Refine
Has Fulltext
- yes (140) (remove)
Year of publication
- 2018 (140) (remove)
Document Type
- Doctoral Thesis (140) (remove)
Keywords
- Fernerkundung (3)
- Magnetismus (3)
- magnetism (3)
- remote sensing (3)
- uncertainty (3)
- Angriffserkennung (2)
- Bakterien (2)
- Big Data (2)
- Bildung (2)
- Biodiversität (2)
Institute
- Institut für Chemie (24)
- Institut für Geowissenschaften (21)
- Institut für Physik und Astronomie (21)
- Institut für Biochemie und Biologie (14)
- Extern (12)
- Hasso-Plattner-Institut für Digital Engineering GmbH (12)
- Wirtschaftswissenschaften (10)
- Sozialwissenschaften (6)
- Department Linguistik (5)
- Department Sport- und Gesundheitswissenschaften (4)
Uncertainty is an essential part of atmospheric processes and thus inherent to weather forecasts. Nevertheless, weather forecasts and warnings are still predominately issued as deterministic (yes or no) forecasts, although research suggests that providing weather forecast users with additional information about the forecast uncertainty can enhance the preparation of mitigation measures. Communicating forecast uncertainty would allow for a provision of information on possible future events at an earlier time. The desired benefit is to enable the users to start with preparatory protective action at an earlier stage of time based on the their own risk assessment and decision threshold. But not all users have the same threshold for taking action. In the course of the project WEXICOM (‘Wetterwarnungen: Von der Extremereignis-Information zu Kommunikation und Handlung’) funded by the Deutscher Wetterdienst (DWD), three studies were conducted between the years 2012 and 2016 to reveal how weather forecasts and warnings are reflected in weather-related decision-making. The studies asked which factors influence the perception of forecasts and the decision to take protective action and how forecast users make sense of probabilistic information and the additional lead time. In a first exploratory study conducted in 2012, members of emergency services in Germany were asked questions about how weather warnings are communicated to professional endusers in the emergency community and how the warnings are converted into mitigation measures. A large number of open questions were selected to identify new topics of interest. The questions covered topics like users’ confidence in forecasts, their understanding of probabilistic information as well as their lead time and decision thresholds to start with preparatory mitigation measures. Results show that emergency service personnel generally have a good sense of uncertainty inherent in weather forecasts. Although no single probability threshold could be identified for organisations to start with preparatory mitigation measures, it became clear that emergency services tend to avoid forecasts based on low probabilities as a basis for their decisions. Based on this findings, a second study conducted with residents of Berlin in 2014 further investigated the question of decision thresholds. The survey questions related to the topics of the perception of and prior experience with severe weather, trustworthiness of forecasters and confidence in weather forecasts, and socio-demographic and social-economic characteristics. Within the questionnaire a scenario was created to determine individual decision thresholds and see whether subgroups of the sample lead to different thresholds. The results show that people’s willingness to act tends to be higher and decision thresholds tend to be lower if the expected weather event is more severe or the property at risk is of higher value. Several influencing factors of risk perception have significant effects such as education, housing status and ability to act, whereas socio-demographic determinants alone are often not sufficient to fully grasp risk perception and protection behaviour. Parallel to the quantitative studies, an interview study was conducted with 27 members of German civil protection between 2012 and 2016. The results show that the latest developments in (numerical) weather forecasting do not necessarily fit the current practice of German emergency services. These practices are mostly carried out on alarms and ground truth in a reactive manner rather than on anticipation based on prognosis or forecasts. As the potential consequences rather than the event characteristics determine protective action, the findings support the call and need for impact-based warnings. Forecasters will rely on impact data and need to learn the users’ understanding of impact. Therefore, it is recommended to enhance weather communication not only by improving computer models and observation tools, but also by focusing on the aspects of communication and collaboration. Using information about uncertainty demands awareness about and acceptance of the limits of knowledge, hence, the capabilities of the forecaster to anticipate future developments of the atmosphere and the capabilities of the user to make sense of this information.
Future magnetic recording industry needs a high-density data storage technology. However, switching the magnetization of small bits requires high magnetic fields that cause excessive heat dissipation. Therefore, controlling magnetism without applying external magnetic field is an important research topic for potential applications in data storage devices with low power consumption. Among the different approaches being investigated, two of them stand out, namely i) all-optical helicity dependent switching (AO-HDS) and ii) ferroelectric control of magnetism. This thesis aims to contribute towards a better understanding of the physical processes behinds these effects as well as reporting new and exciting possibility for the optical and/or electric control of magnetic properties. Hence, the thesis contains two differentiated chapters of results; the first devoted to AO-HDS on TbFe alloys and the second to the electric field control of magnetism in an archetypal Fe/BaTiO3 system.
In the first part, the scalability of the AO-HDS to small laser spot-sizes of few microns in the ferrimagnetic TbFe alloy is investigated by spatially resolving the magnetic contrast with photo-emission electron microscopy (PEEM) and X-ray magnetic circular dichroism (XMCD). The results show that the AO-HDS is a local effect within the laser spot size that occurs in the ring-shaped region in the vicinity of thermal demagnetization. Within the ring region, the helicity dependent switching occurs via thermally activated domain wall motion. Further, the thesis reports on a novel effect of thickness dependent inversion of the switching orientation. It addresses some of the important questions like the role of laser heating and the microscopic mechanism driving AO-HDS.
The second part of the thesis focuses on the electric field control of magnetism in an artificial multiferroic heterostructure. The sample consists of an Fe wedge with thickness varying between 0:5 nm and 3 nm, deposited on top of a ferroelectric and ferroelastic BaTiO3 [001]-oriented single crystal substrate. Here, the magnetic contrast is imaged via PEEM and XMCD as a function of out-of-plane voltage. The results show the evidence of the electric field control of superparamagnetism mediated by a ferroelastic modification of the magnetic anisotropy. The changes in the magnetoelastic anisotropy drive the transition from the superparamagnetic to superferromagnetic state at localized sample positions.
