Journal Articles
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Item Planet population synthesis: the role of stellar encounters(Monthly Notices of the Royal Astronomical Society, 2022-03) Ndugu, N; Abedigamba, O P; Andama, GDepending on the stellar densities, protoplanetary discs in stellar clusters undergo: background heating; disc truncation-driven by stellar encounter; and photoevaporation. Disc truncation leads to reduced characteristic sizes and disc masses that eventually halt gas giant planet formation. We investigate how disc truncation impacts planet formation via pebble-based core accretion paradigm, where pebble sizes were derived from the full grain-size distribution within the disc lifetimes. We make the best-case assumption of one embryo and one stellar encounter per disc. Using planet population synthesis techniques, we find that disc truncation shifts the disc mass distributions to the lower margins. This consequently lowered the gas giant occurrence rates. Despite the reduced gas giant formation rates in clustered discs, the encounter models mostly show as in the isolated field; the cold Jupiters are more frequent than the hot Jupiters, consistent with observation. Moreover, the ratio of hot to cold Jupiters depend on the periastron distribution of the perturbers with linear distribution in periastron ratio showing enhanced hot to cold Jupiters ratio in comparison to the remaining models. Our results are valid in the best-case scenario corresponding to our assumptions of: only one disc encounter with a perturber, ambient background heating, and less rampant photoevaporation. It is not known exactly of how much gas giant planet formation would be affected should disc encounter, background heating, and photoevaporation act in a concert. Thus, our study will hopefully serve as motivation for quantitative investigations of the detailed impact of stellar cluster environments on planet formations.Item Enhancing infrared solar absorption efficiency through plasmonic solar absorber using machine learning-assisted design(Springer Link- Plasmonics, 2024-10-18) Muheki, Jonas; Patel, Shobhit K.; Ainembabazi, Fortunate; Al-Zahrani, Fahad AhmedThis research introduces the architecture of an infrared solar energy absorber coupled with absorption prognosis employing machine learning techniques. Our approach involves creating an efficient absorber tailored for infrared wavelengths complemented by a machine learning model for accurately predicting absorption levels. The absorber's design focuses on maximizing absorption within the 0.7 µm to 4.0 µm range. We optimized the absorber's parameters, including resonator thickness, substrate thickness, and angle of incidence. Simulation results demonstrate excellent absorption performance, capturing over 90% of light within the specified range. At angles between 0° and 40°, the average absorptance exceeds 80%, peaking at 97.16%. However, at an 80° angle of incidence, absorptance drops to 23.3%. The study employs a 1D-CNN regression model to estimate absorption at various wavelengths, which greatly decreases the time required for simulations and experiments. The findings demonstrate the promise of combining metamaterial structures with machine learning approaches to boost the efficiency of solar energy harvesting and conversion processes.Item Computational Insights for interactions between NsP2 and NsP3 of CHIKV and Hormones through DFT computations and Molecular Dynamics Simulations(Chemistry & Biodiversity, 2024-08-13) Raman, Anirudh Pratap Singh; Kumar, Durgesh; Kumari, Kamlesh; Jain, Pallavi; Bahadur, Indra; Abedigamba, Oyirwoth P.; Preetam, Amreeta; Singh, PrashantThe non-structural protein (nsP2 & nsP3) of the CHIKV is responsible for the transmission of viral infection. The main role of nsp is involved in the transcription process at an early stage of the infection. In this work, authors have studied the impact of nsP2 and nsP3 of CHIKV on hormones present in the human body using a computational approach. The ten hormones of chemical properties such as 4-Androsterone-2,17-dione, aldosterone, androsterone, corticosterone, cortisol, cortisone, estradiol, estrone, progesterone and testosterone were taken as a potency. From the molecular docking, the binding energy of the complexes is estimated, and cortisone was found to be the highest negative binding energy (-6.57 kcal/mol) with the nsP2 protease and corticosterone with the nsP3 protease (-6.47 kcal/mol). This is based on the interactions between hormones and NsP2/NsP3, which are types of noncovalent intermolecular interactions categorized into three types: electrostatic interactions, van der Waals interactions, and hydrogen-bonding. To validate the docking results, molecular dynamics simulations and MM-GBSA methods were performed. The change in enthalpy, entropy, and free energy were calculated using MM-GBSA methods. The nsP2 and nsP3 protease of CHIKV interact strongly with the cortisone and corticosterone with free energy changes of -20.55 & -36.08 kcal/mol, respectively.Item Co-sensitization effect of chlorophyll and anthocyanin on optical absorption properties and power conversion efficiency of dye-sensitized solar