114 research outputs found
Effective Rheology of Immiscible Two-Phase Flow in Porous Media
We demonstrate through numerical simulations and a mean field calculation
that immiscible two-phase flow in a porous medium behaves effectively as a
Bingham viscoplastic fluid. This leads to a generalized Darcy equation where
the volumetric flow rate depends quadratically on an excess pressure difference
in the range of flow rates where the capillary forces compete with the viscous
forces. At higher rates, the flow is Newtonian
Dynamic wettability alteration in immiscible two-phase flow in porous media: Effect on transport properties and critical slowing down
The change in contact angles due to the injection of low salinity water or
any other wettability altering agent in an oil-rich porous medium is modeled by
a network model of disordered pores transporting two immiscible fluids. We
introduce a dynamic wettability altering mechanism, where the time dependent
wetting property of each pore is determined by the cumulative flow of water
through it. Simulations are performed to reach steady-state for different
possible alterations in the wetting angle (). We find that deviation
from oil-wet conditions re-mobilizes the stuck clusters and increases the oil
fractional flow. However, the rate of increase in the fractional flow depends
strongly on and as , a critical angle, the system
shows critical slowing down which is characterized by two dynamic critical
exponents.Comment: 8 pages, 9 figure
Isolation of a cdc28 mutation that abrogates the dependence of S phase on completion of M phase of the budding yeast cell cycle
We have isolated a mutation in the budding yeast Saccharomyces cerevisisae CDC28 gene that allows cdc13 cells, carrying damaged DNA, to continue with the cell division cycle. While cdc13 mutant cells are arrested as largebudded cells at the nonpermissive temperature 37°C, the cdc13 cdc28 double mutant culture showed cells with one or more buds, most of which showed apical growth. The additional buds emerged without the intervening steps of nuclear division and cell separation. We suggest that the cdc28 mutation abrogates a checkpoint function and allows cells with damaged or incompletely replicated DNA an entry to another round of cell cycle and bypasses the mitotic phase of the cell cycle
Phase transitions and correlations in fracture processes where disorder and stress compete
We study the effect of the competition between disorder and stress
enhancement in fracture processes using the local load sharing fiber bundle
model, a model that hovers on the border between analytical tractability and
numerical accessibility. We implement a disorder distribution with one
adjustable parameter. The model undergoes a localization transition as a
function of this parameter. We identify an order parameter for this transition
and find that the system is in the localized phase over a finite range of
values of the parameter bounded by a transition to the non-localized phase on
both sides. The transition is first order at the lower transition and second
order at the upper transition. The critical exponents characterizing the second
order transition are close to those characterizing the percolation transition.
We determine the spatiotemporal correlation function in the localized phase. It
is characterized by two power laws as in invasion percolation. We find
exponents that are consistent with the values found in that problem.Comment: 8 pages, 5 figure
Immiscible two-phase flow in porous media: Effective rheology in the continuum limit
It is becoming increasingly clear that there is a regime in immiscible
two-phase flow in porous media where the flow rate depends of the pressure drop
as a power law with exponent different than one. This occurs when the capillary
forces and viscous forces both influence the flow. At higher flow rates, where
the viscous forces dominate, the flow rate depends linearly on the pressure
drop. The question we pose here is what happens to the linear regime when the
system size is increased. Based on analytical calculations using the capillary
fiber bundle model and on numerical simulations using a dynamical network
model, we find that the non-linear regime moves towards smaller and smaller
pressure gradients as the system size grows.Comment: 10 pages, 6 figure
Flow-Area Relations in Immiscible Two-Phase Flow in Porous Media
We present a theoretical framework for immiscible incompressible two-phase
flow in homogeneous porous media that connects the distribution of local fluid
velocities to the average seepage velocities. By dividing the pore area along a
cross-section transversal to the average flow direction up into differential
areas associated with the local flow velocities, we construct a distribution
function that allows us not only to re-establish existing relationships between
the seepage velocities of the immiscible fluids, but also to find new relations
between their higher moments. We support and demonstrate the formalism through
numerical simulations using a dynamic pore-network model for immiscible
two-phase flow with two- and three-dimensional pore networks. Our numerical
results are in agreement with the theoretical considerations.Comment: 12 pages, 5 figure
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