BACKGROUND: Physical activity involving high spinal load has been exposed to possess a crucial impact in the genesis of acute and chronic low back pain and disorder. Vigorous spinal loads are surmised in drop landings, for which strenuous bending loads were formerly evinced for the lower extremity structures. Thus far, clinical studies revealed that repetitive landing impacts can evoke benign structural adaptions or damage to the lumbar vertebrae. Though, causes for these observations are hitherto not conclusively evinced; since actual spinal load has to date not been experimentally documented. Moreover, it is yet undetermined how physiological activation of trunk musculature compensates for landing impact induced spinal loads, and to which extend trunk activity and spinal load are affected by landing demands and performer characteristics. AIMS of this study are 1. the localisation and quantification of spinal bending loads under various landing demands and 2. the identification of compensatory trunk muscular activity pattern, which potentially alleviate spinal load magnitudes. Three consecutive Hypotheses (H1 - H3) were hereto postulated: H1 posits that spinal bending loads in segregated motion planes can feasibly and reliably be evaluated from peak spine segmental angular accelerations. H2 furthermore assumes that vertical drop landings elicit highest spine bending load in sagittal flexion of the lumbar spine. Based on these verifications, a second study shall prove the successive hypothesis (H3) that diversified landing conditions, like performer’s landing familiarity and gender, as an implementation of an instantaneous follow-up task, affect the emerging lumbar spinal bending load. Herein it is moreover surmised that lumbar spinal bending loads under distinct landing conditions are predominantly modulated by herewith disparately deployed conditioned pre-activations of trunk muscles. METHODS: To test the above arrayed hypothesis, two successive studies were carried out. In STUDY 1, 17 subjects were repetitively assessed performing various drop landings (heigth: 15, 30, 45, 60cm; unilateral, bilateral, blindfolded, catching a ball) in a test-retest-design. Herein individual peak angular accelerations [αMAX] were derived from three-dimensional motion data of four trunk-segments (upper thoracic, lower thoracic, lumbar, pelvis). αMAX was herein assessed in flexion, lateral flexion, and rotation of each spinal joint, formed by two adjacent segments. Reliability of αMAX within and between test-days was evaluated by CV%, ICC 2.1, TRV%, and Bland & Altman Analysis (BIAS±LoA). Subsequently, peak flexion acceleration of the lumbo-pelvic joint [αFLEX[LS-PV]] was statistically compared to αMAX expressions of each other assessed spinal joint and motion plane (Mean ±SD, Independent Samples T-test). STUDY 2 deliberately assessed mere peak lumbo-pelvic flexion accelerations [αFLEX[LS-PV]] and electro-myographic trunk pre-activity prior to αFLEX[LS-PV] on 43 subjects performing varied landing tasks (height 45cm; with definite or indefinite predictability of a subsequent instant follow up jump). Subjects were contrasted with respect to their previous landing familiarity ( >1000 vs. <100 landings performed in the past 10 years) and gender. Differences of αFLEX[LS-PV] and muscular pre-activity between contrasted subject groups as between landing tasks were equally statistically tested by three-way mixed ANOVA with Post-hoc tests. Associations between αFLEX[LS-PV] and muscular pre-activity were factor-specifically assessed by Spearman’s rank order correlation coefficient (rS). Complementarily, muscular pre-activity was subdivided by landing phases [DROP, IMPACT] and discretely assessed for phase specific associations to αFLEX[LS-PV]. Each muscular activity was moreover pairwise compared between DROP and IMPACT (Mean ±SD, Dependent Samples T-test). RESULTS: αMAX was presented with overall high variability within test-days (CV =36%). Lowest intra-individual variability and highest reproducibility of αMAX between test-days was shown in flexion of the spine. αFLEX[LS-PV] showed largely consistent sig. higher magnitudes compared to αMAX presented in more cranial spinal joints and other motion planes. αFLEX[LS-PV] moreover gradually increased with escalations in landing heights. Landing unfamiliar subjects presented sig. higher αFLEX[LS-PV] in contrast to landing familiar ones (p=.016). M. Obliquus Int. with M. Transversus Abd. (66 ±32%MVC) and M. Erector Spinae (47 ±15%MVC) presented maredly highest activity in contrast to lowest activity of M. Rectus Abd. (10 ±4%MVC). Landing unfamiliar subjects showed compared to landing familiar ones sig. higher activity of M. Obliquus Ext. (17 ±8%MVC, 12 ±7%MVC, p= .044). M. Obliquus Ext. and its co-contraction ratio with M. Erector Spinae moreover exhibited low but sig. positive correlations to αFLEX[LS-PV] (rs=.39, rs=.31). Each trunk muscule distributed larger shares of its activity to DROP, whereas peak activations of most muscles emerged in the proportionally shorter IMPACT phase. Commonly increased muscular pre-activation particularly at IMPACT was found in landings with a contrived follow up jump and in female subjects, whereby αFLEX[LS-PV] was hereof only marginally affected. DISCUSSION: Highest spine segmental angular accelerations in drop landings emerge in sagittal flexion of the lumbar spine. The compensatory stabilisation of the spine appears to be preponderantly provided by a dorso-ventral co-contraction of M. Obliquus Int., M. Transversus Abd. and M. Erector Spinae. Elevated pre-activity of M. Obliquuis Ext. supposably characterises poor landing experience, which might engender increased bending loads to the lumbar spine. A pervasive large variability of spinal angular accelerations measured across all landing types, suggests a multifarious utilisation of diverse mechanisms compensating for spinal impacts in landing performances. A standardised assessment and valid evaluation of landing evoked lumbar bending loads is hereof largley confined. CONCLUSION: Drop landings elicit most strenuous lumbo-pelvic flexion accelerations, which can be appraised as representatives for high energetic bending loads to the spine. Such entail the highest risk to overload the spinal tissue, when landing demands exceed the individual’s landing skill. Previous landing experience and training appears to effectively improve muscular spine stabilisation pattern, diminishing spinal bending loads.
Magnetotellurics (MT) is a geophysical method that is able to image the electrical conductivity structure of the subsurface by recording time series of natural electromagnetic (EM) field variations. During the data processing these time series are divided into small segments and for each segment spectral values are computed which are typically averaged in a statistical manner to obtain MT transfer functions. Unfortunately, the presence of man-made EM noise sources often deteriorates a significant amount of the recorded time series resulting in disturbed transfer functions. Many advanced processing techniques, e.g. robust statistics, pre-stack data selection or remote reference, have been developed to tackle this problem. The first two techniques reduce the amount of outliers and noise in the data whereas the latter approach removes noise by using data from another MT station. However, especially in populated regions the data processing is still quite challenging even with these approaches. In this thesis, I present two novel pre-stack data confinement and selection criteria for the detection of outliers and noise affected data based on (i) a distance measure of each data segment with regard to the entire sample distribution and (ii) the evaluation of the magnetic polarisation direction of all segments. The first criterion is able to remove data points that scatter around the desired MT distribution and furthermore it can, under some circumstances, even reject complete data cluster originating from noise sources. The second criterion eliminates data points caused by a strongly polarised magnetic signal. Both criteria have been successfully applied to many stations with different noise contaminations showing that they can significantly improve the transfer function estimation. The novel criteria were used to evaluate a MT data set from the Eastern Karoo Basin in South Africa. The corresponding field experiment is part of an extensive research programme to collect information of the current e.g. geological setting in this region prior to a potential shale gas exploitation. The aim was to investigate whether a three-dimensional (3D) inversion of the newly measured data fosters a more realistic mapping of physical properties of the target horizon. For this purpose, a comprehensive 3D model was derived by using all available data. In a second step, I analysed parameters of the target horizon, e.g. its conductivity, that are proxies for physical properties such as thermal maturity and porosity.
New bio-based polymers
(2018)
Redox-responsive polymers, such as poly(disulfide)s, are a versatile class of polymers with potential applications including gene- and drug-carrier systems. Their degradability under reductive conditions allows for a controlled response to the different redox states that are present throughout the body. Poly(disulfide)s are typically synthesized by step growth polymerizations. Step growth polymerizations, however, may suffer from low conversions and therefore low molar masses, limiting potential applications. The purpose of this thesis was therefore to find and investigate new synthetic routes towards the synthesis of amino acid-based poly(disulfide)s.
