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World Wise Words Group

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Mahmood Belozerov
Mahmood Belozerov

Miranda - Phenomena 1996 Download __LINK__


Various techniques have been developed to study this kind of process using microscopy, optical techniques, electrical analysis, etc. (Bauman et al., 2004). For the experimenter it is always important to have access to new, simple, and reliable methodologies. Optical techniques have been also used successfully to study diffusion processes (Almond& Patel, 1996). These techniques are in general based in the study of light transmission at a fixed height of a sample column or illuminating the whole column to detect the change of the system. In this case, the results have been interpreted as a consequence of variations in the optical properties of the system. Photoacoustic effect has been demonstrated to be a useful tool for materials characterization, and in the study of diverse phenomena (Almond& Patel, 1996; Mandelis, 1993; Vargas& Miranda, 1988). Photoacoustics have been also used recently in the study of the evolution of dynamic systems, such as oxygen release in plants, blood sedimentation, evaporation of liquids, etc. (Acosta et al., 1996; Frandas et al., 2000; Landa et al., 2003; Martinez-Torres & Alvarado-Gil, 2007). The photoacoustic (PA) signal is not only directly related to the time evolution of the optical and thermal properties, but also with various physical processes leading to modulated heat and additional changes in the geometry of the sample (Bialkowski, 1996). The PA technique is based on the periodic heating of a sample illuminated with modulated optical radiation. In a gas-microphone configuration, the sample is in contact with the gas-tight cell. In addition to a steady-state temperature gradient, a thermal wave in the material couples back to the gas around the sample and this will result in a periodic fluctuation of the temperature of a thin layer of gas, close to the sample surface. This thin layer of gas will act as an acoustic piston, which will result in the production of a periodic pressure change in the cavity. A sensitive microphone coupled to the sample chamber can be used to detect this pressure fluctuation.




miranda - phenomena 1996 download


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