• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 95
  • 69
  • 17
  • 10
  • 6
  • 5
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 2
  • 2
  • 1
  • Tagged with
  • 240
  • 32
  • 32
  • 23
  • 20
  • 19
  • 19
  • 18
  • 16
  • 15
  • 14
  • 14
  • 13
  • 13
  • 13
  • 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

Estudo do comportamento mecânico de misturas de resíduo da fabricação de papel e solo para utilização na construção rodoviária / Study of the mechanical behavior of paper mill wastes and soil mixtures for their utilization in road construction

Carlos Ernesto Chávez Molina 25 June 2004 (has links)
O resíduo sólido estudado na presente pesquisa e decorrente da associação de lama de calcário e dregs (expressão muito utilizada na indústria do papel, inclusive no Brasil, que poderia ser traduzida como \'borra\'), materiais gerados na fabricação de papel. Tradicionalmente, este resíduo é depositado em aterros sanitários ou em áreas controladas. No entanto, a disponibilidade de espaços adequados para a disposição é pequena, e a conservação dos mesmos é muito dispendiosa, visto que apresentam riscos de contaminação para o ambiente e fauna circundantes. Assim, este tipo de solução não é mais visto como viável a longo prazo. Este trabalho tem como objetivo principal determinar, a partir de ensaios de laboratório, o comportamento mecânico de misturas constituídas com solos e o resíduo em destaque, visando a sua utilização na construção rodoviária. Foram compactados corpos-de-prova com e sem adição de resíduo na energia normal do Proctor, variando-se o tipo de solo, o teor de cal e o tempo de cura, e posteriormente foram submetidos a ensaios de compressão simples, compressão diametral e índice de suporte Califórnia. Complementarmente, foram realizados ensaios de difração de raios-X e microscopia eletrônica por varredura para determinar, respectivamente, a composição química e micro-estrutura do resíduo. Os resultados mostraram que a adição do resíduo da fabricação de papel aos solos não melhora as propriedades mecânicas das misturas compactadas, sendo necessária a utilização de um estabilizante, como a cal, para melhorar as más características. Porém para os solos estudados, as misturas de solo, resíduo e cal apresentaram melhor comportamento mecânico que as misturas de solo-cal, oferecendo uma solução factível para a utilização deste resíduo na construção rodoviária. / The solid waste studied in the present research results from the association of lime mud and dregs, these materials are generated during the paper manufacturing. Traditionally, this waste is disposed of either surface impoundment or landfills. However, there is limited appropriate land availability for these disposal practices, and its maintenance is costly, due to the present contamination risks for the surrounding environment and fauna. Therefore, this kind of solution is no longer seen as long term viable. This work has the main objective of studying, based on laboratory tests, the mechanical behavior of soils and the wastes in focus mixtures, seeking their utilization in road construction. Specimens with and without the addition of waste were compacted at the normal proctor energy, varying the soil type, the lime rate and curing time, afterwards they were submitted to tests of unconfined compressive strength, indirect tensile strength and California bearing ratio. Complementary, tests of ray-X diffraction and spectrum electronic microscopy were executed to respectively determine the chemical composition and microstructure of the waste. The results showed that the addition of paper mill wastes to soils does not improve the mechanical properties of the compacted mixtures, being necessary the use of a stabilizer, such as lime, to improve its poor characteristics. However for the studied soils; the lime stabilized soils and the waste mixtures presented bettermechanical behavior than the lime stabilized soils offering a feasible solution for the use of this waste in road construction.
142

Typologie, architecture et origine des structures d'émission de fluides et leurs interactions avec les processus sédimentaires et tectoniques. Exemple de la Méditerranée Orientale / Typology, architecture and origin of fluid emission structures and their interactions with sedimentary and tectonic processes. Example of the Eastern Mediterranean

