Physics and Material Science

Enhancing sustainable construction through lime and water hyacinth ash -modified compressed earth blocks with improved acoustic properties

Tue, 11 Nov 2025 00:00:00 GMT

Enhancing sustainable construction through lime and water hyacinth ash -modified compressed earth blocks with improved acoustic properties OUMA, Justus Juma Modern construction materials must meet a myriad of requirements, including sustainability, structural integrity, thermal efficiency, and acoustic performance. This study assesses the urgent need for eco-friendly construction materials by investigating the potential of using a blend of lime and water hyacinth ash (WHA) as binders in locally sourced soils from Mayenje ward, Busia County. The primary objective was to fabricate Compressed Soil-Lime-Water Hyacinth Ash (CSL-WHA) blocks with suitable acoustic absorption properties for sustainable building and construction. The specific objectives of this study were as follows; (i) To fabricate compressed earth blocks using a binder mixture of lime and water hyacinth ash, ensuring uniformity and structural integrity (ii) To evaluate the acoustical properties of CSL-WHA blocks by recovering key parameters through inverse modeling of transmission data (iii) To assess how binder ratios (lime vs. WHA) influence acoustic properties of CSL-WHA blocks and (iv) To examine the effect of compaction pressure on the acoustic properties of the blocks. The study delved into the feasibility of acoustical modeling for parameter retrieval, ultimately evaluating the potential of CSL-WHA blocks to meet specified acoustic requirements. A series of sixteen formulations were evaluated across four compaction pressures (25–100 bar) to assess the influence of binder composition and key acoustic parameters, including porosity, airflow resistivity, tortuosity, and viscous characteristic length. The results showed that moderate WHA (≤5%) with high compaction pressure (≥75 bar) could yield balanced porosity (~0.30–0.36) while achieving ideal air flow resistivity, tortuosity and viscous characteristic length ranges for sound absorption, striking a balance between acoustic performance and strength. Inverse modeling using the Johnson-Champoux-Allard-Lafarge (JCAL) framework enabled non-destructive recovery of intrinsic acoustic parameters. These findings offer a design matrix for balancing acoustic absorption and mechanical performance, supporting tailored applications in partition walls, facade systems, and low-frequency noise control. Furthermore, the study pioneers the valorization of invasive water hyacinth biomass for acoustic damping, providing a foundation for localized standardization and contributing to circular economy goals. The integration of WHA as a partial binder advances sustainable construction practices, reinforcing material innovation within environmental and acoustic design frameworks. Master's Thesis

Characterization of meh-ppv: pc71bm blend thin films Deposited on glass substrates by spin-coating and drop-casting techniques for photovoltaic applications

Mon, 01 Jan 2024 00:00:00 GMT

Characterization of meh-ppv: pc71bm blend thin films Deposited on glass substrates by spin-coating and drop-casting techniques for photovoltaic applications ADONIJAH, Oginga Anindo The surge in population growth and modernity since the pre-industrial era has seen an increase in anthropogenic greenhouse gas emissions resulting from increased use of fossil fuels. As a result, there is increase in demand for an alternative clean, sustainable, economical and renewable energy based on photovoltaic technology (PV). This is aimed at reducing greenhouse gas emissions and global average temperature. Kenya receives adequate sunshine, and therefore, photovoltaic technology is the way to go. First generation solar cells technology based on crystalline and polycrystalline silicon solar cells have been widely used to produce electricity for domestic and industrial uses due to their high efficiency of about 20 %. However, their high cost of production is still a challenge. The search for alternative absorber materials have led to intensive research in organic photovoltaic solar cells, which are composed of at least two electronically dissimilar molecules that form a donor-acceptor system. Donor-acceptor molecules form bulk heterojunction, which has been proven to be the best option for a low-cost production of thin film solar cells. Optimizing the active layer blend composition and deposition parameters to improve the layer's properties is an essential stage in producing thin film solar cells with increased efficiency. The choice of materials also plays a major role in ensuring that sufficient energy offset at the donor-acceptor interface take place. The use of fullerene derivatives as electron acceptors has gained popularity due to their favorable electron affinity. These ball-like fully conjugated structures have strong electron affinity and unipolar electron transport that promotes delocalization of electrons. This study focuses on characterization of a blend between poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and fullerene derivatives of phenyl-C71-butyric acid methyl ester (PC71BM) for PVs. The optical and morphological properties of MEH-PPV: PC71BM films were investigated at different spin-coating speed, solution concentration, annealing temperature, acceptor percentage composition in the blend and deposition methods. From the optimized results obtained, deep photoluminescence quenching was observed for MEH-PPV doped with 75 % PC71BM, a signature of improved charge transfer rate. In addition, the band gap energy was reported to reduce to 1.8775 eV, indicating better photon-absorption. It was also found that high spin-coating speeds enhanced film-surface homogeneity and improve light absorption in deposited films. An optimized MEH-PPV: PC71BM system was obtained at spin-coating speed of 2000 revolutions per minute, a thickness of 113 nm, a concentration of 16 mg/ml and an annealing temperature of 150 oC. This system is intended for photovoltaic applications especially in the production of improved thin organic photovoltaic solar cells. Master's Thesis

