Browsing by Author "Makokha, John Wanjala"

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A Framework for Integration of Web 3.0 and Social Media Technologies in Government Portals for Personalized Integrated Service Delivery
(International Journal of Computer Trends and Technology, 2020-06-05) Mwai, Josphat Karani; Makokha, John Wanjala; Karume, Simon Maina
The sustainable development goals (SDGs), which are at the heart of the 2030 Agenda for Sustainable Development, are closely interrelated. The integrated nature of the SDGs has shed new light on the need for integrated service delivery by various governments. An effective e-government portal needs a system with good Integration, interoperability and personalized service delivery. However, most e-government portals lack Integration, interoperability and personalized service delivery. The purpose of this study was to investigate how Web 3.0 and Social Media technologies could be integrated into existing government portals for personalized, integrated service delivery to citizens. The study employed design science research to achieve its objectives. The target population consisted of 94 experts involved in managing social media and portal services for the Kenyan government national portal (eCitizen). The study established that while most government portals had already incorporated social media, social media was being used mostly for information dissemination and not to offer other services like public participation or transactional services. The study developed a framework made of six components that would guide the Integration of web 3.0 and social media technologies within government portals to achieve personalized, integrated service delivery.
Activity Concentration Levels of Natural Radionuclides in the Sediment Samples from Rosterman Gold Mine, Lurambi Sub – County, Kakamega County, Kenya
(International Journal of Research and Innovation in Applied Science, 2020-07-05) Wanyama, Conrad Khisa; Masinde, Fred Wekesa; Makokha, John Wanjala
Rosterman, located in Lurambi sub - county, Kakamega County, Western Kenya consists of gold mining that is done locally (artisanal gold mining). The activity concentration of 238U, 232Th and 40K in sediment samples from the wastes of gold mining were determined by gamma ray spectrometry using NaI (Tl) detector and decomposition of measured gammaspectra. As a measure of radiation hazard to the general population, gamma radiation dose rates were also evaluated. The average activity concentrations of 238U, 232Th and 40K were 85±2.24, 114±5.78and 260±12.18Bqkg-1, respectively. The mean absorbed dose rate in air was 52.5±4.2nGyh-1 while the annual average effective dose rate for indoor and outdoor were 0.4±0.02 and 0.3±0.01mSvy-1 respectively. The absorbed dose rate due to gamma radiation from naturally occurring radioactive materials was below the global average value of 60 nGyh-1. Hence, mining of gold at Rosterman has minimal hazardous health implicationto the general public.
Advection and its applications: Trajectories over Busia County in Kenya
(Climate Change, 2020-12-04) Juma, G. S.; Kituni, Nebat; Makokha, John Wanjala
Advection is defined as a conservative transport of a substance by bulk motion. The substances include pollutants, enthalpy or any material that contains thermal energy. This paper introduces the concept of advection as applied in air pollution modelling of possible pollutants using Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). A three dimensional (3-D) advection equation is specified and a graphical output of a forward air trajectory given over Busia County. The study reveals transboundary flow of air pollutants to the Eastern parts of Uganda and across counties in Western, Central, Rift valley and Eastern Kenya respectively. An intercounty environmental monitoring policy framework is recommended in this study due to the trans county nature of air pollution issues.
