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Towards lattice Boltzmann models for climate sciences : The GeLB programming language with applications
Get PDFThe complexity of Earth system models (ESMs) is continuously increasing a both quantitatively (higher spatio-temporal resolution for existing models) and qualitatively (accounting for additional processes). These trends are sustained by growing capabilities of computers and (equally important) by innovative algorithms. Better algorithms can lead to more accurate and/or more efficient numerical solutions. Efficiency attracted more attention during the last decade when, due to thermal limitations, the driving force behind increased computing performance has shifted from higher clock-frequencies (lower latencies) to more hardware parallelism (higher throughput). Not all numerical algorithms are suited for the new massively-parallel machines a some established approaches can reach plateaus in terms of performance scalability, which motivates ongoing research to find alternatives that thrive on the new hardware. In this thesis the potential of the lattice Boltzmann method (LBM) is analyzed, as a promising alternative for modeling processes relevant to ESMs . During the last two decades, this relatively new approach was successfully applied to many flow problems in engineering (simulation of multi-phase and multi-component flows, melting processes, flows in porous media, and direct numerical simulation (DNS) of turbulence). At the core of any LBM algorithm is a simplified physical landscape inspired by the kinetic theory of gases, with a mesoscopica particles which interact (collisions) and then propagate freely (streaming). This idealized dynamics (usually with local interactions) leads to algorithms which are particularly suited for parallel execution a a key property, which is also interesting for ESMs . However, the impact of LBM on Earth system models was small so far, due to limitations of the early LBM algorithms. The method deserves reconsideration, due to recent advances on improving its stability, a simplified implementation of accurate body-forces, and accurate simulation of thermal flows. This thesis adds two main contributions to this direction: (a) From a computer science (CS) / technical perspective, the new GeLB domain-specific language (DSL) is introduced, to facilitate testing and development of new LBM algorithms. By isolating many of the technical implementation side-issues away from the core physical algorithm, this new tool aims to counteract some of the a fragmentationa of the LBM research, by: (i) shortening the time to develop a parallel simulation from an algorithm idea, (ii) serving as a basis for objective comparisons of different physical algorithms, and by (iii) facilitating sharing of algorithms. (b) From a physical point of view, several flow-problems related to climate sciences are simulated, taking advantage of the recent progress in the LBM research literature. First, the Rayleigh-Benard ( RB ) problem is simulated (in 2D and 3D configurations). The evolution of the flow in this problem is driven by buoyancy forces which can trigger convection (similar to convection in the atmosphere, or to the intermittent bursts of deep-reaching convection, which significantly influence the composition and circulation of oceanic water-masses). As a last application, simulation results are shown for the wind-driven ocean circulation (WDOC) of an idealized barotropic ocean, to which one of the more recent LBM algorithms is applied for the first time (first with an idealized geometry, then with a realistic global land-mask)
Brain maturation throughout adolescence : an EEG study
Get PDFObjective: Adolescence is characterised by a genuine interest in new experiences and an increased sense of responsibility. The aim of this study was to investigate changes in brain maturation that underlie task-relevant behaviour and the relation of these changes to novel impressions during the transition from childhood into adolescence and then young adulthood. We hypothesized that, with development, improved target detection abilities and reduced distractibility will be characterised by an increased involvement of frontal brain regions within the fronto-parietal brain network during novel processing and target detection. Methods: In a cross-sectional study, a classical visual oddball task (n = 159) and a novelty visual oddball task (n = 84) were utilized in combination with EEG measurements to investigate brain maturation between late childhood and young adulthood (8 to 30 years of age). Developmental changes of late ERP components and concurrent delta (0.5 - 4 Hz) and theta (4 - 7 Hz) oscillations were analysed using regression models. Pre-stimulus amplitude and post-stimulus amplitude modulation, inter-trial phase coherence of local maxima and inter-electrode spatial phase coherence were assessed. Results and Discussion: A general decline in reaction time and late ERP latency (novelty N2, P3a and P3b) with age was observed and may depend on task performance. The frontal novelty N2 amplitude decreased while the P3a amplitude increased with age. This opposing