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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

Potential Impacts of Timber Harvesting, Climate, and Conservation on Sediment Accumulation and Dispersal in the South Slough National Estuarine Reserve, Oregon

Mathabane, Nathan 23 February 2016 (has links)
Accurate sediment flux histories are critical data for deciphering the relative importance of climate and land use factors such as logging and road construction on sediment production and deposition. We use 210Pb activities derived from sediment cores taken on the tidal flats of the South Slough of the Coos Bay estuary to establish temporal variations in sediment accumulation rates. We determined that average deposition varied between 0.4 and 0.81 cm/yr based on two ~80 cm sediment cores. Sedimentation accumulation rates approached 2.1 cm/yr during the 1960s when a rainfall event of extreme intensity coincided with vigorous timber activity. Following this peak, a >40% reduction in peak lumber harvests in the latter part of the 20th century was accompanied by a decrease in sedimentation rates. Mean monthly rainfall during the same time period remained seasonably constant, indicating that land use is likely the key factor governing variations in sediment accumulation.
2

A study of '2'1'0Pb in the atmosphere and estuarine sedimentary environment

Murdock, Christopher Paul January 1999 (has links)
No description available.
3

Settling Particulates on the Continental Slope off Northeast Taiwan ¡GMass Flux ¡AGrain Size Distribution and Disequilibrium between Lead-210 and Polonium-210

Hung, Gwo-Wei 01 February 2001 (has links)
Previous studies have shown that the continental shelf and slope area off northeastern Taiwan is a region where the material exchange processes between the East China Sea and open ocean are most rigorous under the influences of the Kuroshio and the monsoons. In order to understand the topographic effects on the particulate flux and the transport path of the settling particles in this region, this study has conducted a series of field measurements using time-series sediment traps and current meters as tools. The temporal and spatial variations on the current, the particulate flux and the particle-size distribution as well as the activity and flux of 210 Pb and 210 Po are presented in this thesis. The biological productivity and the runoff of main rivers from Taiwan were not correlated with the particulate fluxes in our study area. However, the variations of the particulate flux in the canyon and on the slope areas were clearly affected by the tidal currents, showing good positive correlation with their amplitudes. The particulate, 210 Pb and 210 Po fluxes all showed an increase toward the ocean bottom but a decrease away from the shore, suggesting that the transports of particle and particle reactive elements were strongly influenced by the lateral transport process in the study area. Highest fluxes were observed in the Mien-Hua Canyon(MHC) and the lower slope southwest of the canyon. Intermediate values were observed in the South Okinawa Trough and the North Mien-Hua Canyon(NMHC). The intercanyon slope and the shallow traps in the NMHC had lowest values. The particulates and particle reactive elements were transported out of the shelf or upper slope area essentially through the MHC toward the slope southwest of the canyon. The NMHC and the intercanyon area were not major pathways for these materials. The fluxes of particle, 210 Pb and 210 Po in the study area were generally at least an order of magnitude greater than those observed from other continental margins in the world, except for the lowest values at the intercanyon station and the shallow water in the NMHC. Thus the continental margin off northeastern Taiwan is one of the most important areas for material exchanges with open oceans in the world. The trapped particulates were mainly silt with variable sand fractions. High sand contents were observed in the MHC and the lower slope southwest of the canyon, the intermediate values were in the outlet of the MHC and the NMHC, and the lowest in the South Okinawa Trough. This shows that the sand content decreases awayfrom the shore. On the contrary, silt and clay fractions in percent increase away from the shore. Under the influence of tidal currents, the settling sand particles in the MHC and its adjacent lower slope were laterally transported from resuspended sandy sediments of the continental shelf and upper slope area adjoining the head of the MHC. The fluxes of sand, silt and clay all decreased toward the South Okinawa Trough but increased toward the bottom. This particle-size distribution pattern also reflected the effect of lateral transport process in the study area. Variations of the 210 Pb activity in this study area were generally correlated inversely with the particulate flux and the sand content, indicating the effect of dilution of the mass flux and the sand content, but were positively correlated with the silt and clay contents because they were major 210 Pb scavengers. No apparent correlations of 210 Po with the mass flux and the three particle-size fractions were observed, suggesting that the variation of 210 Po activity was not related to the mass fluxes or the three particle-size fractions. High 210 Pb activities were found to be associated with high contents of POC, Mn and Fe. Correlations of 210 Pb with both Mn and Fe indicate that the oxide and hydroxide precipitates of Mn and Fe supplied from sediments on the continental shelf, upper slope area and submarine hydrothermal activities might serve as important mechanisms for enhanced 210 Pb scavenging. The relationship between the 210 Pb activity and the POC content might reflect either the settling mode of the fine particles incorporated with fecal pellets or aggregates, or sharing the same source with fine particles. The variatio ns of 210 Po activity were not correlated with Mn, Fe, major components or biogenic components, implying that the association of 210 Po with biogenic components might be masked by the enormous terrigenous materials. Except for the upper-trap samples collected at the intercanyon slope and the NMHC, the 210 Po activity was lower than the 210 Pb activity with 210 Po/210 Pb ratios less than unity. Based on comparisons of 210 Pb and 210 Po with relevant parameters and references of past studies, we can propose several possible mechanisms to explain why the ratios were less then unity: 1. 210 Pb was preferentially scavenged by advecting and settling particulates of terrigenous origin. 210 Po, known to be biophilic, might remain associated with the suspended organic particulates which could be dissolved or not settling. Moreover, the oxide and hydroxide precipitates of Mn and Fe in the study area would further enhance the scavenging of 210 Pb. 2. The particulates in suspension were favorable for differentiation between 210 Pb and 210 Ponuclides while those settled in sediments would allow them to grow toward the secular equilibrium. Therefore, the trapped particulates might be in frequent suspension and short in deposited sediments during their lateral transport. 3. The 210 Pb supplied from the East Asia aerosol in large quantity was accumulated in water column abd carried by the Kuroshio to the study area. The intrusion and eddies of Kuroshio off northeastern Taiwan could bring large amount of 210 Pb into the region of continental shelf and slope, allowing particulates to scavenge 210 Pb more effectively from the surrounding water. The upper trap in the NMHC and that in the intercanyon site yield lowest particulate flux but highest POC content. With less terrigenous material and more biogenic components in these samples, 210 Po/210 Pb ratios were greater than unity and variations of 210 Pb activity were hardly correlated with those of POC contents but were inversely correlated with those of Mn contents. However, the 210 Po activities of upper trap at the intercanyon site were well positively correlated with POC and PIC contents, indicating effects of the fresh biogenic particles. Based on the mass balance calculations of particulate and 210 Pb fluxes, current data and other related data gathered in this study, we may infer the sedimentation dynamics and transport path of the settling particles below 300m depth in the study area. Under the influence of tidal oscillation, terrigenous sediments on the shelf and the shelf break as well as the upper slope would be resuspended and carried into the MHC and transported further away. Most of the sand particles would deposit in the canyon while part of the silt and clay would be transported to the South Okinawa Trough directly and the rest to the lower slope southwest of the MHC. The particulate flux at the lower slope southwest of MHC might also have a portion of particulates swept from the upper slope by the Kuroshio eddies. As the NMHC and the intercanyon sites are located in the central area of the Kuroshio eddies, the particulates from the continental shelf and upper slope area would be blocked, resulting in very low particulate fluxes. High particulate fluxes observed in the lower NMHC trap should largely be due to resuspension of the sediments from the banks of the canyon.
4

