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Among the multitude of geomorphological processes, aeolian shaping processes are of special character, Pedogenic dust is one of the most important sources of atmospheric aerosols and therefore regarded as a key player for atmospheric processes. Soil dust emissions, being complex in composition and properties, influence atmospheric processes and air quality and has impacts on other ecosystems. In this because even though their immediate impact can be considered low (exceptions exist), their constant and large-scale force makes them a powerful player in the earth system. dissertation, we unravel a novel scientific understanding of this complex system based on a holistic dataset acquired during a series of field experiments on arable land in La Pampa, Argentina. The field experiments as well as the generated data provide information about topography, various soil parameters, the atmospheric dynamics in the very lower atmosphere (4m height) as well as measurements regarding aeolian particle movement across a wide range of particle size classes between 0.2μm up to the coarse sand.
The investigations focus on three topics: (a) the effects of low-scale landscape structures on aeolian transport processes of the coarse particle fraction, (b) the horizontal and vertical fluxes of the very fine particles and (c) the impact of wind gusts on particle emissions.
Among other considerations presented in this thesis, it could in particular be shown, that even though the small-scale topology does have a clear impact on erosion and deposition patterns, also physical soil parameters need to be taken into account for a robust statistical modelling of the latter. Furthermore, specifically the vertical fluxes of particulate matter have different characteristics for the particle size classes. Finally, a novel statistical measure was introduced to quantify the impact of wind gusts on the particle uptake and its application on the provided data set. The aforementioned measure shows significantly increased particle concentrations during points in time defined as gust event.
With its holistic approach, this thesis further contributes to the fundamental understanding of how atmosphere and pedosphere are intertwined and affect each other.
Vom Monomer zum Glykopolymer
(2019)
Glykopolymere sind synthetische und natürlich vorkommende Polymere, die eine Glykaneinheit in der Seitenkette des Polymers tragen. Glykane sind durch die Glykan-Protein-Wechselwirkung verantwortlich für viele biologische Prozesse. Die Beteiligung der Glykanen in diesen biologischen Prozessen ermöglicht das Imitieren und Analysieren der Wechselwirkungen durch geeignete Modellverbindungen, z.B. der Glykopolymere. Dieses System der Glykan-Protein-Wechselwirkung soll durch die Glykopolymere untersucht und studiert werden, um die spezifische und selektive Bindung der Proteine an die Glykopolymere nachzuweisen. Die Proteine, die in der Lage sind, Kohlenhydratstrukturen selektiv zu binden, werden Lektine genannt.
In dieser Dissertationsarbeit wurden verschiedene Glykopolymere synthetisiert. Dabei sollte auf einen effizienten und kostengünstigen Syntheseweg geachtet werden.
Verschiedene Glykopolymere wurden durch funktionalisierte Monomere mit verschiedenen Zuckern, wie z.B. Mannose, Laktose, Galaktose oder N-Acetyl-Glukosamin als funktionelle Gruppe, hergestellt. Aus diesen funktionalisierten Glykomonomeren wurden über ATRP und RAFT-Polymerisation Glykopolymere synthetisiert.
Die erhaltenen Glykopolymere wurden in Diblockcopolymeren als hydrophiler Block angewendet und die Selbstassemblierung in wässriger Lösung untersucht. Die Polymere formten in wässriger Lösung Mizellen, bei denen der Zuckerblock an der Oberfläche der Mizellen sitzt. Die Mizellen wurden mit einem hydrophoben Fluoreszenzfarbstoff beladen, wodurch die CMC der Mizellenbildung bestimmt werden konnte.
Außerdem wurden die Glykopolymere als Oberflächenbeschichtung über „Grafting from“ mit SI-ATRP oder über „Grafting to“ auf verschiedene Oberflächen gebunden. Durch die glykopolymerbschichteten Oberflächen konnte die Glykan Protein Wechselwirkung über spektroskopische Messmethoden, wie SPR- und Mikroring Resonatoren untersucht werden. Hierbei wurde die spezifische und selektive Bindung der Lektine an die Glykopolymere nachgewiesen und die Bindungsstärke untersucht.
Die synthetisierten Glykopolymere könnten durch Austausch der Glykaneinheit für andere Lektine adressierbar werden und damit ein weites Feld an anderen Proteinen erschließen. Die bioverträglichen Glykopolymere wären alternativen für den Einsatz in biologischen Prozessen als Transporter von Medikamenten oder Farbstoffe in den Körper. Außerdem könnten die funktionalisierten Oberflächen in der Diagnostik zum Erkennen von Lektinen eingesetzt werden. Die Glykane, die keine selektive und spezifische Bindung zu Proteinen eingehen, könnten als antiadsorptive Oberflächenbeschichtung z.B. in der Zellbiologie eingesetzt werden.
Vom Gast zum Gastwirt?
(2021)
Die Arbeitsmigration zählt zu den prägenden gesellschaftlichen Wandlungsprozessen der deutschen Nachkriegsgeschichte. 14 Millionen »Gastarbeiter« kamen zwischen 1955 und 1973 in die Bundesrepublik, etwa 3 Millionen von ihnen kehrten nicht in ihre Heimatländer zurück. Vor allem Türkeistämmige blieben nach dem Anwerbestopp häufiger in Deutschland als die Arbeitskräfte aus anderen Ländern. Wie keine andere Stadt steht Berlin bis heute für die Einwanderung aus der Türkei.
Stefan Zeppenfeld untersucht den Wandel der türkischen Arbeitswelten von ihren Anfängen in den 1960er Jahren bis zur Wiedervereinigung. Ausgehend von der »Gastarbeit« im industriellen Großbetrieb spürt er in seiner Studie am Beispiel West-Berlins dem Übergang in andere Branchen nach. Er zeigt, wie der öffentliche Dienst auch für Migrantinnen und Migranten attraktive Aufstiegsmöglichkeiten eröffnete, zeichnet den schwierigen Weg in die gewerbliche Selbstständigkeit nach und legt illegale Beschäftigungsformen als alternative Verdienstmöglichkeit offen.
Damit bettet der Autor die Geschichte der türkischen Arbeitsmigration in die deutsche Zeitgeschichte ein.
Large-scale volcanic deformation recently detected by radar interferometry (InSAR) provides new information and thus new scientific challenges for understanding volcano-tectonic activity and magmatic systems. The destabilization of such a system at depth noticeably affects the surrounding environment through magma injection, ground displacement and volcanic eruptions. To determine the spatiotemporal evolution of the Lazufre volcanic area located in the central Andes, we combined short-term ground displacement acquired by InSAR with long-term geological observations. Ground displacement was first detected using InSAR in 1997. By 2008, this displacement affected 1800 km2 of the surface, an area comparable in size to the deformation observed at caldera systems. The original displacement was followed in 2000 by a second, small-scale, neighbouring deformation located on the Lastarria volcano. We performed a detailed analysis of the volcanic structures at Lazufre and found relationships with the volcano deformations observed with InSAR. We infer that these observations are both likely to be the surface expression of a long-lived magmatic system evolving at depth. It is not yet clear whether Lazufre may trigger larger unrest or volcanic eruptions; however, the second deformation detected at Lastarria and the clear increase of the large-scale deformation rate make this an area of particular interest for closer continuous monitoring.
In the last century, several astronomical measurements have supported that a significant percentage (about 22%) of the total mass of the Universe, on galactic and extragalactic scales, is composed of a mysterious ”dark” matter (DM). DM does not interact with the electromagnetic force; in other words it does not reflect, absorb or emit light. It is possible that DM particles are weakly interacting massive particles (WIMPs) that can annihilate (or decay) into Standard Model (SM) particles, and modern very- high-energy (VHE; > 100 GeV) instruments such as imaging atmospheric Cherenkov telescopes (IACTs) can play an important role in constraining the main properties of such DM particles, by detecting these products. One of the most privileged targets where to look for DM signal are dwarf spheroidal galaxies (dSphs), as they are expected to be high DM-dominated objects with a clean, gas-free environment. Some dSphs could be considered as extended sources, considering the angular resolution of IACTs; their angu- lar resolution is adequate to detect extended emission from dSphs. For this reason, we performed an extended-source analysis, by taking into account in the unbinned maximum likelihood estimation both the energy and the angular extension dependency of observed events. The goal was to set more constrained upper limits on the velocity-averaged cross-section annihilation of WIMPs with VERITAS data. VERITAS is an array of four IACTs, able to detect γ-ray photons ranging between 100 GeV and 30 TeV. The results of this extended analysis were compared against the traditional spectral analysis. We found that a 2D analysis may lead to more constrained results, depending on the DM mass, channel, and source. Moreover, in this thesis, the results of a multi-instrument project are presented too. Its goal was to combine already published 20 dSphs data from five different experiments, such as Fermi-LAT, MAGIC, H.E.S.S., VERITAS and HAWC, in order to set upper limits on the WIMP annihilation cross-section in the widest mass range ever reported.
Air pollution has been a persistent global problem in the past several hundred years. While some industrialized nations have shown improvements in their air quality through stricter regulation, others have experienced declines as they rapidly industrialize. The WHO’s 2021 update of their recommended air pollution limit values reflects the substantial impacts on human health of pollutants such as NO2 and O3, as recent epidemiological evidence suggests substantial long-term health impacts of air pollution even at low concentrations. Alongside developments in our understanding of air pollution's health impacts, the new technology of low-cost sensors (LCS) has been taken up by both academia and industry as a new method for measuring air pollution. Due primarily to their lower cost and smaller size, they can be used in a variety of different applications, including in the development of higher resolution measurement networks, in source identification, and in measurements of air pollution exposure. While significant efforts have been made to accurately calibrate LCS with reference instrumentation and various statistical models, accuracy and precision remain limited by variable sensor sensitivity. Furthermore, standard procedures for calibration still do not exist and most proprietary calibration algorithms are black-box, inaccessible to the public. This work seeks to expand the knowledge base on LCS in several different ways: 1) by developing an open-source calibration methodology; 2) by deploying LCS at high spatial resolution in urban environments to test their capability in measuring microscale changes in urban air pollution; 3) by connecting LCS deployments with the implementation of local mobility policies to provide policy advice on resultant changes in air quality.
In a first step, it was found that LCS can be consistently calibrated with good performance against reference instrumentation using seven general steps: 1) assessing raw data distribution, 2) cleaning data, 3) flagging data, 4) model selection and tuning, 5) model validation, 6) exporting final predictions, and 7) calculating associated uncertainty. By emphasizing the need for consistent reporting of details at each step, most crucially on model selection, validation, and performance, this work pushed forward with the effort towards standardization of calibration methodologies. In addition, with the open-source publication of code and data for the seven-step methodology, advances were made towards reforming the largely black-box nature of LCS calibrations.
With a transparent and reliable calibration methodology established, LCS were then deployed in various street canyons between 2017 and 2020. Using two types of LCS, metal oxide (MOS) and electrochemical (EC), their performance in capturing expected patterns of urban NO2 and O3 pollution was evaluated. Results showed that calibrated concentrations from MOS and EC sensors matched general diurnal patterns in NO2 and O3 pollution measured using reference instruments. While MOS proved to be unreliable for discerning differences among measured locations within the urban environment, the concentrations measured with calibrated EC sensors matched expectations from modelling studies on NO2 and O3 pollution distribution in street canyons. As such, it was concluded that LCS are appropriate for measuring urban air quality, including for assisting urban-scale air pollution model development, and can reveal new insights into air pollution in urban environments.
To achieve the last goal of this work, two measurement campaigns were conducted in connection with the implementation of three mobility policies in Berlin. The first involved the construction of a pop-up bike lane on Kottbusser Damm in response to the COVID-19 pandemic, the second surrounded the temporary implementation of a community space on Böckhstrasse, and the last was focused on the closure of a portion of Friedrichstrasse to all motorized traffic. In all cases, measurements of NO2 were collected before and after the measure was implemented to assess changes in air quality resultant from these policies. Results from the Kottbusser Damm experiment showed that the bike-lane reduced NO2 concentrations that cyclists were exposed to by 22 ± 19%. On Friedrichstrasse, the street closure reduced NO2 concentrations to the level of the urban background without worsening the air quality on side streets. These valuable results were communicated swiftly to partners in the city administration responsible for evaluating the policies’ success and future, highlighting the ability of LCS to provide policy-relevant results.
As a new technology, much is still to be learned about LCS and their value to academic research in the atmospheric sciences. Nevertheless, this work has advanced the state of the art in several ways. First, it contributed a novel open-source calibration methodology that can be used by a LCS end-users for various air pollutants. Second, it strengthened the evidence base on the reliability of LCS for measuring urban air quality, finding through novel deployments in street canyons that LCS can be used at high spatial resolution to understand microscale air pollution dynamics. Last, it is the first of its kind to connect LCS measurements directly with mobility policies to understand their influences on local air quality, resulting in policy-relevant findings valuable for decisionmakers. It serves as an example of the potential for LCS to expand our understanding of air pollution at various scales, as well as their ability to serve as valuable tools in transdisciplinary research.
Alle Organismen sind für ihr Überleben auf Metalle angewiesen. Hierbei gibt es für jedes Metall einen Konzentrationsbereich, der das Optimum zwischen Metallmangel, -bedarf und -toxizität darstellt. Es gilt mittlerweile als erwiesen, dass alle Organismen zur Aufrechterhaltung des Metallgleichgewichts ein komplexes Netzwerk von Proteinen und niedermolekularen Verbindungen entwickelt haben. Die molekularen Komponenten dieses Netzwerks sind nur zu einem Teil bekannt und charakterisiert: In den letzten Jahren wurden einige Proteinfamilien identifiziert, deren Mitglieder Metalle durch Lipidmembranen transportieren. Eine dieser Metalltransporterfamilien ist die Cation Diffusion Facilitator (CDF)-Familie: Alle charakterisierten Mitglieder exportieren Metalle aus dem Zytoplasma – entweder in zelluläre Kompartimente oder aus der Zelle heraus. Von den zwölf Mitgliedern dieser Familie in Arabidopsis thaliana (A. thaliana) – Metall Toleranz Protein (MTP)-1 bis -12 – wurden bisher AtMTP1 und AtMTP3 charakterisiert. In dieser Arbeit wird die Charakterisierung von AtMTP2 beschrieben. Wie die homologen Proteine AtMTP1 und AtMTP3 führt AtMTP2 zu Zn-Toleranz, wenn es heterolog in Zn-sensitiven Hefemutanten exprimiert wird. Mit AtMTP2 transformierte Hefemutanten zeigten darüber hinaus erhöhte Co-Toleranz. Expression von chimären AtMTP2/GFP Fusionsproteinen in Hefe, A.thaliana protoplasten und in stabil transformierten A.thalinana Planzenlinien deutet auf Lokalisation of AtMTP2 in Membranen des Endoplasmatischen Retikulums (ER) hin, wenn GFP an den C-Terminus von MTP2 fusioniert wird. Fusion of GFP an den N-Terminus von AtMTP2 führte zu Lokalisation in der vakuolären Membran, was wahrscheinlichsten auf Fehllokalisierung durch Maskierung eines ER-Retentionsmotivs (XXRR) am N-Terminus von AtMTP2 zurückgeht. Dies legt nahe, dass AtMTP2 die erwähnten Metalle in das Endomembransystem der Zelle transportieren kann. Eine gewebespezifische Lokalisierung wurde mit Pflanzen durchgeführt, die das β-Glucuronidase (GUS)-Reporterprotein bzw. chimäre Fusionsproteine aus EGFP und AtMTP2 unter Kontrolle des nativen pMTP2-Promotors exprimierten. Diese Experimente bestätigten zum einen, dass der pMTP2-Promotor nur unter Zn-Defizienz aktiv ist. GUS-Aktivität wurde unter diesen Bedingungen in zwei Zonen der Wurzelspitze beobachtet: in den isodiametrischen Zellen der meristematischen Zone und in der beginnenden Wurzelhaarzone. Darüber hinaus konnte gezeigt werden, dass die EGFP-Fusionsproteine unter Kontrolle des nativen pMTP2-Promotors nur in epidermalen Zellen exprimiert werden. Für eine homozygote Knockout- Linie, mtp2-S3, konnte bisher kein eindeutiger Phänotyp identifiziert werden. Auf Grundlage der bisher durchgeführten Charakterisierung von AtMTP2 erscheinen zwei Modelle der Funktion von AtMTP2 in der Pflanze möglich: AtMTP2 könnte essentiell für die Versorgung des ER mit Zn unter Zn-Mangelbedingungen sein. Hierfür spricht, dass AtMTP2 in jungen, teilungsaktiven und damit Zn-benötigenden Wurzelzonen exprimiert wird. Die auf die Epidermis beschränkte Lokalisation könnte bei diesem Modell auf die Möglichkeit der zwischenzellulären Zn-Verteilung innerhalb des ER über Desmotubules hindeuten. Alternativ könnte AtMTP2 eine Funktion bei der Detoxifizierung von Zn unter Zn-Schock Bedingungen haben: Es ist bekannt, dass unter Zn- Mangelbedingungen die Expression der zellulären Zn-Aufnahmesysteme hochreguliert wird. Wenn nun die Zn-Verfügbarkeit im Boden z. B durch eine pH-Änderung innerhalb kurzer Zeit stark ansteigt, besteht die Notwendigkeit der Entgiftung von Zn innerhalb der Zelle, bis der starke Einstrom von Zn ins Zytoplasma durch die Deaktivierung der Zn-Aufnahmesysteme und einer geringeren Expression in der Pflanze gedrosselt ist. Ein ähnlicher Mechanismus wurde in der Bäckerhefe S. cerevisae beschrieben, in der darüber hinaus ein Zn-Transporter verstärkt exprimiert wird, der Zn durch Transport in die Vakuole entgiften kann. Es ist durchaus möglich, dass in Arabidopsis AtMTP2 die Zn-Detoxifizierung unter diesen speziellen Bedingungen durch Zn-Transport in das ER oder die Vakuole vermittelt. Zur Identifikation weiterer Komponenten des Metallhomöostasenetzwerks sind verschiedene Ansätze denkbar. In dieser Arbeit wurde in Hefe ein heterologer Screen durchgeführt, um Interaktoren für vier Mitglieder der Arabidopsis-CDF-Familie zu identifizieren. Unter den 11 im Hefesystem bestätigten Kandidaten befindet sich mit AtSPL1 ein AtMTP1-Interaktionskandidat, der möglicherweise eine Rolle bei der Cu-,Zn-Homöostase spielt. Als wahrscheinliche AtMTP3-Interaktionskandidaten wurde die c”-Untereinheit der vakuolären H+-ATPase AtVHA identifiziert sowie mit AtNPSN13 ein Protein, das vermutlich eine Rolle bei Fusionen von Vesikeln mit Zielmembranen spielt. Ein anderer Ansatz zur Identifikation neuer Metallhomöostasegene ist die vergleichende Elementanalyse von natürlichen oder mutagenisierten Pflanzenpopulationen. Voraussetzung für diesen Ansatz ist die schnelle und genaue Analyse des Elementgehalts von Pflanzen. Eine etablierte Methode zur simultanen Bestimmung von bis zu 65 Elementen in einer Probe ist die Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). Der limitierende Faktor für einen hohen Probendurchsatz ist die Notwendigkeit, Proben für die Analyse zu verflüssigen. Eine alternative Methode der Probenzuführung zum Analysegerät ist die elektrothermale Verdampfung (ETV) der Probe. Zur weitgehend automatisierten Analyse von Pflanzenmaterial mit minimiertem Arbeitsaufwand wurde eine Methode entwickelt, die auf der Kopplung der ETV mit der ICP OES basiert.