developmental trend may relate to a compensatory mechanism for immature P3a-related cognitive functions, such as attention control. The pre-stimulus amplitudes of delta and theta oscillations decreased while post-stimulus amplitude enhancements and inter-trial phase coherence increased with age. Both effects seem to underlie maturation of the P3b amplitude, even though this cannot be observed directly in ERP amplitude measurements. Post-stimulus theta inter-electrode spatial phase coherence originating from frontal electrode sites increased with age during novel and target stimulus processing, indicating prolonged maturation of the fronto-parietal network that underlies target detection and novel processing. Conclusion: Functional brain networks involving the frontal cortex, such as the fronto-parietal network, mature until young adulthood, thereby affecting slow-wave oscillations on a local and global scale alongside late frontal ERP components. Brain maturation during adolescence may lead to a reduction of spontaneous slow-wave oscillations and an enhancement of amplitude modulation and regional and inter-regional precision of timing of event-related oscillations within the P3 time-window. Thus, brain maturation underlying task-related behaviour and reduced distractibility is versatile. Significance: Combined analysis of developmental trajectories of late ERPs, concurrent changes in spontaneous and task-modulated brain oscillations and their embedding within functional brain networks (e.g., the fronto-parietal network) is important to estimate how brain maturation relates to abilities of cognitive control during the transition into adolescence and young adulthood. It is critical to extend our understanding of healthy brain maturation as excessive brain plasticity during adolescence raises the sensitivity to the environment and learning experiences, and its outcome may have long-term positive or negative impact on personal opportunities in life and mental health
Macrofaunal impact on biogeochemical turnover in German Bight sediments
No full textMacrofaunal bioturbation is an important mechanism for the enhancement of remineralization and biogeochemical cycling in marine sediments. Reduction of bioturbation activity may accordingly have far-reaching negative implications for general ecosystem performance. This is especially the case for shallow shelf seas, such as the German Bight, which account for 50% of global benthic remineralization, although they cover only 7% of the total sea surface. Increasing anthropogenic activities (e.g. wind farm construction) in these shallow shelf seas have intensified the need for reliable quantifications and predictions of macrofaunal bioturbation activities and resulting biogeochemical processes. The aim of this thesis was,thus, to develop easily applicable concepts that allow for the quantification of sediment reworking and the prediction of bioirrigation. In order to simplify the quantification of sediment reworking, which can so far only be assessed experimentally, I compared two of the most commonly applied methods (sediment profile imaging (SPI) and standard slicing technique (ST)). In addition, the time-saving and easily applicable SPI method was tested for its suitability to assess sediment reworking from cylindrical multi-corer samples (Manuscript I). The results suggested that SPI is suitable and even more accurate than ST for the investigation of sediment reworking activity. This omits the previously necessary need for timeconsuming slicing or the complex transfer into rectangular aquaria. These findings will facilitate studies on spatiotemporal patterns of sediment reworking activity in the German Bight. Such studies are of special interest as the bioturbation potential (BPc), which was previously often applied to estimate the potential of communities to rework the sediment, does not correlate with actual sediment reworking rates (Manuscript II). Surprisingly BPc, which includes sediment reworking traits (i.e. mobility and reworking mode) but no specific bioirrigation traits, rather correlated with bioirrigation activity and nutrient fluxes of silicate, ammonium, nitrate, and nitrite (Manuscript II). To overcome ambiguity of BPc, I developed the irrigation potential (IPc), as an adaptation from BPc (Manuscript III). By incorporation of bioirrigation effect traits (i.e. burrow type, feeding type, injection pocket depth), IPc was specifically designed to predict bioirrigation and its influence on biogeochemical processes (Manuskript III). I could demonstrate that, in contrast to BPc, the modified index provides an accurate quantitative measure of macrofaunal bioirrigation for both single species and entire communities of various infaunal species, if the index is calculated with ash free dry body mass. IPc provided better estimations of phosphate, silicate, ammonium, nitrate and nitrite fluxes than BPc (Manuscript IV). The estimation of silicate, ammonium, nitrate, and nitrite fluxes may be further increased if IPcis calculated in wet body mass instead of ash free dry body mass. Wet body mass thereby serves as a proxy of the irrigated sediment volume. In general, IPc