• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 737
  • 110
  • 75
  • 34
  • 22
  • 18
  • 14
  • 12
  • 10
  • 7
  • 7
  • 7
  • 7
  • 7
  • 7
  • Tagged with
  • 1332
  • 256
  • 231
  • 229
  • 191
  • 158
  • 152
  • 137
  • 125
  • 117
  • 104
  • 94
  • 91
  • 90
  • 87
  • 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.
41

An assessment of current methodologies for mitigating the potential effects of anthropogenic underwater sound on marine life, and recommendations for best practice

Compton, Ross Craig January 2013 (has links)
Underwater sound from anthropogenic sources such as seismic surveys, marine renewable device installations and naval exercises has the potential to disturb and cause injury to a variety of marine species. There is particular concern for the potential effects upon marine mammals, which utilise sound to communicate, hunt and navigate. Observed effects include behavioural changes and reduced sighting rates, with unknown consequences for individuals or populations over time. Potential effects on marine mammals include sound induced damage to auditory systems, altered diving behaviour potentially resulting in decompression sickness, stranding and death. The aim of the thesis was to develop a framework of best practice measures relating to mitigating the potential effects of underwater sound on marine mammals during offshore exploration and development operations. In order to mitigate the potential effects of underwater sound, regulatory guidelines have been developed and implemented around the world, principally for seismic surveys. These guidelines limit the activation of seismic sources when in proximity to marine species, and involve the use of specially trained personnel on survey vessels known as Marine Mammal Observers (MMOs). A critical review of the guidelines identified variation in the level of precaution applied to measures, such as the distance at which species can be sighted before reducing sound output from the operation. MMOs collect sighting information for all encounters with marine species, resulting in large volumes of data detailing species occurrence and behaviour. A sample dataset was found to be subject to variation in quality due to the different academic backgrounds and training levels of personnel. The data highlighted significant differences in relation to sighting distance while the sound source is active or inactive, though lacked detail with regard to behaviours, likely due to the lack of ethological expertise among the observers. A questionnaire was conducted to determine any differences of opinion regarding current mitigation practice and the underlying issue between stakeholder groups. There was no difference of opinion between stakeholders regarding the importance of underwater sound compared to other environmental issues facing marine species such as fisheries by-catch and overfishing. Areas of consensus were evident, with most stakeholders finding current mitigation practice to be only ‘somewhat’ effective, and that sightings data collected by MMOs should be better utilised, with it being more useful for adding to our knowledge of marine mammal distributions than for determining the effects from operations. A framework for enhancing the collection, use and dissemination of MMO data is described with recommendations for the development of a Global Positioning System (GPS) enabled smartphone/ tablet based field data collection system, linked to an internet based geographical information system to enhance species distribution analysis. By coupling this with a simplified mitigation methodology, the outcome would enhance the risk management of operations in relation to where species are known to occur, with mitigation aimed at reducing exposure at critical times or in critical habitats. Simplifying mitigation and enhancing data collection and use will benefit stakeholders in managing essential operations responsibly.
42

Development of an index to rate the completeness and quality of mitigation project definition

Muramatsu, Tadahisa 02 November 2010 (has links)
In the summer of 2008, two hurricanes made landfall along the Texas coast causing billions of dollars in damage. Texas received presidential disaster declarations, which resulted in the state receiving over $350 million in hazard mitigation funds. Over 500 requests for mitigation projects were submitted to the government from communities impacted. Not all requested projects could be funded. As a result, those communities that submitted requests for well-defined mitigation projects were the primary beneficiaries of the federal mitigation funds. To better understand the factors that characterize a “welldefined” mitigation project, this study developed an index to rate the completeness and quality of mitigation project definitions. The study incorporated concepts from research on quality community planning and from project definition rating methods. The rating tool consists of detailed descriptions of the project scope elements along with a scoring method for the completeness and quality of the project’s definition. The rating tool and the detailed descriptions help to develop a “well-defined” mitigation project definition as well as to evaluate it. / text
43

Models of tephra dispersal

Bonadonna, Costanza January 2001 (has links)
No description available.
44

Carbon dioxide sequestration options for British Columbia and mineral carbonation potential of the Tulameen ultramafic complex

Voormeij, Danae Aline. 10 April 2008 (has links)
In an effort to lower atmospheric carbon dioxide (C02) levels, a number of sequestration methods, including geological storage, ocean storage and mineral carbonation of CO2 have been proposed for British Columbia. The selection of a suitable sink depends largely on the geology available for a given region. A methodology for assessment of suitable raw material for the mineral carbonation process has been proposed. The Tulameen ultramafic complex is selected as a promising site for providing the raw feed for mineral C02 sequestration and representative dunites have been collected and examined. Carbonation tests of these dunites took place at the Albany Research Center in Oregon and C02 analyses in reaction products (up to 29.4 wt%) suggest 48-56% conversion to magnesite and silica for the dunites, and 18% conversion for a serpentinized dunite. Based on these results, one tonne of Tulameen dunite could potentially sequester up to 0.4 tomes of C02.
45