Mary, Flore 08 June 2018 (has links)
Depuis le début des années 80, les progrès technologiques de l'imagerie des fonds marins et l'exploration des marges continentales ont permis de découvrir et d'étudier de nombreuses morphologies du fond marin témoignant de la circulation des fluides dans la colonne sédimentaire et de leur expulsion. Dans cette étude des volcans de boue, nous proposons une méthode d'analyse innovante combinant une approche statistique automatisée incluant la détection et l'analyse de paramètres morphométriques avec une étude géologique classique. Nous avons utilisé un vaste jeu de données de géophysiques marines et géologiques, d’origines académiques et industrielles, à l’échelle du bassin oriental de la mer Méditerranée.Il ressort de cette analyse que le mécanisme de formation des volcans de boue est directement lié à une contrainte locale ou régionale pouvant avoir une origine tectonique ou gravitaire.Différents paramètres géologiques conditionnant les dimensions et formes des volcans de boue ont été étudiés permettant de proposer un modèle original de leur formation. La conception de ce modèle, qui se veut générique, permet de regrouper les paramètres constitutifs d’un système de volcan de boue en trois étapes spatiales, depuis la couche source jusqu’à l’expression superficielle. / Since the early 80s, technological advances of seabed imagery and exploration of continental margins allowed to discover and study numerous seabed features recording fluid circulation within the sediment column.In this study of mud volcanoes, we propose an innovative method of analysis combining an automated statistical approach including detection and analysis of morphometric parameters together with a classical geological study. We used broad homogenous academic and industrial marine geophysical and geological dataset, at the scale of Eastern Mediterranean sea.The analysis of these parameters shows that the mechanism of formation of the mud volcanoes is directly related to a local or regional constrain that may have a tectonic or gravitational origin.Various geological parameters conditioning the size and shape of mud volcanoes have been studied and lead to propose an original model for the formation of mud volcanoes. The design of this model, which is intended to be generic, makes it possible to group the constituent parameters of a mud volcano system in three spatial stages, from the source layer to the superficial expression.
143

Multi-User Detection of Overloaded Systems with Low-Density Spreading

Fantuz, Mitchell 11 September 2019 (has links)
Future wireless networks will have applications that require many devices to be connected to the network. Non-orthogonal multiple access (NOMA) is a promising multiple access scheme that allows more users to simultaneously transmit in a common channel than orthogonal signaling techniques. This overloading allows for high spectral efficiencies which can support the high demand for wireless access. One notable NOMA scheme is low-density spreading (LDS), which is a code domain multiple access scheme. Low density spreading operates like code division multiple access (CDMA) in the sense that users use a spreading sequence to spread their data, but the spreading sequences have a low number of nonzero chips, hence the term low-density. The message passing algorithm (MPA) is typically used for multi-user detection (MUD) of LDS systems. The MPA detector has complexity that is exponential to the number of users contributing to each chip. LDS systems suffer from two inherent problems: high computational complexity, and vulnerability to multipath channels. In this thesis, these two problems are addressed. A lower complexity MUD technique is presented, which offers complexity that is proportional to the number of users squared. The proposed detector is based on minimum mean square error (MMSE) and parallel interference cancellation (PIC) detectors. Simulation results show the proposed MUD technique achieves reductions in multiplications and additions by 81.84% and 67.87% with a loss of about 0.25 dB with overloading at 150%. In addition, a precoding scheme designed to mitigate the effects of the multipath channel is also presented. This precoding scheme applies an inverse channel response to the input signal before transmission. This allows for the received signal to eliminate the multipath effects that destroy the low-density structure.
144

Tundra vegetation recovery on 30 year-old seeded and unseeded drilling mud sumps in the Mackenzie River Delta region, NWT

Wunderlich, Nicole Bettina 08 April 2010
Oil and gas exploration conducted in the 1970s left behind a legacy of abandoned well sites in the Mackenzie Delta region of northern Canada, including several in the Kendall Island Migratory Bird Sanctuary and surrounding areas. Evidence of 30 year-old well sites is present in the form of drilling mud sumps, which are mounds of disturbed tundra that contain frozen drilling-wastes. One to two years after the wells were decommissioned some of the sites were seeded with non-native grass species and fertilized to test whether these treatments could accelerate vegetation recovery and prevent erosion. The main objective of this research was to examine the long-term impact of post-disturbance seeding treatments on the vegetation recovery of drilling mud sumps.<p> Surveys of vegetation composition and environmental conditions at 12 sump sites (6 seeded and 6 unseeded) showed that, after over 30 years of recovery, seeded sumps in the Mackenzie Delta did not significantly differ from those left for natural recovery. However, seeded and previously introduced grasses <i>Festuca rubra</i> and <i>Poa pratensis</i> were found on both seeded and unseeded sumps. The undisturbed surrounding tundra seems to be resistant to invasion by these introduced grasses. However, these species could become invasive in the future, particularly in the context of warming in the North and increasing anthropogenic disturbance. The results of this study contribute valuable information on the long-term effects of revegetation treatments that is critical for making informed management decisions about the rehabilitation of industrial disturbances in the Arctic.
145

Tundra vegetation recovery on 30 year-old seeded and unseeded drilling mud sumps in the Mackenzie River Delta region, NWT

