2,956 research outputs found
A remark on nonlocal symmetries for the Calogero-Degasperis-Ibragimov-Shabat equation
We consider the Calogero-Degasperis-Ibragimov-Shabat (CDIS) equation and find
the complete set of its nonlocal symmetries depending on the local variables
and on the integral of the only local conserved density of the equation in
question. The Lie algebra of these symmetries turns out to be a central
extension of that of local generalized symmetries.Comment: arxiv version is already officia
Integrable Systems in n-dimensional Riemannian Geometry
In this paper we show that if one writes down the structure equations for the
evolution of a curve embedded in an (n)-dimensional Riemannian manifold with
constant curvature this leads to a symplectic, a Hamiltonian and an hereditary
operator. This gives us a natural connection between finite dimensional
geometry, infinite dimensional geometry and integrable systems. Moreover one
finds a Lax pair in (\orth{n+1}) with the vector modified Korteweg-De Vries
equation (vmKDV) \vk{t}=
\vk{xxx}+\fr32 ||\vk{}||^2 \vk{x} as integrability condition. We indicate
that other integrable vector evolution equations can be found by using a
different Ansatz on the form of the Lax pair. We obtain these results by using
the {\em natural} or {\em parallel} frame and we show how this can be gauged by
a generalized Hasimoto transformation to the (usual) {\em Fren{\^e}t} frame. If
one chooses the curvature to be zero, as is usual in the context of integrable
systems, then one loses information unless one works in the natural frame
Higher dimensional Automorphic Lie Algebras
The paper presents the complete classification of Automorphic Lie Algebras
based on , where the symmetry group is finite
and the orbit is any of the exceptional -orbits in .
A key feature of the classification is the study of the algebras in the context
of classical invariant theory. This provides on one hand a powerful tool from
the computational point of view, on the other it opens new questions from an
algebraic perspective, which suggest further applications of these algebras,
beyond the context of integrable systems. In particular, the research shows
that Automorphic Lie Algebras associated to the
groups (tetrahedral, octahedral and
icosahedral groups) depend on the group through the automorphic functions only,
thus they are group independent as Lie algebras. This can be established by
defining a Chevalley normal form for these algebras, generalising this
classical notion to the case of Lie algebras over a polynomial ring.Comment: 43 pages, standard LaTeX2
Automorphic Lie Algebras and Cohomology of Root Systems
A cohomology theory of root systems emerges naturally in the context of
Automorphic Lie Algebras, where it helps formulating some structure theory
questions. In particular, one can find concrete models for an Automorphic Lie
Algebra by integrating cocycles. In this paper we define this cohomology and
show its connection with the theory of Automorphic Lie Algebras. Furthermore,
we discuss its properties: we define the cup product, we show that it can be
restricted to symmetric forms, that it is equivariant with respect to the
automorphism group of the root system, and finally we show acyclicity at
dimension two of the symmetric part, which is exactly what is needed to find
concrete models for Automorphic Lie Algebras.
Furthermore, we show how the cohomology of root systems finds application
beyond the theory of Automorphic Lie Algebras by applying it to the theory of
contractions and filtrations of Lie algebras. In particular, we show that
contractions associated to Cartan -filtrations of simple Lie
algebras are classified by -cocycles, due again to the vanishing of the
symmetric part of the second cohomology group.Comment: 26 pages, standard LaTeX2
Equivariant decomposition of polynomial vector fields
To compute the unique formal normal form of families of vector fields with
nilpotent linear part, we choose a basis of the Lie algebra consisting of
orbits under the linear nilpotent. This creates a new problem: to find explicit
formulas for the structure constants in this new basis. These are well known in
the 2D case, and recently expressions were found for the 3D case by ad hoc
methods. The goal of the present paper is to formulate a systematic approach to
this calculation.
We propose to do this using a rational method for the inversion of the
Clebsch-Gordan coefficients. We illustrate the method on a family of 3D vector
fields and compute the unique formal normal form for the Euler family both in
the 2D and 3D case
Versal Normal Form for Nonsemisimple Singularities
The theory of versal normal form has been playing a role in normal form since
the introduction of the concept by V.I. Arnol'd. But there has been no
systematic use of it that is in line with the semidirect character of the group
of formal transformations on formal vector fields, that is, the linear part
should be done completely first, before one computes the nonlinear terms. In
this paper we address this issue by giving a complete description of a first
order calculation in the case of the two- and three-dimensional irreducible
nilpotent cases, which is then followed up by an explicit almost symplectic
calculation to find the transformation to versal normal form in a particular
fluid dynamics problem and in the celestial mechanics problem
Characterization of the human omega-oxidation pathway for omega-hydroxy-very-long-chain fatty acids
Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via beta-oxidation. A defect in peroxisomal beta-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo omega-oxidation, which may provide an alternative route for the breakdown of VLCFAs. The omega-oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce omega-hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from omega-hydroxy-VLCFAs. We demonstrate that very-long-chain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD(+)-dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjogren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of omega-hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of omega-hydroxy-VLCFAs occurs predominantly via the NAD(+)-dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids
Automorphic Lie Algebras with dihedral symmetry
The concept of Automorphic Lie Algebras arises in the context of reduction
groups introduced in the early 1980s in the field of integrable systems.
Automorphic Lie Algebras are obtained by imposing a discrete group symmetry on
a current algebra of Krichever-Novikov type. Past work shows remarkable
uniformity between algebras associated to different reduction groups. For
example, if the base Lie algebra is and the poles
of the Automorphic Lie Algebra are restricted to an exceptional orbit of the
symmetry group, changing the reduction group does not affect the Lie algebra
structure. In the present research we fix the reduction group to be the
dihedral group and vary the orbit of poles as well as the group action on the
base Lie algebra. We find a uniform description of Automorphic Lie Algebras
with dihedral symmetry, valid for poles at exceptional and generic orbits.Comment: 20 pages, 5 tables, standard LaTeX2
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