Department of Physics, Chemistry and Material Science

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A comparative analysis of GNSS-inferred precipitable water vapour at the potential sites for the Africa Millimetre Telescope
(Monthly Notices of the Royal Astronomical Society, 2025) Frans, Lott; Backes, Michael; Falcke, Heino; Venturi, Tiziana
The Event Horizon Telescope (EHT) is a network of antennas across the globe currently used to image supermassive black holes (SMBHs) at a frequency of 230 GHz. Since the release of the image of M87 in 2019 and, subsequently, that of Sgr A in 2022 by the EHT collaboration, the focus has shifted to dynamically imaging SMBHs. This has led to a search for potential sites to extend and fill in the gaps within the EHT network. The Gamsberg Mountain and the High-Energy Stereoscopic System (H.E.S.S.) site are both located within the Khomas highlands and have been identified as potential sites for the Africa Millimetre Telescope (AMT). Precipitable water vapour (PWV) in the atmosphere is the main source of opacity and noise from atmospheric emissions when observing at millimetre to sub-millimetre wavelengths. This study aims to establish the PWV content and the atmospheric transmission at 86, 230, and 345 GHz at the AMT potential sites using Global Navigation Satellite System derived PWV data. Results show both sites have potential for observations at 86 and 230 GHz, with 345 GHz possible at the Gamsberg Mountain during winter. The overall median PWV of 14.27 and 9.25 mm was calculated at the H.E.S.S. site and the Gamsberg Mountain, respectively. The EHT window had PWV medians of 16.62 and 11.20 mm at the H.E.S.S. site and Gamsberg Mountain, respectively. Among the two sites, the Gamsberg Mountain had the lowest PWV conditions, therefore making it the most suitable site for the AMT
A geochemical baseline study of giant kelp (macrocystis pyrifera) at the kelp blue farm to assess carbon sequestration potential
(University of Namibia, 2024) Mutjida, Protasius Shikusho
The raised levels of carbon dioxide (CO2) in the earth’s atmosphere have contributed to global climate change, which has adversely affected a wide range of individuals, communities, and organizations. One of the ways to mitigate climate change is to grow a huge amount of kelp forests that can absorb carbon dioxide from the atmosphere and sequester it in the deep ocean. To grow these forests, the right biogeochemical conditions (temperature, nutrients, oxygen, salinity, pH, trace metals and ions) within the ocean is vital to assess the sequestration potential and the impacts on the ocean health. This study aimed at monitoring the biogeochemical changes at the proposed Kelp Blue farm and surrounding areas further away from the farm. This study also aims to create a baseline of the chemical composition of the farm and Lüderitz areas, which has not been done before. Using the results obtained from the study, the potential of the cultivated giant kelp to sequester CO2 will be evaluated. This study measured the geochemical parameters using both in-situ probes and laboratory analyses at 10 different locations in Lüderitz (both offshore and coastal): offshore (within the Kelp Blue Pilot project farm, upstream of the farm in the Dumfudgeon rocks, downstream of the farm at Boot Bay and further south of Lüderitz at the Halifax island) and the coastal areas which are adjacent to the offshore study areas including at coastal site of Guano Bay which is about 17 km and the coastal area of Grossebucht which is about 20 km south the town of Lüderitz as another control site. This study also collected sediment samples at these offshore sites including further north of Walvis Bay at the different latitudinal transects. The sediments were analysed for trace metals by using a portable XRF and for carbon content by LOI (Loss on Ignition) method. Another geochemical analysis done was the titrimetric method to CO2 determination of seawater by using NaOH as a titrant the end points were determined. The concentrations of nutrients (phosphates and nitrites) in seawater samples were determined by adding them to a 10 mL cuvette, which had been zeroed first. A specific nutrient reagent was then introduced, and using ii prescribed sample preparation techniques, a spectrophotometer was employed to measure the concentrations of the nutrients in µg/L and mg/L. The geochemical parameters changed in relation to the seasonality and geographical positioning. In a season when the upwelling system was strong, the concentration of nutrients, acidity and the value of the pH, salinity, other geochemical parameters increased more, compared to other seasons and the further southern sampling sites resembled to that of the Southern Benguela Upwelling System (SBUS). Higher concentrations of phosphates (614 µg/L) were found in areas close to the islands. This is due to the presence of guanos. These remarkable long duration geochemical measuring results shows that the cultivated kelp can co-exist with other natural existing kelp beds in this ecosystem, and they can thrive more predominantly in season of great influx of nutrients during the season of strong winds. With a dynamic Benguela upwelling eastern boundary, these kelp forests have an enormous potential to grow more and will function as carbon absorber and eventually sequester more carbon when cultivated at larger scale. To quantify the carbon sequestration potential of these giant kelps, there are other areas to be investigated such as developing a sediment carbon baseline using isotopic analyses, lipid biomarkers, identifying sediment hotspots where the kelp will be deposited, developing a carbon dioxide removal model and geochemical dispersion models. All these other areas will be developed from the baseline being developed by this study. This study recommends that a continuous and rigorous monitoring of the water and sediment geochemical changes be done as the kelp forest grows and as the scale of operation expands
Analysis of the accuracy of GNSS inferred precipitable water vapour against that from a 210 GHz WVR at the H.E.S.S. site
