600 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
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
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
Angular momentum sharing in dissipative collisions
Light charged particles emitted by the projectile-like fragment were measured
in the direct and reverse collision of Nb and Sn at 25 AMeV. The
experimental multiplicities of Hydrogen and Helium particles as a function of
the primary mass of the emitting fragment show evidence for a correlation with
net mass transfer. The ratio of Hydrogen and Helium multiplicities points to a
dependence of the angular momentum sharing on the net mass transfer.Comment: 8 pages, 2 figure
Spontaneous emission rates of dipoles in photonic crystal membranes
We show theoretically that finite two-dimensional (2D) photonic crystals in
thin semiconductor membranes strongly modify the spontaneous emission rate of
embedded dipole emitters. Three-dimensional Finite-Difference Time-Domain
calculations show over 7 times inhibition and 15 times enhancement of the
emission rate compared to the vacuum emission rate for judiciously oriented and
positioned dipoles. The vertical index confinement in membranes strongly
enhances modifications of the emission rate as compared to vertically
unconfined 2D photonic crystals. The emission rate modifications inside the
membrane mimic the local electric field mode density in a simple 2D model. The
inhibition of emission saturates exponentially as the crystal size around the
source is increased, with a length that is inversely proportional to the
bandwidth of the emission gap. We obtain inhibition of emission only close to
the slab center. However, enhancement of emission persists even outside the
membrane, with a distance dependence which dependence can be understood by
analyzing the contributions to the spontaneous emission rate of the different
vertically guided modes of the membrane. Finally we show that the emission
changes can even be observed in experiments with ensembles of randomly oriented
dipoles, despite the contribution of dipoles for which no gap exists
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