43 research outputs found
Hele-Shaw limit for a system of two reaction-(cross-)diffusion equations for living tissues
Multiphase mechanical models are now commonly used to describe living tissues
including tumour growth. The specific model we study here consists of two
equations of mixed parabolic and hyperbolic type which extend the standard
compressible porous medium equation, including cross-reaction terms. We study
the incompressible limit, when the pressure becomes stiff, which generates a
free boundary problem. We establish the complementarity relation and also a
segregation result. Several major mathematical difficulties arise in the two
species case. Firstly, the system structure makes comparison principles fail.
Secondly, segregation and internal layers limit the regularity available on
some quantities to BV. Thirdly, the Aronson-B{\'e}nilan estimates cannot be
established in our context. We are lead, as it is classical, to add correction
terms. This procedure requires technical manipulations based on BV estimates
only valid in one space dimension. Another novelty is to establish an L1
version in place of the standard upper bound
Many-particle limit for a system of interaction equations driven by Newtonian potentials
We consider a discrete particle system of two species coupled through
nonlocal interactions driven by the one-dimensional Newtonian potential, with
repulsive self-interaction and attractive cross-interaction. After providing a
suitable existence theory in a finite-dimensional framework, we explore the
behaviour of the particle system in case of collisions and analyse the
behaviour of the solutions with initial data featuring particle clusters.
Subsequently, we prove that the empirical measure associated to the particle
system converges to the unique 2-Wasserstein gradient flow solution of a system
of two partial differential equations (PDEs) with nonlocal interaction terms in
a proper measure sense. The latter result uses uniform estimates of the
-norms of a piecewise constant reconstruction of the density using the
particle trajectories
Nonlocal cross-interaction systems on graphs: Energy landscape and dynamics
We explore the dynamical behavior and energetic properties of a model of two
species that interact nonlocally on finite graphs. The authors recently
introduced the model in the context of nonquadratic Finslerian gradient flows
on generalized graphs featuring nonlinear mobilities. In a continuous and local
setting, this class of systems exhibits a wide variety of patterns, including
mixing of the two species, partial engulfment, or phase separation. This work
showcases how this rich behavior carries over to the graph structure. We
present analytical and numerical evidence thereof.Comment: arXiv admin note: substantial text overlap with arXiv:2107.1128
A multiscale approach for spatially inhomogeneous disease dynamics
In this paper we introduce an agent-based epidemiological model that generalizes the classical SIR model by Kermack and McKendrick. We further provide a multiscale approach to the derivation of a macroscopic counterpart via the mean-field limit. The chain of equations acquired via the multiscale approach is investigated, analytically as well as numerically. The outcome of these results provides strong evidence of the models' robustness and justifies their practicality in describing disease dynamics, in particularly when mobility is involved. The numerical results provide further insights into the applicability of the different scaling limits
Derivation of a macroscopic model for Brownian hard needles
We study the role of anisotropic steric interactions in a system of hard
Brownian needles. Despite having no volume, non-overlapping needles exclude a
volume in configuration space that influences the macroscopic evolution of the
system. Starting from the stochastic particle system, we use the method of
matched asymptotic expansions and conformal mapping to systematically derive a
nonlinear nonlocal partial differential equation for the evolution of the
population density in position and orientation. We consider the regime of high
rotational diffusion, resulting in an equation for the spatial density that
allows us to compare the effective excluded volume of a hard-needles system
with that of a hard-spheres system. We further consider spatially homogeneous
solutions and find an isotropic to nematic transition as density increases,
consistent with Onsager's theory