12,963 research outputs found
Real-time dynamics in Quantum Impurity Systems: A Time-dependent Numerical Renormalization Group Approach
We develop a general approach to the nonequilibrium dynamics of quantum
impurity systems for arbitrary coupling strength. The numerical renormalization
group is used to generate a complete basis set necessary for the correct
description of the time evolution. We benchmark our method with the exact
analytical solution for the resonant-level model. As a first application, we
investigate the equilibration of a quantum dot subject to a sudden change of
the gate voltage and external magnetic field. Two distinct relaxation times are
identified for the spin and charge dynamics.Comment: 5 pages, 5 figure
Chart audit of inpatient treatment of schizophrenic patients: implications for development of coordinated care paths.
This study offers important information regarding the standard of care provided to schizophrenic patients treated at one inpatient facility. The findings were particularly useful in the development of a care path for this specific population. Areas for improvement identified in this research include medical tests, master treatment planning, documentation of care, patient teaching, and discharge planning. Given the limited health care dollars and the lack of a cure for schizophrenia, this research emphasizes the fact that treatment guidelines need to be aggressively tested as to their relevance to practice
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
Topological Optimization of the Evaluation of Finite Element Matrices
We present a topological framework for finding low-flop algorithms for
evaluating element stiffness matrices associated with multilinear forms for
finite element methods posed over straight-sided affine domains. This framework
relies on phrasing the computation on each element as the contraction of each
collection of reference element tensors with an element-specific geometric
tensor. We then present a new concept of complexity-reducing relations that
serve as distance relations between these reference element tensors. This
notion sets up a graph-theoretic context in which we may find an optimized
algorithm by computing a minimum spanning tree. We present experimental results
for some common multilinear forms showing significant reductions in operation
count and also discuss some efficient algorithms for building the graph we use
for the optimization
ALFA & 3D: integral field spectroscopy with adaptive optics
One of the most important techniques for astrophysics with adaptive optics is
the ability to do spectroscopy at diffraction limited scales. The extreme
difficulty of positioning a faint target accurately on a very narrow slit can
be avoided by using an integral field unit, which provides the added benefit of
full spatial coverage. During 1998, working with ALFA and the 3D integral field
spectrometer, we demonstrated the validity of this technique by extracting and
distinguishing spectra from binary stars separated by only 0.26". The
combination of ALFA & 3D is also ideally suited to imaging distant galaxies or
the nuclei of nearby ones, as its field of view can be changed between
1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution
we present new results both on galactic targets, namely young stellar objects,
as well as extra-galactic objects including a Seyfert and a starburst nucleus.Comment: SPIE meeting 4007 on Adaptive Optical Systems Technology, March 200
One-Dimensional Theory of the Quantum Hall System
We consider the lowest Landau level on a torus as a function of its
circumference . When , the ground state at general rational
filling fraction is a crystal with a gap--a Tao-Thouless state. For filling
fractions , these states are the limits of Laughlin's or Jain's
wave functions describing the gapped quantum Hall states when .
For the half-filled Landau level, there is a transition to a Fermi sea of
non-interacting neutral dipoles, or rather to a Luttinger liquid modification
thereof, at magnetic lengths. This state is a version of the
Rezayi-Read state, and develops continuously into the state that is believed to
describe the observed metallic phase as . Furthermore, the
effective Landau level structure that emerges within the lowest Landau level
follows from the magnetic symmetries.Comment: 4 pages, 1 figur
Wilson chains are not thermal reservoirs
Wilson chains, based on a logarithmic discretization of a continuous
spectrum, are widely used to model an electronic (or bosonic) bath for Kondo
spins and other quantum impurities within the numerical renormalization group
method and other numerical approaches. In this short note we point out that
Wilson chains can not serve as thermal reservoirs as their temperature changes
by a number of order Delta E when a finite amount of energy Delta E is added.
This proves that for a large class of non-equilibrium problems they cannot be
used to predict the long-time behavior.Comment: 2 page
Local Responses to Development Pressures : Conflictual Politics of Sprawl and Environmental Conservation
There is an increasing opposition to the absorption of farmland and natural habitats by housing subdivisions and infrastructure, a symptom of urban sprawl. Through an analysis of these challenges at a regional scale, we address the contradictions and tensions in the politics of sprawl and environmental conservation. This article compares environmental conservation on the Oak Ridges Moraine in Richmond Hill and Caledon (two towns in the Greater Toronto Area) and argues that local political cultures, geography, and the density and political influence of citizens and social movements can have an impact on local responses to pressures of development. In the end, however, environmental activism in both towns is subjected to and shaped by an overall growth agenda.Lâenvahissement des terres agricoles et des milieux naturels par des lotissements et des infrastructures rĂ©sidentiels suscite de plus en plus dâopposition. Il en rĂ©sulte des tensions et des contradictions entre les pratiques dâurbanisation et les politiques de conservation de lâenvironnement. Cet article compare la gestion Ă des fins de conservation de la moraine Oak Ridges Ă Richmond Hill et Caledon (deux municipalitĂ©s de la rĂ©gion mĂ©tropolitaine de Toronto). Il est constatĂ© que la culture politique locale, la gĂ©ographie, la densitĂ© et lâinfluence politique des mouvements sociaux peuvent avoir Ă lâĂ©chelle locale un impact sur les pratiques dâurbanisation. Il reste que les mobilisations environnementales dans les deux municipalitĂ©s deviennent, malgrĂ© tout, subjugĂ©es par des objectifs de croissance
Universal Approach to Optimal Photon Storage in Atomic Media
We present a universal physical picture for describing storage and retrieval
of photon wave packets in a Lambda-type atomic medium. This physical picture
encompasses a variety of different approaches to pulse storage ranging from
adiabatic reduction of the photon group velocity and pulse-propagation control
via off-resonant Raman fields to photon-echo based techniques. Furthermore, we
derive an optimal control strategy for storage and retrieval of a photon wave
packet of any given shape. All these approaches, when optimized, yield
identical maximum efficiencies, which only depend on the optical depth of the
medium.Comment: 4 pages, 3 figures. V2: major changes in presentation (title,
abstract, main text), simplification of derivations, new references. V3:
minor changes - final version as published in Phys. Rev. Let
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