UNIBRA / DSEBRA – the German seismological contribution to AlpArray

UNIBRA was a joint initiative of German universities to install and maintain 74 seismic broadband stations at the beginning of the international AlpArray project in 2015 when the proposal for the 100 station broadband array DSEBRA was not yet approved by DFG. In this way, full participation of German teams in the AlpArray project could be secured. Most of these stations were deployed in southern Germany and a few in Austria. After approval in 2017 and installation of DSEBRA in 2018, the UNIBRA stations were replaced and further DSEBRA stations were deployed east of the SWATH-D array and also in Hungary. At that time, DSEBRA made up about one third of AlpArray’s temporary stations. After deinstallation of SWATH-D in autumn 2019 DSEBRA stations were used to reoccupy some of SWATH0-D’s critical sites. In spring 2020, the Covid19 pandemic started in Europe and it became unfeasible to move the DSEBRA stations to new sites. Instead of deinstallation, DFG allowed us to use remaining investment funds to continue the operation of DSEBRA at the current sites. As collaboration partners from Austria, Czech Republic, Poland, Slovakia and Hungary had already relocated many of their AlpArray stations to new sites towards the north-east and east of the Alps before Covid19 started, DSEBRA became part of the PACASE deployment with 214 temporary stations operated by partners from these countries and University of Lausanne. In summer 2022, new funds from DFG could be acquired by RU Bochum and LMU München to move 42 DSEBRA stations to Greece and Northern Macedonia and further 19 stations to Albania, Kosovo and Montenegro as part of the new AdriaArray project. The remaining DSEBRA stations stayed in Austria and Hungary to form a major part of AdriaArray’s backbone circling the Adriatic plate. With little exceptions, the DSEBRA stations have been in the field now without interruption for nearly 6 years. They massively contributed to the collection of a unique, large-scale and long-term seismological dataset which has enabled investigations into the structure of the crust and mantle beneath the greater Alpine area using receiver functions, shear-wave splitting, teleseismic body and surface wave tomography, local earthquake tomography and teleseismic full waveform inversion. Moreover, they allowed new insights into the seismic activity and hazard of active faults. DSEBRA will continue to do so in the framework of AdriaArray as part of an even larger seismic network comprising about 1300 permanent and temporary stations and doubling the size of AlpArray. Noise at the DSEBRA stations on the vertical component stayed below the Peterson high noise model by 20 dB over the entire seismic frequency band. Noise on the horizontal components was partially higher, in particular at low frequencies below 1 Hz. Thanks to special measures to avoid failures of mobile communication and battery charging and efforts to keep the low-power data logger running as long as possible in case of power failures, data availability of the DSEBRA stations reached extremely high values of 98% to 100%. The data were archived and disseminated on the EIDA node at LMU München during the experiment and transferred to the GEOFON for long-term archiving

