Refine
Has Fulltext
- yes (4550) (remove)
Year of publication
Document Type
- Postprint (2089)
- Doctoral Thesis (1731)
- Monograph/Edited Volume (223)
- Preprint (126)
- Working Paper (121)
- Article (86)
- Master's Thesis (59)
- Habilitation Thesis (39)
- Part of Periodical (27)
- Conference Proceeding (26)
Language
- English (4550) (remove)
Is part of the Bibliography
- yes (4550) (remove)
Keywords
- climate change (70)
- Klimawandel (48)
- machine learning (44)
- Modellierung (34)
- diffusion (28)
- morphology (27)
- climate (25)
- model (25)
- Germany (24)
- syntax (23)
Institute
- Institut für Biochemie und Biologie (538)
- Institut für Physik und Astronomie (530)
- Mathematisch-Naturwissenschaftliche Fakultät (482)
- Institut für Geowissenschaften (448)
- Institut für Chemie (361)
- Extern (210)
- Humanwissenschaftliche Fakultät (206)
- Strukturbereich Kognitionswissenschaften (174)
- Wirtschaftswissenschaften (169)
- Institut für Mathematik (168)
Terrestrial landscape dynamics are dominated by the production, mobilisation, transfer and deposition of sediment. Numerous chemical elements are carried by sediments, making them a key component for ecological processes, as soil constitution and thus plants and animal ecosystems depends on them, and by extension the human species. They are also essential for climate evolution and regulation as marine sedimentation acts as a carbon sink. However, the processes at the origin of their production, mobilisation, transfer can occur suddenly with high-energy content – such as volcanic eruption, mass wasting or flooding events and wildfires – shaking ecosystems and shaping landforms. Besides, in the last era, the human species has shown its ability to disturb landscape dynamics and change sediments cycles. Thus, there is a need for predictive understanding of the processes involved. This relies on un-derstanding of the mechanisms of key processes and their controls, and knowledge of the state and evolution of the Earth’s surface. Classic approaches to these challenges include empirical observations and numerical modeling of geochemical fluxes and surface processes, as well as the study of terrestrial sedimentary archives to better understand the parameters at stake in landscape dynamics and climate changes and the different actions and retroactions between the production, mobilisation, transfer and deposition of sediments which ultimately shape landscapes. Environmental seismology complements these approaches.
Environmental seismology is the science topic investigating the source functions and propagation properties of seismic vibrations triggered by processes happening at or near the Earth’s surface, below and above it - cryosphere, hydrosphere, atmosphere, human habitat, biosphere, etc., to obtain insight into all these physical processes. Indeed, from mass wasting event to rivers, from wild species to hu-man, all these processes are generating seismic waves. Environmental seismology is a rather recent field, with new branches rapidly expanding and at various stages of scientific progress. This thesis is motivated by the goal of learning more on two major natural process hazards (river bedload transport and mass wasting) as well as on human-generated acoustic hazard, while covering the axis of funda-mental research progression, from data exploration and method and theory development to proof of concept, with the twin aims of developing a better understanding of the operation of these specific processes, and of advancing the methods we have at our disposal to study them.
First, I provide a benchmark for assessment of the reliability of existing seismic bedload model inver-sion to retrieve bedload flux from seismic data. Bedload flux measurements are essential to better understand river dynamics, and this can be achieved with environmental seismology. However, due to a lack of well-constrained validation data, the accuracy of the resulting inversions is unknown. I address this gap in Chapter 2.2, reporting a seismic field experiment, and comparing the results to high-quality independent bedload measurements to constrain a seismic bedload model. The study shows that the quality of bedload flux estimates from seismic data strongly depends on the quality of the input data for the model. Direct measurements of relevant parameters, chiefly seismic ground proper-ties needed for the Green's function and the grain size distribution of the moving bedload, considerably improve the model quality over generic approaches using empirical or theoretical functions. I also pro-vide a numerical tool to facilitate the use of water turbulence and bedload seismic inversion models: seismic models for bedload flux and water turbulence require painstaking work to constrain parame-ters describing the ground properties by active seismic study or analysis of passive seismic data, and the grain size distribution via independent measurements. Reasonable predictions can be achieved by using a Monte Carlo approach to optimize the free parameters with respect to the target parameters. The validation of the tool, in Chapter 2.3, with independent measurements of water depth and bedload flux at a study site on the Eshtemoa river in Israël makes it available for reliable use at other sites. The work reported in this chapter has been published in Lagarde et al. 2021 and Dietze et al. 2019b.
