11,530 research outputs found
Simulation of spherulite growth using a comprehensive approach to modeling the first-order isotropic/smectic-A mesophase transition
A comprehensive modeling and simulation study of the first-order
isotropic/smectic-A transition is presented and applied to phase diagram
computation and two-dimensional spherulite growth. An approach based on
nonlinear optimization, that incorporates experimental data (from 12CB,
dodecyl-cyanobiphenyl), is used to determine physically realistic model
parameters. These parameters are then used in conjunction with an optimized
phase diagram computation method. Additionally, a time-dependent formulation is
presented and applied to the study of two-dimensional smectic-A spherulite
growth. These results show the growth kinematics and defect dynamics of
nanoscale smectic-A spherulite growth in an isotropic phase with an initially
radial layer configuration
Quantum lattice models at intermediate temperatures
We analyze the free energy and construct the Gibbs-KMS states for a class of
quantum lattice systems, at low temperatures and when the interactions are
almost diagonal in a suitable basis. We study systems with continuous symmetry,
but our results are valid for discrete symmetry breaking only. Such phase
transitions occur at intermediate temperatures where the continuous symmetry is
not broken, while at very low temperature continuous symmetry breaking may
occur.Comment: 25 pages, 6 figure
Quantum limited measurements of atomic scattering properties
We propose a method to perform precision measurements of the interaction
parameters in systems of N ultra-cold spin 1/2 atoms. The spectroscopy is
realized by first creating a coherent spin superposition of the two relevant
internal states of each atom and then letting the atoms evolve under a
squeezing Hamiltonian. The non-linear nature of the Hamiltonian decreases the
fundamental limit imposed by the Heisenberg uncertainty principle to N^(-2), a
factor of N smaller than the fundamental limit achievable with non-interacting
atoms. We study the effect of decoherence and show that even with decoherence,
entangled states can outperform the signal to noise limit of non-entangled
states. We present two possible experimental implementations of the method
using Bose-Einstein spinor condensates and fermionic atoms loaded in optical
lattices and discuss their advantages and disadvantages.Comment: 7 pages, 5 figures. References adde
Wave polarizations for a beam-like gravitational wave in quadratic curvature gravity
We compute analytically the tidal field and polarizations of an exact
gravitational wave generated by a cylindrical beam of null matter of finite
width and length in quadratic curvature gravity. We propose that this wave can
represent the gravitational wave that keep up with the high energy photons
produced in a gamma ray burst (GRB) source.Comment: 5 pages, 3 figures, minor corrections, to appear in CQ
Simulating accelerated atoms coupled to a quantum field
We show an analogy between static quantum emitters coupled to a single mode
of a quantum field and accelerated Unruh-DeWitt detectors. We envision a way to
simulate a variety of relativistic quantum field settings beyond the reach of
current computational power, such as high number of qubits coupled to a quantum
field following arbitrary non-inertial trajectories. Our scheme may be
implemented with trapped ions and circuit QED set-ups.Comment: 5 pages, 2 figures, revtex 4-
Thermodynamics, transition dynamics, and texturing in polymer-dispersed liquid crystals with mesogens exhibiting a direct isotropic/smectic-A transition
Experimental and modeling/simulation studies of phase equilibrium and growth
morphologies of novel polymer-dispersed liquid crystal (PDLC) mixtures of PS
(polystyrene) and liquid crystals that exhibit a direct isotropic/smectic-A
(lamellar) mesophase transition were performed for PS/10CB (decyl-
cyanobiphenyl) and PS/12CB (dodecyl-cyanobiphenyl). Partial phase diagrams were
determined using polarized optical microscopy (POM) and differential scanning
calorimetry (DSC) for different compositions of both materials, determining
both phase separation (liquid/liquid demixing) and phase ordering
(isotropic/smectic-A transition) temperatures. The Flory-Huggins theory of
isotropic mixing and Maier-Saupe-McMillan theory for smectic-A liquid
crystalline ordering were used to computationally determine phase diagrams for
both systems, showing good agreement with the experimental results. In addition
to thermodynamic observations, growth morphology relations were found depending
on phase transition sequence, quench rate, and material composition. Three
stages of liquid crystal-rich domain growth morphology were observed: spherical
macroscale domain growth ("stage I"), highly anisotropic domain growth ("stage
II"), and sub-micron spheroid domain growth ("stage III"). Nano-scale structure
of spheroidal and spherocylindrical morphologies were then determined via
two-dimensional simulation of a high-order Landau-de Gennes model. Morphologies
observed during stage II growth are typical of di- rect isotropic/smectic-A
phase transitions, such as highly anisotropic "batonnets" and filaments. These
morphologies, which are found to be persistent in direct isotropic/smectic-A
PDLCs, could provide new functionality and applications for these functional
materials.Comment: First Revision, 21 pages, 11 figures, submitted to Macromolecules as
an article 17JUL200
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