2,185 research outputs found
SPE water electrolyzers in support of the lunar outpost
During the 1970s, the SPE water electrolyzer, which uses ion exchange membranes as its sole electrolyte, was developed for nuclear submarine metabolic oxygen production. These developments included SPE water electrolyzer operation at up to 3,000 psia and at current densities in excess of 1,000 amps per square foot. The SPE water electrolyzer system is now fully qualified for both the U.S. and U.K. Navies with tens of thousands of system hours accumulated at sea. During the 1980s, the basic SPE water electrolyzer cell structure developed for the Navies was incorporated into several demonstrations for NASA's Space Station Program. Among these were: the SPE regenerative fuel cell for electrical energy storage; the SPE water electrolyzer for metabolic oxygen production; and the high pressure SPE water electrolyzer for reboost propulsion reactant production. In the 1990s, one emphasis will be the development of SPE water electrolyzers for the Lunar Outposts Currently defined potential Lunar Outpost applications for the SPE water electrolyzer include: SPE water electrolyzers for metabolic oxygen and potable water production from reclaimed water; and SPE water electrolyzers operating at high pressure as part of stationary and mobile surface energy storage systems
Spaceborne CO2 laser communications systems
Projections of the growth of earth-sensing systems for the latter half of the 1980's show a data transmission requirement of 300 Mbps and above. Mission constraints and objectives lead to the conclusion that the most efficient technique to return the data from the sensing satellite to a ground station is through a geosynchronous data relay satellite. Of the two links that are involved (sensing satellite to relay satellite and relay satellite to ground), a laser system is most attractive for the space-to-space link. The development of CO2 laser systems for space-to-space applications is discussed with the completion of a 300 Mpbs data relay receiver and its modification into a transceiver. The technology and state-of-the-art of such systems are described in detail
Global Phase Diagram of the High Tc Cuprates
The high Tc cuprates have a complex phase diagram with many competing phases.
We propose a bosonic effective quantum Hamiltonian based on the projected SO(5)
model with extended interactions, which can be derived from the microscopic
models of the cuprates. The global phase diagram of this model is obtained
using mean-field theory and the Quantum Monte Carlo simulation, which is
possible because of the absence of the minus sign problem. We show that this
single quantum model can account for most salient features observed in the high
Tc cuprates, with different families of the cuprates attributed to different
traces in the global phase diagram. Experimental consequences are discussed and
new theoretical predictions are presented.Comment: 19 pages, 20 figures, with updated references, final versio
Vortex avalanches in the non-centrosymmetric superconductor Li2Pt3B
We investigated the vortex dynamics in the non-centrosymmetric superconductor
Li_2Pt_3B in the temperature range 0.1 K - 2.8 K. Two different logarithmic
creep regimes in the decay of the remanent magnetization from the Bean critical
state have been observed. In the first regime, the creep rate is
extraordinarily small, indicating the existence of a new, very effective
pinning mechanism. At a certain time a vortex avalanche occurs that increases
the logarithmic creep rate by a factor of about 5 to 10 depending on the
temperature. This may indicate that certain barriers against flux motion are
present and they can be opened under increased pressure exerted by the
vortices. A possible mechanism based on the barrier effect of twin boundaries
is briefly discussed
Ultraviolet absorption: Experiment MA-059
A technique devised to permit the measurement of atmospheric species concentrations is described. This technique involves the application of atomic absorption spectroscopy and the quantitative observation of resonance fluorescence in which atomic or molecular species scatter resonance radiation from a light source into a detector. A beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation was sent from Apollo to Soyuz. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Results of postflight analysis of the resonance fluorescence data are discussed
Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy
In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and
hole-like states have been found to exhibit spatial modulations in anti-phase
with each other along the Cu-O bonding direction. Some kind of
one-dimensionality has been observed in the vortex core, and it is more clearly
seen in differential conductance maps at lower biases below +-9 mV
Intercomparison of ground-based ozone and NO2 measurements during the MANTRA 2004 campaign
The MANTRA (Middle Atmosphere Nitrogen TRend Assessment) 2004 campaign took place in Vanscoy, Saskatchewan, Canada (52° N, 107° W) from 3 August to 15 September, 2004. In support of the main balloon launch, a suite of five zenith-sky and direct-Sun-viewing UV-visible ground-based spectrometers was deployed, primarily measuring ozone and NO2 total columns. Three Fourier transform spectrometers (FTSs) that were part of the balloon payload also performed ground-based measurements of several species, including ozone. Ground-based measurements of ozone and NO2 differential slant column densities from the zenith-viewing UV-visible instruments are presented herein. They are found to partially agree within NDACC (Network for the Detection of Atmospheric Composition Change) standards for instruments certified for process studies and satellite validation. Vertical column densities of ozone from the zenith-sky UV-visible instruments, the FTSs, a Brewer spectrophotometer, and ozonesondes are compared, and found to agree within the combined error estimates of the instruments (15%). NO2 vertical column densities from two of the UV-visible instruments are compared, and are also found to agree within combined error (15%)
Fourier-Transformed Local Density of States and Tunneling into a -Wave Superconductor with Bosonic Modes
We analyze the effects of the electronic coupling to bosonic modes in a
d-wave superconductor. The role of the scattering due to boson on the momentum
transfer between electronic states in the Brilloine zone is addressed. We
consider specific examples of phonon, breathing mode phonon and spin
resonance at . The Fourier spectrum of the energy derivative local
density of states (LDOS) is calculated. To properly calibrate the effects of
different modes we fix the quasipartilce renormalization at specific momentum
points. It is found that the mode with highly anisotropic
momentum-dependent coupling matrix element gives rise to well definded features
in the Fourier spectrum, at the energy of mode plus gap, with a momentum
transfer along the Cu-O bond direction of cuprates. This result is in a
striking contrast to the cases of the coupling to other modes and also to the
case of no mode coupling. The origin of this difference is explored in detail.
A comparison with the recent STM experiments is briefly discussed.Comment: 9 pages, 4 eps figures include
Absence of large nanoscale electronic inhomogeneities in the Ba(Fe1-xCox)2As2 pnictide
75As NMR and susceptiblity were measured in a Ba(Fe1-xCox)2As2 single crystal
for x=6% for various field H values and orientations. The sharpness of the
superconducting and magnetic transitions demonstrates a homogeneity of the Co
doping x better than +-0.25%. On the nanometer scale, the paramagnetic part of
the NMR spectra is found very anisotropic and very narrow for H//ab which
allows to rule out the interpretation of Ref.[6] in terms of strong Co induced
electronic inhomogeneities. We propose that a distribution of hyperfine
couplings and chemical shifts due to the Co effect on its nearest As explains
the observed linewidths and relaxations. All these measurements show that Co
substitution induces a very homogeneous electronic doping in BaFe2As2, from
nano to micrometer lengthscales, on the contrary to the K doping.Comment: 6 pages, 4 figure
Measurements and analysis of the upper critical field on an underdoped and overdoped compounds
The upper critical field is one of the many non conventional
properties of high- cuprates. It is possible that the
anomalies are due to the presence of inhomogeneities in the local charge
carrier density of the planes. In order to study this point, we
have prepared good quality samples of polycrystalline
using the wet-chemical method, which has demonstrated to produce samples with a
better cation distribution. In particular, we have studied the temperature
dependence of the second critical field, , through the magnetization
measurements on two samples with opposite average carrier concentration
() and nearly the same critical temperature, namely
(underdoped) and (overdoped). The results close to do not
follow the usual Ginzburg-Landau theory and are interpreted by a theory which
takes into account the influence of the inhomogeneities.Comment: Published versio
- âŠ