74 research outputs found
Darcy law for yield stress fluid
Predicting the flow of non-Newtonian fluids in porous structure is still a
challenging issue due to the interplay betwen the microscopic disorder and the
non-linear rheology. In this letter, we study the case of an yield stress fluid
in a two-dimensional structure. Thanks to a performant optimization algorithm,
we show that the system undergoes a continuous phase transition in the behavior
of the flow controlled by the applied pressure drop. In analogy with the
studies of the plastic depinning of vortex lattices in high-
superconductors we characterize the nonlinearity of the flow curve and relate
it to the change in the geometry of the open channels. In particular, close to
the transition, an universal scale free distribution of the channel length is
observed and explained theoretically via a mapping to the KPZ equation.Comment: 5 pages, 4 figures + 1 Supplementary materia
Experimental evidence for three universality classes for reaction fronts in disordered flows
Self-sustained reaction fronts in a disordered medium subject to an external
flow display self-affine roughening, pinning and depinning transitions. We
measure spatial and temporal fluctuations of the front in dimensions,
controlled by a single parameter, the mean flow velocity. Three distinct
universality classes are observed, consistent with the Kardar-Parisi-Zhang
(KPZ) class for fast advancing or receding fronts, the quenched KPZ class
(positive-qKPZ) when the mean flow approximately cancels the reaction rate, and
the negative-qKPZ class for slowly receding fronts. Both quenched KPZ classes
exhibit distinct depinning transitions, in agreement with the theory
The Fate of Shear-Oscillated Amorphous Solids
The behavior of shear-oscillated amorphous materials is studied using a
coarse-grained model. Samples are prepared at different degrees of annealing
and then subject to athermal and quasistatic oscillatory deformations at
various fixed amplitudes. The steady-state reached after several oscillations
is fully determined by the initial preparation and the oscillation amplitude,
as seen from stroboscopic stress and energy measurements. Under small
oscillations, poorly annealed materials display shear-annealing, while
ultra-stabilized materials are insensitive to them. Yet, beyond a critical
oscillation amplitude, both kind of materials display a discontinuous
transition to the same mixed state composed by a fluid shear-band embedded in a
marginal solid. Quantitative relations between uniform shear and the
steady-state reached with this protocol are established. The transient regime
characterizing the growth and the motion of the shear band is also studied.Comment: 6 pages, 4 figure
Pedoanthracology and dendroecology: two complementary approaches applied to old forest history
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