223 research outputs found
Resonance regimes of scattering by small bodies with impedance boundary conditions
The paper concerns scattering of plane waves by a bounded obstacle with
complex valued impedance boundary conditions. We study the spectrum of the
Neumann-to-Dirichlet operator for small wave numbers and long wave asymptotic
behavior of the solutions of the scattering problem. The study includes the
case when is an eigenvalue or a resonance. The transformation from the
impedance to the Dirichlet boundary condition as impedance grows is described.
A relation between poles and zeroes of the scattering matrix in the non-self
adjoint case is established. The results are applied to a problem of scattering
by an obstacle with a springy coating. The paper describes the dependence of
the impedance on the properties of the material, that is on forces due to the
deviation of the boundary of the obstacle from the equilibrium position
On scattering of solitons for the Klein-Gordon equation coupled to a particle
We establish the long time soliton asymptotics for the translation invariant
nonlinear system consisting of the Klein-Gordon equation coupled to a charged
relativistic particle. The coupled system has a six dimensional invariant
manifold of the soliton solutions. We show that in the large time approximation
any finite energy solution, with the initial state close to the solitary
manifold, is a sum of a soliton and a dispersive wave which is a solution of
the free Klein-Gordon equation. It is assumed that the charge density satisfies
the Wiener condition which is a version of the ``Fermi Golden Rule''. The proof
is based on an extension of the general strategy introduced by Soffer and
Weinstein, Buslaev and Perelman, and others: symplectic projection in Hilbert
space onto the solitary manifold, modulation equations for the parameters of
the projection, and decay of the transversal component.Comment: 47 pages, 2 figure
Inverse problems for Schrodinger equations with Yang-Mills potentials in domains with obstacles and the Aharonov-Bohm effect
We study the inverse boundary value problems for the Schr\"{o}dinger
equations with Yang-Mills potentials in a bounded domain
containing finite number of smooth obstacles . We
prove that the Dirichlet-to-Neumann operator on determines
the gauge equivalence class of the Yang-Mills potentials. We also prove that
the metric tensor can be recovered up to a diffeomorphism that is identity on
.Comment: 15 page
High orders of the perturbation theory for hydrogen atom in magnetic field
The states of hydrogen atom with principal quantum number and zero
magnetic quantum number in constant homogeneous magnetic field are
considered. The coefficients of energy eigenvalues expansion up to 75th order
in powers of are obtained for these states. The series for energy
eigenvalues and wave functions are summed up to values of the order
of atomic magnetic field. The calculations are based on generalization of the
moment method, which may be used in other cases of the hydrogen atom
perturbation by a polynomial in coordinates potential.Comment: 16 pages, LaTeX, 6 figures (ps, eps
On the structure of eigenfunctions corresponding to embedded eigenvalues of locally perturbed periodic graph operators
The article is devoted to the following question. Consider a periodic
self-adjoint difference (differential) operator on a graph (quantum graph) G
with a co-compact free action of the integer lattice Z^n. It is known that a
local perturbation of the operator might embed an eigenvalue into the
continuous spectrum (a feature uncommon for periodic elliptic operators of
second order). In all known constructions of such examples, the corresponding
eigenfunction is compactly supported. One wonders whether this must always be
the case. The paper answers this question affirmatively. What is more
surprising, one can estimate that the eigenmode must be localized not far away
from the perturbation (in a neighborhood of the perturbation's support, the
width of the neighborhood determined by the unperturbed operator only).
The validity of this result requires the condition of irreducibility of the
Fermi (Floquet) surface of the periodic operator, which is expected to be
satisfied for instance for periodic Schroedinger operators.Comment: Submitted for publicatio
Bounds on positive interior transmission eigenvalues
The paper contains lower bounds on the counting function of the positive
eigenvalues of the interior transmission problem when the latter is elliptic.
In particular, these bounds justify the existence of an infinite set of
interior transmission eigenvalues and provide asymptotic estimates from above
on the counting function for the large values of the wave number. They also
lead to certain important upper estimates on the first few interior
transmission eigenvalues. We consider the classical transmission problem as
well as the case when the inhomogeneous medium contains an obstacle.Comment: We corrected inaccuracies cost by the wrong sign in the Green formula
(17). In particular, the sign in the definition of \sigma was change
Replica analysis of the generalized p-spin interaction glass model
We investigate stability of replica symmetry breaking solutions in
generalized -spin models. It is shown that the kind of the transition to the
one-step replica symmetry breaking state depends not only on the presence or
absence of the reflection symmetry of the generalized "spin"-operators
but on the number of interacting operators and their individual
characteristics.Comment: 14 pages, 1 figur
Electrocaloric Response of the Dense Ferroelectric Nanocomposites
Using the Landau-Ginzburg-Devonshire approach and effective media models, we
calculated the spontaneous polarization, dielectric, pyroelectric, and
electrocaloric properties of BaTiO core-shell nanoparticles. We predict
that the synergy of size effects and Vegard stresses can significantly improve
the electrocaloric cooling (2- 7 times) of the BaTiO nanoparticles with
diameters (10-100) nm stretched by (1-3)% in comparison with a bulk BaTiO.
To compare with the proposed and other known models, we measured the
capacitance-voltage and current-voltage characteristics of the dense
nanocomposites consisting of (28 -35) vol.% of the BaTiO nanoparticles
incorporated in the poly-vinyl-butyral and ethyl-cellulose polymers covered by
Ag electrodes. We determined experimentally the effective dielectric
permittivity and losses of the dense composites at room temperature. According
to our analysis, to reach the maximal electrocaloric response of the core-shell
ferroelectric nanoparticles incorporated in different polymers, the dense
composites should be prepared with the nanoparticles volume ratio of more than
25 % and fillers with low heat mass and conductance, such as Ag nanoparticles,
which facilitate the heat transfer from the ferroelectric nanoparticles to the
polymer matrix. In general, the core-shell ferroelectric nanoparticles
spontaneously stressed by elastic defects, such as oxygen vacancies or any
other elastic dipoles, which create a strong chemical pressure, are relevant
fillers for electrocaloric nanocomposites suitable for advanced applications as
nano-coolers.Comment: 38 pages, including 10 figures and 2 appendixe
Stimulation of the fluctuation superconductivity by the PT-symmetry
We discuss fluctuations near the second order phase transition where the free
energy has an additional non-Hermitian term. The spectrum of the fluctuations
changes when the odd-parity potential amplitude exceeds the critical value
corresponding to the PT-symmetry breakdown in the topological structure of the
Hilbert space of the effective non-Hermitian Hamiltonian. We calculate the
fluctuation contribution to the differential resistance of a superconducting
weak link and find the manifestation of the PT-symmetry breaking in its
temperature evolution. We successfully validate our theory by carrying out
measurements of far from equilibrium transport in mesoscale-patterned
superconducting wires.Comment: Phys. Rev. Lett 201
Dynamical Systems Gradient method for solving nonlinear equations with monotone operators
A version of the Dynamical Systems Gradient Method for solving ill-posed
nonlinear monotone operator equations is studied in this paper. A discrepancy
principle is proposed and justified. A numerical experiment was carried out
with the new stopping rule. Numerical experiments show that the proposed
stopping rule is efficient. Equations with monotone operators are of interest
in many applications.Comment: 2 figure
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