Browsing by Subject "tomography"
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Item A morphological comparison of Holospira monclovana and Holospira picta (Gastropoda: Urocoptidae) using X-ray computed tomography(2012-05-12) Rilling, Rigel Keith; Rilling, Rigel Keith; Strenth, Ned E.; Maxwell, Terry C.; Negovetich, Nick J.; Cordell-McNulty, Kristi; Angelo State University. Department of Biology.This study was undertaken to re-evaluate the taxonomic placement of two species of xeric-adapted holospirids from near Monclova, Coahuila, Mexico using techniques unavailable to researchers at the time of the original descriptions of these species. X-ray computed tomography was used to scan the complete series of Holospira monclovana (n=24, including holotype) and of Holospira picta (n=27, including holotype), as well as 26 of another series of specimens (assigned to Holospira picta by the original author) from approximately 35 km southeast of Monclova. The program ImageJ was used to analyze Xray CT scans of all specimens. Analyses of Similarities (ANOSIM) were conducted using the statistical suite R to compare the three populations, both pairwise and all together (Null hypothesis: R≈0; dissimilarities within groups ≥ dissimilarities between groups). Analysis shows all three populations to be statistically distinct (R=0.398, p<0.001), supports the retention of H. monclovana within subgenus Holospira, and supports reassignment of both populations of H. picta to the subgenus Bostrichocentrum.Item Seismic tomography constraints on reconstructing the Philippine Sea Plate and its margin(Texas A&M University, 2005-02-17) Handayani, LinaThe Philippine Sea Plate has been surrounded by subduction zones throughout Cenozoic time due to the convergence of the Eurasian, Pacific and Indian-Australian plates. Existing Philippine Sea Plate reconstructions have been made based primarily on magnetic lineations produced by seafloor spreading, rock magnetism and geology of the Philippine Sea Plate. This dissertation employs seismic tomography model to constraint the reconstruction of the Philippine Sea Plate. Recent seismic tomography studies show the distribution of high velocity anomalies in the mantle of the Western Pacific, and that they represent subducted slabs. Using these recent tomography data, distribution maps of subducted slabs in the mantle beneath and surrounding the Philippine Sea Plate have been constructed which show that the mantle anomalies can be related to the various subduction zones bounding the Philippine Sea Plate. The high velocity mantle anomalies are clearly coincident with Wadati-Benioff zones in the upper mantle. The lower mantle anomalies, although distributed in the ?transition zone? (500-1000 km) as stagnant slabs in some cases, can clearly be mapped as continuations of upper mantle subduction zones. Reconstructing the subduction of the slabs now in the mantle best fits Philippine Sea Plate reconstructions that involve the minimal or simplest rotations. Northward movement of the Philippine Sea Plate, WNW subduction of the Pacific Plate since Eocene time (~50 Ma), and northward subduction of the Indian/Australian Plate along Indonesia best explain the subducted slab mantle anomalies. The origin of the eastern plate boundary was a transform zone that evolved into a subduction zone a few million years before the Pacific Plate changed its movement. In addition, the initiation of this subduction zone might possibly be one of the triggers of the Pacific Plate motion changes. The 90 degree rotation of the Philippine Sea Plate including southward plate subduction at its northern boundary proposed in the reconstruction by Hall (2002) is not supported by seismic tomography evidence for slab distribution in the mantle beneath the Philippine Sea region. A hypothesis of minimal rotation of the Philippine Sea Plate, supported by the seismic tomography, guides the reconstruction model presented.Item Ultrasound-modulated optical tomography for biomedical applications(Texas A&M University, 2004-11-15) Li, JunI experimentally studied ultrasound-modulated optical tomography, which holds the promise for biomedical diagnosis. I measured the degree of polarization of laser speckles generated by scattered light transmitted through turbid media, investigated three signal-detection schemes for extracting the intensity of the ultrasound-modulated light, carried out experiments to image thick biological-tissue samples, and studied two techniques providing resolution in the cross-sections containing the ultrasonic axis. The study of degree of polarization presented results important for the understanding of polarization phenomena in turbid media. I explored an optical-filtering based signal detection scheme, improved the parallel-lock-in speckle detection scheme and proposed a speckle-contrast detection scheme. With the speckle-contrast detection scheme, I successfully obtained images of biological-tissue samples up to 50 mm thick. Further I studied frequency-swept ultrasound-modulated optical tomography for sub-millimeter resolution imaging, and developed ultrasound-modulated optical computed tomography that was based on a back-projection image reconstruction method and obtained clear images of biological-tissue samples.