1,598 research outputs found
Spin exchange in quantum rings and wires in the Wigner-crystal limit
We present a controlled method for computing the exchange coupling in
strongly correlated one-dimensional electron systems. It is based on the
asymptotically exact relation between the exchange constant and the
pair-correlation function of spinless electrons. Explicit results are obtained
for thin quantum rings with realistic Coulomb interactions, by calculating this
function via a many-body instanton approach.Comment: 7 pages, 2 figures. Changes in the text and figures to improve
readability; added reference
The Physiology of Political Participation
Political involvement varies markedly across people. Traditional explanations for this variation tend to rely on demographic variables and self-reported, overtly political concepts. In this article, we expand the range of possible explanatory variables by hypothesizing that a correlation exists between political involvement and physiological predispositions. We measure physiology by computing the degree to which electrodermal activity changes on average when a participant sequentially views a full range of differentially valenced stimuli. Our findings indicate that individuals with higher electrodermal responsiveness are also more likely to participate actively in politics. This relationship holds even after the effects of traditional demographic variables are taken into account, suggesting that physiological responsiveness independently contributes to a fuller understanding of the underlying sources of variation in political involvement
Electric field inside a "Rossky cavity" in uniformly polarized water
Electric field produced inside a solute by a uniformly polarized liquid is
strongly affected by dipolar polarization of the liquid at the interface. We
show, by numerical simulations, that the electric "cavity" field inside a
hydrated non-polar solute does not follow the predictions of standard Maxwell's
electrostatics of dielectrics. Instead, the field inside the solute tends, with
increasing solute size, to the limit predicted by the Lorentz virtual cavity.
The standard paradigm fails because of its reliance on the surface charge
density at the dielectric interface determined by the boundary conditions of
the Maxwell dielectric. The interface of a polar liquid instead carries a
preferential in-plane orientation of the surface dipoles thus producing
virtually no surface charge. The resulting boundary conditions for
electrostatic problems differ from the traditional recipes, affecting the
microscopic and macroscopic fields based on them. We show that relatively small
differences in cavity fields propagate into significant differences in the
dielectric constant of an ideal mixture. The slope of the dielectric increment
of the mixture versus the solute concentration depends strongly on which
polarization scenario at the interface is realized. A much steeper slope found
in the case of Lorentz polarization also implies a higher free energy penalty
for polarizing such mixtures.Comment: 9 pages, 8 figure
Beyond Survey Self-Reports: Using Physiology to Tap Political Orientations
Some aspects of our attitudes are composed of things outside of our consciousness. However, traditional survey research does not use measurements that are able to tap into these aspects of public opinion. We describe, recommend, and demonstrate a procedure by which non-self-reported responses can be measured in order to test whether these responses have independent effects on individuals’ preferences. We use one of the better-known physiological measures—electrodermal activity or skin conductance—and illustrate its potential by reporting our own study of attitudes toward President Barack Obama. We find that both self-reported emotional responses and physiological responses to Obama’s image independently correlate with variation in the intensity of attitudes regarding his job approval and his central policy proposal: health-care reform
Models of Emergency Departments for Reducing Patient Waiting Times
In this paper, we apply both agent-based models and queuing models to investigate patient access and patient flow through emergency departments. The objective of this work is to gain insights into the comparative contributions and limitations of these complementary techniques, in their ability to contribute empirical input into healthcare policy and practice guidelines. The models were developed independently, with a view to compare their suitability to emergency department simulation. The current models implement relatively simple general scenarios, and rely on a combination of simulated and real data to simulate patient flow in a single emergency department or in multiple interacting emergency departments. In addition, several concepts from telecommunications engineering are translated into this modeling context. The framework of multiple-priority queue systems and the genetic programming paradigm of evolutionary machine learning are applied as a means of forecasting patient wait times and as a means of evolving healthcare policy, respectively. The models' utility lies in their ability to provide qualitative insights into the relative sensitivities and impacts of model input parameters, to illuminate scenarios worthy of more complex investigation, and to iteratively validate the models as they continue to be refined and extended. The paper discusses future efforts to refine, extend, and validate the models with more data and real data relative to physical (spatial–topographical) and social inputs (staffing, patient care models, etc.). Real data obtained through proximity location and tracking system technologies is one example discussed
