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A dust layer, especially based on high-resistivity dust, at the collecting electrodes may cause a back corona discharge in electrostatic precipitators (ESP). It can significantly reduce the ESP efficiency and as a result cause ecological damages. To study the dust layer influence inside ESPs, it is necessary to derive an adequate model of the ESP precipitation process with a dust layer at the collecting electrode. The research of the present thesis is focused on stationary studies of the precipitation process with a dust layer at the collecting electrode in ESPs. Three mathematical models are proposed as a description of the precipitation process with a dust layer at the collecting electrode. The models are based on Maxwell’s equations and the finite element method (FEM). COMSOL Multiphysics software is used for their implementation. In all models the dust layer has constant conductivity and the air region has constant ion mobility. In the first model there are no coupling conditions, which is required in mathematics, are given between the two regions. The solution found by COMSOL Multiphysics does not provide physically acceptable coupling conditions. In the second model, a continuous transition zone is introduced between the two regions so that no coupling conditions are required. With the large derivatives in the transition zone, the nonlinear solver in COMSOL Multiphysics does not converge. Finally, in the third model, the dust layer and the grounded collecting electrode are replaced with a boundary condition for the air region. The properties of the third model are investigated, and these models can be used to study the influence of the dust layer. The results of these investigations are reported and discussed.

Submarine groundwater discharge (SGD) represents a significant portion of the total discharge from coastal aquifers through diffuse seepage and point source springs, but can be difficult to locate. SGD is important as it can be a source of nutrients to estuaries and other coastal ecosystems. In an effort to evaluate geophysical and thermal methods for detecting SGD on the Florida Gulf coast, a suite of water-borne surveys were run in conjunction with aerial thermal imagery over the lower Suwannee River and estuary in March and September 2005. Thermal imagery exploits temperature differences between discharging groundwater and surface water. Thermal images were collected in March (dry season), at the end of winter, and at night to maximize the differences between warm groundwater and colder surface water. Generally pore waters in zones of concentrated SGD should be fresher, and hence more resistive than "background" values. Marine streaming resistivity data can detect pore water resistivity variations and were collected alongside continuous 222Rn and CH4 sampling from surface waters. Naturally occurring tracers, 222Rn and CH4, are used as the "standard" against which resistivity and thermal images are compared. Based on the expected properties of discharging groundwater, we hypothesize that in zones of elected tracer concentrations, increased thermal image temperatures and increased terrain resistivities will be observed. The data set as a whole supports this hypothesis. However, regional-scale correlations are clearly and significantly influenced by factors other than SGD including thermal-image noise, the presence of the fresh/salt water interface, and a large regional tracer gradient generated by a first-order spring. At local scales (tens to hundreds of meters) there are no significant correlations between thermal image temperature and tracer concentrations, due at least in part to flight-line edge effects that dominate the thermal imagery. After correcting for regional trends,significant correlations between tracer concentration and log resistivity exist only in a subset of the data that lies offshore. Because neither thermal imagery nor streaming resistivity data consistently support the hypotheses, this study suggests that neither method by itself is reliable for detecting SGD in this area

This thesis explores two ways of developing a fracture diagnostics tool capable of estimating hydraulic fracture propped length and orientation. Both approaches make use of an electrically conductive proppant. The fabrication of an electrically conductive proppant is believed to be possible and an option currently on the market is calcined petroleum coke. The first approach for tool development was based on principles of antenna resonance whereas the second approach was based on low frequency magnetic induction. The former approach had limited success due to the lack of resonant features at the stipulated operating conditions. Low frequency induction is a more promising approach as electromagnetic fields showed measurable changes that were dependent on fracture length in simulations. The operation of a logging tool was simulated and the data showed differences in the magnetic field magnitude ranging from 2% to 107% between fracture sizes of 20m, 50m, 80m, and 100m. Continuing research of the topic should focus not only on simulating more diverse fracture scenarios but also on developing an inversion scheme necessary for interpreting field data. / text

Electrical conductivity (or resistivity) of cementitious materials is considered to be a fundamental property and is commonly measured using nondestructive and noninvasive testing techniques. Therefore, electrical measurements are gaining popularity in both research and field applications for structural health monitoring and material characterization of civil engineering infrastructure systems. Based on the results of measurements, the engineer can schedule maintenance more accurately and give an early warning of possible structural failure. Recently, health monitoring systems are capable of significantly increasing the cost efficiency of maintenance and repair by helping engineers improve the safety and maintainability of structures through early damage detection. The research team at the University of Texas at Austin developed a low-cost, passive, wireless conductivity sensor system. Sensors are wirelessly interrogated using external reader during inspection over the service life of the structure to monitor the conductivity variations within concrete. The focus of this work is to assess the condition of cementitious materials by measuring electrical conductivity using passive wireless sensors. By analyzing the measured conductivity data, the condition of the cementitious material, such as extent of hydration, setting and hardening times, and transport phenomena, can be assessed. This document also provides comprehensive information on the design, fabrication, interrogation, and response of conductivity sensor platforms. / text

