| 51. |
- Zainy, Maher T.
(författare)
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Tectonic Evolution of the Zagros Suture-and Imbricate Zones in Iraq
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Orogenic belts are expressions of tectonic activity, often host various natural resources (e.g. petroleum and minerals reserves), and influence the society and environment through hazards (e.g. landslides, earthquakes), climate and cultural divides. The Alpine-Himalayan system is one of the most important orogenic belts in the world with regards to all these aspects. The Zagros Fold-and-Thrust Belt is a part of the central Alpine-Himalayan system, where a wealth of natural resources have been found, including one of the largest petroleum reserves in the world, and many mineral deposits.This thesis focuses on the Imbricate- and Suture zones of the Zagros Fold- and Thrust Belt in Iraq. Research activities here have been limited, mainly due to the apparent relative depletion in natural resources and because of geopolitical security issues.The study area consists of rock masses that have formed as the result of convergence between the Arabian and Eurasian plates from the Late Cretaceous to the present day. Bedrock comprise alternating sequences of Mesozoic siliciclastic and carbonaceous rocks. It is a key area to study ongoing continental collision.The objective of this thesis is to improve the knowledge of the crustal architecture of this relatively unknown part of the Zagros Fold- and Thrust Belt. The results form a basis for future natural resources exploration.The thesis work consists of a local desk study of alluvial fans using remote sensing data (Landsat 8, Operation Land Imager satellite data and Digital Elevation Model), and two seasons of structural geological field work along regional traverses. The study area of field work is 1800 km2 large. The results were subsequently incorporated into a 3D structural framework model in the software Move of Petroleum Experts, Edinburgh, UK (version 2019.1).Remote sensing and GIS techniques were used to analyze neotectonic activity of alluvial fans. Their formation and morphology are influenced by subsurface faulting. Results indicate the location of active faults, and allowed their extrapolation along strike.The aim of field work is to constrain the tectonic history of the area. Structural data were collected from six traverses, varying in length from 4.4 to 25.0 km, using a combination of digital and traditional methods. Based on the style and geometry of the mesoscale folds, buckling is suggested as the dominant mechanism for folding, where flexural slip folding has been followed by shear folding. I have estimated the amount of internal crustal shortening using Ramsey’s equation: Most intense shortening observed close to the Suture zone (~60%). The amount of shortening is about 10% less in the Imbricate zone (~50%).Based on the results above, 3D geological models have constructed. They reveal the structural styles and role of pre-existing faults, and their influence on the crustal architecture of the area. These models act as a base for potential natural resource explorations activities. The structural evolution of thrust sheets within the study area occur as a piggyback sequence. The structural style of the Suture zone is characterized by three main thrust sheets, that are subparallel with the NW-SE striking and NE dipping Main Zagros Fault.The structural framework of the 3D geological models presented in this thesis are derived purely from surface data (field work, remote sensing), and represents the state of art. At this stage, there are no clear candidates for future natural resources exploration. In order to advance the 3D geological models, subsurface data are required, such as seismic and borehole data. These type of data will provide better constraints at depth, which may be key for finding prospects for exploration within the Imbricate and Suture zones.
