698 research outputs found
Coadjoint Orbits of the Generalised Sl(2) Sl(3) Kdv Hierarchies
In this paper we develop two coadjoint orbit constructions for the phase
spaces of the generalised and KdV hierachies. This involves the
construction of two group actions in terms of Yang Baxter operators, and an
Hamiltonian reduction of the coadjoint orbits. The Poisson brackets are
reproduced by the Kirillov construction. From this construction we obtain a
`natural' gauge fixing proceedure for the generalised hierarchies.Comment: 37 page
Generalized Drinfeld-Sokolov Hierarchies II: The Hamiltonian Structures
In this paper we examine the bi-Hamiltonian structure of the generalized
KdV-hierarchies. We verify that both Hamiltonian structures take the form of
Kirillov brackets on the Kac-Moody algebra, and that they define a coordinated
system. Classical extended conformal algebras are obtained from the second
Poisson bracket. In particular, we construct the algebras, first
discussed for the case and by A. Polyakov and M. Bershadsky.Comment: 41 page
Generalized Drinfeld-Sokolov Reductions and KdV Type Hierarchies
Generalized Drinfeld-Sokolov (DS) hierarchies are constructed through local
reductions of Hamiltonian flows generated by monodromy invariants on the dual
of a loop algebra. Following earlier work of De Groot et al, reductions based
upon graded regular elements of arbitrary Heisenberg subalgebras are
considered. We show that, in the case of the nontwisted loop algebra
, graded regular elements exist only in those Heisenberg
subalgebras which correspond either to the partitions of into the sum of
equal numbers or to equal numbers plus one . We prove that the
reduction belonging to the grade regular elements in the case yields
the matrix version of the Gelfand-Dickey -KdV hierarchy,
generalizing the scalar case considered by DS. The methods of DS are
utilized throughout the analysis, but formulating the reduction entirely within
the Hamiltonian framework provided by the classical r-matrix approach leads to
some simplifications even for .Comment: 43 page
SYMMETRIES AND EXACT SOLUTIONS OF CONFORMABLE FRACTIONAL PARTIAL DIFFERENTIAL EQUATIONS
In this paper Lie group analysis is used to investigate invariance properties of
nonlinear fractional partial differential equations with conformable fractional time derivative.
The analysis is applied to Korteweg-de Vries, modified Korteweg-de Vries, Burgers, and modified
Burgers equations. For each equation, all of the vector fields and the Lie symmetries are
obtained. Moreover, exact solutions are given to these equations.In this paper Lie group analysis is used to investigate invariance properties of
nonlinear fractional partial differential equations with conformable fractional time derivative.
The analysis is applied to Korteweg-de Vries, modified Korteweg-de Vries, Burgers, and modified
Burgers equations. For each equation, all of the vector fields and the Lie symmetries are
obtained. Moreover, exact solutions are given to these equations
Gaussian solitary waves and compactons in Fermi-Pasta-Ulam lattices with Hertzian potentials
We consider a class of fully-nonlinear Fermi-Pasta-Ulam (FPU) lattices,
consisting of a chain of particles coupled by fractional power nonlinearities
of order . This class of systems incorporates a classical Hertzian
model describing acoustic wave propagation in chains of touching beads in the
absence of precompression. We analyze the propagation of localized waves when
is close to unity. Solutions varying slowly in space and time are
searched with an appropriate scaling, and two asymptotic models of the chain of
particles are derived consistently. The first one is a logarithmic KdV
equation, and possesses linearly orbitally stable Gaussian solitary wave
solutions. The second model consists of a generalized KdV equation with
H\"older-continuous fractional power nonlinearity and admits compacton
solutions, i.e. solitary waves with compact support. When , we numerically establish the asymptotically Gaussian shape of exact FPU
solitary waves with near-sonic speed, and analytically check the pointwise
convergence of compactons towards the limiting Gaussian profile
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