@article{puckett_daniels_2013, title={Equilibrating Temperaturelike Variables in Jammed Granular Subsystems}, volume={110}, ISSN={["0031-9007"]}, DOI={10.1103/physrevlett.110.058001}, abstractNote={Although jammed granular systems are athermal, several thermodynamiclike descriptions have been proposed which make quantitative predictions about the distribution of volume and stress within a system and provide a corresponding temperaturelike variable. We perform experiments with an apparatus designed to generate a large number of independent, jammed, two-dimensional configurations. Each configuration consists of a single layer of photoelastic disks supported by a gentle layer of air. New configurations are generated by cyclically dilating, mixing, and then recompacting the system through a series of boundary displacements. Within each configuration, a bath of particles surrounds a smaller subsystem of particles with a different interparticle friction coefficient than the bath. The use of photoelastic particles permits us to find all particle positions as well as the vector forces at each interparticle contact. By comparing the temperaturelike quantities in both systems, we find compactivity (conjugate to the volume) does not equilibrate between the systems, while the angoricity (conjugate to the stress) does. Both independent components of the angoricity are linearly dependent on the hydrostatic pressure, in agreement with predictions of the stress ensemble.}, number={5}, journal={PHYSICAL REVIEW LETTERS}, publisher={American Physical Society (APS)}, author={Puckett, James G. and Daniels, Karen E.}, year={2013}, month={Jan} }
@article{puckett_lechenault_daniels_thiffeault_2012, title={Trajectory entanglement in dense granular materials}, journal={Journal of Statistical Mechanics: Theory and Experiment}, author={Puckett, J. G. and Lechenault, F. and Daniels, K. E. and Thiffeault, J. L.}, year={2012} }
@article{puckett_lechenault_daniels_2011, title={Local origins of volume fraction fluctuations in dense granular materials}, volume={83}, ISSN={["1550-2376"]}, DOI={10.1103/physreve.83.041301}, abstractNote={Fluctuations of the local volume fraction within granular materials have previously been observed to decrease as the system approaches jamming. We experimentally examine the role of boundary conditions and interparticle friction $\ensuremath{\mu}$ on this relationship for a dense granular material of bidisperse particles driven under either constant volume or constant pressure. Using a radical Vorono\"{\i} tessellation, we find the variance of the local volume fraction $\ensuremath{\phi}$ monotonically decreases as the system becomes more dense, independent of boundary condition and $\ensuremath{\mu}$. We examine the universality and origins of this trend using experiments and the recent granocentric model [M. Clusel, E. I. Corwin, A. O. N. Siemens, and J. Bruji\ifmmode \acute{c}\else \'{c}\fi{}, Nature (London) 460, 611 (2009); E. I. Corwin, M. Clusel, A. O. N. Siemens, and J. Bruji\ifmmode \acute{c}\else \'{c}\fi{}, Soft Matter 6, 2949 (2010)], modified to draw particle locations from an arbitrary distribution $\mathcal{P}(s)$ of neighbor distances $s$. The mean and variance of the observed $\mathcal{P}(s)$ are described by a single length scale controlled by $\mathrm{\ensuremath{\phi}\ifmmode \bar{}\else \={}\fi{}}$. Through the granocentric model, we observe that diverse functional forms of $\mathcal{P}(s)$ all produce the trend of decreasing fluctuations, but only the experimentally observed $\mathcal{P}(s)$ provides quantitative agreement with the measured $\ensuremath{\phi}$ fluctuations. Thus, we find that both $\mathcal{P}(s)$ and $\mathcal{P}(\ensuremath{\phi})$ encode similar information about the ensemble of observed packings and are connected to each other by the local granocentric model.}, number={4}, journal={PHYSICAL REVIEW E}, author={Puckett, James G. and Lechenault, Frederic and Daniels, Karen E.}, year={2011}, month={Apr} }