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  ______    _____     _  __     ___     _    _   
 /_   _//  |  ___||  | |/ //   / _ \\  | \  / || 
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 /__//     |_____||  |_|\_\\ |_||  |_|||_|\/|_|| 
 `--`      `-----`   `-` --` `-`   `-` `-`  `-`

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Text this: Material characterization of functionally graded material by means of elastic waves and a progressive-learning neural network