Biomedical subjects

M den Nijs

Publications and source records attributed to M den Nijs.

4 recordsLinked to original sources

PubMed2003

Effect of a columnar defect on the shape of slow-combustion fronts.

We report experimental results for the behavior of slow-combustion fronts in the presence of a columnar defect with enhanced or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for enhanced vs reduced driving in the defect clearly demonstrates the existence of a Kardar-Parisi-Zhang-type nonlinear term in the effective evolution equation for the slow-combustion fronts. We also find that slow-combustion fronts display a faceted form for large enough enhanced driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a nonzero enhanced driving in agreement with the simulated behavior of the ASEP model.

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PubMed2001

Anomalous roughness, localization, and globally constrained random walks.

The scaling properties of a random walker subject to the global constraint that it needs to visit each site an even number of times are determined. Such walks are realized in the equilibrium state of one-dimensional surfaces that are subject to dissociative-dimer-type surface dynamics. Moreover, they can be mapped onto unconstrained random walks on a random surface, and the latter corresponds to a non-Hermitian random free fermion model that describes electron localization near a band edge. We show analytically that the dynamic exponent of this random walk is z=d+2 in spatial dimension d. This explains the anomalous roughness, with exponent alpha=1/3, in one-dimensional equilibrium surfaces with dissociative-dimer-type dynamics.

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PubMed2001

Reconstructed rough growing interfaces: ridge-line trapping of domain walls.

We investigate whether surface reconstruction order exists in stationary growing states at all length scales or only below a crossover length l(rec). The latter behavior would be similar to surface roughness in growing crystal surfaces; below the equilibrium roughening temperature they evolve in a layer-by-layer mode within a crossover length scale l(R), but are always rough at large length scales. We investigate this issue in the context of Kardar-Parisi-Zhang (KPZ) type dynamics and a checkerboard type reconstruction, using the restricted solid-on-solid model with negative monatomic step energies. This is a topology where surface reconstruction order is compatible with surface roughness and where a so-called reconstructed rough phase exists in equilibrium. We find that during growth reconstruction order is absent in the thermodynamic limit, but exists below a crossover length l(rec)>l(R), and that this local order fluctuates critically. Domain walls become trapped at the ridge lines of the rough surface, and thus the reconstruction order fluctuations are slaved to the KPZ dynamics.

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PubMed1999

Active width at a slanted active boundary in directed percolation.

The width W of the active region around an active moving wall in a directed percolation process diverges at the percolation threshold p(c) as W approximately Aepsilon(-nu( parallel)) ln(epsilon(0)/epsilon), with epsilon=p(c)-p, epsilon(0) a constant, and nu( parallel)=1.734 the critical exponent of the characteristic time needed to reach the stationary state xi( parallel) approximately epsilon(-nu(parallel)). The logarithmic factor arises from screening the statistically independent needle shaped subclusters in the active region. Numerical data confirm this scaling behavior.

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