could become a valuable tool to support ecosystem management and future investigations on the effects of anthropogenic activities on biogeochemical turnover in shallow shelf seas. Findings of Manuscript IV however also demonstrated that IPc is a crucial but insufficient parameter for the modelling of sediment biogeochemical processes because these also dependent on environmental conditions (e.g. temperature, sediment organic matter content, permeability). A newly proposed temperature term (IcT) (Manuscript III) may provide a tool to identify spatiotemporal variations in macrofaunal bioirrigation activity. There is however a need to determine further how IPcor IcT relate to biogeochemical cycling under different environmental conditions as well as how the respective macrofaunal traits are affected by environmental parameters
Effects of Augmented Reality on Student Achievement and Self-Efficacy in Vocational Education and Training
Get PDFThis study aimed to test the impact of augmented reality (AR) use on student achievement and self-efficacy in vocational education and training. For this purpose, a marker-based AR application, called HardwareAR, was developed. HardwareAR provides information about characteristics of hardware components, ports and assembly. The research design was quasi experimental with pre-test post-test that included a control group. The study was conducted with 46 undergraduate students in the Computer Hardware Course. Computer hardware course achievement test, motherboard assembly self-efficacy questionnaire and unstructured observation form were used in the study for data collection purposes. The control group learned the theoretical and applied information about motherboard assembly by using their textbooks (print material) while students in the experimental group used HardwareAR application for the same purpose. It was found that the use of AR had a positive impact on student achievement in motherboard assembly whereas it had no impact on students self-efficacy related to theoretical knowledge and assembly skills. On the other hand use of AR helped learners to complete the assembly process in a shorter time with less support. It is concluded that compared to control group students, experimental group students were more successful in computer hardware courses. This result shows that AR application can be effective in increasing achievement. It was concluded that AR application had no effect on students motherboard assembly theoretical knowledge self-efficacy and motherboard assembly skills self-efficacy. This result may have been affected from the fact that students had high levels of theoretical knowledge and assembly skills before the implementation. Observations showed that AR application enabled students to assemble motherboard in a shorter time with less support. It is thought that simultaneous interaction between virtual objects and real world provided by the AR application is effective in reducing assembly time. The students who were able to see the process steps and instructions directly with the help of HardwareAR application could complete the assembly by getting less help. Considering these results, it can be argued that, thanks to simultaneous interaction it provides, AR offers an important alternative for topics that need learner application and practice
Construction and Evaluation of Gas Feed-in System, Electrodes and Gas Exhaustion System applied to Low Pressure Plasma Coating Processes
Get PDFPlasma polymerization is a technique used to deposit functional thin film coatings (nanometer until some micrometer thickness) on different materials surface. The thin film coating is deposited directly from a partially ionized precursor gas subjected to the effect of the plasma onto the surface of the substrate, which is placed in a low-pressure plasma chamber. This coating process regarding the achievement of the desired properties is in general well developed. The challenge is based on the scaling up process in respect to a large volume coater. Concerning this aspect only very few and rough information are available for constructors in respect to lay out of low-pressure plasma coater with the aim to achieve homogeneous coating deposition rate as well as homogeneous coating properties over all the products surfaces in contact with the plasma. The aim of the present research work is mainly to investigate the potential of guiding the gas flow inside a large volume plasma polymerization-system and to investigate how this gas guiding directly influences the coating homogeneity as well as the coating properties. Thereby the creation of construction guidelines to support future developments under the frame of low-pressure plasma technology is part of the task. To achieve this purpose, gas feed-in system, gas exhaustion system and electrode geometry were investigated. Taking into consideration that experimentally the local gas flow behavior cannot be directly measured inside a PECVD system computational fluid dynamics (CFD) simulations were carried out using the commercial software Ansys Fluent 16.0A to investigate the gas flow behavior. Additionally, to get more knowledge about the electric