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The global climate crisis is significantly contributing to changing ecosystems, loss of biodiversity and is putting numerous species on the verge of extinction. In principle, many species are able to adapt to changing conditions or shift their habitats to more suitable regions. However, change is progressing faster than some species can adjust, or potential adaptation is blocked and disrupted by direct and indirect human action. Unsustainable anthropogenic land use in particular is one of the driving factors, besides global heating, for these ecologically critical developments. Precisely because land use is anthropogenic, it is also a factor that could be quickly and immediately corrected by human action.
In this thesis, I therefore assess the impact of three climate change scenarios of increasing intensity in combination with differently scheduled mowing regimes on the long-term development and dispersal success of insects in Northwest German grasslands. The large marsh grasshopper (LMG, Stethophyma grossum, Linné 1758) is used as a species of reference for the analyses. It inhabits wet meadows and marshes and has a limited, yet fairly good ability to disperse. Mowing and climate conditions affect the development and mortality of the LMG differently depending on its life stage.
The specifically developed simulation model HiLEG (High-resolution Large Environmental
Gradient) serves as a tool for investigating and projecting viability and dispersal success under different climate conditions and land use scenarios. It is a spatially explicit, stage- and cohort-based model that can be individually configured to represent the life cycle and characteristics of terrestrial insect species, as well as high-resolution environmental data and the occurrence of external disturbances. HiLEG is a freely available and adjustable software that can be used to support conservation planning in cultivated grasslands.
In the three case studies of this thesis, I explore various aspects related to the structure of simulation models per se, their importance in conservation planning in general, and insights regarding the LMG in particular. It became apparent that the detailed resolution of model processes and components is crucial to project the long-term effect of spatially and temporally confined events. Taking into account conservation measures at the regional level has further proven relevant, especially in light of the climate crisis. I found that the LMG is benefiting from global warming in principle, but continues to be constrained by harmful mowing regimes. Land use measures could, however, be adapted in such a way that they allow the expansion and establishment of the LMG without overly affecting agricultural yields.
Overall, simulation models like HiLEG can make an important contribution and add value
to conservation planning and policy-making. Properly used, simulation results shed light
on aspects that might be overlooked by subjective judgment and the experience of individual stakeholders. Even though it is in the nature of models that they are subject to limitations and only represent fragments of reality, this should not keep stakeholders from using them, as long as these limitations are clearly communicated. Similar to HiLEG, models could further be designed in such a way that not only the parameterization can be adjusted as required, but also the implementation itself can be improved and changed as desired. This openness and flexibility should become more widespread in the development of simulation models.
In my doctoral thesis, I examine continuous gravity measurements for monitoring of the geothermal site at Þeistareykir in North Iceland. With the help of high-precision superconducting gravity meters (iGravs), I investigate underground mass changes that are caused by operation of the geothermal power plant (i.e. by extraction of hot water and reinjection of cold water). The overall goal of this research project is to make a statement about the sustainable use of the geothermal reservoir, from which also the Icelandic energy supplier and power plant operator Landsvirkjun should benefit.
As a first step, for investigating the performance and measurement stability of the gravity meters, in summer 2017, I performed comparative measurements at the gravimetric observatory J9 in Strasbourg. From the three-month gravity time series, I examined calibration, noise and drift behaviour of the iGravs in comparison to stable long-term time series of the observatory superconducting gravity meters. After preparatory work in Iceland (setup of gravity stations, additional measuring equipment and infrastructure, discussions with Landsvirkjun and meetings with the Icelandic partner institute ISOR), gravity monitoring at Þeistareykir was started in December 2017. With the help of the iGrav records of the initial 18 months after start of measurements, I carried out the same investigations (on calibration, noise and drift behaviour) as in J9 to understand how the transport of the superconducting gravity meters to Iceland may influence instrumental parameters.
In the further course of this work, I focus on modelling and reduction of local gravity contributions at Þeistareykir. These comprise additional mass changes due to rain, snowfall and vertical surface displacements that superimpose onto the geothermal signal of the gravity measurements. For this purpose, I used data sets from additional monitoring sensors that are installed at each gravity station and adapted scripts for hydro-gravitational modelling. The third part of my thesis targets geothermal signals in the gravity measurements.
Together with my PhD colleague Nolwenn Portier from France, I carried out additional gravity measurements with a Scintrex CG5 gravity meter at 26 measuring points within the geothermal field in the summers of 2017, 2018 and 2019. These annual time-lapse gravity measurements are intended to increase the spatial coverage of gravity data from the three continuous monitoring stations to the entire geothermal field. The combination of CG5 and iGrav observations, as well as annual reference measurements with an FG5 absolute gravity meter represent the hybrid gravimetric monitoring method for Þeistareykir. Comparison of the gravimetric data to local borehole measurements (of groundwater levels, geothermal extraction and injection rates) is used to relate the observed gravity changes to the actually extracted (and reinjected) geothermal fluids. An approach to explain the observed gravity signals by means of forward modelling of the geothermal production rate is presented at the end of the third (hybrid gravimetric) study. Further modelling with the help of the processed gravity data is planned by Landsvirkjun. In addition, the experience from time-lapse and continuous gravity monitoring will be used for future gravity measurements at the Krafla geothermal field 22 km south-east of Þeistareykir.
The complex hierarchical structure of bone undergoes a lifelong remodeling process, where it adapts to mechanical needs. Hereby, bone resorption by osteoclasts and bone formation by osteoblasts have to be balanced to sustain a healthy and stable organ. Osteocytes orchestrate this interplay by sensing mechanical strains and translating them into biochemical signals. The osteocytes are located in lacunae and are connected to one another and other bone cells via cell processes through small channels, the canaliculi. Lacunae and canaliculi form a network (LCN) of extracellular spaces that is able to transport ions and enables cell-to-cell communication. Osteocytes might also contribute to mineral homeostasis by direct interactions with the surrounding matrix. If the LCN is acting as a transport system, this should be reflected in the mineralization pattern. The central hypothesis of this thesis is that osteocytes are actively changing their material environment. Characterization methods of material science are used to achieve the aim of detecting traces of this interaction between osteocytes and the extracellular matrix. First, healthy murine bones were characterized. The properties analyzed were then compared with three murine model systems: 1) a loading model, where a bone of the mouse was loaded during its life time; 2) a healing model, where a bone of the mouse was cut to induce a healing response; and 3) a disease model, where the Fbn1 gene is dysfunctional causing defects in the formation of the extracellular tissue.
The measurement strategy included routines that make it possible to analyze the organization of the LCN and the material components (i.e., the organic collagen matrix and the mineral particles) in the same bone volumes and compare the spatial distribution of different data sets. The three-dimensional network architecture of the LCN is visualized by confocal laser scanning microscopy (CLSM) after rhodamine staining and is then subsequently quantified. The calcium content is determined via quantitative backscattered electron imaging (qBEI), while small- and wide-angle X-ray scattering (SAXS and WAXS) are employed to determine the thickness and length of local mineral particles.
First, tibiae cortices of healthy mice were characterized to investigate how changes in LCN architecture can be attributed to interactions of osteocytes with the surrounding bone matrix. The tibial mid-shaft cross-sections showed two main regions, consisting of a band with unordered LCN surrounded by a region with ordered LCN. The unordered region is a remnant of early bone formation and exhibited short and thin mineral particles. The surrounding, more aligned bone showed ordered and dense LCN as well as thicker and longer mineral particles. The calcium content was unchanged between the two regions.
In the mouse loading model, the left tibia underwent two weeks of mechanical stimulation, which results in increased bone formation and decreased resorption in skeletally mature mice. Here the specific research question addressed was how do bone material characteristics change at (re)modeling sites? The new bone formed in response to mechanical stimulation showed similar properties in terms of the mineral particles, like the ordered calcium region but lower calcium content compared to the right, non-loaded control bone of the same mice. There was a clear, recognizable border between mature and newly formed bone. Nevertheless, some canaliculi went through this border connecting the LCN of mature and newly formed bone.
Additionally, the question should be answered whether the LCN topology and the bone matrix material properties adapt to loading. Although, mechanically stimulated bones did not show differences in calcium content compared to controls, different correlations were found between the local LCN density and the local Ca content depending on whether the bone was loaded or not. These results suggest that the LCN may serve as a mineral reservoir.
For the healing model, the femurs of mice underwent an osteotomy, stabilized with an external fixator and were allowed to heal for 21 days. Thus, the spatial variations in the LCN topology with mineral properties within different tissue types and their interfaces, namely calcified cartilage, bony callus and cortex, could be simultaneously visualized and compared in this model. All tissue types showed structural differences across multiple length scales. Calcium content increased and became more homogeneous from calcified cartilage to bony callus to lamellar cortical bone. The degree of LCN organization increased as well, while the lacunae became smaller, as did the lacunar density between these different tissue types that make up the callus. In the calcified cartilage, the mineral particles were short and thin. The newly formed callus exhibited thicker mineral particles, which still had a low degree of orientation. While most of the callus had a woven-like structure, it also served as a scaffold for more lamellar tissue at the edges. The lamelar bone callus showed thinner mineral particles, but a higher degree of alignment in both, mineral particles and the LCN. The cortex showed the highest values for mineral length, thickness and degree of orientation. At the same time, the lacunae number density was 34% lower and the lacunar volume 40% smaller compared to bony callus. The transition zone between cortical and callus regions showed a continuous convergence of bone mineral properties and lacunae shape. Although only a few canaliculi connected callus and the cortical region, this indicates that communication between osteocytes of both tissues should be possible. The presented correlations between LCN architecture and mineral properties across tissue types may suggest that osteocytes have an active role in mineralization processes of healing.