Arachidonsäurelipoxygenasen (ALOX-Isoformen) sind Lipid-peroxidierenden Enzyme, die bei der Zelldifferenzierung und bei der Pathogenese verschiedener Erkrankungen bedeutsam sind. Im menschlichen Genom gibt es sechs funktionelle ALOX-Gene, die als Einzelkopiegene vorliegen. Für jedes humane ALOX-Gen gibt es ein orthologes Mausgen. Obwohl sich die sechs humanen ALOX-Isoformen strukturell sehr ähnlich sind, unterscheiden sich ihre funktionellen Eigenschaften deutlich voneinander. In der vorliegenden Arbeit wurden vier unterschiedliche Fragestellungen zum Vorkommen, zur biologischen Rolle und zur Evolutionsabhängigkeit der enzymatischen Eigenschaften von Säugetier-ALOX-Isoformen untersucht:
1) Spitzhörnchen (Tupaiidae) sind evolutionär näher mit dem Menschen verwandt als Nagetiere und wurden deshalb als Alternativmodelle für die Untersuchung menschlicher Erkrankungen vorgeschlagen. In dieser Arbeit wurde erstmals der Arachidonsäurestoffwechsel von Spitzhörnchen untersucht. Dabei wurde festgestellt, dass im Genom von Tupaia belangeri vier unterschiedliche ALOX15-Gene vorkommen und die Enzyme sich hinsichtlich ihrer katalytischen Eigenschaften ähneln. Diese genomische Vielfalt, die weder beim Menschen noch bei Mäusen vorhanden ist, erschwert die funktionellen Untersuchungen zur biologischen Rolle des ALOX15-Weges. Damit scheint Tupaia belangeri kein geeigneteres Tiermodel für die Untersuchung des ALOX15-Weges des Menschen zu sein.
2) Entsprechend der Evolutionshypothese können Säugetier-ALOX15-Orthologe in Arachidonsäure-12-lipoxygenierende- und Arachidonsäure-15-lipoxygenierende Enzyme eingeteilt werden. Dabei exprimieren Säugetierspezies, die einen höheren Evolutionsgrad als Gibbons aufweisen, Arachidonsäure-15-lipoxygenierende ALOX15-Orthologe, während evolutionär weniger weit entwickelte Säugetiere Arachidonsäure-12 lipoxygenierende Enzyme besitzen. In dieser Arbeit wurden elf neue ALOX15-Orthologe als rekombinante Proteine exprimiert und funktionell charakterisiert. Die erhaltenen Ergebnisse fügen sich widerspruchsfrei in die Evolutionshypothese ein und verbreitern deren experimentelle Basis. Die experimentellen Daten bestätigen auch das Triadenkonzept.
3) Da humane und murine ALOX15B-Orthologe unterschiedliche funktionelle Eigenschaften aufweisen, können Ergebnisse aus murinen Krankheitsmodellen zur biologischen Rolle der ALOX15B nicht direkt auf den Menschen übertragen werden. Um die ALOX15B-Orthologen von Maus und Mensch funktionell einander anzugleichen, wurden im Rahmen der vorliegenden Arbeit Knock-in Mäuse durch die In vivo Mutagenese mittels CRISPR/Cas9-Technik hergestellt. Diese exprimieren eine humanisierte Mutante (Doppelmutation von Tyrosin603Asparaginsäure+Histidin604Valin) der murinen Alox15b. Diese Mäuse waren lebens- und fortpflanzungsfähig, zeigten aber geschlechtsspezifische Unterschiede zu ausgekreuzten Wildtyp-Kontrolltieren im Rahmen ihre Individualentwicklung.
4) In vorhergehenden Untersuchungen zur Rolle der ALOX15B in Rahmen der Entzündungsreaktion wurde eine antiinflammatorische Wirkung des Enzyms postuliert. In der vorliegenden Arbeit wurde untersucht, ob eine Humanisierung der murinen Alox15b die Entzündungsreaktion in zwei verschiedenen murinen Entzündungsmodellen beeinflusst. Eine Humanisierung der murinen Alox15b führte zu einer verstärkten Ausbildung von Entzündungssymptomen im induzierten Dextran-Natrium-Sulfat-Kolitismodell. Im Gegensatz dazu bewirkte die Humanisierung der Alox15b eine Abschwächung der Entzündungssymptome im Freund‘schen Adjuvans Pfotenödemmodell. Diese Daten deuten darauf hin, dass sich die Rolle der ALOX15B in verschiedenen Entzündungsmodellen unterscheidet.
Climate change is one of the greatest challenges to humanity in this century, and most noticeable consequences are expected to be impacts on the water cycle – in particular the distribution and availability of water, which is fundamental for all life on Earth. In this context, it is essential to better understand where and when water is available and what processes influence variations in water storages. While estimates of the overall terrestrial water storage (TWS) variations are available from the GRACE satellites, these represent the vertically integrated signal over all water stored in ice, snow, soil moisture, groundwater and surface water bodies. Therefore, complementary observational data and hydrological models are still required to determine the partitioning of the measured signal among different water storages and to understand the underlying processes. However, the application of large-scale observational data is limited by their specific uncertainties and the incapacity to measure certain water fluxes and storages. Hydrological models, on the other hand, vary widely in their structure and process-representation, and rarely incorporate additional observational data to minimize uncertainties that arise from their simplified representation of the complex hydrologic cycle.
In this context, this thesis aims to contribute to improving the understanding of global water storage variability by combining simple hydrological models with a variety of complementary Earth observation-based data. To this end, a model-data integration approach is developed, in which the parameters of a parsimonious hydrological model are calibrated against several observational constraints, inducing GRACE TWS, simultaneously, while taking into account each data’s specific strengths and uncertainties. This approach is used to investigate 3 specific aspects that are relevant for modelling and understanding the composition of large-scale TWS variations.
The first study focusses on Northern latitudes, where snow and cold-region processes define the hydrological cycle. While the study confirms previous findings that seasonal dynamics of TWS are dominated by the cyclic accumulation and melt of snow, it reveals that inter-annual TWS variations on the contrary, are determined by variations in liquid water storages. Additionally, it is found to be important to consider the impact of compensatory effects of spatially heterogeneous hydrological variables when aggregating the contribution of different storage components over large areas. Hence, the determinants of TWS variations are scale-dependent and underlying driving mechanism cannot be simply transferred between spatial and temporal scales. These findings are supported by the second study for the global land areas beyond the Northern latitudes as well.
This second study further identifies the considerable impact of how vegetation is represented in hydrological models on the partitioning of TWS variations. Using spatio-temporal varying fields of Earth observation-based data to parameterize vegetation activity not only significantly improves model performance, but also reduces parameter equifinality and process uncertainties. Moreover, the representation of vegetation drastically changes the contribution of different water storages to overall TWS variability, emphasizing the key role of vegetation for water allocation, especially between sub-surface and delayed water storages. However, the study also identifies parameter equifinality regarding the decay of sub-surface and delayed water storages by either evapotranspiration or runoff, and thus emphasizes the need for further constraints hereof.
The third study focuses on the role of river water storage, in particular whether it is necessary to include computationally expensive river routing for model calibration and validation against the integrated GRACE TWS. The results suggest that river routing is not required for model calibration in such a global model-data integration approach, due to the larger influence other observational constraints, and the determinability of certain model parameters and associated processes are identified as issues of greater relevance. In contrast to model calibration, considering river water storage derived from routing schemes can already significantly improve modelled TWS compared to GRACE observations, and thus should be considered for model evaluation against GRACE data.
Beyond these specific findings that contribute to improved understanding and modelling of large-scale TWS variations, this thesis demonstrates the potential of combining simple modeling approaches with diverse Earth observational data to improve model simulations, overcome inconsistencies of different observational data sets, and identify areas that require further research. These findings encourage future efforts to take advantage of the increasing number of diverse global observational data.
In the frame of a world fighting a dramatic global warming caused by human-related activities, research towards the development of renewable energies plays a crucial role. Solar energy is one of the most important clean energy sources and its role in the satisfaction of the global energy demand is set to increase. In this context, a particular class of materials captured the attention of the scientific community for its attractive properties: halide perovskites. Devices with perovskite as light-absorber saw an impressive development within the last decade, reaching nowadays efficiencies comparable to mature photovoltaic technologies like silicon solar cells. Yet, there are still several roadblocks to overcome before a wide-spread commercialization of this kind of devices is enabled. One of the critical points lies at the interfaces: perovskite solar cells (PSCs) are made of several layers with different chemical and physical features. In order for the device to function properly, these properties have to be well-matched.
This dissertation deals with some of the challenges related to interfaces in PSCs, with a focus on the interface between the perovskite material itself and the subsequent charge transport layer. In particular, molecular assemblies with specific properties are deposited on the perovskite surface to functionalize it. The functionalization results in energy level alignment adjustment, interfacial losses reduction, and stability improvement.
First, a strategy to tune the perovskite’s energy levels is introduced: self-assembled monolayers of dipolar molecules are used to functionalize the surface, obtaining simultaneously a shift in the vacuum level position and a saturation of the dangling bonds at the surface. A shift in the vacuum level corresponds to an equal change in work function, ionization energy, and electron affinity. The direction of the shift depends on the direction of the collective interfacial dipole. The magnitude of the shift can be tailored by controlling the deposition parameters, such as the concentration of the solution used for the deposition. The shift for different molecules is characterized by several non-invasive techniques, including in particular Kelvin probe. Overall, it is shown that it is possible to shift the perovskite energy levels in both directions by several hundreds of meV. Moreover, interesting insights on the molecules deposition dynamics are revealed.
Secondly, the application of this strategy in perovskite solar cells is explored. Devices with different perovskite compositions (“triple cation perovskite” and MAPbBr3) are prepared. The two resulting model systems present different energetic offsets at the perovskite/hole-transport layer interface. Upon tailored perovskite surface functionalization, the devices show a stabilized open circuit voltage (Voc) enhancement of approximately 60 meV on average for devices with MAPbBr3, while the impact is limited on triple-cation solar cells. This suggests that the proposed energy level tuning method is valid, but its effectiveness depends on factors such as the significance of the energetic offset compared to the other losses in the devices.
Finally, the above presented method is further developed by incorporating the ability to interact with the perovskite surface directly into a novel hole-transport material (HTM), named PFI. The HTM can anchor to the perovskite halide ions via halogen bonding (XB). Its behaviour is compared to that of another HTM (PF) with same chemical structure and properties, except for the ability of forming XB. The interaction of perovskite with PFI and PF is characterized through UV-Vis, atomic force microscopy and Kelvin probe measurements combined with simulations. Compared to PF, PFI exhibits enhanced resilience against solvent exposure and improved energy level alignment with the perovskite layer. As a consequence, devices comprising PFI show enhanced Voc and operational stability during maximum-power-point tracking, in addition to hysteresis reduction. XB promotes the formation of a high-quality interface by anchoring to the halide ions and forming a stable and ordered interfacial layer, showing to be a particularly interesting candidate for the development of tailored charge transport materials in PSCs.
Overall, the results exposed in this dissertation introduce and discuss a versatile tool to functionalize the perovskite surface and tune its energy levels. The application of this method in devices is explored and insights on its challenges and advantages are given. Within this frame, the results shed light on XB as ideal interaction for enhancing stability and efficiency in perovskite-based devices.
Selenium (Se) is an essential trace element that is ubiquitously present in the environment in small concentrations. Essential functions of Se in the human body are manifested through the wide range of proteins, containing selenocysteine as their active center. Such proteins are called selenoproteins which are found in multiple physiological processes like antioxidative defense and the regulation of thyroid hormone functions. Therefore, Se deficiency is known to cause a broad spectrum of physiological impairments, especially in endemic regions with low Se content. Nevertheless, being an essential trace element, Se could exhibit toxic effects, if its intake exceeds tolerable levels. Accordingly, this range between deficiency and overexposure represents optimal Se supply. However, this range was found to be narrower than for any other essential trace element. Together with significantly varying Se concentrations in soil and the presence of specific bioaccumulation factors, this represents a noticeable difficulty in the assessment of Se
epidemiological status. While Se is acting in the body through multiple selenoproteins, its intake occurs mainly in form of small organic or inorganic molecular mass species. Thus, Se exposure not only depends on daily intake but also on the respective chemical form, in which it is present.
The essential functions of selenium have been known for a long time and its primary forms in different food sources have been described. Nevertheless, analytical capabilities for a comprehensive investigation of Se species and their derivatives have been introduced only in the last decades. A new Se compound was identified in 2010 in the blood and tissues of bluefin tuna. It was called selenoneine (SeN) since it is an isologue of naturally occurring antioxidant ergothioneine (ET), where Se replaces sulfur. In the following years, SeN was identified in a number of edible fish species and attracted attention as a new dietary Se source and potentially strong antioxidant. Studies in populations whose diet largely relies on fish revealed that SeN
represents the main non-protein bound Se pool in their blood. First studies, conducted with enriched fish extracts, already demonstrated the high antioxidative potential of SeN and its possible function in the detoxification of methylmercury in fish. Cell culture studies demonstrated, that SeN can utilize the same transporter as ergothioneine, and SeN metabolite was found in human urine.
Until recently, studies on SeN properties were severely limited due to the lack of ways to obtain the pure compound. As a predisposition to this work was firstly a successful approach to SeN synthesis in the University of Graz, utilizing genetically modified yeasts. In the current study, by use of HepG2 liver carcinoma cells, it was demonstrated, that SeN does not cause toxic effectsup to 100 μM concentration in hepatocytes. Uptake experiments showed that SeN is not bioavailable to the used liver cells.
In the next part a blood-brain barrier (BBB) model, based on capillary endothelial cells from the porcine brain, was used to describe the possible transfer of SeN into the central nervous system (CNS). The assessment of toxicity markers in these endothelial cells and monitoring of barrier conditions during transfer experiments demonstrated the absence of toxic effects from SeN on the BBB endothelium up to 100 μM concentration. Transfer data for SeN showed slow but substantial transfer. A statistically significant increase was observed after 48 hours following SeN incubation from the blood-facing side of the barrier. However, an increase in Se content was clearly visible already after 6 hours of incubation with 1 μM of SeN. While the transfer rate of SeN after application of 0.1 μM dose was very close to that for 1 μM, incubation with 10 μM of SeN resulted in a significantly decreased transfer rate. Double-sided application of SeN caused no side-specific transfer of SeN, thus suggesting a passive diffusion mechanism of SeN across the BBB. This data is in accordance with animal studies, where ET accumulation was observed in the rat brain, even though rat BBB does not have the primary ET transporter – OCTN1. Investigation of capillary endothelial cell monolayers after incubation with SeN and reference selenium compounds showed no significant increase of intracellular selenium concentration. Speciesspecific Se measurements in medium samples from apical and basolateral compartments, as good as in cell lysates, showed no SeN metabolization. Therefore, it can be concluded that SeN may reach the brain without significant transformation.
As the third part of this work, the assessment of SeN antioxidant properties was performed in Caco-2 human colorectal adenocarcinoma cells. Previous studies demonstrated that the intestinal epithelium is able to actively transport SeN from the intestinal lumen to the blood side and accumulate SeN. Further investigation within current work showed a much higher antioxidant potential of SeN compared to ET. The radical scavenging activity after incubation with SeN was close to the one observed for selenite and selenomethionine. However, the SeN effect on the viability of intestinal cells under oxidative conditions was close to the one caused by ET. To answer the question if SeN is able to be used as a dietary Se source and induce the activity of selenoproteins, the activity of glutathione peroxidase (GPx) and the secretion of selenoprotein P (SelenoP) were measured in Caco-2 cells, additionally. As expected, reference selenium compounds selenite and selenomethionine caused efficient induction of GPx activity. In contrast to those SeN had no effect on GPx activity. To examine the possibility of SeN being embedded into the selenoproteome, SelenoP was measured in a culture medium. Even though Caco-2 cells effectively take up SeN in quantities much higher than selenite or selenomethionine, no secretion of SelenoP was observed after SeN incubation.
Summarizing, we can conclude that SeN can hardly serve as a Se source for selenoprotein synthesis. However, SeN exhibit strong antioxidative properties, which appear when sulfur in ET is exchanged by Se. Therefore, SeN is of particular interest for research not as part of Se metabolism, but important endemic dietary antioxidant.
Thermoresponsive Zellkultursubstrate für zeitlich-räumlich gesteuertes Auswachsen neuronaler Zellen
(2019)
Ein wichtiges Ziel der Neurowissenschaften ist das Verständnis der komplexen und zugleich faszinierenden, hochgeordneten Vernetzung der Neurone im Gehirn, welche neuronalen Prozessen, wie zum Beispiel dem Wahrnehmen oder Lernen wie auch Neuropathologien zu Grunde liegt. Für verbesserte neuronale Zellkulturmodelle zur detaillierten Untersuchung dieser Prozesse ist daher die Rekonstruktion von geordneten neuronalen Verbindungen dringend erforderlich. Mit Oberflächenstrukturen aus zellattraktiven und zellabweisenden Beschichtungen können neuronale Zellen und ihre Neuriten in vitro strukturiert werden. Zur Kontrolle der neuronalen Verbindungsrichtung muss das Auswachsen der Axone zu benachbarten Zellen dynamisch gesteuert werden, zum Beispiel über eine veränderliche Zugänglichkeit der Oberfläche.
