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Positron-Impact Excitation of the Lowest Autoionizing State in Rubidium Atom using Distorted Wave Method
(2014-05) Marucha, Alex Magembe
Many calculations on atomic collisions and scattering processes have been performed on electron impact excitation of the lowest autoionizing state of rubidium, but not much attempt has been made with positron impact which is of equally fundamental importance and is receiving attention nowadays with the availability of improved positron beam experiments. So, in this study, total cross-sections, differential cross-sections, lambda parameter, R parameter and the alignment parameter for positron impact excitation of the lowest autoionizing state of rubidium have been calculated using Distorted Wave method. The wave functions used are the Roothan Hatree Fock double zeta and multi zeta wave functions due to Clementi and Roetti. Variations in distortion potential have been made such that the static potential of the initial state of rubidium atom is used as the initial channel distortion potential and a linear combination of static potentials of the initial and final states as the final channel distortion potential to check its effect on cross- sections. Numerical calculations have been done using a modified DWBA1 FORTRAN computer program which was originally made for hydrogen atom. The results for positron impact excitation of the lowest autoionizing state of rubidium have been analyzed and compared with experimental and theoretical results for positron and electron impact excitation of the same state available in literature. From the comparison of the results, it is seen that in general the electron impact excitation cross section results are higher than the positron impact excitation cross section especially near excitation threshold energy. This can be attributed to the exchange process which takes place in the case of electron impact and not in the case of positron impact and also due to larger interaction between the projectile and the target in case of electron impact than in case of positron impact. It is also found from the alignment parameter results that the integral cross section results for m=0 level are larger compared to m=1 level for impact energies up to about 500 eV beyond which integral cross-sections for the magnetic sublevel m=1 become greater. The lambda parameter indicates that more particles are scattered towards m=0 for electron impact compared to positron impact excitation near threshold energy. R parameter results have been calculated to account for phases of scattered amplitudes in the collision process
Design and optimization of HPLWR high pressure Turbine gamma ray shield
(Elsevier, 2014-12-20) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
This work proposes the optimum gamma ray shield thickness around the HPLWR high pressure turbine for different occupancy periods in the turbine building. Monte Carlo method was employed in the design process and only radioactive nitrogen-16 was considered as the source of radiation. Five grades of concrete (ordinary, magnetite, heavy magnetite, steel magnetite and barite) were used as shielding materials. The isotope source term in the high pressure turbine was estimated by modeling the HPLWR three pass core in MCNP and tracking the inventory using a simple algorithm. The high pressure turbine was thereafter modeled in MCNP with a concrete shield arrayed in layers around it. The surface flux tally and ICRP74 dose conversion coefficients were employed to estimate the dose profile across the shield. For some shielding materials, exponential functions were fitted on the calculated data to extrapolate dose values beyond the model thickness. The optimum shield thickness was determined by comparing the calculated dose profiles with dose limit proposals in the IAEA standard (NS-G-1.13) on radiation protection considerations during nuclear power plant design. It was observed that with a 120cm thick heavy concrete shield, the turbine building would be safe for most occupancy periods. However for ordinary concrete the shield would require some extension to guarantee safety. For very long occupancy (more than 10 person hours per week), magnetite shield may also require slight extension. It can therefore be concluded that the shield thickness recommended for BWR turbines (which operate on a direct cycle like HPLWR) could be sufficient for HPLWR if high density concretes are used.