(Oxford University Press, 2025) Frans, Lott; Backes, Michael; Falcke, Heino; Venturi, Tiziana
The High Energy Stereoscopic System (H.E.S.S.) site and the Gamsberg Mountain have been identified as potential sites for the Africa Millimetre Telescope (AMT). The AMT is poised to observe at millimetre and possibly at submillimetre wavelengths. At these wavelengths, precipitable water vapour (PWV) in the atmosphere is the main source of opacity during observations and therefore needs to be accurately assessed at the potential sites for the AMT. In order to investigate the PWV conditions for the AMT, identical Global Navigation Satellite System (GNSS) stations were installed and used to assess the PWV at the two potential sites. In this study, the accuracy of those PWV measurements by the GNSS stations was assessed by comparing the H.E.S.S. installed GNSS station PWV measurements to that from a 210 GHz Water Vapour Radiometer (WVR) also installed at the H.E.S.S. site. A correlation of 98 per cent and an offset of 0.34 mm was found between the GNSS station and the 210 GHz WVR PWV data when on-site pressure and the Nevada Geodetic Laboratory (NGL) weighted mean temperature (⁠ ⁠) were used to calculate the GNSS station PWV data. In comparison, the offset reduces to 0.15 mm when on-site derived and pressure were used to calculate the GNSS station PWV. The results show that the GNSS station with on-site meteorological data can be used with high accuracy to reliably determine the PWV conditions at the H.E.S.S. site
Analysis of tolerable capacity limits of intermittent photovoltaic power connected to the Namibian national electricity grid
(University of Namibia, 2021) Katanga, Lusia Naambo
Grid-connected photovoltaic (PV) systems are being utilized at an increasing level worldwide. Even though the increasing addition of intermittent PV power to the grid systems may lead to grid instability, PV systems feeding power into the Namibian electricity grid system are on the increase. The purpose of the study was to analyse the ability of the Namibian electricity grid system to accommodate intermittent solar PV power and to determine the capacity limit beyond which the Namibian electricity grid system will become unstable due to an increase in intermittent solar PV systems feeding power into the grid system. Data of interest was obtained from collected reports, journal articles, and other documents. This data was analyzed using quantitative methodological approaches and further classified, presented, and discussed. The Namibian grid system is considered strong when certain busbars achieve the SCR of 10 and the majority of the Namibian grid busbars can only connect less than 10MWof intermittent renewable electricity capacity without violating the short circuit ratio (SCR) limit. The capacity limits of intermittent solar PV power for the Namibian national grid system was calculated to be in the range of 38% to 53.4%. This study recommends that more research work and investigation from the perspective of engineering application and academic research are clearly required for more analysis regarding the strength and capacity limits of intermittent PV power of the Namibian grid system.
Assessment of natural radioactivity in the soils of the Ohorongo Cement plant and the town of Otavi, Namibia
(University of Namibia, 2020) Nambinga, Monica Mwadinomo
The activity concentrations of the naturally occurring radionuclides 238U, 232Th, and 40K in soil samples collected from the Ohorongo Cement plant and the town of Otavi, Namibia have been determined using a High-Purity Germanium (HPGe) detector. In addition, an assessment of the radiological hazards due to these natural radionuclides in the soils of the plant and town was carried out. The plant was divided into three geographical areas, and fifty soil samples were collected across the areas. Also, the town of Otavi was divided into ten geographical areas, and fifty soil samples were collected across the areas. These soil samples were processed and 500 g of each sample was placed in a well-labelled 500 ml polythene bottle and analyzed using an HPGe detector. The average activity concentrations of the radionuclides 238U, 232Th, and 40K in the soil samples from the Ohorongo Cement plant were 15.0 ± 4.7 Bq/kg, 25.1 ± 9.9 Bq/kg, and 310.7 ± 97.2 Bq/kg respectively. Similarly, the average activity concentrations of the radionuclides in the soil samples from Otavi were 21.6 ± 7.2 Bq/kg for 238U, 20.3 ± 8.5 Bq/kg for 232Th, and 256.4 ± 113.7 Bq/kg for 40K. The average activity concentrations of 232Th and 40K were found to be higher in the Ohorongo Cement plant than in Otavi. In contrast, the average activity concentration of 238U was higher in Otavi than in the Cement plant. These concentrations were used to calculate the absorbed dose rates and the effective dose rates in air across the different geographical areas in the plant and town. The values of (4.3 ± 1.5) × 10−2 mSv/y and (4.0 ±1.5) × 10−2 mSv/y obtained respectively for the mean effective dose rates in the Cement plant and town are both less than the maximum permissible effective dose rate of 1.0 mSv/y recommended for the public by the International Commission on Radiological Protection. In order to evaluate the associated health hazard, the concentrations were also used to calculate the mean Radium equivalent activity (Raeq) and the mean external hazard index (Hex) for the plant and for the town. The values obtained for Raeq in the Cement plant and town were 74.9 ± 25.6 Bq/kg and 70.4 ± 26.7 Bq/kg, respectively. These values are below the maximum permissible limit of 370 Bq/kg. Furthermore, the values of 0.20 and 0.19 obtained respectively for Hex in the Cement plant and town are again below the maximum permissible limit of 1.0. It is therefore concluded that radiation hazards are negligible in the plant and town and hence the plant and town have normal background radiation. The data generated in this study will contribute to the baseline data on radiological hazards in Namibia.
