25 research outputs found
A New Exponent Characterizing the Effect of Evaporation on Imbibition Experiments
We report imbibition experiments investigating the effect of evaporation on
the interface roughness and mean interface height. We observe a new exponent
characterizing the scaling of the saturated surface width. Further, we argue
that evaporation can be usefully modeled by introducing a gradient in the
strength of the disorder, in analogy with the gradient percolation model of
Sapoval {\it et~al.}. By incorporating this gradient we predict a new critical
exponent and a novel scaling relation for the interface width. Both the
exponent value and the form of the scaling agree with the experimental results.Comment: 12 pages, REVTeX 3.0, figures on request (accepted for PRL
Path Crossing Exponents and the External Perimeter in 2D Percolation
2D Percolation path exponents describe probabilities for
traversals of annuli by non-overlapping paths, each on either occupied
or vacant clusters, with at least one of each type. We relate the probabilities
rigorously to amplitudes of models whose exponents, believed to be
exact, yield . This extends to half-integers
the Saleur--Duplantier exponents for clusters, yields the exact
fractal dimension of the external cluster perimeter, , and also explains the absence of narrow gate fjords, as originally
found by Grossman and Aharony.Comment: 4 pages, 2 figures (EPSF). Revised presentatio
Three dimensional hysdrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media
We report the results of a study of multiphase flow in porous media. A
Darcy's law for steady multiphase flow was investigated for both binary and
ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager
reciprocity were shown to be a good approximation of the simulation data. The
dependence of the relative permeability coefficients on water saturation was
investigated and showed good qualitative agreement with experimental data.
Non-steady state invasion flows were investigated, with particular interest in
the asymptotic residual oil saturation. The addition of surfactant to the
invasive fluid was shown to significantly reduce the residual oil saturation.Comment: To appear in Phys. Rev.
Viscous stabilization of 2D drainage displacements with trapping
We investigate the stabilization mechanisms due to viscous forces in the
invasion front during drainage displacement in two-dimensional porous media
using a network simulator. We find that in horizontal displacement the
capillary pressure difference between two different points along the front
varies almost linearly as function of height separation in the direction of the
displacement. The numerical result supports arguments taking into account the
loopless displacement pattern where nonwetting fluid flow in separate strands
(paths). As a consequence, we show that existing theories developed for viscous
stabilization, are not compatible with drainage when loopless strands dominate
the displacement process.Comment: The manuscript has been substantially revised. Accepted in Phys. Rev.
Let
Scaling properties of driven interfaces in disordered media
We perform a systematic study of several models that have been proposed for
the purpose of understanding the motion of driven interfaces in disordered
media. We identify two distinct universality classes: (i) One of these,
referred to as directed percolation depinning (DPD), can be described by a
Langevin equation similar to the Kardar-Parisi-Zhang equation, but with
quenched disorder. (ii) The other, referred to as quenched Edwards-Wilkinson
(QEW), can be described by a Langevin equation similar to the Edwards-Wilkinson
equation but with quenched disorder. We find that for the DPD universality
class the coefficient of the nonlinear term diverges at the depinning
transition, while for the QEW universality class either or
as the depinning transition is approached. The identification
of the two universality classes allows us to better understand many of the
results previously obtained experimentally and numerically. However, we find
that some results cannot be understood in terms of the exponents obtained for
the two universality classes {\it at\/} the depinning transition. In order to
understand these remaining disagreements, we investigate the scaling properties
of models in each of the two universality classes {\it above\/} the depinning
transition. For the DPD universality class, we find for the roughness exponent
for the pinned phase, and
for the moving phase. For the growth exponent, we find for the pinned phase, and for the moving phase.
Furthermore, we find an anomalous scaling of the prefactor of the width on the
driving force. A new exponent , characterizing the
scaling of this prefactor, is shown to relate the values of the roughnessComment: Latex manuscript, Revtex 3.0, 15 pages, and 15 figures also available
via anonymous ftp from ftp://jhilad.bu.edu/pub/abms/ (128.197.42.52
Reconstruction of individual cumulative radon exposures by low-level in vivo measurements and biokinetic modeling.
In vivo skull measurements of Pb-210 have been performed to assess the individual, chronic exposures of two persons living for 28 years in a house with a distinctly enhanced radon concentration of more than 10,000 Bq/m(3). A partial body counter consisting of 4 HPGe detectors, which were placed close to parietal positions of the head, was used in the study. The lower limit of detection of Pb-210 activity in the skeleton was found to be 40 Bq. Lead-210 activities of up to 152 Bq were found in the test persons, whereas no activity could be measured in an unexposed control person. The cumulative uptake of Pb-210 into the body was assessed for each single test person by using the ICRP respiratory tract and the biokinetic models. A fairly good agreement (within a factor of 2) between in vivo measurements and model was achieved for these two test persons. The technique used in the study may be a useful tool to evaluate assumptions, which have to be made for the reconstruction of individual, cumulative exposures to high radon concentrations