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This thesis deals with the energy system transformation of coal-dependent developing countries in the context of climate change mitigation. It departs from the hypothesis that phasing-out the unabated use of coal for power generation, while scaling up carbon-free alternatives, represents a major challenge for coal-endowed developing countries and emerging economies. This challenge is constituted in multiple economic, political and societal determinants for sustained and expanded coal-use. This thesis adopts a political economy perspective and examines those determinants in detail. It focuses on how different societal and political actors are affected the use of coal, and interprets the distributional implications of reforms away from coal as key restrictions for their political feasibility. Given the heterogeneity in the historical, socio-economic, political, and institutional characteristics that different countries exhibit, which are hypothesized to impact on the drivers behind coal-use, this thesis adopts a case-study based approach. It focuses on two large Asian economies, Indonesia and India, as coal-endowed emerging economics with a pivotal relevance in global climate protection efforts. Three main chapters represent the core of this thesis. The first main chapter of this thesis examines the political economy of the power sector and coal mining in Indonesia, focusing on the drivers for the continued use of coal for electricity generation. It presents an expert-interview case study, based on the perspective of 90 expert stakeholder in Indonesia´s energy and climate policy, at national and subnational level. The study identifies key societal and political actors behind Indonesia´s energy- and climate policies driving coal-use, spells out their objectives, and examines how these actor-specific interests’ effect on energy and climate policies. The second main chapter of this thesis studies the implications of an Indian energy transition away from coal-use along three dimensions: the distributional impacts towards households, the implications for employment, and the impact on competitiveness of industries. The input-output based, distributional- incidence case study analyses the concentration of impacts for key societal groups affected by a coal phase-out and renewable energy phase-in, and its spatial distribution across Indian states and regions. The third main chapter of this thesis studies the cost-competitiveness of renewable energy alternatives to coal in Indonesia. The energy modelling based analysis shows how the cost-optimal composition of Indonesia´s power sector in coming decades would comprise high shares of coal-fired electricity. The three main chapters of this thesis identify political economy challenges to a transition away from coal, outlining how a successful coal phase-out will require focusing on its context-dependent distributional and political implications.
Significance of storm spatiotemporal variability and movement in flood hydrodynamic modelling
(2024)
This dissertation aims to explore the impact of various storm properties on computational flood modelling and to propose a method for integrating them into flood risk assessment. It focuses on three key areas:
Firstly, it examines within-storm variability, investigating how variations in storm intensity, duration, and spatial distribution affect runoff dynamics. Through a systematic theoretical approach, the study generates synthetic rainfall signals with different hyetograph variabilities and applies them to a hydrodynamic model. The results highlight the significant influence of storm spatiotemporal variability on runoff response, affecting peak discharge, hydrograph shapes, and flooded areas. Temporal variability emerges as particularly dominant, overshadowing spatial variability and other storm properties such as return period and volume. The study emphasizes the spatial dependency of these effects within the drainage network.
Secondly, it investigates the role of storm movement in flood modelling, recognizing its potential to alter runoff dynamics and inundation patterns. By generating synthetic rain hyetographs traversing the catchment area at varying velocities and directions, the study shows that storm movement significantly impacts runoff response and flood extents. Higher storm velocities lead to more pronounced peaks and faster runoff onsets, resulting in larger flooded areas. The direction of storm movement plays a crucial role, with storms aligning with the average stream direction causing the highest peaks and flooded areas. The magnitude of this influence varies depending on the location within the catchment.
Finally, the dissertation introduces a dynamic spatiotemporal rainfall model aimed at preserving storm event properties. Using an event-based approach, dynamic precipitation events are identified and regenerated, ensuring the conservation of storm spatiotemporal variability and movement characteristics. This facilitates the generation of more physically plausible and spatiotemporally coherent precipitation time series. The model prioritizes user accessibility, offering a practical tool for integrating storm properties into flood computation modelling and risk analysis frameworks. By addressing these aspects of storm behaviour, the dissertation contributes to enhancing the accuracy and effectiveness of flood modelling, thereby improving flood risk mitigation efforts.
