24 research outputs found
Thermodynamics of Ferrotoroidic Materials: Toroidocaloric Effect
The three primary ferroics, namely ferromagnets, ferroelectrics and
ferroelastics exhibit corresponding large (or even giant)
magnetocaloric,electrocaloric and elastocaloric effects when a phase transition
is induced by the application of an appropriate external field. Recently the
suite of primary ferroics has been extended to include ferrotoroidic materials
in which there is an ordering of toroidic moments in the form of magnetic
vortex-like structures, examples being LiCo(PO_4)_3 and Ba_2CoGe_2O_7. In the
present work we formulate the thermodynamics of ferrotoroidic materials. Within
a Landau free energy framework we calculate the toroidocaloric effect by
quantifying isothermal entropy change (or adiabatic temperature change) in the
presence of an applied toroidic field when usual magnetization and polarization
may also be present simultaneously. We also obtain a nonlinear
Clausius-Clapeyron relation for phase coexistence.Comment: 10 pages, 5 Figure
Effect of Intra-molecular Disorder and Inter-molecular Electronic Interactions on the Electronic Structure of Poly-p-Phenylene Vinylene (PPV)
We investigate the role of intra-molecular conformational disorder and
inter-molecular electronic interactions on the electronic structure of disorder
clusters of poly-p-phenylene vinylene (PPV) oligomers. Classical molecular
dynamics is used to determine probable molecular geometries, and
first-principle density functional theory (DFT) calculations are used to
determine electronic structure. Intra-molecular and inter-molecular effects are
disentangled by contrasting results for densely packed oligomer clusters with
those for ensembles of isolated oligomers with the same intra-molecular
geometries. We find that electron trap states are induced primarily by
intra-molecular configuration disorder, while the hole trap states are
generated primarily from inter-molecular electronic interactions.Comment: 4 pages, 4 figures. Compile with pdflate
Recommended from our members
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
Spherical Vesicles Distorted by a Grafted Latex Bead: An Exact Solution
We present an exact solution to the problem of the global shape description
of a spherical vesicle distorted by a grafted latex bead. This solution is
derived by treating the nonlinearity in bending elasticity through the
(topological) Bogomol'nyi decomposition technique and elastic compatibility. We
recover the ``hat-model'' approximation in the limit of a small latex bead and
find that the region antipodal to the grafted latex bead flattens. We also
derive the appropriate shape equation using the variational principle and
relevant constraints.Comment: 12 pages, 2 figures, LaTeX2e+REVTeX+AmSLaTe
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
Self-Dual Bending Theory for Vesicles
We present a self-dual bending theory that may enable a better understanding
of highly nonlinear global behavior observed in biological vesicles. Adopting
this topological approach for spherical vesicles of revolution allows us to
describe them as frustrated sine-Gordon kinks. Finally, to illustrate an
application of our results, we consider a spherical vesicle globally distorted
by two polar latex beads.Comment: 10 pages, 3 figures, LaTeX2e+IOPar
Peakompactons: Peaked compact nonlinear waves
This paper is meant as an accessible introduction to/tutorial on the analytical construction and numerical simulation of a class of nonstandard solitary waves termed peakompactons. These peaked compactly supported waves arise as solutions to nonlinear evolution equations from a hierarchy of nonlinearly dispersive Korteweg鈥揹e Vries-type models. Peakompactons, like the now-well-known compactons and unlike the soliton solutions of the Korteweg鈥揹e Vries equation, have finite support, i.e., they are of finite wavelength. However, unlike compactons, peakompactons are also peaked, i.e., a higher spatial derivative suffers a jump discontinuity at the wave鈥檚 crest. Here, we construct such solutions exactly by reducing the governing partial differential equation to a nonlinear ordinary differential equation and employing a phase-plane analysis. A simple, but reliable, finite-difference scheme is also designed and tested for the simulation of collisions of peakompactons. In addition to the peakompacton class of solu..
Compactons in PT-symmetric generalized Korteweg-de Vries Equations
In an earlier paper Cooper, Shepard, and Sodano introduced a generalized KdV
equation that can exhibit the kinds of compacton solitary waves that were first
seen in equations studied by Rosenau and Hyman. This paper considers the
PT-symmetric extensions of the equations examined by Cooper, Shepard, and
Sodano. From the scaling properties of the PT-symmetric equations a general
theorem relating the energy, momentum, and velocity of any solitary-wave
solution of the generalized KdV equation is derived, and it is shown that the
velocity of the solitons is determined by their amplitude, width, and momentum.Comment: 12 pages, 5 figure
PT-Symmetric Dimer in a Generalized Model of Coupled Nonlinear Oscillators
Abstract In the present work, we explore the case of a general PT -symmetric dimer in the context of two both linearly and nonlinearly coupled cubic oscillators. To obtain an analytical handle on the system, we first explore the rotating wave approximation converting it into a discrete nonlinear Schr枚dinger type dimer. In the latter context, the stationary solutions and their stability are identified numerically but also wherever possible analytically. Solutions stemming from both symmetric and anti-symmetric special limits are identified. A number of special cases are explored regarding the ratio of coefficients of nonlinearity between oscillators over the intrinsic one of each oscillator. Finally, the considerations are extended to the original oscillator model, where periodic orbits and their stability are obtained. When the solutions are found to be unstable their dynamics is monitored by means of direct numerical simulations