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Stenghel, Alessandro. "Simulazioni numeriche di onde di Alfvén in presenza di resistività." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21065/.
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In questo lavoro di tesi studieremo, con l’ausilio di simulazioni numeriche, le proprietà delle così dette onde di Alfvén in un magnetofluido ideale (ossia con resistività nulla) e non ideale (ossia in presenza di resistività). Dopo aver introdotto il lettore alle principali equazioni della magnetoidrodinamica,
elaborando queste equazioni vedremo come in condizioni ideali (ossia senza resistività) in un plasma nel quale il campo magnetico è uniforme si possano generare delle onde trasversali che si propagano lungo la direzione del campo, le onde di Alfvén. Analizzeremo poi la stessa configurazione in presenza di resistività, la quale avrà come effetto principale uno smorzamento esponenziale dell'ampiezza dell'onda. Infine, effettueremo delle simulazioni numeriche di entrambe queste configurazioni con il codice magnetoidrodinamico Arepo e confronteremo i risultati ottenuti con le previsioni analitiche mostrando il buon accordo tra le simulazioni eseguite e la teoria.
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BOTTACCHI, Marta Caterina. "Studio dell’efficacia dell’OhmMapper (Geometrics Inc.) per indagini geoelettriche in contesti archeologici." Doctoral thesis, Università degli studi di Ferrara, 2010. http://hdl.handle.net/11392/2389294.
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The research project carried out during the PhD work aims to study the effectiveness of the
OhmMapper (Geometrics Inc.) capacitive-coupled resistivity system in archaeological contexts.
In order to verify the effectiveness of this resistivity-meter to identify archaeological features,
we realized a systematic surveys in the Geophysical Test Site of Rovereto (TN - Italy). In particular
we compared both resistance and resistivity profiles realized by OhmMapper capacitively coupled
resistivity-meter and by the Terrameter SAS 1000 (ABEM) galvanic resistivity meter. We realized
these surveys walking along the same acquisition line to intercept a target compatible with an
archaeological feature. The comparison between the profile realized by the two different
instruments allowed us to establish the reliability of the OhmMapper to detect targets characterized
by vertical pattern and resistivity values grater than the context.
After this analysis, we realized several resistivity surveys in archaeological sites using the
OhmMapper. In particular the surveys carried out in five archaeological sites are the most
appropriate to demonstrate the effectiveness of the instrument, because the resistivity results are
comparable with other archaeological or geophysical data. Two of these sites are located in modern
urban contexts (Sacred Area of Medma Greek colony and the roman Aqueduct of Florence); the
other three sites are located in suburban areas (Late-ancient villa near Siena, Accademia of Villa
Adriana and Sentinum roman town).
3
Giammaria, Tommaso. "Realization of a four-probe electrical resistivity apparatus and its noise-reduced data acquisition interface to characterize superconducting materials." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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L’elaborato si basa sulla realizzazione di un sistema di rilevazione sincrona per misure di resistenza elettrica con metodo a quattro terminali. L’obbiettivo, utile alla caratterizzazione di materiali superconduttivi, è quello di misurare la dipendenza tra resistività elettrica e temperatura del campione. L’apparato si suddivide in un sistema di controllo della temperatura e un sistema di acquisizione dotato di amplificatore lock-in digitale.
Gli amplificatori lock-in sono strumenti usati per il recupero di segnali laddove il contributo del rumore di fondo risulta essere preponderante rispetto al segnale d’interesse. L’acquisizione e conversione del segnale analogico viene svolta da una scheda Digilent Analog Discovery 2, il segnale digitalizzato viene elaborato da un amplificatore lock-in digitale. Quest’ultimo è stato sviluppato ad hoc in ambiente labVIEW, ricoprendo un ruolo fondamentale nel lavoro presentato.
Il sistema di controllo della temperatura comprende un impianto criogenico e un sistema di riscaldamento (con circuito di retroazione PID).
I test svolti per definire le performance del sistema di acquisizione hanno rivelato una riserva dinamica stimata di 82 dB ed un segnale minimo misurabile di 200 nV (con un errore del 5%). Successivamente l’apparato è stato utilizzato per caratterizzare due campioni superconduttori appartenenti rispettivamente alla famiglia dei cuprati e a quella dei ferro-pnictidi.
L’apparato è in grado di misurare valori di resistenza con una sensibilità di 200 nV/I (dipende dalla corrente fornita al campione e misurata in Ampere), realizzando un grafico di dipendenza R vs T con 0,05 K di risoluzione. Le temperature critiche misurate per i due campioni sono in accordo con i valori trovati in letteratura.
Il lock-in illustrato in questa tesi presenta possibili applicazioni a scopo educativo o di ricerca, qualora le performance richieste per la misura rientrino in quelle descritte precedentemente.
4
Spinoso, Melissa. "Studio dei processi di dissoluzione nei reattori agitati con alta concentrazione di solido." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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In questo lavoro di tesi si focalizza l’attenzione sullo studio dei fenomeni di dissoluzione nei reattori operanti con miscele bifase solido-liquido meccanicamente agitati, in quanto, queste operazioni sono di largo interesse in campo industriale. La necessità di garantire un’adeguata miscelazione all’interno dei reattori, in cui avvengono reazioni chimiche o dove si verificano scambi di calore e materia, deriva non solo da ragioni economiche, ma anche da aspetti relativi alla sicurezza negli impianti, dato che risulta difficile conoscere il comportamento delle miscele bifase in ogni zona del reattore.
Per seguire dunque l’evoluzione dinamica dei processi ci si è serviti della tomografia elettrica di resistività (ERT) che consente di ricostruire la distribuzione spaziale delle proprietà elettriche del sistema che si sta studiando. Questa apparecchiatura, in maniera non invasiva, consente di valutare, tramite misure di conducibilità elettrica, la concentrazione del prodotto solubile nel tempo all’interno di un reattore agitato. Sono state, inoltre, effettuate misure di distribuzione di solido al variare della velocità di rotazione della girante, per le due differenti classi granulometriche delle particelle utilizzate, in quanto la presenza del solido inerte svolge un’azione di disturbo nei confronti dei fenomeni di dissoluzione. Premesso ciò, sono state dunque condotte numerose prove sperimentali di dissoluzione di cloruro di sodio di tre tagli granulometrici diversi al variare del numero di giri di ciascuna delle due giranti prescelte, ovvero una PBT e una A310. Le prove sono state finalizzate alla valutazione dei tempi di dissoluzione del sale.
La ricerca condotta ha permesso di caratterizzare i fenomeni di scambio di materia nei reattori bifase operanti con miscele solido-liquido, in cui è presente un’elevata concentrazione di solido, proponendo un’interpretazione fenomenologica semplificata del processo di dissoluzione.
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Amaini, Chiara. "Indagini di tomografia geoelettrica sulle dune costiere della Provincia di Ravenna." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8440/.