CHARACTERIZATION OF WATER HYACINTH (EICHHORNIA CRASSIPES) COMPOSITE BRIQUETTE AS AN ALTERNATIVE DOMESTIC ENERGY SOURCE
(University of Eldoret, 2016) Okia, Daniel Otieno
Biomass is one of the most promising energy sources to mitigate greenhouse gas emission during production and utilization. However, majority of biomass are not suitable to be utilized as fuel without an appropriate process since they are bulky, uneven and have low energy density. These characteristics make them difficult in handling, storage, transport and utilization. One of the promising solutions to overcome these problems is the briquetting technology. The study was conducted to characterize water hyacinth composite briquette as an alternative domestic energy source. Water hyacinth was chopped using a shredder and left for two weeks in a heap to partially decompose. The material was thoroughly mixed manually with dried and crushed charcoal dust and cow dung in the ratios of water hyacinth: charcoal dust: cow dung of 100:0:0 (control), 80:10:10, 70:20:10, 70:10:20, 60:30:10, 60:20:20 and 60:10:30 (by weight). The resulting material was then mixed into soupy slurry in water. Simple prototype briquetting mold was fabricated to facilitate densification of these residues into hollow cylindrical briquette at a pressure of 1MPa. The experimental results revealed that the mixture that gave optimal combustion characteristics was 60:30:10 and the calorific values ranged from 16.215 to 21.585 MJ/kg. Water hyacinth alone (100:0:0) gave the best emission characteristics having 28.51 ppm carbon monoxide and 452.80 ppm carbon dioxide though ranking third with 13,623 μg/m3 in particulate matter. For quality control, water hyacinth composite briquette gave good indications on physical parameters that were measured. The results showed that resistance to water penetration range from 79.5% to 88%, durability index range from 57.9% to 99.6% with 60:30:10 and 60:20:20 ratios exhibiting poor index of 57.88% and 59.23 respectively probably due to high charcoal dust content which is known to have low bonding. The rest of mixtures gave 80% and above, with water hyacinth (100:0:0 ratio) showing the highest durability index of 99.63% probably because of partial decomposition which increases the binding effect of biomass. Equilibrium moisture content range from 8.5% to 15.2% at 29 oC and 58% relative humidity; water hyacinth alone was having the highest. This study therefore demonstrates that water hyacinth composite briquette have good physical and combustion characteristics and can therefore be utilized as alternative domestic energy source.
Electrical and Structural Properties of Aluminium Doped tin Oxide Codoped with Sulphur for Solar Energy
(Elsevier, 2016-08) Muramba, Valentine Wabwire; Mageto, Maxwell
Thin films of Tin Oxide co-doped with 28 atomic percentages of Aluminium (i.e. 28 at% Al) and varied concentration of Sulphur were prepared on 1mm thick, 1cm by 1cm glass substrates at 470 0C by Spray Pyrolysis technique. Films were produced from 2.0M solution of hydrous Tin Chloride dissolved in Ethanol with 38% Hydrochloric acid concentration, 1.5M aqueous Aluminium chloride and 2.0M aqueous solution of Ammonium Sulphide. The effects of Sulphur concentration on structural and electrical properties of transparent Tin Oxide thin films were investigated in the atomic percentage of Sulphur content ranging from zero to fifty (i.e. 0at%S -50at%S) with a fixed 28at%Al content. Polycrystalline structures without any second phases were observed with preferential orientations along the (110), (101), (200) and (211) planes. The average grain size as determined from the (110) peaks lay in the range 19.2 nm-47.7nm. The minimum resistivity was found to be 1.15x10-3Ωcm for the Tin Oxide films doped with 32 at% Al content and 9.59x10-3Ωcm for Tin Oxide films co-doped with 28 at% Al and 20 at% S content. It was observed that Aluminium doping lowered the grain size significantly but doping to optimum level of 32 at% Al content increases electrical conductivity of tin oxide. When Sulphur was intentionally introduced in the crystal structure of 28 at% Al doped Tin Oxide, the electrical conductivity decreased appreciably and the grain size increased.
Exhaust Gases Energy Recovered from Internal Combustion Engine for Useful Applications
(IOSR Journal of Mechanical and Civil Engineering, 2017-06-01) Orido, George; Ngunjiri, Prof; Rugiri, Musa
Abstract : The importance of this study is primarily to address the energy problem. The main contribution of this study, in addition to conserving energy through recovery technique, is reduction in the impact of global warming due to exhaust gas emission to the environment. The objective of the research is to recover exhaust gases energy from internal combustion engines for utilization. The experimental set-up consisted of a single cylinder, four-stroke, multi-fuel engine connected to eddy current dynamometer for loading. Thermocouple temperature sensors and transmitters were used to measure exhaust gas to calorimeter inlet temperature and exhaust gas from calorimeter outlet temperature. Exhaust gas mass flow rate and temperature measurements were used to determine the recovered energy. Recovered heat energy was 1.257% of fuel energy when the engine was operated on diesel at 1000 rpm and a torque load of 18 Nm. 3.153% of fuel energy was recovered at 1500 rpm and a torque load of 6 Nm when biodiesel was used. At a speed of 1000 rpm 22.6% and 23.004% of the thermal energy through exhaust was recovered when the engine used diesel and biodiesel at torque loads of 6 Nm and 14 Nm respectively.
