Growth model with restricted surface relaxation

We simulate a growth model with restricted surface relaxation process in d=1 and d=2, where d is the dimensionality of a flat substrate. In this model, each particle can relax on the surface to a local minimum, as the Edwards-Wilkinson linear model, but only within a distance s. If the local minimum is out from this distance, the particle evaporates through a refuse mechanism similar to the Kim-Kosterlitz nonlinear model. In d=1, the growth exponent beta, measured from the temporal behavior of roughness, indicates that in the coarse-grained limit, the linear term of the Kardar-Parisi-Zhang equation dominates in short times (low-roughness) and, in asymptotic times, the nonlinear term prevails. The crossover between linear and nonlinear behaviors occurs in a characteristic time t_c which only depends on the magnitude of the parameter s, related to the nonlinear term. In d=2, we find indications of a similar crossover, that is, logarithmic temporal behavior of roughness in short times and power law behavior in asymptotic times

Crossover effects in a discrete deposition model with Kardar-Parisi-Zhang scaling

We simulated a growth model in 1+1 dimensions in which particles are aggregated according to the rules of ballistic deposition with probability p or according to the rules of random deposition with surface relaxation (Family model) with probability 1-p. For any p>0, this system is in the Kardar-Parisi-Zhang (KPZ) universality class, but it presents a slow crossover from the Edwards-Wilkinson class (EW) for small p. From the scaling of the growth velocity, the parameter p is connected to the coefficient of the nonlinear term of the KPZ equation, lambda, giving lambda ~ p^gamma, with gamma = 2.1 +- 0.2. Our numerical results confirm the interface width scaling in the growth regime as W ~ lambda^beta t^beta, and the scaling of the saturation time as tau ~ lambda^(-1) L^z, with the expected exponents beta =1/3 and z=3/2 and strong corrections to scaling for small lambda. This picture is consistent with a crossover time from EW to KPZ growth in the form t_c ~ lambda^(-4) ~ p^(-8), in agreement with scaling theories and renormalization group analysis. Some consequences of the slow crossover in this problem are discussed and may help investigations of more complex models.Comment: 16 pages, 7 figures; to appear in Phys. Rev.

Modelling of the magnetoelastic behaviour of a polycrystalline ferrimagnetic material

The effect of stresses on the magnetic behaviour of polycrystalline ferrites has been investigated by the use of experiments and a multiscale model. This model is based upon 3 scales: the magnetic domain, the single crystal and the polycrystal. At the scale of the magnetic domain, a minimisation of the potential energy (composed of field energy, anisotropy energy and magneto-elastic energy) gives the orientation of magnetisation under the effect of magnetic field, stresses, and crystal orientation. At the scale of the single crystal, the volume fractions of domains of different orientations are computed from their respective energies through a balance equation that introduces two adjusting parameters. The isotropic polycrystalline behaviour is deduced from the averaging of the behaviour of a sufficient number of grains (of different crystallographic orientations). The adjusting parameters are identified from the magnetisation response of a ring subjected to two different levels of axial compressive stresses. The model is then used to predict the behaviour of the same ring subjected to different levels of radial compressive loading. The predictions are in good agreement with the experimental results

The BaBar detector: Upgrades, operation and performance

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