Correlation between equatorial electrojet and the occurrence of equatorial ionisation anomaly over the East African region during the solar minimum period 2008-2009

Sun, 01 Jan 2023 00:00:00 GMT

Correlation between equatorial electrojet and the occurrence of equatorial ionisation anomaly over the East African region during the solar minimum period 2008-2009 MILIMU, Anekha Hannington In the electron density distribution at the low-latitude ionosphere, equatorial electrodynamics plays a critical role such as forecasting the dynamics and fluctuations of ionospheric plasma densities. The equatorial electrojet (EEJ) and the equatorial ionization anomaly (EIA) are two major phenomena of equatorial electrodynamics. Studies have been carried out on the strength of EEJ as well as the EIA. However, the following gaps still exist: most studies have been done in Indian and American regions during maximum solar years; yet ionospheric dynamics have a dependence on the longitude; correlations have also not been done during both geomagnetically quiet and disturbed conditions. The correlation between EEJ and EIA was required since EEJ is one of the systems that lift plasma in equatorial regions, causing Equatorial Ionization Anomaly, which suggests a connection between EEJ and EIA. Since it is necessary to get a complete picture during both geomagnetically quiet and disturbed conditions, therefore, the problem of the study is that strong scintillations affect communication and navigation systems. Thus, there is a need to investigate the relationship between EEJ and EIA since they are important for ionospheric space weather and also this will help the development of models that can be used to forecast or nowcast scintillations. Based on the aforesaid knowledge gap the problem of this study is on EEJ's impact on the development of the EIA during the low solar activity period over the East African region. Based on this problem the objectives of the study were (i) To determine the strength of EEJ, (ii) To quantify the strength of EIA and (iii) To analyze the correlation between EEJ and EIA. This study used a pair of International Real-time Magnetic Observatory Network (INTERMAGNET) magnetometers located in Addis Ababa (geographic 9.05°N, 38.76°E, geomagnetic 0.16°N, 110.45°E), the African Meridian B-field Education and Research (AMBER) station in Adigrat (geographic 14.26°N, 39.45°E, geomagnetic 6.1°N, 111.04°E) both in Ethiopia and the total electron content (TEC) derived from a set of International Global Navigation Satellite System (GNSS) signals (IGS) receivers within the East African region. The data used during this period was for both geomagnetically disturbed and quiet conditions. The difference in the horizontal component of the geomagnetic field seen by two ground-based magnetometers was used to estimate the EEJ strength. In determining the EIA strength over the region, TEC over the crest to that above the trough was determined to be in a certain ratio. The peak value of EEJ is 110nT and it occurs between 10:00 and 14:00 LT for geomagnetically quiet conditions. This is due to the high rate of photoionization during this period. These variations in the amplitude of EEJ with time and months is attributed to the monthly movement of the Sq foci northward and equatorward in a given year. The EIA’s peak during geomagnetically quiet days is 1.45 and it was recorded between 20:00 – 22:00LT while the peak of EIA during geomagnetically disturbed days is 1.2 and it occurred at 20:00LT. The correlation coefficients were found to vary from moderate to strongest during geomagnetically quiet conditions, ranging from 0.58 to 0.74. During geomagnetically disturbed conditions, the correlation coefficient ranges from 0.28 to 0.45. The significant linear link between EEJ and EIA is caused by the independent increase in the eastward electric field and photo-ionization on TEC. Most panels showed that the ratio of Crest (CT) to trough (TEC) > 1. This research presents patterns in the EEJ and EIA strength over East Africa during the solar minimum period. Since EEJ and EIA influences the occurrence of ionospheric irregularities which in turn lead to scintillations of communication and navigation signals, we recommend simultaneous analysis of EEJ, EIA and scintillation data. This would reveal the influence of EEJ and EIA on the occurrence of scintillations. Master'S Thesis

