Vortex Stability in a Trapped Bose Condensate

A vortex in a trapped Bose-Einstein condensate can experience at least two types of instabilities. (1). Macroscopic hydrodynamic motion of the vortex core relative to the center of mass of the condensate requires some process to dissipate energy. (2). Microscopic small-amplitude normal modes can also induce an instability. In one specific example, the vortex core again moves relative to the overall center of mass, suggesting that there may be only a single physical mechanism.Comment: Latex, 6 pages, no figures, to appear in Proceedings of International Symposium on Quantum Fluids and Solids, 1998 (J. Low Temp. Phys.

Rotating vortex lattice in a Bose-Einstein condensate trapped in combined quadratic and quartic radial potentials

A dense vortex lattice in a rotating dilute Bose-Einstein condensate is studied with the Thomas-Fermi approximation. The upper critical angular velocity Omega_{c2} occurs when the intervortex separation b becomes comparable with the vortex core radius xi. For a radial harmonic trap, the loss of confinement as Omega approaches omega_perp implies a singular behavior. In contrast, an additional radial quartic potential provides a simple model for which Omega_{c2} is readily determined. Unlike the case of a type-II superconductor at fixed temperature, the onset of Omega_{c2} arises not only from decreasing b but also from increasing xi caused by the vanishing of the chemical potential as Omega approaches Omega_{c2}.Comment: 7 pages, 3 figures, accepted for publication in Physical Review

Electron capture rates in a plasma

A new general expression is derived for nuclear electron capture rates within dense plasmas. Its qualitative nature leads us to question some widely accepted assumptions about how to calculate the effects of the plasma on the rates. A perturbative evaluation, though not directly applicable to the strongly interacting case, appears to bear out these suspicions.Comment: 9 page

Energy and Vorticity in Fast Rotating Bose-Einstein Condensates

We study a rapidly rotating Bose-Einstein condensate confined to a finite trap in the framework of two-dimensional Gross-Pitaevskii theory in the strong coupling (Thomas-Fermi) limit. Denoting the coupling parameter by 1/\eps^2 and the rotational velocity by $\Omega$, we evaluate exactly the next to leading order contribution to the ground state energy in the parameter regime |\log\eps|\ll \Omega\ll 1/(\eps^2|\log\eps|) with \eps\to 0. While the TF energy includes only the contribution of the centrifugal forces the next order corresponds to a lattice of vortices whose density is proportional to the rotational velocity.Comment: 19 pages, LaTeX; typos corrected, clarifying remarks added, some rearrangements in the tex

Variation in Organic Standards Prior to the National Organic Program

Interest in establishing nationally uniform certification, labeling, and management standards for organic products grew out of concern that the existence of multiple standards led to consumer and supply chain confusion about, and lack of confidence in, these products. The National Organic Program Final Rule, issued in December 2000, is the result of this interest. We analyze the certification system that was in place prior to the new national rule to evaluate the extent of differences between certification standards and how the national rule is likely to impact the market for organic products. Our analysis suggests that most differences among US certification standards were minor. Also, the most important impacts of the national standard may be in facilitating trade in ingredients and products certified by different certifiers, increasing buyer confidence, and facilitating exports. However, the national rule may decrease the ability of organic certifiers and consumers to place differing emphasis on the multiple goals of organic production and may decrease the flexibility of organic standards to respond to changing market conditions, including new technologies.organic agriculture, organic certification standards, organic labeling, organic market, Agribusiness, Marketing,