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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.
Die vorliegende Studie möchte einen Beitrag zur Erforschung der Frage leisten, inwiefern Rechtsformwechsel bei Stiftungen Auswirkungen auf das Commitment der Beschäftigten haben. Der Fokus liegt dabei auf den Wechselabsichten des Personals beziehungsweise auf dem Absentismus. Im Rahmen einer qualitativen Forschung wurden drei Stiftungen betrachtet, in denen ein Rechtsformwechsel stattgefunden hat. Die Untersuchung wurde mittels Expert/-inneninterview durch eine semistrukturierte Befragung anhand eines Interviewleitfadens durchgeführt. Die Auswertung der Daten erfolgte durch eine qualitative Inhaltsanalyse per QDA-Software. Dabei konnte festgestellt werden, dass bei Einhaltung der Maßnahmen zur Stärkung des Commitments wenige und dann nur positive Auswirkungen zu erkennen sind, da sich Fehlzeiten und Absentismus nicht wesentlich veränderten. Für die Praxis ist relevant, dass die Vorteile der Änderung der Rechtsform einer Stiftung gegenüber den Risiken überwiegen. Weitere Forschungsbedarf,besteht hinsichtlich des nachlassenden Engagements beim Personal im Hinblick auf Änderungen.
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.
In den letzten Jahren erkannten Unternehmen zunehmend die Bedeutung der Entwicklung ihrer Talente, doch eine klare Handlungsstrategie dazu fehlt. Basierend auf dieser Problemstellung entwirft die vorliegende Forschungsarbeit in Form des Nachwuchs-Entwicklungs-Index (NEX) eine praktische Evaluation sowie einen zweckdienlichen Leitfaden zur Integration einer strategischen Nachwuchs-Entwicklungs-Struktur.
Die Forschung zum NEX sah hierfür 3 Forschungsschritte vor: Eine Literaturrecherche, die Experteninterviews sowie die quantitative Indexdefinition.
Damit verbunden wurden folgende Forschungsfragen zur Eingrenzung des Vorhabens festgehalten:
- Sind individuelle Faktoren, welche das individuelle Beziehungsmanagement zu einem Nachwuchsmanager berücksichtigen, entscheidend für die professionelle Nachwuchsmanagemententwicklung?
- Welche Faktoren sind als Ergänzung zum Personalmanagement-Professionalisierungs-Index (PIX) entscheidend für die professionelle Nachwuchsmanagemententwicklung?
- Welche Handlungsempfehlungen entstehen anhand des NEX je nach Reifegrad eines Unternehmens?
Die ersten beiden Forschungsphasen, der theoretischen Aufarbeitung sowie der qualitativen Überprüfung und Eingrenzung der Themenfelder durch Experteninterviews, zeigen auf, dass die Entwicklung von Führungstalenten eine hohe Relevanz im Unternehmensalltag hat. Die quantitative Aufarbeitung dieser Grundlagen hatte einen Index zur Folge, welcher 95 Items umfasst und sich in strukturelle Items (PIX-Ursprung) und personelle Items (eigens entwickelt) unterteilte. Zur Validierung dieser Items wurde eine quantitative Online-Befragung umgesetzt. Schlussendlich konnten N = 159 auswertbare Datensätze zur Quantifizierung des NEX herangezogen werden. Parallel zur Methodik des PIX wurde eine Hauptkomponentenanalyse durchgeführt, um die wesentlichen Komponenten des NEX zu können.
Im weiteren Verlauf zeigten sich zwei übergeordnete Komponenten sowie 16 Frageitems als entscheidend für den NEX. Mit der höchsten Ladung können die folgenden Items beispielhaft als bedeutende Aspekte herangezogen werden:
- Die einzelnen Prozesse des Personalmanagements sind hinreichend miteinander verzahnt.
- Der Kernprozess zum Personaleinsatz ist im Unternehmen eindeutig festgehalten.
- Der Kernprozess zur Personalplanung ist im Unternehmen eindeutig festgehalten.
Im Zusammenhang mit der personellen Komponente sind folgende Maßnahmen beispielhaft wichtige Aspekte, um eine professionelle Nachwuchs-Entwicklungs-Strategie abzubilden:
- Über ein Alumni-Netzwerk wird Kontakt zu ausgeschiedenen Mitarbeitern gehalten.
- Die subjektive Mitarbeiterzufriedenheit wird bei der Mitarbeiterbeurteilung berücksichtigt.
- Mit jedem Mitarbeiter, der aus dem Unternehmen ausscheidet, wird ein strukturiertes Kündigungsgespräch geführt.
Die Ergebnisse ermöglichen es Unternehmen, zukünftig mit einem ökonomisch überschaubaren Aufwand erste Einblicke über den Stand der Professionalisierung ihrer eigenen Nachwuchs-Entwicklungs-Arbeit zu erhalten.
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.