Andrew Oduor - Academia.edu (original) (raw)
Papers by Andrew Oduor
Journal of Applied Physics, 2012
Ab-initio calculations based on density functional theory have been employed to study the structu... more Ab-initio calculations based on density functional theory have been employed to study the structural, electronic, and optical properties of yttrium (Y), scandium (Sc), zirconium (Zr), and niobium (Nb) doped α-Al2O3 with corundum structure. Exchange and correlation effects between electrons have been treated by generalized gradient approximation within the Perdew-Burk-Ezrenhof parameterization and by recently developed Tran-Blaha modified Becke-Johnson approach. Most attention in the work has been paid to the impurity d states, whose energy splitting has been analyzed in terms of the crystal field theory and whose influence on the gap size and the offset of the bands around it has been carefully evaluated. The influence of these states on modification of the optical absorption edge and the static dielectric constant of the doped systems has been also studied. It is concluded that only the Y doped α-Al2O3 (1) preserves the size of the band gap of the pure alumina, (2) does not change ...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 25, 2022
We present a comparative computational study of temperature-dependent elastic constants of silico... more We present a comparative computational study of temperature-dependent elastic constants of silicon (Si), silicon carbide (SiC) and diamond as substrates that are commonly used in the manufacture of Micro-Electromechanical Systems (MEMS) devices. Also mentioned is Cd 2 SnO 4 , whose ground-state elastic constants were determined just recently for the first time. Si is the dominant substrate used in the manufacture of MEMS devices, owing to its desirable electrical, electronic, thermal and mechanical properties. However, its low hardness, brittleness and inability to work under harsh environment such as hightemperature environment, has limited its use in the manufacture of MEMS like mechanical sensors and bioMEMS. Mechanical sensors are fabricated on SiC and diamond due to their high Young's moduli as well as high fracture strength, while the bioMEMS are fabricated on polymers. The effect of temperature on the elastic constants of these substrates will help in giving insight into how their performance vary with temperature.
International Journal of Engineering, Science and Mathematics, 2013
The developments of wind energy systems have enabled an efficient production and use of wind ener... more The developments of wind energy systems have enabled an efficient production and use of wind energy. Three widely used control schemes for wind energy systems are Pitch control, Rotor resistance control and Vector control. A traditional wind energy system consists of a stall regulated or pitch control turbine connected to a synchronous generator through gearbox. The synchronous generator operates at fixed speed and one of the earliest rotor control schemes was the rotor resistance control. The speed of an induction machine is controlled by the external resistance in the rotor circuit. The drawback of the above methods is the inability of wind turbine to capture at low wind speeds. This paper develops a model which maximizes wind energy output. This model asses the effects of friction coefficient and the height of wind above ground(given by the height of turbine from the ground i. e the hub height) on power output. The study considers an already existing model, that is the turbine mo...
The growth of fruits and vegetables is becoming an important component of the agricultural indust... more The growth of fruits and vegetables is becoming an important component of the agricultural industry sector, as sale of dried fruits and vegetables assume commercial scale. However due to lack of processing considerable amount of losses (between 30% and 40%) of these seasonal products occur in many developing countries. Drying is one of the most common methods of preservation of agricultural products. It removes sufficient moisture from the food and prevents decay or spoilage. Majority farmers in developing countries use open-sun method for drying their harvest despite the existence of more efficient methods of drying. This method is time consuming and exposes the produce to destruction by birds, animals and contamination. The areas surrounding Maseno university is agriculturally rich and known for production of vegetables and fruits among other agricultural products. In the wet seasons there is significant waste due to lack of preservation facilities to prolong their shelf life and yet during dry seasons these products are short in supply. In the present work, a model of natural convection solar dryer with twin collectors was designed and tested with and without load under the climatic conditions of Maseno, Kenya for drying of Vegetable kales. Results of test under no load revealed that the humidity in the drying chamber was reduced by 31.4%, while the chamber temperature was raised by 11.5 o C at average air flow rate of 0.39 m/s. The moisture content in the kales was reduced from 84.1% to less than 10% in about 15 hours of drying for an average air flow of 0.39 m/s. The maximum thermal efficiencies obtained were 22.51 % and 25.52 % for collector 1 and 2 respectively. Quality tests performed on both solar dried and wet samples revealed more than 50 % retention of all the nutrients in the solar dried vegetable kales.
