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»Ich kann meinen Mund nicht halten« – Zur Funktion des Schweigens als Sprachform des Widerspruchs bei Anna Baar
No full textPublikation der U Bremen und U Wien internationalen Studierendenkonferenz »Debattieren, Opponieren, Protestieren – Interdisziplinäre Perspektiven auf sprachliche Praktiken des Widersprechens« 2023.11612
Suspension based in-situ re-alloying of metallic materials during laser powder bed fusion
No full textIn der additiven Fertigung metallischer Werkstoffe werden Bauteile zumeist schichtweise aus einem dreidimensionalen Datensatz erzeugt. Dabei wird vor allem von der Möglichkeit profitiert, hochkomplexe Geometrien fertigen zu können, die über die Grenzen konventioneller Fertigungstechnologien hinausgehen. Das pulverbettbasierte Laserstrahlschmelzen (engl. powder bed fusion of metal with laser beam, PBF-LB/M) ist eines der heutzutage am häufigsten industriell eingesetzten Verfahren der additiven Fertigung, in dem einzelne Volumenelemente mit Hilfe einer hochenergetischen Laserquelle sukzessive umgeschmolzen werden. Mit diesem selektiven und schichtweisen Vorgehen entsteht aus einem metallischen Pulver ein nahezu anwendungsfertiges Bauteil. Diese große Individualität des Prozesses ermöglicht neben der Herstellung hochkomplexer Strukturen die einmalige Chance der graduellen Gestaltung des metallischen Gefüges.
In vorliegender Arbeit wurde ein Verfahren zur dreidimensionalen Gradierung entwickelt, das vorliegende Herausforderungen zur Gradierung metallischer Werkstoffe adressiert und die bestehenden Ansätze um eine innovative Methode erweitert. Das in-situ Nachlegieren basiert auf der feindosierten Applikation einer Suspension auf Bereiche innerhalb einzelner Schichten des metallischen Bauteils. Das in der Suspension dispergierte Legierungselement ermöglicht in Folge des Umschmelzvorgangs eine hochpräzise und lokal begrenzte Modifizierung der zugrundeliegenden Mikrostruktur.
Am Beispiel eines ferritischen Edelstahls ermöglichte die Integration eines Dosiersystems in eine PBF-LB/M Anlage sowohl die lokale, als auch die homogene Erhöhung des Kohlenstoffgehalts. Dazu wurde eine über einen Zeitraum von mindestens 24 Stunden stabile Suspension einer Kohlenstoffkonzentration von 2,5 Gew. % formuliert. Unter Verwendung des kommerziellen Dosiersystems konnte das Fluid durch Ausbildung eines Dosierstrahls präzise und reproduzierbar in feinjustierbaren Volumina appliziert werden. Anhand spektroskopischer Analysemethoden, elektronenmikroskopischen Bildgebungen und Mikrohärteprüfungen konnte anschließend die lokale Veränderung des ferritischen Ausgangsgefüges bestätigt und eine zielgenaue Gradierung der Mikrohärte erreicht werden
Paleoclimate data assimilation with CLIMBER-X in transient simulation of the last deglaciation
No full textPaleoclimate studies provide crucial insights into the Earth's climate system drivers and behavior, helping distinguish between natural climate patterns and human-induced changes and providing a context for current climate trends. The last deglaciation marked a period of Earth's history characterized by the retreat of massive ice sheets covering large parts of the planet. During this phase, a drastic transition occurred from the cold Last Glacial Maximum to the warmer and more stable climate of the Holocene. Besides proxy-based reconstructions and climate model simulations, data assimilation (DA) has emerged as a promising reconstruction technique of past climates. DA combines the data and the underlying dynamical principles governing the climate system to provide a state estimate of the system, which is better than that which could be obtained using just the data or the model alone.
As the first step of this dissertation, major uncertainties and forcing factors are evaluated for the last deglaciation using an efficient climate model. Two sets of transient simulations are based on the novel ice-sheet reconstruction PaleoMist and the established GLAC1D. The simulations reveal that the proximity of the Atlantic meridional overturning circulation (AMOC) to a bifurcation point, where it can switch between on- and off-modes, is primarily determined by the interplay of greenhouse gas concentrations, orbital forcing, and freshwater forcing. The impact of deglacial meltwater on AMOC shapes regional temperature patterns. PaleoMist simulation shows a pronounced warming in the Bølling-Allerød (BA), a strong AMOC, and a moderate cooling during the Younger Dryas (YD) with an AMOC weakening. The opposite signature is found for GLAC1D. The PaleoMist simulation replicates, at least qualitatively, the BA/YD sequence: a warming in Greenland and Antarctica in the BA, a cooling northern North Atlantic, and a warming in Antarctica in the YD.
