741 research outputs found
Simulations of collision times in gravity driven granular flow
We use simulations to investigate collision time distributions as one
approaches the static limit of steady-state flow of dry granular matter. The
collision times fall in a power-law distribution with an exponent dictated by
whether the grains are ordered or disordered. Remarkably, the exponents have
almost no dependence on dimension. We are also able to resolve a disagreement
between simulation and experiments on the exponent of the collision time
power-law distribution.Comment: 7 pages, 5 figure
Hydrodynamics of topological defects in nematic liquid crystals
We show that back-flow, the coupling between the order parameter and the
velocity fields, has a significant effect on the motion of defects in nematic
liquid crystals. In particular the defect speed can depend strongly on the
topological strength in two dimensions and on the sense of rotation of the
director about the core in three dimensions.Comment: 4 pages including two figure
Phase Ordering in Nematic Liquid Crystals
We study the kinetics of the nematic-isotropic transition in a
two-dimensional liquid crystal by using a lattice Boltzmann scheme that couples
the tensor order parameter and the flow consistently. Unlike in previous
studies, we find the time dependences of the correlation function, energy
density, and the number of topological defects obey dynamic scaling laws with
growth exponents that, within the numerical uncertainties, agree with the value
1/2 expected from simple dimensional analysis. We find that these values are
not altered by the hydrodynamic flow. In addition, by examining shallow
quenches, we find that the presence of orientational disorder can inhibit
amplitude ordering.Comment: 21 pages, 14 eps figures, revte
Modelling nematohydrodynamics in liquid crystal devices
We formulate a lattice Boltzmann algorithm which solves the hydrodynamic
equations of motion for nematic liquid crystals. The applicability of the
approach is demonstrated by presenting results for two liquid crystal devices
where flow has an important role to play in the switching.Comment: 6 pages including 5 figure
Lattice Boltzmann Algorithm for three-dimensional liquid crystal hydrodynamics
We describe a lattice Boltzmann algorithm to simulate liquid crystal
hydrodynamics in three dimensions. The equations of motion are written in terms
of a tensor order parameter. This allows both the isotropic and the nematic
phases to be considered. Backflow effects and the hydrodynamics of topological
defects are naturally included in the simulations, as are viscoelastic effects
such as shear-thinning and shear-banding. We describe the implementation of
velocity boundary conditions and show that the algorithm can be used to
describe optical bounce in twisted nematic devices and secondary flow in
sheared nematics with an imposed twist.Comment: 12 pages, 3 figure
The Use of New and Innovative DVD Technology to Teach Competitive Youth Horse Judging Teams
Resources for competitive horse judging programs are necessary on several levels. While traditional sources such as printed materials and VHS video have thus far sufficed, the need for more current and technological media is prodigious. The 2003 Rocky Mountain Horse Expo Horse Judging Contest DVD is an interactive and educational DVD that provides users with high quality digital video footage of 10 classes of four horses from the 2003 Rocky Mountain Horse Expo Horse Judging Contest. Additionally, the DVD contains official placings and sample sets of oral reasons from a national champion collegiate horse judging team
Numerical calculations of the phase diagram of cubic blue phases in cholesteric liquid crystals
We study the static properties of cubic blue phases by numerically minimising
the three-dimensional, Landau-de Gennes free energy for a cholesteric liquid
crystal close to the isotropic-cholesteric phase transition. Thus we are able
to refine the powerful but approximate, semi-analytic frameworks that have been
used previously. We obtain the equilibrium phase diagram and discuss it in
relation to previous results. We find that the value of the chirality above
which blue phases appear is shifted by 20% (towards experimentally more
accessible regions) with respect to previous estimates. We also find that the
region of stability of the O5 structure -- which has not been observed
experimentally -- shrinks, while that of BP I (O8-) increases thus giving the
correct order of appearance of blue phases at small chirality. We also study
the approach to equilibrium starting from the infinite chirality solutions and
we find that in some cases the disclination network has to assemble during the
equilibration. In these situations disclinations are formed via the merging of
isolated aligned defects.Comment: 16 pages, 5 figures. Accepted for publication in Phys. Rev.
Hydrodynamics of domain growth in nematic liquid crystals
We study the growth of aligned domains in nematic liquid crystals. Results
are obtained solving the Beris-Edwards equations of motion using the lattice
Boltzmann approach. Spatial anisotropy in the domain growth is shown to be a
consequence of the flow induced by the changing order parameter field
(backflow). The generalization of the results to the growth of a cylindrical
domain, which involves the dynamics of a defect ring, is discussed.Comment: 12 revtex-style pages, including 12 figures; small changes before
publicatio
Elastic response of a nematic liquid crystal to an immersed nanowire
We study the immersion of a ferromagnetic nanowire within a nematic liquid
crystal using a lattice Boltzmann algorithm to solve the full three-dimensional
equations of hydrodynamics. We present an algorithm for including a moving
boundary, to simulate a nanowire, in a lattice Boltzmann simulation. The
nematic imposes a torque on a wire that increases linearly with the angle
between the wire and the equilibrium direction of the director field. By
rotation of these nanowires, one can determine the elastic constants of the
nematic.Comment: 10 pages, 8 figure
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