12,927 research outputs found
Exact Results for 1D Kondo Lattice from Bosonization
We find a solvable limit to the problem of the 1D electron gas interacting
with a lattice of Kondo scattering centers. In this limit, we present exact
results for the problems of incommensurate filling, commensurate filling,
impurity vacancy states, and the commensurate-incommensurate transition.Comment: 4 pages, two columns, Latex fil
A test matrix sequencer for research test facility automation
The hardware and software configuration of a Test Matrix Sequencer, a general purpose test matrix profiler that was developed for research test facility automation at the NASA Lewis Research Center, is described. The system provides set points to controllers and contact closures to data systems during the course of a test. The Test Matrix Sequencer consists of a microprocessor controlled system which is operated from a personal computer. The software program, which is the main element of the overall system is interactive and menu driven with pop-up windows and help screens. Analog and digital input/output channels can be controlled from a personal computer using the software program. The Test Matrix Sequencer provides more efficient use of aeronautics test facilities by automating repetitive tasks that were once done manually
Enhancement of pairing in a boson-fermion model for coupled ladders
Motivated by the presence of various charge inhomogeneities in strongly
correlated systems of coupled ladders, a model of spatially separated bosonic
and fermionic degrees of freedom is numerically studied. In this model, bosonic
chains are connected to fermionic chains by two types of generalized Andreev
couplings. It is shown that for both types of couplings the long-distance
pairing correlations are enhanced. Near quarter filling, this effect is much
larger for the splitting of a pair in electrons which go to the two neighboring
fermionic chains than for a pair hopping process. It is argued that the pairing
enhancement is a result of the nearest neighbor Coulomb repulsion which tunes
the competition between pairing and charge ordering.Comment: 7 pages, 7 eps figures, enlarged version accpeted in Phys. Rev.
The impact of rheumatoid arthritis on foot function in the early stages of disease: a clinical case series
BACKGROUND
Foot involvement occurs early in rheumatoid arthritis but the extent to which this impacts on the structure and function leading to impairment and foot related disability is unknown. The purpose of this study was to compare clinical disease activity, impairment, disability, and foot function in normal and early rheumatoid arthritis (RA) feet using standardised clinical measures and 3D gait analysis.
METHODS
Twelve RA patients with disease duration ≤2 years and 12 able-bodied adults matched for age and sex underwent 3D gait analysis to measure foot function. Disease impact was measured using the Leeds Foot impact Scale (LFIS) along with standard clinical measures of disease activity, pain and foot deformity. For this small sample, the mean differences between the groups and associated confidence intervals were calculated using the t distribution
RESULTS
Moderate-to-high foot impairment and related disability were detected amongst the RA patients. In comparison with age- and sex-matched controls, the patients with early RA walked slower (1.05 m/s Vs 1.30 m/s) and had a longer double-support phase (19.3% Vs 15.8%). In terminal stance, the heel rise angle was reduced in the patients in comparison with normal (-78.9° Vs -85.7°). Medial arch height was lower and peak eversion in stance greater in the RA patients. The peak ankle plantarflexion power profile was lower in the patients in comparison with the controls (3.4 W/kg Vs 4.6 W/kg). Pressure analysis indicated that the RA patients had a reduced lesser toe contact area (7.6 cm2 Vs 8.1 cm2), elevated peak forefoot pressure (672 kPa Vs 553 kPa) and a larger mid-foot contact area (24.6 cm2 Vs 19.4 cm2).
CONCLUSION
Analysis detected small but clinically important changes in foot function in a small cohort of RA patients with disease duration <2 years. These were accompanied by active joint disease and impairment and disability
The differing magnitude distributions of the two Jupiter Trojan color populations
The Jupiter Trojans are a significant population of minor bodies in the
middle Solar System that have garnered substantial interest in recent years.
Several spectroscopic studies of these objects have revealed notable
bimodalities with respect to near-infrared spectra, infrared albedo, and color,
which suggest the existence of two distinct groups among the Trojan population.
