1,902 research outputs found
UAG R-268
This study was supported by the Bureau of Land Management through
interagency agreement with the National Oceanic and Atmospheric Administration
under which a multi-year program responding to need of petroleum development
of the Alaskan continental shelf is managed by the Outer Continental Shelf
Environmental Assessment Program (OCSEAP) Office. Drawings were done by
Debbie Cocci a and Jim Burton. The idea of this project arose during a
conversation between George Edwardson, Jr., and one of the Principal Investigators.
Rachael Craig and Edna MacLean helped in initiating the project and Mrs. Molly
Pederson of the North Slope Borough Inupiaq Language Commission obtained
some of the narratives and interviews and provided translations. Teri
McClung assisted with transcription of interviews and editing. Finally,
the hospitality of the family of Kenneth Toovak during the translation
process is gratefully acknowledged.The objective of this program was to extend the data base on ice hazards
along the Beaufort Sea coast of Alaska backward in time by using the
knowledge and understanding of ice and weather conditions of the local
residents. Information for this pilot project was obtained through direct
interviews with residents, or from narratives supplied by them. The results
of these procedures were evaluated to provide a basis for improving similar
efforts in future. Observations of particular interest obtained from these
interviews and narratives include (1 ) a description of a major motion of the
landfast ice off Harrison Bay in late February, (2) a description of the
formation of ice push ridges and ride-up at Cape Halkett during break up,
(3) reports of whales traveling inshore of Cross Island during the fall
migration and of whales being taken by crews from the Prudhoe Bay area at
that time of year, and 4) descriptions of conditions in the nearshore area
during summer. In addition information of historical and cultural interest
was obtained.Supported by NOAA Contract 03-5-022-55, Task No. 6ABSTRACT -- ACKNOWLEDGEMENTS -- TABLE OF CONTENTS : INTRODUCTION ; PROCEDURES ; RESULTS ; DISCUSSION AND EVALUATION -- APPENDIX I -- APPENDIX II -- APPENDIX II
Spin lifetimes and strain-controlled spin precession of drifting electrons in zinc blende type semiconductors
We study the transport of spin polarized electrons in n-GaAs using spatially
resolved continuous wave Faraday rotation. From the measured steady state
distribution, we determine spin relaxation times under drift conditions and, in
the presence of strain, the induced spin splitting from the observed spin
precession. Controlled variation of strain along [110] allows us to deduce the
deformation potential causing this effect, while strain along [100] has no
effect. The electric field dependence of the spin lifetime is explained
quantitatively in terms of an increase of the electron temperature.Comment: 5 pages, 6 figure
Exact analytic results for the Gutzwiller wave function with finite magnetization
We present analytic results for ground-state properties of Hubbard-type
models in terms of the Gutzwiller variational wave function with non-zero
values of the magnetization m. In dimension D=1 approximation-free evaluations
are made possible by appropriate canonical transformations and an analysis of
Umklapp processes. We calculate the double occupation and the momentum
distribution, as well as its discontinuity at the Fermi surface, for arbitrary
values of the interaction parameter g, density n, and magnetization m. These
quantities determine the expectation value of the one-dimensional Hubbard
Hamiltonian for any symmetric, monotonically increasing dispersion epsilon_k.
