arXiv subjects

A. D. Rutenberg

Publications and source records attributed to A. D. Rutenberg.

14 recordsLinked to original sources

arXiv2001

Curved Tails in Polymerization-Based Bacterial Motility

The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a visually striking signature of actin polymerization-based motility. Similar actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae, the Vaccinia virus, and vesicles and microspheres in related in vitro systems. We show that the torque required to produce the curvature in the tail can arise from randomly placed actin filaments pushing the bacterium or particle. We find that the curvature magnitude determines the number of actively pushing filaments, independent of viscosity and of the molecular details of force generation. The variation of the curvature with time can be used to infer the dynamics of actin filaments at the bacterial surface.

cond-mat.soft↗

arXiv2000

Cluster Persistence: a Discriminating Probe of Soap Froth Dynamics

The persistent decay of bubble clusters in coarsening two-dimensional soap froths is measured experimentally as a function of cluster volume fraction. Dramatically stronger decay is observed in comparison to soap froth models and to measurements and calculations of persistence in other systems. The fraction of individual bubbles that contain any persistent area also decays, implying significant bubble motion and suggesting that T1 processes play an important role in froth persistence.

cond-mat.stat-mech↗

arXiv1999

Triangular anisotropies in Driven Diffusive Systems: reconciliation of Up and Down

Deterministic coarse-grained descriptions of driven diffusive systems (DDS) have been hampered by apparent inconsistencies with kinetic Ising models of DDS. In the evolution towards the driven steady-state, ``triangular'' anisotropies in the two systems point in opposite directions with respect to the drive field. We show that this is non-universal behavior in the sense that the triangular anisotropy ``flips'' with local modifications of the Ising interactions. The sign and magnitude of the triangular anisotropy also vary with temperature. We have also flipped the anisotropy of coarse-grained models, though not yet at the latest stages of evolution. Our results illustrate the comparison of deterministic coarse-grained and stochastic Ising DDS studies to identify universal phenomena in driven systems. Coarse-grained systems are particularly attractive in terms of analysis and computational efficiency.

cond-mat.stat-mech↗

arXiv1999

Dynamical Scaling: the Two-Dimensional XY Model Following a Quench

To sensitively test scaling in the 2D XY model quenched from high-temperatures into the ordered phase, we study the difference between measured correlations and the (scaling) results of a Gaussian-closure approximation. We also directly compare various length-scales. All of our results are consistent with dynamical scaling and an asymptotic growth law $L \sim (t/\ln[t/t_0])^{1/2}$, though with a time-scale $t_0$ that depends on the length-scale in question. We then reconstruct correlations from the minimal-energy configuration consistent with the vortex positions, and find them significantly different from the ``natural'' correlations --- though both scale with $L$. This indicates that both topological (vortex) and non-topological (``spin-wave'') contributions to correlations are relevant arbitrarily late after the quench. We also present a consistent definition of dynamical scaling applicable more generally, and emphasize how to generalize our approach to other quenched systems where dynamical scaling is in question. Our approach directly applies to planar liquid-crystal systems.

cond-mat.stat-mech↗

arXiv1998

Reaction Zones and Quenched Charged-Particle Systems with Long-Range Interactions

We determine the evolving segregated or mixed morphology of charged-particle systems with long-range power-law interactions and overall charge neutrality that have been quenched to a low temperature. Segregated morphology systems are characterized by the size of uniformly charged domains, $L(t)$, the particle separation within the domains, $l_{AA}(t)$, the particle flux-density leaving the domains, $J(t)$, the width of reaction zones between domains, $W(t)$, the particle spacing within the reaction-zones, $l_{AB}(t)$, and the particle lifetime in the reaction-zones, $τ(t)$. Mixed morphology systems are essentially one large reaction zone, with $L \sim l_{AB} \sim l_{AA}$. By relating these quantities through the scaling behavior of particle fluxes and microscopic annihilation rates within reaction-zones, we determine the characteristic time-exponents of these quantities at late times. The morphology of the system, segregated or mixed, is also determined self-consistently. With this unified approach, we consider systems with diffusion and/or long-range interactions, and with either uncorrelated or correlated high-temperature initial conditions. Finally, we discuss systems with particle-like topological defects and electronic systems in various substrate dimensions --- including quantum-hall devices with skyrmions.

cond-mat.stat-mech↗

arXiv1996

Non-equilibrium Phase-Ordering with a Global Conservation Law

In all dimensions, infinite-range Kawasaki spin exchange in a quenched Ising model leads to an asymptotic length-scale $L \sim (ρt)^{1/2} \sim t^{1/3}$ at $T=0$ because the kinetic coefficient is renormalized by the broken-bond density, $ρ\sim L^{-1}$. For $T>0$, activated kinetics recovers the standard asymptotic growth-law, $L \sim t^{1/2}$. However, at all temperatures, infinite-range energy-transport is allowed by the spin-exchange dynamics. A better implementation of global conservation, the microcanonical Creutz algorithm, is well behaved and exhibits the standard non-conserved growth law, $L \sim t^{1/2}$, at all temperatures.

