Recursos de colección

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

Mostrando recursos 1 - 20 de 688

  1. 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)...

  2. 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...

  3. 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...

  4. 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...

  5. Fracturing processes and induced seismicity due to the hydraulic fracturing of rocks

    Gonçalves da Silva, Bruno Miguel
    Hydraulic fracturing is a method used routinely in oil and gas exploitation and in engineered geothermal systems. While used frequently, there are aspects of hydraulic fracturing, such as the propagation of the newly-created fractures and interaction between natural and newly-created fractures, which are not well understood. Since data from field hydraulic stimulations may be difficult to obtain and interpret, laboratory testing and numerical modeling play a major role in understanding the hydraulically fracturing processes. A test setup was developed to simultaneously apply a vertical stress to rock specimens and a hydraulic pressure to pre-cut flaws with various geometries, leading to...

  6. Eumelanin and polydopamine : self-assembly, structure, and properties

    Chen, Chun-Teh
    In this thesis, a detailed hierarchical structure of eumelanin is described and validated in molecular dynamics simulations. For the first time, the gap between primary, secondary, and aggregate structures of eumelanin is bridged. Based on the hierarchical structure, a new explanation of the photoprotective function of eumelanin is proposed. The interplay of geometric order and disorder characteristics of the hierarchical structure results in significant and random excitonic couplings among eumelanin protomolecules. Consequently, these couplings broaden the spectrum and give rise to a relative enhancement of absorption intensity at the higher-energy end. To provide a more in-depth understanding of the structure-property...

  7. Dynamics of fluid-filled porous media under wave action : Excitation of surf-beats in the ocean

    Foda, Mostafa Ameen
    by Mostafa Ameen Foda.

  8. Surveying and harnessing the genetic, (meta)genomic, and metabolic potential of the deep carbonated biosphere

    Freedman, Adam Joshua Ehrich
    The interaction between microbes and supercritical (sc) carbon dioxide represents an increasingly compelling area of research due to use of scCO₂ in geologic carbon sequestration (GCS) and as a sustainable chemical solvent. To investigate the long-term effects of GCS on the in situ deep subsurface biosphere, I conducted a taxonomic, geochemical and metagenomic survey of the McElmo Dome sCCO₂ reservoir, which serves as a natural analog for GCS environments. Through 16S rRNA amplicon and metagenome sequencing, I identified Sulfurospirillum, Rhizobium, Desulfovibrio and members of the Clostridiales family associated with reservoir fluids. Annotations of complete genomes extracted from metagenomes predict diverse...

  9. Microbial cycling of marine high molecular weight dissolved organic matter

    Sosa, Oscar Abraham
    Microorganisms play a central role mediating biogeochemical cycles in the ocean. Marine dissolved organic matter (DOM) - a reservoir of organic solutes and colloids derived from plankton is a major source of carbon, nutrients, and energy to microbial communities. The biological transformation and remineralization of DOM sustains marine productivity by linking the microbial food web to higher trophic levels (the microbial loop) and exerts important controls over the cycles of carbon and bioessential elements, such as nitrogen and phosphorus, in the sea. Yet insight into the underlying metabolism and reactions driving the degradation of DOM is limited partly because its...

  10. A new elasto-viscoplastic model for rate-dependent behavior of clays

    Yuan, Yixing, Ph. D. Massachusetts Institute of Technology
    Viscous properties of clay pertain to numerous geotechnical problems, such as excessive settlements associated with constructed fills on marine clays, or rate-dependent cyclic response of offshore foundations under wave loading. Although there are many observations on rate-dependent characteristics of clays in laboratory tests, none of the existing soil models has attained consistent descriptions of the observed strain-rate effects in shearing, or creep and relaxation in compression. This thesis develops a novel elasto-viscoplastic soil model, MIT-SR, to address these limitations. The proposed I-D formulation introduces a physically-based evolution law that attributes the macroscopic viscoplastic strain rate to an internal strain rate...

  11. Assessing impacts of climate change on the hydrology of the Nile River

    Siam, Mohamed S
    The human population living in the Nile basin is projected to double by 2050, approaching one billion. The increase in water demand associated with this burgeoning population fuels an ongoing water conflict between the riparian countries. Uncertainty regarding potential future changes in the flow of the Nile River as a result of climate change adds further stress to this critical situation. In this thesis, we investigate the impacts of climate change on hydrology and climate of the Nile basin. In particular, we predict and explain the future changes in interannual variability and long-term mean of the flow in Nile river....