Aerosol optical depth and precipitation rate projections over east africa utilizing self organizing map
(The International Journal Of Science & Technoledge, 2017-03-01) Makokha, John Wanjala; Angeyo, H.K.; Muthama, John Nzioka
Assessment of future aerosols impacts on both regional and global climate change requires a comprehensive projection tool that reliably provides information on aerosol evolution characteristics with high fidelity. In the current study, we propose an algorithm based on Self-Organizing Map (SOM) and Community Atmosphere Model 4 (CAM4) for long term Aerosol Optical Depth (AOD) and Precipitation Rate (PR) projections over East Africa. To start with, AOD and PR retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measurement Mission (TRMM) respectively were cross validated with simulation from CAM4 so as to assess the uncertainty between the measured and simulated retrievals from 2000 to 2014.The error analysis between CAM4 simulations and MODIS measurements (from 2000 to 2014)shows a close match where R2 varies from 0.58 to 0.83 with a corresponding RMSE of between 0.014 and 0.065 (for AOD). Likewise, the uncertainty between simulate and measured PR from CAM4 and TRMM showed an estimated R2 to range between 0.40 and 0.78 while the RMSE varied from 0.021 to 0.091 in the same period and study sites. Based on proposed SOM algorithm and simulated CAM4 retrievals over each study site, an increase of between 1.34-2.43 % for AOD and a decrease of between 1.03-1.98 % in PR are projected over the region by 2030.
Annual Effective Dose from Radon-222 Concentration Levels in Underground Water in Bungoma South Sub-County, Kenya
(Journal of Engineering and Technology for Industrial Applications, 2021-04-30) Butik, George Wangila; Makokha, John Wanjala; Masinde, Fred Wekesa; Wanyama, Conrad Khisa
This research measured the concentration levels of radon in groundwater and determined the ingestion and inhalation dose. The study used RAD7 detector with RAD7-H2O accessory from Durridge Company to determine the radon levels. Thirty water samples in granitic dominated regions were collected from various areas of Bungoma County: ten from boreholes (BH), ten from hand dug wells (WL) and ten from springs (SP). The water samples were collected in 250 ml bottles which were tightly covered with lid to avoid radon leakage. The highest value was 303±4.00 KBq/m3 recorded in Kanduyi well and the lowest was 126±11.4kBq/m3 from where most of the samples recorded a high radon concentration with a mean of 269±5.25 KBq/m3 in wells, 213±7.96 KBq/m3 in boreholes and 290±7.70 KBq/m3 in springs. The average ingestion dose was found to be 1.5±0.07mSv/yr, 1.9±0.09 mSv/yr and 2.1±0.1 mSv/yr. The average annual effective dose rate for the samples collected were 2±0.1 mSv/yr for boreholes, 2.6±0.13 mSv/yr for wells and 2.7±0.14 mSv/yr for springs. The samples reported an average.
Anomaly Detection in Selected Aerosol Optical Properties and Associated Climate Variables Using a Multivariate Hidden Markov Model: A Case Study over Kenya
(Open Access Library Journal, 2025-10-23) Wanjala, Dennis W.; Makokha, John Wanjala; Khamala, Geoffrey W.
Understanding aerosol climate interactions is crucial for monitoring atmospheric changes and supporting climate resilience efforts, particularly in vulnerable regions such as Kenya. This study applies a Multivariate Hidden Markov Model (HMM) to detect anomalies in key Aerosol Optical Properties (AOP) i.e., Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA), and Ångström Exponent (AE) alongside associated climate variables; Surface Air Temperature (SAT) and Rainfall Rate (RR), over the period 2000-2022. Satellitebased datasets from MODIS, MERRA-2, and TRMM were used to derive monthly means, and descriptive statistics and linear regression were initially employed to characterize long-term variability. The objectives of this study were to examine the temporal and spatial variability of key aerosol and climate parameters over Kenya, detect and classify anomalies in the multivariate dataset using HMM and to interpret the climatic and environmental implications of detected anomalies and their possible causes. The HMM approach successfully identified temporal patterns and hidden states, enabling the detection of significant anomalous periods, particularly between 2010 and 2016, which aligned with regional biomass burning events and transboundary pollution episodes. Results indicate that AOD and SSA anomalies correspond with periods of elevated temperature and reduced rainfall, highlighting potential climate-aerosol feedbacks. The findings demonstrate the utility of multivariate HMMs in capturing the complex dynamics of aerosol-climate interactions and provide a foundation for improved air quality monitoring and climate impact assessments in Kenya which is critical for improving environmental monitoring and enhancing regional climate adaptation strategies.