Wunderlich, Nicole Bettina 08 April 2010 (has links)
Oil and gas exploration conducted in the 1970s left behind a legacy of abandoned well sites in the Mackenzie Delta region of northern Canada, including several in the Kendall Island Migratory Bird Sanctuary and surrounding areas. Evidence of 30 year-old well sites is present in the form of drilling mud sumps, which are mounds of disturbed tundra that contain frozen drilling-wastes. One to two years after the wells were decommissioned some of the sites were seeded with non-native grass species and fertilized to test whether these treatments could accelerate vegetation recovery and prevent erosion. The main objective of this research was to examine the long-term impact of post-disturbance seeding treatments on the vegetation recovery of drilling mud sumps.<p> Surveys of vegetation composition and environmental conditions at 12 sump sites (6 seeded and 6 unseeded) showed that, after over 30 years of recovery, seeded sumps in the Mackenzie Delta did not significantly differ from those left for natural recovery. However, seeded and previously introduced grasses <i>Festuca rubra</i> and <i>Poa pratensis</i> were found on both seeded and unseeded sumps. The undisturbed surrounding tundra seems to be resistant to invasion by these introduced grasses. However, these species could become invasive in the future, particularly in the context of warming in the North and increasing anthropogenic disturbance. The results of this study contribute valuable information on the long-term effects of revegetation treatments that is critical for making informed management decisions about the rehabilitation of industrial disturbances in the Arctic.
146

An Investigation Of The Leak-off Tests Conducted In Oil And Natural Gas Wells Drilled In Thrace Basin

Kayael, Burak 01 February 2012 (has links) (PDF)
This study aims to analyze the leak-off tests carried out in the Thrace Basin of Turkey by Turkish Petroleum Corporation and find any relationship that may exist between leak-off test results and drilled formations as well as drilling parameters, such as mud weight, depth. The analysis of 77 leak-off tests indicated that there is no close correlation between the mud weight of test fluid and equivalent mud weight (fracture gradient) if the test is carried out within impermeable sections. On the other hand, the correlation between mud weight and equivalent mud weight increase while running the test within permeable-productive zones. It is also found that the leak-off test results are not dependent on the depth but the formation to be tested. The analyzed leak-off test results from Thrace Basin showed that the fracture gradient is not the limiting factor to set the casing of any section unless a gas show is observed during drilling operation which occurred only in 5 wells out of 78 wells analyzed.
147

Evolution of depositional and slope instability processes on Bryant Canyon area, Northwest Gulf of Mexico

Tripsanas, Efthymios 17 February 2005 (has links)
Bryant and Eastern Canyon systems are located on the northwest Gulf of Mexico, and they are characterized by a very complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions of depositional and halokinetic processes. Both canyon systems were active during the low sea-level stand of Oxygen Isotope Stage 6, and provided the pathways for the transport of enormous amounts of sediments on the continental slope and abyssal plain of the northwest Gulf of Mexico. Right after their abandonment, at the beginning of Stage 5, salt diapirs encroached into the canyons, and resulted in their transformation into a network of intraslope basins. The transformation of the canyons resulted in the generation of massive sediment failures. The mid-shelf (Stages 4 and 3) to shelf edge (Stage 2) lowering of the sea-level during the last glacial episode resulted in: 1) extensive river-sourced deposits on the outer shelf and/or upper continental slope that contributed in a seaward mobilization of the underlying salt masses, and 2) the generation of numerous gravity flows and turbidity currents on the outer shelf/upper continental slope. The seaward mobilization of the salt masses resulted in the oversteepening of the flanks of the basins, and consequently in the generation of numerous and massive sediment failures. The turbidity currents were confined on the intraslope basins of the upper continental slope, depositing their coarsest material. However, their most diluted upper and end members were able to continue their downslope propagation depositing characteristic fine-grained turbidites. The frequency of the turbidity currents was highly increased during the last glacial maximum (Stage 2), and three short melt-water pulses centered at 30.5, 36, and 52 ky B.P. The last deglaciation event is characterized by the development of a major melt water event that resulted in the deposition of distinct organic rich sediments, similar to the sapropels of the Eastern Mediterranean. At about 11 ky B.P. the melt water discharges of the North America switched from Mississippi River to St Lawrence Seaway, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico.
148

Effect of predator diet on foraging behavior of panopeus herbstII in response to predator urine cues