Structural Impact Mitigation of Bridge Using Tuned Mass Damper

Hoang, Tu A 04 May 2015 (has links)
This paper investigates the application of tuned mass damper (TMD) systems to bridge pier systems for structural impact damage mitigation and thus reduce the risk of collapses. A bridge superstructure and substructures are designed in accordance with The American Association of State Highway and Transportation Officials (AASHTO) specifications. A variety of vessel collision forces are obtained from collision testing of a scaled reinforced concrete pier. The optimal parameters of TMD systems are then determined such that the drift and displacement of the bridge superstructure are minimized for various impact scenarios. The structural impact mitigation performance of the pier equipped with the proposed optimal TMD system is compared with five different TMD systems employing the benchmark TMD optimal parameters. The uncontrolled responses are used as a baseline. It was demonstrated from the extensive simulations that the control effectiveness of the proposed TMD system was 25% better than all of the existing TMD models in reducing structure responses.
46

A Study of Carbon Dioxide Capture and Catalytic Conversion to Methane using a Ruthenium, “Sodium Oxide” Dual Functional Material: Development, Performance and Characterizations

Wang, Shuoxun January 2018 (has links)
The increasing CO2 level in the atmosphere, mostly attributed to anthropogenic activities, is overwhelmingly accepted to be the main greenhouse gas responsible for climate change. Combustion of fossil fuel is claimed to be the major cause of excess CO2 emission into the atmosphere, but human society will still rely heavily on fossil fuel for energy and feedstock supplements. In order to mitigate the environment-energy crisis and achieve a sustainable developing mode, Carbon Capture, Utilization and Storage (CCUS) is an effective method and attracts considerable interests. Rather than conventional aqueous amine-based liquid absorbent, e.g. the toxic, corrosive and energy intensive monoethanolamine (MEA), solid adsorbents are preferable for CO2 capture. CO2 utilization via CO2 conversion to fuel or other value-added products is favored over CO2 storage. Also it is preferred that no transportation of captured CO2 is required. Capturing and converting CO2 to fuel, such as synthetic natural gas or CH4 is particularly useful if it is produced at the site of CO2 generation. The converted CO2 can then be recycled to the inlet of the power plant or integrated into existed fuel infrastructure eliminating any transportation. This thesis presents a study of the development, performance and characterizations of a newly discovered (second generation) dual functional material (DFM) for CO2 capture and catalytic conversion to methane in two separated steps. This material consists of Ru as the methanation catalyst and “Na2O” obtained from Na2CO3 hydrogenation as the CO2 adsorbent, both of which are deposited on the high surface area γ-Al2O3 support. The Ru, “Na2O” DFM captures CO2 from O2- and steam-containing flue gas at temperature from 250 °C to 350 °C in step 1 and converts it to synthetic natural gas (CH4) at the same temperature with addition of H2 produced from excess renewable energy (solar and/or wind energy) in step 2. The heat generated from methanation drives adsorbed CO2 to Ru by spillover from the adsorption sites and diffuse to Ru for methanation. This approach utilizes the heat in the flue gas for both adsorption and methanation therefore eliminating the need of external energy input. The second generation DFM was developed with a screening process of solid adsorbent candidates. Initial adsorption studies were conducted with powdered samples for CO2 capture capacity, methanation capability, and resistance to an O2-containing simulated flue gas feed. The new composition of DFM was then prepared with tablets for future industrial applications and scaled up to 10 grams suitable for testing in a fixed bed reactor. Parametric and 50-cycle aging studies were conducted in a newly constructed scaled-up fixed bed reactor using 10 grams of DFM tablets in the simulated flue gas atmosphere for CO2 capture. With the presence of O2 in CO2 feed gas for step 1, the Ru catalyst is oxidized but must be rapidly reduced in step 2 to the active metallic state. Parametric studies identified 15% H2 is required for stable operation with no apparent deactivation. The parametric plus 50-cycle aging studies demonstrated excellent stability of the second generation DFM. A kinetic study was also conducted for the methanation step using powdered DFM but prepared via the tablet method to minimize any mass transfer and diffusion influence on the methanation rate. An empirical rate law was developed with kinetic parameters calculated. The methanation rate of captured CO2 is highly dependent on H2 partial pressure (approaching a reaction order of 1) while essentially zero reaction order of CO2 coverage was determined. The kinetic study highlights the importance of H2 partial pressure on the methanation process. Characterizations were conducted on the ground fresh and aged (underwent parametric and aging studies) DFM tablets. BET surface area, H2 chemisorption, X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) images and scanning transmission electron microscope- energy dispersive spectroscopy (STEM-EDS) mapping were utilized to study the material changes between fresh and aged samples. From fresh to aged, similar BET surface area was measured, improved both Ru and “Na2O” dispersion, and decreased Ru cluster size was observed while no definitive proof of the nature of the sodium species was obtained via XRD. The second generation DFM containing 5% Ru, 6.1% “Na2O” / Al2O3 was shown to possess the capability of capturing CO2 from O2-containing simulated flue gas and subsequent methanation with addition of H2 produced from excess renewable energy (or from chemical processes) with twice the CO2 and CH4 capacity relative to the first generation DFM. Activity, selectivity and stability has been demonstrated for the second generation DFM. We envision swing reactors to be utilized commercially where the flue gas feed for step 1 and H2 for step 2 are throttled alternatively between each reactor for continuous operation.
47

