355 research outputs found
Is the Quantum Hall Effect influenced by the gravitational field?
Most of the experiments on the quantum Hall effect (QHE) were made at
approximately the same height above sea level. A future international
comparison will determine whether the gravitational field
influences the QHE. In the realm of (1 + 2)-dimensional phenomenological
macroscopic electrodynamics, the Ohm-Hall law is metric independent
(`topological'). This suggests that it does not couple to . We
corroborate this result by a microscopic calculation of the Hall conductance in
the presence of a post-Newtonian gravitational field.Comment: 4 page
Nonlinear ac conductivity of one-dimensional Mott insulators
We discuss a semiclassical calculation of low energy charge transport in
one-dimensional (1d) insulators with a focus on Mott insulators, whose charge
degrees of freedom are gapped due to the combination of short range
interactions and a periodic lattice potential. Combining RG and instanton
methods, we calculate the nonlinear ac conductivity and interpret the result in
terms of multi-photon absorption. We compare the result of the semiclassical
calculation for interacting systems to a perturbative, fully quantum mechanical
calculation of multi-photon absorption in a 1d band insulator and find good
agreement when the number of simultaneously absorbed photons is large.Comment: Dedicated to Thomas Nattermann on the occasion of his 60th birthday.
To appear in JSTAT. 5 pages, 2 figure
Partition Functions of Non-Abelian Quantum Hall States
Partition functions of edge excitations are obtained for non-Abelian Hall
states in the second Landau level, such as the anti-Read-Rezayi state, the
Bonderson-Slingerland hierarchy and the Wen non-Abelian fluid, as well as for
the non-Abelian spin-singlet state. The derivation is straightforward and
unique starting from the non-Abelian conformal field theory data and solving
the modular invariance conditions. The partition functions provide a complete
account of the excitation spectrum and are used to describe experiments of
Coulomb blockade and thermopower.Comment: 42 pages, 3 figures; published version; minor corrections to sect.
4.
Quantum Zeno effect and parametric resonance in mesoscopic physics
As a realization of the quantum Zeno effect, we consider electron tunneling
between two quantum dots with one of the dots coupled to a quantum point
contact detector. The coupling leads to decoherence and to the suppression of
tunneling. When the detector is driven with an ac voltage, a parametric
resonance occurs which strongly counteracts decoherence. We propose a novel
experiment with which it is possible to observe both the quantum Zeno effect
and the parametric resonance in electric transport.Comment: 4 pages, 2 figure
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One Year Follow-up of a Randomized, Double-Blind, Placebo-Controlled Trial of Percutaneous Peripheral Nerve Stimulation for Chronic Neuropathic Pain Following Amputation
Abstract
INTRODUCTION
Over 85% of patients experience residual limb (RLP) and/or phantom limb (PLP) pain following amputation. Peripheral nerve stimulation (PNS) is a non-opioid approach to relieve postamputation neuropathic pain. A recent multicenter, randomized, double-blind, placebo-controlled study using a novel percutaneous PNS system demonstrated clinically and statistically significant improvements in pain and pain interference with PNS compared to placebo (Gilmore et al, 2019). This work presents prospective 1-yr follow-up to assess durability of pain relief and functional improvements.
METHODS
Over 85% of patients experience residual limb (RLP) and/or phantom limb (PLP) pain following amputation. Peripheral nerve stimulation (PNS) is a non-opioid approach to relieve post-amputation neuropathic pain. A recent multicenter, randomized, double-blind, placebo-controlled study using a novel percutaneous PNS system demonstrated clinically and statistically significant improvements in pain and pain interference with PNS compared to placebo (Gilmore et al, 2019). This work presents prospective one-year follow-up to assess durability of pain relief and functional improvements.
RESULTS
A significantly greater proportion of subjects who completed the 12-mo visit reported = 50% pain relief on the BPI-SF (5/8, 63%; average pain relief = 73% among responders) compared to the placebo group at the time of crossover (0/14, 0%, P = .003; average pain relief = 23%). A majority of subjects also reported = 50% reductions in pain interference at 12 mo (5/8, 63%). Two of 13 (15%) subjects in the placebo group reported sustained improvements in pain interference (P = .06). Average reduction in pain interference among responders in the PNS group was 87%.
CONCLUSION
This work suggests that PNS delivered over 60 d may provide clinically significant and enduring pain relief, enabling improved function and potentially reducing the need for a permanently implanted system
Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels
We observe density induced 90 rotations of the anisotropy axes in
transport measurements at half-filled high Landau levels in the two dimensional
electron system, where stripe states are proposed (=9/2, 11/2, etc). Using
a field effect transistor, we find the transition density to be
cm at =9/2. Hysteresis is observed in the
vicinity of the transition. We construct a phase boundary in the filling
factor-magnetic field plane in the regime . An in-plane magnetic
field applied along either anisotropy axis always stabilizes the low density
orientation of the stripes.Comment: 1 revtex file, 3 eps figure
Magnetic Gaps related to Spin Glass Order in Fermionic Systems
We provide evidence for spin glass related magnetic gaps in the fermionic
density of states below the freezing temperature. Model calculations are
presented and proposed to be relevant for explaining resistivity measurements
which observe a crossover from variable-range- to activated behavior. The
magnetic field dependence of a hardgap and the low temperature decay of the
density of states are given. In models with fermion transport a new
metal-insulator transition is predicted to occur due to the spin-glass gap,
anteceding the spin glass to quantum paramagnet transition at smaller spin
density. Important fluctuation effects due to finite range frustrated
interactions are estimated and discussed.Comment: 4 pages, 1 Postscript figure, revised version accepted for
publication in Physical Review Letter
Edge-State Velocity and Coherence in a Quantum Hall Fabry-Perot Interferometer
We investigate nonlinear transport in electronic Fabry-Perot interferometers
in the integer quantum Hall regime. For interferometers sufficiently large that
Coulomb blockade effects are absent, a checkerboard-like pattern of conductance
oscillations as a function of dc bias and perpendicular magnetic field is
observed. Edge-state velocities extracted from the checkerboard data are
compared to model calculations and found to be consistent with a crossover from
skipping orbits at low fields to E x B drift at high fields. Suppression of
visibility as a function of bias and magnetic field is accounted for by
including energy- and field-dependent dephasing of edge electrons.Comment: related papers at http://marcuslab.harvard.ed
Statistical pairwise interaction model of stock market
Financial markets are a classical example of complex systems as they comprise
many interacting stocks. As such, we can obtain a surprisingly good description
of their structure by making the rough simplification of binary daily returns.
Spin glass models have been applied and gave some valuable results but at the
price of restrictive assumptions on the market dynamics or others are
agent-based models with rules designed in order to recover some empirical
behaviours. Here we show that the pairwise model is actually a statistically
consistent model with observed first and second moments of the stocks
orientation without making such restrictive assumptions. This is done with an
approach based only on empirical data of price returns. Our data analysis of
six major indices suggests that the actual interaction structure may be thought
as an Ising model on a complex network with interaction strengths scaling as
the inverse of the system size. This has potentially important implications
since many properties of such a model are already known and some techniques of
the spin glass theory can be straightforwardly applied. Typical behaviours, as
multiple equilibria or metastable states, different characteristic time scales,
spatial patterns, order-disorder, could find an explanation in this picture.Comment: 11 pages, 8 figure
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