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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Analysis of the benthic Cumacea and Gammaridean Amphipoda from the western Beaufort Sea

Castillo Alarcon, Jorge Gonzalo 18 August 1975 (has links)
A multidisciplinary western Beaufort Sea Ecological Cruise (WEBSEC) was conducted from August 15 to September 20, 1971. During the cruise, one hundred ninety-nine 0.1 m² Smith-McIntyre grabs samples were taken at forty stations located on the continental shelf and slope of the western Beaufort Sea. The Gammaridean Amphipoda and Cumacea collected were sorted and identified. Each sample was analyzed for the number of species and specimens within those groups. The data for all samples at each station were pooled to obtain station data; these were analyzed for abundance, diversity at each station, and similarity between stations. Environmental parameters including sediment data, temperature, salinity and organic carbon content measured during the same cruise were also analyzed for each station. The diversity indices chosen were the Simpson index (SDI) and the Shannon-Wiener index (H'[subscript e]). The results obtained show a e relatively high diversity and animal density in the outer continental shelf, but low diversity values on the inner continental shelf and slope. The lowest SDI value obtained is 0.43 at 2572 m depth. The SDI values on the outer continental shelf are higher than 0.9 and compare well with values obtained in more temperate regions. The similarity between stations is low, and the percentage of rare species found is high. This indicates a patchy distribution of the Amphipoda and Cumacea fauna. The variability of the processes affecting the benthic environment of the western Beaufort Sea suggest that more intensive and seasonal studies are necessary in order to understand the seasonal as well as the annual variation of the infauna of the western Beaufort Sea. / Graduation date: 1976
142

The relationship between morphology and ecology in the spatangoid urchin Brisaster latifrons

Brownell, Charles Lawrence 16 January 1970 (has links)
Graduation date: 1970
143

Phytoplankton of an ice-edge bloom in the Ross Sea, with special reference to the elemental composition of Antarctic diatoms

Carbonell, Maria Consuelo 09 April 1985 (has links)
A phytoplankton bloom dominated by the pennate diatom Nitzschia curta (Van Heurck) Hasle was observed during January-February 1983 at a receding ice-edge in the Western Ross Sea, Antarctica. The core of the bloom was found between 100-150 Km from the ice-edge. Nitzschia curta cell densities up to 22 x 10⁶ cells/1 were observed. The nanoplankton contributed to 18% (average) of the total biomass. The contribution of another pennate diatom, Nitzschia closterium (Ehrenberg) W. Smith, was significant in two offshore stations (22% and 90%). Other diatom species, dinoflagellates and other phytoplankton groups were very few in number. A wind-driven upwelling event occurred along the ice-edge. The presence of off-shore species (e.g. Nitzschia kerguelensis) close to the ice suggests the existence of an eddy circulation. Results of elemental composition experiments with 10 Antarctic diatoms showed that the C:Si:N ratio for Antarctic diatoms, when compared to the Redfield-Richards ratio for diatoms of other environments, have less carbon and more silicon per unit nitrogen. Comparison of laboratory results with the field data confirms the anomalous elemental composition of the major bloom species observed in the Ross Sea. Blooms like the one observed in this study seem to be restricted to the Western part of the Ross Sea and appear to be produced in inshore waters late in the austral summer. / Graduation date: 1985
144

A review and key to the apogonid fishes (Pisces: Perciformes) of the Northwestern Arabian Sea and Southern Gulf of Oman, with description of two new species

