We introduce a new theoretical model to describe the dynamics of transmission for a certain class of bacterial infectious diseases. The propagation mechanism considered is the one concerning direct personal contact. Immunity factors, if present, will be ignored, but in our calculations is included the existence of an incubation period for the contagious infection. The effects of public health campaigns on the spread of the disease are also considered and the inclusion of a certain parameter ε to measure the efficiency of such attempts is proposed.

Introducimos aquí un nuevo modelo teórico para describir la dinámica de transmisión a que responden algunas enfermedades infecciosas bacterianas. El mecanismo de propagación considerado es el de contacto personal directo. La presencia de factores de inmunidad es ignorada, pero el modelo incorpora la existencia de un período de incubación para la enfermedad. Los posibles efectos de campañas educativas de salud pública, orientadas a controlar la propagación, son incluidos y se introduce un cierto parámetro ε para cuantificar la eficiencia de ese tipo de recurso.

The two-photon absorption process is a nonlinear phenomenon that shows very low optical efficiency in bulk semiconductors. For this reason the detection of these processes becomes very difficult from the experimental point of view. Nevertheless, when dealing with semiconductor QD's with few nanometer radii, these transitions are enhanced and the detection is possible. In this contribution we present analytical calculations for the absorption coefficient in CdSe spherical QD's subjected to these second order processes, as a function of the characteristic dot parameters. The intensities of the absorption peaks, as well as the statistical treatment involving QD's ensembles, are also reported.

We introduce a simplified theoretical model to describe a virtual virus propagation process in a set of interacting computers. The propagation mechanisms considered here are those related to the reception of messages through internet as well as the ones concerning the simple exchange of files using recording devices as compact disks or the commonly used floppy disks. In spite of its inherent simplicity, this model provides a good idea of the infection process and trends. From the mathematical point of view, the nonlinear delay integral equation that we obtain here presents certain interesting features which are explored and enlightened in this paper.