1,818 research outputs found
Damping and dispersion of oscillating modes of a multicomponent ionic mixture in a magnetic field
The collective-mode spectrum of a multicomponent magnetized ionic mixture for
small wave number k is studied with the use of magnetohydrodynamics and formal
kinetic theory. Apart from the usual thermal and diffusive modes, the spectrum
contains a set of four oscillating modes. By evaluating the k^2 contributions
to the eigenfrequencies, the damping and the dispersion of these oscillating
modes are determined. The long-range nature of the Coulomb interactions is
shown to imply that Burnett terms with higher-order gradients in the linear
phenomenological laws have to be taken into account in order to obtain a full
description of all damping and dispersion effects.Comment: 25 page
Spontaneous-emission rates in finite photonic crystals of plane scatterers
The concept of a plane scatterer that was developed earlier for scalar waves
is generalized so that polarization of light is included. Starting from a
Lippmann-Schwinger formalism for vector waves, we show that the Green function
has to be regularized before T-matrices can be defined in a consistent way.
After the regularization, optical modes and Green functions are determined
exactly for finite structures built up of an arbitrary number of parallel
planes, at arbitrary positions, and where each plane can have different optical
properties. The model is applied to the special case of finite crystals
consisting of regularly spaced identical planes, where analytical methods can
be taken further and only light numerical tasks remain. The formalism is used
to calculate position- and orientation-dependent spontaneous-emission rates
inside and near the finite photonic crystals. The results show that emission
rates and reflection properties can differ strongly for scalar and for vector
waves. The finite size of the crystal influences the emission rates. For
parallel dipoles close to a plane, emission into guided modes gives rise to a
peak in the frequency-dependent emission rate.Comment: 18 pages, 6 figures, to be published in Phys. Rev.
Continued-fraction representation of the Kraus map for non-Markovian reservoir damping
Quantum dissipation is studied for a discrete system that linearly interacts
with a reservoir of harmonic oscillators at thermal equilibrium. Initial
correlations between system and reservoir are assumed to be absent. The
dissipative dynamics as determined by the unitary evolution of system and
reservoir is described by a Kraus map consisting of an infinite number of
matrices. For all Laplace-transformed Kraus matrices exact solutions are
constructed in terms of continued fractions that depend on the pair correlation
functions of the reservoir. By performing factorizations in the Kraus map a
perturbation theory is set up that conserves in arbitrary perturbative order
both positivity and probability of the density matrix. The latter is determined
by an integral equation for a bitemporal matrix and a finite hierarchy for
Kraus matrices. In lowest perturbative order this hierarchy reduces to one
equation for one Kraus matrix. Its solution is given by a continued fraction of
a much simpler structure as compared to the non-perturbative case. In lowest
perturbative order our non-Markovian evolution equations are applied to the
damped Jaynes-Cummings model. From the solution for the atomic density matrix
it is found that the atom may remain in the state of maximum entropy for a
significant time span that depends on the initial energy of the radiation
field
Quantized Media with Absorptive Scatterers and Modified Atomic Emission Rates
Modifications in the spontaneous emission rate of an excited atom that are
caused by extinction effects in a nearby dielectric medium are analyzed in a
quantummechanical model, in which the medium consists of spherical scatterers
with absorptive properties. Use of the dyadic Green function of the
electromagnetic field near a a dielectric sphere leads to an expression for the
change in the emission rate as a series of multipole contributions for which
analytical formulas are obtained. The results for the modified emission rate as
a function of the distance between the excited atom and the dielectric medium
show the influence of both absorption and scattering processes.Comment: 6 pages, 4 figure
Modified atomic decay rate near absorptive scatterers at finite temperature
The change in the decay rate of an excited atom that is brought about by
extinction and thermal-radiation effects in a nearby dielectric medium is
determined from a quantummechanical model. The medium is a collection of
randomly distributed thermally-excited spherical scatterers with absorptive
properties. The modification of the decay rate is described by a set of
correction functions for which analytical expressions are obtained as sums over
contributions from the multipole moments of the scatterers. The results for the
modified decay rate as a function of the distance between the excited atom and
the dielectric medium show the influence of absorption, scattering and
thermal-radiation processes. Some of these processes are found to be mutually
counteractive. The changes in the decay rate are compared to those following
from an effective-medium theory in which the discrete scatterers are replaced
by a continuum
Field quantization in inhomogeneous anisotropic dielectrics with spatio-temporal dispersion
A quantum damped-polariton model is constructed for an inhomogeneous
anisotropic linear dielectric with arbitrary dispersion in space and time. The
model Hamiltonian is completely diagonalized by determining the creation and
annihilation operators for the fundamental polariton modes as specific linear
combinations of the basic dynamical variables. Explicit expressions are derived
for the time-dependent operators describing the electromagnetic field, the
dielectric polarization and the noise term in the latter. It is shown how to
identify bath variables that generate the dissipative dynamics of the medium.Comment: 24 page
Lack of pupils in German riding schools? A causal-analytical consideration of customer satisfaction in children and adolescents
Not only the horse as a living creature, but also equestrian sport, has a positive influence on the general upbringing and development of young people. Although equestrian sport still exerts a strong fascination, it is becoming more difficult to inspire young people to take part in this time-consuming and costly sport. It is not only the equestrian sport which is affected by this - the majority of sport clubs offering different types of sport have registered diminishing member numbers. Especially those riding schools which consider themselves as being service providers in equestrian sport are confronted with the challenge of binding children and adolescents to their school for a longer term, thereby enabling the schools to manage themselves sustainably. The present study has, therefore, investigated the various factors which influence customer satisfaction in riding schools and their significance by using a structural equation model. A survey of 203 children and adolescents was undertaken in five different German riding schools. Customer satisfaction was particularly influenced by the design of the riding lessons and the school horses. The influence of the riding instructor however, was more indirect (acting over the direct impact on the design of the lessons and the school'horses) than direct. One most noticeable aspect of the results is the strong influence of customer satisfaction on recommendation behaviour. --customer satisfaction,customer loyalty,riding schools,Partial Least Squares (PLS)
Field quantization in inhomogeneous absorptive dielectrics
The quantization of the electromagnetic field in a three-dimensional
inhomogeneous dielectric medium with losses is carried out in the framework of
a damped-polariton model with an arbitrary spatial dependence of its
parameters. The equations of motion for the canonical variables are solved
explicitly by means of Laplace transformations for both positive and negative
time. The dielectric susceptibility and the quantum noise-current density are
identified in terms of the dynamical variables and parameters of the model. The
operators that diagonalize the Hamiltonian are found as linear combinations of
the canonical variables, with coefficients depending on the electric
susceptibility and the dielectric Green function. The complete time dependence
of the electromagnetic field and of the dielectric polarization is determined.
Our results provide a microscopic justification of the phenomenological
quantization scheme for the electromagnetic field in inhomogeneous dielectrics.Comment: 19 page
Eigenmode analysis of the damped Jaynes-Cummings model
The generating functions for density matrix elements of the Jaynes-Cummings
model with cavity damping are analysed in terms of their eigenmodes, which are
characterised by a specific temporal behaviour. These eigenmodes are shown to
be proportional to particular generalised hypergeometric functions. The
relative weights of these eigenmodes in the generating functions are determined
by the initial conditions of the model. These weights are found by deriving
orthogonality relations involving adjoint modes. In an example it is shown how
the time-dependent density matrix elements and the related factorial moments
can be extracted from the eigenmode decompositions of the generating functions
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