A mouse model for the disease marfan syndrome, which includes a genetic defect in the fibrillin-1 gene, was investigated. In humans, Marfan syndrome is characterized by a range of clinical symptoms such as long bone overgrowth, loose joints, reduced bone mineral density, compromised bone microarchitecture, and increased fracture rates. Thus, fibrillin-1 seems to play a role in the skeletal homeostasis. Therefore, the present work studied how marfan syndrome alters LCN architecture and the surrounding bone matrix. The mice with marfan syndrome showed longer tibiae than their healthy littermates from an age of seven weeks onwards. In contrast, the cortical development appeared retarded, which was observed across all measured characteristics, i. e. lower endocortical bone formation, looser and less organized lacuno-canalicular network, less collagen orientation, thinner and shorter mineral particles.
In each of the three model systems, this study found that changes in the LCN architecture spatially correlated with bone matrix material parameters. While not knowing the exact mechanism, these results provide indications that osteocytes can actively manipulate a mineral reservoir located around the canaliculi to make a quickly accessible contribution to mineral homeostasis. However, this interaction is most likely not one-sided, but could be understood as an interplay between osteocytes and extra-cellular matrix, since the bone matrix contains biochemical signaling molecules (e.g. non-collagenous proteins) that can change osteocyte behavior. Bone (re)modeling can therefore not only be understood as a method for removing defects or adapting to external mechanical stimuli, but also for increasing the efficiency of possible osteocyte-mineral interactions during bone homeostasis. With these findings, it seems reasonable to consider osteocytes as a target for drug development related to bone diseases that cause changes in bone composition and mechanical properties. It will most likely require the combined effort of materials scientists, cell biologists, and molecular biologists to gain a deeper understanding of how bone cells respond to their material environment.
The origin and structure of magnetic fields in the Galaxy are largely unknown. What is known is that they are essential for several astrophysical processes, in particular the propagation of cosmic rays. Our ability to describe the propagation of cosmic rays through the Galaxy is severely limited by the lack of observational data needed to probe the structure of the Galactic magnetic field on many different length scales. This is particularly true for modelling the propagation of cosmic rays into the Galactic halo, where our knowledge of the magnetic field is particularly poor.
In the last decade, observations of the Galactic halo in different frequency regimes have revealed the existence of out-of-plane bubble emission in the Galactic halo. In gamma rays these bubbles have been termed Fermi bubbles with a radial extent of ≈ 3 kpc and an azimuthal height of ≈ 6 kpc. The radio counterparts of the Fermi bubbles were seen by both the S-PASS telescopes and the Planck satellite, and showed a clear spatial overlap. The X-ray counterparts of the Fermi bubbles were named eROSITA bubbles after the eROSITA satellite, with a radial width of ≈ 7 kpc and an azimuthal height of ≈ 14 kpc. Taken together, these observations suggest the presence of large extended Galactic Halo Bubbles (GHB) and have stimulated interest in exploring the less explored Galactic halo.
In this thesis, a new toy model (GHB model) for the magnetic field and non-thermal electron distribution in the Galactic halo has been proposed. The new toy model has been used to produce polarised synchrotron emission sky maps. Chi-square analysis was used to compare the synthetic skymaps with the Planck 30 GHz polarised skymaps. The obtained constraints on the strength and azimuthal height were found to be in agreement with the S-PASS radio observations.
The upper, lower and best-fit values obtained from the above chi-squared analysis were used to generate three separate toy models. These three models were used to propagate ultra-high energy cosmic rays. This study was carried out for two potential sources, Centaurus A and NGC 253, to produce magnification maps and arrival direction skymaps. The simulated arrival direction skymaps were found to be consistent with the hotspots of Centaurus A and NGC 253 as seen in the observed arrival direction skymaps provided by the Pierre Auger Observatory (PAO).
The turbulent magnetic field component of the GHB model was also used to investigate the extragalactic dipole suppression seen by PAO. UHECRs with an extragalactic dipole were forward-tracked through the turbulent GHB model at different field strengths. The suppression in the dipole due to the varying diffusion coefficient from the simulations was noted. The results could also be compared with an analytical analogy of electrostatics. The simulations of the extragalactic dipole suppression were in agreement with similar studies carried out for galactic cosmic rays.
„Europäische Bildung beginnt in der Schule.“ Gerade in Zeiten einer Renaissance von Nationalismen und einem spürbaren Rechtsruck in Europa scheint diese Maxime wichtiger denn je zu sein. Die umfassendste Möglichkeit, mittel- und langfristig eine europäische Dimension in den Schulen der EU-Mitgliedsstaaten zu verankern, stellt eine binationale oder sogar internationale Lehramtsausbildung dar. Die Einrichtung derartiger Ausbildungen ist jedoch mit hohen Hürden verbunden. Ihre Anzahl ist überschaubar und allein im deutsch-französischen Kontext vorhanden. Hintergrund hierfür sind erstens die nur schwer zu überwindbaren Hindernisse, die sich aus den stark divergierenden Studien-, Rekrutierungs- und Ausbildungssystemen ergeben. Zweitens ist der Lehramtsbereich besonders stark durch Reformen geprägt. Eine Nutzen-Kosten-Analyse der häufig benötigten und ressourcenintensiven Anpassungen von Programmen auf der einen Seite und der geringen Anzahl der Absolventinnen und Absolventen auf der anderen Seite fällt demnach an vielen Universitäten negativ aus. Ein Rückblick auf die seit 2000 bestehenden Bemühungen der Kooperation Mainz-Dijon hinterlässt eine durchmischte Bilanz. Die Gelegenheit, die lehramtsbezogene binationale Ausbildung dieser Kooperation integrierter zu gestalten, bietet die sich derzeit auf französischer Seite vollziehende Neustrukturierung der französischen Lehramtsausbildung. Die Loi Blanquer vom 26. Juli 2019 führt zu einer Annäherung der beiden Systeme und ermöglicht – auch dank bereits bestehender juristischer Instrumente – eine Verkürzung der Ausbildungszeit sowie eine verbesserte Anerkennungspraxis.
Digitale Logopädie
(2021)
Dysphagieforum
(2014)
Dysphagieforum
(2013)
Dysphagieforum
(2013)
Der Verleger, Kaufhausunternehmer und Mäzen Salman Schocken (1877– 1959)neigte nicht zu übertriebener Bescheidenheit. Als er 1945 in New York seinen amerikanischen Verlag ins Leben rief, kündigte er ihn mit folgenden Worten an:
Schocken ignorierte damit die Arbeit der zahlreichen bestehenden amerikanisch-jüdischen Verlagshäuser, da diese seiner Meinung nach nicht die Aufgabe erfüllten, die ihm vorschwebte: die Rückführung traditionsferner und damit in ihrer Identität unsicherer Juden durch Auseinandersetzung mit ihrem kulturellen Erbe. Dieses Ziel hatte bereits das Programm des Berliner Schocken Verlags (1931– 1938) bestimmt, der die vom Gründer genannten „repräsentative[n] Kostproben des Judentums“ veröffentlicht und damit zur „jüdischen Kulturrenaissance“ der 1930er Jahre beigetragen hatte.² Auch nach seiner Emigration nach Palästina 1934 blieb Schocken einer deutsch-jüdischen Wissenskultur zeitlebens verhaftet. Mit seiner verlegerischen Arbeit in den USA wollte Schocken das Programm seines Berliner Verlags für das amerikanische Nachkriegsjudentum neu auflegen, da sich dieses – seiner Meinung nach – in einer ähnlichen geistigen Situation befand wie das deutsche Judentum der Weimarer Republik. Entsprechend verkündete er 1945 in einer Rede in Jerusalem: „Sie wissen, dass ich jetzt daran arbeite, den Schockenverlag in Amerika zu machen. Das ist eine Imitation des deutschen Verlages. [...] Entfernungen existieren nicht mehr und Einfluss von hier nach dort und dort nach hier ist nicht mehr zu übersehen.“³ In diesen Aussagen klingen bereits verschiedene Schlüsselthemen der Rolle von Schocken Books New York an, dessen Geschichte bisher nur ansatzweise erforscht ist: Der Bezug auf Schockens Erfahrungen in Deutschland und das davon geprägte kulturpolitische Programm, das Kontinuitäten zwischen zwei räumlich und zeitlich fundamental getrennten jüdischen Gemeinschaften postulierte und auf einen transnationalen Kanon jüdischen Wissens zielte. Schocken wirkte mit seinen Verlagen, die er in Deutschland, Palästina/Israel und den USA gründete, nicht nur an drei Schlüsselorten der jüdischen Moderne. Sein Verlagsprogramm stand zudem im Kontext eines Schlüsselprozesses jüdischer Modernisierung: der Transformation traditionell-religiösen Wissens in posttraditionell-kulturelle Formen. Dieser Beitrag stellt anhand von Quellen aus dem Verlagsarchiv, der Nachlässe von Schockens Lektoren in den USA und der Rezeption von Schocken Books in den USA den Verlagsgründer Salman Schocken und die beiden Verlage in Berlin und New York vor. Im Zentrum der Analyse stehen die transnationale Verflechtung der Verlagshäuser und die Frage nach dem in den Publikationsprogrammen angestrebten transnationalen Kanon jüdischen Wissens in der Moderne.
Here, we demonstrate the utility of native membrane derived vesicles (nMVs) as tools for expeditious electrophysiological analysis of membrane proteins. We used a cell-free (CF) and a cell-based (CB) approach for preparing protein-enriched nMVs. We utilized the Chinese Hamster Ovary (CHO) lysate-based cell-free protein synthesis (CFPS) system to enrich ER-derived microsomes in the lysate with the primary human cardiac voltage-gated sodium channel 1.5 (hNaV1.5; SCN5A) in 3 h. Subsequently, CB-nMVs were isolated from fractions of nitrogen-cavitated CHO cells overexpressing the hNaV1.5. In an integrative approach, nMVs were micro-transplanted into Xenopus laevis oocytes. CB-nMVs expressed native lidocaine-sensitive hNaV1.5 currents within 24 h; CF-nMVs did not elicit any response. Both the CB- and CF-nMV preparations evoked single-channel activity on the planar lipid bilayer while retaining sensitivity to lidocaine application. Our findings suggest a high usability of the quick-synthesis CF-nMVs and maintenance-free CB-nMVs as ready-to-use tools for in-vitro analysis of electrogenic membrane proteins and large, voltage-gated ion channels.
