4,494 research outputs found
Interacting Electrons on a Square Fermi Surface
Electronic states near a square Fermi surface are mapped onto quantum chains.
Using boson-fermion duality on the chains, the bosonic part of the interaction
is isolated and diagonalized. These interactions destroy Fermi liquid behavior.
Non-boson interactions are also generated by this mapping, and give rise to a
new perturbation theory about the boson problem. A case with strong repulsions
between parallel faces is studied and solved. There is spin-charge separation
and the square Fermi surface remains square under doping. At half-filling,
there is a charge gap and insulating behavior together with gapless spin
excitations. This mapping appears to be a general tool for understanding the
properties of interacting electrons on a square Fermi surface.Comment: 25 pages, Nordita preprint 94/22
Energy dependent Schrödinger operators and complex Hamiltonian systems on Riemann surfaces
We use so-called energy-dependent Schrödinger operators to establish a link between special classes of solutions on N-component systems of evolution equations and finite dimensional Hamiltonian systems on the moduli spaces of Riemann surfaces. We also investigate the phase-space geometry of these Hamiltonian systems and introduce deformations of the level sets associated to conserved quantities, which results in a new class of solutions with monodromy for N-component systems of PDEs.
After constructing a variety of mechanical systems related to the spatial flows of nonlinear evolution equations, we investigate their semiclassical limits. In particular, we obtain semicalssical asymptotics for the Bloch eigenfunctions of the energy dependent Schrödinger operators, which is of importance in investigating zero-dispersion limits of N-component systems of PDEs
Observations of long period waves in the tropical oceans and atmosphere
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Woods Hole Oceanographic Institution February 1980The existence of resonant, baroclinic, equatorially-trapped inertia-gravity
waves (discovered by Wunsch and Gill (1976)) is confirmed in the
mid-Pacific by spectral analysis of long sea level records. The energy
of the low-mode inertia-gravity waves is found to decrease toward the
meridional boundaries. A simple spectral model, acknowledging the dispersive
characteristics of the equatorial waves, adequately reproduces the
observed mid-Pacific sea level spectra in the 1-6 day band. Model spectra
computed at latitudes outside the equatorial waveguide of the gravest meridional
modes suggest the presence of "inertial" peaks in several observed
sea level spectra. Resonant, low-mode inertia-gravity waves may also
exist in the Indian Ocean.
Sea level fluctuations along the Pacific equator are found to have
Kelvin wave characteristics in the 35-80 day band, and, in particular,
propagation from the western Pacific to the coast of South America is
observed. The Kelvin waves are atmospherically-forced in the central-
western Pacific and have a computed equivalent depth corresponding to
the first-baroc1inic mode.
Outside of the equatorial mid-Pacific, a non-static ocean response to air pressure in the 4-6 day band is dominated by a basin-wide, barotropic, planetary mode.
The low Q of this mode suggests that the ocean is viscous with respect to large-scale barotropic oscillations.
The dynamical components of the observed long-period tides have been
isolated for the first time using the "self-consistent" equilibrium tide
of Agnew and Farrell (1978). The tides are slightly non-equilibrium with
large horizontal scales. The relatively short-scale Rossby modes predicted
by Wunsch (1967) are not observed, perhaps because of the poor spatial
coverage of the dataset. Considering the low Q of the 4-6 day planetary
basin mode, it is suggested that the long-period tides are frictionally-controlled.
The 4- and 5-day equatorial inertia-gravity waves, the 35-80 day
Kelvin waves and the 4-6 day planetary basin mode are clearly atmospherically
forced, and, perhaps surprisingly, they are forced by atmospheric waves
that have similar horizontal structures, i.e., 4-5 day Rossby-gravity waves,
40-50 day Kelvin waves and a 5-day global barotropic mode. The
surface expressions of these atmospheric waves are determined in order to
understand the nature of the oceanic response, e.g., resonant or forced.
Much of the information about the surface atmospheric fields that has
been collected, including frequency-wavenumber descriptions, awaits an
accurate model of the coupling between wind stress and internal ocean
waves.Monetary support for this research was provided by the National
Science Foundation through contract OCE73-0l384. At various times,
tuition and living expenses were paid by funds from the NSF contract
above, the Office of Naval Research (contract N00014-C-75-029l), the
Cecil and Ida Green Professorship in Earth Sciences, the J. P. Luther
Educational Fund and by an M.I.T. Educational Tuition Award
Letter to Sonora Dodd from Luther S. Beard, May 23, 1911
Letter to Sonora Dodd, from Luther S. Beard, News Editor for The North American.https://digitalcommons.whitworth.edu/fathers-day-correspondence/1011/thumbnail.jp
Snow cover monitoring by machine processing of multitemporal LANDSAT MSS data
LANDSAT frames were geometrically corrected and data sets from six different dates were overlaid to produce a 24 channel (six dates and four wavelength bands) data tape. Changes in the extent of the snowpack could be accurately and easily determined using a change detection technique on data which had previously been classified by the LARSYS software system. A second phase of the analysis involved determination of the relationship between spatial resolution or data sampling frequency and accuracy of measuring the area of the snowpack
WHEAT BUFFER STOCKS AND TRADE IN AN EFFICIENT GLOBAL ECONOMY
This study assesses storage and trade of wheat in an integrated global economy. Domestic and international linkages are analyzed using a dynamic rational expectations model of the world wheat market. The results of this study demonstrate the importance of endogenizing both storage and trade in studying commodity markets. Results suggest an optimal US buffer stock level of 150 million bushel. Results indicate that past government stockholdings have not followed efficient market outcomes. Private markets likely would perform better in the absence of government market distortions. Results indicate that elimination of the Export Enhancement Program by the US and of export restitution payments by the EU is unlikely to have a major impact on wheat exports from the two regions, but will save millions of tax dollars in both regions.Crop Production/Industries, International Relations/Trade,
A Follow-up Study of the 1962-66 Graduates Augustana Academy
The functions of the guidance program in today\u27s schools usually consist of five main services. They are: inventory, information, counseling, placement, and follow-up. This paper will center about the last of these services, namely, follow-up. The follow-up service is to education what the customer relations department is to merchandising by means of a continuing follow-up of former students, the educator learns of their .failures, problems, successes, and--most important--obtains their suggestions for improvement. The purpose of this investigation was to conduct a follow-up study of the 1962-66 graduates of Augustana Academy, Canton, South Dakota. Information concerning their evaluations of their former school, their opinions of it, and their_ present status were sought in this survey. At the present time, Augustana Academy is undergoing a retooling operation. With this in mind, it is necessary to evaluate the present curriculum and guidance services. The main purpose of this study was to aid in these revisions
Geometric analysis of optical frequency conversion and its control in quadratic nonlinear media
We analyze frequency conversion and its control among three light waves using a geometric approach that enables the dynamics of the waves to be visualized on a closed surface in three dimensions. It extends the analysis based on the undepleted-pump linearization and provides a simple way to understand the fully nonlinear dynamics. The Poincaré sphere has been used in the same way to visualize polarization dynamics. A geometric understanding of control strategies that enhance energy transfer among interacting waves is introduced, and the quasi-phase-matching strategy that uses microstructured quadratic materials is illustrated in this setting for both type I and II second-harmonic generation and for parametric three-wave interactions
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