In a second study, reported in Chapter 3, I investigate the formation of a failure plane prior to a rock-slide. A better understanding of the dynamics of the preparation phase is essential to determine the timing, volume and mobilization mechanism of a rock slope failure, and this can be achieved with envi-ronmental seismology. I take advantage of a network of seismic stations close to an instable slope recording cracking signals prior to the slope failure, and use a machine learning technique based on hidden Markov models to isolate these signals from the seismic data, retrieving the cumulative number of cracking events in a period of 20 days prior to a large rockslide and 10 days after. The trajectory of the cumulative number of cracks shifts from a rather linear shape in the two weeks prior to the rock-slide to an S-shaped development in the last 27 h before failure. I interpret this change as a switch from initial distributed cracking to localised damage accumulation in the hours prior to the failure. I develop a simple physical model to explain the temporal evolution of crack activity during the S-shape phase, revealing the importance of an internal parameter, the total crack boundary length as the dominant control parameter of failure plane evolution. This study has been published as Lagarde et al. 2023.
Third, I develop a model converting acoustic signals to seismic signals. A part of the acoustic vibrations generated on the Earth’s surface is converted to seismic signals at the ground interface. Consequently, noise pollution may be translated to slope fatigue and rock micro (or macro) fracturing resulting in a degrading effect on landforms. Moreover, this pollution can have negative impacts, such as physical, physiological as well as psychological effects on animal species. At present, the impact of seismic pol-lution generated by acoustic sources is difficult to evaluate. In Chapter 4, I improve and implement a model converting the acoustic pressure generated by a source in the atmosphere to the corresponding seismic signal for a receiver within the ground. The ground is considered to be a porous elastic medium in which wave behaviour can be approximated by the Biot-Stoll model. The model is extended for use of a temporal pressure pulse as an input, and to produce output on a plan 2D map, where the wind effect on the acoustic to seismic coupling can be reproduced. I invest extensive effort in making the model user-friendly, as the project aims at reaching a large audience, comprising, for example, geo-morphologists, biologists and sociologists. Finally, the model is subjected to synthetic testing as well as a qualitative comparison of the predicted ground particle velocity and the seismic signal of a real heli-copter flight as a source of acoustic input.
These studies advance understanding of the operation of specific natural processes in channels and on hillslopes, and bring us closer to designing functioning early warning systems for mass-wasting and flood events. This thesis also raises questions that have not been considered before, such as the con-tribution of human acoustic pollution to the seismic hum and its impact on the natural environment, or the importance of cracks in the self-development of the failure plane prior to slope. Together, these studies question general assumptions usually made regarding the triggering of mass wasting or the hillslope-channel connectivity. Beyond this, the thesis covers the axis of fundamental research progres-sion, from data exploration and method and theory development to proof of concept, and shows how in the rapidly developing field of environmental seismology, an active awareness of progress can help strengthen and accelerate general advances.
On 21 April 2021, the European Commission presented its long-awaited proposal for a Regulation “laying down harmonized rules on Artificial Intelligence”, the so-called “Artificial Intelligence Act” (AIA). This article takes a critical look at the proposed regulation. After an introduction (1), the paper analyzes the unclear preemptive effect of the AIA and EU competences (2), the scope of application (3), the prohibited uses of Artificial Intelligence (AI) (4), the provisions on high-risk AI systems (5), the obligations of providers and users (6), the requirements for AI systems with limited risks (7), the enforcement system (8), the relationship of the AIA with the existing legal framework (9), and the regulatory gaps (10). The last section draws some final conclusions (11).
