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

Mostrando recursos 1 - 20 de 638

  1. The eco-evolutionary dynamics of extrachromosomal elements in environmental vibrio

    Xue, Hong, Ph. D. Massachusetts Institute of Technology
    Plasmids and other extrachromosomal elements (ECEs) are recognized as key factors mediating horizontal gene transfer; however, their diversity and dynamics among ecologically structured host populations in the wild remains poorly understood. Here we take a population-genomic approach to determine carriage of different types of ECEs in a recently established model for ecologically and genetically cohesive bacterial populations, asking whether different ECE types (i) are primarily associated to host phylogeny or ecology, (ii) have distinct transfer (and loss) patterns, and (iii) display different microevolutionary dynamics. We employed two models of environmental bacterial populations: a Vibrio cholerae population isolated from a coastal...

  2. The role of type I collagen heterotrimers and homotrimers in mechanical strength and collagen cleavage

    Chang, Shu-Wei, Ph. D. Massachusetts Institute of Technology
    Collagen is a crucial structural protein, formed through a hierarchical assembly of molecules, arranged in collagen fibrils, which constitutes the basis for larger-scale fibers. Normal type I collagen is a heterotrimer triple-helical molecule consisting of two alpha-1 chains and one alpha-2 chain. A mouse model of the genetic brittle bone disease, osteogenesis imperfecta, oim, is characterized by a replacement of the alpha-2 chain by an alpha-1 chain, resulting in a homotrimer collagen molecule. Experimental studies of oim mice tendon and bone have shown reduced mechanical strength compared to normal mice. The relationship between the molecular content and the decrease in...

  3. Behavior of structural frames subjected to underground explosions

    Matsuda, Fujio
    by Fujio Matsuda.

  4. Analysis of foundation stresses and settlements at the Hayden Library Harl Preslar Aldrich, Jr.

    Aldrich, Harl P
    Thesis (Sc.D.) Massachusetts Institute of Technology. Dept. of Civil and Sanitary Engineering, 1951.

  5. A probabilistic approach to the stability of rock slopes.

    Glynn, Edward Francis
    Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1979.

  6. Numerical and analytical studies of single and multiphase starting jets and plumes

    Wang, Ruo-Qian
    Multiphase starting jets and plumes are widely observed in nature and engineering systems. An environmental engineering example is open-water disposal of sediments. The present study numerically simulates such starting jets/plumes using Large Eddy Simulations. The numerical scheme is first validated for single phase plumes, and the relationship between buoyancy and penetration rate is revealed. Then, the trailing stem behind the main cloud is identified, and the the formation number (critical ratio U[delta]t/D, where U, D and [delta]t are discharge velocity, diameter and duration) that determines its presence is determined as a function of plume buoyancy. A unified relationship for starting...

  7. Dynamic processes on complex networks : from disease spreading to neural activity

    Nicolaides, Christos
    The study of dynamic processes that take place on heterogeneous networks is essential to better understand, forecast, and manage human activities in an increasingly connected world. In this Thesis, we elucidate the role of the network topology as well as the nature of the underlying processes in a variety of phenomena rooted on highly connected network systems. We use real world applications as the motivation to address three distinct questions. The first question is: how is the spread of infectious diseases at the global scale mediated by long-range human travel? We show that network topology, geography, traffic structure and individual...

  8. Demographics of lytic viral infection of coastal ocean vibrio

    Kauffman, Anne Kathryn Marie
    Viral predation on bacteria in the ocean liberates carbon from the particulate fraction, where it is accessible to higher trophic levels, and redirects it to the dissolved fraction, where it supports microbial growth. Although viruses are highly abundant in the ocean little is known about how their interactions with bacteria are structured. This challenge arises because the diversity of both bacteria and viruses is exceedingly high and interactions between them are mediated by specific molecular interactions. This thesis uses heterotrophic bacteria of the genus Vibrio as a model to quantify virus-host interactions in light of host population structure and ecology....

  9. Wind- and thermal-driven air flows and the buoyancy and advection effects on air exchange within urban environments

    Magnusson, Sigurður Pétur
    Human exposure to air pollutants and thermal stress in urban areas are public health concerns. The year 2008 was the first year when more than half of the human population lived in urban areas. Studies of the urban air fluid dynamics can be applied to increase pedestrian comfort and emergency response planning. In this study we focus on thermal effects on urban air flows. The thermal effects are extended beyond what is found in the literature to better understand the thermo fluid processes within urban areas. A field experiment on the air flow within an urban street canyon was performed...

  10. Anomalous transport through porous and fractured media

    Kang, Peter Kyungchul
    Anomalous transport, understood as the nonlinear scaling with time of the mean square displacement of transported particles, is observed in many physical processes, including contaminant transport through porous and fractured geologic media, animal and human foraging patterns, tracer diffusion in biological systems, and transport in complex networks. Understanding the origin of anomalous transport is essential, because it determines the likelihood of high-impact, low-probability events and therefore exerts a dominant control over the predictability of a system. The origin of anomalous transport, however, remains a matter of debate. In this thesis, we first investigate the pore-scale origin of anomalous transport through...

  11. Host/virus interactions in the marine cyanobacterium prochlorococcus

    Frois-Moniz, Katya
    Bacterial viruses shape the diversity, metabolic function, and community dynamics of their microbial hosts. As microbes drive many major biogeochemical cycles, viral infection is therefore a phenomenon of global significance. A significant fraction of primary production in the oceans is performed by the picocyanobacteria Prochlorococcus and Synechococcus. The viruses ('cyanophages') that infect these cyanobacteria are unusual in that their genomes contain a large suite of orthologs to host metabolic genes. These orthologs, known as 'auxiliary metabolic genes' ('AMGs'), encode proteins involved in diverse cellular processes, including photosynthesis, carbon and phosphate metabolism, and nucleotide synthesis. They are thought to benefit phage...