Reduced graphene oxide-germanium quantum dot nanocomposite: electronic, optical and magnetic properties
(IOP Publishing, 2017-11-13) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
Graphene provides numerous possibilities for structural modification and functionalization of its carbon backbone. Localized magnetic moments can, as well, be induced in graphene by the formation of structural defects which include vacancies, edges, and adatoms. In this work, graphene was functionalized using germanium atoms, we report the effect of the Ge ad atoms on the structural, electrical, optical and magnetic properties of graphene. Reduced graphene oxide (rGO)-germanium quantum dot nanocomposites of high crystalline quality were synthesized by the microwave-assisted solvothermal reaction. Highly crystalline spherical shaped germanium quantum dots, of diameter ranging between 1.6–9.0 nm, are anchored on the basal planes of rGO. The nanocomposites exhibit high electrical conductivity with a sheet resistance of up to 16 Ω sq−1. The electrical conductivity is observed to increase with the increase in Ge content in the nanocomposites. High defect-induced magnetization is attained in the composites via germanium adatoms. The evolution of the magnetic moments in the nanocomposites and the coercivity showed marked dependence on the Ge quantum dots size and concentration. Quantum confinement effects is evidenced in the UV–vis absorbance spectra and photoluminescence emission spectra of the nanocomposites which show marked size-dependence. The composites manifest strong absorption in the UV region, strong luminescence in the near UV region, and a moderate luminescence in the visible region.
Analysis of Energy Storage And Return Foot Stiffness By Coupling Musculoskeletal And Finite Element Simulations
(IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE, 2018) Kipkirui, Ngetich Gilbert
Transtibial amputees currently have numerous prostheses in the market which are aimed at improving the control, cosmetics and comfort. Each of the three categories of prosthetic feet namely; conventional, energy storage and return, and bionic feet have different characteristics. Current studies reveal that energy storage and return feet offer better performance as compared with conventional prostheses. In this study, evolution of the prosthesis and the significance of mimicking human ankle-foot biomechanics is highlighted. Lower limb amputations occur due to Peripheral Vascular Disease, Diabetes, War and accidents .It is associated with mortality, morbidity, and disability. Transtibial amputees exhibit loss of plantar flexor musculature [1, 7] resulting in greater intact leg stance times [12] and asymmetrical gait comorbidity in their residual and intact legs [2, 7]. Below-knee amputees lose the functional use of the ankle muscles, which are critical during walking to provide body support, forward propulsion, leg-swing initiation and mediolateral balance [3, 7] . During early and pre-swing, amputees exhibit increased hamstring and rectus femoris activity on residual leg [12] .Prosthetic foot do not allow sufficient dorsiflexion even on level terrain and possess inertia asymmetry. Further improvements ought to be incorporated to adjust the degree of dorsiflexion [4] , absorb shock on impact [10] , and improve inertia gait. Unilateral, transtibial amputees’ clinical efficacy is dependent on appropriate prosthetic foot stiffness [6] .Proper prosthetic foot selection with appropriate design characteristics is critical for successful amputee rehabilitation. Use of laminated composites in the manufacture of prostheses is vital due to their high stiffness and low density. Many researchers have reported that unilateral below-knee amputees (BKA) walk asymmetrically and differently from able-bodied people [1-10, 17] . Researchers have given varied reasons. It is generally believed that socket fit, prosthetic alignment, and prosthetic components (including prosthetic parts' weight and design) can all influence the gait of amputees [2-7,12,18-19]. Others argue that due to loss of plantar flexor muscles, there would be greater intact leg stance times and asymmetrical gait comorbidity in their residual and intact legs. Moreover, degenerative changes in the lumbar spine and knees would occur due to the asymmetrical walking that overloads the musculoskeletal system [7, 12] . This research will come up with an analysis of the energy storage and return foot coupling musculoskeletal and finite element analysis with aim of improving amputee gait. The analysis of the foot is performed using the boundary conditions of ISO-10328 and ISO-22675.The prosthetic foot serves to substitute the loss of tendons and muscles of the intact foot due to amputation. Further series of computer simulation of ESAR foot is performed using Altair Hyper works 14.0 to investigate the effect of stiffness on the tibia section of foot, muscle activity, residual and intact ground reaction forces with aim of coming up with an optimal design. The results of this study would add to the core knowledge regarding prosthetic feet features and their effects on gait, making them directly relevant to prosthesis design and prescription.
Ice Detection Model of Wind Turbine Blades Based on Random Forest Classifier
(Energies, 2018-09-25) Zhang, Lijun; Liu, Kai; Wang, Yufeng; Omariba, Zachary
When wind turbine blades are icing, the output power of a wind turbine tends to reduce, thus informing the selection of two basic variables of wind speed and power. Then other features, such as the degree of power deviation from the power curve fitted by normal sample data, are extracted to build the model based on the random forest classifier with the confusion matrix for result assessment. The model indicates that it has high accuracy and good generalization ability verified with the data from the China Industrial Big Data Innovation Competition. This study looks at ice detection on wind turbine blades using supervisory control and data acquisition (SCADA) data and thereafter a model based on the random forest classifier is proposed. Compared with other classification models, the model based on the random forest classifier is more accurate and more efficient in terms of computing capabilities, making it more suitable for the practical application on ice detection.
Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer
(Elsevier, 2020) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.
Oil and Gas Exploration and Sustainable Environmental Management in Oil Block 13t South Lokichar Basin, Turkana County, Kenya
(Kenyatta University, 2020) Mugendi, Kariuki David
Commercial oil and gas was discovered in Kenya in 2012. Few academic studies have been done on the effects of the mentioned discovery to the environment.The oil and gas resources are expected to transform the economic wellbeing of the locals and the nation at large.However,land degradation, environmental pollution and socio-economic problems have always ensued oil and gas exporation ventures globally.This study aimed at determining the effects of oil and gas exploration on biophysical and socio-economic environments in Oil Block 13T South Lokichar Basin,Turkana South-subcounty and come up with sustainable environmental management strategies in the oil fields.The specific objectives were to review,constitutional,policy,legal and institutional framework governing environmental management in the backdrop of oil and gas exploration in Kenya and determination of oil and gas exploration effects on biophysical and socio-economic environments in the study area.The study adopted an exploratory mixed method research design.Purposive non-probability sampling was applied in determining the study area,sampling the boreholes,sampling the drill cutting samples and sampling the key informants.Probability sampling was used in identifying the manyattas,households and the villages for conducting focused group discussions.Questionnaires,documents review, photography,observation,landsat satellite imageries acquisition and analysis,laboratory analysis using XRF and AAS machines, for drill cuttings and water samples respectively to determine the levels of physicochemical properties were the data collection methods used.The questionnaires were coded into the Statistical Package for Social Sciences version 20.0 software and Excel 10.0.Descriptive and inferential statistics were used in data analysis.The study identified several gaps in the existing environmental policy and legal framework in relation to the oil fields environmental management coupled with poor enforcement of the laws by the relevant agencies.In addition, the study observed a decline in NDVI from 1 to 0.4329 for the rainy season and 0.4107 to 0.1217 jfor the dry season between 2006 and 2017 with a p-value of 0.0091< 0.05 on paired T-test implying a significant change on vegetation cover.The area under forest, shrubland and grassland had significantly reduced at 90% confidence interval with a,value of,0.0718,0.0738 and 0.0609.The drill cuttings whose levels of detected heavy metals concetration for Manganese(Mn),Copper(Cu),Nickel(Ni),Iron(Fe),Calcium(Ca),Lead(Pb),were;1.58,0.21,0.05,70.4,62.57,4.58 respectively were incorrectly being managed onsite.Mn, Feand Pb concentration levels in the drill cuttings were above the WHO and USEPA recommended standards for the reserve pit.The levels of Fe,Ni,Turbidity and Total Dissolved Solids of the sampled water from the study area,were all above the prescribed WHO standards.The study noted improved socio-economic characteristics, physical and social infrastructures in the study area.70% of the respondents felt that water provision, health facilities, education facilities, employment opportunities had improved since oil and gas exploration began with a Cohen kappa coefficient of agreement of 0.608.However,challenges such as population influx,land displacement,lack of adequate engagement of the locals, gender inequalities with a Cronbach’s Alpha of reliability of 0.735, health challenges of the locals and increased number of conflicts cases since 2012 with a statistical p-value of 0.005< 0.05 were noted.The study recommends enforcement of the existing environmental legislations and development of oil specific environmental laws,adoption of advanced oil drilling and drill waste management technologies, as well as participatory environmental management approach in the oil fields.
