Stochastic Methods for Slip Detection in a Sheared Granular System

We develop a flexible methodology for predicting slip events in a sheared granular system. The considered system consists of two-dimensional soft disks between two rigid horizontal walls, where the top wall is exposed to downward pressure and horizontal elastic shearing force, resulting in intermittent stick-slip regimes. The prediction methodology first uses topological data analysis to compute the persistent homology between successive force networks of the system and then quantifies the topological change by placing a metric between the respective persistence diagrams, resulting in a time series. Next, we construct a Bayesian stochastic state space model, which describes the behavior of the time series during the stick regime. We also create similar models for the stick regime behavior of the time series of more traditional measures on the granular system. A model identifies departure from the stick regime by detecting when the predictive error exceeds a specified threshold. The resulting detections demonstrate that this approach can detect the slip events in advance, with further investigation revealing a rough sequence of events. First, a local change appears in the force network and either dissipates or spreads globally. Next, the global change either triggers a slip event or a much smaller ‘micro-slip,’ depending on if its magnitude exceeds a critical threshold

Stochastic methods for slip prediction in a sheared granular system

We consider a sheared granular system experiencing intermittent dynamics of stick-slip type via discrete element simulations. The considered setup consists of a two-dimensional system of soft frictional particles sandwiched between solid walls, one of which is exposed to a shearing force. The slip events are detected using stochastic state space models applied to various measures describing the system. We show that the measures describing the forces between the particles provide earlier detection of an upcoming slip event than the measures based solely on the wall movement. By comparing the detection times obtained from the considered measures, we observe that a typical slip event starts with a local change in the force network. However, some local changes do not spread globally over the force network. For the changes that become global, we find a sharp critical value for their size. If the size of a global change exceeds the critical value, then it triggers a slip event; if it does not, then a much weaker micro-slip follows. Quantification of the changes in the force network is made possible by formulating clear and precise measures describing their static and dynamic properties.Comment: 14 pages, 13 figure

Hybrid cosmic ray measurements using the IceAct telescopes in coincidence with the IceCube and IceTop detectors

IceAct is a proposed surface array of compact (50 cm diameter) and cost-effective Imaging Air Cherenkov Telescopes installed at the site of the IceCube Neutrino Observatory at the geographic South Pole. Since January 2019, two IceAct telescope demonstrators, featuring 61 silicon photomultiplier (SiPM) pixels have been taking data in the center of the IceTop surface array during the austral winter. We present the first analysis of hybrid cosmic ray events detected by the IceAct imaging air-Cherenkov telescopes in coincidence with the IceCube Neutrino Observatory, including the IceTop surface array and the IceCube in-ice array. By featuring an energy threshold of about 10 TeV and a wide field-of-view, the IceAct telescopes show promising capabilities of improving current cosmic ray composition studies: measuring the Cherenkov light emissions in the atmosphere adds new information about the shower development not accessible with the current detectors, enabling significantly better primary particle type discrimination on a statistical basis. The hybrid measurement also allows for detailed feasibility studies of detector cross-calibration and of cosmic ray veto capabilities for neutrino analyses. We present the performance of the telescopes, the results from the analysis of two years of data, and an outlook of a hybrid simulation for a future telescope array