El plateau Andino es el segundo plateau orogénico más grande del mundo y se ubica en los Andes Centrales, desarrollado en un sistema orogénico no colisional. Se extiende desde el sur del Perú (15°S), hasta el norte de Argentina y Chile (27°30´S). A partir de los 24°S y prologándose hacia el sur, el plateau Andino se denomina Puna y está caracterizado por un sistema de cuencas endorreicas y salares delimitados por cordones montañosos. Entre los 26° y 27°30´S, la Puna encuentra su límite austral en una zona de transición entre una zona de subducción normal y una zona de subducción plana o “flat slab” que se prolonga hasta los 33°S. Diversos estudios documentan la ocurrencia de un aumento del espesor cortical, y levantamiento episódico y diacrónico del relieve, alcanzando su configuración actual durante el Mioceno tardío. Posteriormente, el plateau habría experimentado un cambio en el estilo de deformación dominado por procesos extensionales evidenciado por fallas y terremotos de cinemática normal. Sin embargo, en el borde sur del plateau de la Puna y en las áreas delimitadas con el resto del orógeno, la variación del campo de esfuerzo no está del todo comprendida, reflejando una excelente oportunidad para evaluar cómo el campo de esfuerzo puede evolucionar durante el desarrollo del orógeno y cómo puede verse afectado por la presencia/ausencia de un plateau orogénico, así como también por la existencia de anisotropías estructurales propias de cada unidad morfotectónica.
Esta Tesis investiga la relación entre la deformación cortical somera y la evolución en tiempo y espacio del campo de esfuerzos en el sector sur del plateau Andino, durante el cenozoico tardío. Para realizar esta investigación, se utilizaron técnicas de obtención de edades radiométricas con el método Uranio-Plomo (U-Pb), análisis de fallas mesoscópicas para la obtención de tensores de esfuerzos y delimitación de la orientación de los ejes principales de esfuerzos, análisis de anisotropía de susceptibilidad magnética en rocas sedimentarias y volcanoclásticas para estimar direcciones de acortamiento o direcciones de transporte sedimentario, técnicas de modelado cinemático para llegar a una aproximación de las estructuras corticales profundas asociadas a la deformación allí registrada, y un análisis morfométrico para la identificación de indicadores geomorfológicos asociados a deformación producto de la actividad tectónica cuaternaria.
Combinando estos resultados con los antecedentes previamente documentados, el estudio revela una compleja variación del campo de esfuerzo caracterizado por cambios en la orientación y permutaciones verticales de los ejes principales de esfuerzos, durante cada régimen de deformación, durante los últimos ~24 Ma. La evolución del campo de esfuerzos puede ser asociada temporalmente a tres fases orogénicas involucradas con la evolución de los Andes Centrales en esta latitud: (1) una primera fase con un régimen de esfuerzos compresivos de acortamiento E-O documentado desde el Eoceno, Oligoceno tardío hasta el Mioceno medio en el área, coincide con la fase de construcción andina, engrosamiento y crecimiento de la corteza y levantamiento topográfico; (2) una segunda fase caracterizada por un régimen de esfuerzos de transcurrencia, a partir de los ~11 Ma en el borde occidental y compresión y transcurrencia a los~5 Ma en el borde oriental del plateau de la Puna, y un régimen de esfuerzo compresivos en Famatina y las Sierras Pampeanas interpretado como una transición entre la construcción orogénica del Neógeno y la máxima acumulación de deformación y el alzamiento topográfico del plateau de la Puna, y (3) una tercera fase donde el régimen se caracteriza por la transcurrencia en la Puna y en su borde occidental y en su borde oriental con las Sierras Pampeanas, después de ~5-4 Ma, interpretado como un régimen de esfuerzos controlados por el engrosamiento cortical desarrollado a lo largo del borde sur del plateau Altiplano/Puna, previo a un colapso orogénico. Los resultados dejan en evidencia que el borde del plateau experimentó el paso desde un régimen compresivo hacia uno transcurrente, que se diferencia de la extensión documentada hacia el norte en el plateau Andino para el mismo período. Cambios en los esfuerzos similares han sido documentado durante la construcción del plateau Tibetano, en donde un régimen de esfuerzo predominantemente compresivo cambió a un régimen de transcurrente cuando el plateau habría alcanzado la mitad de su elevación actual, y que posteriormente derivó en un régimen extensional, entre 14 y 4 Ma, cuando la altitud del plateau fue superior al 80% respecto a su actitud actual, lo que podría estar indicando que los regímenes transcurrentes representan etapas transicionales entre las zonas externas del plateau bajo compresión y las zonas internas, en las que los regímenes extensionales son más viables de ocurrir.
Familie Veistenauer
(2019)
Steep mountain channels are an important component of the fluvial system. On geological timescales, they shape mountain belts and counteract tectonic uplift by erosion. Their channels are strongly coupled to hillslopes and they are often the main source of sediment transported downstream to low-gradient rivers and to alluvial fans, where commonly settlements in mountainous areas are located. Hence, mountain streams are the cause for one of the main natural hazards in these regions. Due to climate change and a pronounced populating of mountainous regions the attention given to this threat is even growing. Although quantitative studies on sediment transport have significantly advanced our knowledge on measuring and calibration techniques we still lack studies of the processes within mountain catchments. Studies examining the mechanisms of energy and mass exchange on small temporal and spatial scales in steep streams remain sparse in comparison to low-gradient alluvial channels.
In the beginning of this doctoral project, a vast amount of experience and knowledge of a steep stream in the Swiss Prealps had to be consolidated in order to shape the principal aim of this research effort. It became obvious, that observations from within the catchment are underrepresented in comparison to experiments performed at the catchment’s outlet measuring fluxes and the effects of the transported material. To counteract this imbalance, an examination of mass fluxes within the catchment on the process scale was intended. Hence, this thesis is heavily based on direct field observations, which are generally rare in these environments in quantity and quality. The first objective was to investigate the coupling of the channel with surrounding hillslopes, the major sources of sediment. This research, which involved the monitoring of the channel and adjacent hillslopes, revealed that alluvial channel steps play a key role in coupling of channel and hillslopes. The observations showed that hillslope stability is strongly associated with the step presence and an understanding of step morphology and stability is therefore crucial in understanding sediment mobilization. This finding refined the way we think about the sediment dynamics in steep channels and motivated continued research of the step dynamics. However, soon it became obvious that the technological basis for developing field tests and analyzing the high resolution geometry measured in the field was not available. Moreover, for many geometrical quantities in mountain channels definitions and a clear scientific standard was not available. For example, these streams are characterized by a high spatial variability of the channel banks, preventing straightforward calculations of the channel width without a defined reference. Thus, the second and inevitable part of this thesis became the development and evaluation of scientific tools in order to investigate the geometrical content of the study reach thoroughly. The developed framework allowed the derivation of various metrics of step and channel geometry which facilitated research on the a large data set of observations of channel steps. In the third part, innovative, physically-based metrics have been developed and compared to current knowledge on step formation, suggested in the literature. With this analyses it could be demonstrated that the formation of channel steps follow a wide range of hydraulic controls. Due to the wide range of tested parameters channel steps observed in a natural stream were attributed to different mechanisms of step formation, including those based on jamming and those based on key-stones. This study extended our knowledge on step formation in a steep stream and harmonized different, often time seen as competing, processes of step formation. This study was based on observations collected at one point in time. In the fourth part of this project, the findings of the snap-shot observations were extended in the temporal dimension and the derived concepts have been utilized to investigate reach-scale step patterns in response to large, exceptional flood events. The preliminary results of this work based on the long-term analyses of 7 years of long profile surveys showed that the previously observed channel-hillslope mechanism is the responsible for the short-term response of step formation.
The findings of the long-term analyses of step patterns drew a bow to the initial observations of a channel-hillslope system which allowed to join the dots in the dynamics of steep stream. Thus, in this thesis a broad approach has been chosen to gain insights into the complex system of steep mountain rivers. The effort includes in situ field observations (article I), the development of quantitative scientific tools (article II), the reach-scale analyses of step-pool morphology (article III) and its temporal evolution (article IV). With this work our view on the processes within the catchment has been advanced towards a better mechanistic understanding of these fluvial system relevant to improve applied scientific work.
Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes
(2017)
Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures.
In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges.
These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure.
Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67% of this specific capacitance when the scan rate is increased to 200 mV s-1.
In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking.
Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.
Gamification als Motivator in der Sprachtherapie bei Menschen mit intellektueller Beeinträchtigung
(2021)
Gen 32,23-32
(2022)
Generated-X LMS (GXLMS)
(2021)
The quality of the reference signal is essential for the adaptation process of an LMS or one of its derivatives. The reference signal affects the stability, the convergence rate and the maximum achievable attenuation. Since the error signal and the control signal are available as numerical values in the algorithm for the LMS, the reference signal can be calculated from both signals. The error signal is the interference between the control signal and the reference signal. This interference of the control signal and the reference signal can be noted mathematically as a simple addition. It is therefore possible to deduce the reference signal from a known error signal and control signal. This approach is the basis of the generated-x LMS (GxLMS) developed by us. It calculates the reference signal itself without having to rely on an externally supplied reference signal. The advantages of the GxLMS are primarily in fields where the reference signal is difficult or impossible to detect. For example, the detection of the reference signal can be problematic due to design reasons or measurement technology. For example, flow noise could have a negative effect on an acoustic detection of the reference signal. However, the calculation of the reference signal in the GxLMS represents a further feedback signal path, which affects the stability of the algorithm as a whole. Based on the theoretical principles mathematically sufficient convergence conditions can be formulated taking into account the delays existing in the signal paths. The experimental testing took place on an acoustic duct with monofrequency disturb signals. Since the use of an efficient design of experiments (DoE) could be excluded, the measurement was designed as parameter variation (one factor at time) and therefore very time-consuming. The theoretical background of the GxLMS as well as the results from the experiments are presented.
