http://41.89.164.27:8080/xmlui/handle/123456789/29 2026-09-16T00:50:49Z 2026-09-16T00:50:49Z Chonge, Gerald W. Cherop, Hezekiah K. Kanule, Jason http://41.89.164.27:8080/xmlui/handle/123456789/2812 2026-09-10T12:12:50Z 2026-06-01T00:00:00Z

Neutron skin thickness and the transition from cluster decay to spontaneous fission in superheavy nuclei Chonge, Gerald W.; Cherop, Hezekiah K.; Kanule, Jason Understanding the competition between cluster decay and spontaneous fission is essential for elucidating the stability and decay characteristics of neutron-rich superheavy nuclei. In this work, the density- dependent cluster model combined with the Wentzel-Kramers-Brillouin (WKB) approximation is employed to investigate the competing decay modes of selected superheavy nuclei with atomic number Z>103. Cluster-decay penetrabilities, decay constants, together with spontaneous-fission barrier heights and half-lives, are calculated using the AME2020 nuclear mass evaluation and validated against the available experimental data from NUBASE2020. The calculations demonstrate that cluster decay is governed primarily by decay Q-values, barrier penetrability, shell effects, and daughter-nucleus configurations, whereas spontaneous-fission half-lives decrease systematically with increasing fissility as the calculated fission barriers are reduced. To probe the structural evolution of the investigated isotopic chains, the calculated decay characteristics are further analysed in relation to neutron skin thickness. A transition from cluster-decay dominance to spontaneous- fission dominance is observed for nuclei exhibiting larger neutron skin thickness. The observed trends are consistent with the systematic evolution of nuclear structure and decay energetics across the investigated isotopic chains, with neutron skin thickness serving as a structural indicator rather than an independent driver of the calculated decay properties. Comparison with the available experimental spontaneous-fission half-lives yields a root-mean-square deviation of 1.822, demonstrating satisfactory agreement with experiment. The present study establishes a systematic benchmark for assessing the competition between cluster decay and spontaneous fission in superheavy nuclei and provides a reference for the development and validation of microscopic models incorporating neutron-skin-dependent nuclear interactions.

2026-06-01T00:00:00Z Odiwuor, Vincent O. Barasa, Stephen S. Onyambu, Onyambu http://41.89.164.27:8080/xmlui/handle/123456789/2810 2026-09-10T08:59:00Z 2026-08-01T00:00:00Z

Influence of chemical activation on the strength and durability of lime–corn cob ash cement Odiwuor, Vincent O.; Barasa, Stephen S.; Onyambu, Onyambu The slow rate of strength gain and the relatively poor durability of lime–pozzolana binders limit their broader use in sustainable construction applications. This study examined how chemical activation influences the physicochemical characteristics, compressive strength, porosity, and sulfuric acid resistance of lime–corn cob ash (CCA) mortars. CCA was analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and electrical conductivity tests to evaluate its pozzolanic behavior. Mortars containing a 50:50 lime–CCA ratio were prepared using water, 0.5 M NaOH, and 0.5 M Na2SO4 as mixing media. The results indicated that CCA is rich in silica (61.61% SiO2), with a combined SiO2 + Al2O3 + Fe2O3 content of 72.19%, confirming its suitability as a pozzolanic material. The reduction in electrical conductivity of about 28.1% after 240 min suggests moderate pozzolanic reactivity of CCA. Chemical activation markedly enhanced performance. Compressive strength increased from 2.91 MPa in the non-activated system to 5.92 MPa and 7.77 MPa for Na2SO4 and NaOH-activated mortars, respectively. Porosity showed a decreasing trend from L100–H2O to LCCA50–0.5 M NaOH. Under sulfuric acid exposure, activated mortars experienced lower mass and strength losses than non-activated ones, with NaOH activation providing the best resistance. In contrast, pure lime mortar fully disintegrated under acidic conditions. The results confirm that chemical activation significantly improves the mechanical performance and durability of lime–CCA binders. The study demonstrates the viability of corn cob ash as a sustainable pozzolanic material for low-carbon, non-structural construction applications and highlights the effectiveness of different chemical activators in enhancing lime-based systems.

