700 research outputs found
Quantifying Cross-scatter Contamination in Biplane Fluoroscopy Motion Analysis Systems
Biplane fluoroscopy is used for dynamic in vivo three-dimensional motion analysis of various joints of the body. Cross-scatter between the two fluoroscopy systems may limit tracking accuracy. This study measured the magnitude and effects of cross-scatter in biplane fluoroscopic images. Four cylindrical phantoms of 4-, 6-, 8-, and 10-in. diameter were imaged at varying kVp levels to determine the cross-scatter fraction and contrast-to-noise ratio (CNR). Monte Carlo simulations quantified the effect of the gantry angle on the cross-scatter fraction. A cadaver foot with implanted beads was also imaged. The effect of cross-scatter on marker-based tracking accuracy was investigated. Results demonstrated that the cross-scatter fraction varied from 0.15 for the 4-in. cylinder to 0.89 for the 10-in. cylinder when averaged across kVp. The average change in CNR due to cross-scatter ranged from 5% to 36% CNR decreases for the 4- and 10-in. cylinders, respectively. In simulations, the cross-scatter fraction increased with the gantry angle for the 8- and 10-in. cylinders. Cross-scatter significantly increased static-tracking error by 15%, 25%, and 38% for the 6-, 8-, and 10-in. phantoms, respectively, with no significant effect for the foot specimen. The results demonstrated submillimeter marker-based tracking for a range of phantom sizes, despite cross-scatter degradation
Beyond XSPEC: Towards Highly Configurable Analysis
We present a quantitative comparison between software features of the defacto
standard X-ray spectral analysis tool, XSPEC, and ISIS, the Interactive
Spectral Interpretation System. Our emphasis is on customized analysis, with
ISIS offered as a strong example of configurable software. While noting that
XSPEC has been of immense value to astronomers, and that its scientific core is
moderately extensible--most commonly via the inclusion of user contributed
"local models"--we identify a series of limitations with its use beyond
conventional spectral modeling. We argue that from the viewpoint of the
astronomical user, the XSPEC internal structure presents a Black Box Problem,
with many of its important features hidden from the top-level interface, thus
discouraging user customization. Drawing from examples in custom modeling,
numerical analysis, parallel computation, visualization, data management, and
automated code generation, we show how a numerically scriptable, modular, and
extensible analysis platform such as ISIS facilitates many forms of advanced
astrophysical inquiry.Comment: Accepted by PASP, for July 2008 (15 pages
Biplane Fluoroscopy for Hindfoot Motion Analysis during Gait: A Model-based Evaluation
The purpose of this study was to quantify the accuracy and precision of a biplane fluoroscopy system for model-based tracking of in vivo hindfoot motion during over-ground gait. Gait was simulated by manually manipulating a cadaver foot specimen through a biplane fluoroscopy system attached to a walkway. Three 1.6-mm diameter steel beads were implanted into the specimen to provide marker-based tracking measurements for comparison to model-based tracking. A CT scan was acquired to define a gold standard of implanted bead positions and to create 3D models for model-based tracking. Static and dynamic trials manipulating the specimen through the capture volume were performed. Marker-based tracking error was calculated relative to the gold standard implanted bead positions. The bias, precision, and root-mean-squared (RMS) error of model-based tracking was calculated relative to the marker-based measurements. The overall RMS error of the model-based tracking method averaged 0.43â±â0.22 mm and 0.66â±â0.43° for static and 0.59â±â0.10 mm and 0.71â±â0.12° for dynamic trials. The model-based tracking approach represents a non-invasive technique for accurately measuring dynamic hindfoot joint motion during in vivo, weight bearing conditions. The model-based tracking method is recommended for application on the basis of the study results
Ethnic and gender differences in perceptions of mortality risk in a Canadian urban centre
Gilat L Grunau1, Pamela A Ratner1,2, Shahadut Hossain11NEXUS; 2School of Nursing, University of British Columbia, Vancouver, Canada; University of British Columbia, Vancouver, CanadaBackground: Women reportedly do not perceive heart disease (HD) as a major threat to their health; however, men’s perceptions are rarely studied.Purpose: We explored gender and ethnic differences in risk perception of HD mortality.Methods: The survey was completed by 976 people 40+ years of age, in metropolitan Vancouver, Canada.Results: Men, compared with women, were more likely not to know the answer to a question about whether HD is the most common cause of death for women; however, women were more likely not to know the answer to a question about whether HD is the most common cause of death for men. Chinese-Canadian and South Asian-Canadian participants were more likely than participants of other ethnic groups not to know the answer to either question, and the Chinese-Canadian participants were more likely to disagree that HD is the most common cause of death for women.Conclusion: There is a need to educate the Chinese-Canadian and South Asian-Canadian communities about HD as a first step in promoting health behavior change. Men and women must be educated about the other gender’s risk of HD because all adults play integral roles in making decisions about the prevention of and early intervention for HD.Keywords: risk assessment, heart disease, mortality, gender, ethnic group
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Decay Studies of Neutron-Deficient Nuclei Near the Z=64 Subshell: 141Dy, 141Tb, 141Gdg+m, and 141Eum
Dynamic Load Measurement of Ballistic Gelatin Impact Using an Instrumented Tube
Bird strikes are a common problem for the aerospace industry and can cause serious damage to an aircraft. Ballistic gelatin is frequently used as a surrogate for actual bird carcasses in bird strike tests. Numerical simulations of these tests are used to supplement experimental data, therefore it is necessary to use numerical modeling techniques that can accurately capture the dynamic response of ballistic gelatin. An experimental technique is introduced to validate these modeling techniques. A ballistic gelatin projectile is fired into a strike plate attached to a 36 in. long sensor tube. Dynamic load is measured at two locations relative to the strike plate using strain gages configured in a full Wheatstone bridge. Data from these experiments are used to validate a gelatin constitutive model. Simulations of the apparatus are analyzed to investigate its performance
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Space charge behaviour in epoxy laminates under high constant electric field
The development of space charge in insulating materials is one of the main causes of their electrical ageing. The pulsed electro-acoustic method is often used to determine space charge distribution, but the signal analysis in the case of laminate structures is much more complex to analyse. In this paper the authors describe and use a simulated signal in order to study laminates made of epoxy resin and fibre mat. The relatively large conductivity of the fibres compared with that of the resin seems to produce a rapid charge dissociation and recombination in the fibres. Under voltage the presence of fibres close to an electrode seems to promote charge injection
First Principles Study of Structural, Electronic and Magnetic Interplay in Ferroelectromagnetic Yttrium Manganite
We present results of local spin density approximation pseudopotential
calculations for the ferroelectromagnet, yttrium manganite (YMnO3). The origin
of the differences between ferroelectric and non-ferroelectric perovskite
manganites is determined by comparing the calculated properties of yttrium
manganite in its ferroelectric hexagonal and non-ferroelectric orthorhombic
phases. In addition, orthorhombic YMnO3 is compared with the prototypical
non-ferroelectric manganite, lanthanum manganite. We show that, while the
octahedral crystal field splitting of the cubic perovskite structure causes a
centro-symmetric Jahn-Teller distortion around the Mn3+ ion, the markedly
different splitting in hexagonal perovskites creates an electronic
configuration consistent with ferroelectric distortion. We explain the nature
of the distortion, and show that a local magnetic moment on the Mn3+ ion is a
requirement for it to occur.Comment: Replacement of earlier version with error in pseudopotentia
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