Effects of soil carbon and ambient carbon dioxide concentrations on hydrological processes: a modelling study.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF.Publications on page iv-v

Die Lektorierung des Internets durch Öffentliche Bibliotheken : Methoden, Chancen und Schwierigkeiten

Gegenstand der hier vorgestellten Arbeit ist die Lektorierung des Internets durch Öffentliche Bibliotheken. Seit wenigen Jahren haben die Bibliotheken damit begonnen, die Informationsmengen des Internets für ihre Kunden professionell aufzubereiten. Eine einzelne Bibliothek ist allerdings nicht in der Lage das Internet zu erschließen. Diese Dienstleistung können die Öffentlichen Bibliotheken nur erfolgreich gestalten, wenn sie miteinander kooperieren. An den Beispielen ausgewählter Projekte aus den USA, Dänemark, Finnland und Deutschland werden die unterschiedlichen Entwicklungen dargestellt und deren Methoden vorgestellt und ausgewertet. Die Unterschiede und Gemeinsamkeiten der Projekte werden verdeutlicht. Die Chancen, die sich durch die neue Dienstleistung ermöglichen werden ebenso benannt, wie die Schwierigkeiten, die sie mit sich führt

Linkages between selected hydrological ecosystem services and land use changes, as indicated by hydrological responses : a case study on the Mpushini/Mkhondeni Catchments, South Africa.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.Nature provides essential services to humans, including climate regulation, water provisioning and regulation. These so-called ecosystem services have economical, societal and environmental value. This research aims at improving the knowledge on the linkages between selected hydrological ecosystem services and current and proposed land uses within the water-limited Mpushini/Mkhondeni Catchments in South Africa. The research contributes to the recognition of feedback and linkages within the complex ecological-human system, so that informed land use decisions can be made. The research aim is achieved by first reviewing the literature on hydrological ecosystem services, land use in an ecosystem services context and the links between the two. The study area is then sub-delineated into land use determined hydrological response units for baseline natural land cover, as well as for current and proposed land use scenarios. Using an appropriate model, selected hydrological processes are simulated in order to isolate the effects of individual land uses on hydrological responses, both on a local and a more catchment-wide scale. Various land uses were found to affect hydrological responses, such as runoff and its components of stormflows and baseflows, as well as transpiration and sediment yields, differently. These responses were found to be suitable indicators of selected ecosystem services such as water provisioning or flow regulation. Irrigation and high biomass crops, such as sugarcane and wattle plantations were found to reduce downstream water provisioning services. Degraded lands were found to reduce physical water quality through increased sediment yield, to reduce water provisioning during low flow periods, while the degraded lands increased stormflows, thereby reducing regulation of high flows. Urban land uses were found to significantly increase runoff, with increased impervious areas causing a shift from evaporation and transpiration towards runoff. Stormflows increased, with high flow regulation being reduced. Baseflows increased as well, as a result of a spill-over of runoff from impervious to pervious urban areas, which led to increased low flow regulation. In addition, in this study area urban return flows are generated from externally sourced water, further increasing streamflows and especially low flows. While urban areas showed an increase in downstream water quantity provision, the water quality was reduced. The combined effects of the current land use mosaic on the annual streamflows partially cancel each other out, while the proposed urbanisation dominated hydrological responses. Influences of various land uses on hydrological ecosystem services were thereby shown, which contributes to a better understanding of the linkages between the two

Impacts of soil carbon on hydrological responses – a sensitivity study of scenarios across diverse climatic zones in South Africa

Soil organic carbon (SOC) content and the water holding capacity of soils are two properties which link the carbon and hydrological cycles. Hydrological model inputs seldom include soil carbon as a parameter even though soil carbon content is known to influence soil water retention capacities. This study is a sensitivity analysis of changes in hydrological responses when the model inputs include different soil carbon percentages for the topsoil horizon. Sensitivities of hydrological responses such as transpiration, runoff volumes, the stormflow component of runoff and extreme runoff events to SOC content were quantified under various climatic conditions in South Africa. The soil water holding capacities at the drained upper limit (i.e. field capacity), permanent wilting point and saturation were calculated for the topsoil horizon, using SOC dependent pedo (soil)-transfer functions for different soil carbon scenarios and locations in South Africa. These variables, together with other pre-determined soil- and locationrelated inputs, as well as 50 years of daily climate, were then used as inputs in a process-based hydrological model. Overall, it was found that increased SOC content in the topsoil horizon leads to an increase in transpiration, a reduction in runoff, especially in its stormflow component, and a reduction of extreme runoff events. However, these changes are relatively small compared to the influence of climate, particularly of rainfall amount and distribution.Significance: Organic carbon content of the soil and the water holding capacity of soils link the carbon and hydrological cycles. Management interventions that increase SOC lead to win-win situations because, in addition to climate change mitigation, plant water availability improves, and overall surface runoff ‘flashiness’ becomes more regulated. While rainfall amount and distribution over space and time remain the most critical determinants of hydrological responses, increased SOC in the topsoil horizon leads to increases in transpiration and thus plant growth, and to a reduction in runoff, especially in its stormflow component, and hence to a small reduction of severe flooding events

Optimal Treatment Strategies in the Context of ‘Treatment for Prevention’ against HIV-1 in Resource-Poor Settings