The different routes in this thesis include entropy-driven ring opening polymerizations of novel macrocyclic monomers, derived from cystine derivatives. These monomers were obtained with overall yields of up to 77% and were analyzed by mass spectrometry as well as by 1D and 2D NMR spectroscopy. The kinetics of the entropy-driven ring-opening metathesis polymerization (ED-ROMP) were thoroughly investigated in dependence of temperature, monomer concentration, and catalyst concentration. The polymerization was optimized to yield poly(disulfide)s with weight average molar masses of up to 80 kDa and conversions of ~80%, at the thermodynamic equilibrium. Additionally, an alternative metal free polymerization, namely the entropy-driven ring-opening disulfide metathesis polymerization (ED-RODiMP) was established for the polymerization of the macrocyclic monomers. The effect of different solvents, concentrations and catalyst loadings on the polymerization process and its kinetics were studied. Polymers with very high weight average molar masses of up to 177 kDa were obtained. Moreover, various post-polymerization reactions were successfully performed.
This work provides the first example of the homopolymerization of endo-cyclic disulfides by ED-ROMP and the first substantial study into the kinetics of the ED-RODiMP process.
Nervous allies
(2018)
Diese Dissertation untersucht die Entwicklung der diplomatischen Beziehungen zwischen Frankreich, den USA und der Bundesrepublik Deutschland im Zeitraum von 1969-1980. Auf breiter multiarchivarischer Quellengrundlage rekonstruiert sie die interdependente Außenpolitik dieser drei Staaten im Kontext zentraler Themenkomplexe der 1970er Jahre: des Aufstiegs und Verfalls der Entspannungspolitik, des Streits um den Status quo in Europa, die Deutsche Frage und die Zukunft Berlins, der internationalen Wirtschafts- und Währungskrise, der Debatte um Sicherheit und Zukunft des westlichen Bündnisses und des NATO-Doppelbeschlusses. Ebenso betrachtet werden eine Reihe von regionalen Ereignissen und Konflikten mit weitreichenden Auswirkungen wie der Jom-Kippur-Krieg, die Portugiesische Revolution oder die sowjetische Invasion Afghanistans.
Die Untersuchung folgt der zentralen, theoretisch motivierten Fragestellung, in welchem Maß staatliche Außenpolitik und diplomatische Beziehungen von individuellen Akteuren an der Spitze der Regierungen, ihren Agenden, Sichtweisen und persönlichen Beziehungen zu internationalen Partnern geprägt wurden oder in welchem Maß deren Entscheidungsfindung andererseits durch strukturelle Faktoren geopolitischer, ökonomischer oder politischer Natur definiert und limitiert wurde. Um diese Frage zu beantworten, fokussiert sich die Dissertation auf die Analyse von Regierungswechseln und deren Auswirkungen auf Kontinuität und Wandel der Außenpolitik. Die Narrative umfasst sieben solcher Regierungswechsel: von Bundeskanzler Kurt Georg Kiesinger zu Willy Brandt (1969) und von Brandt zu Helmut Schmidt (1974) in Bonn, von Präsident Charles de Gaulle zu Georges Pompidou (1969) und von Pompidou zu Valéry Giscard d’Estaing (1974) in Paris sowie von Lyndon B. Johnson zu Richard M. Nixon (1969), von Nixon zu Gerald R. Ford (1974) und von Ford zu Jimmy Carter (1977) in Washington.
Abseits eines Spektrums empirisch fundierter Erkenntnisse über die Geschichte der internationalen Beziehungen der 1970er Jahre belegt diese Arbeit vor allem hochgradig personalisierte und exklusive außenpolitische Entscheidungsstrukturen und eine deutliche Abhängigkeit der Qualität intergouvernementaler Beziehungen von den persönlichen Beziehungen außenpolitischer Führungspersönlichkeiten. Zugleich werden jedoch strukturelle Grenzen ihres Handlungsspielraums im internationalen System deutlich, die von Faktoren wie militärischer Sicherheit und geopolitischer Lage, Zugang zu Ressourcen und ökonomischer Leistungsfähigkeit sowie politischem Druck aus dem In- und Ausland abhängen. Die Dissertation kommt zu dem zentralen Ergebnis, dass Regierungswechsel zwar bisweilen drastische Einschnitte in Inhalt und Stil der auswärtigen Beziehungen nach sich zogen und Bonn, Paris und Washington im Laufe der Dekade mit vielerlei neuen Herausforderungen konfrontiert wurden, dass in der Gesamtschau jedoch pfadabhängige strukturelle Druckszenarien zu höherer politischer Kontinuität im internationalen System führten, als oft mit den für tiefgreifenden historischen Wandel bekannten 1970er Jahren assoziiert wird.
This research addressed the question, if it is possible to simplify current microcontact printing systems for the production of anisotropic building blocks or patchy particles, by using common chemicals while still maintaining reproducibility, high precision and tunability of the Janus-balance
Chapter 2 introduced the microcontact printing materials as well as their defined electrostatic interactions. In particular polydimethylsiloxane stamps, silica particles and high molecular weight polyethylenimine ink were mainly used in this research. All of these components are commercially available in large quantities and affordable, which gives this approach a huge potential for further up-scaling developments. The benefits of polymeric over molecular inks was described including its flexible influence on the printing pressure. With this alteration of the µCP concept, a new method of solvent assisted particle release mechanism enabled the switch from two-dimensional surface modification to three-dimensional structure printing on colloidal silica particles, without changing printing parameters or starting materials. This effect opened the way to use the internal volume of the achieved patches for incorporation of nano additives, introducing additional physical properties into the patches without alteration of the surface chemistry.
The success of this system and its achievable range was further investigated in chapter 3 by giving detailed information about patch geometry parameters including diameter, thickness and yield. For this purpose, silica particles in a size range between 1µm and 5µm were printed with different ink concentrations to change the Janus-balance of these single patched particles. A necessary intermediate step, consisting of air-plasma treatment, for the production of trivalent particles using "sandwich" printing was discovered and comparative studies concerning the patch geometry of single and double patched particles were conducted. Additionally, the usage of structured PDMS stamps during printing was described. These results demonstrate the excellent precision of this approach and opens the pathway for even greater accuracy as further parameters can be finely tuned and investigated, e.g. humidity and temperature during stamp loading.
The performance of these synthesized anisotropic colloids was further investigated in chapter 4, starting with behaviour studies in alcoholic and aqueous dispersions. Here, the stability of the applied patches was studied in a broad pH range, discovering a release mechanism by disabling the electrostatic bonding between particle surface and polyelectrolyte ink. Furthermore, the absence of strong attractive forces between divalent particles in water was investigated using XPS measurements. These results lead to the conclusion that the transfer of small PDMS oligomers onto the patch surface is shielding charges, preventing colloidal agglomeration. However, based on this knowledge, further patch modifications for particle self-assembly were introduced including physical approaches using magnetic nano additives, chemical patch functionalization with avidin-biotin or the light responsive cyclodextrin-arylazopyrazoles coupling as well as particle surface modification for the synthesis of highly amphiphilic colloids. The successful coupling, its efficiency, stability and behaviour in different solvents were evaluated to find a suitable coupling system for future assembly experiments. Based on these results the possibility of more sophisticated structures by colloidal self-assembly is given.
Certain findings needed further analysis to understand their underlying mechanics, including the relatively broad patch diameter distribution and the decreasing patch thickness for smaller silica particles. Mathematical assumptions for both effects are introduced in chapter 5. First, they demonstrate the connection between the naturally occurring particle size distribution and the broadening of the patch diameter, indicating an even higher precision for this µCP approach. Second, explaining the increase of contact area between particle and ink surface due to higher particle packaging, leading to a decrease in printing pressure for smaller particles.