A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta Universi... more A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta University, Physics Department; 1988; The QC 321.7.T45 O3
A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta Universi... more A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta University, Physics Department; 1988; The QC 321.7.T45 O3
Case Studies in Construction Materials
International Journal of Environment and Waste Management
Solid State Communications
American Journal of Materials Science, 2019
Spray Pyrolysis Technique was used in depositing thin films of cadmium stannate, doped with iron ... more Spray Pyrolysis Technique was used in depositing thin films of cadmium stannate, doped with iron metal. The precursor solutions used were sprayed onto the pre – heated glass slides that were kept at a constant temperature of 450°C. The transmittance and reflectance measurements were made in the spectral wavelength range of 300 – 1100 nm. It was found out that both the concentration of the reactants and doping had an effect on the optical properties of the deposited thin films. At the upper end of the visible spectrum (718 nm wavelength), the values of the optical constants were: Transmittance of up to 70.45%, thickness of 323 – 594 nm, refractive index of 2.108 – 3.542, absorption coefficient of 7.385 x 103 cm-1 – 2.2784 cm-1, extinction coefficient of 0.042 cm – 0.130 cm and a band gap energy of 3.9 eV.
Spray Pyrolysis Technique (SPT) was used to deposit thin films (TFs) of cadmium stannate, doped w... more Spray Pyrolysis Technique (SPT) was used to deposit thin films (TFs) of cadmium stannate, doped with iron (Fe) for the first time. The precursor solutions that were used wereprepared at a concentration of 0.1M, doped with Feand then sprayed onto the pre-heated glass slides immediately at deposition temperatures of 350 ± 7°C, 400 ± 7°C and 450 ± 7°C. The optical properties of the deposited Fe-doped TFs were studied in the wavelength range of 300-1100nm. The X-Ray diffraction (XRD) studies showed that the TFs were orthorhombic with growth orientation along the (2 0 0) direction. Film thickness of 85 ± 10 nm was obtained. It was found out that anincrease in the deposition temperature increased transmittance and band gap, but decreased absorption coefficient, extinction coefficient and refractive index, which was attributed to the improvement in crystallinity of the deposited TFs. Doping reduced transmittance and band gap, but increased refractive index, absorption coefficient and extin...
The electronic and optical properties of hexagonal and cubic Ge2Sb2Te5 have been calculated using... more The electronic and optical properties of hexagonal and cubic Ge2Sb2Te5 have been calculated using the QUANTUM ESPRESSO and Yambo codes. The study has considered t he variation of electronic band gaps with lattice c onstants using the LDA with non-linear correction, where it was es tablished that both phases are apparently metallic at equilibrium. Upon increasing a, it was found that the hexagonal phase had a maxim um gap of 0.22 eV at a c/a value of 3.49 whereas the cubic phase had a maximum gap of 0.23 eV at a much higher c/a value of 10.62. Findings of the optical absorption spectra of both hexagonal and cubic Ge2Sb2Te5 obtained using time dependent density functional t heory (TDDFT) and the partially selfconsistent GW (GW0) are also reported. The absorption edge has been o bserved at 0.48 eV using TDDFT and at 0.21 eV using GW0 for the hexagonal phase.
