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    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.
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    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.
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    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.
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    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.
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    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.
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    Optimization of Hole Transport Layer Materials for a Lead-Free Perovskite Solar Cell Based on Formamidinium Tin Iodide
    (Energy Technology, 2021-10-31) Rono, Nicholas; Merad, Abdelkrim E.; Kibet, Joshua K.; Martincigh, Bice S.; Nyamori, Vincent O.
    Recently, lead-based perovskite solar cells have been mainly studied; however, these cells suffer from two main problems: the toxicity of lead and the instability of the devices, which limit their commercialization. Herein, a theoretical investigation of a lead-free perovskite solar cell based on formamidinium tin iodide (HC(NH2)2SnI3) with the general architecture: glass/FTO/WS2/HC(NH2)2SnI3/HTL/Au is reported. All calculations are performed with the SCAPS-1D solar cell simulator. Two inorganic (CuSCN and Cu2O) and two organic (P3HT and D-PBTTT-14) hole transport layer (HTL) materials are tested in this model. The effect of the external operating temperature and different metal work functions of the back contact of the cell on the overall performance of the devices is also studied. Simulations showed that, with the introduction of CuSCN, Cu2O, and P3HT as HTLs, the device can attain a remarkable efficiency of ≈21%. All the modeled devices showed remarkable performance of above 20% at higher temperatures of 380–420 K but degraded slightly when this range is exceeded. Relatively cheaper Pt, Ni, and Pd metals perform better, thus, can replace gold. These simulation results can provide avenues and directions for future advancement of the performance of lead-free perovskite solar cells.
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    Structural, Electronic and Mechanical Properties of Re Doped FeMnP0.67A0.33 (A=Ga and Ge): A DFT Study
    (International Journal of Physics, 2022-02-14) Chirchir, Gabriel Kipkemei; Mulwa, Winfred Mueni; Adetunji, Bamidele Ibrahim
    The structural, electronic and mechanical properties of Re doped FeMnP0.67A0.33 (A= Ga and Ge) were examined by use of density functional theory (DFT) within the generalized gradient approximations as demonstrated in Quantum ESPRESSO code. The optimized structural parameters as well as derived lattice parameters are in consistent with other computational and achievable experimental results. The computed independent elastic constants confirm the mechanical stability of the investigated materials. The computed Poisson’s and Pugh’s ratios as well as Cauchy pressure, verify that FeMn0.67Re0.33P0.67Ga0.33 is the most ductile among the studied compounds. The calculated values of bulk modulus, shear modulus and Young’s modulus confirm high values of bond strength, hardness and stiffness of the investigated materials respectively. Therefore, the four compounds considered may be appropriate for industrial applications. The results report that FeMn0.67Re0.33P0.67Ga0.33 compound is more ductile and mechanically stable compared to other investigated compounds. This is the first qualitative computational prediction of the elastic properties of FeMnP0.67Ge0.33, FeMnP0.67Ga0.33, FeMn0.67Re0.33P0.67Ge0.33 and FeMn0.67Re0.33P0.67Ga0.33 compounds and this awaits experimental ratification. The calculated electronic density of states confirms that the Re_2p states are located in the conduction band (CB) in the unite cell while Re_3d dominate the CB in the supercell. Results from the doped compounds could not be compared with experimental or computational findings because to the best of our knowledge, this has not been done.
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    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.