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Questa tesi Magistrale è frutto di un'attività di ricerca, che consiste nella realizzazione di un'indagine geofisica di tipo geoelettrico (ERT Electrical Resistivity Tomography). Lo scopo è quello di caratterizzare l'idrogeologia di una porzione limitata dell'acquifero freatico costiero ravennate, situato nella Pineta Ramazzotti di Lido di Dante, cercando di apportare nuove conoscenze sulle dinamiche che favoriscono l'ingressione marina (problema di forte attualità)che potrebbero contribuire a migliorare la gestione e la tutela delle risorse idriche. In questo contesto la tesi si pone come obiettivo quello di valutare l'applicabilità del metodo geoelettrico verificando se questo è in grado d'individuare efficacemente l'interfaccia acqua dolce-salata e le strutture presenti nel sottosuolo, in due tipologie di ambiente, con e senza un sistema di dune. I risultati dimostrano che dal punto di vista scientifico, il metodo geoelettrico ha verificato il principio di Ghyben-Herzberg, il quale suppone che vi sia una relazione inversa tra quota topografica e limite superiore della zona satura con acqua salata, inoltre si è riscontrata una certa stagionalità tra i profili acquisiti in momenti diversi (influenzati dalla piovosità). Mentre dal punto di vista tecnologico, il metodo, è di difficile utilizzo negli ambienti di transizione tanto ché chi si occupa professionalmente di questi rilievi preferisce non eseguirli. Questo è dovuto alla mancanza di un protocollo per le operazioni di acquisizione e a causa dell'elevato rumore di fondo che si riscontra nelle misurazioni. Con questo studio è stato possibile calibrare e sviluppare un protocollo, utilizzabile con diverse spaziature tra gli elettrodi, che è valido per l'area di studio indagata. Si è riscontrato anche che l'utilizzo congiunto delle informazioni delle prospezioni e quelle dei rilievi classici (monitoraggio della superficie freatica, parametri chimico-fisici delle acque sotterranee, rilievo topografico e sondaggi geognostici), generino un prodotto finale di semplice interpretazione e di facile comprensione per le dinamiche in atto.
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Signora, Alessandro. "Monitoraggio geoelettrico time lapse di lungo periodo come strumento di indagine e di incremento del rendimento energetico di una discarica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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Nel lavoro in oggetto si presenta lo studio dell’evoluzione di una discarica RSU, sita in provincia di Trento, attraverso tecniche di prospezione geoelettrica in continuo. Lo scopo dello studio è di comprendere se i risultati del monitoraggio geoelettrico in continuo siano effettivamente utili nella pratica della gestione delle discariche, la quale è alla costante ricerca di soluzioni in equilibrio fra qualità ed economia.
Nel dettaglio sono state eseguite misure geoelettriche passive (PS) ed attive (ERT) senza interruzioni per 5 anni (2015-2020), attraverso una matrice permanente di 72 elettrodi gestita da una centralina programmata per acquisire giornalmente due rilievi completi di potenziale e otto misure di resistività. Questo lungo monitoraggio ad alta frequenza combinato con la decisione di mantenere fissa la posizione degli elettrodi sono gli elementi originalità che verranno valutati maggiormente nel corso di questo studio.
Nel corso del lavoro ci concentreremo anche sulla variazione dei parametri chimico-fisici che può essere associata all’azione delle comunità batteriche produttrici dei biogas. Tenteremo di monitorare l’attività di queste ultime e di correlarla con l’evoluzione della discarica a tre scale temporali molto diverse fra loro: i cambiamenti strutturali di lungo periodo, le variazioni stagionali e gli eventi “istantanei”.
Le tecniche di acquisizione passive ed attive utilizzate si sono rivelate complementari ed il loro impiego congiunto ha permesso di definire sia le dinamiche temporali (PS) che quelle fisico-chimiche (resistività) degli eventi studiati. Grazie all’elevata frequenza di misura è stato possibile caratterizzare con buona accuratezza l’evoluzione della discarica a tutte le scale temporali proposte, consentendo interpretazioni potenzialmente utili per la gestione dell’impianto.
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Vanella, Daniela. "Monitoring and modeling fluxes transfer processes in soil-plant-atmosphere continuum across scales." Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/4084.
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Alle interazioni tra le diverse componenti del sistema suolo-pianta-atmosfera (SPA) è attribuito un ruolo critico nel ciclo idrologico e della biosfera terrestre.
La comunità scientifica specializzata è sempre più consapevole della necessità di portare avanti studi a carattere interdisciplinare per la comprensione delle interazioni funzionali tra le risorse naturali ed i relativi problemi di sostenibilità del sistema SPA.
All interno di tali studi interdisciplinari, l analisi delle interazioni suolo-radice risulta rilevante anche per la gestione ottimale dell'irrigazione, in particolare nelle zone caratterizzate da scarsa disponibilità idrica, come le aree mediterranee. A tal fine nasce l esigenza di valutare, ad alta risoluzione sia spaziale che temporale, le dinamiche idrologiche del sistema SPA, sino alla scala dell apparato radicale.
Il contributo della tesi di dottorato consiste nell applicazione di tecniche di monitoraggio avanzate e minimamente invasive, per valutare gli scambi di massa ed energia all'interno del sistema SPA.
L aspetto innovativo del lavoro di tesi consiste nell integrazione di tecniche geofisiche con misure micrometeorologiche e dati di traspirazione, al fine di interpretare alcuni dei principali processi di trasferimento di flussi nel sistema SPA (evapotraspirazione ed assorbimento radicale) in ambiente semi-arido.
Tale approccio, è stato applicato a due Casi studio con l obiettivo di monitorare le complesse interazioni del sistema suolo-pianta, con particolare riferimento al processo di assorbimento radicale di alberi di agrume.
Nel primo Caso studio, la tecnica della tomografia di resistività elettrica (ERT) tridimensionale è stata integrata con dati di traspirazione, misure micrometeorologiche e modellistica idrologica al fine di delineare la porzione di suolo non satura interessata dalle radici attive di un aranceto adulto.
Nel secondo Caso studio, il monitoraggio ERT è stato integrato con misure di traspirazione al fine di delineare i pattern di RWU di alberi di arancio irrigati in regime di deficit.
I risultati del lavoro di tesi dimostrano l abilità della tecnica di monitoraggio geofisico ERT nello spiegare le dinamiche idriche del suolo e la risposta fisiologica della pianta, in termini di attività delle radici nel processo di uptake, contribuendo, in tal senso, a migliorare la conoscenza dei processi di assorbimento radicale.
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Garipova, Yulia V. "Borehold resistivity inversion." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/53031.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997.Includes bibliographical references (leaves 110-111).
by Yulia V. Garipova.
M.S.
9
Morelli, Roberto. "Resistivity testing of concrete." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/15425.
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Marklund, Per. "A 2D Electrical Resistivity Survey of Palsas in Tavvavuoma, sub-arctic Sweden." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-219932.
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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.
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Eidem, Per Anders. "Electrical Resistivity of Coke Beds." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5027.
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Winterton, Stephen S. (Stephen Scott) Carleton University Dissertation Engineering Electrical. "The measurement of contact resistivity." Ottawa, 1989.
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Penz, Sébastien. "Modélisation et inversion de données électriques en courant continu : vers une prise en compte efficace de la topographie." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00796438.
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L'imagerie électrique est un outil de plus en plus important pour un large domaine d'applications relatives à la caractérisation de la subsurface proche. D'importants développements ont été réalisés au cours des vingt dernières années pour l'amélioration des systèmes d'acquisitions et des algorithmes d'inversions. L'acquisition et le traitement de gros jeux de données reste toutefois une tâche délicate, en particulier en présence de topographie. Afin d'améliorer la gestion de la topographie, nous avons développé un nouvel algorithme d'inversion électrique 2.5D et 3D. Nous avons proposé deux nouvelles formulations pour supprimer la singularité à la source. Le problème direct est résolu en utilisant la méthode des Différences Finies Généralisées et des maillages non structurés, permettant une représentation précise de la topographie. Le code d'inversion utilise la méthode de l'état adjoint pour calculer le gradient de la fonction objective de manière économique. Cette approche a donné de bons résultats avec des données synthétiques. Les premiers résultats sur des données réelles ont permis de retrouver les principales structures de la subsurface, ainsi que plusieurs zones de faibles résistivités pouvant correspondre à des zones fracturées.
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Kalscheuer, Thomas. "Improvement and Assessment of Two-Dimensional Resistivity Models Derived from Radiomagnetotelluric and Direct-Current Resistivity Data." Doctoral thesis, Uppsala universitet, Geofysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9366.
