42 research outputs found
Optimal error estimation for H(curl)-conforming p-interpolation in two dimensions
In this paper we prove an optimal error estimate for the H(curl)-conforming
projection based p-interpolation operator introduced in [L. Demkowicz and I.
Babuska, p interpolation error estimates for edge finite elements of variable
order in two dimensions, SIAM J. Numer. Anal., 41 (2003), pp. 1195-1208]. This
result is proved on the reference element (either triangle or square) K for
regular vector fields in H^r(curl,K) with arbitrary r>0. The formulation of the
result in the H(div)-conforming setting, which is relevant for the analysis of
high-order boundary element approximations for Maxwell's equations, is provided
as well
Universal Spin Transport in a Strongly Interacting Fermi Gas
Transport of fermions is central in many elds of physics. Electron transport runs modern technology,
de ning states of matter such as superconductors and insulators, and electron spin, rather
than charge, is being explored as a new carrier of information [1]. Neutrino transport energizes
supernova explosions following the collapse of a dying star [2], and hydrodynamic transport of the
quark-gluon plasma governed the expansion of the early Universe [3]. However, our understanding
of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold
gases of fermionic atoms realize a pristine model for such systems and can be studied in real time
with the precision of atomic physics [4, 5]. It has been established that even above the super
uid
transition such gases
ow as an almost perfect
uid with very low viscosity [3, 6] when interactions
are tuned to a scattering resonance. However, here we show that spin currents, as opposed to
mass currents, are maximally damped, and that interactions can be strong enough to reverse spin
currents, with opposite spin components reflecting off each other. We determine the spin drag coefficient, the spin di usivity, and the spin susceptibility, as a function of temperature on resonance and
show that they obey universal laws at high temperatures. At low temperatures, the spin di usivity
approaches a minimum value set by ħ/m, the quantum limit of di usion, where ħ is the reduced
Planck's constant and m the atomic mass. For repulsive interactions, our measurements appear to
exclude a metastable ferromagnetic state [7{9].National Science Foundation (U.S.)United States. Office of Naval ResearchUnited States. Army Research Office (DARPA OLE programme)Alfred P. Sloan FoundationUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeUnited States. Army Research Office. Multidisciplinary University Research InitiativeUnited States. Defense Advanced Research Projects Agency. Young Faculty AwardDavid & Lucile Packard Foundatio