1,018 research outputs found
Contamination of spacecraft by recontact of dumped liquids
Liquids partially freeze when dumped from spacecraft producing particles which are released into free space at various velocities. Recontact of these particles with the spacecraft is possible for specific particle sizes and velocities and, therefore, can become contamination for experiments within the spacecraft or released experiments as a result of waste and potable water dumped from Space Shuttle. An examination of dump characteristics was conducted on STS-29 using both on-board video records and ground based measurements. A preliminary analysis of data from this flight indicates particle velocities are in the range of 30 to 75 ft/sec and recontact is possible for limited particle sizes
Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions
We compute the frequency and magnetic field dependencies of the reflectivity
in layered superconductors with two alternating intrinsic Josephson
junctions with different critical current densities and quasiparticle
conductivities for the electric field polarized along the c-axis. The parameter
describing the electronic compressibility of the layers and the charge
coupling of neighboring junctions was extracted for the
SmLaSrCuO superconductor from two independent
optical measurements, the fit of the loss function at zero magnetic
field and the magnetic field dependence of the peak positions in .
The experiments are consistent with a free electron value for near
the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte
Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors
We consider the magnetic field dependence of the plasma resonance frequency
in pristine and in irradiated BiSrCaCuO crystals near . At
low magnetic fields we relate linear in field corrections to the plasma
frequency to the average distance between the pancake vortices in the
neighboring layers (wandering length). We calculate the wandering length in the
case of thermal wiggling of vortex lines, taking into account both Josephson
and magnetic interlayer coupling of pancakes. Analyzing experimental data, we
found that (i) the wandering length becomes comparable with the London
penetration depth near T and (ii) at small melting fields ( G) the
wandering length does not change much at the melting transition. This shows
existence of the line liquid phase in this field range. We also found that
pinning by columnar defects affects weakly the field dependence of the plasma
resonance frequency near .Comment: RevTex, 4 pages, 2 PS figures, Submitted to Phys. Rev.
New superconducting phases in field-induced organic superconductor lambda-(BETS)2FeCl4
We derive the parallel upper critical field, Hc2, as a function of the
temperature T in quasi-2D organic compound lambda-(BETS)2FeCl4, accounting for
the formation of the nonuniform LOFF state. To further check the 2D LOFF model
we propose to study the Hc2(T) curve at low T in tilted fields, where the
vortex state is described by the high Landau level functions characterized by
the index n. We predict a cascade of first order transitions between vortex
phases with different n, between phases with different types of the symmetry at
given n and the change of the superconducting transition from the second order
to the first order as FeCl4 ions are replaced partly by GaCl4 ions.Comment: 4 pages, 3 figures, to be published in PR
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
The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river
Ocean acidification threatens to reduce pH and aragonite saturation state
(ΩA) in estuaries, potentially damaging their ecosystems.
However, the impact of highly variable river total alkalinity (TA) and
dissolved inorganic carbon (DIC) on pH and ΩA in these
estuaries is unknown. We assess the sensitivity of estuarine surface pH and
ΩA to river TA and DIC using a coupled biogeochemical model
of the Strait of Georgia on the Canadian Pacific coast and place the results
in the context of global rivers. The productive Strait of Georgia estuary has
a large, seasonally variable freshwater input from the glacially fed,
undammed Fraser River. Analyzing TA observations from this river plume and pH
from the river mouth, we find that the Fraser is moderately alkaline
(TA 500–1000 µmol kg−1) but relatively DIC-rich. Model
results show that estuarine pH and ΩA are sensitive to
freshwater DIC and TA, but do not vary in synchrony except at high
DIC : TA. The asynchrony occurs because increased freshwater TA is
associated with increased DIC, which contributes to an increased estuarine
DIC : TA and reduces pH, while the resulting higher carbonate ion
concentration causes an increase in estuarine ΩA. When
freshwater DIC : TA increases (beyond  ∼  1.1), the shifting chemistry
causes a paucity of the carbonate ion that overwhelms the simple
dilution/enhancement effect. At this high DIC : TA ratio, estuarine
sensitivity to river chemistry increases overall. Furthermore, this increased
sensitivity extends to reduced flow regimes that are expected in future.
Modulating these negative impacts is the seasonal productivity in the estuary
which draws down DIC and reduces the sensitivity of estuarine pH to
increasing DIC during the summer season
Josephson Plasma Resonance as a Structural Probe of Vortex Liquid
Recent developments of the Josephson plasma resonance and transport c-axis
measurements in layered high T superconductors allow to probe Josephson
coupling in a wide range of the vortex phase diagram. We derive a relation
between the field dependent Josephson coupling energy and the density
correlation function of the vortex liquid. This relation provides a unique
opportunity to extract the density correlation function of pancake vortices
from the dependence of the plasma resonance on the -component of the
magnetic field at a fixed -axis component.Comment: 4 pages, 1 fugure, accepted to Phys. Rev. Let
Research priorities of people living with Turner syndrome
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148393/1/ajmgc31676.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148393/2/ajmgc31676_am.pd
Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments
We present an experimental study of thermally activated flux creep in a
superconducting ring-shaped epitaxial YBCO film as well as a new way of
analyzing the experimental data. The measurements were made in a wide range of
temperatures between 10 and 83 K. The upper temperature limit was dictated by
our experimental technique and at low temperatures we were limited by a
crossover to quantum tunneling of vortices. It is shown that the experimental
data can very well be described by assuming a simple thermally activated
hopping of vortices or vortex bundles over potential barriers, whereby the
hopping flux objects remain the same for all currents and temperatures. The new
procedure of data analysis also allows to establish the current and temperature
dependencies of the flux-creep activation energy U, as well as the temperature
dependence of the critical current Ic, from the flux-creep rates measured at
different temperatures. The variation of the activation energy with current,
U(I/Ic), is then used to reconstruct the profile of the potential barriers in
real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review
High-Field Quasiparticle Tunneling in Bi_2Sr_2CaCu_2O_8+delta: Negative Magnetoresistance in the Superconducting State
We report on the c-axis resistivity rho_c(H) in Bi_2Sr_2CaCu_2O_{8+\delta}
that peaks in quasi-static magnetic fields up to 60 T. By suppressing the
Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity
\sigma_c (H), we find that the negative slope of \rho_c(H) above the peak is
due to quasiparticle tunneling conductivity \sigma_q(H) across the CuO_2 layers
below H_{c2}. At high fields (a) \sigma_q(H) grows linearly with H, and (b)
\rho_c(T) tends to saturate (sigma_c \neq 0) as T->0, consistent with the
scattering at the nodes of the d-gap. A superlinear sigma_q(H) marks the normal
state above T_c.Comment: 4p., 5 fig. (.eps), will be published in Phys. Rev. Let
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