224 research outputs found
Equilibrium microphase separation in the two-leaflet model of lipid membranes
Because of the coupling between local lipid composition and the thickness of the membrane, microphase separation in two-component lipid membranes can take place; such effects may underlie the formation of equilibrium nanoscale rafts. Using a kinetic description, this phenomenon is analytically and numerically investigated. The phase diagram is constructed through the stability analysis for linearized kinetic equations, and conditions for microphase separation are discussed. Simulations of the full kinetic model reveal the development of equilibrium membrane nanostructures with various morphologies from the initial uniform state
Asymptotic Dynamics of Breathers in Fermi-Pasta-Ulam Chains
We study the asymptotic dynamics of breathers in finite Fermi-Pasta-Ulam
chains at zero and non-zero temperatures. While such breathers are essentially
stationary and very long-lived at zero temperature, thermal fluctuations tend
to lead to breather motion and more rapid decay
Nonequilibrium orientational patterns in two-component Langmuir monolayers
A model of a phase-separating two-component Langmuir monolayer in the
presence of a photo-induced reaction interconvering two components is
formulated. An interplay between phase separation, orientational ordering and
treaction is found to lead to a variety of nonequilibrium self-organized
patterns, both stationary and traveling. Examples of the patterns, observed in
numerical simulations, include flowing droplets, traveling stripes, wave
sources and vortex defects.Comment: Submitted to the Physical Review
Energy Relaxation in Nonlinear One-Dimensional Lattices
We study energy relaxation in thermalized one-dimensional nonlinear arrays of
the Fermi-Pasta-Ulam type. The ends of the thermalized systems are placed in
contact with a zero-temperature reservoir via damping forces. Harmonic arrays
relax by sequential phonon decay into the cold reservoir, the lower frequency
modes relaxing first. The relaxation pathway for purely anharmonic arrays
involves the degradation of higher-energy nonlinear modes into lower energy
ones. The lowest energy modes are absorbed by the cold reservoir, but a small
amount of energy is persistently left behind in the array in the form of almost
stationary low-frequency localized modes. Arrays with interactions that contain
both a harmonic and an anharmonic contribution exhibit behavior that involves
the interplay of phonon modes and breather modes. At long times relaxation is
extremely slow due to the spontaneous appearance and persistence of energetic
high-frequency stationary breathers. Breather behavior is further ascertained
by explicitly injecting a localized excitation into the thermalized array and
observing the relaxation behavior
Enhanced Pulse Propagation in Non-Linear Arrays of Oscillators
The propagation of a pulse in a nonlinear array of oscillators is influenced
by the nature of the array and by its coupling to a thermal environment. For
example, in some arrays a pulse can be speeded up while in others a pulse can
be slowed down by raising the temperature. We begin by showing that an energy
pulse (1D) or energy front (2D) travels more rapidly and remains more localized
over greater distances in an isolated array (microcanonical) of hard springs
than in a harmonic array or in a soft-springed array. Increasing the pulse
amplitude causes it to speed up in a hard chain, leaves the pulse speed
unchanged in a harmonic system, and slows down the pulse in a soft chain.
Connection of each site to a thermal environment (canonical) affects these
results very differently in each type of array. In a hard chain the dissipative
forces slow down the pulse while raising the temperature speeds it up. In a
soft chain the opposite occurs: the dissipative forces actually speed up the
pulse while raising the temperature slows it down. In a harmonic chain neither
dissipation nor temperature changes affect the pulse speed. These and other
results are explained on the basis of the frequency vs energy relations in the
various arrays
Thermal Resonance in Signal Transmission
We use temperature tuning to control signal propagation in simple
one-dimensional arrays of masses connected by hard anharmonic springs and with
no local potentials. In our numerical model a sustained signal is applied at
one site of a chain immersed in a thermal environment and the signal-to-noise
ratio is measured at each oscillator. We show that raising the temperature can
lead to enhanced signal propagation along the chain, resulting in thermal
resonance effects akin to the resonance observed in arrays of bistable systems.Comment: To appear in Phys. Rev.
Fractal entropy of a chain of nonlinear oscillators
We study the time evolution of a chain of nonlinear oscillators. We focus on
the fractal features of the spectral entropy and analyze its characteristic
intermediate timescales as a function of the nonlinear coupling. A Brownian
motion is recognized, with an analytic power-law dependence of its diffusion
coefficient on the coupling.Comment: 6 pages, 3 figures, revised version to appear in Phys. Rev.
Equilibrium microphase separation in the two-leaflet model of lipid membranes
Because of the coupling between local lipid composition and the thickness of the membrane, microphase separation in two-component lipid membranes can take place; such effects may underlie the formation of equilibrium nanoscale rafts. Using a kinetic description, this phenomenon is analytically and numerically investigated. The phase diagram is constructed through the stability analysis for linearized kinetic equations, and conditions for microphase separation are discussed. Simulations of the full kinetic model reveal the development of equilibrium membrane nanostructures with various morphologies from the initial uniform state
Reactive dynamics of inertial particles in nonhyperbolic chaotic flows
Anomalous kinetics of infective (e.g., autocatalytic) reactions in open,
nonhyperbolic chaotic flows are important for many applications in biological,
chemical, and environmental sciences. We present a scaling theory for the
singular enhancement of the production caused by the universal, underlying
fractal patterns. The key dynamical invariant quantities are the effective
fractal dimension and effective escape rate, which are primarily determined by
the hyperbolic components of the underlying dynamical invariant sets. The
theory is general as it includes all previously studied hyperbolic reactive
dynamics as a special case. We introduce a class of dissipative embedding maps
for numerical verification.Comment: Revtex, 5 pages, 2 gif figure
- …