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While estimated numbers of past and future climate migrants are alarming, the growing empirical evidence suggests that the association between adverse climate-related events and migration is not universally positive. This dissertation seeks to advance our understanding of when and how climate migration emerges by analyzing heterogeneous climatic influences on migration in low- and middle-income countries. To this end, it draws on established economic theories of migration, datasets from physical and social sciences, causal inference techniques and approaches from systematic literature review. In three of its five chapters, I estimate causal effects of processes of climate change on inequality and migration in India and Sub-Saharan Africa. By employing interaction terms and by analyzing sub-samples of data, I explore how these relationships differ for various segments of the population. In the remaining two chapters, I present two systematic literature reviews. First, I undertake a comprehensive meta-regression analysis of the econometric climate migration literature to summarize general climate migration patterns and explain the conflicting findings. Second, motivated by the broad range of approaches in the field, I examine the literature from a methodological perspective to provide best practice guidelines for studying climate migration empirically. Overall, the evidence from this dissertation shows that climatic influences on human migration are highly heterogeneous. Whether adverse climate-related impacts materialize in migration depends on the socio-economic characteristics of the individual households, such as wealth, level of education, agricultural dependence or access to adaptation technologies and insurance. For instance, I show that while adverse climatic shocks are generally associated with an increase in migration in rural India, they reduce migration in the agricultural context of Sub-Saharan Africa, where the average wealth levels are much lower so that households largely cannot afford the upfront costs of moving. I find that unlike local climatic shocks which primarily enhance internal migration to cities and hence accelerate urbanization, shocks transmitted via agricultural producer prices increase migration to neighboring countries, likely due to the simultaneous decrease in real income in nearby urban areas. These findings advance our current understanding by showing when and how economic agents respond to climatic events, thus providing explicit contexts and mechanisms of climate change effects on migration in the future. The resulting collection of findings can guide policy interventions to avoid or mitigate any present and future welfare losses from climate change-related migration choices.
Das Ziel des hier beschriebenen Masterprojekts war es, eine Methode zu etablieren, mit der Insekten in Gießharz eingeschlossen werden können, damit sie dauerhaft konserviert für mikroskopische Untersuchungen im Biologieunterricht zur Verfügung stehen. Die Masterarbeit enthält eine ausführliche Anleitung zur Herstellung von Gießharzpräparaten mit darin eingebetteten Insekten. Sie soll als Handreichung vor allem für Biologie-Lehrkräfte dienen, um selbstständig hochwertige Lehrpräparate für ihren Unterricht herstellen zu können. Aufgrund der Komplexität des Themas werden Naturschutzbestimmungen und die Beschaffung der Insekten genauso beleuchtet wie deren anschließende Präparation, die Konstruktion einer eigenen Gießform, die Einbettung der Insekten in Gießharz und die Nachbehandlung des Gießlings. Wichtige Einflussfaktoren, die die Qualität der Präparate entscheidend beeinflussen und mögliche Fehlerquellen, werden ausführlich erläutert. Mittels dieser detaillierten Eingießanleitung können mit relativ einfachen und kostengünstigen Mitteln faszinierende Studienobjekte für einen anschaulichen Biologieunterricht entstehen.
Portal Wissen = Zusammen
(2022)
Darüber, was den Menschen zum Menschen macht – und von anderen Lebewesen auf der Erde unterscheidet – wird schon lange und bis heute eifrig diskutiert. Als „Homo sapiens“ ist die wissenschaftliche Selbstbeschreibung unserer Art schon die Charakterisierung als „verstehender, weiser, wissender Mensch“. Dieses Mehr an Wissen verdanken wir, so ließe sich argumentieren, dem Wesenszug, dass wir unseresgleichen (grundsätzlich) besonders verbunden sind. Wir sind, was wir sind, vor allem, vielleicht sogar ausschließlich: zusammen. Die Entwicklung, durch die aus Gemeinschaften irgendwann Gesellschaften wurden, in deren Zuge Kultur und Wissen entstanden, ließe sich durchaus als eine Geschichte des mehr oder weniger Zusammens erzählen. Erfolgreich waren Menschen immer dann, wenn sie miteinander statt gegeneinander lebten, später Bestauntes entstand, wenn sie zusammenarbeiteten, Wissen, das als Fortschritt Geschichte machte, wurde von Köpfen entwickelt, die ins Gespräch kamen.
Umso verwunderlicher, dass dieses „Erfolgsrezept“ in Zeiten, wo es mehr denn je gebraucht wird, in den Hintergrund gedrängt wird. Wir leben infolge der Corona- Pandemie in einer Zeit, in der die Welt vor eine – wörtlich genommen – allumfassende Aufgabe gestellt ist, die sie, wie bereits vielfach geäußert, nur zusammen bewältigen kann. Und doch sorgen sich viele Menschen auf vielfältige Weise vor allem um ihr eigenes Wohl – nicht selten ohne zu reflektieren, dass auf diesem Wege das Wohl vieler anderer leidet und möglicherweise letztlich sogar ihr eigenes. Wenn es mehr Zusammen braucht, wo viel über Spaltung gesprochen wird, zeigt sich, dass der Erfolg des Miteinander kein Selbstläufer ist: Wenn wir zusammen etwas erreichen wollen, müssen wir über die Ziele und den Weg dorthin immer im Gespräch bleiben.
