https://repository.seku.ac.ke/handle/123456789/19 2026-08-17T00:45:29Z https://repository.seku.ac.ke/handle/123456789/8419 Natural radioactivity and radiological risks in soil and irish potatoes in Mt. Elgon region, Bungoma County, Kenya Wanyama, Conrad; Nakitare, Michael; Linturi, James M. This study examines the exposure levels and the consequent radiological effects of natural radioactivity on the people of Mt. Elgon Kenya. Soil and Irish potato samples were obtained for this purpose. The gathered samples were processed and evaluated using gamma ray spectrometry at the physics laboratory of South Eastern University Kenya. The mean activity concentration of Ra-226, Th-232, and K-40 were determined to be: 68 ± 3.42, 359 ± 17.98 and 394 ± 19.73 Bq/kg for soil; 38 ± 1.93, 308 ± 15.44 and 776 ± 38.83 Bq/kg for Irish potatoes. The soil annual effective dosage measured indoors for Ra-226, Th-232, and K-40 falls within the following range of 0.12 – 0.25 mSv/y with an average of 0.18 mSv/y. The average outdoor annual effective doses in soil averaged at 0.12 mSv/y. The average radium equivalent, internal hazard index, external hazard index, absorbed dose rate and were below the recommended standards of 370 Bq/kg, 100 mSvy-1, 60 nGyh-1 and 300 mSvy-1 respectively annual gonadal index (AGED) for all examined soil samples were 332 ± 16.53 Bq/kg, 1.3 ± 0.06 mSvy-1, 1.4 ± 0.07 mSvy-1, 51 ± 2.56 nGyh-1 and 254 ± 12.7 mSvy-1 respectively. All the radiological parameters set by ICRP, with the exception of a few soil samples. The translocation of radionuclides from soils-to-Irish potatoes were 0.5 ± 0.02, 0.8 ± 0.04 and 1.9 ± 0.09 for 226Ra, 232Th and 40K respectively. Hence, soils obtained from the study area are rich in potassium minerals, thorium minerals and uranium minerals. DOI 10.24200/jonra.2026.2031.1231 2026-08-01T00:00:00Z https://repository.seku.ac.ke/handle/123456789/8404 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 https://repository.seku.ac.ke/handle/123456789/8393 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 https://repository.seku.ac.ke/handle/123456789/8391 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