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This dissertation aimed to determine differential expressed miRNAs in the context of chronic pain in polyneuropathy. For this purpose, patients with chronic painful polyneuropathy were compared with age matched healthy patients. Taken together, all miRNA pre library preparation quality controls were successful and none of the samples was identified as an outlier or excluded for library preparation. Pre sequencing quality control showed that library preparation worked for all samples as well as that all samples were free of adapter dimers after BluePippin size selection and reached the minimum molarity for further processing. Thus, all samples were subjected to sequencing. The sequencing control parameters were in their optimal range and resulted in valid sequencing results with strong sample to sample correlation for all samples. The resulting FASTQ file of each miRNA library was analyzed and used to perform a differential expression analysis. The differentially expressed and filtered miRNAs were subjected to miRDB to perform a target prediction. Three of those four miRNAs were downregulated: hsa-miR-3135b, hsa-miR-584-5p and hsa-miR-12136, while one was upregulated: hsa-miR-550a-3p. miRNA target prediction showed that chronic pain in polyneuropathy might be the result of a combination of miRNA mediated high blood flow/pressure and neural activity dysregulations/disbalances. Thus, leading to the promising conclusion that these four miRNAs could serve as potential biomarkers for the diagnosis of chronic pain in polyneuropathy.
Since TRPV1 seems to be one of the major contributors of nociception and is associated with neuropathic pain, the influence of PKA phosphorylated ARMS on the sensitivity of TRPV1 as well as the part of AKAP79 during PKA phosphorylation of ARMS was characterized. Therefore, possible PKA-sites in the sequence of ARMS were identified. This revealed five canonical PKA-sites: S882, T903, S1251/52, S1439/40 and S1526/27. The single PKA-site mutants of ARMS revealed that PKA-mediated ARMS phosphorylation seems not to influence the interaction rate of TRPV1/ARMS. While phosphorylation of ARMST903 does not increase the interaction rate with TRPV1, ARMSS1526/27 is probably not phosphorylated and leads to an increased interaction rate. The calcium flux measurements indicated that the higher the interaction rate of TRPV1/ARMS, the lower the EC50 for capsaicin of TRPV1, independent of the PKA phosphorylation status of ARMS. In addition, the western blot analysis confirmed the previously observed TRPV1/ARMS interaction. More importantly, AKAP79 seems to be involved in the TRPV1/ARMS/PKA signaling complex. To overcome the problem of ARMS-mediated TRPV1 sensitization by interaction, ARMS was silenced by shRNA. ARMS silencing resulted in a restored TRPV1 desensitization without affecting the TRPV1 expression and therefore could be used as new topical therapeutic analgesic alternative to stop ARMS mediated TRPV1 sensitization.
Cardiovascular diseases are the main cause of death worldwide, and their prevalence is expected to rise in the coming years. Polymer-based artificial replacements have been widely used for the treatment of cardiovascular diseases. Coagulation and thrombus formation on the interfaces between the materials and the human physiological environment are key issues leading to the failure of the medical device in clinical implantation. The surface properties of the materials have a strong influence on the protein adsorption and can direct the blood cell adhesion behavior on the interfaces. Furthermore, implant-associated infections will be induced by bacterial adhesion and subsequent biofilm formation at the implantation site. Thus, it is important to improve the hemocompatibility of an implant by altering the surface properties. One of the effective strategies is surface passivation to achieve protein/cell repelling ability to reduce the risk of thrombosis.
This thesis consists of synthesis, functionalization, sterilization, and biological evaluation of bulk poly(glycerol glycidyl ether) (polyGGE), which is a highly crosslinked polyether-based polymer synthesized by cationic ring-opening polymerization. PolyGGE is hypothesized to be able to resist plasma protein adsorption and bacterial adhesion due to analogous chemical structure as polyethylene glycol and hyperbranched polyglycerol. Hydroxyl end groups of polyGGE provide possibilities to be functionalized with sulfates to mimic the anti-thrombogenic function of the endothelial glycocalyx.