In dieser Arbeit wurde untersucht, ob mit thermoresponsiven Polymeren (TRP) beschichtete Zellkultursubstrate für eine dynamische Kontrolle des Auswachsens neuronaler Zellen geeignet sind. TRP können über die Temperatur von einem zellabweisenden in einen zellattraktiven Zustand geschaltet werden, womit die Zugänglichkeit der Oberfläche für Zellen dynamisch gesteuert werden kann. Die TRP-Beschichtung wurde mikrostrukturiert, um einzelne oder wenige neuronale Zellen zunächst auf der Oberfläche anzuordnen und das Auswachsen der Zellen und Neuriten über definierte TRP-Bereiche in Abhängigkeit der Temperatur zeitlich und räumlich zu kontrollieren. Das Protokoll wurde mit der neuronalen Zelllinie SH-SY5Y etabliert und auf humane induzierte Neurone übertragen. Die Anordnung der Zellen konnte bei Kultivierung im zellabweisenden Zustand des TRPs für bis zu 7 Tage aufrecht erhalten werden. Durch Schalten des TRPs in den zellattraktiven Zustand konnte das Auswachsen der Neuriten und Zellen zeitlich und räumlich induziert werden. Immunozytochemische Färbungen und Patch-Clamp-Ableitungen der Neurone demonstrierten die einfache Anwendbarkeit und Zellkompatibilität der TRP-Substrate.
Eine präzisere räumliche Kontrolle des Auswachsens der Zellen sollte durch lokales Schalten der TRP-Beschichtung erreicht werden. Dafür wurden Mikroheizchips mit Mikroelektroden zur lokalen Jouleschen Erwärmung der Substratoberfläche entwickelt. Zur Evaluierung der generierten Temperaturprofile wurde eine Temperaturmessmethode entwickelt und die erhobenen Messwerte mit numerisch simulierten Werten abgeglichen. Die Temperaturmessmethode basiert auf einfach zu applizierenden Sol-Gel-Schichten, die den temperatursensitiven Fluoreszenzfarbstoff Rhodamin B enthalten. Sie ermöglicht oberflächennahe Temperaturmessungen in trockener und wässriger Umgebung mit hoher Orts- und Temperaturauflösung. Numerische Simulationen der Temperaturprofile korrelierten gut mit den experimentellen Daten. Auf dieser Basis konnten Geometrie und Material der Mikroelektroden hinsichtlich einer lokal stark begrenzten Temperierung optimiert werden. Ferner wurden für die Kultvierung der Zellen auf den Mikroheizchips eine Zellkulturkammer und Kontaktboard für die elektrische Kontaktierung der Mikroelektroden geschaffen.
Die vorgestellten Ergebnisse demonstrieren erstmalig das enorme Potential thermoresponsiver Zellkultursubstrate für die zeitlich und räumlich gesteuerte Formation geordneter neuronaler Verbindungen in vitro. Zukünftig könnte dies detaillierte Studien zur neuronalen Informationsverarbeitung oder zu Neuropathologien an relevanten, humanen Zellmodellen ermöglichen.
The Andes are a ~7000 km long N-S trending mountain range developed along the South American western continental margin. Driven by the subduction of the oceanic Nazca plate beneath the continental South American plate, the formation of the northern and central parts of the orogen is a type case for a non-collisional orogeny. In the southern Central Andes (SCA, 29°S-39°S), the oceanic plate changes the subduction angle between 33°S and 35°S from almost horizontal (< 5° dip) in the north to a steeper angle (~30° dip) in the south. This sector of the Andes also displays remarkable along- and across- strike variations of the tectonic deformation patterns. These include a systematic decrease of topographic elevation, of crustal shortening and foreland and orogenic width, as well as an alternation of the foreland deformation style between thick-skinned and thin-skinned recorded along- and across the strike of the subduction zone. Moreover, the SCA are a very seismically active region. The continental plate is characterized by a relatively shallow seismicity (< 30 km depth) which is mainly focussed at the transition from the orogen to the lowland areas of the foreland and the forearc; in contrast, deeper seismicity occurs below the interiors of the northern foreland. Additionally, frequent seismicity is also recorded in the shallow parts of the oceanic plate and in a sector of the flat slab segment between 31°S and 33°S. The observed spatial heterogeneity in tectonic and seismic deformation in the SCA has been attributed to multiple causes, including variations in sediment thickness, the presence of inherited structures and changes in the subduction angle of the oceanic slab. However, there is no study that inquired the relationship between the long-term rheological configuration of the SCA and the spatial deformation patterns. Moreover, the effects of the density and thickness configuration of the continental plate and of variations in the slab dip angle in the rheological state of the lithosphere have been not thoroughly investigated yet. Since rheology depends on composition, pressure and temperature, a detailed characterization of the compositional, structural and thermal fields of the lithosphere is needed. Therefore, by using multiple geophysical approaches and data sources, I constructed the following 3D models of the SCA lithosphere: (i) a seismically-constrained structural and density model that was tested against the gravity field; (ii) a thermal model integrating the conversion of mantle shear-wave velocities to temperature with steady-state conductive calculations in the uppermost lithosphere (< 50 km depth), validated by temperature and heat-flow measurements; and (iii) a rheological model of the long-term lithospheric strength using as input the previously-generated models.
The results of this dissertation indicate that the present-day thermal and rheological fields of the SCA are controlled by different mechanisms at different depths. At shallow depths (< 50 km), the thermomechanical field is modulated by the heterogeneous composition of the continental lithosphere. The overprint of the oceanic slab is detectable where the oceanic plate is shallow (< 85 km depth) and the radiogenic crust is thin, resulting in overall lower temperatures and higher strength compared to regions where the slab is steep and the radiogenic crust is thick. At depths > 50 km, largest temperatures variations occur where the descending slab is detected, which implies that the deep thermal field is mainly affected by the slab dip geometry.
The outcomes of this thesis suggests that long-term thermomechanical state of the lithosphere influences the spatial distribution of seismic deformation. Most of the seismicity within the continental plate occurs above the modelled transition from brittle to ductile conditions. Additionally, there is a spatial correlation between the location of these events and the transition from the mechanically strong domains of the forearc and foreland to the weak domain of the orogen. In contrast, seismicity within the oceanic plate is also detected where long-term ductile conditions are expected. I therefore analysed the possible influence of additional mechanisms triggering these earthquakes, including the compaction of sediments in the subduction interface and dehydration reactions in the slab. To that aim, I carried out a qualitative analysis of the state of hydration in the mantle using the ratio between compressional- and shear-wave velocity (vp/vs ratio) from a previous seismic tomography. The results from this analysis indicate that the majority of the seismicity spatially correlates with hydrated areas of the slab and overlying continental mantle, with the exception of the cluster within the flat slab segment. In this region, earthquakes are likely triggered by flexural processes where the slab changes from a flat to a steep subduction angle.
First-order variations in the observed tectonic patterns also seem to be influenced by the thermomechanical configuration of the lithosphere. The mechanically strong domains of the forearc and foreland, due to their resistance to deformation, display smaller amounts of shortening than the relatively weak orogenic domain. In addition, the structural and thermomechanical characteristics modelled in this dissertation confirm previous analyses from geodynamic models pointing to the control of the observed heterogeneities in the orogen and foreland deformation style. These characteristics include the lithospheric and crustal thickness, the presence of weak sediments and the variations in gravitational potential energy.
Specific conditions occur in the cold and strong northern foreland, which is characterized by active seismicity and thick-skinned structures, although the modelled crustal strength exceeds the typical values of externally-applied tectonic stresses. The additional mechanisms that could explain the strain localization in a region that should resist deformation are: (i) increased tectonic forces coming from the steepening of the slab and (ii) enhanced weakening along inherited structures from pre-Andean deformation events. Finally, the thermomechanical conditions of this sector of the foreland could be a key factor influencing the preservation of the flat subduction angle at these latitudes of the SCA.
Widespread landscape changes are presently observed in the Arctic and are most likely to
accelerate in the future, in particular in permafrost regions which are sensitive to climate warming. To assess current and future developments, it is crucial to understand past
environmental dynamics in these landscapes. Causes and interactions of environmental variability can hardly be resolved by instrumental records covering modern time scales. However, long-term
environmental variability is recorded in paleoenvironmental archives. Lake sediments are important archives that allow reconstruction of local limnogeological processes as well as past environmental changes driven directly or indirectly by climate dynamics. This study aims at
reconstructing Late Quaternary permafrost and thermokarst dynamics in central-eastern Beringia,
the terrestrial land mass connecting Eurasia and North America during glacial sea-level low stands. In order to investigate development, processes and influence of thermokarst dynamics, several sediment cores from extant lakes and drained lake basins were analyzed to answer the
following research questions:
1. When did permafrost degradation and thermokarst lake development take place and what were enhancing and inhibiting environmental factors?
2. What are the dominant processes during thermokarst lake development and how are
they reflected in proxy records?
3. How did, and still do, thermokarst dynamics contribute to the inventory and properties of organic matter in sediments and the carbon cycle?
Methods applied in this study are based upon a multi-proxy approach combining
sedimentological, geochemical, geochronological, and micropaleontological analyses, as well as
analyses of stable isotopes and hydrochemistry of pore-water and ice. Modern field observations of water quality and basin morphometrics complete the environmental investigations.
The investigated sediment cores reveal permafrost degradation and thermokarst dynamics on different time scales. The analysis of a sediment core from GG basin on the northern Seward
Peninsula (Alaska) shows prevalent terrestrial accumulation of yedoma throughout the Early to
Mid Wisconsin with intermediate wet conditions at around 44.5 to 41.5 ka BP. This first wetland
development was terminated by the accumulation of a 1-meter-thick airfall tephra most likely originating from the South Killeak Maar eruption at 42 ka BP. A depositional hiatus between 22.5 and 0.23 ka BP may indicate thermokarst lake formation in the surrounding of the site which forms a yedoma upland till today. The thermokarst lake forming GG basin initiated 230 ± 30 cal a
BP and drained in Spring 2005 AD. Four years after drainage the lake talik was still unfrozen below 268 cm depth.
A permafrost core from Mama Rhonda basin on the northern Seward Peninsula preserved a
full lacustrine record including several lake phases. The first lake generation developed at 11.8 cal ka BP during the Lateglacial-Early Holocene transition; its old basin (Grandma Rhonda) is still partially preserved at the southern margin of the study basin. Around 9.0 cal ka BP a shallow and more dynamic thermokarst lake developed with actively eroding shorelines and potentially intermediate shallow water or wetland phases (Mama Rhonda). Mama Rhonda lake drainage at 1.1 cal ka BP was followed by gradual accumulation of terrestrial peat and top-down refreezing of the lake talik. A significant lower organic carbon content was measured in Grandma Rhonda deposits (mean TOC of 2.5 wt%) than in Mama Rhonda deposits (mean TOC of 7.9 wt%) highlighting the impact of thermokarst dynamics on biogeochemical cycling in different lake generations by thawing and mobilization of organic carbon into the lake system.
Proximal and distal sediment cores from Peatball Lake on the Arctic Coastal Plain of Alaska revealed young thermokarst dynamics since about 1,400 years along a depositional gradient based on reconstructions from shoreline expansion rates and absolute dating results. After its initiation as a remnant pond of a previous drained lake basin, a rapidly deepening lake with increasing oxygenation of the water column is evident from laminated sediments, and higher Fe/Ti and Fe/S ratios in the sediment. The sediment record archived characterizing shifts in depositional regimes and sediment sources from upland deposits and re-deposited sediments from drained thaw lake basins depending on the gradually changing shoreline configuration. These changes are evident from alternating organic inputs into the lake system which highlights the potential for thermokarst lakes to recycle old carbon from degrading permafrost deposits of its catchment.
The lake sediment record from Herschel Island in the Yukon (Canada) covers the full Holocene period. After its initiation as a thermokarst lake at 11.7 cal ka BP and intense thermokarst activity until 10.0 cal ka BP, the steady sedimentation was interrupted by a depositional hiatus at 1.6 cal ka BP which likely resulted from lake drainage or allochthonous slumping due to collapsing shore lines. The specific setting of the lake on a push moraine composed of marine deposits is reflected in the sedimentary record. Freshening of the maturing lake is indicated by decreasing electrical conductivity in pore-water. Alternation of marine to freshwater ostracods and foraminifera confirms decreasing salinity as well but also reflects episodical re-deposition of allochthonous marine sediments.
Based on permafrost and lacustrine sediment records, this thesis shows examples of the Late Quaternary evolution of typical Arctic permafrost landscapes in central-eastern Beringia and the complex interaction of local disturbance processes, regional environmental dynamics and global climate patterns. This study confirms that thermokarst lakes are important agents of organic matter recycling in complex and continuously changing landscapes.
Current climate warming is affecting arctic regions at a faster rate than the rest of the world. This has profound effects on permafrost that underlies most of the arctic land area. Permafrost thawing can lead to the liberation of considerable amounts of greenhouse gases as well as to significant changes in the geomorphology, hydrology, and ecology of the corresponding landscapes, which may in turn act as a positive feedback to the climate system. Vast areas of the east Siberian lowlands, which are underlain by permafrost of the Yedoma-type Ice Complex, are particularly sensitive to climate warming because of the high ice content of these permafrost deposits. Thermokarst and thermal erosion are two major types of permafrost degradation in periglacial landscapes. The associated landforms are prominent indicators of climate-induced environmental variations on the regional scale. Thermokarst lakes and basins (alasses) as well as thermo-erosional valleys are widely distributed in the coastal lowlands adjacent to the Laptev Sea. This thesis investigates the spatial distribution and morphometric properties of these degradational features to reconstruct their evolutionary conditions during the Holocene and to deduce information on the potential impact of future permafrost degradation under the projected climate warming. The methodological approach is a combination of remote sensing, geoinformation, and field investigations, which integrates analyses on local to regional spatial scales. Thermokarst and thermal erosion have affected the study region to a great extent. In the Ice Complex area of the Lena River Delta, thermokarst basins cover a much larger area than do present thermokarst lakes on Yedoma uplands (20.0 and 2.2 %, respectively), which indicates that the conditions for large-area thermokarst development were more suitable in the past. This is supported by the reconstruction of the development of an individual alas in the Lena River Delta, which reveals a prolonged phase of high thermokarst activity since the Pleistocene/Holocene transition that created a large and deep basin. After the drainage of the primary thermokarst lake during the mid-Holocene, permafrost aggradation and degradation have occurred in parallel and in shorter alternating stages within the alas, resulting in a complex thermokarst landscape. Though more dynamic than during the first phase, late Holocene thermokarst activity in the alas was not capable of degrading large portions of Pleistocene Ice Complex deposits and substantially altering the Yedoma relief. Further thermokarst development in existing alasses is restricted to thin layers of Holocene ice-rich alas sediments, because the Ice Complex deposits underneath the large primary thermokarst lakes have thawed completely and the underlying deposits are ice-poor fluvial sands. Thermokarst processes on undisturbed Yedoma uplands have the highest impact on the alteration of Ice Complex deposits, but will be limited to smaller areal extents in the future because of the reduced availability of large undisturbed upland surfaces with poor drainage. On Kurungnakh Island in the central Lena River Delta, the area of Yedoma uplands available for future thermokarst development amounts to only 33.7 %. The increasing proximity of newly developing thermokarst lakes on Yedoma uplands to existing degradational features and other topographic lows decreases the possibility for thermokarst lakes to reach large sizes before drainage occurs. Drainage of thermokarst lakes due to thermal erosion is common in the study region, but thermo-erosional valleys also provide water to thermokarst lakes and alasses. Besides these direct hydrological interactions between thermokarst and thermal erosion on the local scale, an interdependence between both processes exists on the regional scale. A regional analysis of extensive networks of thermo-erosional valleys in three lowland regions of the Laptev Sea with a total study area of 5,800 km² found that these features are more common in areas with higher slopes and relief gradients, whereas thermokarst development is more pronounced in flat lowlands with lower relief gradients. The combined results of this thesis highlight the need for comprehensive analyses of both, thermokarst and thermal erosion, in order to assess past and future impacts and feedbacks of the degradation of ice-rich permafrost on hydrology and climate of a certain region.
The foreland of the Andes in South America is characterised by distinct along strike changes in surface deformational styles. These styles are classified into two end-members, the thin-skinned and the thick-skinned style. The superficial expression of thin-skinned deformation is a succession of narrowly spaced hills and valleys, that form laterally continuous ranges on the foreland facing side of the orogen. Each of the hills is defined by a reverse fault that roots in a basal décollement surface within the sedimentary cover, and acted as thrusting ramp to stack the sedimentary pile. Thick-skinned deformation is morphologically characterised by spatially disparate, basement-cored mountain ranges. These mountain ranges are uplifted along reactivated high-angle crustal-scale discontinuities, such as suture zones between different tectonic terranes.
Amongst proposed causes for the observed variation are variations in the dip angle of the Nazca plate, variation in sediment thickness, lithospheric thickening, volcanism or compositional differences. The proposed mechanisms are predominantly based on geological observations or numerical thermomechanical modelling, but there has been no attempt to understand the mechanisms from a point of data-integrative 3D modelling. The aim of this dissertation is therefore to understand how lithospheric structure controls the deformational behaviour. The integration of independent data into a consistent model of the lithosphere allows to obtain additional evidence that helps to understand the causes for the different deformational styles. Northern Argentina encompasses the transition from the thin-skinned fold-and-thrust belt in Bolivia, to the thick-skinned Sierras Pampeanas province, which makes this area a well suited location for such a study. The general workflow followed in this study first involves data-constrained structural- and density-modelling in order to obtain a model of the study area. This model was then used to predict the steady-state thermal field, which was then used to assess the present-day rheological state in northern Argentina.
The structural configuration of the lithosphere in northern Argentina was determined by means of data-integrative, 3D density modelling verified by Bouguer gravity. The model delineates the first-order density contrasts in the lithosphere in the uppermost 200 km, and discriminates bodies for the sediments, the crystalline crust, the lithospheric mantle and the subducting Nazca plate. To obtain the intra-crustal density structure, an automated inversion approach was developed and applied to a starting structural model that assumed a homogeneously dense crust. The resulting final structural model indicates that the crustal structure can be represented by an upper crust with a density of 2800 kg/m³, and a lower crust of 3100 kg/m³. The Transbrazilian Lineament, which separates the Pampia terrane from the Río de la Plata craton, is expressed as a zone of low average crustal densities.