Applied Acoustics, 2021
When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms whi... more When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms which are switched on or o as the excitation frequency varies. The classical way of measuring acoustic energy loss in porous materials uses the Kundt impedance tube. However, due to its short length, measurements are made in the steady state harmonic regimes. Its lower cuto frequency is often limited to a few hundreds of Hertz. Two long acoustic waveguides were assembled from water pipes and mounted to create test-rigs for the low-frequency acoustic characterization of monolayer and stratied airsaturated poroelastic materials. The rst waveguide was straight and had a length of 120 m, while the second was coiled to gain space and was 135 m long. The long waveguides appeal to very low frequency measurements using impulsive acoustic waves (with rich spectral content) because the incident waves can be separated in time from echoes o the extremities of the guides. The transmission coecient of porous materials recovered using the two waveguides compared well with those from the transfer matrix method (TMM) used here in combination with Biot's 1962 theory to describe propagation in porous dissipative media. This wave-material interaction model permitted the recovery of the properties of poroelastic materials from transmitted acoustic waves propagating in air. The parameters involved are the Young's moduli, Poisson ratio and microstructural properties such as tortuosity and permeability. Being able to descend to lower frequencies guarantees the correct verication of the magnitude of the measured transmission coecient which approaches unity towards the static frequency. The coiled and straight 1 waveguides were found to be equivalent and provided data down to frequencies of the order of ≈ Hz.
![Research paper thumbnail of Corrigendum on “Microstructural and elastic properties of stable aluminium-rich TiAl and TiAl2 formed phase intermetallics” [Mater. Lett. 287 (2021) 129295]](https://attachments.academia-assets.com/99201924/thumbnails/1.jpg)
](Materials Letters, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Materials Letters, 2021
We studied aluminium-rich Ti-Al (Ti32Al68 and Ti40Al60) binary alloys that were composed of TiAl ... more We studied aluminium-rich Ti-Al (Ti32Al68 and Ti40Al60) binary alloys that were composed of TiAl and TiAl2 lamellar microstructures. The law of mixtures was employed in calculating the theoretical Young's moduli. The lattice parameters of the alloys showed that both were tetragonal crystals. In the computational study, we made use of our modified method for the stress-strain calculation of elastic constants. The alloys at the respective chemical compositions were modelled by creating titanium (Ti) supercells, which were then doped by replacing some of the Ti atoms with aluminium atoms. The values of elastic moduli were verified by the ab initio calculation in this work, which showed a perfect agreement. The Pugh's ratio showed that both the alloys are ductile.
We examined changes in rheological properties of nonequilibrated spin-coated thin films of isotac... more We examined changes in rheological properties of nonequilibrated spin-coated thin films of isotactic polystyrene (iPS) and isotactic poly(para-methylstyrene) and blends thereof by dewetting experiments. For 200 nm thick films and a systematic variation of dewetting temperature, we focused on changes in the amount of residual stresses and the corresponding relaxation times as a function of iPS content. We found that both parameters increased in an approximately logarithmic fashion with iPS content, suggesting an increased tendency for the formation of transient clusters in blends with increased iPS content. Assuming linear elasticity, we determined a nonequilibrium shear modulus and a nonequilibrium viscosity, which we compared with published data of the equilibrium properties. Particularly for the viscosity, huge deviations from published values were observed. We provide a tentative explanation.
Journal of Technology Innovations in Renewable Energy, 2018
This paper reports on the effect of reverse bias (RB) on dye-sensitized solar cells (DSSCs) that ... more This paper reports on the effect of reverse bias (RB) on dye-sensitized solar cells (DSSCs) that were investigated outdoor in Wajir (1 o 44'50'' North, 40 o 4' 8'' East), Vihiga (35 o 0' East, 0 o 15' North), Kitui (3 o 0' South, 37 o 50' East) and Kajiado (360 o 5' East, 30 o 0' South) in Kenya. The DSSCs' J-V characteristics, namely, Voc, Jsc, FF and η, were studied under varied RB potentials. This was achieved through partial, as well as complete shading of the DSSCs during their operation in the study sites, using a thick piece of black cloth, and measuring the obtaining J-V characteristics. Findings of the study reveal that subjecting the DSSC module that was investigated in Wajir to RB of between 1V and 4V triggered between 25.53% and 23.53% drop in the module's efficiency (η), followed by its total breakdown thereafter. The modules studied in Vihiga, Kitui and Kajiado exhibited a similar trend, but with variations in η under the different RB regimes. The DSSCs' breakdown under RB regimes of over half their voltage ratings could be attributed to the damaging of their dye constituents. These findings are important for context-informed DSSC dye choices, as well as DSSCintegrated designs that appeal to local cultural textile fabrics, like shawls, kanzu (long robes) and light coats that women and men dress in, respectively, in Wajir, and blankets that both men and women wrap around their shoulders in Kajiado, as well as in local architectures. The findings underscore the existence of vast prospects for localized industries that innovate in DSSC-integrated designs for local espousal. They could form foundations for programs that mentor people, especially children and youths at local levels to engage in climate change-mitigating enterprises.
