3,674 research outputs found
Gauss Sums and Quantum Mechanics
By adapting Feynman's sum over paths method to a quantum mechanical system
whose phase space is a torus, a new proof of the Landsberg-Schaar identity for
quadratic Gauss sums is given. In contrast to existing non-elementary proofs,
which use infinite sums and a limiting process or contour integration, only
finite sums are involved. The toroidal nature of the classical phase space
leads to discrete position and momentum, and hence discrete time. The
corresponding `path integrals' are finite sums whose normalisations are derived
and which are shown to intertwine cyclicity and discreteness to give a finite
version of Kelvin's method of images.Comment: 14 pages, LaTe
The Zel'dovich effect and evolution of atomic Rydberg spectra along the Periodic Table
In 1959 Ya. B. Zel'dovich predicted that the bound-state spectrum of the
non-relativistic Coulomb problem distorted at small distances by a short-range
potential undergoes a peculiar reconstruction whenever this potential alone
supports a low-energy scattering resonance. However documented experimental
evidence of this effect has been lacking. Previous theoretical studies of this
phenomenon were confined to the regime where the range of the short-ranged
potential is much smaller than Bohr's radius of the Coulomb field. We go beyond
this limitation by restricting ourselves to highly-excited s states. This
allows us to demonstrate that along the Periodic Table of elements the
Zel'dovich effect manifests itself as systematic periodic variation of the
Rydberg spectra with a period proportional to the cubic root of the atomic
number. This dependence, which is supported by analysis of experimental and
numerical data, has its origin in the binding properties of the ionic core of
the atom.Comment: 17 pages, 12 figure
Interface states in junctions of two semiconductors with intersecting dispersion curves
A novel type of shallow interface state in junctions of two semiconductors
without band inversion is identified within the envelope function
approximation, using the two-band model. It occurs in abrupt junctions when the
interband velocity matrix elements of the two semiconductors differ and the
bulk dispersion curves intersect. The in-plane dispersion of the interface
state is found to be confined to a finite range of momenta centered around the
point of intersection. These states turn out to exist also in graded junctions,
with essentially the same properties as in the abrupt case.Comment: 1 figur
Excitation of propagating spin waves with global uniform microwave fields
Copyright © 2011 American Institute of PhysicsWe demonstrate a magnonic architecture that converts global free-space uniform microwaves into spin waves propagating in a stripe magnonic waveguide. The architecture is based upon dispersion mismatch between the narrow magnonic waveguide and a wide "antenna" patch, both patterned from the same magnetic film. The spin waves injected into the waveguide travel to distances as large as several tens of micrometers. The antennas can be placed at multiple positions on a magnonic chip and used to excite mutually coherent multiple spin waves for magnonic logic operations. This demonstration paves way for "magnonics" to become a pervasive technology for information processing
Enhancement of spontaneous and stimulated emission of a rhodamine 6G dye by an Ag aggregate
We have demonstrated that by adding the solution of aggregated silver nanoparticles to the solution of rhodamine 6G dye, one can enhance the efficiency of spontaneous and stimulated emission. We attribute an increase of the spontaneous emission intensity of dye to the increase of the absorption efficiency caused by the field enhancements in metallic nanostructures associated with surface plasmons. The enhancement of the stimulated emission of dye, which has the same nature as the enhancement of absorption, was observed in the pump-probe and laser experiments
Tight-binding study of interface states in semiconductor heterojunctions
Localized interface states in abrupt semiconductor heterojunctions are
studied within a tight-binding model. The intention is to provide a microscopic
foundation for the results of similar studies which were based upon the
two-band model within the envelope function approximation. In a two-dimensional
description, the tight-binding Hamiltonian is constructed such that the
Dirac-like bulk spectrum of the two-band model is recovered in the continuum
limit. Localized states in heterojunctions are shown to occur under conditions
equivalent to those of the two-band model. In particular, shallow interface
states are identified in non-inverted junctions with intersecting bulk
dispersion curves. As a specific example, the GaSb-AlSb heterojunction is
considered. The matching conditions of the envelope function approximation are
analyzed within the tight-binding description.Comment: RevTeX, 11 pages, 3 figures, to appear in Phys. Rev.
Development of the MESH modelling system for hydrological ensemble forecasting of the Laurentian Great Lakes at the regional scale
International audienceEnvironment Canada has been developing a community environmental modelling system (Modélisation Environmentale Communautaire ? MEC), which is designed to facilitate coupling between models focusing on different components of the earth system. The ultimate objective of MEC is to use the coupled models to produce operational forecasts. MESH (MEC ? Surface and Hydrology), a configuration of MEC currently under development, is specialized for coupled land-surface and hydrological models. To determine the specific requirements for MESH, its different components were implemented on the Laurentian Great Lakes watershed, situated on the Canada-US border. This experiment showed that MESH can help us better understand the behaviour of different land-surface models, test different schemes for producing ensemble streamflow forecasts, and provide a means of sharing the data, the models and the results with collaborators and end-users. This modelling framework is at the heart of a testbed proposal for the Hydrologic Ensemble Prediction Experiment (HEPEX) which should allow us to make use of the North American Ensemble Forecasting System (NAEFS) to improve streamflow forecasts of the Great Lakes tributaries, and demonstrate how MESH can contribute to a Community Hydrologic Prediction System (CHPS)
Using the MESH modelling system for hydrological ensemble forecasting of the Laurentian Great Lakes at the regional scale
International audienceEnvironment Canada has been developing a community environmental modelling system (Modélisation Environmentale Communautaire ? MEC), which is designed to facilitate coupling between models focusing on different components of the earth system. The ultimate objective of MEC is to use the coupled models to produce operational forecasts. MESH (MEC ? Surface and Hydrology), a configuration of MEC currently under development, is specialized for coupled land-surface and hydrological models. To determine the specific requirements for MESH, its different components were implemented on the Laurentian Great Lakes watershed, situated on the Canada?U.S. border. This experiment showed that MESH can help us better understand the behaviour of different land-surface models, test different schemes for producing ensemble streamflow forecasts, and provide a means of sharing the data, the models and the results with collaborators and end-users. This modelling framework is at the heart of a testbed proposal for the Hydrologic Ensemble Prediction Experiment (HEPEX) which should allow us to make use of the North American Ensemble Forecasting System (NAEFS) to improve streamflow forecasts of the Great Lakes tributaries, and demonstrate how MESH can contribute to a Community Hydrologic Prediction System (CHPS)
Edge electron states for quasi-one-dimensional organic conductors in the magnetic-field-induced spin-density-wave phases
We develop a microscopic picture of the electron states localized at the
edges perpendicular to the chains in the Bechgaard salts in the quantum Hall
regime. In a magnetic-field-induced spin-density-wave state (FISDW)
characterized by an integer N, there exist N branches of chiral gapless edge
excitations. Localization length is much longer and velocity much lower for
these states than for the edge states parallel to the chains. We calculate the
contribution of these states to the specific heat and propose a time-of-flight
experiment to probe the propagating edge modes directly.Comment: 4 pages, 2 figures. V.2: Minor changes to the final version published
in PR
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