58,745 research outputs found
Predicting image quality using a modular image difference model
The paper is focused on the implementation of a modular color image difference model, as described in [1], with aim to predict visual magnitudes between pairs of uncompressed images and images compressed using lossy JPEG and JPEG 2000. The work involved programming each pre-processing step, processing each image file and deriving the error map, which was further reduced to a single metric. Three contrast sensitivity function implementations were tested; a
Laplacian filter was implemented for spatial localization and the contrast masked-based local contrast enhancement method, suggested by Moroney, was used for local contrast detection. The error map was derived using the CIEDE2000 color difference formula on a pixel-by-pixel basis. A final single value was obtained by calculating the median value of the error map. This metric was finally tested against relative quality differences between original and compressed images, derived from psychophysical investigations on the same dataset. The outcomes revealed a grouping of images which was attributed to correlations between the busyness of the test scenes (defined as image property indicating the presence or absence of high frequencies) and different clustered results. In conclusion, a method for accounting for the amount of detail in test is required for a more accurate prediction of image quality
Role of three-body interactions in formation of bulk viscosity in liquid argon
With the aim of locating the origin of discrepancy between experimental and
computer simulation results on bulk viscosity of liquid argon, a molecular
dynamic simulation of argon interacting via ab initio pair potential and
triple-dipole three-body potential has been undertaken. Bulk viscosity,
obtained using Green-Kubo formula, is different from the values obtained from
modeling argon using Lennard-Jones potential, the former being closer to the
experimental data. The conclusion is made that many-body inter-atomic
interaction plays a significant role in formation of bulk viscosity.Comment: 4 pages, 3 figure
Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes
The rates of axion emission by nucleon-nucleon bremsstrahlung are calculated
with the inclusion of the full momentum contribution from a nuclear one pion
exchange (OPE) potential. The contributions of the neutron-neutron (nn),
proton-proton (pp) and neutron-proton (np) processes in both the nondegenerate
and degenerate limits are explicitly given. We find that the finite momentum
corrections to the emissivities are quantitatively significant for the
non-degenerate regime and temperature-dependent, and should affect the existing
axion mass bounds. The trend of these nuclear effects is to diminish the
emissivities
Plasmas generated by ultra-violet light rather than electron impact
We analyze, in both plane and cylindrical geometries, a collisionless plasma
consisting of an inner region where generation occurs by UV illumination, and
an un-illuminated outer region with no generation. Ions generated in the inner
region flow outwards through the outer region and into a wall. We solve for
this system's steady state, first in the quasi-neutral regime (where the Debye
length vanishes and analytic solutions exist) and then in the
general case, which we solve numerically. In the general case a double layer
forms where the illuminated and un-illuminated regions meet, and an
approximately quasi-neutral plasma connects the double layer to the wall
sheath; in plane geometry the ions coast through the quasi-neutral section at
slightly more than the Bohm speed . The system, although simple, therefore
has two novel features: a double layer that does not require counter-streaming
ions and electrons, and a quasi-neutral plasma where ions travel in straight
lines with at least the Bohm speed. We close with a pr\'{e}cis of our
asymptotic solutions of this system, and suggest how our theoretical
conclusions might be extended and tested in the laboratory.Comment: 10 pages, 3 figures, accepted by Physics of Plasma
Polarisation rotation of slow light with orbital angular momentum in ultracold atomic gases
We consider the propagation of slow light with an orbital angular momentum
(OAM) in a moving atomic medium. We have derived a general equation of motion
and applied it in analysing propagation of slow light with an OAM in a rotating
medium, such as a vortex lattice. We have shown that the OAM of slow light
manifests itself in a rotation of the polarisation plane of linearly polarised
light. To extract a pure rotational phase shift, we suggest to measure a
difference in the angle of the polarisation plane rotation by two consecutive
light beams with opposite OAM. The differential angle is
proportional to the rotation frequency of the medium
and the winding number of light, and is inversely proportional to the
group velocity of light. For slow light the angle should
be large enough to be detectable. The effect can be used as a tool for
measuring the rotation frequency of the medium.Comment: 5 pages, 1 figur
IRS 16SW - A New Comoving Group of Young Stars in the Central Parsec of the Milky Way
One of the most perplexing problems associated with the supermassive black
hole at the center of our Galaxy is the origin of the young stars in its close
vicinity. Using proper motion measurements and stellar number density counts
based on 9 years of diffraction-limited K(2.2 micron)-band speckle imaging at
the W. M. Keck 10-meter telescopes, we have identified a new comoving group of
stars, which we call the IRS 16SW comoving group, located 1.9" (0.08 pc, in
projection) from the central black hole. Four of the five members of this
comoving group have been spectroscopically identified as massive young stars,
specifically He I emission-line stars and OBN stars. This is the second young
comoving group within the central parsec of the Milky Way to be recognized and
is the closest, by a factor of 2, in projection to the central black hole.
