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Publication
2022-02-26Zeitschriftenartikel
Social learning as an underlying mechanism for sustainability in neglected communities: The Brazilian case of the Bucket Revolution project
(Lebenswissenschaftliche Fakultät) Bonatti, Michelle; Erismann, Carla; Askhabalieva, Ayna; Borba, Juliano; Pope, Kamila; Reynaldo, Renata; Eufemia, Luca; Turetta, Ana Paula; Sieber, Stefan
In neglected communities, waste and organic residues are not only a vector of several problems, like diseases and water pollution, but also a contributor to increasing forms of vulnerability and marginalization. At the same time, these communities also have presented innovative local initiatives and transformative learning about natural resources management that can be a vehicle for achieving more sustainable food systems. In the south of Brazil, community-based organic residue management has shown an extraordinary potential to improve food security and livelihoods for (≈1600) community members of a vulnerable urban territory. In this context, the overall objective of this article is (a) To better understand what Social Learning (SL) processes related to successful organic residues management in neglected communities exist and (b) To identify what knowledge systems are created in one empirical case. The study case is based on a communitarian waste management project, the Bucket Revolution Project (BRP). The analytical framework builds upon social learning theory and its triple-loop process focusing on four specific phenomena. The applied mixed-methods approach was made in four steps: 1. a focus group to investigate collective community issues; 2. semi-structured interviews to investigate specific and individual issues in the context of the BRP; 3. social media analysis to better understand the BRP narratives; and finally 4. participant observation in community and institutional meetings. Mainly using MaxQda software and coding indicators of SL, the data show that “Diversity of knowledge integration” is the most identified SL indicator in the interviews (52%). For BRP, identity development, community conditions improvement, and environment understanding are three key components of the knowledge system enhanced through an underlying process of social learning. Furthermore, the study also shows that there are endogenous and exogenous social learning processes at work.
Publication
2024-10-15Dissertation
Modular Graph Forms and one-loop closed-string amplitudes
(Mathematisch-Naturwissenschaftliche Fakultät) Doroudiani, Mehregan; Nicolai, Hermann; Plefka, Jan; Green, Michael
Diese Dissertation konzentriert sich auf die perturbative Berechnung von Streuamplituden in der Stringtheorie, insbesondere auf Ein-Schleifen-Amplituden für geschlossene Strings. In diesem Fall ist die Weltfläche ein Torus oder eine Riemannsche Fläche vom Geschlecht eins, wobei Punktierungen externe Strings repräsentieren. Der Torus besitzt eine SL(2,Z)-Symmetrie (die modulare Gruppe), die reiche mathematische Eigenschaften offenbart, die für das Verständnis der Amplituden in der Stringtheorie von zentraler Bedeutung sind. Die Niedrigenergie-Entwicklung der Streuamplituden für geschlossene Strings auf Genus-eins-Niveau wird durch die Integration von Korrelatoren der konformen Feldtheorie über den Modulraum des punktierten Torus bestimmt. Dieser Prozess zerfällt in zwei Integrale: eines über den Konfigurationsraum der Einfügungspunkte und eines über den Modulraum der Tori. Das erste Integral führt zu nicht-holomorphen modularen Formen, die als modulare Graphenformen (MGFs) bekannt sind. Diese Arbeit wendet Techniken aus der algebraischen Geometrie und Zahlentheorie an, um MGFs als iterierte Integrale von holomorphen Eisensteinreihen und deren komplexer Konjugation zu analysieren. Mithilfe von Zetageneratoren zeigt die Fourier-Entwicklung der MGFs das Auftreten von mehrfachen Zetawerten und deren einfachwertigen Versionen. Der Prozess wird auf nicht-holomorphe modulare Formen ausgeweitet, die aus iterierten Integralen holomorpher modularer Formen konstruiert sind und holomorphe Spitzenformen einbeziehen. Diese Konstrukte helfen bei der Definition der modularen Vervollständigung der dreifachen Eisenstein-Integrale, wobei Koeffizienten auftreten, die multiple Zetawerte, L-Werte der Spitzenformen und neue Perioden enthalten. Auf modularer Tiefe drei wird eine Basis der MGFs unter Verwendung von Lösungen der Laplace-Gleichungen konstruiert, die es ermöglicht, MGFs über den Modulraum des Torus zu integrieren.
