66 research outputs found
The Evolution of Cavitation Events with Speed and Scale of the Flow
This paper focuses on the different forms that individual cavitating events may take when the cavitation number is below the inception value (but not so low as to produce only attached cavities) and individual nuclei trigger individual cavitation events. It is a sequel to those of Kuhn de Chizelle et al. (1992a, 1992b, 1995) which described a set of cavitation scaling observations on simple Schiebe headforms conducted in the US Navy Large Cavitation Channel (LCC). The most common events observed in those experiments were traveling, hemi-spherical shaped bubbles which grew and collapsed as they were convected through the low pressure region on the headform. Several interesting variations were also observed, including the development of bubble tails and the triggering of patches, or local regions of attached cavitation. In the present paper, the frequency of occurrence of the various types of events is analyzed as well as how those probabilities changed with cavitation number, velocity and headform size. In general, the probabilities of tails and patches increased with decreasing cavitation number, but they also increased with increasing headform size and increasing velocity. A specific parametric dependence on these variables is suggested
Void Fraction Measurment Beneath a Stationary Breaking Wave
Impedance based techniques have been used to quantify air entrainment by a stationary breaking wave at the bow of a ship. The present paper describes an impedance based void fraction meter which was developed to make measurements in this high speed, unsteady, multiphase flow, and details of its calibration are provided. In addition, air entrainment data from an experimental simulation of a bow wave are presented. The local, time averaged void fraction was mapped for flow cross sections beneath the plunging wave jet, revealing the location of the clouds of bubbles formed by that jet impacting the incoming water surface. Size distribution functions for the bubbles within the bubble clouds are also presented. The results are correlated with the wave structure described in Waniewski et al. (1997)
Bubble Measurements Downstream of Hydraulic Jumps
A phase Doppler anemometer (PDA) system was used to measure the velocity profiles and air bubble size distributions downstream of two-dimensional hydraulic jumps for different upstream flow conditions in a 1.92m long laboratory flume. The PDA detected bubbles from 1 to 500 [microns] in diameter, and more were found at the bottom of the downstream flow near the elevation of the upstream free surface. This distribution was more marked for smaller bubbles, those with diameters less that 100 [microns]. The migration of the bubbles is controlled by the effects of buoyancy and by turbulent mixing; the relative magnitude of their effects on bubble distribution depends strongly on bubble size, and also on the energy of the upstream flow
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The short-chain fatty acid acetate reduces appetite via a central homeostatic mechanism
Increased intake of dietary carbohydrate that is fermented in the colon by the microbiota has been reported to decrease body weight, although the mechanism remains unclear. Here we use in vivo11C-acetate and PET-CT scanning to show that colonic acetate crosses the bloodâbrain barrier and is taken up by the brain. Intraperitoneal acetate results in appetite suppression and hypothalamic neuronal activation patterning. We also show that acetate administration is associated with activation of acetyl-CoA carboxylase and changes in the expression profiles of regulatory neuropeptides that favour appetite suppression. Furthermore, we demonstrate through 13C high-resolution magic-angle-spinning that 13C acetate from fermentation of 13C-labelled carbohydrate in the colon increases hypothalamic 13C acetate above baseline levels. Hypothalamic 13C acetate regionally increases the 13C labelling of the glutamateâglutamine and GABA neuroglial cycles, with hypothalamic 13C lactate reaching higher levels than the âremaining brainâ. These observations suggest that acetate has a direct role in central appetite regulation
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