These calculations ultimately lead to the development of a new mechanical microcontact printing approach, using centrifugal forces for high pressure control and excellent parallel alignment of printing substrates. First results with this device and the comparison with previously conducted by-hand experiments conclude this research. It furthermore displays the advantages of such a device for future applications using a mechanical printing approach, especially for accessing even smaller nano particles with great precision and excellent yield.
In conclusion, this work demonstrates the successful adjustment of the µCP approach using commercially available and affordable silica particles and polyelectrolytes for high flexibility, reduced costs and higher scale-up value. Furthermore, its was possible to increase the modification potential by introducing three-dimensional patches for additional functionalization volume. While keeping a high colloidal stability, different coupling systems showed the self-assembly capabilities of this toolbox for anisotropic particles.
Gamma-ray astronomy has proven to provide unique insights into cosmic-ray accelerators in the past few decades. By combining information at the highest photon energies with the entire electromagnetic spectrum in multi-wavelength studies, detailed knowledge of non-thermal particle populations in astronomical objects and systems has been gained: Many individual classes of gamma-ray sources could be identified inside our galaxy and outside of it. Different sources were found to exhibit a wide range of temporal evolution, ranging from seconds to stable behaviours over many years of observations. With the dawn of both neutrino- and gravitational wave astronomy, additional messengers have come into play over the last years. This development presents the advent of multi-messenger astronomy: a novel approach not only to search for sources of cosmic rays, but for astronomy in general.
In this thesis, both traditional multi-wavelength studies and multi-messenger studies will be presented. They were carried out with the H.E.S.S. experiment, an imaging air Cherenkov telescope array located in the Khomas Highland of Namibia. H.E.S.S. has entered its second phase in 2012 with the addition of a large, fifth telescope. While the initial array was limited to the study of gamma-rays with energies above 100 GeV, the new instrument allows to access gamma-rays with energies down to a few tens of GeV. Strengths of the multi-wavelength approach will be demonstrated at the example of the galaxy NGC253, which is undergoing an episode of enhanced star-formation. The gamma-ray emission will be discussed in light of all the information on this system available from radio, infrared and X-rays. These wavelengths reveal detailed information on the population of supernova remnants, which are suspected cosmic-ray accelerators. A broad-band gamma-ray spectrum is derived from H.E.S.S. and Fermi-LAT data. The improved analysis of H.E.S.S. data provides a measurement which is no longer dominated by systematic uncertainties. The long-term behaviour of cosmic rays in the starburst galaxy NGC253 is finally characterised.
In contrast to the long time-scale evolution of a starburst galaxy, multi-messenger studies are especially intriguing when shorter time-scales are being probed. A prime example of a short time-scale transient are Gamma Ray Bursts. The efforts to understand this phenomenon effectively founded the branch of gamma-ray astronomy. The multi-messenger approach allows for the study of illusive phenomena such as Gamma Ray Bursts and other transients using electromagnetic radiation, neutrinos, cosmic rays and gravitational waves contemporaneously. With contemporaneous observations getting more important just recently, the execution of such observation campaigns still presents a big challenge due to the different limitations and strengths of the infrastructures.
An alert system for transient phenomena has been developed over the course of this thesis for H.E.S.S. It aims to address many follow-up challenges in order to maximise the science return of the new large telescope, which is able to repoint much faster than the initial four telescopes. The system allows for fully automated observations based on scientific alerts from any wavelength or messenger and allows H.E.S.S. to participate in multi-messenger campaigns. Utilising this new system, many interesting multi-messenger observation campaigns have been performed. Several highlight observations with H.E.S.S. are analysed, presented and discussed in this work. Among them are observations of Gamma Ray Bursts with low latency and low energy threshold, the follow-up of a neutrino candidate in spatial coincidence with a flaring active galactic nucleus and of the merger of two neutron stars, which was revealed by the coincidence of gravitational waves and a Gamma-Ray Burst.
Over the last decades mechanisms of recognition of morphologically complex words have been extensively examined in order to determine whether all word forms are stored and retrieved from the mental lexicon as wholes or whether they are decomposed into their morphological constituents such as stems and affixes. Most of the research in this domain focusses on English. Several factors have been argued to affect morphological processing including, for instance, morphological structure of a word (e.g., existence of allomorphic stem alternations) and its linguistic nature (e.g., whether it is a derived word or an inflected word form). It is not clear, however, whether processing accounts based on experimental evidence from English would hold for other languages. Furthermore, there is evidence that processing mechanisms may differ across various populations including children, adult native speakers and language learners. Recent studies claim that processing mechanisms could also differ between older and younger adults (Clahsen & Reifegerste, 2017; Reifegerste, Meyer, & Zwitserlood, 2017).
The present thesis examined how properties of the morphological structure, types of linguistic operations involved (i.e., the linguistic contrast between inflection and derivation) and characteristics of the particular population such as older adults (e.g., potential effects of ageing as a result of the cognitive decline or greater experience and exposure of older adults) affect initial, supposedly automatic stages of morphological processing in Russian and German. To this end, a series of masked priming experiments was conducted.
In experiments on Russian, the processing of derived -ost’ nouns (e.g., glupost’ ‘stupidity’) and of inflected forms with and without allomorphic stem alternations in 1P.Sg.Pr. (e.g., igraju – igrat’ ‘to play’ vs. košu – kosit’ ‘to mow’) was examined. The first experiment on German examined and directly compared processing of derived -ung nouns (e.g., Gründung ‘foundation’) and inflected -t past participles (e.g., gegründet ‘founded’), whereas the second one investigated the processing of regular and irregular plural forms (-s forms such as Autos ‘cars’ and -er forms such as Kinder ‘children’, respectively).
The experiments on both languages have shown robust and comparable facilitation effects for derived words and regularly inflected forms without stem changes (-t participles in German, forms of -aj verbs in Russian). Observed morphological priming effects could be clearly distinguished from purely semantic or orthographic relatedness between words. At the same time, we found a contrast between forms with and without allomorphic stem alternations in Russian and regular and irregular forms in German, with significantly more priming for unmarked stems (relative to alternated ones) and significantly more priming for regular (compared) word forms. These findings indicate the relevance of morphological properties of a word for initial stages of processing, contrary to claims made in the literature holding that priming effects are determined by surface form and meaning overlap only. Instead, our findings are more consistent with approaches positing a contrast between combinatorial, rule-based and lexically-stored forms (Clahsen, Sonnenstuhl, & Blevins, 2003).
The doctoral dissertation also addressed the role of ageing and age-related cognitive changes on morphological processing. The results obtained on this research issue are twofold. On the one hand, the data demonstrate effects of ageing on general measures of language performance, i.e., overall longer reaction times and/or higher accuracy rates in older than younger individuals. These findings replicate results from previous studies, which have been linked to the general slowing of processing speed at older age and to the larger vocabularies of older adults. One the other hand, we found that more specific aspects of language processing appear to be largely intact in older adults as revealed by largely similar morphological priming effects for older and younger adults. These latter results indicate that initial stages of morphological processing investigated here by means of the masked priming paradigm persist in older age. One caveat should, however, be noted. Achieving the same performance as a younger individual in a behavioral task may not necessarily mean that the same neural processes are involved. Older people may have to recruit a wider brain network than younger individuals, for example. To address this and related possibilities, future studies should examine older people’s neural representations and mechanisms involved in morphological processing.