  12. Spatiotemporal variability of hydrologic response : an entropy-based approach using a distributed hydrologic model

    Castillo, Aldrich Edra
    Basin hydrologic response pertains to the partitioning of precipitation into stream-flow, evapotranspiration, and change in storage. The ability to explain or predict the response has many applications e.g. flood forecasting, water budget studies, and design of hydrological observing systems. However, explaining the response is challenging because it is the combined manifestation of many complex and interrelated factors that naturally vary in space and time, and act over a variety of scales. A possible key is better understanding of the space-time dynamics of the hydrologic state variable - the soil moisture field. This thesis uses the distributed hydrologic model MOBIDIC that...

  13. The consolidation and strength behavior of mechanically compressed fine-grained sediments

    Casey, Brendan (Brendan Anthony)
    This thesis investigates the consolidation and shear strength behavior of saturated fine-grained sediments over the effective stress range of 0.1 to 100 MPa. The research makes use of samples which are resedimented in the laboratory from natural soils. In addition to practical benefits, resedimentation allows for isolation and quantification of individual factors influencing behavior such as composition, consolidation stress and overconsolidation ratio (OCR). Ko-consolidated triaxial compression tests were performed on eight resedimented soils at room temperature. The results demonstrate conclusively that the conventional assumption of these soils exhibiting constant normalized properties is not valid when behavior is evaluated over a...

  14. Managing risks in energy capital projects -- the value of contractual risk-sharing in CCS-EOR

    Agarwal, Anna
    This thesis addresses the question of how to maximize the value of energy capital projects in light of the various risks faced by these projects. The risks can be categorized as exogenous risks (not in control of involved entities) and endogenous risks (arising from sub-optimal decisions by involved entities). A dominant reason for poor project performance is the endogenous risks associated with weak incentives to deliver optimal project outcomes. A key objective of this research is to illustrate that risk-sharing through contracts is central to incentivize the involved entities to maximize overall project value. The thesis presents a risk management...

  15. Permeability anisotropy and resistivity anisotropy of mechanically compressed mudrocks

    Adams, Amy Lynn
    Permeability anisotropy (the ratio of the horizontal to vertical permeability) is an important parameter used in sedimentary basin models and geotechnical design to model fluid flow, locate hydrocarbon reserves and estimate stress and pressure evolution. The magnitude of the permeability anisotropy for a given mudrock is difficult to measure; further, whether the permeability anisotropy is a constant value or evolves with the basin state is of active debate. This thesis experimentally investigates the development of permeability anisotropy in mechanically compressed mudrocks. A novel measurement method is developed using resedimented cubic specimens. The permeability anisotropy of Resedimented Boston Blue Clay (RBBC)...

  16. Settlement of structures on shallow foundations: a probabilistic analysis.

    Diaz Padilla Guerrero, Jorge
    Massachusetts Institute of Technology. Dept. of Civil Engineering. Thesis. 1974. Ph.D.

  17. Hydrodynamic and transport phenomena at the interface between flow and aquatic vegetation : from the forest to the blade scale

    Rominger, Jeffrey T. (Jeffrey Tsaros)
    From the canopy scale to the blade scale, interactions between fluid motion and kelp produce a wide array of hydrodynamic and scalar transport phenomena. At the kilometer scale of the kelp forest, coastal currents transport nutrients, microorganisms and spores. But, kelp forests exert a drag force on currents, causing the flow to decelerate and divert as it encounters the canopy, affecting the fate of species transported by the current. We identify a dimensionless flow-blockage parameter, based on canopy width and density, that controls both the length of the flow deceleration region and the total flow in the canopy. We further...

  18. Flow through porous media : from mixing of fluids to triggering of earthquakes

    Jha, Birendra, Ph. D. Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
    Enhanced oil recovery by displacing oil with solvents such as carbon dioxide requires development of miscibility between the two fluids to maximize the displacement efficiency. Prevention of inadvertent triggering of earthquakes due to injection or production of fluids in the underground requires understanding of coupling between flow and deformation processes. In this Dissertation, we study flow through porous media in two different contexts: effect of viscosity on mixing of fluids, and triggering of earthquakes due to coupling between flow and deformation. We show that miscible viscous fingering-the hydrodynamic instability that arises when a less viscous fluid displaces the more viscous...

  19. The dynamics of surface detachment and quorum sensing in spatially controlled biofilm colonies of Pseudomonas aeruginosa

    Jang, Hongchul
    Biofilms represent a highly successful life strategy of bacteria in a very broad range of environments and often have negative implications for industrial and clinical applications, as their removal from surfaces and the prevention of biofouling in the first place represent formidable and to date unmet challenges. At the same time, biofilms modulate important natural processes, including nutrient cycling in rivers and streams and the clogging of porous materials. Biofilm development is a dynamic process, dependent on a host of cellular and environmental parameters that include, among others, hydrodynamic environment and the communication among cells (QS). Here we used microfluidics...

  20. Multiscale modeling of clay-water systems

    Ebrahimi, Davoud
    The engineering properties of soils are highly affected by clay content and clay-water interactions. However, existing macro-scale continuum models have no length scale to describe the evolution of the clay microstructure and its role in affecting macroscopic properties. This research proposes a bottom-up multiscale modeling approach to understand the physics underlying macroscopic clay behavior. Atomistic models are developed to understand clay-water interactions using the ClayFF force field. We simulate water adsorption between clay layers for a reference mineral, Wyoming montmorillonite (Na-smectite) using molecular dynamics simulations. The elastic properties of the system are found to vary with the hydration state (amount...

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