Reliability assessment of pipeline failure factors has become a major concern for industrial firms involved in the transmission of oil and gas, where the requirement to limit these failure factors and their consequences, such as maintenance costs, is particularly significant. Pipelines were constructed throughout time to include safety precautions in order to offer a theoretical minimal failure rate for the pipeline's whole life. This strategy also includes the management of various failure causes as well as routine-based maintenance to assure the dependability of pipelines during their service life. However, the requirement to reduce the impact of these failure factors on pipelines has bolstered the use of reliability evaluation of failure factors on petroleum pipelines. The purpose of this study is to evaluate the reliability of oil pipelines in Nigeria, with emphasis on proposing operational and technical changes to enhance their resilience against unexpected failures. The thesis uses the regular Poisson, empirical, and compound Poisson processes to describe the number of common failure causes owing to corrosion, third-party damage, mechanically induced failure, operational mistakes, and natural hazards in repairable systems. The statistical analysis results serve as the foundation for time to failure modeling of petroleum pipelines utilizing Bayesian inference of the three-parameter Exponentiated Weibull distribution. The thesis also includes reliability probabilistic methods for assessing the influence of uncertainties in pipelines by comparing the First order reliability method (FORM) with the Second order reliability method (SORM) with demonstration on five distinct petroleum pipelines. The probability of failure and the reliability index for the five pipelines were calculated, along with the target reliability. Additionally, the influence of specific pipeline design parameters on the probability of failure was analyzed through sensitivity analysis. This analysis helps identify which design factors have the most significant impact on the likelihood of pipeline failure, allowing for more informed decisions in pipeline design and maintenance practices. By understanding these influences, it is possible to enhance the overall reliability and safety of the pipeline infrastructure. The framework developed in this thesis can be applied to enhance the performance of existing pipelines and serve as a good foundation for the design and implementation of new pipelines and similar infrastructures.
Benign prostatic hyperplasia (BPH) is considered an age-related disease of men with unknown etiopathophysiology. Chronic inflammation represents one of the most important pathophysiological mechanisms in this context, and there is also evidence for the involvement of autoimmune responses in an inflammatory environment in the prostate. Conventional therapeutic approaches for BPH are limited; however, immunosuppression by TNF (tumor necrosis factor)-𝛼 blockers seems to reduce symptoms in BPH patients due to the reduction of epithelial hyperplasia and macrophage-triggered inflammation. Therefore, this cumulative dissertation addresses biomarker-based BPH diagnosis by lens epithelium-derived growth factor splice variant 75 kDa (LEDGF/p75). LEDGF/p75 is an autoantigen that is overexpressed in solid tumors and functions as a stress-related transcriptional co-activator. It also plays an important role in cancer and DNA damage repair (DDR). The generation of CRISPR/Cas9-modified HEp-2 LEDGF deficient (KO) and HEp-2 LEDGF/p75 overexpressing (OE) cell lines provided new insights for the diagnosis and therapy of cancer and genetic disorders. Herein, IgG autoantibody reactivity to LEDGF/p75 was detected in patients with prostate cancer (PCa, n=89), bladder cancer (BCa, n=116), benign prostatic hyperplasia (BPH, n=103) and blood donors (BD, n=60) by indirect immunofluorescence assay (IFA) linear immunoassay (LIA) and Chritidia luciliae immunofluorescence test (CLIFT). In addition, proliferation and migration capacity as well as chemosensitivity of genome-edited cells were determined by optimized all-in-one approach, followed by investigation of DDR signaling pathways by Western blot and immunofluorescence. Surprisingly, no increased binding of autoantibodies (autoAbs) to LEDGF/p75 was detected in cancer patients, but autoAb reactivity to LEDGF/p75 O/E cells was unexpectedly increased in approximately 50% of patients with BPH. At the molecular level, LEDGF-deficient cells exhibit decreased proliferation and migration and increased sensitivity to the chemotherapeutic agent etoposide. A significantly Decreased DNA damage response could also be visualized. New diagnostic capabilities using HEp-2 cells overexpressing LEDGF/p75 or mitochondrial DNA as autoimmune targets could be used to identify BPH patients with autoimmune responses. Furthermore, this Thesis shows that LEDGF is not only involved in the recruitment of DNA damage response proteins, but also affects the proteosomal regulation of DDR signaling molecules.
The hetero-integration of group IV and III-V epitaxial layers on silicon (Si) substrates enables novel devices for optoelectronic and high-power applications. However, lattice and thermal mismachtes lead to an unavoidable formation of defects in hetero-epitaxy. The consideration of these defects is important in semiconductor devices as they affect material properties and impair the device performances. Besides the structural characterization of the unintentional introduced defects and the question of it’s origin, it is essential to evaluate their electrical activity in order to describe their impact on the device performance.
This work explores the electrical activity of threading dislocations (TDs) in Ge-rich SiGe heterostructures integrated on Si substrates as well as the electrical active defects introduced by the growth of aluminium-nitride (AlN) seed layers for the integration of gallium-nitride (GaN) on Si substrates.
