We introduce a Markov decision process in continuous time for the optimal control of a simple symmetrical immigration-emigration process by the introduction of total catastrophes. It is proved that a particular control-limit policy is average cost optimal within the class of all stationary policies by verifying that the relative values of this policy are the solution of the corresponding optima...

Chronic inflammatory disease is accompanied by structural changes that appear to relate to disease severity and duration, and are often considered to be poorly reversible, if at all. The processes underpinning the structural changes are varied, complex and not well understood. It is clear that these structural changes contribute to tissue dysfunction. In asthma, remodelling comprises changes in...

Identifying source-sink dynamics is of fundamental importance for conservation but is often limited by an inability to determine how immigration and emigration influence population processes. We demonstrate two ways to assess the role of immigration on population processes without directly observing individuals dispersing from one population to another and apply these methods to a population of...

Most previously used measures of immigrant labor market assimilation will be biased if there is non-random emigration of immigrants. We use longitudinal data on immigration to Sweden 1970-1990 to examine the extent and pattern of immigrant emigration and its consequences for measures of assimilation. Large fractions of the immigrants leave the host country shortly after arrival; within five yea...

A compartmental network is formulated in which each of N compartments represents a possible behavioral state of a discrete population immigrating from outside sources. The network contains absorbing states (sinks) sufficient to maintain an accounting record of every individual that enters the network. Time dependent distributions of counts of individuals in every compartment are given for the c...

responding to critical shortages of physicians, most sub-saharan countries have scaled up training of nonphysician clinicians (npcs), resulting in a gradual but decisive shift to npcs as the cornerstone of healthcare delivery. this development should unfold in parallel with strategic rethinking about the role of physicians and with innovations in physician education and in-service training. in ...

Many habitat fragmentation experiments make the prediction that animal population density will be positively related to fragment, or patch, size. The mechanism that is supposed to result in this prediction is unclear, but several recent reviews have demonstrated that population density often is negatively related to patch size. Immigration behavior is likely to have an important effect on popul...