Digitalisation in industry – also called “Industry 4.0” – is seen by numerous actors as an opportunity to reduce the environmental impact of the industrial sector. The scientific assessments of the effects of digitalisation in industry on environmental sustainability, however, are ambivalent. This cumulative dissertation uses three empirical studies to examine the expected and observed effects of digitalisation in industry on environmental sustainability. The aim of this dissertation is to identify opportunities and risks of digitalisation at different system levels and to derive options for action in politics and industry for a more sustainable design of digitalisation in industry. I use an interdisciplinary, socio-technical approach and look at selected countries of the Global South (Study 1) and the example of China (all studies). In the first study (section 2, joint work with Marcel Matthess), I use qualitative content analysis to examine digital and industrial policies from seven different countries in Africa and Asia for expectations regarding the impact of digitalisation on sustainability and compare these with the potentials of digitalisation for sustainability in the respective country contexts. The analysis reveals that the documents express a wide range of vague expectations that relate more to positive indirect impacts of information and communication technology (ICT) use, such as improved energy efficiency and resource management, and less to negative direct impacts of ICT, such as electricity consumption through ICT. In the second study (section 3, joint work with Marcel Matthess, Grischa Beier and Bing Xue), I conduct and analyse interviews with 18 industry representatives of the electronics industry from Europe, Japan and China on digitalisation measures in supply chains using qualitative content analysis. I find that while there are positive expectations regarding the effects of digital technologies on supply chain sustainability, their actual use and observable effects are still limited. Interview partners can only provide few examples from their own companies which show that sustainability goals have already been pursued through digitalisation of the supply chain or where sustainability effects, such as resource savings, have been demonstrably achieved. In the third study (section 4, joint work with Peter Neuhäusler, Melissa Dachrodt and Marcel Matthess), I conduct an econometric panel data analysis. I examine the relationship between the degree of Industry 4.0, energy consumption and energy intensity in ten manufacturing sectors in China between 2006 and 2019. The results suggest that overall, there is no significant relationship between the degree of Industry 4.0 and energy consumption or energy intensity in manufacturing sectors in China. However, differences can be found in subgroups of sectors. I find a negative correlation of Industry 4.0 and energy intensity in highly digitalised sectors, indicating an efficiency-enhancing effect of Industry 4.0 in these sectors. On the other hand, there is a positive correlation of Industry 4.0 and energy consumption for sectors with low energy consumption, which could be explained by the fact that digitalisation, such as the automation of previously mainly labour-intensive sectors, requires energy and also induces growth effects. In the discussion section (section 6) of this dissertation, I use the classification scheme of the three levels macro, meso and micro, as well as of direct and indirect environmental effects to classify the empirical observations into opportunities and risks, for example, with regard to the probability of rebound effects of digitalisation at the three levels. I link the investigated actor perspectives (policy makers, industry representatives), statistical data and additional literature across the system levels and consider political economy aspects to suggest fields of action for more sustainable (digitalised) industries. The dissertation thus makes two overarching contributions to the academic and societal discourse. First, my three empirical studies expand the limited state of research at the interface between digitalisation in industry and sustainability, especially by considering selected countries in the Global South and the example of China. Secondly, exploring the topic through data and methods from different disciplinary contexts and taking a socio-technical point of view, enables an analysis of (path) dependencies, uncertainties, and interactions in the socio-technical system across different system levels, which have often not been sufficiently considered in previous studies. The dissertation thus aims to create a scientifically and practically relevant knowledge basis for a value-guided, sustainability-oriented design of digitalisation in industry.
Gruppierung von Daten
(2022)
Dieser Beitrag beinhaltet einen Vergleich zwischen den Methoden der Topologischen Datenanalyse (TDA) und statistischen Clusterverfahren bei der Gruppierung von Daten. Es werden Gemeinsamkeiten und Unterschiede bei der Bildung der Cluster und Zuordnung der statistischen Einheiten identifiziert. Hierzu werden zwei empirische Datensätze aus der Biologie und Medizin herangezogen.
Zusammengefasst haben sich die Verfahren der TDA als ein praktikables Werkzeug bei der Gruppierung von Objekten erwiesen. Vor allem mit dem Mapper-Algorithmus konnten adäquate Cluster erkannt werden. Beim Iris Flower-Datensatz hat die TDA ähnliche Ergebnisse wie die Clusteranalyse erzielt. Der Heart Disease-Datensatz war schwieriger zu behandeln. Die genutzten clusteranalytischen Verfahren waren nicht geeignet, die beiden Gruppen von Patienten korrekt zu identifizieren. Im Vergleich zu den Standardverfahren der Clusteranalyse zeigte sich eine leichte Überlegenheit der topologischen Verfahren.
The concept of hydrologic connectivity summarizes all flow processes that link separate regions of a landscape. As such, it is a central theme in the field of catchment hydrology, with influence on neighboring disciplines such as ecology and geomorphology. It is widely acknowledged to be an important key in understanding the response behavior of a catchment and has at the same time inspired research on internal processes over a broad range of scales. From this process-hydrological point of view, hydrological connectivity is the conceptual framework to link local observations across space and scales.
This is the context in which the four studies this thesis comprises of were conducted. The focus was on structures and their spatial organization as important control on preferential subsurface flow. Each experiment covered a part of the conceptualized flow path from hillslopes to the stream: soil profile, hillslope, riparian zone, and stream.
For each study site, the most characteristic structures of the investigated domain and scale, such as slope deposits and peat layers were identified based on preliminary or previous investigations or literature reviews. Additionally, further structural data was collected and topographical analyses were carried out. Flow processes were observed either based on response observations (soil moisture changes or discharge patterns) or direct measurement (advective heat transport). Based on these data, the flow-relevance of the characteristic structures was evaluated, especially with regard to hillslope to stream connectivity.
Results of the four studies revealed a clear relationship between characteristic spatial structures and the hydrological behavior of the catchment. Especially the spatial distribution of structures throughout the study domain and their interconnectedness were crucial for the establishment of preferential flow paths and their relevance for large-scale processes. Plot and hillslope-scale irrigation experiments showed that the macropores of a heterogeneous, skeletal soil enabled preferential flow paths at the scale of centimeters through the otherwise unsaturated soil. These flow paths connected throughout the soil column and across the hillslope and facilitated substantial amounts of vertical and lateral flow through periglacial slope deposits.
In the riparian zone of the same headwater catchment, the connectivity between hillslopes and stream was controlled by topography and the dualism between characteristic subsurface structures and the geomorphological heterogeneity of the stream channel. At the small scale (1 m to 10 m) highest gains always occurred at steps along the longitudinal streambed profile, which also controlled discharge patterns at the large scale (100 m) during base flow conditions (number of steps per section). During medium and high flow conditions, however, the impact of topography and parafluvial flow through riparian zone structures prevailed and dominated the large-scale response patterns.
In the streambed of a lowland river, low permeability peat layers affected the connectivity between surface water and groundwater, but also between surface water and the hyporheic zone. The crucial factor was not the permeability of the streambed itself, but rather the spatial arrangement of flow-impeding peat layers, causing increased vertical flow through narrow “windows” in contrast to predominantly lateral flow in extended areas of high hydraulic conductivity sediments.
These results show that the spatial organization of structures was an important control for hydrological processes at all scales and study areas. In a final step, the observations from different scales and catchment elements were put in relation and compared. The main focus was on the theoretical analysis of the scale hierarchies of structures and processes and the direction of causal dependencies in this context. Based on the resulting hierarchical structure, a conceptual framework was developed which is capable of representing the system’s complexity while allowing for adequate simplifications.
The resulting concept of the parabolic scale series is based on the insight that flow processes in the terrestrial part of the catchment (soil and hillslopes) converge. This means that small-scale processes assemble and form large-scale processes and responses. Processes in the riparian zone and the streambed, however, are not well represented by the idea of convergence. Here, the large-scale catchment signal arrives and is modified by structures in the riparian zone, stream morphology, and the small-scale interactions between surface water and groundwater. Flow paths diverge and processes can better be represented by proceeding from large scales to smaller ones. The catchment-scale representation of processes and structures is thus the conceptual link between terrestrial hillslope processes and processes in the riparian corridor.
Die Fachtagungen HDI (Hochschuldidaktik Informatik) beschäftigen sich mit den unterschiedlichen Aspekten informatischer Bildung im Hochschulbereich. Neben den allgemeinen Themen wie verschiedenen Lehr- und Lernformen, dem Einsatz von Informatiksystemen in der Hochschullehre oder Fragen der Gewinnung von geeigneten Studierenden, deren Kompetenzerwerb oder auch der Betreuung der Studierenden widmet sich die HDI immer auch einem Schwerpunktthema.
Im Jahr 2021 war dies die Berücksichtigung von Diversität in der Lehre. Diskutiert wurden beispielsweise die Einbeziehung von besonderen fachlichen und überfachlichen Kompetenzen Studierender, der Unterstützung von Durchlässigkeit aus nichtakademischen Berufen, aber auch die Gestaltung inklusiver Lehr- und Lernszenarios, Aspekte des Lebenslangen Lernens oder sich an die Diversität von Studierenden adaptierte oder adaptierende Lehrsysteme.
