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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.
1

Environmental Influences on the Genetic Diversity of Bacterial Communities in Arctic Streams

Larouche, Julia 13 February 2009 (has links)
The National Park Service (NPS) Inventory and Monitoring (I&M) Program is designed to collect baseline data on “vital sign” indicators across the entire NPS system. The project presented in this thesis was designed to supplement to efforts of the Artic Network (ARCN) to catalogue the physical, chemical and biological metrics associated with the Stream Communities and Ecosystems vital sign and to foster a better understanding of the basic structure and function of these remote systems. This data is essential to assess the impacts of current and future environmental change in the ARCN parks. The primary objective of this project was to quantify the genetic diversity of microbial communities of selected arctic stream ecosystems. Microbes are a fundamentally important but poorly understood component of arctic stream ecosystems. They are responsible for recycling organic matter and regenerating nutrients that are essential to the food webs of aquatic ecosystems. Recent research (Jorgenson et al. 2002) in the ARCN parks has shown that two fundamentally different lithologies – ultramafic and non-carbonate – influence terrestrial productivity and impart different geochemical characteristics to stream water. Microbes are found in different stream habitats – sediment (epipssamon) and rock (epilithon) biofilms. In this work we test the hypothesis that these differences in lithology and stream habitat influence the genetic diversity of bacterial biofilm communities in arctic streams and whether these patterns can be correlated to stream biogeochemistry. A microbial community fingerprinting method, T-RFLP, as well as 16S rRNA gene sequencing were used to explore the genetic diversity of microbial communities in sediment and epilithic biofilms in stream reaches that drain watersheds with contrasting lithologies in the Noatak National Preserve, Alaska. Differing patterns in bacterial community composition at both the large-scale (lithology) and small-scale (stream habitat) were observed. Non-metric multidimensional scaling (NMDS) ordination of T-RFLP peaks and Analysis of Similarity (ANOSIM) showed a high degree of separation (ANOSIM P < 0.001) between the non-carbonate and ultramafic lithologies, as well as the two habitats, sediment and epilithon. Significant (P < 0.005, Bonferroni corrected) positive correlations were detected between particular nutrients, base cations, and dissolved organic carbon and bacterial community structure unique to each lithology. Although clone libraries indicated high bacterial OTU diversity within and across stream sites, biogeographical patterns were observed depending on locality type. Rarefaction analyses indicated that streams arising from the non-carbonate lithology may be more diverse than streams arising from the ultramafic lithology. Analysis of MOlecular VAriance (AMOVA) indicated that sediment and epilithon samples had genetically different microbial communities (P = 0.01) and taxonomic identifications revealed markedly different bacterial residents between sediment and epilithon habitats. Our results show relationships at large- and small-scales at the landscape level and in ecological niches within a single stream.
2

Predation and the prey community of a headwater stream

Schofield, K. January 1988 (has links)
No description available.
3

The Electrochemistry Of Metal Ions In Industrial Streams

Van Aswegen, Anton 24 April 2006 (has links)
Degree: Master of Science Department: Engineering / The electrochemical recovery of low concentrations ( < 200 1 l mg − ) of palladium and platinum from a selected refinery effluent was investigated. Cyclic Voltammetry (CV) provided qualitative evidence that palladium and platinum contained in an effluent with an acid chloride matrix could be deposited on a graphite cathode. Experimental techniques related to (i) the use of synthetic solutions (ii) the variation of potential scan ranges, (iii) the use of a witness ion ( + 3 Fe ), and (iv) the use of glassy carbon or platinum disc working electrodes were used to assist with the interpretation of voltammograms. Exhaustive electrolysis experiments via a graphite working electrode demonstrated the recovery of palladium and platinum in the refinery effluent to concentrations of < 1 1 l mg − . Copper present in the effluent was co-deposited with the precious metals. Exchange current densities ( o j ), electron transfer coefficients ( á), standard rate constants ( s k ) and mass transfer coefficients ( m k ) were determined for selected reduction-oxidation (redox) couples via a custom made Rotating Disc Electrode (RDE).
4

