In a model of overlapping generations with a continuum of finitely lived individuals, the aggregate price dynamics is characterized by a functional differential equation of mixed type. Delays and advances are exogenous when age at retirement is mandatory; they become state-dependent when...

We analyze a mathematical model of the simultaneous transmission of two HIV subtypes and their control by vaccines. Two vaccines are analyzed which utilize different mechanisms, one in which the vaccine take differs for each subtype, and the other in which a different level of reduced...

A simple theoretical framework is presented that addresses the question of how different vaccination strategies work against a pathogen which infects two species. This is first studied in purely theoretical terms to determine which equilibria will be stable for which parameter combinations. Two...

Realistic models have a larger number of parameters than simple models do. In such realistic models some of the parameter values will be less realistic because of the availability and the difficulty in estimation. On the contrary, a simple model with a smaller number of parameters of which...