https://repository.seku.ac.ke/handle/123456789/19 2026-07-24T11:48:01Z 2026-07-24T11:48:01Z Ngumbi, Paul K. Mugo, Simon W. Ngaruiya, James M. https://repository.seku.ac.ke/handle/123456789/8404 2026-07-23T08:20:47Z 2018-07-01T00:00:00Z

Determination of gold nanoparticles sizes via surface plasmon resonance Ngumbi, Paul K.; Mugo, Simon W.; Ngaruiya, James M. Surface plasmon resonance technique has been highly employed in determination of the sizes of metallic nanoparticles (NPs). Generally, NP size has been viewed as a function of SPR wavelength value only, with every value of this wavelength being associated with one particular size. In this paper, gold NPs (AuNPs) prepared through the citrate reduction method with a variation in the amount of citrate used on gold (III) chloride precursor was studied. Using UV-Vis spectra analysis of the synthesized NPs in colloidal form, SPR absorption band with a wavelength ranging from 518 to 520 nm was detected. At 518 and 519 nm peaks, the recorded average NP size was 12 nm while 520 nm coincided with NPs of diameters 11 and 13 nm. This indicated that small and large AuNPs within the plasmonic size can present similar high resonance. We attribute this observation to the atomic interactions within the NPs solution hence the availability of the high density of the surface (resonance) electrons from the NPs surface atoms. DOI: 10.9790/5736-1107012529

2018-07-01T00:00:00Z Jalloh, Abdul A. Yusuf, Abdullahi A. Khamis, Fathiya M. Sevgan, Subramanian https://repository.seku.ac.ke/handle/123456789/8393 2026-07-02T09:34:41Z 2026-06-24T00:00:00Z

Impacts of multitrophic interactions in diversified cropping systems for sustainable management of Spodoptera frugiperda Jalloh, Abdul A.; Yusuf, Abdullahi A.; Khamis, Fathiya M.; Sevgan, Subramanian Background: Rapid population growth has made the sustainable intensification of agricultural productivity essential for meeting global food demands while maintaining environmental integrity and biodiversity. Diversified cropping systems, such as intercropping, push-pull systems, and cover cropping, are recognized as agroecological strategies to enhance plant growth and protection, and suppress major pests, including the fall armyworm (FAW, Spodoptera frugiperda). These systems influence complex above-andbelow ground interactions among herbivorous pests, plants, soil microbes, and their natural enemies. Aims: This review synthesizes current knowledge on how diversified cropping systems shape multitrophic interactions that affect soil health, plant performance, S. frugiperda suppression, and biocontrol within agroecosystems. Methods: We critically reviewed the impact of below-and-above ground interactions and synthesized recent knowledge from soil microbiology, entomology, ecology, and agronomy to examine how diversified cropping systems shape plant-microbe-pest interactions. Particular emphasis is given to the roles of soil microbial communities, plant defensive responses, and natural enemies contributing to S. frugiperda suppression. Results and Conclusions: This review provides a comprehensive understanding of below-and-above ground interactions and the contribution of soil microbes in crop protection. Evidence indicates that diversified cropping systems can reduce S. frugiperda infestations through multiple ecological mechanisms. These include increased activity of natural enemy, improved plant defense traits, and beneficial changes in soil microbial communities. These systems also promote improved soil structure, nutrient cycling, and crop productivity. Integrating these ecological interactions into crop management offers a promising integrated pest management strategy for sustainable S. frugiperda management, particularly smallholder farming systems in sub-Saharan Africa and other regions affected by S. frugiperda. https://doi.org/10.1079/ab.2026.0037

2026-06-24T00:00:00Z Ndede, Charles O. Ojiambo, Viona Abonyo, Jeconia O. Ngesa, Joel O. https://repository.seku.ac.ke/handle/123456789/8391 2026-06-15T08:42:30Z 2026-03-01T00:00:00Z

