31,943 research outputs found
Kinetic Inflation in Stringy and Other Cosmologies
An inflationary epoch driven by the kinetic energy density in a dynamical
Planck mass is studied. In the conformally related Einstein frame it is easiest
to see the demands of successful inflation cannot be satisfied by kinetic
inflation alone. Viewed in the original Jordan-Brans-Dicke frame, the obstacle
is manifest as a kind of graceful exit problem and/or a kind of flatness
problem. These arguments indicate the weakness of only the simplest
formulation. {}From them can be gleaned directions toward successful kinetic
inflation.Comment: 26 pages, LaTeX, CITA-94-2
Distinguishing Marks of Simply-connected Universes
A statistical quantity suitable for distinguishing simply-connected
Robertson-Walker (RW) universes is introduced, and its explicit expressions for
the three possible classes of simply-connected RW universes with an uniform
distribution of matter are determined. Graphs of the distinguishing mark for
each class of RW universes are presented and analyzed.There sprout from our
results an improvement on the procedure to extract the topological signature of
multiply-connected RW universes, and a refined understanding of that
topological signature of these universes studied in previous works.Comment: 13 pages, 4 figures, LaTeX2e. To appear in Int. J. Mod. Phys. D
(2000
Entanglement of two-qubit photon beam by magnetic field
We have studied the possibility of affecting the entanglement measure of
2-qubit system consisting of two photons with different fixed frequencies but
with two arbitrary linear polarizations, moving in the same direction, by the
help of an applied external magnetic field. The interaction between the
magnetic field and the photons in our model is achieved through intermediate
electrons that interact with both the photons and the magnetic field. The
possibility of exact theoretical analysis of this scheme is based on known
exact solutions that describe the interaction of an electron subjected to an
external magnetic field (or a medium of electrons not interacting with each
other) with a quantized field of two photons. We adapt these exact solutions to
the case under consideration. Using explicit wave functions for the resulting
electromagnetic field, we calculate the entanglement measure of the photon beam
as a function of the applied magnetic field and parameters of the electron
medium
Predictions for Impurity-Induced Tc Suppression in the High-Temperature Superconductors
We address the question of whether anisotropic superconductivity is
compatible with the evidently weak sensitivity of the critical temperature Tc
to sample quality in the high-Tc copper oxides. We examine this issue
quantitatively by solving the strong-coupling Eliashberg equations numerically
as well as analytically for s-wave impurity scattering within the second Born
approximation. For pairing interactions with a characteristically low energy
scale, we find an approximately universal dependence of the d-wave
superconducting transition temperature on the planar residual resistivity which
is independent of the details of the microscopic pairing. These results, in
conjunction with future systematic experiments, should help elucidate the
symmetry of the order parameter in the cuprates.Comment: 13 pages, 4 figures upon request, revtex version
Blind Normalization of Speech From Different Channels
We show how to construct a channel-independent representation of speech that
has propagated through a noisy reverberant channel. This is done by blindly
rescaling the cepstral time series by a non-linear function, with the form of
this scale function being determined by previously encountered cepstra from
that channel. The rescaled form of the time series is an invariant property of
it in the following sense: it is unaffected if the time series is transformed
by any time-independent invertible distortion. Because a linear channel with
stationary noise and impulse response transforms cepstra in this way, the new
technique can be used to remove the channel dependence of a cepstral time
series. In experiments, the method achieved greater channel-independence than
cepstral mean normalization, and it was comparable to the combination of
cepstral mean normalization and spectral subtraction, despite the fact that no
measurements of channel noise or reverberations were required (unlike spectral
subtraction).Comment: 25 pages, 7 figure
Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism
Tensegrity mechanisms have several interesting properties that make them
suitable for a number of applications. Their analysis is generally challenging
because the static equilibrium conditions often result in complex equations. A
class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three
linear springs is analyzed in detail in this paper. The kinetostatic equations
are derived and solved under several loading and geometric conditions. It is
shown that these mechanisms exhibit up to six equilibrium configurations, of
which one or two are stable. Discriminant varieties and cylindrical algebraic
decomposition combined with Groebner base elimination are used to classify
solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May
2017, Poitiers, France. 201
Exact asymptotic expansions for the cylindrical Poisson-Boltzmann equation
The mathematical theory of integrable Painleve/Toda type systems sheds new
light on the behavior of solutions to the Poisson-Boltzmann equation for the
potential due to a long rod-like macroion. We investigate here the case of
symmetric electrolytes together with that of 1:2 and 2:1 salts. Short and large
scale features are analyzed, with a particular emphasis on the low salinity
regime. Analytical expansions are derived for several quantities relevant for
polyelectrolytes theory, such as the Manning radius. In addition, accurate and
practical expressions are worked out for the electrostatic potential, which
improve upon previous work and cover the full range of radial distances
Monopole solutions to the Bogomolny equation as three-dimensional generalizations of the Kronecker series
The Dirac monopole on a three-dimensional torus is considered as a solution
to the Bogomolny equation with non-trivial boundary conditions. The analytical
continuation of the obtained solution is shown to be a three-dimensional
generalization of the Kronecker series. It satisfies the corresponding
functional equation and is invariant under modular transformations.Comment: 13 pages, 1 figur
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