133 research outputs found
Anomalous elasticity in nematic and smectic elastomer tubule
We study anomalous elasticity in the tubule phases of nematic and smectic
elastomer membranes, which are flat in one direction and crumpled in another.
These phases share the same macroscopic symmetry properties including
spontaneously-broken in-plane isotropy and hence belong to the same
universality class. Below an upper critical value of the membranes'
intrinsic dimension D, thermal fluctuations renormalize the elasticity with
respect to elastic displacements along the tubule axis so that elastic moduli
for compression along the tubule axis and for bending the tubule axis become
length-scale dependent. This anomalous elasticity belongs to the same
universality class as that of d-dimensional conventional smectics with D taking
on the role of d. For physical tubule, D=2, this anomaly is of power-law type
and thus might by easier to detect experimentally than the logarithmic anomaly
in conventional smectics.Comment: 4 pages, 1 figur
Multifractal current distribution in random diode networks
Recently it has been shown analytically that electric currents in a random
diode network are distributed in a multifractal manner [O. Stenull and H. K.
Janssen, Europhys. Lett. 55, 691 (2001)]. In the present work we investigate
the multifractal properties of a random diode network at the critical point by
numerical simulations. We analyze the currents running on a directed
percolation cluster and confirm the field-theoretic predictions for the scaling
behavior of moments of the current distribution. It is pointed out that a
random diode network is a particularly good candidate for a possible
experimental realization of directed percolation.Comment: RevTeX, 4 pages, 5 eps figure
First-order phase transitions in outbreaks of co-infectious diseases and the extended general epidemic process
In co-infections, positive feedback between multiple diseases can accelerate
outbreaks. In a recent letter Chen, Ghanbarnejad, Cai, and Grassberger (CGCG)
introduced a spatially homogeneous mean-field model system for such
co-infections, and studied this system numerically with focus on the possible
existence of discontinuous phase transitions. We show that their model
coincides in mean-field theory with the homogenous limit of the extended
general epidemic process (EGEP). Studying the latter analytically, we argue
that the discontinuous transition observed by CGCG is basically a spinodal
phase transition and not a first-order transition with phase-coexistence. We
derive the conditions for this spinodal transition along with predictions for
important quantities such as the magnitude of the discontinuity. We also shed
light on a true first-order transition with phase-coexistence by discussing the
EGEP with spatial inhomogeneities.Comment: 6 pages, 3 figure
Dynamics of smectic elastomers
We study the low-frequency, long-wavelength dynamics of liquid crystal
elastomers, crosslinked in the smectic- phase, in their smectic-, biaxial
smectic and smectic- phases. Two different yet related formulations are
employed. One formulation describes the pure hydrodynamics and does not
explicitly involve the Frank director, which relaxes to its local equilibrium
value in a non-hydrodynamic time. The other formulation explicitly treats the
director and applies beyond the hydrodynamic limit. We compare the
low-frequency, long-wavelength dynamics of smectic- elastomers to that of
nematics and show that the two are closely related. For the biaxial smectic and
the smectic- phases, we calculate sound velocities and the mode structure in
certain symmetry directions. For the smectic- elastomers, in addition, we
discuss in some detail their possible behavior in rheology experiments.Comment: 19 pages, 3 figure
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