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    Effects of 15th January 2010 Annular Solar Eclipse on Traveling Ionospheric Disturbances and Equatorial Plasma Bubbles over Low Latitude Regions of East Africa
    (Hindawi Publishing Corporation, 2022-09-21) Athwart, Davis Odhiambo; Ndinya, Boniface; Baki, Paul
    The influence of the 15th January 2010 annular solar eclipse on traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) is studied using data from six global navigation and satellite system (GNSS) receivers spread across the path of annularity over the low latitude region of East Africa. The GNSS receivers are stationed at Nairobi (RCMN), Malindi (MAL2), and Eldoret (MOIU) in Kenya; Mbarara (MBAR) in Uganda; Kigali (NURK) in Rwanda; and Mtwara (MTWA) in Tanzania. The study period ranges from 12th to 18th January 2010, three days before and after the 15th January 2010 annular solar eclipse. The year 2010 marked the beginning phase of solar cycle 24, evidently observed in low total electron content (TEC) values and the disturbed storm time index (Dst). The eclipse started at 7 : 06 LT and ended at 10 : 14 LT, with MOIU and RCMN experiencing eclipse magnitudes of 0.946 and 0.93, respectively. The maximum obscuration occurred between 8 : 21 LT and 8 : 34 LT across most of the stations. A detrending on vertical TEC (VTEC) derived from GNSS receivers across or close to the path of totality revealed a reduction of ∼2-3 TECU during the maximum phase of the eclipse. The level of reduction was highly close to the totality path and decreased smoothly away from the totality path. Using a background polynomial fitting technique on diurnal TEC, we analyzed TIDs along NURK-MBAR-MOIU and MOIU-RCMN-MAL2 GPS arrays. The results revealed a wavelike perturbation with a virtual horizontal velocity of 830m/s and ∼1 TECU amplitude propagating eastward along the MOIU-RCMN-MAL2 GPS array. The study reports a moderate scintillation activity of 0.5 ≤ ROTI ≤ 0.9 values, demonstrating the presence of few EPBs over the region. The results show a latitudinal variation in GPS-TEC scintillation activities and suggest a possible influence of the eclipse on the observed increase in average scintillation levels across East Africa.
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    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.
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    Sustainable insulating porous building materials for energy-saving perspective: Stones to environmentally friendly bricks
    (Elsevier, 2022-02-07) Anjum, Farah; Yasin Naz, Muhammad; Ghaffar, Abdul; Kamran, Kashif; Shukrullah, Shazia; Ullah, Sami
    The growing gap between energy demand and supply and the risk of environmental pollution, especially in the developing countries due to population growth and subsequent progress in the construction industry, is a challenging issue of this era. Many studies have been carried out to elucidate the thermophysical properties of building materials in terms of energy transfer and mitigation of environmental risks. This review provides a brief insight into the past literature and ongoing research work on thermophysical properties of building materials to establish the intellectual context of the study. The thermophysical properties of the rocks under the influence of moisture and temperature are reviewed. The influence of salt weathering on building materials' physical and thermal properties is also an important issue to be addressed in building structures. As fired clay bricks undergo several physical and chemical changes during sintering, a review of the existing literature on the effect of the mineralogy of clay, sintering time, and temperature on the physical and thermal properties of the bricks is also presented in this article. The construction of eco-friendly and thermally insulated bricks by adding waste materials is also examined in depth in terms of energy saving capacity and mechanical strength, with a relation to the contemporary challenges.
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    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.
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    Effects of Energy Intensification of Pressure-Swing Distillation on Energy Consumption and Controllability
    (ACS omega, 2022-12-22) Mtogo, JonathanWavomba; Toth, Andras Jozsef; Fozer, Daniel; Mizsey, Péter; Szanyi, Agnes
    , The aim of processintegration is the efficient use of energy andnatural resources. However, process integration can result in a moreprecise process operation, that is, it influences controllability.Pressure-swing distillation processes are designed for the separationof azeotropic mixtures, but their inherent heat integration optioncan be utilized to significantly reduce their energy consumption.One maximum-boiling and three minimum-boiling azeotropes are consideredto study and compare the nonintegrated and integrated alternativeswith the tool of mathematical modeling where ASPEN Plus and MATLABsoftware are used. The results show that the heat-integrated alternativesresult in 32–45% energy savings that are proportional to theemission reduction and the consumption of natural resources. As faras the operability is concerned, the heat-integrated alternativesshow worse controllability features than the nonintegrated base case.This can be due to the loss of one controllability degree of freedom.This recommends using more sophisticated control structures for thesake of safe operation if process integration is applied.
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    Effects of Energy Intensification of Pressure-Swing Distillation on Energy Consumption and Controllability
    (ACS Omega, 2023-12-22) Mtogo, Jonathan Wavomba; Toth, Andras Jozsef; Fozer, Daniel; Mizsey, Péter; Szanyi, Agnes
    The aim of process integration is the efficient use of energy and natural resources. However, process integration can result in a more precise process operation, that is, it influences controllability. Pressure-swing distillation processes are designed for the separation of azeotropic mixtures, but their inherent heat integration option can be utilized to significantly reduce their energy consumption. One maximum-boiling and three minimum-boiling azeotropes are considered to study and compare the nonintegrated and integrated alternatives with the tool of mathematical modeling where ASPEN Plus and MATLAB software are used. The results show that the heat-integrated alternatives result in 32–45% energy savings that are proportional to the emission reduction and the consumption of natural resources. As far as the operability is concerned, the heat-integrated alternatives show worse controllability features than the nonintegrated base case. This can be due to the loss of one controllability degree of freedom. This recommends using more sophisticated control structures for the sake of safe operation if process integration is applied.