In an excursion, we demonstrate in another study, that the gravity inversion method developed to obtain intra-crustal density structures, is also applicable to obtain density variations in the uppermost lithospheric mantle. Densities in such sub-crustal depths are difficult to constrain from seismic tomographic models due to smearing of crustal velocities. With the application to the uppermost lithospheric mantle in the north Atlantic, we demonstrate in Tan et al. (2018) that lateral density trends of at least 125\,km width are robustly recovered by the inversion method, thereby providing an important tool for the delineation of subcrustal density trends.
Due to the genetic link between subduction, orogenesis and retroarc foreland basins the question rises whether the steady-state assumption is valid in such a dynamic setting. To answer this question, I analysed (i) the impact of subduction on the conductive thermal field of the overlying continental plate, (ii) the differences between the transient and steady-state thermal fields of a geodynamic coupled model. Both studies indicate that the assumption of a thermal steady-state is applicable in most parts of the study area. Within the orogenic wedge, where the assumption cannot be applied, I estimated the transient thermal field based on the results of the conducted analyses.
Accordingly, the structural model that had been obtained in the first step, could be used to obtain a 3D conductive steady-state thermal field. The rheological assessment based on this thermal field indicates that the lithosphere of the thin-skinned Subandean ranges is characterised by a relatively strong crust and a weak mantle. Contrarily, the adjacent foreland basin consists of a fully coupled, very strong lithosphere. Thus, shortening in northern Argentina can only be accommodated within the weak lithosphere of the orogen and the Subandean ranges. The analysis suggests that the décollements of the fold-and-thrust belt are the shallow continuation of shear zones that reside in the ductile sections of the orogenic crust. Furthermore, the localisation of the faults that provide strain transfer between the deeper ductile crust and the shallower décollement is strongly influenced by crustal weak zones such as foliation. In contrast to the northern foreland, the lithosphere of the thick-skinned Sierras Pampeanas is fully coupled and characterised by a strong crust and mantle. The high overall strength prevents the generation of crustal-scale faults by tectonic stresses. Even inherited crustal-scale discontinuities, such as sutures, cannot sufficiently reduce the strength of the lithosphere in order to be reactivated. Therefore, magmatism that had been identified to be a precursor of basement uplift in the Sierras Pampeanas, is the key factor that leads to the broken foreland of this province. Due to thermal weakening, and potentially lubrication of the inherited discontinuities, the lithosphere is locally weakened such that tectonic stresses can uplift the basement blocks. This hypothesis explains both the spatially disparate character of the broken foreland, as well as the observed temporal delay between volcanism and basement block uplift.
This dissertation provides for the first time a data-driven 3D model that is consistent with geophysical data and geological observations, and that is able to causally link the thermo-rheological structure of the lithosphere to the observed variation of surface deformation styles in the retroarc foreland of northern Argentina.
In the here presented work we discuss a series of results that are all in one way or another connected to the phenomenon of trapping in black hole spacetimes.
First we present a comprehensive review of the Kerr-Newman-Taub-NUT-de-Sitter family of black hole spacetimes and their most important properties. From there we go into a detailed analysis of the bahaviour of null geodesics in the exterior region of a sub-extremal Kerr spacetime. We show that most well known fundamental properties of null geodesics can be represented in one plot. In particular, one can see immediately that the ergoregion and trapping are separated in phase space.
We then consider the sets of future/past trapped null geodesics in the exterior region of a sub-extremal Kerr-Newman-Taub-NUT spacetime. We show that from the point of view of any timelike observer outside of such a black hole, trapping can be understood as two smooth sets of spacelike directions on the celestial sphere of the observer. Therefore the topological structure of the trapped set on the celestial sphere of any observer is identical to that in Schwarzschild.
We discuss how this is relevant to the black hole stability problem.
In a further development of these observations we introduce the notion of what it means for the shadow of two observers to be degenerate. We show that, away from the axis of symmetry, no continuous degeneration exists between the shadows of observers at any point in the exterior region of any Kerr-Newman black hole spacetime of unit mass. Therefore, except possibly for discrete changes, an observer can, by measuring the black holes shadow, determine the angular momentum and the charge of the black hole under observation, as well as the observer's radial position and angle of elevation above the equatorial plane. Furthermore, his/her relative velocity compared to a standard observer can also be measured. On the other hand, the black hole shadow does not allow for a full parameter resolution in the case of a Kerr-Newman-Taub-NUT black hole, as a continuous degeneration relating specific angular momentum, electric charge, NUT charge and elevation angle exists in this case.
We then use the celestial sphere to show that trapping is a generic feature of any black hole spacetime.
In the last chapter we then prove a generalization of the mode stability result of Whiting (1989) for the Teukolsky equation for the case of real frequencies. The main result of the last chapter states that a separated solution of the Teukolsky equation governing massless test fields on the Kerr spacetime, which is purely outgoing at infinity, and purely ingoing at the horizon, must vanish. This has the consequence, that for real frequencies, there are linearly independent fundamental solutions of the radial Teukolsky equation which are purely ingoing at the horizon, and purely outgoing at infinity, respectively. This fact yields a representation formula for solutions of the inhomogenous Teukolsky equation, and was recently used by Shlapentokh-Rothman (2015) for the scalar wave equation.
Systemic inflammation is a hallmark of cancer cachexia. Among tumor-host interactions, the white adipose tissue (WAT) is an important contributor to inflammation as it suffers morphological reorganization and lipolysis, releasing free fatty acids (FA), bioactive lipid mediators (LM) and pro-inflammatory cytokines, which accentuate the activation of pro-inflammatory signaling pathways and the recruitment of immune cells to the tissue. This project aimed to investigate which inflammatory factors are involved in the local adipose tissue inflammation and what is the influence of such factors upon enzymes involved in FA or LM metabolism in healthy individuals (Control), weight stable gastro-intestinal cancer patients (WSC) and cachectic cancer patients (CC). The results demonstrated that the inflammatory signature of systemic inflammation is different from local adipose tissue inflammation. The systemic inflammation of the cachectic cancer patients was characterized by higher levels of circulating saturated fatty acids (SFA), tumor-necrosis-factor-α (TNF-α), interleukins IL-6, IL-8 and CRP while levels of polyunsaturated fatty acids (PUFAs), especially n3-PUFAs, were lower in CC than in the other groups. In vitro and in adipose tissue explants, pro-inflammatory cytokines and SFAs were shown to increase the chemokines IL-8 and CXCL10 that were found to be augmented in adipose tissue inflammation in CC which was more profound in the visceral adipose tissue (VAT) than in subcutaneous adipose tissue (SAT). Systemic inflammation was negatively associated with the expression of PUFA synthesizing enzymes, though gene and protein expression did hardly differ between groups. The effects of inflammatory factors on enzymes in the whole tissue could have been masked by differentiated modulation of the diverse cell types in the same tissue. In vitro experiments showed that the expression of FA-modifying enzymes such as desaturases and elongases in adipocytes and macrophages was regulated into opposing directions by TNF-α, IL-6, LPS or palmitate. The higher plasma concentration of the pro-resolving LM resolvin D1 in CC cannot compensate the overall inflammatory status and the results indicate that inflammatory cytokines interfere with synthesis pathways of pro-resolving LM. In summary, the data revealed a complex inter-tissue and inter-cellular crosstalk mediated by pro-inflammatory cytokines and lipid compounds enhancing inflammation in cancer cachexia by feed-forward mechanisms.
The spread of antibiotic-resistant bacteria poses a globally increasing threat to public health care. The excessive use of antibiotics in animal husbandry can develop resistances in the stables. Transmission through direct contact with animals and contamination of food has already been proven. The excrements of the animals combined with a binding material enable a further potential path of spread into the environment, if they are used as organic manure in agricultural landscapes. As most of the airborne bacteria are attached to particulate matter, the focus of the work will be the atmospheric dispersal via the dust fraction.
Field measurements on arable lands in Brandenburg, Germany and wind erosion studies in a wind tunnel were conducted to investigate the risk of a potential atmospheric dust-associated spread of antibiotic-resistant bacteria from poultry manure fertilized agricultural soils. The focus was to (i) characterize the conditions for aerosolization and (ii) qualify and quantify dust emissions during agricultural operations and wind erosion.
PM10 (PM, particulate matter with an aerodynamic diameter smaller than 10 µm) emission factors and bacterial fluxes for poultry manure application and incorporation have not been previously reported before. The contribution to dust emissions depends on the water content of the manure, which is affected by the manure pretreatment (fresh, composted, stored, dried), as well as by the intensity of manure spreading from the manure spreader. During poultry manure application, PM10 emission ranged between 0.05 kg ha-1 and 8.37 kg ha-1. For comparison, the subsequent land preparation contributes to 0.35 – 1.15 kg ha-1 of PM10 emissions. Manure particles were still part of dust emissions but they were accounted to be less than 1% of total PM10 emissions due to the dilution of poultry manure in the soil after manure incorporation. Bacterial emissions of fecal origin were more relevant during manure application than during the subsequent manure incorporation, although PM10 emissions of manure incorporation were larger than PM10 emissions of manure application for the non-dried manure variants.
Wind erosion leads to preferred detachment of manure particles from sandy soils, when poultry manure has been recently incorporated. Sorting effects were determined between the low-density organic particles of manure origin and the soil particles of mineral origin close above the threshold of 7 m s-1. In dependence to the wind speed, potential erosion rates between 101 and 854 kg ha-1 were identified, if 6 t ha-1 of poultry manure were applied. Microbial investigation showed that manure bacteria got detached more easily from the soil surface during wind erosion, due to their attachment on manure particles.
Although antibiotic-resistant bacteria (ESBL-producing E. coli) were still found in the poultry barns, no further contamination could be detected with them in the manure, fertilized soils or in the dust generated by manure application, land preparation or wind erosion. Parallel studies of this project showed that storage of poultry manure for a few days (36 – 72 h) is sufficient to inactivate ESBL-producing E. coli. Further antibiotic-resistant bacteria, i.e. MRSA and VRE, were only found sporadically in the stables and not at all in the dust. Therefore, based on the results of this work, the risk of a potential infection by dust-associated antibiotic-resistant bacteria can be considered as low.
The Andean Cordillera is a mountain range located at the western South American margin and is part of the Eastern- Circum-Pacific orogenic Belt. The ~7000 km long mountain range is one of the longest on Earth and hosts the second largest orogenic plateau in the world, the Altiplano-Puna plateau. The Andes are known as a non-collisional subduction-type orogen which developed as a result of the interaction between the subducted oceanic Nazca plate and the South American continental plate. The different Andean segments exhibit along-strike variations of morphotectonic provinces characterized by different elevations, volcanic activity, deformation styles, crustal thickness, shortening magnitude and oceanic plate geometry. Most of the present-day elevation can be explained by crustal shortening in the last ~50 Ma, with the shortening magnitude decreasing from ~300 km in the central (15°S-30°S) segment to less than half that in the southern part (30°S-40°S). Several factors were proposed that might control the magnitude and acceleration of shortening of the Central Andes in the last 15 Ma. One important factor is likely the slab geometry. At 27-33°S, the slab dips horizontally at ~100 km depth due to the subduction of the buoyant Juan Fernandez Ridge, forming the Pampean flat-slab. This horizontal subduction is thought to influence the thermo-mechanical state of the Sierras Pampeanas foreland, for instance, by strengthening the lithosphere and promoting the thick-skinned propagation of deformation to the east, resulting in the uplift of the Sierras Pampeanas basement blocks. The flat-slab has migrated southwards from the Altiplano latitude at ~30 Ma to its present-day position and the processes and consequences associated to its passage on the contemporaneous acceleration of the shortening rate in Central Andes remain unclear. Although the passage of the flat-slab could offer an explanation to the acceleration of the shortening, the timing does not explain the two pulses of shortening at about 15 Ma and 4 Ma that are suggested from geological observations. I hypothesize that deformation in the Central Andes is controlled by a complex interaction between the subduction dynamics of the Nazca plate and the dynamic strengthening and weakening of the South American plate due to several upper plate processes. To test this hypothesis, a detailed investigation into the role of the flat-slab, the structural inheritance of the continental plate, and the subduction dynamics in the Andes is needed. Therefore, I have built two classes of numerical thermo-mechanical models: (i) The first class of models are a series of generic E-W-oriented high-resolution 2D subduction models thatinclude flat subduction in order to investigate the role of the subduction dynamics on the temporal variability of the shortening rate in the Central Andes at Altiplano latitudes (~21°S). The shortening rate from the models was then validated with the observed tectonic shortening rate in the Central Andes. (ii) The second class of models are a series of 3D data-driven models of the present-day Pampean flat-slab configuration and the Sierras Pampeanas (26-42°S). The models aim to investigate the relative contribution of the present-day flat subduction and inherited structures in the continental lithosphere on the strain localization. Both model classes were built using the advanced finite element geodynamic code ASPECT.
The first main finding of this work is to suggest that the temporal variability of shortening in the Central Andes is primarily controlled by the subduction dynamics of the Nazca plate while it penetrates into the mantle transition zone. These dynamics depends on the westward velocity of the South American plate that provides the main crustal shortening force to the Andes and forces the trench to retreat. When the subducting plate reaches the lower mantle, it buckles on it-self until the forced trench retreat causes the slab to steepen in the upper mantle in contrast with the classical slab-anchoring model. The steepening of the slab hinders the trench causing it to resist the advancing South American plate, resulting in the pulsatile shortening. This buckling and steepening subduction regime could have been initiated because of the overall decrease in the westwards velocity of the South American plate. In addition, the passage of the flat-slab is required to promote the shortening of the continental plate because flat subduction scrapes the mantle lithosphere, thus weakening the continental plate. This process contributes to the efficient shortening when the trench is hindered, followed by mantle lithosphere delamination at ~20 Ma. Finally, the underthrusting of the Brazilian cratonic shield beneath the orogen occurs at ~11 Ma due to the mechanical weakening of the thick sediments covered the shield margin, and due to the decreasing resistance of the weakened lithosphere of the orogen.
The second main finding of this work is to suggest that the cold flat-slab strengthens the overriding continental lithosphere and prevents strain localization. Therefore, the deformation is transmitted to the eastern front of the flat-slab segment by the shear stress operating at the subduction interface, thus the flat-slab acts like an indenter that “bulldozes” the mantle-keel of the continental lithosphere. The offset in the propagation of deformation to the east between the flat and steeper slab segments in the south causes the formation of a transpressive dextral shear zone. Here, inherited faults of past tectonic events are reactivated and further localize the deformation in an en-echelon strike-slip shear zone, through a mechanism that I refer to as “flat-slab conveyor”. Specifically, the shallowing of the flat-slab causes the lateral deformation, which explains the timing of multiple geological events preceding the arrival of the flat-slab at 33°S. These include the onset of the compression and of the transition between thin to thick-skinned deformation styles resulting from the crustal contraction of the crust in the Sierras Pampeanas some 10 and 6 Myr before the Juan Fernandez Ridge collision at that latitude, respectively.
In recent decades, astronomy has seen a boom in large-scale stellar surveys of the Galaxy. The detailed information obtained about millions of individual stars in the Milky Way is bringing us a step closer to answering one of the most outstanding questions in astrophysics: how do galaxies form and evolve? The Milky Way is the only galaxy where we can dissect many stars into their high-dimensional chemical composition and complete phase space, which analogously as fossil records can unveil the past history of the genesis of the Galaxy. The processes that lead to large structure formation, such as the Milky Way, are critical for constraining cosmological models; we call this line of study Galactic archaeology or near-field cosmology.
At the core of this work, we present a collection of efforts to chemically and dynamically characterise the disks and bulge of our Galaxy. The results we present in this thesis have only been possible thanks to the advent of the Gaia astrometric satellite, which has revolutionised the field of Galactic archaeology by precisely measuring the positions, parallax distances and motions of more than a billion stars. Another, though not less important, breakthrough is the APOGEE survey, which has observed spectra in the near-infrared peering into the dusty regions of the Galaxy, allowing us to determine detailed chemical abundance patterns in hundreds of thousands of stars. To accurately depict the Milky Way structure, we use and develop the Bayesian isochrone fitting tool/code called StarHorse; this software can predict stellar distances, extinctions and ages by combining astrometry, photometry and spectroscopy based on stellar evolutionary models. The StarHorse code is pivotal to calculating distances where Gaia parallaxes alone cannot allow accurate estimates.
We show that by combining Gaia, APOGEE, photometric surveys and using StarHorse, we can produce a chemical cartography of the Milky way disks from their outermost to innermost parts. Such a map is unprecedented in the inner Galaxy. It reveals a continuity of the bimodal chemical pattern previously detected in the solar neighbourhood, indicating two populations with distinct formation histories. Furthermore, the data reveals a chemical gradient within the thin disk where the content of 𝛼-process elements and metals is higher towards the centre. Focusing on a sample in the inner MW we confirm the extension of the chemical duality to the innermost regions of the Galaxy. We find stars with bar shape orbits to show both high- and low-𝛼 abundances, suggesting the bar formed by secular evolution trapping stars that already existed. By analysing the chemical orbital space of the inner Galactic regions, we disentangle the multiple populations that inhabit this complex region. We reveal the presence of the thin disk, thick disk, bar, and a counter-rotating population, which resembles the outcome of a perturbed proto-Galactic disk. Our study also finds that the inner Galaxy holds a high quantity of super metal-rich stars up to three times solar suggesting it is a possible repository of old super-metal-rich stars found in the solar neighbourhood.
We also enter into the complicated task of deriving individual stellar ages. With StarHorse, we calculate the ages of main-sequence turn-off and sub-giant stars for several public spectroscopic surveys. We validate our results by investigating linear relations between chemical abundances and time since the 𝛼 and neutron capture elements are sensitive to age as a reflection of the different enrichment timescales of these elements. For further study of the disks in the solar neighbourhood, we use an unsupervised machine learning algorithm to delineate a multidimensional separation of chrono-chemical stellar groups revealing the chemical thick disk, the thin disk, and young 𝛼-rich stars. The thick disk is shown to have a small age dispersion indicating its fast formation contrary to the thin disk that spans a wide range of ages.
With groundbreaking data, this thesis encloses a detailed chemo-dynamical view of the disk and bulge of our Galaxy. Our findings on the Milky Way can be linked to the evolution of high redshift disk galaxies, helping to solve the conundrum of galaxy formation.
Over the last years there is an increasing awareness that historical land cover changes and associated land use legacies may be important drivers for present-day species richness and biodiversity due to time-delayed extinctions or colonizations in response to historical environmental changes. Historically altered habitat patches may therefore exhibit an extinction debt or colonization credit and can be expected to lose or gain species in the future. However, extinction debts and colonization credits are difficult to detect and their actual magnitudes or payments have rarely been quantified because species richness patterns and dynamics are also shaped by recent environmental conditions and recent environmental changes.
