5,570 research outputs found
Describing the set of words generated by interval exchange transformation
Let be an infinite word over finite alphabet . We get combinatorial
criteria of existence of interval exchange transformations that generate the
word W.Comment: 17 pages, this paper was submitted at scientific council of MSU,
date: September 21, 200
Spatially dispersive finite-difference time-domain analysis of sub-wavelength imaging by the wire medium slabs
In this paper, a spatially dispersive finite-difference time-domain (FDTD)
method to model wire media is developed and validated. Sub-wavelength imaging
properties of the finite wire medium slabs are examined. It is demonstrated
that the slab with its thickness equal to an integer number of half-wavelengths
is capable of transporting images with sub-wavelength resolution from one
interface of the slab to another. It is also shown that the operation of such
transmission devices is not sensitive to their transverse dimensions, which can
be made even comparable to the wavelength. In this case, the edge diffractions
are negligible and do not disturb the image formation.Comment: 14 pages, 13 figures, submitted to Optics Expres
State-Selective High-Energy Excitation of Nuclei by Resonant Positron Annihilation
In the annihilation of a positron with a bound atomic electron, the virtual
gamma photon created may excite the atomic nucleus. We put forward this effect
as a spectroscopic tool for an energy-selective excitation of nuclear
transitions. This scheme can efficiently populate nuclear levels of arbitrary
multipolarities in the MeV regime, including monopole transitions and giant
resonances. In certain cases, it may have a higher cross sections than the
conventionally used Coulomb excitation
On Shirshov bases of graded algebras
We prove that if the neutral component in a finitely-generated associative
algebra graded by a finite group has a Shirshov base, then so does the whole
algebra.Comment: 4 pages; v2: minor corrections in English; to appear in Israel J.
Mat
Geometrical Description of the Local Integrals of Motion of Maxwell-Bloch Equation
We represent a classical Maxwell-Bloch equation and related to it positive
part of the AKNS hierarchy in geometrical terms. The Maxwell-Bloch evolution is
given by an infinitesimal action of a nilpotent subalgebra of affine Lie
algebra on a Maxwell-Bloch phase space treated as a homogeneous
space of . A space of local integrals of motion is described using
cohomology methods. We show that hamiltonian flows associated to the
Maxwell-Bloch local integrals of motion (i.e. positive AKNS flows) are
identified with an infinitesimal action of an abelian subalgebra of the
nilpotent subalgebra on a Maxwell- Bloch phase space. Possibilities of
quantization and latticization of Maxwell-Bloch equation are discussed.Comment: 16 pages, no figures, plain TeX, no macro
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