Protocol Dependence and State Variables in the Force-Moment Ensemble

Condensed Matter journal club

Protocol Dependence and State Variables in the Force-Moment Ensemble

  • Event time: 11:30am until 12:30pm
  • Event date: 8th February 2019
  • Location: 2511

Event details

Stress-based ensembles incorporating temperaturelike variables have been proposed as a route to an equation of state for granular materials. To test the efficacy of this approach, we perform experiments on a two-dimensional photoelastic granular system under three loading conditions: uniaxial compression, biaxial compression, and simple shear. From the interparticle forces, we find that the distributions of the normal component of the coarse-grained force-moment tensor are exponential tailed, while the deviatoric component is Gaussian distributed. This implies that the correct stress-based statistical mechanics conserves both the force-moment tensor and the Maxwell-Cremona force-tiling area. As such, two variables of state arise: the tensorial angoricity (^α ) and a new temperaturelike quantity associated with the force-tile area which we name keramicity (κ ). Each quantity is observed to be inversely proportional to the global confining pressure; however, only κ exhibits the protocol independence expected of a state variable, while ^α behaves as a variable of process.►

Event resources

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