Gas transfer through clay barriers

Gas transport through clay-rocks can occur by different processes that can be basically subdivided into pressure-driven flow of a bulk gas phase and transport of dissolved gas either by molecular diffusion or advective water flow (Figure 1, Marschall et al., 2005). The relative importance of these transport mechanisms depends on the boundary conditions and the scale of the system. Pressure-driven volume flow (“Darcy flow”) of gas is the most efficient transport mechanism. It requires, however, pressure gradients that are sufficiently large to overcome capillary forces in the typically water-saturated rocks (purely gas-saturated argillaceous rocks are not considered in the present context). These pressure gradients may form as a consequence of the gravity field (buoyancy, compaction) or by gas generation processes (thermogenic, microbial, radiolytic). Dissolved gas may be transported by water flow along a hydraulic gradient. This process is not affected by capillary forces but constrained by the solubility of the gas. It has much lower transport efficiency than bulk gas phase flow. Molecular diffusion of dissolved gas, finally, is occurring essentially without constraints, ubiquitously and perpetually. Effective diffusion distances are, however, proportional to the square root of time, which limits the relevance of this transport process to the range of tens to hundreds of metres on a geological time scale (millions of years). 2 Process understanding and the quantification of the controlling parameters, like diffusion coefficients, capillary gas breakthrough pressures and effective gas permeability coefficients, is of great importance for up-scaling purposes in different research disciplines and applications. During the past decades, gas migration through fully water-saturated geological clay-rich barriers has been investigated extensively (Thomas et al., 1968, Pusch and Forsberg, 1983; Horseman et al., 1999; Galle, 2000; Hildenbrand et al., 2002; Marschall et al., 2005; Davy et al., 2009; Harrington et al., 2009, 2012a, 2014). All of these studies aimed at the analysis of experimental data determined for different materials (rocks of different lithotype, composition, compaction state) and pressure/temperature conditions. The clay-rocks investigated in these studies, ranged from unconsolidated to indurated clays and shales, all characterised by small pores (2-100 nm) and very low hydraulic conductivity (K < 10-12 m·s-1) or permeability coefficients (k < 10-19 m²). Studies concerning radioactive waste disposal include investigations of both the natural host rock formation and synthetic/engineered backfill material at a depth of a few hundred meters (IAEA, 2003, 2009). Within a geological disposal facility, hydrogen is generated by anaerobic corrosion of metals and through radiolysis of water (Rodwell et al., 1999; Yu and Weetjens, 2009). Additionally, methane and carbon dioxide are generated by microbial degradation of organic wastes (Rodwell et al., 1999; Ortiz et al., 2002; Johnson, 2006; Yu and Weetjens, 2009). The focus of carbon capture and storage (CCS) studies is on the analysis of the long-term sealing efficiency of lithologies above depleted reservoirs or saline aquifers, typically at larger depths (hundreds to thousands of meters). During the last decade, several studies were published on the sealing integrity of clay-rocks to carbon dioxide (Hildenbrand et al., 2004; Li et al., 2005; Hangx et al., 2009; Harrington et al., 2009; Skurtveit et al., 2012; Amann-Hildenbrand et al., 2013). In the context of petroleum system analysis, a significant volume of research has been undertaken regarding gas/oil expulsion mechanisms from sources rocks during burial history (Tissot & Pellet, 1971; Appold & Nunn, 2002), secondary migration (Luo et al., 2008) and the capillary sealing capacity of caprocks overlying natural gas accumulations (Berg, 1975; Schowalter, 1979; Krooss, 1992; Schlömer and Kross, 2004; Li et al., 2005; Berne et al., 2010). Recently, more attention has been paid to investigations of the transport efficiency of shales in the context of oil/gas shale production (Bustin et al., 2008; Eseme et al., 2012; Amann-Hildenbrand et al., 2012; Ghanizadeh et al., 2013, 2014). Analysis of the migration mechanisms within partly unlithified strata becomes important when explaining the 3 origin of overpressure zones, sub-seafloor gas domes and gas seepages (Hovland & Judd, 1988; Boudreau, 2012). The conduction of experiments and data evaluation/interpretation requires a profound process understanding and a high level of experience. The acquisition and preparation of adequate samples for laboratory experiments usually constitutes a major challenge and may have serious impact on the representativeness of the experimental results. Information on the success/failure rate of the sample preparation procedure should therefore be provided. Sample specimens “surviving” this procedure are subjected to various experimental protocols to derive information on their gas transport properties. The present overview first presents the theoretical background of gas diffusion and advective flow, each followed by a literature review (sections 2 and 3). Different experimental methods are described in sections 4.1 and 4.2. Details are provided on selected experiments performed at the Belgian Nuclear Research Centre (SCK-CEN, Belgium), Ecole Centrale de Lille (France), British Geological Survey (UK), and at RWTH-Aachen University (Germany) (section 4.3). Experimental data are discussed with respect to different petrophysical parameters outlined above: i) gas diffusion, ii) evolution of gas breakthrough, iii) dilation-controlled flow, and iv) effective gas permeability after breakthrough. These experiments were conducted under different pressure and temperature conditions, depending on sample type, burial depth and research focus (e.g. radioactive waste disposal, natural gas exploration, or carbon dioxide storage). The interpretation of the experimental results can be difficult and sometimes a clear discrimination between different mechanisms (and the controlling parameters) is not possible. This holds, for instance, for gas breakthrough experiments where the observed transport can be interpreted as intermittent, continuous, capillary- or dilation-controlled flow. Also, low gas flow rates through samples on the length-scale of centimetres can be equally explained by effective two-phase flow or diffusion of dissolved gas

Nicht-Periodische Parkettierungen auf Basis von Eckkacheln für die Computergraphik

Rendering computer-generated images is both memory and runtime intensive. This is particularly true in realtime computer graphics where large amounts of content have to be produced very quickly and from limited data. Tile-based methods offer a solution to this problem by generating large portions of a specific content out of a much smaller data set of tiles. This dissertation investigates the use of corner tiles for this purpose—unit square tiles with color-coded corners. They tile the plane by placing them without gaps or overlaps such that tiles have matching corner colors. We present efficient algorithms to perform such a tiling that are both more flexible and less prone to artifacts than existing algorithms. We also present solutions to combinatorial problems that arise when using corner tiles, and introduce high-quality methods to perform the tile-based generation of two fundamental components of any rendering system: textures and two-dimensional sample point sets. The results of this dissertation are advantageous for both realtime and offline rendering systems where they improve state-of-the-art results in texture synthesis, image plane sampling, and lighting computations based on numerical integration

Marketing strategies for video games

Der Video- und Computerspielmarkt ist auch im Jahr 2013 sehr attraktiv und hat vor allem wegen den kommenden Konsolen der 8. Generation enormes Potenzial. Die Bachelorarbeit behandelt diesen Markt und geht darauf ein, wie eine erfolgreiche Teilnahme am elektronischen Unterhaltungsmarkt erzielt werden kann. Im Mittelpunkt der Analyse liegen hierbei die Wichtigkeit von Marketingstrategien im Prozess eines Marketingplans und die Antwort auf die Frage, welche Marketinginstrumente in der Kommunikationspolitik effizient sind. Dabei werden auch die unterschiedlichen Erfolge von klassischen und nicht-klassischen Medien untersucht und zwei crossmediale Fallbeispiele analysiert