I demonstrated a defect-related p-type conductivity of intrinsically grown Si ₀ ̣₀₆Ge ₀ ̣₉₄/Ge that reaffirms previous work of similar intrinsic Ge-based material. Moreover, I detailed the threading dislocation related leakage currents in rectifying devices, revealing a power law dependence on the threading dislocation density (TDD). By a variation of temperature I determined the dominant mechanism of transport of this leakage currents in different temperature regimes, for which I suggested possible interactions with TD related defect states. Through the reduction of leakage currents in the fabricated MOS capacitors I was able to examine an effective carrier concentration of 5-6x10¹⁵cm⁻³ in the nominally intrinsic Si ₀ ̣₀₆Ge ₀ ̣₉₄ epitaxial layer, which decreases down to 1x10¹⁵cm⁻³in the Ge buffer underneath. By applying deep level transient spectroscopy (DLTS) I found one dominant hole trap at mid-gap position confirming the presence of an TD-related effective generation-recombination center. In addition, I investigated the hole trapping kinetics of this defect level and associated it with point defects that are trapped in the strain field around threading dislocations.
I obtained insights into defect formation in the Si substrate and at the AlN/Si interface in dependence of the AlN growth temperature. A low temperature growth step prevented a deep in-diffusion of Al atoms into the Si substrate with simultaneous increase of the maximal p-type doping in the vicinity of the AlN/Si interface. Furthermore, I found a bulk hole trap inside the Si substrate at mid-gap position that showed an increase in density by applying a low temperature growth step. In contrast, the defect states at the AlN/Si interface decreased when a low temperature growth step was applied, in comparison to AlN layers grown at continuous high temperatures.
By the year 2539 almost 75% of all freshwater mollusc species within Europe will be lost. The transformation of natural ecosystems, the extension of infrastructure, as well as agriculture are the main threats. The Roman snail (Helix pomatia L. 1758) has been part of human culture for centuries and is protected by law as an endangered species in several regions, and at the same time regarded and treated as a pest, making the conservation of this species difficult.
The aim of this thesis was to create a better understanding of H. pomatia and its functional role within the ecosystem. Eight subpopulations were studied regarding its role within the food web, the use of empty shells as a mircohabitat and its influence on vegetation by showing food preferences. The latter, due to the fact, that a strong predation pressure can minimize habitats, which leads to higher pressure on the local vegetation and a limited possibility of shells being used as a microhabitat.
First, the relationships between H. pomatia individuals, subpopulations and their predators were analysed. The total number and percentage of shells that showed external attack marks by predators (32%) and internal utilization marks by Diptera pupae (45%) were analysed and correlated to morphometric traits of shells. Signs of external attack and internal utilization marks were positively correlated (R = 0.79; P = 0.020). External attacks were more regular in larger shells and internal utilization was more frequent in shells with higher body density.
The second chapter focuses on the shells of H. pomatia and their value as microhabitat for shell adopters in different vegetation forms and during two sample periods. Out of 618 collected shells, 91.4 % were inhabited and the average was 1.5 time higher in summer, than in autumn. The number of shell adopters per shell was 1.5 times higher in herbaceous vegetation, than in areas dominated by trees. Shell width (P = 0.008), but not shell height (P = 0.078) had a significant higher influence.
Finally, food preferences of H. pomatia were analysed, showing a pronounced preference for Urtica dioica (35% of all 697 feeding interactions) and plant litter (44%). Only 27 out of 143 available plant species were eaten and a literature review confirmed U. dioica as a food plant for 19 other terrestrial snail species. The width and height of the snail shells were related to the feeding height as smaller, juvenile snails fed higher in vegetation (384mm ± 327mm) compared to adult individuals (68mm ± 194mm) (P<0.001).
These results highlight the importance of H. pomatia in the studied ecosystem. H. pomatia is an important food source for predators and host for parasitoids, the shells offer habitat and refuge for soil organisms and as a relatively specialized herbivore and decomposer H. pomatia contributes to herbivory and nutrient cycling in ecosystems.
Hopefully this study may help to motivate future conservation efforts.
Due to environmental impacts from anthropomorphic climate change, countries from around the world are committed to an energy transition from fossil fuels to renewable and sustainable energy sources. The heating and cooling sector represents the largest share of total energy consumption globally, not only for domestic use but also for commercial and industrial purposes of which only 11% is covered by renewable energy. One renewable source, geothermal energy, has the potential to cover much of this demand, particularly heating demand, for the agriculture and food sector. Geothermal use in the agri-food industry continues to be positive overall, yet slow adoption and inconsistent growth have not met its potential as claimed by experts. This trend may be explained by a lack of coherent policy and initiatives from regulating government bodies. This research explores the relationship and the degree of correlation between government support, expressed in terms of policy incentives, and the growth of geothermal energy use in the agri-food sector. Two hypotheses are constructed to test this relationship. The first assumes that government support through policy leads to positive growth in geothermal argi-food, and the second assumes that no relationship exists. The research is a multiple case study of twelve countries from 2010 to 2020. Methods used in this study include Likert summative scale, a statistical and content analysis of secondary sources such as policy documents, laws, and other government acts. The results show a strong correlation between policy incentives and adoption of geothermal energy in agri-food sector. However, only 23% of growth in capacity in case countries can be explained by the levels of government support. Additionally, not all policies hold equal weight in that they are implemented on different levels of governance (global, national, and local). The study observes that between these three levels, national policies have the most correlative effect on geothermal energy adoption, while global and local policies do not seem to have significant influence. These effects vary but the overall market trends are influenced heavily by leading performers. Countries that show the most growth are – Hungary, Iceland, the Netherlands, and Türkiye. They all share strong government support on a national level, targeted policies for geothermal agri-food, and geothermal energy is economically competitive when compared to other forms of energy.
