• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 41
  • 20
  • 9
  • 6
  • 3
  • 2
  • 1
  • 1
  • Tagged with
  • 84
  • 38
  • 36
  • 24
  • 23
  • 19
  • 19
  • 19
  • 19
  • 19
  • 17
  • 12
  • 12
  • 12
  • 11
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

3-D inversion of helicopter-borne electromagnetic data

Scheunert, Mathias 27 November 2015 (has links)
In an effort to improve the accuracy of common 1-D analysis for frequency domain helicopter-borne electromagnetic data at reasonable computing costs, a 3-D inversion approach is developed. The strategy is based on the prior localization of an entire helicopter-borne electromagnetic survey to parts which are actually affected by expected local 3-D anomalies and a separate inversion of those sections of the surveys (cut-&-paste strategy). The discrete forward problem, adapted from the complete Helmholtz equation, is formulated in terms of the secondary electric field employing the finite difference method. The analytical primary field calculation incorporates an interpolation strategy that allows to effectively handle the enormous number of transmitters. For solving the inverse problem, a straightforward Gauss-Newton method and a Tikhonov-type regularization scheme are applied. In addition, different strategies for the restriction of the domain where the inverse problem is solved are used as an implicit regularization. The derived linear least squares problem is solved with Krylov-subspace methods, such as the LSQR algorithm, that are able to deal with the inherent ill-conditioning. As the helicopter-borne electromagnetic problem is characterized by a unique transmitter-receiver relation, an explicit representation of the Jacobian matrix is used. It is shown that this ansatz is the crucial component of the 3-D HEM inversion. Furthermore, a tensor-based formulation is introduced that provides a fast update of the linear system of the forward problem and an effective handling of the sensitivity related algebraic quantities. Based on a synthetic data set of a predefined model problem, different application examples are used to demonstrate the principal functionality of the presented algorithm. Finally, the algorithm is applied to a data set obtained from a real field survey in the Northern German Lowlands. / Die vorliegende Arbeit beschäftigt sich mit der 3-D Inversion von Hubschrauberelektromagnetikdaten im Frequenzbereich. Das vorgestellte Verfahren basiert auf einer vorhergehenden Eingrenzung des Messgebiets auf diejenigen Bereiche, in denen tatsächliche 3-D Strukturen im Untergrund vermutet werden. Die Resultate der 3-D Inversion dieser Teilbereiche können im Anschluss wieder in die Ergebnisse der Auswertung des komplementären Gesamtdatensatzes integriert werden, welche auf herkömmlichen 1-D Verfahren beruht (sog. Cut-&-Paste-Strategie). Die Diskretisierung des Vorwärtsproblems, abgeleitet von einer Sekundärfeldformulierung der vollständigen Helmholtzgleichung, erfolgt mithilfe der Methode der Finiten Differenzen. Zur analytischen Berechnung der zugehörigen Primärfelder wird ein Interpolationsansatz verwendet, welcher den Umgang mit der enorm hohen Anzahl an Quellen ermöglicht. Die Lösung des inversen Problems basiert auf dem Gauß-Newton-Verfahren und dem Tichonow-Regularisierungsansatz. Als Mittel der zusätzlichen impliziten Regularisierung dient eine räumliche Eingrenzung des Gebiets, auf welchem das inverse Problem gelöst wird. Zur iterativen Lösung des zugrundeliegenden Kleinste-Quadrate-Problems werden Krylov-Unterraum-Verfahren, wie der LSQR Algorithmus, verwendet. Aufgrund der charakteristischen Sender-Empfänger-Beziehung wird eine explizit berechnete Jakobimatrix genutzt. Ferner wird eine tensorbasierte Problemformulierung vorgestellt, welche die schnelle Assemblierung leitfähigkeitsabhängiger Systemmatrizen und die effektive Handhabung der zur Berechnung der Jakobimatrix notwendigen algebraischen Größen ermöglicht. Die Funktionalität des beschriebenen Ansatzes wird anhand eines synthetischen Datensatzes zu einem definierten Testproblem überprüft. Abschließend werden Inversionsergebnisse zu Felddaten gezeigt, welche im Norddeutschen Tiefland erhoben worden.
82