Submarine groundwater discharge (SGD) can be an important pathway for nutrients entering coastal systems. However SGD flow paths can be difficult to identify and flow volumes difficult to quantify. This study assesses whether geophysical techniques are potentially cost effective methods for detecting the presence or lack of SGD within an estuary environment found in Sarasota Bay, Florida. In this area, a rapid increase in urbanization has led to increased nitrogen loading into the bay, with some 10% of this loading attributed to SGD. Discharging groundwater is expected to be fresher and hence higher resistivity, than "background" surface waters. Thus resistivity surveys sensitive to seafloor conductivities may be useful for identifying zones of SGD. However, terrain resistivities are influenced by matrix geology as well as pore water resistivity. In this study we compare the results of marine resistivity surveys against both geochemical measures of SGD (radon tra cers) and seismic profiles indicative of subsurface structure to better determine the relative impacts of geology and SGD on marine resistivity measurements in Sarasota Bay. On both regional (kilometers to tens of kilometers) and local scales (hundreds of meters) the relationship between marine resistivity and tracer-based SGD estimates does not follow the expected pattern of higher resistivities associated with higher SGD flux. Seafloor resistivities instead appear primarily influenced by stratigraphy, particularly the presence of a clay layer at ~10-15 m depth in the southern part of the bay. In the southern bay, resistivities decrease at the depths associated with the clay layer. On the local (hundreds of meters) scale, lateral variations in resistivities derived from inversions of resistivity data were not found to be reproducible; nearly-coincident lines collected 30 minutes apart in time show different local signatures. This apparent local lateral variability in the resistivi ty profiles is inferred to be a result of inversion of noisy streaming resistivity data.

The integrated use of Electromagnetic Ground Conductivity, Ground Electrical Resistivity and Seismic Refraction geophysics methods was made in Alia valley, Eritrea for the aim of developing a methodology best suited for ground water exploration in hard rock areas with limited professional and financial resources. A total area of 25 square kilometer was covered with the geophysical surveys. The effective use of information from wells and geological information from outcrops and existing literature helped to create a preliminary conceptual hydrogeologic model that in turn provided a general picture of the research site in terms of its groundwater potential and related factors. The optimum configuration of the geophysical methods and their interpretation was researched by the use of synthetic mathematical models and experimental surveys in areas of known hydrogeological characteristics like lithology and depth of water table. Two approximately parallel electromagnetic ground conductivity profile lines crossed the survey area in approximately north-south direction to assess the variation in the electrical conductivity of the major geological structures. Vertical electrical sounding (VES) surveys were conducted close to existing wells with lithological information and at some selected sites. Survey sites for the two dimensional electrical resistivity imaging and the seismic refraction surveys were selected based on the results from the electromagnetic ground conductivity surveys. The formal geophysical surveys results were correlated with nearby boreholes and with each other. The responses of the different geophysical methods for each lithological layer were recognized. In addition, the location and characteristics of the major geological structures of the area were studies based on the information from the geophysical surveys and other available information. At the end of the research, parts of the research area with better groundwater potential were identified. As a result of the research, an efficient and cost effective geophysical approach was developed for groundwater exploration in hard rock areas of Eritrea and similar places of the world. Recommendations were made on the wider and effective use of the approach with due consideration for the limited financial, human resource and material capacities available for ground water exploration in most countries of Africa and other countries of the world.