Distribution Patterns of Lead-210 and Polonium-210 Along the Gaoping Submarine Canyon

Shen, Ya-ting 09 September 2008 (has links)
Abstract The purposes of this study are to understand the variations of the particulate and dissolved 210Pb and 210Po profiles in the water column of Gaoping Submarine Canyon(GSC) and to compare the distributions of the two nuclides in settling particles and sediments. Different types of samples taken in this area were analyzed for 210Pb and 210Po in order to understand processes involved in the particulate transport. Seawater samples were collected from Ocean Researcher III Cruise (ORIII-1192 in Nov, 2006). Sediment trap was deployed on Jun 21, 2000 and recovered on Jul 20, 2000 (ORIII-634). Sediments cores collected from ORIII-642 on Jul 21, 2000 (Core A-B) and ORIII-696 on Apr 7, 2001 (Core D-F) using multicorer. The profiles of 210Pb and 210Po in water column could be divided into two types one is estuarine and the other is oceanic. The profiles of dissolved nuclides in estuarine stations (CW1 to 3) are lower than in the oceanic stations (CW4-5). Because stations CW1 to 3 are controlled by large amount of terrigenous particles, scavenging in the three stations is quite obvious. The nuclide activities of the settling particles decrease with depth, probably due to dilution by resuspended surface sediment of lower activities, similar to observations in this study area. The downcore distributions of 210Pb and 210Po show clearly disequilibria between the two nuclides and suggested that sediment deposited in GSC has been disturbed down to 40-50 cm deep. All the data indicate the 210Po in the water column and in the settling particles as well as in the surface sediments is strongly deficient relative to its parent, 210Pb. Using a box-model and considering the influence of horizontal transports, we may calculate the residence times of 210Po in the 100m water layer in the GSC, to be 2.1d for the dissolved phase and 7.0 d for the particulate phase with a total 210Pb residence time is 3.8d.
5

