23,474 research outputs found
Folds and Buckles at the Nanoscale: Experimental and Theoretical Investigation of the Bending Properties of Graphene Membranes
The elastic properties of graphene crystals have been extensively investigated, revealing unique properties in the linear and nonlinear regimes, when the membranes are under either stretching or bending loading conditions. Nevertheless less knowledge has been developed so far on folded graphene membranes and ribbons. It has been recently suggested that fold-induced curvatures, without in-plane strain, can affect the local chemical reactivity, the mechanical properties, and the electron transfer in graphene membranes. This intriguing perspective envisages a materials-by-design approach through the engineering of folding and bending to develop enhanced nano-resonators or nano-electro-mechanical devices. Here we present a novel methodology to investigate the mechanical properties of folded and wrinkled graphene crystals, combining transmission electron microscopy mapping of 3D curvatures and theoretical modeling based on continuum elasticity theory and tight-binding atomistic simulations
Dynamical heterogeneity in soft particle suspensions under shear
We present experimental measurements of dynamical heterogeneities in a dense
system of microgel spheres, sheared at different rates and at different packing
fractions in a microfluidic channel, and visualized with high speed digital
video microscopy. A four-point dynamic susceptibility is deduced from video
correlations, and is found to exhibit a peak that grows in height and shifts to
longer times as the jamming transition is approached from two different
directions. In particular, the time for particle-size root-mean square relative
displacements is found to scale as where is the strain rate and
is the distance from the random close packing volume
fraction. The typical number of particles in a dynamical heterogeneity is
deduced from the susceptibility peak height and found to scale as . Exponent uncertainties are less than ten
percent. We emphasize that the same power-law behavior is found at packing
fractions above and below . Thus, our results considerably extend a
previous observation of for granular heap flow at
fixed packing below . Furthermore, the implied result compares well with expectation from mode-coupling theory and
with prior observations for driven granular systems
Simulating Organogenesis in COMSOL: Tissue Mechanics
During growth, tissue expands and deforms. Given its elastic properties,
stresses emerge in an expanding and deforming tissue. Cell rearrangements can
dissipate these stresses and numerous experiments confirm the viscoelastic
properties of tissues [1]-[4]. On long time scales, as characteristic for many
developmental processes, tissue is therefore typically represented as a liquid,
viscous material and is then described by the Stokes equation [5]-[7]. On short
time scales, however, tissues have mainly elastic properties. In discrete
cell-based tissue models, the elastic tissue properties are realized by springs
between cell vertices [8], [9]. In this article, we adopt a macroscale
perspective of tissue and consider it as homogeneous material. Therefore, we
may use the "Structural Mechanics" module in COMSOL Multiphysics in order to
model the viscoelastic behavior of tissue. Concretely, we consider two
examples: first, we aim at numerically reproducing published [10] analytical
results for the sea urchin blastula. Afterwards, we numerically solve a
continuum mechanics model for the compression and relaxation experiments
presented in [4]
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