We describe briefly a perturbative method for problems with two critical arguments developed elsewhere (Henrard and Lemaître 1986). This perturbative method is based upon the numerical evaluation of a set of angle-action variables valid globaly on the phase space of a one-degree of freedom resonance problem. Applied ot the resonance 2/1 of the elliptic restricted planar three body problem, this perturbative method enables us to distinguish two mechanisms of formation of chaotic behavior and to identify features found in numerical experiments by previous authors. Questions relative ot the formation of the Kirkwood gaps in the asteroid belt are also briefly reviewed.
Cryptosporidium parvum, the protozoan responsible for cryptosporidiosis, continues to defy eradication with existing therapies. A review of the anticryptosporidial activity of several drugs in the dexamethasone-immunosuppressed rat model illustrates the multitude of factors that may contribute to the difficulty of assessing a drug’s therapeutic efficacy against the protozoan and provides possible explanation for drug failure at the level of host-parasite interaction.