Mee, Jonathan K. L. 25 March 1996 (has links)
Field collections in the Southern Gulf of Oman and the Northwestern Arabian Sea, and examination of museum collections from this study area, yielded 7 genera and 33 species of apogonid fishes. Twenty one species of Apogon, one Archamia, four Cheilodipterus, three Fowleria, one Rhabdamia, two Siphamia, and one Holapogon are reviewed and illustrated. The Dhofar Cardinalfish, Apogon dhofar, nov. sp. is described from 21 specimens collected in the Arabian Sea, off southern Oman. It differs from the very similar A. pseudotaeniatus Gon, 1986 in its higher gill-raker count (12-17 developed rakers vs. 9-11) and coloration. Apogon dhofar has narrower dark vertical bars (one scale row or less wide vs. two or more for A. pseudotaeniatus) which are often indistinct or absent in life and tend to fade with size; and a caudal spot which is much smaller (2-3% SL vs. 4-6% SL for pseudotaeniatus) and often absent in life. Both A. dhofar and A. pseudotaeniatus have small dark chromatophores covering their bodies, but A. dhofar differs in having these chromatophores concentrated under the posterior edge of each scale producing a reticulate pattern on the body. The Cryptic Cardinalfish, Apogon species C., is described from 19 specimens collected in the Gulf of Oman and Arabian Gulf It differs from the similar A. taeniatus Ehrenberg, 1828 in its lower gill-raker count (8 developed rakers vs. 10-15) and horizontal stripes (7-8 dark stripes vs. 5-6 indistinct stripes). Apogon species C. also has 3-4 short brown stripes radiating away from the eye whereas A. taeniatus occasionally has one narrow dark stripe. Apogon species C. lacks any caudal spot which is usually present in A. taeniatus. Apogon thurstoni Day, 1888 is shown to be a junior synonym of Apogon nigripinnis Cuvier, 1828, and Apogon smithvanizi Allen and Randall, 1994 is shown to be a junior synonym of Apogon gularis Fraser and Lachner, 1986. Apogon pharaonis Bellotti, 1874, formerly considered a junior synonym of Apogon nigripinnis Cuvier, 1828, is shown to be a valid species occurring in the Red Sea and western Indian Ocean, and the range of A. nigripinnis is redefined as eastern Indian to western Pacific. Apogon suezi Sauvage, 1883 is shown to be a junior synonym of A. pharaonis. A review is presented of the systematic literature of the apogonid fishes from the study area, and a key to genera and species is provided. Included in the key are 33 apogonid species known from the area and an additional 7 species (and one genus) not yet recorded but likely to occur. / Graduation date: 1997
145

Aspects of Late Helladic sea trade

Bachhuber, Christoph Stephen 30 September 2004 (has links)
The trade mechanisms joining the Mycenaean Aegean to the greater Levant have intrigued and eluded Bronze Age scholarship since the earliest discoveries of foreign objects in Mycenaean burials. In the past decade, topics of interregional trade in the eastern Mediterranean have enjoyed renewed discussions, inspired in no small part by the excavation of the Uluburun shipwreck. Data generated from the shipwreck is amounting to an extraordinary body of evidence for contact between the Aegean and the Near East. The proposed Mycenaean presence on board the Uluburun ship requires that the sum of evidence and hypotheses for trade between the two regions be re-examined. By attempting to demonstrate the role the Mycenaeans had performed on the last journey of the Uluburun ship, an important mechanism of trade may be revealed between the Aegean and Semitic worlds.
146

An investigation of array elements for enhanced single echo acquisition imaging

Dominick, Colleen Elizabeth 30 October 2006 (has links)
Rapid MR imaging has facilitated the development of a variety of medical tools such as MR guided surgeries, drug delivery, stent placement, biopsies, and blood flow imaging. This rapid imaging is largely attributable to the development of parallel imaging techniques. In one such technique, single echo acquisition (SEA) imaging, scan time is reduced by substituting the lengthy phase encoding process with spatial information from an extensive receiver coil array. In order to easily construct and obtain images from this coil array, an ideal set of coil elements would be easily decoupled and tuned, possess high SNR and penetration depth, and would allow for operation in both transmit and receive mode. Several types of coils have been considered for use in massive coil arrays, including the planar pair coil, the loop coil and the stripline coil. This thesis investigates each of these coils for use in massive arrays for SEA imaging with enhanced penetration. This investigation includes: improving the currents on the planar pair coil, determining the feasibility of the loop coil and the stripline coil at the scale required for SEA, and comparing the salient properties of each coil type. This investigation revealed that the stripline coil appears to be the best coil element for SEA imaging with enhanced penetration.
147