Assessing the Long-Term Changes in Selected Meteorological Parameters over the North-Rift, Kenya: A Regional Climatology Perspective
(Hydrology, 2024-12-03) Makokha, John Wanjala; Masayi, Nelly Nambande; Barasa, Peter; Ikoha, Peters Anselemo; Konje, Martha Muthoni; Mutonyi, Jonathan; Okello, Victor Samuel; Wechuli, Alice Nambiro; Majengo, Collins Otieno; Khamala, Geoffrey Wanjala
Understanding long-term trends in climatic variables is essential for assessing climate change impacts on regional ecosystems and human livelihoods. A regional analysis of climatic variables over some domains is inevitable due to their geographical location and importance to the agricultural sector. Due to the aforementioned demands, the current study analyzes, trends in precipitation (from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS)), and minimum and maximum temperatures (from TerraClimate) over the North-Rift region of Kenya for over thirty (30) years using satellite data. The seasonal decomposition analysis was performed for each variable to explore the trends and residual components. The findings by the current study indicate that most counties, have experienced enhance precipitation which corresponds to a declining diurnal temperature from 2019 onwards. The seasonality component reveals repeated patterns or variations occurring at steady intervals within each region's data, hence suggesting a distinct regional seasonal trend in the selected meteorological parameters over time. Basically, all counties have reported a relatively constant variability in both maximum and minimum temperatures during the study period except from 2017 onwards where significant variability in the two properties is recorded. In conclusion, the foregoing results that the selected climatic variables exhibit significant spatiotemporal and interannual variability
Assessment of Natural Radioactivity Levels in Tailings From Lurambi Rosterman Gold Mine, Kakamega County Kenya.
(Global Scientific Journal, 2020-07-04) Wanyama, Conrad Khisa; Makokha, John Wanjala; Masinde, Fred Wekesa
Thirty samples were analyzed in the assessment of the activity concentration levels associated with naturally occurring radionuclides materials from Rosterman gold mine. Activity concentration with regard to gamma ray spectrometric analysis was 245±12.39 Bqkg-1; 110±5.15Bqkg-1 and84±4.23Bqkg-1 for 40K, 232Th and 238Urespectively. Averagely, the absorbed dose rate was53.65±6.2 nGy-1, the annual effective dose of 0.4±0.02𝑚𝑚𝑆𝑆𝑣𝑣𝑦𝑦−1 for indoor and 0.3±0.01𝑚𝑚𝑆𝑆𝑣𝑣𝑦𝑦−1 for outdoor were reported. The radiological parameters were averagely valued as 0.7±0.03 𝑚𝑚𝑆𝑆𝑣𝑣𝑦𝑦−1, 0.8±0.04 𝑚𝑚𝑆𝑆𝑣𝑣𝑦𝑦−1 and 278±13.08 Bq/Kg for internal hazard index, external hazard index and radium equivalent respectively. All the radiological parameters were within the recommended permissible values. This therefore points out that gold mining at Rosterman has no significant radiological health implication on the miners and population around.
Baseline Survey on ICT Infrastructure for Online and Digital Learning during and Post Covid_19 in Selected Kenyan Universities
(Asian Journal of Social Science and Management Technology, 2022-04-05) Mbuguah, Samuel Mungai; Njuguna, Alice; Makokha, John Wanjala; Njoki, Catherine
The onset of COVID-19 Pandemic forced the closure of institutions of higher learning to curb the spread of the virus. This led to new scenarios that required education institutions to rapidly adopt. The Solution was mainly online/digital learning. This study sought to investigate the status of ICT infrastructure a key enabler of online/ digital learning. This was achieved through a survey of selected eleven Universities in Kenya. The findings indicated that even though the universities had adopted blended learning the ICT infrastructure was still a challenge. The Paper recommended the need for the institutions to come up with strategies to improve on the ICT infrastructure and hence enhance the quality of learning and reduce digital exclusion.
