950 research outputs found
Tree Recruitment Limitation by Introduced Snowshoe Hares, Lepus americanus, on Kent Island, New Brunswick
Species introductions often have negative consequences for native plant and animal communities of islands. Herbivores introduced to islands lacking predators can attain high population densities and alter native plant communities by selective consumption of palatable plants. We examined the legacy of the 1959 introduction of Snowshoe Hares (Lepus americanus) to Kent Island, New Brunswick, by reconstructing a history of tree recruitment on Kent Island and on nearby Outer Wood Island, which lacks Snowshoe Hares. Tree-ring records show pronounced recruitment peaks associated with farm abandonment in the 1930s for Kent Island and in the 1950s for Outer Wood Island. Following the introduction of Snowshoe Hares to Kent Island, tree recruitment plummeted and has remained low ever since. In contrast, trees continued to establish throughout the latter 20th century on Outer Wood Island. The high rates of seedling mortality on Kent Island associated with Snowshoe Hare browsing coupled with high rates of canopy tree mortality threaten to degrade severely the forest of this important seabird nesting sanctuary
Transient Response of the Induction Coil Loading in the Initial Startup Phase of rf Indiction Thermal Plasmas
Development of an intense positron source using a crystal--amorphous hybrid target for linear colliders
In a conventional positron source driven by a few GeV electron beam, a high
amount of heat is loaded into a positron converter target to generate intense
positrons required by linear colliders, and which would eventually damage the
converter target. A hybrid target, composed of a single crystal target as a
radiator of intense gamma--rays, and an amorphous converter target placed
downstream of the crystal, was proposed as a scheme which could overcome the
problem.This paper describes the development of an intense positron source with
the hybrid target. A series of experiments on positron generation with the
hybrid target has been carried out with a 8--GeV electron beam at the KEKB
linac. We observed that positron yield from the hybrid target increased when
the incident electron beam was aligned to the crystal axis and exceeded the one
from the conventional target with the converter target of the same thickness,
when its thickness is less than about 2 radiation length. The measurements in
the temperature rise of the amorphous converter target was successfully carried
out by use of thermocouples. These results lead to establishment to the
evaluation of the hybrid target as an intense positron source.Comment: 17pages, 10figure
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