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Two-dimensional (2-D) models of electrical resistivity are improved by jointly inverting radiomagnetotelluric (RMT) and direct-current resistivity (DCR) data or by allowing for displacement currents in the inversion of RMT data collected on highly resistive bedrock. Uniqueness and stability of the 2-D models are assessed with a model variance and resolution analysis that allows for the non-linearity of the inverse problem. Model variance and resolution are estimated with a truncated singular value decomposition (TSVD) of the sensitivity matrix. In the computation of model errors, inverse singular values are replaced by non-linear semi-axes and the number of included eigenvectors is increased until a given error threshold is reached. Non-linear error estimates are verified with most-squares inversions. For the obtained truncation levels, model resolution matrices are computed. For RMT data, non-linear error appraisals are smaller than linearized ones. Hence, the consideration of the non-linearity in RMT data leads to reduced model errors or enhanced model resolution. The dielectric effect on RMT data is investigated with a new 2-D forward and inverse code that allows for displacement currents. As compared to the quasi-static approximation, apparent resistivities and phases of the impedance tensor elements are found to be significantly smaller and the vertical magnetic transfer function exhibits more distinct sign reversals. More reliable models of electrical resistivity are obtained from areas with highly resistive bedrock, if displacement currents are allowed for. In contrast, inversions with a quasi-static scheme introduce artefactual structures with extremely low or high resistivities. A smoothness-constrained 2-D joint inversion of RMT and DCR data is presented. The non-linear model variance and resolution analysis is applied to single and joint inverse models. For DCR data, the errors estimated by most-squares inversions are consistently larger than those estimated by the non-linear semi-axes, indicating that DCR models are poorly resolved. Certain areas of the joint inverse models are better resolved than in the single inverse models.
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Gebregiorgis, Ashenafi Weldemariam. "Local Resistivity Measurement on Multicrystalline Silicon." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19278.
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Even though in the past the photovoltaic industry was dominated by single-crystalline silicon this days multi-crystalline silicon is consider to be on of the most promising material for application in low manufacturing cost solar photovoltaic arrays, consequently it has a huge potential to dominate the single-crystalline silicon in the photovoltaic industry in the next decades. However the presence of crystal defects such as dislocation and grain boundaries in multi-crystalline solar cells hugely reducing the conversion efficiency of this material compared to single crystalline silicon solar cell. Hence realizing the widespread utilization of this material will require understanding and control of the effects of this defects on the photovoltaic cell performance. Therefor we will examine the local resistivity of a given multi-crystalline sample in a dark and how it is affected by the presence of grain boundaries and the electrical activity when we cross or with in the grain boundary or twin boundaries. We have measured the resistivity of a number of samples of multi-crystalline silicon using a multi-height four-point probe.
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Par, Andrew R. "DC Resistivity Inversion for Structural Information." Thesis, Colorado School of Mines, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10744014.
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The DC resistivity method has been an important tool for mineral exploration for the direct detection of conductive bodies with economic value. It has also been used for the structural mapping of lithology and alteration where boundaries are zones of economic interest and the detection of edges is the primary goal of surveying. Edge preserving inversion has been explored extensively within the context of potential field methods but has seen relatively little attention for the DC resistivity method. The focus of this thesis is to develop and implement methods which employ specific advantages of the DC method to aid the recovery of edges in the earth’s resistivity distribution.
I begin by utilizing sparse a priori geologic knowledge to create a geologic concept of pervasive blocky resistivity. l1 and l0 approximating measures of model values and model gradients are used as a vehicle to inject the a priori knowledge into a regularized inversion. An iterative method is used to solve for the model that minimizes a total objective function using these general measures.
A series of synthetic modelling and inversion scenarios demonstrate the effectiveness of l1 and minimum gradient support regularization to recover boundaries when compared to traditional sum-of-squares regularization. These blocky inversion schemes also exhibit an improved recovery of the resistivity value of distinct bodies. Additionally, I recognize that the various regularization types have different strengths and weaknesses. I exploit this property to create a new composite regularization that combines smooth model and blocky model regularization. This composite regularization exhibits the strengths of both regularization styles and less of the weaknesses.
A case study on field data from the Sabajo gold deposit was performed utilizing this methodology. Sharp lithologic contacts from drillholes informed the creation of a sharp resistivity concept. A blocky inversion was performed to recover a blocky model that was consistent with this concept and compared to the results of a smooth model inversion. Important differences were noted with their economic implications. I observed that the blocky regularized inversion may have recovered better estimates of the conductivity of features and this can greatly aid prioritization of targets for drilling. Finally, the differences between the inversions utilizing diverse regularization styles provided a proxy for model uncertainty.
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Jordan, David. "The Electrical Resistivity of Archaeological Remains." Thesis, University of Reading, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519871.
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Jönsson, Clara, and Linn Larsson. "Kartläggning av kvicklera med hjälp av flygresistivitetsmätningar." Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Byggnadsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-37057.
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Purpose: One of the major soil problems that the construction industry may face is the presence of a certain type of highly sensitive marine clay, known as quick clay. The quick clay possesses properties that allow the clay to move from being relatively stable to on mechanical impact losing virtually all shear strength and act as a viscous mass. The majority of the Swedish, Norwegian and Canadian landslides, caused by quick clay, have caused significant consequences due to lack of bearing capacity of quick clay. In order to prevent these landslides knowledge about where there is quick clay is required. A large-scale mapping work has therefore been ongoing for a long time. The government has for some time been researching how to streamline mapping work and the result has shown a connection between quick clay attendance and increased resistivity. The purpose of this study is to develop a theoretical framework for areas with higher risk for presence of quick clay based on linking the resistivity to geotechnical properties. Method: The study has mainly applied quantitative data collection methods in the form of data analyzes combined with literature studies. Measurement data used in the study comprise of data collected through geotechnical and geophysical surveys. Literature studies have mainly been supported by reports from previous research in the field. Result: The result of the study points to a variety of geological factors that can give rise to increased risk of quick clay existence such as good permeability, artesian groundwater and uneven mountain subsidence etc. The study also shows a possible link between resistivity and sensitivity. Consequences: The study demonstrates the possibility of linking resistivity to the geotechnical property sensitivity to facilitate and streamline the mapping of quick clay through airborne resistivity measuring. Limitations: The study is limited to studying two research areas in south western Sweden, Strömstad and Lödöse. The study intends to examine the evidence from previous surveys and no further supplementary studies are conducted. The work is also delimited to study the geotechnical and geophysical properties of quick clay (in terms of resistivity). Chemical aspects are not taken into account.Syfte: Ett av de större markproblem bygg- och anläggningsbranschen kan tvingas stå inför är förekomsten av en viss typ av högsensitiv havsavsatt lera, kallad kvicklera. Kvickleran besitter egenskaper som innebär att leran kan gå från relativt stabil till att vid mekanisk påverkan förlora praktiskt taget all sin skjuvhållfasthet och uppträder som en trögflytande massa. Majoriteten av de svenska, norska och kanadensiska lerskred som medfört betydande konsekvenser har varit ett resultat av kvicklerans bristande bärighet. För att förebygga dessa kvickleraskred krävs vetskap om var kvicklera förekommer. Ett omfattande kartläggningsarbete har därför pågått under en lång tid. Staten har under en tid bedrivit forskning för att effektivisera kartläggningsarbetet och resultatet har visat på ett samband mellan kvickleraförekomst och förhöjd resistivitet. Syftet med detta examensarbete är att ta fram ett teoretiskt ramverk för områden med större risk för förekomst av kvicklera baserat på att koppla samband mellan resistivitet och geotekniska egenskaper i form av vattenkvot, sensitivitet och densitet. Metod: I studien har i huvudsak kvantitativa datainsamlingsmetoder i form av dataanalyser tillämpats i kombination med litteraturstudier. Mätdatat som studien omfattar är insamlad via geotekniska och geofysiska undersökningar, litteraturstudierna har främst tagit stöd i rapporter från tidigare forskning inom området. Resultat: Resultatet pekar på en rad olika geologiska faktorer som kan ge upphov till ökad risk för kvickleraförekomst, exempelvis god permeabilitet, artesiskt grundvatten samt ojämn bergunderyta etc. Studien visar även på en möjlig koppling mellan resistivitet och sensitivitet. Konsekvenser: Studien visar på möjligheten att koppla resistivitet till den geotekniska egenskapen sensitivitet för att underlätta och effektivisera kartläggningen av kvicklera genom flygburna resistivitetsmätningar. Begränsningar: Uppsatsen begränsas till att studera två undersökningsområden i sydvästra Sverige, Strömstad och Lödöse. Studien avser granska underlag från tidigare utförda undersökningar och inga ytterligare kompletterande undersökningar har utförts. Arbetet avgränsas till att studera kvicklerans geotekniska egenskaper samt dess resistivitetsegenskaper. Arbetet tar således inte hänsyn till kemiska aspekter.