Was Menschen miteinander erreichen können und wie Wissenschaft das „Geheimnis des Zusammens“ an vielen Stellen zu ergründen versucht, haben wir für dieses Heft zusammengetragen. Wir haben ein Team von Umweltwissenschaftlerinnen und -wissenschaftlern besucht, die gemeinsam mit engagierten Bürgerinnen und Bürgern Waldgärten entwickeln – als grüne Oasen mitten in der Stadt. Wir haben Psychologinnen über die Schulter geschaut, die untersuchen, wie sich sexuelle Aggression unter jungen Menschen verringern lässt, und zwar gemeinsam. Eine Altphilologin hat uns erklärt, warum Mensch und Tier in antiken Fabeln eine ganz besondere Beziehung eingehen, und wir haben einen ersten Blick auf den Prototypen einer nationalen Bildungsplattform geworfen, die digitales Lernen aller Art künftig bündeln soll. Außerdem stellen wir zwei Modellprojekte vor, die auf unterschiedlichen Wegen Lehrenden sowie Schülerinnen und Schülern dabei helfen wollen, antidemokratischen Tendenzen und Hatespeech vorzubeugen. Nicht zuletzt präsentiert das Heft eine kleine Auswahl aus der Vielfalt der Kooperationen über Fach- und Ländergrenzen: Wir zeigen, wie Forschende aus der Rechtsund der Politikwissenschaft zusammen das Auf und Ab des Völkerrechts in den Blick nehmen, warum Religionswissenschaftlerinnen und -wissenschaftler aus Potsdam und dem Irak voneinander profitieren und wie die Uni Potsdam und die Europauniversität Viadrina in Frankfurt/Oder gemeinsam jüdische Friedhöfe in Brandenburg und Westpolen wiederentdecken.
Natürlich bringt das Heft darüber hinaus die ganze Breite der Forschung an der Uni Potsdam zusammen, versprochen! Wir haben uns schlau gemacht, wie aus Starkregen „flash floods“ werden und wie man sich darauf vorbereiten kann. Wir haben mit der Vizepräsidentin für Forschung Prof. Barbara Höhle über Anfänge und Zukünfte gesprochen, einen Migrationsforscher befragt und einen Geoforscher besucht, den es auf Berg und Tal gleichermaßen zieht. Es geht um – oft ungeschriebene – „body rules“ im Alltag, die höfische Minne und was sie uns heute noch zu sagen hat, die Erforschung unseres Blicks mithilfe Künstlicher Intelligenz, 33 Antworten voller Komplexität und die Mathematik im Unendlichen. Genug der Worte. Lesen Sie selbst – allein oder zusammen. Wie Sie wollen!
Portal Wissen = Together
(2022)
What makes humans human – and what distinguishes them from other creatures on Earth – has long been fervently discussed and is still being discussed today. “Homo sapiens”, the scientific self-description of our species, is already the characterization as an “understanding, wise, knowledgeable human being”. It could be argued that we owe this additional knowledge to our trait of (basically) feeling particularly attached to our equals. We are what we are, above all, and perhaps even exclusively: together. The development that eventually turned communities into societies in the course of which culture and knowledge emerged, could well be told as a story of more and less togetherness. People were always successful when they lived with instead of against each other. Things that were much admired later came into being when people worked together, knowledge that made history as progress was developed by minds that came into a conversation.
It is therefore all the more surprising that this “recipe for success” is being pushed into the background at a time when it is needed more than ever. As a result of the Corona pandemic, we are living in a time in which the world is faced with a – literally – all-encompassing task which it can only overcome together, as has already been said many times. And yet, many people are primarily concerned about their own well-being in various ways – not infrequently without reflecting that the well-being of many others, and possibly ultimately even their own, suffers as a consequence. When there is a need for more togetherness while there is a lot of talk about division, it becomes clear that the success of togetherness is not a foregone conclusion: If we want to achieve something together, we must always keep talking about the goals and the way to get there.
For this issue, we have collected what people can achieve together and how research is trying to fathom the “secret of togetherness” in many ways. We visited a team of environmental scientists who are developing forest gardens together with committed residents – as green oases in the middle of cities. We took a first look at the prototype of a national education platform that will bundle all kinds of digital learning in the future. We also present a model project that aims to help teachers and students prevent hate speech. Last but not least, the issue presents a small selection of various collaborations across disciplinary and national borders: We show how researchers from law and political science are working together to examine the ups and downs of international law, and why religious studies scholars from Potsdam and Iraq benefit from each other.
Of course, the issue also brings together the entire spectrum of research at the University of Potsdam, we promise! We found out how heavy rain turn into flash floods and how to prepare for such events. We interviewed a migration researcher and visited a geoscientist who is drawn to mountains and valleys alike. It’s about – often unwritten – “body rules” in everyday life, the exploration of our gaze with the help of artificial intelligence, 33 answers full of complexity, and about mathematics at infinity. Enough words. Read for yourself – alone or together. Just as you like!
Portal Wissen = Humans
(2022)
When humans write and talk about humans, you notice right away: It’s their favorite topic. It is not only that everyone (usually) is closest to themselves. As a species, Homo sapiens also attaches distinct importance to themselves. Aristotle was concerned about the order of things and ranked the human being – as the seemingly most complicated one – at the “very top.” The book of Genesis in the Bible seems to take this up, calling the human being in a way the final point or “pride of creation” who should “rule” over Earth and all living beings. An impressive story, but it did not stand the test of time. The theory of evolution changed the pyramid into a far-branched tree and the human being to a little branch among many others. What has remained is that humans are not so easy to understand, especially to themselves. Or, as Marie von Ebner-Eschenbach said, “The simplest human is still a very complicated being.”