Simulation of unsteady magnetohydrodynamic flow of hybrid nanofluid in solar thermal collectors Ndede, Charles O.; Ojiambo, Viona; Abonyo, Jeconia O.; Ngesa, Joel O. The urgent challenge of climate change calls for innovative energy solutions that reduce greenhouse gas emissions and strengthen system resilience. Solar thermal technology, when enhanced by advanced fluid dynamics, offers a promising pathway towards sustainable clean energy. This study simulates the performance of hybrid nanofluids, specifically copper and titanium dioxide nanoparticles dispersed in water, to improve heat transfer efficiency in parabolic solar thermal collectors. The governing nonlinear partial differential equations describing mass, momentum, energy, concentration, and magnetic induction are reduced to ordinary differential equations using similarity transformations and solved using MATLAB’s collocation based bvp4c solver. The model assumes two-dimensional laminar flow, thermal equilibrium between fluid phases, and temperature dependent hybrid nanofluid properties. Parametric analysis shows that Brownian diffusion and thermophoresis significantly influence velocity, temperature, and nanoparticle concentration, while Prandtl and thermal Grashof numbers strongly govern convective transport and MHD coupling. The findings provide deeper physical insight into hybrid nanofluid dynamics under electromagnetic influences and support the optimization of solar thermal collectors for enhanced thermal performance. The study contributes to Sustainable Development Goals 13 by advancing efficient and climate resilient clean energy technologies.

2026-03-01T00:00:00Z Onyango, Ephine A. Kituyi, Sarah N. Hunja, Carol W. Kimatu, Josphert N. Nyaboga, Evans N. https://repository.seku.ac.ke/handle/123456789/8390 2026-06-15T07:13:15Z 2026-01-01T00:00:00Z

Preliminary report of epicoccum spp. associated with brown leaf spot on cassava in Kenya Onyango, Ephine A.; Kituyi, Sarah N.; Hunja, Carol W.; Kimatu, Josphert N.; Nyaboga, Evans N. Cassava brown leaf spot (BLS) is among the most damaging diseases that significantly reduce cassava root yields and quality. In this study, drought-resistant cassava varieties were screened on an experimental farm in Kitui County, Kenya. One variety, Kasukari, exhibited abnormal morphological aberrations suggesting BLS and necessitated systematic studies to establish the causal agents. Fungi were isolated from symptomatic leaves and purified on Potato Dextrose Agar (PDA) with antibiotics. Fungal pathogens were identified using morpho-cultural characteristics and molecular characterization through polymerase chain reaction (PCR) amplification and sequencing of the internal transcribed spacer (ITS). 162 Kasukari samples were used to determine the prevalence and severity of the disease, while 15 samples were used to determine the effects of the disease. Pathogenicity tests of ten isolates were conducted in vitro using detached leaves of the healthy Kasukari variety. The results indicated that the prevalence within the plots had no significant difference (χ2 = 6, p-value = 0.1991). However, there was a significant difference in severity (χ2 = 53.013, p-value = 1.166e-09). PCR with the ITS marker identified the fungal pathogens from the genera Alternaria, Epicoccum, Preussia, and Cladosporium. Epicoccum spp. had colonies of white clusters that formed concentric rings, while the reverse had grey-brown colonies and a regular margin. Conidia produced on PDA were oval, hyaline, unicellular, and aseptate, consistent with Epicoccum morphology. Based on ITS identification and pathogenicity assays, this study provides a preliminary report of an Epicoccum sp. associated with brown leaf spot (BLS) disease in cassava in Kenya. However, due to the absence of multi-locus sequence data and the limited number of isolates tested, the causal role of Epicoccum remains suggestive. These findings form the basis for future studies to confirm the causal role of Epicoccum spp. and clarify its epidemiology. The study will also help inform prevention and management strategies, including breeding programs and targeted control measures. https://doi.org/10.1016/j.heliyon.2026.e45093

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