Determination of endogenous and dietary-derived nitric oxide production in exhaled air of adult humans
(University of Namibia, 2022) Keendjele, Tuwilika P.T.
The production of nitric oxide (NO) has been demonstrated in the human body. Studies have elucidated that NO can either be produced endogenously via enzymatic action or through exogenous factors from dietary nitrate reduction. Exhaled nitric oxide (eNO) levels were also observed to be increased in inflammatory conditions, such as asthma and rhinitis, compared to normal physiological conditions. The aim of this study was to observe the production of NO in the body, the influence of dietary nitrate on eNO and factors affecting NO production. In this cross-sectional study, eNO in healthy, control participants (n=25) and compared to exhaled NO in participants with asthma (n=6) and participants with seasonal rhinitis (n=7). Exhaled NO in 20 healthy controls was also after supplementation with dietary nitrate. Asthmatic participant’s eNO concentrations (41±25 ppb) were higher compared to eNO in the control participants (12±12 ppb; p=0.04). There was no difference between eNO concentrations in participants with rhinitis (30±31 ppb) compared to control participants (12±12 ppb; p=0.21). There was also no dose-response relationship between the amount of dietary nitrate (nitrate-rich beetroot juice) and eNO concentration where eNO concentrations of 31±16 ppb, 34±31 ppb and 38±30 ppb; p=0.42 were measured for 35 mL, 70 mL and 140 mL of beetroot juice, respectively. A transient increase in eNO was observed after 30 minutes post-nitrate ingestion (20±8 ppb) compared to baseline eNO concentrations (6±5 ppb; p=0.03). The use of antibacterial mouthwash also reduced eNO concentrations post nitrate-ingestion (18±15 ppb) compared to beetroot ingestion without prior use of mouthwash (34±31 ppb; p=0.02). Exhaled NO levels were not reduced after antacid administration (p=0.791). The results of this study may indicate that the transient impact of dietary nitrate on eNO could account for the variations demonstrated in literature.
Determination of natural radioactivity in the soil of Omaruru, Namibia
(University of Namibia, 2022) Mbuende, Mercey
In this study, the level of natural radioactivity and associated hazards has been evaluated for 50 soil samples from the town of Omaruru in western Namibia. Activity concentrations (Bqkg-1) of the primordial radionuclides 238U, 232Th and 40K in these soil samples were determined using a gamma-ray spectroscopy system with a High Purity Germanium detector (HPGe). These activity concentrations of the primordial radionuclides were calculated by using the intensities of selected gamma lines in the spectra as emitted by the radionuclides. The samples were collected from ten geographical areas which are inhabited localities in the town. The obtained results of activity concentrations for every soil sample was compared with the worldwide average values as recommended by UNSCEAR 2000. The values of activity concentration of 238U have been found to lie in the range of 39.4 - 111.1 Bq kg-1, with an average value of 63.9 ± 15.4 Bq kg-1, the values of activity concentration of 232Th ranged from 49.5 - 231.7 Bq kg-1 with an average value of 120.0 ± 42.9 Bq kg-1 and the values of activity concentration of 40K ranged from 692.4 - 1425.5 Bq kg-1, with an average value of 1136.7 ± 197.8 Bq kg-1 . The absorbed dose rates and annual effective dose as well as the radiation hazard indices in the soil samples, were calculated by employing the determined activity concentration values of 238U, 232Th and 40K. The total absorbed dose rate varied from 90.9 to 230.2 nGyh-1, with the average value of 149.4 ± 35.2 nGyh-1 and subsequently the annual effective dose ranged between 0.112 to 0.282 mSvy -1, with an average value of 0.183 ± 0.043 mSvy-1. This result of the annual effective dose is much lower than the recommended maximum permissible dose rate of 1.0 mSvy-1. The implication thereof is that the town of Omaruru has a normal background radiation. Additionally, the average value of the radium equivalent activity was 323.0 ± 80.2 Bq kg-1, and is lower than the recommended maximum value of 370 Bq kg-1. Furthermore, the average external hazard index, which was 0.87 ± 0.22, is also below the recommended safe level of 1. Based on these results, the radiological hazard is low in Omaruru. The results obtained in this study would be useful in establishing a baseline data to serve as a future reference in confirming possible changes in the environmental radioactivity as a result of any nuclear and related activities.
