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The Effect of Population and Structural Biases on Social Media-based Algorithms - A Case Study in Geolocation Inference Across the Urban-Rural Spectrum
Get PDFMuch research has shown that social media platforms have substantial population biases. However, very little is known about how these population biases affect the many algorithms that rely on social media data. Focusing on the case study of geolocation inference algorithms and their performance across the urban-rural spectrum, we establish that these algorithms exhibit significantly worse performance for underrepresented populations (i.e. rural users). We further establish that this finding is robust across both text- and network-based algorithm designs. However, we also show that some of this bias can be attributed to the design of algorithms themselves rather than population biases in the underlying data sources. For instance, in some cases, algorithms perform badly for rural users even when we substantially overcorrect for population biases by training exclusively on rural data. We discuss the implications of our findings for the design and study of social media-based algorithms
Applying Global Governance agenda in post-Soviet states : the case of EITI in Kazakhstan and Kyrgyzstan
Get PDFCurrent explanations of global governance fail to incorporate in their analysis the importance of both structural domestic and contextual factors in which global governance initiatives operate. More specifically, it is necessary to further investigate what global governance means for specific non-democratic regions and actors involved in the process of global governance. Current research on global governance is characterised by the concept of a static dichotomy between the international and domestic spheres. In contrast, the present thesis aims to offer a more sophisticated account of the interplay between these two spheres; it therefore presents an empirical and theoretical framework that is able to capture the transboundary character of global governance encompassing both the international and domestic context. Using the case of an international governance initiative, the Extractive Industries Transparency Initiative (EITI), this PhD thesis investigates how the standardised practices of global governance arrangements are implemented in the post-Soviet and autocratic states of Kazakhstan and Kyrgyzstan. Adopting a comparative case study perspective, the study examines, first, how shared self-regulatory governance practices as prescribed under the EITI function in authoritarian countries, second, whom or which constituencies they serve, and, finally, how the initiativea s legitimacy can be assessed. Most importantly, in analysing the EITI, the thesis aims to assess the role of different actors (state and non-state) within non-democratic countries. Furthermore, in light of the EITIa s focus on fighting corruption in the extractive sector, the project aims to contribute to the debate on the resource curse in the political economy. The results of my thesis indicate that the EITI in Kazakhstan and Kyrgyzstan operates as a dysfunctional platform for cooperation that is detached from its initial purpose. The research further demonstrates that the regime type, the countrya s political institutions and the inherited Soviet legacy have considerably affected the functioning of the Initiative. In light of these observations, the thesis urges scholars and policy practitioners to more thoroughly consider the context in which global governance takes place
North Atlantic Current in model and observations: Transport variability, flow paths and hydrography
Get PDFThe North Atlantic Current (NAC) is subject to variability on multiannual to decadal time scales, influencing the transport of volume, heat and freshwater from the subtropical to the eastern subpolar North Atlantic (NA). Current observational time series are either too short or too episodic to comprehensively study the processes involved, therefore models are used to complement the observations. For this study, moored and ship-based observations from three sections along the NAC pathway, satellite altimetry data and 1/20 degree hindcast VIKING20 model configuration (1960-2008) output are used. They are investigated and compared to describe hydrography, flow field and transport time series. The flow into and out of the NA is monitored at 47 degree N, the flow from the western into the eastern basin of the NA is captured by a section at the western flank of the Mid-Atlantic Ridge (MAR), and the distribution in the eastern basin of the NA is observed at the OVIDE line. These three sections thus provide an extensive picture of the flow
Versorgungsforschung bei Demenz
Get PDFBackground: In the last few years, health services research has become an important field of research and has attracted higher attention than ever before. As the so called last mile of the health care System the field is supposed to analyze complex and conflicting problems of health care and eventually develop and evaluate measures to improve health care. The aim of the present endeavor is to integrate three conducted research studies on specific questions in dementia care into the current health services research activities in dementia. It provides an overview of the current care situation, examined topics and used methods. Methodology: In the present study, a systematic literature search has been conducted investigating the health care situation of persons with dementia in Germany between 2011 and 2016. Current research activities are presented as well as the actual health care situation of dementia patients, including the used methods and data sources. The cumulative dissertation at hand includes the author s studies investigating and analyzing trends in the use of antipsychotics, time until nursing home admission and feeding tube provision in dementia patients. Results: An increase of research activities in the field of health care research in dementia could be observed during the past five years. The identified studies reveal a very broad thematic variety. The research landscape is characterized by quantitative studies, mainly in outpatient settings and by observational studies. Mostly, a connection between primary and secondary data is not established. In some areas of pharmaceutical supply deficits have been revealed. In addition, an examination of the care situation is often independent of the stage of the disease and the palliative phase of dementia is frequently not considered. A clear research gap can also be shown for inpatient hospital care. Conclusion: Over the last few years, health care research has evolved into an important discipline and will continue to grow due to current policy measures in Germany. Also, an increase in studies in health services research investigating dementia could be identified in recent years. The wide range of topics covered by the fielda s research reveals deficits. The author s three pioneering studies provide information on specific care situations and the status quo of the care of dementia patients for the first time