Experimental and computational studies of properties of thin films of cadmium-tin-oxide for manufacture of micro-electromechanical systems and for noise control

Sat, 01 Jan 2022 00:00:00 GMT

Experimental and computational studies of properties of thin films of cadmium-tin-oxide for manufacture of micro-electromechanical systems and for noise control ONGWEN, Nicholas Ogada The recent advancement in electronics have stimulated the high demand for semiconductor substrate materials for the printing of electronic circuits, some of which are used in the Micro-Electromechanical Systems (MEMS) devices. The most commonly used substrate for the printing of these devices is silicon (Si), which is preferred because, compared to the other semiconductor substrate materials like silicon nitride and gallium arsenide, it: Has better electrical, mechanical and thermal properties that are desirable for the fabrication of MEMS devices; is readily available, and is also relatively cheaper. Despite the advantages above, Si has serious drawbacks, including rarely occurring as a pure element and being brittle, which call for alternative substrate materials such as cadmium tin oxide (CTO), whose thin films (TFs) have been studied and proved to possess excellent optical and electrical properties, as well as flexibility. However, the mechanical and thermal properties of CTO have not been explored extensively. This study employed ab initio calculations to determine the mechanical and thermal properties of CTO. The specific objectives of the study were: i) to find out the effect of concentration of cadmium and tin on the structural properties of CTO, (ii) to develop a simplified method that applies stress and strain in calculating elastic constants of materials, (iii) to find out the effect of concentration of cadmium and tin on the mechanical properties of CTO, and (iv) to find out the effect of concentration of cadmium and tin on the thermal properties of CTO. The TFs of CTO were prepared by dissolving cadmium chloride and tin II chloride separately in distilled water to form 0.4 M of each solution. The two solutions were then mixed at ratios of 1:5, 2:4, 3:3 4:2 and 5:1 by volume. The final solutions were then sprayed onto the preheated microscope glass substrates by spray pyrolysis at a temperature of 450 °C. The measurement of film thickness was done using surface profiler, the X-Ray diffraction measurements were taken using Expert Pro from 2θ = 10-70° at a step of 0.02°, the chemical composition was measured using X-Ray Fluorescence. The ab initio calculations were done using density functional theory with PBESOL functionals as implemented in the Quantum Espresso code. Stress-strain method was developed for the study of mechanical properties. The outcome of the study showed that all the properties of CTO are very sensitive to the number of cadmium atoms. The optimum properties obtained were: crystallite size of 60.75 nm, density of 7.636 g/cm3, bulk modulus of 149.1 GPa, shear modulus of 53.2 GPa, Young’s modulus of 142.7 GPa, Vickers hardness of 3.757 GPa, Poisson’s ratio of 0.367, Pugh’s ratio of 3.422, Debye temperature of 377.68 K, melting temperature of 1558.07 K, vibrational energy of 8.557 x 10-2 Ry/cell, Gibbs free energy of 0.1584 Ry/cell, entropy of 7.984 x 10-4 Ry/cell/K, and specific heat at constant volume of 2.659 x 10-4 Ry/cell/K. Due to the comparable mechanical and thermal properties of CTO to Si, it can replace Si in the manufacture of MEMS. The ductile nature of CTO is ideal for manufacture of flexible MEMS such as biomedical MEMS, microbolometers, image sensors, and microbridges, which require softer and dultile substrates. PhD Thesis

Geomagnetic field variations at African equatorial regions during the ascending phase of the solar cycle 24