Dieser Band enthält ausgewählte Beiträge der 9. Fachtagung 2021, die in besonderer Weise die Konferenz und die dort diskutierten Themen repräsentieren.
Hydraulic-driven fractures play a key role in subsurface energy technologies across several scales. By injecting fluid at high hydraulic pressure into rock with intrinsic low permeability, in-situ stress field and fracture development pattern can be characterised as well as rock permeability can be enhanced. Hydraulic fracturing is a commercial standard procedure for enhanced oil and gas production of rock reservoirs with low permeability in petroleum industry. However, in EGS utilization, a major geological concern is the unsolicited generation of earthquakes due to fault reactivation, referred to as induced seismicity, with a magnitude large enough to be felt on the surface or to damage facilities and buildings. Furthermore, reliable interpretation of hydraulic fracturing tests for stress measurement is a great challenge for the energy technologies. Therefore, in this cumulative doctoral thesis the following research questions are investigated. (1): How do hydraulic fractures grow in hard rock at various scales?; (2): Which parameters control hydraulic fracturing and hydro-mechanical coupling?; and (3): How can hydraulic fracturing in hard rock be modelled?
In the laboratory scale study, several laboratory hydraulic fracturing experiments are investigated numerically using Irazu2D that were performed on intact cubic Pocheon granite samples from South Korea applying different injection protocols. The goal of the laboratory experiments is to test the concept of cyclic soft stimulation which may enable sustainable permeability enhancement (Publication 1).
In the borehole scale study, hydraulic fracturing tests are reported that were performed in boreholes located in central Hungary to determine the in-situ stress for a geological site investigation. At depth of about 540 m, the recorded pressure versus time curves in mica schist with low dip angle foliation show atypical evolution. In order to provide explanation for this observation, a series of discrete element computations using Particle Flow Code 2D are performed (Publication 2).
In the reservoir scale study, the hydro-mechanical behaviour of fractured crystalline rock due to one of the five hydraulic stimulations at the Pohang Enhanced Geothermal site in South Korea is studied. Fluid pressure perturbation at faults of several hundred-meter lengths during hydraulic stimulation is simulated using FracMan (Publication 3).
The doctoral research shows that the resulting hydraulic fracturing geometry will depend “locally”, i.e. at the length scale of representative elementary volume (REV) and below that (sub-REV), on the geometry and strength of natural fractures, and “globally”, i.e. at super-REV domain volume, on far-field stresses. Regarding hydro-mechanical coupling, it is suggested to define separate coupling relationship for intact rock mass and natural fractures. Furthermore, the relative importance of parameters affecting the magnitude of formation breakdown pressure, a parameter characterising hydro-mechanical coupling, is defined. It can be also concluded that there is a clear gap between the capacity of the simulation software and the complexity of the studied problems. Therefore, the computational time of the simulation of complex hydraulic fracture geometries must be reduced while maintaining high fidelity simulation results. This can be achieved either by extending the computational resources via parallelization techniques or using time scaling techniques. The ongoing development of used numerical models focuses on tackling these methodological challenges.
Emotions are a complex concept and they are present in our everyday life. Persons on the autism spectrum are said to have difficulties in social interactions, showing deficits in emotion recognition in comparison to neurotypically developed persons. But social-emotional skills are believed to be positively augmented by training. A new adaptive social cognition training tool “E.V.A.” is introduced which teaches emotion recognition from face, voice and body language. One cross-sectional and one longitudinal study with adult neurotypical and autistic participants were conducted. The aim of the cross-sectional study was to characterize the two groups and see if differences in their social-emotional skills exist. The longitudinal study, on the other hand, aimed for detecting possible training effects following training with the new training tool. In addition, in both studies usability assessments were conducted to investigate the perceived usability of the new tool for neurotypical as well as autistic participants. Differences were found between autistic and neurotypical participants in their social-emotional and emotion recognition abilities. Training effects for neurotypical participants in an emotion recognition task were found after two weeks of home training. Similar perceived usability was found for the neurotypical and autistic participants. The current findings suggest that persons with ASC do not have a general deficit in emotion recognition, but are in need for more time to correctly recognize emotions. In addition, findings suggest that training emotion recognition abilities is possible. Further studies are needed to verify if the training effects found for neurotypical participants also manifest in a larger ASC sample.
Enhanced geothermal systems (EGS) are considered a cornerstone of future sustainable energy production. In such systems, high-pressure fluid injections break the rock to provide pathways for water to circulate in and heat up. This approach inherently induces small seismic events that, in rare cases, are felt or can even cause damage. Controlling and reducing the seismic impact of EGS is crucial for a broader public acceptance. To evaluate the applicability of hydraulic fracturing (HF) in EGS and to improve the understanding of fracturing processes and the hydromechanical relation to induced seismicity, six in-situ, meter-scale HF experiments with different injection schemes were performed under controlled conditions in crystalline rock in a depth of 410 m at the Äspö Hard Rock Laboratory (Sweden).
I developed a semi-automated, full-waveform-based detection, classification, and location workflow to extract and characterize the acoustic emission (AE) activity from the continuous recordings of 11 piezoelectric AE sensors. Based on the resulting catalog of 20,000 AEs, with rupture sizes of cm to dm, I mapped and characterized the fracture growth in great detail. The injection using a novel cyclic injection scheme (HF3) had a lower seismic impact than the conventional injections. HF3 induced fewer AEs with a reduced maximum magnitude and significantly larger b-values, implying a decreased number of large events relative to the number of small ones. Furthermore, HF3 showed an increased fracture complexity with multiple fractures or a fracture network. In contrast, the conventional injections developed single, planar fracture zones (Publication 1).
An independent, complementary approach based on a comparison of modeled and observed tilt exploits transient long-period signals recorded at the horizontal components of two broad-band seismometers a few tens of meters apart from the injections. It validated the efficient creation of hydraulic fractures and verified the AE-based fracture geometries. The innovative joint analysis of AEs and tilt signals revealed different phases of the fracturing process, including the (re-)opening, growth, and aftergrowth of fractures, and provided evidence for the reactivation of a preexisting fault in one of the experiments (Publication 2). A newly developed network-based waveform-similarity analysis applied to the massive AE activity supports the latter finding.
To validate whether the reduction of the seismic impact as observed for the cyclic injection schemes during the Äspö mine-scale experiments is transferable to other scales, I additionally calculated energy budgets for injection experiments from previously conducted laboratory tests and from a field application. Across all three scales, the cyclic injections reduce the seismic impact, as depicted by smaller maximum magnitudes, larger b-values, and decreased injection efficiencies (Publication 3).
The trace gases CO2 and CH4 pertain to the most relevant greenhouse gases and are important exchange fluxes of the global carbon (C) cycle. Their atmospheric quantity increased significantly as a result of the intensification of anthropogenic activities, such as especially land-use and land-use change, since the mid of the 18th century. To mitigate global climate change and ensure food security, land-use systems need to be developed, which favor reduced trace gas emissions and a sustainable soil carbon management. This requires the accurate and precise quantification of the influence of land-use and land-use change on CO2 and CH4 emissions. A common method to determine the trace gas dynamics and C sink or source function of a particular ecosystem is the closed chamber method. This method is often used assuming that accuracy and precision are high enough to determine differences in C gas emissions for e.g., treatment comparisons or different ecosystem components.
However, the broad range of different chamber designs, related operational procedures and data-processing strategies which are described in the scientific literature contribute to the overall uncertainty of closed chamber-based emission estimates. Hence, the outcomes of meta-analyses are limited, since these methodical differences hamper the comparability between studies. Thus, a standardization of closed chamber data acquisition and processing is much-needed.
Within this thesis, a set of case studies were performed to: (I) develop standardized routines for an unbiased data acquisition and processing, with the aim of providing traceable, reproducible and comparable closed chamber based C emission estimates; (II) validate those routines by comparing C emissions derived using closed chambers with independent C emission estimates; and (III) reveal processes driving the spatio-temporal dynamics of C emissions by developing (data processing based) flux separation approaches.
The case studies showed: (I) the importance to test chamber designs under field conditions for an appropriate sealing integrity and to ensure an unbiased flux measurement. Compared to the sealing integrity, the use of a pressure vent and fan was of minor importance, affecting mainly measurement precision; (II) that the developed standardized data processing routines proved to be a powerful and flexible tool to estimate C gas emissions and that this tool can be successfully applied on a broad range of flux data sets from very different ecosystem; (III) that automatic chamber measurements display temporal dynamics of CO2 and CH4 fluxes very well and most importantly, that they accurately detect small-scale spatial differences in the development of soil C when validated against repeated soil inventories; and (IV) that a simple algorithm to separate CH4 fluxes into ebullition and diffusion improves the identification of environmental drivers, which allows for an accurate gap-filling of measured CH4 fluxes.
Overall, the proposed standardized data acquisition and processing routines strongly improved the detection accuracy and precision of source/sink patterns of gaseous C emissions. Hence, future studies, which consider the recommended improvements, will deliver valuable new data and insights to broaden our understanding of spatio-temporal C gas dynamics, their particular environmental drivers and underlying processes.
Improving permafrost dynamics in land surface models: insights from dual sensitivity experiments
(2024)
The thawing of permafrost and the subsequent release of greenhouse gases constitute one of the most significant and uncertain positive feedback loops in the context of climate change, making predictions regarding changes in permafrost coverage of paramount importance. To address these critical questions, climate scientists have developed Land Surface Models (LSMs) that encompass a multitude of physical soil processes. This thesis is committed to advancing our understanding and refining precise representations of permafrost dynamics within LSMs, with a specific focus on the accurate modeling of heat fluxes, an essential component for simulating permafrost physics.