DFT calculations of elastic, electronic and thermal properties of TiB2Mo
(Oxford Open Materials Science, 2022-02-02) Wafula, Job W.; Manyali, George S.; Makokha, John Wanjala
Ceramics are materials with good mechanical properties; however, low fracture toughness, intrinsic brittleness and poor resistance against oxidation at high temperatures are challenges limiting their applications. TiB2Mo is a ceramic material whose all elastic properties have not been calculated. In this study, we investigated the elastic, electronic and thermal properties of TiB2Mo structure using first principles calculations. All first principles calculations were based on the density functional theory as implemented in Quantum ESPRESSO code with the help of Thermopw as a post-processing code. Obtained lattice parameters of TiB2Mo structure were in good agreement with other previous theoretical studies. TiB2Mo structure was found to be mechanically and dynamically stable at ground state conditions. The results also show that TiB2Mo is brittle, anisotropic and metallic in nature. Based on the calculated Vicker’s hardness Hv, we noted that TiB2Mo is classified as a hard material with fracture toughness of above 7MPam0:5; therefore, it is a promising ultra-high temperature ceramic.
DFT study of structural, mechanical, electronic, and thermoelectric properties of YNbNi2X2 (X=Si or Ge) double half-Heusler alloy
(Results in Materials, 2025-12-28) Wafula, Job W.; Manyali, George S.; Makokha, John Wanjala
This work examines the structural, mechanical, electronic, and thermoelectric characteristics of YNbNi2X2 (X = Si, Ge) double half-Heusler alloys using density functional theory (DFT) computations. Thermodynamic stability was demonstrated by formation energy estimates, and mechanical parameters show ductile behavior with good mechanical stability. YNbNi2Si2 and YNbNi2Ge2 exhibit semiconducting characteristics, with indirect band gaps of 0.51 eV and 0.56 eV, respectively. The Boltzmann transport equation is used to investigate thermoelectric properties, which yield promising Seebeck coefficients and electrical conductivities. The dimensionless figure of merit (ZT) for YNbNi2Ge2 and YNbNi2Si2 peaks at 0.85 and 0.68 at 300 K respectively. However, these values should be regarded as upper limits, as only the electronic contribution to thermal conductivity was considered, and the lattice contribution was not explicitly calculated. The figure of merit (𝑍𝑇 ) increases with temperature suggesting that these are potential materials for energy harvesting applications at high temperature.
DFT+U investigation of electronic, optical, and thermoelectric properties of YAuX (X=Si or Ge or Sn) half-Heusler alloys
(Results in Physics, 2024-05-06) Wafula, Job W.; Manyali, George S.; Makokha, John Wanjala; Madallah, Yusuf; Bouhmaidi, Soukaina; Setti, Larbi
Half-heusler alloys are fascinating thermoelectric materials because they have superior mechanical and transport properties. In this study, we used dft+u calculations and the Boltztrap equation to examine the electronic, optical, and thermoelectric properties of YAuSi, YAuGe, and YAuSn half-heusler alloys. The DFT+U approach predicted band gaps of 1.2767 eV, 0.611 eV, and 1.5741 eV for YAuGe, YAUSn, and YAuSi, respectively. We also observed that all materials under consideration have a broad absorption spectrum ranging from 1 eV to 12 eV, with notable peaks in the visible and UV ranges. The obtained opto-electronic properties position the three alloys as promising candidates for photovoltaic applications. Finally, thermoelectric property calculations revealed that the figure of merit values for YAuSi, YAuGe, and YAuSn HH alloys were 0.730, 0.726, and 0.736 at 800 K, respectively suggesting the materials are also suitable candidates for application in the field of thermoelectricity
EDXRF spectroscopic elemental analysis for efficacy of Kibabii University sewage treatment System
(Open Access Library Journal, 2018-10-18) Situma, Yonah; Odhiambo, Jared Oloo; Makokha, John Wanjala
