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Now showing items 71-80 of 202
Working paper
Petropolitics
(2023)
• The dominant trend was that oil and natural gas were first and foremost a matter of market mechanisms and competition rules, even if they interacted with politics and geopolitics.
• The WTO persisted in treating hydrocarbons as commodities like any other, ignoring both their commons character and their impact on the environment and climate.
• The conflict in Ukraine has caused an upheaval. Within a few months, Europe faced a serious threat of energy shortages.
• In a few months, the rehabilitation of coal and ...
Dissertation
Plastic packaging waste management in Germany: Evaluating and optimizing material flows and environmental impacts
(2023)
Since 1990, the annual plastic packaging consumption by private end users in Germany more than doubled. This trend can be attributed to plastic's advantageous properties such as its low weight, cost-effectiveness, and customizable features. However, plastic packaging is also widely criticized due to its dependency on fossil fuels, short lifespan, and potential contribution to marine littering. The tension between the popularity of plastic packaging and the environ-mental challenges associated with a short-term product ...
Dissertation
Investigation and Elimination of Substructures in Formal Concept Analysis focusing on Boolean Suborders and Subcontexts
(2023)
In the field of Formal Concept Analysis, data is mainly presented in so-called formal contexts, which assign to a set of objects their respective attributes. From those concept lattices can be generated, where the objects are grouped with respect to their common attributes to represent the relationships in the data in a way that enhances the understandability for humans. However, since a concept lattice can be of exponential size compared to its associated formal context, the presented relationships often become hard ...
Aufsatz
Experimental Analysis of Residual Stresses in CFRPs through Hole-Drilling Method: The Role of Stacking Sequence, Thickness, and Defects
(2023-05-09)
Carbon fiber reinforced plastics (CFRPs) gained high interest in industrial applications because of their excellent strength and low specific weight. The stacking sequence of the unidirectional plies forming a CFRP laminate, and their thicknesses, primarily determine the mechanical performance. However, during manufacturing, defects, e.g., pores and residual stresses, are induced, both affecting the mechanical properties. The objective of the present work is to accurately measure residual stresses in CFRPs as well ...
Aufsatz
Exploring the mechanical properties of additively manufactured carbon-rich zirconia 3D microarchitectures
(2023-07-11)
Two-photon lithography (TPL) is a promising technique for manufacturing ceramic microstructures with nanoscale resolution. The process relies on tailor-made precursor resins rich in metal–organic and organic constituents, which can lead to carbon-based residues incorporated within the ceramic microstructures. While these are generally considered unwanted impurities, our study reveals that the presence of carbon-rich residues in the form of graphitic and disordered carbon in tetragonal (t-) ZrO₂ can benefit the ...
Aufsatz
Describing mechanical damage evolution through in situ electrical resistance measurements
(2023-02-27)
The fatigue properties of metallizations used as electrical conductors in flexible electronic devices have been thoroughly studied over the years. Most studies use time-intensive characterization methods to evaluate mechanical damage. For their ease of access, in situ electrical resistance measurements are often performed along with other characterization methods. However, the data are mostly used as an indicator of failure and a thorough analysis is usually missing. This work presents some deeper analysis methods ...
Aufsatz
Influence of Cu Addition and Microstructural Configuration on the Creep Resistance and Mechanical Properties of an Fe-Based α/α′/α″ Superalloy
(2023-01-14)
Introducing Cu nanoparticles is an effective mechanism for strengthening and toughening Fe-based materials such as ultra-high-strength steels. Herein, the effect of Cu on the mechanical properties of a novel Fe-based α/α′/α″ superalloy is studied. Compared to a Cu-free reference alloy, nanoindentation reveals an increase in hardness, which was associated with the formation of Cu nanoparticles. Both alloys show room temperature (RT) compressive plastic strain at maximum stress greater than 8%, irrespective of the ...
Aufsatz
Elevated Temperature Mechanical Characteristics and Fracture Behavior of a Novel Beta Titanium Alloy
(2023-02-03)
In the present work, the elevated-temperature deformation characteristics and microstructural evolution of a Ti-5V-5Mo-5Cr-4Al alloy in solution-treatment conditions were studied under a tensile load at temperatures in the range of 25 to 550 °C and strain rates between 0.001 and 0.1 s-¹. The results obtained indicated that, essentially, dynamic recovery (DRV) was the dominant softening mechanism in the case of the regimes considered. An analysis based on transmission electron microscopy (TEM) and the assessment of ...
Dissertation
Regulatory mechanisms of Protein kinase A - Isoform mediated fine-tuning
(2023)
cAMP-dependent protein kinase (PKA) is a crucial part in eukaryotic signal transduction and controls biological processes. With a multitude of substrates, a great variety of cellular functions are regulated by PKA. Regulation of metabolism, cell growth and -differentiation, conductivity of ion channels, movement of sperm cells, embryonic development, neuroplasticity as well as conversion of short- to long-term memory are just examples for the many tasks of the kinase. To achieve and coordinate these diverse functions, ...