6,913 research outputs found
Manual for extending the laser specklegram technique to strain analysis of rotating components
The theory, techniques, and equipment necessary for extending laser speckle techniques to analyze stresses in rotating blades are described. Details for setting up the equipment, for timing the events, for data recording, and for data analysis are discussed. Finite element techniques are investigated for analysis of speckle data. Advantages and limitations of the finite element analysis for the speckle data are discussed. The finite element program is listed
Meson distribution amplitudes in holographic models
We study the wave functions of light and heavy mesons in both hard-wall (HW)
and soft-wall (SW) holographic models which use AdS/CFT correspondence. In the
case of massless constituents, the asymptotic behaviors of the electromagnetic
form factor, the distribution amplitudes, and the decay constants for the two
models are the same, if the relation between the dilaton scale parameter and
the size of meson is an inverse proportion. On the other hand, by introducing a
quark mass dependence in the wave function, the differences of the distribution
amplitudes between the two models are obvious. In addition, for the SW model,
the dependences of the decay constants of meson on the dilaton scale parameter
differ; especially f_{Qq}\sim \kappa^3/m_Q^2 is consistent with the
prediction of the heavy quark effective theory if \kappa\sim m_Q^{1/2}. Thus
the parameters of the two models are fit by the decay constants of the distinct
mesons; the distribution amplitudes and the \xi-moments are calculated and
compared.Comment: 30 pages, 11 figures, 2 tables, minor modifications and one short
paragraph added, some references added and removed, accepted for publication
in PR
Comparative Study of BCS-BEC Crossover Theories above : the Nature of the Pseudogap in Ultra-Cold Atomic Fermi Gases
This paper presents a comparison of two finite-temperature BCS-Bose Einstein
condensation (BEC) crossover theories above the transition temperature:
Nozieres Schmitt-Rink (NSR) theory and finite -extended BCS-Leggett theory.
The comparison is cast in the form of numerical studies of the behavior of the
fermionic spectral function both theoretically and as constrained by
(primarily) radio frequency (RF) experiments. Both theories include pair
fluctuations and exhibit pseudogap effects, although the nature of this
pseudogap is very different. The pseudogap in finite -extended BCS-Leggett
theory is found to follow a BCS-like dispersion which, in turn, is associated
with a broadened BCS-like self energy, rather more similar to what is observed
in high temperature superconductors (albeit, for a d-wave case). The fermionic
quasi-particle dispersion is different in NSR theory and the damping is
considerably larger. We argue that the two theories are appropriate in
different temperature regimes with the BCS-Leggett approach more suitable
nearer to condensation. There should, in effect, be little difference at higher
as the pseudogap becomes weaker and where the simplifying approximations
used in the BCS-Leggett approach break down. On the basis of
momentum-integrated radio frequency studies of unpolarized gases, it would be
difficult to distinguish which theory is the better. A full comparison for
polarized gases is not possible since there is claimed to be inconsistencies in
the NSR approach (not found in the BCS-Leggett scheme). Future experiments
along the lines of momentum resolved experiments look to be very promising in
distinguishing the two theories.Comment: 16 pages, 11 figure
Development of basic theories and techniques for determining stresses in rotating turbine or compressor blades
A method for measuring in-plane displacement of a rotating structure by using two laser speckle photographs is described. From the displacement measurements one can calculate strains and stresses due to a centrifugal load. This technique involves making separate speckle photographs of a test model. One photograph is made with the model loaded (model is rotating); the second photograph is made with no load on the model (model is stationary). A sandwich is constructed from the two speckle photographs and data are recovered in a manner similar to that used with conventional speckle photography. The basic theory, experimental procedures of this method, and data analysis of a simple rotating specimen are described. In addition the measurement of in-plane surface displacement components of a deformed solid, and the application of the coupled laser speckle interferometry and boundary-integral solution technique to two dimensional elasticity problems are addressed
Model-independent analysis for determining mass splittings of heavy baryons
We study the hyperfine mass differences of heavy hadrons in the heavy quark
effect theory (HQET). The effects of one-gluon exchange interaction are
considered for the heavy mesons and baryons. Base on the known experimental
data, we predict the masses of some heavy baryons in a model-independent way.Comment: 14 pages, 1 figur
Dynamical mean-field equations for strongly interacting fermionic atoms in a potential trap
We derive a set of dynamical mean-field equations for strongly interacting
fermionic atoms in a potential trap across a Feshbach resonance. Our derivation
is based on a variational ansatz, which generalizes the crossover wavefunction
to the inhomogeneous case, and the assumption that the order parameter is
slowly varying over the size of the Cooper pairs. The equations reduce to a
generalized time-dependent Gross-Pitaevskii equation on the BEC side of the
resonance. We discuss an iterative method to solve these mean-field equations,
and present the solution for a harmonic trap as an illustrating example to
self-consistently verify the approximations made in our derivation.Comment: replaced with the published versio
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