Answer Set Programming (ASP) is a declarative problem solving approach, combining a rich yet simple modeling language with high-performance solving capabilities. Although this has already resulted in various applications, certain aspects of such applications are more naturally modeled using variables over finite domains, for accounting for resources, fine timings, coordinates, or functions. Our goal is thus to extend ASP with constraints over integers while preserving its declarative nature. This allows for fast prototyping and elaboration tolerant problem descriptions of resource related applications. The resulting paradigm is called Constraint Answer Set Programming (CASP).
We present three different approaches for solving CASP problems. The first one, a lazy, modular approach combines an ASP solver with an external system for handling constraints. This approach has the advantage that two state of the art technologies work hand in hand to solve the problem, each concentrating on its part of the problem. The drawback is that inter-constraint dependencies cannot be communicated back to the ASP solver, impeding its learning algorithm. The second approach translates all constraints to ASP. Using the appropriate encoding techniques, this results in a very fast, monolithic system. Unfortunately, due to the large, explicit representation of constraints and variables, translation techniques are restricted to small and mid-sized domains. The third approach merges the lazy and the translational approach, combining the strength of both while removing their weaknesses. To this end, we enhance the dedicated learning techniques of an ASP solver with the inferences of the translating approach in a lazy way. That is, the important knowledge is only made explicit when needed.
By using state of the art techniques from neighboring fields, we provide ways to tackle real world, industrial size problems. By extending CASP to reactive solving, we open up new application areas such as online planning with continuous domains and durations.
Die deutsche Berufsausbildung hat in den vergangenen Jahren stark an Zuspruch verloren. Dies trifft insbesondere auch auf die duale kaufmännische Berufsausbildung zu. Galt sie vor einigen Jahren noch als ein möglicher Ausbildungsweg für leistungsstarke Schüler/-innen, präferieren diese heute zum großen Teil das Studium. Die wachsende Anzahl an Studienabbrechern belegt jedoch, dass dadurch auch Potenzial verloren geht, weil sich Jugendliche mit dem Studium für einen Ausbildungsweg entscheiden, der für sie nicht geeignet ist. Bisherige Bemühungen zur Etablierung alternativer Bildungswege wie zum Beispiel Berufsakademien weisen zwar Erfolge auf, basieren jedoch auf einem Konzept, das sich ausschließlich am Bedarf der Wirtschaft orientiert. Es ist jedoch die Überzeugung der Autorin, dass neue innovative Bildungswege auch die Bedürfnisse und Vorstellungen derjenigen berücksichtigen müssen, für die sie entworfen werden. Denn die Generation der heutigen Jugendlichen zeichnet sich dadurch aus, dass sie ein anderes Wertekonzept als ihre Vorgängergenerationen aufweist. Die Dissertation entwickelt daher ein Modell einer wirtschaftsorientierten Ausbildung, welches sich aus unterschiedlichen motivationstheoretischen Elementen ableitet und zugleich die Werte der Generation der heutigen Jugend-lichen berücksichtigt. Es umfasst sowohl die Anreiz-Beitrags-Theorie nach Barnard als auch die Inhalts-Erwartungstheorie nach Vroom. Zudem liegt ein Hauptaugenmerk dieser Arbeit auf der Anpassung der Zwei-Faktoren-Theorie nach Herzberg auf die heutige Zeit.
Empirisch basiert die Dissertation auf einem dreistufigen Untersuchungsdesign. Die erste Stufe umfasst eine quantitative Befragung von insgesamt 459 Abiturienten/-innen und 100 Studierenden. In der zweiten Stufe wurden 10 Studieren-de und 12 Abiturienten/-innen qualitativ befragt. Eine Validierung der Ergebnis-se erfolgte in der dritten Stufe mittels Experteninterviews. Das Ziel der empirischen Untersuchung bestand in der Überprüfung von vier Hypothesen als Basis zur Modellableitung:
Hypothese H1 - Flexibilität erhöht die Attraktivität einer wirtschaftsorientierten Ausbildung: Der Faktor Flexibilität wurde als ein relevanter Motivator für die Wahl eines Ausbildungsweges identifiziert. Jugendliche wollen sich heutzutage nicht sofort bzw. nicht zu früh festlegen müssen.
Hypothese H2 - Auslandsaufenthalte erhöhen die Attraktivität einer wirtschaftsorientierten Ausbildung: Es wurde bestätigt, dass Auslandsaufenthalte die Attraktivität einer wirtschaftsorientierten Ausbildung steigert, es besteht jedoch eine Reihe von Barrieren, die Jugendliche (obwohl sie den grundsätzlichen Vor-teil sehen) davon abhalten, einen Auslandsaufenthalt für sich selbst in Betracht zu ziehen.
Hypothese H3 - Das Aufzeigen einer Karriereperspektive erhöht die Attraktivität einer wirtschaftsorientierten Ausbildung: Für die Generation der heutigen Jugendlichen steht bezüglich der Wahl ihres Ausbildungsweges die Aussicht auf eine Tätigkeit im Vordergrund, die ein gesichertes Einkommen und somit ein gutes Leben ermöglicht und zudem aus ihrer Sicht eine gewisse Sinnhaftigkeit hat. Führungspositionen, in denen auch höhere Verantwortung übernommen wird, strebt nur eine Minderheit an.
Hypothese H4 - Zusätzliche monetäre Anreize erhöhen die Attraktivität einer wirtschaftsorientierten Ausbildung: Vergütungsbestandteile werden grundsätzlich nicht abgelehnt (das wäre auch irrational), haben jedoch auch nicht die Anreizfunktion, die ihr auf Basis der Voruntersuchung im Rahmen dieser Arbeit hätte unterstellt werden können. Für die Entscheidungsfindung bezüglich eines Ausbildungsweges spielen sie nur eine untergeordnete Rolle. Dennoch trägt die Vergütung zur Attraktivität eines Ausbildungsweges bei.
Basierend auf den zuvor genannten Ergebnissen wurde das Modell einer wirtschaftsorientieren Ausbildung abgeleitet, das sowohl horizontal als auch vertikal flexibel ist. Horizontale Flexibilität ist dadurch gegeben, dass innerhalb eines Ausbildungsjahres unterschiedliche Unternehmen und Branchen kennengelernt werden (Jahr 1 und Jahr 2). Eine Spezialisierung erfolgt erst in den späteren Ausbildungsjahren. Durch die Möglichkeit, nach jedem Ausbildungsjahr mit einem Abschluss ins Berufsleben zu wechseln und die Ausbildung gegebenenfalls zu einem späteren Zeitpunkt fortzusetzen, ist auch eine vertikale Flexibilität gegeben. Zudem bietet das Modell Studienabbrechern/-innen die Möglichkeit, im Ausbildungsjahr 2 bzw. 3 in die Ausbildung einzusteigen. Im Jahr 2 und/oder Jahr 3 sind Auslandsaufenthalte integriert. Diese werden fakultativ an-geboten. Bereits ab dem Jahr 1 besteht die Möglichkeit, Vorbereitungskurse zu belegen. Der hohen Bedeutung der Karriereperspektive wird im abgeleiteten Modell auf mehreren Ebenen Rechnung getragen. So werden nach jedem Ausbildungsjahr anerkannte Abschlüsse erreicht. Während diese in den Jahren 1 und 2 mit IHK-Abschlüssen gleichzusetzen sind, beginnen ab Jahr 3 die akademischen Graduierungen (Jahr 3 Bachelor, Jahr 4 Master). Die Vergütung wird Bestandteil einer wirtschaftsorientierten Ausbildung, wobei ihre Höhe mit Dauer der Ausbildung zunimmt.
