Experimental investigations are crucial to the development of our
understanding of complex systems, and the establishment of the CATS
Center has made it possible to launch an experimental effort
commensurate with the level of already existing theoretical activity.
Currently we have ongoing experiments in
chemical reactions (quenching analysis, invariant manifolds, chemical waves),
fluid dynamics (turbulence in pipe flows, capillary waves, hydraulic jumps,
thin film flows),
acoustics (spectroscopy of high-*Q* resonators of various geometries),
physics of biological systems
(measurement of
protein folding transitions),
and
granular flows.

**Macromolecular dynamics:**

One of the advances made possible by CATS SNF funding was
the first mechanical measurements
of protein folding transitions on nanometer scales.
Using a mechanical technique developed here
it was observed
that the dynamics of protein folding is characterized by discrete
steps in time.
These measurements suggest
a hierarchical organization within the protein molecule,
motivating
exploration of hierarchically
structured statistical mechanics models pursued by CATS theorists.

**Granular flows:**

Granular matter has properties that do not resemble those of other states
of matter. In particular, granular flows do not behave like fluids,
their discrete nature having manifest consequences.
CATS experimentalists study the dynamics of
rapid granular flows in simple geometries,
focusing on the basic underlying mechanisms,
such as steady flows, intermittent flows,
and shock waves.

**Acoustics:**

High resolution acoustic spectroscopy is used to study aspects of
quantum chaos. The acoustic wave-equation is clearly very different
from the Schrödinger equation (notably the displacement field is a
vector field), but the basic features are similar enough to allow very
useful analogies. For example Random Matrix Theory which is now used
extensively to characterize chaos in quantum systems is tested to
levels not previously inaccessible experimentally. In addition we study
symmetries and symmetry-breaking which are specific to the elastic
systems. We study parametric level dynamics where the parameter varied
is either the shape of the object or the temperature. We measure
wavefunctions of stationary states as well as the transient development
of a wavefront following a sharp blow.

**Turbulence:**

Particle Motion in Capillary Waves:

We have followed the motion of particles floating on a water surface
in a cylindrical dish oscillated vertically so as to create
capillary waves.
For the single-particle motion, a cross-over in
the diffusion motion is observed, from a strongly anomalous diffusion
at length scales below the wave length to a motion closer to
Brownian at larger length scales.
For the relative particle motion, the non-Brownian character of the
flow is very pronounced. We have determined the relative diffusivity
and studied its dependence on distance.

Pipe flow turbulence:

Turbulence is produced in a pipe flow behind a grid, and the velocity
fluctuations are measured using laser Doppler anemometry. The
distributions and their moments of these fluctuations are determined
at various temporal scales and Reynolds number. At intermediate
Reynolds numbers the moments do not follow a power law in scale,
but they still follow a power law when one moment is plotted versus
another. We investigate how the exponents obtained in this way depend
on the Reynolds number.

Hydraulic jump:

The circular hydraulic jump is used as a convenient laboratory
for studying
in detail the transition from laminar to turbulent flow. A sequence of
states is observed involving different numbers of vortexes with varying
degrees of symmetry breaking.

Fri Feb 21 15:17:28 MET 1997