Elemental analysis of sewage effluents in Kibabii sewage treatment system was achieved via Energy-Dispersive X-Ray Fluorescence (EDXRF) spectroscopy with the aim of assessing the efficacy of the treatment system. Concentrations of lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As) were measured based on clay soil “standards” in concentration range for Pb, Hg and As as 12.7 ppm, 14.3 ppm and 8.83 ppm respectively for certification. Among other probable reference materials, clay soil “standards” were used for certification in this work because of similarity in matrix composition with the sediments. The concentration for Hg, Pb, and As in the sewage sediments were 10.65 ± 2.28 ppm, 8.86 ± 2.92 ppm and 3.41 ± 2.18 ppm respectively in lagoon A. In lagoon B the levels were 3.82 ± 0.56 ppm, 6.35 ± 1.50 ppm and 1.67 ± 0.53 ppm respectively. Lagoon C showed a reduction in the levels with 3.74 ± 1.39 ppm for Hg and 2.30 ± 0.27 ppm for Pb. As was not detected in lagoon C, on the other hand, Cd was not detected in all the lagoons. The efficacies in the treatment varied from 30.34% - 51.78%, 37.63% - 65.41% and 76.63% - 84.81% for lagoon A, B and C respectively. The study was successful in quantifying the heavy elements in the lagoons from which the efficacy in the treatment process was determined. The study provided awareness on the elemental concentration levels in the Kibabii University sewage treatment system, hence creating awareness on what is released into River Kibabii. With this information, the surrounding community and the University can partner in order to mitigate the effects of heavy metals in the effluents in future due to the growth of the University day by day.
Effect of Internal Energy on Specific Heat of Cuprates using s-Wave and d-Wave Hybrid Model
(International Journal of Research and Innovation in Applied Science, 2020-07-05) Wanyonyi, Andrew Munyasia; Waswa, Michael Nakitare; Makokha, John Wanjala
The observation of an exponential decay of the specific heat at low temperatures shows that specific heat (Cv) of cuprates depend on the energy spectrum of a superconductor. This means that devising ways of varying internal energy of a system without necessarily varying temperature can help achieve room temperature superconductivity. In this paper, the relationship between internal energy and specific heat is investigated using a Hamiltonian generated from a Hybrid of swave and d-wave. The Hamiltonian was diagonalized by Bogoliubov-Valatin (BVT) formalism and used to analyze specific heat of Bismuth cuprates. The graph of Cv versus temperature was a skewed Gaussian shaped curve. Maximum Cv was observed at Tc (32 K, 94 K and 108 K) respectively as 2750 eV/K, for Bi-2201, Bi-2212 and Bi-2223. Increasing the number of copper oxide layers can therefore help increase binding energy and increase the temperature at which maximum Cv of the system is attained, a prerequisite for attaining high transition temperature (Tc). As a consequence, room temperature superconductivity can be achieved by varying the binding energy (increasing copper oxide planes) in a lattice of a cuprate superconductor.
Energy of plasmon-mediated boson-fermion pair condensate in high temperature superconductors
(Physica B: Condensed Matter, 2021-10-01) Mukubwa, Abel; Makokha, John Wanjala
Interaction between particles in condensate state is nontrivial in understanding charge pairing that defines high-temperature superconductivity . A Bose-Einstein Condensate (BEC) of a non-zero-momentum Cooper pair constitutes a composite boson. A two-component electronic BEC - bosons and fermions -harbours some properties that are closely related to those of high temperature superconductors. We demonstrated that quantum coherence of a boson-fermion condensate is controlled by plasmons. A binary electronic system has an associated response function, given by the zero of longitudinal dielectric function. The response function has both long and short-wavelength branches, at least in layered superconductors. Coulomb screening of bosons by the electron cloud, in the long-wavelength branch, drives plasmon mediation in boson-fermion (BF) pairing. This study reveals that: the attractive potential in boson-fermion pair condensate (BFPC) is anisotropic, the magnitude of collective BEC excitations is in the order of an energy gap and that boson-fermion coherence under plasmon-mediation occurs at 10-9 m.