In particular for nearest-neighbor hopping and densities away from half filling
the Gutzwiller wave function is found to predict ferromagnetic behavior for
sufficiently large interaction U.Comment: REVTeX 4, 32 pages, 8 figure
Turning a First Order Quantum Phase Transition Continuous by Fluctuations: General Flow Equations and Application to d-Wave Pomeranchuk Instability
We derive renormalization group equations which allow us to treat order
parameter fluctuations near quantum phase transitions in cases where an
expansion in powers of the order parameter is not possible. As a prototypical
application, we analyze the nematic transition driven by a d-wave Pomeranchuk
instability in a two-dimensional electron system. We find that order parameter
fluctuations suppress the first order character of the nematic transition
obtained at low temperatures in mean-field theory, so that a continuous
transition leading to quantum criticality can emerge
Soft Fermi Surfaces and Breakdown of Fermi Liquid Behavior
Electron-electron interactions can induce Fermi surface deformations which
break the point-group symmetry of the lattice structure of the system. In the
vicinity of such a "Pomeranchuk instability" the Fermi surface is easily
deformed by anisotropic perturbations, and exhibits enhanced collective
fluctuations. We show that critical Fermi surface fluctuations near a d-wave
Pomeranchuk instability in two dimensions lead to large anisotropic decay rates
for single-particle excitations, which destroy Fermi liquid behavior over the
whole surface except at the Brillouin zone diagonal.Comment: 12 pages, 2 figures, revised version as publishe
d-wave superconductivity and Pomeranchuk instability in the two-dimensional Hubbard model
We present a systematic stability analysis for the two-dimensional Hubbard
model, which is based on a new renormalization group method for interacting
Fermi systems. The flow of effective interactions and susceptibilities confirms
the expected existence of a d-wave pairing instability driven by
antiferromagnetic spin fluctuations. More unexpectedly, we find that strong
forward scattering interactions develop which may lead to a Pomeranchuk
instability breaking the tetragonal symmetry of the Fermi surface.Comment: 4 pages (RevTeX), 4 eps figure
Slave-Boson Mean-Field Theory of the Antiferromagnetic State in the Doubly Degenerate Hubbard Model - the Half-Filled Case -
The antiferromagnetic ground state of the half-filled Hubbard model with the
doubly degenerate orbital has been studied by using the slave-boson mean-field
theory which was previously proposed by the present author. Numerical
calculations for the simple cubic model have shown that the metal-insulator
transition does not take place except at the vanishing interaction point, in
strong contrast with its paramagnetic solution. The energy gap in the density
of states of the antiferromagnetic insulator is much reduced by the effect of
electron correlation. The exchange interaction plays an important role in
the antiferromagnetism: although for the sublattice magnetic moment
in our theory is fairly smaller than obtained in the Hartree-Fock
approximation, for (: the Coulomb interaction) is increased
to become comparable to . Surprisingly, the antiferromagnetic state is
easily destroyed if a small, negative exchange interaction () is
introduced.Comment: Latex 18 pages, 12 figures available on request to
[email protected] Note: published in Phys. Rev. B with some minor
modification
Quantum phase transitions and collapse of the Mott gap in the dimensional half-filled Hubbard model
We study the low-energy asymptotics of the half-filled Hubbard model with a
circular Fermi surface in continuous dimensions, based on the
one-loop renormalization-group (RG) method. Peculiarity of the
dimensions is incorporated through the mathematica structure of the elementary
particle-partcile (PP) and particle-hole (PH) loops: infrared logarithmic
singularity of the PH loop is smeared for . The RG flows indicate
that a quantum phase transition (QPT) from a metallic phase to the Mott
insulator phase occurs at a finite on-site Coulomb repulsion for
. We also discuss effects of randomness.Comment: 12 pages, 10 eps figure
Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy
A slave-boson functional-integral method has been developed for the Hubbard
model with arbitrary, orbital degeneracy . Its saddle-point mean-field
theory is equivalent to the Gutzwiller approximation, as in the case of
single-band Hubbard model. Our theory is applied to the doubly degenerate () model, and numerical calculations have been performed for this model in the
paramagnetic states. The effect of the exchange interaction on the
metal-insulator (MI) transition is discussed. The critical interaction for the
MI transition is analytically calculated as functions of orbital degeneracy and
electron occupancy.Comment: Latex 20 pages, 9 figures available on request to
[email protected] Note: published in J. Physical Society of Japan with
some minor modification
Numerical renormalization group study of the symmetric Anderson-Holstein model: phonon and electron spectral functions
We study the symmetric Anderson-Holstein (AH) model at zero temperature with
Wilson's numerical renormalization group (NRG) technique to study the interplay
between the electron-electron and electron-phonon interactions. An improved
method for calculating the phonon propagator using the NRG technique is
presented, which turns out to be more accurate and reliable than the previous
works in that it calculates the phonon renormalization explicitly and satisfies
the boson sum rule better. The method is applied to calculate the renormalized
phonon propagators along with the electron propagators as the onsite Coulomb
repulsion and electron-phonon coupling constant are varied. As is
increased, the phonon mode is successively renormalized, and for crosses over to the regime where the mode splits into two components,
one of which approaches back to the bare frequency and the other develops into
a soft mode. The initial renormalization of the phonon mode, as is
increased from 0, depends on and the hybridization ; it gets
softened (hardened) for . Correlated with
the emergence of the soft mode is the central peak of the electron spectral
function severely suppressed. These NRG calculations will be compared with the
standard Green's function results for the weak coupling regime to understand
the phonon renormalization and soft mode.Comment: 18 pages, 4 figures. Submitted to Phys. Rev.
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