High-frequency ultrasound

Ultrasound (high frequency) devices are already marketed commercially as a means of clearing rodents from restaurants and other sites. The physical effects on rats and mice are sufficient to drive them from the area. Although intensity levels are selected to be relatively... 

Ultrasound High-frequency sound waves can promote ligand dissociation and other reactions of organometallic species as a result of the high local temperatures that can be achieved by cavitation (the opening and closing of small bubbles of vapor in the solvent). ... 

The previous subsection described single-experiment perturbations by J-jumps or P-jumps. By contrast, sound and ultrasound may be used to induce small periodic perturbations of an equilibrium system that are equivalent to periodic pressure and temperature changes. A temperature amplitude 0.002 K and a pressure amplitude 5 P ss 30 mbar are typical in experiments with high-frequency ultrasound. Fignre B2.5.4 illustrates the situation for different rates of chemical relaxation with the angular frequency of the sound wave... 

The attenuation of ultrasound (acoustic spectroscopy) or high frequency electrical current (dielectric spectroscopy) as it passes through a suspension is different for weU-dispersed individual particles than for floes of those particles because the floes adsorb energy by breakup and reformation as pressure or electrical waves josde them. The degree of attenuation varies with frequency in a manner related to floe breakup and reformation rate constants, which depend on the strength of the interparticle attraction, size, and density (inertia) of the particles, and viscosity of the Hquid. 

In the contact mode, a metal rod acts as a waveguide. When it touches a surface, it is stimulated by the high frequencies, ultrasound, on the opposite side of the surface. This technique is used to locate turbulent flow and or flow restriction in process piping. 

Ultra-sound emissions typically occur when male rodents are exposed to female odours or altricial neonates to maternal sources (Whitney, 1974 Conely and Bell, 1978). Without the VNO, sexually inexperienced male mice do not utter emissions at ultra-high frequencies (UHF), whereas those with prior experience vocalise after VN-x, as discussed above (Chap. 5). Female mouse urine contains a unique UHF-eliciting component which is non-volatile but ephemeral (Sipos et al., 1995). The signal is degraded by oxidation and disappears within 15 to 18 hours of deposition. Direct contact with freshly voided urine must occur before males will vocalise (sexually experienced or inexperienced). At least one of the olfactory systems is needed for UHF to be elicited by fresh urine complete deafferentation abolishes the response (Sipos et al., 1993). Exposure to females permits UHF to be elicited by other than chemical cues (Labov and Wysocki, 1989). Nocturnal or cryptic species conceivably use ultrasound to advertise male presence whether this is to deter other males or assist with female location is unclear. 

The gas-driven transducers are simply whistles with high frequency output. Dog whistles and sirens can be given as the two examples of gas-driven transducers. These transducers can be used to break down foams and agglomerates of dust and for the acceleration of drying processes. However, these types do not have any significant chemical applications, as it is not possible to achieve a sufficiently high-pressure intensity in airborne ultrasound by this method. 

The pioneering work on the chemical applications of ultrasound was conducted in the 1920 s by Richards and Loomis in their classic survey of the effects of high frequency sound waves on a variety of solutions, solids and pure liquidsQ). Ultrasonic waves are usually defined as those sound waves with a frequency of 20 kHz or higher. The human ear is most sensitive to frequencies in the 1-5 kHz range with upper and lower limits of 0.3 and 20 kHz, respectively. A brief but useful general treatment of the theory and applications of ultrasound has been given by Cracknel 1(2). 

Welding is easy using thermal processes, possible with ultrasound methods but impossible with the high-frequency technique. 

Welding is possible using thermal processes and by ultrasound but impossible by the high-frequency technique. 

PVDC is appreciated for its barrier effect to water vapour, gases and aromas as well as its chemical resistance (except to certain solvents), its relative flexibility, fireproofing, the possibility of food contact for special grades, transparency, gloss, scalability (including by high frequency and ultrasound), printability. 

Welding is easy by the thermal processes and possible with ultrasound but the high-frequency technique is unsuitable. 

Welding is possible for certain grades by the thermal processes, high frequencies, induction and by ultrasound. The strength of the joints can be 10-40% of the PMMA used. Gluing generally gives better results. 

Welding is possible by all the processes thermal, friction, ultrasound and high frequencies. Gluing is also possible with solvents. Preliminary tests are essential. 

The basis for the present-day generation of ultrasound was established as far back as 1880 with the discovery of the piezoelectric effect by the Curies [1-3]. Most modern ultrasonic devices rely on transducers (energy converters) which are composed of piezoelectric material. Such materials respond to the application of an electrical potential across opposite faces with a small change in dimension. This is the inverse of the piezoelectric effect and will be dealt with in detail later (Chapter 7). If the potential is alternated at high frequencies the crystal converts the electrical energy to mechanical... 

Essentially all imaging from medical ultrasound to non-destructive testing relies upon the same pulse-echo type of approach but with considerably refined electronic hardware. The refinements enable the equipment not only to detect reflections of the sound wave from the hard, metallic surface of a submarine in water but also much more subtle changes in the media through which sound passes (e. g. those between different tissue structures in the body). It is high frequency ultrasound (in the range 2 to 10 MHz) which is used primarily in this type of application because by using these... 

The first area involves low amplitude (higher frequency) sound and is concerned with the physical effect of the medium on the wave and is commonly referred to as low power or high frequency ultrasound . Typically, low amplitude waves are used for analytical purposes to measure the velocity and absorption coefficient of the wave in a medium in the 2 to 10 MHz range. Information from such measurements can used in medical imaging, chemical analysis and the study of relaxation phenomena and this will be dealt with later. 

The potential of sonochemistry was identified over sixty years ago in a wide ranging paper entitled The Physical and Biological Effects of High Frequency Sound-Waves of Great Intensity [13]. Over the few years which followed this paper a great deal of pioneering work in sonochemistry was carried out and, as a result of this, two reviews on the applications of ultrasound in polymer and chemical processes were published... 

A. Mues and A. Peiffer, Design of ultrasound systems for low and high frequencies, Ultrasound in Environmental Engineering, A. Tiehm and U. Neis (eds.),... 

Table 6.15 shows the product mixture from an unstirred (silent) reaction in which the only mixing is by convection, an arrangement not normally used in electrosynthesis. (All electrosyntheses are normally agitated mechanically in some way and therefore still conditions cannot practically be achieved.) For these conditions, the major product was the isomeric mixture of diphenyl methane derivatives. This was similiar to the product mix obtained at 800 kHz. Thus the use of high frequency ultrasound... 

Sonication, the application of high-intensity ultrasound at frequencies beyond the range of human hearing (16 kHz), of a monomer results in radical polymerization. Initiation results from the effects of cavitation—the formation and collapse of cavities in the liquid. The collapse (implosion) of the cavities generates very high local temperatures and pressures. This results in the formation of excited states that leads to bond breakage and the formation of... 

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