field created by the RF-electrode in combination with the powered electrode, electrostatic simulations were done using the commercial software Ansys Maxwell 16.0A . Gas flow simulations showed clearly that the gas exhaustion system influences the local gas flow much more (in intensity and range) in comparison to the gas feed-in system. In this regard, a perforated polymeric plate was developed to reduce the influence of the gas exhaustion system and it was named under the frame of this work as a Baffle Platea . Coating experiments exhibited a clear improvement in the coating deposition homogeneity due to the installation of the Baffle Plate. The construction guidelines for gas feed-in systems and gas exhaustion systems were defined using gas flow simulations. To evaluate the simulation results, a non-uniformity coefficient was defined to define a construction border. For this work, the construction border was established at non-uniformity coefficient equals 5%. It means that construction layout which leads to non-uniformity coefficient higher than 5% will be not recommended for this application. From the analyzed parameters of the gas feed-in system, the pipe section area was the most relevant influencing the homogeneity of gas distribution. Regarding the gas exhaustion system, the simulation results showed that the distance between the Baffle Plate and the top of the chamber has a huge influence in the homogeneity of the gas exhaustion. Coating experiments were performed to correlate the distribution of the coating deposition rate in addition to the coating properties with the local gas velocity and the local electric field. Therefore, the construction guidelines must be supplemented with hints how to handle the influence of the walls (chamber, electrodes and product holder systems). The selected construction guidelines revealed to be useful for the development and construction of a new low-pressure plasma chamber of about 3 mA . Following the knowledge acquired from this research work the realized coating showed on an area of 2 mA a standard deviation of the deposition rate less than 17%. With this it had been demonstrated, that especially for large volume PECVD-systems following the rules of the construction guidelines is essential
Dust variability and provenance in the Pacific and Atlantic sectors of the Southern Ocean
Get PDFThe effect of dust on the global climate results from processes in the atmosphere and in the ocean. On the one hand, dust in the atmosphere scatters or absorbs incoming sunlight (a direct influence on climate) or modifies cloud properties (an indirect influence on climate). On the other hand, dust can stimulate the marine productivity by supplying iron to the ocean (iron fertilization). Increased dust fluxes, especially during glacial periods, may have enhanced the marine productivity in the Southern Ocean, which was likely responsible for an atmospheric CO2 reduction of 40 ppmv. Subsequently, the Southern Ocean is a crucial component of the global climate system. Analyzing marine dust records deposited downwind of the major Southern Hemisphere dust source areas provides valuable information on paleoclimate changes in source areas characteristics (e.g. aridity, precipitation, wind) and within the dust transporting winds. Based on these analyses, this dissertation aims to contribute to a better understanding of paleoclimate changes inferred from the dust variability of marine dust records from the Southern Ocean. To achieve this goal, four manuscripts are presented in chapters 3, 4, 5 and 6, which each utilizes different methodical approaches. A comprehensive set of sediment surface samples and sediment cores from the Pacific and Atlantic sectors of the Southern Ocean was used to conduct dust provenance, grain size and biomarker analyses. Manuscript one (chapter 3) presents the first combined lithogenic flux and dust provenance analysis extracted from sediment surface samples from the Pacific sector of the Southern Ocean, which allows to better understand Holocene dust variability. The lowest lithogenic fluxes detected in open ocean surface sediments are interpreted as solely derived from atmospheric dust. The provenance analysis reveals that sources in central and southeast Australia dominate the dust supply to the Pacific sector of the Southern Ocean during the Holocene. The second manuscript (chapter 4) aims to identify dust fluctuations over glacial-interglacial timescales. Grain size analysis were performed on two sediment cores located in the Pacific and Atlantic sectors of the Southern Ocean, respectively. The results reveal opposing grain size patterns with coarser glacial grain sizes in the Pacific sector compared to finer glacial grain sizes in the Atlantic sector. Additional iron and lithogenic flux records provide consistent results for both sectors with increased glacial values indicating that more dust was available in potential source areas. The inconsistent grain size patterns are the result of different responses to glacial climate conditions in the source areas coupled with variations within the Southern Westerly Winds favoring or hampering the erosion of coarse dust