Energy Loss from a Moving Vortex in Superfluid Helium

We present measurements on both energy loss and pinning for a vortex terminating on the curved surface of a cylindrical container. We vary surface roughness, cell diameter, fluid velocity, and temperature. Although energy loss and pinning both arise from interactions between the vortex and the surface, their dependences on the experimental parameters differ, suggesting that different mechanisms govern the two effects. We propose that the energy loss stems from reconnections with a mesh of microscopic vortices that covers the cell wall, while pinning is dominated by other influences such as the local fluid velocity.Comment: 8 pages, 6 figure

Ray stability in weakly range-dependent sound channels

Ray stability is investigated in environments consisting of a range-independent background sound-speed profile on which a range-dependent perturbation, such as that produced by internal waves in deep ocean environments, is superimposed. Numerical results show that ray stability is strongly influenced by the background sound speed profile. Ray instability is shown to increase with increasing magnitude of alpha := I omega^{prime} / omega, where 2 pi / omega(I) is the range of a ray double loop and I is the ray action variable. The mechanism, shear-induced instability enhancement, by which alpha controls ray instability is described.Comment: To appear in JAS

THE SUPERMARKET INDUSTRY AT THE START OF THE 21st CENTURY: KEY FINDINGS FROM THE 2000 SUPERMARKET PANEL

The 2000 Supermarket Panel gathered data on store characteristics, management practices, and operating performance from a representative, nation-wide sample of supermarkets. The Panel is unique because the unit of analysis is the individual store, and the same stores will be surveyed over time. Linking information on management practices and store and market characteristics with measures for key performance measures provides useful information for both strategic and tactical decisions. Descriptive findings are presented for stores groups by ownership group size and format. Results from a multivariate analysis of relationships between store performance and key performance drivers also are presented.Agribusiness,

Tate Objects in Exact Categories

We study elementary Tate objects in an exact category. We characterize the category of elementary Tate objects as the smallest subcategory of admissible Ind-Pro objects which contains the categories of admissible Ind-objects and admissible Pro-objects, and which is closed under extensions. We compare Beilinson’s approach to Tate modules to Drinfeld’s. We establish several properties of the Sato Grassmannian of an elementary Tate object in an idempotent complete exact category (e.g., it is a directed poset). We conclude with a brief treatment of n-Tate modules and n-dimensional adèles. An appendix due to J. Šťovíček and J. Trlifaj identifies the category of flat Mittag-Leffler modules with the idempotent completion of the category of admissible Ind-objects in the category of finitely generated projective modules