Department of Energy and Power Engineering

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    Analysis of Electromagnetic Field Radiation from a Rectangular Cavity-Backed Slot Antenna Using ADI-FDTD Method
    (2012) Musyoki, Stephen; Ouma, Heywood A.; K’Onditi, Dominic B.O.; Nyaory, George M.
    In this paper, a rectangular Cavity Backed Slot Antenna (CBSA) Model excited by a probe is investigated. The analysis is carried out using the Alternating Direction Implicit - Finite Difference Time Domain (ADI-FDTD) Method which is applied to investigate its characteristics in terms of radiation patterns and power. This is because the method is capable of providing a more accurate definition of the electromagnetic fields within the rectangular apertures, while eliminating the Courant-Friedrich-Levy (CFL) stability condition which is present in the regular Finite Difference Time Domain (FDTD) method. A cavity-backed slot antenna structure with dimensions of 14cm×22cm×30cm is analyzed with the slot and aperture measurements done at 3GHz. Results showing current distribution on the material surrounding the apertures are presented and a discussion on the physical aspects of the aperture radiation phenomenon is also presented.
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    Auto-resonant eniotron oscillator using a magnetron type cavity
    (1991) Musyoki, Stephen; Yokoo, Kuniyoshi; Sato, Nobuyuki; Ono, Shoichi
    In 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 characteristics
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    Auto-resonant peniotron amplifier with a down tapered DC magnetic field
    (Taylor & Francis, 1990-02) Musyoki, Stephen; Yokoo, Kuniyoshi; Sato, Nabuyi; Ono, Shoichi
    High efficiency operation of an auto-resonant peniotron amplifier operating with a down tapered DC magnetic field is discussed and the basic design concepts for a 200 GHz experimental prototype tube are described.
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    Biocontainment of PCBs on flat concrete surfaces and coprecipitation of PCBs and metals in boiler chemical cleaning wastewater by microbial carbonate precipitation
    (2010) Okwadha, GDO
    Some 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 system
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    Biocontainment of polychlorinated biphenyls (PCBs) on flat concrete surfaces by microbial carbonate precipitation
    (2011) Li, Jin; Okwdha, GDO
    In 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.
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    Bit Error Rate Performance Analysis of a Wideband Code Division Multiple Access System Model in an Indoor Environment using Convolution Coding over Additive White Gaussian Channel
    (Volume 3, Issue 5 October 2014, 2014) Musyoki, Stephen; Kibet, Philip; Ombongi, Filbert
    The research entails the development of a WCDMA system model in an indoor environment that transmits data over an Additive White Gaussian Noise channel. In this environment the data rate is taken as 2Mbps. The performance of this model is enhanced by employing convolution coding scheme which reduced the error rate encountered in the system. The results show that the performance of the system improves when convolution coding is implemented. The performance of QPSK is found to be better that that of 16-QAM which means that QPSK is an efficient modulation scheme but its throughput is less that of 16-QAM. Therefore, there must be a trade-off between the modulation format to be applied in a given system and the error rate generates at the receiver by that format. The convolution coding improves the power efficiency of the system when it is incorporated into the system.
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    Casting of semi-solid cast iron slurry using combination of cooling slope and pressurisation
    (2004) Muumbo, A; Nomura, H; Takita, M
    A system developed at Nagoya University combining a cooling slope, gravity pouring and pressurisation was utilised to cast components from hypoeutectic cast iron in the semi-solid state. Investigation of resulting microstructure and attendant defects was carried out, which revealed significant improvements in primary particle size refinement and globularity in components produced through semi-solid casting (SSC) when compared with normal gravity die casting (GDC) of super-heated melt. Sub-surface anomalies such as chilling tendency and skin-deep shrinkage cavities were unavoidable in components cast under pressure in a metallic mould at room temperature but, increasing the mould preheat temperature reduced the anomalies whereas increased pressurisation improved melt feeding and drastically reduced porosity attributed to gas entrapment and solidification shrinkage
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    Challenges of Implementing E-Learning in Kenya: A Case of Kenyan Public Universities
    (2015) Tarus, John K; Gichoya, David; Muumbo, Alex M
    In 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.