In addition, as the main goal, this study presents an efficient method for assimilating the temporal evolution of surface temperatures for the last deglaciation. In applying an ensemble Kalman filter approach, the study makes use of the advances in the parallel DA framework (PDAF). It is found that the DA solution depends strongly on the background evolution of the decaying ice sheets rather than the assimilated temperatures. Further, the influence of DA is more pronounced on regional scales than on the global mean. In particular, DA has a stronger effect during millennial warming and cooling phases, such as BA and YD, especially at high latitudes with heterogeneous temperature patterns.
In the final step, the DA technique is developed to assimilate the subsurface temperatures. The results show the DA of subsurface temperatures modifies the precipitation pattern, which can consequently change the timing and magnitude of climate events such as BA and YD. The DA technique introduced and developed in this dissertation facilitates the paleoclimate DA on multi-millennial time scales and can also be employed to study future warming scenarios
Trophic ecology of Arctic gelatinous zooplankton
No full textThe overarching goal of this dissertation is to reject the hypothesis of gelatinous zooplankton (GZP) as a trophic dead end for the Arctic and sub-Arctic seas. To do so, I investigated the role of GZP in the diet of different invertebrate and fish species, during different seasons and at different locations. To do so, I used DNA metabarcoding of the stomach contents of bentho-pelagic amphipods and demersal and bathypelagic fish species. I also, aimed to prove the usefulness of DNA metabarcoding in diet studies and the detection of GZP, which are rapidly digested and due to that often overlooked with traditional methods. Furthermore, I aimed to investigate the role of GZP species in the marine food web, which was investigated using stable isotope analysis, to determine the trophic level of GZP and fish species in Porsangerfjorden. Overall, I was able to show that GZP was consumed regularly by many predators in the Arctic and sub-Arctic seas during different seasons. Furthermore, I showed that GZP should be considered as different groups in food web models rather than being pooled into one term
An HCI approach to privacy and security in mobile and ubiquitous applications
No full textPrivacy and security decisions are omnipresent in our digital lives, shaping and influencing our interactions across a broad spectrum of mobile and ubiquitous applications. In today’s interconnected world, where personal data flows through numerous digital channels, our privacy and security choices have far-reaching implications. These decisions impact our safety and confidentiality and our trust in digital platforms and services. From managing sensitive information on social media to protecting financial transactions on mobile banking apps, our daily activities are intertwined with navigating and watching our digital identities. As technology advances, the complexity of these decisions grows, necessitating thoughtful consideration and informed choices to maintain control over our privacy and security in an increasingly interconnected and data-driven environment.
This dissertation explores the pivotal role of HCI strategies in improving user understanding, engagement, and decision-making in privacy and security tasks within mobile and ubiquitous applications. Through a variety of research methods and approaches, this work shows how techniques such as gamification, visualization, and augmented reality interfaces improve users’ confidence in their ability to manage their privacy and security, enhance their knowledge of these concepts, and empower their overall engagement with privacy and security practices.
Findings emphasize that while privacy concerns are critical, bolstering knowledge and self-efficacy through interactive tools is essential for promoting informed and proactive privacy and security behaviors. The conducted studies advocate a paradigm shift towards empowering users with clear, actionable privacy goals and settings supported by intuitive, accessible interfaces. The implications of this work extend to what developers should consider when designing privacy and security mechanisms. By leveraging HCI approaches, developers can empower user ability and comprehension in mobile and ubiquitous environments, which enhances users’ self-efficacy and motivation, enabling them to make informed decisions in digital environments
Praxisbeispiele der Stadt- und Regionalentwicklung in Wrocław
No full textGeländetage oder Exkursionen gehören zu den angestammten Lernformaten der Geographie. Sie werden durch die unmittelbare Auseinandersetzung mit Gegebenheiten vor Ort als besonders sinnstiftendes Lernen wahrgenommen. Der vorliegende Band ist im Kontext einer fünftägigen Exkursion nach Wrocław von Studierenden im Master „Stadt- und Regionalentwicklung“ an der Universität Bremen entstanden, die Anfang September 2024 durchgeführt wurde. Die Inhalte und Programmpunkte wurden maßgeblich von den Studierenden erarbeitet. Im Anschluss an eine kurze Einleitung finden sich sechs Kapitel zu folgenden Themen:
(1) Erinnerungskultur und Herrschaftsansprüche: Welche symbolische Wirkung haben geographische Namen auf raumbezogene Identitäten? Das Beispiel Wrocław vs. Breslau
(2) (Post-)Sozialistische Stadtentwicklung – Erkundungen am Beispiel des Stadtteils Szczepin in Wrocław
(3) Street Art in Wrocław
(4) Orte des Erinnerns: Die Jüdische Geschichte Wrocławs und ihre Gegenwart
(5) Klimaanpassung in Wrocław - Das Beispiel des GrowGreen Projekts
(6) Wer bestimmt, was sehenswert ist? Tourismus und Stadtentwicklung am Beispiel eines Stadtrundgangs durch Wrocław1-202
Adiabatic Charging in SAR ADCs
No full textSuccessive Approximation Register (SAR) is an established and well-rounded (Analog-to-Digital Converter) ADC architecture allowing for medium resolution and medium conversion speed while being energy efficient and relatively small in area. Switched-capacitor (Digital-to-Analog Converter) DAC being an essential component of the SAR architecture in certain design configurations might contribute significantly to the overall ADC power consumption. Adiabatic capacitor charging is a method that allows for increasing the charging efficiency using linear
voltage or constant current to charge a capacitor. A variation of this approach uses a series of small voltage steps instead of a voltage ramp, which is particularly suitable for switched-capacitor circuits as it does not require analog circuitry such as a voltage ramp generator or a current source.
