In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any nonzero temperature gradient. We study analogous instabilities in degenerate collisional plasmas, i.e., when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residua...

We prove Calegari’s conjecture that every quasigeodesic flow on a closed hyperbolic 3-manifold has closed orbits.

We show that the multi-commodity max-flow/min-cut gap for series-parallel graphs can be as bad as 2, matching a recent upper bound [8] for this class, and resolving one side of a conjecture of Gupta, Newman, Rabinovich, and Sinclair. This also improves the largest known gap for planar graphs from 32 to 2, yielding the first lower bound that doesn’t follow from elementary calculations. Our appro...

Effective navigation and locomotion depend critically on an observer's ability to judge direction of linear self-motion, i.e., heading. The vestibular cue to heading is the direction of inertial acceleration that accompanies transient linear movements. This cue is transduced by the otolith organs. The otoliths also respond to gravitational acceleration, so vestibular heading discrimination coul...

Dissipative Particle Dynamics (DPD) simulations of wall-bounded flows exhibit density fluctuations that depend strongly on the no-slip boundary condition and increase with the level of coarse graining. We develop an adaptive model for wall-particle interactions that eliminates such oscillations and can target prescribed density profiles. Comparisons are made with ideal no-slip boundary conditio...