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| 52. |
- Zhang, Hanzhu, 1991-
(författare)
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High-entropy boron-carbide and its composites
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-entropy alloy (HEA) is a multicomponent alloy material that contains five or more principal elements in equi- or near equi-atomic ratios. The entropy stabilisation leads to the formation of a crystalline solid solution accommodating the principal elements. The HEA solid solution has characteristic features such as lattice distortion, sluggish diffusion and cocktail effect that contribute to the superior properties of HEA including high strength, high hardness, excellent thermal and chemical stability, etc. The concept of HEA has been extended to ceramic materials to process high-entropy ceramic (HEC) that consists of multiple ceramic compounds such as metallic oxides, nitrides or carbides. The HECs have shown entropy stabilisation and formed single-phase ceramic solid solutions. However, the formation mechanism of high-entropic phase in HECs remains unclear and unpredictable. Generally, in order to maximise the probability of forming a high-entropy solid solution in a ceramic system, ceramic compounds with least difference in the crystal structure, preferably with only one anionic constituent element, are favoured when designing HECs, which limits the potential of discovering and developing new HECs. In this project, a multicomponent ceramic system containing six ultra-high temperature ceramics (UHTCs), B4C, HfC, Mo2C, TaC, TiC and SiC, was used to investigate the formation of high-entropy ceramics, UHTC composites, as well as the microstructure evolution, properties and high temperature applications. A ceramic composite composed of SiC and a high-entropy boron-carbide with hexagonal crystal structure was successfully processed from the carbide system in spite of the difference in the crystal structures of precursors (face-centred cubic, hexagonal and rhombohedral). The hexagonal HEC solid solution exhibited a unique AlB2 structure with alternating layers of metal and non-metal C/B atoms according to the experimental and simulation investigations. The HEC/SiC composite showed superior mechanical properties such as ultra-high hardness, excellent wear and oxidation resistance. The addition of B4C was discovered to be the key factor in the formation of the hexagonal high-entropy boron-carbide solid solution, while the final phase composition was tailored by utilising precursors of different particle size. Additionally, SiC as the reinforcement component in the HEC/SiC composite was used to tailor the microstructure, phase evolution and mechanical properties of the high-entropy boron-carbide composite. Higher content of SiC resulted in enhanced mechanical properties such as hardness and fracture toughness, as well as promoted the formation of the hexagonal high-entropy boron-carbide solid solution. To extend the investigation on the high-entropy boron-carbide composite to application, B4C, HfC, Mo2C, TaC and TiC were consolidated into a target for magnetron sputtering. The target was used to deposit oxidation-resistant high-entropy coatings using magnetron sputtering on carbon-carbon composites. The coatings showed superior mechanical performance and high temperature oxidation resistance at 2000 °C on carbon-carbon composite, suggesting potential applications of high-entropy boron-carbide ceramics as a protective coating material against oxidation at elevated temperature. This work pointed out the possibilities of synthesising high-performance HECs with superior properties from components with vast elemental and structure diversity, and thereby advanced the design criteria of HECs and provided more potential research directions for the new high-performance ceramic materials.
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| 53. |
- Öhman, Johan, 1991-
(författare)
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Polarization-Resolved Particle Holography
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, measurement of particle fields using digital holography is the main subject. The questions investigated consider positioning, identification and sizing of nanometer and micrometer particles. The thesis explore these topics using both simulations and experimental measurements. Measuring particles is inherently a three-dimensional problem. Digital holography is, therefore, chosen as the measurement technique since it can record three-dimensional information in the interference pattern.Two main digital holographic setups are considered in this work, one single-view and one dual-view, both with off-axis configuration for the reference wave. Methods for positioning along the optical axis is the central question for the single-view system. This work presents a new method for axial positioning based on the wavefront curvature of the scattered light. In the reconstructed volume, along the optical axis, the scattered wave changes from converging to diverging around its location. This assumption is verified using simulations. An estimation of the position where this change occurs, hence, is an estimation of the actual axial position. Two different methods for quantification of the wavefront curvature is presented. The first uses the finite difference method of the reconstructed phase. The second uses a Chebyshev model for the phase-response. The difference between the two methods is that the one based on the Chebyshev model is more robust and less sensitive to noise.The dual-view system is an extension of the single-view setup where an identical system is placed perpendicular with the first system. The sample is illuminated from below, making the angle between the illumination and the two systems $90^\circ$. The concept of polarization-resolved registration is also incorporated in the detection. This detection is made possible by using two reference waves with linear and mutually orthogonal polarization at different off-axis tilts. One hologram can, therefore, be reconstructed into two complex amplitudes, one for each polarization component. The measurements using this system focus on how particle properties influence the polarization-response. The transition from single to dual-view polarization-resolved detection increases the complexity in the reconstruction. There is a need for accurate calibrations for this type of setup. The thesis contains details on calibrations of both the spatial mapping and polarization detection.The first application of the dual-view polarization-resolved setup is for identification and size estimation of nanometer-sized particles. The T-matrix method is used to establish a model for the sizing of spherical and spheroid particles. It is possible to estimate the size unambiguously up to approximately 200 nm for smooth particles. The sizing is limited to this lower size range.The second application investigates how the detected polarization varies for different kinds of microplastics. The measurements show that the microplastics have a complex polarization-response, indicating an irregular and non-spherical shape. In general, for both sizing and identification, the problem becomes more complex as the size increases and the particle shape is less smooth.This thesis shows that it is possible to estimate particle information from the polarization-response. However, the method is constricted both by the size and complexity of the particles.
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