8,034 research outputs found
Novel Method of Measuring Electron Positron Colliding Beam Parameters
Through the simultaneous measurement of the transverse size as a function of
longitudinal position, and the longitudinal distribution of luminosity, we are
able to measure the (vertical envelope function at the collision
point), vertical emittance, and bunch length of colliding beams at the Cornell
Electron-positron Storage Ring (CESR). This measurement is possible due to the
significant ``hourglass'' effect at CESR and the excellent tracking resolution
of the CLEO detector.Comment: 11 pages, 4 figures, submitted to NIM
Habitat conversion and global avian biodiversity loss
The magnitude of the impacts of human activities on global biodiversity has been documented at several organizational levels. However, although there have been numerous studies of the effects of local-scale changes in land use (e.g. logging) on the abundance of groups of organisms, broader continental or global-scale analyses addressing the same basic issues remain largely wanting. None the less, changing patterns of land use, associated with the appropriation of increasing proportions of net primary productivity by the human population, seem likely not simply to have reduced the diversity of life, but also to have reduced the carrying capacity of the environment in terms of the numbers of other organisms that it can sustain.
Here, we estimate the size of the existing global breeding bird population, and then make a first approximation as to how much this has been modified as a consequence of land-use changes wrought by human activities. Summing numbers across different land-use classes gives a best current estimate of a global population of less than 100 billion breeding bird individuals. Applying the same methodology to estimates of original land-use distributions suggests that conservatively this may represent a loss of between a fifth and a quarter of pre-agricultural bird numbers. This loss is shared across a range of temperate and tropical land-use types
Volume Comparison for Hypersurfaces in Lorentzian Manifolds and Singularity Theorems
We develop area and volume comparison theorems for the evolution of
spacelike, acausal, causally complete hypersurfaces in Lorentzian manifolds,
where one has a lower bound on the Ricci tensor along timelike curves, and an
upper bound on the mean curvature of the hypersurface. Using these results, we
give a new proof of Hawking's singularity theorem.Comment: 15 pages, LaTe
Single-Particle Diffusion-Coefficient on Surfaces with Ehrlich-Schwoebel-Barriers
The diffusion coefficient of single particles in the presence of
Ehrlich-Schwoebel barriers (ESB)is considered. An exact expression is given for
the diffusion coefficient on linear chains with random arrangements of ESB. The
results are extended to surfaces having ESB with uniform extension in one or
both directions. All results are verified by Monte Carlo simulations.Comment: 11 pages, LaTeX2e, 6 eps-figure
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