### Abstract

In the paper, we study some ‘a priori’ properties of mild solutions to a single reaction–diffusion equation with discontinuous nonlinear reaction term on the two-dimensional sphere close to its poles. This equation is the counterpart of the well-studied bistable reaction–diffusion equation on the Euclidean plane. The investigation of this equation on the sphere is mainly motivated by the phenomenon of the fertilization of oocytes or recent studies of wave propagation in a model of immune cells activation, in which the cell is modeled by a ball. Because of the discontinuous nature of reaction kinetics, the standard theory cannot guarantee the solution existence and its smoothness properties. Moreover, the singular nature of the diffusion operator near the north/south poles makes the analysis more involved. Unlike the case in the Euclidean plane, the (axially symmetric) Green's function for the heat operator on the sphere can only be represented by an infinite series of the Legendre polynomials. Our approach is to consider a formal series in Legendre polynomials obtained by assuming that the mild solution exists. We show that the solution to the equation subject to the Neumann boundary condition is C^{1} smooth in the spatial variable up to the north/south poles and Hölder continuous with respect to the time variable. Our results provide also a sort of ‘a priori’ estimates, which can be used in the existence proofs of mild solutions, for example, by means of the iterative methods.

Original language | English |
---|---|

Pages (from-to) | 5349-5369 |

Number of pages | 21 |

Journal | Mathematical Methods in the Applied Sciences |

Volume | 40 |

Issue number | 14 |

DOIs | |

Publication status | Published - 2017 Sep 30 |

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### Keywords

- discontinuous reaction term
- sphere
- stationary fronts

### ASJC Scopus subject areas

- Mathematics(all)
- Engineering(all)

### Cite this

*Mathematical Methods in the Applied Sciences*,

*40*(14), 5349-5369. https://doi.org/10.1002/mma.4390

**Regularity of solutions to a reaction–diffusion equation on the sphere : the Legendre series approach.** / Bialecki, Slawomir; Kaźmierczak, Bogdan; Nowicka, Dominika; Tsai, Je-Chiang.

Research output: Contribution to journal › Article

*Mathematical Methods in the Applied Sciences*, vol. 40, no. 14, pp. 5349-5369. https://doi.org/10.1002/mma.4390

}

TY - JOUR

T1 - Regularity of solutions to a reaction–diffusion equation on the sphere

T2 - the Legendre series approach

AU - Bialecki, Slawomir

AU - Kaźmierczak, Bogdan

AU - Nowicka, Dominika

AU - Tsai, Je-Chiang

PY - 2017/9/30

Y1 - 2017/9/30

N2 - In the paper, we study some ‘a priori’ properties of mild solutions to a single reaction–diffusion equation with discontinuous nonlinear reaction term on the two-dimensional sphere close to its poles. This equation is the counterpart of the well-studied bistable reaction–diffusion equation on the Euclidean plane. The investigation of this equation on the sphere is mainly motivated by the phenomenon of the fertilization of oocytes or recent studies of wave propagation in a model of immune cells activation, in which the cell is modeled by a ball. Because of the discontinuous nature of reaction kinetics, the standard theory cannot guarantee the solution existence and its smoothness properties. Moreover, the singular nature of the diffusion operator near the north/south poles makes the analysis more involved. Unlike the case in the Euclidean plane, the (axially symmetric) Green's function for the heat operator on the sphere can only be represented by an infinite series of the Legendre polynomials. Our approach is to consider a formal series in Legendre polynomials obtained by assuming that the mild solution exists. We show that the solution to the equation subject to the Neumann boundary condition is C1 smooth in the spatial variable up to the north/south poles and Hölder continuous with respect to the time variable. Our results provide also a sort of ‘a priori’ estimates, which can be used in the existence proofs of mild solutions, for example, by means of the iterative methods.

AB - In the paper, we study some ‘a priori’ properties of mild solutions to a single reaction–diffusion equation with discontinuous nonlinear reaction term on the two-dimensional sphere close to its poles. This equation is the counterpart of the well-studied bistable reaction–diffusion equation on the Euclidean plane. The investigation of this equation on the sphere is mainly motivated by the phenomenon of the fertilization of oocytes or recent studies of wave propagation in a model of immune cells activation, in which the cell is modeled by a ball. Because of the discontinuous nature of reaction kinetics, the standard theory cannot guarantee the solution existence and its smoothness properties. Moreover, the singular nature of the diffusion operator near the north/south poles makes the analysis more involved. Unlike the case in the Euclidean plane, the (axially symmetric) Green's function for the heat operator on the sphere can only be represented by an infinite series of the Legendre polynomials. Our approach is to consider a formal series in Legendre polynomials obtained by assuming that the mild solution exists. We show that the solution to the equation subject to the Neumann boundary condition is C1 smooth in the spatial variable up to the north/south poles and Hölder continuous with respect to the time variable. Our results provide also a sort of ‘a priori’ estimates, which can be used in the existence proofs of mild solutions, for example, by means of the iterative methods.

KW - discontinuous reaction term

KW - sphere

KW - stationary fronts

UR - http://www.scopus.com/inward/record.url?scp=85018555614&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85018555614&partnerID=8YFLogxK

U2 - 10.1002/mma.4390

DO - 10.1002/mma.4390

M3 - Article

VL - 40

SP - 5349

EP - 5369

JO - Mathematical Methods in the Applied Sciences

JF - Mathematical Methods in the Applied Sciences

SN - 0170-4214

IS - 14

ER -