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Adams, Christopher Hugh, and c. adams@student rmit edu au. "Capacitive Array Resistivity with an Inductive Source." RMIT University. Applied Sciences, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090527.142304.
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The aim of this research was to develop an instrument that fills a niche in geophysical instrumentation for a tool that is fast, non-contact or minimal contact, and specifically optimised for discrete, near-surface, electrically resistive targets in resistive and conductive environments. This aim was sought to be achieved through the development of a new Capacitive Array Resistivity with Inductive Source (CARIS) system. Two CARIS systems were produced and thoroughly tested. A first prototype instrument CARIS-1, operating at 100KHz, was developed for proof of concept in the laboratory and initial field testing. A second prototype CARIS-2, operating at 5kHz, was developed for further fielding testing and trial mapping experiments. Several major conclusions have been reached through the development and testing of the CARIS systems. Firstly, the CARIS system can clearly detect objects in a conductive homogeneous liquid, with high repeatability of data. This result reinforced the concept of the CARIS method, and established the stability of the instrumentation in laboratory environments. The approach was validated by close correlation between measurements and modelling. Secondly, the CARIS system is able to measure responses to near-surface conductivity variation in field conditions with high repeatability. Data collected also showed spatial consistency with GPR, Resistivity and mapped culture. It was determined that properties of the near surface, such as moisture content and soil consolidation, can significantly affect the electrical homogeneity of the medium and thus the uniformity of the background reading. The CARIS systems thus had a limitation that they proved to be quite sensitive to variations of this nature. Thirdly, foll owing from the second conclusion, although the aim of the CARIS system was to detect the presence of discrete buried objects, CARIS proved to be more responsive to the effects of the burial process rather than the objects themselves. It was concluded therefore that the method of excavation, burial, and refill material were of high significance in CARIS interpretation. This conclusion was reinforced by the results of theoretical modelling which showed that shallow boundaries of small conductivity contrast could quite easily produce more significant anomalies than target objects which are deeper and have higher contrast.
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Lawson, N. S. "The electrical resistivity of dilute cadmium alloys." Thesis, Lancaster University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355340.
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Loke, Meng Heng. "The inversion of two-dimensional resistivity data." Thesis, University of Birmingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496050.
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Strange, Kathryn Louise. "The integration of ground resistivity with GPS." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405095.
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Snyder, Jeffrey Z. 1974. "Accuracy and resolution in 2D resistivity inversion." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/59096.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.Includes bibliographical references.
Two-dimensional resistivity inversion employing regularization enforces a constraint of smoothness that minimizes error and avoids unrealistically complex solutions to the inverse problem. The insensitivity of surface array data to deeper targets typically presents an under-determined problem for solution by the inversion algorithm, and the smoothing function within the algorithm tends to "smear" tomographic imagery. Together, the physical challenges of electrical resistivity as a geophysical method and the numerical challenges inherent in solving the inverse problem introduce errors in the accuracy of 2D resistivity imagery. It is important to know what surface array geometry will provide data that yields the best results from the inversion. Testing this inversion algorithm on data from several array geometries provides the opportunity to determine the comparative performance of each survey method. By introducing two types of resistive anomalies and varying their location within a synthetic homogeneous half-space, it is possible to generate synthetic data with a forward model algorithm. The data from each array geometry is then inverted in order to illustrate the accuracy and resolution response of the inversion algorithm. The inversion images are converted into binary images after defining a critical resistivity that describes the contrast between background resistivity and target resistivity. The binary images are used as interpretive tools that allow the user to overcome the "smearing" introduced by the inversion. Because of its consistent performance from the margins to the center of an array, a left-right sweep geometry combined with a pseudo section geometry appears to be the best choice for a surface array when there is no knowledge of the subsurface structure or resistivity distribution. The critical resistivity and the area of the anomaly are used to describe the performance of the inversion. When taken as functions of increasing depth, the critical resistivity decreases and the area of anomaly increases, providing a respective correlation with the current density and the degree of smoothness. Initial results by forming a product of critical resistivity and area suggest that it is possible to approximate the product from the original forward model, but further testing is warranted to provide more conclusive results.
by Jeffrey Z. Snyder.
S.M.
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Schippan, Frank. "The contactless measurement of the electrical resistivity." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/14732.
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Physicists are interested in understanding the processes of nature. Within the field of Solid State Physics the characterisation of materials and the measurement of their properties is the first step towards identifiying new and interesting areas of scientific activities. The electrical resistivity of conductive materials is an important property which provides information about the electronic behaviour of the material. An elegant method to determine this characteristic is the measurement without using electrical contacts. Such a method avoids a whole set of experimental problems connected with the physics of electrical contacts to the sample. This Master-thesis gives an introduction into this experimental technique. A detailed theoretical description is developed. The experimental activity has involved the design, construction and testing of the apparatus. In the process of testing the method novel aspect emerged: The measurement at resonance point. These measurements can yield separate values for two different physical quantities: the electrical resistivity e and the magnetic susceptibility x. The innovation of this project is the simultaneous characterisation of both values for the material under investigation. The report starts by giving the theoretical background within which the first part of the detailed theoretical predictions are discussed. The second part contains experiments and a description of the experimental set-up. This design is the result of a long period of optimisation and testing. The working of the apparatus is demonstrated by the measurement of some samples.
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Perren, Lee John. "Investigating the Performance Of Electrical Resistivity Arrays." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/35240.
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2D inversion modeling of synthetic data is used to evaluate the performance of five electrical resistivity arrays, with the primary criteria being the reproduction of sharp model boundaries. 2D synthetic noise free data were calculated simulating a modern fixed spacing multi-electrode cable. Twelve 2D synthetic models, resembling a number of different geologic situations, were used to investigate performance of the dipole-dipole, pole-dipole, pole-pole, Wenner and Schlumberger arrays
Although the synthetic, noise-free data were well matched for all inversions, many of the inversion results exhibit substantial mismatches from the true model. The greatest resistivity mismatches are near model discontinuities. Resistivity mismatches become worse with depth and the geometry of geologic boundaries in the deep portion of the models are not well reproduced by any of the arrays. Field surveys must be designed so that the geologic target is in the middle of the data constrained region. Different arrays performed best for different models and a practical table is presented allowing the practitioner to choose the optimal array for the particular geologic situation under investigation. Although the dipole-dipole and pole-dipole arrays may not be the optimal array for a given geology, they rarely fail for any model, and thus are recommended for reconnaissance or preliminary investigations in regions of unknown geology.
Contrary to traditional advice found in textbooks, based on 1D profiling and sounding, and data plot comparison, this study, using 2D data and 2D inversion, finds the Wenner and Schlumberger arrays, thought to perform poorly for vertical boundaries, performed well for a vertical boundary and a thin vertical resistor. Similarly, the dipole-dipole and pole-dipole arrays, thought to perform poorly for horizontal and dipping boundaries, performed well for several models containing those geometries. Another interesting finding is that changing the polarity of geologic units from resistors to conductors changed relative array performance in most models.Master of Science
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Hägerbrand, Jonathan. "Measurements of resistivity in transformer insulation liquids." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413804.