The Central Mozambique continental margin : Its tectonic evolution as the centrepiece of the initial Gondwana break-up
Get PDFA consolidated knowledge of the formation and dispersal of the former supercontinents reveals important evidence for the eartha s climate and biosphere in the past and contribute to the prediction of their future evolution. Nowadays, a main objective is the investigation of the initial break-up of the continental assembly of Gondwana that serves as a constraint for its subsequent dispersal and the evolution of all oceans and seas in the southern hemisphere. Evidence of the early rifting stages are expected at the margins of Southeast Africa and East Antarctica, whereas the latter one is difficult to access, due to its remote position and ice coverage. To understand the driving forces and the chronology of the break-up and of the massive volcanism additional detailed knowledge of the crustal setting along the margins of Southeast Africa is required. Therefor, a new geophysical dataset was acquired with the RV Sonne in the northern Mozambique Basin at the beginning of year 2014. This comprises a deep seismic sounding profile across a so-far unknown structural high, the Beira High. Additional gravity and magnetic data were systematically recorded across the entire northern Mozambique Basin. Based on velocity, amplitude, density and magnetic modelling, a geological model of the continental margin of Central Mozambique was prepared. A new compilation of all available magnetic data in the Mozambique Basin reveals information about the age of the sea floor, which serves as constraint for the reconstruction of the initial Gondwana break-up. The study depicts a continental origin of up to 23 km thick and partly highly intruded crust at Beira High. In the adjacent coastal areas of the south-western part of Central Mozambique, 7 km thin crust is observed, which is covered by more than 11 km thick sediments and implies the continuation of the continent-ocean transition towards onshore Mozambique. This is in clear contrast to the narrow transition observed in the north-eastern part of the margin and reveals a clear asymmetric crustal setting as supposed for the conjugate margin in the Riiser-Larsen Sea in Antarctica and consequently suggests a complex break-up scenario. The presence of a pronounced high-velocity lower crustal body is interpreted as magmatic material, which underplates the crust and extends about 200 km from the Central Mozambican margin towards the Mozambique Basin and testifies for the massive volcanism during the break-up. The distribution of further volcanics along the entire margin clearly depicts the continuation of the north-eastern branch of the Karoo large igneous province and are mainly emplaced between 177-157 Ma. The magmatism in Southeast Africa seemed to be continuous throughout the initial break-up, which points to the presence of either a mantle plume or a thermal anomaly as source of the giant magmatism. An additional late stage of rift-volcanism mainly affected the margin of Dronning Maud Land and causes the difference in the magnetic signature of the conjugate margins. The tracing of continuous fractures throughout the Africa-Antarctica Corridor leads to the reconstruction of a tight Gondwana fit prior rifting, which reveals several geological links between the plates. A main structure of the East African-Antarctic Orogen extends from the Namama Shear Zone in Central Mozambique across the Orvin Shear Zone towards the Forster magnetic anomaly in Dronning Maud Land. During the initial Gondwana break-up at 182 Ma, Beira High started to separate from West Gondwana along this suture until it demerged as well from East Gondwana by a rift jump. The investigation of further partly unknown tectonic structures along the western and southern coast of Mozambique revealed a possible oceanic origin of the southern part of the Mozambique Coastal Plains, due to similarities of the magnetic signature to the oceanic crust south of Beira High as well as the tentative identification of magnetic spreading anomalies. The subsequent emplaced Mozambique Ridge moved southwards as part of a micro plate during an additional active spreading centre in the Northern Natal Valley. The resulting reconstruction of the initial Gondwana break-up in the Africa-Antarctica Corridor accounts for all present-day available geological, geophysical and geodynamic constraints and might serve as a basis for the investigation of the subsequent dispersal of Gondwana
Parity-based Error Detection with Recomputation for Fault-tolerant Spaceborne Computing
Get PDFIn radiation environment (e.g., space, nuclear reactor), electronics can fail due to bitflips in the flipflops of integrated circuits. A common solution is to triplicate the flipflops and connect their outputs to a voter. If one of the three bits is flipped, then the voter outputs the majority value and tolerates the error. This method is called triple modular redundancya (TMR). TMR can cause about 300% area redundancy. An alternative way is error detection with on-demand recomputation, where the recomputation is done by repeating the failed processing request to the processing circuit. The computation is done in consecutive transactions, which we call transaction-based processing. We implemented and evaluated the aforementioned alternative approach using parity checking on the Microsemi ProASIC3 FPGA, which is often used in space applications. The results show that parity-based error detection with our system recovery approach can save up to 54% of the area overhead that would be caused by the TMR, and achieve in most circuits slightly better timing results than TMR on ProASIC3. This area saving can be the key for fitting the application to a space-constrained chip
Identity and function of key bacterial groups in Arctic deep-sea surface sediments
