443 research outputs found
Epidemiological studies on radiation carcinogenesis in human populations following acute exposure: nuclear explosions and medical radiation.
The present review provides an understanding of our current knowledge of the carcinogenic effect of low-dose radiation in man, and surveys the epidemiological studies of human populations exposed to nuclear explosions and medical radiation. Discussion centers on the contributions of quantitative epidemiology to present knowledge, the reliability of the dose-incidence data, and those relevant epidemiological studies that provide the most useful information for risk estimation of cancer induction in man. Reference is made to dose-incidence relationships from laboratory animal experiments where they may obtain, for problems and difficulties in extrapolation from data obtained at high doses to low doses, and from animal data to the human situation. The paper describes the methods of application of such epidemiological data for estimation of excess risk of radiation-induced cancer in exposed human populations and discusses the strengths and limitations of epidemiology in guiding radiation protection philosophy and public health policy
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Geovisualization of dynamics, movement and change: key issues and developing approaches in visualization research
Enhancement of the Benjamin-Feir instability with dissipation
It is shown that there is an overlooked mechanism whereby some kinds of
dissipation can enhance the Benjamin-Feir instability of water waves. This
observation is new, and although it is counterintuitive, it is due to the fact
that the Benjamin-Feir instability involves the collision of modes with
opposite energy sign (relative to the carrier wave), and it is the negative
energy perturbations which are enhanced.Comment: 15 pages, 2 figures To download more papers, go to
http://www.cmla.ens-cachan.fr/~dias. Physics of Fluids (2007) to appea
Scale Invariance in Road Networks
We study the topological and geographic structure of the national road
networks of the United States, England and Denmark. By transforming these
networks into their dual representation, where roads are vertices and an edge
connects two vertices if the corresponding roads ever intersect, we show that
they exhibit both topological and geographic scale invariance. That is, we show
that for sufficiently large geographic areas, the dual degree distribution
follows a power law with exponent 2.2 < alpha < 2.4, and that journeys,
regardless of their length, have a largely identical structure. To explain
these properties, we introduce and analyze a simple fractal model of road
placement that reproduces the observed structure, and suggests a testable
connection between the scaling exponent alpha and the fractal dimensions
governing the placement of roads and intersections.Comment: 6 pages, 10 figures; revision incorporates more rigorous statistical
analyses; matches journal versio
Active feedback scheme for minimization of helicity-dependent instrumental asymmetries
A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5
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