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This thesis focuses on measuring techniques and results of resistivity in four commercially available insulating transformer oils: mineral oil, ester oil and two isoparaffin oils. Two measuring techniques, the industrially used diagnostic system for electrical insulation IDA and the Labview implemented Triangular Method, are used for resistivity measurements and the techniques are compared, a correction algorithm to the triangular method is suggested. Dielectric properties of mineral & ester and isoparaffin A&B mixtures are investigated, it is experimentally shown that the transformer oils that show high resistivity also show low loss factor. The effect moisture has on resistivity in mineral and ester oil are shown both in terms of relative humidity and actual water content in parts per million. A previous measurement cell is redesigned, the cell is manufactured in copper and gold. It is found that the material choice of the cell significantly affects the resistivity measurements. The electrical double layer and contact resistance between the oil and cell are investigated as a way to explain the difference in measured resistivity. These experiments are limited to the mineral oil and isoparaffin oil A, it is found that contact resistance is a plausible explanation. The electrical double layer is fairly constant for both oils and the Debye length of the double layer is negligible compared to the total distance between the electrodes of the cell. Lastly, the field of insulating transformer oils and its future is discussed, from data obtained regarding the dielectric properties and environmental aspects of the four transformer oils used in this study. A positive trend which combines the high insulating properties with good biodegradability qualities is found. Suggesting a positive future in the field of insulating transformer oils. The results found in this thesis can be used as a basis for future theses regarding transformer oils used for HVDC applications.
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Kiflu, Henok Gidey. "Improved 2D and 3D resistivity surveys using buried electrodes and optimized arrays: The multi-electrode resistivity implant technique (MERIT)." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6524.
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This thesis presents a novel resistivity method called Multi-Electrode resistivity technique (MERIT) that is used for high resolution imaging of complex geologic features at depth and near the edges of survey lines. The MERIT electrodes are especially shaped and designed to be self-driven using a robust-direct push technique. Measurements are taken using optimized arrays that are generated using a modified version of the “Compare-R” optimization algorithm. This work focused on both two-dimensional (MERIT2D) and three-dimensional (MERIT3D) applications of the buried array and show the relevance of the additional information gained by the addition of deep electrodes especially in sites with limited survey area. Numerical and laboratory studies are used to test and develop the technique and are later applied to image complex subsurface geologic structures on the field.
The configuration of MERIT arrays brings some additional problems in terms the sensitivity of the deep MERIT arrays to a problem of non-uniqueness, mis-information, geometric error and resolution break between the two layers of electrodes. Multiple vertical resolution characteristic curves (RC curves) are analyzed to study the effect of array type, resistivity contrast, target resistivity and implant depth on the above-mentioned problems. Results show that MERIT measurements taken using standard dipole -dipole and wenner arrays along the surface and deep electrodes will strongly suffer from the problem of non-uniqueness or ambiguity while measurements taken using optimized arrays is suitable for MERIT configuration and will not suffer from any problem of ambiguity or non-uniqueness. Based on our result, a procedural guideline is developed to determine optimal MERIT implant depth and resolution cutoff that can be used for successful field implementation and for controlling misinformation during data interpretation.
Numerical studies involving simple shapes and complex geometries mostly based on actual geological cross-sections from karst environments were used to compare the effectiveness of MERIT2D in terms its high depth resolution and is compared in detail with traditional 2D and 3D surface resistivity methods of equal foot prints. Similar comparison was made between MERIT3D technique and 3D surface resistivity measurements. Results show that both methods achieve high depth resolution compared to their equivalent traditional resistivity methods. Laboratory experiment conducted using a complex analogue model mimicking actual sinkhole structure is used to test MERIT2D. Also laboratory experiment involving a 3D printed plastic cave model mimicking an actual cave was conducted using MERIT3D approach. Both results show the promise of MERIT approach to image and solve complex geological structures or problems.
Finally, the method is applied to collect field data in three case study sites involving complex karst related sinkhole structures and an old landfill site. The result shows the promising capability of the MERIT technique to study challenging geologic conditions with high depth resolution.
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Sabo, Stephen Henry. "Evaluation of Capacitively-Coupled Electrical Resistivity for Locating Solution Cavities Overlain by Clay-rich Soils." Bowling Green State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1219092853.
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Watts, Paul CristoÌir Patrick. "Electrically conducting carbon nanotube polystyrene composites." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288865.
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Akbari-Moghanjoughi, Massoud. "Temperature dependence of the electrical resistivity in quasicrystals." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/10382.
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The applicability of the weak-localization theory to highly ordered quasicrystals raises the question of whether or not the long-range order in these alloys can be reconciled with the electronic disorder. This study did not detect any unusual structure-induced contribution to the resistivity at low temperatures other than those known for metallic glasses. The temperature dependence of the resistivity in icosahedral quasicrystals of high structural quality showed that the transport behaviour of these alloys at low temperatures can be satisfactorily explained in terms of conventional weak-localization and electron-electron interaction theories. The temperature dependence of the resistivity in weakly disordered (low-resistivity) alloys can be explained qualitatively in terms of the classical theories extended to liquids and disordered alloys. The experimental evidence shows the existence of a close relationship between the icosahedral quasicrystalline structure and the weak localization tendency of the electronic states at the Fermi level. To explain the temperature dependence of the resistivity at high temperatures additional models based on the concept of the band transition and hopping have to be invoked. In the high-resistivity stable icosahedral Al-Cu-Ru alloy the insulating-like (electron hopping) behaviour was found to dominate the electron transport even at low temperatures. This causes the deviations from the weak-localization theory and is due to the enhancement of the density of localized electronic states at the Fermi level. Consequently, the Anderson localization is collapsed in the vicinity of the metal-insulator transition. The values of the correlation gap in the Al-Cu-Fe-Mn icosahedral system suggest a considerably different nature for the pseudogap around the Fermi level in amorphous and icosahedral phases. However, unless an ideal quasicrystal belongs to the metal-insulator transition region (if it exists), the weak-localization theory will be the most appropriate tool to investigate the low temperature electron transport properties in icosahedral phases.
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Aaltonen, Jaana. "Ground Monitoring using Resistivity Measurements in Glaciated Terrains." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3177.
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Coleman, Brendan James Joseph. "Some aspects of IP/resistivity modelling and methodology /." Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09SB/09sbc6921.pdf.
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Muchaidze, Iana. "Imaging in karst terrain using electrical resistivity tomography." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Muchaidze_09007dcc80534d1b.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 26, 2008) Includes bibliographical references (p. 66-67).
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Fenn, Michael. "Electrical resistivity of thin metal films and multilayers." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325924.
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Adetunji, Ademola Quadri. "Resistivity structure of the Precambrian Grenville Province, Canada." Tectonophysics, 2014. http://hdl.handle.net/1993/23450.
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As part of the southern Ontario POLARIS project, this thesis uses magnetotelluric methods to investigate the lithospheric architecture of the Proterozoic Grenville Province and its margin with the Archean Superior Province. The first multi-dimensional crustal and lithospheric resistivity images for this region are presented.
The resistivity structure of the Phanerozoic sedimentary rocks in the lower Great Lakes region was determined using 1-D methods. The responses are strongly affected by a 20-23 S conductive layer within the sedimentary rocks, interpreted to be associated with Upper Ordovician shale units. This layer excludes resolution of resistivity structure of underlying crust.