Determination of the suitability of MT Gamsberg in Namibia for millimetre wave stronomy by measurements of the precipitable water vapour
(University of Namibia, 2020) Frans, Lott Ndeyanale
Precipitable Water Vapour (PWV) is the amount of water vapour in the atmospheric column above a location equivalent to the amount of liquid precipitation that would result if all the water vapour in the column was condensed. Water vapour is the main source of opacity in the Earth’s atmosphere at infrared and millimetre to sub-millimetre wavelengths. The Event Horizon Telescope (EHT) is a large network of millimetre to sub-millimetre telescopes across the globe that is used to image supermassive black holes. The Africa Millimetre Telescope (AMT) is planned to be built on Mt Gamsberg in Namibia and aims to complement the EHT. In this study, PWV at Mt Gamsberg and at the H.E.S.S. site was determined in order to asses the two sites regarding their suitability to conduct millimetre wave astronomy and for the AMT to be built on Mt Gamsberg. PWV at the H.E.S.S. site was indirectly determined from sky temperature data which was taken from 2004 to 2019 by radiometers on four of the H.E.S.S. Cherenkov Telescopes (CT). The PWV at H.E.S.S. as a function of sky temperature as given by the CT radiometers was determined by relationships given by data from two other equipment present at the H.E.S.S. site, namely the NASA AERONET station and an ATMOSCOPE with the equipment recording PWV and sky temperature, respectively. The PWV at Mt Gamsberg was determined by scaling the PWV from the H.E.S.S. site to what it would be at the height of Mt Gamsberg. The relative frequency distribution of PWV, monthly mean PWV along with its seasonal variations were comiputed for both sites. The presented results indicate Mt Gamsberg is a suitable site for millimetre wave astronomy and to host the AMT. However it was recommended that direct PWV measurements should be taken at Mt Gamsberg to confirm the result of this study, as these were not based on direct in-situ measurements.
An efficient method for the synthesis of dihydropyridine by hantzsch reaction with Fe/SiO2 nano heterogeneous catalysts
(2020) Rahman, Ateeq; Nehemia, P.N.; Nyambe, Moola M.
An efficient method for the synthesis of dihydropyridines (DHPs) by Hantzsch reaction with Fe/SiO2 heterogeneous catalysts was developed. The Fe/SiO2 catalysts was prepared by impregnation method. The catalysts were characterized by IR and SEM instruments. The SEM results indicated that Fe/SiO2 nano spheres were formed. The reaction procedure involved reaction of aldehyde, ethyl acetoacetate (EAA), ammonium acetate (NH4OAc) and ethanol under reflux. The study was focused on optimizing reactions conditions: Standardization of catalyst, substrate of study and solvent study. In order to iden-tify the best active catalysts, five different ratios of catalyst were synthesized and evaluated for the ti-tle reaction under similar conditions. To standardize the active catalysts, different temperature condi-tions (i.e. room temperature, 60 ºC and 80 ºC) as well as catalysts amounts were evaluated. Under these established conditions, 2.5% Fe/SiO2 was the best active catalysts that resulted. Benzaldehyde and p-anisaldehyde were used to study the effect of having various substrates on the conversion and reaction time, especially the substituted aldehydes. The best results were obtained by reacting p-anisaldehyde with EAA, NH4OAc, and ethanol at 60 ºC with 0.3 grams of 2.5% Fe/SiO2 heterogeneous catalysts. Thin Layer Chromatography (TLC) monitoring of the reaction mixture showed no selectivity at high temperatures (80 ºC) with 15% Fe/SiO2. Standardization of solvent study was executed with two solvents, ethanol and acetonitrile. The product dihydropyridines were analyzed using gas chroma-tography-mass spectrometry (GC-MS). The melting points of the products were compared with authen-tic samples reported in the literature. Hence, the Fe/SiO2 catalysts is eco-friendly and economically de-veloped for the title reaction.
An evaluation of the natural radioactivity in the soils of Okahandja and Karibib, Namibia
(University of Namibia, 2018) Midzi, Wilfred
The natural radioactivity and associated hazards in the soils of the towns of Karibib and Okahandja have been studied by gamma spectroscopy. Each town was divided into ten geographical areas and five soil samples were collected across each area. These samples were processed and placed in well-labelled 500 ml plastic bottles. A High Purity Germanium detector (HPGe) was used to measure the gamma ray spectra of the samples. The intensities of selected gamma lines were used to calculate the activity concentrations of the gamma emitting radionuclides 238U, 232Th, and 40K. The average activity concentrations of 238U, 232Th, and 40K in Karibib are 29.4 ± 5.8 Bq/kg, 49.0 ± 8.6 Bq/kg, and 824.3 ± 153.5 Bq/kg respectively while they are 40.9 ± 8.6 Bq/kg, 57.9 ± 19.4 Bq/kg, and 562.4 ± 125.4 Bq/kg respectively in Okahandja. Consequently, the average activity concentrations of 238U and 232Th are much higher in Okahandja than in Karibib, while the average activity concentration of 40K is much higher in Karibib than in Okahandja. These concentrations were used to calculate the absorbed dose rates and effective dose rates in air in the two towns. The average absorbed dose rate in air in Okahandja is 77.3 ± 18.0 nGy/hr while that in Karibib is 77.6 ± 10.9 nGy/hr. However, the resulting average effective dose rate in Okahandja and Karibib are the same and equal to 9.5 𝑥 10-2 mSv/yr. The average absorbed dose rate in air in each of the two towns is relatively high than the world average of 51 nGy/hr. However, the corresponding average effective dose rate in both towns is much below the recommended maximum permissible dose rate of 1.0 mSv/yr. This result implies that the two towns have normal background radiation. Also, the results of 163.0 ± 22.6 Bq/kg and 167.1 ± 40.1 Bq/kg obtained for the Radium equivalent activities, Raeq, in Karibib and Okahandja respectively are much lower than the recommended maximum value of 370 Bq/kg thus confirming that both towns have normal background radiation. Furthermore, the average external hazard indices determined for Karibib and Okahandja are respectively 0.4 ± 0.1 and 0.5 ± 0.1. These values are again far less than the recommended safe level of unity. This result further confirms that radiological hazard is negligible in Karibib and Okahandja. The results obtained in this study would be useful in establishing a baseline data that will serve as a reference to ascertain possible changes in environmental radioactivity due to nuclear and related activities in future.