Patterns and drivers of recent peatland carbon accumulation in northeastern Canada

Sanderson, Nicole Katherine January 2016 (has links)
Northern peatlands are an important component of the global carbon (C) cycle and have been a net sink of atmospheric C during the Holocene. Under current climate warming conditions, the future sink-source balance of these peatlands is uncertain. In particular, peatlands near the southern limit of permafrost are likely to be sensitive to changes in topography as well as climate. In order to predict how the sink-source balance may change, this thesis focuses on determining the generality of observed patterns of C accumulation in Northeastern Canada. The methodological approach in this thesis is unique. A total of 30 cores were taken from 9 peatlands located in 3 ecoclimatic regions along the North Shore of the Gulf of St Lawrence. This replication of records allows for climate-scale (allogenic) signals to be separated from the internal or local factors (autogenic), and for statistical testing of differences between regions and within sites over time. Trends in carbon accumulation rates (CAR) were analysed on three levels: (1) within individual sites along a hydrological or microtopography gradient, (2) between overall regions located along a climatic or permafrost gradient, and (3) over time on a multi-centennial scale. Lead-210 (210Pb) dating was used throughout the analysis to increase temporal resolution for the last 150-200 years of C accumulation. The method was thoroughly tested from preparation to analysis and found to produce reliable results, comparable with other dating methods. These dates were then used to develop combined age-depth models for longer-term context. Replicated records of 210Pb inventories and fallout rates were also used to address questions of deposition patterns and post-depositional mobility in peat profiles. Total inventories decreased with water table depth, with lichen hummocks having significantly higher inventories. One site also received significantly higher 210Pb deposition than the other two, as it is more sheltered from the Gulf influence. Recent carbon accumulation rates for the 150-year period for all microforms across all regions was 62.1 ± 4.4 g C m-2 a-1, and were highest for Sphagnum hummocks (79.9 ± 8.9 g C m-2 a-1) and lowest for dry lichen hummocks (42.7 ± 6.2 g C m-2 a-1). Patterns and trends at this scale were mainly driven by autogenic processes, including incomplete decomposition in the acrotelm peat. Models of peat accumulation related to acrotelm thickness were found to be overly simplistic, as carbon accumulation for intermediate microforms showed large natural variability driven by changing ecohydrological feedbacks, in part due to permafrost degradation at one of the sites. Over a multi-centennial scale, carbon accumulation rates were driven by a combination of climatic changes and ecohydrological feedbacks due to shifts in the microform configuration in response to permafrost degradation. Changes in carbon accumulation rates were detected and coincided with Little Ice Age temperature/solar minima (including the Spörer, Maunder and Dalton Minima), permafrost degradation since the 1950s, and recent climatic changes in the mid-1990s. Snow cover and exposure of sites and microforms were found to play an important role, rather than solely climatic variables. Rapid Sphagnum re-establishment in post-permafrost degraded features and increasing temperatures meant that carbon accumulation was highest for the northernmost site in the transect. Age-depth models using a combination of lead-210 and radiocarbon dates allowed for the calculation of carbon accumulation rates at a decadal resolution. While peat carbon sequestration is projected to increase in northern regions, the fate of peatland C near the southern limit of permafrost is complex. Future studies seeking to interpret recent changes should include multiple cores and consider both regional climatic and local ecohydrological drivers.
6

Determinacao de sup210 Pb e sup210 Po em aguas minerais radioativas

NIERI, ARTIDORO 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:40:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:27Z (GMT). No. of bitstreams: 1 04024.pdf: 3628243 bytes, checksum: 85a871f2396f235238f333eefec1e8ab (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
7

Determinacao de sup210 Pb e sup210 Po em aguas minerais radioativas

NIERI, ARTIDORO 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:40:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:27Z (GMT). No. of bitstreams: 1 04024.pdf: 3628243 bytes, checksum: 85a871f2396f235238f333eefec1e8ab (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
8

Human skeletal uptake of natural alpha radioactivity from '2'1'0Pb-supported '2'1'0Po

Oyedepo, Aderonke Caroline January 1998 (has links)
No description available.
9

Natural #alpha#-radionuclides in children's teeth

James, Patrick R. January 1999 (has links)
No description available.
10

Distribuição do Pb-210 em sedimentos de bacias hidrográficas à mina de urânio de Caldas - MG