Fast and contrast-enhanced phase-sensitive magnetic resonance imaging

Son, Jong Bum 15 May 2009 (has links)
Phase-sensitive magnetic resonance (MR) imaging has a number of important clinical applications, such as phase-sensitive inversion recovery (PSIR) and Dixon water/fat imaging. PSIR and Dixon techniques are widely used in neurological and body imaging to improve tissue-contrast, the former by extending the dynamic range of image intensity and the later by suppressing unnecessary fat signals. Several important limitations, however, occur in these techniques: (1) Dixon techniques cannot decompose two signals if the resonance frequencies are close. For example, in MR mammography, it is difficult to separate silicone breast implants signals (4.0 ppm) from fat signals (3.5 ppm); (2) the signal dynamic range of images acquired using Dixon techniques is limited by the equilibrium magnetization; and (3) long image acquisition time. These limitations have hindered the applications of phase-sensitive Dixon imaging techniques on breast implant imaging or as a screening tool where fast acquisition is required. In this work, novel phase-sensitive MRI techniques were developed to enhance the capability, image-contrast, and scan-efficiency of Dixon imaging techniques. Specifically, we developed (1) a generalized chemical-shift imaging technique to separate spectrally overlapped signals both T1-contrast and chemical-shift; (2) a contrast-enhanced Dixon technique to extend the signal dynamic range of Dixon images; and (3) a single-echo acquisition (SEA) imaging technique integrated with phase-sensitive MR imaging to provide ultra-fast image acquisitions. Phantom studies, performed on 1.5 T and 4.7 T MR scanners, demonstrated the developed generalized chemical-shift imaging technique could clearly separate breast silicone implant signals (4.0 ppm) from fat (3.5 ppm). The contrast-enhanced Dixon technique, by extending the dynamic range of signal intensity from positive levels to positive/negative levels, could improve image-contrast by 1.6 times, compared with a conventional single-point Dixon technique. Phantom studies, using a 64-channel SEA imaging system, showed the integrated Dixon technique with SEA could acquire decomposed 2-D water-only and fat-only images with ultra-fast frame-rates up to 1/TR, while providing improved image-contrast (by 2.4 times in this experiment) compared with a conventional SEA imaging technique.
148

Interannual variability and future changes of the Southern Ocean sea ice cover

Lefebvre, Wouter 16 November 2007 (has links)
The interannual variability of the sea ice in the Southern Ocean and its evolution projected for the end of the 21st century are investigated using observations and different types of models. First of all, none of the known atmospheric modes of variability are able to explain much of the total sea ice extent variability in the Southern Ocean. However, they have large influences on the local and regional scales. In particular, the response of the sea ice to the Southern Annular Mode is characterized by a dipole between the Ross Sea and the region around the Antarctic Peninsula caused by a low pressure anomaly in the Amundsen Sea in high SAM-index years. Secondly, the sea ice extent in the different regions seems to be mostly uncorrelated, showing that the total sea ice cover cannot be seen as a single entity, but merely as a combination of regional covers. Finally, it is shown why the projected distribution of sea ice is not a simple extrapolation of the current sea ice trends. The mechanisms responsible for the regional variability of the future sea-ice extents are discussed.
149