Da mit der Einführung des Modells einer wirtschaftsorientierten Ausbildung die Überwindung von institutionellen Paradigmen und Schranken verbunden sind, erfolgte im Rahmen des Ausblicks der Arbeit eine weitere Expertenbefragung bezüglich seiner Umsetzbarkeit. Es setzt eine Beweglichkeit von institutioneller Seite voraus (hierbei insbesondere auch von den Kammern), die von der Mehr-zahl der Experten derzeit skeptisch gesehen wird. Die konzeptionelle Ausgestaltung findet grundsätzlichen Zuspruch, wobei in einigen Details, zum Beispiel in der Dauer der Ausbildung, noch Klärungsbedarf besteht.
Grundsätzlich schließen sich die Experten/-innen der Meinung der Autorin an, dass ein Sinneswandel in der deutschen Ausbildungslandschaft gewünscht und gefordert wird. Dies betrifft insbesondere auch den kaufmännischen Bereich. Diese Arbeit liefert mit dem Modell der wirtschaftsorientierten Ausbildung einen wichtigen Beitrag zur Diskussion über neue Ausbildungswege.
East Africa is a natural laboratory: Studying its unique geological and biological history can help us better inform our theories and models. Studying its present and future can help us protect its globally important biodiversity and ecosystem services. East African vegetation plays a central role in all these aspects, and this dissertation aims to quantify its dynamics through computer simulations.
Computer models help us recreate past settings, forecast into the future or conduct simulation experiments that we cannot otherwise perform in the field. But before all that, one needs to test their performance. The outputs that the model produced using the present day-inputs, agreed well with present-day observations of East African vegetation. Next, I simulated past vegetation for which we have fossil pollen data to compare. With computer models, we can fill the gaps of knowledge between sites where we have fossil pollen data from, and create a more complete picture of the past. Good level of agreement between model and pollen data where they overlapped in space further validated our model performance.
Once the model was tested and validated for the region, it became possible to probe one of the long standing questions regarding East African vegetation: How did East Africa lose its tropical forests? The present-day vegetation in the tropics is mainly characterized by continuous forests worldwide except in tropical East Africa, where forests only occur as patches. In a series of simulation experiments, I was able to show under which conditions these forest patches could have been connected and fragmented in the past. This study showed the sensitivity of East African vegetation to climate change and variability such as those expected under future climate change.
El Niño Southern Oscillation (ENSO) events that result from the fluctuations in temperature between the ocean and atmosphere, bring further variability to East African climate and are predicted to increase in intensity in the future. But climate models are still not good at capturing the pattens of these events. In a study where I quantified the influence of ENSO events on East African vegetation, I showed how different the future vegetation could be from what we currently predict with these climate models that lack accurate ENSO contribution. Consideration of these discrepancies is important for our future global carbon budget calculations and management decisions.
Business process automation improves organizations’ efficiency to perform work. Therefore, a business process is first documented as a process model which then serves as blueprint for a number of process instances representing the execution of specific business cases. In existing business process management systems, process instances run independently from each other. However, in practice, instances are also collected in groups at certain process activities for a combined execution to improve the process performance. Currently, this so-called batch processing is executed manually or supported by external software. Only few research proposals exist to explicitly represent and execute batch processing needs in business process models. These works also lack a comprehensive understanding of requirements.
This thesis addresses the described issues by providing a basic concept, called batch activity. It allows an explicit representation of batch processing configurations in process models and provides a corresponding execution semantics, thereby easing automation. The batch activity groups different process instances based on their data context and can synchronize their execution over one or as well multiple process activities. The concept is conceived based on a requirements analysis considering existing literature on batch processing from different domains and industry examples. Further, this thesis provides two extensions: First, a flexible batch configuration concept, based on event processing techniques, is introduced to allow run time adaptations of batch configurations. Second, a concept for collecting and batching activity instances of multiple different process models is given. Thereby, the batch configuration is centrally defined, independently of the process models, which is especially beneficial for organizations with large process model collections. This thesis provides a technical evaluation as well as a validation of the presented concepts. A prototypical implementation in an existing open-source BPMS shows that with a few extensions, batch processing is enabled. Further, it demonstrates that the consolidated view of several work items in one user form can improve work efficiency. The validation, in which the batch activity concept is applied to different use cases in a simulated environment, implies cost-savings for business processes when a suitable batch configuration is used. For the validation, an extensible business process simulator was developed. It enables process designers to study the influence of a batch activity in a process with regards to its performance.
The development of self-adaptive software requires the engineering of an adaptation engine that controls the underlying adaptable software by a feedback loop. State-of-the-art approaches prescribe the feedback loop in terms of numbers, how the activities (e.g., monitor, analyze, plan, and execute (MAPE)) and the knowledge are structured to a feedback loop, and the type of knowledge. Moreover, the feedback loop is usually hidden in the implementation or framework and therefore not visible in the architectural design. Additionally, an adaptation engine often employs runtime models that either represent the adaptable software or capture strategic knowledge such as reconfiguration strategies. State-of-the-art approaches do not systematically address the interplay of such runtime models, which would otherwise allow developers to freely design the entire feedback loop.
This thesis presents ExecUtable RuntimE MegAmodels (EUREMA), an integrated model-driven engineering (MDE) solution that rigorously uses models for engineering feedback loops. EUREMA provides a domain-specific modeling language to specify and an interpreter to execute feedback loops. The language allows developers to freely design a feedback loop concerning the activities and runtime models (knowledge) as well as the number of feedback loops. It further supports structuring the feedback loops in the adaptation engine that follows a layered architectural style. Thus, EUREMA makes the feedback loops explicit in the design and enables developers to reason about design decisions.
To address the interplay of runtime models, we propose the concept of a runtime megamodel, which is a runtime model that contains other runtime models as well as activities (e.g., MAPE) working on the contained models. This concept is the underlying principle of EUREMA. The resulting EUREMA (mega)models are kept alive at runtime and they are directly executed by the EUREMA interpreter to run the feedback loops. Interpretation provides the flexibility to dynamically adapt a feedback loop. In this context, EUREMA supports engineering self-adaptive software in which feedback loops run independently or in a coordinated fashion within the same layer as well as on top of each other in different layers of the adaptation engine. Moreover, we consider preliminary means to evolve self-adaptive software by providing a maintenance interface to the adaptation engine.
This thesis discusses in detail EUREMA by applying it to different scenarios such as single, multiple, and stacked feedback loops for self-repairing and self-optimizing the mRUBiS application. Moreover, it investigates the design and expressiveness of EUREMA, reports on experiments with a running system (mRUBiS) and with alternative solutions, and assesses EUREMA with respect to quality attributes such as performance and scalability.
The conducted evaluation provides evidence that EUREMA as an integrated and open MDE approach for engineering self-adaptive software seamlessly integrates the development and runtime environments using the same formalism to specify and execute feedback loops, supports the dynamic adaptation of feedback loops in layered architectures, and achieves an efficient execution of feedback loops by leveraging incrementality.
