678 research outputs found
Collective modes of CP(3) Skyrmion crystals in quantum Hall ferromagnets
The two-dimensional electron gas in a bilayer quantum Hall system can sustain
an interlayer coherence at filling factor nu=1 even in the absence of tunneling
between the layers. This system has low-energy charged excitations which may
carry textures in real spin or pseudospin. Away from filling factor nu =1 a
finite density of these is present in the ground state of the 2DEG and forms a
crystal. Depending on the relative size of the various energy scales, such as
tunneling (Delta_SAS), Zeeman coupling (Delta_Z) or electrical bias (Delta_b),
these textured crystal states can involve spin, pseudospin, or both
intertwined. In this article, we present a comprehensive numerical study of the
collective excitations of these textured crystals using the GRPA. For the pure
spin case, at finite Zeeman coupling the state is a Skyrmion crystal with a
gapless phonon mode, and a separate Goldstone mode that arises from a broken
U(1) symmetry. At zero Zeeman coupling, we demonstrate that the constituent
Skyrmions break up, and the resulting state is a meron crystal with 4 gapless
modes. In contrast, a pure pseudospin Skyrme crystal at finite tunneling has
only the phonon mode. For Delta_SAS=0, the state evolves into a meron crystal
and supports an extra gapless U(1) mode in addition to the phonon. For a CP(3)
Skyrmion crystal, we find a U(1) gapless mode in the presence of the
symmetry-breaking fields. In addition, a second mode with a very small gap is
present in the spectrum.Comment: 16 pages and 12 eps figure
Effects of a Six-Month Walking Intervention on the Physical Activity Measures Among Older Adults
Please refer to the pdf version of the abstract located adjacent to the title
Networks of nonlinear superconducting transmission line resonators
We investigate a network of coupled superconducting transmission line
resonators, each of them made nonlinear with a capacitively shunted Josephson
junction coupling to the odd flux modes of the resonator. The resulting
eigenmode spectrum shows anticrossings between the plasma mode of the shunted
junction and the odd resonator modes. Notably, we find that the combined device
can inherit the complete nonlinearity of the junction, allowing for a
description as a harmonic oscillator with a Kerr nonlinearity. Using a dc SQUID
instead of a single junction, the nonlinearity can be tuned between 10 kHz and
4 MHz while maintaining resonance frequencies of a few gigahertz for realistic
device parameters. An array of such nonlinear resonators can be considered a
scalable superconducting quantum simulator for a Bose-Hubbard Hamiltonian. The
device would be capable of accessing the strongly correlated regime and be
particularly well suited for investigating quantum many-body dynamics of
interacting particles under the influence of drive and dissipation.Comment: 18 pages, 3 figure
Effect of a Walking Program on Functional Fitness Measures in Older Adults
Please refer to the pdf version of the abstract located adjacent to the title
Changes in Balance Measures During a Pedometer-Based Senior Citizen Walking Program
Please refer to the pdf version of the abstract located adjacent to the title
Comparing Short Physical Performance Battery Results in Active vs. Non-Active Geriatric Individuals
Please refer to the pdf version of the abstract located adjacent to the title
Changes in Balance Measures During a Six-Month Senior Citizen Walking Program
Please see the pdf version of the abstract
Dynamics of electrons in the quantum Hall bubble phases
In Landau levels N > 1, the ground state of the two-dimensional electron gas
(2DEG) in a perpendicular magnetic field evolves from a Wigner crystal for
small filling of the partially filled Landau level, into a succession of bubble
states with increasing number of guiding centers per bubble as the filling
increases, to a modulated stripe state near half filling. In this work, we show
that these first-order phase transitions between the bubble states lead to
measurable discontinuities in several physical quantities such as the density
of states and the magnetization of the 2DEG. We discuss in detail the behavior
of the collective excitations of the bubble states and show that their spectra
have higher-energy modes besides the pinned phonon mode. The frequencies of
these modes, at small wavevector k, have a discontinuous evolution as a
function of filling factor that should be measurable in, for example, microwave
absorption experiments.Comment: 13 pages, 7 figures. Corrected typos in eqs. (38),(39),(40
UK Housing Market: Time Series Processes with Independent and Identically Distributed Residuals
The paper examines whether a univariate data generating process can be identified which explains the data by having residuals that are independent and identically distributed, as verified by the BDS test. The stationary first differenced natural log quarterly house price index is regressed, initially with a constant variance and then with a conditional variance. The only regression function that produces independent and identically distributed standardised residuals is a mean process based on a pure random walk format with Exponential GARCH in mean for the conditional variance. There is an indication of an asymmetric volatility feedback effect but higher frequency data is required to confirm this. There could be scope for forecasting the index but this is tempered by the reduction in the power of the BDS test if there is a non-linear conditional variance process
Trend and variability in ozone in the tropical lower stratosphere over 2.5 solar cycles observed by SAGE II and OSIRIS
We have extended the satellite-based ozone anomaly time series to the
present (December 2012) by merging SAGE II (Stratospheric Aerosol and Gas Experiment
II) with OSIRIS (Optical Spectrograph and Infrared Imager System)
and correcting for the small bias (~0.5%) between them,
determined using their temporal overlap of 4 years. Analysis of the merged
data set (1984–2012) shows a statistically significant negative trend at all
altitudes in the 18–25 km range, including a trend of (−4.6 ± 2.6)% decade<sup>−1</sup>
at 19.5 km where the relative standard error is a minimum. We are
also able to replicate previously reported decadal trends in the tropical
lower-stratospheric ozone anomaly based on SAGE II observations.
Uncertainties are smaller on the merged trend than the SAGE II trend at all
altitudes. Underlying strong fluctuations in ozone anomaly due to El Niño–Southern Oscillation (ENSO), the altitude-dependent quasi-biennial
oscillation, and tropopause pressure need to be taken into account to reduce
trend uncertainties and, in the case of ENSO, to accurately determine the
linear trend just above the tropopause. We also compare the observed ozone
trend with a calculated trend that uses information on tropical upwelling
and its temporal trend from model simulations, tropopause pressure trend
information derived from reanalysis data, and vertical profiles from SAGE II
and OSIRIS to determine the vertical gradient of ozone and its trend. We
show that the observed trend agrees with the calculated trend and that the
magnitude of the calculated trend is dominated by increased tropical
upwelling, with minor but increasing contribution from the vertical ozone
gradient trend as the tropical tropopause is approached. Improvements are
suggested for future regression modelling efforts which could reduce trend
uncertainties and biases in trend magnitudes, thereby allowing accurate
trend detection to extend below 18 km
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