Sat, 01 Jan 2022 00:00:00 GMT

Geomagnetic field variations at African equatorial regions during the ascending phase of the solar cycle 24 ATIENO, Lucy. Obuya The Earth’s magnetic field is the field of force that extends from the interior of the Earth to the outer space where it interconnects with the Interplanetary Magnetic Field (IMF). It is characterized by regular and irregular variations. Previous researches have shown the geomagnetic field variations at different sectors of the world. Despite the significance of knowledge on geomagnetic field variations to industry, communication and navigation as well as the localized nature of ionospheric dynamics, geomagnetic field variation studies in Africa is still not fully exploited. Therefore, knowledge gaps that this study has bridged are: the solar quiet seasonal and annual variations; the seasonal and annual variations of Equatorial Electrojet current (EEJ) strength as well as the storm time variations of the Earth’s magnetic field in the African equatorial regions during the ascending phase of the 24th solar cycle, comparing different stations within the African equatorial region. Based on the aforementioned knowledge gaps, the problem of this study was the little accessible information on the Geomagnetic field variations in the African equatorial region during the ascending phase of solar cycle 24 from the year 2009-2014 to help establish its solar quiet and storm time variations in Addis Ababa, Adigrat, Mbour and Yaoundé stations and to estimate the EEJ strength in Mbour and Addis Ababa for the period 2009 to 2014 for identification of the specific and unique trends within this region, that may be useful for industries and space agencies in the region for purposes of planning and preparations for space weather eventualities. The objectives set to be achieved by this study were: to establish the solar quiet seasonal and annual variations of Earth’s magnetic field; to determine the storm time variations of the geomagnetic field at Adigrat (ETHI) , Addis Ababa(AAE), Yaoundé(CMRN) and Mbour(MBO) during the Ascending phase of the solar cycle 24 from the year 2009 to 2014; and to estimate the seasonal and annual Equatorial Electrojet (EEJ) strength at Addis Ababa and Mbour for the period from 2009 to 2014. The Solar quiet (Sq) variations were calculated by method of non-cyclic variation and EEJ strength estimated using the two station method. The monthly values were averaged for months in a season to give seasonal variations while the average monthly values for a particular year provided the annual variations. The storm perturbations were obtained by subtracting the Sq of the most quiet day of every month from the Storm time variation of that day under study. Sq showed a seasonal variation which recorded the highest magnitudes of 110nT, 70nT, 65nT and 75nT for AAE, CMRN, ETHI and MBO respectively in the Equinoxes and lowest magnitudes of 50nT, 40nT, 40nT and 45nT for AAE, CMRN, ETHI and MBO respectively during the June solstices. Both the annual and seasonal variations showed solar activity, longitude and the local time dependence. The seasonal and annual variations in the EEJ strength showed larger magnitudes at Addis Ababa as compared to Mbour but larger peaks of westward Counter Electrojet (CEJ) current in Mbour as compared to Addis Ababa. The EEJ annual variation peaks during low solar activity years occurred earlier at about 1200LT as compared to peaks during high solar activity years which occurred between 1300LT and 1400LT, an outcome attributed to earlier ionization peaks during low solar activity leading to increased ionospheric conductivity. The storm time variation had a latitudinal variation. The results are useful for long term forecasting on the impact of geomagnetic field variations to help mitigate the effects of storms on the economic and ecological environment. This study recommends further research into the lack of seasonal variation on the CEJ in this region and the cause of the latitudinal storm time variation. Masters Thesis

Photon Anti-Bunching Properties of the Anti-Jaynes-Cummings Model

Fri, 01 Jan 2021 00:00:00 GMT

Photon Anti-Bunching Properties of the Anti-Jaynes-Cummings Model MUGA, Owiny Patrick This thesis present anti-Jaynes interaction, an interaction where anti-rotating light mode couples to a two-level atom. The anti-bunching properties of the anti-Jaynes-Cummings model was explicitly demonstrated, a model which researchers have always shied away from studying due to the notion that it was non-energy conserving. The energy conservation property was recently addressed hence creating a wider gap which need to be addressed. The anti-Jaynes-Cummings interaction was redefined as a generator of the anti-polariton qubit. Anti-polariton qubit is a two-state quantized particle specified by state vectors, Hamiltonian, conserved excitation number, identity, state transition, U(1) symmetry operators. Formation of anti-polariton qubit involves absorption or emission of negative energy photon by field mode triggered by initial emission or absorption of negative energy photon by the atom. Superposition of qubit state vectors provides the eigenvectors and eigenvalues of the anti JC Hamiltonian. The mean photon number, photon number fluctuation, density operator and atomic inversion are easily evaluated. The result of the mean and its fluctuation were used in the Mandel operator to explicitly demonstrate the anti-bunching properties of the anti-JC interaction. Exact solution of the long standing problem is of importance in understanding the statistical properties and physical properties of the interacting two level atom system which shall be of great importance in the optimization of the technological application, especially in the emerging areas of quantum teleportation and quantum computing. Attention can now be refocused in studying the practical application of the anti JC model such as quantum computing.