2026-08-01T00:00:00Z Odiwuor, Vincent O. Samita, Fidelis N. Wetungu, Martin W. http://41.89.164.27:8080/xmlui/handle/123456789/2809 2026-09-10T08:45:25Z 2026-07-01T00:00:00Z

Performance and Durability of Chemically Activated Lime-Based Cement Blended With Rice Husk Ash Odiwuor, Vincent O.; Samita, Fidelis N.; Wetungu, Martin W. Lime–pozzolana binders ofer a low-carbon alternative to conventional materials; however, their practical application is limited by slow strength development and insufcient durability, particularly under aggressive chemical environments. In addition, existing studies on chemical activation have largely focused on OPC-based systems, with limited attention to lime-based binders and their durability performance. This study investigates the efect of chemical activation on the performance and durability of lime–rice husk ash (RHA) mortars. The objective was to evaluate how sodium hydroxide (NaOH) and sodium sulfate (Na2SO4) infuence compressive strength, porosity, and resistance to sulfuric acid attack of lime mortars. Physicochemical characterization confrmed that the RHA contained 94.95% SiO2 with high amorphous content and strong pozzolanic reactivity (> 60% conductivity loss). Results showed that RHA incorporation improved lime mortar performance, while chemical activation signifcantly enhanced these properties. NaOH activation increased compressive strength by 132%, compared to 53% for Na2SO4, relative to the non- activated system. Porosity decreased progressively across the systems, with the lowest values observed in NaOH-activated mortars. Under acid exposure, all RHA-containing mortars outperformed pure lime, which disintegrated completely. Strength and mass losses were lower in activated systems, particularly with NaOH. Deterioration was more severe in 3% H2SO4 than in a 0.5% solution. The fndings indicate that chemical activation improves the short-term performance of lime–RHA mortars, although reaction products were not directly quantifed. These results highlight the potential of chemically activated lime–RHA mortars as sus- tainable construction materials, particularly in resource-constrained regions.

2026-07-01T00:00:00Z Odiwuor, Vincent O. Ayabei, Kiplagat Okoth, Maurice O. Munyao, Onesmus M. http://41.89.164.27:8080/xmlui/handle/123456789/2808 2026-09-10T07:25:48Z 2026-06-01T00:00:00Z

Using Pozzolanic Materials to Improve Mechanical Properties of Lime-Based Mortar Odiwuor, Vincent O.; Ayabei, Kiplagat; Okoth, Maurice O.; Munyao, Onesmus M. The environmental impact associated with the production of Portland cement has intensifed interest in sustainable alternatives such as lime-based binders. However, their application is constrained by low early strength and slow hardening. This study evaluates rice husk ash (RHA) and sugarcane bagasse ash (SCBA) as pozzolanic additives to enhance the mechanical performance and durability of lime mortars. Hydrated lime was partially replaced (50%) with RHA or SCBA, and the mortars were air-cured for 28 days. Both ashes satisfed the standard pozzolanicity requirements. RHA exhibited a higher amorphous silica content and greater reactivity, whereas SCBA demonstrated slower but sustained pozzolanic activity. The incorporation of these pozzolans signifcantly improved performance. Compressive strength increased from 0.43 MPa for pure lime to 4.64 and 3.84 MPa for RHA and SCBA mortars, respectively. Flexural strength improved from 0.17 to 2.70 MPa and 0.97 MPa for RHA and SCBA mortars, respectively. Water absorption was substantially reduced in the modifed mortars, indicating improved pore structure and du- rability. RHA provided superior strength development and lower permeability, while SCBA ofered moderate strength en- hancement with improved fexibility. These characteristics make both materials suitable for nonstructural applications, including heritage conservation and restoration. The fndings demonstrate that agricultural waste ashes can serve as efective, low-carbon pozzolanic materials for durable lime-based construction.

