12,916 research outputs found
Robust oscillations in SIS epidemics on adaptive networks: Coarse-graining by automated moment closure
We investigate the dynamics of an epidemiological
susceptible-infected-susceptible (SIS) model on an adaptive network. This model
combines epidemic spreading (dynamics on the network) with rewiring of network
connections (topological evolution of the network). We propose and implement a
computational approach that enables us to study the dynamics of the network
directly on an emergent, coarse-grained level. The approach sidesteps the
derivation of closed low-dimensional approximations. Our investigations reveal
that global coupling, which enters through the awareness of the population to
the disease, can result in robust large-amplitude oscillations of the state and
topology of the network.Comment: revised version 6 pages, 4 figure
A new ghost cell/level set method for moving boundary problems:application to tumor growth
In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth
Numerical Simulation of Grain Boundary Grooving By Level Set Method
A numerical investigation of grain-boundary grooving by means of a Level Set
method is carried out. An idealized polygranular interconnect which consists of
grains separated by parallel grain boundaries aligned normal to the average
orientation of the surface is considered. The surface diffusion is the only
physical mechanism assumed. The surface diffusion is driven by surface
curvature gradients, and a fixed surface slope and zero atomic flux are assumed
at the groove root. The corresponding mathematical system is an initial
boundary value problem for a two-dimensional Hamilton-Jacobi type equation. The
results obtained are in good agreement with both Mullins' analytical "small
slope" solution of the linearized problem (W.W. Mullins, 1957) (for the case of
an isolated grain boundary) and with solution for the periodic array of grain
boundaries (S.A. Hackney, 1988).Comment: Submitted to the Journal of Computational Physics (19 pages, 8
Postscript figures, 3 tables, 29 references
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