Publication
2022-08-06Zeitschriftenartikel
Modelling cropland expansion and its drivers in Trans Nzoia County, Kenya
(Lebenswissenschaftliche Fakultät) Kipkulei, Harison Kiplagat; Bellingrath-Kimura, Sonoko Dorothea; Lana, Marcos; Ghazaryan, Gohar; Boitt, Mark; Sieber, Stefan
Population growth and increasing demand for agricultural production continue to drive global cropland expansions. These expansions lead to the overexploitation of fragile ecosystems, propagating land degradation, and the loss of natural diversity. This study aimed to identify the factors driving land use/land cover changes (LULCCs) and subsequent cropland expansion in Trans Nzoia County in Kenya. Landsat images were used to characterize the temporal LULCCs in 30 years and to derive cropland expansions using change detection. Logistic regression (LR), boosted regression trees (BRTs), and evidence belief functions (EBFs) were used to model the potential drivers of cropland expansion. The candidate variables included proximity and biophysical, climatic, and socioeconomic factors. The results showed that croplands replaced other natural land covers, expanding by 38% between 1990 and 2020. The expansion in croplands has been at the expense of forestland, wetland, and grassland losses, which declined in coverage by 33%, 71%, and 50%, respectively. All the models predicted elevation, proximity to rivers, and soil pH as the critical drivers of cropland expansion. Cropland expansions dominated areas bordering the Mt. Elgon forest and Cherangany hills ecosystems. The results further revealed that the logistic regression model achieved the highest accuracy, with an area under the curve (AUC) of 0.96. In contrast, EBF and the BRT models depicted AUC values of 0.86 and 0.77, respectively. The findings exemplify the relationships between different potential drivers of cropland expansion and contribute to developing appropriate strategies that balance food production and environmental conservation.
Publication
2022-10-21Zeitschriftenartikel
Assessment of Maize Yield Response to Agricultural Management Strategies Using the DSSAT–CERES-Maize Model in Trans Nzoia County in Kenya
(Lebenswissenschaftliche Fakultät) Kipkulei, Harison Kiplagat; Bellingrath-Kimura, Sonoko Dorothea; Lana, Marcos; Ghazaryan, Gohar; Baatz, Roland; Boitt, Mark; Chisanga, Charles B.; Rotich, Brian; Sieber, Stefan
Maize production in low-yielding regions is influenced by climate variability, poor soil fertility, suboptimal agronomic practices, and biotic influences, among other limitations. Therefore, the assessment of yields to various management practices is, among others, critical for advancing site-specific measures for production enhancement. In this study, we conducted a multiseason calibration and evaluation of the DSSAT–CERES-Maize model to assess the maize yield response of two common cultivars grown in Trans Nzoia County in Kenya under various agricultural strategies, such as sowing dates, nitrogen fertilization, and water management. We then applied the Mann–Kendall (MK), and Sen’s Slope Estimator (SSE) tests to establish the yield trends and magnitudes of the different strategies. The evaluated model simulated long-term yields (1984–2021) and characterized production under various weather regimes. The model performed well in simulating the growth and development of the two cultivars, as indicated by the model evaluation results. The RMSE for yield was 333 and 239 kg ha −1 for H614 and KH600-23A, respectively, representing a relative error (RRMSE) of 8.1 and 5.1%. The management strategies assessment demonstrated significant feedback on sowing dates, nitrogen fertilization, and cultivars on maize yield. The sowing date conducted in mid-February under fertilization of 100 kg of nitrogen per hectare proved to be the best strategy for enhancing grain yields in the region. Under the optimum sowing dates and fertilization rate, the average yield for cultivar KH600-23A was 7.1% higher than that for H614. The MK and SSE tests revealed a significant (p < 0.05) modest downwards trend in the yield of the H614 cultivar compared to the KH600-23A. The eastern part of Trans Nzoia County demonstrated a consistent downwards trend for the vital yield enhancement strategies. Medium to high nitrogen levels revealed positive yield trends for more extensive coverage of the study area. Based on the results, we recommend the adoption of the KH600-23A cultivar which showed stability in yields under optimum nitrogen levels. Furthermore, we recommend measures that improve soil quality and structure in the western and northern parts, given the negative model response on maize yield in these areas. Knowledge of yield enhancement strategies and their spatial responses is of utmost importance for precision agricultural initiatives and optimization of maize production in Trans Nzoia County.
Publication
2023-02-27Zeitschriftenartikel
Seasonal and diurnal patterns of littoral microhabitat use by fish in gravel pit lakes, with special reference to supplemented deadwood brush piles
(Lebenswissenschaftliche Fakultät) Maday, Andreas; Matern, Sven; Monk, Christopher T.; Klefoth, Thomas; Wolter, Christian; Arlinghaus, Robert
The habitat quality of the littoral zone is of key importance for almost all lentic fish species. In anthropogenically created gravel pit lakes, the littoral zone is often structurally homogenized with limited fish habitats. We supplemented deadwood brush piles in the littoral zone of eight gravel pit lakes and investigated the diurnal and seasonal use of this and other typical microhabitats by six dominant fish species. Shoreline habitats were sampled using point abundance electrofishing during day and night in all four seasons, and patterns of fish abundance were compared amongst unstructured littoral habitats, emerged macrophytes and brush piles. We caught a total of 14,458 specimens from 15 species in the gravel pit lakes. Complex shoreline structures were used by all fish species that we examined, especially during daytime, whilst the use of unstructured habitats was highest during night. The newly added brush piles constituted suitable microhabitats for selected fish species, perch ( Perca fluviatilis ), roach ( Rutilus rutilus ) and pike ( Esox lucius ), particularly during winter. Supplemented deadwood provides suitable fish habitat in gravel pit lakes and may to some degree compensate for the loss of submerged macrophytes in winter by offering refuge and foraging habitat for selected fish species.