Department of Energy and Power Engineering
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Item Parameter optimization in design of a rectangular microstrip patch antenna using adaptive neuro-fuzzy inference system technique(2012) Rop, K.V; Konditi, D.B.O; Ouma, H.A; Musyoki, S.MModern wireless system s are placing greater emphasis on antenna designs for future development in communication technology becau se the antenna is a key element in the overall communication system. A Microstrip Antenna is well suited for wireless communication due to its light weight, low volume and low profile planar configuration which can be easily conformed to the host surface. In this paper, an optimization method based on adaptive neuro-fuzzy inference system (ANFIS) for determining the parameters used in the design of a rectangular microstrip patch antenna is presented. The ANFIS has the advantages of expert knowledge of fuzzy inference system (FIS) and the learning capability of artificia l neural network (ANN). By calculating and optimizing the patch dimensions and the feed point of a rectangular microstrip antenna, this paper shows that ANFIS produces good results that are in agreement with Ansoft HFSS 13.0 simulation results.Item Traffic Analysis in the Reduction of Power Consumption in Cellular Radio Access Network(2015) Kimanthi, Shadrack; Kibet, P. L; Musyoki, SAll over the world cellular network communication has become an integral part of people’s lives. This has changed how people behave and their demand for connectivity is anywhere and anytime. Understanding the subscriber calling patterns and behaviour is very important when planning for the network resources and carrying out network design. Traffic analysis is carried and is aimed at improving Quality of Service, determining the busy hour, estimating subscriber traffic usage, determining the amount of capacity (channel) required to satisfy a given number of subscribers in a cell or network among other reasons. This paper investigates the telecommunication traffic of a selected region. An analysis of the subscriber calling pattern will be carried out and a solution will be proposed on how to reduce power consumption in the cellular network based on traffic load.Item Improving the Bandwidth of a Circular Microstrip Patch Antenna through Shape Modification(2014) Langat, Benard Kipkorir; Langat, Kibet P; Musyoki, StephenAn antenna is used in a communication system to radiate or receive radio waves. The most desired antenna is one which is small in size, light in weight, cheap and can easily fit to the surface attached. All these features are inherently possessed by microstrip patch antennas. However, no antenna is perfect. Microstrip patch antennas like all other types of antennas do have their associated disadvantages. One of the major disadvantages of this type of antenna is narrow bandwidth. In this study, the narrow bandwidth of a circular microstrip patch antenna was improved through shape modification. The bandwidth of the antenna was optimized by adding some parts to and removing some parts from the initial circular patch. Although the main aim was to improve the bandwidth, it had to be ensured that other important parameters of the antenna such as radiation efficiency, impedance matching and gain are not degraded in the process. Microstrip line feeding technique was utilized in the design. HFSS 13.0 full wave simulator based on Finite Element Method (FEM) was used to simulate the antenna. Simulation results were then presented. Simulation results of return loss showed that the antenna achieved a bandwidth of 13.16% at 1.755 GHz and a very broad bandwidth from 3.315-20 GHz. This is a great improvement when compared with the bandwidth of a conventional microstrip patch antenna of less than 3%. Simulation results of Z11 parameters showed that the antenna achieved satisfactory impedance matching with a 50Ω transmission line at 1.755 GHz, 3.65 GHz, 4.668 GHz and 7.031 GHz and with a 75Ω transmission line at 9.366 GHz, 14.634 GHz, 16.461 GHz, 17.304 GHz and 18.265 GHz. The antenna recorded satisfactory gains and excellent radiation efficiencies in all these frequencies. The antenna can be used for a wide range of applications because of its wider bandwidth.Item Performance Analysis of Pulse Shaping Filter for WCDMA Applications(2014) Ombongi, Filbert Onkundi; Kibet, Philip Langat; Musyoki, Stephen MThe wireless systems with spreading of a signal experiences time delay which has to be smaller compar ed to symbol period of the data. The condition can’t be met in high data rate transmissions which make this delay to be greater than that of the data symbol period which results in inter - symbol interference (ISI) due to serial transmission. Therefore, a p erformance of pulse shaping filter for use in WCDMA needs to be optimized to reduce ISI for a rate of 2Mbps. The system is simulated in MATLAB with 16 - QAM modulation and channel coding . The error rates are determined with a variation in the f ilter roll off factor (α) . The results have shown that the performance of a wireless communication