Enhancing climate resilience: A data-driven north rift weather prediction system for real-time forecasting and agricultural decision support
(Heliyon, 2025-02-07) Makokha, John Wanjala; Barasa, Peter Wawire; Khamala, Geoffrey W.
This study presents the development and integration of predictive models for the Normalized Difference Vegetation Index (NDVI) and Bare Soil Index (BSI) using the XGBoost algorithm within the North Rift Weather Prediction System (NRWPS) to enhance ecosystem monitoring in Kenya’s North Rift region. Trained on a comprehensive dataset spanning 1995 to 2020, which includes precipitation (from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS)), temperature (TerraClimate), historical NDVI (Landsat 4–5 Thematic Mapper (from 1995 to 2013) and Landsat 7 Enhanced Thematic Mapper plus (ETM+) (from 2014 to 2020)), and BSI (SoilGrids) data, the models effectively capture the complex relationships between environmental factors and vegetation health. The BSI model achieved an MSE of 0.029, an MAE of 0.019, and an R-squared score of 0.93, while the NDVI model yielded an MSE of 0.002, an MAE of 0.024, and an R-squared score of 0.945. These results demonstrate the models’ strong predictive accuracy, enabling precise assessments of vegetation health and bare soil exposure. By analyzing temporal variations in vegetation health and land degradation from 1995 to 2020, the study identifies a significant inverse relationship between NDVI and BSI, where increasing bare soil exposure corresponds to declining vegetation health. The analysis also reveals that climatic factors particularly temperature (minimum and maximum) and precipitation play a critical role in shaping these trends, with high temperatures after 2000 associated with reduced NDVI, while regions with higher precipitation show healthier vegetation and lower BSI. The successful development of the NRWPS model provides significant opportunities for informing land management strategies, conservation efforts, and agricultural practices, enabling data-driven decision- making. Moreover, its integration into larger decision support systems allows for proactive interventions to mitigate land degradation and climate change stressors. This study emphasizes the importance of sustainable land-use practices and climate adaptation strategies to preserve vegetation health and manage ecosystem vulnerabilities effectively in the wake of regional climate change with the North Rift region most affected.
Environmental Radiation Exposure and Lifetime Cancer Risk at Lumoru Dumpsite, Western Kenya
(Open Access Library Journal, 2025-11-18) Wanjala, Bilha; Nyukuri, Robert Wanjala; Kibe, Horace Eyinda; Makokha, John Wanjala
This study quantified the activity concentrations of natural radionuclides 238U, 232Th, and 40K in soils from the Lumoru Dumpsite, Bungoma County, Kenya, using a NaI (Tl) gamma spectrometer. The mean concentrations were 7 ± 0.4 Bq/kg for 238U, 57 ± 2.0 Bq/kg for 232Th, and 25 ± 1.3 Bq/kg for 40K. From these values, the absorbed dose rate was estimated at 39 ± 3.4 nGy/h, the outdoor annual effective dose equivalent at 0.09 ± 0.01 mSv/y, and the radium equivalent activity at 91 ± 3.4 Bq/kg. The hazard indices (Hex = 0.25 ± 0.01; Hin = 0.28 ± 0.01) were all within international safety limits, while the mean excess lifetime cancer risk was 0.30 ± 0.03 × 10−3. Compared with similar dumpsites in Kenya and across Africa, Lumoru exhibited lower activity concentrations and radiological risks than Machinjoni, Nigerian, and Ukrainian landfills, though its risks remain comparable to food-chain pathways in Bungoma. These findings establish Lumoru as a moderately impacted site and provide a critical baseline for monitoring cumulative exposures from environmental and household sources in Western Kenya.