Open Journal of Ecology, 2020
Lake Victoria the second largest fresh water body in the world located in East Africa is a shared... more Lake Victoria the second largest fresh water body in the world located in East Africa is a shared resource between Kenya, Tanzania and Uganda and enjoys a wide range of streams and rivers from as far as Burundi and Rwanda. The lake has environmentally undergone physical, chemical and biological changes in the last four decades, particularly rise in its trophic condition and decline in oxygen level, which affects the water quality and fish population dynamics. This study therefore set out to determine the quality of water in selected fishing beaches of Lake Victoria, Kenya with a view to report the possible pollution levels. pH was highest at Nyamasari and Kotieno (9.3 ± 0.1) and lowest at Nyachebe and Kichinjio (7.08 ± 0.1) whereas temperature was highest at Nyamasari (29.5˚C ± 0.0˚C) and lowest at Kichinjio (23.4˚C ± 0.2˚C). DO was highest at Kotieno (10.3 ± 0.2 mgL) and lowest at Seka (2.4 ± 0.1 mgL). Turbidity was highest at Uyoga (125.5 ± 0.90 NTU) and lowest at Osieko (2.7 ± 0.1 NTU). Ammoniacal nitrogen was highest at Dunga (1278.3 ± 0.8 μg•l −1) and lowest at Nyamasari (12.4 ± 0.8), all a factor of human activities, lake substratum and effluents from rivers and surface runoff. All parameters assessed showed significant differences across sampling sites and depth except pH which did not vary significantly with distance from lakeshore. Further, all parameters did not show a clear pattern with respect to distance from the lakeshore possibly due to adequate mixing in the gulf. There is a need for further water quality monitoring by seasons to inform policy decisions towards sustainable lake exploitation.
Journal of Applied Physics, 2012
Ab-initio calculations based on density functional theory have been employed to study the structu... more Ab-initio calculations based on density functional theory have been employed to study the structural, electronic, and optical properties of yttrium (Y), scandium (Sc), zirconium (Zr), and niobium (Nb) doped α-Al2O3 with corundum structure. Exchange and correlation effects between electrons have been treated by generalized gradient approximation within the Perdew-Burk-Ezrenhof parameterization and by recently developed Tran-Blaha modified Becke-Johnson approach. Most attention in the work has been paid to the impurity d states, whose energy splitting has been analyzed in terms of the crystal field theory and whose influence on the gap size and the offset of the bands around it has been carefully evaluated. The influence of these states on modification of the optical absorption edge and the static dielectric constant of the doped systems has been also studied. It is concluded that only the Y doped α-Al2O3 (1) preserves the size of the band gap of the pure alumina, (2) does not change ...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 25, 2022
We present a comparative computational study of temperature-dependent elastic constants of silico... more We present a comparative computational study of temperature-dependent elastic constants of silicon (Si), silicon carbide (SiC) and diamond as substrates that are commonly used in the manufacture of Micro-Electromechanical Systems (MEMS) devices. Also mentioned is Cd 2 SnO 4 , whose ground-state elastic constants were determined just recently for the first time. Si is the dominant substrate used in the manufacture of MEMS devices, owing to its desirable electrical, electronic, thermal and mechanical properties. However, its low hardness, brittleness and inability to work under harsh environment such as hightemperature environment, has limited its use in the manufacture of MEMS like mechanical sensors and bioMEMS. Mechanical sensors are fabricated on SiC and diamond due to their high Young's moduli as well as high fracture strength, while the bioMEMS are fabricated on polymers. The effect of temperature on the elastic constants of these substrates will help in giving insight into how their performance vary with temperature.
