2,922 research outputs found
Measurement of spin-exchange rate constants between 129Xe and alkali metals
By measuring the relaxation rates of the nuclear spin polarization of Xe-129 in the presence of alkali-metal vapor at different densities, we have extracted the spin-exchange rates between Xe-129 and the three alkali metals K, Rb, and Cs. By studying the alkali-metal-Xe-129 spin-exchange rates as functions of the cell number density from 0.2 to 0.7 amagat, the binary collision and van der Waals molecular terms are separated, and constants governing both mechanisms are determined. The results from our work can be used to optimize the parameter space for polarizing Xe-129, a promising agent for magnetic resonance imaging and other applications
Stability of two-dimensional steady Euler flows with concentrated vorticity
In this paper, we study the stability two-dimensional (2D) steady Euler flows
with sharply concentrated vorticity in a simply-connected bounded domain. These
flows are obtained as maximizers of the kinetic energy subject to the
constraint that the vorticity is compactly supported in a finite number of
disjoint regions of small diameter. We prove the nonlinear stability of these
flows when the vorticity is concentrated in one small region, or in two small
regions with opposite signs. The proof is achieved by showing that these flows
constitute a compact and isolated set of local maximizers of the kinetic energy
on an isovortical surface. The separation property of the stream function plays
a crucial role in validating the isolatedness.Comment: 41 pages, proof of existence for multiple vortices was adde
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