Application of the residue number system to the matrix multiplication problem

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Spatial variation in red deer density in a transboundary forest ecosystem

Forests in Europe are exposed to increasingly frequent and severe disturbances. The resulting changes in the structure and composition of forests can have profound consequences for the wildlife inhabiting them. Moreover, wildlife populations in Europe are often subjected to differential management regimes as they regularly extend across multiple national and administrative borders. The red deer Cervus elaphus population in the Bohemian Forest Ecosystem, straddling the Czech-German border, has experienced forest disturbances, primarily caused by windfalls and bark beetle Ips typographus outbreaks during the past decades. To adapt local management strategies to the changing environmental conditions and to coordinate them across the international border, reliable estimates of red deer density and abundance are highly sought-after by policymakers, wildlife managers, and stakeholders. Covering a 1081-km2 study area, we conducted a transnational non-invasive DNA sampling study in 2018 that yielded 1578 genotyped DNA samples from 1120 individual red deer. Using spatial capture-recapture models, we estimated total and jurisdiction-specific abundance of red deer throughout the ecosystem and quantified the role of forest disturbance and differential management strategies in shaping spatial heterogeneity in red deer density. We hypothesised that (a) forest disturbances provide favourable habitat conditions (e.g., forage and cover), and (b) contrasting red deer management regimes in different jurisdictions create a differential risk landscape, ultimately shaping density distributions. Overall, we estimated that 2851 red deer (95% Credible Interval = 2609–3119) resided in the study area during the sampling period, with a relatively even overall sex ratio (1406 females, 95% CI = 1229–1612 and 1445 males, 95% CI = 1288–1626). The average red deer density was higher in Czechia (3.5 km−2, 95% CI = 1.2–12.3) compared to Germany (2 km−2, 95% CI = 0.2–11). The effect of forest disturbances on red deer density was context-dependent. Forest disturbances had a positive effect on red deer density at higher elevations and a negative effect at lower elevations, which could be explained by partial migration and its drivers in this population. Density of red deer was generally higher in management units where hunting is prohibited. In addition, we found that sex ratios differed between administrative units and were more balanced in the non-intervention zones. Our results show that the effect of forest disturbances on wild ungulates is modulated by additional factors, such as elevation and ungulate management practices. Overall density patterns and sex ratios suggested strong gradients in density between administrative units. With climate change increasing the severity and frequency of forest disturbances, population-level monitoring and management are becoming increasingly important, especially for wide-ranging species as both wildlife and global change transcend administrative boundaries.publishedVersio

Leistungssteigerung metallgestützter Festelektrolyt-Brennstoffzellen (MSCs) durch gezielte Optimierungen des Anoden / Elektrolytverbunds

This work addressed the perfomance increase of metal-supported solid oxide fuel cells (MSCs) by optimization of the anode/electrolyte interface. Properties of the anode are strongly influenced by process parameters of the used screen printing process, a powder-based process. In comparison, properties of the electrolyte are influenced by process parameters of a specific physical vapor deposition (PVD) method. In this work, both processes were adapted to increase cell performance by improving cell design, cell layer thicknesses and microstructures. The goal of this work was the increase of the electrochemically active surface and the decrease of polarization resistances of the anode functional layer and ohmic resistances of the electrolyte. In a first step, cells developed in the PhD thesis of Rojek-Wöckner were reproduced and acted as a reference for further development. In a second step, the electrochemically active surface of the anode functional layer was raised. By reducing the sintering temperature, reduced coarsening of the microstructure resulted during processing. However, this was found to be detrimental due to undesired side effects. At low anode thicknesses, mechanical stability of the layered composite anode suffered because of low sintering between the particles. In addition, at high anode functional layer thicknesses, gas permeability suffered because of a both thick and fine-pored layer. Availability of fuel gas in the layered composite anode decreased, leading to increased anode polarization resistance. By increasing the layer thickness, a positive side effect appeared by lowering the surface roughness. A low surface roughness is a requirement for a gas-tight PVD-thin film electrolyte. Therefore, this concept with a thicker anode functional layer was used to successfully implement a cell design with a 2 μm thick PVD-electrolyte. This can be taken as starting point for future improvement of a 2 μm thin-film electrolyte. By increasing the sintering temperature of the functional layer in this design as well, stability and permeability of the layered composite anode were increased. Still, signs of gas diffusion limitation at high current densities became visible. To overcome this, a further improved cell design was implemented. An electrochemically inactive Ni/YSZ-interlayer was exchanged by an electrochemically active Ni/GDC-layer. Compared to the reference cell concept of Rojek-Wöckner, the improved cell design with a double-layered Ni/GDC-anode functional layer enabled a performance increase from 1,29 A/cm$^{2}$ to 1,79 A/cm$^{2}$ and therefore by 38%. The active surface and the permeability of the layered composite anode were increased. Moreover, mechanical stability and reproducibility were enhanced. Furthermore, the cell showed lower deflection after processing easing the handling of the cell during next processing steps like stack assembling [...