A contribution to the online monitoring of partial discharges in high-voltage grid components
(2024)
Increasing utilization of HV power cable lines, and particularly the advent of long HVDC underground links, results in the need to sensitively monitor their condition, such as by tracking the emergence and development of partial discharges. This study demonstrates that existing solutions are poorly suited to the case of HVDC lines, and that a new, more sophisticated monitoring system needs to address a wide array of diverse problems. First of all, the overview of the task and main functional blocks of the monitoring system is given. Following this, selected blocks are subject to detailed examination in subsequent chapters.
The first of these blocks, a high-frequency current transformer (HFCT), is responsible for capturing the signal in the power line and transferring it to the electronics. This component receives in-depth coverage: general design considerations, computation of leakage inductance, operation in presence of a power current, resonant behavior, balanced design. Particular attention is given to the application of Finite Element Analysis (FEA) in relation to the HFCT, however, the demonstrated techniques can also be applied to other magnetic devices. Last section of the chapter presents various stages of development, experimental setups, prototypes, and the final device which has been put into series production.
The next block addresses extraction of signals from noise. A literature analysis is conducted concerning noise suppression in partial discharge recordings, and the application of the signal separation approach based on Linear Predictive Coding is shown.
In the section on localization, examples illustrating problems encountered during the development of a partial discharge localization algorithm are presented.
In the chapter devoted to laboratory tests, various auxiliary experiments conducted during the system's development are compiled, where some of them are: Time Domain Reflectometry (TDR) TDR-based line characterization, estimation of monitoring sensitivity, measurement of the cable attenuation and reflection coefficients of the accessories.
In the final chapter – field tests – the installation of the system on a 110 kV line and the measured transfer function are demonstrated.
Plenty of semiconductor devices are developed to operate with private data. To guarantee data privacy cryptographic algorithms are used, where the secrecy is based on the used keys. Theoretically, the cryptographic algorithms using keys with recommended lengths are secure. The issue is that a potential attacker can steal the devices and attack in a lab. Physical attacks are usually aimed to perturb normal operation of a device and to extract cryptographic keys, e.g. by means of fault injection (FI). One class of FI attacks exploits the sensitivity of semiconductor devices to light and are performed using a laser as the light source.
This work investigates the sensitivity of different logic and memory cells to optical Fault Injection attacks. Front-side attacks against cells manufactured in different IHP technologies were performed using two different red lasers controlled by Riscure software. To reach the repeatability of the experimental results and to increase the comparability of the results with attack results published in literature the setup parameters as well as setting parameters of the Riscure software were experimentally evaluated. Attacks were performed against inverter, NAND, NOR, flip-flop cells from standard libraries, radiation-hard flip-flops based on Junction Isolated Common Gate technique, radiation-tolerant Triple Modular Redundancy registers as well as non-volatile Resistive Random Access Memory (RRAM) cells. The results of attacks against volatile circuits were successful transient bit-set and bit-reset as well permanent stuck-at faults. The results of attacks against RRAM cells were successful in the sense that manipulation of all RRAM logic states was feasible. The faults injected during the performed experiments were repeatable and reproducible.
The goal of this work was not only to achieve successful FI but also to determine cell area(s) sensitive to laser illumination. Knowledge about areas sensitive to laser illumination can be used by designers to implement corresponding countermeasure(s) at the initial stage of chip development and is the necessary step to design appropriate countermeasures. For example, metal fillers can be applied as optical obstacles reducing the success of front-side FI attacks, i.e. as a possible low-cost countermeasure. Based on the knowledge of the sensitive cell areas, the placement of the metal fillers can be automated in the future, i.e. the findings given in the work can serve as a basis for a methodology development for improving resistance against optical FI attacks at the initial stage of chip development. Such methodology can be adapted for each chip manufacturing technology.