Post-restoration evaluation of two urban streams in Austin, Texas, USA

Meier, Megan Driskill 15 May 2009 (has links)
Rapid urban growth of Austin, Texas, has resulted in significant alteration of the surface characteristics of the Colorado River Watershed. These changes have increased the runoff and accelerated erosion of the banks of stream channels. To minimize the threat of stream erosion to real estate and infrastructure, the City of Austin began restoring unstable channel reaches through the placement of rock armor on the banks, construction of rock grade controls, and planting of riparian vegetation. Since the late 1990s, approximately thirty channel reaches have been restored in the Austin area. Considerable discussion is taking place regarding the true impact of restoration on streams. Few studies have attempted to conduct post-project evaluation to assess the impact of restoration efforts. Because it has been several years since steps were taken to stabilize these streams, a sufficient time period for stabilization to occur has passed. Thus, we believe these projects now can be assessed for the temporal impact of restoration on these streams. We studied the restored and natural reaches of two of these streams. The natural reaches served as ergodic surrogates for temporal channel development of the restored reaches. We used Rosgen’s (2001) methodology of channel stability assessment and repeat ground photography (Graf, 1985) to evaluate the stability of Waller Creek and Tannehill Branch. Variables of channel morphology analyzed included riparian vegetation cover, vertical stability, scour/deposition potential, and bed sediment composition. From our analysis, restoration enlarged stream channels, decreased bank height ratios and reduced flood prone width. Bed sediment analysis revealed that pools contain a higher percentage of fines whereas riffles are coarser in restored reaches than pre-restoration reaches. Visual examination of ground photographs and scores from the Pfankuch channel stability evaluation indicate that restoration increased vegetative cover and deposition. Thus, restoration efforts worked on these two streams. Data from the assessments of stream channel stability provide the basis upon which longer-term monitoring and evaluation can be conducted. Knowledge gained from long-term monitoring can be used to improve the effectiveness of the current and future restoration projects in Texas and elsewhere.
5

Implementations of Splitting and Merging Mechanisms for SVC Streams on Mixed Wired and Wireless Networks

Hsieh, Yi-Chuen 01 July 2010 (has links)
In this thesis, we propose two mechanisms, stream splitting and merging, to fully utilize the bandwidth in a mixed wired and wireless network. The two mechanisms implemented on a SVC Streaming Gateway (SSG) mainly exploit the characteristics of multi-layer SVC (Scalable Video Coding). In the stream splitting mechanism, the available bandwidth can be calculated on SSG, so that an adequate number of layers of a SVC stream can be determined for splitting. In the stream merging mechanism, when the available bandwidth is increased, a stream with more number of enhancement layers can be extracted to merge onto a stream with less number of layers. Additionally, when two streams pass through SSG concurrently, one stream may arrive at SSG faster due to different traffic conditions. If one stream with more SVC layers is faster than the one with less SVC layers, we buffer the packets of the faster stream on SSG, so that the buffered packets can be merged to the top of SVC layers of the slow stream. On the other hand, if one stream with more SVC layers is slower than the one with less SVC layers, to effectively merge the enhancement layers of the slow stream onto the faster stream, SSG will delay the packets of the faster stream to wait for the packets of the slow stream. Finally, we implement these two mechanisms on the Linux platform. In the experiments, we measure buffer delay, queue length, and the number of merged packets to demonstrate that the two proposed mechanisms can effectively improve the picture freeze-up and mosaic phenominon.
6