Get PDFThe deep-sea floor covers about 65% of the Earth s surface and benthic biomass is dominated by highly diverse bacterial communities. Bacterial carbon cycling in deep-sea sediments plays a crucial role in global biogeochemical cycles, and remineralization efficiency of organic carbon can be more than 97%. However, key bacteria relevant for carbon turnover and ecosystem functioning remain unknown. Benthic bacteria mainly depend on organic carbon supply from the surface ocean, and will therefore likely be affected by changing surface ocean conditions. The Arctic Ocean is already impacted by environmental changes more rapidly here than in any other ocean region and will be impacted even more in the future. This turns the Arctic Ocean into an important study site to understand the effects of environmental changes on bacterial communities and ecosystem functioning, such as carbon cycling. At the same time, the Arctic Ocean remains to a large extent understudied, and little is known about the identity of key bacterial groups, which could be useful as indicators to describe the state of the ecosystem and to monitor community response to changing environmental conditions. Consequently, the goals of this thesis include the identification of indigenous key bacteria in deep-sea sediments and their metabolic potential, as well as the development of a better understanding of the specific response of Arctic deep-sea bacterial communities to changes in the supply of organic matter. The Long-Term Ecological Research site HAUSGARTEN (HG) is one out of two open ocean, long-term observatories in a polar region, and therefore provided a unique opportunity to study key bacterial groups from Arctic deep-sea sediments. Chapters I and II present one of the first characterizations of a globally sequence-abundant sediment bacterial group, the JTB255 marine benthic group (JTB255). Cell counts with newly designed probes evidenced high cell abundances in coastal (Chapter I) and deep-sea sediments (Chapter II). Labeling experiments together with metatranscriptomic data suggested a chemolithoautotrophic lifestyle, with a potential high importance for sulfur-based carbon fixation in coastal sediments (Chapter II). Furthermore, genomic analyses of single cells emerged as a powerful means to provide first insights into the metabolic potential of JTB255 representatives in deep-sea sediments, suggesting a heterotrophic lifestyle with oxygen as terminal electron acceptor (Chapter II). Genomic analysis showed that JTB255 encode enzymes for the oxidative degradation of polymeric cell material such as membranes and cell walls, suggesting recalcitrant organic carbon sources in marine sediments. Therefore, it is hypothesized for the first time that some representatives of JTB255 might be involved in the cycling of a major class of refractory sediment organic matter, potentially explaining their global ecological success. In an ex situ experimental approach, the response of Arctic benthic bacterial deep-sea communities at HG to different types of detritus was explored (Chapter III). This is the first experimental study investigating the response of bacterial deep-sea communities to the addition of natural food sources by combining measurements of community function with the analysis of high resolution taxonomic community structure. Our results provide evidence that differences in organic matter composition lead to significant changes in bacterial community structure and function at the seafloor, which can affect carbon turnover and retention in the deep sea. In addition, opportunistic groups of bacteria were identified that may serve as indicator taxa for different organic matter sources at this site. In Chapter IV, a pilot study is presented which addresses an issue often discussed in deep-sea research, i.e. the unknown effects of sample retrieval from high-pressure environments on bacterial communities. Therefore, the influence of de- and recompression on deep-sea sediment bacteria, as inherently imposed during sediment retrieval and subsequent laboratory experiments, was studied in a small-scale experiment. Results indicated few effects of de- and recompression on bacterial community structure within the experimental time frame, but contained evidence for changes in the metabolic activity of specific taxa, after the retrieval of decompressed samples from the seafloor. These observations remain to be verified with further sample replication. In summary, this thesis contributes to the identification of candidate key bacterial groups. It further provides valuable insights into bacterial diversity and function in Arc-tic deep-sea sediments and will help to assess impacts of future climate scenarios on pelago-benthic coupling in the Arctic
Microbial Ecology of Subtidal Sandy Sediments
Get PDFIn marine subtidal sandy sediments, water column-derived organic matter is readily remineralized by heterotrophic benthic microorganisms. Little is known about these microbial communities. The aims of this thesis were, therefore, the identification of the microbial diversity and community structure, estimations of specific bacterial abundances and the analysis whether sediment permeability and tight coupling with the water column influences benthic communities. Combining the insights obtained in this thesis will allow for targeted studies on key clades to specifically identify cellular processes contributing to the high organic matter turnover known for sandy permeable surface sediments
Bacterial Response to Elevated Dissolved Organic Carbon in Coral Reef Ecosystems
Get PDFCoastal pollution and algal cover are increasing in many coral reefs, resulting in higher dissolved organic carbon (DOC) concentrations. High DOC concentrations are shown to have highly detrimental effects on coral reefs through the stimulation of bacterial growth and the accumulation of suspended particles (i.e., aggregate formation). In this thesis, aggregate formation processes and gene expression of planktonic coral reef microbial populations under elevated concentrations of naturally abundant monosaccharides (glucose, galactose,mannose, and xylose) in algal exudates and sewage inputs, were investigated. The results of this thesis show evidence of the detrimental effects of high DOC concentrations on coral reefs by promoting aggregate formation and microbial activity. Furthermore, this thesis shows that elevated DOC concentrations mediate the expression of virulence factors involved in invasion, iron chelation, accumulation of toxic substances, suggesting to be important for feeding the positive loop of coral reef degradation