The first research question overviews fundamental model prerequisites for the representation of permafrost soils within land surface modeling. It includes a first-of-its-kind comparison between LSMs in CMIP6 to reveal their differences and shortcomings in key permafrost physics parameters. Overall, each of these LSMs represents a unique approach to simulating soil processes and their interactions with the climate system. Choosing the most appropriate model for a particular application depends on factors such as the spatial and temporal scale of the simulation, the specific research question, and available computational resources.
The second research question evaluates the performance of the state-of-the-art Community Land Model (CLM5) in simulating Arctic permafrost regions. Our approach overcomes traditional evaluation limitations by individually addressing depth, seasonality, and regional variations, providing a comprehensive assessment of permafrost and soil temperature dynamics. I compare CLM5's results with three extensive datasets: (1) soil temperatures from 295 borehole stations, (2) active layer thickness (ALT) data from the Circumpolar Active Layer Monitoring Network (CALM), and (3) soil temperatures, ALT, and permafrost extent from the ESA Climate Change Initiative (ESA-CCI). The results show that CLM5 aligns well with ESA-CCI and CALM for permafrost extent and ALT but reveals a significant global cold temperature bias, notably over Siberia. These results echo a persistent challenge identified in numerous studies: the existence of a systematic 'cold bias' in soil temperature over permafrost regions. To address this challenge, the following research questions propose dual sensitivity experiments.
The third research question represents the first study to apply a Plant Functional Type (PFT)-based approach to derive soil texture and soil organic matter (SOM), departing from the conventional use of coarse-resolution global data in LSMs. This novel method results in a more uniform distribution of soil organic matter density (OMD) across the domain, characterized by reduced OMD values in most regions. However, changes in soil texture exhibit a more intricate spatial pattern. Comparing the results to observations reveals a significant reduction in the cold bias observed in the control run. This method shows noticeable improvements in permafrost extent, but at the cost of an overestimation in ALT. These findings emphasize the model's high sensitivity to variations in soil texture and SOM content, highlighting the crucial role of soil composition in governing heat transfer processes and shaping the seasonal variation of soil temperatures in permafrost regions.
Expanding upon a site experiment conducted in Trail Valley Creek by \citet{dutch_impact_2022}, the fourth research question extends the application of the snow scheme proposed by \citet{sturm_thermal_1997} to cover the entire Arctic domain. By employing a snow scheme better suited to the snow density profile observed over permafrost regions, this thesis seeks to assess its influence on simulated soil temperatures. Comparing this method to observational datasets reveals a significant reduction in the cold bias that was present in the control run. In most regions, the Sturm run exhibits a substantial decrease in the cold bias. However, there is a distinctive overshoot with a warm bias observed in mountainous areas. The Sturm experiment effectively addressed the overestimation of permafrost extent in the control run, albeit resulting in a substantial reduction in permafrost extent over mountainous areas. ALT results remain relatively consistent compared to the control run. These outcomes align with our initial hypothesis, which anticipated that the reduced snow insulation in the Sturm run would lead to higher winter soil temperatures and a more accurate representation of permafrost physics.
In summary, this thesis demonstrates significant advancements in understanding permafrost dynamics and its integration into LSMs. It has meticulously unraveled the intricacies involved in the interplay between heat transfer, soil properties, and snow dynamics in permafrost regions. These insights offer novel perspectives on model representation and performance.
Städte sind aufgrund ihrer Agglomeration von Bevölkerung, Sachwerten und Infrastrukturen in besonderem Maße von extremen Wetterereignissen wie Starkregen und Hitze betroffen. Zahlreiche Überflutungsereignisse infolge von Starkregen traten in den letzten Jahren in verschiedenen Regionen Deutschlands auf und führten nicht nur zu Schäden in zwei- bis dreistelliger Millionenhöhe, sondern auch zu Todesopfern. Und auch Hitzewellen, wie sie in den vergangenen Jahren vermehrt aufgetreten sind, bergen gesundheitliche Risiken, welche sich auch in verschiedenen Schätzungen zu Hitzetodesfällen wiederfinden.
Um diesen Risiken zu begegnen und Schäden infolge von Wetterextremen zu reduzieren, entwickeln viele Kommunen bereits Strategien und Konzepte im Kontext der Klimaanpassung und/oder setzen Anpassungsmaßnahmen um. Neben der Entwicklung und Umsetzung eigener Ideen orientieren sich Städte dabei u. a. an Leitfäden und Beispielen aus der Literatur, Erfahrungen aus anderen Städten oder an Ergebnissen aus Forschungsprojekten. Dieser Lern- und Transferprozess, der eine Übertragung von Maßnahmen oder Instrumenten der Klimaanpassung von einem Ort auf einen anderen beinhaltet, ist bislang noch unzureichend erforscht und verstanden.
Der vorliegende Bericht untersucht deshalb ebendiesen Lern- und Transferprozess zwischen sowie innerhalb von Städten sowie das Transferpotenzial konkreter Wissenstransfer-Medien, Instrumente und Maßnahmen. Damit wird das Ziel verfolgt, ein besseres Verständnis dieser Prozesse zu entwickeln und einen Beitrag zur Verbesserung des Transfers von kommunalen Klimaanpassungsaktivitäten zu leisten. Der vorliegende Inhalt baut dabei auf einer vorangegangenen Analyse des Forschungsstands zum Transfer von Policies durch Haupt et al. (2021) auf und versucht, den bereits generierten Wissensstand auf der Ebene von Policies nun um die Ebene konkreter Instrumente und Maßnahmen zu ergänzen sowie durch empirische Befunde zu ausgewählten Maßnahmen zu untermauern. Die Wissens- und Datengrundlage dieses Berichts umfasst einen Mix aus verschiedenen (Online)-Befragungen und Interviews mit Vertreter:innen relevanter Akteursgruppen, vor allem Vertreter:innen von Stadtverwaltungen, sowie den Erfahrungswerten der drei ExTrass-Fallstudienstädte Potsdam, Remscheid und Würzburg.
Nach einer Einleitung beschäftigt sich Kapitel 2 mit übergeordneten Faktoren der Übertragbarkeit bzw. des Transfers. Kapitel 2.1 bietet hierbei eine Zusammenfassung zum aktuellen Wissensstand hinsichtlich des Transfers von Policies im Bereich der städtischen Klimapolitik gemäß Haupt et al. (2021). Hier werden zentrale Kriterien für einen erfolgreichen Transfer herausgearbeitet, um einen Anknüpfungspunkt für die folgenden Inhalte und empirischen Befunde auf der Ebene konkreter Instrumente und Maßnahmen zu bieten. Kapitel 2.2 schließt hieran an und präsentiert Erkenntnisse aus einer weitreichenden Kommunalbefragung. Hierbei wurde untersucht ob und welche Klimaanpassungsmaßnahmen in den Städten bereits umgesetzt werden, welche fördernden und hemmenden Aspekte es dabei gibt und welche Erfahrungen beim Transfer von Wissen und Ideen bereits vorliegen.
Kapitel 3 untersucht die Rolle verschiedener Medien des Wissenstransfers und widmet sich dabei beispielhaft Leitfäden zur Klimaanpassung und Maßnahmensteckbriefen. Kapitel 3.1 beantwortet dabei Fragen nach der Relevanz und Zugänglichkeit von Leitfäden, deren Stärken und Schwächen, sowie konkreten Anforderungen vonseiten befragter Personen. Außerdem werden acht ausgewählte Leitfäden vorgestellt und komprimiert auf ihre Transferpotenziale hin eingeschätzt. Kapitel 3.2 betrachtet Maßnahmensteckbriefe als Medien des Wissenstransfers und arbeitet zentrale Aspekte für einen praxisrelevanten inhaltlichen Aufbau heraus, um basierend darauf einen Muster-Maßnahmensteckbrief für Klimaanpassungsmaßnahmen zu entwickeln und vorzuschlagen.
Kapitel 4 beschäftigt sich mit sehr konkreten kommunalen Erfahrungen rund um den Transfer von sieben ausgewählten Instrumenten und Maßnahmen und bietet zahlreiche empirische Befunde aus den Kommunen, basierend auf der Kommunalbefragung, verschiedenen Interviews und den Erfahrungen aus der Projektarbeit. Die folgenden sieben Instrumente und Maßnahmen wurden ausgewählt, um eine große Breite städtischer Klimaanpassungsaktivitäten zu betrachten: 1) Klimafunktionskarten (Stadtklimakarten), 2) Starkregengefahrenkarten, 3) Checklisten zur Klimaanpassung in der Bauleitplanung, 4) Verbot von Schottergärten in Bebauungsplänen, 5) Fassadenbegrünungen, 6) klimaangepasste Gestaltung von Grün- und Freiflächen sowie 7) Handlungsempfehlungen für Betreuungseinrichtungen zum Umgang mit Hitze und Starkregen. Für jede dieser Klimaanpassungsaktivitäten wird auf Ebene der Kommunen Ziel, Verbreitung und Erscheinungsformen, Umsetzung anhand konkreter Beispiele, fördernde und hemmende Faktoren sowievorliegende Erfahrungen zu und Hinweisen auf Transfer dargestellt.
Kapitel 5 schließt den vorliegenden Bericht ab, indem zentrale Transfer-Barrieren aus den gewonnenen Erkenntnissen aufgegriffen und entsprechende Empfehlungen an verschiedene Ebenen der Politik ausgesprochen werden. Diese Empfehlungen zur Verbesserung des Transfers von klimaanpassungsrelevanten Instrumenten, Strategien und Maßnahmen umfassen 1) die Verbesserung des Austauschs zwischen verschiedenen Städten, 2) die Verbesserung der Zugänglichkeit von Wissen und Erfahrungen, 3) die Schaffung von Vernetzungsstrukturen innerhalb von Städten sowie 4) bestehende Wissenslücken zu schließen.