cells(Springer, 2024-04) Mukhokosi, Emma Panzi; Mohammed, Tibenkana; Loyce, Namanya; Botha, Nandipha L.; Maaza, Maliki; Velauthapillai, DhayalanIn this article, the chemical structure, optical absorption and photoluminescence properties of un/adsorbed dyes of hibiscus flower (H), pumpkin leaf (P), sweet potato leaf (S) and their composites (H: P & H: S) have been studied. The chemical structural properties revealed the O–H, C–C and C = O as the main anchoring functional groups. The optical absorption properties revealed two definite bands in between 450–500 nm and 600–680 nm wavelength for chlorophyll-based dyes and a peak at 526 nm for anthocyanin based dye extract. The composite dye extracts revealed optical absorption bands corresponding to chlorophyll and anthocyanin pigments with enhanced absorption of light. Five different solar cells based on H, P, S, H:P-3:1 and H:S-3:1 were developed and revealed an efficiency of ~ 0.08, 0.3, 0.5, 0.7 and ~ 1% respectively. The efficiency was reduced by half after 30 days. The composites had the highest power conversion efficiency due to more O–H, C–C and C = O binding sites on TiO2 nanoparticles, reduced rate of electron–hole pair recombination and a wide range of optical absorption. These studies suggest that co-pigmentation can be an alternative strategy to increasing the power conversion efficiency in DSSCs.Item Characterisation of copper indium gallium diselenide solar module in the Ugandan climate(Kyambogo University [unpublished work], 2014-01) Kisitu, Zawedde SarahThe photovoltaic solar energy from copper indium gallium diselenide (CIGS) solar module is one of the most promising sources of solar energy for large scale production of clean energy at competitive prices. The focus of the study was to determine the performance of CIGS solar module in terms of its performance parameters in the tropical region. The goal of this dissertation was hence to characterise the performance of CIGS solar modules in the Ugandan climate. The performance of the CIGS module was assessed when put out doors by measuring the current-voltage (1-V) characteristic of the device. A variable resistor was connected to the CIGS module and was varied from minimum (0 Ω) to maximum (l00 Ω) and the corresponding current and voltage were measured. The electrical performance parameters such as short circuit current, open circuit voltage, maximum power, fill factor and efficiency were then obtained from 1-V characteristic curves. The short circuit current obtained was l.03A that is 1.9% lower than the rated value. The open circuit voltage obtained was 19.25V that is 35.8% lower than the rated value. The maximum current obtained was 0.7 lA that is 12.3% lower than the rated value. The maximum voltage obtained was 13.4V that is 37.9% lower than the rated value. The maximum power obtained was 9.5W that is 36.7% lower than the rated value. There was no change in the fill factor. The efficiency obtained was 6.1 % that is 24.7% lower than the rated value. The study shows that out of the seven parameters it was only the fill factor which had the same value with the rated value. The short circuit current was close to the rated value while other parameters were significantly lower than the rated value varying between 12.3% and 37.9%. Basing on the findings of this study, it is recommended that a further study should be done over a longer period of time for example a year in both dry and wet seasons to cross check the reliability of the findings of this study. The results of this study will be useful to compare the performance of this type of module with others in the market to find out if they would give similar values. Current-voltage (1-V) characteristics measurements under the dark should also be considered to determine the performance of the CIGS solar modules. This would determine other electrical parameters such as series resistance, shunt resistance and diode parameters (ideality factor and reverse saturation current).Item Radiological hazard levels due to gamma emmiting radionuclides in natural water bodies in selected sub-counties of Mubende district(Kyambogo University [unpublished work], 2016-01) John, CandiaThis study was carried out to investigate the health hazard levels due to gamma rays emitted by radionuclides in natural water bodies in selected sub-counties in Mubende District. Owing to the interaction between underground water wells with the mineral rich geological components of the landscape; and the link that the minerals have with gamma emitting radionuclides, the population of Mubende is exposed to unknown levels of ionizing radiation. In the study, a representative of 60 natural water samples from the sub-counties of Bukuya, K.asambya, Kassanda and Kitumbi were analyzed for radiological hazard levels using a NaI (Tl) gamma-ray detector. Specific activities due to 226Ra, 232Th, 238 U, and 40 K. were obtained and then used to calculate the absorbed dose rates, annual effective dose equivalents and the radiological health hazard indices. To ensure quality control, the samples were collected from the sites in rinsed empty mineral water bottles which were sealed and labeled. They were transp01ied in paper boxes