From bouncing to floating: noncoalescence of drops on a fluid bath.

When a drop of a viscous fluid is deposited on a bath of the same fluid, it is shown that its coalescence with this substrate is inhibited if the system oscillates vertically. Small drops lift off when the peak acceleration of the surface is larger than g. This leads to a steady regime where a drop can be kept bouncing for any length of time. It is possible to inject more fluid into the drop to increase its diameter up to several centimeters. Such a drop remains at the surface, forming a large sunk hemisphere. When the oscillation is stopped, the two fluids remain separated by a very thin air film, which drains very slowly (approximately 30 min). An analysis using lubrication theory accounts for most of the observations.

Relationships between startle and cardiovascular reactivity.

Although startle and cardiovascular reactivity have been studied extensively, little is known about their relationship. In the present study, we examined cardiovascular responses and affective startle modulation in 112 normotensive individuals varying in self-reported fearfulness and parental cardiovascular health history. An initial intense noise burst elicited a phasic cardiac acceleration that was larger for fearful individuals. Startle blink responses were larger during aversive than during pleasant relaxing imagery but did not differ with fear group. Cognitive challenge tasks elicited heart rate and blood pressure increases that were unrelated to fearfulness or parental health history. However, greater startle potentiation by aversive imagery predicted larger pressor responses to cognitive challenge, especially among men. The observed relationship between startle and cardiovascular reactivity suggests a common mechanism for their affective modulation.

Fearfulness and startle potentiation during aversive visual stimuli.

Recent experimental research suggests an association between negative affect and potentiation of the human startle reflex, as well as enhancement of this effect among fearful compared to low fear subjects. In the present study, 32 undergraduates were selected for high or low total Fear Survey Schedule scores. Acoustic startle probes were presented while subjects received warned presentations of aversive and neutral photographic slides. High fear but not low fear subjects showed potentiated short-latency cardiac acceleration and blink magnitude, and reduced blink latency, during aversive compared to neutral slides. These results support the hypothesis that affective modulation of startle is enhanced among high fear compared to low fear subjects. Considered in the context of prior findings, the results suggest that this individual difference effect generalizes across psychophysiological components of the startle reflex and diverse procedures for manipulating affect.

Role of sympathetic innervation in cardiac development in oculo.

Embryonic heart cultured in oculo differentiates into adult-like heart tissue, increases in size, and maintains spontaneous activity driven by a defined pacemaker. The growth and beating rate of embryonic heart maturing in oculo are modulated by its neural milieu. Culture in a sympathetically denervated eye chamber compromised growth and increased intrinsic beating rate. Exposure to an additional source of sympathetic neurons increased parasympathetic control of heart rate but did not alter growth or intrinsic beating rate. Because eye chamber sympathectomy alters neurotransmitter expression in parasympathetic and sensory neurons, it is possible that the growth inhibition observed in heart grafts is not a direct consequence of preventing sympathetic innervation. This possibility is being tested in additional experiments.