Representing vegetation in experimental models of river systems.

The physical behaviour of fluvial systems have been studied in detail and as have their representations of the impact and interaction between hydraulic and sedimentological features within these river systems. However, there is limited understanding of the interaction and impact of organic features like vegetation. Vegetation, in particular riparian vegetation on the banks and floodplains of rivers, is closely intertwined with river behaviour. Rivers can be growth enhancing, by deposition of nutrient rich sediments and the supply of water, or growth inhibiting during periods of low flow or erosive floods. Furthermore, vegetation itself influences the river system by, for example, increasing bank strength and flow resistance.Vegetation is a living organism interacting with the fluvial system, and its behaviour is dynamic over time (both in terms of growth and decay). Vegetation not only strengthens itself and the substrate it grows in, but it also evolves over time and thrives differently over the seasons in a year. In systems that exhibit dynamic equilibrium this temporal variance of vegetation adjusts into the resulting river morphology and the vegetation itself follows the dynamics of the fluvial system as well. However, present-day predictions of climate change can significantly change river systems. Firstly, flood events may increase in magnitude and frequency; and secondly droughts may increase in length. Simultaneously, changes in temperature and rainfall will affect vegetation growth and decay and may change species types within a given area. These predicted effects will change the behaviour of systems over the next decades, a timescale that is significantly faster than most ‘natural’ changes in fluvial systems. Hence, it is essential to be able to model these fluvial systems and understand their changes over the next decades.Physical modelling offers a solution to modelling these systems, and enables time to be compressed by reducing the scale of the river systems. In analogue physical models, surrogates are often used to represent vegetation in small-scale models. Surrogate vegetation enables modellers to incorporate vegetation density, growth and decay into models of fluvial environments since the surrogate vegetation represents the cohesive effect of plant roots, introducing the biotic forcing produced by vegetation in scaled physical models of hydraulic and sediment behaviour. However, despite the rapid growth that can be achieved with surrogate vegetation, it still takes a significant time to representative vegetation in an experiment which has a significant financial cost.This research consists of a number of different experiments that: (i) elucidate how different stages of surrogate vegetation (Alfalfa) affects bank stability and the dynamics of a braided river system; and (ii) demonstrate how chemical surrogates that have instantaneous effects on sediment cohesion can be used as an alternative to growing surrogate vegetation. These experiments are conducted across different scales, with small bank erosion experiments to determine erosion rates for different ages and densities of surrogate vegetation followed by larger scale braided river experiments to demonstrate how the dynamic behaviour of the system is dependent on threshold ages of vegetation. These experiments include the novel use of chemical surrogates such as xanthan gum and sodium alginate which can be used in different concentrations to represent the behaviour of surrogate vegetation in both controlled bank erosion experiments as in dynamic braided systems.Finally, this research introduces a new method to control the cohesive strength of these chemical surrogates. This method enables experiments to mimic the growth and decay of surrogate vegetation without the need to alter the sediment itself, thereby maintaining the characteristic existing morphology of previous stages. Experiments demonstrate that the chemical surrogates can be used to simulate sequences of vegetation growth, simulating either seasonal or longer-term climate induced changes in vegetation impacts of fluvial systems. Therefore this method significantly extends analogue scale modelling of complex fluvial systems

Chang’aa Drinking in Kibera Slum: The Harmful Effects of Contemporary Changes in the Production and Consumption of Traditional Spirits

This article examines the harmful effects of drinking chang’aa, an illegal spirit produced locally, in Kibera slum in Nairobi, Kenya. The negative impact of chang’aa on the community’s physical, social and economic life is traced, in part, to contemporary changes in consumption patterns as well as the production of chang’aa during the late 1990s. This article also analyzes the efforts of a local Catholic parish to launch a campaign to raise awareness on the dangers of chang’aa and to lobby the government to enforce its ban on the sale and use of the illicit brew. The parish was limited in its efforts primarily due to fears of violent reprisal by local government officials and chang’aa sellers who profited from the illegal, but lucrative trade. Key Words: Chang’aa, Kibera, Kenya, traditional drinks, spirits, alcoho

Interferon in Sjögren's Syndrome and Other Systemic Autoimmune Diseases: A driver of disease pathogenesis and potential treatment target

In this thesis we study the role of interferon (IFN) and its downstream signaling pathways on the pathogenesis of several systemic autoimmune diseases, with primary Sjögren’s syndrome (pSS) being the main focus

Stable divisorial gonality is in NP

Divisorial gonality and stable divisorial gonality are graph parameters, which have an origin in algebraic geometry. Divisorial gonality of a connected graph $G$ can be defined with help of a chip firing game on $G$. The stable divisorial gonality of $G$ is the minimum divisorial gonality over all subdivisions of edges of $G$. In this paper we prove that deciding whether a given connected graph has stable divisorial gonality at most a given integer $k$ belongs to the class NP. Combined with the result that (stable) divisorial gonality is NP-hard by Gijswijt, we obtain that stable divisorial gonality is NP-complete. The proof consist of a partial certificate that can be verified by solving an Integer Linear Programming instance. As a corollary, we have that the number of subdivisions needed for minimum stable divisorial gonality of a graph with $n$ vertices is bounded by $2^{p(n)}$ for a polynomial $p$

Cystic fibrosis liver disease and the enterohepatic circulation of bile acids

Cystic fibrosis (CF) is one of the most frequently occurring life threatening congenital diseases. This progressive disease manifests itself in several organ systems. The disease is caused by a mutation in the CFTR protein. The studies in the thesis focused on the development and treatment of CF in the liver and intestine, in particular the role of bile salts. Bile salts are essential in metabolism and play a crucial role in intestinal dietary fat and vitamin absorption in the gut. The experiments were performed in mice models with a mutation in the CFTR protein. With respect to CF disease in the gut we found that a disturbance in the bile salt metabolism, together with e.g. changes in the intestinal microbial flora, could be related to the clinical finding of persistent decrease of intestinal fat absorption in CF, despite adequate medication. These findings could be related to the decreased growth in CF conditions. With respect to CF disease in the liver we found that the currently used treatment for CF related liver disease (Ursodeoxycholaat or UDCA) can potentially be effective. We were particularly interested to investigate whether the severe form of cirrhotic CF related liver disease is caused by the altered bile salt metabolism. This was not the case. We did however find that normal liver growth is impaired in CF. This is most likely due to the important interaction between the mutated CFTR protein, the intestinal microbial flora, and the altered bile metabolism

Immunity to Influenza and Future Vaccination Strategies

Influenza viruses are very small pathogens (typically 80-120 nm) belonging to the family of the Orthomyxoviridae together with four other genera: Thogoto virus, Isavirus and influenza B and C viruses. The influenza viruses are distinguished based on the membrane channel protein, genome size and surface glycoproteins. The influenza A viruses are further subdivided into subtypes based on the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). At present, 16 subtypes of the HA and 9 subtypes of the NA are known