http://en.wikipedia.org/wiki/Gyrator
http://inst.eecs.berkeley.edu/~ee100/su07/handouts/ChuaNotesFall04/ChuaFall04_Gyrator_Guide.pdf
http://www.falstad.com/circuit/e-gyrator.html
http://www.beigebag.com/case_gyrator.htm
http://en.wikipedia.org/wiki/Negative_impedance_converter
http://www.falstad.com/circuit/e-nic-r.html
http://mysite.du.edu/~etuttle/electron/elect66.htm
http://www.ee.nmt.edu/~rhb/spr05-ee212/lab/lab06.html
http://www.matheonics.com/Tutorials/Introduction.html