In this thesis we aimed to determine patterns of herb-layer species richness and recent species richness dynamics of forest herb layer plants and link those patterns and dynamics to historical land cover changes and associated land use legacies. The study was conducted in the Prignitz, NE-Germany, where the forest distribution remained stable for the last ca. 100 years but where a) the deciduous forest area had declined by more than 90 per cent (leaving only remnants of "ancient forests"), b) small new forests had been established on former agricultural land ("post-agricultural forests"). Here, we analyzed the relative importance of land use history and associated historical land cover changes for herb layer species richness compared to recent environmental factors and determined magnitudes of extinction debt and colonization credit and their payment in ancient and post-agricultural forests, respectively.
We showed that present-day species richness patterns were still shaped by historical land cover changes that ranged back to more than a century. Although recent environmental conditions were largely comparable we found significantly more forest specialists, species with short-distance dispersal capabilities and clonals in ancient forests than in post-agricultural forests. Those species richness differences were largely contingent to a colonization credit in post-agricultural forests that ranged up to 9 species (average 4.7), while the extinction debt in ancient forests had almost completely been paid. Environmental legacies from historical agricultural land use played a minor role for species richness differences. Instead, patch connectivity was most important. Species richness in ancient forests was still dependent on historical connectivity, indicating a last glimpse of an extinction debt, and the colonization credit was highest in isolated post-agricultural forests. In post-agricultural forests that were better connected or directly adjacent to ancient forest patches the colonization credit was way smaller and we were able to verify a gradual payment of the colonization credit from 2.7 species to 1.5 species over the last six decades.
The increasing number of known exoplanets raises questions about their demographics and the mechanisms that shape planets into how we observe them today. Young planets in close-in orbits are exposed to harsh environments due to the host star being magnetically highly active, which results in high X-ray and extreme UV fluxes impinging on the planet. Prolonged exposure to this intense photoionizing radiation can cause planetary atmospheres to heat up, expand and escape into space via a hydrodynamic escape process known as photoevaporation. For super-Earth and sub-Neptune-type planets, this can even lead to the complete erosion of their primordial gaseous atmospheres. A factor of interest for this particular mass-loss process is the activity evolution of the host star. Stellar rotation, which drives the dynamo and with it the magnetic activity of a star, changes significantly over the stellar lifetime. This strongly affects the amount of high-energy radiation received by a planet as stars age. At a young age, planets still host warm and extended envelopes, making them particularly susceptible to atmospheric evaporation. Especially in the first gigayear, when X-ray and UV levels can be 100 - 10,000 times higher than for the present-day sun, the characteristics of the host star and the detailed evolution of its high-energy emission are of importance.
In this thesis, I study the impact of stellar activity evolution on the high-energy-induced atmospheric mass loss of young exoplanets. The PLATYPOS code was developed as part of this thesis to calculate photoevaporative mass-loss rates over time. The code, which couples parameterized planetary mass-radius relations with an analytical hydrodynamic escape model, was used, together with Chandra and eROSITA X-ray observations, to investigate the future mass loss of the two young multiplanet systems V1298 Tau and K2-198. Further, in a numerical ensemble study, the effect of a realistic spread of activity tracks on the small-planet radius gap was investigated for the first time. The works in this thesis show that for individual systems, in particular if planetary masses are unconstrained, the difference between a young host star following a low-activity track vs. a high-activity one can have major implications: the exact shape of the activity evolution can determine whether a planet can hold on to some of its atmosphere, or completely loses its envelope, leaving only the bare rocky core behind. For an ensemble of simulated planets, an observationally-motivated distribution of activity tracks does not substantially change the final radius distribution at ages of several gigayears. My simulations indicate that the overall shape and slope of the resulting small-planet radius gap is not significantly affected by the spread in stellar activity tracks. However, it can account for a certain scattering or fuzziness observed in and around the radius gap of the observed exoplanet population.
Most of the matter in the universe consists of hydrogen. The hydrogen in the intergalactic medium (IGM), the matter between the galaxies, underwent a change of its ionisation state at the epoch of reionisation, at a redshift roughly between 6>z>10, or ~10^8 years after the Big Bang. At this time, the mostly neutral hydrogen in the IGM was ionised but the source of the responsible hydrogen ionising emission remains unclear. In this thesis I discuss the most likely candidates for the emission of this ionising radiation, which are a type of galaxy called Lyman alpha emitters (LAEs). As implied by their name, they emit Lyman alpha radiation, produced after a hydrogen atom has been ionised and recombines with a free electron. The ionising radiation itself (also called Lyman continuum emission) which is needed for this process inside the LAEs could also be responsible for ionising the IGM around those galaxies at the epoch of reionisation, given that enough Lyman continuum escapes. Through this mechanism, Lyman alpha and Lyman continuum radiation are closely linked and are both studied to better understand the properties of high redshift galaxies and the reionisation state of the universe.
Before I can analyse their Lyman alpha emission lines and the escape of Lyman continuum emission from them, the first step is the detection and correct classification of LAEs in integral field spectroscopic data, specifically taken with the Multi-Unit Spectroscopic Explorer (MUSE). After detecting emission line objects in the MUSE data, the task of classifying them and determining their redshift is performed with the graphical user interface QtClassify, which I developed during the work on this thesis. It uses the strength of the combination of spectroscopic and photometric information that integral field spectroscopy offers to enable the user to quickly identify the nature of the detected emission lines. The reliable classification of LAEs and determination of their redshifts is a crucial first step towards an analysis of their properties.
Through radiative transfer processes, the properties of the neutral hydrogen clouds in and around LAEs are imprinted on the shape of the Lyman alpha line. Thus after identifying the LAEs in the MUSE data, I analyse the properties of the Lyman alpha emission line, such as the equivalent width (EW) distribution, the asymmetry and width of the line as well as the double peak fraction. I challenge the common method of displaying EW distributions as histograms without taking the limits of the survey into account and construct a more independent EW distribution function that better reflects the properties of the underlying population of galaxies. I illustrate this by comparing the fraction of high EW objects between the two surveys MUSE-Wide and MUSE-Deep, both consisting of MUSE pointings (each with the size of one square arcminute) of different depths. In the 60 MUSE-Wide fields of one hour exposure time I find a fraction of objects with extreme EWs above EW_0>240A of ~20%, while in the MUSE-Deep fields (9 fields with an exposure time of 10 hours and one with an exposure time of 31 hours) I find a fraction of only ~1%, which is due to the differences in the limiting line flux of the surveys. The highest EW I measure is EW_0 = 600.63 +- 110A, which hints at an unusual underlying stellar population, possibly with a very low metallicity.
With the knowledge of the redshifts and positions of the LAEs detected in the MUSE-Wide survey, I also look for Lyman continuum emission coming from these galaxies and analyse the connection between Lyman continuum emission and Lyman alpha emission. I use ancillary Hubble Space Telescope (HST) broadband photometry in the bands that contain the Lyman continuum and find six Lyman continuum leaker candidates. To test whether the Lyman continuum emission of LAEs is coming only from those individual objects or the whole population, I select LAEs that are most promising for the detection of Lyman continuum emission, based on their rest-frame UV continuum and Lyman alpha line shape properties. After this selection, I stack the broadband data of the resulting sample and detect a signal in Lyman continuum with a significance of S/N = 5.5, pointing towards a Lyman continuum escape fraction of ~80%. If the signal is reliable, it strongly favours LAEs as the providers of the hydrogen ionising emission at the epoch of reionisation and beyond.
Aging is associated with bone loss, which can lead to osteoporosis and high fracture risk. This coincides with the enhanced formation of bone marrow adipose tissue (BMAT), suggesting a negative effect of bone marrow adipocytes on skeletal health. Increased BMAT formation is also observed in pathologies such as obesity, type 2 diabetes and osteoporosis. However, a subset of bone marrow adipocytes forming the constitutive BMAT (cBMAT), arise early in life in the distal skeleton, contain high levels of unsaturated fatty acids and are thought to provide a physiological function. Regulated BMAT (rBMAT) forms during aging and obesity in proximal regions of the bone and contain a large proportion of saturated fatty acids. Paradoxically, BMAT accumulation is also enhanced during caloric restriction (CR), a life-span extending dietary intervention. This indicates, that different types of BMAT can form in response to opposing nutritional stimuli with potentially different functions.
To this end, two types of nutritional interventions, CR and high fat diet (HFD), that are both described to induce BMAT accumulation were carried out. CR markedly increased BMAT formation in the proximal tibia and led to a higher proportion of unsaturated fatty acids, making it similar to the physiological cBMAT. Additionally, proximal and diaphyseal tibia regions displayed higher adiponectin expression. In aged mice, CR was associated with an improved trabecular bone structure. Taken together, these findings demonstrate, that the type of BMAT that forms during CR might provide beneficial effects for local bone stem/progenitor cells and metabolic health. The HFD intervention performed in this thesis showed no effect on BMAT accumulation and bone microstructure. RNA Seq analysis revealed alterations in the composition of the collagen-containing extracellular matrix (ECM).
In order to investigate the effects of glucose homeostasis on osteogenesis, differentiation capacity of immortalized multipotent mesenchymal stromal cells (MSCs) and osteochondrogenic progenitor cells (OPCs) was analyzed. Insulin improved differentiation in both cell types, however, combination of with a high glucose concentration led to an impaired mineralization of the ECM. In the MSCs, this was accompanied by the formation of adipocytes, indicating negative effects of the adipocytes formed during hyperglycemic conditions on mineralization processes. However, the altered mineralization pattern and structure of the ECM was also observed in OPCs, which did not form any adipocytes, suggesting further negative effects of a hyperglycemic environment on osteogenic differentiation.
In summary, the work provided in this thesis demonstrated that differentiation commitment of bone-resident stem cells can be altered through nutrient availability, specifically glucose. Surprisingly, both high nutrient supply, e.g. the hyperglycemic cell culture conditions, and low nutrient supply, e.g. CR, can induce adipogenic differentiation. However, while CR-induced adipocyte formation was associated with improved trabecular bone structure, adipocyte formation in a hyperglycemic cell-culture environment hampered mineralization. This thesis provides further evidence for the existence of different types of BMAT with specific functions.
The comprehension of figurative language : electrophysiological evidence on the processing of irony
(2008)
This dissertation investigates the comprehension of figurative language, in particular the temporal processing of verbal irony. In six experiments using event-related potentials(ERP) brain activity during the comprehension of ironic utterances in relation to equivalent non-ironic utterances was measured and analyzed. Moreover, the impact of various language-accompanying cues, e.g., prosody or the use of punctuation marks, as well as non-verbal cues such as pragmatic knowledge has been examined with respect to the processing of irony. On the basis of these findings different models on figurative language comprehension, i.e., the 'standard pragmatic model', the 'graded salience hypothesis', and the 'direct access view', are discussed.
Technologically important, environmentally friendly InP quantum dots (QDs) typically used as green and red emitters in display devices can achieve exceptional photoluminescence quantum yields (PL QYs) of near-unity (95-100%) when the-state-of-the-art core/shell heterostructure of the ZnSe inner/ZnS outer shell is elaborately applied. Nevertheless, it has only led to a few industrial applications as QD liquid crystal display (QD–LCD) which is applied to blue backlight units, even though QDs has a lot of possibilities that able to realize industrially feasible applications, such as QD light-emitting diodes (QD‒LEDs) and luminescence solar concentrator (LSC), due to their functionalizable characteristics.
Before introducing the main research, the theoretical basis and fundamentals of QDs are described in detail on the basis of the quantum mechanics and experimental synthetic results, where a concept of QD and colloidal QD, a type-I core/shell structure, a transition metal doped semiconductor QDs, the surface chemistry of QD, and their applications (LSC, QD‒LEDs, and EHD jet printing) are sequentially elucidated for better understanding. This doctoral thesis mainly focused on the connectivity between QD materials and QD devices, based on the synthesis of InP QDs that are composed of inorganic core (core/shell heterostructure) and organic shell (surface ligands on the QD surface). In particular, as for the former one (core/shell heterostructure), the ZnCuInS mid-shell as an intermediate layer is newly introduced between a Cu-doped InP core and a ZnS shell for LSC devices. As for the latter one (surface ligands), the ligand effect by 1-octanethiol and chloride ion are investigated for the device stability in QD‒LEDs and the printability of electro-hydrodynamic (EHD) jet printing system, in which this research explores the behavior of surface ligands, based on proton transfer mechanism on the QD surface.
Chapter 3 demonstrates the synthesis of strain-engineered highly emissive Cu:InP/Zn–Cu–In–S (ZCIS)/ZnS core/shell/shell heterostructure QDs via a one-pot approach. When this unconventional combination of a ZCIS/ZnS double shelling scheme is introduced to a series of Cu:InP cores with different sizes, the resulting Cu:InP/ZCIS/ZnS QDs with a tunable near-IR PL range of 694–850 nm yield the highest-ever PL QYs of 71.5–82.4%. These outcomes strongly point to the efficacy of the ZCIS interlayer, which makes the core/shell interfacial strain effectively alleviated, toward high emissivity. The presence of such an intermediate ZCIS layer is further examined by comparative size, structural, and compositional analyses. The end of this chapter briefly introduces the research related to the LSC devices, fabricated from Cu:InP/ZCIS/ZnS QDs, currently in progress.
Chapter 4 mainly deals with ligand effect in 1-octanethiol passivation of InP/ZnSe/ZnS QDs in terms of incomplete surface passivation during synthesis. This chapter demonstrates the lack of anionic carboxylate ligands on the surface of InP/ZnSe/ZnS quantum dots (QDs), where zinc carboxylate ligands can be converted to carboxylic acid or carboxylate ligands via proton transfer by 1-octanethiol. The as-synthesized QDs initially have an under-coordinated vacancy surface, which is passivated by solvent ligands such as ethanol and acetone. Upon exposure of 1-octanethiol to the QD surface, 1-octanthiol effectively induces the surface binding of anionic carboxylate ligands (derived from zinc carboxylate ligands) by proton transfer, which consequently exchanges ethanol and acetone ligands that bound on the incomplete QD surface. The systematic chemical analyses, such as thermogravimetric analysis‒mass spectrometry and proton nuclear magnetic resonance spectroscopy, directly show the interplay of surface ligands, and it associates with QD light-emitting diodes (QD‒LEDs).
Chapter 5 shows the relation between material stability of QDs and device stability of QD‒LEDs through the investigation of surface chemistry and shell thickness. In typical III–V colloidal InP quantum dots (QDs), an inorganic ZnS outermost shell is used to provide stability when overcoated onto the InP core. However, this work presents a faster photo-degradation of InP/ZnSe/ZnS QDs with a thicker ZnS shell than that with a thin ZnS shell when 1-octanethiol was applied as a sulfur source to form ZnS outmost shell. Herein, 1-octanethiol induces the form of weakly-bound carboxylate ligand via proton transfer on the QD surface, resulting in a faster degradation at UV light even though a thicker ZnS shell was formed onto InP/ZnSe QDs. Detailed insight into surface chemistry was obtained from proton nuclear magnetic resonance spectroscopy and thermogravimetric analysis–mass spectrometry. However, the lifetimes of the electroluminescence devices fabricated from InP/ZnSe/ZnS QDs with a thick or a thin ZnS shell show surprisingly the opposite result to the material stability of QDs, where the QD light-emitting diodes (QD‒LEDs) with a thick ZnS shelled QDs maintained its luminance more stable than that with a thin ZnS shelled QDs. This study elucidates the degradation mechanism of the QDs and the QD light-emitting diodes based on the results and discuss why the material stability of QDs is different from the lifetime of QD‒LEDs.
Chapter 6 suggests a method how to improve a printability of EHD jet printing when QD materials are applied to QD ink formulation, where this work introduces the application of GaP mid-shelled InP QDs as a role of surface charge in EHD jet printing technique. In general, GaP intermediate shell has been introduced in III–V colloidal InP quantum dots (QDs) to enhance their thermal stability and quantum efficiency in the case of type-I core/shell/shell heterostructure InP/GaP/ZnSeS QDs. Herein, these highly luminescent InP/GaP/ZnSeS QDs were synthesized and applied to EHD jet printing, by which this study demonstrates that unreacted Ga and Cl ions on the QD surface induce the operating voltage of cone jet and cone jet formation to be reduced and stabilized, respectively. This result indicates GaP intermediate shell not only improves PL QY and thermal stability of InP QDs but also adjusts the critical flow rate required for cone-jet formation. In other words, surface charges of quantum dots can have a significant role in forming cone apex in the EHD capillary nozzle. For an industrially convenient validation of surface charges on the QD surface, Zeta potential analyses of QD solutions as a simple method were performed, as well as inductively coupled plasma optical emission spectrometry (ICP-OES) for a composition of elements.
Beyond the generation of highly emissive InP QDs with narrow FWHM, these studies talk about the connection between QD material and QD devices not only to make it a vital jumping-off point for industrially feasible applications but also to reveal from chemical and physical standpoints the origin that obstructs the improvement of device performance experimentally and theoretically.