The 'cultural appropriation' of traditional textiles from Mexico : an analysis of 3 case studies
(2023)
This doctoral thesis intended to examine the phenomenon of ‘cultural appropriation’ of traditional textiles from Mexico through an analysis of 3 case studies. This research had the objective of understanding the phenomenon through the relationships, perspectives, and discourses of the social actors involved, by following the development of controversies involving different objects of material culture from different communities: the xaam nïxuy Ayuujk (Mixe) blouse from Santa Maria Tlahuitoltepec, Oaxaca; the Hñuhú and Hñahñ (Otomi) “Tenango” embroideries from the communities of Tenago de Doria and San Nicolas in Hidalgo; and the mestizo gabanes from Santa Clara del Cobre and Nahuatzen in the State of Michoacán.
This doctoral examination was sustained through theoretical approximations that located the occurrences within transnational/ transcultural processes, engaging with qualitative methodologies and multi-sited ethnographies in order to obtain data that elucidated on the diversity of objects, actors, relationships, understandings, perceptions, values, and discourses involved in the ‘cultural appropriation’ of traditional textiles controversies in the country.
The content analysis of this doctoral research dissected a number of different processes, effects, and consequences of the phenomenon as it developed in dissimilar locations and periods of time. The examination revealed a complex intersection of meanings, productions, circulations, and consumptions of culture, that simultaneously affected cultural meanings, relationships, and processes, raising concerns over the management of traditional textiles as objects of cultural heritage, and the unviability of protecting communal creative domains through national legal mechanisms.
The contribution of community involvement in heritage management : a cultural mapping project
(2023)
Heritage has been lately the matter of debate regarding its definition, conservation and management approaches. In the last few years, there has been an increasing demand for the involvement of the local community in heritage management. Too often, the involvement perspectives of key stakeholders in general and the community members, in particular, are entirely different. While the theoretical ground of community involvement is somehow well set, heritage management has been slow in applying the involvement approach. Practically, it is not easy to find the balance to achieve all the goals of key stakeholders in any involvement project. Subsequently, there are a few numbers of empirical works on the practical implications of understanding heritage management effective tools and limited indication to convince recent ‘power-holders’ such as governmental organizations to distribute their power with local community members.
This doctoral research project explores community involvement in heritage management as an effective solution to building a strong management system. The study aims to examine the level and the quality of involvement in the management of heritage sites in general through a cultural mapping-based approach. This is applied to a case study which is the Religious Complex in Historic Cairo World Heritage Site. The research outcomes indicate the importance of involving the local community in heritage management and planning processes. Ultimately, the study provides critical empirical evidence and draws valuable theoretical and practical assumptions that spread knowledge of cultural mapping in critical issues, such as the drivers of involvement and cooperative decision-making.
Brain-computer interfacing (BCI) is a relatively new field of study that involves engineering, neuroscience, psychology, and physiology. A BCI is a system that allows direct communication between the brain and the environment, using signals from electroencephalography (EEG) to identify a user's intentions and mental states. This can be used for human-machine interaction (HMI) to adapt software or control a device. Particularly passive BCIs are the most promising for the general population, as they can detect and interpret a user's mental state without requiring their attention. This can enable neuroadaptive technology (NAT), which allows a machine to learn over time how the user perceives and interprets the world. However, there are still obstacles to be overcome before BCI technology can be applied in real-world situations for NAT.
In this work I firstly address the issue of subject dependence in training data collection for classifier calibration, which can be time-consuming and impractical. I investigated the training of a subject-independent predictive model that is trained on a group of other users' data and applied to online-testing data of a new person. This was done in the context of training an automatic classifier for error detection and correction. Results showed that a classifier model can be trained without user-specific calibration and with high accuracy. The number of electrodes used in training the model was also reduced. Further it was validated that the trained classifier models were based on cortical sources and not other modalities.
In a second study I address the issue of task-dependence. To that end I tested the application of a potentially task-independent calibration paradigm for mental workload assessment in a new task. This new task was a speed reading context, where subjects read texts of varying difficulty and speed. The study found that the mental workload prediction model was accurate in classifying mental workload in different reading tasks, indicating that it can be used as a task-independent classifier for mental workload.
In a third study I examine if it is possible to measure neural correlates of human moral assessment using a passive BCI on a single-trial basis. A calibration paradigm was developed using pictures that were ranked as morally unacceptable and morally neutral. However, the results showed low classification accuracies and it was not possible to reliably distinguish between a user's subjective moral evaluations on a single-trial basis using current classification approaches.
The results presented in this thesis provide solutions towards real-world applicability of NAT enabled by passive BCIs, as examples of a subject-independent and a task-independent classifier are demonstrated and discussed. Further, approaches for increased versatility of passive BCI technology are presented, that could make passive BCIs more feasible for use in future real-world human-machine interaction settings.
