6,464 research outputs found
Iterated Differential Forms II: Riemannian Geometry Revisited
A natural extension of Riemannian geometry to a much wider context is
presented on the basis of the iterated differential form formalism developed in
math.DG/0605113 and an application to general relativity is given.Comment: 12 pages, extended version of the published note Dokl. Math. 73, n. 2
(2006) 18
Algebraic theories of brackets and related (co)homologies
A general theory of the Frolicher-Nijenhuis and Schouten-Nijenhuis brackets
in the category of modules over a commutative algebra is described. Some
related structures and (co)homology invariants are discussed, as well as
applications to geometry.Comment: 14 pages; v2: minor correction
On the continuous spectral component of the Floquet operator for a periodically kicked quantum system
By a straightforward generalisation, we extend the work of Combescure from
rank-1 to rank-N perturbations. The requirement for the Floquet operator to be
pure point is established and compared to that in Combescure. The result
matches that in McCaw. The method here is an alternative to that work. We show
that if the condition for the Floquet operator to be pure point is relaxed,
then in the case of the delta-kicked Harmonic oscillator, a singularly
continuous component of the Floquet operator spectrum exists. We also provide
an in depth discussion of the conjecture presented in Combescure of the case
where the unperturbed Hamiltonian is more general. We link the physics
conjecture directly to a number-theoretic conjecture of Vinogradov and show
that a solution of Vinogradov's conjecture solves the physics conjecture. The
result is extended to the rank-N case. The relationship between our work and
the work of Bourget on the physics conjecture is discussed.Comment: 25 pages, published in Journal of Mathematical Physic
Presymplectic current and the inverse problem of the calculus of variations
The inverse problem of the calculus of variations asks whether a given system
of partial differential equations (PDEs) admits a variational formulation. We
show that the existence of a presymplectic form in the variational bicomplex,
when horizontally closed on solutions, allows us to construct a variational
formulation for a subsystem of the given PDE. No constraints on the
differential order or number of dependent or independent variables are assumed.
The proof follows a recent observation of Bridges, Hydon and Lawson and
generalizes an older result of Henneaux from ordinary differential equations
(ODEs) to PDEs. Uniqueness of the variational formulation is also discussed.Comment: v2: 17 pages, no figures, BibTeX; minor corrections, close to
published versio
Electromagnetic wave refraction at an interface of a double wire medium
Plane-wave reflection and refraction at an interface with a double wire
medium is considered. The problem of additional boundary conditions (ABC) in
application to wire media is discussed and an ABC-free approach, known in the
solid state physics, is used. Expressions for the fields and Poynting vectors
of the refracted waves are derived. Directions and values of the power density
flow of the refracted waves are found and the conservation of the power flow
through the interface is checked. The difference between the results, given by
the conventional model of wire media and the model, properly taking into
account spatial dispersion, is discussed.Comment: 17 pages, 11 figure
Heat Transfer of Non-Newtonian Dilatant Power Law Fluids in Square and Rectangular Cavities
Steady two-dimensional natural convection in fluid filled cavities is numerically investigated for the case of non-
Newtonian shear thickening power law liquids. The conservation equations of mass, momentum and energy under the
assumption of a Newtonian Boussinesq fluid have been solved using the finite volume method for Newtonian and
non-Newtonian fluids. The computations were performed for a Rayleigh number, based on cavity height, of 105 and a
Prandtl number of 100. In all of the numerical experiments, the channel is heated from below and cooled from the top
with insulated side-walls and the inclination angle is varied. The simulations have been carried out for aspect ratios of
1 and 4. Comparison between the Newtonian and the non-Newtonian cases is conducted based on the dependence of
the average Nusselt number on angle of inclination. It is shown that despite significant variation in heat transfer rate
both Newtonian and non-Newtonian fluids exhibit similar behavior with the transition from multi-cell flow structure
to a single-cell regime
The graded Jacobi algebras and (co)homology
Jacobi algebroids (i.e. `Jacobi versions' of Lie algebroids) are studied in
the context of graded Jacobi brackets on graded commutative algebras. This
unifies varios concepts of graded Lie structures in geometry and physics. A
method of describing such structures by classical Lie algebroids via certain
gauging (in the spirit of E.Witten's gauging of exterior derivative) is
developed. One constructs a corresponding Cartan differential calculus (graded
commutative one) in a natural manner. This, in turn, gives canonical generating
operators for triangular Jacobi algebroids. One gets, in particular, the
Lichnerowicz-Jacobi homology operators associated with classical Jacobi
structures. Courant-Jacobi brackets are obtained in a similar way and use to
define an abstract notion of a Courant-Jacobi algebroid and Dirac-Jacobi
structure. All this offers a new flavour in understanding the
Batalin-Vilkovisky formalism.Comment: 20 pages, a few typos corrected; final version to be published in J.
Phys. A: Math. Ge
Channel spaser
We show that net amplification of surface plasmons is achieved in channel in
a metal plate due to nonradiative excitation by quantum dots. This makes
possible lossless plasmon transmission lines in the channel as well as the
amplification and generation of coherent surface plasmons. As an example, a
ring channel spaser is considered
Inverse Borrmann effect in photonic crystals
The Borrmann effect, which is related to the microscopic distribution of the
electromagnetic field inside the primitive cell, is studied in photonic and
magnetophotonic crystals. This effect, well-known in x-ray spectroscopy, is
responsible for the enhancement or suppression of various linear and nonlinear
optical effects when the incidence angle and/or the frequency change. It is
shown that by design of the primitive cell this effect can be suppressed and
even inverted
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