This and the ongoing interest of humans in themselves ensure that many sciences also deal with him, her, or us, again and again and from every conceivable angle. Medicine and linguistics, educational research and psychology, history and sociology – many disciplines revolve around human(kind) and their actions. Therefore, it is hardly difficult to take a small exemplary human research journey through the University of Potsdam with this issue of “Portal Wissen.” We begin with a visit to the BabyLAB, where you can rewardingly watch even the youngest children learn languages. An economist points out that differences between men and women on their paychecks are anything but acceptable, and a start-up team showed us an app that can help you do something against dementia before it’s too late.
Besides, it should have been clear long ago: If we want to understand ourselves, we must always look at what is surrounding us. This means the social interactions that challenge and shape us on both a small and large scale. That’s why we talked to historians who are investigating corruption in the ancient world. But it also includes the environment, both living and non-living, on which we leave our mark and which, in turn, constantly influences us. A specialist in ancient DNA, for example, is investigating whether even Neanderthals left an ecological footprint, while an ecologist is searching for the consequences of climate change for biodiversity in Africa. And a media scientist has spent years analyzing how various images can help communicate scientific findings on climate change in such a way that they are understood.
We have not forgotten that the coronavirus continues to influence both our lives and research: A psychologist is working with partners throughout Germany to study how children and young people with chronic diseases get through the pandemic.
In addition, we naturally do not leave aside the diversity of research – created by humans – at the University of Potsdam: We introduce one of Germany’s best gravitational wave researcher and talk about the role of mathematics in earthquake research. Last but not least, we had the work of the new research center for digital data law explained to us.
Portal Wissen = Mensch
(2022)
Wenn Mensch über Mensch schreibt oder erzählt, dann merkt man gleich: Es ist sein Lieblingsthema. Nicht nur jede oder jeder Einzelne ist sich (meist) selbst der oder die Nächste. Auch als Art nimmt sich Homo sapiens unverkennbar wichtig. Aristoteles war um eine Ordnung der Dinge bemüht und sortierte den Menschen – als das am kompliziertesten erscheinende Wesen – ganz „nach oben“. Die Schöpfungsgeschichte in der Bibel scheint das aufzugreifen, benennt den Menschen gewissermaßen als Schlusspunkt oder „Krone der Schöpfung“, der über Erde und alles Lebendige „herrschen“ soll. Machte was her, hatte aber keinen Bestand. Die Evolutionstheorie hat aus der Pyramide einen weitverzweigten Baum und den Menschen zu einem Zweiglein unter vielen gemacht. Geblieben ist, dass Mensch nicht so einfach zu verstehen ist, vor allem nicht für sich selbst. Oder, wie Marie von Ebner-Eschenbach sagte: „Der einfachste Mensch ist immer noch ein sehr kompliziertes Wesen.“
Dies und das anhaltende Interesse des Menschen an sich selbst sorgen dafür, dass auch viele Wissenschaften sich immer wieder und aus allen erdenklichen Blickwinkeln mit ihm, ihr bzw. uns beschäftigen: Medizin und Linguistik, Bildungsforschung und Psychologie, Geschichte und Soziologie – viele Disziplinen kreisen unentwegt um Mensch(heit) und deren Wirken. Deshalb fällt es kaum schwer, mit dieser Ausgabe der „Portal Wissen“ eine kleine exemplarische Mensch-Forschungsreise durch die Universität Potsdam zu unternehmen. Wir beginnen mit einem Besuch im BabyLAB, wo schon den Kleinsten gewinnbringend beim Sprachenlernen zugeschaut wird, und lassen uns von Bildungsforschenden erklären, wie ihre Erkenntnisse in die Schule kommen. Eine Wirtschaftsexpertin zeigt auf, dass Unterschiede zwischen Männern und Frauen auf dem Gehaltszettel alles andere als akzeptabel sind, und ein Gründungstrio hat uns eine App vorgeführt, mit der man etwas gegen Demenz tun kann, bevor es zu spät ist.
Außerdem sollte eigentlich längst klar sein: Wenn wir uns verstehen wollen, müssen wir immer auch den Blick richten auf das, was uns umgibt. Das meint jenes soziale Miteinander, das uns im Kleinen wie im Großen fordert und prägt. Wir haben deshalb mit Historikern gesprochen, die Korruption in der Antike untersuchen, und Forschende aus der Soziologie gefragt, wohin unsere Gesellschaft steuert. Es meint aber auch die Umwelt, belebt wie unbelebt, der wir den Stempel aufdrücken, und die umgekehrt auch uns unentwegt beeinflusst. Ein Spezialist für alte DNA erforscht beispielsweise, ob schon der Neandertaler einen ökologischen Fußabdruck hinterließ, während eine Ökologin den Folgen des Klimawandels auf die Biodiversität in Afrika auf der Spur ist. Und eine Medienwissenschaftlerin hat über Jahre hinweg analysiert, wie Bilder aller Art dabei helfen können, wissenschaftliche Erkenntnisse zum Klimawandel so zu kommunizieren, dass sie auch verstanden werden.
Nicht vergessen haben wir, dass das Coronavirus nach wie vor unser Leben und auch die Forschung beeinflusst – und stellen deshalb drei Projekte vor, die verschiedene Facetten der Pandemie genauer unter die Lupe nehmen: Ein Team aus den Verwaltungswissenschaften hat analysiert, wie sich Deutschland im Vergleich zu anderen Ländern im Krisenmanagement schlägt, das Harding- Zentrum entwickelt Infomaterial, um Menschen aufgeklärt Entscheidungen in Sachen Impfen zu ermöglichen und eine Psychologin will mit Partnern in ganz Deutschland untersuchen, wie Kinder und Jugendliche mit chronischen Erkrankungen durch die Pandemie kommen.
