20,107 research outputs found
Local and Global Casimir Energies for a Semitransparent Cylindrical Shell
The local Casimir energy density and the global Casimir energy for a massless
scalar field associated with a -function potential in a 3+1
dimensional circular cylindrical geometry are considered. The global energy is
examined for both weak and strong coupling, the latter being the well-studied
Dirichlet cylinder case. For weak-coupling,through ,
the total energy is shown to vanish by both analytic and numerical arguments,
based both on Green's-function and zeta-function techniques. Divergences
occurring in the calculation are shown to be absorbable by renormalization of
physical parameters of the model. The global energy may be obtained by
integrating the local energy density only when the latter is supplemented by an
energy term residing precisely on the surface of the cylinder. The latter is
identified as the integrated local energy density of the cylindrical shell when
the latter is physically expanded to have finite thickness. Inside and outside
the delta-function shell, the local energy density diverges as the surface of
the shell is approached; the divergence is weakest when the conformal stress
tensor is used to define the energy density. A real global divergence first
occurs in , as anticipated, but the proof is supplied
here for the first time; this divergence is entirely associated with the
surface energy, and does {\em not} reflect divergences in the local energy
density as the surface is approached.Comment: 28 pages, REVTeX, no figures. Appendix added on perturbative
divergence
A near infrared line list for \NH: Analysis of a Kitt Peak spectrum after 35 years
A Fourier Transform (FT) absorption spectrum of room temperature NH3 in the
region 7400 - 8600 cm-1 is analysed using a variational line list and ground
state energies determined using the MARVEL procedure. The spectrum was measured
by Dr Catherine de Bergh in 1980 and is available from the Kitt Peak data
center. The centers and intensities of 8468 ammonia lines were retrieved using
a multiline fitting procedure. 2474 lines are assigned to 21 bands providing
1692 experimental energies in the range 7000 - 9000 cm-1. The spectrum was
assigned by the joint use of the BYTe variational line list and combination
differences. The assignments and experimental energies presented in this work
are the first for ammonia in the region 7400 - 8600 cm-1, considerably
extending the range of known vibrational-excited statesComment: 27 pages, 6 table, 5 figures. Accepted for publication in Journal of
Molecular Spectroscop
Relic Abundances and the Boltzmann Equation
I discuss the validity of the quantum Boltzmann equation for the calculation
of WIMP relic densities.Comment: 5 pages, no figures; talk given at Dark Matter 2000; an important
reference is added in the revised versio
Computer program to predict noise of general aviation aircraft: User's guide
Program NOISE predicts General Aviation Aircraft far-field noise levels at FAA FAR Part 36 certification conditions. It will also predict near-field and cabin noise levels for turboprop aircraft and static engine component far-field noise levels
A review of residual stress analysis using thermoelastic techniques
Thermoelastic Stress Analysis (TSA) is a full-field technique for experimental stress analysis
that is based on infra-red thermography. The technique has proved to be extremely effective for
studying elastic stress fields and is now well established. It is based on the measurement of the
temperature change that occurs as a result of a stress change. As residual stress is essentially a
mean stress it is accepted that the linear form of the TSA relationship cannot be used to
evaluate residual stresses. However, there are situations where this linear relationship is not
valid or departures in material properties due to manufacturing procedures have enabled
evaluations of residual stresses. The purpose of this paper is to review the current status of
using a TSA based approach for the evaluation of residual stresses and to provide some
examples of where promising results have been obtained
Surface Divergences and Boundary Energies in the Casimir Effect
Although Casimir, or quantum vacuum, forces between distinct bodies, or
self-stresses of individual bodies, have been calculated by a variety of
different methods since 1948, they have always been plagued by divergences.
Some of these divergences are associated with the volume, and so may be more or
less unambiguously removed, while other divergences are associated with the
surface. The interpretation of these has been quite controversial. Particularly
mysterious is the contradiction between finite total self-energies and surface
divergences in the local energy density. In this paper we clarify the role of
surface divergences.Comment: 8 pages, 1 figure, submitted to proceedings of QFEXT0
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