The cooling effect of air on flat plate solar energy collectors

Fri, 01 Jan 2021 00:00:00 GMT

The cooling effect of air on flat plate solar energy collectors ADUOGO, Peter Onyango Use of solar energy devices requires that they be exposed to receive maximum solar radiation. Unfortunately, the intensity of solar radiation incident on these devices varies throughout the day with the position of the sun in the sky hence making these devices to under-perform. Moreover, high temperature associated with the heating effect of the much needed solar radiation also destroys solar PV cells whose optimal operation temperature is 25oC. This is contrary to solar thermal energy collectors whose performance improves with increased temperature. To improve the performance of flat plate solar PV and thermal energy collectors, it is important to determine their optimal angle of orientation with respect to solar radiation and wind. To address these challenges, it was important to achieve the study objectives which were to investigate cooling effect of air with a view to improving the performance of flat plate solar energy collectors, determine the dependence of wind-related heat transfer coefficient (hw) on angle of incidence of wind onto the flat plate solar energy collectors and to develop the currently lacking single expression of (hw) for the full possible range of angles of incidence of wind onto the flat plate solar energy collectors from 0o to 90o. To achieve these study objectives, it was important to understand the effect of air velocity (u), angle of incidence of wind (𝜃i) and temperature variation on the performance of these devices. To study the effect of these variables on the performance of flat plate solar energy devices, a laboratory experiment was set up having a flat plate inside a wind tunnel to collect data on cooling effect of air at different angles of inclination of the plate (𝜃p). Velocity and temperature at different angles of orientation of the plate were measured using thermo-anemometer and digital data logger respectively. Data collected under steady state condition were used to determine wind-related heat transfer coefficient (hw). The dimensionless numbers associated with this study were Nusselt (Nu), Reynolds (Re) and Prandtl (Pr). These are correlated by Nu = 𝛾 (RePr) n which links (hw) with 𝜃p, 𝜃i and u. To show variation of (hw) with (u) and (θi), graphs of (hw) against (u) and (θi) were plotted by OriginPro. The values of (hw) under different conditions were used to determine suitable orientation of flat plate solar energy devices with reference to wind and solar radiation, for their optimum performance. The study found that in a relatively low air velocity, the value of (hw) was insensitive to incident angles of wind onto plate. However, as air velocity increased, the variation of (𝜃i) with (𝜃p) strongly influenced the plate’s steady state temperature which in turn influenced the magnitude of (hw). The incident angles of wind yielding low and high values of (hw) were found suitable for optimum operation of solar thermal and PV energy collectors respectively. The study recommends that the optimal tilt angles of solar PV panels and solar thermal panels would be 0o and 45o respectively relative to wind. The results of this study will serve as reference for

Sensitivity of thermally deposited titanium Dioxide thin film for Liquefied petroleum gas sensing application

Fri, 01 Jan 2010 00:00:00 GMT

Sensitivity of thermally deposited titanium Dioxide thin film for Liquefied petroleum gas sensing application OSUMBAH, Paul Otieno Titanium dioxide thin films have a wide scope of application including gas sensing. Other studies have been carried on the sensing ability ofTi02 to natural gases (02, CO2 and H2) and hydrocarbons (ethanol and butane). This study investigated if thermally deposited Ti02 thin film is sensitive to LPG by identifying thermal deposition conditions, assessing the variation in sheet resistivity of Ti02 when exposed to LPG and correlating the sensitivity to the optical properties of the Ti02 films. Ti02 films were thermally deposited on microscope glass slides in a square pattern to allow for a four point probe using Van der Pauw setup to measure the sheet resistivity of the films using Keithley 2400 sourcemeter. The resistivity was mea sured in three phases; before, during and after exposure to LPG at room temperature. In all the samples tested, there was a decline in resistance between 0.009 kn and 0.04 kn when the film' was exposed to LPG and about 90% recovery when withdrawn from the LPG rich environment. The change in sheet resistivity was used to deduce film sensitivity to LPG. The film's refractive index was obtained in the range of 1.67 to 1.88 at 550 nm wavelength from the transmittance spectra and used to calculate film porosity. The film thickness was measured using Alpha-step IQ (surface profilometer). The sensitivity of the film was observed to increase with increase in refractive index and decrease in film thickness and film porosity. The improved response of the thinner films over thicker films shows that conduction mainly occurs at the pore phase rather than at the solid phase. This study reveals that Ti02 thin film is sensitive to LPG at room temperature and hence the material is viable for use in fabricating LPG sensors.