Quantifying Greenhouse Gas Emissions and Carbon Stocks in Maize-Soybean Cropping Systems in Siaya County, Kenya
(Kenyatta University, 2020) Karanja, Anne Njeri
As climate change continues to threaten ecosystems’ functions, agriculture remains one of the major source of greenhouse gas (GHG) emissions that are responsible for global warming. The major GHG in agriculture are; carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Unfortunately, agriculture is also one of the most affected sectors by climate change. There is therefore need to reduce emissions by adopting agricultural practices with mitigation potential. This is by enhancing soil carbon sequestration to offset emissions, or reducing emissions while safeguarding crop yields. However, little is still known about GHG quantities and intensities that major cropping systems in Kenya emmit. Site specific studies on GHG emissions to establish interventions for mitigation of climate change and enhanced crop production is therefore of essence. The objective of this study was to examine the effect of reduced tillage, crop residue retention and use of controlled release urea (CRU) in maize-soybean cropping systems on GHG emissions, soil N mineralization, organic carbon stocks and yields. Field measurements were carried out in a 13 year old researcher-managed trial in Siaya county, Kenya between March 2016 and January 2017. Four treatment combinations: ZT M-S NU (reduced tilage+maize soybean rotation+normal urea), ZT M-S CRU (reduced tillage+maize soybean rotation+controlled release urea), ZT M/S (reduced tillage+maize soybean intercrop without urea), CT M-S NU (Conventional tillage+maize soybean rotation+normal urea) were tested. The treatments were laid out in a randomized complete block design. DAYCENT model was used to simulate soil carbon, N2O emissions and maize yields. Results showed that daily fluxes of N2O ranged between -0.5-26 g ha-1 d-1 and -2-10 g ha-1 d-1 in the long and short rainy seasons respectively. Cumulatively, N2O emissions were between 0.2 - 0.7 kg ha-1 and 0.2 - 0.4 kg ha-1 in the long and short rainy seasons respectively. In the long rainy season, ZT M-S CRU had significantly higher N2O fluxes than the other treatments (P=0.05). In the short rainy season there were no significant effects of treatment on N2O emissions. In the long rainy season, CO2 daily fluxes were between 9 to 42 kg ha-1 while the cumulative emissions ranged between 2.5 to 2.8 t ha -1. In the short rainy season daily CO2 fluxes ranged between 6 to 30 kg ha-1 while cumulative emissions were 1.8- 2.5 t ha -1. There was no significant effect of treatment on CO2 emissions. Methane emissions were largely negative, and did not differ significantly among treatments. Yield was significantly low for ZT M/S but N2O emission intensities were not significantly different among treatments. DAYCENT simulated soil carbon and maize yield within the same ranges observed by measurement. N2O emissions by DAYCENT were higher during the peak of the seasons, but were comparable with observed measurements later in the seasons. Even though the long rainy season had higher N2O and CO2 emissions, the difference was not significant. These results indicate that emissions in the study area were low.These results further indicate that the current soil management practices in Siaya County influence GHG emissions, and the higher emissions observed with ZT M-S CRU in the long rainy season calls for further investigations of the effect of CRU on N2O emissions. The lower emission intensity shown by ZT M/S despite having lower yield points to the need of evaluating cropping systems for climate change mitigation and adaptation. These results indicated that DAYCENT model can be used to simulate soil carbon and yield but not N2O emissions in the study area.
Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer
(Elsevier, 2020-11) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.
A Hybrid of Fuzzy Logic and Sliding Mode Techniques for Photovoltaic Maximum Power Point Tracking Systems Under Partial Shading
(University of Nairobi Research Archive, 2020-11-20) Gathoni, Robinson N.
Solar energy harvesting using photovoltaic (PV) modules have been one of the most commonsources of renewable energy for several decades. These modules have been used as a sourceof electricity for households, industries, in stand-alone, and grid-connected solar plants. Themodules consist of semi-conductor solar cells combined in series and parallel. In order to makea solar system, the modules are usually linked in series. The performance of a solar system isaffected by environmental factors like varying radiance and temperatures, shadowing caused byhigh-rise buildings, birds, fog, trees and dust. Such varying environmental conditions affect asolar cell's efficiency. Nevertheless, given all the effort made to mitigate the impact of all theseenvironmental threats, some of the natural occurrences such as varying radiance, clouds, dust,wind-speed and change in temperature, can not be done away with. To improve the e ciencyof the entire solar system, power extraction must be optimized under all weather conditions.Fuzzy logic and sliding mode techniques are e cient, fast and reliable methods of trackingthe maximum power point that have been used in this study. The application of these twoapproaches substantially increases system e ciency for all environmental conditions includingpartial shading instances. The sliding mode technique is a very fast, stable and robust algorithmthat work e ectively under very stable weather condition while the fuzzy logic has beenexploited under partial shading conditions. Both methods rely heavily on a good understandingof the characteristics of PV modules, which are studied using I-V, P-V or P-I curves. In thiswork, three new algorithms have been used to simulate and model the characteristics of a PVmodule.The algorithms are based on a single diode equivalent circuit, which has been chosen dueto the simplicity of simulation and modeling and provides a fast convergence time. The algorithmsare classi ed according to the method of obtaining the best values of the unknownve parameters of the diode model. Ideality factor (A), saturation current (Io), photocurrentiv(Iph), series (Rs) and parallel (Rp) resistances are the ve unknown parameters to be determinedfor characterization of a PV module using a diode model. These parameters have beenextracted using the I-V curve's three critical points at short circuit point (SCP), open circuitpoint (OCP) and maximum power point (MPP). The rst algorithm has been based on thechoice of ideality factor below the optimal ideality factor (Ao), such that 0 A Ao, whereasthe other parameters depends heavily on the choice of A. The second algorithm has been basedon the choice of ideality factor in the neighborhood of Ao and the third algorithm has beenbased on A Ao. The three methods have been utilized to characterize the solar module usingI-V and P-V curves and have output power errors of less than 0.5%.For proof of concept of the three algorithms, PV module with IEC61215 speci cations havecarefully selected from Kyocera- KC130CGT. Additional experimental work has been carriedout at Solinc Kenya Ltd using Solinc 60Wp and 250Wp PV modules, similar to those mountedon the rooftop of the building in Chiromo at School of Physical Sciences.
Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals In Ortum, West Pokot County, Kenya
(Kenyatta University, 2021) Wanjala, Felix Omonya
The background radiation in air, the activity concentration of selected radionuclides in soil and rock samples, the radon and thoron concentration in selected mud houses and elemental concentration of heavy metals in soil and water samples from Ortum, West Pokot County in Kenya was determined in this study. Ortum was chosen due to the presence of granitic and silicon rocks which are associated with high levels of background radiation. The activity concentration of 238U, 232Th and 40K in soil was determined using the High Purity Germanium detector (HPGe) and the average values were 40 ± 3 Bq/kg, 56 ± 4 Bq/kg and 425 ± 19 Bq/kg respectively which is within the world average range. The activity concentration of 238U and 232Th in soil samples reduced with increasing depth while that of 40K increased slightly with increase in depth. The average activity concentration of 238U, 232Th, and 40K in soil samples was higher than in the rock samples implying that the soils originate from other regions. The average outdoor absorbed dose rate in air at 1 m above the ground was found to be 112 ± 30 nGy/h which is almost double the world average value of 60 nGy/h. The average Raeq was 153 ± 49 Bq/kg which is less than the limit of 300 Bq/kg and the external hazard indices (Hex) and the internal hazard index (Hin) were 0.41 ± 0.13 and 0.52 ± 0.16 respectively which is below the limit values of unity (>1). This implies that soil and rocks in Ortum poses low radiological risk and they can therefore, be used for construction of houses, industrial and agricultural purposes. The average radon and thoron concentration in mud houses was determined using RADUET detector and found to be 40 ± 19 Bq/m3 and 54 ± 30 Bq/m3 respectively which is below the ICRP recommended lower and upper limit of 100 Bq/m3 and 300 Bq/m3 respectively. The elemental concentration of Ni, Cu, Zn, Pb, K, Ca, Fe, Ti, Mn, Rb, Sr, Zr and Nb in soil was determined using the Energy dispersive X-Ray Fluorescence Spectrometer (EDXRF) and found to be below the WHO recommended limits. The mean concentration of trace elements Pb, Zn and Cu in soil samples reduced with increasing depth while that of Ni increased with increasing depth. The Geoaccumulation Index (Igeo), Potential Ecological Risk Index (Ei) and synthesized potential ecological risk index (Er) were evaluated and found to be -0.40, 4.92 and 19.69 respectively. The results show that soil from Ortum is moderately polluted and the risk associated with exposure to heavy metals in soil is low. The concentration of Ni, Cu, Pb, Zn, Ag, Al, As, Ba, Ca, Cd, Co, Cr, Fe, K, Mg, Mn, Mo, Na and Se in water samples was determine using Agilent-5100 Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The elemental concentrations in water samples from the two rivers was found to be lower than the WHO permissible limits, except for calcium (Ca) which was higher than the permissible levels in borehole water. Hence, water from rivers in Ortum is unpolluted and fit for use except for borehole water which has high calcium levels. The lifetime cancer risk due to background radiation (LTCRBR) and elemental pollution in water (LTCREP) was found to be 1.47 x 10-3 and 1.92 x 10-6 respectively which is within the recommended safe limits. The lifetime cancer risk due to exposure to background radiation evaluated using RESRAD programme for a resident farmer in Ortum was found to be 0.011 or 1.1%. This implies that cancer risk due to exposure to background radiation in Ortum is low.
A Review of the Current Trends in the Production and Consumption of Bioenergy
(Sami Publishing Company(SPC), 2021) Korir, Benjamin K.; Kibet, Joshua; Mosonik, Bornes C.