Die Autor:innen des vorliegenden Berichts hoffen, durch die vielfältigen Untersuchungsaspekte einen Beitrag zum besseren Verständnis der Lern- und Transferprozesse und zur Verbesserung des Transfers kommunaler Klimaanpassungsaktivitäten zu leisten.
The NAC transcription factor (TF) JUNGBRUNNEN1 (JUB1) is an important negative regulator of plant senescence, as well as of gibberellic acid (GA) and brassinosteroid (BR) biosynthesis in Arabidopsis thaliana. Overexpression of JUB1 promotes longevity and enhances tolerance to drought and other abiotic stresses. A similar role of JUB1 has been observed in other plant species, including tomato and banana. Our data show that JUB1 overexpressors (JUB1-OXs) accumulate higher levels of proline than WT plants under control conditions, during the onset of drought stress, and thereafter. We identified that overexpression of JUB1 induces key proline biosynthesis and suppresses key proline degradation genes. Furthermore, bZIP63, the transcription factor involved in proline metabolism, was identified as a novel downstream target of JUB1 by Yeast One-Hybrid (Y1H) analysis and Chromatin immunoprecipitation (ChIP). However, based on Electrophoretic Mobility Shift Assay (EMSA), direct binding of JUB1 to bZIP63 could not be confirmed. Our data indicate that JUB1-OX plants exhibit reduced stomatal conductance under control conditions. However, selective overexpression of JUB1 in guard cells did not improve drought stress tolerance in Arabidopsis. Moreover, the drought-tolerant phenotype of JUB1 overexpressors does not solely depend on the transcriptional control of the DREB2A gene. Thus, our data suggest that JUB1 confers tolerance to drought stress by regulating multiple components. Until today, none of the previous studies on JUB1´s regulatory network focused on identifying protein-protein interactions. We, therefore, performed a yeast two-hybrid screen (Y2H) which identified several protein interactors of JUB1, two of which are the calcium-binding proteins CaM1 and CaM4. Both proteins interact with JUB1 in the nucleus of Arabidopsis protoplasts. Moreover, JUB1 is expressed with CaM1 and CaM4 under the same conditions. Since CaM1.1 and CaM4.1 encode proteins with identical amino acid sequences, all further experiments were performed with constructs involving the CaM4 coding sequence. Our data show that JUB1 harbors multiple CaM-binding sites, which are localized in both the N-terminal and C-terminal regions of the protein. One of the CaM-binding sites, localized in the DNA-binding domain of JUB1, was identified as a functional CaM-binding site since its mutation strongly reduced the binding of CaM4 to JUB1. Furthermore, JUB1 transactivates expression of the stress-related gene DREB2A in mesophyll cells; this effect is significantly reduced when the calcium-binding protein CaM4 is expressed as well. Overexpression of both genes in Arabidopsis results in early senescence observed through lower chlorophyll content and an enhanced expression of senescence-associated genes (SAGs) when compared with single JUB1 overexpressors. Our data also show that JUB1 and CaM4 proteins interact in senescent leaves, which have increased Ca2+ levels when compared to young leaves. Collectively, our data indicate that JUB1 activity towards its downstream targets is fine-tuned by calcium-binding proteins during leaf senescence.
Die vorliegende kumulative Promotionsarbeit beschäftigt sich mit leistungsstarken Schülerinnen und Schülern, die seit 2015 in der deutschen Bildungspolitik, zum Beispiel im Rahmen von Förderprogrammen wieder mehr Raum einnehmen, nachdem in Folge des „PISA-Schocks“ im Jahr 2000 zunächst der Fokus stärker auf den Risikogruppen lag. Während leistungsstärkere Schülerinnen und Schüler in der öffentlichen Wahrnehmung häufig mit „(Hoch-)Begabten“ identifiziert werden, geht die Arbeit über die traditionelle Begabungsforschung, die eine generelle Intelligenz als Grundlage für Leistungsfähigkeit von Schülerinnen und Schülern begreift und beforscht, hinaus. Stattdessen lässt sich eher in den Bereich der Talentforschung einordnen, die den Fokus weg von allgemeinen Begabungen auf spezifische Prädiktoren und Outcomes im individuellen Entwicklungsverlauf legt. Der Fokus der Arbeit liegt daher nicht auf Intelligenz als Potenzial, sondern auf der aktuellen schulischen Leistung, die als Ergebnis und Ausgangspunkt von Entwicklungsprozessen in einer Leistungsdomäne doppelte Bedeutung erhält.
Die Arbeit erkennt die Vielgestaltigkeit des Leistungsbegriffs an und ist bestrebt, neue Anlässe zu schaffen, über den Leistungsbegriff und seine Operationalisierung in der Forschung zu diskutieren. Hierfür wird im ersten Teil ein systematisches Review zur Operationalisierung von Leistungsstärke durchgeführt (Artikel I). Es werden Faktoren herausgearbeitet, auf welchen sich die Operationalisierungen unterscheiden können. Weiterhin wird ein Überblick gegeben, wie Studien zu Leistungsstarken sich seit dem Jahr 2000 auf diesen Dimensionen verorten lassen. Es zeigt sich, dass eindeutige Konventionen zur Definition schulischer Leistungsstärke noch nicht existieren, woraus folgt, dass Ergebnisse aus Studien, die sich mit leistungsstarken Schülerinnen und Schülern beschäftigen, nur bedingt miteinander vergleichbar sind. Im zweiten Teil der Arbeit wird im Rahmen zwei weiterer Artikel, welche sich mit der Leistungsentwicklung (Artikel II) und der sozialen Einbindung (Artikel III) von leistungsstarken Schülerinnen und Schülern befassen, darauf aufbauend der Ansatz verfolgt, die Variabilität von Ergebnissen über verschiedene Operationalisierungen von Leistungsstärke deutlich zu machen. Damit wird unter anderem auch die künftige Vergleichbarkeit mit anderen Studien erleichtert. Genutzt wird dabei das Konzept der Multiversumsanalyse (Steegen et al., 2016), bei welcher viele parallele Spezifikationen, die zugleich sinnvolle Alternativen für die Operationalisierung darstellen, nebeneinandergestellt und in ihrem Effekt verglichen werden (Jansen et al., 2021). Die Multiversumsanalyse knüpft konzeptuell an das bereits vor längerem entwickelte Forschungsprogramm des kritischen Multiplismus an (Patry, 2013; Shadish, 1986, 1993), erhält aber als spezifische Methode aktuell im Rahmen der Replizierbarkeitskrise in der Psychologie eine besondere Bedeutung. Dabei stützt sich die vorliegende Arbeit auf die Sekundäranalyse großangelegter Schulleistungsstudien, welche den Vorteil besitzen, dass eine große Zahl an Datenpunkten (Variablen und Personen) zur Verfügung steht, um Effekte unterschiedlicher Operationalisierungen zu vergleichen.
Inhaltlich greifen Artikel II und III Themen auf, die in der wissenschaftlichen und gesellschaftlichen Diskussion zu Leistungsstarken und ihrer Wahrnehmung in der Öffentlichkeit immer wieder aufscheinen: In Artikel II wird zunächst die Frage gestellt, ob Leistungsstarke bereits im aktuellen Regelunterricht einen kumulativen Vorteil gegenüber ihren weniger leistungsstarken Mitschülerinnen und Mitschülern haben (Matthäus-Effekt). Die Ergebnisse zeigen, dass an Gymnasien keineswegs von sich vergrößernden Unterschieden gesprochen werden kann. Im Gegenteil, es verringerte sich im Laufe der Sekundarstufe der Abstand zwischen den Gruppen, indem die Lernraten bei leistungsschwächeren Schülerinnen und Schülern höher waren. Artikel III hingegen betrifft die soziale Wahrnehmung von leistungsstarken Schülerinnen und Schülern. Auch hier hält sich in der öffentlichen Diskussion die Annahme, dass höhere Leistungen mit Nachteilen in der sozialen Integration einhergehen könnten, was sich auch in Studien widerspiegelt, die sich mit Geschlechterstereotypen Jugendlicher in Bezug auf Schulleistung beschäftigen. In Artikel III wird unter anderem erneut das Potenzial der Multiversumsanalyse genutzt, um die Variation des Zusammenhangs über Operationalisierungen von Leistungsstärke zu beschreiben. Es zeigt sich unter unterschiedlichen Operationalisierungen von Leistungsstärke und über verschiedene Facetten sozialer Integration hinweg, dass die Zusammenhänge zwischen Leistung und sozialer Integration insgesamt leicht positiv ausfallen. Annahmen, die auf differenzielle Effekte für Jungen und Mädchen oder für unterschiedliche Fächer abzielen, finden in diesen Analysen keine Bestätigung.
Die Dissertation zeigt, dass der Vergleich unterschiedlicher Ansätze zur Operationalisierung von Leistungsstärke — eingesetzt im Rahmen eines kritischen Multiplismus — das Verständnis von Phänomenen vertiefen kann und auch das Potenzial hat, Theorieentwicklung voranzubringen.
Extreme flooding displaces an average of 12 million people every year. Marginalized populations in low-income countries are in particular at high risk, but also industrialized countries are susceptible to displacement and its inherent societal impacts. The risk of being displaced results from a complex interaction of flood hazard, population exposed in the floodplains, and socio-economic vulnerability. Ongoing global warming changes the intensity, frequency, and duration of flood hazards, undermining existing protection measures. Meanwhile, settlements in attractive yet hazardous flood-prone areas have led to a higher degree of population exposure. Finally, the vulnerability to displacement is altered by demographic and social change, shifting economic power, urbanization, and technological development. These risk components have been investigated intensively in the context of loss of life and economic damage, however, only little is known about the risk of displacement under global change.