Fast and contrast-enhanced phase-sensitive magnetic resonance imaging

Son, Jong Bum 15 May 2009 (has links)
Phase-sensitive magnetic resonance (MR) imaging has a number of important clinical applications, such as phase-sensitive inversion recovery (PSIR) and Dixon water/fat imaging. PSIR and Dixon techniques are widely used in neurological and body imaging to improve tissue-contrast, the former by extending the dynamic range of image intensity and the later by suppressing unnecessary fat signals. Several important limitations, however, occur in these techniques: (1) Dixon techniques cannot decompose two signals if the resonance frequencies are close. For example, in MR mammography, it is difficult to separate silicone breast implants signals (4.0 ppm) from fat signals (3.5 ppm); (2) the signal dynamic range of images acquired using Dixon techniques is limited by the equilibrium magnetization; and (3) long image acquisition time. These limitations have hindered the applications of phase-sensitive Dixon imaging techniques on breast implant imaging or as a screening tool where fast acquisition is required. In this work, novel phase-sensitive MRI techniques were developed to enhance the capability, image-contrast, and scan-efficiency of Dixon imaging techniques. Specifically, we developed (1) a generalized chemical-shift imaging technique to separate spectrally overlapped signals both T1-contrast and chemical-shift; (2) a contrast-enhanced Dixon technique to extend the signal dynamic range of Dixon images; and (3) a single-echo acquisition (SEA) imaging technique integrated with phase-sensitive MR imaging to provide ultra-fast image acquisitions. Phantom studies, performed on 1.5 T and 4.7 T MR scanners, demonstrated the developed generalized chemical-shift imaging technique could clearly separate breast silicone implant signals (4.0 ppm) from fat (3.5 ppm). The contrast-enhanced Dixon technique, by extending the dynamic range of signal intensity from positive levels to positive/negative levels, could improve image-contrast by 1.6 times, compared with a conventional single-point Dixon technique. Phantom studies, using a 64-channel SEA imaging system, showed the integrated Dixon technique with SEA could acquire decomposed 2-D water-only and fat-only images with ultra-fast frame-rates up to 1/TR, while providing improved image-contrast (by 2.4 times in this experiment) compared with a conventional SEA imaging technique.
150

The future of the Salton Sea under proposed lower Colorado River basin water management scenarios

Kjelland, Michael Edward 2008 December 1900 (has links)
The Salton Sea, situated in the Lower Colorado River Basin (LCRB), is under duress due to, among other things, increased water demands of cities like San Diego, California and Mexicali, Mexico. This research developed a tool to investigate the implications of water transfers on the health and sustainability of the Salton Sea Ecosystem. The Salton Sea model is a spatially-explicit, stochastic, simulation model representing water flow, i.e., water volume and quantity of Total Dissolved Salts (TDS) and Phosphorus (P), in the LCRB as it enters the Salton Sea. The model is formulated as a compartment model based on difference equations with a daily time step using STELLA® 8.0 software. The model was developed, evaluated, and applied to simulate the potential effects on the population dynamics of selected fish and avian species at the Salton Sea under six different scenarios. Oneway ANOVAs and Bonferroni Multiple Comparison Post Hoc Tests were performed for the water management scenarios and selected variables involving the fish and bird population dynamics using SPSS version 12.0.1 (SPSS Inc., 2003). Weather station daily data were collected for both precipitation and Eto for a 25- year period (1980-2004) for the Salton Sea area. Thirty-four probability distributions were fit to the monthly datasets. Monthly distributions were used to preserve seasonality when modeling future climate scenarios. Additionally, binomial and multinomial logistic regression models were utilized to determine the relationships concerning precipitation events and Eto levels. Further, two strategies were employed in modeling the uncertainty in future climate patterns, namely deterministic and stochastic versions of the driving variables. A climate sensitivity analysis was also conducted and results showed that the cumulative effects and change of plus or minus 10 percent in Salton Sea inflows can have significant effects on sea elevation and salinity. Both of the Salton Sea impoundment scenarios significantly (P<0.05) lowered the salinity in the north or main sea impoundments compared to future downward trends in sea elevation and upward trends in salinity under baseline conditions. Further, the elevations of the north or main sea impoundments were stabilized at -220 by the end of 2024. Should action be taken to stabilize the sea and reduce salinity, the impoundment scenarios demonstrated the most success in the present study. If no such action is taken, the simulation results demonstrate that the current community dynamics of the Salton Sea will be further impaired as a result.

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