Real- Time Human Immunodeficiency Virus test Analyzer Based on Digital Image Processing

Sat, 01 Jan 2011 00:00:00 GMT

Real- Time Human Immunodeficiency Virus test Analyzer Based on Digital Image Processing ADEM, Jack Abibo Manykinds of HIV testing kits have recently become available to be used in determining whetheran individual's blood contains HIV virus or not. In the determine method of the HIV rapidtestprocedure, when a drop of blood is introduced at the lower testing region of the test kit, a redhorizontal line appears on the test section indicating the presence of the HIV virus. The <:...absenceof the red line shows that the blood does not contain the virus. However, a similar red linemustappear at the control section of the kit to show that the test procedure is successful and complete.The reading, interpretation and confidentiality of the HIV test result has often been abusedby the medics and the counselors. There has been an immense widespread of HIV due to people's ignorance of their status. The spread can be curbed by introducing a human friendly, confidential,automatic and reliable testing system that has been developed by this study. In this study,an electronic system that automatically acquires the red color signals that appear on the testkitshas been developed. The system analyses the color signals, processes them, displays and relaysthe test result to the client. The main objective of the study was to design and develop a real-timeHIV test analyzer based on computer aided image processing technique and. An image processing software in a client/server system was created. The system used Complementary metal-oxide-semiconductor (CMOS), digitalcamera to capture the image and the programmed software,developed in C#, processes the captured image and sends the testing results to the displayunit. This technique will not only eliminate the human error associated with the use of HNtesting kits, but will also improve the testing productivity in comparison to those achieved by the trained technicians. It will also enhance the confidentiality of the test result hence reducingthe stigma associated with the disease and encourage more people to know their HIV status.The system can be installed in our medical facilities and at the Voluntary Counseling and Testing(VCT) to aid the medical personnel in HIV screening and testing. The system has been testedsuccessfully and the testing results have proved that the system is reliable

Characterization of variability of Total Electron Content (TEC) over Malindi

Tue, 01 Jan 2013 00:00:00 GMT

Characterization of variability of Total Electron Content (TEC) over Malindi ONDEDE, George Ochieng The dynamics of the ionosphere depends largely on solar activity. The attenuation of radio signals as they propagate through the ionosphere can be determined through a parameter called the Total Electron Content (TEC),which is a measure of the number of electrons along a line of sight. The variability of TEC is critical around the dip equatorial region especially within 15° North and South where we experience anomalously enhanced TEC in the ionosphere. This study focused on the characterization of the variability of TECover Malindi, Kenya (03.03°N, 40.13°E), and the variability studies were carried out using inter-quartile range as the parameter, with goal of coming up with a morphological description of TECthat would be useful in the understanding of the space weather conditions over Kenya. The objectives of the study were to obtain plots of TECagainst time for each day of the four months, January, April, July and October, representing four seasons, of the years 1999, 2000, 2001 and 2002 and to characterize the variability of the TEC during the period of study. The diurnal variability was greatest during the early morning and late evening hours of the local time and minimum during the midday and midnight. The seasonal variability was greatest during the March equinox, moderate during the summer equinox and least during the solstices. There was observed enhanced night-time variability just before midnight, which could be attributed to neutral winds. Of the four years studied, 2000 and 2001 experienced the highest level of TEC variability and a TECvariability level of between 12 and 30 TECU was thought to be significant enough to depict the occurrence of scintillations. The research findings would be useful to aviation industry, the marine industry, the communication service providers and other technological systems whose operations may be affected by the space weather conditions.