These comoving groups may be the surviving cores of massive infalling star
clusters that are undergoing disruption in the strong tidal field of the
central supermassive black hole.Comment: 10 pages, 1 figure, accepted for ApJL, uses emulateap
Daemons and DAMA: Their Celestial-Mechanics Interrelations
The assumption of the capture by the Solar System of the electrically charged
Planckian DM objects (daemons) from the galactic disk is confirmed not only by
the St.Petersburg (SPb) experiments detecting particles with V<30 km/s. Here
the daemon approach is analyzed considering the positive model independent
result of the DAMA/NaI experiment. We explain the maximum in DAMA signals
observed in the May-June period to be associated with the formation behind the
Sun of a trail of daemons that the Sun captures into elongated orbits as it
moves to the apex. The range of significant 2-6-keV DAMA signals fits well the
iodine nuclei elastically knocked out of the NaI(Tl) scintillator by particles
falling on the Earth with V=30-50 km/s from strongly elongated heliocentric
orbits. The half-year periodicity of the slower daemons observed in SPb
originates from the transfer of particles that are deflected through ~90 deg
into near-Earth orbits each time the particles cross the outer reaches of the
Sun which had captured them. Their multi-loop (cross-like) trajectories
traverse many times the Earth's orbit in March and September, which increases
the probability for the particles to enter near-Earth orbits during this time.
Corroboration of celestial mechanics calculations with observations yields
~1e-19 cm2 for the cross section of daemon interaction with the solar matter.Comment: 12 pages including 5 figure
[N]pT Monte Carlo Simulations of the Cluster-Crystal-Forming Penetrable Sphere Model
Certain models with purely repulsive pair interactions can form cluster
crystals with multiply-occupied lattice sites. Simulating these models'
equilibrium properties is, however, quite challenging. Here, we develop an
expanded isothermal-isobaric ensemble that surmounts this problem by
allowing both particle number and lattice spacing to fluctuate. We apply the
method with a Monte Carlo simulation scheme to solve the phase diagram of a
prototypical cluster-crystal former, the penetrable sphere model (PSM), and
compare the results with earlier theoretical predictions. At high temperatures
and densities, the equilibrium occupancy of
face-centered cubic (FCC) crystal increases linearly. At low temperatures,
although plateaus at integer values, the crystal
behavior changes continuously with density. The previously ambiguous crossover
around is resolved
Quantum Spinodal Decomposition
We study the process of spinodal decomposition in a scalar quantum field
theory that is quenched from an equilibrium disordered initial state at to a final state at . The process of formation and growth
of correlated domains is studied in a Hartree approximation. We find an
approximate scaling law for the size of the domains at long times for weakly coupled theories, with the zero
temperature correlation length.Comment: REVTEX 13 pages(2 figures not included),PITT 93-0
Casimir effect for massless minimally coupled scalar field between parallel plates in de Sitter spacetime
Casimir effect for massless minimally coupled scalar field is studied. An
explicit answer for de Sitter spacetime is obtained and analized. Cosmological
implications of the result are discussed.Comment: 7 pages, 2 figure
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