8,418 research outputs found
On transport in quantum Hall systems with constrictions
Motivated by recent experimental findings, we study transport in a simple
phenomenological model of a quantum Hall edge system with a gate-voltage
controlled constriction lowering the local filling factor. The current
backscattered from the constriction is seen to arise from the matching of the
properties of the edge-current excitations in the constriction () and
bulk () regions. We develop a hydrodynamic theory for bosonic edge
modes inspired by this model, finding that a competition between two tunneling
process, related by a quasiparticle-quasihole symmetry, determines the fate of
the low-bias transmission conductance. In this way, we find satisfactory
explanations for many recent puzzling experimental results.Comment: 4 pages, 4 figure
The Intensities of Cosmic Ray H and He Nuclei at ~250 MeV/nuc Measured by Voyagers 1 and 2 - Using these Intensities to Determine the Solar Modulation Parameter in the Inner Heliosphere and the Heliosheath Over a 40 Year Time Period
We have determined the solar modulation potential, phi, vs. time that is
observed at Voyager 1 and 2 from measurements of the H and He nuclei
intensities at a common energy of 250 MeVnuc. The H nuclei have a rigidity 0.7
GV, the He nuclei 1.4 GV. These measurements cover a 40 year time period, which
includes almost 4 cycles of solar 11 year sunspot variations, throughout the
inner heliosphere out to the HTS at distances of 95 AU and 85 AU, respectively
at V1 and V2, and then beyond in the heliosheath. Inside the HTS the modulation
potential vs. time curves at V1 and V2 show a very similar temporal structure
to those observed at the Earth. During a later period of maximum solar
modulation from 2000.0 to 2005.0 when V1 and V2 are in the outer heliosphere
between 60-94 AU, the main temporal features of the modulation potential curves
at all 3 locations match up with appropriate time delays at V1 and V2 if it is
assumed that spatially coherent structures are moving outward past V1 and V2,
with outward speeds of up to 700 Kms negative 1. After 2004.0 V1 and V2 are at
latitudes of positive 35 and negative 30 respectively, placing lower limits on
the latitude extent of these structures. Beyond the HTS in the heliosheath the
modulation potential slowly decreases at both spacecraft with only a weak
evidence of the unusual modulation minimum observed at the Earth in 2009, for
example. A sudden decrease of the modulation potential 50 MV for both H and He
nuclei occurs at V1 just before the heliopause crossing at about 122 AU. This
decrease has not yet been observed at V2, which is now at 113 AU and still
observing a modulation potential 60 MV.Comment: 28 pages, 9 Figure
Economic Value of Groundwater Resources and Irrigated Agriculture in the Oklahoma Panhandle
An economic optimization model was developed using available groundwater resources in the Oklahoma Panhandle to estimate value of water for irrigated agriculture in the area. The model will serve as policy tool to analyze alternative water management strategies and conservation programs to assess the economic impact of depleting Ogallala Aquifer.Ogallala Aquifer, Irrigated Agriculture, Groundwater Conservation, Water Management Policy, Oklahoma Panhandle, Resource /Energy Economics and Policy,
Termination shock particle spectral features
Spectral features of energetic H ions accelerated at the termination shock may be evidence of two components. At low energies the energy spectrum is ~E^(–1.55), with break at ~0.4 MeV to E^(–2.2). A second component appears above ~1 MeV with a spectrum of E^(–1.27) with a break at ~3.2 MeV. Even though the intensities upstream are highly variable, the same spectral break energies are observed, suggesting that these are durable features of the source spectrum. The acceleration processes for the two components may differ, with the lower energy component serving as the injection source for diffusive shock acceleration of the higher energy component. Alternatively, the spectral features may result from the energy dependence of the diffusion tensor that affects the threshold for diffusive shock acceleration
- …