International Journal of Engineering, Science and Mathematics, 2013
The developments of wind energy systems have enabled an efficient production and use of wind ener... more The developments of wind energy systems have enabled an efficient production and use of wind energy. Three widely used control schemes for wind energy systems are Pitch control, Rotor resistance control and Vector control. A traditional wind energy system consists of a stall regulated or pitch control turbine connected to a synchronous generator through gearbox. The synchronous generator operates at fixed speed and one of the earliest rotor control schemes was the rotor resistance control. The speed of an induction machine is controlled by the external resistance in the rotor circuit. The drawback of the above methods is the inability of wind turbine to capture at low wind speeds. This paper develops a model which maximizes wind energy output. This model asses the effects of friction coefficient and the height of wind above ground(given by the height of turbine from the ground i. e the hub height) on power output. The study considers an already existing model, that is the turbine mo...
The growth of fruits and vegetables is becoming an important component of the agricultural indust... more The growth of fruits and vegetables is becoming an important component of the agricultural industry sector, as sale of dried fruits and vegetables assume commercial scale. However due to lack of processing considerable amount of losses (between 30% and 40%) of these seasonal products occur in many developing countries. Drying is one of the most common methods of preservation of agricultural products. It removes sufficient moisture from the food and prevents decay or spoilage. Majority farmers in developing countries use open-sun method for drying their harvest despite the existence of more efficient methods of drying. This method is time consuming and exposes the produce to destruction by birds, animals and contamination. The areas surrounding Maseno university is agriculturally rich and known for production of vegetables and fruits among other agricultural products. In the wet seasons there is significant waste due to lack of preservation facilities to prolong their shelf life and yet during dry seasons these products are short in supply. In the present work, a model of natural convection solar dryer with twin collectors was designed and tested with and without load under the climatic conditions of Maseno, Kenya for drying of Vegetable kales. Results of test under no load revealed that the humidity in the drying chamber was reduced by 31.4%, while the chamber temperature was raised by 11.5 o C at average air flow rate of 0.39 m/s. The moisture content in the kales was reduced from 84.1% to less than 10% in about 15 hours of drying for an average air flow of 0.39 m/s. The maximum thermal efficiencies obtained were 22.51 % and 25.52 % for collector 1 and 2 respectively. Quality tests performed on both solar dried and wet samples revealed more than 50 % retention of all the nutrients in the solar dried vegetable kales.
A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta Universi... more A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta University, Physics Department; 1988; The QC 321.7.T45 O3
A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta Universi... more A thesis submitted in partial fulfilment for the degree of Master of Science in Kenyatta University, Physics Department; 1988; The QC 321.7.T45 O3
Case Studies in Construction Materials
International Journal of Environment and Waste Management
Solid State Communications
American Journal of Materials Science, 2019
Spray Pyrolysis Technique was used in depositing thin films of cadmium stannate, doped with iron ... more Spray Pyrolysis Technique was used in depositing thin films of cadmium stannate, doped with iron metal. The precursor solutions used were sprayed onto the pre – heated glass slides that were kept at a constant temperature of 450°C. The transmittance and reflectance measurements were made in the spectral wavelength range of 300 – 1100 nm. It was found out that both the concentration of the reactants and doping had an effect on the optical properties of the deposited thin films. At the upper end of the visible spectrum (718 nm wavelength), the values of the optical constants were: Transmittance of up to 70.45%, thickness of 323 – 594 nm, refractive index of 2.108 – 3.542, absorption coefficient of 7.385 x 103 cm-1 – 2.2784 cm-1, extinction coefficient of 0.042 cm – 0.130 cm and a band gap energy of 3.9 eV.
