2,870 research outputs found
Quantum graph as a quantum spectral filter
We study the transmission of a quantum particle along a straight
input--output line to which a graph is attached at a point. In the
point of contact we impose a singularity represented by a certain properly
chosen scale-invariant coupling with a coupling parameter . We show
that the probability of transmission along the line as a function of the
particle energy tends to the indicator function of the energy spectrum of
as . This effect can be used for a spectral analysis
of the given graph . Its applications include a control of a
transmission along the line and spectral filtering. The result is illustrated
with an example where is a loop exposed to a magnetic field. Two more
quantum devices are designed using other special scale-invariant vertex
couplings. They can serve as a band-stop filter and as a spectral separator,
respectively.Comment: 15 pages, 8 figures. Copyright (2013) American Institute of Physics.
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Discovery of Reflection Nebulosity Around Five Vega-like Stars
Coronagraphic optical observations of six Vega-like stars reveal reflection
nebulosities, five of which were previously unknown. The nebulosities
illuminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemble
that of the Pleiades, indicating an interstellar origin for dust grains. The
reflection nebulosity around HD 123160 has a double-arm morphology, but no
disk-like feature is seen as close as 2.5 arcsec from the star in K-band
adaptive optics data. We demonstrate that uniform density dust clouds
surrounding HD 23362, HD 23680 and HD 123160 can account for the observed
12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD
49662 an additional emission source, such as from a circumstellar disk or
non-equilibrium grain heating, is required to fit the 12-25 micron data. These
results indicate that in some cases, particularly for Vega-like stars located
beyond the Local Bubble (>100 pc), the dust responsible for excess thermal
emission may originate from the interstellar medium rather than from a
planetary debris system.Comment: The Astrophysical Journal, in press for March, 2002 (32 pages, 13
figures
Geochemistry of volcanic rocks from the Wawa greenstone belt
The Wawa greenstone belt is located in the District of Algoma and extends east-northeast from Lake Superior to the western part of the Sudbury District in Ontario, Canada. Recent mapping by Attoh has shown that an unconformity at the base of the Dore' Formation and equivalent sedimentary rocks marks a significant stratigraphic break which can be traced throughout the volcanic belt. This break has been used to subdivide the volcanic-sedimentary into pre- and post-Dore' sequences. The pre-Dore' sequence includes at least two cycles of mafic-to-felsic volcanism, each capped by an iron-formation unit. The post-Dore' sequence includes an older mafic-to-felsic unit, which directly overlies sedimentary rocks correlated with the Dore' Formation, and a younger felsic breccia unit interpreted to have formed as debris flows from a felsic volcanic center. In the present study, samples of both the pre-and post-Dore' volcanic sequences were analyzed for major and trace elements, incuding rare earths (REE). This preliminary study is part of an ongoing program to assess the petrogenesis of the volcanic rocks of the Wawa greenstone belt
Rhyolitic components of the Michipicoten greenstone belt, Ontario: Evidence for late Archaen intracontinental rifts or convergent plate margins in the Canadian Shield?
Rhyolitic rocks often are the dominant felsic end member of the biomodal volcanic suites that characterize many late Archean greenstone belts of the Canadian Shield. The rhyolites primarily are pyroclastic flows (ash flow tuffs) emplaced following plinian eruptions, although deposits formed by laval flows and phreatomagmatic eruptions also are presented. Based both on measured tectono-stratigraphic sections and provenance studies of greenstone belt sedimentary sequences, the rhyolites are believed to have been equal in abundance to associated basaltic rocks. In many recent discussions of the tectonic setting of late Archean Canadian greenstone belts, rhyolites have been interpreted as products of intracontinental rifting . A study of the tectono-stratigraphic relationships, rock associations and chemical characteristics of the particularly ell-exposed late Archean rhyolites of the Michipicoten greenstone belt, suggests that convergent plate margin models are more appropriate
Four new and five overlooked records of vascular plants from high elevation puna grasslands of the southern Peruvian Andes
Area Potentials and Deformation Quantization
Systems built out of N-body interactions, beyond 2-body interactions, are
formulated on the plane, and investigated classically and quantum mechanically
(in phase space). Their Wigner Functions--the density matrices in phase-space
quantization--are given and analyzed.Comment: LaTeX, 7 page
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