Stability in a metapopulation model with density-dependent dispersal.

A spatially explicit metapopulation model with positive density-dependent migration is analysed. We obtained conditions under which a previously stable system can be driven to instability caused by a density-dependent migration mechanism. The stability boundary depends on the rate of increase of the number of migrants on each site at local equilibrium, on the intrinsic rate of increase at local level, on the number of patches, and on topological aspects regarding the connectivity between patches. A concrete example is presented illustrating the dynamics on the dispersal-induced unstable regime.

Synchronism in a metapopulation model.

We consider a spatially explicit meta-population model with interaction among the two nearest neighbors to relate, with a simple mathematical expression, chaos in the local, uncoupled, populations, the degree of interaction among patches, size of the meta-population, and the stability of the synchronized attractor. Since synchronism is strongly correlated with extinction, our results can provide useful information on factors leading to population extinction.

Characterization of anti-erythrocyte autoantibodies in non-Hodgkin's lymphoma patients in Brazil.

The existence of an association between autoimmune phenomena and lymphoproliferative neoplasms is well known. In Campinas at the University Hospital, seventy-seven adult patients with non-Hodgkin's lymphoma (NHL) were studied at diagnosis. The histological subgroup of NHL was performed using Kiel criteria and all patients were characterized by clinical and laboratory examinations according to the Ann Arbor staging. The results of the immunohaematological evaluation of our patients with NHL showed that: 28% presented erythrocyte autoantibodies (auto anti-I or auto-IgG without specificity) but only one developed haemolytic anaemia. There was a weak correlation between low-grade lymphoma and erythrocyte autoantibodies.