This thesis aims to improve our understanding of flood-induced displacement risk under global climate change and socio-economic change. This objective is tackled by addressing the following three research questions. First, by focusing on the choice of input data, how well can a global flood modeling chain reproduce flood hazards of historic events that lead to displacement? Second, what are the socio-economic characteristics that shape the vulnerability to displacement? Finally, to what degree has climate change potentially contributed to recent flood-induced displacement events?
To answer the first question, a global flood modeling chain is evaluated by comparing simulated flood extent with satellite-derived inundation information for eight major flood events. A focus is set on the sensitivity to different combinations of the underlying climate reanalysis datasets and global hydrological models which serve as an input for the global hydraulic model. An evaluation scheme of performance scores shows that simulated flood extent is mostly overestimated without the consideration of flood protection and only for a few events dependent on the choice of global hydrological models. Results are more sensitive to the underlying climate forcing, with two datasets differing substantially from a third one. In contrast, the incorporation of flood protection standards results in an underestimation of flood extent, pointing to potential deficiencies in the protection level estimates or the flood frequency distribution within the modeling chain.
Following the analysis of a physical flood hazard model, the socio-economic drivers of vulnerability to displacement are investigated in the next step. For this purpose, a satellite- based, global collection of flood footprints is linked with two disaster inventories to match societal impacts with the corresponding flood hazard. For each event the number of affected population, assets, and critical infrastructure, as well as socio-economic indicators are computed. The resulting datasets are made publicly available and contain 335 displacement events and 695 mortality/damage events. Based on this new data product, event-specific displacement vulnerabilities are determined and multiple (national) dependencies with the socio-economic predictors are derived. The results suggest that economic prosperity only partially shapes vulnerability to displacement; urbanization, infant mortality rate, the share of elderly, population density and critical infrastructure exhibit a stronger functional relationship, suggesting that higher levels of development are generally associated with lower vulnerability.
Besides examining the contextual drivers of vulnerability, the role of climate change in the context of human displacement is also being explored. An impact attribution approach is applied on the example of Cyclone Idai and associated extreme coastal flooding in Mozambique. A combination of coastal flood modeling and satellite imagery is used to construct factual and counterfactual flood events. This storyline-type attribution method allows investigating the isolated or combined effects of sea level rise and the intensification of cyclone wind speeds on coastal flooding. The results suggest that displacement risk has increased by 3.1 to 3.5% due to the total effects of climate change on coastal flooding, with the effects of increasing wind speed being the dominant factor.
In conclusion, this thesis highlights the potentials and challenges of modeling flood- induced displacement risk. While this work explores the sensitivity of global flood modeling to the choice of input data, new questions arise on how to effectively improve the reproduction of flood return periods and the representation of protection levels. It is also demonstrated that disentangling displacement vulnerabilities is feasible, with the results providing useful information for risk assessments, effective humanitarian aid, and disaster relief. The impact attribution study is a first step in assessing the effects of global warming on displacement risk, leading to new research challenges, e.g., coupling fluvial and coastal flood models or the attribution of other hazard types and displacement events. This thesis is one of the first to address flood-induced displacement risk from a global perspective. The findings motivate for further development of the global flood modeling chain to improve our understanding of displacement vulnerability and the effects of global warming.
The Greenland Ice Sheet is the second-largest mass of ice on Earth. Being almost 2000 km long, more than 700 km wide, and more than 3 km thick at the summit, it holds enough ice to raise global sea levels by 7m if melted completely. Despite its massive size, it is particularly vulnerable to anthropogenic climate change: temperatures over the Greenland Ice Sheet have increased by more than 2.7◦C in the past 30 years, twice as much as the global mean temperature. Consequently, the ice sheet has been significantly losing mass since the 1980s and the rate of loss has increased sixfold since then. Moreover, it is one of the potential tipping elements of the Earth System, which might undergo irreversible change once a warming threshold is exceeded. This thesis aims at extending the understanding of the resilience of the Greenland Ice Sheet against global warming by analyzing processes and feedbacks relevant to its centennial to multi-millennial stability using ice sheet modeling.
One of these feedbacks, the melt-elevation-feedback is driven by the temperature rise with decreasing altitudes: As the ice sheet melts, its thickness and surface elevation decrease, exposing the ice surface to warmer air and thus increasing the melt rates even further. The glacial isostatic adjustment (GIA) can partly mitigate this melt-elevation feedback as the bedrock lifts in response to an ice load decrease, forming the negative GIA feedback. In my thesis, I show that the interaction between these two competing feedbacks can lead to qualitatively different dynamical responses of the Greenland Ice Sheet to warming – from permanent loss to incomplete recovery, depending on the feedback parameters. My research shows that the interaction of those feedbacks can initiate self-sustained oscillations of the ice volume while the climate forcing remains constant.
Furthermore, the increased surface melt changes the optical properties of the snow or ice surface, e.g. by lowering their albedo, which in turn enhances melt rates – a process known as the melt-albedo feedback. Process-based ice sheet models often neglect this melt-albedo feedback. To close this gap, I implemented a simplified version of the diurnal Energy Balance Model, a computationally efficient approach that can capture the first-order effects of the melt-albedo feedback, into the Parallel Ice Sheet Model (PISM). Using the coupled model, I show in warming experiments that the melt-albedo feedback almost doubles the ice loss until the year 2300 under the low greenhouse gas emission scenario RCP2.6, compared to simulations where the melt-albedo feedback is neglected,
and adds up to 58% additional ice loss under the high emission scenario RCP8.5. Moreover, I find that the melt-albedo feedback dominates the ice loss until 2300, compared to the melt-elevation feedback.
Another process that could influence the resilience of the Greenland Ice Sheet is the warming induced softening of the ice and the resulting increase in flow. In my thesis, I show with PISM how the uncertainty in Glen’s flow law impacts the simulated response to warming. In a flow line setup at fixed climatic mass balance, the uncertainty in flow parameters leads to a range of ice loss comparable to the range caused by different warming levels.
While I focus on fundamental processes, feedbacks, and their interactions in the first three projects of my thesis, I also explore the impact of specific climate scenarios on the sea level rise contribution of the Greenland Ice Sheet. To increase the carbon budget flexibility, some warming scenarios – while still staying within the limits of the Paris Agreement – include a temporal overshoot of global warming. I show that an overshoot by 0.4◦C increases the short-term and long-term ice loss from Greenland by several centimeters. The long-term increase is driven by the warming at high latitudes, which persists even when global warming is reversed. This leads to a substantial long-term commitment of the sea level rise contribution from the Greenland Ice Sheet.
Overall, in my thesis I show that the melt-albedo feedback is most relevant for the ice loss of the Greenland Ice Sheet on centennial timescales. In contrast, the melt-elevation feedback and its interplay with the GIA feedback become increasingly relevant on millennial timescales. All of these influence the resilience of the Greenland Ice Sheet against global warming, in the near future and on the long term.
Mit den ›Nachträgen‹ liegt nun der letzte Schriftenband der Jubiläumsausgabe vor. Er ergänzt die ›Jubiläumsausgabe‹ um Texte und Briefe, die entweder erst nach Erscheinen des jeweiligen Bandes entdeckt wurden oder bei Fortsetzung der Ausgabe nach dem Krieg als verschollen galten. Bei den philosophischen Fragmenten handelt es sich u.a. um bisher unbekannte Entwürfe für die ›Morgenstunden‹ und ›An die Freunde Lessings‹. Zu den Judaica zählen Mendelssohns Übertragungen hebräischer Gedichte des 18. Jahrhunderts, seine Übersetzung der Grundartikel des Judentums und seine Anmerkungen zu Michaelis’ Rezension von Dohms ›Ueber die bürgerliche Verbesserung der Juden‹. Zu Mendelssohns Briefpartnern zählen u.a. Abbt, Iselin, Lessing, Friedrich II., Engel, Lavater, Michaelis, Penzel, Nicolai, Dohm, Kuh, Lowth, Carmer und Ramler.
Moss-microbe associations are often characterised by syntrophic interactions between the microorganisms and their hosts, but the structure of the microbial consortia and their role in peatland development remain unknown.
In order to study microbial communities of dominant peatland mosses, Sphagnum and brown mosses, and the respective environmental drivers, four study sites representing different successional stages of natural northern peatlands were chosen on a large geographical scale: two brown moss-dominated, circumneutral peatlands from the Arctic and two Sphagnum-dominated, acidic peat bogs from subarctic and temperate zones.
The family Acetobacteraceae represented the dominant bacterial taxon of Sphagnum mosses from various geographical origins and displayed an integral part of the moss core community. This core community was shared among all investigated bryophytes and consisted of few but highly abundant prokaryotes, of which many appear as endophytes of Sphagnum mosses. Moreover, brown mosses and Sphagnum mosses represent habitats for archaea which were not studied in association with peatland mosses so far. Euryarchaeota that are capable of methane production (methanogens) displayed the majority of the moss-associated archaeal communities. Moss-associated methanogenesis was detected for the first time, but it was mostly negligible under laboratory conditions. Contrarily, substantial moss-associated methane oxidation was measured on both, brown mosses and Sphagnum mosses, supporting that methanotrophic bacteria as part of the moss microbiome may contribute to the reduction of methane emissions from pristine and rewetted peatlands of the northern hemisphere.
Among the investigated abiotic and biotic environmental parameters, the peatland type and the host moss taxon were identified to have a major impact on the structure of moss-associated bacterial communities, contrarily to archaeal communities whose structures were similar among the investigated bryophytes. For the first time it was shown that different bog development stages harbour distinct bacterial communities, while at the same time a small core community is shared among all investigated bryophytes independent of geography and peatland type.
The present thesis displays the first large-scale, systematic assessment of bacterial and archaeal communities associated both with brown mosses and Sphagnum mosses. It suggests that some host-specific moss taxa have the potential to play a key role in host moss establishment and peatland development.