26,403 research outputs found
Field-guided proton acceleration at reconnecting X-points in flares
An explicitly energy-conserving full orbit code CUEBIT, developed originally
to describe energetic particle effects in laboratory fusion experiments, has
been applied to the problem of proton acceleration in solar flares. The model
fields are obtained from solutions of the linearised MHD equations for
reconnecting modes at an X-type neutral point, with the additional ingredient
of a longitudinal magnetic field component. To accelerate protons to the
highest observed energies on flare timescales, it is necessary to invoke
anomalous resistivity in the MHD solution. It is shown that the addition of a
longitudinal field component greatly increases the efficiency of ion
acceleration, essentially because it greatly reduces the magnitude of drift
motions away from the vicinity of the X-point, where the accelerating component
of the electric field is largest. Using plasma parameters consistent with flare
observations, we obtain proton distributions extending up to gamma-ray-emitting
energies (>1MeV). In some cases the energy distributions exhibit a bump-on-tail
in the MeV range. In general, the shape of the distribution is sensitive to the
model parameters.Comment: 14 pages, 4 figures, accepted for publication in Solar Physic
Control of the persistent currents in two interacting quantum rings through the Coulomb interaction and inter-ring tunneling
The persistent current in two vertically coupled quantum rings containing few
electrons is studied. We find that the Coulomb interaction between the rings in
the absence of tunneling affects the persistent current in each ring and the
ground state configurations. Quantum tunneling between the rings alters
significantly the ground state and the persistent current in the system.Comment: accepted for publication in Phys. Rev.
Determination of the Baryon Density from Large Scale Galaxy Redshift Surveys
We estimate the degree to which the baryon density, , can be
determined from the galaxy power spectrum measured from large scale galaxy
redshift surveys, and in particular, the Sloan Digital Sky Survey. A high
baryon density will cause wiggles to appear in the power spectrum, which should
be observable at the current epoch. We assume linear theory on scales and do not include the effects of redshift distortions, evolution,
or biasing. With an optimum estimate of to ,
the uncertainties in are roughly 0.07 and 0.016 in flat
and open () cosmological models, respectively. This result
suggests that it should be possible to test for consistency with big bang
nucleosynthesis estimates of if we live in an open universe.Comment: 23 Pages, 10 Postscript figure
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
Development of life-test methodology for long-life mechanical components. Phase 1: Development of methodology. Phase 2: Demonstration of methodology
THE EFFECTS OF WATER RIGHTS AND IRRIGATION TECHNOLOGY ON STREAMFLOW AUGMENTATION COST IN THE SNAKE RIVER BASIN
Three species of salmon in the Snake River Basin have been listed as endangered. Recovery efforts for these fish include attempts to obtain increased quantities of water during smolt migration periods to improve habitat in the lower basin. Agriculture is the dominant user of surface flows in this region. This study investigates farmer cost of a contingent water contract requiring the agricultural release of stored irrigation supplies in low flow years during critical flow periods. Results show that contingent contracts can provide substantial quantities of water at a relatively modest cost without significantly affecting the agricultural base of the area.Resource /Energy Economics and Policy,
Herwig++ 2.0 Release Note
A new release of the Monte Carlo program Herwig++ (version 2.0) is now
available. This is the first version of the program which can be used for
hadron-hadron physics and includes the full simulation of both initial- and
final-state QCD radiation.Comment: Source code and additional information available at
http://hepforge.cedar.ac.uk/herwig
Artificial molecular quantum rings: Spin density functional theory calculations
The ground states of artificial molecules made of two vertically coupled
quantum rings are studied within the spin density functional theory for systems
containing up to 13 electrons. Quantum tunneling effects on the electronic
structure of the coupled rings are analyzed. For small ring radius, our results
recover those of coupled quantum dots. For intermediate and large ring radius,
new phases are found showing the formation of new diatomic artificial ring
molecules. Our results also show that the tunneling induced phase transitions
in the coupled rings occur at much smaller tunneling energy as compared to
those for coupled quantum dot systems.Comment: 10 pages, 6 figure
Development of life-test methodology for long-life mechanical components. Phase 1: Development of methodology
Kinetic energy spectrum of horizontal motions in middle-atmosphere models
Data from several middle-atmosphere general circulation models are used to calculate kinetic energy spectra as a function of total horizontal wavenumber n. The horizontal and vertical resolution between models varies but all have upper. boundaries at heights greater than or similar to 80 km. Tropospheric spectra show power-law behavior with slopes slightly shallower than -3 for wavenumbers n greater than or similar to 10 (horizontal wavelengths less than or similar to 4000 km) and are dominated by the rotational part of the flow. These spectra agree well with those calculated using data obtained from a global assimilation model and with the results of previous observational studies. Stratospheric spectra have larger amplitudes than tropospheric ones at planetary scales and smaller amplitudes at smaller scales. Mesospheric spectra are characterized by enhanced spectral amplitudes at all wavenumbers compared to the stratosphere and spectral slopes in the wavenumber range n greater than or similar to 10 are generally shallower. Stratospheric and mesospheric spectra include approximately equal contributions from the rotational and divergent parts of the flow for n greater than or similar to 20 in all models. These features appear to be independent of model resolution. The divergent part of the flow, presumably associated with explicitly resolved inertiogravity waves in the models, increases more rapidly with height above the lower stratosphere than the rotational part. The divergent part is fairly insensitive to season, whereas the rotational part changes considerably between January and July in the middle-atmosphere region. Spectral amplitudes and vertical growth rates of both parts vary widely between models for a given season. The horizontal diffusion schemes used by the models are compared in an attempt to explain some of these differences
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