particles. A biomarker perspective on different terrigenous and marine proxies (dust, productivity and sea surface temperature) from the polar and subpolar zones of the Pacific sector of Southern Ocean is given in the third manuscript (chapter 5). Reconstructed sea surface temperatures reveal modern summer temperatures confirming that the analyzed surface samples are representative for the Holocene. The results inferred from n-alkanes and brGDGTs (organic tracers for terrigenous material) clearly reveal that the samples located in the open ocean were solely derived from atmospheric dust. In the fourth manuscript (chapter 6), the Drake Passage throughflow is reconstructed using the sortable silt mean grain size as proxy for changes in bottom current speed. The results illustrate a substantial glacial throughflow reduction, which is consistent with a decrease of the Southern Westerly Winds core zone over Patagonia. The weakened winds reduce, in addition to other factors (e.g. sea ice), the strength of the Antarctic Circumpolar Current, which in turn affects the bottom current speed. The Southern Westerly Winds are the main dust transport medium in the Southern Hemisphere, so that changes within this wind belt can affect the long-range dust transport. Ultimately, this thesis advances the understanding of the Southern Ocean dust variability with implications for paleoclimate reconstructions and clearly illustrates the versatile application of dust analyses in paleoclimate studies. The combination of different methods, the large spatial coverage and the temporal resolution of the surface samples and sediment cores used provide a unique dataset for the Southern Ocean
Multiferroic bismuth ferrates : Synthesis, structure-property relationships and phase transformations
Get PDFNowadays, great efforts are made to understand the rich physics of materials that show interesting magnetic, electronic, optic, photocatalytic or even multiferroic properties. Within the scope of this dissertation two of such potentially very promising compounds, perovskite-type (Bi1-xFex)FeO3 and mullite-type Bi2Fe4O9, were synthesized and studied. The primary focus was placed to understand the synthesis conditions that strongly influence the resulting phase composition, structures and corresponding properties. The second main focus was to study the structure-property relationships based on the average crystallite size, chemical composition and phase composition of the materials. It could be shown that the phase system Bi2O3 - Fe2O3 is very complex and sensitive to a lot of synthesis parameters such as the type of complexing agent, pH value as well as calcination time and temperature
Professional Desires and Career Decisions: Effects of Professional Interests, Role Models, and Internship in Lower Secondary School
Get PDFContext: Following the social cognitive career theory of Lent, Brown, and Hackett (1994), the current study examines the effect of role models professions and practical internship experiences on the choice of professional environment independent of professional interests. Embedded in the Swiss context with its strong vocational training system, the paper outlines to what extent the desired professional environment is realized in the chosen apprenticeship two years later and how this realization can be predicted. The theoretical model proposes that students form direct professional experiences during their first internship(s). If those experiences are positive, students choose an apprenticeship in the same professional environment. Students have indirect (vicarious) professional experiences through their role models. If those experiences are positive, students choose an apprenticeship in the role model s professional environment. The study examined whether, independent of professional interests, direct experiences in internships and indirect experiences through role models professions predict the realization of a desired professional environment in an apprenticeship. Method: The longitudinal sample consists of N = 348 seventh- and ninth-grade students from four German-speaking Swiss cantons. Professional interests and environments were measured using standardized questionnaires. The professional environments of the desired professions, the chosen apprenticeships, the role model s professions, and the internship s professions were coded using Holland s (1997) interest types: realistic, investigative, artistic, social, enterprising, and conventional (RIASEC). Results: In 53% of the cases, students chose an apprenticeship in the professional environment they desired. In 53% of the cases, the chosen professional environment corresponded with the professional environment of the student s two most important role models. In 39% of the cases, those role models were their parents. By means of logistic regression analyses, we can show that role models professional environments and the professional environment of the first internship influenced the realization of the desired professional environment at the end of lower secondary school, independent of the effect of the individuals interests. Conclusions: Results show that direct professional experiences in internships and indirect experiences of role models influence the realization of the desired professional environment, independent of professional interests. In a contextual approach, career counselling should include the role model s profession and how it corresponds with the client s interests and professional desires. Moreover, role models, especially parents, have a responsibility to reflect on how their goals influence students career choice processes
