101,028 research outputs found
Dirac zero-modes in compact U(1) gauge theory
We study properties of the zero and near-zero eigenmodes of the overlap Dirac
operator in compact U(1) gauge theory. In the confinement phase the exact
zero-modes are localized as found by studying the values of the inverse
participation ratio and other features. Non-zero-eigenmodes are less localized
in the confinement phase. In the Coulomb phase no zero-modes are observed and
the eigenmodes show no localization at all.Comment: Minor corrections, 15 pages, 5 figures, LaTeX styl
High-Dimensional Diffusive Growth
We consider a model of aggregation, both diffusion-limited and ballistic,
based on the Cayley tree. Growth is from the leaves of the tree towards the
root, leading to non-trivial screening and branch competition effects. The
model exhibits a phase transition between ballistic and diffusion-controlled
growth, with non-trivial corrections to cluster size at the critical point.
Even in the ballistic regime, cluster scaling is controlled by extremal
statistics due to the branching structure of the Cayley tree; it is the
extremal nature of the fluctuations that enables us to solve the model.Comment: 5 pages, 3 figures; reference adde
Defining, Valuing, and Providing Ecosystem Goods and Services
Ecosystem services are the specific results of ecosystem processes that either directly sustain or enhance human life (as does natural protection from the sun's harmful ultraviolet rays) or maintain the quality of ecosystem goods (as water purification maintains the quality of streamflow). "Ecosystem service" has come to represent several related topics ranging from the measurement to the marketing of ecosystem service flows. In this article we examine several of these topics by first clarifying the meaning of "ecosystem service" and then (1) placing ecosystem goods and services within an economic framework, emphasizing the role and limitations of substitutes; (2) summarizing the methods for valuation of ecosystem goods and services; and (3) reviewing the various approaches for their provision and financing.Many ecosystem services and some ecosystem goods are received without monetary payment. The "marketing" of ecosystem goods and services is basically an effort to turn such recipients - those who benefit without ownership- into buyers, thereby providing market signals that serve to help protect valuable goods and services. We review various formal arrangements for making this happen
A consumer's guide to regional economic multipliers
Regional economics ; Multiplier (Economics)
Have federal spending and taxation contributed to the divergence of state per capita incomes in the 1980s?
Taxation ; Income
Development of a comprehensive software engineering environment
The generation of a set of tools for software lifecycle is a recurring theme in the software engineering literature. The development of such tools and their integration into a software development environment is a difficult task because of the magnitude (number of variables) and the complexity (combinatorics) of the software lifecycle process. An initial development of a global approach was initiated in 1982 as the Software Development Workbench (SDW). Continuing efforts focus on tool development, tool integration, human interfacing, data dictionaries, and testing algorithms. Current efforts are emphasizing natural language interfaces, expert system software development associates and distributed environments with Ada as the target language. The current implementation of the SDW is on a VAX-11/780. Other software development tools are being networked through engineering workstations
Crossover to Potential Energy Landscape Dominated Dynamics in a Model Glass-forming Liquid
An equilibrated model glass-forming liquid is studied by mapping successive
configurations produced by molecular dynamics simulation onto a time series of
inherent structures (local minima in the potential energy). Using this
``inherent dynamics'' approach we find direct numerical evidence for the long
held view that below a crossover temperature, , the liquid's dynamics can
be separated into (i) vibrations around inherent structures and (ii)
transitions between inherent structures (M. Goldstein, J. Chem. Phys. {\bf 51},
3728 (1969)), i.e., the dynamics become ``dominated'' by the potential energy
landscape. In agreement with previous proposals, we find that is within
the vicinity of the mode-coupling critical temperature . We further find
that at the lowest temperature simulated (close to ), transitions between
inherent structures involve cooperative, string like rearrangements of groups
of particles moving distances substantially smaller than the average
interparticle distance.Comment: Expanded from 4 to 7 page
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