Post-restoration evaluation of two urban streams in Austin, Texas, USA

Meier, Megan Driskill 15 May 2009 (has links)
Rapid urban growth of Austin, Texas, has resulted in significant alteration of the surface characteristics of the Colorado River Watershed. These changes have increased the runoff and accelerated erosion of the banks of stream channels. To minimize the threat of stream erosion to real estate and infrastructure, the City of Austin began restoring unstable channel reaches through the placement of rock armor on the banks, construction of rock grade controls, and planting of riparian vegetation. Since the late 1990s, approximately thirty channel reaches have been restored in the Austin area. Considerable discussion is taking place regarding the true impact of restoration on streams. Few studies have attempted to conduct post-project evaluation to assess the impact of restoration efforts. Because it has been several years since steps were taken to stabilize these streams, a sufficient time period for stabilization to occur has passed. Thus, we believe these projects now can be assessed for the temporal impact of restoration on these streams. We studied the restored and natural reaches of two of these streams. The natural reaches served as ergodic surrogates for temporal channel development of the restored reaches. We used Rosgen’s (2001) methodology of channel stability assessment and repeat ground photography (Graf, 1985) to evaluate the stability of Waller Creek and Tannehill Branch. Variables of channel morphology analyzed included riparian vegetation cover, vertical stability, scour/deposition potential, and bed sediment composition. From our analysis, restoration enlarged stream channels, decreased bank height ratios and reduced flood prone width. Bed sediment analysis revealed that pools contain a higher percentage of fines whereas riffles are coarser in restored reaches than pre-restoration reaches. Visual examination of ground photographs and scores from the Pfankuch channel stability evaluation indicate that restoration increased vegetative cover and deposition. Thus, restoration efforts worked on these two streams. Data from the assessments of stream channel stability provide the basis upon which longer-term monitoring and evaluation can be conducted. Knowledge gained from long-term monitoring can be used to improve the effectiveness of the current and future restoration projects in Texas and elsewhere.
7

Numerical analysis of source-water dynamics for stream-bounded alluvial aquifers

Webb, Sarah E., January 2003 (has links)
Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 119 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references.
8

The impact of subglacial hydrology on force balance for a physically modeled ice stream

Wagman, Benjamin Moore 20 July 2012 (has links)
We use a physical model to investigate how changes in the distribution of subglacial hydrology affect ice motion of Antarctic ice streams. Ice streams are modeled using silicone polymer placed over a thin water layer to mimic ice flow dominated by basal sliding. Dynamic similarity between modeled and natural ice streams is achieved through direct comparison of the model force balance and the observed force balance of Whillans Ice Stream (WIS). The WIS force balance has evolved over time due to increased basal resistance. We test two hypotheses: 1) the subglacial water distribution influences the ice flow speed and thus the force balance and; 2) shear margins are locations where transitions in water layer thickness occur. The velocity and force balance are sensitive to pulsed water discharge events and changes in lubrication associated with sticky spots, and model shear margins tend to overlie water lubrication boundaries. Local changes in basal lubrication near margins (possibly as a result of the presence of sticky spots or subglacial lakes) influences the stability of the margin position and may be responsible for large and rapid shifts in margin location. / text
9

Heterogeneous video transcoding for matching network-bandwidth and end-system constraints

Shanableh, Tamer Jamal January 2001 (has links)
No description available.
10

Effects of anthropogenic alterations to ephemeral and intermittent headwater drainage features on downstream fish communities

Hennigar, Julie Michelle January 2012 (has links)
Headwater drainage features (HDFs) in the GTA are commonly subjected to land-use modifications including agricultural uses and urbanization. A temporal study design approach was used to test whether the runoff being exported from previously modified HDFs differed from runoff exported from less disturbed forested channels. Drift nets were deployed in the permanent reaches of streams and in the HDF channels, to give an indication of the quality and quantity of drifting materials. Gastric lavage was used to remove stomach contents from creek chub living downstream from HDFs and these contents were used to determine if invertebrates in HDF runoff could act as food immediately upon reaching fish-bearing sections of stream. Reaches of streams associated with forested HDFs were found to have more fish than either those associated with agricultural or urban HDFs (203, 184 and 145 fish per forested, agricultural and urban site, respectively). Sites associated with forested catchments also had a greater number of salmonids per site. Conditions of high flow in the stream and the HDF coincided with an increased quantity of drifting invertebrates in all site types and land uses, as well as a decrease in the proportion of creek chub with empty stomachs. Overall, aquatic Diptera were the most numerous invertebrates captured in drift nets and in the stomach contents of creek chub. Hymenoptera, terrestrial Oligochaeta and Diplopoda also made major contributions to the diets of creek chub. Results indicate that HDFs in all land uses are exporting both aquatic and terrestrial invertebrates to main streams at times of high flow. Creek chub consume more prey at times of high flow, and this often includes terrestrial invertebrates, which must have been imported from terrestrial sources to the aquatic environment, however the degree to which they are exported by HDFs is still not clear. The series of complex interactions occurring at the HDF/main stream interface requires further study.

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