In this paper, we analyze the magnitude distributions of these two groups,
which we refer to as the red and less red color populations. By compiling
spectral and photometric data from several previous works, we show that the
observed bimodalities are self-consistent and categorize 221 of the 842 Trojans
with absolute magnitudes in the range H<12.3 into the two color populations. We
demonstrate that the magnitude distributions of the two color populations are
distinct to a high confidence level (>95%) and fit them individually to a
broken power law, with special attention given to evaluating and correcting for
incompleteness in the Trojan catalog as well as incompleteness in our
categorization of objects. A comparison of the best-fit curves shows that the
faint-end power-law slopes are markedly different for the two color
populations, which indicates that the red and less red Trojans likely formed in
different locations. We propose a few hypotheses for the origin and evolution
of the Trojan population based on the analyzed data.Comment: Published in AJ; 26 pages, 7 figure
Theory of doped Mott insulators: duality between pairing and magnetism
By bosonizing the electronic t-J model exactly on any two-dimensional (2D)
lattices, and integrating out the gauge fluctuations combined to slave
particles beyond mean fields, we get a theory in terms of physical Cooper pair
and spin condensates. In the sense of mutual Berry phase they turns out to be
dual to each other. The mutual-duality is the missing key in the
resonant-valance-bond idea\cite{rvb} to work as a paradigm of doped 2D Mott
insulators. We argue that essential aspects of high- phenomenology find
natural solutions in the theory. We also provide interesting predictions for
systems on hexagonal lattices.Comment: 4 pages, no figures, Submitted to Phys. Rev. Let
True infliximab resistance in rheumatoid arthritis: a role for lymphotoxin α?
Background: The combination of methotrexate and the anti-tumour necrosis factor (TNF) antibody infliximab is a very effective treatment for rheumatoid arthritis (RA). However, a proportion of patients are not responsive to this treatment. Inefficacy may represent a TNF independent disease or insufficient drug at the site of action.
Case report: A patient with RA resistant to repeated high dose infliximab infusions and intra-articular infliximab into an inflamed knee is described. No beneficial clinical effect was observed. Pre-injection arthroscopic biopsy of the study knee demonstrated TNF staining but also confirmed the presence of lymphotoxin (LT or TNFß) on immunohistochemistry. Subsequent treatment with etanercept (which blocks LT as well as TNF) resulted in clinical remission of disease.
Conclusion: This case suggests that resistance to TNF blockade may occur when TNF is not the dominant inflammatory cytokine and suggests that LT may have a pathogenic role in RA
Particle-hole symmetry in the antiferromagnetic state of the cuprates
In the layered cuprate perovskites, the occurence of high-temperature
superconductivity seems deeply related to the unusual nature of the hole
excitations. The limiting case of a very small number of holes diffusing in the
antiferromagnetic (AF) background may provide important insights into this
problem. We have investigated the transport properties in a series of crystals
of , and found that the temperature dependences of the Hall
coefficient and thermopower change abruptly as soon as the AF phase
boundary is crossed. In the AF state at low temperatures , both and
are unexpectedly suppressed to nearly zero over a broad interval of . We
argue that this suppression arises from near-exact symmetry in the
particle-hole currents. From the trends in and , we infer that the
symmetry is increasingly robust as the hole density becomes very small
(). We discuss implications for electronic properties both within
the AF state and outside.Comment: 8 pages, 7 figure
Sea surface velocities from visible and infrared multispectral atmospheric mapping sensor imagery
High resolution (100 m), sequential Multispectral Atmospheric Mapping Sensor (MAMS) images were used in a study to calculate advective surface velocities using the Maximum Cross Correlation (MCC) technique. Radiance and brightness temperature gradient magnitude images were formed from visible (0.48 microns) and infrared (11.12 microns) image pairs, respectively, of Chandeleur Sound, which is a shallow body of water northeast of the Mississippi delta, at 145546 GMT and 170701 GMT on 30 Mar. 1989. The gradient magnitude images enhanced the surface water feature boundaries, and a lower cutoff on the gradient magnitudes calculated allowed the undesirable sunglare and backscatter gradients in the visible images, and the water vapor absorption gradients in the infrared images, to be reduced in strength. Requiring high (greater than 0.4) maximum cross correlation coefficients and spatial coherence of the vector field aided in the selection of an optimal template size of 10 x 10 pixels (first image) and search limit of 20 pixels (second image) to use in the MCC technique. Use of these optimum input parameters to the MCC algorithm, and high correlation and spatial coherence filtering of the resulting velocity field from the MCC calculation yielded a clustered velocity distribution over the visible and infrared gradient images. The velocity field calculated from the visible gradient image pair agreed well with a subjective analysis of the motion, but the velocity field from the infrared gradient image pair did not. This was attributed to the changing shapes of the gradient features, their nonuniqueness, and large displacements relative to the mean distance between them. These problems implied a lower repeat time for the imagery was needed in order to improve the velocity field derived from gradient imagery. Suggestions are given for optimizing the repeat time of sequential imagery when using the MCC method for motion studies. Applying the MCC method to the infrared brightness temperature imagery yielded a velocity field which did agree with the subjective analysis of the motion and that derived from the visible gradient imagery. Differences between the visible and infrared derived velocities were 14.9 cm/s in speed and 56.7 degrees in direction. Both of these velocity fields also agreed well with the motion expected from considerations of the ocean bottom topography and wind and tidal forcing in the study area during the 2.175 hour time interval
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