89 research outputs found
Filling the void in confined polymer nematics: phase transitions in a minimal model of dsDNA packing
Inspired to understand the complex spectrum of space-filling organizations
the dsDNA genome within the capsid of bacterial viruses, we study a minimal,
coarse-grained model of single chains densely-packed into a finite spherical
volume. We build the three basic elements of the model--i) the absence of chain
ends ii) the tendency of parallel-strand alignment and iii) a preference of
uniform areal density of chain segments--into a polymer nematic theory for
confined chains. Given the geometric constraints of the problem, we show that
axially symmetric packings fall into one of three topologies: the coaxial
spool; the simple solenoid; and the twisted-solenoid. Among these, only the
twisted-solenoid fills the volume without the presence of line-like
disclinations, or voids, and are therefore generically preferred in the
incompressible limit. An analysis of the thermodynamics behavior of this simple
model reveals a rich behavior, a generic sequence of phases from the empty
state for small container sizes, to the coaxial spool configuration at
intermediate sizes, ultimately giving way, via a second-order,
symmetry-breaking transition, to the twisted-solenoid structure above a
critical sphere size.Comment: 7 pages; 3 figure
Frustrated Polyelectrolyte Bundles and T=0 Josephson-Junction Arrays
We establish a one-to-one mapping between a model for hexagonal
polyelectrolyte bundles and a model for two-dimensional, frustrated
Josephson-junction arrays. We find that the T=0 insulator-to-superconductor
transition of the {\it quantum} system corresponds to a continuous
liquid-to-solid transition of the condensed charge in the finite temperature
{\it classical} system. We find that the role of the vector potential in the
quantum system is played by elastic strain in the classical system. Exploiting
this correspondence we show that the transition is accompanied by a spontaneous
breaking of chiral symmetry and that at the transition the polyelectrolyte
bundle adopts a universal response to shear.Comment: 4 pages, 2 figures, 1 table minor changes to text, reference adde
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