For the first time stabilizer-free vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical CO₂. Polymerizations were carried out at 140°C, 1500 bar and were initiated with di-tert-butyl peroxide (DTBP). In-line FT-NIR (Fourier Transform- Near Infrared) spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography (SEC) and polymer end group analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g∙mol−1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. To allow for isothermal reactions high CO₂ contents ranging from 61 to 83 wt.% were used. The high-temperature, high-pressure conditions were required for homogeneous phase polymerization. These conditions did not alter the amount of defects in VDF chaining. Scanning electron microscopy (SEM) indicated that regular stack-type particles were obtained upon expansion of the homogeneous polymerization mixture. To reduce the required amount of initiator, further VDF polymerizations using chain transfer agents (CTAs) to control molecular weights were carried out in homogeneous phase with supercritical carbon dioxide (scCO₂) at 120 °C and 1500 bar. Using perfluorinated hexyl iodide as CTA, polymers of low polydispersity ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol·L-1 were obtained. Electrospray ionization- mass spectroscopy (ESI-MS) indicates the absence of initiator derived end groups, supporting livingness of the system. The “livingness” is based on the labile C-I bond. However, due to the weakness of the C-I bond perfluorinated hexyl iodide also contributes to initiation. To allow for kinetic analyses of VDF polymerizations the CTA should not contribute to initiation. Therefore, additional CTAs were applied: BrCCl3, C6F13Br and C6F13H. It was found that C6F13H does not contribute to initiation. At 120°C and 1500 bar kp/kt0.5~ 0.64 (L·mol−1·s−1)0.5 was derived. The chain transfer constant (CT) at 120°C has been determined to be 8·10−1, 9·10−2 and 2·10−4 for C6F13I, C6F13Br and C6F13H, respectively. These CT values are associated with the bond energy of the C-X bond. Moreover, the labile C-I bond allows for functionalization of the polymer to triazole end groups applying click reactions. After substitution of the iodide end group by an azide group 1,3 dipolar cycloadditions with alkynes yield polymers with 1,2,3 triazole end groups. Using symmetrical alkynes the reactions may be carried out in the absence of any catalyst. This end-functionalized poly (vinylidene fluoride) (PVDF) has higher thermal stability as compared to the normal PVDF. PVDF samples from homogeneous phase polymerizations in supercritical CO₂ and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs and morphology. Upon expansion the polymer was obtained as white powder. Scanning electron microscopy (SEM) showed that DTBP derived polymer end groups led to stack-type particles whereas sponge- or rose-type particles were obtained in case of CTA fragments as end groups. Fourier-Transform Infrared spectroscopy and wide angle X-ray diffraction indicated that the type of polymorph, α or β crystal phase was significantly affected by the type of end group. The content of β-phase material, which is responsible for piezoelectricity of PVDF, is the highest for polymer with DTBP-derived end groups. In addition, the crystallinity of the material, as determined via differential scanning calorimetry is affected by the end groups and polymer molecular weights. For example, crystallinity ranges from around 26 % for DTBP-derived end groups to a maximum of 62 % for end groups originating from perfluorinated hexyl iodide for polymers with Mn ~2200 g·mol–1. Expansion of the homogeneous polymerization mixture results in particle formation by a non-optimized RESS (Rapid Expansion from Supercritical Solution) process. Thus, it was tested how polymer end groups affect the particles size distribution obtained from RESS process under controlled conditions (T = 50°C and P = 200 bar). In all RESS experiments, small primary PVDF with diameters less than 100 nm without the use of liquid solvents, surfactants, or other additives were produced. A strong correlation between particle size and particle size distribution with polymer end groups and molecular weight of the original material was observed. The smallest particles were found for RESS of PVDF with Mn~ 4000 g·mol–1 and PFHI (C6F13I) - derived end groups.
This thesis covers the synthesis of conjugates of 2-Deoxy-D-ribose-5-phosphate aldolase (DERA) with suitable polymers and the subsequent immobilization of these conjugates in thin films via two different approaches.
2-Deoxy-D-ribose-5-phosphate aldolase (DERA) is a biocatalyst that is capable of converting acetaldehyde and a second aldehyde as acceptor into enantiomerically pure mono- and diyhydroxyaldehydes, which are important structural motifs in a number of pharmaceutically active compounds. Conjugation and immobilization renders the enzyme applicable for utilization in a continuously run biocatalytic process which avoids the common problem of product inhibition. Within this thesis, conjugates of DERA and poly(N-isopropylacrylamide) (PNIPAm) for immobilization via a self-assembly approach were synthesized and isolated, as well as conjugates with poly(N,N-dimethylacrylamide) (PDMAA) for a simplified and scalable spray-coating approach. For the DERA/PNIPAm-conjugates different synthesis routes were tested, including grafting-from and grafting-to, both being common methods for the conjugation. Furthermore, both lysines and cysteines were addressed for the conjugation in order to find optimum conjugation conditions. It turned out that conjugation via lysine causes severe activity loss as one lysine plays a key role in the catalyzing mechanism. The conjugation via the cysteines by a grafting-to approach using pyridyl disulfide (PDS) end-group functionalized polymers led to high conjugation efficiencies in the presence of polymer solubilizing NaSCN. The resulting conjugates maintained enzymatic activity and also gained high acetaldehyde tolerance which is necessary for their use later on in an industrial relevant process after their immobilization.
The resulting DERA/PNIPAm conjugates exhibited enhanced interfacial activity at the air/water interface compared to the single components, which is an important pre-requisite for the immobilization via the self-assembly approach. Conjugates with longer polymer chains formed homogeneous films on silicon wafers and glass slides while the ones with short chains could only form isolated aggregates. On top of that, long chain conjugates showed better activity maintenance upon the immobilization.
The crosslinking of conjugates, as well as their fixation on the support materials, are important for the mechanical stability of the films obtained from the self-assembly process. Therefore, in a second step, we introduced the UV-crosslinkable monomer DMMIBA to the PNIPAm polymers to be used for conjugation. The introduction of DMMIBA reduced the lower critical solution temperature (LCST) of the polymer and thus the water solubility at ambient conditions, resulting in lower conjugation efficiencies and in turn slightly poorer acetaldehyde tolerance of the resulting conjugates. Unlike the DERA/PNIPAm, the conjugates from the copolymer P(NIPAM-co-DMMIBA) formed continuous, homogenous films only after the crosslinking step via UV-treatment. For a firm binding of the crosslinked films, a functionalization protocol for the model support material cyclic olefin copolymer (COC) and the final target support, PAN based membranes, was developed that introduces analogue UV-reactive groups to the support surface. The conjugates immobilized on the modified COC films maintained enzymatic activity and showed good mechanical stability after several cycles of activity assessment. Conjugates with longer polymer chains, however, showed a higher degree of crosslinking after the UV-treatment leading to a pronounced loss of activity. A porous PAN membrane onto which the conjugates were immobilized as well, was finally transferred to a dead end filtration membrane module to catalyze the aldol reaction of the industrially relevant mixture of acetaldehyde and hexanal in a continuous mode. Mono aldol product was detectable, but yields were comparably low and the operational stability needs to be further improved
Another approach towards immobilization of DERA conjugates that was followed, was to generate the conjugates in situ by simply mixing enzyme and polymer and spray coat the mixture onto the membrane support. Compared to the previous approach, the focus was more put on simplicity and a possible scalability of the immobilization. Conjugates were thus only generated in-situ and not further isolated and characterized. For the conjugation, PDMAA equipped with N-2-thiolactone acrylamide (TlaAm) side chains was used, an amine-reactive comonomer that can react with the lysine residues of DERA, as well as with amino groups introduced to a desired support surface. Furthermore disulfide formation after hydrolysis of the Tla groups causes a crosslinking effect. The synthesized copolymer poly(N,N-Dimethylacrylamide-co-N-2-thiolactone acrylamide) (P(DMAA-co-TlaAm)) thus serves a multiple purpose including protein binding, crosslinking and binding to support materials. The mixture of DERA and polymer could be immobilized on the PAN support by spray-coating under partial maintenance of enzymatic activity. To improve the acetaldehyde tolerance, the polymer in used was further equipped with cysteine reactive PDS end-groups that had been used for the conjugation as described in the first part of the thesis. The generated conjugates indeed showed good acetaldehyde tolerance and were thus used to be coated onto PAN membrane supports. Post treatment with a basic aqueous solution of H2O2 was supposed to further crosslink the spray-coated film hydrolysis and oxidation of the thiolactone groups. However, a washing off of the material was observed. Optimization is thus still necessary.
Ein viel diskutiertes Thema unserer Zeit ist die Zukunft der Energiegewinnung und Speicherung. Dabei nimmt die Nanowissenschaft eine bedeutende Rolle ein; sie führt zu einer Effizienzsteigerung bei der Speicherung und Gewinnung durch bereits bekannte Materialien und durch neue Materialien. In diesem Zusammenhang ist die Chemie Wegbereiter für Nanomaterialien. Allerdings führen bisher die meisten bekannten Synthesen von Nanopartikeln zu undefinierten Partikeln. Eine einfache, kostengünstige und sichere Synthese würde die Möglichkeit einer breiten Anwendung und Skalierbarkeit bieten. In dieser Arbeit soll daher die Darstellung der einfachen Synthese von Mangannitrid-, Aluminiumnitrid-, Lithiummangansilicat-, Zirkonium-oxinitrid- und Mangancarbonatnanopartikel betrachtet werden. Dabei werden die sogenannte Harnstoff-Glas-Route als eine Festphasensynthese und die Solvothermalsynthese als typische Flüssigphasensynthese eingesetzt. Beide Synthesewege führen zu definierten Partikelgrößen und interessanten Morphologien und ermöglichen eine Einflussnahme auf die Produkte. Im Falle der Synthese der Mangannitridnanopartikel mithilfe der Harnstoff-Glas-Route führt diese zu Nanopartikeln mit Kern-Hülle-Struktur, deren Einsatz als Konversionsmaterial erstmalig vorgestellt wird. Mit dem Ziel einer leichteren Anwendung von Nanopartikeln wird eine einfache Beschichtung von Oberflächen mit Nanopartikeln mithilfe der Rotationsbeschichtung beschrieben. Es entstand ein Gemisch aus MnN0,43/MnO-Nanopartikeln, eingebettet in einem Kohlenstofffilm, dessen Untersuchung als Konversionsmaterial hohe spezifische Kapazitäten (811 mAh/g) zeigt, die die von dem konventionellen Anodenmaterial Graphit (372 mAh/g) übersteigt. Neben der Synthese des Anodenmaterials wurde ebenfalls die des Kathodenmaterials Li2MnSiO4-Nanopartikeln mithilfe der Harnstoff-Glas-Route vorgestellt. Mithilfe der Synthese von Zirkoniumoxinitridnanopartikeln Zr2ON2 kann eine einfache Einflussnahme auf das gewünschte Produkt durch die Variation derReaktionsbedingungen, wie Harnstoffmenge oder Reaktionstemperatur, bei der Harnstoff-Glas-Route demonstriert werden. Der Zusatz von kleinsten Mengen an Ammoniumchlorid vermeidet, dass sich Kohlenstoff im Endprodukt bildet und führt so zu gelben Zr2ON2-Nanopartikeln mit einer Größe d = 8 nm, die Halbleitereigen-schaften besitzen. Die Synthese von Aluminiumnitridnanopartikeln führt zu kristallinen Nanopartikeln, die in eine amorphe Matrix eingebettet sind. Die Solvothermalsynthese von Mangancarbonatnanopartikel lässt neue Morphologien in Form von Nanostäbchen entstehen, die zu schuppenartigen sphärischen Überstrukturen agglomeriert sind.
Sustainable urban growth
(2022)
This dissertation explores the determinants for sustainable and socially optimalgrowth in a city. Two general equilibrium models establish the base for this evaluation, each adding its puzzle piece to the urban sustainability discourse and examining the role of non-market-based and market-based policies for balanced growth and welfare improvements in different theory settings. Sustainable urban growth either calls for policy actions or a green energy transition. Further, R&D market failures can pose severe challenges to the sustainability of urban growth and the social optimality of decentralized allocation decisions. Still, a careful (holistic) combination of policy instruments can achieve sustainable growth and even be first best.
The utilization of lignin as renewable electrode material for electrochemical energy storage is a sustainable approach for future batteries and supercapacitors. The composite electrode was fabricated from Kraft lignin and conductive carbon and the charge storage contribution was determined in terms of electrical double layer (EDL) and redox reactions. The important factors at play for achieving high faradaic charge storage capacity contribute to high surface area, accessibility of redox sites in lignin and their interaction with conductive additives. A thinner layer of lignin covering the high surface area of carbon facilitates the electron transfer process with a shorter pathway from the active sites of nonconductive lignin to the current collector leading to the improvement of faradaic charge storage capacity.
Composite electrodes from lignin and carbon would be even more sustainable if the fluorinated binder can be omitted. A new route to fabricate a binder-free composite electrode from Kraft lignin and high surface area carbon has been proposed by crosslinking lignin with glyoxal. A high molecular weight of lignin is obtained to enhance both electroactivity and binder capability in composite electrodes. The order of the processing step of crosslinking lignin on the composite electrode plays a crucial role in achieving a stable electrode and high charge storage capacity. The crosslinked lignin based electrodes are promising since they allow for more stable, sustainable, halogen-free and environmentally benign devices for energy storage applications. Furthermore, improvement of the amount of redox active groups (quinone groups) in lignin is useful to enhance the capacity in lithium battery applications. Direct oxidative demethylation by cerium ammonium nitrate has been carried out under mild conditions. This proves that an increase of quinone groups is able to enhance the performance of lithium battery. Thus, lignin is a promising material and could be a good candidate for application in sustainable energy storage devices.
Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.
Supernovae are known to be the dominant energy source for driving turbulence in the interstellar medium. Yet, their effect on magnetic field amplification in spiral galaxies is still poorly understood. Analytical models based on the uncorrelated-ensemble approach predicted that any created field will be expelled from the disk before a significant amplification can occur. By means of direct simulations of supernova-driven turbulence, we demonstrate that this is not the case. Accounting for vertical stratification and galactic differential rotation, we find an exponential amplification of the mean field on timescales of 100Myr. The self-consistent numerical verification of such a “fast dynamo” is highly beneficial in explaining the observed strong magnetic fields in young galaxies. We, furthermore, highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field. This finding impressively confirms the classical picture of a dynamo based on cyclonic turbulence.
Stimuli-promoted in situ formation of hydrogels with thiol/thioester containing peptide precursors
(2022)
Hydrogels are potential synthetic ECM-like substitutes since they provide functional and structural similarities compared to soft tissues. They can be prepared by crosslinking of macromolecules or by polymerizing suitable precursors. The crosslinks are not necessarily covalent bonds, but could also be formed by physical interactions such as π-π interactions, hydrophobic interactions, or H-bonding. On demand in situ forming hydrogels have garnered increased interest especially for biomedical applications over preformed gels due to the relative ease of in vivo delivery and filling of cavities. The thiol-Michael addition reaction provides a straightforward and robust strategy for in situ gel formation with its fast reaction kinetics and ability to proceed under physiological conditions. The incorporation of a trigger function into a crosslinking system becomes even more interesting since gelling can be controlled with stimulus of choice. The use of small molar mass crosslinker precursors with active groups orthogonal to thiol-Michael reaction type electrophile provides the opportunity to implement an on-demand in situ crosslinking without compromising the fast reaction kinetics.
It was postulated that short peptide sequences due to the broad range structural-function relations available with the different constituent amino acids, can be exploited for the realisation of stimuli-promoted in situ covalent crosslinking and gelation applications. The advantages of this system over conventional polymer-polymer hydrogel systems are the ability tune and predict material property at the molecular level.
The main aim of this work was to develop a simplified and biologically-friendly stimuli-promoted in situ crosslinking and hydrogelation system using peptide mimetics as latent crosslinkers. The approach aims at using a single thiodepsipeptide sequence to achieve separate pH- and enzyme-promoted gelation systems with little modification to the thiodepsipeptide sequence. The realization of this aim required the completion of three milestones.
In the first place, after deciding on the thiol-Michael reaction as an effective in situ crosslinking strategy, a thiodepsipeptide, Ac-Pro-Leu-Gly-SLeu-Leu-Gly-NEtSH (TDP) with expected propensity towards pH-dependent thiol-thioester exchange (TTE) activation, was proposed as a suitable crosslinker precursor for pH-promoted gelation system. Prior to the synthesis of the proposed peptide-mimetic, knowledge of the thiol-Michael reactivity of the would-be activated thiol moiety SH-Leu, which is internally embedded in the thiodepsipeptide was required. In line with pKa requirements for a successful TTE, the reactivity of a more acidic thiol, SH-Phe was also investigated to aid the selection of the best thiol to be incorporated in the thioester bearing peptide based crosslinker precursor. Using ‘pseudo’ 2D-NMR investigations, it was found that only reactions involving SH-Leu yielded the expected thiol-Michael product, an observation that was attributed to the steric hindrance of the bulkier nature of SH-Phe. The fast reaction rates and complete acrylate/maleimide conversion obtained with SH-Leu at pH 7.2 and higher aided the direct elimination of SH-Phe as a potential thiol for the synthesis of the peptide mimetic.
Based on the initial studies, for the pH-promoted gelation system, the proposed Ac-Pro-Leu-Gly-SLeu-Leu-Gly-NEtSH was kept unmodified. The subtle difference in pKa values between SH-Leu (thioester thiol) and the terminal cysteamine thiol from theoretical conditions should be enough to effect a ‘pseudo’ intramolecular TTE. In polar protic solvents and under basic aqueous conditions, TDP successfully undergoes a ‘pseudo’ intramolecular TTE reaction to yield an α,ω-dithiol tripeptide, HSLeu-Leu-Gly-NEtSH. The pH dependence of thiolate ion generation by the cysteamine thiol aided the incorporation of the needed stimulus (pH) for the overall success of TTE (activation step) – thiol-Michael addition (crosslinking) strategy.
Secondly, with potential biomedical applications in focus, the susceptibility of TDP, like other thioesters, to intermolecular TTE reaction was probed with a group of thiols of varying thiol pKa values, since biological milieu characteristically contain peptide/protein thiols. L-cysteine, which is a biologically relevant thiol, and a small molecular weight thiol, methylthioglycolate both with relatively similar thiol pKa, values, led to an increase concentration of the dithiol crosslinker when reacted with TDP. In the presence of acidic thiols (p-NTP and 4MBA), a decrease in the dithiol concentration was observed, an observation that can be attributed to the inability of the TTE tetrahedral intermediate to dissociate into exchange products and is in line with pKa requirements for successful TTE reaction. These results additionally makes TDP more attractive and the potentially the first crosslinker precursor for applications in biologically relevant media.
Finally, the ability of TDP to promote pH-sensitive in situ gel formation was probed with maleimide functionalized 4-arm polyethylene glycol polymers in tris-buffered media of varying pHs. When a 1:1 thiol: maleimide molar ratio was used, TDP-PEG4MAL hydrogels formed within 3, 12 and 24 hours at pH values of 8.5, 8.0 and 7.5 respectively. However, gelation times of 3, 5 and 30 mins were observed for the same pH trend when the thiol: maleimide molar was increased to 2:1.
A direct correlation of thiol content with G’ of the gels at each pH could also be drawn by comparing gels with thiol: maleimide ratios of 1:1 to those with 2:1 thiol: maleimide mole ratios. This is supported by the fact that the storage modulus (G') is linearly dependent on the crosslinking density of the polymer. The values of initial G′ for all gels ranged between (200 – 5000 Pa), which falls in the range of elasticities of certain tissue microenvironments for example brain tissue 200 – 1000 Pa and adipose tissue (2500 – 3500 Pa).
