Macroscopic theory of cavitation

Speaker: 

V. Shneidman

Institution: 

New Jersey Institute of Technology

Time: 

Tuesday, October 2, 2018 - 2:00pm

Location: 

rh 340p

The classical description of nucleation of cavities in a stretched fluid relies on a one-dimensional Fokker-Planck equation (FPE) in the space of their sizes, with the diffusion coefficient  constructed from macroscopic hydrodynamics and thermodynamics, as shown by Zeldovich. When additional variables (e.g., vapor pressure) are required to describe the state of a bubble, a similar approach to construct a diffusion tensor  generally works only in the direct vicinity of the thermodynamic saddle point corresponding to the critical nucleus. We show, nevertheless, that “proper” kinetic variables to describe a cavity can be selected, allowing to introduce a diffusion tensor in the entire domain of parameters. In this way, for the first time, complete FPE’s are constructed for viscous volatile and inertial fluids. 

Bright solitons in an optical lattice

Speaker: 

M. Olshanii

Institution: 

U Mass Boston

Time: 

Thursday, September 20, 2018 - 2:00pm

Location: 

rh 306

We discuss ultracold atomic gas with attractive interactions in a one-dimensional optical lattice. We find that its excitation spectrum displays a quantum soliton band, corresponding to N-particle bound states, and a continuum band of other, mostly extended, states. For a system of a finite size, the two branches are degenerate in energy for weak interactions, while a gap opens above a threshold value for the interaction strength. We find that the interplay between degenerate extended and bound states has important consequences for both static and dynamical properties of the system.

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