報告題目: The response of jammed packings to thermal fluctuations

報告人：Prof. Corey O'Hern（Yale University）

報告時間：2018年5月3日15:00

報告地點：明故宮校區A18-526

主辦單位: 國際合作處、科協、機械結構力學及控制國家重點實驗室、航空宇航學院

報告摘要：

We focus on the response of mechanically stable (MS) packings of frictionless, bidisperse disks to thermal fluctuations, with the aim of quantifying how nonlinearities affect system properties at finite temperature. In contrast, numerous prior studies characterized the structural and mechanical properties of MS packings of frictionless spherical particles at zero temperature.  Packings of disks with purely repulsive contact interactions possess two main types of nonlinearities, one from the form of the interaction potential and one from the breaking (or forming) of interparticle contacts. To identify the temperature regime at which the contact-breaking nonlinearities begin to contribute, we first calculated the minimum temperatures required to break a single contact in the MS packing. We find that the temperature required to break a single contact for equal velocity-amplitude perturbations involving all eigenmodes approaches the minimum value obtained for a perturbation in the direction connecting disk pairs with the smallest overlap.  We then studied deviations in the constant volume specific heat and deviations of the average disk positions from their zero-temperature values. We find that the deviation in the specific heat per particle relative to the zero temperature value can grow rapidly above the temperature required to break a single contact, however, the deviation decreases with increasing system size. To characterize the relative strength of contact-breaking versus form nonlinearities, we measured the ratio of the average position deviations for single- and double-sided linear and nonlinear spring interactions.  We find relative position deviations that are larger than two orders of magnitude for linear spring interactions and independent of system size.  This result emphasizes that contact-breaking nonlinearities are dominant over form nonlinearities in the low temperature range for model jammed systems.

報告人簡介：

Professor Corey O’Hern joined the faculty of the School of Engineering and Applied Science at Yale with joint appointments in the Department of Mechanical Engineering & Materials Science (MEMS), Applied Physics, and Physics in July 2002 after postdoctoral fellowships in physics at the University of Chicago and the University of California, Los Angeles.  He received tenure at Yale in 2011 and became a full professor in 2018. The O’Hern research group tackles a broad range of fundamental questions in soft matter and biological physics using a combination of theoretical and computational techniques.  He has authored more than 100 manuscripts in peer-reviewed journals and given more than 150 seminars, colloquia, and presentations at universities and scientific meetings in the US and abroad. He has served in a number of leadership positions in the US soft matter research community, including the Chair of the Topical Group on Statistical and Nonlinear Physics of the American Physical Society.  In 2017, he was elected as a Fellow of the American Physical Society.