Spray Pyrolysis Technique (SPT) was used to deposit thin films (TFs) of cadmium stannate, doped w... more Spray Pyrolysis Technique (SPT) was used to deposit thin films (TFs) of cadmium stannate, doped with iron (Fe) for the first time. The precursor solutions that were used wereprepared at a concentration of 0.1M, doped with Feand then sprayed onto the pre-heated glass slides immediately at deposition temperatures of 350 ± 7°C, 400 ± 7°C and 450 ± 7°C. The optical properties of the deposited Fe-doped TFs were studied in the wavelength range of 300-1100nm. The X-Ray diffraction (XRD) studies showed that the TFs were orthorhombic with growth orientation along the (2 0 0) direction. Film thickness of 85 ± 10 nm was obtained. It was found out that anincrease in the deposition temperature increased transmittance and band gap, but decreased absorption coefficient, extinction coefficient and refractive index, which was attributed to the improvement in crystallinity of the deposited TFs. Doping reduced transmittance and band gap, but increased refractive index, absorption coefficient and extin...
The electronic and optical properties of hexagonal and cubic Ge2Sb2Te5 have been calculated using... more The electronic and optical properties of hexagonal and cubic Ge2Sb2Te5 have been calculated using the QUANTUM ESPRESSO and Yambo codes. The study has considered t he variation of electronic band gaps with lattice c onstants using the LDA with non-linear correction, where it was es tablished that both phases are apparently metallic at equilibrium. Upon increasing a, it was found that the hexagonal phase had a maxim um gap of 0.22 eV at a c/a value of 3.49 whereas the cubic phase had a maximum gap of 0.23 eV at a much higher c/a value of 10.62. Findings of the optical absorption spectra of both hexagonal and cubic Ge2Sb2Te5 obtained using time dependent density functional t heory (TDDFT) and the partially selfconsistent GW (GW0) are also reported. The absorption edge has been o bserved at 0.48 eV using TDDFT and at 0.21 eV using GW0 for the hexagonal phase.
Applied Acoustics, 2021
When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms whi... more When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms which are switched on or o as the excitation frequency varies. The classical way of measuring acoustic energy loss in porous materials uses the Kundt impedance tube. However, due to its short length, measurements are made in the steady state harmonic regimes. Its lower cuto frequency is often limited to a few hundreds of Hertz. Two long acoustic waveguides were assembled from water pipes and mounted to create test-rigs for the low-frequency acoustic characterization of monolayer and stratied airsaturated poroelastic materials. The rst waveguide was straight and had a length of 120 m, while the second was coiled to gain space and was 135 m long. The long waveguides appeal to very low frequency measurements using impulsive acoustic waves (with rich spectral content) because the incident waves can be separated in time from echoes o the extremities of the guides. The transmission coecient of porous materials recovered using the two waveguides compared well with those from the transfer matrix method (TMM) used here in combination with Biot's 1962 theory to describe propagation in porous dissipative media. This wave-material interaction model permitted the recovery of the properties of poroelastic materials from transmitted acoustic waves propagating in air. The parameters involved are the Young's moduli, Poisson ratio and microstructural properties such as tortuosity and permeability. Being able to descend to lower frequencies guarantees the correct verication of the magnitude of the measured transmission coecient which approaches unity towards the static frequency. The coiled and straight 1 waveguides were found to be equivalent and provided data down to frequencies of the order of ≈ Hz.
Materials Letters, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Materials Letters, 2021
We studied aluminium-rich Ti-Al (Ti32Al68 and Ti40Al60) binary alloys that were composed of TiAl ... more We studied aluminium-rich Ti-Al (Ti32Al68 and Ti40Al60) binary alloys that were composed of TiAl and TiAl2 lamellar microstructures. The law of mixtures was employed in calculating the theoretical Young's moduli. The lattice parameters of the alloys showed that both were tetragonal crystals. In the computational study, we made use of our modified method for the stress-strain calculation of elastic constants. The alloys at the respective chemical compositions were modelled by creating titanium (Ti) supercells, which were then doped by replacing some of the Ti atoms with aluminium atoms. The values of elastic moduli were verified by the ab initio calculation in this work, which showed a perfect agreement. The Pugh's ratio showed that both the alloys are ductile.
