1,554 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
Matrix Metalloproteinase-9 in Pneumococcal Meningitis: Activation via an Oxidative Pathway
In experimental bacterial meningitis, matrix metalloproteinases (MMPs) and reactive oxygen species (ROS) contribute to brain damage. MMP-9 increases in cerebrospinal fluid (CSF) during bacterial meningitis and is associated with the brain damage that is a consequence of the disease. This study assesses the origin of MMP-9 in bacterial meningitis and how ROS modulate its activity. Rat brain-slice cultures and rat polymorphonuclear cells (PMNs) that had been challenged with capsule-deficient heat-inactivated Streptococcus pneumoniae R6 (hiR6) released MMP-9. Coincubation with either catalase, with the myeloperoxidase inhibitor azide, or with the hypochlorous acid scavenger methionine almost completely prevented activation, but not the release, of MMP-9, in supernatants of human PMNs stimulated with hiR6. Thus, in bacterial meningitis, both brain-resident cells and invading PMNs may act as sources of MMP-9, and stimulated PMNs may activate MMP-9 via an ROS-dependent pathway. MMP-9 activation by ROS may represent a target for therapeutic intervention in bacterial meningiti
Low Frequency Quantum Transport in a Three-probe Mesoscopic Conductor
The low frequency quantum transport properties of a three-probe mesoscopic
conductor are studied using B\"uttiker's AC transport formalism. The static
transmission coefficients and emittance matrix of the system were computed by
explicitly evaluating the various partial density of states (PDOS). We have
investigated the finite size effect of the scattering volume on the global
PDOS. By increasing the scattering volume we observed a gradual improvement in
the agreement of the total DOS as computed externally or locally. Our numerical
data permits a particular fitting form of the finite size effect.Comment: 13 pages, LaTeX, submitted to Phys. Rev.
An improved continuous compositional-spread technique based on pulsed-laser deposition and applicable to large substrate areas
A new method for continuous compositional-spread (CCS) thin-film fabrication
based on pulsed-laser deposition (PLD) is introduced. This approach is based on
a translation of the substrate heater and the synchronized firing of the
excimer laser, with the deposition occurring through a slit-shaped aperture.
Alloying is achieved during film growth (possible at elevated temperature) by
the repeated sequential deposition of sub-monolayer amounts. Our approach
overcomes serious shortcomings in previous in-situ implementations of CCS based
on sputtering or PLD, in particular the variations of thickness across the
compositional spread and the differing deposition energetics as function of
position. While moving-shutter techniques are appropriate for PLD-approaches
yielding complete spreads on small substrates (i.e. small as compared to
distances over which the deposition parameters in PLD vary, typically about 1
cm), our method can be used to fabricate samples that are large enough for
individual compositions to be analyzed by conventional techniques, including
temperature-dependent measurements of resistivity and dielectric and magnetic
and properties (i.e. SQUID magnetometry). Initial results are shown for spreads
of (Sr,Ca)RuO.Comment: 6 pages, 8 figures, accepted for publication in Rev. Sci. Instru
Charge injection instability in perfect insulators
We show that in a macroscopic perfect insulator, charge injection at a
field-enhancing defect is associated with an instability of the insulating
state or with bistability of the insulating and the charged state. The effect
of a nonlinear carrier mobility is emphasized. The formation of the charged
state is governed by two different processes with clearly separated time
scales. First, due to a fast growth of a charge-injection mode, a localized
charge cloud forms near the injecting defect (or contact). Charge injection
stops when the field enhancement is screened below criticality. Secondly, the
charge slowly redistributes in the bulk. The linear instability mechanism and
the final charged steady state are discussed for a simple model and for
cylindrical and spherical geometries. The theory explains an experimentally
observed increase of the critical electric field with decreasing size of the
injecting contact. Numerical results are presented for dc and ac biased
insulators.Comment: Revtex, 7pages, 4 ps figure
A catalog of Nearby Poor Clusters of Galaxies
A catalog of 732 optically selected, nearby poor clusters of galaxies
covering the entire sky north of declination is presented. The
poor clusters, called WBL clusters, were identified as concentrations of 3 or
more galaxies with photographic magnitudes brighter than 15.7, possessing a
galaxy surface overdensity of . These criteria are consistent with
those used in the identification of the original Yerkes poor clusters, and this
new catalog substantially increases the sample size of such objects. These poor
clusters cover the entire range of galaxy associations up to and including
Abell clusters, systematically including poor and rich galaxy systems spanning
over three orders of magnitude in the cluster mass function. As a result, this
new catalog contains a greater diversity of richness and structures than other
group catalogs, such as the Hickson or Yerkes catalogs. The information on
individual galaxies includes redshifts and cross-references to other galaxy
catalogs. The entries for the clusters include redshift (where available) and
cross-references to other group and cluster catalogs.Comment: 27 pages, 7 figures, + one 20-page landscape table, accepted for
publication in A
New supersymmetric quartet of nuclei in the A=190 mass region
We present evidence for a new supersymmetric quartet in the A=190 region of
the nuclear mass table. New experimental information on transfer and neutron
capture reactions to the odd-odd nucleaus 194 Ir strongly suggests the
existence of a new supersymmetric quartet, consisting of the 192,193 Os and
193,194 Ir nuclei. We make explicit predictions for the odd-neutron nucleus 193
Os, and suggest that its spectroscopic properties be measured in dedicated
experiments.Comment: 5 pages, 4 figures, updated figures and revised text, Physical Review
C, Rapid Communication, in pres
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