10,314 research outputs found
Radio sky mapping from satellites at very low frequencies
Wave Distribution Function (WDF) analysis is a procedure for making sky maps of the sources of natural electromagnetic waves in space plasmas, given local measurements of some or all of the three magnetic and three electric field components. The work that still needs to be done on this subject includes solving basic methodological problems, translating the solution into efficient algorithms, and embodying the algorithms in computer software. One important scientific use of WDF analysis is to identify the mode of origin of plasmaspheric hiss. Some of the data from the Japanese satellite Akebono (EXOS D) are likely to be suitable for this purpose
Effluent sampling of Titan 3 C vehicle exhaust
Downwind in situ ground-level measurements of the exhaust from a Titan 3 C launch vehicle were made during a normal launch. The measurement activity was conducted as part of an overall program to obtain field data for comparison with the multilayer dispersion model currently being used to predict the behavior of rocket vehicle exhaust clouds. All measurements were confined to land, ranging from the launch pad to approximately 2 kilometers downwind from the pad. Measurement systems included detectors for hydrogen chloride (HCl), carbon dioxide (CO2), and particulates (Al2O3). Airborne and ground-based optical systems were employed to monitor exhaust cloud rise, growth, and movement. These measurement systems, located along the ground track (45 deg azimuth from the launch pad) of the exhaust cloud, showed no effluents attributable to the launch. Some hydrogen chloride and aluminum oxide were detected in the surface wind direction (15 deg azimuth) from the pad. Comparisons with the model were made in three areas: (1) assumption of cloud geometry at stabilization; (2) prediction of cloud stabilization altitude; and (3) prediction of the path of cloud travel. In addition, the importance of elemental analyses of the particulate samples is illustrated
Data synthesis and display programs for wave distribution function analysis
At the National Space Science Data Center (NSSDC) software was written to synthesize and display artificial data for use in developing the methodology of wave distribution analysis. The software comprises two separate interactive programs, one for data synthesis and the other for data display
Saddle-point van Hove singularity and the phase diagram of high-Tc cuprates
We examine the generic phase behavior of high-Tc cuprate superconductors in
terms a universal van Hove singularity in the strongly overdoped region. Using
a rigid ARPES-derived dispersion we solve the BCS gap equation and show that
the pairing interaction or pairing energy cutoff must be a rapidly declining
function of doping. This result is prejudicial to a phonon-based pairing
interaction and more consistent with a magnetic or magnetically enhanced
interaction.Comment: 5 pages, 2 figures, submitted to Physical Review
Electron pockets and pseudogap asymmetry observed in the thermopower of underdoped cuprates
We calculate the diffusion thermoelectric power of high-Tc cuprates using the
resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang
(YRZ). In this model, reconstruction of the energy-momentum dispersion results
in a pseudogap in the density of states that is heavily asymmetric about the
Fermi level. The subsequent asymmetry in the spectral conductivity is found to
account for the large magnitude and temperature dependence of the thermopower
observed in underdoped cuprates. In addition we find evidence in experimental
data for electron pockets in the Fermi surface, arising from a YRZ-like
reconstruction, near the onset of the pseudogap in the slightly overdoped
regime.Comment: 6 pages, 7 figures, accepted for publication in EP
Two-component electron fluid in underdoped high- cuprate superconductors
Evidence from NMR of a two-component spin system in cuprate high-
superconductors is shown to be paralleled by similar evidence from the
electronic entropy so that a two-component quasiparticle fluid is implicated.
We propose that this two-component scenario is restricted to the optimal and
underdoped regimes and arises from the upper and lower branches of the
reconstructed energy-momentum dispersion proposed by Yang, Rice and Zhang (YRZ)
to describe the pseudogap. We calculate the spin susceptibility within the YRZ
formalism and show that the doping and temperature dependence reproduces the
experimental data for the cuprates.Comment: 5 pages, 2 figures, accepted for publication in European Physics
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