With the current traditional fossil fuels depleting at an alarming rate coupled with environmental degradation because of toxic emissions, there is a mounting desire in search of renewable and sustainable energy resources. In this regard, bioenergy is considered one of the greatest potential to address the global energy demands in order to foster confidence in energy security, economic sustainability, and environmental protection. Global use of biomass to generate electricity and enhanced green energy transport is expected to increase in the near future. Accordingly, the demand for renewable energy is aimed at minimizing energy poverty and mitigation against climate change. Bioenergy despite bioconversion challenges is one of the key solutions to the world’s current energy demands. Model bioenergy plant sources – Croton megalocarpus, palm oil, Jatropha, and soybeans are briefly discussed in this review as major sources of bioenergy. The increased focus on bioenergy has been necessitated by high oil and gas prices, and the desire for sustainable energy resources. Nonetheless, corrupt practices and lack of political goodwill has hampered efforts towards achieving the full utilization of bioenergy. Corruption has been widely cited as a major setback to bioenergy development in a range of global jurisdictions. In order to minimize environmental damage, carbon trade has been projected as a necessary action by developing countries to reduce carbon emissions. Generally, the analysis of the use of fossil fuels across the world shows a strong interrelationship involving energy utilization, degradation of air quality, and environmental health concerns.
Energy recovery from biomethanation of vinasse and its potential application in ozonation post-treatment for removal of biorecalcitrant organic compounds
(Elsevier, 2021) Otieno, Benton; Apollo, Seth
Vinasse is characterized by a high chemical oxygen demand (COD) and dark brown colour, which requires abatement before disposal to prevent the pollution of receiving streams. Anaerobic digestion (AD) usually applied for vinasse treatment can only reduce the COD with the colour remaining unabated. This study investigated the feasibility of combining AD and ozonation for vinasse treatment. The AD process alone achieved high COD removal of 95 %, at a best organic loading rate of 15 kgCOD/m3/d. However, the anaerobic effluent still had an intense dark brown colour caused by a considerable amount of residual biorecalcitrant COD of 4.5 g/L. The ozonation post-treatment of the anaerobic effluent removed 80 % of the colour with up to 92 % ozone transfer at optimal parameters of pH 4, substrate dilution factor of 2, and 90 mg/L/min ozone dosage. Kinetic analysis showed that for a constant feed flow combined system, the ratio of the anaerobic reactor unit to the ozonation reactor unit is recommended to be 20:1. Also, from energy analysis, application of the bioenergy produced from AD to supplement the total energy requirement of the combined system could lead to 50 % savings on energy, and a carbon dioxide emission reduction of 122 kg CO2/m3 of vinasse treated. The combined system is thus a promising technology for vinasse treatment and can contribute to combating greenhouse gas emissions.
Investigation of magnetic properties of FeMnP1-xAx (A = In, Se and Sn, where x = 0.33) by use of GGA functionals
(Elsevier, 2021-07) Vincent, Otieno; Mulwa, Winfred Mueni; Kirui, M. S. K.
Magnetic properties of stable iron-based compounds (FeMnP1-xAx (A = Si, In, Se and Sn) were investigated by use of Quantum Espresso (QE) within the Density Functional Theory (DFT) formalism as a viable magnetic refrigerant. In this research work, DFT technique was the first principle theoretical approach that was employed along with the planewave pseudopotentials (ultrasoft), and the projected augmented wave (PAW) within the generalized gradient approximation (GGA) to describe the electronic structure and investigation of magnetic properties. Magnetic stability is described as the repeated magnetic performance of a material under specific conditions over the life of a magnet. In this case our reference compound, FeMnP0.67 Si0.33 was optimized and its properties were examined in both ferromagnetic (FM) and antiferromagnetic (AFM) states. Two Si atoms were later substituted with atoms of post-transitional metals in period four and five which has shown first-order magnetic transition at near room temperatures. In, Se and Sn were chosen to replace silicon since they would easily mimic the bond, their availability and nontoxic nature. The results showed that only ferromagnetic states of both host and doped compounds gave promising magnetic properties that can be applied in magnetocaloric effect phenomenon. Their band structure results indicated that they were all metals. Antiferromagnetic states showed no magnetic properties as the spin-polarized graph resulted in perfect symmetry of spin up projected density of states (PDOS) and spin down PDOS. From the thermo_pw calculations, it was realized that FeMnP0.67 In0.33 is the best candidate for near room temperature magnetic refrigeration among the studied compounds.
