Tanzania Journal of Science

Investigation of a Choke Valve Erosion in the Gas Lifted Systems

2024-06-26T12:41:09+00:00

Erosion is one of the common causes of failure in subsea operations. However, erosion of subsea systems has many patterns, trends and uncertainties. This has led to production losses due to the failure of prediction of the useful life of the components in the gas lifted system. This work experimentally studied the effect of flow rate and pressure variations on the erosion of the choke valve in the gas lifted system by using flow streams containing either liquid or liquid injected with gas. Cameras installed on both sides of the erosion box captured images of the probe after every one second, followed by image analysis using the RGB model in MATLAB. Erosion consistently occurred after 120 minutes, followed by a significant reduction of the probe area with time. Severe erosion was observed on the liquid streams with no injected gas. Differential pressure in the erosion box varied with higher flow rates. High volumetric flow rates are found to increase erosion of the choke valve. Adding sand in the rig is crucial on establishing the trends of the erosion of the choke valve because of eminent production of sand in the matured gas wells.

Levels of Aflatoxins in Selected Spices Marketed in Dar es Salaam and Zanzibar, Tanzania

2024-06-26T12:25:19+00:00

Aflatoxins are produced by fungi species known as Aspergillus flavus and Aspergillus parasiticus which invade crops like maize, oilseeds, and spices. This study investigated the levels of aflatoxins in four selected types of spices marketed in Dar es Salaam and Zanzibar in Tanzania to determine the incidence of human exposure to aflatoxin through the consumption of spices as food additives. A total of 72 samples of selected spices (25 cinnamon, 16 ginger, 20 cloves, and 11 mixed spices) were collected from farms (Zanzibar), markets and stores in Dar es Salaam and Zanzibar. Aflatoxins B₁, B₂, G₁, G₂, and total aflatoxins were determined using high-performance liquid chromatography with fluorescence detection. The findings revealed that 24 (33%) samples out of 72 were contaminated by aflatoxin B₁ but did not exceed the maximum tolerable level of 5 ngg^-1; whereas, total aflatoxins contaminated 53 (73.6%) samples out of 72, with 2 samples exceeding the maximum permissible limits of 10 ngg^-1. Although the detected levels were within acceptable limits, the risk of aflatoxicosis due to the consumption of spiced foods may be high; hence, necessitating regulatory bodies in the country to constantly monitor for aflatoxins in the marketed spices.

Effects of Coagulant Dosage, Particle Size, and Settling Time on Pond Water Treatment with Cactus Pads and Watermelon Seeds

2024-07-02T03:03:26+00:00

Most Tanzanians who live in villages still struggle to get enough drinking water due to limited supply, so they use pond water for drinking and household purposes. Treatment of this water is crucial especially during the rainy season to reduce its turbidity. The performance of two natural coagulants (i.e., Cactus pads and watermelon seeds) was evaluated in their effectiveness in purifying pond water. The jar test method was used to analyze the effects of coagulant particle size, dosage, and settling time on the treatment of pond water. Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) was used for characterizing the functional groups of the coagulants. The presence of proteins and carboxylic acid groups in both coagulants demonstrates their potential for use in water purification. The effectiveness of removing turbidity in pond water with Cactus and watermelon seed coagulants was determined to be 78.58% and 94.18%, respectively. For both coagulants, the longer the settling time, the more turbidity was removed. The study indicates that watermelon and cactus pads can be used as coagulants to replace synthetic coagulants.

Thermal Behavior of Bio-Fibers Reinforced Paving Bricks

2024-07-02T03:09:37+00:00

Paved areas are among sources of ambient temperature rise due to heat radiation that has been absorbed by pavement materials and then released into the air. The materials that are widely used in paving grounds include concrete, asphalt concrete and cement sand bricks. The paved surfaces absorb the incoming solar radiation from the sun, which is converted into heat, resulting into higher surface temperature than the ambient air temperature, thus contributing to the global warming. In an attempt to solve this problem, a study on paving bricks reinforced with bio-fibers has been done aiming at establishing the thermal behavior of the bricks. Bio-fibers from grass and coconut coir were studied for their heat insulation, and then were included in the green mix of cement-sand (1:6 ratio) during manufacturing of bricks. On attaining the testing age, the bricks were tested for compressive strength and heat flow. The results showed that bio-fibers reinforced bricks meet the compressive strength specifications of ASTM C 902 and their heat flow rate was less when compared with traditional cement sand bricks. Also, during cooling, bio-fibers reinforced bricks cooled faster than traditional bricks, indicating that they are suitable for paving streets and grounds as they offer good thermal resistance that lowers the Urban Heat Island by 9 ° C below that of traditional bricks.

