893 research outputs found
Homogeneous variational problems: a minicourse
A Finsler geometry may be understood as a homogeneous variational problem,
where the Finsler function is the Lagrangian. The extremals in Finsler geometry
are curves, but in more general variational problems we might consider extremal
submanifolds of dimension . In this minicourse we discuss these problems
from a geometric point of view.Comment: This paper is a written-up version of the major part of a minicourse
given at the sixth Bilateral Workshop on Differential Geometry and its
Applications, held in Ostrava in May 201
Hilbert forms for a Finsler metrizable projective class of sprays
The projective Finsler metrizability problem deals with the question whether
a projective-equivalence class of sprays is the geodesic class of a (locally or
globally defined) Finsler function. In this paper we use Hilbert-type forms to
state a number of different ways of specifying necessary and sufficient
conditions for this to be the case, and we show that they are equivalent. We
also address several related issues of interest including path spaces, Jacobi
fields, totally-geodesic submanifolds of a spray space, and the equivalence of
path geometries and projective-equivalence classes of sprays.Comment: 23 page
The Cartan form for constrained Lagrangian systems and the nonholonomic Noether theorem
This paper deals with conservation laws for mechanical systems with
nonholonomic constraints. It uses a Lagrangian formulation of nonholonomic
systems and a Cartan form approach. We present what we believe to be the most
general relations between symmetries and first integrals. We discuss the
so-called nonholonomic Noether theorem in terms of our formalism, and we give
applications to Riemannian submanifolds, to Lagrangians of mechanical type, and
to the determination of quadratic first integrals.Comment: 25 page
Invariant Lagrangians, mechanical connections and the Lagrange-Poincare equations
We deal with Lagrangian systems that are invariant under the action of a
symmetry group. The mechanical connection is a principal connection that is
associated to Lagrangians which have a kinetic energy function that is defined
by a Riemannian metric. In this paper we extend this notion to arbitrary
Lagrangians. We then derive the reduced Lagrange-Poincare equations in a new
fashion and we show how solutions of the Euler-Lagrange equations can be
reconstructed with the help of the mechanical connection. Illustrative examples
confirm the theory.Comment: 22 pages, to appear in J. Phys. A: Math. Theor., D2HFest special
issu
Linearization of nonlinear connections on vector and affine bundles, and some applications
A linear connection is associated to a nonlinear connection on a vector
bundle by a linearization procedure. Our definition is intrinsic in terms of
vector fields on the bundle. For a connection on an affine bundle our procedure
can be applied after homogenization and restriction. Several applications in
Classical Mechanics are provided
Lifetimes of Stark-shifted image states
The inelastic lifetimes of electrons in image-potential states at Cu(100)
that are Stark-shifted by the electrostatic tip-sample interaction in the
scanning tunneling microscope are calculated using the many-body GW
approximation. The results demonstrate that in typical tunneling conditions the
image state lifetimes are significantly reduced from their field-free values.
The Stark-shift to higher energies increases the number of inelastic scattering
channels that are available for decay, with field-induced changes in the image
state wave function increasing the efficiency of the inelastic scattering
through greater overlap with final state wave functions.Comment: 10 pages, 4 figure
Homogeneity and projective equivalence of differential equation fields
We propose definitions of homogeneity and projective equivalence for systems
of ordinary differential equations of order greater than two, which allow us to
generalize the concept of a spray (for systems of order two). We show that the
Euler-Lagrange fields of parametric Lagrangians of order greater than one which
are regular (in a natural sense that we define) form a projective equivalence
class of homogeneous systems. We show further that the geodesics, or base
integral curves, of projectively equivalent homogeneous differential equation
fields are the same apart from orientation-preserving reparametrization; that
is, homogeneous differential equation fields determine systems of paths
The inverse problem for Lagrangian systems with certain non-conservative forces
We discuss two generalizations of the inverse problem of the calculus of
variations, one in which a given mechanical system can be brought into the form
of Lagrangian equations with non-conservative forces of a generalized Rayleigh
dissipation type, the other leading to Lagrangian equations with so-called
gyroscopic forces. Our approach focusses primarily on obtaining coordinate-free
conditions for the existence of a suitable non-singular multiplier matrix,
which will lead to an equivalent representation of a given system of
second-order equations as one of these Lagrangian systems with non-conservative
forces.Comment: 28 page
The Berwald-type linearisation of generalised connections
We study the existence of a natural `linearisation' process for generalised
connections on an affine bundle. It is shown that this leads to an affine
generalised connection over a prolonged bundle, which is the analogue of what
is called a connection of Berwald type in the standard theory of connections.
Various new insights are being obtained in the fine structure of affine bundles
over an anchored vector bundle and affineness of generalised connections on
such bundles.Comment: 25 page
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