Biomedical subjects

MJ Alava

Publications and source records attributed to MJ Alava.

12 recordsLinked to original sources

PubMed2000

Energy landscapes in random systems, driven interfaces, and wetting

We discuss the zero-temperature susceptibility of elastic manifolds with quenched randomness. It diverges with system size due to low-lying local minima. The distribution of energy gaps is deduced to be constant in the limit of vanishing gaps by comparing numerics with a probabilistic argument. The typical manifold response arises from a level-crossing phenomenon and implies that wetting in random systems begins with a discrete transition. The associated "jump field" scales as approximately L-5/3 and L-2.2 for (1+1) and (2+1) dimensional manifolds with random bond disorder.

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PubMed2000

Scaling and noise in slow combustion of paper

We present results of high resolution experiments on kinetic roughening of slow combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of slow combustion fronts cannot be explained by standard theories of kinetic roughening.

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PubMed2000

Elasticity of Poissonian fiber networks

An effective-medium model is introduced for the elasticity of two-dimensional random fiber networks. These networks are commonly used as basic models of heterogeneous fibrous structures such as paper. Using the exact Poissonian statistics to describe the microscopic geometry of the network, the tensile modulus can be expressed by a single-parameter function. This parameter depends on the network density and fiber dimensions, which relate the macroscopic modulus to the relative importance of axial and bending deformations of the fibers. The model agrees well with simulation results and experimental findings. We also discuss the possible generalizations of the model.

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PubMed2000

Scaling of interfaces in brittle fracture and perfect plasticity

The roughness properties of two-dimensional fracture surfaces as created by the slow failure of random fuse networks are considered and compared to yield surfaces of perfect plasticity with similar disorder. By studying systems up to a linear size L=350 it is found that in the cases studied the fracture surfaces exhibit self-affine scaling with a roughness exponent close to 2/3, which is asymptotically exactly true for plasticity though finite-size effects are evident for both. The overlap of yield or minimum energy and fracture surfaces with exactly the same disorder configuration is shown to be a decreasing function of the system size and to be of a rather large magnitude for all cases studied. The typical "overlap cluster" length between pairs of such interfaces converges to a constant with increasing L.

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PubMed2000

Roughening of a propagating planar crack front

A numerical model of the front of a planar crack propagating between two connected elastic plates is investigated. The plates are modeled as square lattices of elastic beams. The plates are connected by similar but breakable beams with a randomly varying stiffness. The crack is driven by pulling both plates at one end in Mode I at a constant rate. We find zeta=1/3, z=4/3, and beta=1/4 for the roughness, dynamical, and growth exponents, respectively, that describe the front behavior. This is similar to continuum limit analyses based on a perturbative stress-intensity treatment of the front [H. Gao and J. R. Rice, J. Appl. Mech. 56, 828 (1989)]. We discuss the differences to recent experiments.

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PubMed2000

Periodic elastic medium in which periodicity is relevant

We analyze, in both (1+1) and (2+1) dimensions, a periodic elastic medium in which the periodicity is such that at long distances the behavior is always in the random-substrate universality class. This contrasts with the models with an additive periodic potential in which, according to the field-theoretic analysis of Bouchaud and Georges and more recently of Emig and Nattermann, the random manifold class dominates at long distances in (1+1) and (2+1) dimensions. The models we use are random-bond Ising interfaces in hypercubic lattices. The exchange constants are random in a slab of size L(d-1)xlambda and these coupling constants are periodically repeated, with a period lambda, along either 10 or 11 [in (1+1) dimensions] and 100 or 111 [in (2+1) dimensions]. Exact ground-state calculations confirm scaling arguments which predict that the surface roughness w behaves as w approximately L(2/3), L< >L(c) with L(c) approximately lambda(3/2) in (1+1) dimensions, and w approximately L0.42,L< >L(c) with L(c) approximately lambda(2. 38) in (2+1) dimensions.

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PubMed2000

Dynamic scaling in one-dimensional cluster-cluster aggregation

We study the dynamic scaling properties of an aggregation model in which particles obey both diffusive and driven ballistic dynamics. The diffusion constant and the velocity of a cluster of size s follow D(s) approximately s(gamma) and v(s) approximately s(delta), respectively. We determine the dynamic exponent and the phase diagram for the asymptotic aggregation behavior in one dimension in the presence of mixed dynamics. The asymptotic dynamics is dominated by the process that has the largest dynamic exponent with a crossover that is located at delta=gamma-1. The cluster size distributions scale similarly in all cases but the scaling function depends continuously on gamma and delta. For the purely diffusive case the scaling function has a transition from exponential to algebraic behavior at small argument values as gamma changes sign, whereas in the drift dominated case the scaling function always decays exponentially.

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PubMed1996