This work investigates the stepwise capacitor charging approach applied to DAC in SAR ADC in terms of the architectural modifications and their influence on the resulting efficiency improvement.
The study begins with an estimation of the stepwise charging applied to a conventional DAC switching scheme. The average energy consumption is derived as a function of the number of charging steps and resolution, the results are verified in MATLAB. For the implementation of the approach, other switching schemes were considered, the selected monotonic switching scheme was then also modelled in MATLAB to evaluate the efficiency improvement depending on the number of charging steps in that case. Stepwise charging requires several intermediate voltage levels in addition to the regular reference voltage. The work includes the discussion and implementation of the onboard DC-DC converter and the MATLAB model includes its influence on energy savings, allowing for a design optimization as well as the selection of the converter’s configuration in regards to the number of charging steps, resolution, and DAC unit capacitor size.
Finally, the work describes a fabricated IC with two proof-of-concept ADC prototypes featuring 4-step charging applied to a 10-bit monotonic SAR ADC. The circuits differ in terms of the DAC capacitance and conversion speed. The first prototype has a sampling rate of 165 kS/s and achieves SNDR of 57.63 dB. The second prototype has a sampling rate of 1 MS/s and achieves SNDR of 56.52 dB. The architecture is designed with separated circuits for the SAR register and
adiabatic charging control logic in order to better differentiate the control logic penalty related to stepwise charging. To further identify the power savings in both prototypes, the 1-step versions of each prototype with adiabatic circuitry removed from the layout are simulated in CAD and compared to the 4-step counterparts.
The evaluation of the first prototype shows a 26% reduction of the DAC power consumption including all the extra circuitry, whereas the second prototype establishes the limitation of the approach where the energy savings were overpowered by the control logic penalty and DC-DC converter switching losses. The work discusses this limitation in detail describing the applicability area of adiabatic charging. The proposed method allows the inclusion of these types of losses to optimize the configuration and estimate the benefits of the adiabatic switching in each case
Impact of powder application in metal binder jetting
No full textMetal Binder Jetting (MBJ) ist ein additives Fertigungsverfahren, bei dem ein Binder lokalisiert schichtweise in ein aufgetragenes Pulverbett eingebracht wird. Nach dem Aushärten des Binders werden die Grünteile entpulvert und in einem Entbinder- und Sinterprozess zu einem dichten Bauteil konsolidiert. Das Verdichtungsverhalten hängt von der Homogenität des Grünteils, seiner Packungsdichte und der Sinteraktivität ab.
In einer umfassenden Varianzanalyse zu den Prozessparametern des Pulverauftrags anhand des Edelstahls 316L wurde festgestellt, dass sowohl die Trocknung von Pulvern den Einfluss der Pulverauftragsparameter erhöht. Die Schichtstärke zeigte sich als einer der einflussreichsten Parameter. Eine höhere Schichtstärke führt zu einer geringeren Grünteildichte und inhomogeneren Grünteilen. Der Pulverauftrag mittels gegenläufig rotierendem Roller und der Bindereintrag verursachen Dichteschwankungen und Entmischungen der Partikel im Grünteil, die bei höherer Schichtdicke stärker ausgeprägt sind. Daraus resultiert eine lokal niedrigere Pulverpackung in den Grünteilen, die einerseits in Zwischenschichtporosität von Sinterteilen und niedrigeren Sinterdichten führen. Andererseits ist das anisotrope Schwindungsverhalten des MBJ darauf zurückführen.
Bei der Verarbeitung von Pulvern mit mittleren Partikelgrößen D50 zwischen 5 und 26 µm nimmt die Pulverbettdichte bei kleineren Partikelgrößen ab. Die höchsten Grünteildichten werden bei mittleren Partikelgrößen erreicht, da bei gröberen Pulvern aufgrund ihrer geringeren Kohäsion durch den Tropfenaufprall des Bindereintrags ein höherer Anteil an Partikeln ausgeschossen wird.