whose background radiation emissions were measured with an identifier. The mean Specific Activities in Bq/kg due to 226Ra, 232Th, 238U and 40K obtained from the laboratory investigations were 103.10 ± 2.59, 80.69 ± 1.33, 24.94 ± 0.42 and 16.02 ± 1.32, respectively. The mean absorbed dose rate was 97.45 nGyh-1 which was higher than the published reference value of 55 nGyh-1. The mean Annual Effective Dose Equivalent was 0.30 mSv year -1, above the reference level of 0.12 mSv year-1. The calculated radium equivalent was 219.50 Bqkg-1, below the reference level of 370 Bqkg-1 The mean external hazard index was 0.60 while the mean internal hazard index was 0.88. Though the Specific Activities, the mean absorbed dose rate and the annual effective dose equivalent were higher than reference values, the radiological hazard indices indicate that consuming these waters did not pose a significant threat to the health of the population but precautions should be taken against high radiation water sources. The study recommended that background radiation emissions in these sites of water collection be done by Uganda Atomic Energy Council (AEC) in collaboration with Uganda National Bureau of Standards (UNBS) and National water and sewerage cooperation (NWSC). In addition, it also recommended for periodic monitoring of the radioactivity levels due to the gamma emitting radionuclides in the natural and drinking waters of the district. Finally, the study recommended that a research be carried out on radiation hazard levels posed by water bodies this study did not look at in Mubende district.Item Assessing the radiological hazards due to radionuclides in sediments and tailings around Kilembe copper mines, Western Uganda(International Journal of Environmental Analytical Chemistry, 2024-03-19) Evarist, Turyahabwa R. S.; Farooq, Kyeyune; Eric, Mucunguzi; Akisophel, Kisolo; Manny, MathuthuCopper mining in Kilembe Valley, Western Uganda, between 1956 and 1982 resulted in multiple tailing sites, raising concerns about potential increases in the natural background radiation. In this study, the radioactivity concentrations of 226Ra, 232Th, and 40K in 31 sediments and tailing samples from the Kilembe copper mines area were determined using HPGe-based gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K in sediment samples were 38.6 ± 8.9, 37.4 ± 7.8, and 708.0 ± 147.3 Bq kg−1, respectively. While in tailing samples, the mean values were 171.3 ± 31.7, 34.8 ± 14.9, and 792.4 ± 208.2 Bq kg−1, respectively. These values exceeded global averages of 35, 30, and 400 Bq kg−1 for 226Ra, 232Th, and 40K, respectively. To assess the radiological hazards due to radionuclides in sediments and tailings, several parameters such as the radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), gamma representative index (Iγ), absorbed dose rate (D), total annual effective dose (Etot), and total excess lifetime cancer risk (ELCRtot) were determined. In sediments, most of these hazard parameters were above the world’s average values, except Raeq, Iγ, Hex, and Hin. While in tailings, all the hazard parameters surpassed the global average values except Raeq and Hex. Pearson correlation coefficient and hierarchical cluster analysis showed that 226Ra was the main contributor to the assessed radiological hazards. The study suggests potential radiological risks linked to natural radioactivity from sediments and mine tailings, especially when used as building materials.Item Influence of device architectures and mobility on response/recovery time of metal halide perovskites: A review(Journal of Materials Science, 2022-01) Emma, Panzi Mukhokosi; Maliki, MaazaOrganic–Inorganic perovskite materials have attracted great interest in the research community for photo-detector and solar energy applications. For various photo-detector applications, the response time is a very important parameter. In telecommunication, a high response speed is required and for this special class of materials, a fast response time in the order of ns has been realized by some authors. The main challenge is their stability. It is established that the response time is primarily controlled by the electron/hole mobility, electrode spacing and the depletion width. In this review, we discuss the recent developments of photo-detector devices composed of mixed halide perovskites and their performance with the main emphasis on the role played by mobility and internally generated electric field to the response/recovery speed. We discuss how the response speed clear relates to charge carrier mobility and depletion width. We further suggest ways on how to improve the response speed to match those of the conventional commercial photo-detectors like Si and InGaAs. We hope this article will find a suitable audience who will utilize this knowledge in the design and construction of ultra-fast photo-detectors.Item Optical absorption and photoluminescence properties of Cucurbita maxima dye adsorption on TiO2 nanoparticles(IOP Publishing Materials Research Express, 2023-04) Emma, Panzi Mukhokosi; Maliki, Maaza; Muhammed, Tibenkana; Nandipha, L Botha; Loyce, Namanya; Madiba, I G; Michael, OkulloDye-sensitised solar cells (DSSCs) are 