Daneben lassen wir selbstverständlich nicht die – menschengemachte – Vielfalt der Forschung an der Uni Potsdam links liegen: Wir stellen einen der besten deutschen Gravitationswellenforscher vor, sprechen über links und rechts in der Pflanzenwelt und die Rolle der Mathematik in der Erdbebenforschung. Nicht zuletzt haben wir uns die Arbeit der neuen Forschungsstelle für digitales Datenrecht erklären lassen und der Direktorin des Moses-Mendelssohn-Zentrums 33 Fragen gestellt. Sie hat sie alle beantwortet – als Wissenschaftlerin und als Mensch.
Distances affect economic decision-making in numerous situations. The time at which we make a decision about future consumption has an impact on our consumption behavior. The spatial distance to employer, school or university impacts the place where we live and vice versa. The emotional closeness to other individuals influences our willingness to give money to them. This cumulative thesis aims to enrich the literature on the role of distance for economic decision-making. Thereby, each of my research projects sheds light on the impact of one kind of distance for efficient decision-making.
Against the background of the increasingly discussed “Linguistic Saving Hypothesis” (Chen, 2013), I studied whether the targeted use of a present tense (close tense) and a future tense (distant tense) within the same language have an impact on intertemporal decision-making. In a monetarily incentivized laboratory experiment in Germany, I implemented two different treatments on intertemporal choices. The treatments differed in the tense in which I referred to future rewards. My results show that individuals prefer to a greater extent rewards which are associated with a present tense (close tense). This result is in line with my prediction and the first empirical support for the Linguistic Saving Hypothesis within one language. However, this result holds exclusively for males. Females seem to be unaffected by the linguistic manipulation. I discuss my findings in the context of “gender-as-culture” as well as their potential policy-implications.
Privacy regulations and the physical distribution of heterogeneous data are often primary concerns for the development of deep learning models in a medical context. This paper evaluates the feasibility of differentially private federated learning for chest X-ray classification as a defense against data privacy attacks. To the best of our knowledge, we are the first to directly compare the impact of differentially private training on two different neural network architectures, DenseNet121 and ResNet50. Extending the federated learning environments previously analyzed in terms of privacy, we simulated a heterogeneous and imbalanced federated setting by distributing images from the public CheXpert and Mendeley chest X-ray datasets unevenly among 36 clients. Both non-private baseline models achieved an area under the receiver operating characteristic curve (AUC) of 0.940.94 on the binary classification task of detecting the presence of a medical finding. We demonstrate that both model architectures are vulnerable to privacy violation by applying image reconstruction attacks to local model updates from individual clients. The attack was particularly successful during later training stages. To mitigate the risk of a privacy breach, we integrated Rényi differential privacy with a Gaussian noise mechanism into local model training. We evaluate model performance and attack vulnerability for privacy budgets ε∈{1,3,6,10}�∈{1,3,6,10}. The DenseNet121 achieved the best utility-privacy trade-off with an AUC of 0.940.94 for ε=6�=6. Model performance deteriorated slightly for individual clients compared to the non-private baseline. The ResNet50 only reached an AUC of 0.760.76 in the same privacy setting. Its performance was inferior to that of the DenseNet121 for all considered privacy constraints, suggesting that the DenseNet121 architecture is more robust to differentially private training.
Biofilms are complex living materials that form as bacteria get embedded in a matrix of self-produced protein and polysaccharide fibres. The formation of a network of extracellular biopolymer fibres contributes to the cohesion of the biofilm by promoting cell-cell attachment and by mediating biofilm-substrate interactions. This sessile mode of bacteria growth has been well studied by microbiologists to prevent the detrimental effects of biofilms in medical and industrial settings. Indeed, biofilms are associated with increased antibiotic resistance in bacterial infections, and they can also cause clogging of pipelines or promote bio-corrosion. However, biofilms also gained interest from biophysics due to their ability to form complex morphological patterns during growth. Recently, the emerging field of engineered living materials investigates biofilm mechanical properties at multiple length scales and leverages the tools of synthetic biology to tune the functions of their constitutive biopolymers.
This doctoral thesis aims at clarifying how the morphogenesis of Escherichia coli (E. coli) biofilms is influenced by their growth dynamics and mechanical properties. To address this question, I used methods from cell mechanics and materials science. I first studied how biological activity in biofilms gives rise to non-uniform growth patterns. In a second study, I investigated how E. coli biofilm morphogenesis and its mechanical properties adapt to an environmental stimulus, namely the water content of their substrate. Finally, I estimated how the mechanical properties of E. coli biofilms are altered when the bacteria express different extracellular biopolymers.
On nutritive hydrogels, micron-sized E. coli cells can build centimetre-large biofilms. During this process, bacterial proliferation and matrix production introduce mechanical stresses in the biofilm, which release through the formation of macroscopic wrinkles and delaminated buckles. To relate these biological and mechanical phenomena, I used time-lapse fluorescence imaging to track cell and matrix surface densities through the early and late stages of E. coli biofilm growth. Colocalization of high cell and matrix densities at the periphery precede the onset of mechanical instabilities at this annular region. Early growth is detected at this outer annulus, which was analysed by adding fluorescent microspheres to the bacterial inoculum. But only when high rates of matrix production are present in the biofilm centre, does overall biofilm spreading initiate along the solid-air interface. By tracking larger fluorescent particles for a long time, I could distinguish several kinematic stages of E. coli biofilm expansion and observed a transition from non-linear to linear velocity profiles, which precedes the emergence of wrinkles at the biofilm periphery. Decomposing particle velocities to their radial and circumferential components revealed a last kinematic stage, where biofilm movement is mostly directed towards the radial delaminated buckles, which verticalize. The resulting compressive strains computed in these regions were observed to substantially deform the underlying agar substrates. The co-localization of higher cell and matrix densities towards an annular region and the succession of several kinematic stages are thus expected to promote the emergence of mechanical instabilities at the biofilm periphery. These experimental findings are predicted to advance future modelling approaches of biofilm morphogenesis.