2026-06-01T00:00:00Z Odiwuor, Vincent O. Wambu, Enos W. Okoth, Maurice O. Kipkemboi, Pius K. http://41.89.164.27:8080/xmlui/handle/123456789/2807 2026-09-10T06:58:15Z 2026-08-01T00:00:00Z

Pozzolanic reactivity and mortar performance of sugarcane bagasse and sawdust ashes in lime based binders Odiwuor, Vincent O.; Wambu, Enos W.; Okoth, Maurice O.; Kipkemboi, Pius K. The growing energy demand, rising production costs, and environmental impacts associated with ordinary Portland cement have intensified the search for sustainable, low-carbon binders. Lime–pozzolana systems incorporating agricultural waste ashes present a viable alternative; however, their development is often based primarily on strength results, limiting insight into the role of material structure and reactivity. This study comparatively evaluates sugarcane bagasse ash (SCBA) and sawdust ash (SDA) as supplementary cementitious materials in lime-based binders, with emphasis on linking physicochemical properties to performance. The ashes were produced under controlled calcination at 600–700 °C and characterized for oxide composition, mineralogy, particle size distribution, specific surface area, and loss on ignition. SCBA exhibited a high combined content of SiO2 + Al2O3 + Fe2O3 (86.60%) and was predominantly amorphous, whereas SDA showed a significantly lower content (23.16%), higher loss on ignition (15.33%), and a largely crystalline structure, despite possessing a higher specific surface area. Pozzolanic activity was assessed via electrical conductivity measurements. The results revealed faster early reactivity for SDA, attributed to its higher surface area, while SCBA demonstrated more sustained reactivity due to its high amorphous silica content. At 28 days, SCBA–lime mortars achieved compressive strengths of 2.98–3.72 MPa, compared to 1.51–2.52 MPa for SDA–lime mortars across pozzolan-to-lime ratios of 3:1 to 1:1. Similarly, SCBA mortars exhibited higher bulk density (930.6 kg/m3) and lower water absorption (14.14%) than SDA mortars (812.4 kg/m3 and 18.14%, respectively). All mixes exceeded the minimum strength requirement of 2 MPa for lime–pozzolana binders, although they remained significantly lower than the OPC control (48.06 MPa). Overall, SDA enhances early-age reactivity, whereas SCBA provides superior long-term mechanical performance. These findings establish a clear relationship between material characteristics, pozzolanic behavior, and mortar performance, offering practical guidance for the selection of locally available agricultural ashes in sustainable construction.

2026-08-01T00:00:00Z Odiwuor, Vincent Onyango, Wambu, Enos W. Okoth, Maurice O. Kipkemboi, Pius K. http://41.89.164.27:8080/xmlui/handle/123456789/2806 2026-09-09T12:19:44Z 2026-08-01T00:00:00Z

Physicochemical And Mechanical Performance Of Lime- Based Binders Incorporating Rice Husk Ash And Calcined Clay Odiwuor, Vincent Onyango,; Wambu, Enos W.; Okoth, Maurice O.; Kipkemboi, Pius K. The environmental concerns linked to ordinary Portland cement have increased the demand for alternative binder systems that utilize locally available resources efficiently and still provide adequate performance. This study investigates the potential of rice husk ash (RHA) and calcined clay (CC) as supplementary pozzolanic materials in lime-based binders. The objective was to comparatively evaluate the influence of these materials on physicochemical properties, reactivity, and mechanical performance and to establish relationships between these parameters. RHA and CC were produced under controlled calcination conditions and characterized using chemical, mineralogical, and surface analyses. Pozzolanic reactivity was assessed through electrical conductivity measurements, while performance was evaluated using water absorption and compressive strength tests. The results showed that both materials satisfied standard chemical requirements for pozzolans; however, their reactivity differed significantly due to variations in structure and surface characteristics. RHA exhibited a predominantly amorphous structure and a high specific surface area, resulting in faster reaction kinetics, greater calcium hydroxide consumption, and slightly higher compressive strength when used in lime-based mortars. In contrast, CC displayed a mixed amorphous–crystalline composition and lower surface area, leading to slower but sustained reactivity. The incorporation of both pozzolans improved compressive strength and reduced water absorption compared to pure lime mortar. After 28 days, blended mortars achieved strengths of approximately 4.2–4.3 MPa, indicating suitability for non-structural applications. The findings demonstrate that binder performance is governed by the combined effects of chemical composition, phase structure, surface properties, and reaction kinetics rather than composition alone. This study provides a systematic comparative assessment of RHA and CC in lime-based systems and highlights the importance of integrating physicochemical characteristics with reactivity measurements to better understand and optimize the performance of sustainable binder materials.