The resistivity structure of the Precambrian crust and lithosphere was determined using 2-D methods. Different strike azimuths were determined for the crust, the upper lithospheric mantle and the deeper mantle layer. The crustal resistivity model for a profile from 50oN79oW to 43oN76oW images resistive Laurentian margin rocks dipping southeast to the base of the crust, bounded by the Grenville Front and the Central Metasedimentary Belt Boundary Zone. In a 2-D model of the mantle lithosphere for the same profile, a conductor at 70-150 km depth, located along-strike from the Mesozoic Kirkland Lake and Cobalt kimberlite fields, is interpreted to be due to mantle re-fertilization. Results from multiple MT profiles indicate conductive (<10 Ω.m) lithospheric mantle beneath the Central Metasedimentary Belt and show that the northwestern Grenville Province is characterized by large-scale, resistive lithosphere (>10,000 Ω.m) extending for about 300 km beneath the Grenville Province and 800 km along strike. Lithospheric thickness is interpreted to be 280 km; local decreases in this depth are attributed to refertilization of the lower mantle lithosphere by fluids associated with Cretaceous kimberlite magmatism.
Anisotropic 2-D modeling reveals minimal electrical anisotropy (<10%) at mantle depths in contrast to the factor of 15 anisotropy determined in earlier 1-D studies. This result suggests that observed MT response anisotropy is caused by large-scale structures. Strike direction in the upper lithospheric mantle is interpreted to be related to the Archean fabric of the Superior craton and in the deeper, conductive, mantle it is interpreted to have been established in the Cretaceous.
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Coles, Darrell Ardon 1971. "Optimal experimental design applied to DC resistivity problems." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/42921.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 317-323).
The systematic design of experiments to optimally query physical systems through manipulation of the data acquisition strategy is termed optimal experimental design (OED). This dissertation introduces the state-of-the-art in OED theory and presents a new design methodology, which is demonstrated by application to DC resistivity problems. The primary goal is to minimize inversion model errors and uncertainties, where the inversion is approached via nonlinear least squares with L1 smoothness constraints. An equally important goal is to find ways to expedite experimental design to make it practical for a wider variety of surveying situations than is currently possible.A fast, sequential ED strategy is introduced that designs surveys accumulatively by an efficient method that maximizes the determinant of the Jacobian matrix. An analysis of electrode geometries for multielectrode data acquisition systems reveals that experiment-space can be usefully decimated by using special subsets of observations, reducing design CPU times. Several techniques for decimating model-space are also considered that reduce design times.A law of diminishing returns is observed; compact, information-dense designed surveys produce smaller model errors than comparably sized random and standard surveys, but as the number of observations increases the utility of designing surveys diminishes. Hence, the prime advantage of OED is its ability to generate small, high-quality surveys whose data are superior for inversion.Designed experiments are examined in a Monte Carlo framework, compared with standard and random experiments on 1D, 2D and borehole DC resistivity problems in both noiseless and noisy data scenarios and for homogeneous and heterogeneous earth models. Adaptive methods are also investigated, where surveys are specifically tailored to a heterogeneous target in real time or in a two-stage process.
(cont) The main contributions this thesis makes to geophysical inverse theory are: 1) a fast method of OED that minimizes a measure of total parameter uncertainty; 2) novel techniques of experiment-space and model-space decimation that expedite design times; 3) new methods of adaptive OED that tailor surveys to specific targets; and 4) though the OED method is demonstrated on geoelectrical problems, it can be applied to any inverse problem where the user controls data acquisition.
by Darrell A. Coles.
Ph.D.
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Barghout, Jeries Y. J. "Microstructural features that affect resistivity of aluminium conductors." Thesis, University of Manchester, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630500.
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Before privatisation of the electrical generation and distribution industries in the United Kingdom, the CEGB, owner and operator of the national grid, distributed electricity from electrical power stations to areas local to those stations. After the privatisation of the electrical industry the National Grid Company was formed and is obliged to supply the consumer with the cheapest supplier of electricity, irrespective of supplier and user, and this has caused an increased demand on the national grid. Due to the difficulty of obtaining the right of way for new overhead electricity transmission lines, the National Grid Company plc has focused its attention on developing an electrical conductor which has higher electrical conductivity than the present conductor alloy but with similar mechanical properties. To develop a new conductor it is important to gain an understanding of the factors that affect the electrical resistivity of aluminium conductors. The aim of the present research has been to investigate the effect of microstructural features on the electrical resistivity of aluminium and to measure the individual contribution of those features. The microstructural features examined in the present work are: intermetallic particles, dislocations, grain and sub-grain boundaries. The research involved manufacturing aluminium-based wires which contained a number of alloying additions that were subjected to varying levels of deformation up to true strains of 4. By using various thermo-mechanical treatments, it was possible to produce sets of aluminium wires of 1.18mm in diameter which contained varying volume fraction of intermetallic particles, varying dislocation densities and varying sub-grain sizes and grain sizes. The electrical resistivity of the wires was measured and related to their microstructure. Microstructural characterisation of the sets of wires was mainly carried out by transmission electron microscopy, scanning electron microscopy and optical metallography. This involved measuring dislocation density, grain/sub-grain size, sub-grain misorientation and volume fraction of intermetallic particles. The electrical resistance of the wires was measured using the four probe method. It was found that all microstructural features described above increased the resistivity of pure aluminium. The relationship between volume fraction of intermetallic particles and resistivity was found to be linear for volume fractions of less than 5%. The resistivity of the alloy could be calculated by considering the intermetallic particles and the aluminium matrix as two resistors in parallel. Cold working aluminium and aluminium alloys caused an increase in the resistivity. For the aluminium-iron alloys the rate of increase in resistivity was dependent on the volume fraction of intermetallic particles. The particles increased the rate of generation of dislocations as the alloy was deformed due to the plastic incompatibility between the matrix and the particles. For the aluminium-magnesium alloys the rate of increase in resistivity was dependent on the concentration of magnesium is solid solution. The rate of increase in resistivity when the wires were cold worked up to true strains of 1 was larger than when the wires were cold worked from true stains of 1 to 4. The microstructure of the wires that were cold worked to true strains of up to 1 was found to be dominated by dislocations. The relationship between dislocation density and resistivity was found to obey a power-law relationship. At low levels of deformation «0.3 true strain) the dislocations were randomly distributed and acted as individual electron scattering centres. As the dislocation density increased the dislocations became tangled and the degree of scattering of conduction electrons for each dislocation decreased. As the samples were deformed in the plastic strain range of 1 to 4, the dislocations formed dislocation cells / sub-grains. The increase in resistivity was found to be inversely proportional with sub-grain size due to scattering of conduction electrons by sub-grain boundaries. The relationship between grain size and resistivity was found to be inversely proportional to the grain size. This was the same relationship as that between sub-grain size and resistivity. The findings reported in this thesis provide an understanding of the way in which particles, dislocations and grain boundaries affect the resistivity of electrical conductors. The results show that, in general, factors which increase conductivity also increase strength. This information is vital when attempting to develop a conductor that combines high conductivity and high strength.
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Karim, Md Zahidul. "Characterizing soil erosion potential using electrical resistivity imaging." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32899.
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Master of ScienceDepartment of Civil Engineering
Stacey Tucker-Kulesza
The erosion rate, or erodibility, of soil depends on many soil characteristics including: plasticity, water content, grain size, percent clay, compaction, and shear strength. Many of these characteristics also influence soil in situ bulk electrical resistivity (ER) measurements. The objective of this study was to characterize soil erosion potential by correlating the in situ ER of soil with erodibility measured in the Kansas State University Erosion Function Apparatus (KSU-EFA). ER surveys were conducted at eleven bridge sites. Soil samples were also collected at each site with a drill rig from the surface to three meters using thin-walled Shelby tubes. Five samples were collected at each site, tested in the KSU-EFA, and classified according to the Unified Soil Classification System. Analysis showed that the rapid in situ data obtained from an ER survey can be used to categorize the level of erodibility. As such, ER surveys may be used to characterize the soils at future bridge sites or prioritize existing bridges for additional testing to measure the scour potential. Moreover, ER surveys may be used to determine which existing bridges should be closed or closely monitored for scour potential during a flood event. Analytical models to predict critical shear stress using ER and other soil parameters were constructed.