Jurisdiction
(2022)
Strength of weakness
(2020)
The paper investigates quality management in teaching and learning in higher education institutions from a principal-agent perspective. Based on data gained from semi-structured interviews and from a nation-wide survey with quality managers of German higher education institutions, the study shows how quality managers position themselves in relation to their perception of the interests of other actors in higher education institutions. The paper describes the various interests and discusses the main implications of this constellation of actors. It argues that quality managers, although they may be considered as rather weak actors within the higher education institution, may be characterised as having a strength of weakness due to diverging interests of their principals.
Strategic social media use positively influences organizational goals such as the long-term accrual of social capital, and thus social media information governance has become an increasingly important organizational objective. It is particularly important for humanitarian nongovernmental organizations (HNGOs), whose work relies on accurate and timely information regarding socially altruistic behavior (donations, volunteerism, etc.). Despite the potential of social media for increasing social capital, tensions in governing social media information across an organization's different operational levels (regional, intermediate, and national) pose a difficult challenge. Prominent governance frameworks offer little guidance, as their focus on control and incremental policymaking is largely incompatible with the processes, roles, standards, and metrics needed for managing self-governing social media. This study offers a notion of dynamic and co-evolutionary process management of multi-level organizations as a means of conceptualizing social media information governance for the accrual of organizational social capital. Based on interviews with members of HNGOs, this study reveals tensions that emerge within eight focus areas of accruing social capital in multi-level organizations, explains how dynamic process management can ease those tensions, and proposes corresponding strategy recommendations.
With the latest technological developments and associated new possibilities in teaching, the personalisation of learning is gaining more and more importance. It assumes that individual learning experiences and results could generally be improved when personal learning preferences are considered. To do justice to the complexity of the personalisation possibilities of teaching and learning processes, we illustrate the components of learning and teaching in the digital environment and their interdependencies in an initial model. Furthermore, in a pre-study, we investigate the relationships between the learner's ability to (digital) self-organise, the learner’s prior- knowledge learning in different variants of mode and learning outcomes as one part of this model. With this pre-study, we are taking the first step towards a holistic model of teaching and learning in digital environments.
Alcohol use disorder (AUD) is the most common substance use disorder worldwide. Although dopamine-related findings were often observed in AUD, associated neurobiological mechanisms are still poorly understood. Therefore, in the present study, we investigate D2/3 receptor availability in healthy participants, participants at high risk (HR) to develop addiction (not diagnosed with AUD), and AUD patients in a detoxified stage, applying F-18-fallypride positron emission tomography (F-18-PET). Specifically, D2/3 receptor availability was investigated in (1) 19 low-risk (LR) controls, (2) 19 HR participants, and (3) 20 AUD patients after alcohol detoxification. Quality and severity of addiction were assessed with clinical questionnaires and (neuro)psychological tests. PET data were corrected for age of participants and smoking status. In the dorsal striatum, we observed significant reductions of D2/3 receptor availability in AUD patients compared with LR participants. Further, receptor availability in HR participants was observed to be intermediate between LR and AUD groups (linearly decreasing). Still, in direct comparison, no group difference was observed between LR and HR groups or between HR and AUD groups. Further, the score of the Alcohol Dependence Scale (ADS) was inversely correlated with D2/3 receptor availability in the combined sample. Thus, in line with a dimensional approach, striatal D2/3 receptor availability showed a linear decrease from LR participants to HR participants to AUD patients, which was paralleled by clinical measures. Our study shows that a core neurobiological feature in AUD seems to be detectable in an early, subclinical state, allowing more individualized alcohol prevention programs in the future.
