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- ItemPerformance Assessment of Satellite and DACCIWA Optical Gauge Rainfall Products for the Analysis of Trends and Drivers of Rainfall Extremes in Ghana(KNUST, 2018-11) Atia Winifred AyinpogbillaRainfall plays an important role in the socio-economic development of any nation. Below or above normal rainfall conditions have serious consequences on key socioeconomic sectors such as agriculture. This is particularly true for countries where rain-fed agriculture is a predominant practice as such, rainfall impact studies are important. In this thesis, rainfall impact studies in Ghana were examined in three different areas. The first part of the study evaluated the performance of satellites and merged rainfall products over Ghana in order to examine their reliability as surrogate ground-based gauge measurements for areas where gauge networks are sparse. Satellite products (TAMSAT, TRMM, ARC2, CMAP, GPCP and CHIRPs) and gauge-only products (CRU and GPCC) were validated with gridded rainfall data from the Ghana Meteorological Agency (GMet) on monthly to annual time scales using a suite of statistical analysis. The results showed that, the performance of the satellites and merged rainfall products is a function of the scales and locations used in the validation. While ARC2 showed large biases on both monthly and annual time scales, all other products, especially, TRMM and TAMSAT showed relatively good skills on the monthly scale (r > 0.90) than the annual. On the countrywide basis, CHIRPs and CRU markedly revealed better skills on both time scales. In all the four agro-ecological zones of the country, the products were able to capture the respective rainfall patterns, onset, cessation and spells (wet and dry) of each zone. Thus, TRMM and TAMSAT will serve as better surrogates at monthly time scale whereas CHIRPS and CRU would be better substitutes to ground-based gauge data for both time scales over the entire country and in the four ecological zones. In the second part of the study, the performance of the new Dynamic Aerosol Chemistry-Cloud Interactions in West Africa (DACCIWA) optical rain gauge (DOG) measurements over the Ashanti region of Ghana were assessed. The study further examined the validities of subdaily rainfall data from IMERG and TRMM over the region for their exploits in the key socio-economic activities of the country such as agriculture, hydrology and water resource management. Daily rainfall data for nine co-located stations from the Ghana Meteorological agency (GMet) were used to assess the validity of the DOGs. A point-point assessment of IMERG and TRMM from 2016–2017 for the nine stations were then performed using the DOGs. The outcome of the assessment revealed that the DOGs were able to capture the diurnal and monthly rainfall patterns in the region. IMERG revealed a better skill in capturing the daily rainfall than TRMM although both products showed some similarities in the June–August (JJA) season. Both products slightly over-estimated gauge measurements (<2 mm/day) in all selected stations. The third part of the study examined the climatologies and trends of extreme rainfall events in Ghana. The study further probed the links between the rainfall extremes and SST anomalies at the oceanic basin. The trend analysis revealed that CDD, CWD, R10mm and R20mm were in the range of 5–140, 5–14, 25–60 and 2–26 days per year respectively. Moreover, PRCPTOT, R95p, R99p, SDII, RX1day and RX5day were in the range of 800-1800 mm, 150–450 mm, 30–130 mm, 6–14 mm, 30–100 mm and 60–190 mm per year respectively. The maximum of temporally averaged intensity rainfall indices have shown to cover southwestern Ghana while the minimum of these indices covered northwestern and eastern coasts of Ghana. Significant decreasing trends in wet indices were observed over the Volta lake and central Ghana while low positive trends were dominant over the northern sectors of the country. In most cases, with the exception of the CDD and CWD indices, there were significant positive (negative) correlations with the Atlantic (Pacific and Indian) basins SSTs. IOD had a dipole effect on rainfall indices with the central and southern sectors generally covered by negative correlations while northern and coastal Ghana have shown positive correlations. The R95p index over central Ghana had negative correlations with AMO while positive correlations dominated some isolated parts of the country in the south and northeast. The impacts of AMO on PRCPTOT index were insignificant over most parts of the country with a few exceptions over southeastern and northern boarder regions. These results have implications on the improvement of monthly-annual forecasts of the Ghanaian rainfall and its extremes, and also provides prior knowledge for better understanding of multidecadal modulations of global inter-annual teleconnections
- ItemModelling Customers Response to Service offers using game Theory Case Study; MTN and Vodafone in Bolgatanga Polytechnic(2011-11-18) Issahaku, Abdul-MajeedGame theory is being found to be one of the useful tools for analysing strategic situations that involve competitors or rivals who struggle against each other for supremacy...
