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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 421 (2003), S. 321-321 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ...Experimental oncology is awash with data. In 2001 alone, over 21,000 articles on characterizing, diagnosing and treating malignancies were published. The powerful techniques of molecular biology have demonstrated innumerable cancer-related alterations in the structure and function of ...
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 56 (1994), S. 1163-1172 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 380 (1996), S. 678-678 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Kondo and Asai1 interpret observ-ations on the time evolution of skin patterns of the angelfish (Pomacanthus) as the first instance of a Turing (reac-tion-diffusion) pattern in biology. But we believe that reaction-diffusion systems per se cannot provide a mechanistic basis for one of the ...
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 35 (1997), S. 713-728 
    ISSN: 1432-1416
    Keywords: Key words: Sharp fronts ; Degenerate diffusion ; Hamiltonian ; Bifurcation of heteroclinic trajectories
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract.  In this paper we study the existence of one-dimensional travelling wave solutions u(x, t)=φ(x−ct) for the non-linear degenerate (at u=0) reaction-diffusion equation u t =[D(u)u x ] x +g(u) where g is a generalisation of the Nagumo equation arising in nerve conduction theory, as well as describing the Allee effect. We use a dynamical systems approach to prove: 1. the global bifurcation of a heteroclinic cycle (two monotone stationary front solutions), for c=0, 2. The existence of a unique value c *〉0 of c for which φ(x−c * t) is a travelling wave solution of sharp type and 3. A continuum of monotone and oscillatory fronts for c≠c *. We present some numerical simulations of the phase portrait in travelling wave coordinates and on the full partial differential equation.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 37 (1998), S. 381-417 
    ISSN: 1432-1416
    Keywords: Key words: Turing bifurcation ; Reaction diffusion ; Weakly nonlinear ; Pattern formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract . The Turing bifurcation is the basic bifurcation generating spatial pattern, and lies at the heart of almost all mathematical models for patterning in biology and chemistry. In this paper the authors determine the structure of this bifurcation for two coupled reaction diffusion equations on a two-dimensional square spatial domain when the diffusion coefficients have a small explicit variation in space across the domain. In the case of homogeneous diffusivities, the Turing bifurcation is highly degenerate. Using a two variable perturbation method, the authors show that the small explicit spatial inhomogeneity splits the bifurcation into two separate primary and two separate secondary bifurcations, with all solution branches distinct. This splitting of the bifurcation is more effective than that given by making the domain slightly rectangular, and shows clearly the structure of the Turing bifurcation and the way in which the! var ious solution branches collapse together as the spatial variation is reduced. The authors determine the stability of the solution branches, which indicates that several new phenomena are introduced by the spatial variation, including stable subcritical striped patterns, and the possibility that stable stripes lose stability supercritically to give stable spotted patterns..
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 41 (2000), S. 493-512 
    ISSN: 1432-1416
    Keywords: Key words: Turing systems – Pattern formation – Generalised morphogen – Activator-inhibitor system – Differential-flow instability (DIFI)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract. We present necessary and sufficient conditions on the stability matrix of a general n(≥2)-dimensional reaction-diffusion system which guarantee that its uniform steady state can undergo a Turing bifurcation. The necessary (kinetic) condition, requiring that the system be composed of an unstable (or activator) and a stable (or inhibitor) subsystem, and the sufficient condition of sufficiently rapid inhibitor diffusion relative to the activator subsystem are established in three theorems which form the core of our results. Given the possibility that the unstable (activator) subsystem involves several species (dimensions), we present a classification of the analytically deduced Turing bifurcations into p (1 ≤p≤ (n− 1)) different classes. For n = 3 dimensions we illustrate numerically that two types of steady Turing pattern arise in one spatial dimension in a generic reaction-diffusion system. The results confirm the validity of an earlier conjecture [12] and they also characterise the class of so-called strongly stable matrices for which only necessary conditions have been known before [23, 24]. One of the main consequences of the present work is that biological morphogens, which have so far been expected to be single chemical species [1–9], may instead be composed of two or more interacting species forming an unstable subsystem.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 33 (1994), S. 163-192 
    ISSN: 1432-1416
    Keywords: Travelling waves ; Non-linear diffusion equations ; Sharp solutions ; Wavespeed ; Degenerate diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In this paper we use a dynamical systems approach to prove the existence of a unique critical value c * of the speed c for which the degenerate density-dependent diffusion equation u ct = [D(u)u x ] x + g(u) has: 1. no travelling wave solutions for 0 〈 c 〈 c *, 2. a travelling wave solution u(x, t) = ϕ(x - c * t) of sharp type satisfying ϕ(− ∞) = 1, ϕ(τ) = 0 ∀τ ≧ τ*; ϕ'(τ*−) = − c */D'(0), ϕ'(τ*+) = 0 and 3. a continuum of travelling wave solutions of monotone decreasing front type for each c 〉 c *. These fronts satisfy the boundary conditions ϕ(− ∞) = 1, ϕ'(− ∞) = ϕ(+ ∞) = ϕ'(+ ∞) = 0. We illustrate our analytical results with some numerical solutions.
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  • 8
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We present a model for the formation of parallel rows of scale cells in the developing adult wing of moths and butterflies. Precursors of scale cells differentiate throughout each epithelial monolayer and migrate into rows that are roughly parallel to the body axis. Grafting experiments have revealed what appears to be a gradient of adhesivity along the wing. What is more, cell adhesivity character is maintained after grafting. Thus we suggest that it is a cell’s location prior to migration that determines its interactions during migration. We use nonlinear bifurcation analysis to show that differential origin-dependent cell adhesion can result in the stabilization of rows over spots.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1093-1120 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We investigate the sequence of patterns generated by a reaction—diffusion system on a growing domain. We derive a general evolution equation to incorporate domain growth in reaction—diffusion models and consider the case of slow and isotropic domain growth in one spatial dimension. We use a self-similarity argument to predict a frequency-doubling sequence of patterns for exponential domain growth and we find numerically that frequency-doubling is realized for a finite range of exponential growth rate. We consider pattern formation under different forms for the growth and show that in one dimension domain growth may be a mechanism for increased robustness of pattern formation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 59 (1997), S. 517-532 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Ensembles of mutually coupled ultradian cellular oscillators have been proposed by a number of authors to explain the generation of circadian rhythms in mammals. Most mathematical models using many coupled oscillators predict that the output period should vary as the square root of the number of participating units, thus being inconsistent with the well-established experimental result that ablation of substantial parts of the suprachiasmatic nuclei (SCN), the main circadian pacemaker in mammals, does not eliminate the overt circadian functions, which show no changes in the phases or periods of the rhythms. From these observations, we have developed a theoretical model that exhibits the robustness of the circadian clock to changes in the number of cells in the SCN, and that is readily adaptable to include the successful features of other known models of circadian regulation, such as the phase response curves and light resetting of the phase.
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