Several others have already responded to this request but I'll add my own
URL for some quicktime movies of wave packets moving with various
combinations of phase and group velocity.
I confess; they are only Maple simulations. However, if I look hard
enough, I can almost imagine that I see a 39 degree bow shock forming in
one of them.
John
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A. John Mallinckrodt http://www.intranet.csupomona.edu/~ajm
Professor of Physics mailto:ajmallinckro@csupomona.edu
Physics Department voice:909-869-4054
Cal Poly Pomona fax:909-869-5090
Pomona, CA 91768-4031 office:Building 8, Room 223