We examined changes in rheological properties of nonequilibrated spin-coated thin films of isotac... more We examined changes in rheological properties of nonequilibrated spin-coated thin films of isotactic polystyrene (iPS) and isotactic poly(para-methylstyrene) and blends thereof by dewetting experiments. For 200 nm thick films and a systematic variation of dewetting temperature, we focused on changes in the amount of residual stresses and the corresponding relaxation times as a function of iPS content. We found that both parameters increased in an approximately logarithmic fashion with iPS content, suggesting an increased tendency for the formation of transient clusters in blends with increased iPS content. Assuming linear elasticity, we determined a nonequilibrium shear modulus and a nonequilibrium viscosity, which we compared with published data of the equilibrium properties. Particularly for the viscosity, huge deviations from published values were observed. We provide a tentative explanation.
Journal of Technology Innovations in Renewable Energy, 2018
This paper reports on the effect of reverse bias (RB) on dye-sensitized solar cells (DSSCs) that ... more This paper reports on the effect of reverse bias (RB) on dye-sensitized solar cells (DSSCs) that were investigated outdoor in Wajir (1 o 44'50'' North, 40 o 4' 8'' East), Vihiga (35 o 0' East, 0 o 15' North), Kitui (3 o 0' South, 37 o 50' East) and Kajiado (360 o 5' East, 30 o 0' South) in Kenya. The DSSCs' J-V characteristics, namely, Voc, Jsc, FF and η, were studied under varied RB potentials. This was achieved through partial, as well as complete shading of the DSSCs during their operation in the study sites, using a thick piece of black cloth, and measuring the obtaining J-V characteristics. Findings of the study reveal that subjecting the DSSC module that was investigated in Wajir to RB of between 1V and 4V triggered between 25.53% and 23.53% drop in the module's efficiency (η), followed by its total breakdown thereafter. The modules studied in Vihiga, Kitui and Kajiado exhibited a similar trend, but with variations in η under the different RB regimes. The DSSCs' breakdown under RB regimes of over half their voltage ratings could be attributed to the damaging of their dye constituents. These findings are important for context-informed DSSC dye choices, as well as DSSCintegrated designs that appeal to local cultural textile fabrics, like shawls, kanzu (long robes) and light coats that women and men dress in, respectively, in Wajir, and blankets that both men and women wrap around their shoulders in Kajiado, as well as in local architectures. The findings underscore the existence of vast prospects for localized industries that innovate in DSSC-integrated designs for local espousal. They could form foundations for programs that mentor people, especially children and youths at local levels to engage in climate change-mitigating enterprises.
Open Journal of Ecology, 2020
Lake Victoria the second largest fresh water body in the world located in East Africa is a shared... more Lake Victoria the second largest fresh water body in the world located in East Africa is a shared resource between Kenya, Tanzania and Uganda and enjoys a wide range of streams and rivers from as far as Burundi and Rwanda. The lake has environmentally undergone physical, chemical and biological changes in the last four decades, particularly rise in its trophic condition and decline in oxygen level, which affects the water quality and fish population dynamics. This study therefore set out to determine the quality of water in selected fishing beaches of Lake Victoria, Kenya with a view to report the possible pollution levels. pH was highest at Nyamasari and Kotieno (9.3 ± 0.1) and lowest at Nyachebe and Kichinjio (7.08 ± 0.1) whereas temperature was highest at Nyamasari (29.5˚C ± 0.0˚C) and lowest at Kichinjio (23.4˚C ± 0.2˚C). DO was highest at Kotieno (10.3 ± 0.2 mgL) and lowest at Seka (2.4 ± 0.1 mgL). Turbidity was highest at Uyoga (125.5 ± 0.90 NTU) and lowest at Osieko (2.7 ± 0.1 NTU). Ammoniacal nitrogen was highest at Dunga (1278.3 ± 0.8 μg•l −1) and lowest at Nyamasari (12.4 ± 0.8), all a factor of human activities, lake substratum and effluents from rivers and surface runoff. All parameters assessed showed significant differences across sampling sites and depth except pH which did not vary significantly with distance from lakeshore. Further, all parameters did not show a clear pattern with respect to distance from the lakeshore possibly due to adequate mixing in the gulf. There is a need for further water quality monitoring by seasons to inform policy decisions towards sustainable lake exploitation.