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Mass transfers during fluid-rock interactions at divergent and convergent plate boundaries
Get PDFFluids and reactions between fluids and rock evoke significant mass and energy transfers in the marine realm. Phyllosilicate-rich shear zone rocks from a detachment fault zone (Mid-Atlantic Ridge) formed by hydrothermal alteration of hybrid ultramafica mafic rocks. Extensional strain and deformation focus in these weak lithologies and initiate a feedback loop between hydration and strain localization, which likely play a key role in detachment faults worldwide. Carbonates, precipitated from CO2-rich, oxidizing fluids, have formed in veins in metavolcanic and -sedimentary clasts at depths <20 km within the subduction channel (Mariana subduction system). Their existence proofs of C mobilization from the slab at shallow portions of subduction zones. Serpentinites from the basal plane of the mantle wedge (Mariana subduction zone) contain high contents of fluid-mobile elements (Li, B, Sr, Rb, Cs, Ba) that were mobilized during dehydration of the slab. Element concentrations vary with slab-depths and the sources of the serpentinization fluids, and provide a continuous record of slab dehydration reactions
Matter-wave Interferometry for space-borne Inertial Sensors
Get PDFInertial sensors based on matter-wave interferometry are currently approaching the precision and accuracy of state-of-the-art classical sensors. While these devices are often realised with ultracold but not Bose-condensed atoms as matter waves, employing Bose-Einstein Condensates (BEC) promises to overcome certain limitations, especially those related to the ensemble's expansion. The point-source like character of BECs also enables utilising spatial interference patterns to measure e.g. rotation rates in single-shot experiments. Matter wave-based inertial sensors are considered for experiments ranging from Gravitational Wave detection to tests of the Universality of Free Fall (UFF) to gain insight into the joint between Quantum Mechanics and General Relativity. In the scope of this thesis, matter-wave interferometry with BECs was demonstrated for the first time in a microgravity environment with the QUANTUS-1 apparatus. The same instrument was then employed as a quantum tiltmeter utilising a novel beam-splitting mechanism known as Bragg Double Diffraction. To this end, the QUANTUS-1 apparatus designed as a BEC instrument to be operated in the drop tower at ZARM at University of Bremen was equipped with optics and laser systems required for performing matter-wave interferometry based on Bragg Diffraction. The apparatus employs an atom chip to create BECs of around 10000 Rubidium 87 atoms within 15 s. With a Mach-Zehnder like interferometer scheme, spatial interference fringes were observed after a free evolution time in the interferometer of up to 677 ms. To achieve these long time scales, a method known as Delta-Kick Collimation (DKC) was adapted to slow the expansion of the BEC to a kinetic energy equivalent below 1 nK, and the atoms were transferred to a non-magnetic Zeeman state via an adiabatic rapid passage (ARP). A similar interferometer scheme with a newly developed beam-splitter mechanism known as Bragg Double Diffraction was used to measure the tilt of the instrument on ground with a precision of up to 4.4 AA rad. This thesis presents an overview of the apparatus including ground-based characterisations of all required experimental steps. Results from over 400 free fall experiments are evaluated for expansion studies of the BEC and matter-wave interferometry in microgravity. The time-evolution of first and second order Bragg Double Diffraction beam splitters is studied, and an interferometer sensitive to the tilt of the instrument is implemented. Based on this work, a gravimeter with a new launch mechanism comprising Bragg beam splitters and Bloch oscillations to enable atomic fountains in atom-chip based devices was developed. The microgravity experiments were adapted for the MAIUS-1 sounding-rocket instrument to create the first man-made BEC in outer space and study the feasibility of operating matter-wave interferometers on space-borne platforms. The results of this thesis lay the groundwork for future space-borne missions using matter-wave interferometry for precision measurements of inertial forces
Hydroclimate variations in the Caspian Sea region from the late Quaternary to the future : a model perspective
