This work seeks to obtain in a systematic manner the symbolic normal modes of beams and plates in terms of the impulse response of an associated fourth-order ordinary differential equation and its derivatives. The problem of finding the modes of a beam su

Over a period of five years, samples were taken from a population of the mite Tetranychus urticae and its natural enemies with the purpose of finding a model that predicts the abundance of these populations. Research was carried out as a statistical investigation directed to the study of spatial distribution. We succeeded in establishing a logistic model that creates a value for the presence–absence of the plague. In this paper, we propose an ecological model in order to express the prey–predator relationship.