PolyGGE was synthesized by polymerization of the commercially available monomer glycerol glycidyl ether, which was characterized as a mixture of mono-, di- and tri-glycidyl ether. Cationic ring opening-polymerization of this monomer was carried out by ultraviolet (UV) initiation of the photo-initiator diphenyliodonium hexafluorophosphate. With the increased UV curing time, more epoxides in the side chains of the monomers participated in chemical crosslinking, resulting in an increase of Young’s modulus, while the value of elongation at break of polyGGE first increased due to the propagation of the polymer chains then decreased with the increase of crosslinking density. Eventually, the chain propagation can be effectively terminated by potassium hydroxide aqueous solution. PolyGGE exhibited different tensile properties in hydrated conditions at body temperature compared to the values in the dry state at room temperature. Both Young’s modulus and values of elongation at break were remarkably reduced when tested in water at 37 °C, which was above the glass transition temperature of polyGGE. At physiological conditions, entanglements of the ployGGE networks unfolded and the free volume of networks were replaced by water molecules as softener, which increased the mobility of the polymer chains, resulting in a lower Young’s modulus.
Protein adsorption analysis was performed on polyGGE films with 30 min UV curing using an enzyme-linked immunosorbent assay. PolyGGE could effectively prevent the adsorption of human plasma fibrinogen, albumin, and fibronectin at the interface of human plasma and polyGGE films. The protein resistance of polyGGE was comparable to the negative controls: the hemocompatible polydimethylsiloxane (PDMS), showing its potential as a coating material for cardiovascular implants. Moreover, antimicrobial tests of bacterial activity using isothermal microcalorimetry and the microscopic image of direct bacteria culturing demonstrated that polyGGE could directly interfere biofilm formation and growth of both Gram-negative and antibiotic-resistant Gram-positive bacteria, indicating the potential application of polyGGE for combating the risk of hospital-acquired infections and preventing drug-resistant superbug spreading.
To investigate its cell compatibility, polyGGE films were extracted by different solvents (ethanol, chloroform, acetone) and cell culture medium. Indirect cytotoxicity tests showed extracted polyGGE films still had toxic effects on L929 fibroblast cells. High-performance liquid chromatography/electrospray ionization mass spectrometry revealed the occurrence of organochlorine-containing compounds released during the polymer-cell culture medium interaction. A constant level of those organochlorine-containing compounds was confirmed from GGE monomer by a specific peak of C-Cl stretching in infrared spectra of GGE. This is assumed to be the main reason causing the increased cell membrane permeability and decreased metabolic activity, leading to cell death. Attempts as changing solvents were made to remove toxic substances, however, the release of these small molecules seems to be sluggish. The densely crosslinked polyGGE networks can possibly contribute to the trapping of organochlorine-containing compounds. These results provide valuable information for exploring the potentially toxic substances, leaching from polyGGE networks, and propose a feasible strategy for minimizing the cytotoxicity via reducing their crosslinking density.
Sulfamic acid/ N-Methyl-2-pyrrolidone (NMP) were selected as the reagents for the sulfation of polyGGE surfaces. Fourier transform attenuated total reflection infrared spectroscopy (ATR-FT-IR) was used to monitor the functionalization kinetics and the results confirmed the successful sulfate grafting on the surface of polyGGE with the covalent bond -C-O-S-. X-ray photoelectron spectroscopy was used to determine the element composition on the surface and the cross-section of the functionalized polyGGE and sulfation within 15 min guarantees the sulfation only takes place on the surface while not occurring in the bulk of the polymer. The concentration of grafted sulfates increased with the increasing reaction time. The hydrophilicity of the surface of polyGGE was highly increased due to the increase of negatively charged end groups. Three sterilization techniques including autoclaving, gamma irradiation, and ethylene oxide (EtO) sterilization were used for polyGGE sulfates. Results from ATR-FT-IR and Toluidine Blue O quantitative assay demonstrated the total loss of the sulfates after autoclave sterilization, which was also confirmed by the increased water contact angle. Little influence on the concentration of sulfates was found for gamma-irradiated and autoclaving sterilized polyGGE sulfates. To investigate the thermal influence on polyGGE sulfates, one strategy was to use poly(hydroxyethyl acrylate) sulfates (PHEAS) for modeling. The thermogravimetric analysis profile of PHEAS demonstrated that sulfates are not thermally stable independent of the substrate materials and decomposition of sulfates occurs at around 100 °C. Although gamma irradiation also showed little negative effect on the sulfate content, the color change in the polyGGE sulfates indicates chemical or physical change might occur in the polymer. EtO sterilization was validated as the most suitable sterilization technique to maintain the chemical structure of polyGGE sulfates.
