2,328 research outputs found
Phase-ordering dynamics of binary mixtures with field-dependent mobility in shear flow
The effect of shear flow on the phase-ordering dynamics of a binary mixture
with field-dependent mobility is investigated. The problem is addressed in the
context of the time-dependent Ginzburg-Landau equation with an external
velocity term, studied in self-consistent approximation. Assuming a scaling
ansatz for the structure factor, the asymptotic behavior of the observables in
the scaling regime can be analytically calculated. All the observables show
log-time periodic oscillations which we interpret as due to a cyclical
mechanism of stretching and break-up of domains. These oscillations are dumped
as consequence of the vanishing of the mobility in the bulk phase.Comment: 9 pages, 4 figures, EPJ styl
Switching dynamics in cholesteric blue phases
Blue phases are networks of disclination lines, which occur in cholesteric
liquid crystals near the transition to the isotropic phase. They have recently
been used for the new generation of fast switching liquid crystal displays.
Here we study numerically the steady states and switching hydrodynamics of blue
phase I (BPI) and blue phase II (BPII) cells subjected to an electric field.
When the field is on, there are three regimes: for very weak fields (and strong
anchoring at the boundaries) the blue phases are almost unaffected, for
intermediate fields the disclinations twist (for BPI) and unzip (for BPII),
whereas for very large voltages the network dissolves in the bulk of the cell.
Interestingly, we find that a BPII cell can recover its original structure when
the field is switched off, whereas a BPI cell is found to be trapped more
easily into metastable configurations. The kinetic pathways followed during
switching on and off entails dramatic reorganisation of the disclination
networks. We also discuss the effect of changing the director field anchoring
at the boundary planes and of varying the direction of the applied field.Comment: 17 pages, 11 figure
15N NMR study of a mixture of uniformly labeled tRNAs
15N NMR spectra were taken of 15N-enriched tRNA extracted from bakers yeast; ammonium sulfate was used as a nitrogen source. The increase in the degree of denaturation of tRNA, which occurs with increase in temperature from 30 degrees C to 70 degrees C, resulted in no large changes in 15N chemical shifts at acidic and neutral pH but quite pronounced changes in proton-15N nuclear Overhauser effects
Enhancement of structural rearrangement in glassy systems under shear flow
We extend the analysis of the mean field schematic model recently introduced
for the description of glass forming liquids to the case of a supercooled fluid
subjected to a shear flow of rate . After quenching the system to a low
temperature , a slow glassy regime is observed before stationarity is
achieved at the characteristic time . is of the order of the
usual equilibration time without shear for weak shear, , local rearrangement of
dense regions is instead enhanced by the flow, and .Comment: 8 pages, 3 figures, changed content Pacs{64}{70.Pf}{Glass
transitions} Pacs{05}{70.Ln}{Non-equilibrium thermodynamics, irreversible
processes} Pacs{83}{50.Ax}{Steady shear flows
Bistable defect structures in blue phase devices
Blue phases (BPs) are liquid crystals made up by networks of defects, or
disclination lines. While existing phase diagrams show a striking variety of
competing metastable topologies for these networks, very little is known as to
how to kinetically reach a target structure, or how to switch from one to the
other, which is of paramount importance for devices. We theoretically identify
two confined blue phase I systems in which by applying an appropriate series of
electric field it is possible to select one of two bistable defect patterns.
Our results may be used to realise new generation and fast switching
energy-saving bistable devices in ultrathin surface treated BPI wafers.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let
Kinetics of Phase Separation in Fluids: A Molecular Dynamics Study
We present results from extensive 3-d molecular dynamics (MD) simulations of
phase separation kinetics in fluids. A coarse-graining procedure is used to
obtain state-of-the-art MD results. We observe an extended period of temporally
linear growth in the viscous hydrodynamic regime. The morphological similarity
of coarsening in fluids and solids is also quantified. The velocity field is
characterized by the presence of monopole-like defects, which yield a
generalized Porod tail in the corresponding structure factor.Comment: 4 pages, 4 figure
Hydrodynamics and growth laws in lamellar ordering
Ordering of lamellar phases described by a free-energy functional with short-range interactions is numerically investigated in two dimensions by means of a pseudo-spectral method. The ordering process is found to depend on the fluid viscosity: it is arrested for large viscosity values and proceeds as a power law for small ones, with a crossover regime for intermediate values. At varying the free energy parameters, strong evidence has been found that the ordering law, unlike binary mixtures, is not unique. Copyright c (c) EPLA, 2007
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