Ultrasonic power levels

Once experimental conditions have been fixed, the aerosol production efficiency also depends on physical parameters related to the liquid nature. It has been shown (Gershenzon, 1964) that, at constant ultrasonic power level, the production yield is an increasing function of the ratio r. 

Low-intensity ultrasound uses power levels (typically < 1 W cm 2) that are considered to be so small that the ultrasonic wave causes no physical or chemical alterations in the properties of the material through which the wave passes, i.e. it is nondestructive. However,... 

The first requirement for the level of ultrasonic power required to cause chemical effects in a reaction is that sufficient acoustic energy must be supplied to overcome the cavitation threshold of the medium. Once this has been exceeded then the region of... 

In another report, an ultrasonic mixer was constructed on a PDMS-quartz chip using a ZnO film. The ZnO film (8 pm) was deposited on the quartz plate with a patterned Au electrode (300 nm) for excitation. Operation frequency was 450 MHz. No heating or bubble formation were observed with a power level of 15 dBm (or 30 mW at 1.2 VJ [489]. 

The effect of ultrasonic treatment on com particles was examined by sonicating both cooked and raw corn slurry samples and the resulting particle size was compared with nonsonicated samples (controls). The peak of the particle size distribution curve shifted from 800 pm to around 80 pm following sonication at high-power levels for cooked corn slurry samples. In addition, the particle size reduction was directly related to the power level and sonication time. The particle size reduction at the... 

As shown in Figure 9.7, Aoki et al. [34] were able to explain why the mean diameter of the ag omerates first decreased and then increased, with increased exposure time to the ultrasonic radiation at power levels above that necessary for cavity formation. These results show the competitive nature of the two processes (deag omeration and ag omeration) taking place in the viltrasonic bath. This increase in particle size is real in that observations of the particle size without... 

FIGURE 9.8 Centrifuged eediment densities (3000 G for 1 hr) of ultrasonically treated powders as a function of power level. Dispersims were treated for 5 min. The powders were dispersed in Oloa-h ane. The Oloa content was 20% of the powder wei it. All SiC powders B064, B082, and G009 are similar to one another. Taken from Aoki et al. [34]. Reprinted by permission of the American Ceramic Society. 

In the most common bath design, the ultrasonic transducer is attached to the underside of the metallic base of the bath and the strongest power level occurs directly above the transducer. However, the ultrasonic power profile in the bath liquid varies in a non-uniform manner with the distance from the base. This has been ascribed to the fact that US is driven through the liquid as waves, so there are points where the irradiation amplitude is maximal and others where it is zero. Maxima are always desirable and can be calculated as multiples of the half-wavelength of sound X) in the medium. Such distances can be calculated from the equation ... 

High-speed observations of the ice crystals produced by an ultrasonic horn (a) comparison of the bubble cloud (1.0°C) and bubble cloud containing ice crystals (-2.8°C) in pure water at ultrasonic power output 7 (0.1-sec pulse) (b) density population of ice crystals observed in a 15wt% sucrose solution (—3.8°C) at increasing ultrasonic output levels (0.1-sec pulse) (t = 0.41 sec). 

Figure 48.1(b) shows the population density of crystals filmed under increasing ultrasonic power output levels. A single 0.1-sec pulse of ultrasound was applied at — 3.8°C in a 15wt% sucrose solution. The growing crystals are shovm 0.40 sec later. These results highlight that a commercial ultrasonic horn can be used to control the nucleation and the size distribution of ice crystals produced within the supercooled liquid. Further results by the first author have shown that as the power output level is increased, the level of transient cavitation increases (Chow-McGarva, 2004). This increase in transient cavitation could be correlated to an increase in the primary nucleation events and thus explain the increase in the observed number of crystals. 

The number of ice crysfals produced af increasing ultrasonic output levels of fhe ulfrasonic horn was observed fo increase as the power output level was increased. Microscopic studies using a unique ultrasonic cold-stage device have shown that this may occur by the fragmentation of preexisting ice dendrifes by cavifafion bubbles. 

In vivo experiments were performed using para-aminohippuric acid (PAH) as a marker inside the polymers. Data of rats PAH concentration in the urine after implantation showed that the PAH concentration in the urine was pronounced during the exposure and mainly in the timespan just after the exposure. The delay was presumably the diffusion time from the implantation site to the bloodstream and then the removal by the kidneys. When control animals were treated by the same procedure, i.e., placing the ultrasonic applicator head over the treated area with the power level of the ultrasound set to zero, no effect of the ultrasound could be detected... 

The milled rice straw pulp fiber was soaked in distilled water for more than 24 h, and then treated by high intensity ultrasonication (Sonics Materials. INC, CT, 20kHz, Model 1500 W) for 30 min with 80% power level. After ultrasonication treatment, the obtained RSF aqua compound was kept in frozen. 

For whole body extractions, 100 female or male alates were ultrasonicated (Sonic Dismembrator 60, Fisher Scientific) in 10 mL hexane for 1 min (power level 3). The hexane was filtered (0.45 pm, PTFE) and stored at -20 C. TMS derivatization was carried out by adding 5 pL BSA and sonicating (15 min) while concentrating to 95 pL under a stream of nitrogen. Another 5 pL BSA was added and the solution was sonicated for 1 hr. 

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