http://physics.about.com/od/quantump...ringtheory.htm
http://www.sukidog.com/jpierre/strings/basics.htm
http://library.thinkquest.org/04apr/.../whatis_st.htm

I think if you use your own words, then most all of it, since it is a theory that has to be spelled out in a certain way, no one can patent, nor plagerize the example.