White mica and tourmaline are the dominant hydrothermal alteration minerals at the world-class Panasqueira W-Sn-Cu deposit in Portugal. Thus, understanding the controls on their chemical composition helps to constrain ore formation processes at this deposit and determine their usefulness as pathfinder minerals for mineralization in general. We combine whole-rock geochemistry of altered and unaltered metasedimentary host rocks with in situ LA-ICP-MS measurements of tourmaline and white mica from the alteration halo. Principal component analysis (PCA) is used to better identify geochemical patterns and trends of hydrothermal alteration in the datasets. The hydrothermally altered metasediments are enriched in As, Sn, Cs, Li, W, F, Cu, Rb, Zn, Tl, and Pb relative to unaltered samples. In situ mineral analyses show that most of these elements preferentially partition into white mica over tourmaline (Li, Rb, Cs, Tl, W, and Sn), whereas Zn is enriched in tourmaline. White mica has distinct compositions in different settings within the deposit (greisen, vein selvages, wall rock alteration zone, late fault zone), indicating a compositional evolution with time. In contrast, tourmaline from different settings overlaps in composition, which is ascribed to a stronger dependence on host rock composition and also to the effects of chemical zoning and microinclusions affecting the LA-ICP-MS analyses. Hence, in this deposit, white mica is the better recorder of the fluid composition. The calculated trace-element contents of the Panasqueira mineralizing fluid based on the mica data and estimates of mica-fluid partition coefficients are in good agreement with previous fluid-inclusion analyses. A compilation of mica and tourmaline trace-element compositions from Panasqueira and other W-Sn deposits shows that white mica has good potential as a pathfinder mineral, with characteristically high Li, Cs, Rb, Sn, and W contents. The trace-element contents of hydrothermal tourmaline are more variable. Nevertheless, the compiled data suggest that high Sn and Li contents are distinctive for tourmaline from W-Sn deposits.
In nature, plants are constantly exposed to many transient, but recurring, stresses. Thus, to complete their life cycles, plants require a dynamic balance between capacities to recover following cessation of stress and maintenance of stress memory. Recently, we uncovered a new functional role for macroautophagy/autophagy in regulating recovery from heat stress (HS) and resetting cellular memory of HS inArabidopsis thaliana. Here, we demonstrated that NBR1 (next to BRCA1 gene 1) plays a crucial role as a receptor for selective autophagy during recovery from HS. Immunoblot analysis and confocal microscopy revealed that levels of the NBR1 protein, NBR1-labeled puncta, and NBR1 activity are all higher during the HS recovery phase than before. Co-immunoprecipitation analysis of proteins interacting with NBR1 and comparative proteomic analysis of annbr1-null mutant and wild-type plants identified 58 proteins as potential novel targets of NBR1. Cellular, biochemical and functional genetic studies confirmed that NBR1 interacts with HSP90.1 (heat shock protein 90.1) and ROF1 (rotamase FKBP 1), a member of the FKBP family, and mediates their degradation by autophagy, which represses the response to HS by attenuating the expression ofHSPgenes regulated by the HSFA2 transcription factor. Accordingly, loss-of-function mutation ofNBR1resulted in a stronger HS memory phenotype. Together, our results provide new insights into the mechanistic principles by which autophagy regulates plant response to recurrent HS.
Induced point mutations are important genetic resources for their ability to create hypo- and hypermorphic alleles that are useful for understanding gene functions and breeding. However, such mutant populations have only been developed for a few temperate maize varieties, mainly B73 and W22, yet no tropical maize inbred lines have been mutagenized and made available to the public to date. We developed a novel Ethyl Methanesulfonate (EMS) induced mutation resource in maize comprising 2050 independent M2 mutant families in the elite tropical maize inbred ML10. By phenotypic screening, we showed that this population is of comparable quality with other mutagenized populations in maize. To illustrate the usefulness of this population for gene discovery, we performed rapid mapping-by-sequencing to clone a fasciated-ear mutant and identify a causal promoter deletion in ZmCLE7 (CLE7). Our mapping procedure does not require crossing to an unrelated parent, thus is suitable for mapping subtle traits and ones affected by heterosis. This first EMS population in tropical maize is expected to be very useful for the maize research community. Also, the EMS mutagenesis and rapid mapping-by-sequencing pipeline described here illustrate the power of performing forward genetics in diverse maize germplasms of choice, which can lead to novel gene discovery due to divergent genetic backgrounds.