Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- Dynamics of a Non-Autonomous ODE System Occurring in Coagulation TheoryPublication . Costa, Fernando Pestana da; Sasportes, RafaelWe consider a constant coefficient coagulation equation with Becker–D¨oring type interactions and power law input of monomers J1(t)=αtω, with α > 0 and ω>−1 2 . For this infinite dimensional system we prove solutions converge to similarity profiles as t and j converge to infinity in a similarity way, namely with either j/ς or (j −ς)/√ς constants, where ς =ς(t) is a function of t only. This work generalizes to the non-autonomous case a recent result of da Costa et al. (2004). Markov Processes Relat. Fields 12, 367–398. and provides a rigorous derivation of formal results obtained by Wattis J. Phys. A: Math. Gen. 37, 7823–7841. The main part of the approach is the analysis of a bidimensional non-autonomous system obtained through an appropriate change of variables; this is achieved by the use of differential inequalities and qualitative theory methods. The results about rate of convergence of solutions of the bidimensional system thus obtained are fed into an integral formula representation for the solutions of the infinite dimensional system which is then estimated by an adaptation of methods used by da Costa et al. (2004). Markov Processes Relat. Fields 12, 367–398.
- Long-time behaviour and self-similarity in a coagulation equation with input of monomersPublication . Costa, Fernando Pestana da; Roessel, Henry J. van; Wattis, Jonathan ADFor a coagulation equation with Becker-Doring type interactions and time-independent monomer input we study the detailed long-time behaviour of nonnegative solutions and prove the convergence to a self-similar function
- A hierarchical cluster system based on Horton-Strahler rules for river networksPublication . Costa, Fernando Pestana da; Grinfeld, Michael; Wattis, Jonathan ADWe consider a cluster system in which each cluster is characterized by two parameters: an \order" i; following Horton-Strahler's rules, and a \mass" j following the usual additive rule. Denoting by ci;j (t) the concen- tration of clusters of order i and mass j at time t; we derive a coagulation- like ordinary di erential system for the time dynamics of these clusters. Results about existence and the behaviour of solutions as t ! 1 are ob- tained, in particular we prove that ci;j (t) ! 0 and Ni(c(t)) ! 0 as t ! 1; where the functional Ni( ) measures the total amount of clusters of a given xed order i: Exact and approximate equations for the time evolution of these functionals are derived. We also present numerical results that sug- gest the existence of self-similar solutions to these approximate equations and discuss its possible relevance for an interpretation of Horton's law of river numbers
- Convergence to self-similarity in an addition model with power-like time-dependent input of monomersPublication . Costa, Fernando Pestana da; Sasportes, Rafael; Pinto, João TeixeiraIn this note we extend the results published in Ref. 1 to a coagulation system with Becker-Doring type interactions and time-dependent input of monomers $J_{1}(t)$ of power–like type: $J_{1}(t)/(\alpha t^{\omega }) \rightarrow 1$ as $t \rightarrow \infty$, with $\alpha > 0$ and $\omega > − \frac{1}{2}$. The general framework of the proof follows Ref. 1 but a different strategy is needed at a number of points.
- Mathematical aspects of coagulation-fragmentation equationsPublication . Costa, Fernando Pestana daWe give an overview of the mathematical literature on the coagulation-like equations, from an analytic deterministic perspective. In Section 1 we present the coagulation type equations more commonly encountered in the scientific and mathematical literature and provide a brief historical overview of relevant works. In Section 2 we present results about existence and uniqueness of solutions in some of those systems, namely the discrete Smoluchowski and coagulation-fragmentation: we start by a brief description of the functional spaces, and then review the results on existence of solutions with a brief description of the main ideas of the proofs. This part closes with the consideration of uniqueness results. In Sections 3 and 4 we are concerned with several aspects of the solutions behaviour.We pay special attention to the long time convergence to equilibria, self-similar behaviour, and density conservation or lack thereof.
- A nonautonomous predator-prey system arising from coagulation theoryPublication . Costa, Fernando Pestana da; Pinto, João TeixeiraA recent investigation of Budác et al. on the selfsimilar behaviour of solutions to a model of coagulation with maximum size [Oxford Center for Nonlinear PdE, Report no. OxPDE-10/01, June 2010] led us to consider a related nonautonomous Lotka-Volterra predator-prey system in which the vector field of the predator equation converges to zero as t\rightarrow +\infty. The solutions of the system show a behaviour distinct from those of either autonomous or periodic analogs. A partial numerical and analytical study of these systems is initiated. An ecological interpretation of this type of systems is proposed.
- The continuous Redner–Ben-Avraham–Kahng coagulation system: well-posedness and asymptotic behaviourPublication . Verma, Pratibha; Giri, Ankik Kumar; Costa, Fernando Pestana daThis paper examines the existence of solutions to the continuous Redner-Ben-Avraham-Kahng coagulation system under specific growth conditions on unbounded coagulation kernels at infinity. Moreover, questions related to uniqueness and continuous dependence on the data are also addressed under additional restrictions. Finally, the large-time behaviour of solutions is also investigated.