A hybrid analysis approach to the high energy stereoscopic system phase II mono-analysis
(University of Namibia, 2020) Shapopi, Jimmy Ndawedapo
The High Energy Stereoscopic System (H.E.S.S.) is an array of imaging atmospheric Cherenkov telescopes located in the Khomas highlands of Namibia. Their primary purpose is to detect Cherenkov light (CL) produced by particles in extensive air showers which are produced by incident high energy particles (gamma rays or cosmic rays) on the Earth's atmosphere. The array consists of four 107 m2 optical telescopes and a larger 614 m2 collective surface area telescope in the center of the array. The larger telescope has the ability of detecting showers induced by lower energy gamma rays therefore, it's addition to the array meant a lower threshold for the entire array. This can be accomplished by sophisticated analysis techniques, however, the analysis techniques that have thus far been used have not increased the integral sensitivity of the array as a whole as would be expected, but perform worse than the standard analysis technique at medium and high energies. Data taken by the H.E.S.S. telescopes is analyzed by fitting parameterized shower model images to actual images produced when observing a source, (Model++ Analysis) using a goodness of fit approach. This work explores the distribution of a shower parameter introduced in 2009, the depth of first interaction. Adjustments to the primary depth selection criteria to distinguish signal against noise are made and applied for a more sensitive result. Multi-wavelength lag studies from Cygnus X-3 are also presented. Light curve correlations between hard/soft X-rays versus radio emissions over long periods are studied. These studies are layed out as supporting suggestions that, lowering energy threshold while maintaining integral sensitivity to those energies would assist in the study of micro-quasars and possibly infer properties of quasars.
Investigating electronic pedestals of the analoque front-end boards of the upgraded high-energy stereoscopic system (H.E.S.S.I) cameras
(University of Namibia, 2017) Shiningayamwe, Kleopas P.
The High-Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes located in the Khomas Highland in Namibia, dedicated to very-high-energy (VHE, 100 GeV { 100 TeV) gamma-ray astronomy. It consists of four identical 12 m diameter telescopes (H.E.S.S.-I) which started operating in 2003 and a large 28 m diameter telescope (H.E.S.S.-II) which was brought online in 2012 [1]. The H.E.S.S.-I camera upgrade project was aimed to increase the stability and performances of the camera operation by replacing the 13 years old camera electronics with modern-day technologies. The most delicate part of the upgraded electronics are the readout boards of the drawers, which have been upgraded with a new analog memory [2, 3]. A significant level of cross-talk has been observed in the analog front-end boards of the H.E.S.S.-I camera upgrade [3], and investigating the electronic pedestals of these analog boards could help understand the origin of such a cross-talk. A C++ code written in ROOT modular scientific software framework has been developed for the analysis of the data taken with a drawer on the Test bench at DESY in Zeuthen, Germany. So far, from the computation of the autocorrelation function and Fourier transform of the electronic pedestals, no characteristic patterns have been found to explain the level of cross-talk observed. The upgrade of the cameras is ongoing, and the investigations of the noise level of the rear part of the electronic boards will be continued.
Investigation of the dependence of sheet resistance on the thickness of spin coated poly (3-Hexylthiophene) thin films
(University of Namibia, 2024) Mutenda, Oliver Sibenga
Sheet resistance (R□) and thickness of as-cast and post-treated poly(3- hexylthiophene) (P3HT) thin films fabricated on non-conductive glass substrates by the spin coating method, were determined under dark, and illuminated conditions. R□ of P3HT thin films of different thicknesses were compared, to examine the effect of illumination on the R□, and hence on the resistivity of the films. Commercially available P3HT was purchased and dissolved in chloroform (CHCl3). Glass slides were cleaned using detergent, acetone, and alcohol, in an ultrasonic bath, followed by cleaning in distilled water. P3HT thin films were fabricated by spin coating CHCl3 based solutions on cleaned, dry glass substrates, in ambient air. The films were annealed at a controlled temperature, and then the R□ of each thin film was measured, using the in-line four-point probe method. The thicknesses of the thin films were varied by varying the spin speed (ω) of the spin coater. The results showed a correlation between the R□ and the P3HT thin films’ thickness. The R□ reduces as the thicknesses of the P3HT thin films increase in the light, and in the dark, for as-cast, and annealed, P3HT thin films. Annealing also reduced the R□ of the P3HT thin films, and R□ showed some reductions when measured in the dark. The four-point probe method can be used to characterise materials
Laser induced fluorescence for stress studies on maize plants under control conditions
(University of Namibia, 2015) Van Kent, Alfred A.