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    Improvement of Ceramic Insulation of Cook Stoves Using Carbonized Organic Waste
    (Journal of Energy Research and Reviews, 2023-06-29) Kyuvi, Esther; Nyangaya, James; Aganda, Alex
    Many households and small hotels in Kenya source their energy from biomass; mainly wood and charcoal. For the urban poor, their energy source is basically charcoal. With increasing population, rural urban migration, tough economic times, the use of charcoal must be as efficient as possible. In cognizance of this need, development of energy efficient biomass (charcoal) cook stoves is paramount. The main objective of the project was to optimize the insulating properties of ceramic insulation used in ceramic cook stoves using carbonized organic waste as the burnout additive. Carbonized organic waste herein referred to as char was collected and ground to fine dust. The char was used as a burnout medium in the clay to create pores, reduce density and increase porosity thereby improving insulation properties of the fired clay. Optimization was achieved by using different ratios of clay to char. Testing of biomass cook stove is provided for in ISO- 19867-0; the harmonized laboratory test protocol. The results showed that the apparent porosity of the sample increased from 34% with no char to 87% when the sample had 50% char. On the other hand, the bulk density reduced from 2.8 g/cm3 with no char to 1.2 g/m3 with 50% char. The prototype thermal efficiency was 33% and 25.8% for the control cook stove. The prototype and control cook stove cooking power were 0.97kW and 0.71kW respectively. The prototype PM2.5 emissions estimated to be 76 mg/MJd and CO emissions at 21 g/MJd which were lower than the Kenya standard KS 1814:2019 maximum emission of 137 mg/MJd and 25 g/MJd respectively This study has shown that when clay was mixed with char, there was a significant increase in desirable characteristics, which results in increased efficiency of biomass (charcoal) cook stoves and lower emissions.
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    (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.
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    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.
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    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.
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    Relativistic Distorted Wave Approach to Electron Impact Excitation of Heavy Rare Gases Using a Complex Potential
    (Kenyatta University, 2022) Marucha, Alex Magembe
    Data on excitation of rare gases is important in the study of plasma displays, lighting and lasers.From literature, both relativistic and non-relativistic computations performed on electron impact excitation of low-lying states of rare gases often fail to give satisfactory agreement with available experimental data mostly at low impact energies and at intermediate scattering angles. With this in view, in the present study, we have applied relativistic effects in a fully-relativistic distorted-wave approach to excitation of the lowest lying resonance states of argon, krypton and xenon gases, by modifying the electron-atom interaction distortion potential in such a way that the complex part, the absorption potential, and the real part, which includes an energy dependent polarization potential, exchange and electrostatic potentials, form the complex distortion potential used in calculating radial wavefunctions. The atomic wavefunctions are constructed in the multi-configuration Dirac-Fock approach by modifying the general-purpose relativistic atomic structure code GRASP for numerical procedures. In this study, the WKB approximation is used to compute the free continuum electron wavefunctions which are then used in computing scattering cross sections and angular parameters using our program RDWBA1. Present results from this study predict that use of a complex distortion potential in the relativistic approach to excitation of argon, krypton and xenon generally lowers integral cross sections as impact energies of the incident electron increases, compared to those obtained using real distortion potentials only. For argon, the effect of the absorption potential, which accounts for loss of flux into other open scattering channels is more visible at electron impact energies above 50 eV, while for krypton, absorption becomes more dominant above 100 eV. For xenon, which is the heaviest of the three, absorption in the distortion potential generally has minimal effect on cross sections at impact energies below 50 eV then significantly improves these results when compared with experiments as kinetic energy of the electron increases. Furthermore, for all the rare gases under investigation, it is the energy dependent polarization potential adopted, that plays a major role in improving shapes of cross-sections at low and near threshold impact energies, where available distorted-wave methods fail to give satisfactory results when compared to experiments. We have also obtained angular correlation parameters lambda to predict the magnetic sublevel responsible for most excitations, and Stokes parameters to predict the polarization of the emitted photon during atomic decay. Cross section results obtained from this study are in good agreement with experiments at all impact energies under investigation, therefore it will be interesting to see how these cross sections vary when this present approach is used to investigate excitation of the metastable states of rare gases with both electron and positron impact.
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    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.