In dieser Arbeit wurde ein Zusammenhang zwischen den Partikeleigenschaften und der Pulverbettdichte herausgearbeitet. Die spezifische Oberfläche des Pulvers, die Partikelgrößenverteilung und die Schichtstärke ermöglichen eine präzise Vorhersage der Pulverbettdichte. Die spezifische Oberfläche des Pulvers und die Schichtstärke besitzen den größten Einfluss auf die Pulverbettdichte. Je gröber das Pulver und je niedriger die Schichtstärke, desto höher ist die Pulverbettdichte
Entlassung von Arzneimitteln aus der Verschreibungspflicht. Eine Analyse von OTC-Switches unter pharmakologischen und versorgungsrelevanten Gesichtspunkten
No full textProspektive Analyse von Wirkstoffen und Wirkstoffkombinationen hinsichtlich ihrer Geeignetheit für einen OTC-Switch anhand der EU-Switch-Leitlinie und Bewertung nach einem Ampelschema. Retrospektive Betrachtung bereits erfolgter OTC-Switches bezüglich ihrer Auswirkungen auf die AMTS anhand von Krankenkassendaten und Nebenwirkungsmeldungen sowie auf die Versorgungssituation in der GKV
Using fluorescence in situ hybridization to study intracellular properties
No full textMicroorganisms dominate the surface ocean and significantly shape biogeochemical cycles, particularly the carbon cycle. Through photosynthesis, primary producers fix inorganic carbon and produce organic matter. The phytoplankton-derived organic matter fuels differently specialized heterotrophic bacteria that remineralize large proportions of it. At the same time, phages, which are viruses that infect bacteria, shape the bacterial community composition through top-down controls. Environmental microbial ecology often uses microscopically derived changes in cell abundance or incubation experiments with labeled substrates to derive bacterial growth or activity. However, the former does not account for mortality, while the latter is prone to biases by bottle effects and substrate preferences. Nevertheless, marine microbial ecology requires a thorough understanding of bacterial growth and mortality to understand the effects on, e.g., the carbon cycle. Additionally, microbial ecologists have little understanding of the effect of phages on the heterotrophic community. For example, no studies have quantified the amount of phage-infected heterotrophs in complex marine samples to date.
For this thesis, I studied the bacterial life cycle, from cell division to cell death, in environmental samples. To do so, I used fluorescence in situ hybridization (FISH) techniques and high-throughput image cytometry, complemented with metagenomic analyses. A significant focus was on bacteria of the SAR11 clade. SAR11 are specialized to grow in oligotrophic habitats that are nutrient and substrate-depleted. They are assumed to be outcompeted by specialized bacteria during high-substrate conditions, such as phytoplankton blooms. Additionally, there is an ongoing debate on whether phage infection has a considerable effect on SAR11 communities. In this thesis, I demonstrate rapidly dividing SAR11 communities during phytoplankton blooms with a concomitantly high phage infection rate.
In Chapter 2, I used FISH in combination with a fluorescent DNA stain to study the frequency of dividing cells by visualizing the intracellular DNA distribution. During a cell replication cycle, the dublicated genomes need to be separated into the future daughter cells. The correlation with experimentally derived in situ cell division rates allowed the calculation of cell division across an entire phytoplankton bloom. Measurements revealed faster SAR11 cell division rates than anticipated by cell counts. Hence, calculated mortality rates were high during these times. As the mortality was taxon-specific, I hypothesized phage-induced lysis as a cause.
In Chapter 3, I designed direct-geneFISH probes to visualize phage-infected SAR11 cells in the environment. I could thereby provide the missing link between cell division and mortality rates, as revealed in Chapter 2. The highest amounts of phage-infected SAR11 cells (up to 19\% of the SAR11 cells) were detected when taxon-specific mortality and cell division rates were highest. Additionally, I found a phenomenon of phage-infected, ribosome-depleted cells, which I dubbed ‘zombie cells’. I thoroughly discuss possible explanations for their emergence and propose that nucleotides from ribosomal RNA are used as substrates for phage genome synthesis. Additionally, I show that both phage-infected and zombie cells occur globally.
In Chapter 4, I assessed the influences of future ocean scenarios and a marine heatwave on the microbial community, including cell division and grazing rates. Anthropogenic influences shape the ocean as a habitat with unknown consequences for the microbial community. I found no significant influences of the mild marine heatwave, while the future ocean scenarios caused differences in bacterial abundances. Overall, the results indicate a stable and adaptable marine microbial community in the face of a changing ocean.
In the general discussion (Chapter 5), I discuss the methodological approaches used in this thesis to study bacterial cell division rate and the viral community. I further summarize and discuss the insights into SAR11 ecology gained through this thesis, as well as the importance and emergence of zombie cells. The discussion is rounded off with an outlook, proposing directions for future research projects to understand further the interplay of bacterial hosts and their phages, as well as zombie cells