system depends on the filter roll off factor. Therefore, there must be a trade - off between filter complexity and power efficiency in determining an optimum roll - off factor which gives minimum error rateItem Simulation of the influence of secondary electrons on the performance of potential depressed collectors for TWTs(2000) Musyoki, Stephen; Takahashi, M; Uchikawa, TSignificant differences have been found between measured and simulated data for collectors designed with codes which disregard the influence of secondary electrons. To solve this problem, various codes have been developed. These codes assume that secondary electrons are only emitted in a single direction and ignore their spatial distribution. We have developed a code in which secondary electron yield is calculated from an empirical formula and the emitted secondary electrons are assumed to have cosine spatial distribution. To represent this distribution, for each primary beam point of impact, the emitted secondary beam is split into 3 beams; one beam normal to the impact surface and the other two at an angle to the normal. The normal beam carries half of the current and the rest of the current is divided equally between the side beams. The code uses a two dimensional, axis symmetric Finite Element Method (FEM) for modeling. FEM has been chosen because of its ability to model accurately arbitrary shaped structures. We designed a ku-band (14.25 GHz), 2-stage TWT by using the developed code.Item A new method of emittance measurement for electron beams from the Micro-emitter(1994) Ishizuka, Hiroshi; Nakahara, Yuriko; Kawasaki, Sunao; Musyoki, Stephen; Shimizu, Hiroshi; Watanabe, Akihiko; Shiho, MakotoRecently a new type of cathode called Micor-emitter has been put in progress. This cathode is a microfabricated field emitter having the characteristics of very low emittance and high brightness. We cannot measure the emittance of the cathode with conventional methods like the pepper-pot method. The reasons are: (1) the angle between the electron orbit and the axis is very small and (2) we cannot focus the electron beam in the vacuum or on the surface of the material since the current density of the cathode is extremely high. For the emittance measurement for such low emittance and high brightness cathode, we need to expand the beam, and measure the beam's cross section without any slits or apertures. We studied and proposed a new emittance measurement method for the Micro-emitter.Item Auto-resonant eniotron oscillator using a magnetron type cavity(1991) Musyoki, Stephen; Yokoo, Kuniyoshi; Sato, Nobuyuki; Ono, ShoichiIn an ideal auto-resonant eniotron oscillator (ARPO), all the electrons are able to give almost all their kinetic energy to an electromagnetic wave, resulting in a conversion efficiency of nearly 100%. However, the electric field strength required to drive a highly efficient interaction is difficult to achieve in an ordinary rectangular or circular waveguide cavity because of the low interaction coupling between electrons and the electromagnetic wave in the cavity. In this aper, we describe our investigation of an ARPO with a magnetron type cavity in lace of that above. In this cavity, the coupling becomes sufficiently strong to confirm experimentally the romising features of an ARPO. Additionally, the experiments should be useful for developing highly efficient medium-power oscillators in the microwave region. Here we resent our rocedure for designing such an experimental tube and our computer simulation results for its operational characteristicsItem An overview of the Faculty of Infomation Technology in 2009.(2009) Marwanga, Reuben OItem Influence of graphite morphology, matrix structure on gray iron machining(2000) Marwanga, Reuben O; Robert, C. Voigt; Paul, H. CohenItem Biocontainment of PCBs on flat concrete surfaces and coprecipitation of PCBs and metals in boiler chemical cleaning wastewater by microbial carbonate precipitation(2010) Okwadha, GDOSome industrial equipment such as electric transformers and capacitors are located in vaults and substations on flat concrete surfaces. Due to accidents, normal routine maintenance or replacements, these equipments may spill oil which may contain PCBs on these surfaces. These spills must be cleaned up in accordance with United States Environmental Protection Agency's (USEPA) guidelines. Current cleanup operations are abiotic in nature, encompassing both physical and chemical methods. These methods generate enormous amounts of impacted wastewater and solid wastes which have to be disposed of carefully at a cost. In addition, some chemicals used are harmful to both humans and other organisms. Epoxy coatings have been used to encapsulate PCBs on concrete surfaces. However, these coating systems can be ineffective because the adhesion with concrete is easily damaged by elevated temperatures causing failure of the coating systemItem Evaluation of Surface Water Runoff from Fly Ash–Stabilized and Nonstabilized Soil Surfaces(2010) Dombrowski, Frank J; Ramme, Bruce W; Okwadha, GDO; Kollakowsky, DaveThis study evaluated the constituent