In conclusion, the conducted work proved that bulk polyGGE can be used as an antifouling coating material and shows its antimicrobial potential. Sulfates functionalization can be effectively realized using sulfamic acid/NMP. EtO sterilization is the most suitable sterilization technique for grafted sulfates. Besides, this thesis also offers a good strategy for the analysis of toxic leachable substances using suitable physicochemical characterization techniques. Future work will focus on minimizing/eliminating the release of toxic substances via reducing the crosslinking density. Another interesting aspect is to study whether grafted sulfates can meet the need for anti-thrombogenicity.
Climate change is one of the greatest challenges to humanity in this century, and most noticeable consequences are expected to be impacts on the water cycle – in particular the distribution and availability of water, which is fundamental for all life on Earth. In this context, it is essential to better understand where and when water is available and what processes influence variations in water storages. While estimates of the overall terrestrial water storage (TWS) variations are available from the GRACE satellites, these represent the vertically integrated signal over all water stored in ice, snow, soil moisture, groundwater and surface water bodies. Therefore, complementary observational data and hydrological models are still required to determine the partitioning of the measured signal among different water storages and to understand the underlying processes. However, the application of large-scale observational data is limited by their specific uncertainties and the incapacity to measure certain water fluxes and storages. Hydrological models, on the other hand, vary widely in their structure and process-representation, and rarely incorporate additional observational data to minimize uncertainties that arise from their simplified representation of the complex hydrologic cycle.
In this context, this thesis aims to contribute to improving the understanding of global water storage variability by combining simple hydrological models with a variety of complementary Earth observation-based data. To this end, a model-data integration approach is developed, in which the parameters of a parsimonious hydrological model are calibrated against several observational constraints, inducing GRACE TWS, simultaneously, while taking into account each data’s specific strengths and uncertainties. This approach is used to investigate 3 specific aspects that are relevant for modelling and understanding the composition of large-scale TWS variations.
The first study focusses on Northern latitudes, where snow and cold-region processes define the hydrological cycle. While the study confirms previous findings that seasonal dynamics of TWS are dominated by the cyclic accumulation and melt of snow, it reveals that inter-annual TWS variations on the contrary, are determined by variations in liquid water storages. Additionally, it is found to be important to consider the impact of compensatory effects of spatially heterogeneous hydrological variables when aggregating the contribution of different storage components over large areas. Hence, the determinants of TWS variations are scale-dependent and underlying driving mechanism cannot be simply transferred between spatial and temporal scales. These findings are supported by the second study for the global land areas beyond the Northern latitudes as well.
This second study further identifies the considerable impact of how vegetation is represented in hydrological models on the partitioning of TWS variations. Using spatio-temporal varying fields of Earth observation-based data to parameterize vegetation activity not only significantly improves model performance, but also reduces parameter equifinality and process uncertainties. Moreover, the representation of vegetation drastically changes the contribution of different water storages to overall TWS variability, emphasizing the key role of vegetation for water allocation, especially between sub-surface and delayed water storages. However, the study also identifies parameter equifinality regarding the decay of sub-surface and delayed water storages by either evapotranspiration or runoff, and thus emphasizes the need for further constraints hereof.
The third study focuses on the role of river water storage, in particular whether it is necessary to include computationally expensive river routing for model calibration and validation against the integrated GRACE TWS. The results suggest that river routing is not required for model calibration in such a global model-data integration approach, due to the larger influence other observational constraints, and the determinability of certain model parameters and associated processes are identified as issues of greater relevance. In contrast to model calibration, considering river water storage derived from routing schemes can already significantly improve modelled TWS compared to GRACE observations, and thus should be considered for model evaluation against GRACE data.
Beyond these specific findings that contribute to improved understanding and modelling of large-scale TWS variations, this thesis demonstrates the potential of combining simple modeling approaches with diverse Earth observational data to improve model simulations, overcome inconsistencies of different observational data sets, and identify areas that require further research. These findings encourage future efforts to take advantage of the increasing number of diverse global observational data.
Sustainable urban growth
(2022)
This dissertation explores the determinants for sustainable and socially optimalgrowth in a city. Two general equilibrium models establish the base for this evaluation, each adding its puzzle piece to the urban sustainability discourse and examining the role of non-market-based and market-based policies for balanced growth and welfare improvements in different theory settings. Sustainable urban growth either calls for policy actions or a green energy transition. Further, R&D market failures can pose severe challenges to the sustainability of urban growth and the social optimality of decentralized allocation decisions. Still, a careful (holistic) combination of policy instruments can achieve sustainable growth and even be first best.
