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Other Publications (10)
 Physical Review Letters
 Physical Review Letters
 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
 The Review of Scientific Instruments
 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
 Physical Review Letters
 Physical Review Letters
 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
 Physical Review Letters
Articles by Greg A. Voth in JoVE
Other articles by Greg A. Voth on PubMed



Failure and Strengthening of Granular Slopes Under Horizontal Vibration
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics.
Nov, 2006 
Pubmed ID: 17279902 We present experimental measurements of a granular slope under horizontal vibration. We use optical particle tracking to measure the motion of surface beads as the slope fails. We find that for all but the largest inclination angles, initial bead motion leads to strengthening rather than an avalanche. The initial motion of the beads is usually intermittent and evolves differently for different preparations, slope angles, and rates of increase in the vibration amplitude. When a specific criterion is chosen to define failure, the Coulomb friction model adequately describes the average acceleration required to produce failure, as long as slope preparation and experimental protocol are constant. However, the observed intermittent motion and rate dependence indicate that strengthening microrearrangements are important features that affect failure of slopes under external perturbations.


Experimental Measurements of the Collapse of a Twodimensional Granular Gas Under Gravity
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics.
Oct, 2008 
Pubmed ID: 18999413 We experimentally measure the decay of a quasitwodimensional granular gas under gravity. A granular gas is created by vibrofluidization, after which the energy input is halted, and the timedependent statistical properties of the decaying gas are measured with video particle tracking. There are two distinct cooling stages separated by a high temperature settling shock. In the final stage, the temperature of a fluid packet decreases as a power law T proportional, variant(t{c}t);{alpha} just before the system collapses to a static state. The measured value of alpha ranges from 3.3 to 6.1 depending on the height, significantly higher than the exponent of 2 found in theoretical work on this problem [D. Volfson, B. Meerson, and L. S. Tsimring, Phys Rev. E 73, 61305 (2006)]. We also address the question of whether the collapse occurs simultaneously at different heights in the system.




Simulations of Granular Gravitational Collapse
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics.
Dec, 2013 
Pubmed ID: 24483431 A freely cooling granular gas in a gravitational field undergoes a collapse to a multicontact state in a finite time. Previous theoretical [D. Volfson et al., Phys. Rev. E 73, 061305 (2006)] and experimental work [R. Son et al., Phys. Rev. E 78, 041302 (2008)] have obtained contradictory results about the rate of energy loss before the gravitational collapse. Here we use a molecular dynamics simulation in an attempt to recreate the experimental and theoretical results to resolve the discrepancy. We are able to nearly match the experimental results, and find that to reproduce the power law predicted in the theory we need a nearly elastic system with a constant coefficient of restitution greater than 0.993. For the more realistic velocitydependent coefficient of restitution, there does not appear to be a powerlaw decay and the transition from granular gas to granular solid is smooth, making it difficult to define a time of collapse.

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