Estimation of radiative forcing due to aerosols over selected sites in Kenya
(Kenya Meteorological Society : Journal of Meteorology and Related Sciences, 2013-01-01) Makokha, John Wanjala; Angeyo, H.K.
Variations in the radiative characteristics of aerosols can be used to quantify their effects on climate. This study evaluated the temporal-spatial variability of aerosol radiative characteristics at λ = 440 nm, λ = 675 nm, λ = 870 nm and λ = 1020 nm over the Nairobi-1°S, 36°E, Mbita-0°S, 34°E and Malindi-2°S, 40°E sites of Kenya. Aerosol optical properties from AERONET were used as inputs in the Coupled Ocean Atmosphere Radiative Transfer (COART) code to model aerosol radiative effects. The results over Nairobi showed an increase in reflectance of 2.6%, 6.7%, 7.2% and 2.4% for 2006–2007 at the specified wavelengths, respectively. Drops of 2.7%, 12.2%, 50.6% and 25.6% were noted in the same wavelengths for the 2007–2008 period. The reflectance over Mbita (0.2284) was higher than that over Nairobi (0.1396) at λ = 675 nm for 2007, due to biomass burning at site. Maritime conditions and aerosols coupled with long range transport of monsoon winds explain the higher reflectance observed over Malindi when compared to Nairobi, except for λ = 440 nm in 2008. This is as a result of aerosols from vehicular and industrial emissions that dominate the λ = 440 nm over Nairobi. The variability of downward and upward spectral irradiance measured at the surface and 12 km levels depended on the wavelength of measurement, but was temporally invariant. Upward irradiance decreased with increasing Solar Zenith Angles (SZAs) due to strong Fresnel reflection at large angles. The equality in the upwelling irradiances at the two atmospheric levels at all sites for λ = 870 nm and λ = 1020 nm was due to the near IR absorption by aerosols. The radiant flux lost in the spectral range 440–1020 nm remained relatively constant over the study sites, and thus the influence of aerosols on radiative characteristics was independent of both site and period of study.
First-principles calculations to investigate structural, elastic, electronic and thermodynamic properties of NbCoSn and VRhSn Half-Heusler compounds
(Results in Physics, 2022-11-30) Wafula, Job W.; Makokha, John Wanjala; Manyali, George S.
In this study, we investigated the structural, elastic, electronic, and thermodynamic properties of NbCoSn and VRhSn HH compounds using the first-principles calculations as implemented in the density functional theory (DFT). The computed lattice constants of NbCoSn and VRhSn compounds were found to be consistent with the available theoretical as well as the experimental data. The compounds are mechanically stable since their elastic constants satisfy the Born-Huang criteria for cubic system stability. Due to the absence of imaginary phonons, NbCoSn is dynamically stable, whereas VRhSn is unstable. NbCoSn is harder than VRhSn HH because it has a higher Vicker’s hardness and shear modulus. Both compounds feature band gaps, indicating that they are semiconductors. When compared to NbCoSn HH compound, VRhSn has a narrow band gap. Furthermore, thermodynamic properties are computed and thoroughly explored. As a result of the findings, NbCoSn and VRhSn HH compounds are viable thermoelectric materials; however, doping and alloying could be employed to enhance the stability of VRhSn HH compound.
Gauge-Invariant Wigner Function Extended to High Temperature Superconductivity
(Social Science Research Network, 2021-11-02) Mukubwa, Abel; Makokha, John Wanjala
The realization of gauge-invariant Wigner function (GIWF) has revolutionized studies on quantized and classical electromagnetic fields and has been adapted to a magnetostatic phenomenon in superconducting systems. We apply the quantum fluid moment hierarchy equations in solving the conservative moment equation of the gauge-invariant Wigner operator. The results show that the lower critical field (𝐻𝑐1), the vortex radius (𝑟0) and the penetration depth (𝜆) show dependence on Cooper pair excitation energy (𝐸𝑘).