Recursos de colección

DSpace at MIT (100.801 recursos)

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

Mostrando recursos 1 - 20 de 734

  1. Exploring the absorption properties and direct radiative impact of atmospheric carbonaceous aerosols

    Wang, Xuan, Ph. D. Massachusetts Institute of Technology
    Atmospheric aerosols are important due to their adverse effects on human health and their direct and indirect radiative effects on climate, which are significant and very uncertain factors contributing to global climate change. In estimating the direct radiative effect (DRE), the absorption from carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC, a component of organic aerosol, OA), are highly uncertain. This thesis addresses this uncertainty by combining models and observations to better constrain the optical properties and radiative impact of carbonaceous aerosols. First, a global model simulation (GEOS-Chem) of BC is expanded to separately treat both the aging...

  2. Observations and mechanistic modelling of the role of Aedes mosquitoes in dengue transmission in Singapore

    Seidahmed, Osama M. E. (Osama Mohamed Elmekki)
    Dengue is the most prevalent human arboviral disease in the world with an estimate of 390 million cases per year. The disease is mainly transmitted by two mosquitoes: Aedes aegypti and Ae. albopictus. Despite the continuous efforts to curb the spread of the disease in Singapore, there is an upsurge in dengue epidemics. In this thesis, the role of Aedes mosquitoes in shaping the spatiotemporal patterns of dengue transmission in Singapore is investigated. Field surveys are carried out to study the effect of monsoons on the disease vectors; the impact of urban housing on spatial patterns of dengue transmission is...

  3. Adaptation of granular solid hydrodynamics for modeling sand behavior

    Panagiotidou, Andriani Ioanna
    The development of constitutive models that can realistically represent the effective stress-strain-strength of the soil properties is essential for making accurate predictions using finite element analysis. Currently, most of the existing constitutive models are based on the framework of incrementally-linearized elasto-plasticity. However, most of these models do not typically consider energy conservation and are also phenomenological. This means that they can only be used to predict the behavior/ loading conditions for which they have been developed and that they often employ artificial mathematical formulations. This research proposes an improved constitutive model for sands based on the framework of Granular Solid...

  4. Investigation of the impact of desalination on the salinity of the Persian Gulf

    Ibrahim, Hamed D. (Hamed Dare)
    The Persian Gulf (also known as the Arabian Gulf) is a shallow marginal sea located in a region of Southwest Asia with arid climate. Because of this aridity, evaporation from the Gulf is extremely high (1.84 meters per year) and far exceeds the sum of freshwater inflow to the Gulf, mainly from precipitation and some from river flow. A residual circulation exists between the Gulf and the Indian Ocean such that saline water flows into the Gulf from the Indian Ocean in order to balance the freshwater deficit due to high evaporation rate; and since evaporation only removes freshwater, the...

  5. Carbon fluxes from tropical peatlands : methane, carbon dioxide, and peatland subsidence

    Hoyt, Alison May
    Tropical peatlands in Southeast Asia have sequestered carbon over thousands of years and are an important global carbon stock. In natural peat swamp forests, high water levels inhibit decomposition due to anoxic conditions. However, they are being rapidly deforested and drained, releasing stored carbon to the atmosphere. In this thesis, we investigate the carbon dioxide and methane fluxes from both pristine and degraded peat swamp forests in Borneo using field measurements, modeling and remote sensing. We first study methane fluxes from natural peatlands. We use an isotope-based mass transport model to evaluate the extent of methane production, transport and oxidation....

  6. Field observations and numerical model simulations of a migrating inlet system

    Hopkins, Julia A
    Waves, currents, and bathymetric change observed along 11 km of the southern shoreline of Martha's Vineyard include storm events, strong tidal flows (> 2 m/s), and an inlet migrating 2.5 km in ~7 years. A field-verified Delft3D numerical model developed for this system is used to examine the hydrodynamics in the nearshore and their effect on the migrating inlet. An initial numerical experiment showed that the observed 700 tidal modulation of wave direction in the nearshore was owing to interactions with tidal currents, and not to depth-induced refraction as waves propagated over complex shallow bathymetry. A second set of simulations...

  7. Using polyethylene passive sampling to assess transport of polychlorinated biphenyls (PCBs) between contaminated sediments, water, and biota

    Apell, Jennifer Nicole
    Polychlorinated biphenyls (PCBs), which were a widely used group of chemicals before their manufacture was banned in 1979 in the United States, still contaminate numerous aquatic systems. Although there are ongoing efforts to remediate these sites, our ability to implement effective remediation strategies has been hindered by a limited understanding of how PCBs are transported in the environment as well as how they bioaccumulate into aquatic animals. Investigations of contaminated sites often rely on sediment measurements since PCB concentrations are highest in the sediment phase. However, previous research has shown that sediment concentrations are a poor predictor of contaminant fate...

  8. Optimal land and water allocation to agriculture and hydropower in the Upper Blue Nile basin

    Allam, Mariam M. (Mariam Mohammed Nasr El Din Ibrahim)
    The Nile basin is an ecosystem under stress due to rapid population growth, urgent needs for more efficient utilization of natural resources, potential impacts of climate change, and persistent conflicts between riparian countries on the limited set of resources. This thesis develops a framework for optimal allocation of land and water resources to agriculture and hydropower production in the upper Blue Nile (UBN) basin, which contributes about 60 percent of the Nile river flow. The framework consists of three optimization models that aim to: (a) provide accurate estimates of the basin water budget components, (b) allocate land and water resources...

  9. The significance of ion concentration in the anaerobic biochemical decomposition of acetate

    McCarty, Perry L
    by Perry Lee McCarty.

  10. The significance of ion concentration in the anaerobic biochemical decomposition of acetate

    McCarty, Perry L
    by Perry Lee McCarty.

  11. Activated sludge metabolism of certain quaternary carbon compounds

    Mohanrao, Govindaraju Jagan
    by Govindaraju Jagan Mohanrao.

  12. 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...

  13. 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...

  14. 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...

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

    Bryant, Jessica A.
    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...

  16. 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...

  17. 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...

  18. 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...

  19. 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...

  20. 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...

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