944 research outputs found
An improved method for testing performance of vidicons during vibration
Vidicon electron beam modulation is used for checking the performance of vidicons in mechanical vibration tests. The vidicon electron beam is modulated with an external signal during the write period thereby storing the image on the vidicon face
Calibration of the Langley 16-foot transonic tunnel with test section air removal
The Langley 16-foot transonic tunnel with test section air removal (plenum suction) was calibrated to a Mach number of 1.3. The results of the calibration, including the effects of slot shape modifications, test section wall divergence, and water vapor condensation, are presented. A complete description of the wind tunnel and its auxiliary equipment is included
Cooperon propagator description of high temperature superconductivity
A phenomenological description of the high-Tc superconductors based on the
Cooperon propagator is presented. This model allows one to study the effects of
local pairing correlations and long-range phase fluctuations on the same
footing, both above and below Tc. Based on numerical calculations, it is shown
that the two types of correlations contribute to the gap/pseudogap in the
single-particle excitation spectra. The concourse of these two effects can
induce low energy states, which should be observable in underdoped materials at
very low temperature.Comment: LaTeX, 6 pages, 2 EPS figures; paper presented at New^3SC-3, Hawaii,
01/2001. To appear in Physica
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Important Considerations in Plasmon-Enhanced Electrochemical Conversion at Voltage-Biased Electrodes.
In this perspective we compare plasmon-enhanced electrochemical conversion (PEEC) with photoelectrochemistry (PEC). PEEC is the oxidation or reduction of a reactant at the illuminated surface of a plasmonic metal (or other conductive material) while a potential bias is applied. PEC uses solar light to generate photoexcited electron-hole pairs to drive an electrochemical reaction at a biased or unbiased semiconductor photoelectrode. The mechanism of photoexcitation of charge carriers is different between PEEC and PEC. Here we explore how this difference affects the response of PEEC and PEC systems to changes in light, temperature, and surface morphology of the photoelectrode
Cooperative localization-delocalization in the high Tc cuprates
The intrinsic metastable crystal structure of the cuprates results in local
dynamical lattice instabilities, strongly coupled to the density fluctuations
of the charge carriers. They acquire in this way simultaneously both,
delocalized and localized features. It is responsible for a partial fractioning
of the Fermi surface, i.e., the Fermi surface gets hidden in a region around
the anti-nodal points, because of the opening of a pseudogap in the normal
state, arising from a partial charge localization. The high energy localized
single-particle features are a result of a segregation of the homogeneous
crystal structure into checker-board local nano-size structures, which breaks
the local translational and rotational symmetry. The pairing in such a system
is dynamical rather than static, whereby charge carriers get momentarily
trapped into pairs in a deformable dynamically fluctuating ligand environment.
We conclude that the intrinsically heterogeneous structure of the cuprates must
play an important role in this type of superconductivity.Comment: 14 pages, 8 figures, Proceedings of the "International Conference on
Condensed Matter Theories", Quito, 2009 Int. J. Mod. Phys. B 2010 (Accepted
Cofinite Graphs and Their Profinite Completions
We generalize the idea of cofinite groups, due to B. Hartley, [2]. First we define cofinite spaces in general. Then, as a special situation, we study cofinite graphs and their uniform completions.The idea of constructing a cofinite graph starts with defining a uniform topological graph , in an appropriate fashion. We endow abstract graphs with uniformities corresponding to separating filter bases of equivalence relations with finitely many equivalence classes over . It is established that for any cofinite graph there exists a unique cofinite completion
Measurement of the complex Faraday angle in thin-film metals and high temperature superconductors
A sensitive polarization modulation technique uses photoelastic modulation
and hetrodyne detection to simultaneously measure the Faraday rotation and
induced ellipticity in light transmitted by semiconducting and metallic
samples. The frequencies measured are in the mid-infrared and correspond to the
spectral lines of a CO2 laser. The measured temperature range is continuous and
extends from 35 to 330K. Measured samples include GaAs and Si substrates, gold
and copper films, and YBCO and BSCCO high temperature superconductors.Comment: 12 pages of text, 6 figures, fixed typos in formulas, added figur
Probing Pseudogap by Josephson Tunneling
We propose here an experiment aimed to determine whether there are
superconducting pairing fluctuations in the pseudogap regime of the high-
materials. In the experimental setup, two samples above are brought into
contact at a single point and the differential AC conductivity in the presence
of a constant applied bias voltage between the samples, , should be
measured. We argue the the pairing fluctuations will produce randomly
fluctuating Josephson current with zero mean, however the current-current
correlator will have a characteristic frequency given by Josephson frequency
. We predict that the differential AC conductivity
should have a peak at the Josephson frequency with the width determined by the
phase fluctuations time.Comment: 4 pages, 2 eps figure
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