Ultrasonic emission

In this scenario, Antonelli et al. (2005) found a decrease in the rate of separation-induced ultrasonic emission in the 10-day-old rat pups prenatal exposed to WIN55,212-2, revealing a decreased emotional reactivity in such offspring. In a recent study, we focused on the effects induced by exposure to... 

As the fracture propagates, the elastic energy released due to the micro-fractures occurring within the sample can be measured. This ultrasonic emission due to micro-fracture aftershock relaxation has recently been measured for various laboratory samples. Petri et al (1994) measured the ultrasonic emission amplitude distribution in a large number of stressed solid samples under different experimental conditions. A power law decay for the cumulative energy release distribution n Er) with the released energy amplitude Er was observed in all cases n Er) E (see Fig. 3.21). This is indeed very similar to the Guttenberg-Richter law for the frequency distribution of earthquakes, as discussed briefly in Chapter 1, and will be discussed in detail in the next chapter. 

The role of disorder, in particular of the fractal structure of the earthquake faults (discussed in Section 4.4), are not clearly understood. As discussed in an earlier chapter (Section 3.8), the dynamics of fracture in disordered solids also indicate similar (Guttenberg-Richter type) power law behaviour in the power spectrum of the ultrasonic emission from such solids, as the fracture propagates. No doubt the understanding of the connections between the dynamics of fracture in disordered solids and the dynamics of earthquakes will become much clearer in the near future, because of the intensive efforts which are being made currently. 

Rettelbach T, Sauberlich J, Korder S, Fricke J (1995) Thermal conductivity of silica aerogel powders at temperatures from 10 to 275K. J Non-Cryst Solids 186 278-284 Shen Q, Toyoda T (2003) Dependence of thermal conductivity of porous silicon on porosity characterized by photoacoustic technique. Rev Sci Instr 74 601-603 Shinoda H, Nakajima T, Ueno K, Koshida N (1999) Thermally induced ultrasonic emission from porous silicon. Nature 400 853-855... 

Low-intensity ultrasonic waves are used for nondestructive probing to locate flaws in materials for which complete reliability is mandatory, such as those used in spacecraft components and nuclear reactor vessels. When an ultrasonic transducer emits a pulse of energy into the test object, flaws reflect the wave and are detected. Because objects subjected to stress emit ultrasonic waves, these signals may be used to interpret the condition of the material as it is increasingly stressed. Another application is ultrasonic emission testing, which records the ultrasound emitted by porous rock when natural gas is pumped into cavities formed by the rock to determine the maximum pressure these natural holding tanks can withstand. 

Furthermore, the ultrasonic irradiation of alkanes in the presence of N2 (or NH or amines) gives emission from CN excited states, but not from N2 excited states. Emission from N2 excited states would have been expected if the MBSL originated from microdischarge, whereas CN emission is typically observed from thermal sources. When oxygen is present, emission from excited states of CO2, CH-, and OH- is observed, again similar to flame emission. 

Nondestmctive evaluation, also termed nondestmctive testing or nondestmctive inspection, is extensively used in weld testing (14). Nondestmctive tests do no impair the serviceabiUty of the material or component under stress. The most widely used tests for evaluation of welds are Hquid penetrant, magnetic particle, ultrasonics, and radiography. Acoustic-emission tests are increasingly used. Nondestmctive tests detect and characterize, in terms of size, shape, and location, the various types of weld discontinuities that can occur. 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Visual identification prior to failure is difficult due to the typical tightness of stress-corrosion cracks. A low-power hand lens will greatly aid determination. Crack enhancement may be achieved through the use of dye penetrants. Severe cracking may be detectable using ultrasonic, radiographic, or acoustic emission techniques. 

Nondestructive testing (NDT) is used to assess a component or structure during its operational lifetime. Radiography, ultrasonics, eddy currents, acoustic emissions, and other methods are used to detect and monitor flaws that develop during operation (Chapter 7). 

Balasubrahmanyam A, Pandit AB (2009) Oscillating bubble concentration and its size distribution using acoustic emission spectra. Ultrason Sonochem 16 105-115... 

Moholkar VS, Sable SP, Pandit AB (2000) Mapping the cavitation intensity in an ultrasonic bath using the acoustic emission. AIChE J 46 684—694... 

Francoise L-M, Voglet N, Thierry L, Rudi A (2001) Evidence for the emission of alkali-metal-noble-gas van der Waals molecules from cavitation bubbles. Ultrason Sonochem 8(2) 151—158... 

The experimental system for measuring the sonoluminescence spectrum of alkali-metal atom emission from an aqueous solution is similar to that for measuring the MBSL spectrum from water. Degassing the solution is an important procedure because the presence of dissolved air affects the emission intensity. In an air-saturated solution, no observation of alkali-metal atom emission has been reported, whereas continuum emission can be observed. A typical experimental apparatus using ultrasonic standing waves is shown in Fig. 13.3 [8]. The cylindrical sample container is made of stainless steel, and its size is 46 mm in diameter and 150 mm in... 

Fig. 13.7 Spectra of Na atom emission from 2 M NaCl solutions after adding ethanol with concentrations of 0.5 mM (b), 1 mM (c), 1.5 mM (d) and 2 mM (e). Line a denotes the spectrum obtained without adding ethanol. The ultrasonic frequency is 138 kHz and the power is 7.3 W [21] (Reprinted from American Chemical Society. With permission)...

C. Sonoluminescence Emission from exposure to ultrasonic sound waves in solution... 

Unlike the known approaches we develop the use of water- fuel emulsions with the soluble in water catalytic non- corroding additions and ultrasonic mixing by the sharp superheated steam for reduction of the oxides of nitrogen and soot emission in the combustion engines. Our know how is also the use of the electro-activated water for emulgation. The first results testily the technical and economic expedience of the chosen direction. 

Photoluminescence spectroscopy is used to analyze the electronic properties of semiconducting CNTs [64]. The emission wavelength is particularly sensitive to the tube diameter [65] and chemical defects [66], However, a more dedicated sample preparation is required in order to eliminate van der Waals and charge transfer interactions between bundled CNTs. This can be done via ultrasonication or treatment of the bundles with surfactants that separate individual CNTs and suppress interactions between them [67]. 

From the above one might be tempted to attribute ultrasonically enhanced chemical reactivity mainly to the mechanical effects of sonication. However this cannot be the whole reason for the effect of ultrasound on reactivity because there are a variety of homogeneous reactions which are also affected by ultrasonic irradiation. How, for example, can we explain the way in which power ultrasound can cause the emission of light from sonicated water (sonoluminescence), the fragmentation of liquid alkanes, the liberation of iodine from aqueous potassium iodide or the acceleration of homogeneous solvolysis reactions ... 

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