Die Kernfrage der vorliegenden Arbeit lautet: Sichert die Schuldenbremse die fiskalische Nachhaltigkeit in Deutschland? Zur Beantwortung dieser Frage wird zunächst untersucht, welche Vor-Wirkungen die Einführung der Schuldenbremse im Zeitraum 2010-16 auf die deutschen Bundesländer zeitigte. Dafür wurden die beobachtete Konsolidierungsleistung und der 2009 bestehende Konsolidierungsanreiz bzw. –druck der Bundesländer mit Hilfe einer eigens zu diesem Zweck entwickelten Scorecard evaluiert. Mittels multipler Regressionsanalyse wurde dann analysiert, wie die Faktoren der Scorecard die Konsolidierungsleistung der Bun- desländer beeinflussen. Dabei wurde festgestellt, dass beinahe 90% der Variation, durch die unabhängigen Variablen Haushaltslage, Schuldenlast, Einnahmenwachstum und Pensionslast erklärt werden und der Schuldenbremse bei der Konsolidierungsepisode 2009-2016 eher eine untergeordnete Rolle zugefallen sein dürfte. Anschließend wurde mithilfe der in 65 Expertinneninterviews gesammelten Daten analysiert, welche Grenzen der neuen Fiskalregel in ihrem Wirken gesetzt sind, bzw. welche Risiken zukünftig die Einhaltung der Schuldenbremse erschweren oder verhindern könnten: Kommunalverschuldung, FEUs, Eventualverpflichtungen in Form von Bürgschaften für Finanzinstitute und Pensionsverpflichtungen. Die häufig geäußerten Kritikpunkte, die Schuldenbremse sei eine Konjunktur- und Investitionsbremse werden ebenfalls überprüft und zurückgewiesen. Schließlich werden potentielle zukünftige Entwicklungen hinsichtlich der Schuldenbremse und der öffentlichen Verwaltung in Deutschland sowie der Konsolidierungsbemühungen der Länder erörtert.
Plastic pollution is ubiquitous on the planet since several millions of tons of plastic waste enter aquatic ecosystems each year. Furthermore, the amount of plastic produced is expected to increase exponentially shortly. The heterogeneity of materials, additives and physical characteristics of plastics are typical of these emerging contaminants and affect their environmental fate in marine and freshwaters. Consequently, plastics can be found in the water column, sediments or littoral habitats of all aquatic ecosystems. Most of this plastic debris will fragment as a product of physical, chemical and biological forces, producing particles of small size. These particles (< 5mm) are known as “microplastics” (MP). Given their high surface-to-volume ratio, MP stimulate biofouling and the formation of biofilms in aquatic systems.
As a result of their unique structure and composition, the microbial communities in MP biofilms are referred to as the “Plastisphere.” While there is increasing data regarding the distinctive composition and structure of the microbial communities that form part of the plastisphere, scarce information exists regarding the activity of microorganisms in MP biofilms. This surface-attached lifestyle is often associated with the increase in horizontal gene transfer (HGT) among bacteria. Therefore, this type of microbial activity represents a relevant function worth to be analyzed in MP biofilms. The horizontal exchange of mobile genetic elements (MGEs) is an essential feature of bacteria. It accounts for the rapid evolution of these prokaryotes and their adaptation to a wide variety of environments. The process of HGT is also crucial for spreading antibiotic resistance and for the evolution of pathogens, as many MGEs are known to contain antibiotic resistance genes (ARGs) and genetic determinants of pathogenicity.
In general, the research presented in this Ph.D. thesis focuses on the analysis of HGT and heterotrophic activity in MP biofilms in aquatic ecosystems. The primary objective was to analyze the potential of gene exchange between MP bacterial communities vs. that of the surrounding water, including bacteria from natural aggregates. Moreover, the thesis addressed the potential of MP biofilms for the proliferation of biohazardous bacteria and MGEs from wastewater treatment plants (WWTPs) and associated with antibiotic resistance. Finally, it seeks to prove if the physiological profile of MP biofilms under different limnological conditions is divergent from that of the water communities. Accordingly, the thesis is composed of three independent studies published in peer-reviewed journals. The two laboratory studies were performed using both model and environmental microbial communities. In the field experiment, natural communities from freshwater ecosystems were examined.
In Chapter I, the inflow of treated wastewater into a temperate lake was simulated with a concentration gradient of MP particles. The effects of MP on the microbial community structure and the occurrence of integrase 1 (int 1) were followed. The int 1 is a marker associated with mobile genetic elements and known as a proxy for anthropogenic effects on the spread of antimicrobial resistance genes. During the experiment, the abundance of int1 increased in the plastisphere with increasing MP particle concentration, but not in the surrounding water. In addition, the microbial community on MP was more similar to the original wastewater community with increasing microplastic concentrations. Our results show that microplastic particles indeed promote persistence of standard indicators of microbial anthropogenic pollution in natural waters.
In Chapter II, the experiments aimed to compare the permissiveness of aquatic bacteria towards model antibiotic resistance plasmid pKJK5, between communities that form biofilms on MP vs. those that are free-living. The frequency of plasmid transfer in bacteria associated with MP was higher when compared to bacteria that are free-living or in natural aggregates. Moreover, comparison increased gene exchange occurred in a broad range of phylogenetically-diverse bacteria. The results indicate a different activity of HGT in MP biofilms, which could affect the ecology of aquatic microbial communities on a global scale and the spread of antibiotic resistance.
Finally, in Chapter III, physiological measurements were performed to assess whether microorganisms on MP had a different functional diversity from those in water. General heterotrophic activity such as oxygen consumption was compared in microcosm assays with and without MP, while diversity and richness of heterotrophic activities were calculated by using Biolog® EcoPlates. Three lakes with different nutrient statuses presented differences in MP-associated biomass build up. Functional diversity profiles of MP biofilms in all lakes differed from those of the communities in the surrounding water, but only in the oligo-mesotrophic lake MP biofilms had a higher functional richness compared to the ambient water. The results support that MP surfaces act as new niches for aquatic microorganisms and can affect global carbon dynamics of pelagic environments.
Overall, the experimental works presented in Chapters I and II support a scenario where MP pollution affects HGT dynamics among aquatic bacteria. Among the consequences of this alteration is an increase in the mobilization and transfer efficiency of ARGs. Moreover, it supposes that changes in HGT can affect the evolution of bacteria and the processing of organic matter, leading to different catabolic profiles such as demonstrated in Chapter III. The results are discussed in the context of the fate and magnitude of plastic pollution and the importance of HGT for bacterial evolution and the microbial loop, i.e., at the base of aquatic food webs. The thesis supports a relevant role of MP biofilm communities for the changes observed in the aquatic microbiome as a product of intense human intervention.
The continuously increasing pollution of aquatic environments with microplastics (plastic particles < 5 mm) is a global problem with potential implications for organisms of all trophic levels. For microorganisms, trillions of these floating microplastics particles represent a huge surface area for colonization. Due to the very low biodegradability, microplastics remain years to centuries in the environment and can be transported over thousands of kilometers together with the attached organisms. Since also pathogenic, invasive, or otherwise harmful species could be spread this way, it is essential to study microplastics-associated communities.
