Robert W. Gammon
||Robert W. Gammon
Light passing through materials is scattered by the thermal fluctuations
in positions of the atoms. The wavelength dependence of this scattering
leads to the blue color of the sunlit sky. What is less familiar is that
the dynamics of the atomic motions can be measured by studying the
spectrum of the scattered light. Professor Gammon and his students have
been studying the internal motions of materials near critical phase
transitions using techniques of laser light scattering spectroscopy.
Fluids at the liquid-vapor critical point develop strong density profiles
on earth due to gravity. A microgravity experiment was successfully
proposed by the group. They received the prime contract to build and
operate a photon-correlation, light scattering experiment. The experiment
is named Zeno and measured the
critical fluctuation space-time correlation
functions of a xenon sample in orbit on the Space Shuttle, where the
residual gravitational acceleration was a few micro-g's. The experiment
flew twice, in 1994 and 1996. At the present time the publications from
the experiment and its apparatus development are being prepared. The
archival data set presentation together with a first analysis of the
scaling of the transport coefficients (thermal conductivity and viscosity)
will be the primary publication from this work. New work centers around
experiments to test new ideas about microscopic chaos and to study
cross-over of critical phenomena in systems in which there are competing
- Equilibration near the liquid-vapor critical point in microgravity, R. Allen Wilkinson,
G.A. Zimmerli, Hong Hao, Michael R. Moldover, Robert F. Berg, William L. Johnson, Richard
A. Ferrell, Robert W. Gammon, Phys. Rev. E 57, 436-447 (1998).
- Experimental Evidence for Microscopic Chaos, P. Gaspard, M.E. Briggs, M.K. Francis, J.V.
Sengers, R.W. Gammon, J.R. Dorfman, R.V. Calabrese, Nature 394, 865-868 (1998).
- Concentration Fluctuations in a Polymer Solution under a Temperature Gradient, W.B. Li,
K.J. Zhang, J.V. Sengers, R.W. Gammon, and J.M. Ortiz de Zarates, Phys. Rev. Lett. 81,
Graph of the scattering intensity as the critical point is crossed comparing data from
flight with data at one g (ground): transition is very sharp in low gravity.