E. coli biofilm morphogenesis is further anticipated to depend on external stimuli from the environment. To clarify how the water could be used to tune biofilm material properties, we quantified E. coli biofilm growth, wrinkling dynamics and rigidity as a function of the water content of the nutritive substrates. Time-lapse microscopy and computational image analysis revealed that substrates with high water content promote biofilm spreading kinetics, while substrates with low water content promote biofilm wrinkling. The wrinkles observed on biofilm cross-sections appeared more bent on substrates with high water content, while they tended to be more vertical on substrates with low water content. Both wet and dry biomass, accumulated over 4 days of culture, were larger in biofilms cultured on substrates with high water content, despite extra porosity within the matrix layer. Finally, the micro-indentation analysis revealed that substrates with low water content supported the formation of stiffer biofilms. This study shows that E. coli biofilms respond to the water content of their substrate, which might be used for tuning their material properties in view of further applications.
Biofilm material properties further depend on the composition and structure of the matrix of extracellular proteins and polysaccharides. In particular, E. coli biofilms were suggested to present tissue-like elasticity due to a dense fibre network consisting of amyloid curli and phosphoethanolamine-modified cellulose. To understand the contribution of these components to the emergent mechanical properties of E. coli biofilms, we performed micro-indentation on biofilms grown from bacteria of several strains. Besides showing higher dry masses, larger spreading diameters and slightly reduced water contents, biofilms expressing both main matrix components also presented high rigidities in the range of several hundred kPa, similar to biofilms containing only curli fibres. In contrast, a lack of amyloid curli fibres provides much higher adhesive energies and more viscoelastic fluid-like material behaviour. Therefore, the combination of amyloid curli and phosphoethanolamine-modified cellulose fibres implies the formation of a composite material whereby the amyloid curli fibres provide rigidity to E. coli biofilms, whereas the phosphoethanolamine-modified cellulose rather acts as a glue. These findings motivate further studies involving purified versions of these protein and polysaccharide components to better understand how their interactions benefit biofilm functions.
All three studies depict different aspects of biofilm morphogenesis, which are interrelated. The first work reveals the correlation between non-uniform biological activities and the emergence of mechanical instabilities in the biofilm. The second work acknowledges the adaptive nature of E. coli biofilm morphogenesis and its mechanical properties to an environmental stimulus, namely water. Finally, the last study reveals the complementary role of the individual matrix components in the formation of a stable biofilm material, which not only forms complex morphologies but also functions as a protective shield for the bacteria it contains. Our experimental findings on E. coli biofilm morphogenesis and their mechanical properties can have further implications for fundamental and applied biofilm research fields.
In the present thesis I investigate the lattice dynamics of thin film hetero structures of magnetically ordered materials upon femtosecond laser excitation as a probing and manipulation scheme for the spin system. The quantitative assessment of laser induced thermal dynamics as well as generated picosecond acoustic pulses and their respective impact on the magnetization dynamics of thin films is a challenging endeavor. All the more, the development and implementation of effective experimental tools and comprehensive models are paramount to propel future academic and technological progress.
In all experiments in the scope of this cumulative dissertation, I examine the crystal lattice of nanoscale thin films upon the excitation with femtosecond laser pulses. The relative change of the lattice constant due to thermal expansion or picosecond strain pulses is directly monitored by an ultrafast X-ray diffraction (UXRD) setup with a femtosecond laser-driven plasma X-ray source (PXS). Phonons and spins alike exert stress on the lattice, which responds according to the elastic properties of the material, rendering the lattice a versatile sensor for all sorts of ultrafast interactions. On the one hand, I investigate materials with strong magneto-elastic properties; The highly magnetostrictive rare-earth compound TbFe2, elemental Dysprosium or the technological relevant Invar material FePt. On the other hand I conduct a comprehensive study on the lattice dynamics of Bi1Y2Fe5O12 (Bi:YIG), which exhibits high-frequency coherent spin dynamics upon femtosecond laser excitation according to the literature. Higher order standing spinwaves (SSWs) are triggered by coherent and incoherent motion of atoms, in other words phonons, which I quantified with UXRD. We are able to unite the experimental observations of the lattice and magnetization dynamics qualitatively and quantitatively. This is done with a combination of multi-temperature, elastic, magneto-elastic, anisotropy and micro-magnetic modeling.
