A non-linear model for a sexually transmitted disease with contact tracing.

A non-linear model is developed for an epidemic with contact tracing, and its dynamic is studied. We present the data for the Cuban HIV/AIDS epidemic and fit the non-linear model, we obtain estimates for the size of the Cuban HIV epidemic, and for the mean time for detecting a person that is infected with HIV.

A two-type model for the Cuban national programme on HIV/AIDS.

We study deterministic and stochastic versions of a birth and death process for a two-type population with immigration for both types. For the stochastic model we consider the case where the rates are time dependent, and also when they are constant, as is the case in our AIDS application. We derive the probability generating function of the bivariate process and the expectations of the marginal processes. We also study the marginal behaviour of the bivariate process in a particular case where we suppose that the first event is an immigration, and examine the behaviour of the marginal processes divided by their expectations. Finally, we apply some of these results to a sexual-partner notification system, as in the Cuban national programme on HIV/AIDS.

The right brain hemisphere is dominant in human infants.

The development of functional brain asymmetry during childhood is confirmed by changes in cerebral blood flow measured at rest using dynamic single photon emission computed tomography. Between 1 and 3 years of age, the blood flow shows a right hemispheric predominance, mainly due to the activity in the posterior associative area. Asymmetry shifts to the left after 3 years. The subsequent time course of changes appear to follow the emergence of functions localized initially on the right, but later on the left hemisphere (i.e. visuospatial and later language abilities). These findings support the hypothesis that, in man, the right hemisphere develops its functions earlier than the left.

A multicentre study of acute in vitro cytotoxicity in rat liver cells.

A multicentre validation study of the acute in vitro cytotoxicity of drugs involving six French laboratories from INSERM or pharmaceutical companies has been carried out. Thirty liquid or solid chemicals such as antibiotics, anticancer drugs and solvents were selected and incubated for 20 hr with normal rat hepatocytes and FaO hepatoma cells. Miniaturized and automated methods were defined for the evaluation of cytotoxic effects. Four endpoints were evaluated: the ratio of extracellular lactate dehydrogenase to total lactate dehydrogenase, total cellular protein content, reduction of a tetrazolium salt, and neutral red uptake. For each test IC(50) values were calculated. A good interlaboratory reproducibility was demonstrated. The neutral red assay was found to be the most sensitive and the least reproducible endpoint. More compounds were shown to be cytotoxic to hepatocytes than to hepatoma cells (18 v. 12). On the basis of the IC(50) values a few compounds were found to be much less cytotoxic than predicted from in vivo data, suggesting that a simple experimental protocol and non-specific cytotoxicity parameters are not sufficient to test certain drug families. However, such methods appear to provide a useful means of defining the concentration range of the drug that will be selected for further analysis using more specific tests.

A two-type population epidemic problem.

We consider a two-type population such that the birth rate of the second type depends on the size of the population of the first type. This problem was formulated by Kendall (1949) and Goodman (1953), then solved for constant parameters by Tapaswi & Roychoudhury (1984) and Gani & Tin (1984) (where the first type was female, and the second type, male). We generalize the known results to cases where the parameters are time dependent. Analytic expressions for the first two moments are found. For constant parameters, we derive the asymptotic law for the process.