Connolly, Lauren E. 08 June 2015 (has links)
The ability of prey to detect and respond appropriately to predator risk is important to overall prey fitness. Many aquatic organisms assess risk through the use of chemical cues that can change with predator diet. Two variable characteristics of diet are: 1. prey type and 2. prey mass. To assess the effect of these two characteristics on the assessment of risk by the mud crab Panopeus herbstii, I exposed mud crabs to the urine of the blue crab Callinectes sapidus fed one of 5 diet treatments: 10g of oyster shell free wet mass, 5g of oyster shell free wet mass, 10g crushed mud crabs, 5g crushed mud crabs, and a mix of 5g of oyster shell free wet mass and 5g crushed mud crab. Effects on P. herbstii foraging were tested in a previously developed bioassay by measuring shrimp consumption over a 4 hour period. I hypothesized that P. herbstii would have a larger magnitude response to urine from C. sapidus fed a diet of crushed mud crabs than to urine from C. sapidus fed a diet of oysters. I further hypothesized that P. herbstii would have a larger magnitude response to urine from C. sapidus fed a high mass diet relative to a lower mass diet. Contrary to expectations there was no observed effect of urine on P. herbstii foraging in any of the treatments. Results suggest that bioassay protocol may be unreliable suggesting further replication to determine the difference between this study and previous results. Future studies examining how P. herbstii varies with urine concentration will aid in understanding the ecological scale of this predator cue system. Determining the role of other potential cue sources will improve the predictive abilities of these studies.
149

Second language learning in an online computer game: insights from theories of social interaction, practice, and nonlinear dynamics

Reese, Curtis Lee, 1971- 29 August 2008 (has links)
Research in second language acquisition has typically focused on classroom and laboratory settings. This study explores second language use in a non-classroom setting. It is based on research from divergent fields including theories of social interaction from sociology, theories of practice from anthropology, and nonlinear dynamics from the physical sciences. This study is a qualitative study, which employs both ethnographic and discourse analytic methods. The study examines native and non-native English speaker interactions on a MUD, a text-based online game. Data was collected for one year. The data for analysis consist primarily of logs of online interactions. The major conclusion of this study was that individuals acquire language appropriate to a particular environment by interacting with others in that environment. As individuals come to an environment and strive towards particular non-linguistic goals, they necessarily interact with others in the environment. As they do, they create shared ways of interacting. Through interaction, they refine the ways in which they speak. By employing multiple perspectives to guide the analysis, new insights into second language use and interaction can be obtained. This broadens our understanding of second language use in non-classroom settings. Implications for pedagogy in foreign language education are discussed.
150

Construction of static and dynamic multi-layer petrophysical models in Camisea gas reservoirs, Peru

Gandhi, Ankur 03 January 2011 (has links)
Estimation of static and dynamic petrophysical properties of multi-layer hydrocarbon reservoirs is crucial for the assessment of storage and flow capacities, compartmentalization, and for best primary or enhanced recovery practices. Interactive numerical simulation to reproduce field logs and core data is a reliable procedure to estimate static and dynamic petrophysical properties of complex rock formations. Previously, Voss et al. (2009) introduced the concept of Common Stratigraphic Framework (CSF) to construct and cross-validate multi-layer static/dynamic petrophysical models by invoking the interactive, numerical simulation of well logs both before and after invasion. This thesis documents the successful implementation of the CSF concept to examine and quantify the effects of mud-filtrate invasion on apparent resistivity, nuclear, and magnetic resonance logs acquired in San Martin, Cashiriari and Pagoreni gas fields in Camisea, Peru. Conventional petrophysical interpretation methods yield abnormally high estimates of water saturation in some of the reservoir units that produce gas with null water influx. This anomalous behavior is due to relatively low values of deep apparent electrical resistivity, and has otherwise been attributed to the presence of clay-coating grains and/or electrically conductive grain minerals. On the other hand, electrical resistivity logs exhibit substantial invasion effects as evidenced by the separation of apparent resistivity logs (both LWD and wireline) with multiple radial lengths of investigation. In extreme cases, apparent resistivity logs “stack” because of very deep invasion. We diagnose and quantify invasion effects on resistivity and nuclear logs with interactive numerical modeling before and after invasion. The assimilation of such effects in the interpretation consistently decreases previous estimates of water saturation to those of irreducible water saturation inferred from core data. It is shown that capillary pressure effects are responsible for the difference in separation of resistivity curves in some of the reservoir units. The final multi-layer CSF is in agreement with gas production measurements and permits reliable flow predictions to assist in reservoir engineering and production studies. / text

Page generated in 0.0551 seconds