Knowledge so far gained from the study on the ability to design and tune the exchange reaction of thioester containing peptide mimetic will give those working in the field further insight into the development of new sequences tailored towards specific applications.
TTE substrate design using peptide mimetic as presented in this work has revealed interesting new insights considering the state-of-the-art. Using the results obtained as reference, the strategy provides a possibility to extend the concept to the controlled delivery of active molecules needed for other robust and high yielding crosslinking reactions for biomedical applications. Application for this sequentially coupled functional system could be seen e.g. in the treatment of inflamed tissues associated with urinary tract like bladder infections for which pH levels above 7 were reported. By the inclusion of cell adhesion peptide motifs, the hydrogel network formed at this pH could act as a new support layer for the healing of damage epithelium as shown in interfacial gel formation experiments using TDP and PEG4MAL droplets.
The versatility of the thiodepsipeptide sequence, Ac-Pro-Leu-Gly-SLeu-Leu-Gly-(TDPo) was extended for the design and synthesis of a MMP-sensitive 4-arm PEG-TDPo conjugate. The purported cleavage of TDPo at the Gly-SLeu bond yields active thiol units for subsequent reaction of orthogonal Michael acceptor moieties. One of the advantages of stimuli-promoted in situ crosslinking systems using short peptides should be the ease of design of required peptide molecules due to the predictability of peptide functions their sequence structure. Consequently the functionalisation of a 4-arm PEG core with the collagenase active TDPo sequence yielded an MMP-sensitive 4-arm thiodepsipeptide-PEG conjugate (PEG4TDPo) substrate.
Cleavage studies using thiol flourometric assay in the presence of MMPs -2 and -9 confirmed the susceptibility of PEG4TDPo towards these enzymes. The resulting time-dependent increase in fluorescence intensity in the presence of thiol assay signifies the successful cleavage of TDPo at the Gly-SLeu bond as expected. It was observed that the cleavage studies with thiol flourometric assay introduces a sigmoid non-Michaelis-Menten type kinetic profile, hence making it difficult to accurately determine the enzyme cycling parameters, kcat and KM .
Gelation studies with PEG4MAL at 10 % wt. concentrations revealed faster gelation with MMP-2 than MMP-9 with 28 and 40 min gelation times respectively. Possible contributions by hydrolytic cleavage of PEG4TDPo has resulted in the gelation of PEG4MAL blank samples but only after 60 minutes of reaction. From theoretical considerations, the simultaneous gelation reaction would be expected to more negatively impact the enzymatic than hydrolytic cleavage. The exact contributions from hydrolytic cleavage of PEG4TDPo would however require additional studies.
In summary this new and simplified in situ crosslinking system using peptide-based crosslinker precursors with tuneable properties exhibited in situ crosslinking gelation kinetics on similar levels with already active dithiols reported. The advantageous on-demand functionality associated with its pH-sensitivity and physiological compatibility makes it a strong candidate worth further research as biomedical applications in general and on-demand material synthesis is concerned.
Results from MMP-promoted gelation system unveils a simple but unexplored approach for in situ synthesis of covalently crosslinked soft materials, that could lead to the development of an alternative pathway in addressing cancer metastasis by making use of MMP overexpression as a trigger. This goal has so far not being reach with MMP inhibitors despite the extensive work this regard.
I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae. I supplement my {3+1} GR hydrodynamic simulations with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on (1) the late postbounce gravitational wave emission owing to convective overturn, anisotropic neutrino emission and protoneutron star pulsations, and (2) on the gravitational wave signature of accretion-induced collapse of white dwarfs to neutron stars.
Stars under influence: evidence of tidal interactions between stars and substellar companions
(2023)
Tidal interactions occur between gravitationally bound astrophysical bodies. If their spatial separation is sufficiently small, the bodies can induce tides on each other, leading to angular momentum transfer and altering of evolutionary path the bodies would have followed if they were single objects. The tidal processes are well established in the Solar planet-moon systems and close stellar binary systems. However, how do stars behave if they are orbited by a substellar companion (e.g. a planet or a brown dwarf) on a tight orbit?
Typically, a substellar companion inside the corotation radius of a star will migrate toward the star as it loses orbital angular momentum. On the other hand, the star will gain angular momentum which has the potential to increase its rotation rate. The effect should be more pronounced if the substellar companion is more massive. As the stellar rotation rate and the magnetic activity level are coupled, the star should appear more magnetically active under the tidal influence of the orbiting substellar companion. However, the difficulty in proving that a star has a higher magnetic activity level due to tidal interactions lies in the fact that (I) substellar companions around active stars are easier to detect if they are more massive, leading to a bias toward massive companions around active stars and mimicking the tidal interaction effect, and that (II) the age of a main-sequence star cannot be easily determined, leaving the possibility that a star is more active due to its young age.
In our work, we overcome these issues by employing wide stellar binary systems where one star hosts a substellar companion, and where the other star provides the magnetic activity baseline for the host star, assuming they have coevolved, and thereby provides the host's activity level if tidal interactions have no effect on it. Firstly, we find that extrasolar planets can noticeably increase the host star's X-ray luminosity and that the effect is more pronounced if the exoplanet is at least Jupiter-like in mass and close to the star. Further, we find that a brown dwarf will have an even stronger effect, as expected, and that the X-ray surface flux difference between the host star and the wide stellar companion is a significant outlier when compared to a large sample of similar wide binary systems without any known substellar companions. This result proves that substellar hosting wide binary systems can be good tools to reveal the tidal effect on host stars, and also show that the typical stellar age indicators as activity or rotation cannot be used for these stars. Finally, knowing that the activity difference is a good tracer of the substellar companion's tidal impact, we develop an analytical method to calculate the modified tidal quality factor Q' of individual host stars, which defines the tidal dissipation efficiency in the convective envelope of a given main-sequence star.
This thesis is focussed on the electronic properties of the new material class named topological insulators. Spin and angle resolved photoelectron spectroscopy have been applied to reveal several unique properties of the surface state of these materials. The first part of this thesis introduces the methodical background of these quite established experimental techniques.
In the following chapter, the theoretical concept of topological insulators is introduced. Starting from the prominent example of the quantum Hall effect, the application of topological invariants to classify material systems is illuminated. It is explained how, in presence of time reversal symmetry, which is broken in the quantum Hall phase, strong spin orbit coupling can drive a system into a topologically non trivial phase. The prediction of the spin quantum Hall effect in two dimensional insulators an the generalization to the three dimensional case of topological insulators is reviewed together with the first experimental realization of a three dimensional topological insulator in the Bi1-xSbx alloys given in the literature.
The experimental part starts with the introduction of the Bi2X3 (X=Se, Te) family of materials. Recent theoretical predictions and experimental findings on the bulk and surface electronic structure of these materials are introduced in close discussion to our own experimental results. Furthermore, it is revealed, that the topological surface state of Bi2Te3 shares its orbital symmetry with the bulk valence band and the observation of a temperature induced shift of the chemical potential is to a high probability unmasked as a doping effect due to residual gas adsorption.
The surface state of Bi2Te3 is found to be highly spin polarized with a polarization value of about 70% in a macroscopic area, while in Bi2Se3 the polarization appears reduced, not exceeding 50%. We, however, argue that the polarization is most likely only extrinsically limited in terms of the finite angular resolution and the lacking detectability of the out of plane component of the electron spin. A further argument is based on the reduced surface quality of the single crystals after cleavage and, for Bi2Se3 a sensitivity of the electronic structure to photon exposure.
We probe the robustness of the topological surface state in Bi2X3 against surface impurities in Chapter 5. This robustness is provided through the protection by the time reversal symmetry. Silver, deposited on the (111) surface of Bi2Se3 leads to a strong electron doping but the surface state is observed up to a deposited Ag mass equivalent to one atomic monolayer. The opposite sign of doping, i.e., hole-like, is observed by exposing oxygen to Bi2Te3. But while the n-type shift of Ag on Bi2Se3 appears to be more or less rigid, O2 is lifting the Dirac point of the topological surface state in Bi2Te3 out of the valence band minimum at $\Gamma$. After increasing the oxygen dose further, it is possible to shift the Dirac point to the Fermi level, while the valence band stays well beyond. The effect is found reversible, by warming up the samples which is interpreted in terms of physisorption of O2.
For magnetic impurities, i.e., Fe, we find a similar behavior as for the case of Ag in both Bi2Se3 and Bi2Te3. However, in that case the robustness is unexpected, since magnetic impurities are capable to break time reversal symmetry which should introduce a gap in the surface state at the Dirac point which in turn removes the protection. We argue, that the fact that the surface state shows no gap must be attributed to a missing magnetization of the Fe overlayer. In Bi2Te3 we are able to observe the surface state for deposited iron mass equivalents in the monolayer regime. Furthermore, we gain control over the sign of doping through the sample temperature during deposition.
Chapter6 is devoted to the lifetime broadening of the photoemission signal from the topological surface states of Bi2Se3 and Bi2Te3. It is revealed that the hexagonal warping of the surface state in Bi2Te3 introduces an anisotropy for electrons traveling along the two distinct high symmetry directions of the surface Brillouin zone, i.e., $\Gamma$K and $\Gamma$M. We show that the phonon coupling strength to the surface electrons in Bi2Te3 is in nice agreement with the theoretical prediction but, nevertheless, higher than one may expect. We argue that the electron-phonon coupling is one of the main contributions to the decay of photoholes but the relatively small size of the Fermi surface limits the number of phonon modes that may scatter off electrons. This effect is manifested in the energy dependence of the imaginary part of the electron self energy of the surface state which shows a decay to higher binding energies in contrast to the monotonic increase proportional to E$^2$ in the Fermi liquid theory due to electron-electron interaction.
Furthermore, the effect of the surface impurities of Chapter 5 on the quasiparticle life- times is investigated. We find that Fe impurities have a much stronger influence on the lifetimes as compared to Ag. Moreover, we find that the influence is stronger independently of the sign of the doping. We argue that this observation suggests a minor contribution of the warping on increased scattering rates in contrast to current belief. This is additionally confirmed by the observation that the scattering rates increase further with increasing silver amount while the doping stays constant and by the fact that clean Bi2Se3 and Bi2Te3 show very similar scattering rates regardless of the much stronger warping in Bi2Te3.
In the last chapter we report on a strong circular dichroism in the angle distribution of the photoemission signal of the surface state of Bi2Te3. We show that the color pattern obtained by calculating the difference between photoemission intensities measured with opposite photon helicity reflects the pattern expected for the spin polarization. However, we find a strong influence on strength and even sign of the effect when varying the photon energy. The sign change is qualitatively confirmed by means of one-step photoemission calculations conducted by our collaborators from the LMU München, while the calculated spin polarization is found to be independent of the excitation energy. Experiment and theory together unambiguously uncover the dichroism in these systems as a final state effect and the question in the title of the chapter has to be negated: Circular dichroism in the angle distribution is not a new spin sensitive technique.
This PhD thesis presents the spatio-temporal distribution of terrestrial carbon fluxes for the time period of 1982 to 2002 simulated by a combination of the process-based dynamic global vegetation model LPJ and a 21-year time series of global AVHRR-fPAR data (fPAR – fraction of photosynthetically active radiation). Assimilation of the satellite data into the model allows improved simulations of carbon fluxes on global as well as on regional scales. As it is based on observed data and includes agricultural regions, the model combined with satellite data produces more realistic carbon fluxes of net primary production (NPP), soil respiration, carbon released by fire and the net land-atmosphere flux than the potential vegetation model. It also produces a good fit to the interannual variability of the CO2 growth rate. Compared to the original model, the model with satellite data constraint produces generally smaller carbon fluxes than the purely climate-based stand-alone simulation of potential natural vegetation, now comparing better to literature estimates. The lower net fluxes are a result of a combination of several effects: reduction in vegetation cover, consideration of human influence and agricultural areas, an improved seasonality, changes in vegetation distribution and species composition. This study presents a way to assess terrestrial carbon fluxes and elucidates the processes contributing to interannual variability of the terrestrial carbon exchange. Process-based terrestrial modelling and satellite-observed vegetation data are successfully combined to improve estimates of vegetation carbon fluxes and stocks. As net ecosystem exchange is the most interesting and most sensitive factor in carbon cycle modelling and highly uncertain, the presented results complementary contribute to the current knowledge, supporting the understanding of the terrestrial carbon budget.
Ziel der Studie war die Untersuchung individueller und familialer Faktoren für den sozialen Status eines Kindes in seiner Schulklasse. Durch die Unterscheidung von Akzeptanz und Einfluss als zweier Hauptdimensionen des sozialen Status konnte die Arbeit aufklären, welche Rolle verschiedene Attribute für das Erreichen von Akzeptanz oder Einfluss spielen. 234 Dritt- und Fünftklässler aus Berliner Grundschulen erhielten soziometrische Maße, durch welche der soziale Status erhoben wurde (Akzeptanz und Einfluss). Individuelle und familiale Faktoren wurden mittels Peernominationen über das Verhalten der Kinder (Fremdurteil), Schulnoten (Lehrerangabe)und Maße des sozio-ökonomischen Status der Eltern (Elternangabe)erhoben. Die Ergebnisse zeigen, dass Akzeptanz positiv mit prosozialem und negativ mit aggressivem Verhalten eines Kindes assoziiert ist. Die Zusammenhänge dieser Verhaltensweisen mit Einfluss wiesen in dieselbe Richtung, waren aber deutlich geringer. Ideenreichtum und Humor hingen mit Akzeptanz und Einfluss gleichermaßen positiv zusammen, sowie Traurigsein gleichermaßen negativ mit beiden Statusdimensionen verbunden war. Das Verhalten eines Kindes vermittelte den Zusammenhang zwischen Merkmalen wie Geschlecht, relativem Alter, Schulnoten und der Akzeptanz und dem Einfluss eines Kindes. Zum Beispiel war die positive Beziehung zwischen Schulnoten und dem sozialen Status überwiegend auf die mit(guten)Schulnoten assoziierten Verhaltensweisen Prosozialität und (geringe) Aggressivität zurückzuführen. Die größere Akzeptanz von Mädchen ließ sich ebenso durch deren größere Prosozialität und geringere Aggressivität erklären. Jungen waren im Hinblick auf ihren Einfluss sowohl am oberen als auch am unteren Ende der Hierarchie überrepräsentiert. Sowohl sehr einflussreiche als auch einflusslose Jungen zeichneten sich durch eine erhöhte Aggressivität aus. Komplexere Analysen wiesen daraufhin, dass Jungen negative Auswirkungen von aggressivem Verhalten durch Humor und Ideenreichtum auf ihren Status kompensieren konnten. Der moderate Zusammenhang zwischen dem elterlichen sozioökonomischen Status und dem sozialen Status des Kindes wurde vollständig durch das Verhalten des Kindes mediiert. Das Elternhaus war wichtiger für die Akzeptanz als für den Einfluss eines Kindes. Kinder mit Migrationshintergrund waren sowohl weniger akzeptiert als auch weniger einflussreich in ihrer Klasse. Elterliche Trennung trug nicht zur sozialen Position eines Kindes bei.
Major challenges during geothermal exploration and exploitation include the structural-geological characterization of the geothermal system and the application of sustainable monitoring concepts to explain changes in a geothermal reservoir during production and/or reinjection of fluids. In the absence of sufficiently permeable reservoir rocks, faults and fracture networks are preferred drilling targets because they can facilitate the migration of hot and/or cold fluids. In volcanic-geothermal systems considerable amounts of gas emissions can be released at the earth surface, often related to these fluid-releasing structures.
In this thesis, I developed and evaluated different methodological approaches and measurement concepts to determine the spatial and temporal variation of several soil gas parameters to understand the structural control on fluid flow. In order to validate their potential as innovative geothermal exploration and monitoring tools, these methodological approaches were applied to three different volcanic-geothermal systems. At each site an individual survey design was developed regarding the site-specific questions.
The first study presents results of the combined measurement of CO2 flux, ground temperatures, and the analysis of isotope ratios (δ13CCO2, 3He/4He) across the main production area of the Los Humeros geothermal field, to identify locations with a connection to its supercritical (T > 374◦C and P > 221 bar) geothermal reservoir. The results of the systematic and large-scale (25 x 200 m) CO2 flux scouting survey proved to be a fast and flexible way to identify areas of anomalous degassing. Subsequent sampling with high resolution surveys revealed the actual extent and heterogenous pattern of anomalous degassing areas. They have been related to the internal fault hydraulic architecture and allowed to assess favourable structural settings for fluid flow such as fault intersections. Finally, areas of unknown structurally controlled permeability with a connection to the superhot geothermal reservoir have been determined, which represent promising targets for future geothermal exploration and development.
In the second study, I introduce a novel monitoring approach by examining the variation of CO2 flux to monitor changes in the reservoir induced by fluid reinjection. For that reason, an automated, multi-chamber CO2 flux system was deployed across the damage zone of a major normal fault crossing the Los Humeros geothermal field. Based on the results of the CO2 flux scouting survey, a suitable site was selected that had a connection to the geothermal reservoir, as identified by hydrothermal CO2 degassing and hot ground temperatures (> 50 °C). The results revealed a response of gas emissions to changes in reinjection rates within 24 h, proving an active hydraulic communication between the geothermal reservoir and the earth surface. This is a promising monitoring strategy that provides nearly real-time and in-situ data about changes in the reservoir and allows to timely react to unwanted changes (e.g., pressure decline, seismicity).
The third study presents results from the Aluto geothermal field in Ethiopia where an area-wide and multi-parameter analysis, consisting of measurements of CO2 flux, 222Rn, and 220Rn activity concentrations and ground temperatures was conducted to detect hidden permeable structures. 222Rn and 220Rn activity concentrations are evaluated as a complementary soil gas parameter to CO2 flux, to investigate their potential to understand tectono-volcanic degassing. The combined measurement of all parameters enabled to develop soil gas fingerprints, a novel visualization approach. Depending on the magnitude of gas emissions and their migration velocities the study area was divided in volcanic (heat), tectonic (structures), and volcano-tectonic dominated areas. Based on these concepts, volcano-tectonic dominated areas, where hot hydrothermal fluids migrate along permeable faults, present the most promising targets for future geothermal exploration and development in this geothermal field. Two of these areas have been identified in the south and south-east which have not yet been targeted for geothermal exploitation. Furthermore, two unknown areas of structural related permeability could be identified by 222Rn and 220Rn activity concentrations.
