Strukturierter Entwurf selbstoptimierender mechatronischer Systeme

von Oliver OberschelpPaderborn, Univ., Diss., 200

A Probabilistic Proof of the nCPA to CCA Bound

We provide a new proof of Maurer, Renard, and Pietzak's result that the sum of the nCPA advantages of random permutations $P$ and $Q$ bound the CCA advantage of $P^{-1} \circ Q$. Our proof uses probability directly, as opposed to information theory, and has the advantage of providing an alternate sufficient condition of low CCA advantage. Namely, the CCA advantage of a random permutation can be bounded by its separation distance from the uniform distribution. We use this alternate condition to improve the best known bound on the security of the Swap or Not shuffle in the special case of having fewer queries than the square root of the number of cards

Entwicklung eines Konstantstromladers mit Weitbereichseingang und neuartigem Snubberkonzept

Diese Veröffentlichung behandelt eine neuartige Konstantstromladertopologie für Hochspannungskondensatoren, welche sich besonders für den mobilen Einsatz bei variablen Eingangsspannungen mit hohen Ausgangsleistungen eignet. Als besondere Anforderung ergibt sich hierbei die hohe geforderte Effizienz durch die begrenzt verfügbare Energiemenge der Batterieversorgung in Verbindung mit den benötigten sehr hohen Eingangsströmen. Weiterhin erfordert der mobile Einsatz eine Topologie, die möglichst wenig Volumen einnimmt und ein niedriges Gewicht bietet. Ein 2 kW Prototyp mit 50 kV Ausgangsspannung wurde entwickelt und in Betrieb genommen, der mit einer Eingangsspannung zwischen 20 und 50 V versorgt wird, wodurch sich Eingangsströme über 100 A ergeben. Zur Reduktion der Verlustleistung wurde eine neues Snubberkonzept entwickelt, das Überspannungen an den Halbleiterschaltern eliminiert, indem eine schnellere Kommutierung erfolgt, wodurch auch Schalter mit niedrigeren Sperrspannungen und daraus folgend niedrigerem Durchgangswiderstand eingesetzt werden können

Simulation des modularen Mehrpunkt-Umrichters (M2C) im Niederspannungsbereich

In dieser Arbeit werden die Ergebnisse einer Simulation des modularen Mehrpunkt-Umrichters (M2C) dargestellt. Der ursprünglich für den Hochspannungsbereich entwickelte M2C wurde in den Niederspannungsbereich portiert, um hier seine Vorteile gegenüber den überwiegend eingesetzten Zweipunkt-Wechselrichtern ausspielen zu können. Simuliert wurde ein dreizehnstufiger Wechselrichter an einer dreiphasigen, ohmsch-induktiven Last. Zur Ansteuerung der einzelnen Submodule des Systems wurde eine Pulsweitenmodulation (PDPWM- Verfahren) eingesetzt. Zur Symmetrierung der Submodulspannungen musste zusätzlich ein Sortieralgorithmus in die Ansteuerkette implementiert werden. Die Simulation wurde mit dem Programm Plecs von Plexim durchgeführt

Internationale Wissenschaftlerinnen und Wissenschaftler an deutschen Hochschulen: Von der Postdoc-Phase zur Professur (InWiDeHo); Eine Analyse von Herausforderungen und Gelingensbedingungen

In Deutschland gelingt bislang nur wenigen internationalen Wissenschaftler*innen der Zugang zu einer Universitätsprofessur. Dies zeigt sich im internationalen Maßstab, aber auch im Vergleich mit dem sonstigen wissenschaftlichen Personal an Universitäten. Das Forschungsprojekt InWiDeHo hat untersucht, ob und ggf. welche Hürden beim Übergang von der Postdoc-Phase auf eine Professur für diese Personengruppe bestehen. Der Bericht stellt die Kernbefunde und Handlungsempfehlungen der qualitativen Studie vor, für die im Rahmen von Expert*inneninterviews internationale Postdocs und Neuberufene sowie Mitglieder von Universitätsleitungen befragt wurden. Außerdem wurden Gruppendiskussionen mit Mitarbeitenden an Universitäten durchgeführt

Petrochemicals and Climate Change : Tracing Globally Growing Emissions and Key Blind Spots in a Fossil-Based Industry

With the risk of climate breakdown becoming ever more pressing as the world is on track for 2.7 degrees warming, pressure is increasing on all sectors of the economy to break with fossil fuel dependence and reduce greenhouse gas (GHG) emissions. In this context, the chemical industry and the production of important basic chemicals is a key sector to consider. Although historically a driver of economic development, the sector is highly dependent on fossil resources for use as both feedstock and fuel in the production of as well organic as inorganic chemicals. The chemical industry demands both petroleum fractions and natural gas. Petroleum fractions such as naphtha and petroleum gases are used as feedstocks for building block chemicals and polymers (e.g., benzene and polyethylene), while natural gas is used for methanol and ammonia. Indeed, the sector is associated with both large process emissions as well as energy related emissions. Our results demonstrate that in 2020 direct GHG emissions from the petrochemical sector amounted to 1.8 Gt CO2eq which is equivalent to 4% of global GHG emissions. Indirect GHG emissions resulting from the activities in other industries supplying inputs for the petrochemical industry accounted for another 3.8 Gt CO2eq. The petrochemical industry is thus associated with a total of 5.6Gt CO2eq of GHG emissions, equivalent to ~10% of global emissions. Over the past 25 years, emissions associated with petrochemicals have doubled and the sector is the third most GHG emitting industry. This increase is fueled by large growth of petrochemicals production as well as growth in regions with high indirect emissions, i.e., in energy systems with high dependence on coal and other fossil fuels. Over the past decades, the industry has grown rapidly in the Asia-Pacific region especially in China which in 2020 was the source for about 47% of global GHG emissions associated with petrochemicals. USA accounts for 6% of the emissions from the industry and Europe for 5%. The BRIC group of countries, which except for China also includes Brazil, India, and Russia, currently accounts for 57% of GHG emissions from petrochemicals, showing that the emissions from this sector are more geographically clustered in these countries than emissions from other sectors.Proper disaggregated and comparative analyses of key products is currently not possible. Data confidentiality and a high reliance on proxy data limit the reliability of LCA and stands in the way of mapping climate impacts. A strong demand of chemicals life cycle inventory (LCI) data for environmental footprinting has resulted in a general increase of chemicals data in many LCI databases, but the energy demands both for heat and electricity are typically not well-documented for production processes outside the main bulk chemicals. If incinerated at end-of-life plastics and other chemical products will emit embodied carbon as CO2 and if landfilled there is a risk of slow degradation with associated methane emissions. Global estimates based on most LCA datasets will thus significantly underestimate emissions from the chemical industry.The multitude of value chains dependent on the petrochemical industry makes it an important contribution to life cycle emissions in many sectors of the economy. Petrochemicals are used as an intermediate input in many industries and the emissions associated with them thus propagate through the economy, with final demand in manufacturing industries and services being associated with the largest shares of emissions from chemicals. The impacts and emissions downstream in value chains is however poorly understood and disclosure by petrochemical producers is lacking and insufficient. While disclosure of emissions in the industry has increased over the past decades, it remains partial and shows inconsistencies over time. This is due to issues such as different reporting standards, large discrepancies in the extent of disclosure as well as various other gaps and inconsistencies in reporting. This holds for all scopes, although Scope 1 emissions are better covered. Only some firms disclose information about downstream Scope 3 emissions including end-of-life for final products. Emission targets set by firms in the industry do not correspond to the challenge of large and rapid emission reductions. Many targets include only parts of operations and transparent, standardized target-setting is lacking. Reported emission reduction initiatives to achieve targets are far from sufficient focusing mainly on efficiency improvements or insubstantial parts of the operation. Shifting to renewable energy is a key for rapid emission reductions in the industry, yet few firms report strategic targets for this shift. As the industry has historically been closely linked to and integrated with the energy sector it holds a great potential for engaging with the deployment and adoption of renewable energy, although this implies a transformation of the knowledge base and resource allocation in the industry which is still focused on fossil fuels. Roadmaps and scenario analyses show that apart from a shift to renewable energy, a transformation of the industry relies on the deployment of key technologies which are not yet fully developed. This includes new technologies for hydrogen production, e.g., electrolytic (green) hydrogen or hydrogen produced with carbon capture and storage (CCS). New chemical synthesis pathways based on captured carbon, so called carbon capture and utilization (CCU) is also highlighted, but the massive demand for renewable energy associated with this pathway is a significant barrier to its adoption in the near term. The report shows how efficiency improvements continues to be the main focus for reducing the climate impact of petrochemicals, but that this is a completely inadequate approach for achieving the emissions reductions necessary in the coming decades. Breakthrough technologies are unlikely to be deployed at a rate consistent with international climate targets, and there is a great risk in relying on the promises of technologies which are yet to be proven at scale. The large knowledge gaps that remain are key barriers for effective governance of the transition