18 research outputs found
Systematic quantum corrections to screening in thermonuclear fusion
We develop a series expansion of the plasma screening length away from the
classical limit in powers of . It is shown that the leading order
quantum correction increases the screening length in solar conditions by
approximately 2% while it decreases the fusion rate by approximately .
We also calculate the next higher order quantum correction which turns out to
be approximately 0.05%
Influence of supercoiling on the disruption of dsDNA
We propose that supercoiling energizes double-stranded DNA (dsDNA) so as to
facilitate thermal fluctuations to an unzipped state. We support this with a
model of two elastic rods coupled via forces that represent base pair
interactions. Supercoiling is shown to lead to a spatially localized higher
energy state in a small region of dsDNA consisting of a few base pairs. This
causes the distance between specific base pairs to be extended, enhancing the
thermal probability for their disruption. Our theory permits the development of
an analogy between this unzipping transition and a second order phase
transition, for which the possibility of a new set of critical exponents is
identified
Mesoscopic theory of the viscoelasticity of polymers
We have advanced our previous static theory of polymer entanglement involving
an extended Cahn-Hilliard functional, to include time-dependent dynamics. We go
beyond the Gaussian approximation, to the one-loop level, to compute the
frequency dependent storage and loss moduli of the system. The three parameters
in our theory are obtained by fitting to available experimental data on
polystyrene melts of various chain lengths. This provides a physical
representation of the parameters in terms of the chain length of the system. We
discuss the importance of the various terms in our energy functional with
respect to their contribution to the viscoelastic response of the polymeric
system.Comment: Submitted to Phys. Rev.
Onset of entanglement
We have developed a theory of polymer entanglement using an extended
Cahn-Hilliard functional, with two extra terms. One is a nonlocal attractive
term, operating over mesoscales, which is interpreted as giving rise to
entanglement, and the other a local repulsive term indicative of excluded
volume interactions. We show how such a functional can be derived using notions
from gauge theory. We go beyond the Gaussian approximation, to the one-loop
level, to show that the system exhibits a crossover to a state of entanglement
as the average chain length between points of entanglement decreases. This
crossover is marked by critical slowing down, as the effective diffusion
constant goes to zero. We have also computed the tensile modulus of the system,
and we find a corresponding crossover to a regime of high modulus.Comment: 18 pages, with 4 figure