Systems that require a driving force of some kind are very common in physical and biological settings. Driving forces in a biological context are usually referred to as rhythms, pulses or clocks. Here we are interested in the effect of adding a square wave periodic driving force to a biological model. This is intended to model inputs from biological circuits with all-or-none or switch-like resposes. We study a model of cell division proposed by Novak and Tyson. Our switched input is intended to model the interaction of the mitotic oscillator with an ultradian clock. We thoroughly characterize the behaviour as a function of the durations of the active and inactive phases. We also study a model of vein formation in plant leaves proposed by Mitchison. Pulsed hormonal release greatly accelerates vein formation in this model. / x, 105 leaves : ill. (some col.) ; 29 cm.

This thesis assessed the impacts of acute and chronic phase-shifting on learning and memory in male and female rats. Previous research has revealed impaired retention immediately following circadian disruption and on the acquisition of new associations. However, whether behaviour resumes normality following circadian re-entrainment is unresolved. Following circadian re-entrainment, retention of pre-phase-shift acquired associations on Morris water task (MWT) and a visual discrimination task designed on the 8-arm radial maze were tested. Subsequently, an extradimensional set shift (EDS) using the 8-arm radial maze was performed. Acute circadian disruption negatively impacted retention in males and females, but only male rats without running wheels exhibited impairment following chronic phase-shifting on MWT performance. Retention on the visual discrimination task was impaired following chronic, but not acute, circadian disruption. Chronic, but not acute, phase-shifting negatively impacted performance on the EDS. Generally, phase-shifting produced differential negative impacts on cognitive function in rats. / xiv, 181 leaves : ill. (some col.) ; 29 cm