76,883 research outputs found
Quadrature domains and kernel function zipping
It is proved that quadrature domains are ubiquitous in a very strong sense in
the realm of smoothly bounded multiply connected domains in the plane. In fact,
they are so dense that one might as well assume that any given smooth domain
one is dealing with is a quadrature domain, and this allows access to a host of
strong conditions on the classical kernel functions associated to the domain.
Following this string of ideas leads to the discovery that the Bergman kernel
can be zipped down to a strikingly small data set. It is also proved that the
kernel functions associated to a quadrature domain must be algebraic.Comment: 13 pages, to appear in Arkiv for matemati
Exact General Solutions to Extraordinary N-body Problems
We solve the N-body problems in which the total potential energy is any
function of the mass-weighted root-mean-square radius of the system of N point
masses. The fundamental breathing mode of such systems vibrates non-linearly
for ever. If the potential is supplemented by any function that scales as the
inverse square of the radius there is still no damping of the fundamental
breathing mode. For such systems a remarkable new statistical equilibrium is
found for the other coordinates and momenta, which persists even as the radius
changes continually.Comment: 15 pages, LaTeX. Accepted for publication in Proc. Roy. Soc.
Relaxation to a Perpetually Pulsating Equilibrium
Paper in honour of Freeman Dyson on the occasion of his 80th birthday.
Normal N-body systems relax to equilibrium distributions in which classical
kinetic energy components are 1/2 kT, but, when inter-particle forces are an
inverse cubic repulsion together with a linear (simple harmonic) attraction,
the system pulsates for ever. In spite of this pulsation in scale, r(t), other
degrees of freedom relax to an ever-changing Maxwellian distribution. With a
new time, tau, defined so that r^2d/dt =d/d tau it is shown that the remaining
degrees of freedom evolve with an unchanging reduced Hamiltonian. The
distribution predicted by equilibrium statistical mechanics applied to the
reduced Hamiltonian is an ever-pulsating Maxwellian in which the temperature
pulsates like r^-2. Numerical simulation with 1000 particles demonstrate a
rapid relaxation to this pulsating equilibrium.Comment: 9 pages including 4 figure
Complexity in complex analysis
We show that the classical kernel and domain functions associated to an
n-connected domain in the plane are all given by rational combinations of three
or fewer holomorphic functions of one complex variable. We characterize those
domains for which the classical functions are given by rational combinations of
only two or fewer functions of one complex variable. Such domains turn out to
have the property that their classical domain functions all extend to be
meromorphic functions on a compact Riemann surface, and this condition will be
shown to be equivalent to the condition that an Ahlfors map and its derivative
are algebraically dependent. We also show how many of these results can be
generalized to finite Riemann surfaces.Comment: 30 pages, to appear in Advances in Mat
Particle acceleration by shocks in supernova remnants
Particle acceleration occurs on a range of scales from AU in the heliosphere
to Mpc in clusters of galaxies and to energies ranging from MeV to EeV. A
number of acceleration processes have been proposed, but diffusive shock
acceleration (DSA) is widely invoked as the predominant mechanism. DSA operates
on all these scales and probably to the highest energies. DSA is simple, robust
and predicts a universal spectrum. However there are still many unknowns
regarding particle acceleration. This paper focuses on the particular question
of whether supernova remnants (SNR) can produce the Galactic CR spectrum up to
the knee at a few PeV. The answer depends in large part on the detailed physics
of diffusive shock acceleration.Comment: Invited talk at the 33rd International Cosmic Ray Conference, Rio de
Janeiro, Brazil, 2-9 July 2013. Submitted for publication in a special issue
of the Brazilian Journal of Physic
The Green's function and the Ahlfors map
The classical Green's function associated to a simply connected domain in the
complex plane is easily expressed in terms of a Riemann mapping function. The
purpose of this paper is to express the Green's function of a finitely
connected domain in the plane in terms of a single Ahlfors mapping of the
domain, which is a proper holomorphic mapping of the domain onto the unit disc
that is the analogue of the Riemann map in the multiply connected setting.Comment: 14 page
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