Pedro Henrique Dutra 29 April 2014 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O empreendimento das Indústrias Nucleares do Brasil INB Caldas, Minas Gerais, o primeiro complexo mínero-industrial de urânio instalado no Brasil e inaugurado em 1982, está em fase de fechamento e de descomissionamento. Esse empreendimento está situado a mina de urânio a céu aberto Osamu Utsumi e a usina de extração de minério de urânio. Em relação a esta área, está sendo desenvolvido o Projeto Caracterização, monitoramento da qualidade ambiental e recuperação de áreas degradadas pela indústria mineral, incluindo a recuperação de metais de resíduos e de efluentes industriais em uma das linhas de pesquisa do Instituto Nacional de Ciência e Tecnologia em Recursos Minerais, Água e Biodiversidade (INCT-Acqua). Dentre as diversas atividades deste projeto, está a avaliação da qualidade da água e sedimentos no entorno do empreendimento, no município de Caldas, levando em conta os focos de contaminação em potencial e a verificação de impacto da mina em termos da presença de radionuclídeos provenientes da série de decaimento radioativo natural do 238U. A área de estudo é constituída pela Bacia Hidrográfica do Rio Taquari, subdividida por seus três principais sub-bacias: córrego da Consulta, ribeirão Soberbo e rio Taquari. Assim, atendendo a um dos objetivos do projeto, foi realizado este estudo no qual visando verificar a distribuição de 210Pb no entorno da mina, onde os resultados de concentrações da atividade do radionuclídeo em amostras de sedimento coletadas em 4 campanhas, estações seca e chuvosa, em diversos pontos das sub-bacias, foram a base para ser aplicada a técnica de geoprocessamento utilizando as concentrações da atividade de 210Pb medidas. As medidas da concentração de atividade 210Pb foram obtidas por espectrometria gama em detectores de alta e de baixa energias. Para se comparar os resultados obtidos foi calculada a razão entre os resultados dos detectores e normalizados em relação às médias das razões por campanha. Em 12 pontos de coleta foram produzidos 48 resultados, sendo que deste total, 77,1% apresentaram afastamento de apenas 5% em relação à média das razões normalizadas, 12,5 % apresentaram afastamento maior do que 10%, sendo que destes 4,2% acima de 20% de afastamento. Baseando-se nestes percentuais, pode-se afirmar que o desempenho dos detectores foi similar. Assim, verificou-se que a determinação de 210Pb em amostras de sedimento pode ser realizada tanto em detector de alta energia do tipo HPGe com janela de carbono quanto no de baixa energia do tipo HPGe janela de berílio. Em termos de distribuição da atividade de 210Pb nas campanhas e por sub-bacia, pode-se verificar que a proximidade dos corpos dágua de pontos-fonte, descarga de um rio em outro, ações antropogênicas na área e sazonalidade influenciam na variação da concentração de atividade do radionuclídeo. Quanto à aplicação da técnica de geoprocessamento, ela foi útil ao mapear a distribuição espacial do radionuclídeo, realçando as áreas de maior concentração. Os resultados indicam que a mina Osamu Utsumi está influenciando na distribuição de 210Pb no seu entorno. Estudos mais detalhados devem ser conduzidos de modo a identificar ocorrência de anomalias geológicas na região, ainda não identificadas, poderiam estar contribuindo para o aumento da atividade de 210Pb. As medidas da concentração de atividade 210Pb foram obtidas por espectrometria gama em detectores de alta e de baixa energias. Para se comparar os resultados obtidos foi calculada a razão entre os resultados dos detectores e normalizados em relação às médias das razões por campanha. Em 12 pontos de coleta foram produzidos 48 resultados, sendo que deste total, 77,1% apresentaram afastamento de apenas 5% em relação à média das razões normalizadas, 12,5 % apresentaram afastamento maior do que 10%, sendo que destes 4,2% acima de 20% de afastamento. Baseando-se nestes percentuais, pode-se afirmar que o desempenho dos detectores foi similar. Assim, verificou-se que a determinação de 210Pb em amostras de sedimento pode ser realizada tanto em detector de alta energia do tipo HPGe com janela de carbono quanto no de baixa energia do tipo HPGe janela de berílio. Em termos de distribuição da atividade de 210Pb nas campanhas e por sub-bacia, pode-se verificar que a proximidade dos corpos dágua de pontos-fonte, descarga de um rio em outro, ações antropogênicas na área e sazonalidade influenciam na variação da concentração de atividade do radionuclídeo. Quanto à aplicação da técnica de geoprocessamento, ela foi útil ao mapear a distribuição espacial do radionuclídeo, realçando as áreas de maior concentração. Os resultados indicam que a mina Osamu Utsumi está influenciando na distribuição de 210Pb no seu entorno. Estudos mais detalhados devem ser conduzidos de modo a identificar ocorrência de anomalias geológicas na região, ainda não identificadas, poderiam estar