Low axial resolution data such as multi-slice CT(MSCT) used for coronary artery disease screening
must balance the potential loss in image clarity, detail and partial volume effects with the benefits to the
patient such as faster acquisition time leading to lower dose exposure. In addition, tracking of the coronary
arteries can aid the location of objects contained within, thus helping to differentiate them from similar in
appearance, difficult to discern neighbouring regions.
A fully automated system has been developed to segment and track the main coronary arteries and
visualize the results. Automated heart isolation is carried out for each slice of an MSCT image using
active contour methods. Ascending aorta and artery root segmentation is performed using a combination of
active contours, morphological operators and geometric analysis of coronary anatomy to identify a starting
point for vessel tracking. Artery tracking and backtracking employs analysis of vessel position combined
with segmented region shape analysis to obtain artery paths. Robust, accurate threshold parameters are
calculated for segmentation utilizing Gaussian Mixture Model fitting and analysis.
The low axial resolution of our MSCT data sets, in combination with poor image clarity and noise
presented the greatest challenge. Classification techniques such as shape analysis have been utilized to
good effect and our results to date have shown that such deficiencies in the data can be overcome, further
promoting the positive benefits to patients.
The analysis of particles produced by solid rocket motor fuels relates to two types of studies: the effect of these particles on the Earth's ozone layer, and the dynamic flight behavior of solid fuel boosters used by the NASA Space Shuttle. Since laser backscatter depends on the particle size and concentration, a lidar system can be used to analyze the particle distributions inside a solid rocket plume in flight. We present an analytical model that simulates the lidar returns from solid rocket plumes including effects of beam profile, spot size, polarization and sensing geometry. The backscatter and extinction coefficients of alumina particles are computed with the T-matrix method that can address non-spherical particles. The outputs of the model include time-resolved return pulses and range-Doppler signatures. Presented examples illustrate the effects of sensing geometry.
A general-purpose remote sensing lidar system model has been developed for use with aerosol targets as well as hard targets in various atmospheric conditions and battlefield aerosol smoke conditions to model the actual analogue return waveform. A description of the model with equations and some of the aerosol parameters are presented. An empirically determined impulse response function from a commercially developed short-range system that operates at 0.905 micrometers is used in the prediction of the analogue output waveform for this particular system. The computed waveforms show the effects of backscatter for aerosol smoke conditions. Some experimental validation of the model for a hard target in military fog oil smoke is shown. This model will be used to predict performance of the current lidar sensor as well as other senors under various other atmospheric and battlefield smoke conditions.
Neutron irradiation of sapphire with 1 x 1022 neutrons(<EQ MeV)/m2 increases the c-axis compressive strength by a factor of 3 at 600 degree(s)C. The mechanism of strength enhancement is the retardation of r-plane twin propagation by radiation-induced defects. 1-B and Cd shielding was employed during irradiation to filter our thermal neutrons (<EQ1 eV), thereby reducing residual radioactivity in the sapphire to background levels in a month. Yellow-brown irradiated sapphire is nearly decolorized to pale yellow by annealing at 600 degree(s)C with no loss of mechanical strength. Annealing at sufficiently high temperature (such as 1200 degree(s)C for 24 h) reduces the compressive strength back to its baseline value. Neutron irradiation decreases the flexure strength of sapphire at 600 degree(s)C by 0-20% in some experiments. However, the c- plane ring-on-ring flexure strength at 600 degree(s)C is doubled by irradiation. Elastic constants of irradiated sapphire are only slightly changed by irradiation. Infrared absorption and emission and thermal conductivity of sapphire are not affected by irradiation at the neutron fluence used in this study. Defects that might be correlated with strengthening were characterized by electron paramagnetic resonance spectroscopy. Color centers observed in the ultraviolet absorption spectrum were not clearly correlated with mechanical response. No radiation-induced changes could be detected by x-ray topography or x-ray diffraction.
Submerged spectral reflectance measurements made on paint samples using two different techniques are compared. With the first technique spectral measurements are made with a simple thin water film measurement technique originally used for photopic viewing. A comparison of these measurements with a second technique in which the measured sample is immersed in water in a cylindrical container and the submerged reflectance is measured with a goniophotometer shows good agreement for wavelengths from 420 to 700 nm.