The growth of plants is affected by several environmental parameters of which light (particularly UV) is the most important. It is a well established fact that similar plants grow differently in different regions, due to the fact that the local environmental conditions vary from place to place. Stratospheric ozone depletion has caused an increase in the amount of ultraviolet-A (UV-A) and ultraviolet-B (UV-B) radiation reaching the earth’s surface. In Namibia, excessive ultraviolet (UV) radiation is one of the main factors that adversely effects the growth of vegetation and therefore the study of its influence on the growth of plants is very vital. For this study, an advanced technique of Laser-Induced Fluorescence (LIF) is used. When plant leaves are irradiated by ultraviolet (UV) radiation, fluorescence spectrum shows four peaks centered at wavelengths of 450nm, 530nm, 685nm and. The ratio of blue (450nm) to red (730nm) fluorescence differs from plant to plant and is considered a stress indicator. For laboratory measurement of fluorescence spectra from the leaves of maize plants grown under controlled conditions such as humidity, temperature, water and mineral stresses, and exposed to UV-A and UV-B radiation over different timelines are used. The emission spectrum of the third leaf from the bottom side of each maize seedling were obtained using a AvaLight- D(H)S Deuterium-Halogen light sources (337 nm), which was connected to Ava Spec-2048 Fiber Optic Spectrometer and a computer for displaying the results in a graph format. In this study, the intensity ratios of these peaks as 𝐅𝟒𝟏𝟎𝐅𝟒𝟑𝟎 , 𝐅𝟒𝟏𝟎𝐅𝟓𝟓𝟎, and 𝐅𝟓𝟓𝟎𝐅𝟓𝟗𝟎 corresponding to blue to green, blue to red, and chlorophyll fluorescence were calculated and analyzed. This study focused on maize plants due to socio-economic importance of maize in Namibia. The ratio 𝐹410𝐹430 , that is blue to green, has decreased from 0.4 to 0.2, that is a 50% decrease, while the ratio 𝐹410𝐹550, that is blue to red, increase from 0.2 to 0.4, which is an increase of 100%. On the other hand, it was found that the ratio 𝐹550𝐹590 , the chlorophyll flurescence, has decreased from 2.9 to 1.6, which is a decrease of 44.8%. The decease in the ratio 𝐹550𝐹590 , the chlorophyll flurescence is due to the reduction in photosynthesis activity and hence the health status of plants, whereas the decrease in the ratio F410F430 (blue to green fluorescence) reflects the chlorophyll and carotenoid pigmentation in green leaves. The increase in the ratio of F410F550 (blue to red) with the increase of UV-A and UV-B radiation, could be due to the reabsorbtion on the red light in the the inner leaf with high concentrations of flavonoids and anthocynanins. Furthermore, it was found that UV-B was more destructive than UV-A. From measurements taken of the growth parameters, such as number of leaves, width of the leave, diameter of the stem and height of seedling, the following were observed. When exposed to UV–A, the width of the leave reduces from 1.7 to 0.7 (58%), the diameter of the stem reduced from 0.4 to 0.1 (75%), and the height of the seedling from 41 to 19 (53%). In this study it is thus observed that UV and in particular UV-B has significant impacts on the total biomass and the growth of plants. This is in agreement with other reports that plants are more susceptible to long-wave UV-B irradiation and that this difference is more apparent from the changes in total area of leaves and dry mass of shoots, rather than from the parameters of chlorophyll fluorescence and net photosynthetic rate. It is recommended that the continued advancement of laser research and the further development of laser remote sensing techniques for atmospheric, environmental and further vegetative studies be actively promoted and motivated.
Measurement and comparison of refractive index of the water samples collected from different surface water sources in Namibia
(University of Namibia, 2015) Shafudah, Natangue H.
Refractive index is an important optical parameter that exhibits the optical properties of materials. Single-Diffraction Method (SDM) and Abbe’s Refractometer Method (ARM) have been used for the measurements of refractive indices of twelve water samples collected from different surface water sources in Namibia. SDM employs a diffraction grating, rectangular glass cell and Ne-He laser emitting a monochromatic light of 632.5 nm. Refractive indices of water samples were measured without knowledge of refractive indices of the diffraction grating and the rectangular glass cell, and without measuring the angles of refraction, reflection and diffraction of the laser light. Experimental values obtained for refractive indices of the twelve water samples are presented. By comparison of refractive index values from SDM and ARM, their refractive index uncertainties values were lower than 0.1. This uncertainty error could be attributed to SDM instrument limitation error. More-over, turbidity, salinity, hydrogen ions (pH) and density values were measured for the water samples. From the statistical model, there exist non linear regression between salinity, pH and turbidity and the results from refractive indices from both methods. However, a linear correlation between SDM and ARM refractive index values was found to exist. Moreover, the correlation seems to exist between refractive index and density of water samples which is more notable in sea water samples. The root test was found to be 0.9535~1 for refractive index measurements from SDM and ARM.