make up of simulated rainwater runoff from Class C fly ash–stabilized and nonstabilized clay soil using laboratory test pads to assess the potential for impacts to surface water from the use of uncovered fly ash–stabilized soils as potential roadbed material. Recirculated runoff from test pads was sampled and tested during three simulated rainfall events over an 84-day trial period. All samples were analyzed for trace metals. Analytical results from the simulated runoff were screened to identify five indicator parameters in the runoff that were used as the basis for assessing potential environmental effects to surface waters. Runoff water results from fly ash–stabilized test pads for these indicator parameters were compared to water quality benchmarks. Based on the low concentrations measured in runoff relative to applicable criteria, and on the conservative nature of the experimental methods relative to typical field conditions, we concluded that surface runoff from fly ash–stabilized soil would not present significant adverse effects to surface water if used uncovered on low traffic exposed surfacesItem Thermal removal of mercury in spent powdered activated carbon from Toxecon process(2009) Okwadha, GDO; Li, Jin; Ramme, Bruce; Michaud, Dave; Kollakowsky, DaveThis research developed and demonstrated a technology to liberate Hg adsorbed onto powdered activated carbon (PAC) by the TOXECON process using pilot-scale high temperature air slide (HTAS) and bench-scale thermogravimetric analyzer (TGA). The HTAS removed 65, 83, and 92% of Hg captured with PAC when ran at 900°F , 1,000°F , and 1,200°F , respectively, while the TGA removed 46 and 100% of Hg at 800°F and 900°F , respectively. However, addition of CuO–Fe2O3 mixture and CuCl catalysts enhanced Hg removal and PAC regeneration at lower temperatures. CuO–Fe2O3 mixture performed better than CuCl in PAC regeneration. Scanning electron microscopy images and energy dispersive X-ray analysis show no change in PAC particle aggregation or chemical composition. Thermally treated sorbents had higher surface area and pore volume than the untreated samples indicating regeneration. The optimum temperature for PAC regeneration in the HTAS was 1,000°F . At this temperature, the regenerated sorbent had sufficient adsorption capacity similar to its virgin counterpart at 33.9% loss on ignition. Consequently, the regenerated PAC may be recycled back into the system by blending it with virgin PAC.Item Biocontainment of polychlorinated biphenyls (PCBs) on flat concrete surfaces by microbial carbonate precipitation(2011) Li, Jin; Okwdha, GDOIn this study, a biosealant obtained from microbial carbonate precipitation (MCP) was evaluated as an alternative to an epoxy-coating system. A bacterium Sporosarcina pasteurii strain ATCC 11859, which metabolizes urea and precipitates calcite in a calcium-rich environment, was used in this study to generate the biosealant on a PCB-contaminated concrete surface. Concrete cylinders measuring 3 in (76.2 mm) by 6 in (152.4 mm) were made in accordance with ASTM C33 and C192 and used for this purpose. The PCB, urea, Ca2+, and bacterial cell concentrations were set at 10 ppm, 666 mM, 250 mM, and about 2.1 × 108 cells mL−1, respectively. The results indicate that the biosealed surfaces reduced water permeability by 1–5 orders of magnitude, and had a high resistance to carbonation. Since the MCP biosealant is thermally stable under temperatures of up to 840 °C, the high temperatures that normally exist in the surrounding equipment, which may contain PCB-based fluids, have no effect on the biosealed surfaces. Consequently, there is greater potential to obtain a stronger, coherent, and durable surface by MCP. No measurable amount of PCBs was detected in the permeating water, indicating that the leaching water, if any, will have a minimum impact on the surrounding environment.Item Optimum conditions for microbial carbonate precipitation(2010) Okwadha, George D.O; Li, JinThe type of bacteria, bacterial cell concentration, initial urea concentration, reaction temperature, the initial Ca2+ concentration, ionic strength, and the pH of the media are some factors that control the activity of the urease enzyme, and may have a significant impact on microbial carbonate precipitation (MCP). Factorial experiments were designed based on these factors to determine the optimum conditions that take into consideration economic advantage while at the same time giving quality results. Sporosarcina pasteurii strain ATCC 11859 was used at constant temperature (25 °C) and ionic strength with varying amounts of urea, Ca2+, and bacterial cell concentration. The results indicate that the rate of ureolysis (kurea) increases with bacterial cell concentration, and the bacterial cell concentration had a greater influence on kurea than initial urea concentration. At 25 mM Ca2+ concentration, increasing bacterial cell concentration from 106 to 108 cells mL−1 increased the CaCO3 precipitated and CO2 sequestrated by over 30%. However, when the Ca2+ concentration was increased 10-fold to 250 mM Ca2+, the amount