994 research outputs found
Drainage in a model stratified porous medium
We show that when a non-wetting fluid drains a stratified porous medium at
sufficiently small capillary numbers Ca, it flows only through the coarsest
stratum of the medium; by contrast, above a threshold Ca, the non-wetting fluid
is also forced laterally, into part of the adjacent, finer strata. The spatial
extent of this partial invasion increases with Ca. We quantitatively understand
this behavior by balancing the stratum-scale viscous pressure driving the flow
with the capillary pressure required to invade individual pores. Because
geological formations are frequently stratified, we anticipate that our results
will be relevant to a number of important applications, including understanding
oil migration, preventing groundwater contamination, and sub-surface CO
storage
Strain-induced alignment in collagen gels
Collagen is the most abundant extracellular-network-forming protein in animal
biology and is important in both natural and artificial tissues, where it
serves as a material of great mechanical versatility. This versatility arises
from its almost unique ability to remodel under applied loads into anisotropic
and inhomogeneous structures. To explore the origins of this property, we
develop a set of analysis tools and a novel experimental setup that probes the
mechanical response of fibrous networks in a geometry that mimics a typical
deformation profile imposed by cells in vivo. We observe strong fiber alignment
and densification as a function of applied strain for both uncrosslinked and
crosslinked collagenous networks. This alignment is found to be irreversibly
imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for
tissue organization at the microscale. However, crosslinked networks display
similar fiber alignment and the same geometrical properties as uncrosslinked
gels, but with full reversibility. Plasticity is therefore not required to
align fibers. On the contrary, our data show that this effect is part of the
fundamental non-linear properties of fibrous biological networks.Comment: 12 pages, 7 figures. 1 supporting material PDF with 2 figure
Dripping, Jeting, Drops and Wetting: The Magic of Microfluidics
This talk will discuss some of the new opportunities that arise by precisely controlling fluid flow and mixing using microfluidic devices. I describe studies to elucidate the instabilities that lead to drop formation and use these to create new materials that are difficult to achieve with any other method. I also show how the exquisite control afforded by the microfluidic devices provides enabling technology to use droplets as nanoreactors to qualitatively increase the rate of screening of biological reactions, and will demonstrate how this can be used in new applications relevant for biotechnology
Local pore size correlations determine flow distributions in porous media
The relationship between the microstructure of a porous medium and the
observed flow distribution is still a puzzle. We resolve it with an analytical
model, where the local correlations between adjacent pores, which determine the
distribution of flows propagated from one pore downstream, predict the flow
distribution. Numerical simulations of a two-dimensional porous medium verify
the model and clearly show the transition of flow distributions from
-function-like via Gaussians to exponential with increasing disorder.
Comparison to experimental data further verifies our numerical approach.Comment: 5 pages, 3 figures, supplemental materia
- …