An estimated 2.7 million new HIV-1 infections occurred in 2010. `Treatment- for-prevention’ may strongly prevent HIV-1 transmission. The basic idea is that immediate treatment initiation rapidly decreases virus burden, which reduces the number of transmittable viruses and thereby the probability of infection. However, HIV inevitably develops drug resistance, which leads to virus rebound and nullifies the effect of `treatment-for-prevention’ for the time it remains unrecognized. While timely conducted treatment changes may avert periods of viral rebound, necessary treatment options and diagnostics may be lacking in resource-constrained settings. Within this work, we provide a mathematical platform for comparing different treatment paradigms that can be applied to many medical phenomena. We use this platform to optimize two distinct approaches for the treatment of HIV-1: (i) a diagnostic-guided treatment strategy, based on infrequent and patient-specific diagnostic schedules and (ii) a pro-active strategy that allows treatment adaptation prior to diagnostic ascertainment. Both strategies are compared to current clinical protocols (standard of care and the HPTN052 protocol) in terms of patient health, economic means and reduction in HIV-1 onward transmission exemplarily for South Africa. All therapeutic strategies are assessed using a coarse-grained stochastic model of within-host HIV dynamics and pseudo-codes for solving the respective optimal control problems are provided. Our mathematical model suggests that both optimal strategies (i)-(ii) perform better than the current clinical protocols and no treatment in terms of economic means, life prolongation and reduction of HIV-transmission. The optimal diagnostic-guided strategy suggests rare diagnostics and performs similar to the optimal pro-active strategy. Our results suggest that ‘treatment-for-prevention’ may be further improved using either of the two analyzed treatment paradigms

Partial mean-field model for neurotransmission dynamics

This article addresses reaction networks in which spatial and stochastic effects are of crucial importance. For such systems, particle-based models allow us to describe all microscopic details with high accuracy. However, they suffer from computational inefficiency if particle numbers and density get too large. Alternative coarse-grained-resolution models reduce computational effort tremendously, e.g., by replacing the particle distribution by a continuous concentration field governed by reaction-diffusion PDEs. We demonstrate how models on the different resolution levels can be combined into hybrid models that seamlessly combine the best of both worlds, describing molecular species with large copy numbers by macroscopic equations with spatial resolution while keeping the stochastic-spatial particle-based resolution level for the species with low copy numbers. To this end, we introduce a simple particle-based model for the binding dynamics of ions and vesicles at the heart of the neurotransmission process. Within this framework, we derive a novel hybrid model and present results from numerical experiments which demonstrate that the hybrid model allows for an accurate approximation of the full particle-based model in realistic scenarios.Comment: 16 pages + 2 pages appendix, 5 figures. Submitted to Mathematical Bioscience

From interacting agents to density-based modeling with stochastic PDEs

Many real-world processes can naturally be modeled as systems of interacting agents. However, the long-term simulation of such agent-based models is often intractable when the system becomes too large. In this paper, starting from a stochastic spatio-temporal agent-based model (ABM), we present a reduced model in terms of stochastic PDEs that describes the evolution of agent number densities for large populations. We discuss the algorithmic details of both approaches; regarding the SPDE model, we apply Finite Element discretization in space which not only ensures efficient simulation but also serves as a regularization of the SPDE. Illustrative examples for the spreading of an innovation among agents are given and used for comparing ABM and SPDE models

Stochastic pH Oscillations in a Model of the Urea−Urease Reaction Confined to Lipid Vesicles

ABSTRACT: The urea−urease clock reaction is a pH switch from acid to basic that can turn into a pH oscillator if it occurs inside a suitable open reactor. We numerically study the confinement of the reaction to lipid vesicles, which permit the exchange with an external reservoir by differential transport, enabling the recovery of the pH level and yielding a constant supply of urea molecules. For microscopically small vesicles, the discreteness of the number of molecules requires a stochastic treatment of the reaction dynamics. Our analysis shows that intrinsic noise induces a significant statistical variation of the oscillation period, which increases as the vesicles become smaller. The mean period, however, is found to be remarkably robust for vesicle sizes down to approximately 200 nm, but the periodicity of the rhythm is gradually destroyed for smaller vesicles. The observed oscillations are explained as a canardlike limit cycle that differs from the wide class of conventional feedback oscillators

Genetic Variation in ABCC4 and CFTR and Acute Pancreatitis during Treatment of Pediatric Acute Lymphoblastic Leukemia

Background: Acute pancreatitis (AP) is a serious, mechanistically not entirely resolved side effect of L-asparaginase-containing treatment for acute lymphoblastic leukemia (ALL). To find new candidate variations for AP, we conducted a genome-wide association study (GWAS). Methods: In all, 1,004,623 single-nucleotide variants (SNVs) were analyzed in 51 pediatric ALL patients with AP (cases) and 1388 patients without AP (controls). Replication used independent patients. Results: The top-ranked SNV (rs4148513) was located within the ABCC4 gene (odds ratio (OR) 84.1; p = 1.04 × 10−14). Independent replication of our 20 top SNVs was not supportive of initial results, partly because rare variants were neither present in cases nor present in controls. However, results of combined analysis (GWAS and replication cohorts) remained significant (e.g., rs4148513; OR = 47.2; p = 7.31 × 10−9). Subsequently, we sequenced the entire ABCC4 gene and its close relative, the cystic fibrosis associated CFTR gene, a strong AP candidate gene, in 48 cases and 47 controls. Six AP-associated variants in ABCC4 and one variant in CFTR were detected. Replication confirmed the six ABCC4 variants but not the CFTR variant. Conclusions: Genetic variation within the ABCC4 gene was associated with AP during the treatment of ALL. No association of AP with CFTR was observed. Larger international studies are necessary to more conclusively assess the risk of rare clinical phenotypes