Liquidphase-Infiltration of porous carbon bodies with copper alloys

Zusammenfassung in englischer SpracheAbweichender Titel nach Übersetzung der Verfasserin/des VerfassersZiel dieser Arbeit war, durch den Zusatz von Legierungselementen zu Kupfer die Benetzbarkeit und die physikalischen Eigenschaften von gasdruck-infiltrierten Kohlekörpern zu verbessern. Beginnend mit einer Literaturrecherche wurden Benetzungswinkel, mechanische und elektrische Eigenschaften von Kupfer und Kupferlegierungen ermittelt und Kupferlegierungen für die experimentelle Durchführung ausgewählt. Im Rahmen der praktischen Arbeit wurden zunächst die Ausgangsmaterialien untersucht. In weiterer Folge wurden von ausgewählten Kupferlegierungen Benetzungsversuche auf Kohlenstoffsubstraten unter unterschiedlichen Atmosphären und Versuchsaufbauten durchgeführt. Die Gasdruck-Infiltration wurde mit ausgewählten Kupferlegierungen wiederholt und die physikalischen Eigenschaften der Komposite bestimmt.The aim of this master thesis was to improve wettability and physical properties of copper-carbon composites by adding alloying elements and using gas-pressure infiltration. Starting with a literature research, contact angles, mechanical and electrical properties of copper and copper-alloys were investigated. Copper alloys were used to do wettability experiments on carbon substrates by using different atmospheres and different experimental set-ups. After selection of appropriate copper alloys the infiltration was repeated by these alloys and physical properties of the composites were evaluated.11

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells

Sexual segregation results in pronounced sex-specific density gradients in the mountain ungulate, Rupicapra rupicapra

Abstract Sex-specific differences in habitat selection and space use are common in ungulates. Yet, it is largely unknown how this behavioral dimorphism, ultimately leading to sexual segregation, translates to population-level patterns and density gradients across landscapes. Alpine chamois (Rupicapra rupicapra r.) predominantly occupy habitat above tree line, yet especially males may also take advantage of forested habitats. To estimate male and female chamois density and determinants thereof, we applied Bayesian spatial capture-recapture (SCR) models in two contrasting study areas in the Alps, Germany, during autumn. We fitted SCR models to non-invasive individual encounter data derived from genotyped feces. Sex-specific densities were modeled as a function of terrain ruggedness, forest canopy cover, proportion of barren ground, and site severity. We detected pronounced differences in male and female density patterns, driven primarily by terrain ruggedness, rather than by sex-specific effects of canopy cover. The positive effect of ruggedness on density was weaker for males which translated into a higher proportion of males occupying less variable terrain, frequently located in forests, compared to females. By estimating sex-specific variation in both detection probabilities and density, we were able to quantify and map how individual behavioral differences scale up and shape spatial patterns in population density

Optimized Cell Processing As the Key to High Electrochemical Performance of Metal-Supported Solid Oxide Fuel Cells

Metal-supported solid oxide fuel cells (MSCs) are promisingcandidates for non-stationary applications like auxiliary powerunits (APUs) in heavy duty trucks or range extender systems forbattery electric vehicles. Due to limited space available forintegrating such systems especially in passenger cars, achievinghigh power density of MSCs is essential. The MSC concept ofPlansee SE, Austria was stepwise optimized by improvedprocessing of the electrodes and tailoring of the interfaces.Variations of cathode composition and sintering conditions wereinvestigated. Using LSC or LSC/GDC cathodes and Ni/GDCanodes with higher electrochemically active volume increased thecell performance significantly. Moreover, reducing the electrolyteto 2 μm resulted in further improvement of the performance.Finally, preliminary results of long-term operation of the PlanseeMSC for more than 1.000 h at 700 °C and 300 mA cm-2, as well aspost-mortem analyses, are presented