contribuindo para o aumento da atividade de 210Pb.As medidas da concentração de atividade 210Pb foram obtidas por espectrometria gama em detectores de alta e de baixa energias. Para se comparar os resultados obtidos foi calculada a razão entre os resultados dos detectores e normalizados em relação às médias das razões por campanha. Em 12 pontos de coleta foram produzidos 48 resultados, sendo que deste total, 77,1% apresentaram afastamento de apenas 5% em relação à média das razões normalizadas, 12,5 % apresentaram afastamento maior do que 10%, sendo que destes 4,2% acima de 20% de afastamento. Baseando-se nestes percentuais, pode-se afirmar que o desempenho dos detectores foi similar. Assim, verificou-se que a determinação de 210Pb em amostras de sedimento pode ser realizada tanto em detector de alta energia do tipo HPGe com janela de carbono quanto no de baixa energia do tipo HPGe janela de berílio. Em termos de distribuição da atividade de 210Pb nas campanhas e por sub-bacia, pode-se verificar que a proximidade dos corpos dágua de pontos-fonte, descarga de um rio em outro, ações antropogênicas na área e sazonalidade influenciam na variação da concentração de atividade do radionuclídeo. Quanto à aplicação da técnica de geoprocessamento, ela foi útil ao mapear a distribuição espacial do radionuclídeo, realçando as áreas de maior concentração. Os resultados indicam que a mina Osamu Utsumi está influenciando na distribuição de 210Pb no seu entorno. Estudos mais detalhados devem ser conduzidos de modo a identificar ocorrência de anomalias geológicas na região, ainda não identificadas, poderiam estar contribuindo para o aumento da atividade de 210Pb   / The Nuclear Industries of Brazil - INB Caldas, State of Minas Gerais, was the first mineral-industrial complex in Brazil. It has been installed since 1982 and at the moment it is under conclusion and decommissioning. This complex consists of an open air uranium mining called Osamu Utsumi, and a unit of process in the extraction of uranium ore. Concerning this area, a project Characterization, monitoring of environment quality and recovering of degraded areas by mining industry, including recovering metals from waste and industrial effluents is one of researches of National Institute for Science and Technology in Mining Resources, Water and Biodiversity (INCT-Acqua). Among the several activities of this project, it is related to the evaluation of water quality and sediment around the complex in Caldas, taking into account the potential sources of contamination and the assessment of the impact of the mine basing on the presence of radionuclides from the radioactive decay series of natural 238U.The study area consists of the Taquari watershed, sub-divided by its three major sub-basins: Consultation stream, Soberbo stream and Taquari river. Therefore, in order to answer one of the objectives of the project, this research was carried to verify the distribution of 210Pb around the mining. The radionuclide activity concentrations were measured in sediment samples that were collected during 4 campaigns, dry and rainy seasons, in several collecting points. The values were the data basis for applying the geoprocessing technique. The results of the 210Pb concentration activity were obtained by gamma spectrometry performed in a high energy detector and also low energy detector. In order to compare the results, the ratio between the measurements on detectors was calculated and normalized related to the average of the ratios per caper detector. Summarizing, in 12 sampling points, 48 results were obtained: 77.1% of the total presented distance of only 5% related to the normalized average; 12.5% presented distance higher than 10% (4.2% above than 20%). Basing on these results, it is possible to state that the detectors had similar performance. Therefore, it was possible to verify that the 210Pb determination in sediment samples can be carried out in both types of detector HPGe, one suitable for measuring high gamma energy with composed carbon window and other suitable for low gamma energy with beryllium window. In relation to the distribution of 210Pb activity during the campaigns, it was possible to verify the influence of the proximity of the water bodies to source-points, discharge of a river into another, anthropogenic activities in the area and seasonality on the variation of the concentration of the radionuclide activity. The use of geoprocessing technique was useful mapping the spatial distribution of 210Pb activity. In the maps, the areas with higher activity were enhanced. The results point out that the Osamu Utsumi mining is influencing on the distribution of 210Pb activity in its neighbourhood. However, more detailed study should be done in order to identify if there is another source of 210Pb like geological anomaly occurrence in the region that may contributing to the 210Pb activity. 

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