http://www.eas.uccs.edu/wickert/ece2610/lecture_notes/ece2610_chap9.pdf
http://courses.ece.ubc.ca/359/lectures/chapter2.pdf
http://www.site.uottawa.ca/~jpyao/courses/ELG3120_files/ch2.pdf
http://www.javaquant.net/papers/Laplacetransform.pdf
http://www.secs.oakland.edu/~frick/ECE276_W11_ICN/Laplace_Notes.pdf