Performance evaluation of Photovoltaic (PV) modules under different deployment conditions
(University of Namibia, 2021) Michael, Poland Amutenya
The purpose of this thesis is to evaluate the performance of solar modules, comprising various PV technologies, subject to different climatic conditions. The assessed PV technologies comprises of commercially available technologies and included Cadmium Telluride (CdTe), Copper Indium diSelenide (CIS), amorphous silicon (a-Si)and polycrystalline silicon (p-Si) modules. Commercially available photovoltaic (PV) modules currently are comprised of two main groups: crystalline silicon modules and thin film modules. The thin film modules are cheaper due to lower production cost. They also exhibit lower temperature coecients compared to crystalline silicon. There is a perception in the PV industry that thin film modules exhibit superior performance in hot climates and that they show better tolerance and performance in lower solar radiation locations. Our task was to determine if there is scientificc evidence for such perceptions. Measurements were done at two stations in South Africa with different climates: Port Elizabeth (PE), having a humid, relatively cool and with high cloud cover and Johannesburg (JB), having a warm, semi-arid and low cloud cover climate. In PE, one year of operation data for power output and module temperature measured at one minute time resolution were collected from the site while the GHI and ambient temperatures were measured from the site but downloaded from the SAURAN website. In JB, the power output and module temperature data measured at one minute time resolution were collected for a period of 6 months. The assessment was based on the following performance indicators: specific yield (SY), specific yield per unit land/roof area occupied by modules (SY/A) and the relative module efficiency ( rel:) for sunny (high irradiance) days and cloudy (low irradiance) days in each location. Statistical assessment of the performance indicators for each module type was performed with ANOVA test. The Tukey post-hoc test at 5% significance level was used for comparison of the daily SY, SY/A, rel: and average module temperatures between the different technologies at each location. A regression model was created to determine the extent of the impact of ambient conditions on the energy output of the modules. Our findings indicate that the solar radiation and ambient temperature have a strong impact on the module's SY, with the SY increasing linearly with the solar radiation while decreasing linearly with the ambient temperature during sunny days. Our findings further shows that the performance of all PV technology types are comparable in cloudy conditions at both locations. Under sunny conditions, CIS shows the highest SY in both locations, CdTe shows the highest SY/A in the warm and sunny JB climate while p-Si shows the highest SY/A under the cool and cloudy climate of PE, and a-Si shows the lowest SY, SY/A and rel: in PE. Furthermore, CIS remained the coolest and p-Si the hottest in the JB location. In PE, all modules were equally cool on average. In conclusion, significant difference in performance between different PV technologies is only observed during sunny conditions. In addition, the established differences during sunny conditions were not technology specific but rather dependent of the type of performance indicator assessed. Thin film technologies have shown vast differences in performance between technologies and between climatic conditions. The superior performance of thin film technologies in cloudy conditions could not be established. These results are based only on the first year of module deployment and can be expected to change with time due to module degradation.
Photophysical, electrochemical, and DFT studies of the novel azacrownbridged dinuclear ruthenium dye sensitizers for solar cells
(University of Namibia, 2019) Uahengo, Veikko; Cai, Ping; Naimhwaka, Johannes; Rahman, Ateeq; Daniel, Likius S.; Bhakhoa, Hanusha; Rhyman, Lydia; Ramasani, Ponnadurai
A dinuclear ruthenium bipyridyl complex with 1,10-diaza-18-crown-6 bridging ligand was synthesized and characterized. Its photophysical and electrochemical properties were also studied. DFT computations were performed to complement the experimental investigations. Analysis of the results indicates that the path in which charges move from one metal center to the other is significant for effective electronic coupling. However, electron transfer between the two ruthenium centers is hindered by the azacrown bridging ligand, compared to the smooth electronic transfer reported for a related dye involving an azo bridging ligand.
Properties of front-end electronics of the compact high energy camera prototype for gamma-ray astronomy
(University of Namibia, 2022) Nekwaya, Mwashana Susana
Electronics are a key component for all modern detector systems. The Compact High Energy Camera (CHEC) is a full-waveform camera designed for the dual-mirror Small Sized Telescopes (SST) of the Cherenkov Telescope Array (CTA). Some of the main components of the front-end electronics for CHEC are photo-sensors, preamplifiers and TARGET modules. CTA is planned to be a large observatory with up to 70 SSTs, with thousands of photosensor pixels per telescope (2048 camera channels per SST). The readout electronics for an array with such a high number of channels will cer tainly require a highly integrated and modular recording technology. In this study pulse waveforms generated by the camera channels and output by the preamplifier channels were analysed and parameterised in order to identify the different characteristics of the pulse waveforms. Characterising the pulse waveforms will help to better under stand the behaviour of different electronic channels during camera mass production and during observations as well. An automated analysis procedure that will be able to identify faulty camera channels has been established. A cubic spline has been fit to the data in order to get a good representation of the data and for better comparison of the behaviour of the different electronics channels. The interpolated pulse waveform has a gradually rounded peak, while the actual pulse waveform has a rather sharp peak. In addition, for comparing the behaviour of the different electronic channels, the fre quency distribution of the different characteristics are determined. In this study, it was found that the rise time of the pulse waveform is on average (7.0 ± 0.3) ns , with an average fall time of (15.0 ± 0.8) ns, while the interpolated fit has an average rise time of (6.0 ± 0.6) ns, thus showing consistency in the behaviour of the different channels.