Eventually, the fourth study presents a novel measurement approach to detect structural controlled CO2 degassing, in Ngapouri geothermal area, New Zealand. For the first time, the tunable diode laser (TDL) method was applied in a low-degassing geothermal area, to evaluate its potential as a geothermal exploration method. Although the sampling approach is based on profile measurements, which leads to low spatial resolution, the results showed a link between known/inferred faults and increased CO2 concentrations. Thus, the TDL method proved to be a successful in the determination of structural related permeability, also in areas where no obvious geothermal activity is present. Once an area of anomalous CO2 concentrations has been identified, it can be easily complemented by CO2 flux grid measurements to determine the extent and orientation of the degassing segment.
With the results of this work, I was able to demonstrate the applicability of systematic and area-wide soil gas measurements for geothermal exploration and monitoring purposes. In particular, the combination of different soil gases using different measurement networks enables the identification and characterization of fluid-bearing structures and has not yet been used and/or tested as standard practice. The different studies present efficient and cost-effective workflows and demonstrate a hands-on approach to a successful and sustainable exploration and monitoring of geothermal resources. This minimizes the resource risk during geothermal project development. Finally, to advance the understanding of the complex structure and dynamics of geothermal systems, a combination of comprehensive and cutting-edge geological, geochemical, and geophysical exploration methods is essential.
The central gas in half of all galaxy clusters shows short cooling times. Assuming unimpeded cooling, this should lead to high star formation and mass cooling rates, which are not observed. Instead, it is believed that condensing gas is accreted by the central black hole that powers an active galactic nuclei jet, which heats the cluster. The detailed heating mechanism remains uncertain. A promising mechanism invokes cosmic ray protons that scatter on self-generated magnetic fluctuations, i.e. Alfvén waves. Continuous damping of Alfvén waves provides heat to the intracluster medium. Previous work has found steady state solutions for a large sample of clusters where cooling is balanced by Alfvénic wave heating. To verify modeling assumptions, we set out to study cosmic ray injection in three-dimensional magnetohydrodynamical simulations of jet feedback in an idealized cluster with the moving-mesh code arepo. We analyze the interaction of jet-inflated bubbles with the turbulent magnetized intracluster medium.
Furthermore, jet dynamics and heating are closely linked to the largely unconstrained jet composition. Interactions of electrons with photons of the cosmic microwave background result in observational signatures that depend on the bubble content. Those recent observations provided evidence for underdense bubbles with a relativistic filling while adopting simplifying modeling assumptions for the bubbles. By reproducing the observations with our simulations, we confirm the validity of their modeling assumptions and as such, confirm the important finding of low-(momentum) density jets.
In addition, the velocity and magnetic field structure of the intracluster medium have profound consequences for bubble evolution and heating processes. As velocity and magnetic fields are physically coupled, we demonstrate that numerical simulations can help link and thereby constrain their respective observables. Finally, we implement the currently preferred accretion model, cold accretion, into the moving-mesh code arepo and study feedback by light jets in a radiatively cooling magnetized cluster. While self-regulation is attained independently of accretion model, jet density and feedback efficiencies, we find that in order to reproduce observed cold gas morphology light jets are preferred.
Cosmic rays (CRs) constitute an important component of the interstellar medium (ISM) of galaxies and are thought to play an essential role in governing their evolution. In particular, they are able to impact the dynamics of a galaxy by driving galactic outflows or heating the ISM and thereby affecting the efficiency of star-formation. Hence, in order to understand galaxy formation and evolution, we need to accurately model this non-thermal constituent of the ISM. But except in our local environment within the Milky Way, we do not have the ability to measure CRs directly in other galaxies. However, there are many ways to indirectly observe CRs via the radiation they emit due to their interaction with magnetic and interstellar radiation fields as well as with the ISM.
In this work, I develop a numerical framework to calculate the spectral distribution of CRs in simulations of isolated galaxies where a steady-state between injection and cooling is assumed. Furthermore, I calculate the non-thermal emission processes arising from the modelled CR proton and electron spectra ranging from radio wavelengths up to the very high-energy gamma-ray regime.
I apply this code to a number of high-resolution magneto-hydrodynamical (MHD) simulations of isolated galaxies, where CRs are included. This allows me to study their CR spectra and compare them to observations of the CR proton and electron spectra by the Voyager-1 satellite and the AMS-02 instrument in order to reveal the origin of the measured spectral features.
Furthermore, I provide detailed emission maps, luminosities and spectra of the non-thermal emission from our simulated galaxies that range from dwarfs to Milk-Way analogues to starburst galaxies at different evolutionary stages. I successfully reproduce the observed relations between the radio and gamma-ray luminosities with the far-infrared (FIR) emission of star-forming (SF) galaxies, respectively, where the latter is a good tracer of the star-formation rate. I find that highly SF galaxies are close to the limit where their CR population would lose all of their energy due to the emission of radiation, whereas CRs tend to escape low SF galaxies more quickly. On top of that, I investigate the properties of CR transport that are needed in order to match the observed gamma-ray spectra.
Furthermore, I uncover the underlying processes that enable the FIR-radio correlation (FRC) to be maintained even in starburst galaxies and find that thermal free-free-emission naturally explains the observed radio spectra in SF galaxies like M82 and NGC 253 thus solving the riddle of flat radio spectra that have been proposed to contradict the observed tight FRC.
Lastly, I scrutinise the steady-state modelling of the CR proton component by investigating for the first time the influence of spectrally resolved CR transport in MHD simulations on the hadronic gamma-ray emission of SF galaxies revealing new insights into the observational signatures of CR transport both spectrally and spatially.
Natural extreme events are an integral part of nature on planet earth. Usually these events are only considered hazardous to humans, in case they are exposed. In this case, however, natural hazards can have devastating impacts on human societies. Especially hydro-meteorological hazards have a high damage potential in form of e.g. riverine and pluvial floods, winter storms, hurricanes and tornadoes, which can occur all over the globe. Along with an increasingly warm climate also an increase in extreme weather which potentially triggers natural hazards can be expected. Yet, not only changing natural systems, but also changing societal systems contribute to an increasing risk associated with these hazards. These can comprise increasing exposure and possibly also increasing vulnerability to the impacts of natural events. Thus, appropriate risk management is required to adapt all parts of society to existing and upcoming risks at various spatial scales. One essential part of risk management is the risk assessment including the estimation of the economic impacts. However, reliable methods for the estimation of economic impacts due to hydro-meteorological hazards are still missing. Therefore, this thesis deals with the question of how the reliability of hazard damage estimates can be improved, represented and propagated across all spatial scales. This question is investigated using the specific example of economic impacts to companies as a result of riverine floods in Germany.
Flood damage models aim to describe the damage processes during a given flood event. In other words they describe the vulnerability of a specific object to a flood. The models can be based on empirical data sets collected after flood events. In this thesis tree-based models trained with survey data are used for the estimation of direct economic flood impacts on the objects. It is found that these machine learning models, in conjunction with increasing sizes of data sets used to derive the models, outperform state-of-the-art damage models. However, despite the performance improvements induced by using multiple variables and more data points, large prediction errors remain at the object level. The occurrence of the high errors was explained by a further investigation using distributions derived from tree-based models. The investigation showed that direct economic impacts to individual objects cannot be modeled by a normal distribution. Yet, most state-of-the-art approaches assume a normal distribution and take mean values as point estimators. Subsequently, the predictions are unlikely values within the distributions resulting in high errors. At larger spatial scales more objects are considered for the damage estimation. This leads to a better fit of the damage estimates to a normal distribution. Consequently, also the performance of the point estimators get better, although large errors can still occur due to the variance of the normal distribution. It is recommended to use distributions instead of point estimates in order to represent the reliability of damage estimates.
In addition current approaches also mostly ignore the uncertainty associated with the characteristics of the hazard and the exposed objects. For a given flood event e.g. the estimation of the water level at a certain building is prone to uncertainties. Current approaches define exposed objects mostly by the use of land use data sets. These data sets often show inconsistencies, which introduce additional uncertainties. Furthermore, state-of-the-art approaches also imply problems of missing consistency when predicting the damage at different spatial scales. This is due to the use of different types of exposure data sets for model derivation and application. In order to face these issues a novel object-based method was developed in this thesis. The method enables a seamless estimation of hydro-meteorological hazard damage across spatial scales including uncertainty quantification. The application and validation of the method resulted in plausible estimations at all spatial scales without overestimating the uncertainty.
Mainly newly available data sets containing individual buildings make the application of the method possible as they allow for the identification of flood affected objects by overlaying the data sets with water masks. However, the identification of affected objects with two different water masks revealed huge differences in the number of identified objects. Thus, more effort is needed for their identification, since the number of objects affected determines the order of magnitude of the economic flood impacts to a large extent.
In general the method represents the uncertainties associated with the three components of risk namely hazard, exposure and vulnerability, in form of probability distributions. The object-based approach enables a consistent propagation of these uncertainties in space. Aside from the propagation of damage estimates and their uncertainties across spatial scales, a propagation between models estimating direct and indirect economic impacts was demonstrated. This enables the inclusion of uncertainties associated with the direct economic impacts within the estimation of the indirect economic impacts. Consequently, the modeling procedure facilitates the representation of the reliability of estimated total economic impacts. The representation of the estimates' reliability prevents reasoning based on a false certainty, which might be attributed to point estimates. Therefore, the developed approach facilitates a meaningful flood risk management and adaptation planning.
The successful post-event application and the representation of the uncertainties qualifies the method also for the use for future risk assessments. Thus, the developed method enables the representation of the assumptions made for the future risk assessments, which is crucial information for future risk management. This is an important step forward, since the representation of reliability associated with all components of risk is currently lacking in all state-of-the-art methods assessing future risk.
In conclusion, the use of object-based methods giving results in the form of distributions instead of point estimations is recommended. The improvement of the model performance by the means of multi-variable models and additional data points is possible, but small. Uncertainties associated with all components of damage estimation should be included and represented within the results. Furthermore, the findings of the thesis suggest that, at larger scales, the influence of the uncertainty associated with the vulnerability is smaller than those associated with the hazard and exposure. This leads to the conclusion that for an increased reliability of flood damage estimations and risk assessments, the improvement and active inclusion of hazard and exposure, including their uncertainties, is needed in addition to the improvements of the models describing the vulnerability of the objects.
The highly conserved protein complex containing the Target of Rapamycin (TOR) kinase is known to integrate intra- and extra-cellular stimuli controlling nutrient allocation and cellular growth. This thesis describes three studies aimed to understand how TOR signaling pathway influences carbon and nitrogen metabolism in Chlamydomonas reinhardtii. The first study presents a time-resolved analysis of the molecular and physiological features across the diurnal cycle. The inhibition of TOR leads to 50% reduction in growth followed by nonlinear delays in the cell cycle progression. The metabolomics analysis showed that the growth repression is mainly driven by differential carbon partitioning between anabolic and catabolic processes. Furthermore, the high accumulation of nitrogen-containing compounds indicated that TOR kinase controls the carbon to nitrogen balance of the cell, which is responsible for biomass accumulation, growth and cell cycle progression. In the second study the cause of the high accumulation of amino acids is explained. For this purpose, the effect of TOR inhibition on Chlamydomonas was examined under different growth regimes using stable 13C- and 15N-isotope labeling. The data clearly showed that an increased nitrogen uptake is induced within minutes after the inhibition of TOR. Interestingly, this increased N-influx is accompanied by increased activities of nitrogen assimilating enzymes. Accordingly, it was concluded that TOR inhibition induces de-novo amino acid synthesis in Chlamydomonas. The recognition of this novel process opened an array of questions regarding potential links between central metabolism and TOR signaling. Therefore a detailed phosphoproteomics study was conducted to identify the potential substrates of TOR pathway regulating central metabolism. Interestingly, some of the key enzymes involved in carbon metabolism as well as amino acid synthesis exhibited significant changes in the phosphosite intensities immediately after TOR inhibition. Altogether, these studies provide a) detailed insights to metabolic response of Chlamydomonas to TOR inhibition, b) identification of a novel process causing rapid upshifts in amino acid levels upon TOR inhibition and c) finally highlight potential targets of TOR signaling regulating changes in central metabolism. Further biochemical and molecular investigations could confirm these observations and advance the understanding of growth signaling in microalgae.
Recurrences in past climates
(2023)
Our ability to predict the state of a system relies on its tendency to recur to states it has visited before. Recurrence also pervades common intuitions about the systems we are most familiar with: daily routines, social rituals and the return of the seasons are just a few relatable examples. To this end, recurrence plots (RP) provide a systematic framework to quantify the recurrence of states. Despite their conceptual simplicity, they are a versatile tool in the study of observational data. The global climate is a complex system for which an understanding based on observational data is not only of academical relevance, but vital for the predurance of human societies within the planetary boundaries. Contextualizing current global climate change, however, requires observational data far beyond the instrumental period. The palaeoclimate record offers a valuable archive of proxy data but demands methodological approaches that adequately address its complexities. In this regard, the following dissertation aims at devising novel and further developing existing methods in the framework of recurrence analysis (RA). The proposed research questions focus on using RA to capture scale-dependent properties in nonlinear time series and tailoring recurrence quantification analysis (RQA) to characterize seasonal variability in palaeoclimate records (‘Palaeoseasonality’).
In the first part of this thesis, we focus on the methodological development of novel approaches in RA. The predictability of nonlinear (palaeo)climate time series is limited by abrupt transitions between regimes that exhibit entirely different dynamical complexity (e.g. crossing of ‘tipping points’). These possibly depend on characteristic time scales. RPs are well-established for detecting transitions and capture scale-dependencies, yet few approaches have combined both aspects. We apply existing concepts from the study of self-similar textures to RPs to detect abrupt transitions, considering the most relevant time scales. This combination of methods further results in the definition of a novel recurrence based nonlinear dependence measure. Quantifying lagged interactions between multiple variables is a common problem, especially in the characterization of high-dimensional complex systems. The proposed ‘recurrence flow’ measure of nonlinear dependence offers an elegant way to characterize such couplings. For spatially extended complex systems, the coupled dynamics of local variables result in the emergence of spatial patterns. These patterns tend to recur in time. Based on this observation, we propose a novel method that entails dynamically distinct regimes of atmospheric circulation based on their recurrent spatial patterns. Bridging the two parts of this dissertation, we next turn to methodological advances of RA for the study of Palaeoseasonality. Observational series of palaeoclimate ‘proxy’ records involve inherent limitations, such as irregular temporal sampling. We reveal biases in the RQA of time series with a non-stationary sampling rate and propose a correction scheme.
In the second part of this thesis, we proceed with applications in Palaeoseasonality. A review of common and promising time series analysis methods shows that numerous valuable tools exist, but their sound application requires adaptions to archive-specific limitations and consolidating transdisciplinary knowledge. Next, we study stalagmite proxy records from the Central Pacific as sensitive recorders of mid-Holocene El Niño-Southern Oscillation (ENSO) dynamics. The records’ remarkably high temporal resolution allows to draw links between ENSO and seasonal dynamics, quantified by RA. The final study presented here examines how seasonal predictability could play a role for the stability of agricultural societies. The Classic Maya underwent a period of sociopolitical disintegration that has been linked to drought events. Based on seasonally resolved stable isotope records from Yok Balum cave in Belize, we propose a measure of seasonal predictability. It unveils the potential role declining seasonal predictability could have played in destabilizing agricultural and sociopolitical systems of Classic Maya populations.
The methodological approaches and applications presented in this work reveal multiple exciting future research avenues, both for RA and the study of Palaeoseasonality.
This paper introduces a novel measure to assess similarity between event hydrographs. It is based on Cross Recurrence Plots and Recurrence Quantification Analysis which have recently gained attention in a range of disciplines when dealing with complex systems. The method attempts to quantify the event runoff dynamics and is based on the time delay embedded phase space representation of discharge hydrographs. A phase space trajectory is reconstructed from the event hydrograph, and pairs of hydrographs are compared to each other based on the distance of their phase space trajectories. Time delay embedding allows considering the multi-dimensional relationships between different points in time within the event. Hence, the temporal succession of discharge values is taken into account, such as the impact of the initial conditions on the runoff event. We provide an introduction to Cross Recurrence Plots and discuss their parameterization. An application example based on flood time series demonstrates how the method can be used to measure the similarity or dissimilarity of events, and how it can be used to detect events with rare runoff dynamics. It is argued that this methods provides a more comprehensive approach to quantify hydrograph similarity compared to conventional hydrological signatures.
In this thesis we mainly generalize two theorems from Mackaay-Picken and Picken (2002, 2004). In the first paper, Mackaay and Picken show that there is a bijective correspondence between Deligne 2-classes $\xi \in \check{H}^2(M,\mathcal{D}^2)$ and holonomy maps from the second thin-homotopy group $\pi_2^2(M)$ to $U(1)$. In the second one, a generalization of this theorem to manifolds with boundaries is given: Picken shows that there is a bijection between Deligne 2-cocycles and a certain variant of 2-dimensional topological quantum field theories. In this thesis we show that these two theorems hold in every dimension. We consider first the holonomy case, and by using simplicial methods we can prove that the group of smooth Deligne $d$-classes is isomorphic to the group of smooth holonomy maps from the $d^{th}$ thin-homotopy group $\pi_d^d(M)$ to $U(1)$, if $M$ is $(d-1)$-connected. We contrast this with a result of Gajer (1999). Gajer showed that Deligne $d$-classes can be reconstructed by a different class of holonomy maps, which not only include holonomies along spheres, but also along general $d$-manifolds in $M$. This approach does not require the manifold $M$ to be $(d-1)$-connected. We show that in the case of flat Deligne $d$-classes, our result differs from Gajers, if $M$ is not $(d-1)$-connected, but only $(d-2)$-connected. Stiefel manifolds do have this property, and if one applies our theorem to these and compare the result with that of Gajers theorem, it is revealed that our theorem reconstructs too many Deligne classes. This means, that our reconstruction theorem cannot live without the extra assumption on the manifold $M$, that is our reconstruction needs less informations about the holonomy of $d$-manifolds in $M$ at the price of assuming $M$ to be $(d-1)$-connected. We continue to show, that also the second theorem can be generalized: By introducing the concept of Picken-type topological quantum field theory in arbitrary dimensions, we can show that every Deligne $d$-cocycle induces such a $d$-dimensional field theory with two special properties, namely thin-invariance and smoothness. We show that any $d$-dimensional topological quantum field theory with these two properties gives rise to a Deligne $d$-cocycle and verify that this construction is surjective and injective, that is both groups are isomorphic.
Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change. Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance. Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments. Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests. The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau.