42 research outputs found
Knots in Charged Polymers
The interplay of topological constraints and Coulomb interactions in static
and dynamic properties of charged polymers is investigated by numerical
simulations and scaling arguments. In the absence of screening, the long-range
interaction localizes irreducible topological constraints into tight molecular
knots, while composite constraints are factored and separated. Even when the
forces are screened, tight knots may survive as local (or even global)
equilibria, as long as the overall rigidity of the polymer is dominated by the
Coulomb interactions. As entanglements involving tight knots are not easy to
eliminate, their presence greatly influences the relaxation times of the
system. In particular, we find that tight knots in open polymers are removed by
diffusion along the chain, rather than by opening up. The knot diffusion
coefficient actually decreases with its charge density, and for highly charged
polymers the knot's position appears frozen.Comment: Revtex4, 9 pages, 9 eps figure
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes
A chromosphere is a universal attribute of stars of spectral type later than
~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae
binaries) show extended and highly turbulent chromospheres, which develop into
slow massive winds. The associated continuous mass loss has a significant
impact on stellar evolution, and thence on the chemical evolution of galaxies.
Yet despite the fundamental importance of those winds in astrophysics, the
question of their origin(s) remains unsolved. What sources heat a chromosphere?
What is the role of the chromosphere in the formation of stellar winds? This
chapter provides a review of the observational requirements and theoretical
approaches for modeling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including physical
models that have recently been proposed. It describes the successes that have
been achieved so far by invoking acoustic and MHD waves to provide a physical
description of plasma heating and wind acceleration, and discusses the
challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript;
accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake
(Berlin: Springer