Collapse

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in a Driven Granular Monolayer.

		gas phase
		collapse phase
Instantaneous Image	1 sec. Time-Average	D.I.L. '98

The above images are a visual demonstration of collapse in the 2D granular gas. The collapse images above are of one-quarter of the total collapse. The instantaneous and time-averaged images of the total collapse can be seen by clicking back to our front page.

In the gas phase, the time-averaged motion is completely random, or uncorrelated, as demonstrated by the nearly uniform distribution of particles in the composite image.

In the collapse phase, however, the ordered lattice corresponds to particles that have come to rest relative to one another and the driving plate. The light reflects off only a portion of the top of each particle, so the above picture does not detail that the particles in the collapse are actually all in contact with one another in their motionless state. The image below has been added to demonstrate this characteristic of the condensate.


A picture with different lighting


The collapse phase is more accurately a two-phase steady state. The time-averaged image of the collapse conveys the random gas-like behavior of the particles that remain in motion. Below is an animated gif that demonstrates this more clearly:





As long as the driving is maintained, the particles in the co-existing gas phase remain in motion.

The clusters are nucleation points for collapse as the driving is lowered. For the above images, the number of particles is 8000. The acceleration, or driving, in the gas phase is 1.0g, while the acceleration in the collapse phase is 0.76g, where g is the acceleration due to gravity. To return the collapsed particles to motion, the acceleration must be increased.