Frameless rendering

This thesis studies a render paradigm of computer graphics called "frameless rendering". Breaking with the traditional approach in computer graphics, it allows an image to be displayed even when it has not been finished yet. It ensures that the user is constantly provided with the possibility to immediately see the results of his interactions on screen - even if this means to see only partially up-to-date imagery. The idea differs from classic single-buffered approaches in two aspects. First, the image is not rendered from top to bottom; rather the next to-be-computed pixel is always chosen at random. Second, the approach allows to display the currently available image at every point in time. In the most strict consequence this means that there really are no coherent images anymore, no connected image sequences, no frames per second, no frames at all - hence the name "frameless rendering". Frameless rendering has evolved to an alternative render paradigm, moving from a camera-based to a perception-based way to understand the image generation process in computer graphics. However, only very few researchers have dedicated their work to this idea since its introduction. No "theory" of frameless rendering has been developed ever since and only a couple of researchers have tried to formalize the process in some way. We fill this gap by providing an in-depth exploration of this novel approach to digital image synthesis. We examine the effectiveness of the traditional random pattern as a sampling order during frameless rendering and analyze the suitability of alternative deterministic approaches. In addition, we reformulate the rendering equation to account for the frameless rendering approach and show that by finding a suitable reconstruction filter, frameless rendering can deliver better imagery than traditional rendering approaches in scenarios of a very limited computational budget

Accurate spectral analysis of two-dimensional point sets

We investigate accuracy issues regarding the spectral analysis of two-dimensional point sets. We demonstrate the sensitivity of amplitude/power spectrum and radial statistics to the type of Fourier transform and formulate recommendations for crucial analysis and formatting parameters. The goal of these recommendations is to facilitate the comparison of different point-set generation methods with respect to their spectral characteristics

Semi-Stochastic Tilings for Example-Based Texture Synthesis

We investigate semi-stochastic tilings based on Wang or corner tiles for the real-time synthesis of example-based textures. In particular, we propose two new tiling approaches: (1) to replace stochastic tilings with pseudo-random tilings based on the Halton low-discrepancy sequence, and (2) to allow the controllable generation of tilings based on a user-provided probability distribution. Our first method prevents local repetition of texture content as common with stochastic approaches and yields better results with smaller sets of utilized tiles. Our second method allows to directly influence the synthesis result which—in combination with an enhanced tile construction method that merges multiple source textures—extends synthesis tasks to globally-varying textures. We show that both methods can be implemented very efficiently in connection with tile-based texture mapping and also present a general rule that allows to significantly reduce resulting tile sets

Towards a Standardized Spectral Analysis of Point Sets with Applications in Graphics

We investigate common pitfalls in the spectral analysis of point sets based on amplitude/power spectrum and radial statistics. We demonstrate the sensitivity of these measurements to the type of Fourier transform and formulate recommendations for crucial analysis and formatting parameters. Following these guidelines elevates comparability between different point generation methods with respect to their spectral characteristics.

Blue noise sampling with controlled aliasing

In this article we revisit the problem of blue noise sampling with a strong focus on the spectral properties of the sampling patterns. Starting from the observation that oscillations in the power spectrum of a sampling pattern can cause aliasing artifacts in the resulting images, we synthesize two new types of blue noise patterns: step blue noise with a power spectrum in the form of a step function and single-peak blue noise with a wide zero-region and no oscillations except for a single peak. We study the mathematical relationship of the radial power spectrum to a spatial statistic known as the radial distribution function to determine which power spectra can actually be realized and to construct the corresponding point sets. Finally, we show that both proposed sampling patterns effectively prevent structured aliasing at low sampling rates and perform well at high sampling rates

Farthest-Point Optimized Point Sets with Maximized Minimum Distance

δX=0.009, ¯ δX=0.469 input δX=0.049, ¯ δX=0.645 1/4 iteration δX=0.079, ¯ δX=0.756 1/2 iteration δX=0.772, ¯ δX=0.865 1 iteration δX=0.814, ¯ δX=0.905 2 iterations δX=0.925, ¯ δX=0.932 63 iterations Figure 1: Farthest-point optimization of a random point set with 1024 points. Both the global minimum distance δX and the average minimum distance ¯ δX increase rapidly using our optimization technique. After one iteration the point set is already well-distributed. Efficient sampling often relies on irregular point sets that uniformly cover the sample space. We present a flexible and simple optimization strategy for such point sets. It is based on the idea of increasing the mutual distances by successively moving each point to the “farthest point, ” i.e., the location that has the maximum distance from the rest of the point set. We present two iterative algorithms based on this strategy. The first is our main algorithm which distributes points in the plane. Our experimental results show that the resulting distributions have almost optimal blue noise properties and are highly suitable for image plane sampling. The second is a variant of the main algorithm that partitions any point set into equally sized subsets, each with large mutual distances; the resulting partitionings yield improved results in more general integration problems such as those occurring in physically based rendering