It has been shown that for dead marine diatom cells or diatom cells which are severely stressed metabolically, larger cells sink faster than small cells as dictated by Stokes' Law. In these cases, the slope of the sinking rate versus cell volume relationship within a culture reaches a maximum. Within cultures of rapidly dividing cells, larger cells' s~n k i n g rate is reduced physiologically to that of smaller cells and the slope of this relationship approaches zero. In several marine d~a t o m species between 5 and 100 pm in diameter, dev~ations from the maximum slope of the volume versus sinking rate relationship could b e used to quantify the physiological reduction of sinking rates. This allowed us to differentiate 2 different components of sinking rate control, the ballasting component (driven by changes in cell composition and volume) which, when dominant, causes sinking rates to be proport~o n a l to cell volume a n d the energy-requiring, protoplast and vacuolar component which, when active, allows si.nklng rates to become independent of cell volume Across the 9 species of diatoms examined, ~ncluding the 3 single-celled species (Ditylun~ brightwellii, Thalassiosira pseudonana, and 7. weissflogii), 4 chain-forming coastal bloom diatoms (T aestivalis, Skeletonema costatum. Chaetoceros debilis and C. cornpressuni) and 2 large floating open ocean species (Ethrnodiscus sp. a n d entire Rhizosolenia spp. mats), there was a strong correlation between log cell volume and sinking rate only for cells that were metabolically inactivated either through extended dark treatment or through treatment with the respiratory inhibitor KCN This was true both within and between cultures. However, no correlation between s~n k i n g rate and cell volume was found for rapidly growlng cells maintamed at saturating irradiances. This supports the notion that there is no obligate correlation between cell volume and sinking rate for metabolically active cells. This potential for cellular modification of the sinking rate versus volume relationship suggests that physiological state may be a n important feature to include in models where carbon flux is predicted on the basis of particle size spectra. We suggest that the minimum cell volume necessary for active sinking rate control is ca 200 pm3, and that this represents a lower limit for Villareal's (1988; Deep Sea Kes 35:1037-1045) theoretical minimum volume necessary for posltlve buoyancy.

Two experiments are reported which test the hypothesis that heart rate increases will be seen in response to monetary incentives during performance on a continuous motor task. In the first study, heart rate was significantly higher when subjects were paid 20 for each success feedback compared to subjects who received feedback only. In contrast, there was no effect of varying the probability of success (10% versus 90% success). Study 2 replicated the monetary incentive effect on heart rate, this time employing 100% success feedback. In neither study were subjects' response rates significantly affected by monetary incentive. In addition, control groups responding much faster on the task as a result of making it more predictable did not show increased heart rate. Consequently, these incentive effects eire di£Bcult to explain with a cardiacsomatic coupling interpretation. It was concluded that cardiac acceleration does occur in response to monetary incentives, even in the absence of failure feedback, and it was proposed that this incentive effect reflects the activation of an appetitive motivational system. Possible applications of the assessment of appetitive responses are suggested.

No abstract

Previous demonstrations of monetary incentive effects on heart rate during a continuous motor task were extended by employing different magnitudes of incentive: 0« (feedback only), li, and H per response. The influence of the total amount of monetary incentive for the experiment was examined by providing monetary incentives either for only 2 trials or for all S trials. This procedure also provided an evaluation of the effect on heart rate during the later trials of discontinuing the incentive after 2 trials. The results showed aclear and graded effect of the amount of incentive per response, but no significant effects were obtained for the total amount of incentive, in spite of providing subjects with clear feedback as to how much money they could expect. Discontinuing incentives produced a significant decrease in heart rate, compared to subjects who continued to receive incentives.No effect was found for the magnitude of incentive on the rate of responding on the motor task, rendering unlikely an explanation for the results in terms of cardiac-somatic coupling. Also, any possible contribution to the heart rate results from fnistrative nonreward feedback was eliminated by avoiding any suggestion of failure feedback on the task. It was concluded that the effects are attributable to the incentive value of the monetary reward and that they are large enough to be of considerable interest.

We have investigated a thiamine-dependent enzyme, transketolase, in cultured fibroblasts from 41 human subjects, including patients with alcoholism-associated Wernicke-Korsakoff syndrome (n = 3), familial chronic alcoholic males (a = 7), their sons (n = 7), nonalcoholic men (n = 7), their male offspring (a = 7), and three generations of an Amish family (n = 10)