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Civil and Environmental Engineering - Ph.D. / Sc.D.

Mostrando recursos 1 - 20 de 722

  1. The impact of Arctic amplification on the extratropical jets

    Whittleston, David Patrick
    Since the 1990's, greenhouse gas forcing has warmed the Arctic at twice the rate of lower latitudes, coinciding with a dramatic decline in Arctic sea ice extent. This manifestation of climate change has ignited a lively and ongoing debate regarding if Arctic warming will significantly influence extreme weather in the extra-tropics. This thesis offers three distinct contributions to the dialogue. Firstly, results are presented from a suite of targeted climate model experiments designed to establish how ice-forced and snow-forced anomalies interact and propagate through the atmosphere. Results suggest that high snow anomalies can suppress the October-November atmospheric response by interfering...

  2. Dimensions of microbial biodiversity in the North Pacific subtropical Gyre

    Bryant, Jessica, 1983-
    Microorganisms support all life in the oceans and are fundamental to maintaining a habitable biosphere on Earth. However an understanding of their taxonomic and functional distributions across space and time are just beginning to emerge and numerous niches within the marine environment are still awaiting exploration. The motivation for this thesis is to improve our understanding of distributions of microbes and their metabolic potential at Station ALOHA, a long-term study site representative of the North Pacific Subtropical Gyre (NPSG). We observed changes in diversity and community composition at Station ALOHA across time, ocean depth and on plastic debris, a new...

  3. Dimensions of microbial biodiversity in the North Pacific subtropical Gyre

    Bryant, Jessica, 1983-
    Microorganisms support all life in the oceans and are fundamental to maintaining a habitable biosphere on Earth. However an understanding of their taxonomic and functional distributions across space and time are just beginning to emerge and numerous niches within the marine environment are still awaiting exploration. The motivation for this thesis is to improve our understanding of distributions of microbes and their metabolic potential at Station ALOHA, a long-term study site representative of the North Pacific Subtropical Gyre (NPSG). We observed changes in diversity and community composition at Station ALOHA across time, ocean depth and on plastic debris, a new...

  4. Microbial communities as predictors of outcomes in industrial and clinical applications

    Perrotta, Allison Rose
    Environmental and host associated microbial communities provide an extensive reservoir of genetic and functional diversity. This diversity represents a wealth of potential for applications in many fields. To harness this potential for engineering applications, the impact of temporal dynamics need to be better understood. Yet most of the data we have are in the form of static surveys of diversity. In this thesis, I use 16S rRNA sequencing analysis to measure community composition across time series to predict outcomes for three applications: bioreactor function; a non-invasive diagnostic of endometriosis; and commercial chicken rearing. I identify bacteria that exhibit distinct temporal...

  5. Microbial communities as predictors of outcomes in industrial and clinical applications

    Perrotta, Allison Rose
    Environmental and host associated microbial communities provide an extensive reservoir of genetic and functional diversity. This diversity represents a wealth of potential for applications in many fields. To harness this potential for engineering applications, the impact of temporal dynamics need to be better understood. Yet most of the data we have are in the form of static surveys of diversity. In this thesis, I use 16S rRNA sequencing analysis to measure community composition across time series to predict outcomes for three applications: bioreactor function; a non-invasive diagnostic of endometriosis; and commercial chicken rearing. I identify bacteria that exhibit distinct temporal...

  6. Multiphase flow in porous media with phase transitions : from CO₂ sequestration to gas hydrate systems

    Fu, Xiaojing, Ph. D. Massachusetts Institute of Technology
    Ongoing efforts to mitigate climate change include the understanding of natural and engineered processes that can impact the global carbon budget and the fate of greenhouse gases (GHG). Among engineered systems, one promising tool to reduce atmospheric emissions of anthropogenic carbon dioxide (CO₂) is geologic sequestration of CO₂ , which entails the injection of CO₂ into deep geologic formations, like saline aquifers, for long-term storage. Among natural contributors, methane hydrates, an ice-like substance commonly found in seafloor sediments and permafrost, hold large amounts of the world's mobile carbon and are subject to an increased risk of dissociation due to rising...

  7. Multiphase flow in porous media with phase transitions : from CO₂ sequestration to gas hydrate systems

    Fu, Xiaojing, Ph. D. Massachusetts Institute of Technology
    Ongoing efforts to mitigate climate change include the understanding of natural and engineered processes that can impact the global carbon budget and the fate of greenhouse gases (GHG). Among engineered systems, one promising tool to reduce atmospheric emissions of anthropogenic carbon dioxide (CO₂) is geologic sequestration of CO₂ , which entails the injection of CO₂ into deep geologic formations, like saline aquifers, for long-term storage. Among natural contributors, methane hydrates, an ice-like substance commonly found in seafloor sediments and permafrost, hold large amounts of the world's mobile carbon and are subject to an increased risk of dissociation due to rising...

