157,438 research outputs found
Accurate measurement of the piezoelectric coefficient of thin films by eliminating the substrate bending effect using spatial scanning laser vibrometry
One of the major difficulties in measuring the piezoelectric coefficient d(33,f)
for thin films is the elimination of the contribution from substrate bending. We
show by theoretical analysis and experimental measurements that by bonding thin
film piezoelectric samples to a substantial holder, the substrate bending can be
minimized to a negligible level. Once the substrate bending can be effectively
eliminated, single-beam laser scanning vibrometry can be used to measure the
precise strain distribution of a piezoelectric thin film under converse
actuation. A significant strain increase toward the inside edge of the top
electrode (assuming a fully covered bottom electrode) and a corresponding strain
peak in the opposite direction just outside the electrode edge were observed.
These peaks were found to increase with the increasing Poisson's ratio and
transverse piezoelectric coefficient of the piezoelectric thin film. This is due
to the non-continuity of the electric field at the edge of the top electrode,
which leads to the concentration of shear stress and electric field in the
vicinity of the electrode edge. The measured d(33,f) was found to depend not
only on the material properties such as the electromechanical coefficients of
the piezoelectric thin films and elastic coefficients of the thin film and the
substrate, but also on the geometry factors such as the thickness of the
piezoelectric films, the dimensions of the electrode, and also the thickness of
the substrate
Neutrino oscillations in de Sitter space-time
We try to understand flavor oscillations and to develop the formulae for
describing neutrino oscillations in de Sitter space-time. First, the covariant
Dirac equation is investigated under the conformally flat coordinates of de
Sitter geometry. Then, we obtain the exact solutions of the Dirac equation and
indicate the explicit form of the phase of wave function. Next, the concise
formulae for calculating the neutrino oscillation probabilities in de Sitter
space-time are given. Finally, The difference between our formulae and the
standard result in Minkowski space-time is pointed out.Comment: 13 pages, no figure
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
A code to unfold scintillation spectrometer polyenergetic gamma photon experimental distributions
FORTRAN code to unfold sodium iodide scintillation spectrometer polyenergetic gamma photon experimental distribution
Technicolor corrections to b\bar{b} -> W^{\pm}\pi^{\mp}_t at the CERN Large Hadron Collider
In this paper we calculate the technicolor correction to the production of a
charged top pion in association with a W boson via b\bar{b} annihilation at the
CERN Large Hadron Collider in the context of the topcolor assisted technicolor
model. We find that the cross section of pp \rightarrow b\bar{b} ->
W^{\pm}\pi_t^{\mp} at the tree level can reach a few hundred femtobarns for
reasonable ranges of the parameters, roughly corresponding to the result of the
process pp -> b\bar{b} -> W^{\pm}H^{\mp} in the minimal supersymmetric standard
model; the relative corrections arising from the one-loop diagrams are about a
few percent to two dozen percent, and they will increase the cross section at
the tree level. As a comparison, we also discuss the size of the hadron cross
section via the other subprocess gg -> W^{\pm}\pi_t^{\mp}.Comment: 6 pages, 5 figure
From insulator to quantum Hall liquid at low magnetic fields
We have performed low-temperature transport measurements on a GaAs
two-dimensional electron system at low magnetic fields. Multiple
temperature-independent points and accompanying oscillations are observed in
the longitudinal resistivity between the low-field insulator and the quantum
Hall (QH) liquid. Our results support the existence of an intermediate regime,
where the amplitudes of magneto-oscillations can be well described by
conventional Shubnikov-de Haas theory, between the low-field insulator and QH
liquid.Comment: Magneto-oscillations governed by Shubnikov-de Haas theory are
observed between the low-field insulator and quantum Hall liqui
Assessment of closure coefficients for compressible-flow turbulence models
A critical assessment is made of the closure coefficients used for turbulence length scale in existing models of the transport equation, with reference to the extension of these models to compressible flow. It is shown that to satisfy the compressible 'law of the wall', the model coefficients must actually be functions of density gradients. The magnitude of the errors that result from neglecting this dependence on density varies with the variable used to specify the length scale. Among the models investigated, the k-omega model yields the best performance, although it is not completely free from errors associated with density terms. Models designed to reduce the density-gradient effect to an insignificant level are proposed
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