331 research outputs found
Rossby and Drift Wave Turbulence and Zonal Flows: the Charney-Hasegawa-Mima model and its extensions
A detailed study of the Charney-Hasegawa-Mima model and its extensions is
presented. These simple nonlinear partial differential equations suggested for
both Rossby waves in the atmosphere and also drift waves in a
magnetically-confined plasma exhibit some remarkable and nontrivial properties,
which in their qualitative form survive in more realistic and complicated
models, and as such form a conceptual basis for understanding the turbulence
and zonal flow dynamics in real plasma and geophysical systems. Two idealised
scenarios of generation of zonal flows by small-scale turbulence are explored:
a modulational instability and turbulent cascades.
A detailed study of the generation of zonal flows by the modulational
instability reveals that the dynamics of this zonal flow generation mechanism
differ widely depending on the initial degree of nonlinearity. A numerical
proof is provided for the extra invariant in Rossby and drift wave turbulence
-zonostrophy and the invariant cascades are shown to be characterised by the
zonostrophy pushing the energy to the zonal scales.
A small scale instability forcing applied to the model demonstrates the
well-known drift wave - zonal flow feedback loop in which the turbulence which
initially leads to the zonal flow creation, is completely suppressed and the
zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner
which has been mathematically predicted.
The insights gained from this simple model could provide a basis for
equivalent studies in more sophisticated plasma and geophysical fluid dynamics
models in an effort to fully understand the zonal flow generation, the
turbulent transport suppression and the zonal flow saturation processes in both
the plasma and geophysical contexts as well as other wave and turbulence
systems where order evolves from chaos.Comment: 64 pages, 33 figure
L\'evy flights on a comb and the plasma staircase
We formulate the problem of confined L\'evy flight on a comb. The comb
represents a sawtooth-like potential field , with the asymmetric teeth
favoring net transport in a preferred direction. The shape effect is modeled as
a power-law dependence within the sawtooth period,
followed by an abrupt drop-off to zero, after which the initial power-law
dependence is reset. It is found that the L\'evy flights will be confined in
the sense of generalized central limit theorem if (i) the spacing between the
teeth is sufficiently broad, and (ii) , where is the fractal
dimension of the flights. In particular, for the Cauchy flights (),
. The study is motivated by recent observations of
localization-delocalization of transport avalanches in banded flows in the Tore
Supra tokamak and is intended to devise a theory basis to explain the observed
phenomenology.Comment: 13 pages; 3 figures; accepted for publication in Physical Review
Asymptotic spreading speeds for a predator-prey system with two predators and one prey
This paper investigates the large time behaviour of a three species
reaction-diffusion system, modelling the spatial invasion of two predators
feeding on a single prey species. In addition to the competition for food, the
two predators exhibit competitive interactions and under some parameter
conditions (), they can also be considered as two mutants. When
mutations occur in the predator populations, the spatial spread of invasion
takes place at a definite speed, identical for both mutants. When the two
predators are not coupled through mutation, the spreading behaviour exhibits a
more complex propagating pattern, including multiple layers with different
speeds. In addition, some parameter conditions reveal situations where a
nonlocal pulling phenomenon occurs and in particular where the spreading speed
is not linearly determined
Partial Differential Equations in Ecology
Partial differential equations (PDEs) have been used in theoretical ecology research for more than eighty years. Nowadays, along with a variety of different mathematical techniques, they remain as an efficient, widely used modelling framework; as a matter of fact, the range of PDE applications has even become broader. This volume presents a collection of case studies where applications range from bacterial systems to population dynamics of human riots
Traveling Wave in a Ratio-dependent Holling-Tanner System with Nonlocal Diffusion and Strong Allee Effect
In this paper, a ratio-dependent Holling-Tanner system with nonlocal
diffusion is taken into account, where the prey is subject to a strong Allee
effect. To be special, by applying Schauder's fixed point theorem and iterative
technique, we provide a general theory on the existence of traveling waves for
such system. Then appropriate upper and lower solutions and a novel sequence,
similar to squeeze method, are constructed to demonstrate the existence of
traveling waves for c>c*. Moreover, the existence of traveling wave for c=c* is
also established by spreading speed theory and comparison principle. Finally,
the nonexistence of traveling waves for c<c* is investigated, and the minimal
wave speed then is determined
Pursuit-Evasion Dynamics for Bazykin-Type Predator-Prey Model with Indirect Predator Taxis
publishedVersio
Differential Equations arising from Organising Principles in Biology
This workshop brought together experts in modeling and analysis of organising principles of multiscale biological systems such as cell assemblies, tissues and populations. We focused on questions arising in systems biology and medicine which are related to emergence, function and control of spatial and inter-individual heterogeneity in population dynamics. There were three main areas represented of differential equation models in mathematical biology. The first area involved the mathematical description of structured populations. The second area concerned invasion, pattern formation and collective dynamics. The third area treated the evolution and adaptation of populations, following the Darwinian paradigm. These problems led to differential equations, which frequently are non-trivial extensions of classical problems. The examples included but were not limited to transport-type equations with nonlocal boundary conditions, mixed ODE-reaction-diffusion models, nonlocal diffusion and cross-diffusion problems or kinetic equations
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