Recursos de colección

DSpace at MIT (91.223 recursos)

This site is a university repository providing access to the publication output of the institution. Registered users can set up email alerts to notify them of newly added relevant content. A certain level of encryption and security is embedded in the site which may cause some users accessibility problems.

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

Mostrando recursos 1 - 20 de 680

  1. 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...

  2. 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...

  3. 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....

  4. 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...

  5. 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...

  6. 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,...

  7. 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,...

  8. 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...

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

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

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

    McKinney, Ross E
    by Ross E. McKinney.

  11. 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...

  12. 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...

  13. Effective mechanical Properties of material models with random heterogeneities

    Dimas, Leon Sokratis Scheie
    In this thesis we obtain analytical approximations to the probability distribution of the elastic tensor and fracture strengths of material models with random heterogeneities. We start by investigating the effective elastic properties of one-, two-, and three-dimensional rectangular blocks whose Young's modulus varies spatially as a lognormal random field. We decompose the spatial fluctuations of the Young's log-modulus F = In E into first- and higher-order terms and find the joint distribution of the effective elastic tensor by multiplicatively combining the term-specific effects. Through parametric analysis of the analytical solutions, we gain insight into the effective elastic properties of this...

  14. From clay slurries to mudrocks : a cryo-SEM investigation of the development of the porosity and microstructure

    Deirieh, Amer (Amer Mohammad)
    This thesis investigates the microstructure of smectitic and illitic rich mudrocks that are resedimented in the laboratory from the Gulf of Mexico and Boston Blue clay natural sediments. The resedimentation technique consists of mixing clay sediments with saline water to form a slurry, which is then subjected to a wide range of effective stresses. Cryo-SEM and conventional SEM techniques are used to investigate the microstructure of the clay slurry and resedimented mudrocks. Cryo-SEM enables the imaging of samples in their in-situ conditions, while conventional SEM is used to image oven-dried samples. Two techniques are used to prepare the slurry samples...

  15. Biological nutrients and growth in anaerobic digestion

    Speece, Richard Eugene
    by Richard Eugene Speece.

  16. Clustering of motile bacteria around phytoplankton in a turbulent ocean

    Bowen, James Douglas
    by James Douglas Bowen.

  17. A static evaluation of soil plug behavior with application to the pile plugging problem

    Paikowsky, Samuel G
    by Samuel G. Paikowsky.

  18. A stochastic live load model for buildings.

    Peir, Jong-cherng
    Massachusetts Institute of Technology, Dept. of Civil Engineering. Thesis. 1972. Ph. D.

  19. Investigating the evolution and formation of coastlines and the response to sea-level rise

    Ortiz, Alejandra C
    To understand how waves and sea level shape sandy shoreline profiles, I use existing energetics-based equations of cross-shore sediment flux to describe shoreface evolution and equilibrium profiles, utilizing linear Airy wave theory instead of shallow-water wave assumptions. By calculating a depth-dependent characteristic diffusivity timescale, I develop a morphodynamic depth of shoreface closure for a given time envelope, with depth increasing as temporal scale increases. To assess which wave events are most important in shaping the shoreface in terms of occurrence and severity, I calculate the characteristic effective wave conditions for both cross-shore and alongshore shoreline evolution. Extreme events are formative...

  20. An experimental and numerical study on the fracturing processes in Opalinus shale

    Morgan, Stephen Philip
    The extraction of hydrocarbons from unconventional oil and gas reservoirs relies on a detailed understanding of the fracture processes in shale. Also, underground structures designed for nuclear waste repositories are typically constructed in shale due to its characteristic low permeability. To understand the behavior of shale it is important to know how cracks initiate, propagate and coalesce. Although there have been many studies on the cracking processes in rock, cracking in shale is not well understood mainly due to its anisotropy, which is caused by naturally formed bedding planes. Natural bedding planes are weak zones along which cracks can initiate...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.