Importance Of Cavitation Research Articles

Effects of ultrasonic amplitude on sapphire ultrasonic vibration assisted chemical mechanical polishing by experimental and CFD method

Sapphire possesses chemically inert and high hardness. Therefore, it is difficult to get idea material removal rate (MRR) and low surface roughness through chemical mechanical polishing (CMP). Ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) can effectively increase the MRR and decrease the roughness of sapphire surface by combining ultrasonic with CMP. In this article, computational fluid dynamics was adopted to research the effects of ultrasonic amplitude on slurry behavior in UV-CMP. The distribution and variations of physical properties such as velocity, pressure, and air volume fraction were characterized at the microscopic level. The importance of cavitation in UV-CMP was discussed. The accuracy of numerical results was verified by the experiments of sapphire UV-CMP. The results show that the amplitude has a vital influence on the polishing effects. The ultrasonic vibration, f = 40 kHz and P = 60 W, can make the MRR and polished surface roughness Ra of sapphire reach 0.96 μm/h and 0.095 nm, respectively. It is much better than 0.66 μm/h and 0.261 nm of sapphire CMP.

Starch Hydrolysis and Vessel Occlusion Related to Wilt Symptoms in Olive Stems of Susceptible Cultivars Infected by Verticillium dahliae.

This study investigated starch content, amount of pathogen DNA and density of occluded vessels in healthy and Verticillium dahliae infected olive shoots and stems. Starch hydrolysis is considered a mechanism to refill xylem vessels that suffered cavitation by either, drought conditions or pathogen infections. The main objective of this work was to evaluate this mechanism in olive plants subjected to V. dahliae infection or to drought conditions, in order to know the importance of cavitation in the development of wilting symptoms. In initial experiments starch content in the shoots was studied in trees of cultivars differing in the level of resistance growing in fields naturally infested with V. dahliae. The starch content, esteemed by microscopic observation of stem transversal sections stained with lugol, decreased with the level of symptom severity. Results were confirmed in a new experiment developed with young plants of cultivars ‘Picual’ (highly susceptible), ‘Arbequina’ (moderately susceptible) and ‘Frantoio’ (resistant), growing in pots under greenhouse conditions, either inoculated or not with V. dahliae. In this experiment, the pathogen DNA content, quantified by real-time PCR, and the density of occluded vessels, recorded by microscopic observations of transversal sections stained with toluidine blue, were related to the symptoms severity caused by the pathogen. Finally, a drought experiment was established with young plants of the cultivar ‘Picual’ grown in pots under greenhouse conditions in order to compare the effects caused by water deficit with those caused by the pathogen infection. In both cases, results show that starch hydrolysis occurred, what indirectly evidence the importance of xylem cavitation in the development of the symptoms caused by V. dahliae but in the water stressed plants no vessel occlusion was detected.

Ultrasound Emulsification—An Overview

ABSTRACT Fundamentals and applications of ultrasound emulsification are reviewed. The importance of cavitation is stressed, as also is power input to the multiphase fluid. The influence of surfactants, polymeric stabilizers, temperature, pressure, and ultrasonic parameters such as frequency, residence time, acoustic intensity, and energy density are described. The effects of other physicochemical parameters such as emulsifier concentration, disperse phase volume fraction, and viscosity are discussed. Applications to both water-in-oil and oil-in-water emulsions are discussed.

Shock wave characteristics in liquids and extracorporal lithotripsy

Reliable determinations of shock wave parameters such as risetime, pulse width, and positive and negative pressure amplitudes are prerequisites for a study and comparison of different stone destruction mechanisms in lithotripsy. In comparing stone destruction mechanisms, it is found that the fiber-optic probe hydrophone is ideally suited for reliable shock-wave measurements, especially also in the negative pulse range. Different stone destruction mechanisms as a direct action of the shock wave penetrating into the stone, the sound soft reflection, i.e., the Hopkinson effect, the importance of cavitation, and finally the action of evanescent waves in the stone caused by the passing pressure wave in the liquid are discussed in their dependence on shock wave parameters. The results are compared with experiment.

Sea urchin cavitation of giant kelp ( Macrocystis pyrifera C. Agardh) holdfasts and its effects on kelp mortality across a large California forest

Sea urchins, Strongylocentrotus franciscanus (A. Agassiz) and especially S. purpuratus (Stimpson) sheltering in holdfasts of giant kelp, Macrocystis pyrifera, feed on haptera, eventually creating cavitation damage that leads to structural failure of the holdfast when the plants are stressed by large waves. Periodically giant kelp plants on permanent transects in a large Southern California forest were categorized for their degree of urchin infestation and cavitation damage, and subsequent survival followed for 5 yr. Plants with a high degree of urchin damage had significantly higher rates of mortality than plants with little damage during several assessment periods. There was a decreasing gradient in the degree of urchin damage and importance of cavitation from the deep (18 m), outer edge of the Point Loma forest, through the center (15 m), to the inner (12 m) edge of the forest which paralleled urchin abundance and recruitment rates. This gradient acts to reduce the impact of the gradient of giant kelp mortality caused by storms, which is much greater in shallow water and decreases seaward.

The nonlinear dynamics of journal bearings

The journal bearing is ubiquitous in moving mechanical systems, and is a major potential target for study in the field of lubrication theory. Despite this, theoretical understanding of its dynamic behaviour is far from complete ; in particular the essentially nonlinear interplay of rotor dynamics and fluid dynamics of the lubricant has been studied only very recently. Our own investigations have been mainly numerical, and have revealed a wide range of qualitative behaviour. They have confirmed the great importance of cavitation of the lubricant, and the sensitivity to geometrical features of the bearing. Additionally they have enabled us to identify the crucial non-dimensional parameters and their critical values. Finally they have stimulated analytical approaches (e.g. searches for Hopf bifurcations). In this paper we exploit the conceptual approach of dynamical systems theory to present many of our results in a succinct form. Our aim is to make clear not only the extent of understanding of the problem, but also the present shortcomings of theory that require further study.

Primary cavitating tuberculosis in childhood

Eleven cases of pulmonary cavitating primary tuberculosis are described. Ten of these had evidence of haematogenous dissemination. Thus the importance of cavitation in primary tuberculosis should alert the physician to other sites of infection and is an indication for intensive therapy.