  8. Advancing accessibility : public transport and urban space

    Stewart, Anson F. (Anson Forest)
    After decades of academic research, urban accessibility metrics are beginning to see adoption in transportation and metropolitan planning practice. Such metrics capture the potential for reaching destinations enabled by transport (e.g. number of jobs available within a given commute time), not just the mobility benefits accruing from the use of transport (e.g. time and emissions reductions for a given commute), and have well-established advantages. From a transportation equity perspective, for example, measuring the potential for reaching destinations instead of actual travel avoids bias against groups who travel infrequently due to current or historical barriers to access. This dissertation elaborates on...

  9. Advancing accessibility : public transport and urban space

    Stewart, Anson F. (Anson Forest)
    After decades of academic research, urban accessibility metrics are beginning to see adoption in transportation and metropolitan planning practice. Such metrics capture the potential for reaching destinations enabled by transport (e.g. number of jobs available within a given commute time), not just the mobility benefits accruing from the use of transport (e.g. time and emissions reductions for a given commute), and have well-established advantages. From a transportation equity perspective, for example, measuring the potential for reaching destinations instead of actual travel avoids bias against groups who travel infrequently due to current or historical barriers to access. This dissertation elaborates on...

  10. Elastic properties and failure behavior of disordered porous solids : a potential-of-mean-force-based lattice element approach

    Laubie, Hadrien Hyacinthe
    The effective mechanical properties of multiphase materials not only depend on the volume fraction and chemical composition of their constituents but also on details of their local texture. Yet, most homogenization methods do not take this texture effect into account. Understanding how local texture affects the overall elastic and failure properties of heterogeneous solids is the focus of this thesis. Emphasis is placed on porous media that are critical for many industry sectors, that either aim at engineering the porosity and its distribution in synthesized materials to reach desired properties; or at predicting the behavior of naturally-occurring porous materials given...

  11. Elastic properties and failure behavior of disordered porous solids : a potential-of-mean-force-based lattice element approach

    Laubie, Hadrien Hyacinthe
    The effective mechanical properties of multiphase materials not only depend on the volume fraction and chemical composition of their constituents but also on details of their local texture. Yet, most homogenization methods do not take this texture effect into account. Understanding how local texture affects the overall elastic and failure properties of heterogeneous solids is the focus of this thesis. Emphasis is placed on porous media that are critical for many industry sectors, that either aim at engineering the porosity and its distribution in synthesized materials to reach desired properties; or at predicting the behavior of naturally-occurring porous materials given...

  12. Analysis of large deformation offshore geotechnical problems in soft clay

    Orazalin, Zhandos Y
    Although finite element (FE) methods are well established for modeling geotechnical problems in soil masses and soil-structure interaction, most prior research on large deformation problems has been limited to simplified assumptions on drainage conditions and constitutive behavior. This thesis investigates two large deformation problems in soft clay and proposes a methodology for performing coupled flow and deformation analyses with advanced effective stress models. The first part of the research focuses on realistic 3-D finite element analyses (using AbaqusTM Standard) of a conductor (steel pipe pile) embedded within soft marine clay subjected to large lateral deformations caused by drift/drive-off of a...

  13. Analysis of large deformation offshore geotechnical problems in soft clay

    Orazalin, Zhandos Y
    Although finite element (FE) methods are well established for modeling geotechnical problems in soil masses and soil-structure interaction, most prior research on large deformation problems has been limited to simplified assumptions on drainage conditions and constitutive behavior. This thesis investigates two large deformation problems in soft clay and proposes a methodology for performing coupled flow and deformation analyses with advanced effective stress models. The first part of the research focuses on realistic 3-D finite element analyses (using AbaqusTM Standard) of a conductor (steel pipe pile) embedded within soft marine clay subjected to large lateral deformations caused by drift/drive-off of a...

  14. Bus network sketch planning with origin-destination travel data

    Viggiano, Cecilia A. (Cecilia Ann)
    Public transport plays an important role in urban mobility. Public transport planners seek to improve existing public transport networks to better serve existing passengers and recruit new passengers, particularly as demand patterns change with evolving demographics and land use. One strategy for network improvement is to add new routes, which can improve service by reducing circuity in the network. In large, complex, and multi-modal public transport networks, it is challenging to determine where new routes should be added. A systematic approach for incremental network improvements, such as adding new bus services, is needed. This research proposes a new approach to...