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Earl, Simeon J. "Estimation of subsurface electrical resistivity values in 3D." Thesis, University of Bristol, 1998. http://hdl.handle.net/1983/e7842879-bf35-43eb-86d6-d4624fae9c3c.
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Meheni, Youcef. "Cartographie de resistivite electrique en geophysique de subsurface." Paris 6, 1995. http://www.theses.fr/1995PA066161.
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L'evaluation, par le biais d'une etude comparative, des avantages et limites de trois methodes de cartographie en prospection geophysique - la methode electrique wenner, la methode slingram et la methode m. T-vlf - basees sur la mesure de la resistivite electrique et adaptees a la reconnaissance du proche sous-sol, constitue l'objectif de ce travail. Apres un rappel theorique de ces methodes, plusieurs points ont ete abordes: sensibilite aux structures 1d et 3d, bruit geophysique, anisotropie apparente et inversion 1d sur un parametre. Pour illustrer et verifier les resultats theoriques, cinq sites caracterises par des structures situees a quelques metres de profondeur ont ete cartographies et ont servi de cadre de confrontation aux trois methodes. Au vu des resultats de cette etude: ? la methode electrique wenner, la moins affectee par le bruit geophysique, apparait comme la plus performante pour caracteriser les parametres de structures quasi-tabulaires. La methode. Mt-vlf, en plus de sa plus grande profondeur d'investigation, a le meilleur pouvoir de detection des structures 3d. ? l'effet d'anisotropie apparente est pratiquement inexistant en configuration dipole-dipole pour un dispositif wenner. Pour les autres methodes, une structure allongee presentant un contraste de resistivite produira une anomalie plus marquee lorsque le dispositif de mesure est parallele a la structure pour les methodes electrique wenner normal et slingram vcp, et lorsque le champ electrique primaire est perpendiculaire a la structure pour la methode m. T-vlf ? dans les conditions d'application, l'inversion 1d donne de bons resultats. Cependant, en m. T-vlf l'epaisseur est surestimee. Les resultats experimentaux sont caracterises globalement par la coherence et la similitude des cartes de resistivite apparente obtenues par les trois differentes methodes, et par une bonne correspondance avec les modeles theoriques
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Giouse, Hélène. "Proprietes petrophysiques et resistivite des gres argileux petroliferes." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0060.
Full textAbstract:
La presence d'argile dispersee dans les reservoirs de petrole greseux pose un probleme d'interpretation des diagraphies de resistivite a cause de leur conductivite de surface. On presente une revue bibliographique des phenomenes physiques mis en jeu au sein du reservoir et une analyse critique des formations existantes: on examine en particulier les formules de waxman et smits et celle du dual water. L'etude experimentale des proprietes petrophysiques des roches magasins met en evidence l'importance de la texture de l'argile. Une nouvelle equation "double conducteur-double effet" est proposee. Des mesures de resistivite sur echantillons partiellement satures en huile ont montre qu'il est necessaire de distinguer plusieurs domaines de saturation en eau avec des lois differentes
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Zhang, Jie. "Microstructure study of cementitious materials using resistivity measurement /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202008%20ZHANG.
Full text
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Amidu, Sikiru Adetona Dunbar John A. "Electrical resistivity imaging for characterizing dynamic hydrologic systems." Waco, Tex. : Baylor University, 2008. http://hdl.handle.net/2104/5207.
Full text
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Safarjameh, Kourosh 1961. "Fast-neutron-induced resistivity change in power MOSFETs." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277011.
Full textAbstract:
Fast neutron irradiation tests were performed to determine the correlation of change of drain-source resistance and neutron fluence for power MOSFETs. The Objectives of the tests were: (1) to detect and measure the degradation of critical MOSFET device parameters as a function of neutron fluence (2) to compare the experimental results and the theoretical model. In general, the drain-source resistance increased from 1 Ohm to 100 Ohm after exposure to fast neutron fluence of 3 x 1014 neut/cm2, and decreased by a factor of five after high temperature annealing.
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Kamkar-Rouhani, Abolghasem. "Development and application of processing techniques for signal enhancement using multisystem resistivity measurements." Thesis, Curtin University, 1998. http://hdl.handle.net/20.500.11937/1314.
Full textAbstract:
DC electrical surveying involves the injection of current into the earth, and the measurement of the electrical potential differences this produces. A number of electrode configurations such as the Schlumberger and Wenner arrays, dipole-dipole and pole-pole geometries are in common use for electrical surveying. New acquisition systems enable the convenient collection of data with a number of common configurations at the same time. It is found however that while the recovery of layered structure from electrical surveys can be effective, the sensitivity and resolving power of such systems in detecting the presence of anomalous three-dimensional (3-D) bodies is poor. This is mainly due to the dominance of conduction pathways through the layered earth compared to the influence of small 3-D conductivity anomalies.Theoretical relationships between the responses of various survey geometries to the layered earth may be established as is shown in this thesis, but their response to 3-D targets differs strongly. This thesis introduces a new procedure for anomalous target detection by the computation of an apparent resistivity residual using multi-electrode configuration survey data. This procedure, applicable to a variety of electrode geometries, reduces the dominance of the layered earth response and enhances the signal from 3-D structures.In the development and testing of this new apparent resistivity residual, numerically modelled data were used. In order to obtain suitable test data of high accuracy it was necessary to make improvements to modelling software. For this purpose, recently developed techniques in numerical modelling such as the biconjugate gradient method, new digital linear filters for computation of Hankel transforms, and spectral formalism were employed in an integral equation approach for the software developed in this thesis.The computed apparent resistivity residual was found to depend on the array type and dimensions, the nature of the anomalous zone, geological layer geometries, and resistivity contrasts of the layers involved. While the apparent resistivity residual signature requires some measure of interpretation, it is shown to enhance the resolution and detectability of 3-D targets in a layered environment.The presence of random noise produces some degradation in the performance of the residual technique, but a normalisation procedure has been developed to alleviate the problem. A preliminary field trial showed that survey profiles of apparent resistivity residual were able to locate a subsurface conductive anomaly in an area in Western Australia.A transitional zone is defined as a layer in the earth where resistivity varies as a continuous function of depth. A theoretical formulation for the electrical response of an earth structure composed of anomalous 3-D bodies in the presence of transitional layers is introduced. Tests on synthetic survey data showed that the apparent resistivity residual is an effective anomaly detector in transitional layer environments.A multi-system method of computing an apparent resistivity residual has been developed theoretically and tested on both synthetic and field data. This new approach when applied to resistivity profiling is more sensitive to, and gives greater resolution of, localised anomalies than is possible using conventional profiling procedures.
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Rücker, Carsten. "Advanced Electrical Resistivity Modelling and Inversion using Unstructured Discretization." Doctoral thesis, Universitätsbibliothek Leipzig, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-69066.
Full textAbstract:
In this dissertation an approach is presented for the three-dimensional electrical resistivity tomography (ERT) using unstructured discretizations.
The geoelectrical forward problem is solved by the finite element method using tetrahedral meshes with linear and quadratic shape functions.
Unstructured meshes are suitable for modelling domains of arbitrary geometry (e.g., complicated topography).
Furthermore, the best trade-off between accuracy and numerical effort can be achieved due to the capability of problem-adapted mesh refinement.
Unstructured discretizations also allow the consideration of spatial extended finite electrodes.
Due to a corresponding extension of the forward operator using the complete electrode model, known from medical impedance tomography, a study about the influence of such electrodes to geoelectrical measurements is given.
