Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 19 of 19 for “"diffusive flux"”.
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An analysis of a diffusive-flux-limited model for groundwater cleanup rate estimation using air sparging
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1997.
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Microfluidic Flow Creation in the Insect Respiratory System
… this dissertation, we examine how advective and diffusive flows are created in the insect respiratory system, using a combination of direct biological studies and computational fluid dynamics simulations. The insect respiratory system differs significantly from the vertebrate respiratory system. …
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The ramifications of diffusive volume transport in classical fluid mechanics
… represents the heretofore largely ignored diffusive transport of volume. We will begin by giving a motivating discussion containing example problems which point to the possible need for a change in the constitutive choice for in. This will be followed by a brief outline of the kinematic …
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Streams, stromatolites and the geometry of growth
… focus on two systems which grow in response to a diffusive flux. The first system is a microbial mat which overlays a layer of precipitated mineral. The microbial mat grows in response to the diffusion of nutrients while the mineral layer grows in response to the precipitation of dissolved ions …
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Mechanisms of metal release from contaminated coastal sediments
… giving a solid phase enrichment. There is a diffusive flux of copper to the water column throughout the year, while silver is released only in winter. Lead is strongly scavenged and is rarely released to the overlying waters.
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Mercury in water, porewaters, sediments and fish from the Medway Estuary, Southeast England
… comparison with overlying waters, suggesting a diffusive release of mercury from the bottom sediments to the water column. The calculated diffusive flux was 6 kg year-1, demonstrating that mercury is mobile in this system. Mercury in sediment core samples ranged between 382-1888 µg kg-1 (dry …
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Exploring Novel Biophysical Mechanisms In Evolved Optical Systems
… mechanism used by giant clams to increase diffusive flux of photosynthetic product from symbiotic algae. Over 50 years ago, it was reported that the addition of clam homogenate to algae stimulated photosynthate release, but the molecular effectors and mechanism of this “host release factor” …
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Mechanisms of metal release from contaminated coastal sediments
… giving a solid phase enrichment. There is a diffusive flux of copper to the water column throughout the year, while silver is released only in winter. Lead is strongly scavenged and is rarely released to the overlying waters. Analysis of reduced sulfur compounds in the porewaters has shown …
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Ageing of HDPE Geomembranes Used to Contain Landfill Leachate or Hydrocarbon Spills
… reducing the concentration gradient and outward diffusive flux of antioxidants. Fourth, diffusion modelling is used to evaluate the results from immersion and composite liner simulation tests. Diffusion modelling provided a means for predicting the performance of the GMs in conditions other than …
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Invariant-region-preserving discontinuous Galerkin methods for systems of hyperbolic conservation laws
… viscous p-system by using the direct DG (DDG) diffusive flux proposed in [H. Liu and J. Yan., Communications in Computational Physics, 2010], considering the p-system and its viscous counterpart share the same invariant region. Numerical tests validate the desired properties of the IRP limiter …
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Evaluating the combined use of three-dimensional hydrodynamic modeling and polyethylene passive sampling in the Lower Duwamish Waterway
… are most likely located and what mass flux is required to produce the measured concentrations. This evaluation was completed for the Lower Duwamish Waterway (LDW), a salt wedge estuary located in Seattle, Washington. The LDW was selected for its idealized conditions (straight channel …
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Estuarine sediment nutrient exchange: the importance of physical transport mechanisms and benthic micro-communities
… transport mechanisms on sediment nutrient flux were investigated for two nearshore sediment types on Virginia’s Eastern Shore. Subtidal sandy mineral sediments were conducive to water transport and subsequently influenced by groundwater discharge to a greater degree than less permeable …
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The biogeochemistry of 210Pb and 210Po in fresh waters and sediments
… that might influence the distribution and fluxes of the radionuclide in ways that could effect 210Pb sediment dating. A mass balance for the epilimnion showed that 210Pb inputs by precipitation were matched by outputs on settling particles, indicating that direct uptake by bottom sediments …
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Time series analysis and machine learning studies of biophotovoltaic systems
… age resulted in larger cell surface area for diffusive flux of electron mediators, partially accounting for the gradual increase in mediated electron export rates over time. To avoid the hard-to-predict STL remainder, the Hilbert-Huang transform (HHT) was applied to decompose current profiles. …
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Dynamic forcing of oxygen, iron, and manganese fluxes at the sediment-water interface in lakes and reservoirs
… sediment oxygen demand) and other sediment-water fluxes. In response to the growing need for alternative approaches for improving water quality, we conducted highly interdisciplinary research to evaluate how O₂, Fe, and Mn cycling at the sediment-water interface is influenced by both natural and …
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Box models of thermohaline circulation
… and tracer through a closed basin with buoyancy fluxes supplied at the top and bottom boundaries and, in both chapters, we compare the two cases in which the mixing either occurs uniformly across the tank or is locally confined to one portion. In chapter 2 we establish the simplest case in which …
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Soil-Bentonite Cutoff Walls: Hydraulic Conductivity and Contaminant Transport
… were developed that can be used to estimate the flux through a cutoff wall based on knowledge of the average hydraulic conductivity of the wall and an estimate of the variability in hydraulic conductivity. Data sets of hydraulic conductivity from lab tests on soil-bentonite samples from four …
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Carbon dioxide and methane emissions from the Te Arawa lakes of Rotorua, New Zealand
… in many other eutrophic lakes, the net CO₂ flux was mostly from the atmosphere to the lake. However, CO₂, together with CH₄, escaped from the lake as a pulsed emission in winter. Using a simple annual mass balance model it was calculated that, ~31% of CH₄ sourced from the sediment escaped to …
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Plutonium isotopes in the North Atlantic
… (Kd's <104 in cores from water depths >2500m). Diffusive flux calculations based upon the observed Pu pore water gradients suggest that since its introduction, negligible Pu has been remobilized out of the sediments at all of the sites. On a time scale of 102 -103 years however, Pu …