53,941 research outputs found
Parametric resonant acceleration of particles by gravitational waves
We study the resonant interaction of charged particles with a gravitational
wave propagating in the non-empty interstellar space in the presence of a
uniform magnetic field. It is found that this interaction can be cast in the
form of a parametric resonance problem which, besides the main resonance,
allows for the existence of many secondary ones. Each of them is associated
with a non-zero resonant width, depending on the amplitude of the wave and the
energy density of the interstellar plasma. Numerical estimates of the
particles' energisation and the ensuing damping of the wave are given.Comment: LaTeX file, 16 page
Generalized surface current method in the macroscopic theory of diffraction radiation
The surface current method known in the theory of electromagnetic waves
diffraction is generalized to be applied for the problems of diffraction
radiation generated by a charged particle moving nearby an ideally-conducting
screen in vacuum. An expression for induced surface current density leading to
the exact results in the theory of transition radiation is derived, and by
using this expression several exact solutions of diffraction radiation problems
are found. Limits of applicability for the earlier known models based on the
surface current conception are indicated. Properties of radiation from a
semi-plane and from a slit in cylinder are investigated at the various
distances to observer.Comment: 8 pages, 8 figure
Gaussian solitary waves and compactons in Fermi-Pasta-Ulam lattices with Hertzian potentials
We consider a class of fully-nonlinear Fermi-Pasta-Ulam (FPU) lattices,
consisting of a chain of particles coupled by fractional power nonlinearities
of order . This class of systems incorporates a classical Hertzian
model describing acoustic wave propagation in chains of touching beads in the
absence of precompression. We analyze the propagation of localized waves when
is close to unity. Solutions varying slowly in space and time are
searched with an appropriate scaling, and two asymptotic models of the chain of
particles are derived consistently. The first one is a logarithmic KdV
equation, and possesses linearly orbitally stable Gaussian solitary wave
solutions. The second model consists of a generalized KdV equation with
H\"older-continuous fractional power nonlinearity and admits compacton
solutions, i.e. solitary waves with compact support. When , we numerically establish the asymptotically Gaussian shape of exact FPU
solitary waves with near-sonic speed, and analytically check the pointwise
convergence of compactons towards the limiting Gaussian profile
Dibaryon Condensate in Nuclear Matter and Neutron Stars: Exact Analysis in One-Dimensional Models
We investigate dense nuclear matter with a dibaryon Bose-Einstein condensate
as a possible intermediate state before the quark-gluon phase transition. An
exact analysis of this state of matter is presented in a one-dimensional model.
The analysis is based on a reduction of the quantization rules for the N-body
problem to N coupled algebraic transcendental equations. We observe that when
the Fermi momentum approaches the resonance momentum, the one-particle
distribution function increases near the Fermi surface. When the Fermi momentum
is increased beyond the resonance momentum, the equation of state becomes
softer. The observed behavior can be interpreted in terms of formation of a
Bose-Einstein condensate of two-fermion resonances (dibaryons). In cold nuclear
matter, it should occur if 2(m_N + epsilon_F) is greater or equal to m_D, where
m_N and m_D are respectively the nucleon and dibaryon masses and epsilon_F is
the nucleon Fermi energy.Comment: 25 pages, LaTeX, 2 Postscript figures, to appear in Annals of Physic
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