Cities are major contributors to climate change and biodiversity loss, and at the same time particularly affected by some of their consequences. Urban green can help address these challenges and provide numerous other benefits to people. Economic valuation can estimate the value that people assign to these diverse urban ecosystem services. The environmental economics literature uses several valuation methods. This work examines the valuation of urban ecosystem services with choice experiments. It includes five articles that use empirical analysis to address three overarching research goals: First, to improve understanding of the value of urban ecosystem services to urban residents. Second, to contribute to improving the validity of choice experiments. Third, to develop modeling of spatial patterns in the value of urban ecosystem services.
Chapter 1 describes the background and motivation of the valuation of urban ecosystem services with choice experiments, gives an overview over the relevant literature, and sets out the research objectives and methods of this dissertation.
Chapter 2 presents a choice experiment on green spaces, street trees and green roofs in Bremen. It analyzes the effect of additional information that these measures are part of a climate adaptation strategy. The results show greater willingness to pay among informed respondents. Part of the effect can be explained by a higher credibility of the survey.
Chapter 3 describes a choice experiment on urban gardens in Berlin and Stuttgart. It explores how respondents process the information provided in the questionnaire. It finds that questions about the information do not significantly affect either recall or the responses in the choice experiment.
Chapter 4 is based on choice experiments on street trees, green spaces, and greenways in four German cities. It examines how choice experiment surveys should elicit perceived consequentiality. The results show advantages of elicitation before the choice experiment over the usual elicitation afterwards.
Chapter 5 explores how valid policy makers perceive the results of choice experiments on urban green in several German cities, and what consequences this has for their use of the results. Interviews show that most policy makers use the results in their city to raise awareness or justify positions. Perceptions of validity are mixed, but do not play a major role in this type of use.
Chapter 6 examines the spatial distribution of the value of urban ecosystem services using choice experiments on green spaces, urban trees, green roofs, and green facades in Berlin and Leipzig. It develops and tests new choice models that may better represent than the common approach how the value of urban green space decreases with distance.
Based on the findings of the articles, Chapter 7 derives recommendations for practitioners of choice experiments and for urban green policy makers. Finally, it identifies research gaps that would be promising for future studies.
This thesis is dedicated to the structured sheet metals topic. Structured sheet metals are semi-finished products with the honeycomb (cell) shape, made by cold forming of the flat sheets. They represent an innovative technology in the field of lightweight construction. In recent years, this technology has undergone dynamic development what gives to researchers possibilities to improve the level of knowledge about structured sheets metals properties and explore new application fields for them.
The structuring improves basic properties, such as stiffness, compared to the flat sheet material. Due to these advantages, the use of structured sheet metals offers enormous innovation potential for efficient lightweight construction in many industrial sectors such as aerospace, rail transport technology, architectural products. Structured sheets have already been implementing in lighting technology, in the manufacture of household appliances and even in automotive industry. So that, the question arises if it possible to apply this kind of material successfully in other areas such as building industry.
This work contains an overview of the lightweight constructions historical development and stiffening elements in the steel industry, also the creation process of structured sheet metals, manufacturing investigated specimens, further bending tests, numerical simulations, analysis and comparison of resulting data and possible further use of lightweight beams with structured sheet elements as a building construction.
In this work beams compound of structured and flat plates are investigated. Steps of structured plates manufacturing process are described: hydroforming, point- and laser welding and bending. As a result, lightweight beams of two main shapes are manufactured: C- and square sectioned. There are four types of beams for each of the shapes are investigated. Every type has same geometrical dimensions, but thicknesses vary.
The series of laboratory tests with created beams under load is made. Three- and four-points bending tests are chosen for that.
This work also presents numerical analysis based on conducted experiments: buckling and global non-linear behavior of specimens by use of the software package ABAQUS/CAE are obtained. The behavior of the beams with structured and flat sheets under load is analyzed and the comparison of parameters such as load bearing capacity and stiffnesses is made.
Finally, in addition to laboratory and simulations, parametric modelling is done. Also, based on parametric calculations, the proposal for calculation the beams stiffness for with higher thicknesses is given. It allows to predict the behavior of beams with structured sheets with different thicknesses without manufacturing and conducting the expensive and time-taking laboratory experiments.
In conclusion, the recommendations for the simplifying of manufacturing process and for the improving of the beams stiffnesses are given.