of CaCO3 precipitated and CO2 sequestrated increased by over 100% irrespective of initial urea concentration. Consequently, the optimum conditions for MCP under our experimental conditions were 666 mM urea and 250 mM Ca2+ at 2.3 × 108 cells mL−1 bacterial cell concentration. However, a greater CaCO3 deposition is achievable with higher concentrations of urea, Ca2+, and bacterial cells so long as the respective quantities are within their economic advantage. X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray analyzes confirmed that the precipitate formed was CaCO3 and composed of predominantly calcite crystals with little vaterite crystals.Item Challenges of Implementing E-Learning in Kenya: A Case of Kenyan Public Universities(2015) Tarus, John K; Gichoya, David; Muumbo, Alex MIn this paper, we discuss the challenges experienced by Kenyan public universities in implementation of e-learning and recommend possible solutions towards its successful implementation. In the last few years, most Kenyan public universities have adopted e-learning as a new approach to teaching and learning. However, the implementation challenges faced by these universities have continued to impact negatively on its effective utilization. This paper presents the findings from a survey of 148 staff of three Kenyan public universities who are currently using e-learning in blended mode approach. The purpose of this study was to investigate the challenges hindering the implementation of e-learning in Kenyan public universities. Data was collected through questionnaires, in-depth interviews and document analysis. The findings reveal that e-learning comes with some challenges that must be addressed by Kenyan public universities before successful implementation can be realized. However, the benefits and opportunities presented by e-learning far outweigh the challenges. The paper finally recommends some possible solutions that public universities could embrace towards successful implementation of e-learning.Item Colour and Nutrient Removal from Textile Waste Water Using an Enhanced Fluidised Bed Bioreactor(2011) Nzila, C; Wambua, P; Githaiga, J; Tuigong, D; Kiriamiti, HK; Kiambi, S-L; Muumbo, ATextile waste water contains an array of chemicals with different biodegradation characteristics that often presents chronic colour and nutrient removal problems. Conventional and advanced methods commonly applied to treat textile wastewater are normally costly and require substantial investment costs. Enhanced anaerobic digestion (E.A.D) of textile wastewater, in comparison with other processes, seems to be most promising since it drastically reduces the organic and colour load of the wastewater at substantially minimised costs. This possibility offers textile industries an opportunity to cost effectively treat their effluents. This study evaluated colour and COD removal from raw textile waste water by means of an enhanced fluidised bed bioreactor. The enhancement of the bioreactor entailed pretreatment of the raw waste water using a coagulant (AlCl3) and a polyelectrolyte organic flocculant (Calflock 2900) to remove the suspended solids. The enhanced system was operated semi-continuously under laboratory conditions for 1680 hours. The fluidised bed anaerobic bioreactor was operated at a Bv of 2.6g COD/L.d and HRT of 12 hours. The enhancement process on average achieved respectively 40 ± 13 per cent and 68 per cent COD and colour removal efficiencies. The combined system on average achieved 72 ± 7per cent and 87 ± 4 per cent COD and colour removal efficiencies respectively however the bioreactor produced a low amount of biogas. The bioreactor operated without the need to discharge regularly the biological excess of sludge produced. The implementation of the combined system proved to be quite promising thus a new approach for the treatment of textile wastewater is thus proposed.Item A Study on Agricultural Residues as a Substitute to Fire Wood in Kenya: a Review on Major Crops(2014) Kimutai, Stephen K; Muumbo, Alex M; Siagi, Zachary O; Kiprop, Ambrose KFor Kenya, the use of fire wood is enormous that the exploitation of other energy resources such as biomass from agricultural residues is little known. Therefore, the main aim of this study is to investigate agricultural residues estimates for use as a substitute to fire wood and charcoal in Kenya. This solution is in line to the urgent needs of finding the alternative for the depleting fossil fuels. The study found that Kenya agricultural residue energy potential is about 187,000 TJ which enough to substitute fire wood in most regions if converted with suitable technologies. If all the available agricultural residues are used as substitution fuel for fire wood, Kenya could reinstate the 10% forest cover as recommended from the current 1.7%.Item The use of ICT in enhancing quality in public universities: case of Moi University(2009) Ataro, E; Nzila, C; Muumbo, AItem A precast concrete technology for affordable housing in Kenya. Pt. 2(2008) Shitote, SM; Nyomboi, T; Muumbo, A; Wanjala, RS; Khadambi, EL; Orowe, J; Sakwa, F; Apollo, A