Plate tectonics describes the movement of rigid plates at the surface of the Earth as well as their complex deformation at three types of plate boundaries: 1) divergent boundaries such as rift zones and mid-ocean ridges, 2) strike-slip boundaries where plates grind past each other, such as the San Andreas Fault, and 3) convergent boundaries that form large mountain ranges like the Andes. The generally narrow deformation zones that bound the plates exhibit complex strain patterns that evolve through time. During this evolution, plate boundary deformation is driven by tectonic forces arising from Earth’s deep interior and from within the lithosphere, but also by surface processes, which erode topographic highs and deposit the resulting sediment into regions of low elevation. Through the combination of these factors, the surface of the Earth evolves in a highly dynamic way with several feedback mechanisms. At divergent boundaries, for example, tensional stresses thin the lithosphere, forcing uplift and subsequent erosion of rift flanks, which creates a sediment source. Meanwhile, the rift center subsides and becomes a topographic low where sediments accumulate. This mass transfer from foot- to hanging wall plays an important role during rifting, as it prolongs the activity of individual normal faults. When rifting continues, continents are eventually split apart, exhuming Earth’s mantle and creating new oceanic crust. Because of the complex interplay between deep tectonic forces that shape plate boundaries and mass redistribution at the Earth’s surface, it is vital to understand feedbacks between the two domains and how they shape our planet.
In this study I aim to provide insight on two primary questions: 1) How do divergent and strike-slip plate boundaries evolve? 2) How is this evolution, on a large temporal scale and a smaller structural scale, affected by the alteration of the surface through erosion and deposition? This is done in three chapters that examine the evolution of divergent and strike-slip plate boundaries using numerical models. Chapter 2 takes a detailed look at the evolution of rift systems using two-dimensional models. Specifically, I extract faults from a range of rift models and correlate them through time to examine how fault networks evolve in space and time. By implementing a two-way coupling between the geodynamic code ASPECT and landscape evolution code FastScape, I investigate how the fault network and rift evolution are influenced by the system’s erosional efficiency, which represents many factors like lithology or climate. In Chapter 3, I examine rift evolution from a three-dimensional perspective. In this chapter I study linkage modes for offset rifts to determine when fast-rotating plate-boundary structures known as continental microplates form. Chapter 4 uses the two-way numerical coupling between tectonics and landscape evolution to investigate how a strike-slip boundary responds to large sediment loads, and whether this is sufficient to form an entirely new type of flexural strike-slip basin.
In the present thesis I investigate the lattice dynamics of thin film hetero structures of magnetically ordered materials upon femtosecond laser excitation as a probing and manipulation scheme for the spin system. The quantitative assessment of laser induced thermal dynamics as well as generated picosecond acoustic pulses and their respective impact on the magnetization dynamics of thin films is a challenging endeavor. All the more, the development and implementation of effective experimental tools and comprehensive models are paramount to propel future academic and technological progress.
In all experiments in the scope of this cumulative dissertation, I examine the crystal lattice of nanoscale thin films upon the excitation with femtosecond laser pulses. The relative change of the lattice constant due to thermal expansion or picosecond strain pulses is directly monitored by an ultrafast X-ray diffraction (UXRD) setup with a femtosecond laser-driven plasma X-ray source (PXS). Phonons and spins alike exert stress on the lattice, which responds according to the elastic properties of the material, rendering the lattice a versatile sensor for all sorts of ultrafast interactions. On the one hand, I investigate materials with strong magneto-elastic properties; The highly magnetostrictive rare-earth compound TbFe2, elemental Dysprosium or the technological relevant Invar material FePt. On the other hand I conduct a comprehensive study on the lattice dynamics of Bi1Y2Fe5O12 (Bi:YIG), which exhibits high-frequency coherent spin dynamics upon femtosecond laser excitation according to the literature. Higher order standing spinwaves (SSWs) are triggered by coherent and incoherent motion of atoms, in other words phonons, which I quantified with UXRD. We are able to unite the experimental observations of the lattice and magnetization dynamics qualitatively and quantitatively. This is done with a combination of multi-temperature, elastic, magneto-elastic, anisotropy and micro-magnetic modeling.
