2,281 research outputs found
Anomalous Dynamic Scaling in Locally-Conserved Coarsening of Fractal Clusters
We report two-dimensional phase-field simulations of locally-conserved
coarsening dynamics of random fractal clusters with fractal dimension D=1.7 and
1.5. The correlation function, cluster perimeter and solute mass are measured
as functions of time. Analyzing the correlation function dynamics, we identify
two different time-dependent length scales that exhibit power laws in time. The
exponents of these power laws are independent of D, one of them is apparently
the classic exponent 1/3. The solute mass versus time exhibits dynamic scaling
with a D-dependent exponent, in agreement with a simple scaling theory.Comment: 5 pages, 4 figure
Four-year clinical experience with Ad Hoc fractional flow reserve measurement to guide ravascularization strategy
Semiclassical theory of electron drag in strong magnetic fields
We present a semiclassical theory for electron drag between two parallel
two-dimensional electron systems in a strong magnetic field, which provides a
transparent picture of the most salient qualitative features of anomalous drag
phenomena observed in recent experiments, especially the striking sign reversal
of drag at mismatched densities. The sign of the drag is determined by the
curvature of the effective dispersion relation obeyed by the drift motion of
the electrons in a smooth disorder potential. Localization plays a role in
explaining activated low temperature behavior, but is not crucial for anomalous
drag per se.Comment: 10 page
Phase Field Modeling of Fast Crack Propagation
We present a continuum theory which predicts the steady state propagation of
cracks. The theory overcomes the usual problem of a finite time cusp
singularity of the Grinfeld instability by the inclusion of elastodynamic
effects which restore selection of the steady state tip radius and velocity. We
developed a phase field model for elastically induced phase transitions; in the
limit of small or vanishing elastic coefficients in the new phase, fracture can
be studied. The simulations confirm analytical predictions for fast crack
propagation.Comment: 5 pages, 11 figure
Breakdown of Scale Invariance in the Phase Ordering of Fractal Clusters
Our numerical simulations with the Cahn-Hilliard equation show that
coarsening of fractal clusters (FCs) is not a scale-invariant process. On the
other hand, a typical coarsening length scale and interfacial area of the FC
exhibit power laws in time, while the mass fractal dimension remains invariant.
The initial value of the lower cutoff is a relevant length scale. A
sharp-interface model is formulated that can follow the whole dynamics of a
diffusion controlled growth, coarsening, fragmentation and approach to
equilibrium in a system with conserved order parameter.Comment: 4 pages, 4 figures, RevTex, submitted to PR
Thermal roughening of an SOS-model with elastic interaction
We analyze the effects of a long-ranged step-step interaction on thermal
roughening within the framework of a solid-on-solid model of a crystal surface
by means of Monte Carlo simulation. A repulsive step-step interaction is
modeled by elastic dipoles located on sites adjacent to the steps. In order to
reduce the computational effort involved in calculating interaction energy
based on long-ranged potentials, we employ a multi-grid scheme. As a result of
the long-range character of the step interaction, the roughening temperature
increases drastically compared to a system with short-range cutoff as a
consequence of anti-correlations between surface defects
The universality class of fluctuating pulled fronts
It has recently been proposed that fluctuating ``pulled'' fronts propagating
into an unstable state should not be in the standard KPZ universality class for
rough interface growth. We introduce an effective field equation for this class
of problems, and show on the basis of it that noisy pulled fronts in {\em d+1}
bulk dimensions should be in the universality class of the {\em (d+1)+1}D KPZ
equation rather than of the {\em d+1}D KPZ equation. Our scenario ties together
a number of heretofore unexplained observations in the literature, and is
supported by previous numerical results.Comment: 4 pages, 2 figure
Multiscale Random-Walk Algorithm for Simulating Interfacial Pattern Formation
We present a novel computational method to simulate accurately a wide range
of interfacial patterns whose growth is limited by a large scale diffusion
field. To illustrate the computational power of this method, we demonstrate
that it can be used to simulate three-dimensional dendritic growth in a
previously unreachable range of low undercoolings that is of direct
experimental relevance.Comment: 4 pages RevTex, 6 eps figures; substantial changes in presentation,
but results and conclusions remain the sam
Nonlinear lattice model of viscoelastic Mode III fracture
We study the effect of general nonlinear force laws in viscoelastic lattice
models of fracture, focusing on the existence and stability of steady-state
Mode III cracks. We show that the hysteretic behavior at small driving is very
sensitive to the smoothness of the force law. At large driving, we find a Hopf
bifurcation to a straight crack whose velocity is periodic in time. The
frequency of the unstable bifurcating mode depends on the smoothness of the
potential, but is very close to an exact period-doubling instability. Slightly
above the onset of the instability, the system settles into a exactly
period-doubled state, presumably connected to the aforementioned bifurcation
structure. We explicitly solve for this new state and map out its
velocity-driving relation
Near-Field Spectroscopy of Individual Asymmetric Split-Ring Terahertz Resonators
Metamaterial resonators have become an efficient and versatile platform in the terahertz frequency range, finding applications in integrated optical devices, such as active modulators and detectors, and in fundamental research, e.g., ultrastrong light–matter investigations. Despite their growing use, characterization of modes supported by these subwavelength elements has proven to be challenging and it still relies on indirect observation of the collective far-field transmission/reflection properties of resonator arrays. Here, we present a broadband time-domain spectroscopic investigation of individual metamaterial resonators via a THz aperture scanning near-field microscope (a-SNOM). The time-domain a-SNOM allows the mapping and quantitative analysis of strongly confined modes supported by the resonators. In particular, a cross-polarized configuration presented here allows an investigation of weakly radiative modes. These results hold great potential to advance future metamaterial-based optoelectronic platforms for fundamental research in THz photonics.
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