822 research outputs found
Conserved Dynamics and Interface Roughening in Spontaneous Imbibition : A Critical Overview
Imbibition phenomena have been widely used experimentally and theoretically
to study the kinetic roughening of interfaces. We critically discuss the
existing experiments and some associated theoretical approaches on the scaling
properties of the imbibition front, with particular attention to the
conservation law associated to the fluid, to problems arising from the actual
structure of the embedding medium, and to external influences such as
evaporation and gravity. Our main conclusion is that the scaling of moving
interfaces includes many crossover phenomena, with competition between the
average capillary pressure gradient and its fluctuations setting the maximal
lengthscale for roughening. We discuss the physics of both pinned and moving
interfaces and the ability of the existing models to account for their
properties.Comment: 9 pages, Late
Comment on: "Roughness of Interfacial Crack Fronts: Stress-Weighted Percolation in the Damage Zone"
This is a comment on J. Schmittbuhl, A. Hansen, and G. G. Batrouni, Phys.
Rev. Lett. 90, 045505 (2003). They offer a reply, in turn.Comment: 1 page, 1 figur
Energy landscapes, lowest gaps, and susceptibility of elastic manifolds at zero temperature
We study the effect of an external field on (1+1) and (2+1) dimensional
elastic manifolds, at zero temperature and with random bond disorder. Due to
the glassy energy landscape the configuration of a manifold changes often in
abrupt, ``first order'' -type of large jumps when the field is applied. First
the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact
ground state calculations and an extreme statistics argument. The scaling has a
logarithmic prefactor originating from the number of the minima in the
landscape, and reads ,
where is the roughness exponent and is the energy fluctuation
exponent of the manifold, is the linear size of the manifold, and is
the system height. The gap scaling is extended to the case of a finite external
field and yields for the susceptibility of the manifolds . We also present a mean field argument
for the finite size scaling of the first jump field, .
The implications to wetting in random systems, to finite-temperature behavior
and the relation to Kardar-Parisi-Zhang non-equilibrium surface growth are
discussed.Comment: 20 pages, 22 figures, accepted for publication in Eur. Phys. J.
Optimization in random field Ising models by quantum annealing
We investigate the properties of quantum annealing applied to the random
field Ising model in one, two and three dimensions. The decay rate of the
residual energy, defined as the energy excess from the ground state, is find to
be with in the range ,
depending on the strength of the random field. Systems with ``large clusters''
are harder to optimize as measured by . Our numerical results suggest
that in the ordered phase whereas in the paramagnetic phase the
annealing procedure can be tuned so that .Comment: 7 pages (2 columns), 9 figures, published with minor changes, one
reference updated after the publicatio
Elastic lines on splayed columnar defects studied numerically
We investigate by exact optimization method properties of two- and
three-dimensional systems of elastic lines in presence of splayed columnar
disorder. The ground state of many lines is separable both in 2d and 3d leading
to a random walk -like roughening in 2d and ballistic behavior in 3d.
Furthermore, we find that in the case of pure splayed columnar disorder in
contrast to point disorder there is no entanglement transition in 3d.
Entanglement can be triggered by perturbing the pure splay system with point
defects.Comment: 9 pages, 11 figures. Accepted for publication in PR
Surface criticality in random field magnets
The boundary-induced scaling of three-dimensional random field Ising magnets
is investigated close to the bulk critical point by exact combinatorial
optimization methods. We measure several exponents describing surface
criticality: for the surface layer magnetization and the surface
excess exponents for the magnetization and the specific heat, and
. The latter ones are related to the bulk phase transition by the
same scaling laws as in pure systems, but only with the same violation of
hyperscaling exponent as in the bulk. The boundary disorders faster
than the bulk, and the experimental and theoretical implications are discussed.Comment: 6 pages, 9 figures, to appear in Phys. Rev.
Multilevel modelling of cost data: an application to thrombolysis and primary angioplasty in the UK NHS
Cost data are frequently collected from several locations and tend to be non negative and skewed. Generalised linear multilevel models provide a means of dealing with each of these issues. This paper compares several statistical models within this class using data drawn from an observational study of 3,000 patients treated for heart attack in 15 UK NHS hospitals. A number of alternative link functions and covariates were considered. We demonstrate that whilst it is important to take account of clustering in the data, the precise manner in which this is done is equally important. Models which allow for correlation between the random effects components and heteroskedasticity across all hospitals performed best in terms of model fit and made substantial di¤erences to cost estimates
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