2,593 research outputs found
Control of reaction-diffusion equations on time-evolving manifolds
Among the main actors of organism development there are morphogens, which are
signaling molecules diffusing in the developing organism and acting on cells to
produce local responses. Growth is thus determined by the distribution of such
signal. Meanwhile, the diffusion of the signal is itself affected by the
changes in shape and size of the organism. In other words, there is a complete
coupling between the diffusion of the signal and the change of the shapes. In
this paper, we introduce a mathematical model to investigate such coupling. The
shape is given by a manifold, that varies in time as the result of a
deformation given by a transport equation. The signal is represented by a
density, diffusing on the manifold via a diffusion equation. We show the
non-commutativity of the transport and diffusion evolution by introducing a new
concept of Lie bracket between the diffusion and the transport operator. We
also provide numerical simulations showing this phenomenon
Turing conditions for pattern forming systems on evolving manifolds
The study of pattern-forming instabilities in reaction-diffusion systems on
growing or otherwise time-dependent domains arises in a variety of settings,
including applications in developmental biology, spatial ecology, and
experimental chemistry. Analyzing such instabilities is complicated, as there
is a strong dependence of any spatially homogeneous base states on time, and
the resulting structure of the linearized perturbations used to determine the
onset of instability is inherently non-autonomous. We obtain general conditions
for the onset and structure of diffusion driven instabilities in
reaction-diffusion systems on domains which evolve in time, in terms of the
time-evolution of the Laplace-Beltrami spectrum for the domain and functions
which specify the domain evolution. Our results give sufficient conditions for
diffusive instabilities phrased in terms of differential inequalities which are
both versatile and straightforward to implement, despite the generality of the
studied problem. These conditions generalize a large number of results known in
the literature, such as the algebraic inequalities commonly used as a
sufficient criterion for the Turing instability on static domains, and
approximate asymptotic results valid for specific types of growth, or specific
domains. We demonstrate our general Turing conditions on a variety of domains
with different evolution laws, and in particular show how insight can be gained
even when the domain changes rapidly in time, or when the homogeneous state is
oscillatory, such as in the case of Turing-Hopf instabilities. Extensions to
higher-order spatial systems are also included as a way of demonstrating the
generality of the approach
Geometry-induced patterns through mechanochemical coupling
Intracellular protein patterns regulate a variety of vital cellular processes
such as cell division and motility, which often involve dynamic changes of cell
shape. These changes in cell shape may in turn affect the dynamics of
pattern-forming proteins, hence leading to an intricate feedback loop between
cell shape and chemical dynamics. While several computational studies have
examined the resulting rich dynamics, the underlying mechanisms are not yet
fully understood. To elucidate some of these mechanisms, we explore a
conceptual model for cell polarity on a dynamic one-dimensional manifold. Using
concepts from differential geometry, we derive the equations governing
mass-conserving reaction-diffusion systems on time-evolving manifolds.
Analyzing these equations mathematically, we show that dynamic shape changes of
the membrane can induce pattern-forming instabilities in parts of the membrane,
which we refer to as regional instabilities. Deformations of the local membrane
geometry can also (regionally) suppress pattern formation and spatially shift
already existing patterns. We explain our findings by applying and generalizing
the local equilibria theory of mass-conserving reaction-diffusion systems. This
allows us to determine a simple onset criterion for geometry-induced
pattern-forming instabilities, which is linked to the phase-space structure of
the reaction-diffusion system. The feedback loop between membrane shape
deformations and reaction-diffusion dynamics then leads to a surprisingly rich
phenomenology of patterns, including oscillations, traveling waves, and
standing waves that do not occur in systems with a fixed membrane shape. Our
work reveals that the local conformation of the membrane geometry acts as an
important dynamical control parameter for pattern formation in mass-conserving
reaction-diffusion systems
A computational method for the coupled solution of reaction–diffusion equations on evolving domains and manifolds: application to a model of cell migration and chemotaxis
In this paper, we devise a moving mesh finite element method for the approximate solution of coupled bulk–surface reaction–diffusion equations on an evolving two dimensional domain. Fundamental to the success of the method is the robust generation of bulk and surface meshes. For this purpose, we use a novel moving mesh partial differential equation (MMPDE) approach. The developed method is applied to model problems with known analytical solutions; these experiments indicate second-order spatial and temporal accuracy. Coupled bulk–surface problems occur frequently in many areas; in particular, in the modelling of eukaryotic cell migration and chemotaxis. We apply the method to a model of the two-way interaction of a migrating cell in a chemotactic field, where the bulk region corresponds to the extracellular region and the surface to the cell membrane
Invariant manifolds and the geometry of front propagation in fluid flows
Recent theoretical and experimental work has demonstrated the existence of
one-sided, invariant barriers to the propagation of reaction-diffusion fronts
in quasi-two-dimensional periodically-driven fluid flows. These barriers were
called burning invariant manifolds (BIMs). We provide a detailed theoretical
analysis of BIMs, providing criteria for their existence, a classification of
their stability, a formalization of their barrier property, and mechanisms by
which the barriers can be circumvented. This analysis assumes the sharp front
limit and negligible feedback of the front on the fluid velocity. A
low-dimensional dynamical systems analysis provides the core of our results.Comment: 14 pages, 11 figures. To appear in Chaos Focus Issue:
Chemo-Hydrodynamic Patterns and Instabilities (2012
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