Radionuclide analysis of soil samples taken from Outjo, Namibia
(University of Namibia, 2019) Hanga, Lusina Venomufenu
Naturally occurring radionuclides such as Uranium (238U), Thorium (232Th) and Potassium (40K), exist in the soil where they continuously disintegrate and emit ionising radiation which could pose health hazards to the inhabitants of a given location if the concentrations of the radionuclides are very high. In this work, the concentrations of the radionuclides 238U, 232Th and 40K in the soil samples taken from Outjo have been studied by gamma spectrometry. The town of Outjo was divided into ten geographical areas and five samples were collected across each area. These samples were dried under laboratory temperature, passed through a 2 mm mesh screen and sealed in 500 ml polythene bottles. The samples were analysed using a liquid nitrogen cooled High Purity Germanium (HPGe) detector (by Canberra). The Python Code was used to calculate the activity concentrations of- and Hazard indices due tothe radionuclides 238U, 232Th and 40K from the intensities of the gamma lines emitted. The results obtained show that the concentrations of radionuclides in the soils of the town of Outjo vary from 11. 7 ± 1.6 to 29. 8 ± 2.0 Bq kg-1 with an average of 20.5 ± 3.5 Bq kg-1 for 238U, 15.2 ± 1.8 to 58.3 ± 4.2 Bq kg-1 with an average of 31.4 ± 8.9 Bq kg-1 for 232Th and 206.2 ± 12.9 to 819.6 ± 31.9 Bq kg-1 with an average of 350.6 ± 124.6 Bq kg-1 for 40K. The average concentrations for 238U and 40K are lower than the worldwide averages of 35.0 Bq kg-1 and 400.0 Bq kg-1 respectively. In contrast, the average concentration for 232Th is slightly higher than the worldwide average of 30.0Bq kg-1. The average outdoor air absorbed dose rate due to terrestrial gamma rays at 1m abovethe ground was found to be 43.0 ± 10.6 nGyh-1 which is below the worldwide averagevalue of 58.0 nGyh-1. Also, the corresponding average effective dose was found to be0.05 ± 0.01 mSvy-1 which is below the maximum permissible limit of 1.0 mSvy-1. These results imply that the background radiation in the town is not high. The average values of Raeq and Hex are 92.4 ± 22.5 Bq kg-1 and 0.25 ± 0.06 which are below the recommended maximum limit of 370.0 Bq kg-1 and 1 respectively. Furthermore, the average values obtained for the other hazard parameters are all below the recommended maximum values, thus confirming that the town have normal background radiation so that radiation hazard is negligible in the town. All the results obtained in this study will contribute to the national baseline data of activity concentrations of radionuclides in the soils of Namibia.
Radionuclide concentrations and radiation hazard assessment in the soil of Otjiwarongo, Namibia
(University of Namibia, 2020) Kapofi, Naeman Tuyoleni
The natural radioactivity and associated hazards in soil samples collected from the town of Otjiwarongo, Namibia, have been studied by gamma ray spectroscopy. The town was divided into ten geographical areas and five soil samples were collected across each area. The samples were dried, homogenized and 500 g of each sample was placed in a clearly-labelled 500 mL polythene bottle and sealed for four weeks. HPGe detector was subsequently used to obtain gamma ray spectra of the samples. The intensities of selected gamma lines were used to determine the activity concentrations of the primordial radionuclides 238U, 232Th, and 40K in the soil samples. The mean activity concentrations of the radionuclides in the ten geographical areas vary from 37.6 ± 7.4 to a high of 97.8 ± 46.2 Bq/kg for 238U, from 81.9 ± 16.7 to a very high of 852.8 ± 533.0 Bq/kg for 232Th and from 498.7 ± 55.7 to 807.1 ± 94.5 Bq/kg for 40K. All these mean activity concentrations are higher than the corresponding world-wide average values of 33.0 Bq/kg, 45.0 Bq/ kg and 420.0 Bq/kg for 238U, 232Th and 40K respectively, according to United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 report. Furthermore, the mean activity concentrations of some of the radionuclides in some areas are more than double those of the other areas thus indicating that the distribution of radionuclides in the soil of the town is not uniform. In order to assess the hazards associated with the radionuclides, different radiation hazard parameters such as absorbed dose rate, effective dose rate, radium equivalent activity (Raeq), and external radiation hazard index (Hex), were calculated from the activity concentrations of the radionuclides. The mean absorbed dose rates in the ten areas vary from 90.0 ± 13.7 to 593.9 ± 347.2 nGy h-1 and are all higher than the world average value of 60.0 nGy h-1 . However, the ii corresponding mean effective dose rates vary from 0.11 ± 0.01 to 0.73 ± 0.43 mSv/y which are all below the maximum permissible limit of 1 mSv/y, according to the International Commission on Radiological Protection (ICRP) reference level for public exposure control. Furthermore, the mean effective dose rates in seven of the areas are relatively low and below 0.2 mSv/y while those in the other three areas are relatively high and above 0.2 mSv/y. These results indicate that the level of radiation varies across the town and it is low in seven geographical areas but higher in three areas. The mean values of the radium equivalent activity in the ten areas vary from 197.9 ± 31.5 to a very high value of 1379.5 ± 815.7 Bq/kg. Again, the mean Raeq in the seven geographical areas are low and below the maximum permissible limit of 370 Bq/kg while they are high and above the permissible limit in the other three areas. Similarly, the mean values of Hex in the seven geographical areas are below the maximum permissible limit of unity but they are above the permissible limit in the other three areas. These results confirm that the level of ionizing radiation in most areas of Otjiwarongo is well-below the maximum permissible limit while the level in three other areas of the town is high and the hazard indices are above the maximum permissible limit

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