The collective data from UXRD, to probe the lattice, and time-resolved magneto-optical Kerr effect (tr-MOKE) measurements, to monitor the magnetization, were previously collected at different experimental setups. To improve the precision of the quantitative assessment of lattice and magnetization dynamics alike, our group implemented a combination of UXRD and tr-MOKE in a singular experimental setup, which is to my knowledge, the first of its kind. I helped with the conception and commissioning of this novel experimental station, which allows the simultaneous observation of lattice and magnetization dynamics on an ultrafast timescale under identical excitation conditions. Furthermore, I developed a new X-ray diffraction measurement routine which significantly reduces the measurement time of UXRD experiments by up to an order of magnitude. It is called reciprocal space slicing (RSS) and utilizes an area detector to monitor the angular motion of X-ray diffraction peaks, which is associated with lattice constant changes, without a time-consuming scan of the diffraction angles with the goniometer. RSS is particularly useful for ultrafast diffraction experiments, since measurement time at large scale facilities like synchrotrons and free electron lasers is a scarce and expensive resource. However, RSS is not limited to ultrafast experiments and can even be extended to other diffraction techniques with neutrons or electrons.
StudyMe
(2022)
N-of-1 trials are multi-crossover self-experiments that allow individuals to systematically evaluate the effect of interventions on their personal health goals. Although several tools for N-of-1 trials exist, there is a gap in supporting non-experts in conducting their own user-centric trials. In this study, we present StudyMe, an open-source mobile application that is freely available from https://play.google.com/store/apps/details?id=health.studyu.me and offers users flexibility and guidance in configuring every component of their trials. We also present research that informed the development of StudyMe, focusing on trial creation. Through an initial survey with 272 participants, we learned that individuals are interested in a variety of personal health aspects and have unique ideas on how to improve them. In an iterative, user-centered development process with intermediate user tests, we developed StudyMe that features an educational part to communicate N-of-1 trial concepts. A final empirical evaluation of StudyMe showed that all participants were able to create their own trials successfully using StudyMe and the app achieved a very good usability rating. Our findings suggest that StudyMe provides a significant step towards enabling individuals to apply a systematic science-oriented approach to personalize health-related interventions and behavior modifications in their everyday lives.
The Greenland Ice Sheet is the second-largest mass of ice on Earth. Being almost 2000 km long, more than 700 km wide, and more than 3 km thick at the summit, it holds enough ice to raise global sea levels by 7m if melted completely. Despite its massive size, it is particularly vulnerable to anthropogenic climate change: temperatures over the Greenland Ice Sheet have increased by more than 2.7◦C in the past 30 years, twice as much as the global mean temperature. Consequently, the ice sheet has been significantly losing mass since the 1980s and the rate of loss has increased sixfold since then. Moreover, it is one of the potential tipping elements of the Earth System, which might undergo irreversible change once a warming threshold is exceeded. This thesis aims at extending the understanding of the resilience of the Greenland Ice Sheet against global warming by analyzing processes and feedbacks relevant to its centennial to multi-millennial stability using ice sheet modeling.
One of these feedbacks, the melt-elevation-feedback is driven by the temperature rise with decreasing altitudes: As the ice sheet melts, its thickness and surface elevation decrease, exposing the ice surface to warmer air and thus increasing the melt rates even further. The glacial isostatic adjustment (GIA) can partly mitigate this melt-elevation feedback as the bedrock lifts in response to an ice load decrease, forming the negative GIA feedback. In my thesis, I show that the interaction between these two competing feedbacks can lead to qualitatively different dynamical responses of the Greenland Ice Sheet to warming – from permanent loss to incomplete recovery, depending on the feedback parameters. My research shows that the interaction of those feedbacks can initiate self-sustained oscillations of the ice volume while the climate forcing remains constant.
Furthermore, the increased surface melt changes the optical properties of the snow or ice surface, e.g. by lowering their albedo, which in turn enhances melt rates – a process known as the melt-albedo feedback. Process-based ice sheet models often neglect this melt-albedo feedback. To close this gap, I implemented a simplified version of the diurnal Energy Balance Model, a computationally efficient approach that can capture the first-order effects of the melt-albedo feedback, into the Parallel Ice Sheet Model (PISM). Using the coupled model, I show in warming experiments that the melt-albedo feedback almost doubles the ice loss until the year 2300 under the low greenhouse gas emission scenario RCP2.6, compared to simulations where the melt-albedo feedback is neglected,
and adds up to 58% additional ice loss under the high emission scenario RCP8.5. Moreover, I find that the melt-albedo feedback dominates the ice loss until 2300, compared to the melt-elevation feedback.
Another process that could influence the resilience of the Greenland Ice Sheet is the warming induced softening of the ice and the resulting increase in flow. In my thesis, I show with PISM how the uncertainty in Glen’s flow law impacts the simulated response to warming. In a flow line setup at fixed climatic mass balance, the uncertainty in flow parameters leads to a range of ice loss comparable to the range caused by different warming levels.
While I focus on fundamental processes, feedbacks, and their interactions in the first three projects of my thesis, I also explore the impact of specific climate scenarios on the sea level rise contribution of the Greenland Ice Sheet. To increase the carbon budget flexibility, some warming scenarios – while still staying within the limits of the Paris Agreement – include a temporal overshoot of global warming. I show that an overshoot by 0.4◦C increases the short-term and long-term ice loss from Greenland by several centimeters. The long-term increase is driven by the warming at high latitudes, which persists even when global warming is reversed. This leads to a substantial long-term commitment of the sea level rise contribution from the Greenland Ice Sheet.
Overall, in my thesis I show that the melt-albedo feedback is most relevant for the ice loss of the Greenland Ice Sheet on centennial timescales. In contrast, the melt-elevation feedback and its interplay with the GIA feedback become increasingly relevant on millennial timescales. All of these influence the resilience of the Greenland Ice Sheet against global warming, in the near future and on the long term.
