We follow the discussion presented in ref. [8].

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They were derived, according to several textbooks, on the basis of experimental observations. In fact it seems that the laws were modeled by Fick after the work by Fourier on heat transmission. For a further discussion of this point see for instance ref. [10].

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The programs have been written in Bologna by M. Deninno, F. Fabbri, F.-L. Navarria and F. Rimondi

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