Strategies for Mitigating Supply Chain Disruptions

Bowman Jr, Johnny 01 January 2015 (has links)
Disruptions in the supply chain are becoming more common as supply chains become more complex, and supply chain managers of warehouse distribution centers need strategies to minimize the impact of disruptions. In this study, the focus of the research questions was on strategies supply chain managers could use to mitigate the impact of disruptions. The conceptual frameworks for this study were the resource dependence theory and the normal accident theory, which link supply chain disruptions with resource availability and the inability to eliminate disruptions. An exploratory case study involved exploring how supply chain managers of a warehouse distribution center in Jacksonville, Florida, successfully used strategies to mitigate the impact of a disruption after it occurred. Data came from responses to semistructured interview questions from these managers (n = 6) and archival documents related to policies, procedures, and business continuity planning of a warehouse distribution center in Jacksonville, Florida. I analyzed the data by using Atlas.ti qualitative analysis software. There were 6 themes that emerged: collaborating to minimize the impact of disruptions, disruptions precursors, identifying and assessing impact of disruptions, resources used to minimize impact of disruption, strategies to mitigate disruptions, and supplier relationships. The results could contribute to social change by minimizing the negative effects disruptions have on an organization's profitability and performance. Social change can come from business leaders who are able to maintain and sustain their businesses after a supply chain disruption has occurred.
48

Radar Signal Processing for Interference Mitigation

Geng, Zhe 23 March 2018 (has links)
It is necessary for radars to suppress interferences to near the noise level to achieve the best performance in target detection and measurements. In this dissertation work, innovative signal processing approaches are proposed to effectively mitigate two of the most common types of interferences: jammers and clutter. Two types of radar systems are considered for developing new signal processing algorithms: phased-array radar and multiple-input multiple-output (MIMO) radar. For phased-array radar, an innovative target-clutter feature-based recognition approach termed as Beam-Doppler Image Feature Recognition (BDIFR) is proposed to detect moving targets in inhomogeneous clutter. Moreover, a new ground moving target detection algorithm is proposed for airborne radar. The essence of this algorithm is to compensate for the ground clutter Doppler shift caused by the moving platform and then to cancel the Doppler-compensated clutter using MTI filters that are commonly used in ground-based radar systems. Without the need of clutter estimation, the new algorithms outperform the conventional Space-Time Adaptive Processing (STAP) algorithm in ground moving target detection in inhomogeneous clutter. For MIMO radar, a time-efficient reduced-dimensional clutter suppression algorithm termed as Reduced-dimension Space-time Adaptive Processing (RSTAP) is proposed to minimize the number of the training samples required for clutter estimation. To deal with highly heterogeneous clutter more effectively, we also proposed a robust deterministic STAP algorithm operating on snapshot-to-snapshot basis. For cancelling jammers in the radar mainlobe direction, an innovative jamming elimination approach is proposed based on coherent MIMO radar adaptive beamforming. When combined with mutual information (MI) based cognitive radar transmit waveform design, this new approach can be used to enable spectrum sharing effectively between radar and wireless communication systems. The proposed interference mitigation approaches are validated by carrying out simulations for typical radar operation scenarios. The advantages of the proposed interference mitigation methods over the existing signal processing techniques are demonstrated both analytically and empirically.
49

Carbon Capture and Storage in the European Union : The role for combating climate change

Zetterman, Eric January 2007 (has links)
<p>The urgency of climate change is pressing on the development of different technologies to reduce greenhouse gas emissions among which carbon dioxide (CO2) is the most abundant. A great source of CO2 is the burning of fossil fuels. The installation of carbon capture and storage (CCS) technology could reduce the amount of CO2 released from larger combustion processes by up to 90%. Fossil fuels stand for a great part of the total consumption of energy in the society today. To replace it so rapidly that strict climate change objectives will be reached with only increased energy efficiency and renewable energy would be difficult and would not be the most cost-efficient strategy. To be able to stabilize the atmospheric CO2 level within this decade and in a cost-efficient manner, the development of CCS technologies is clearly needed as a complementary strategy.</p>
50

Carbon Capture and Storage in the European Union : The role for combating climate change

Zetterman, Eric January 2007 (has links)
The urgency of climate change is pressing on the development of different technologies to reduce greenhouse gas emissions among which carbon dioxide (CO2) is the most abundant. A great source of CO2 is the burning of fossil fuels. The installation of carbon capture and storage (CCS) technology could reduce the amount of CO2 released from larger combustion processes by up to 90%. Fossil fuels stand for a great part of the total consumption of energy in the society today. To replace it so rapidly that strict climate change objectives will be reached with only increased energy efficiency and renewable energy would be difficult and would not be the most cost-efficient strategy. To be able to stabilize the atmospheric CO2 level within this decade and in a cost-efficient manner, the development of CCS technologies is clearly needed as a complementary strategy.

Page generated in 0.0618 seconds