Überzeugungen zum Lehren und Lernen sind als Teil der professionellen Kompetenz von Lehrkräften bereits im Lehramtsstudium relevant und haben insbesondere in längeren Praxisphasen Entwicklungspotenzial. Welche Faktoren für die Entwicklung von Überzeugungen in Praxisphasen von Bedeutung sind, ist bislang aber nur unzureichend erforscht. In Interviews haben wir N = 16 Studierende befragt, welche Lerngelegenheiten für die Entwicklung ihrer Überzeugungen im Praxissemester eine Rolle spielten. Dabei konnten wir mittels Inhaltsanalyse vier übergeordnete Faktoren identifizieren: die universitäre Lernbegleitung, die Mentorinnen und Mentoren, die Schülerinnen und Schüler und die Reflexion eigener Unterrichtserfahrungen. Den Faktoren wurden untergeordnete Faktoren (z. B. Hospitationen durch Universitätsdozierende) zugeordnet und es wird dargestellt, warum und unter welchen Umständen diese Lerngelegenheiten für die Entwicklung der Überzeugungen aus Studierendensicht relevant sind.
The world energy consumption has constantly increased every year due to economic development and population growth. This inevitably caused vast amount of CO2 emission, and the CO2 concentration in the atmosphere keeps increasing with economic growth. To reduce CO2 emission, various methods have been developed but there are still many bottlenecks to be solved. Solvents easily absorbing CO2 such as monoethanol-amine (MEA) and diethanolamine, for example, have limitations of solvent loss, amine degradation, vulnerability to heat and toxicity, and the high cost of regeneration which is especially caused due to chemisorption process. Though some of these drawbacks can be compensated through physisorption with zeolites and metal-organic frameworks (MOFs) by displaying significant adsorption selectivity and capacity even in ambient conditions, limitations for these materials still exist. Zeolites demand relatively high regeneration energy and have limited adsorption kinetics due to the exceptionally narrow pore structure. MOFs have low stability against heat and moisture and high manufacturing cost.
Nanoporous carbons have recently received attention as an attractive functional porous material due to their unique properties. These materials are crucial in many applications of modern science and industry such as water and air purification, catalysis, gas separation, and energy storage/conversion due to their high chemical and thermal stability, and in particular electronic conductivity in combination with high specific surface areas. Nanoporous carbons can be used to adsorb environmental pollutants or small gas molecules such as CO2 and to power electrochemical energy storage devices such as batteries and fuel cells. In all fields, their pore structure or electrical properties can be modified depending on their purposes.
This thesis provides an in-depth look at novel nanoporous carbons from the synthetic and the application point of view. The interplay between pore structure, atomic construction, and the adsorption properties of nanoporous carbon materials are investigated. Novel nanoporous carbon materials are synthesized by using simple precursor molecules containing heteroatoms through a facile
templating method. The affinity, and in turn the adsorption capacity, of carbon materials toward polar gas molecules (CO2 and H2O) is enhanced by the modification of their chemical construction. It is also shown that these properties are important in electrochemical energy storage, here especially for supercapacitors with aqueous electrolytes which are basically based on the physisorption of ions on carbon surfaces. This shows that nanoporous carbons can be a “functional” material with specific physical or chemical interactions with guest species just like zeolites and MOFs.
The synthesis of sp2-conjugated materials with high heteroatom content from a mixture of citrazinic acid and melamine in which heteroatoms are already bonded in specific motives is illustrated. By controlling the removal procedure of the salt-template and the condensation temperature, the role of salts in the formation of porosity and as coordination sites for the stabilization of heteroatoms is proven. A high amount of nitrogen of up to 20 wt. %, oxygen contents of up to 19 wt.%, and a high CO2/N2 selectivity with maximum CO2 uptake at 273 K of 5.31 mmol g–1 are achieved. Besides, the further controlled thermal condensation of precursor molecules and advanced functional properties on applications of the synthesized porous carbons are described. The materials have different porosity and atomic construction exhibiting a high nitrogen content up to 25 wt. % as well as a high porosity with a specific surface area of more than 1800 m2 g−1, and a high performance in selective CO2 gas adsorption of 62.7. These pore structure as well as properties of surface affect to water adsorption with a remarkably high Qst of over 100 kJ mol−1 even higher than that of zeolites or CaCl2 well known as adsorbents. In addition to that, the pore structure of HAT-CN-derived carbon materials during condensation in vacuum is fundamentally understood which is essential to maximize the utilization of porous system in materials showing significant difference in their pore volume of 0.5 cm3 g−1 and 0.25 cm3 g−1 without and with vacuum, respectively.
The molecular designs of heteroatom containing porous carbon derived from abundant and simple molecules are introduced in the presented thesis. Abundant precursors that already containing high amount of nitrogen or oxygen are beneficial to achieve enhanced interaction with adsorptives. The physical and chemical properties of these heteroatom-doped porous carbons are affected by mainly two parameters, that is, the porosity from the pore structure and the polarity from the atomic composition on the surface. In other words, controlling the porosity as well as the polarity of the carbon materials is studied to understand interactions with different guest species which is a fundamental knowledge for the utilization on various applications.
Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.