2026-08-01T00:00:00Z Ashibambo, Nancy Shichika, Julius Bii, Albert http://41.89.164.27:8080/xmlui/handle/123456789/2805 2026-09-08T13:21:56Z 2025-08-01T00:00:00Z

Mathematical Modelling of Malaria Transmission Dynamics in Kenya: The Role of Seasonality, Drug Resistance, and Human Movement Ashibambo, Nancy; Shichika, Julius; Bii, Albert Background: Although there has been a remarkable improvement in controlling malaria, the clinical problem is still of public health importance in Kenya and especially in areas where there is climatic variation, which affects the transmission pattern. Seasonal rainfall has been explored as a central factor in the breeding of mosquitoes and the ensuing outbreaks of malaria, but most models have not included these ecological forces together with drug resistance and human mobility. Objective: The purpose of the study is to formulate and examine a seasonally driven malaria transmission model to represent the interaction of the dynamics of mosquito infection, antimalarial drug resistance, and human mobility in the Kenyan setting. Methods: We developed a compartmental model with drug-susceptible and drug-resistant parasite strains, categorised by stages of human infections, and mosquitoes. The model proposes seasonalforcing in a sinusoidal representation, which is staggered with the Kenyan rainfall pattern, which drives the mosquito recruitment. Inter-regional human migration is thought to take the form of a toggling migration parameter. The deSolve package in R was then used to simulate the model within a 2-year horizon. Monthly averages were then used to determine the peaks of the infection rates, and these were equated to the long (March to May) and short (October to December) rainy seasons in Kenya. Results: It was found that the results of simulations identified clear infection spikes closely corresponding to two periods of rainfall in Kenya (bimodal). The post-rainy periods when mosquitoes infected with the malaria parasites reach their peak (Q), as well as when humans are infected, were consistent, making a difference to resistant infections, which do not drop as fast as susceptible infections. The circulation of human movements enhanced the continuation and propagation of resistant infections. This indicated the environmental drivers of seasonal forcing that explained the time and magnitude of outbreaks. Conclusion: Noting the inclusion of seasonality, drug resistance, and movement in the models of malaria transmission increases their reality and predictability to a great extent. The syncing of the most significant infection-containing seasons with rainy seasons necessitates climate-tactful surveillance and intervention time. In Kenya, where the mobility of the population is high based on trade, labour migration, and between urban and rural regions, the modelling of such mobility is very important in gaining an understanding of the management of the epidemic. The model can be of great benefit in optimising vector control, deploying drugs and allocating resources regionally to malaria-endemic countries such as Kenya.

2025-08-01T00:00:00Z Ruto, Faith Bii, Albert Shichikha, Maremwa http://41.89.164.27:8080/xmlui/handle/123456789/2803 2026-09-08T09:30:37Z 2026-08-01T00:00:00Z

Navier-stokes Based Modelling of Airflows in Forest Canopies and Its Influence on Local Climate Dynamics Ruto, Faith; Bii, Albert; Shichikha, Maremwa Background: Forest canopies strongly influence atmospheric airflow, turbulence generation, heat exchange, water transport, and carbon dioxide distribution, thereby regulating the local climate. However, accurately representing airflow dynamics within forests remains challenging because of vegetation drag and turbulent mixing. Aims: This study developed a mathematical model based on the Navier–Stokes equations to investigate airflow behaviour within forest canopies and assess its influence on local climate dynamics. Study Design: This was a computational fluid dynamics (CFD)-based modelling study employing the Reynolds-averaged Navier–Stokes (RANS) equations coupled with the standard k–ε turbulence model.Place and Duration of Study: Department of Mathematics and Computer Science, University of Eldoret, Kenya, between July 2025 and April 2026. Methodology: The incompressible Navier–Stokes equations were used to model airflow within and above forest canopies. Vegetation effects were represented using a canopy drag-force term based on leaf area density. Turbulence was simulated using the standard k–ε model, while additional transport equations described temperature, water vapour, and carbon dioxide dynamics. The governing equations were discretised using the Finite Volume Method (FVM) and solved numerically in MATLAB. Simulations were performed for dense, medium, and sparse canopy configurations over a 30 m computational domain. Results: Airflow velocity increased with height in all canopy configurations, with dense canopies showing the greatest attenuation. At canopy height, velocities were approximately 1.45 m/s, 1.95 m/s, and 2.65 m/s for dense, medium, and sparse canopies, respectively. Turbulent kinetic energy (TKE) peaked near the canopy top, reaching approximately 66 m2/s2, 44 m2/s2, and 22 m2/s2, respectively. Temperature increased with height, while moisture and carbon dioxide concentrations decreased because of enhanced turbulent mixing. Dense canopies retained higher moisture and carbon dioxide levels than medium and sparse canopies. Conclusion: Forest canopy density significantly influenced airflow structure, turbulence production, and scalar transport. Dense canopies provided stronger microclimatic regulation through enhanced momentum attenuation, moisture retention, and carbon storage. The developed modelling framework provides a useful tool for studying canopy–atmosphere interactions and local climate dynamics.