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    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, A
    Textile 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.
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    Design of a high power, 10 GHz auto-resonant peniotron amplifier
    (1992) Musyoki, Stephen; Sakamoto, Keishi; Watanabe, Akihiko
    The autoresonant peniotron amplifier is a suitable source of high power RF radiation because of its high gain, high power, high frequency and high efficiency operation features. In this report we present our simulation results of a 10 GHz, 2.2 GW autoresonant peniotron amplifier with an electron energy conversion efficiency of 72.5 % and a gain of about 58 dB
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    Design of a high power, 2.75 GHz relativistic peniotron oscillator
    (1992-10) Musyoki, Stephen; Sakamoto, Keishi; Watanabe, Akihiko
    In the peniotron oscillator, the kinetic energy of relativistic electrons can be efficiently converted to an electromagnetic wave. This feature makes the peniotron a very attractive source of high power microwaves, which is required in heating of fusion plasma in tokamaks and high gradient particle accelerators. In this report we present the design of a 2.75 GHz relativistic peniotron oscillator which is capable of generating a microwave radiation of 30 megawatt with an efficiency of about 60 %. The experimental test results of the designed cavity are also presented
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    Development of a Medical Expert System as an Expert Knowledge Sharing Tool on Diagnosis and Treatment of Hypertension in Pregnancy
    (2012) Gudu, J; Gichoya, D; Nyongesa, P; Muumbo, A
    This paper outlines the development a Medical Expert System for the diagnosis and treatment Hypertension in Pregnancy to be used in the Reproductive Health Division, at Moi Teaching and Referral Hospital in Eldoret, Kenya. The Diagnostic and Treatment Expert System for Hypertension in Pregnancy has so far remained at the testing phase of its life cycle and is yet to be implemented. During the research, it was found that there is an acute shortage of specialist obstetricians in the Reproductive Health Division which implies that there is also scarce expert knowledge on the diagnosis and treatment of Hypertension in Pregnancy, yet the condition continues to kill many women of reproductive age in Kenya, hence the need to develop the Medical Expert System (MES) as an expert knowledge sharing tool to be used by other medical personnel within the Reproductive Health Division who are not specialists in diagnosis and treatment of Hypertension in Pregnancy
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    Development of a Renewable Energy Database System for East Africa – Survey on Biogas Usage and Potency of Various Agricultural Bio-wastes in Kenya
    (2014) Nzila, C; Muasya, R; Muumbo, A; Kiriamiti, K; Githaiga, J; Dewulf, J
    Kenya being an agricultural based economy produces vast amounts of agricultural bio-waste such as maize/corn stalks, rice and wheat straws, tea and coffee waste, sugarcane, banana and barley residues, sisal and cotton wastes as well as other forest residues. Most of these residues are regarded as of no immediate value hence they are wasted in the farms through burning or uncontrolled decay thus leading to nutrient leakage and eutrophication to the surrounding water bodies as well as contributing to odour and green-house gas emission through release of volatile and un-burnt hydrocarbons. The main objective of the researchwas to identify and develop biogas data variables in Kenya through a structured use of anaerobic digestion as a means of producing biogas from agricultural bio-waste including animal manure and crop residues. The short term target of the project was a phased development of well-defined/structured data variables suitable for a multilayered database system on biogas energy in Kenya, which could later form a basis for the development of a real time biogas information dissemination platform that can be replicated in other regions across Africa. Literature review was done by means of desk-study and field surveys were conducted to gather qualitative as well as quantitative data for analysis and in-putting onto a Geographic Information System (GIS) based data mapping. Direct interviews were based on a schedule that employed a combination of direct site visits, emails and phone calls.Laboratory-based physical/bio-chemical characterization of biogas feedstock was also conducted. Discussions with diverse biogas stake holders elicited 100% support from respondents in addition to yielding an array of recommendations. The bio‐methane results further demonstrated the suitability of coffee pulp residue, cotton residue and maize stover as complementary biogas feedstock.The biogas quality in terms of hydrogen supplied (H2S) and methane (CH4) content was quite promising. The biogas H2S content (ppmv) for all the substrates ranged from as low as 105 (for maize stover) to 1100 (sugarcane leaves) whereas the CH4 content varied from 40% (sugar cane leaves) to 62%(cotton residue).Generally CH4 content is required to be above 50% whereas the presence of contaminants such as H2S is supposed to be less than 1000ppmv. From the results, biogas from coffee pulp residue, sugarcane bagasse, maize stover, cotton residue and banana stalks can be regarded as suitable alternatives for domestic biogas production.