The collective data from UXRD, to probe the lattice, and time-resolved magneto-optical Kerr effect (tr-MOKE) measurements, to monitor the magnetization, were previously collected at different experimental setups. To improve the precision of the quantitative assessment of lattice and magnetization dynamics alike, our group implemented a combination of UXRD and tr-MOKE in a singular experimental setup, which is to my knowledge, the first of its kind. I helped with the conception and commissioning of this novel experimental station, which allows the simultaneous observation of lattice and magnetization dynamics on an ultrafast timescale under identical excitation conditions. Furthermore, I developed a new X-ray diffraction measurement routine which significantly reduces the measurement time of UXRD experiments by up to an order of magnitude. It is called reciprocal space slicing (RSS) and utilizes an area detector to monitor the angular motion of X-ray diffraction peaks, which is associated with lattice constant changes, without a time-consuming scan of the diffraction angles with the goniometer. RSS is particularly useful for ultrafast diffraction experiments, since measurement time at large scale facilities like synchrotrons and free electron lasers is a scarce and expensive resource. However, RSS is not limited to ultrafast experiments and can even be extended to other diffraction techniques with neutrons or electrons.
Abzug unter Beobachtung
(2022)
Mehr als vier Jahrzehnte lang beobachteten die Streitkräfte und Militärnachrichtendienste der NATO-Staaten die sowjetischen Truppen in der DDR. Hierfür übernahm in der Bundesrepublik Deutschland der Bundesnachrichtendienst (BND) die militärische Auslandsaufklärung unter Anwendung nachrichtendienstlicher Mittel und Methoden. Die Bundeswehr betrieb dagegen taktische Fernmelde- und elektronische Aufklärung und hörte vor allem den Funkverkehr der „Gruppe der sowjetischen Streitkräfte in Deutschland“ (GSSD) ab. Mit der Aufstellung einer zentralen Dienststelle für das militärische Nachrichtenwesen, dem Amt für Nachrichtenwesen der Bundeswehr, bündelte und erweiterte zugleich das Bundesministerium für Verteidigung in den 1980er Jahren seine analytischen Kapazitäten. Das Monopol des BND in der militärischen Auslandsaufklärung wurde von der Bundeswehr dadurch zunehmend infrage gestellt.
Nach der deutschen Wiedervereinigung am 3. Oktober 1990 befanden sich immer noch mehr als 300.000 sowjetische Soldaten auf deutschem Territorium. Die 1989 in Westgruppe der Truppen (WGT) umbenannte GSSD sollte – so der Zwei-plus-Vier-Vertrag – bis 1994 vollständig abziehen. Der Vertrag verbot auch den drei Westmächten, in den neuen Bundesländern militärisch tätig zu sein. Die für die Militäraufklärung bis dahin unverzichtbaren Militärverbindungsmissionen der Westmächte mussten ihre Dienste einstellen. Doch was geschah mit diesem „alliierten Erbe“? Wer übernahm auf deutscher Seite die Aufklärung der sowjetischen Truppen und wer kontrollierte den Truppenabzug?
Die Studie untersucht die Rolle von Bundeswehr und BND beim Abzug der WGT zwischen 1990 und 1994 und fragt dabei nach Kooperation und Konkurrenz zwischen Streitkräften und Nachrichtendiensten. Welche militärischen und nachrichtendienstlichen Mittel und Fähigkeiten stellte die Bundesregierung zur Bewältigung des Truppenabzugs zur Verfügung, nachdem die westlichen Militärverbindungsmissionen aufgelöst wurden? Wie veränderten sich die Anforderungen an die militärische Auslandsaufklärung des BND? Inwieweit setzten sich Konkurrenz und Kooperation von Bundeswehr und BNDbeim Truppenabzug fort? Welche Rolle spielten dabei die einstigen Westmächte? Die Arbeit versteht sich nicht nur als Beitrag zur Militärgeschichte, sondern auch zur deutschen Nachrichtendienstgeschichte.
One aspect of achieving a more sustainable chemical industry is the minimization of the usage of solvents and chemicals. Thus, optimization and development of chemical processes for large-scale production is favourably performed in small batches. The critical step in this approach is upscaling the batches from the small reaction systems to the large reactors mandatory for cost efficient production in an industrial environment. Scaling up the bulk volume always goes along with increasing the surface where the reaction medium is in contact with the confining vessel. Since volume scales proportional with the cubic dimension while the surface scales quadratic, their ratio is size-dependent. The influence of reaction vessel walls can change the reaction performance. A number of phenomena occurring at the surface-liquid interface can affect reaction rates and yields, resulting in possible difficulties in predicting and extrapolating from small size production scale to large industrial processes. The application of levitated droplets as a containerless reaction vessels provides a promising possibility to avoid the above-mentioned issues.