  12. Feedbacks between plants, flow, and particle fate

    Follett, Elizabeth (Elizabeth Marie)
    Environmental flows carry a wide variety of particles that interact with vegetation. Vegetated canopies are anchored by sediment, release pollen and seeds to colonize new ground, rely on nutrients carried by sediment, and may be killed by disease spores. While the influence of vegetation on flow profiles has been investigated, the transport of particles within vegetated canopies remains poorly understood. In this thesis I present the results from laboratory experiments and numerical modeling that investigated particle fate and transport around emergent and submerged model vegetation canopies. The effect of canopy mediated flow on particle transport was explored in experimental studies...

  13. Navigating congested cities : understanding urban mobility using new data sources

    C̦olak, Serdar
    Rapid urbanization and technological innovations sparked the generation of massive volumes of data that is continually improving in resolution. In particular, mobile phones, having reached penetration levels above 97% in Europe and Americas according to the World Bank, transformed into passive sensors of urban mobility by signaling movement at the individual level. The data generated by these devices has a wide range of applications concerning how people and cities interact through the infrastructure. This thesis presents new analysis tools that utilize large geolocated datasets to provide new insights towards human mobility, road networks, congestion, and energy. In the first part...

  14. Expansion and shrinkage of early age cementitious materials under saturated conditions : the role of colloidal eigenstresses

    Abuhaikal, Muhannad (Muhannad A. R.)
    Mixing water with anhydrous cement powder and other additives results in a viscid cement slurry and triggers a set of complex exothermic reactions. As the cement slurry transitions from a suspension to a gel and ultimately to a stone-like porous solid, the material develops mechanical properties. This transition, however, is also accompanied by bulk volume changes, which -if restrained- lead to premature cracking of materials and structures. The main objective of this study is to relate bulk volume changes as measured at a macroscopic scale to their finer colloidal origin under controlled temperature and pressure conditions. To achieve this goal,...

  15. Spatiotemporal variability of methane ebullition from lake sediments

    Scandella, Benjamin P. (Benjamin Paul)
    Methane is a potent greenhouse gas, and natural sources to the atmosphere include inland waterways and shallow oceans. However, the magnitude of these emissions and their potential for feedbacks with climate change remain poorly constrained. In many settings the majority of atmospheric methane emissions is delivered by bubbles, and the spatiotemporal heterogeneity of ebullition makes measurement challenging and impacts bubble dissolution and atmospheric emissions. In this thesis, we present an analysis of both the episodicity and spatial structure of methane venting from soft sediments in a eutrophic lake over a range of spatial scales, from 1 cm to 20 m,...

  16. Video camera-based vibration measurement of infrastructure

    Chen, Justin Gejune
    Functional infrastructure-including transportation, energy, and buildings and other facilities - is key to the economic production of a country and the daily lives of its people. Due to deterioration and potential damage, timely inspections and repairs are necessary to keep infrastructure functioning at full capacity. Visual testing is one of the oldest and most widely used methods for condition assessment; however, this technique is limited since it is based on an inspector's subjective rating rather than on an objective quantitative measure of structural condition. Quantitative alternatives to visual testing have emerged over time. These include vibration analysis, in which a...

  17. Kinetics of the removal of soluble substrates by activated sludge

    Garrett, Melrose Truett, 1925-
    by Melrose Truett Garrett, Jr.

  18. Biology and biochemistry of the micro-organisms in activated sludge

    McKinney, Ross E
    by Ross E. McKinney.

  19. Stiffness characterization of mechanically-compressed cohesive soils using wave propagation

    Marjanovic, Jana
    Wave propagation through soils is a non-destructive method used to characterize soil stiffness properties and is the basis for geophysical interpretations. Due to the difficulty of measuring shear waves through soft cohesive soils with ultrasonic transducers, bender elements are typically used, which couple to the soft clay. Unfortunately, the stress limitation of bender elements precludes it from testing above 1.5 MPa. A novel setup using ultrasonic transducers, with electronic conditioning, is developed in order to overcome the difficulties of transmitting a shear wave through a soft material. The successful fabrication of triaxial cell endcaps fitted with ultrasonic piezoceramic elements has...

  20. Indoor navigation for passengers in underground transit stations using smartphones

    Wang, Yin, Ph. D. Massachusetts Institute of Technology
    People are increasingly relying on smartphones to solve a lot of their daily problems, among which navigation is one of the most fundamental tasks. Estimating the locations of pedestrians and tracking them in an indoor environment is a long sought after research goal. This thesis develops a smartphone-based indoor navigation system specifically designed for transit stations, but which also allows easy extension to other navigation scenarios. The thesis' system requires no extra hardware installation in the indoor environment or on the phone and few assumptions are made about the indoor space and the path tile user is taking, unlike previous...

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