With the increasing consciousness of the value of wetland ecological and environmental functions and its fast rate of decline in the size of this important and rich ecosystem globally, the Niger Delta ecosystem has been reported to be undergoing tremendous change, hence the need for this research, to identify the challenges and proffer solutions. This study focuses on ascertaining if a change has occurred in the Upper Orashi Forest Reserved wetland, to know and evaluate the policies used in managing the wetland in the region and Nigeria. To ascertain the wetland change, land cover change detection was carried out using Geographic Information Systems and Remote Sensing to produce paradigm or data to detect change occurrence in the wetland area. Supervised classification of land use and land cover change was carried out using LANDSAT data from 2002, 2008, and 2019. Thereafter, the land cover transition was mapped for the period 2002 to 2019 and this was computed for the net land cover change for the period of study. The site was classified into three different classes and each class was analyzed using the land use and land cover change model formula. The result from this part shows that there is a consistent decrease in the wetland area for the period under review and in the other two identified classes, some interchangeable compositions were observed for the period of study. To validate this result, the opinion of experts and the host community is needed. Two sets of questionnaires were designed for experts and local community dwellers to sample their opinion in relation to the wetland and its management. The information collected was analyzed using Microsoft excel and the result shows that changes have occurred in the wetland of Upper Orashi Forest (decrease in size and other challenging issues with respect to policies and regulations). This study has identified critical challenging issues facing wetlands in the region or driving factors of wetland loss in the study area. Thereafter making recommendations that will help address these issues to actualize environmental sustainability and sustainable wetland in the region and Nigeria at large.
This thesis summarizes the author’s developments of combustion models and multi-objective optimization methods for gasoline and diesel engines. The combustion models belong to the family of zero-dimensional stochastic reactor models introduced in the 1990s to improve the prediction of emissions with detailed chemistry in partially stirred reactors.
The first part introduces the fundamentals of the physical and chemical models describing the combustion process. As a novelty, k−ε turbulence models were implemented in the stochastic reactor model to predict the turbulent time and length scales in gasoline and diesel engines. This development allowed an improvement of the models for convective heat transfer, fuel evaporation, gas exchange across the valves, turbulent flame propagation and crevice flow, which depend on the turbulent time and length scales.
In the second part, the multi-objective optimization platform for automatic training of the stochastic reactor model is presented. The optimization method considers multiple operating points to find a set of model parameters that predict performance and emissions over the entire engine map. The Non-domination Sorting Genetic Algorithm II is combined with the stochastic reactor model and response surface models to find the best Pareto front. Multi-criteria decision making is used to select the best designs from the Pareto front.
Finally, the third part of this thesis deals with the validation of the stochastic reactor model and the multi-objective optimization platform. For this purpose, experiments of two single-cylinder research engines with spark ignition, one passenger car engine with compression ignition and one heavy duty engine with compression ignition are used. For the spark ignition engines, a set of model parameters was found that predicts well the power and emissions over the whole engine map. The calculated turbulent kinetic energy, dissipation, and angular momentum follow the trends of the three-dimensional computational fluid dynamic simulations to a good approximation for various operating points. For the two compression ignition engines, the prediction of combustion progress and nitrogen oxide emissions are in good agreement with the experiments. Larger discrepancies were found for the prediction of carbon monoxide and unburned hydrocarbon. Optimization of the soot model parameters improves the prediction of soot mass for operating points throughout the engine map.
Programmable Logic Controllers (PLCs) are pivotal in Critical Infrastructures (CIs) and Industrial Control Systems (ICSs), governing processes in nuclear power plants, petrochemical factories, and water treatment systems. Despite their importance, PLCs are vulnerable to security threats, notably control logic injection attacks, aiming to sabotage physical processes. This thesis delves into PLC security, analyzing vulnerabilities in non-cryptographically and cryptographically protected PLCs, particularly Siemens S7-300 and S7-1500 models.
Siemens, an automation market leader, utilizes S7-300 PLCs in millions of applications, reflecting the broader ICS security landscape. The S7-1500 line claims resistance to cyberattacks, including control logic injections. The thesis evaluates authentication in non-cryptographically protected PLCs, introducing a stealthy control logic injection attack scenario using an S7-300 PLC and S7Comm protocol.
The second part explores integrity checks in cryptographically protected S7-1500 PLCs. Findings, encompassing disclosed vulnerabilities, lead to a severe control logic injection attack with a malicious interrupt block, conducted in an industrial setting using the S7-1500 and S7CommPlus protocol.
The final segment focuses on Profinet protocol security and an injection attack scenario. The study demonstrates adversaries manipulating critical data without prior knowledge, causing harm to physical processes. A real-world attack on a Profinet-based system with two S7-300 PLCs is executed.
The thesis concludes by proposing mitigation solutions, enhancing PLC and communication protocol security. This contribution elevates the security posture of millions of operating devices globally, advancing PLC security research.
Energy efficiency is vital for future low-power electronic applications. This ultra-low power consumption requirement enables the research beyond the conventional charge-based memories. Further, reliability, high scalability, fast switching, CMOS compatibility, high endurance, etc., are some of the characteristics envisaged by the new generation of emerging non-volatile memories (NVMs). A memristor or OxRAM is one among the many emerging NVMs, which can exhibit the aforementioned characteristics, and it has the potential to replace the power-hungry conventional NVMs.
