510 research outputs found
Evaluation of turbulence-related high-frequency tidal current velocity fluctuation
Within the development needed for economy viability of tidal stream energy, adaptability of laboratory converters to sea flow conditions is a milestone. The objective of this work is to investigate the high frequency fluctuations in current velocity magnitude and direction related to the turbulent nature of the flow and present a new method for their prediction. With this purpose, high frequency data measured by two ADV (32 Hz) and two ADCP (8 Hz) at four different points in the sea area surrounding Goto Islands (Japan) are analyzed. The data were divided in short-time samples (3-min data for ADV and 5-min data for ADCP) and treated separately. Velocity magnitude fits a normal distribution, with prediction levels higher than 95% for a margin of error of 0.25 m/s when comparing different percentiles between 0.1 and 99.9. Flow direction is analyzed in terms of opening angle between two representative percentiles equidistant from the median (99.9-0.1, 95-5, …), giving as a result a leptokurtic distribution, more outlier-prone than normal. Empirically, for opening angles 99.9-0.1, 97.7-2.3 and 95-5, slopes of 6.79 (6 in normal distribution), 4.17 (4) and 3.38 (3.29) were found, with results similar to a theoretical normal distribution for narrower angles. The new prediction method for high frequency fluctuations is based in this direct correlation between velocity magnitude and direction fluctuations with turbulence intensity and transverse turbulence intensity, respectively. These two parameters can be estimated indirectly by numerical models, giving rise to a tool for the prediction of turbulence-related high frequency fluctuationThe authors would like to thank the Ministry of Environment of Japan for permission to publish of the data used in this study, which were obtained through the project for Promotion of Realization of Tidal Current Power Generation supported by the ministry in 2014 and 2015S
Nicotinic Acid Adenine Dinucleotide Phosphate-induced Ca2+ Release INTERACTIONS AMONG DISTINCT Ca2+ MOBILIZING MECHANISMS IN STARFISH OOCYTES
An intracellular mechanism activated by nicotinic acid adenine dinucleotide phosphate (NAADP(+)) contributes to intracellular Ca(2+) release alongside inositol 1,4,5-trisphosphate (Ins-P(3)) and ryanodine receptors. The NAADP(+)-sensitive mechanism has been shown to be operative in sea urchin eggs, ascidian eggs, and pancreatic acinar cells. Furthermore, most mammalian cell types can synthesize NAADP(+), with nicotinic acid and NADP(+) as precursors. In this contribution, NAADP(+)-induced Ca(2+) release has been investigated in starfish oocytes. Uncaging of injected NAADP(+) induced Ca(2+) mobilization in both immature oocytes and in oocytes matured by the hormone 1-methyladenine (1-MA). The role of extracellular Ca(2+) in NAADP(+)-induced Ca(2+) mobilization, which was minor in immature oocytes, was instead essential in mature oocytes. Thus, the NAADP(+)-sensitive Ca(2+) pool, which is known to be distinct from those sensitive to inositol 1,4,5-trisphosphate or cyclic ADPribose, apparently migrated closer to (or became part of) the plasma membrane during the maturation process. Inhibition of both Ins-P(3) and ryanodine receptors, but not of either alone, substantially inhibited NAADP(+)-induced Ca(2+) mobilization in both immature and mature oocytes. The data also suggest that NAADP(+)-induced Ca(2+) mobilization acted as a trigger for Ca(2+) release via Ins-P(3) and ryanodine receptors
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