cond-mat↗

arXiv1996

Stress-free Spatial Anisotropy in Phase-Ordering

We find spatial anisotropy in the asymptotic correlations of two-dimensional Ising models under non-equilibrium phase-ordering. Anisotropy is seen for critical and off-critical quenches and both conserved and non-conserved dynamics. We argue that spatial anisotropy is generic for scalar systems (including Potts models) with an anisotropic surface tension. Correlation functions will not be universal in these systems since anisotropy will depend on, e.g., temperature, microscopic interactions and dynamics, disorder, and frustration.

cond-mat↗

arXiv1995

Comment on ``Theory of Spinodal Decomposition''

I comment on a paper by S. B. Goryachev [PRL vol 72, p.1850 (1994)] that presents a theory of non-equilibrium dynamics for scalar systems quenched into an ordered phase. Goryachev incorrectly applies only a global conservation constraint to systems with local conservation laws.

cond-mat↗

arXiv1995

Scaling Violations with Textures in Two-Dimensional Phase-Ordering

Scaling violations are found in the phase-ordering two-dimensional Heisenberg [$O(3)$] model, which has non-singular topological textures, under dissipative non-conserved dynamics. Three separate length-scales are found: $L_T$ characterizes the scale of individual textures, $L_N$ characterizes the separation between textures, and $L_C$ characterizes the distance between oppositely charged textures.

cond-mat↗

arXiv1994

The Energy-Scaling Approach to Phase-Ordering Growth Laws

We present a simple, unified approach to determining the growth law for the characteristic length scale, $L(t)$, in the phase ordering kinetics of a system quenched from a disordered phase to within an ordered phase. This approach, based on a scaling assumption for pair correlations, determines $L(t)$ self-consistently for purely dissipative dynamics by computing the time-dependence of the energy in two ways. We derive growth laws for conserved and non-conserved $O(n)$ models, including two-dimensional XY models and systems with textures. We demonstrate that the growth laws for other systems, such as liquid-crystals and Potts models, are determined by the type of topological defect in the order parameter field that dominates the energy. We also obtain generalized Porod laws for systems with topological textures.

cond-mat↗

arXiv1994

Phase Ordering of 2D XY Systems Below T_{KT}

We consider quenches in non-conserved two-dimensional XY systems between any two temperatures below the Kosterlitz-Thouless transition. The evolving systems are defect free at coarse-grained scales, and can be exactly treated. Correlations scale with a characteristic length $L(t) \propto t^{1/2}$ at late times. The autocorrelation decay exponent, $\barλ = (η_i+η_f)/2$, depends on both the initial and the final state of the quench through the respective decay exponents of equilibrium correlations, $C_{EQ}(r) \sim r^{-η}$. We also discuss time-dependent quenches.

cond-mat↗

arXiv1994

Unwinding Scaling Violations in Phase Ordering

The one-dimensional $O(2)$ model is the simplest example of a system with topological textures. The model exhibits anomalous ordering dynamics due to the appearance of two characteristic length scales: the phase coherence length, $L \sim t^{1/z}$, and the phase winding length, $L_{w} \sim L^χ$. We derive the scaling law $z=2+μχ$, where $μ=0$ ($μ=2$) for nonconserved (conserved) dynamics and $χ=1/2$ for uncorrelated initial orientations. From hard-spin equations of motion, we consider the evolution of the topological defect density and recover a simple scaling description. (please email ar@v2.ph.man.ac.uk for a hard copy by mail)

cond-mat↗

arXiv1994

Phase Ordering Kinetics of One-Dimensional Non-Conserved Scalar Systems

We consider the phase-ordering kinetics of one-dimensional scalar systems. For attractive long-range ($r^{-(1+σ)}$) interactions with $σ>0$, ``Energy-Scaling'' arguments predict a growth-law of the average domain size $L \sim t^{1/(1+σ)}$ for all $σ>0$. Numerical results for $σ=0.5$, $1.0$, and $1.5$ demonstrate both scaling and the predicted growth laws. For purely short-range interactions, an approach of Nagai and Kawasaki is asymptotically exact. For this case, the equal-time correlations scale, but the time-derivative correlations break scaling. The short-range solution also applies to systems with long-range interactions when $σ\rightarrow \infty$, and in that limit the amplitude of the growth law is exactly calculated.

cond-mat↗

arXiv1993

Growth Laws for Phase Ordering

We determine the characteristic length scale, $L(t)$, in phase ordering kinetics for both scalar and vector fields, with either short- or long-range interactions, and with or without conservation laws. We obtain $L(t)$ consistently by comparing the global rate of energy change to the energy dissipation from the local evolution of the order parameter. We derive growth laws for O(n) models, and our results can be applied to other systems with similar defect structures.

cond-mat↗