http://www.ece.jhu.edu/~cooper/courses/214/signalsandsystemsnotes.pdf
http://158.132.21.81/class/EIE312/LS102_LTIS.pdf
http://itee.uq.edu.au/~coms3100/Lecture%20Notes/lec04.pdf
http://www.cis.hut.fi/Opinnot/T-61.140/Luennot/Ch2.pdf
http://faemino.ucsd.edu/~soniamartinez/teaching/143a_SignalsSystems/data/impulse-response.pdf
http://www.ece.mcgill.ca/~mvu5/ES150/8-lti_psd.pdf
http://en.wikipedia.org/wiki/Laplace_transform
http://www.intmath.com/laplace-transformation/10-applications.php
http://www.vis.uky.edu/~cheung/courses/ee422g/lecture6.pdf
http://fourier.eng.hmc.edu/e102/lectures/Laplace_Transform/node3.html
http://fourier.eng.hmc.edu/e101/lectures/Laplace_Transform/node8.html
http://en.wikipedia.org/wiki/Routh%E2%80%93Hurwitz_stability_criterion
http://www.egr.msu.edu/classes/me451/jchoi/Fall2011/notes/ME451_L10_RouthHurwitz.pdf
http://www.atp.ruhr-uni-bochum.de/rt1/syscontrol/node40.html
http://www.ece.rutgers.edu/~npuri/research/stable_poly.pdf