1,367 research outputs found
Use of kinematic algorithms to distinguish people with chronic non-specific low back pain from asymptomatic subjects: A validation study
Objective: To determine whether kinematic algorithms can distinguish subjects with chronic non-specific low back pain from asymptomatic subjects and subjects simulating low back pain, during trunk motion tasks.Design: Comparative cohort study.Subjects: A total of 90 subjects composed 3 groups; 45 chronic non-specific low back pain patients in the CLBP group; 45 asymptomatic controls people in the asymptomatic controls group. 20/45 subjects from the asymptomatic controls group composed the CLBP simulators group as well. Method: During performance of 7 standardized trunk motion tasks 6 spinal segments from the kinematic spine model were recorded by 8 infrared cameras. Two logit scores, for range of motion and speed, were used to investigate differences between the groups. Group allocation based on logit scores was also calculated, allowing the assessment of sensitivity and specificity of the algorithms. Results: For the 90 subjects (pooled data), the logit scores for range of motion and speed demonstrated highly significant differences between groups (p<0.001). The logit score means and standard deviation (SD) values in the asymptomatic group (n = 45) and chronic non-specific low back pain group (n = 45), respectively, were -1.6 (SD 2.6) and 2.8 (SD 2.8) for range of motion and -2.6 (SD 2.5) and 1.2 (SD 1.9) for speed. The sensitivity and specificity (n = 90) for logit score for range of motion were 0.80/0.82 and for logit score for speed were 0.80/0.87, respectively. Conclusion: These results support the validity of using 2 movement algorithms, range of motion and speed, to discriminate asymptomatic subjects from those with low back pain. However, people simulating low back pain cannot be distinguished from those with real low back pain using this method
Summary Abstract: A theoretical study of the effect of lateral interactions on molecular adsorption and desorption
The effect of lateral interactions between coadsorbed molecules on adsorbate island growth and the kinetics of adsorption and desorption have been studied within the constraints of a lattice gas model incorporating a combination of deterministic rate equations with a stochastic formulation. The adsorption and desorption of molecular nitrogen on Ru(001) has been investigated in detail. Recent experiments performed at 77 K reveal an unusual functional dependence of the probability of adsorption which displays a maximum at a coverage of approximately 0.2 monolayer [1,2]. EEL spectra indicate chemisorption of molecular nitrogen occurs only at atop sites with the molecular axis oriented perpendicular to the surface plane [2]. Saturation coverage is achieved at approximately 0.5 monolayer [1,2]. Thermal desorption spectra suggest the presence of two distinct chemisorption states at coverages greater than 0.25 monolayer. Quantitative agreement between calculated and experimental thermal desorption spectra as well as the coverage-dependent probability of adsorption is obtained
Onset of dielectric modes at 110K and 60K due to local lattice distortions in non-superconducting YBa_{2}Cu_{3}O_{6.0} crystals
We report the observation of two dielectric transitions at 110K and 60K in
the microwave response of non-superconducting YBa_{2}Cu_{3}O_{6.0} crystals.
The transitions are characterized by a change in polarizability and presence of
loss peaks, associated with overdamped dielectric modes. An explanation is
presented in terms of changes in polarizability of the apical O atoms in the
Ba-O layer, affected by lattice softening at 110K, due to change in buckling of
the Cu-O layer. The onset of another mode at 60K strongly suggests an
additional local lattice change at this temperature. Thus microwave dielectric
measurements are sensitive indicators of lattice softening which may be
relevant to superconductivity.Comment: 5 pages, 3 ps format figure
Coupling between electronic and structural degrees of freedom in the triangular lattice conductor NaxCoO2
The determination by powder neutron diffraction of the ambient temperature
crystal structures of compounds in the NaxCoO2 family, for 0.3 < x <= 1.0, is
reported. The structures consist of triangular CoO2 layers with Na ions
distributed in intervening charge reservoir layers. The shapes of the CoO6
octahedra that make up the CoO2 layers are found to be critically dependent on
the electron count and on the distribution of the Na ions in the intervening
layers, where two types of Na sites are available. Correlation of the shapes of
cobalt-oxygen octahedra, the Na ion positions, and the electronic phase diagram
in NaxCoO2 is made, showing how structural and electronic degrees of freedom
can be coupled in electrically conducting triangular lattice systems.Comment: 15 pages, 1 tables, 6 figures Submitted to Physical Review
From Black Strings to Black Holes
Using recently developed numerical methods, we examine neutral compactified
non-uniform black strings which connect to the Gregory-Laflamme critical point.