This study examined the spoken narrative skills of a group of bilingual Mandarin–English speaking 3–6-year-olds (N = 25) in Australia, using a remote online story-retell task. Bilingual preschoolers are an understudied population, especially those who are speaking typologically distinct languages such as Mandarin and English which have fewer structural overlaps compared to language pairs that are typologically closer, reducing cross-linguistic positive transfer. We examined these preschoolers’ spoken narrative skills as measured by macrostructures (the global organization of a story) and microstructures (linguistic structures, e.g., total number of utterances, nouns, verbs, phrases, and modifiers) across and within each language, and how various factors such as age and language experiences contribute to individual variability. The results indicate that our bilingual preschoolers acquired spoken narrative skills similarly across their two languages, i.e., showing similar patterns of productivity for macrostructure and microstructure elements in both of their two languages. While chronological age was positively correlated with macrostructures in both languages (showing developmental effects), there were no significant correlations between measures of language experiences and the measures of spoken narrative skills (no effects for language input/output). The findings suggest that although these preschoolers acquire two typologically diverse languages in different learning environments, Mandarin at home with highly educated parents, and English at preschool, they displayed similar levels of oral narrative skills as far as these macro−/micro-structure measures are concerned. This study provides further evidence for the feasibility of remote online assessment of preschoolers’ narrative skills.
We introduce and study a Lévy walk (LW) model of particle spreading with a finite propagation speed combined with soft resets, stochastically occurring periods in which an harmonic external potential is switched on and forces the particle towards a specific position. Soft resets avoid instantaneous relocation of particles that in certain physical settings may be considered unphysical. Moreover, soft resets do not have a specific resetting point but lead the particle towards a resetting point by a restoring Hookean force. Depending on the exact choice for the LW waiting time density and the probability density of the periods when the harmonic potential is switched on, we demonstrate a rich emerging response behaviour including ballistic motion and superdiffusion. When the confinement periods of the soft-reset events are dominant, we observe a particle localisation with an associated non-equilibrium steady state. In this case the stationary particle probability density function turns out to acquire multimodal states. Our derivations are based on Markov chain ideas and LWs with multiple internal states, an approach that may be useful and flexible for the investigation of other generalised random walks with soft and hard resets. The spreading efficiency of soft-rest LWs is characterised by the first-passage time statistic.
Flood risk management in Germany follows an integrative approach in which both private households and businesses can make an important contribution to reducing flood damage by implementing property-level adaptation measures. While the flood adaptation behavior of private households has already been widely researched, comparatively less attention has been paid to the adaptation strategies of businesses. However, their ability to cope with flood risk plays an important role in the social and economic development of a flood-prone region. Therefore, using quantitative survey data, this study aims to identify different strategies and adaptation drivers of 557 businesses damaged by a riverine flood in 2013 and 104 businesses damaged by pluvial or flash floods between 2014 and 2017. Our results indicate that a low perceived self-efficacy may be an important factor that can reduce the motivation of businesses to adapt to flood risk. Furthermore, property-owners tended to act more proactively than tenants. In addition, high experience with previous flood events and low perceived response costs could strengthen proactive adaptation behavior. These findings should be considered in business-tailored risk communication.
Einleitung: Bisherige Untersuchungen deuten darauf hin, dass etwa 30-40 % der PatientInnen in der kardiologischen Rehabilitation eine besondere berufliche Problemlage (BBPL) aufweisen. Die hindernden und fördernden Faktoren des beruflichen Wiedereinstiegs wurden vielfach untersucht. Beispielsweise können eine positive Gesundheitswahrnehmung, Beschwerdefreiheit und Berufszufriedenheit als Förderfaktoren, und Komorbiditäten, die Krankheitsschwere, motivationale Gründe sowie das Alter beispielhaft als Hindernisse benannt werden. In dieser Arbeit sollten die Faktoren, die die subjektiven Berufsaussichten von PatientInnen in der kardiologischen Anschlussheilbehandlung (AHB) bestimmen, identifiziert und beschrieben werden. Daraus sollten Impulse für ein patientInnenzentriertes Vorgehen in der AHB abgeleitet werden.
Methode: In einer qualitativen, monozentrischen Interviewstudie wurden insgesamt 20 PatientInnen mit und ohne BBPL in der kardiologischen AHB als ExpertInnen gefragt, um die subjektiven Erwerbserwartungen zu eruieren und die PatientInnenperspektive besser zu verstehen. Die Interviews wurden aufgezeichnet, transkribiert und codiert. Die Auswertung erfolgte mittels der thematischen Analyse.
Ergebnisse: Es wurden sieben Schlüsselthemen identifiziert. Hierzu gehörten die krankheitsbezogenen Vorerfahrungen sowie Zukunftsvorstellungen als perspektivische Einflussfaktoren. Außerdem wurden interne und externe Aspekte, darunter die Gesundheitswahrnehmung (inkl. Belastbarkeitseinschätzung), die Veränderbarkeit der Arbeitsbedingungen und die Angst, erneut zu erkranken, als bedeutsame Themen ermittelt. Deutlich wurde auch, dass die BBPL-PatientInnen in das Berufsleben zurückkehren wollten, das kardiologische Ereignis jedoch zu einer wahrgenommenen Notwendigkeit für Lebensstil- und Prioritätenänderungen geführt hat. Zur Umsetzung dieser wollten sich die PatientInnen Zeit nehmen, auch das soziale Umfeld unterstützte die Priorisierung der Gesundheit.
Schlussfolgerung: Hieraus ergibt sich die Notwendigkeit einer multiprofessionellen, dabei individuell-differenzierten Herangehensweise in der kardiologischen AHB. Ein besonderer Fokus sollte auf der Berücksichtigung der Selbsterwartung, der individuellen Zielsetzung im Hinblick auf die Berufszukunft und dem Einbeziehen des sozialen Umfelds liegen. Des Weiteren wird eine Überarbeitung des BBPL-Begriffes vorgeschlagen, da die Zuweisung einer solchen Problemlage durch den Kostenträger paradox und stigmatisierend erscheint.