4,471 research outputs found
Boundary conditions in the Dirac approach to graphene devices
We study a family of local boundary conditions for the Dirac problem
corresponding to the continuum limit of graphene, both for nanoribbons and
nanodots. We show that, among the members of such family, MIT bag boundary
conditions are the ones which are in closest agreement with available
experiments. For nanotubes of arbitrary chirality satisfying these last
boundary conditions, we evaluate the Casimir energy via zeta function
regularization, in such a way that the limit of nanoribbons is clearly
determined.Comment: 10 pages, no figure. Section on Casimir energy adde
Undulated cylinders of charged diblock copolymers
We study the cylinder to sphere morphological transition of diblock
copolymers in aqueous solution with a hydrophobic block and a charged block. We
find a metastable undulated cylinder configuration for a range of charge and
salt concentrations which, nevertheless, occurs above the threshold where
spheres are thermodynamically favorable. By modeling the shape of the cylinder
ends, we find that the free energy barrier for the transition from cylinders to
spheres is quite large and that this barrier falls significantly in the limit
of high polymer charge and low solution salinity. This suggests that observed
undulated cylinder phases are kinetically trapped structures
- …