By studying the geometry of the horizon we give evidence that this branch of
solutions may connect to the black hole solutions, as conjectured by Kol. We
find the geometry of the topology changing solution is likely to be nakedly
singular at the point where the horizon radius is zero. We show that these
solutions can all be expressed in the coordinate system discussed by Harmark
and Obers.Comment: 6 pages, 5 figures, RevTe
Summary Abstract: A theoretical study of the effect of lateral interactions on molecular adsorption and desorption
Adaptation and enslavement in endosymbiont-host associations
The evolutionary persistence of symbiotic associations is a puzzle.
Adaptation should eliminate cooperative traits if it is possible to enjoy the
advantages of cooperation without reciprocating - a facet of cooperation known
in game theory as the Prisoner's Dilemma. Despite this barrier, symbioses are
widespread, and may have been necessary for the evolution of complex life. The
discovery of strategies such as tit-for-tat has been presented as a general
solution to the problem of cooperation. However, this only holds for
within-species cooperation, where a single strategy will come to dominate the
population. In a symbiotic association each species may have a different
strategy, and the theoretical analysis of the single species problem is no
guide to the outcome. We present basic analysis of two-species cooperation and
show that a species with a fast adaptation rate is enslaved by a slowly
evolving one. Paradoxically, the rapidly evolving species becomes highly
cooperative, whereas the slowly evolving one gives little in return. This helps
understand the occurrence of endosymbioses where the host benefits, but the
symbionts appear to gain little from the association.Comment: v2: Correction made to equations 5 & 6 v3: Revised version accepted
in Phys. Rev. E; New figure adde
Phonons from neutron powder diffraction
The spherically averaged structure function \soq obtained from pulsed
neutron powder diffraction contains both elastic and inelastic scattering via
an integral over energy. The Fourier transformation of \soq to real space, as
is done in the pair density function (PDF) analysis, regularizes the data, i.e.
it accentuates the diffuse scattering. We present a technique which enables the
extraction of off-center phonon information from powder diffraction experiments
by comparing the experimental PDF with theoretical calculations based on
standard interatomic potentials and the crystal symmetry. This procedure
(dynamics from powder diffraction(DPD)) has been successfully implemented for
two systems, a simple metal, fcc Ni, and an ionic crystal, CaF. Although
computationally intensive, this data analysis allows for a phonon based
modeling of the PDF, and additionally provides off-center phonon information
from powder neutron diffraction
Correlated local distortions of the TlO layers in TlBaCuO: An x-ray absorption study
We have used the XAFS (x-ray-absorption fine structure) technique to
investigate the local structure about the Cu, Ba, and Tl atoms in orthorhombic
Tl-2201 with a superconducting transition temperature T=60 K. Our results
clearly show that the O(1), O(2), Cu, and Ba atoms are at their ideal sites as
given by the diffraction measurements, while the Tl and O(3) atoms are more
disordered than suggested by the average crystal structure. The Tl-Tl distance
at 3.5 \AA{ } between the TlO layers does not change, but the Tl-Tl distance at
3.9 \AA{ } within the TlO layer is not observed and the Tl-Ba and Ba-Tl peaks
are very broad. The shorter Tl-O(3) distance in the TlO layer is about 2.33
\AA, significantly shorter than the distance calculated with both the Tl and
O(3) atoms at their ideal sites ( 0 or ). A model based
on these results shows that the Tl atom is displaced along the
directions from its ideal site by about 0.11 \AA; the displacements of
neighboring Tl atoms are correlated. The O(3) atom is shifted from the $4e$
site by about 0.53 \AA{ } roughly along the directions. A comparison of
the Tl L-edge XAFS spectra from three samples, with T=60 K, 76 K,
and 89 K, shows that the O environment around the Tl atom is sensitive to T
while the Tl local displacement is insensitive to T and the structural
symmetry. These conclusions are compared with other experimental results and
the implications for charge transfer and superconductivity are discussed. This
paper has been submitted to Phys. Rev. B.Comment: 20 pages plus 14 ps figures, REVTEX 3.
- …