25,546 research outputs found
A comprehensive treatment of electromagnetic interactions and the three-body spectator equations
We present a general derivation the three-body spectator (Gross) equations
and the corresponding electromagnetic currents. As in previous paper on
two-body systems, the wave equations and currents are derived from those for
Bethe-Salpeter equation with the help of algebraic method using a concise
matrix notation. The three-body interactions and currents introduced by the
transition to the spectator approach are isolated and the matrix elements of
the e.m. current are presented in detail for system of three indistinguishable
particles, namely for elastic scattering and for two and three body break-up.
The general expressions are reduced to the one-boson-exchange approximation to
make contact with previous work. The method is general in that it does not rely
on introduction of the electromagnetic interaction with the help of the minimal
replacement. It would therefore work also for other external fields
Discrimination of Coastal Vegetation and Biomass Using AIS Data
The Airborne Imaging Spectrometer (AIS) was flown over a coastal wetlands region near Lewes, Delaware, adjacent to the Delaware Bay on 16 August 1984. Using the AIS data, it was possible to discriminate between four different types of wetland vegetation canopies: (1) trees; (2) broadleaf herbaceous plants (e.g., Acnida cannabina, Hisbiscus moscheutos); (3) the low marsh grass Spartina alterniflora; and (4) the high marsh grasses Distichlis spicata and Spartina patens. The single most useful region of the spectrum was that between 1.40 and 1.90 microns, where slopes of portions of the radiance curve and ratios of radiance at particular wavelengths were significantly different for the four canopy types. The ratio between the highest digital number in the 1.40 to 1.90 microns and .84 to .94 microns regions and a similar ratio between the peaks in radiance in the 1.12 to 1.40 microns and .84 to .94 microns spectral regions were also very effective at discriminating between vegetation types. Differences in radiance values at various wavelengths between samples of the same vegetation type could potentially be used to estimate biomass
Spin and angular momentum in the nucleon
Using the covariant spectator theory (CST), we present the results of a
valence quark-diquark model calculation of the nucleon structure function f(x)
measured in unpolarized deep inelastic scattering (DIS), and the structure
functions g1(x) and g2(x) measured in DIS using polarized beams and targets.
Parameters of the wave functions are adjusted to fit all the data. The fit
fixes both the shape of the wave functions and the relative strength of each
component. Two solutions are found that fit f(x) and g1(x), but only one of
these gives a good description of g2(x). This fit requires the nucleon CST wave
functions contain a large D-wave component (about 35%) and a small P-wave
component (about 0.6%). The significance of these results is discussed.Comment: 27 pages; 13 figure
Two-pion exchange potential and the amplitude
We discuss the two-pion exchange potential which emerges from a box diagram
with one nucleon (the spectator) restricted to its mass shell, and the other
nucleon line replaced by a subtracted, covariant scattering amplitude
which includes , Roper, and isobars, as well as contact terms
and off-shell (non-pole) dressed nucleon terms. The amplitude satisfies
chiral symmetry constraints and fits data below 700 MeV pion
energy. We find that this TPE potential can be well approximated by the
exchange of an effective sigma and delta meson, with parameters close to the
ones used in one-boson-exchange models that fit data below the pion
production threshold.Comment: 9 pages (RevTex) and 7 postscript figures, in one uuencoded gzipped
tar fil
Thermal fluctuations in the lattice Boltzmann method for non-ideal fluids
We introduce thermal fluctuations in the lattice Boltzmann method for
non-ideal fluids. A fluctuation-dissipation theorem is derived within the
Langevin framework and applied to a specific lattice Boltzmann model that
approximates the linearized fluctuating Navier-Stokes equations for fluids
based on square-gradient free energy functionals. The obtained thermal noise is
shown to ensure equilibration of all degrees of freedom in a simulation to high
accuracy. Furthermore, we demonstrate that satisfactory results for most
practical applications of fluctuating hydrodynamics can already be achieved
using thermal noise derived in the long wavelength-limit.Comment: 15 pages, 5 figure
Imaging of a vibrating object by Sideband Digital Holography
We obtain quantitative measurements of the oscillation amplitude of vibrating
objects by using sideband digital holography. The frequency sidebands on the
light scattered by the object, shifted by n times the vibration frequency, are
selectively detected by heterodyne holography, and images of the object are
calculated for different orders n. Orders up to n=120 have been observed,
allowing the measurement of amplitudes of oscillation that are significantly
larger than the optical wavelength. Using the positions of the zeros of
intensity for each value of n, we reconstruct the shape of vibration the
object.Comment: 6 page
Tropical eigenwave and intermediate Jacobians
Tropical manifolds are polyhedral complexes enhanced with certain kind of
affine structure. This structure manifests itself through a particular
cohomology class which we call the eigenwave of a tropical manifold. Other wave
classes of similar type are responsible for deformations of the tropical
structure.
If a tropical manifold is approximable by a 1-parametric family of complex
manifolds then the eigenwave records the monodromy of the family around the
tropical limit. With the help of tropical homology and the eigenwave we define
tropical intermediate Jacobians which can be viewed as tropical analogs of
classical intermediate Jacobians.Comment: 38 pages, 8 figure
Fluctuating Multicomponent Lattice Boltzmann Model
Current implementations of fluctuating lattice Boltzmann equations (FLBE)
describe single component fluids. In this paper, a model based on the continuum
kinetic Boltzmann equation for describing multicomponent fluids is extended to
incorporate the effects of thermal fluctuations. The thus obtained fluctuating
Boltzmann equation is first linearized to apply the theory of linear
fluctuations, and expressions for the noise covariances are determined by
invoking the fluctuation-dissipation theorem (FDT) directly at the kinetic
level. Crucial for our analysis is the projection of the Boltzmann equation
onto the ortho-normal Hermite basis. By integrating in space and time the
fluctuating Boltzmann equation with a discrete number of velocities, the FLBE
is obtained for both ideal and non-ideal multicomponent fluids. Numerical
simulations are specialized to the case where mean-field interactions are
introduced on the lattice, indicating a proper thermalization of the system.Comment: 30 pages, 6 figure
Confinement and the analytic structure of the one body propagator in Scalar QED
We investigate the behavior of the one body propagator in SQED. The self
energy is calculated using three different methods: i) the simple bubble
summation, ii) the Dyson-Schwinger equation, and iii) the Feynman-Schwinger
represantation. The Feynman-Schwinger representation allows an {\em exact}
analytical result. It is shown that, while the exact result produces a real
mass pole for all couplings, the bubble sum and the Dyson-Schwinger approach in
rainbow approximation leads to complex mass poles beyond a certain critical
coupling. The model exhibits confinement, yet the exact solution still has one
body propagators with {\it real} mass poles.Comment: 5 pages 2 figures, accepted for publication in Phys. Rev.
Measuring and engineering entropy and spin squeezing in weakly linked Bose-Einstein condensates
We propose a method to infer the single-particle entropy of bosonic atoms in
an optical lattice and to study the local evolution of entropy, spin squeezing,
and entropic inequalities for entanglement detection in such systems. This
method is based on experimentally feasible measurements of
non-nearest-neighbour coherences. We study a specific example of dynamically
controlling atom tunneling between selected sites and show that this could
potentially also improve the metrologically relevant spin squeezing
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