- ItemMechanistic Studies and Mathematical Models for Mycolactone Toxin and Autoinhibitory WASP: Model Mechanisms for Buruli ulcer Initiation and Spread.(2015-11-09) Nyarko, Peter RomeoThe Wiskott-Aldrich Syndrome Protein (WASP) has been implicated in many diseases such as Wiskott-Aldrich Syndrome (WAS) and Buruli ulcer. Mycobactrium ulcerans is the main causative organism of Buruli ulcer (BU) disease. The bacteria secretes a polyketide lipid toxin (Mycolactone). The toxin not only di uses through the cell membranes, but also binds, hijacks and disrupts the normal functions of WASP in the cytoplasm leading to over polymerization of actin lament, cytoskeletal rearrangement and eventually cell death through necrosis. In pre-ulcerative BU disease, toxins extend beyond the actual size of the lesion. A mathematical model is developed to describe the binding mechanism of the two conformations of WASP and the complexes formed using the idea of isomerization. The formulation utilizes ligand concentration-dependence (ligand-receptor), equilibrium and conservation principles. By this approach, we are able to determine the fractional response of WASP against change in concentration of its activators;
- ItemPreparation and characterization of fat particles-in-water emulsions for the encapsulation of bioactive compounds using allanblackia seed fat and tween 20 and sodium alginate as emulsifying agents(2015-11-09) Badu, MercyEffective delivery of poorly water-soluble bioactive ingredients has been considered a great challenge in the pharmaceutical, food and cosmetic industries. The compartmentalized hydrophobic and hydrophilic regions of emulsion systems give them the advantage to encapsulate polar and non-polar compounds for effective delivery. However, the challenge associated with emulsions is their thermodynamic instability. This study investigated the stabilisation process of fully crystallised fat globules as a dispersed phase in an oil-in-water emulsion system prepared from a naturally occurring vegetable fat, a nonionic surfactant and a polysaccharide biopolymer. The crystallisation profiles of the fats from Allanblackia seed and shea nuts were determined. Based on the results Allanblackia seed fat was selected and used as the dispersed phase in the oil-in-water emulsion system. The emulsion was formulated in the presence of Tween 20 and sodium alginate. The mixed emulsifier system gave stability against aggregation of the fat particles hence preventing coalescing, creaming and flocculation and this was more significant at 2 % to 4 % sodium alginate content. The emulsion particle size and microstructure were dependent on the fat/water ratio and a viscoelastic system with G′ > G′′ at the lower frequencies and G′′ > G′ at higher frequencies (where G and G are….). The dispersed fat particles emulsion system was used to encapsulate sudan orange dye (a water insoluble dye) and the efficiency of the encapsulation was characterized by an increase in particle size (ranging from 246 to 250 nm) and varying size distribution. UV-Vis spectrophotometric analysis of the dye loading capacity, release rate and leaching capacity showed a successful entrapment of the dye in the fat matrix. This confirms Allanblackia seed fat as a potential solid fat for its application in the formulation of oil-in-water emulsions.
- ItemThe kinetics of mycolactone in relation to the microbiological, clinical and immunological responses to antibiotic therapy for mycobacterium ulcerans disease.(2014-11-20) Sarfo, Fred StephenBackground: Mycobacterium ulcerans is the causative agent for a chronic necrotising skin infection called Buruli ulcer. Pathology of the disease is closely linked with the elaboration of a unique lipid toxin, mycolactone, which has potent cytotoxic and immunomodulatory properties. In this study, assays were developed to detect and quantify mycolactone concentrations in tissues during curative antibiotic therapy in mice and in humans to understand its dynamics in pathogenesis and to explore its potential as a biomarker for diagnosis and monitoring of patients with Buruli ulcer disease on antibiotic therapy. The currently recommended antibiotic regimen for the management of Buruli ulcer is a combination of daily intramuscular injections of streptomycin and oral rifampicin for 8 weeks (RS8). This regimen was compared with streptomycin/rifampicin for 2 weeks followed by clarithromycin/rifampicin (RS2RC6) for 6 weeks in patients to determine the clinical and bacteriological effectiveness in a pilot study. Methods: Biopsies were obtained from infected human skin tissues and BALB/c mouse hind footpads before, during and after 8-weeks of rifampicin-containing combination antibiotic therapy. Lipids were extracted from tissues using organic solvents, mycolactone concentrations were measured using a cytotoxicity assay and mass spectrometry. Trends in mycolactone concentrations and clinical, bacteriological and immuno-histopathological responses were determined. Concentrations of cytokines in supernates of whole blood assays in humans or murine splenocytes after stimulation with mycobacterial antigens/T-cell mitogens were measured using ELISA. iv Results: Eighty-three patients with confirmed Buruli ulcer were randomized to RS8 or RS2RC6 and monitored for recurrence free-healing. Bacterial load in tissue samples before and after treatment for 6 and 12 weeks was monitored in samples obtained by 4mm punch biopsy by semi-quantitative culture. There was no difference in using RS8 or RS2RC6 with respect to healing rate or the proportion healed in each group after 4, 8, 12, 16, 20, 24 and up to 52 weeks. The success rate was 93% in each group and there was no recurrence after 12-month follow-up. There was no difference in the number of bacteria cultured at the different time points for the two regimens. Mycolactone was detectable in 92% and 77% of human samples (n=80) using cytotoxicity assays and mass spectrometry respectively. Antibiotic therapy was associated with a decline in tissue concentration of mycolactone in both human and murine-infected tissues which was paralleled by resolution of clinical lesions, reductions in bacteriological counts and restoration of local and systemic immune responses. Discussions/Conclusions: This study shows that mycolactone concentrations in tissues is closely associated with the presence of M. ulcerans and provides useful proof-of-concept data that mycolactone detection could potentially be used to monitor response to antibiotic therapy as well as for diagnosis of Buruli ulcer disease. The findings from the pilot study indicate that rifampicin combined with clarithromycin can replace rifampicin and streptomycin for the continuation phase after rifampicin-streptomycin treatment for 2 weeks without any apparent loss of efficacy. The implication is that a controlled trial of fully oral therapy using rifampicin and clarithromycin for 8 weeks (RC8) is justified.