For this doctoral thesis, eukaryotic communities were analyzed for the first time on microplastics in brackish environments and compared to communities in the surrounding water and on the natural substrate wood. With Illumina MiSeq high-throughput sequencing, more than 500 different eukaryotic taxa were detected on the microplastics samples. Among them were various green algae, dinoflagellates, ciliates, fungi, fungal-like protists and small metazoans such as nematodes and rotifers. The most abundant organisms was a dinoflagellate of the genus Pfiesteria, which could include fish pathogenic and bloom forming toxigenic species. Network analyses revealed that there were numerous interaction possibilities among prokaryotes and eukaryotes in microplastics biofilms. Eukaryotic community compositions on microplastics differed significantly from those on wood and in water, and compositions were additionally distinct among the sampling locations. Furthermore, the biodiversity was clearly lower on microplastics in comparison to the diversity on wood or in the surrounding water.
In another experiment, a situation was simulated in which treated wastewater containing microplastics was introduced into a freshwater lake. With increasing microplastics concentrations, the resulting bacterial communities became more similar to those from the treated wastewater. Moreover, the abundance of integrase I increased together with rising concentrations of microplastics. Integrase I is often used as a marker for anthropogenic environmental pollution and is further linked to genes conferring, e.g., antibiotic resistance.
This dissertation gives detailed insights into the complexity of prokaryotic and eukaryotic communities on microplastics in brackish and freshwater systems. Even though microplastics provide novel microhabitats for various microbes, they might also transport toxigenic, pathogenic, antibiotic-resistant or parasitic organisms; meaning their colonization can pose potential threats to humans and the environment. Finally, this thesis explains the urgent need for more research as well as for strategies to minimize the global microplastic pollution.
Metamaterial devices
(2018)
Digital fabrication machines such as 3D printers excel at producing arbitrary shapes, such as for decorative objects. In recent years, researchers started to engineer not only the outer shape of objects, but also their internal microstructure. Such objects, typically based on 3D cell grids, are known as metamaterials. Metamaterials have been used to create materials that, e.g., change their volume, or have variable compliance.
While metamaterials were initially understood as materials, we propose to think of them as devices.
We argue that thinking of metamaterials as devices enables us to create internal structures that offer functionalities to implement an input-process-output model without electronics, but purely within the material’s internal structure. In this thesis, we investigate three aspects of such metamaterial devices that implement parts of the input-process-output model: (1) materials that process analog inputs by implementing mechanisms based on their microstructure, (2) that process digital signals by embedding mechanical computation into the object’s microstructure, and (3) interactive metamaterial objects that output to the user by changing their outside to interact with their environment. The input to our metamaterial devices is provided directly by the users interacting with the device by means of physically pushing the metamaterial, e.g., turning a handle, pushing a button, etc.
The design of such intricate microstructures, which enable the functionality of metamaterial devices, is not obvious. The complexity of the design arises from the fact that not only a suitable cell geometry is necessary, but that additionally cells need to play together in a well-defined way. To support users in creating such microstructures, we research and implement interactive design tools. These tools allow experts to freely edit their materials, while supporting novice users by auto-generating cells assemblies from high-level input. Our tools implement easy-to-use interactions like brushing, interactively simulate the cell structures’ deformation directly in the editor, and export the geometry as a 3D-printable file. Our goal is to foster more research and innovation on metamaterial devices by allowing the broader public to contribute.
This text is a contribution to the research on the worldwide success of evangelical Christianity and offers a new perspective on the relationship between late modern capitalism and evangelicalism. For this purpose, the utilization of affect and emotion in evangelicalism towards the mobilization of its members will be examined in order to find out what similarities to their employment in late modern capitalism can be found. Different examples from within the evangelical spectrum will be analyzed as affective economies in order to elaborate how affective mobilization is crucial for evangelicalism’s worldwide success. Pivotal point of this text is the exploration of how evangelicalism is able to activate the voluntary commitment of its members, financiers, and missionaries. Gathered here are examples where both spheres—evangelicalism and late modern capitalism—overlap and reciprocate, followed by a theoretical exploration of how the findings presented support a view of evangelicalism as an inner-worldly narcissism that contributes to an assumed re-enchantment of the world.
Movement and navigation are essential for many organisms during some parts of their lives. This is also true for bacteria, which can move along surfaces and swim though liquid environments. They are able to sense their environment, and move towards environmental cues in a directed fashion.
These abilities enable microbial lifecyles in biofilms, improved food uptake, host infection, and many more. In this thesis we study aspects of the swimming movement - or motility - of the soil bacterium (P. putida). Like most bacteria, P. putida swims by rotating its helical flagella, but their arrangement differs from the main model organism in bacterial motility research: (E. coli). P. putida is known for its intriguing motility strategy, where fast and slow episodes can occur after each other. Up until now, it was not known how these two speeds can be produced, and what advantages they might confer to this bacterium.
Normally the flagella, the main component of thrust generation in bacteria, are not observable by ordinary light microscopy. In order to elucidate this behavior, we therefore used a fluorescent staining technique on a mutant strain of this species to specifically label the flagella, while leaving the cell body only faintly stained. This allowed us to image the flagella of the swimming bacteria with high spacial and temporal resolution with a customized high speed fluorescence microscopy setup. Our observations show that P. putida can swim in three different modes. First, It can swim with the flagella pushing the cell body, which is the main mode of swimming motility previously known from other bacteria. Second, it can swim with the flagella pulling the cell body, which was thought not to be possible in situations with multiple flagella. Lastly, it can wrap its flagellar bundle around the cell body, which results in a speed wich is slower by a factor of two. In this mode, the flagella are in a different physical conformation with a larger radius so the cell body can fit inside. These three swimming modes explain the previous observation of two speeds, as well as the non strict alternation of the different speeds.
Because most bacterial swimming in nature does not occur in smoothly walled glass enclosures under a microscope, we used an artificial, microfluidic, structured system of obstacles to study the motion of our model organism in a structured environment. Bacteria were observed in microchannels with cylindrical obstacles of different sizes and with different distances with video microscopy and cell tracking. We analyzed turning angles, run times, and run length, which we compared to a minimal model for movement in structured geometries. Our findings show that hydrodynamic interactions with the walls lead to a guiding of the bacteria along obstacles. When comparing the observed behavior with the statics of a particle that is deflected with every obstacle contact, we find that cells run for longer distances than that model.
Navigation in chemical gradients is one of the main applications of motility in bacteria. We studied the swimming response of P. putida cells to chemical stimuli (chemotaxis) of the common food preservative sodium benzoate. Using a microfluidic gradient generation device, we created gradients of varying strength, and observed the motion of cells with a video microscope and subsequent cell tracking. Analysis of different motility parameters like run lengths and times, shows that P. putida employs the classical chemotaxis strategy of E. coli: runs up the gradient are biased to be longer than those down the gradient. Using the two different run speeds we observed due to the different swimming modes, we classify runs into `fast' and `slow' modes with a Gaussian mixture model (GMM). We find no evidence that P. putida's uses its swimming modes to perform chemotaxis.
In most studies of bacterial motility, cell tracking is used to gather trajectories of individual swimming cells. These trajectories then have to be decomposed into run sections and tumble sections. Several algorithms have been developed to this end, but most require manual tuning of a number of parameters, or extensive measurements with chemotaxis mutant strains. Together with our collaborators, we developed a novel motility analysis scheme, based on generalized Kramers-Moyal-coefficients. From the underlying stochastic model, many parameters like run length etc., can be inferred by an optimization procedure without the need for explicit run and tumble classification. The method can, however, be extended to a fully fledged tumble classifier. Using this method, we analyze E. coli chemotaxis measurements in an aspartate analog, and find evidence for a chemotactic bias in the tumble angles.