154,128 research outputs found
Front Propagation in Evanescent Media
We investigate the time evolution of waves in evanescent media generated by a
source within this medium and observed at some distance away from the location
of the source. The aim is to find a velocity which describes a causal process
and is thus, for a medium with relativistic dispersion, limited by the velocity
of light. The wave function consists of a broad frequency forerunner generated
by the onset of the source, and of a monochromatic front which carries the
oscillation frequency of the source. For a medium with Schr\"{o}dinger-like
dispersion the monochromatic front propagates with a velocity which is in
agreement with the traversal time, and in the relativistic case the velocity of
the fronts is limited by the velocity of light. For sources with a sharp onset,
the forerunners are not attenuated and in magnitude far exceed the
monochromatic front. In contrast, for sources which are frequency-band limited,
the forerunners are also attenuated and become comparable to the monochromatic
front: like in the propagating case, there exists a time at which a broad
frequency forerunner is augmented by a monochromatic wave
His+ reversions Caused in Salmonella typhimurium by different types of ionizing radiation
The yield of his+ reversions in the Ames Salmonella tester strain TA2638 has been determined for 60Co γ rays, 140 kV X rays, 5.4 keV characteristic X rays, 2.2 MeV protons, 3.1 MeV α particles, and 18 MeV/U Fe ions. Inactivation studies were performed with the same radiations. For both mutation and inactivation, the maximum effectiveness per unit absorbed dose was obtained for the characteristic X rays, which have a dose averaged linear energy transfer (LET) of roughly 10 keV/μm. The ratio of the effectiveness of this radiation to γ rays was 2 for inactivation and about 1.4 for the his+ reversion. For both end points the effectiveness decreases substantially at high LET, i.e., for the α particles and the Fe ions. The composition of the bottom and the top agar was the one recommended by Maron and Ames [Mutat. Res. 113, 173-215 (1983)] for application in chemical mutagenicity tests. The experiments with the less penetrating radiations differed from the usual protocol by utilization of a technique of plating the bacteria on the surface of the top agar. As in an earlier study [Roos et al., Radiat. Res. 104, 102-108 (1985)] greatly enhanced yields of mutations, relative to the spontaneous reversion rate, were obtained in these experiments by performing the irradiations 6 h after plating, which differs from the conventional procedure to irradiate the bacteria shortly after plating
Dust interferometers in plasmas
An interferometric imaging technique has been proposed to instantly measure
the diameter of individual spherical dust particles suspended in a gas
discharge plasma. The technique is based on the defocused image analysis of
both spherical particles and their binary agglomerates. Above a critical
diameter, the defocused images of spherical particles contain stationary
interference fringe patterns and the fringe number increases with particle
diameters. Below this critical diameter, the particle size has been measured
using the rotational interference fringe patterns which appear only on the
defocused images of binary agglomerates. In this case, a lower cut-off limit of
particle diameter has been predicted, below which no such rotational fringe
patterns are observed for the binary agglomerates. The method can be useful as
a diagnostics for complex plasma experiments on earth as well as under
microgravity condition
Effect of Auto Plant Openings on Net Migration in the Auto Corridor, 1980-1997
In linking demographic trends of the last two decades to the geographic dispersion of the auto industry, this article finds that the addition of a large plant significantly influences the migration experience of the host county as well as counties adjacent to it
Synthesis of Telechelic Polyisoprene via Ring-Opening Metathesis Polymerization in the Presence of Chain Transfer Agent
Telechelic polyisoprene was synthesized via the ring-opening metathesis polymerization (ROMP) of 1,5-dimethyl-1,5-cyclooctadiene (DMCOD) in the presence of cis-1,4-diacetoxy-2-butene as a chain transfer agent (CTA). This method afforded telechelic polymer in excellent yield, and the acetoxy groups were successfully removed to yield α,ω-hydroxy end-functionalized polyisoprene with potential for subsequent reactions. Efficient, quantitative incorporation of CTA was achieved, and NMR spectroscopy was utilized to confirm the chemical identity of the polymer end groups. Polymerization of discrete DMCOD monomer generated polyisoprene with excellent regioregularity in the polymer backbone. Successful ROMP of sterically challenging DMCOD in the presence of a CTA for chain end-functionalization was borne out through screening of a variety of Ru-based olefin metathesis catalysts
Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates
A new type of quasi-two-dimensional complex plasma system was observed which
consisted of monodisperse microspheres and their binary agglomerations
(dimers). The particles and their dimers levitated in a plasma sheath at
slightly different heights and formed two distinct sublayers. The sys- tem did
not crystallize and may be characterized as disordered solid. The dimers were
identified based on their characteristic appearance in defocused images, i.e.,
rotating interference fringe pat- terns. The in-plane and inter-plane particle
separations exhibit nonmonotonic dependence on the discharge pressure which
agrees well with theoretical predictions
Synthesis of improved feeds for large circular paraboloids
Synthesis of low-noise feeds for large circular paraboloids using hybrid modes propagated in cylindrical waveguides - antenna field pattern
Cold dilute neutron matter on the lattice I: Lattice virial coefficients and large scattering lengths
We study cold dilute neutron matter on the lattice using an effective field
theory. We work in the unitary limit in which the scattering length is much
larger than the interparticle spacing. In this paper we focus on the equation
of state at temperatures above the Fermi temperature and compare lattice
simulations to the virial expansion on the lattice and in the continuum. We
find that in the unitary limit lattice discretization errors in the second
virial coefficient are significantly enhanced. As a consequence the equation of
state does not show the universal scaling behavior expected in the unitary
limit. We suggest that scaling can be improved by tuning the second virial
coefficient rather than the scattering length.Comment: 17 pages, 12 figure
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