Electrical resistivity tomography (ERT) is a commonly used geophysical method to investigate permafrost in the mountain environment, but few studies have employed this method in a permafrost affected peatland. For this thesis, 5 ERT profiles were measured over 17 palsas and peat-plateaus in a palsa peatland environment in Tavvavuoma, northern Sweden, where the primary aim was to investigate the depth to the base of permafrost under the mounds. These depths are also used to estimate the excess ice fraction (EIF), which is indicative of the proportion of segregation ice in the frozen core under the mounds. The internal structure of palsas and the spatial distribution of permafrost was also investigated from the inverted resistivity models. Permafrost thickness was found to range from 5 – 17 m, with the thickest permafrost in the west end of the study area. EIF values range between 0,04 to 0,58, with the lowest values in the same end as the deepest permafrost, where also low mound elevations are found. The deep permafrost combined with low mound elevations are suggested to be attributed to the presence of coarse grained (glaciofluvial) sediments where ice segregation formation is limited, thus small amounts of frost heave. Deep permafrost is possibly underlying at least two thermokarst depressions/fens in the area, which is suggested to obstruct their drainage. The height of the mounds was surprisingly found to decrease with permafrost thickness, a relationship that is likely to be an effect of the varied underlying sediment cover. This thesis demonstrates the applicability of ERT in peatland permafrost research, but also considers the limitations of the method. / Elektrisk resistivitetstomografi (ERT) är en geofysisk metod som har använts flitigt vid undersökningar av alpin permafrost, men få studier har hittills tillämpat denna teknik vid undersökningar av permafrost i myrmarker. Under detta examensarbete på masternivå mättes 5 ERT-profiler över 17 palsar samt torvplatåer i ett palsmyrkomplex med sporadisk permafrost i Tavvavuoma, norra Sverige, med det primära målet att undersöka permafrostens mäktighet under dessa. De beräknade permafrostdjupen används även för att uppskatta isöverskottsfraktionen (EIF), vilket ger en indikation på andelen segregationsis i den frusna kärnan under respektive pals/torvplatå. Palsarnas interna struktur och den rumsliga utbredningen av permafrost i myren diskuteras också kvalitativt utifrån resistivitetsmodellerna. Permafrostmäktigheten under palsar och torvplatåer bestämdes till mellan 5 – 17 meter, med den djupaste permafrosten i den västra delen av studieområdet. Isöverskottsfraktionen varierar mellan 0,04 – 0,58, med de lägsta värdena i samma del av studieområdet som den djupaste permafrosten fanns, här är även palshöjderna låga. Den djupa permafrosten i kombination med låga palshöjder föreslås tillskrivas förekomst av grovkorniga (glaciofluviala) sediment i denna del av studieområdet, där bildningen av segregationsis begränsas. I och med detta begränsas mängden frosthävning, med låga palshöjder som resultat. Djup permafrost kan finnas under minst två thermokarstsänkor i området, vilket kan hindra dränering av dessa. Ett oväntat resultat var att palshöjd minskar med ökat permafrostdjup bland de studerade objekten, vilket bäst kan förklaras med det varierade sedimentunderlaget, som ger mycket olika förutsättningar för segregationsisbildning. Denna masteruppsats visar på tillämpligheten av ERT i myrmarker med permafrost, men beaktar även metodens begränsningar för denna tillämpning.

Remote determination of the hydrate content of marine sediments remains a challenging problem. In the absence of boreholes, the most commonly used approach involves the measurement of Pwave velocities from seismic experiments. A range of seismic effective medium methods has been developed to interpret these velocities in terms of hydrate content, but uncertainties about the pore-scale distribution of hydrate can lead to large uncertainties in this interpretation. Where borehole geophysical measurements are available, electrical resistivity is widely used as a proxy for hydrate content, and the measurement of resistivity using controlled source electromagnetic methods shows considerable promise. However, resistivity is commonly related to hydrate content using Archie’s law, an empirical relationship with no physical basis that has been shown to fail for hydrate-bearing sediments. We have developed an electrical effective medium method appropriate to hydrate-bearing sediments based on the application of a geometric correction to the Hashin-Shrikman conductive bound, and tested this method by making resistivity measurements on artificial sediments of known porosity. We have adapted our method to deal with anisotropic grains such as clay particles, and combined it with a well-established seismic effective medium method to develop a strategy for estimating the hydrate content of marine sediments based on a combination of seismic and electrical methods. We have applied our approach to borehole geophysical data from Integrated Ocean Drilling Program Expedition 311 on the Vancouver Island margin. Hydrate saturations were determined from resistivity logs by adjusting the geometric factor in areas of the log where hydrate was not present. This value was then used over the entire resistivity log. Hydrate saturations determined using this method match well those determined from direct measurements of the methane content of pressurized cores.

In this research, we study high resistivity fractures found in unconsolidated clay sediments on logging-while-drilling borehole resistivity images from Indian continental margin collected during the National Gas Hydrate Program Expedition 01. These fractures, found at Sites 5, 6, 7, and 10 are likely filled with natural gas hydrate. Gas hydrate is identified on borehole logs and images as high resistivity responses without associated density increases or indications of free gas. The local state of stress at the time of fracturing can be determined by fracture orientations. In Holes 5A, 5B, 6A an 7A the gas hydrate-filled fractures have an aligned, preferred orientation likely associated with a local stress regime. At Site 10, where 130 m of gas hydrate-filled fractures were observed, fracturing is chaotic, likely due to high gas flux.