Dynamic scaling for 2D superconductors, Josephson junction arrays and superfluids
The value of the dynamic critical exponent is studied for two-dimensional
superconducting, superfluid, and Josephson Junction array systems in zero
magnetic field via the Fisher-Fisher-Huse dynamic scaling. We find
, a relatively large value indicative of non-diffusive
dynamics. Universality of the scaling function is tested and confirmed for the
thinnest samples. We discuss the validity of the dynamic scaling analysis as
well as the previous studies of the Kosterlitz-Thouless-Berezinskii transition
in these systems, the results of which seem to be consistent with simple
diffusion (). Further studies are discussed and encouraged.Comment: 19 pages in two-column RevTex, 8 embedded EPS figure
Renormalization group approach to layered superconductors
A renormalization group theory for a system consisting of coupled
superconducting layers as a model for typical high-temperature superconducters
is developed. In a first step the electromagnetic interaction over infinitely
many layers is taken into account, but the Josephson coupling is neglected. In
this case the corrections to two-dimensional behavior due to the presence of
the other layers are very small. Next, renormalization group equations for a
layered system with very strong Josephson coupling are derived, taking into
account only the smallest possible Josephson vortex loops. The applicability of
these two limiting cases to typical high-temperature superconductors is
discussed. Finally, it is argued that the original renormalization group
approach by Kosterlitz is not applicable to a layered system with intermediate
Josephson coupling.Comment: RevTeX, 15 pages, 4 figures can be obtained from the author by
conventional mail; accepted for publication in Phys. Rev.
Observation of low-lying isomeric states in Cs: a new avenue for dark matter and solar neutrino detection in xenon detectors
We report on new measurements establishing the existence of low-lying
isomeric states in Cs using rays produced in
Xe(p,n)Cs reactions. Two states with ~ns
lifetimes are placed in the decay sequence of the Cs levels that are
populated in charged-current interactions of solar neutrinos and fermionic dark
matter with Xe. Xenon-based experiments can therefore exploit a
delayed-coincidence tag of these interactions, greatly suppressing backgrounds
to enable spectroscopic studies of solar neutrinos and dark matter.Comment: Supplemental material available upon request. Version accepted by
Phys.Rev.Let
Alpha Antihydrogen Experiment
ALPHA is an experiment at CERN, whose ultimate goal is to perform a precise
test of CPT symmetry with trapped antihydrogen atoms. After reviewing the
motivations, we discuss our recent progress toward the initial goal of stable
trapping of antihydrogen, with some emphasis on particle detection techniques.Comment: Invited talk presented at the Fifth Meeting on CPT and Lorentz
Symmetry, Bloomington, Indiana, June 28-July 2, 201
Decoherence of electron spin qubits in Si-based quantum computers
Direct phonon spin-lattice relaxation of an electron qubit bound by a donor
impurity or quantum dot in SiGe heterostructures is investigated. The aim is to
evaluate the importance of decoherence from this mechanism in several important
solid-state quantum computer designs operating at low temperatures. We
calculate the relaxation rate as a function of [100] uniaxial strain,
temperature, magnetic field, and silicon/germanium content for Si:P bound
electrons. The quantum dot potential is much smoother, leading to smaller
splittings of the valley degeneracies. We have estimated these splittings in
order to obtain upper bounds for the relaxation rate. In general, we find that
the relaxation rate is strongly decreased by uniaxial compressive strain in a
SiGe-Si-SiGe quantum well, making this strain an important positive design
feature. Ge in high concentrations (particularly over 85%) increases the rate,
making Si-rich materials preferable. We conclude that SiGe bound electron
qubits must meet certain conditions to minimize decoherence but that
spin-phonon relaxation does not rule out the solid-state implementation of
error-tolerant quantum computing.Comment: 8 figures. To appear in PRB-July 2002. Revisions include: some
references added/corrected, several typos fixed, a few things clarified.
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