In the presented work, an efficient coupling of acoustically levitated droplets to an ion mobility (IM) spectrometer, operating at ambient conditions, was designed for real-time monitoring of chemical reactions. The design of the system comprises noncontact sampling and ionization of the droplet realised by laser desorption/ionization at 2,94 µm. The scope of the work includes fundamental studies covering understanding of laser irradiation of droplets enclosed in an acoustical field. Understanding of this phenomenon is crucial to comprehending the effects of temporal and spatial resolution of the generated ion plume that influence the resolution of the system.
The set-up includes an acoustic trap, laser irradiation and ion manipulation electrostatic lenses operating at high voltage at ambient pressure. The complexity of the design needs to fully be considered for an effective ion transfer at the interface region between the levitated droplet and IM spectrometer. For sampling and ionization, two distinct laser pulse lengths were evaluated, ns and µs. Irradiation via µs laser pulses provides several advantages: i) the droplet volume is not extensively impinged, as in case of ns laser pulses, allowing the sampling of only the small volume of the droplet; ii) the lower fluence results in less pronounced oscillations of the droplet confined in the acoustic field. The droplet will not be dissipated out of the acoustic field leading to loss of the sample; iii) the mild laser irradiation results in better spatial and temporal ion plume confinement, leading to better resolution of the detected ion packets. Finally, this knowledge allows the application of ion optics necessary to induce ion flow between the droplet suspended in the acoustic field and the IM spectrometer. The ion optics, composed of 2 electrostatic lenses placed in the near vicinity of the droplet, allow effective focusing of the ion plume and its redirection directly to the IM spectrometer entrance. This novel coupling has proved to be successful for detection of some simple molecules ionizable at the 2.94 µm wavelength. To further demonstrate the applicability of the system, a proof-of-principle reaction was selected, fulfilling the requirements of the system, and was subjected to comprehensive investigation of its performance. Herein, the reaction between N-Boc cysteine methyl ester and allyl alcohol has been performed in a batch reactor and on-line monitored via 1H NMR to establish reaction propagation. With the additional assessment, it was confirmed that the thiol-ene coupling can be performed within first 20 minutes of the irradiation with a reaction yield above 50%, proving that the reaction can be applied as a study case to assess the possibilities of the developed system.
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 echo chamber model describes the development of groups in heterogeneous social networks. By heterogeneous social network we mean a set of individuals, each of whom represents exactly one opinion. The existing relationships between individuals can then be represented by a graph. The echo chamber model is a time-discrete model which, like a board game, is played in rounds. In each round, an existing relationship is randomly and uniformly selected from the network and the two connected individuals interact. If the opinions of the individuals involved are sufficiently similar, they continue to move closer together in their opinions, whereas in the case of opinions that are too far apart, they break off their relationship and one of the individuals seeks a new relationship. In this paper we examine the building blocks of this model. We start from the observation that changes in the structure of relationships in the network can be described by a system of interacting particles in a more abstract space.
These reflections lead to the definition of a new abstract graph that encompasses all possible relational configurations of the social network. This provides us with the geometric understanding necessary to analyse the dynamic components of the echo chamber model in Part III. As a first step, in Part 7, we leave aside the opinions of the inidividuals and assume that the position of the edges changes with each move as described above, in order to obtain a basic understanding of the underlying dynamics. Using Markov chain theory, we find upper bounds on the speed of convergence of an associated Markov chain to its unique stationary distribution and show that there are mutually identifiable networks that are not apparent in the dynamics under analysis, in the sense that the stationary distribution of the associated Markov chain gives equal weight to these networks.
In the reversible cases, we focus in particular on the explicit form of the stationary distribution as well as on the lower bounds of the Cheeger constant to describe the convergence speed.
The final result of Section 8, based on absorbing Markov chains, shows that in a reduced version of the echo chamber model, a hierarchical structure of the number of conflicting relations can be identified.
We can use this structure to determine an upper bound on the expected absorption time, using a quasi-stationary distribution. This hierarchy of structure also provides a bridge to classical theories of pure death processes. We conclude by showing how future research can exploit this link and by discussing the importance of the results as building blocks for a full theoretical understanding of the echo chamber model. Finally, Part IV presents a published paper on the birth-death process with partial catastrophe. The paper is based on the explicit calculation of the first moment of a catastrophe. This first part is entirely based on an analytical approach to second degree recurrences with linear coefficients. The convergence to 0 of the resulting sequence as well as the speed of convergence are proved. On the other hand, the determination of the upper bounds of the expected value of the population size as well as its variance and the difference between the determined upper bound and the actual value of the expected value. For these results we use almost exclusively the theory of ordinary nonlinear differential equations.