2026-08-01T00:00:00Z Obande, Ruth Kandie, Joseph Bii, Albert http://41.89.164.27:8080/xmlui/handle/123456789/2802 2026-09-08T06:21:27Z 2026-08-01T00:00:00Z

Hydrodynamic Modelling of Mixing Efficiency and Optimal Bio-methane Production in Anaerobic Digesters Using a Two-Dimensional Navier–Stokes Framework Obande, Ruth; Kandie, Joseph; Bii, Albert Background: Anaerobic digestion (AD) is a proven technology for renewable bio-methane production, but digester efficiency is often limited by poor hydrodynamic mixing rather than by microbial kinetics alone; most existing models, however, assume idealised, fully homogeneous reactors. Objective: This study investigates the influence of hydrodynamics on mixing efficiency and bio-methane production potential in anaerobic digesters using mathematical modelling. Methods: A two-dimensional incompressible Navier–Stokes model was coupled with a tracer advection– diffusion equation to simulate slurry flow and mixing behaviour. The governing equations were non- dimensionalised using the Reynolds and Péclet numbers, discretised using the finite difference method, and solved numerically in MATLAB. An optimisation framework that treated inlet velocity as the control variable, together with an adjoint sensitivity analysis, was used to evaluate and improve mixing efficiency. Results: At a Reynolds number of 2100, the flow exhibited transitional characteristics, with a dead zone fraction of approximately 35.1%. Velocity contours revealed limited circulation, whereas the tracer distribution showed a non-uniform concentration pattern across the domain. The dead zone fraction declined exponentially as Re increased, with values above 4000 projected to reduce it below 15%. At Pe = 10,000, transport was strongly advection-dominated, and the adjoint sensitivity analysis identified the inlet/impeller region as offering the greatest leverage over mixing performance. Conclusion: Hydrodynamic conditions play a critical role in determining mixing efficiency and, consequently, bio-methane production potential. The developed model provides a computationally efficient framework for analysing and optimising anaerobic digester performance and offers a foundation for future integration with biochemical reaction models.

2026-08-01T00:00:00Z Kegwaro, Winnie King’ang’i, Denis Meli, Collins http://41.89.164.27:8080/xmlui/handle/123456789/2800 2026-09-07T12:01:28Z 2026-06-01T00:00:00Z

On the Norm of Jordan Elementary Operators in Tensor Product of C ∗ -Algebras Kegwaro, Winnie; King’ang’i, Denis; Meli, Collins Elementary operators have been studied over years, with their norms being of significant interest in operator theory. The study includes the derivation of formulas that describe norms in terms of their coefficient operators, which is traced back to Stampfli`s Theorem that used the property of Numerical range as a foundation for the study of norms. Other properties of Elementary operators have been studied ever since, but little is known on Jordan Elementary operators in tensor products of C ∗ - algebras. This paper aims to extend the determination of norms of Jordan Elementary operators in the tensor product of C ∗ - algebra by determining the lower bound of the norm using the maximal numerical range by employing the technique of tensor product, finite rank operator and inner product. A lower bound of Jordan elementary operator in tensor product of C ∗algebras is obtained.

2026-06-01T00:00:00Z