1,919 research outputs found
Asymptotic Series and Precocious Scaling
Some of the basic concepts regarding asymptotic series are reviewed. A heuristic proof is given that the divergent QCD perturbation series is asymptotic. By treating it as an asymptotic expansion we show that it makes sense to keep only the first few terms. The example of e^+e^- annihilation is considered. It is shown that by keeping only the first few terms one can get within a per cent (or smaller) of the complete sum of the series even at very low momenta where the coupling is large. More generally, this affords an explanation of the phenomena of precocious scaling and why keeping only leading order corrections generally works so well
Predicting Whole Forest Structure, Primary Productivity, and Biomass Density From Maximum Tree Size and Resource Limitations
In the face of uncertain biological response to climate change and the many
critiques concerning model complexity it is increasingly important to develop
predictive mechanistic frameworks that capture the dominant features of
ecological communities and their dependencies on environmental factors. This is
particularly important for critical global processes such as biomass changes,
carbon export, and biogenic climate feedback. Past efforts have successfully
understood a broad spectrum of plant and community traits across a range of
biological diversity and body size, including tree size distributions and
maximum tree height, from mechanical, hydrodynamic, and resource constraints.
Recently it was shown that global scaling relationships for net primary
productivity are correlated with local meteorology and the overall biomass
density within a forest. Along with previous efforts, this highlights the
connection between widely observed allometric relationships and predictive
ecology. An emerging goal of ecological theory is to gain maximum predictive
power with the least number of parameters. Here we show that the explicit
dependence of such critical quantities can be systematically predicted knowing
just the size of the largest tree. This is supported by data showing that
forests converge to our predictions as they mature. Since maximum tree size can
be calculated from local meteorology this provides a general framework for
predicting the generic structure of forests from local environmental parameters
thereby addressing a range of critical Earth-system questions.Comment: 26 pages, 4 figures, 1 Tabl
A New Approach to y-scaling and the Universal Features of Scaling Functions and Nucleon Momentum Distributions
Some systematic general features of y-scaling structure functions, which are
essentially independent of detailed dynamics, are pointed out. Their physical
interpretation in terms of general characteristics, such as a mean field
description and nucleon-nucleon correlations, is given and their relationship
to the momentum distributions illustrated. A new relativistic scaling variable
is proposed which incorporates the momentum dependence of the excitation energy
of the (A-1) system, with the resulting scaling function being closely related
to the longitudinal momemtum distributions and being free from removal-energy
scaling violating effects.Comment: 17 pages, RevTeX, 4 ps Figures, to appear in Physics Letters
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