172 research outputs found
Elastic Moduli in Nano-Size Samples of Amorphous Solids: System Size Dependence
This Letter is motivated by some recent experiments on pan-cake shaped
nano-samples of metallic glass that indicate a decline in the measured shear
modulus upon decreasing the sample radius. Similar measurements on crystalline
samples of the same dimensions showed a much more modest change. In this Letter
we offer a theory of this phenomenon; we argue that such results are
generically expected for any amorphous solid, with the main effect being
related to the increased contribution of surfaces with respect to bulk when the
samples get smaller. We employ exact relations between the shear modulus and
the eigenvalues of the system's Hessian matrix to explore the role of surface
modes in affecting the elastic moduli
Long-time evolution of sequestered CO in porous media
CO sequestration in subsurface reservoirs is important for limiting
atmospheric CO concentrations. However, a complete physical picture able to
predict the structure developing within the porous medium is lacking. We
investigate theoretically reactive transport in the long-time evolution of
carbon in the brine-rock environment. As CO is injected into a brine-rock
environment, a carbonate-rich region is created amid brine. Within the
carbonate-rich region minerals dissolve and migrate from regions of high
concentration to low concentration, along with other dissolved carbonate
species. This causes mineral precipitation at the interface between the two
regions. We argue that precipitation in a small layer reduces diffusivity, and
eventually causes mechanical trapping of the CO. Consequently, only a small
fraction of the CO is converted to solid mineral; the remainder either
dissolves in water or is trapped in its original form. We also study the case
of a pure CO bubble surrounded by brine and suggest a mechanism that may
lead to a carbonate-encrusted bubble due to structural diffusion
The dynamics of cracks in torn thin sheets
Motivated by recent experiments, we present a study of the dynamics of cracks
in thin sheets. While the equations of elasticity for thin plates are well
known, there remains the question of path selection for a propagating crack. We
invoke a generalization of the principle of local symmetry to provide a
criterion for path selection and demonstrate qualitative agreement with the
experimental findings. The nature of the singularity at the crack tip is
studied with and without the interference of nonlinear terms.Comment: 7 pages, 11 figure
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