Simulated performance of a novel solid-state dye-sensitized solar cell based on phenyl-C61-butyric acid methyl ester (PC61BM) electron transport layer
(Optical and Quantum Electronics, 2021-07-01) Korir, Benjamin K.; Kibet, Joshua K.; Ngari, Silas M.
Climate change has approached a major crisis limit worldwide due to exhaust emissions arising from the use of traditional transport fuels. Solar energy, therefore, appears to be the most promising alternative energy that can mitigate air quality and environmental degradation. Herein, we report numerical simulation of a novel model solid-state dye-sensitized solar cell consisting of solid-state layers with the configuration FTO/PC61BM/N719/CuSCN/Au using 1-dimensional solar cell capacitance simulator software (SCAPS-1D). The motivation underpinning the numerical simulation of the solar cell architecture proposed in this study was to optimize phenyl-C61-butyric acid methyl ester (PC61BM) performance as the electron transport layer. In this model, the effects of varying several parameters—temperature, absorber thickness, defect density, and metallic back contact on the overall solar cell performance have been critically examined. After optimizing the input parameters, the optimal conversion efficiency was 5.38% while the optimized open-circuit voltage was 0.885 V. Besides, 70.94% was the optimum fill factor and the peak short-circuit current of 8.563 mA cm−2 was achieved. Built-in voltage of ~ 1.0 V was estimated from the Mott–Schottky curve and the cell band diagram. The power conversion efficiency obtained in this study is robust for this cell configuration, and is toxic-free compared to the lead-based perovskite solar cells. These findings are therefore useful in the advancement and fabrication of high-performance dye-based photovoltaic devices for large-scale industrial production.
Design and Testing of a Demand Response Q-Learning Algorithm for a Smart Home Energy Management System
(Institute of Electrical and Electronics Engineers (IEEE), 2021-09-28) Angano, Walter; Musau, Peter; Wekesa, Cyrus Wabuge
Growth in energy demand stimulates a need to meet this demand which is achieved either through wired solutions like investment in new or expansion of existing generation, transmission and distribution systems or non-wired solutions like Demand Response (DR). This paper proposes a Q-learning algorithm, an off-policy Reinforcement Learning technique, to implement DR in a residential energy system adopting a static Time of Use (ToU) tariff structure, reduce its learning speed by introducing a knowledge base that updates fuzzy logic rules based on consumer satisfaction feedback and minimize dissatisfaction error. Testing was done in a physical system by deploying the algorithm in Matlab and through serial communication interfacing the physical environment with the Arduino Uno. Load curve generated from appliances and ToU data was used to test the algorithm. The designed algorithm minimized electricity cost by 11 % and improved the learning speed of its agent within 500 episodes.
Use and Efficiency Of Low Temoerature Plasma In Foods: Promising Intervention On Aflatoxin Control In Maize In Kenya – A Review
(Journal of pure and applied scinces, 2021-10-16) Nyaguti W. O
Abstract The Refractance window dryer (RWD) is a fourth generation dehydration technology. RWD is used to dry heat-sensitive materials because it retains high nutrient content, colour, flavour, aroma and bioactive compounds. The dehydrated products have a high sensory quality. There were no RWD in East Africa despite their excellent performance hence need for local fabrication of RWD Prototypes that can meet the technical, economical and socio-economical requirements. This paper describes the performance evaluation and economic analysis of the RWD prototype developed at the Kenya Industrial and Development Institute (KIRDI), Kenya. Indicators such as drying rate and drying time were used to assess its technical performance. The economic performance of the dryer was appraised using Net Present Value (NPV), Internal Rate of Return (IRR), Benefit-Cost Ratio (BCR), and Payback Period (PBP). Mango pulp and African leafy vegetables were dried using the RWD prototype at KIRDI between May-July, 2021. During drying process, moisture content of mango pulp was reduced from 88% to 15% in one hour while African leafy vegetable from 88% to 5% in 40 minutes. The economic evaluation of the dryer revealed an IRR of 31%, NPV of 808223.515 @ 24% and PBP of 3.6 years. KIRDI RWD prototype is a versatile technology that can be deployed in remote settings resulting to reduction of post-harvest losses as well as carbon emission. Currently, sun drying, solar drying, cabinet drying, spray drying, drum drying, fluidized bed drying and freeze drying are available in Kenya. They possess various advantages and equally significant drawbacks. Therefore the adoption of KIRDI’s Refractance window dryer would be beneficial to Micro Small and Medium enterprises in providing timely drying services and improve their socio-economic status.

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