3rd generation photovoltaic device that imitate photosynthesis in plants. The fundamental concept of a DSSCs is that the photoanode is covered by the dye as a sensitiser. Natural dyes from plant-based extracts have gained attention as alternatives to toxic and expensive commercial dye sensitisers. Various studies have been conducted on the use of natural plant dye extracts for DSSCs . However, more fundamental studies on their adsorption on TiO2 photoanode nanoparticles are still not well understood. In this study, we investigated the crystal structure, optical absorption, and photoluminescence properties of TiO2, Cucurbita maxima, and Cucurbita maxima dyes adsorbed on TiO2 nanoparticles as potential materials for DSSCs. Raman spectra confirmed the anatase phase of the TiO2 nanoparticles. The particle size of 12 ± 2 nm was confirmed through the transmission electron microscope. The optical absorption properties of Cucurbita maxima show two distinct absorption bands: blue visible (450–500 nm) and red visible (635–674 nm). The photoluminescence spectra of the dye extract and its adsorption onto the TiO2 nanoparticles showed two prominent peaks in the blue and red regions of the electromagnetic spectrum. No significant peak is observed in the green region of the electromagnetic spectrum. These studies shed more light on the fundamental properties of chlorophyll adsorption on TiO2 nanoparticles and their optical and photoluminescence properties for applications as sensitisers in DSSCs.Item Biomarker Raman bands of estradiol, follicle-stimulating, luteinizing, and progesterone hormones in blood(Vibrational Spectroscopy, 2022-08) Annah, M. Ondieki; Zephania, Birech; Kenneth, A. Kaduki; Catherine, K. Kaingu; Anne, N. Ndeke; Loyce, NamanyaVariation of the levels of reproductive hormones outside the normal range indicates health problems that include cancer, infertility, and menstrual difficulties. This work reports on a potentially novel method of screening four (estradiol, follicle-stimulating hormone, FSH; luteinizing hormone, LH; and progesterone) hormones. The work involved first determining the characteristic Raman spectra of their standards. Thereafter, the Raman marker bands of the respective hormones in blood were determined experimentally. Simulate samples were prepared by mixing, at varying concentrations, the respective standard hormone samples with male mouse’s blood and concentration-sensitive Raman bands identified upon 785 nm laser excitation. The samples were applied, separately, onto prepared conductive silver paste smeared microscope glass slides. Spectral data analyses were done using both Principal Component Analysis (PCA) and Analysis of variance (ANOVA). The spectral profiles of respective standard hormones (with no blood) displayed common bands at 483, 1005, 1244, and 1455 cm−1 which were tentatively attributed to C-C stretching of glucose, lipid bands, and CH2/CH3 scissoring respectively. Other bands were observed at 542 cm−1 (for LH and progesterone), 859 cm−1 (for estradiol and FSH), 837 cm−1 (for FSH and LH) and at 1360 cm−1 (for progesterone). In blood, a large comparative Raman spectral intensity variation was observed at around 483 and 1450 cm−1 in LH; 902 and 1569 cm−1 in estradiol. These bands could be used as biomarker Raman bands for the respective hormones. The bands centered at 668 and 1219 cm−1 displayed almost identical intensity variation in the four hormones (estradiol, FSH, LH, and progesterone) and could be used as marker bands for level determination for the four combined. This work has shown the power of Raman spectroscopy in potential hormone concentration level determination when respective biomarker bands are employed.Item Structural and mechanical properties of non-glazed ceramic tiles developed from selected mineral deposits in Uganda(Nano-Horizons: Journal of Nanosciences and Nanotechnologies, 2023-07) George, William Mukwaya; Ben, Enjiku; Emma, Panzi MukhokosiUganda is well endowed with clay resources; however, comprehensive knowledge about the composition, structure and suitability of these clays for ceramic tile production is lacking. In this study, we provide a comprehensive characterisation of locally sourced clays in Uganda and their suitability for ceramic tile production. In the study, we developed ceramic tiles using feldspar, kaolin, ball clay and sand from four different sites in Uganda. We focused on analysing the surface morphology, crystallographic structure and mineralogical composition of the raw materials. In addition, we examined the mechanical properties of the developed tiles with the different mixture ratios of the clay types. The surface morphology of the raw materials was analysed by using a scanning electron microscope. The structural analysis of the raw clay materials was done using X-ray diffraction. The mineralogical composition of the raw materials was investigated using energy dispersive X-ray spectroscopy and X- ray fluorescence spectroscopy. The results indicated that the strength and rapture modulus are influenced by the composition of kaolin and feldspar. We concluded that the selected mineral deposits can be used in the production of ceramic tiles in Uganda.