Abstract

The motion of a body through a superfluid can generate phenomena distinct from a normal viscous fluid. This includes the absence of drag below a critical body speed with the shedding of quantized vortices and non-zero drag above this speed. In this talk, the speaker will investigate the drag experienced by a penetrable circular disk that is moving in a superfluid described by the Gross-Pitaevksii equation. Using analytical theory and numerical simulations, he will show that the drag varies non-monotonically with the disk velocity, leading to complex dynamical behavior. These results advance understanding of the motion of bodies with finite penetrability, which is relevant to laser experiments probing the superfluidity of Bose-Einstein condensates. 

About the Speaker

Prof. John E. SADER gained his PhD from the University of New South Wales in Electrical Engineering and then joined the University of Melbourne in 1992 as a Research Fellow, progressing to Professor of Applied Mathematics before moving to the California Institute of Technology in 2022 as a Research Professor of Aerospace and Applied Physics. In 2026, he was also appointed Program Director for Research in the Physical Sciences at the W. M. Keck Foundation.

Prof. Sader is an applied mathematician with over 30 years of experience in collaborative research that have focused on a broad range of areas, including fluid and solid mechanics, colloid science, plasmonics, and advanced scientific instrumentation. He is perhaps best known for developing experimental techniques that are widely used in atomic force microscopy, including the Sader Method which is implemented in commercial instruments. He is elected to Fellow of the American Physical Society, the Australian Academy of Science, the Australian Mathematical Society, and the Australasian Fluid Mechanics Society.

For Attendees' Attention

Seating is on a first come, first served basis.