profiles in contacts of newly diagnosed leprosy patients. We hypothesize that the effects of both interventions may be complementary, causing the combined preventive outcome to be significant and long-lasting.Methods/design: Through a cluster randomized controlled trial we compare immunization with BCG alone with BCG plus SDR in contacts of new leprosy cases. Contact groups of around 15 persons will be established for each of the 1300 leprosy patients included in the trial, resulting in approximately 20,000 contacts in total. BCG will be administered to the intervention group followed by SDR, 2 months later. The control group will receive BCG only. In total 10,000 contacts will be included in both intervention arms over a 2-year period. Follow-up will take place one year as well as two years after intake. The primary outcome is the occurrence of clinical leprosy within two years. Simultaneously with vaccination and SDR, blood samples for in vitro analyses will be obtained from 300 contacts participating in the trial to determine the effect of these chemo- and immunoprophylactic interventions on immune and genetic host parameters.Discussion: Combined chemoprophylaxis and immunoprophylaxis is potentially a very powerful and innovative tool aimed at contacts of leprosy patients that could reduce the transmission of M. leprae markedly. The trial intends to substantiate this potential preventive effect. Evaluation of immune and genetic biomarker profiles will allow identification of pathogenic versus (BCG-induced) protective host biomarkers and could lead to effective prophylactic interventions for leprosy using optimized tools for identification of individuals who are most at risk of developing disease.Trial registration: Netherlands Trial Register: NTR3087
Undertstanding the Home Market Effect and the Gravity Equation: The Role of Differentiating Goods
This paper argues that the theoretical foundations for the gravity equation are general, while the empirical performance of the gravity equation is specific to the type of goods examined. Most existing theory for the gravity equation depends on the assumption of differentiated goods. We show that the gravity equation can also be derived from a reciprocal dumping' model of trade in homogeneous goods. The different theories have different testable implications. Theoretically, the gravity equation should have a lower domestic income elasticity for exports of homogeneous goods than of differentiated goods, because of a home market' effect which depends on barriers to entry. We quantify the home market effect empirically using cross-sectional gravity equations, and find that domestic income export elasticities are indeed substantially higher for differentiated goods than for homogeneous goods.
Multi-Harmony: detecting functional specificity from sequence alignment
Many protein families contain sub-families with functional specialization, such as binding different ligands or being involved in different proteināprotein interactions. A small number of amino acids generally determine functional specificity. The identification of these residues can aid the understanding of protein function and help finding targets for experimental analysis. Here, we present multi-Harmony, an interactive web sever for detecting sub-type-specific sites in proteins starting from a multiple sequence alignment. Combining our Sequence Harmony (SH) and multi-Relief (mR) methods in one web server allows simultaneous analysis and comparison of specificity residues; furthermore, both methods have been significantly improved and extended. SH has been extended to cope with more than two sub-groups. mR has been changed from a sampling implementation to a deterministic one, making it more consistent and user friendly. For both methods Z-scores are reported. The multi-Harmony web server produces a dynamic output page, which includes interactive connections to the Jalview and Jmol applets, thereby allowing interactive analysis of the results. Multi-Harmony is available at http://www.ibi.vu.nl/ programs/shmrwww
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