Get PDFThe northern hemispheric glacial-interglacial climate states during the late Quaternary period drove Caspian Sea level (CSL) changes of up to 150 m and can be used as an analogue for assessing present and future climate impacts. Geologic reconstructions of these paleo-lake levels and potential links with different climate events remain complex while future declines in modelled lake levels vary widely and are uncertain. The key drivers for such CSL include variations in the water budget balance between precipitation and evaporation (P-E). This thesis employs a climate modeling approach to investigate long-term changes in the Caspian Sea (CS) hydroclimate during different climate states from the late Quaternary to the end of the 21st century. The new results from the Community Earth System Model (CESM1.2.2), contribute to an improved interpretation of reconstructed paleo-lake levels with respect to changing P-E patterns and identify key drivers for future CSL changes. This study produced new modeling results for the late Quaternary period, that constrain the timings and identify the climate conditions favourable for major CS transgressions and regressions, in comparison with selected geological reconstructions; under three glacial (Marine Isotope 3 (MIS3), Last Glacial Maximum (LGM), Heinrich event 1 (H1)) and two interglacial (last interglacial (LIG) and early Holocene (EH)) climate states. The two interglacial climate states suggest favourable climate conditions (higher temperature and precipitation) for the CS that result in a positive water budget (LIG-P-E anomalies of 14.6 meter/1000 years and the EH-P-E anomalies 5 meter/1000yr). The results propose a transgression was initiated by the summer large-scale and convective precipitation, triggered by enhanced summer insolation and the associated wind anomalies. The warmer and wetter MIS3 interstadial climate is identified as being responsible for a transgression with P-E anomalies of 16 meter/1000yr. The colder and drier LGM climate favours a regression with P-E of -12 meter/ 1000yr. These P-E anomalies and climate conditions agree with the reconstructions. However, our simulated P-E anomalies (for the H1); do not capture the magnitude of the reconstructed highstands during the deglaciation, and it is clear that meltwater into the CS is responsible for this highstand; and as our model does not include a sophisticated meltwater routing into the CS; hence comparisons with selected reconstructions remain complicated. This study also assessed different CESM horizontal resolutions and model setups to identify the best version that can represent the CS climate and climate modes of variability such as North Atlantic Oscillation (NAO) for the period 1850-2000 CE, as well as presenting new CSL under two new emission scenarios by the end of the 21st century. CESM1.2.2 with 1AAAdegree CAM5 is identified as the best skill in simulating the NAO and its effects on CS catchment hydrology. Projections under the Representative Concentration Pathways RCP4.5 and RCP8.5 confirm the winter NAO remains the major winter variability with a significant impact on the Caspian catchment hydroclimate. However, under global warming, the evaporation over the sea is the key driver for a CSL decrease of about 9 m and 18 m between 2020 and 2100 for the RCP4.5 and RCP8.5 scenarios, respectively. The new CSL values are larger than previous projections of CSL, and include an overestimated total evaporation due to a larger CS surface area in CESM. Despite the clear potential for this, current global climate models neglect to include accurate representations of CS area. This study generated new results to notably aid in evaluating the impacts of different CS surface areas on the regional and large-scale climate. Regionally, the presence of a larger CS area has a clear impact as higher evaporation over the sea and higher precipitation over the south-west catchment, while reducing (summer) and increasing (winter) surface air temperatures and vice versa for smaller CS area. Most importantly, this summer temperature disturbs the upper atmospheric circulation (at the 200 hPa and the 500 hPa level) with a southward shift and increase in speed of the summer jet stream. This leads to enhanced summer precipitation over central Asia and increased winter warming over the north-western Pacific. An accurate Caspian Sea area representation is thus vital in global climate models for paleo and future scenarios and share serious implications for expanding coastal communities, agricultural activities, fisheries and the ecosystem
The functional Role of Gamma-Band Synchronization in selective Routing and Network Configuration within the visual Cortex
