46 research outputs found
A simple Discrete-Element-Model of Brazilian Test
We present a statistical model which is able to capture some interesting
features exhibited in the Brazilian test. The model is based on breakable
elements which break when the force experienced by the elements exceed their
own load capacity. In this model when an element breaks, the capacity of the
neighboring elements are decreased by a certain amount assuming weakening
effect around the defected zone. We numerically investigate the stress-strain
behavior, the strength of the system, how it scales with the system size and
also it's fluctuation for both uniformly and weibull distributed breaking
threshold of the elements in the system. We find that the strength of the
system approaches it's asymptotic value and for
uniformly and Weibull distributed breaking threshold of the elements
respectively. We have also shown the damage profile right at the point when the
stress-strain curve reaches at it's maximum and then it is compared with our
experimental observations
Conformation and dynamics of partially active linear polymers
We perform numerical simulations of isolated, partially active polymers,
driven out-of-equilibrium by a fraction of their monomers. We show that, if the
active beads are all gathered in a contiguous block, the position of the
section along the chain determines the conformational and dynamical properties
of the system. Notably, one can modulate the diffusion coefficient of the
polymer from {active-like to passive-like} just by changing the position of the
active block. Further, in special cases, enhancement of diffusion can be
achieved by decreasing the overall polymer activity. Our findings may help in
the modelization of active biophysical systems, such as filamentous bacteria or
worms.Comment: 12 pages, 10 figures + supplemental 4 pages, 7 figure
Inequality of avalanche sizes in models of fracture
Prediction of an imminent catastrophic event in a driven disordered system is
of paramount importance - from the laboratory scale controlled fracture
experiment to the largest scale of mechanical failure i.e., earthquakes. It has
been long conjectured that the statistical regularities in the energy emission
time series mirrors the "health" of such driven systems and hence have the
potential for forecasting imminent catastrophe. Among other statistical
regularities, a measure of how unequal the avalanche sizes are, is potentially
a crucial indicator of imminent failure. The inequalities of avalanche sizes
are quantified using inequality indices traditionally used in socio-economic
systems: the Gini index (g), the Hirsch index (h) and the Kolkata index (k). It
is then shown analytically (for mean field) and numerically (for non mean
field) in models of quasi-brittle materials that the indices show universal
behavior near the breaking points in such models and hence could serve as
indicators of imminent breakdown of stressed disordered systems.Comment: Accepted for publication in Phys. Rev.
Machine learning understands knotted polymers
Simulated configurations of flexible knotted rings confined inside a
spherical cavity are fed into long-short term memory neural networks (LSTM NNs)
designed to distinguish knot types. The results show that they perform well in
knot recognition even if tested against flexible, strongly confined and
therefore highly geometrically entangled rings. In agreement with the
expectation that knots are delocalized in dense polymers, a suitable
coarse-graining procedure on configurations boosts the performance of the LSTMs
when knot identification is applied to rings much longer than those used for
training. Notably, when the NNs fail, usually the wrong prediction still
belongs to the same topological family of the correct one. The fact that the
LSTMs are able to grasp some basic properties of the ring's topology is
corroborated by a test on knot types not used for training. We also show that
the choice of the NN architecture is important: simpler convolutional NNs do
not perform so well. Finally, all results depend on the features used for
input: surprisingly, coordinates or bond directions of the configurations
provide the best accuracy to the NNs, even if they are not invariant under
rotations (while the knot type is invariant). Other rotational invariant
features we tested are based on distances, angles, and dihedral angles
Jamming and percolation in the random sequential adsorption of a binary mixture on the square lattice
We study the competitive irreversible adsorption of a binary mixture of
monomers and square-shaped particles of linear size on the square lattice.
With the random sequential adsorption model, we investigate how the jamming
coverage and percolation properties depend on the size ratio and relative
flux . We find that the onset of percolation of monomers is always lower for
the binary mixture than in the case with only monomers (). Moreover, for
values below a critical value, the higher is the flux or size of the
largest species, the lower is the value of the percolation threshold for
monomers.Comment: Submitted to a special issue of Journal of Physics A: Mathematical
and Theoretical to mark the 70th Birthday of Robert M. Zif