8,070 research outputs found
Software to compute infinitesimal symmetries of exterior differenial systems, with applications
A description is given of a software package to compute symmetries of partial differential equations, using computer algebra. As an application, the computation of higher-order symmetries of the classical Boussinesq equation is given leading to the recursion operator for symmetries in a straightforward way. Nonlocal symmetries for the Federbush model are obtained yielding the linearization of the model
The N=2 supersymmetric unconstrained matrix GNLS hierarchies
The generalization of the N=2 supersymmetric chiral matrix (k|n,m)--GNLS
hierarchy (Lett. Math. Phys. 45 (1998) 63, solv-int/9711009) to the case when
matrix entries are bosonic and fermionic unconstrained N=2 superfields is
proposed. This is done by exhibiting the corresponding matrix Lax--pair
representation in terms of N=2 unconstrained superfields. It is demonstrated
that when matrix entries are chiral and antichiral N=2 superfields, it
reproduces the N=2 chiral matrix (k|n,m)-GNLS hierarchy, while in the scalar
case, k=1, it is equivalent to the N=2 supersymmetric multicomponent hierarchy
(J. Phys. A29 (1996) 1281, hep-th/9510185). The simplest example --the N=2
unconstrained (1|1,0)--GNLS hierarchy-- and its reduction to the N=2
supersymmetric {\alpha}=1 KdV hierarchy are discussed in more detail, and its
rich symmetry structure is uncovered.Comment: 11 pages, LaTex, misprints correcte
On symmetries and cohomological invariants of equations possessing flat representations
We study the equation E_fc of flat connections in a fiber bundle and discover
a specific geometric structure on it, which we call a flat representation. We
generalize this notion to arbitrary PDE and prove that flat representations of
an equation E are in 1-1 correspondence with morphisms f: E\to E_fc, where E
and E_fc are treated as submanifolds of infinite jet spaces. We show that flat
representations include several known types of zero-curvature formulations of
PDE. In particular, the Lax pairs of the self-dual Yang-Mills equations and
their reductions are of this type. With each flat representation we associate a
complex C_f of vector-valued differential forms such that its first cohomology
describes infinitesimal deformations of the flat structure, which are
responsible, in particular, for parameters in Backlund transformations. In
addition, each higher infinitesimal symmetry S of E defines a 1-cocycle c_S of
C_f. Symmetries with exact c_S form a subalgebra reflecting some geometric
properties of E and f. We show that the complex corresponding to E_fc itself is
0-acyclic and 1-acyclic (independently of the bundle topology), which means
that higher symmetries of E_fc are exhausted by generalized gauge ones, and
compute the bracket on 0-cochains induced by commutation of symmetries.Comment: 30 page
Time and energy budgets of Oystercatchers <i>Haematopus ostralegus</i> occupying territories of different quality
Validity of the Impact on Participation and Autonomy questionnaire ā a comparison between the Netherlands and the UK
Optimizing the real-world impact of rehabilitation reviews: increasing the relevance and usability of systematic reviews in rehabilitation
Content-based video indexing for the support of digital library search
Presents a digital library search engine that combines efforts of the AMIS and DMW research projects, each covering significant parts of the problem of finding the required information in an enormous mass of data. The most important contributions of our work are the following: (1) We demonstrate a flexible solution for the extraction and querying of meta-data from multimedia documents in general. (2) Scalability and efficiency support are illustrated for full-text indexing and retrieval. (3) We show how, for a more limited domain, like an intranet, conceptual modelling can offer additional and more powerful query facilities. (4) In the limited domain case, we demonstrate how domain knowledge can be used to interpret low-level features into semantic content. In this short description, we focus on the first and fourth item
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