Get PDFFirst psychophysical experiments performed more than 100 years ago by the German psychologist and physicist Hermann von Helmholtz, showed that visual attention is a central component of perception and, therefore, of substantial relevance for successful behavior. In the decades that followed, much research has been performed to investigate how attention modulates neuronal activity in order to explain the effects of attention on behavior and perception. A well-described finding is that visual neurons responding to the same attended object synchronize their activity in the gamma-frequency range (30 - 100 Hz). In chapter 2, I present the results of an experiment that was designed to find evidence for a causal role of gamma-band synchronization in selective information routing and processing. The underlying idea is that neurons, which synchronize their activity deliver their respective outputs (spikes) more precisely at times the receiving neuron is sensitive for it, i.e. the incoming spikes are more likely to evoke spikes of the receiving neuron. The selective synchronization between input and receiver neurons representing an attended and therefore relevant object could constitute a powerful selection mechanism. To test this gamma recorded neuronal activity in area V4 of two macaque monkeys while applying single electrical pulses to neurons located in area V2. Those V2 neurons delivered afferent input to the recorded V4 population, including the electrically evoked spikes. By relating the effects of these electrically evoked spikes to the gamma-oscillation in V4, I could show that the impact of stimulation on behavior and neuronal activity is causally dependent on the gamma-phase. In chapter 3, I investigated whether the effective processing of a given object requires a specific level of gamma-band synchronization within a local neuronal population. I hypothesized that different objects require different combinations of neurons of the same population to be functionally coupled with one another for effective processing. Furthermore, we hypothesized that this dynamic establishment of functional connections is implemented by gamma-band synchronization, resulting in a specific level of gamma-band synchronization for a specific stimulus. I tested these predictions by first recording neuronal activity in area V4 and quantifying the level of gamma-synchronization in response to two different single stimuli, which had to be attended. Second, I compared these levels to the level of gamma-synchronization when neurons received input of both stimuli simultaneously, and one of them was attended. The level of gamma-synchronization was almost 'as if' the attended stimulus was presented alone, strongly indicating that the processing of this stimulus requires this specific gamma-synchronization level. Chapter 4 describes and characterizes a method that I used for analyzing multi-unit activity in area V4. It does not rely on setting up an amplitude-threshold for separating spikes from background noise as standard procedures do. Thus, this measure takes the entire spike activity into account, which I, therefore, refer to as ESA. I used semi-chronically recorded data of five macaque monkeys in order to quantify the sensitivity of the ESA to detect neuronal responses. The ESA-signal was significantly more sensitive than the standard procedures, especially for data with low signal-to-noise ratio, but preserves information about receptive field sizes and orientation selectivity of the underlying neuronal population. The fifth chapter is describing a method for offline stimulation-artifact removal and restoration of the original broadband neuronal signal. I could show that in contrast to existing methods the here described procedure does not disturb the original signal and therefore allows for analysis of neuronal activity even shortly after electrical stimulation. In summary, the results presented here give further insight into the functional roles of gamma-band synchronization. I could show that (1) gamma-phase synchronization plays a causal role in selective information processing and routing, and (2) that a specific pattern of intra-areal gamma-synchronization is required for effective processing of a given stimulus
Analysis of tribological behavior of surface modifications for a dry deep drawing process
