Recursos de colección

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

Mostrando recursos 1 - 20 de 706

  1. 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...

  2. 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...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. Nonlinear effects in soil structure interaction

    Scaletti Farina, Hugo Victor Luis
    by Hugo Scaletti Farina.

  12. Nonlinear effects in soil structure interaction

    Scaletti Farina, Hugo Victor Luis
    by Hugo Scaletti Farina.

  13. Multiphase flow in porous media: the impact of capillarity and wettability from field-scale to pore-scale

    Zhao, Benzhong
    Multiphase flow in the context of this Thesis refers to the simultaneous flow of immiscible fluids. It differs significantly from single-phase flow due to the existence of fluid-fluid interfaces, which are subject to capillary forces. Multiphase flow in porous media is important in many natural and industrial processes, including geologic carbon dioxide (CO₂) sequestration, enhanced oil recovery, and water infiltration into soil. Despite its importance, much of our current description of multiphase flow in porous media is based on semi-empirical extensions of single-phase flow theories, which miss key physical mechanisms that are unique to multiphase systems. One challenging aspect of...

  14. Water quality and hydrological assessment and modeling of bioretention basins in tropical cities

    Wang, Jia, Ph. D. Massachusetts Institute of Technology
    The bioretention basin is a form of stormwater best management practice that originated in temperate regions and is becoming increasingly popular in tropical regions. Nevertheless, it is a poorly evaluated system in the tropics due to the limited availability of long-term, high-resolution hydrological and multi-component water quality data on completed basins. The resulting gaps in data and knowledge limit the ability of environmental managers to control nonpoint source pollution by stormwater. In this thesis, we provide a survey of basin performance in treating 15 water quality parameters in the Balam Estate Rain Garden in Singapore. We then use a combination...

  15. Simulating fluid-solid interaction using smoothed particle hydrodynamics method

    Pan, Kai, Ph. D. Massachusetts Institute of Technology
    The fluid-solid interaction (FSI) is a challenging process for numerical models since it requires accounting for the interactions of deformable materials that are governed by different equations of state. It calls for the modeling of large deformation, geometrical discontinuity, material failure, including crack propagation, and the computation of flow induced loads on evolving fluid-solid interfaces. Using particle methods with no prescribed geometric linkages allows high deformations to be dealt with easily in cases where grid-based methods would introduce difficulties. Smoothed Particle Hydrodynamics (SPH) method is one of the oldest mesh-free methods, and it has gained popularity over the last decades...

  16. Spectral modeling of an idealized atmospheric surface layer

    McColl, Kaighin Alexander
    Almost all of humanity resides in the atmospheric surface layer (ASL), so its state (e.g., temperature, humidity, wind velocity) is relevant to a range of applications in human health, agriculture, and ecosystem health. However, the ASL is turbulent, and therefore characterized by complex dynamics across a wide range of spatial and temporal scales. Explicitly modelling turbulent motions in the ASL at all scales is computationally expensive and beyond current capabilities. In this thesis, a framework is proposed for parsimoniously modelling a broad range of turbulent motions in wall-bounded turbulent flows such as the ASL, using spectra of turbulent fluctuations as...

  17. Long-term ground response For borehole heat exchangers in clay

    Zymnis, Despina M
    The use of ground source heat pumps to transfer heat to and from the ground via borehole heat exchangers is among the most energy efficient techniques for space heating and cooling. Designs for seasonal heat exchange systems are becoming increasingly popular in urban environments to reduce energy costs and contribute in decreasing carbon emissions. Broader applications require more careful evaluation of hydro-mechanical behavior of soil to understand the long-term ground response to seasonal cycles of heating and cooling and the impacts on adjacent structures. The goal of this thesis is to develop reliable methods for studying the coupled thermo-hydro-mechanical (THM)...

  18. Exploring the effects of proteorhodopsin on the physiology of native and heterologous hosts

    Valliere, Michael (Michael Finian)
    Photoheterotrophic microbes use proteorhodopsin (PR) and other types of microbial rhodopsin photosystems to harness energy directly from sunlight. This thesis explores the photophysiology of PR in the context of a natural marine isolate, Dokdonia sp. strain MED 134, and by establishing Escherichia coli as a heterologous host to experimentally determine conditions under which the PR photosystem is capable of enhancing growth rate and yield. In Dokdonia sp. MED 134, PR and 11 other genes were discovered to be significantly induced by light but the induction of these genes increased growth rate and yield in an extremely carbon-limited environment; in richer...

  19. Material diversification in pavement management : a technique to proactively deal with an uncertain future

    Swei, Omar Abdullah
    Pavement management systems are important tools that planning agencies depend upon for the effective maintenance of roadway systems. Although uncertainty is an inherent trait of these systems, the current approaches generally exclude its consideration from the analysis. Consequently, decision-makers disregard opportunities to embed sources of flexibility that may be advantageous to deploy if future conditions unfold differently from expectations. One potential source of flexibility available to planners is the incorporation of a broader range of paving materials and designs as part of their pavement preservation strategy. More specifically, this thesis hypothesizes that the inclusion of concrete-based maintenance alternatives by an...

  20. Ensemble-based reservoir history matching using hyper-reduced-order models

    Yoon, Seonkyoo
    Subsurface flow modeling is an indispensable task for reservoir management, but the associated computational cost is burdensome owing to model complexity and the fact that many simulation runs are required for its applications such as production optimization, uncertainty quantification, and history matching. To relieve the computational burden in reservoir flow modeling, a reduced-order modeling procedure based on hyper-reduction is presented. The procedure consists of three components: state reduction, constraint reduction, and nonlinearity treatment. State reduction based on proper orthogonal decomposition (POD) is considered, and the impact of state reduction, with different strategies for collecting snapshots, on accuracy and predictability is...

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