  15. Bus network sketch planning with origin-destination travel data

    Viggiano, Cecilia A. (Cecilia Ann)
    Public transport plays an important role in urban mobility. Public transport planners seek to improve existing public transport networks to better serve existing passengers and recruit new passengers, particularly as demand patterns change with evolving demographics and land use. One strategy for network improvement is to add new routes, which can improve service by reducing circuity in the network. In large, complex, and multi-modal public transport networks, it is challenging to determine where new routes should be added. A systematic approach for incremental network improvements, such as adding new bus services, is needed. This research proposes a new approach to...

  16. Computationally efficient simulation-based optimization algorithms for large-scale urban transportation problems

    Chong, Linsen
    In this thesis, we propose novel computationally efficient optimization algorithms that derive effective traffic management strategies to reduce congestion and improve the efficiency of urban transportation systems. The proposed algorithms enable the use of high-resolution yet computationally inefficient urban traffic simulators to address large-scale urban transportation optimization problems in a computationally efficient manner. The first and the second part of this thesis focus on large-scale offline transportation optimization problems with stochastic simulation-based objective functions, analytical differentiable constraints and high-dimensional decision variables. We propose two optimization algorithms to solve these problems. In the first part, we propose a simulation-based metamodel algorithm...

  17. Computationally efficient simulation-based optimization algorithms for large-scale urban transportation problems

    Chong, Linsen
    In this thesis, we propose novel computationally efficient optimization algorithms that derive effective traffic management strategies to reduce congestion and improve the efficiency of urban transportation systems. The proposed algorithms enable the use of high-resolution yet computationally inefficient urban traffic simulators to address large-scale urban transportation optimization problems in a computationally efficient manner. The first and the second part of this thesis focus on large-scale offline transportation optimization problems with stochastic simulation-based objective functions, analytical differentiable constraints and high-dimensional decision variables. We propose two optimization algorithms to solve these problems. In the first part, we propose a simulation-based metamodel algorithm...

  18. Molecular structure, hierarchical assembly and stimuli-responsive mechanics of tropoelastin and elastin biomaterials

    Tarakanova, Anna
    The elastin polymer, assembled from its molecular precursor tropoelastin, is the dominant component of elastic fibers, which confer elasticity and structural integrity to skin, lung, connective and vascular tissue. Historically, elastin's dynamic nature has precluded traditional approaches such as X-ray crystallography to understand its detailed features. Solving tropoelastin's atomistic structure is key to characterizing elastin's complex biological function, disease-related mechanisms associated with mutations therein, and assembly process, to replicate natural function upon impairment. From the materials perspective, elastin-based materials display tunable thermal sensitivity, presenting opportunities to mimic and control these responsive features for biomedical applications. First, we develop and validate...

  19. Molecular structure, hierarchical assembly and stimuli-responsive mechanics of tropoelastin and elastin biomaterials

    Tarakanova, Anna
    The elastin polymer, assembled from its molecular precursor tropoelastin, is the dominant component of elastic fibers, which confer elasticity and structural integrity to skin, lung, connective and vascular tissue. Historically, elastin's dynamic nature has precluded traditional approaches such as X-ray crystallography to understand its detailed features. Solving tropoelastin's atomistic structure is key to characterizing elastin's complex biological function, disease-related mechanisms associated with mutations therein, and assembly process, to replicate natural function upon impairment. From the materials perspective, elastin-based materials display tunable thermal sensitivity, presenting opportunities to mimic and control these responsive features for biomedical applications. First, we develop and validate...

  20. Malaria transmission around the Koka Reservoir in Ethiopia : field observations, model predictions, and strategies for prevention

    Endo, Noriko Ph. D. Massachusetts Institute of Technology
    New dam construction is likely to exacerbate malaria transmission in Africa. The vectors of malaria - Anopheles mosquitoes - use bodies of water as breeding sites. Thus, dams and their reservoirs are associated with elevated risks of malaria. In Africa, more than 150 dams are currently under construction or proposed, and most of them are designed without satisfactory considerations for the potential of enhancing malaria transmission. Precise environmental mechanisms of malaria transmission around reservoirs are yet to be identified. Understanding of these mechanisms should lead to a better assessment of the impacts of dam construction. Moreover, incorporation of such understanding...

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