615,306 research outputs found
Effective slip in pressure-driven flow past super-hydrophobic stripes
Super-hydrophobic array of grooves containing trapped gas (stripes), have the
potential to greatly reduce drag and enhance mixing phenomena in microfluidic
devices. Recent work has focused on idealized cases of stick-perfect slip
stripes, with limited guidance. Here, we analyze the experimentally relevant
situation of a pressure-driven flow past striped slip-stick surfaces with
arbitrary local slip at the gas sectors. We derive analytical formulas for
maximal (longitudinal) and minimal (transverse) directional effective slip
lengths that can be used for any surface slip fraction (validated by numerical
calculations). By representing eigenvalues of the slip length-tensor, they
allow us to obtain the effective slip for any orientation of stripes with
respect to the mean flow. Our results imply that flow past stripes is
controlled by the ratio of the local slip length to texture size. In case of a
large (compared to the texture period) slip at the gas areas, surface
anisotropy leads to a tensorial effective slip, by attaining the values
predicted earlier for a perfect local slip. Both effective slip lengths and
anisotropy of the flow decrease when local slip becomes of the order of texture
period. In the case of small slip, we predict simple surface-averaged,
isotropic flows (independent of orientation). These results provide a framework
for the rational design of super-hydrophobic surfaces and devices.Comment: 10 pages, 4 figures, revised versio
Slip avalanches in a fiber bundle model
We study slip avalanches in disordered materials under an increasing external
load in the framework of a fiber bundle model. Over-stressed fibers of the
model do not break, instead they relax in a stick-slip event which may trigger
an entire slip avalanche. Slip avalanches are characterized by the number
slipping fibers, by the slip length, and by the load increment, which triggers
the avalanche. Our calculations revealed that all three quantities are
characterized by power law distributions with universal exponents. We show by
analytical calculations and computer simulations that varying the amount of
disorder of slip thresholds and the number of allowed slips of fibers, the
system exhibits a disorder induced phase transition from a phase where only
small avalanches are formed to another one where a macroscopic slip appears.Comment: 6 pages, 6 figure
Fluctuation phenomena in crystal plasticity - a continuum model
On microscopic and mesoscopic scales, plastic flow of crystals is
characterized by large intrinsic fluctuations. Deformation by crystallographic
slip occurs in a sequence of intermittent bursts ('slip avalanches') with
power-law size distribution. In the spatial domain, these avalanches produce
characteristic deformation patterns in the form of slip lines and slip bands
which exhibit long-range spatial correlations. We propose a generic continuum
model which accounts for randomness in the local stress-strain relationships as
well as for long-range internal stresses that arise from the ensuing plastic
strain heterogeneities. The model parameters are related to the local dynamics
and interactions of lattice dislocations. The model explains experimental
observations on slip avalanches as well as the associated slip and surface
pattern morphologies
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Daily measurement of slow slip from low-frequency earthquakes is consistent with ordinary earthquake scaling.
Slow slip transients on faults can last from seconds to months and stitch together the earthquake cycle. However, no single geophysical instrument is able to observe the full range of slow slip because of bandwidth limitations. Here, we connect seismic and geodetic data from the Mexican subduction zone to explore an instrumental blind spot. We establish a calibration of the daily median amplitude of the seismically recorded low-frequency earthquakes to the daily geodetically recorded moment rate of previously established slow slip events. This calibration allows us to use the precise evolution of low-frequency earthquake activity to quantitatively measure the moment of smaller, subdaily slip events that are unresolvable by geodesy alone. The resulting inferred slow slip moments scale with duration and inter-event time like ordinary earthquakes. These new quantifications help connect slow and fast events in a broad spectrum of transient slip and suggest that slow slip events behave much like ordinary earthquakes
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