Get PDFThe global trend towards more environment-friendly and sustainable production motivates the development of efficient manufacturing processes. Forming technology has great potential regarding that due to its high material efficiency. Research is necessary to improve the sustainability of established forming processes such as deep drawing. One possibility to improve the environmental friendliness of deep drawing is the realization of lubricant-free processes. This avoids the usage of harmful lubricants. Additionally, it has the potential to shorten process chains by eliminating cleaning steps. However, dry deep drawing is associated with challenges. Due to the lack of a lubricant between tool and workpiece, friction and wear increase. An approach to overcome these challenges is the usage of modified tool surfaces. In this context, the aim of this research is to investigate dry deep drawing operations under application-oriented conditions. Firstly, the cause-effect relationships between the properties and tribological performance for a-C:H and ta-C coating systems as well as laserbased micro-textures are investigated in strip drawing tests using the workpiece materials DC04 and AA5182. Therefore, different amorphous carbon coating approaches for DC04 and AA5182 are evaluated. Beside of coatings, diverse laser micro-texturings are investigated and applied on forming tools. Key parameters are identified, which result in low friction and adhesion. Based on these findings, the different modifications are evaluated. Promising modifications are selected and applied in a novel test rig under application-oriented conditions to analyze their durability. The test rig enables the time- and material-efficient forming of a great number of parts. In this regard, in addition to the occurring process forces, the tool and component topographies are determined at periodic intervals in order to derive the cause-effect relationships between friction, wear and component quality as well as to demonstrate the feasibility of dry deep drawing operations under application-oriented forming conditions
An Optical DipoleTrap in Microgravity
Get PDFOptical interferometers are well known for their high precession in several measurement situations. They are based on a readout of phase differences between optical path length. In contrast, atom interferometers rely on the De Broglie wavelength of atoms and their corresponding phase. A cloud of atoms is split and recombined with light pulses, while in between, the atoms are moving freely. These precise quantum tools will enhance a broad variety of measurements, ranging from large scale phenomena like gravitational wave detection to short scale Casimir-Polder forces and everything in between. The sensitivity of atom interferometers scales with the time squared between light pulses, which is generally limited by gravity and temperature. One technical challenging sollution is the realization of atom interferometers in microgravity. While ultra cold atoms can be prepared in optical and magnetic traps, under weightlessness their preparation is limited to magnetic traps until now. These experiments are based on atom chips with highly asymmetric trapping potentials. The improved symmetry of optical traps can improve the most advanced cooling technique, called delta kick collimation, leading to atomic clouds in the yet unreached femtokelvin range. This thesis is about the first realization of an optical trapping potential in microgravity. It describes the experimental setup, identifies a molasseses technique as the optimal process for dipole trap loading and investigates the further cooling process under the influence and in the absence of gravity. In optical and magnetic traps, the preparation of ultracold atoms is based on evaporation. However, the underlying physics to drive this process are fundamentally different and for optical traps, evaporation is driven by gravity. It is demonstrated that evaporation from an optical potential performs approximately equal with and without gravity, due to a strong mixing of the trapping potentials in all three spatial dimensions. These findings are confirmed with computational simulations, based on the Direct Simulation Monte Carlo method. Atomic ensembles of rubidium-87 with temperatures as low as a 300 nK were generated in the microgravity environment of the drop tower in Bremen with an evaporation time as short as 0.5 s. The final confining trap was too shallow to be reproduced in a laboratory environment. The findings of this thesis will possibly guide the way to improved atom interferometers, with countless applications in precise sensing. Furthermore, optical potentials in microgravity on their own will open up a broad field of fundamental physical experiments. One example is the applicability of magnetic Feshbach resonances. Allowing almost arbitrary tuning of the interatomic scattering length offers new insights in scattering processes or miscibility scenarios
Dynamics of the vegetation in oak forests in Northwest Germany - Effects of environment and management