The memristive devices have the advantage of monolithic integration with the CMOS logic, which enables the widening of their application areas. Despite their various advantages, the reliability, forming voltages, and variability of the devices pose a hurdle to their wide commercial usage. Hence, it is crucial to identify these factors and mitigate them. This thesis addresses these issues through fabrication process improvements, electrical characterization techniques, and device-engineering methods.
The improvements in the fabrication processes reduced the pristine state currents of the memristive devices. It impacted the reliability and resistive switching performance of the memristive devices directly. To further improve the performance, the memristive devices are integrated into the 130 nm BiCMOS baseline technology of IHP. Additionally, dedicated test structures are developed to monitor and control the fabrication process steps through in-line electrical characterization.
Further, the forming current and voltage values, along with their dispersions in the 4 kbit memristive arrays, were reduced by utilizing the electrical characterization techniques. Accordingly, the forming operations were performed at high operating temperatures using incremental step pulse and verify algorithm (ISPVA). In contrast to the well-known method of increasing the current compliance (1R) or the gate voltage of the transistor (1T-1R) to increase the conduction filament size, a thin layer of Al2O3 is added. This device engineering technique reduced the variability in both LRS and HRS currents of the memristive devices. Additionally, the conduction filament properties in both states are modeled by using the quantum point contact (QPC) model. Finally, harnessing the intrinsic variability of the memristive devices for neuromorphic computing applications is demonstrated. The reliability of the devices is assessed through endurance and retention characteristics.
Numerical investigation and extension of quadrature-based moment methods for population balances
(2023)
Particulate systems can be described by a number density function (NDF) with respect to a vector of internal coordinates. The evolution of the NDF is governed by the typically high-dimensional population balance equation (PBE). A common approach to reduce the dimensionality of the problem is to solve only for a set of moments instead of the NDF. The derived system of moment equations, however, includes unclosed integral terms that still contain the unknown NDF. One way to close the system of moment equations is to approximate the unclosed integral terms using a Gaussian quadrature computed from the moments. The procedure of taking a set of moments to compute a Gaussian quadrature, which is, in turn, used to close the moment equations, is known as the quadrature method of moments (QMOM). It gave rise to an entire family of methods, the quadrature-based moment methods (QBMMs), which are the primary focus of this work. The presented research can be divided into three major parts. The first part involves the formulation of a common Lagrangian droplet breakup model for QBMMs and the numerical investigation with the QMOM as well as the more sophisticated extended QMOM (EQMOM). The results indicate that the approximations are reasonably accurate when at least six moment equations are solved, with the EQMOM providing no advantages for the investigated configurations. In the second part, a quadrature-based moment model for the effects of fluid turbulence on particle velocities is formulated. The resulting moment equations contain non-smooth integrands that are the source of large errors when using common QBMMs. As an alternative, the Gauss/anti-Gauss QMOM (GaG-QMOM) is proposed that uses the average of a Gaussian and an anti-Gaussian quadrature. Numerical studies show that the GaG-QMOM is able to significantly reduce the previously observed large errors. Another novelty proposed in this context is the modification of the second-order strong-stability preserving Runge-Kutta method to guarantee the preservation of moment realizability in the presence of phase-space diffusion. The third part is concerned with the numerical exploration of the core algorithm of most QBMMs in terms of performance and accuracy. The algorithm consists of, first, computing the recurrence coefficients of the orthogonal polynomials associated with a set of moments, second, solving a symmetric tridiagonal eigenvalue problem to obtain the quadrature nodes and weights, and third, evaluating the integral terms in the moment equations. The results indicate that the contribution of the first step to compute the recurrence coefficients from moments to the overall computational costs is negligible. Instead, the primary focus should be on the fast solution of the eigenvalue problem and, possibly, on the efficient implementation of the moment source term evaluation, which becomes important when second-order processes are considered.
The current global warming caused by the enormous negative effects of climate change rings alarm bells to humanity. It requires a colossal cooperation of scientific researchers and practitioners in all professions to invent innovating solutions to reduce the impact of global warming. In fact, the use of kinetic facades in architecture helps to save up to 50% of energy used in office space and to reduce 20% of CO2 emissions of entire building. Thus, how effective can the use of kinetic facades be in different climate regions? This research employs Grasshopper to design kinetic facades based on Minimal surfaces. DIVA 4.1 and LadyBug software based on the EnergyPlus are used to generate output data of energy use for cooling system of kinetic facade and 06 conventional facades in Berlin, Ho Chi Minh and Las Vegas in two SRES scenarios (A1FI and B1) of the IPCC in 2020, 2050 and 2080. The output data shows that the performance of the kinetic facade is approximately 40% higher than the facade with high-performance double glazing. Meaning, there is great potential to apply kinetic facades in various places on Earth in the current context of severe climate change.