2,683 research outputs found
Are tibial angles measured with inertial sensors useful surrogates for frontal plane projection angles using 2-dimensional video analysis during single leg squat tasks? A reliability and agreement analysis in elite football (soccer) players
During single leg squats (SLS), tibial angle (TA) quantification using inertial measurement units (IMU) may offer
a practical alternative to frontal plane projection angle (FPPA) measurement using 2-dimensional (2D) video
analysis. This study determined: (i) the reliability of IMUs and 2D video analysis for TA measurement, and 2D
video analysis for FPPA measurement; (ii) the agreement between IMU TA and both 2D video TA and FPPA
measurements during single leg squats in elite footballers. 18 players were tested on consecutive days. Absolute
TA (ATA) and relative TA (RTA) were measured with IMUs. ATA and FPPA were measured concurrently using
2D video analysis. Within-session reliability for all measurements varied across days (intraclass correlation
coefficient (ICC) range=0.27â0.83, standard error of measurement (SEM) range=2.12â6.23°, minimal detectable
change (MDC) range=5.87â17.26°). Between-sessions, ATA reliability was good for both systems
(ICCs=0.70â0.74, SEMs=1.64â7.53°, MDCs=4.55â7.01°), while IMU RTA and 2D FPPA reliability ranged
from poor to good (ICCs=0.39â0.72, SEMs=2.60â5.99°, MDCs=7.20â16.61°). All limits of agreement exceeded
a 5° acceptability threshold. Both systems were reliable for between-session ATA, although agreement
was poor. IMU RTA and 2D video FPPA reliability was variable. For SLS assessment, IMU derived TAs are not
useful surrogates for 2D video FPPA measures in this population
Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradientârecalled echo measurement
Purpose
To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientationâdependent part of R*2 using a single gradientârecalled echo (GRE) measurement.
Methods
The proposed method utilized a temporal secondâorder approximation of the hollowâcylinderâfiber model, in which the parameter describing the linear signal decay corresponded to the orientationâindependent part of R*2. The estimated parameters were compared to the classical, monoâexponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientationâdependent and âindependent parts.
Results
Using the phenomenological method on the classical signal model, the wellâknown separation of R*2 into orientationâdependent and âindependent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed.
Conclusions
Since the proposed secondâorder model features orientationâdependent and âindependent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement
Institutional and policy issues in the management of fisheries and coastal resources in Cambodia
Fishery management, Governments, Fishery policies, Resource conservation, Resource management, Cambodia,
Scaling of the anomalous Hall effect in SrCaRuO
The anomalous Hall effect (AHE) of ferromagnetic thin films of
SrCaRuO (0 0.4) is studied as a function of
and temperature . As increases, both the transition temperature
and the magnetization are reduced and vanish near 0.7. For all
compositions, the transverse resistivity varies non-monotonously
with , and even changes sign, thus violating the conventional expression
( is the magnetic induction, while
and are the ordinary and anomalous Hall coefficients). From the rather
complicated data of , we find a scaling behavior of the transverse
conductivity with , which is well reproduced by the
first-principles band calculation assuming the intrinsic origin of the AHE.Comment: REVTeX 4 style; 5 pages, 3 figures; revised 23/2 and accepted for
publicatio
The Johnson-Segalman model with a diffusion term in Couette flow
We study the Johnson-Segalman (JS) model as a paradigm for some complex
fluids which are observed to phase separate, or ``shear-band'' in flow. We
analyze the behavior of this model in cylindrical Couette flow and demonstrate
the history dependence inherent in the local JS model. We add a simple gradient
term to the stress dynamics and demonstrate how this term breaks the degeneracy
of the local model and prescribes a much smaller (discrete, rather than
continuous) set of banded steady state solutions. We investigate some of the
effects of the curvature of Couette flow on the observable steady state
behavior and kinetics, and discuss some of the implications for metastability.Comment: 14 pp, to be published in Journal of Rheolog
Measurement of statistical nuclear spin polarization in a nanoscale GaAs sample
We measure the statistical polarization of quadrupolar nuclear spins in a
sub-micrometer (0.6 um^3) particle of GaAs using magnetic resonance force
microscopy. The crystalline sample is cut out of a GaAs wafer and attached to a
micro-mechanical cantilever force sensor using a focused ion beam technique.
Nuclear magnetic resonance is demonstrated on ensembles containing less than 5
x 10^8 nuclear spins and occupying a volume of around (300 nm)^3 in GaAs with
reduced volumes possible in future experiments. We discuss how the further
reduction of this detection volume will bring the spin ensemble into a regime
where random spin fluctuations, rather than Boltzmann polarization, dominate
its dynamics. The detection of statistical polarization in GaAs therefore
represents an important first step toward 3D magnetic resonance imaging of
III-V materials on the nanometer-scale.Comment: 20 pages, 6 figures, 1 supplementary fil
Propagator Resolved Transverse Relaxation Exchange Spectroscopy
We use the propagator resolved transverse relaxation exchange technique to look at the movement of fluid in three different types of rock samples. The two pore model previously used to fit molecular exchange simulations to the experimental data is expanded to accommodate the three site exchange seen in two of the samples. Estimated values for pore space characteristics from the simulations were compared to values calculated from XâRay CT data of the samples. While discrepancies exist between the NMR and XâRay CT results, the molecular exchange behavior estimated from the three samples reflects well with their morphology
Structural properties of crumpled cream layers
The cream layer is a complex heterogeneous material of biological origin
which forms spontaneously at the air-milk interface. Here, it is studied the
crumpling of a single cream layer packing under its own weight at room
temperature in three-dimensional space. The structure obtained in these
circumstances has low volume fraction and anomalous fractal dimensions. Direct
means and noninvasive NMR imaging technique are used to investigate the
internal and external structure of these systems.Comment: 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phy
DJ-1 interacts with and regulates paraoxonase-2, an enzyme critical for neuronal survival in response to oxidative stress.
Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP+ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2
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