8 research outputs found
Thermally Induced Local Failures in Quasi-One-Dimensional Systems: Collapse in Carbon Nanotubes, Necking in Nanowires and Opening of Bubbles in DNA
We present a general framework to explore thermally activated failures in
quasi one dimensional systems. We apply it to the collapse of carbon nanotubes,
the formation of bottlenecks in nanowires, both of which limit conductance, and
the opening of local regions or "bubbles" of base pairs in strands of DNA that
are relevant for transcription and danaturation. We predict an exponential
behavior for the probability of the opening of bubbles in DNA, the average
distance between flattened regions of a nanotube or necking in a nanowire as a
monotonically decreasing function of temperature, and compute a temperature
below which these events become extremely rare. These findings are difficult to
obtain numerically, however, they could be accessible experimentally.Comment: 4 pages, 2 figures, to be submitte
Microstructure from ferroelastic transitions using strain pseudospin clock models in two and three dimensions: a local mean-field analysis
We show how microstructure can arise in first-order ferroelastic structural
transitions, in two and three spatial dimensions, through a local meanfield
approximation of their pseudospin hamiltonians, that include anisotropic
elastic interactions. Such transitions have symmetry-selected physical strains
as their -component order parameters, with Landau free energies that
have a single zero-strain 'austenite' minimum at high temperatures, and
spontaneous-strain 'martensite' minima of structural variants at low
temperatures. In a reduced description, the strains at Landau minima induce
temperature-dependent, clock-like hamiltonians, with
-component strain-pseudospin vectors pointing to
discrete values (including zero). We study elastic texturing in five such
first-order structural transitions through a local meanfield approximation of
their pseudospin hamiltonians, that include the powerlaw interactions. As a
prototype, we consider the two-variant square/rectangle transition, with a
one-component, pseudospin taking values of , as in a
generalized Blume-Capel model. We then consider transitions with two-component
() pseudospins: the equilateral to centred-rectangle ();
the square to oblique polygon (); the triangle to oblique ()
transitions; and finally the 3D cubic to tetragonal transition (). The
local meanfield solutions in 2D and 3D yield oriented domain-walls patterns as
from continuous-variable strain dynamics, showing the discrete-variable models
capture the essential ferroelastic texturings. Other related hamiltonians
illustrate that structural-transitions in materials science can be the source
of interesting spin models in statistical mechanics.Comment: 15 pages, 9 figure
Viscoelastic Properties of Dynamically Asymmetric Binary Fluids Under Shear Flow
We study theoretically the viscoelastic properties of sheared binary fluids
that have strong dynamical asymmetry between the two components. The dynamical
asymmetry arises due to asymmetry between the viscoelastic stresses,
particularly the bulk stress. Our calculations are based on the two-fluid model
that incorporates the asymmetric stress distribution. We simulate the phase
separation process under an externally imposed shear and compare the asymmetric
case with the usual phase separation under a shear flow without viscoelastic
effects. We also simulate the behavior of phase separated stable morphologies
under applied shear and compute the stress relaxation.Comment: 10 pages text, 9 figure
Domain Size Dependence of Piezoelectric Properties of Ferroelectrics
The domain size dependence of piezoelectric properties of ferroelectrics is
investigated using a continuum Ginzburg-Landau model that incorporates the
long-range elastic and electrostatic interactions. Microstructures with desired
domain sizes are created by quenching from the paraelectric phase by biasing
the initial conditions. Three different two-dimensional microstructures with
different sizes of the domains are simulated. An electric field is
applied along the polar as well as non-polar directions and the piezoelectric
response is simulated as a function of domain size for both cases. The
simulations show that the piezoelectric coefficients are enhanced by reducing
the domain size, consistent with recent experimental results of Wada and
Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered
Comment: submitted to Physical Review
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Bridging properties of multiblock copolymers.
Using self-consistent field theory, we attempt to elucidate the links between microscopically determined properties, such as the bridging fraction of chains, and mechanical properties of multiblock copolymer materials. We determine morphological aspects such as period and interfacial width and calculate the bridging fractions, and compare with experimental data
Bogomol'nyi Decomposition for Vesicles of Arbitrary Genus
We apply the Bogomol'nyi technique, which is usually invoked in the study of
solitons or models with topological invariants, to the case of elastic energy
of vesicles. We show that spontaneous bending contribution caused by any
deformation from metastable bending shapes falls in two distinct topological
sets: shapes of spherical topology and shapes of non-spherical topology
experience respectively a deviatoric bending contribution a la Fischer and a
mean curvature bending contribution a la Helfrich. In other words, topology may
be considered to describe bending phenomena. Besides, we calculate the bending
energy per genus and the bending closure energy regardless of the shape of the
vesicle. As an illustration we briefly consider geometrical frustration
phenomena experienced by magnetically coated vesicles.Comment: 8 pages, 1 figure; LaTeX2e + IOPar