Freshwater variability in the Arctic Ocean and subarctic North Atlantic
Get PDFIn the past decades, observations in the upper Arctic Ocean and subpolar North Atlantic have shown signicant freshwater changes that were in each region mainly attributed to independent processes. Both regions are sensitive to changes in the density stratication with possible implications for the ocean/atmsophere heat exchange and the deep convection. Thus changes in the freshwater content of the Arctic Ocean and subpolar North Atlantic have the potential to impact the climate locally and globally. The objectives of the present study are to investigate the freshwater content (co)variability of the upper Arctic Ocean and subpolar North Atlantic, to identify the processes causing the observed changes in freshwater content and to analyse possible drivers of these processes. To investigate the freshwater content variability I used objectively mapped salinity fields for the subpolar North Atlantic and Nordic Seas, and objectively mapped liquid freshwater inventories and sea ice volume estimates from the Pan-Arctic Ice Ocean Modeling and Assimilation product for the upper Arctic Ocean. To explore possible links, I compared the liquid freshwater content of the subarctic North Atlantic (SANA; combination of subpolar North Atlantic and Nordic Seas) with the sum of liquid and solid freshwater content of the upper Arctic Ocean from the observational and assimilation products. I found a distinct anti-correlation of the freshwater anomalies in these two regions between 1992 and 2013 with anomalies of the same magnitude. An analysis of freshwater fluxes from the global Finite Element Sea ice Ocean Model and the Common Ocean-ice Reference Experiment version 2 atmospheric forcing data set suggested that the observed freshwater variations resulted from changing freshwater transports. Variations in the Arctic freshwater export to the North Atlantic are found to be most important for the total freshwater content variability of the upper Arctic Ocean and for the liquid freshwater content variability of the western SANA. The eastern SANA freshwater content seems to be mainly influenced by the exchange with the subtropical North Atlantic. Furthermore, this study reveals that the observed freshwater changes are correlated with the Arctic and North Atlantic Oscillation indices. Therefore I suggest that a changing freshwater export from the Arctic Ocean to the SANA responds to decadal alternations of the dominant large-scale atmospheric variability. Thereby the export through the Canadian Arctic Archipelago is associated to different patterns of the atmospheric and oceanic pressure and circulation than the export through the Fram Strait and Barents Sea Opening. I propose, that the recently observed rapid changes in the SANA and upper Arctic Ocean freshwater content resulted from an interplay of these different driving patterns causing parallel changes in the freshwater export on both sides of Greenland. According to the present phase of the decadal alternations of the atmospheric variability and the final years in my freshwater content time series, the fresh water accumulated in the Arctic Ocean during the previous decades started to be released into the SANA. This release might continue in the following years and could have the potential to impact the Atlantic Meridional Overturning Circulation and the oceanic heat release to the Arctic atmosphere and sea ice
Livelihood Vulnerability of Coastal Communities in Fiji and Solomon Islands to Changes in Reef Resource Availability and Climate Change
Get PDFFisheries support the livelihoods of millions of people globally. In the Pacific Islands most coastal communities have traditionally been highly dependent on marine resources. Coral reefs are particularly important to these communities as their main source of animal protein and livelihoods. Climate change and human-induced stresses have led to high mortality of coral reefs globally. These changes can lead to a decline in reef fisheries resources, thereby affecting the livelihoods of fisheries-dependent communities. The high dependence of coastal communities on marine resources potentially makes them highly vulnerable to any change in the status of these resources. This research examined the livelihood vulnerability of coastal communities in Fiji and Solomon Islands to a decrease in reef resources resulting from social-ecological changes and the capacity of households and communities to cope with or adapt to these changes. Data from household interviews, key informant interviews and focus group discussions were collected using mixed methods from ten communities in Fiji and nine in the Solomon Islands