Get PDFThe main aim of this thesis is to detect and understand long-term changes of the vegetation in the four oak forest types occurring in NW Germany. The following main questions were addressed: (1) How has the vegetation of Alluvial hardwood oak forests, Thermophilious oak-hornbeam forests, Sub-atlantic oak-hornbeam forests and Acidophilous oak forests changed over the past decades? (2) What are the drivers of the changes in the vegetation in these oak forests? (3) Do the observed changes and the drivers differ between the different oak forest ecosystems
Indie and Dojin Games : a Multilayered Cross-Cultural Comparison
Get PDFThe article provides a comparative account of two paradigms of independent videogame production: the Japanese dojin (doujin) games and the increasingly global indie games. Through a multilayered analysis, it expounds the conceptual metaphors associated with indie and d jin games, traces the two movements respective histories, situates them in wider media environments, and compares their characteristic traits
Die Müllproblematik ( Littering ) im Nationalpark Schwarzwald : Entwicklung von Maßnahmen und einer Aufklärungskampagne zur Prävention und Vermeidung von Littering
Get PDFNaturtourismus stellt eine beliebte Urlaubsform der Deutschen dar. Die steigenden Besucherströme in Großschutzgebieten haben allerdings gravierende Folgen, wie beispielsweise die Müllproblematik ( Littering ). In der vorliegenden Bachelor-Thesis wird exemplarisch am Beispiel des Nationalparks Schwarzwald untersucht, wie diesem Problem entgegengewirkt werden kann. Für die empirische Untersuchung wurde ein Methodenmix aus Sekundär- und Primärforschung angewandt. Neben den theoretischen Erkenntnissen wurde eine Besucherblitzlichtbefragung und Ortserkundung durchgeführt. Das Hauptaugenmerk der Arbeit liegt auf den Experteninterviews, die einen tieferen Einblick in die Thematik geben. Hundebesitzer, Raucher, Kinder und Jugendliche konnten als spezifische Zielgruppen identifiziert werden. Das Ergebnis zeigt, dass sich insbesondere Maßnahmen, die auf die Besuchersensibilisierung abzielen, als besonders effektiv erweisen. Neben Umweltbildung, partizipativen Maßnahmen, Öffentlichkeitsarbeit und Kampagnen ist es essentiell, das Abfallaufkommen zu quantifizieren und zu qualifizieren, um die Abfallmenge, -zusammensetzung und die Hotspots von Littering zu identifizieren sowie genaue Aussagen über die Effektivität von Maßnahmen treffen zu können. In diesem Sinne werden Handlungsempfehlungen unter Berücksichtigung der Besonderheiten eines Nationalparks erarbeitet, die zu geeigneten Maßnahmen der Abfallvermeidung führen können. Zusätzlich wird ein Konzeptentwurf für eine Abfallkampagne vorgestellt
The economic impact of international uncertainties : Sanctioning effects, foreign direct Investment and firm behaviour in Russia
Get PDFThis thesis contributes to following fields of studies: international economics, political economy, international business and industrial organization literature, as well as institutional and innovation economics. In the introductory chapter we provide the necessary foundation for placing the empirical evidence that is presented in Chapters 2 - 4 in a broader economic context. By doing this, the first chapter gives an overview of the main milestones in Russian economic history and outlines Russia's integration into the global economy. Hereby we concentrate on Foreign Direct Investment (FDI) and trade as they are the most relevant components of Russia's globalization process, a process that is currently being reversed as a result of geopolitical tensions. Chapters 2 - 4 form the empirical part of this dissertation. In Chapter 2, we quantify the economic cost for the sanction sender, the EU-27, in the aftermath of the geopolitical crisis, triggered by Russia's involvement in the Ukrainian conflict. We find that direct costs are mainly born by the countries closely connected with Russia in terms of trade, whereas indirect costs are mainly induced by the tight embeddedness in the European trade network. In the empirical part that follows, we turn to the question of whether political risks affect the behaviour of multinational companies (MNCs) in Russia. The research shows that political risks not only affect FDI exits in the host economy, but that their impact is intensified through sanctioning policies. In our final empirical analysis, we take a different perspective that is still highly relevant for an emerging economy stuck in the geopolitical crisis while simultaneously requiring reforms that would guarantee sustainable long-term growth. This growth becomes possible by boosting productivity and building institutions that foster investment in human and physical capital, as well as innovation, in both the high and low-tech manufacturing sectors. Thus, in the empirical study on the innovation-performance link, we scrutinize the factors that might contribute to an improved efficiency of the Russian manufacturing sector