Geochemical and isotope investigations of carbonate sinter – 2000 years of water supply management in Palestine

Sabri, Raghid N. R. 04 November 2016 (has links)
Over thousands of years, the eastern part of the Mediterranean has developed ways to supply and manage its water resources. The most important evidence of this is the water networks that are distributed in the area. Case studies involving a literature review, fieldwork, sample collection and analysis were conducted that focused on two areas in the West Bank: Nablus city and the northern part of Jordan Valley. These locations were chosen because Nablus city and its vicinity have many of Roman tunnels and aqueducts while the Jordan Valley has many watermills. This study aims to examine the changes in water quality over time in various ways; in an attempt to explain environmental degradation, to understand archeological aspects relating to the water management system, and to piece together what sustained the past environmental development. Throughout centuries carbonate deposits have accumulated along the sidewalls of the water system, containing and archiving geochemical and hydraulic information. These carbonate deposits were sampled from the walls of tunnels together with water samples from the tunnel and surrounding springs in the area. In addition, carbonate sinter has accumulated at the outlet of the watermill on the water shaft. This sinter was also sampled along with water samples from the springs and the water in the Wadi in the area. Water and carbonate samples were analyzed. Water analysis included major cations and anions, trace elements, rare earth elements, 18O/16O isotope ratio, and 87Sr/86Sr isotope ratio. Results indicate the presence of different underground water bodies and Sr resources. Furthermore, thin sections were made from the carbonate samples for SEM–EDX analyses and microscopic investigations. The microscope analysis showed that the distribution of minerals precipitated differs within one sample. Likewise, SEM–EDX results show a variation in element distribution along the growth axis. After finishing the analysis of water samples and thin sections, the layers of the carbonate samples were acidified and trace elements and rare earth elements were measured by means of ICP–MS. Then selected layers were prepared for isotope analyses (18O, 13C, and 87Sr/86Sr) and subsequently measured. The carbonate samples were dated using the U–Th method. Rare earth elements and trace elements measurements provide clear evidence that urbanization has an adverse effect on groundwater quality. Different groundwater bodies were identified by means of geochemical analysis. In the same way, the water sources used to feed the ancient water system were also identified. Through petrological and geochemical analysis, the sustainability of the watermill concept could be demonstrated. This study recommends a more controlled regulation of urbanization expansion. It will only be possible to continue living in this region with sufficient amounts of groundwater and innovative techniques for water supply and management that are environmentally sustainable, as it used to be centuries ago.:Declaration V Acknowledgment VI Abstract VIII List of Figures X List of Tables XVI List of Abbreviations XVII Terms and definitions XIX 1. Introduction 1 1.1 Structure of the thesis 1 1.2 General information, background 2 1.2.1 Spiritual value of water in Palestine 2 1.2.2 Water resources and management condition in Palestine 3 1.2.3 Water crisis in Palestine 4 1.3 Motivation 5 1.4 Hypothesis 6 1.5 Location of study area 6 1.5.1 Description of geology and hydrogeology of the study area 8 1.5.2 Climate 13 2. Literature review 18 2.1 Research history of aqueducts 18 2.2 Aqueducts in Palestine 18 2.2.1 Agricultural aqueducts (related to watermills) in Palestine 20 2.3 Utilization of springs in Palestine 21 2.3.1 Ancient water system in Nablus–Sebestia 22 2.4 Carbonate sinter accumulation in aqueducts and artificial water network 24 2.4.1 Research history of secondary carbonate sinter 26 2.4.2 Growth mechanism of secondary carbonate 29 2.4.3 Carbonate sinter analysis 30 3. Methodology 33 3.1 Literature review 33 3.2 Fieldwork 34 3.3 Sampling and analysis 37 3.3.1 Water samples: 37 3.3.2 Carbonate samples 38 3.3.3 U–Th series dating 41 3.4 Software used 43 3.5 Challenges 43 4. Results and discussion (Nablus area) 45 4.1 Ancient water system description 45 4.2 Water sample results and discussion 54 4.2.1 Stable isotope 59 4.2.2 Strontium isotope analysis (87Sr/86Sr) 60 4.2.3 Saturation index 62 4.2.4 Discussion 63 4.3 Carbonate analysis (host rock) 64 4.4 Aqueduct building material 65 4.5 Secondary carbonate analysis 66 4.5.1 Ras Al Ein location (S-2) 66 4.5.2 Ijnisinya location (S-9) 72 4.5.3 Harun Location (S-8) 79 4.5.4 Water tunnel Location (A-1) 86 4.5.5 Water aqueduct Location (A-4) 99 4.6 Discussion 101 4.6.1 Is urbanization a source of groundwater quality degradation? 101 4.6.3 Paleoclimate calculations 105 5. Results and discussion (Al Malih area) 107 5.1 Water system description 107 5.2 Geochemical results (water) 108 5.3 Geochemical results (Carbonate) 111 5.3 Sustainability of watermills 113 6. Conclusions and recommendation 115 6.1 Conclusions 115 6.2 Recommendations 116 6.2.1 Recommendation for further research 116 6.2.2 Recommendation for policy makers 116 References 118
83

