Browsing by Author "Makokha, John W."

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    Characterization of Kenyan ceramics for production of medium duty alumina firebrick incinerator linings
    (2018) Makokha, John W.; Kariuki, DK.; Mwitari, PG.
    The aim of this study was to evaluate locally available ceramic raw materials for the manufacture of Medium Duty Alumina Refractory Firebrick for incinerator lining.The clays were collected from two sites, Eburru in Nakuru County and Mukurwe-ini in Nyeri County in Kenya. Atomic Absorption Spectrophotometer and X-Ray Diffraction analytical methods were used to determine the chemical composition of the respective clays before and after firing at 1000OC for two hours.Atomic Absorption Spectrophotometer results revealed that Eburru Kaolin contained the highest amount of silica at72.64% SiO2but had the lowest of all other oxides. All the three raw materials were found to increase their oxide percentages after firing due to the loss in moisture and organic matter and reflected on their aluminasilica ratio. The X-Ray Diffraction results showed that the refractory formulated using the clays at a ratio of 2:2:1 Eburru Kaolin : Eburru Fireclay: Mukuruweini Ballclay attained good structural properties after firing at 1000OC for two hours and was comparable to commercial products in the market in addition to meeting the standards of a Medium Duty Refractory Firebrick.This is suitable for manufacture of incinerator linings.
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    Long term assessment of aerosol radiative forcing over selected sites of East Africa
    (Scientific Research Publishing Inc., 2018-04-02) Makokha, John W.; Odhiambo, Jared O.; Shem, Godfrey Juma
    Atmospheric aerosols have contributed to radiative forcing through direct and indirect mechanisms. Aerosol effects are important in computing radiative forcing estimates for the past, current and future climate. In this study, a comprehensive assessment of regional aerosol radiative forcing, Optical Properties of Aerosol and Clouds (OPAC) model (wavelength range of 0.25 - 4.0 μm) over selected sites in East Africa was done. Aerosol optical properties constituted the inputs of a Radiative Transfer Model (RTM). Optical properties investigated included Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA) and Asymmetry Parameter (AP). Aerosol Radiative Forcing (ARF) during the study period at the surface (SFC), top of the atmosphere (TOA) and the atmosphere (ATM) was estimated to be –18.4 ± 1.4 W∙m−2 , +1.1 ± 0.3 W∙m−2 and +19.5 ± 2.5 W∙m−2 , respectively. This corresponds to an increment in net atmospheric forcing at a heating rate of about 0.55 ± 0.05 K/day (0.41 ± 0.03 to 0.78 ± 0.03 K/day) in the lower troposphere. The study points out the significant role played by atmospheric aerosols in climate modification over the area of study. It is recommended that a further assessment be done in view of uncertainties that may impact on the findings and which were not within the scope of this research.
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    Retrieval of aerosol optical depth over ecologically stressed east African land surfaces from top of atmosphere radiance utilizing the aerosol free vegetation index
    (Dept. of Geography, Bahir Dar University, 2005) Makokha, John W.; Angeyo, JW.
    Traditional satellite based AOD retrieval techniques with a coarse resolution such as collection 5 hardly provides a high spatial detail suitable for accurate AOD retrieval particularly over the ecologically stressed sites of East Africa. Furthermore, AOD retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS-collection 5) require a linear mixing model that utilizes the normalized difference vegetation index (NDVI) to calculate surface reflectance. Since NDVI is affected by the presence of aerosols in the atmosphere, an empirical linear relationship between short wave infrared (SWIR) and visible reflectance were estimated in order to calculate a modified aerosol free vegetation index (AFRI). Based on AFRI and the minimum reflectance technique (MRT), an improved linear mixing model was developed. Calculated Vis/SWIR ratio diverges from the one used in the hypothetical model for AOD retrieval. Likewise, the regression coefficients between retrieved AOD for the developed algorithm and AERONET were higher as compared to that of MODIS collection 5 and AERONET. These emphasize the need of using AFRI plus accurate selection of surface characteristics and aerosol type for accurate AOD retrieval over East Africa that is addressed by the developed algorithm. At low AERONET AOD values, the two algorithms i.e. MODIS and developed agree but as the AERONET AOD value increases, a discrepancy is noted between the two as a result of usingNDVI and AFRIin the MODIS and developed algorithms respectively.