This paper shows how the presence of unstable equilibrium configurations of elastic continua is reflected in the behaviour of transients induced by large perturbations. A beam that is axially loaded beyond its critical state typically exhibits two buckled stable equilibrium configurations, separated by one or more unstable equilibria. If the beam is then loaded laterally (effectively like a shallow arch) it may snapthrough between these states, including the case in which the loading is applied dynamically and of short duration, i.e. an impact. Such impacts, if applied at random locations and of random strength, will generate an ensemble of transient trajectories that explore the phase space. Given sufficient variety, some of these trajectories will possess initial energy that is close to (just less than or just greater than) the energy required to cause snap-through and will have a tendency to slowdown as they pass close to an unstable configuration: a saddle point in a potential energy surface, for example. Although this closeencounter is relatively straightforward in a system characterized by a single degree of freedom, it is more challenging to identify in a higher order or continuous system, especially in a (necessarily) noisy experimental system. This paper will show how the identification of unstable equilibrium configurations can be achieved using transient dynamics.

No abstract

The squirrel monkey (Saimiri boliviensis boliviensis) has a well-defined breeding season during which adult males undergo androgen-dependent morphological changes, with acquisition of active spermatogenesis. To assess the hormonal events of this annual cycle, blood samples were obtained weeklyfromtenadult males,andserumwasassayedfortestosterone(T), androstenedione (AA), and dehydroepiandrosterone (DHEA). A significant seasonal variation was noted in mean serum T (P < 0.02), AA (P < 0.02), and DHEA (P < 0.001) concentrations. Mean AA concentrations increased from a nonbreeding season nadir of 91.4 f 12.9 ng/ml (mean f standard error) to a prebreeding concentration of 139 f 10.5 ng/ml and breeding season peak of 167.5 f 15.4 ng/ml (P < 0.05). Mean DHEA concentrations increased from a nonbreeding season nadir of 8.3 & 0.8 to a breeding season peak of 14.3 k 1.2 (P < 0.001). Mean T levels in the nonbreeding (52.2 & 11.6 ng/ ml) and prebreeding season (48.6 f 7.4) were similar. However, T significantly increased during the breeding season to 103.5 k 12.8 ng/ml 8 < 0.05). Progressive changes in body weight and morphology paralleled the rise in serum AA levels. The pattern of peripheral serum androgen concentrations throughout the year would suggest annual activation of the hypothalamic-pituitary-adrenal and/or hypothalamic-pituitary-gonadal axes.

No abstract

No abstract