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Secondary Current and Classification of River Channels

Applied Mathematics 2013年第1期4卷 70-78页

作者： Kaguchwa john njenga Kwanza Jackson Kioko Gathia Patricia Wanjiru Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya Mathematics Department Egerton University Egerton Kenya

In this research, the secondary current theory is used in investigating the role of phase shift angle between the secondary current and the channel axis displacement in stability analysis of a river channel. To achieve this, a small-perturbation stability analysis is developed for investigation of the role of the secondary current accompanying channel curvature in the initiation and early development of meanders in open channels. The secondary currents are generating in planes perpendicular to the primary direction of motion. The secondary currents form a helical motion in which the water in the upper part of the river is driven outward, whereas the water near the bottom is driven inward in a bend. Force-momentum equations for longitudinal and transverse direction in open channel bends were utilized. Assuming that the transverse force contributed by the bed is negligible, the pressure force associated with the transverse surface inclination is balanced by the centripetal force. Existing equations of the transverse velocity profile were analyzed. Since the magnitude of the vertical velocity is negligible compared to the transverse velocity in secondary currents, this study concentrates on the transverse velocity which is the radial component of the secondary current. This formulation leads to a linear differential equation which is solved for its orthogonal components which give the rates of meander growth and downstream migration. It is shown that instability increases with decrease in phase shift angle. Transition from straight to meandering and then from meandering to braiding occurs when phase shift angle is reduced.

关键词： Secondary Flow Phase Shift Meandering Braiding Stability

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Epidemiology of <i>Staphylococcus aureus</i>Infections in Kenya: Current State, Gaps and Opportunities

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Open Journal of Medical Microbiology 2020年第4期10卷 204-221页

作者： Justin Nyasinga Geoffrey Omuse njenga john Andrew Nyerere Shima Abdulgader Mae Newton Andrew Whitelaw Gunturu Revathi Department of Pathology Aga Khan University Nairobi Kenya Department of Biomedical Sciences and Technology The Technical University of Kenya Nairobi Kenya Pan-African University-Institute of Science Technology and Innovation/Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya Department of Biomedical Sciences Stellenbosch University Stellenbosch South Africa

Staphylococcus aureus has maintained its clinical relevance as a major cause of hospital and community acquired infections globally with a high burden of antimicrobial resistance (AMR). Though reported, the burden of infection, antimicrobial resistance and molecular epidemiology of S. aureus are not well defined in Kenya. This descriptive review evaluated reported data on the detection and characterization of S. aureus infections in Kenya. Published data between 2000 and 2020 were evaluated. S. aureus isolation frequencies varied from 1% in blood specimens to 52.6% among skin and soft tissues infections while MRSA rates ranged from 1% to 84.1%. While penicillin resistance has consistently been high, last line and recent antibiotics such as vancomycin, linezolid, teicoplanin and daptomycin have retained their efficacy. Data on MRSA carriage in the community, among HCWs and inpatients is limited. Global clones (CC1, CC5, CC8, CC22, CC30, CC45 and CC239) alongside a few novel MRSA strains have been reported with staphylococcal protein A (spa) sequence based clustering yielding four major clusters (spa

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Trace Element Concentrations in Some Traditional Diets Consumed in Selected Parts of Eastern Province of Kenya

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Journal of Environmental Protection 2012年第7期3卷 617-623页

作者： David M. Maina Lydia W. njenga john M. Onyari Benjamin N. Kyalo Department of Chemistry School of Physical Sciences University of Nairobi Nairobi Kenya Institute of Nuclear Science and Technology University of Nairobi Nairobi Kenya

Dietary quality is vital in maintaining sound nutritional status. The ecological conditions thus influence the type of diets and their nutritional quality. The purpose of this study was to determine the trace element/mineral content of some of the commonly consumed diets in Machakos, Kitui, Makueni and Mwingi districts. Decorticated maize, beans and finger millet flour samples were purchased from the local markets. For each category, a total of ten samples were collected from each district. The samples were put in plastic bags, sealed and transported to the laboratory in the Institute of Nuclear Science & Technology, University of Nairobi for preparation and analysis. The cooking of the samples was carried out according to local traditional methods. In the decorticated samples, mean copper concentrations were observed to be below 20 μg·g-1;mean zinc concentrations ranged from 34 to 63 μg·g-1 and mean manganese concentrations were in a similar range of 34 to 78 μg·g-1. The mean iron concentrations were significantly high with a range of 161 μg·g-1 to 287 μg·g-1. A similar trend was observed in the beans where the mean copper concentrations varied from 11 to 33 μg·g-1, mean zinc concentrations ranged from a low value of 24 μg·g-1 to a high value of 35 μg·g-1, mean manganese concentrations varied from 33 μg·g-1 to 98 μg·g-1 and the mean iron concentrations ranged from 227 μg·g-1 to 647 μg·g-1. The cooked Muthokoi samples from Machakos district had relatively high mean trace element concentrations: manganese—109 μg·g-1;iron—280 μg·g-1;copper—19 μg·g-1;and zinc—41 μg·g-1. The only exception was mean iron concentrations which were extremely high in samples from Mwingi District where the concentrations varied from 73 μg·g-1 to 1597 μg·g-1. In finger millet flour, the mean manganese concentrations varied from 95 to 290 μg·g-1, whereas the mean iron concentrations ranged from 127 μg·g-1 to 259 μg·g-1. In contrast, the mean copper and zinc concentrations were low in compariso

