Prosperetti's Phi calculator

Returns the Phi argument given by Prosperetti's, The thermal behaviour of oscillating gas bubbles.

Phi returns the Phi argument given by Prosperetti's article, The thermal behaviour of oscillating gas bubbles, JASA 1991.
Chad A. Greene, May 2012

INPUTS: (can be arrays)
gamma = ratio of specific heats (~1.4 for air)
Dg = thermal diffusivity of the gas (~1.9e-5 for air)
omega = angular frequency of bubble oscillation (rad/s)
ro = nominal radius of bubble

Good resources for gas properties are found here:
http://www.peacesoftware.de/einigewerte/einigewerte_e.html and
http://encyclopedia.airliquide.com/encyclopedia.asp