Der Geologische Dienst in Sachsen: Festband zum Jubiläum 150 Jahre Landesgeologie

Büchner, Jörg, Dietel, Sabine, Dommaschk, Peter, Döring, Ines, Duteloff, Tobias, Fischer, Petra, Franke-Laske, Daniel, Gahlert, Anna, Görne, Sascha, Görz, Ines, Grafe, Friedemann, Hofmann, Karina, Hübschmann, Mathias, Kleeberg, Katrin, Korb, Daniel, Kulikov, Sabine, Kupetz, Manfred, Lapp, Manuel, Lehmann, Uwe, Loos, Denis, Reinhardt, Katrin, Reinhardt, Silke, Repstock, Alexander, Richter, Marcus, Rommel, Axel, Schneider, Sandra, Schreiber, Andrea, Schulz, Carsten, Sentek, Susann, Thiele, Lisa, Ussath, Maria, Walter, Harald 22 July 2022 (has links)
Der Geologische Dienst von Sachsen feiert im Jahr 2022 sein 150-jähriges Jubiläum – am 6. April 1872 wurde die Geologische Landesuntersuchung im Königreich Sachsen gegründet. Auf 153 Seiten der Reihe „Geoprofil“ werden Einblicke in die Arbeit des Geologischen Dienstes im LfULG, seinen Aufgaben und die Dienste als zuständige Fachbehörde gegeben. Die elf Einzelbeiträge zeigen die aktuellen Herausforderungen und Chancen, die sich aus den Themenbereichen Umwelt, Naturschutz und Geologie für Sachsen stellen. Im Einzelnen geht es in den Beiträgen um die sächsische Rohstoffstrategie, die Suche nach einem Endlagerstandort für radioaktive Abfälle, Erdwärme, Hydrogeologie, die Eisenbahn Neubaustrecke Dresden – Prag, Naturgefahren, das geowissenschaftliche Archiv, Träger öffentlicher Belange (TöB), Geoparks und einen Blick in die 150 jährige Geschichte. Redaktionsschluss: 30.11.2021
84

Zakládání na objemově nestálých zeminách / Foundations in Volume Unstable Soils

Legut, Dana Unknown Date (has links)
This dissertation is concerned with the foundations in volume unstable soils and objects disorders which are related to this. The thesis was focused on the study of clay and loess soils which are abundant in the geological profile of the Czech Republic. First, the formation of the two groups of soils is introduced, then their properties are examined and finally the influence of vegetation on the former type and the influence of collapsibility in the latter type are investigated. The conclusion is, in fact, a recommendation on the design of structures so that the system of clay / structure is not damaged and that structures are not subject to renovations. Several instance of problems with structures are discussed which were subject to structural repairs employing both a civil and geotechnical engineers.

Page generated in 0.0383 seconds