关键词： Trace Elements Diets Semi-Arid Kenya

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Antimicrobial Properties of Actinomycetes Isolated from Menengai Crater in Kenya

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CellBio 2017年第2期6卷 13-26页

作者： Paul njenga Waithaka Francis B. Mwaura john M. Wagacha Eliud M. Gathuru Benson M. Githaiga School of Biological Sciences University of Nairobi Nairobi Kenya Department of Biological Sciences Egerton University Njoro Kenya

A study was carried out to isolate and screen actinomycetes for antimicrobials from Menengai Crater in Kenya. The actinomycetes were isolated using starch casein agar, Luria Bertani agar and starch nitrate agar. Primary screening for antagonism was carried out using perpendicular method while secondary screening was done using agar disk technique. Extraction of the antimicrobials was carried out using ethyl acetate. Sensitivity testing of the crude extracts against Staphylococcus aureus, Bacillus subtilis, Escherichia faecalis, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Xanthomonas campestris, Erwinia carotovora, Candida albicans, Alternaria alternate and Fusarium oxysporum was carried out using agar well technique. Biochemical tests and carbon source requirements were used in characterization of the selected antimicrobial producers. M1 was the best agar medium for isolation of actinomycetes. The number of actinomycetes from regions A, B, C, and D in the crater varied significantly (F = 27.50 P = 0.000). Out of the 156 actinomycetes isolates, 20 isolates were positive for both primary and secondary screening for antimicrobials. There was no significant difference in the zones of inhibition in primary screening of the actinomycetes for antagonistic properties against the test pathogens (F = 1.6957 P = 0.0838). The zones of inhibition after secondary screening varied significantly (F = 2.4473 P = 0.0089). Likewise, there was a significant difference (F = 6.6046 P = 0.001338) in the zones of inhibition after exposing the pathogens to ethyl extracts of the selected antagonistic actinomycetes. There is need to purify and characterize the antimicrobials obtained from the present study.

关键词： Actinomycetes Antimicrobials Crater Menengai Metabolites Sensitivity

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Optimization and Characterization of Cellulose Extraction from Grevillea robusta (Silky Oak) Leaves by Soda-Anthraquinone Pulping Using Response Surface Methodology

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Green and Sustainable Chemistry 2024年第3期14卷 43-65页

作者： Catherine N. Muya john M. Onyari Lydia W. njenga Joab O. Onyango Wilson M. Gitari Department of Chemistry The University of Nairobi Nairobi Kenya School of Chemical and Material Science The Technical University of Kenya Nairobi Kenya

Response surface methodology (RSM) using the central composite design (CCD) was applied to examine the impact of soda-anthraquinone pulping conditions on Grevillea robusta fall leaves. The pulping factors studied were: NaOH charge 5% to 20% w/v, pulping time 30 to 180 minutes, and the anthraquinone charge 0.1 to 0.5% w/w based on the oven-dried leaves. The responses evaluated were the pulp yield, cellulose content, and the degree of delignification. Various regression models were used to evaluate the effects of varying the pulping conditions. The optimum conditions attained were;NaOH charge of 14.63%, 0.1% anthraquinone, and a pulping period of 154 minutes, corresponding to 20.68% pulp yield, 80.56% cellulose content, and 70.34% lignin removal. Analysis of variance (ANOVA), was used to determine the most important variables that improve the extraction process of cellulose. The experiment outcomes matched those predicted by the model (Predicted R2 = 0.9980, Adjusted R2 = 0.9994), demonstrating the adequacy of the model used. FTIR analysis confirmed the elimination of the non-cellulosic fiber constituents. The lignin and hemicellulose-related bands (around 1514 cm−1, 1604 cm−1, 1239 cm−1, and 1734 cm−1) decreased with chemical treatment, indicating effective cellulose extraction by the soda-anthraquinone method. Similar results were obtained by XRD, SEM and thermogravimetric analysis of the extracted cellulose. Therefore, Grevillea robusta fall leaves are suitable renewable, cost-effective, and environmentally friendly non-wood biomass for cellulose extraction.

关键词： Cellulose Extraction Response Surface Methodology Central Composite Design Delignification

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