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    E-Medical Consultation for Diagnosis and Treatment of Hyperten sion in Pregnancy: an Opportunity to achieve the 5 th Millennium Development Goal in Kenya
    (2012) Gudu, Jael; Gichoya, David; Muumbo, AM; Nyongesa, Paul
    This study sought to establ ish the challenges that the Reproductive Health Division (Hi gh Risk Pregnancy Clinic) at Moi Teaching and Referral Hospital based in Eldoret city, one of the two referral hospitals in Kenya, faces in adopting e-medical consultation as a way of impr oving maternal healthcare for patients with hypertension in pregnancy and reducing maternal deaths. In this paper, an outline of the strategies and pillars that the Clinic needs to adopt to embrace the use of e-medical consultation for the diagnosis, treatment and management of hypertension in pregnancy is pr esented. The survey conducted established that the division is still lagging behind and has not adopted the use of e-he alth, especially in the consultation sessions between the doctors and patients. The outlined strategies when implemented will help steer the Reproductive Health Division (High Risk Pregnancy Clinic) to wards making healthcare services available in an efficient and effective way to expectant women with the condition. The model could be adopted to extend the same to less endowed areas around the globe, where specialist: patient ratio is low.
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    The Effects of a Human Hand on a Wireless Mouse Antenna
    (2015) Musyoki, Stephen; Konditi, B. O.; Njoroge, Dominic; Rainsford, K
    In this paper, Finite Difference Time Domain (FDTD) method is used to analyze the effect of a human hand on a wireless mouse antenna. The need for this analysis is based on the fact that human tissues are dielectric in nature and they can, therefore, be treated as electromagnetic absorbers. In the first part, hand effect on reflection coefficient, input resistance, bandwidth and radiation efficiency are studied. In the second part, the variation of radiation efficiency with the position of the hand from the antenna feed point is estimated. The Method of Moments is used to validate the results.
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    Emittance measurement of high-brightness microbeams
    (Japanese Journal of Applied Physics, 1994) Musyoki, Stephen; Ishizuka, Hiroshi; Nakahara, Yuriko; Kawasaki, Sunao; Shimizu, Hiroshi; Watanabe, Akihiko; Shiho, Makoto
    Arrays of microtriodes have recently become available due to the development of microfabricated field-emission electron sources. Computer simulation has shown that the brightness of beams emitted by them is significantly higher than that of the common microbeams, and possible application of the accelerated beam to free electron lasers has been discussed. Experimentation on beam generation has started, but methods for diagnosing the beam have not yet been established. Difficulty is predicted, because of the high brightness, in applying the conventional methods of emittance measurement. In this paper we propose a new method that determines the emittance without using apertures. The cross section of a converging beam is elongated by a quadrupole lens, and parameters of the emittance ellipse are obtained from the beam size on a screen when changing either the strength or the axial position of the quadrupole lens.
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    Evaluation of Surface Water Runoff from Fly Ash–Stabilized and Nonstabilized Soil Surfaces
    (2010) Dombrowski, Frank J; Ramme, Bruce W; Okwadha, GDO; Kollakowsky, Dave
    This 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 surfaces
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    Improving the Bandwidth of a Circular Microstrip Patch Antenna through Shape Modification
    (2014) Langat, Benard Kipkorir; Langat, Kibet P; Musyoki, Stephen
    An 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.