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In this article, we address the phenomenon of temporal, self-sustained oscillations for a solid oxide fuel cell which utilises a humidified methane fuel stream. Our objective is to uncover the fundamental mechanisms giving rise to current oscillations that have been observed experimentally. To this end, we develop a model based on the fundamental chemical kinetics and transfer processes which take place within the fuel cell. This leads to a three-dimensional dynamical system, which, under typical operating conditions, is rationally reducible to a planar dynamical system. This planar dynamical system was studied in (Sands et al., Proc. R. Soc. Lond. A 470 (2014)) for the case where the parameter ¯c0 ⪡ 1, corresponding with a weakly humidified fuel stream. In the present article, the structural dynamics of the planar dynamical system for the case where the parameter ¯c0 = O(1), which corresponds with a humidified fuel stream, are studied in detail. Self-sustained oscillations are shown to arise through Hopf bifurcations in this planar dynamical system, and the key parameter ranges for the occurrence of such oscillations are identified. Fuel stream humidification is also shown to significantly alter the fuel cell dynamics, leading to hysteresis. [ABSTRACT FROM AUTHOR]

The relationship of stressful life events to decline in intellectual abilities in 112 women aged 65-92 was assessed. A ratio of crystal/fluid abilities was used to estimate decline. The Vocabulary and Comprehension subtests of the Wechsler Adult Intelligence Scale (WAIS) were used to assess crystalized abilities, and the Block Design and Object Assembly subtests of the WAIS were used to assess fluid abilities. The Holmes and Rahe Schedule of Recent Events (SRE) was used as a measure of stress along with a method for quantifying individual estimates of stress experience. In addition, the relationship of subsets of actual events experienced to intellectual functioning was analyzed. Stress was found to be related to the ratio used to estimate decline. Changes in personal health and changes in health of a family member were positively related and vacations were negatively related to decline in intellectual functioning.

Adults from different age groups (18-24, 30-40, and 65-86) were tested to determine if they differ in their perception of certain stressful life events. Twenty adults from each age group were asked to rate a series of events according to their perceived relative stressfulness; included were events thought to be particularly salient for elderly adults. Amster and Krauss' list of events and Holmes and Rahe's procedure for quantifying stress were used. Group differences were not found for the elderly salient events; however it was found that elderly adults perceive death-related events as less stressful than do younger adults.