http://www.ece.jhu.edu/~cooper/courses/214/signalsandsystemsnotes.pdf
http://www.javaquant.net/papers/Laplacetransform.pdf
http://www.secs.oakland.edu/~frick/ECE276_W11_ICN/Laplace_Notes.pdf
http://www.svce.ac.in/departments/maths/Lapref.pdf
http://www.ece.rochester.edu/courses/ECE113/homework/soln_11.pdf