11,218 research outputs found
Nonlinear supratransmission in multicomponent systems
A method is proposed to solve the challenging problem of determining the
supratransmission threshold (onset of instability of harmonic boundary driving
inside a band gap) in multicomponent nonintegrable nonlinear systems. It is
successfully applied to the degenerate three-wave resonant interaction in a
birefringent quadratic medium where the process generates spatial gap solitons.
No analytic expression is known for this model showing the broad applicability
of the method to nonlinear systems.Comment: 4 pages, 3 figure
Dynamic Precompression Treatment - A Case History
An unusual case history of a condominium apartment building, originally designed for eleven storeys, to which four additional floors were added after the footings had already been constructed and was successfully completed to fifteen storeys in height . The use of rather high soil-bearing values, from 7 ksf ( 350 kPa) in the original design to over 12 ksf ( 600 kPa) . The project site , underlain by erratic soil profiles containing layers of soft fine-grained soils to about 20 ft (6 m) below the surface, had been effectively improved with an intense application of the Dynamic Precompression Treatment (OPT) . A historical background of the OPT and extensive general and specific details of the implementation of this technique are presented together with selection of design parameters, results of conventional in-situ testing and non-conventional stress-strain tests for determination of soil compressibility moduli. Stress settlement analyses and settlement records are also provided
An analytic model for the transition from decelerated to accelerated cosmic expansion
We consider the scenario where our observable universe is devised as a
dynamical four-dimensional hypersurface embedded in a five-dimensional bulk
spacetime, with a large extra dimension, which is the {\it generalization of
the flat FRW cosmological metric to five dimensions}. This scenario generates a
simple analytical model where different stages of the evolution of the universe
are approximated by distinct parameterizations of the {\it same} spacetime. In
this model the evolution from decelerated to accelerated expansion can be
interpreted as a "first-order" phase transition between two successive stages.
The dominant energy condition allows different parts of the universe to evolve,
from deceleration to acceleration, at different redshifts within a narrow era.
This picture corresponds to the creation of bubbles of new phase, in the middle
of the old one, typical of first-order phase transitions. Taking today, we find that the cross-over from deceleration to acceleration
occurs at , regardless of the equation of state in the very
early universe. In the case of primordial radiation, the model predicts that
the deceleration parameter "jumps" from to at . At the present time and the equation of state of the
universe is , in agreement with observations and some
theoretical predictions.Comment: The abstract and introduction are improved and the discussion section
is expanded. A number of references are adde
Bistability in sine-Gordon: the ideal switch
The sine-Gordon equation, used as the representative nonlinear wave equation,
presents a bistable behavior resulting from nonlinearity and generating
hysteresis properties. We show that the process can be understood in a
comprehensive analytical formulation and that it is a generic property of
nonlinear systems possessing a natural band gap. The approach allows to
discover that sine-Gordon can work as an it ideal switch by reaching a
transmissive regime with vanishing driving amplitude.Comment: Phys. Rev. E, (to be published, May 2005
Wave-like Solutions for Bianchi type-I cosmologies in 5D
We derive exact solutions to the vacuum Einstein field equations in 5D, under
the assumption that (i) the line element in 5D possesses self-similar symmetry,
in the classical understanding of Sedov, Taub and Zeldovich, and that (ii) the
metric tensor is diagonal and independent of the coordinates for ordinary 3D
space. These assumptions lead to three different types of self-similarity in
5D: homothetic, conformal and "wave-like". In this work we present the most
general wave-like solutions to the 5D field equations. Using the standard
technique based on Campbell's theorem, they generate a large number of
anisotropic cosmological models of Bianchi type-I, which can be applied to our
universe after the big-bang, when anisotropies could have played an important
role. We present a complete review of all possible cases of self-similar
anisotropic cosmologies in 5D. Our analysis extends a number of previous
studies on wave-like solutions in 5D with spatial spherical symmetry
Nonlinear Discrete Systems with Nonanalytic Dispersion Relations
A discrete system of coupled waves (with nonanalytic dispersion relation) is
derived in the context of the spectral transform theory for the Ablowitz Ladik
spectral problem (discrete version of the Zakharov-Shabat system). This 3-wave
evolution problem is a discrete version of the stimulated Raman scattering
equations, and it is shown to be solvable for arbitrary boundary value of the
two radiation fields and initial value of the medium state. The spectral
transform is constructed on the basis of the D-bar approach.Comment: RevTex file, to appear in Journ. Math. Phy
Electroweak Baryogenesis with Vector-like Leptons and Scalar Singlets
We investigate the viability of electroweak baryogenesis in a model with a
first order electroweak phase transition induced by the addition of two gauge
singlet scalars. A vector-like lepton doublet is introduced in order to provide
CP violating interactions with the singlets and Standard Model leptons, and the
asymmetry generation dynamics are examined using the vacuum expectation value
insertion approximation. We find that such a model is readily capable of
generating sufficient baryon asymmetry while satisfying electron electric
dipole moment and collider phenomenology constraints.Comment: 38 pages, 8 figures. Citations added. Benchmarks, figures and tables
updated, error fixed in calculations. Matches version published in JHE
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