14,907 research outputs found
Simultaneous Measurements of Microwave Photoresistance and Cyclotron Reflection in the Multi-Photon Regime
We simultaneously measure photoresistance with electrical transport and
plasmon-cyclotron resonance (PCR) using microwave reflection spectroscopy in
high mobility GaAs/AlGaAs quantum wells under a perpendicular magnetic field.
Multi-photon transitions are revealed as sharp peaks in the resistance and the
cyclotron reflection on samples with various carrier densities. Our main
finding is that plasmon coupling is relevant in the cyclotron reflection
spectrum but has not been observed in the electrical conductivity signal. We
discuss possible mechanisms relevant to reflection or dc conductivity signal to
explain this discrepancy. We further confirm a trend that higher order
multi-photon features can be observed using higher carrier density samples.Comment: 19 pages, 5 figure
Global Action-Angle Variables for Non-Commutative Integrable Systems
In this paper we analyze the obstructions to the existence of global
action-angle variables for regular non-commutative integrable systems (NCI
systems) on Poisson manifolds. In contrast with local action-angle variables,
which exist as soon as the fibers of the momentum map of such an integrable
system are compact, global action-angle variables rarely exist. This fact was
first observed and analyzed by Duistermaat in the case of Liouville integrable
systems on symplectic manifolds and later by Dazord-Delzant in the case of
non-commutative integrable systems on symplectic manifolds. In our more general
case where phase space is an arbitrary Poisson manifold, there are more
obstructions, as we will show both abstractly and on concrete examples. Our
approach makes use of a few new features which we introduce: the action bundle
and the action lattice bundle of the NCI system (these bundles are canonically
defined) and three foliations (the action, angle and transverse foliation),
whose existence is also subject to obstructions, often of a cohomological
nature
Smallholder Agriculture, Wage Labour, and Rural Poverty Alleviation in Mozambique: What Does the Evidence Tell Us?
Ministry of Agriculture and Rural Development, Directorate of Economics, Republic of Mozambiquefood security, food policy, Mozambique, smallholder agriculture, commercial agriculture, Food Security and Poverty, Q18,
Thermopower and Nernst measurements in a half-filled lowest Landau level
Motivated by recent proposal by Potter et al. [Phys. Rev. X 6, 031026 (2016)]
concerning possible thermoelectric signatures of Dirac composite fermions, we
perform a systematic experimental study of thermoelectric transport of an
ultrahigh-mobility GaAs/AlxGa1-xAs two dimensional electron system at filling
factor v = 1/2. We demonstrate that the thermopower Sxx and Nernst Sxy are
symmetric and anti-symmetric with respect to B = 0 T, respectively. The
measured properties of thermopower Sxx at v = 1/2 are consistent with previous
experimental results. The Nernst signals Sxy of v = 1/2, which have not been
reported previously, are non-zero and show a power law relation with
temperature in the phonon-drag dominant region. In the electron-diffusion
dominant region, the Nernst signals Sxy of v = 1/2 are found to be
significantly smaller than the linear temperature dependent values predicted by
Potter et al., and decreasing with temperature faster than linear dependence.Comment: 23 pages, 5 figure
Spin-dependent Fano resonance induced by conducting chiral helimagnet contained in a quasi-one-dimensional electron waveguide
Fano resonance appears for conduction through an electron waveguide
containing donor impurities. In this work, we consider the thin-film conducting
chiral helimagnet (CCH) as the donor impurity in a one-dimensional waveguide
model. Due to the spin spiral coupling, interference between the direct and
intersubband transmission channels gives rise to spin-dependent Fano resonance
effect. The spin-dependent Fano resonance is sensitively dependent on the
helicity of the spiral. By tuning the CCH potential well depth and the incident
energy, this provides a potential way to detect the spin structure in the CCH.Comment: 14 pages, 6 figure
Nonparametric inference procedure for percentiles of the random effects distribution in meta-analysis
To investigate whether treating cancer patients with
erythropoiesis-stimulating agents (ESAs) would increase the mortality risk,
Bennett et al. [Journal of the American Medical Association 299 (2008)
914--924] conducted a meta-analysis with the data from 52 phase III trials
comparing ESAs with placebo or standard of care. With a standard parametric
random effects modeling approach, the study concluded that ESA administration
was significantly associated with increased average mortality risk. In this
article we present a simple nonparametric inference procedure for the
distribution of the random effects. We re-analyzed the ESA mortality data with
the new method. Our results about the center of the random effects distribution
were markedly different from those reported by Bennett et al. Moreover, our
procedure, which estimates the distribution of the random effects, as opposed
to just a simple population average, suggests that the ESA may be beneficial to
mortality for approximately a quarter of the study populations. This new
meta-analysis technique can be implemented with study-level summary statistics.
In contrast to existing methods for parametric random effects models, the
validity of our proposal does not require the number of studies involved to be
large. From the results of an extensive numerical study, we find that the new
procedure performs well even with moderate individual study sample sizes.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS280 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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