Based on the forward operator, the so-called triple-grid-technique is developed to solve the geoelectrical inverse problem.
Due to unstructured discretization, the ERT can be applied by using a resolution dependent parametrization on arbitrarily shaped two-dimensional and three-dimensional domains. A~Gauss-Newton method is used with inexact line search to fit the data within error bounds.
A global regularization scheme is applied using special smoothness constraints.
Furthermore, an advanced regularization scheme for the ERT is presented based on unstructured meshes, which is able to include
a-priori information into the inversion and significantly improves the resulting ERT images.
Structural information such as material interfaces known from other geophysical techniques
are incorporated as allowed sharp resistivity contrasts.
Model weighting functions can define individually the allowed deviation of the final resistivity model from given start or reference values.
As a consequent further development the region concept is presented where the parameter domain is subdivided into lithological or geological regions with individual inversion and regularization parameters.
All used techniques and concepts are part of the open source C++ library GIMLi, which has been developed during this thesis as an advanced tool for the method-independent solution of the inverse problem.
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Seehafer, Norbert, and Jörg Schumacher. "Resistivity profile and instability of the plane sheet pinch." Universität Potsdam, 1998. http://opus.kobv.de/ubp/volltexte/2007/1468/.
Full textAbstract:
The stability of the quiescent ground state of an incompressible, viscous and electrically conducting fluid sheet, bounded by stress-free parallel planes and driven by an external electric field tangential to the boundaries, is studied numerically. The electrical conductivity varies as cosh–2(x1/a), where x1 is the cross-sheet coordinate and a is the half width of a current layer centered about the midplane of the sheet. For a <~ 0.4L, where L is the distance between the boundary planes, the ground state is unstable to disturbances whose wavelengths parallel to the sheet lie between lower and upper bounds depending on the value of a and on the Hartmann number. Asymmetry of the configuration with respect to the midplane of the sheet, modelled by the addition of an externally imposed constant magnetic field to a symmetric equilibrium field, acts as a stabilizing factor.
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Kramvis, Sotiris C. "Application of electrical resistivity in groundwater exploration in Cyprus." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/35057.
Full textAbstract:
A number of geophysical methods have been used in groundwater exploration in Cyprus. Of these, electrical resistivity has found the widest application in the investigation of the mostly unconsolidated extensive aquifers of the Mesaoria Plain and the alluvial aquifers of the rivers draining the Troodos massif. Special emphasis has been given in this study on the detailed investigation by means of electrical resistivity of the aquifers of Western Mesaoria, Central Mesaoria and the three main Paphos rivers of Dhiarizos, Xeros and Ezusa where the nature of the deposits and the scarcity of exposures diminish the effectiveness of conventional hydrogeological methods. Existing hydrogeological information and specially conducted resistivity measurements of the magnitude and extent of lateral and orientational resistivity variations indicate that conditions in Western Mesaoria, the Paphos rivers and the larger part of Central Mesaoria are on the main suitable for the application of the electrical sounding technique. Over 120 correlation soundings measured in these areas show close correspondence between hydrogeological and electrical layers and enable the establishment of working geoelectrical models according to which the rest of the 904 soundings have been interpreted. In Western Mesaoria subsurface conditions are fairly simple and laterally persistent and two subaquifers to the Western Mesaoria Upper Aquifer are indicated by the electrical and hydrogeological results. In Central Mesaoria subsurface conditions are more variable while groundwater salinity variations complicate the picture. Interpretation of sounding measurements has been based on several geoelectrical models. In the Paphos rivers subsurface conditions are simple and the basic geoelectrical model assumes the presence of two alluvial layers with different physical properties. Aquifer geometry and configuration are accurately defined by the electrical-hydrogeological results. The electrical properties of the aquifers and associated rocks are derived while aquifer potential and hydraulic transmissivity appear to be related directly to the aquifer transverse resistance.
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Andriyas, Tushar. "Particle Dynamics and Resistivity Characteristics in Bifurcated Current Sheets." DigitalCommons@USU, 2013. http://digitalcommons.usu.edu/etd/1513.
Full textAbstract:
Charged particle chaos and its collective effects in different magnetic geometries are investigated in a sequence of various numerical experiments. The fields generated by the particles as a result of interaction with the background electric and magnetic fields is not accounted for in the simulation. An X-line is first used to describe the geometry of the magnetotail prior to magnetic reconnection and a study of the behavior of charged particles is done from a microscopic viewpoint. Another important geometry in the magnetotail prior to substorm onset is Bifurcated Current Sheet. The same analysis is done for this configuration. The existence of at least one positive Lyapunov exponent shows that the motion of the particles is chaotic. By using statistical mechanics, the macroscopic properties of this chaotic motion are studied. Due to particles being charged, an electric field (perpendicular to the magnetic field in weak magnetic field region) accelerates the particles on average. Finite average velocity in the direction of electric field gives rise to an effective resistivity even in a collisionless regime such as solar corona and the magnetotail. Starting from initial velocities that are chosen randomly from a uniform distribution, the evolution of these distributions tends to a Maxwellian by the end of the simulation that is somewhat analogous to collisions in a Lorentz gas model. The effective resistivity due to such collisions is estimated. Ohmic heating is found to occur as a result of such an effective resistivity. Such collisions due to collective particle effects are essentially a different mechanism from classical collision notion. These experiments are done for two types of ions found in the plasma sheet prior to substorm onset, viz., protons and oxygen ions. Observational evidence of oxygen ions in the central plasma sheet, which flow out along open field lines from the ionosphere, were also simulated in the same manner. Oxygen ions have been found to influence the bifurcation of the current sheet and are also important in reconnection and other nonohmic instabilities, such as Kelvin Helmholtz instability, due to their mass. It is found that acceleration in X-line scales with the mass of ion species and the resistivity remains constant for different electric field strengths. In a Bifurcated Current Sheet, the acceleration scales with the square of mass of ion species and the resistivity scales with the electric field. Also, the overall resistivity values found in a Bifurcated Current Sheet are an order of magnitude lower than that found in an X-line.
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Adams, Amy Lynn. "Permeability anisotropy and resistivity anisotropy of mechanically compressed mudrocks." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90036.
Full textAbstract:
Thesis: Ph. D. in Geotechnical and Geoenvironmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 313-322).
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) is systematically measured to determine both the magnitude and evolution of the permeability anisotropy. The permeability anisotropy predicted using measurements of the mudrock fabric is compared with the measured permeability anisotropy to understand the relationship between fabric evolution and permeability anisotropy. Finally, resistivity anisotropy is compared with permeability anisotropy to reveal useful field correlations. The results of the RBBC study are contrasted with additional measurements made using mudrocks covering a range of plasticity, clay fraction and mineralogical composition. The permeability anisotropy and the conductivity anisotropy (inverse of the resistivity anisotropy) of uniform RBBC increase from 1.2 to 1.9 as the porosity decreases from 0.49 to 0.36. The permeability decreases by over one order of magnitude and the formation factor triples over this porosity range. Platy particles rotate from ~ 42 to 28 degrees to the horizontal, driving permeability anisotropy development. Further decreasing the porosity of RBBC below porosity 0.36 decreases both the permeability anisotropy and the conductivity anisotropy. Finally, the conductivity anisotropy is shown to equal to the permeability anisotropy within +/-20%. This general behaviour is characteristic of all mudrocks studied. Though small (<2), the permeability anisotropy of uniform mudrocks can significantly increase the permeability anisotropy of larger systems, as shown through layered system models. These models also reveal that the large scale conductivity anisotropy is not equal to the permeability anisotropy, though the relationship identified for uniform mudrocks may still be useful for sites with high measurement resolution.
by Amy Lynn Adams.
Ph. D. in Geotechnical and Geoenvironmental Engineering