6,795 research outputs found
USGS/NOAA Workshop on Mycobacteriosis in Striped Bass, May 7-10, 2006, Annapolis, Maryland
As a Federal trust species, the well-being of the striped bass (Morone saxatilis) population along the Eastern Seaboard is of major concern to resource users. Striped bass are an extremely valuable commercial and recreational resource. As a principal piscivore in Chesapeake Bay, striped bass directly or indirectly interact with multiple trophic levels within the ecosystem and are therefore very sensitive to biotic and abiotic ecosystem changes. For reasons that have yet to be defined, the species has a high intrinsic susceptibility to mycobacteriosis. This disease has been impacting Chesapeake Bay striped bass since at least the 1980s as indicated by archived tissue samples. However, it was not until heightened incidences of fish with skin lesions in the Pocomoke River and other tributaries of the Chesapeake Bay were reported in the summer and fall of 1996 and 1997 that a great deal of public and scientific interest was stimulated about concerns for fish disease in the Bay. (PDF contains 50 pages
Work function and surface stability of tungsten-based thermionic electron emission cathodes
Materials that exhibit a low work function and therefore easily emit
electrons into vacuum form the basis of electronic devices used in applications
ranging from satellite communications to thermionic energy conversion. W-Ba-O
is the canonical materials system that functions as the thermionic electron
emitter used commercially in a range of high power electron devices. However,
the work functions, surface stability, and kinetic characteristics of a
polycrystalline W emitter surface are still not well understood or
characterized. In this study, we examined the work function and surface
stability of the eight lowest index surfaces of the W-Ba-O system using Density
Functional Theory methods. We found that under the typical thermionic cathode
operating conditions of high temperature and low oxygen partial pressure, the
most stable surface adsorbates are Ba-O species with compositions in the range
of Ba0.125O to Ba0.25O per surface W atom, with O passivating all dangling W
bonds and Ba creating work function-lowering surface dipoles. Wulff
construction analysis reveals that the presence of O and Ba significantly
alters the surface energetics and changes the proportions of surface facets
present under equilibrium conditions. Analysis of previously published data on
W sintering kinetics suggests that fine W particles in the size range of
100-500 nm may be at or near equilibrium during cathode synthesis, and thus may
exhibit surface orientation fractions well-described by the calculated Wulff
construction
Configuration of the Crucial Set for a Quadratic Rational Map
Let be a complete, algebraically closed non-archimedean valued field, and
let have degree two. We describe the crucial set of
in terms of the multipliers of at the classical fixed
points, and use this to show that the crucial set determines a stratification
of the moduli space related to the reduction type of
. We apply this to settle a special case of a conjecture of Hsia
regarding the density of repelling periodic points in the non-archimedean Julia
set
Perverse performances by skilful liars : Shakespeare\u27s lago and Mamet\u27s Billy and Mike
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