In-situ investigation of Kinetics of Phase Transformation of Ti54M Titanium Alloy by Electrical Resistivity

2024-07-02T03:15:44+00:00

The kinetics of phase transformation of Ti54M titanium alloy was investigated using electrical resistivity measurement for different heating cycles. The resulting microstructure parameters were analyzed using Aphelion software. It was found that α-phase starts to decompose to β-phase is between 600°C and 780°C. The temperature at which 100% β-phase was formed is 965°C. Beyond the temperature at which α-phase starts to decompose and despite the high heating rate of 10 °C/s, a rapid decrease of electrical resistivity which is attributed to dissolution of a-phase was observed. During isothermal holding, equilibrium was reached in about 15 minutes regardless of the holding temperature and differences in electrical resistivity observed at room temperature. A rapid increase in electrical resistivity during quenching which is attributed to martensitic transformation was observed and enhanced with increasing holding temperature. As expected, the fraction of α-phase, the surface density and average equivalent diameter of α-nodules decreased with increasing holding temperature. A good correlation between the variation of electrical resistivity and the fraction of a-phase obtained by image analysis after isothermal holding at different temperatures confirms that in-situ measurement of electrical resistivity can be used to determine the kinetics of phase transformation.

Effect of Increasing Amount of Sisal Fabric on Density, Compressive Strength and Flexural Strength of Sisal Fabric Reinforced Concrete Composite

2024-07-02T03:21:51+00:00

This study examines the impact of adding plain-woven sisal fibres on the mechanical characteristics of sisal reinforced concrete composites. Analysis of the mechanical strength was done in relation to their density, compressive strength, and flexural strength. The sisal fabric composite matrix contained up to four layers of sisal fabric, which was either NaOH treated or untreated. The properties of sisal fabric reinforced concrete were compared to those of steel reinforced concrete. With addition of layers of sisal fabric, the flexural strength of both NaOH-treated and untreated concrete composites increased to a maximum of 18.2 MPa, which was less than steel reinforced at 20.59 MPa. As the number of fabric layers increased, both NaOH-treated and untreated composites’ compressive strength decreased. Although the compressive strength for treated sisal fabric composites decreased by 14.6%, it remained above the desired level of 30 MPa. For untreated sisal fabric composites compressive strength decreased by 18.0% and decreased below the target compressive strength of 30 MPa for up to four layers of fabric added. In comparison to control concrete, the density of concrete with treated sisal fabric decreased to up to 6.05% while for concrete with NaOH treated fabric decreased by 4.90%.

Performance Evaluation of the Physical and Combustion Properties of Faecal Sludge Derived Briquettes Using Different Binding Materials

2024-07-02T03:30:27+00:00

This research aimed at evaluating the performance of faecal sludge briquettes on the quality of briquettes produced in terms physical and combustion properties. Specifically, the research determined the physical and combustion properties of briquette produced from faecal sludge bond with cassava peel, sunflower cake, banana peel and waste paper binders. Physical and combustion properties of the binder materials and briquettes produced were analysed in the Water Resource Engineering laboratory. The laboratory analysis of the combustion properties showed that the Sunflower cake binder had highest calorific value of 16.24 MJ/Kg when compared to other binders including banana peels, cassava peels and waste papers. Similarly, sunflower cake bond briquettes were found to have highest calorific value of 10.81 MJ/Kg than other binders bound briquettes. The drying rates were higher for waste paper, a bond briquette which was observed to be within 6 days from the day of briquette production. The density of faecal sludge briquette was higher in banana peels bond briquettes having the density of 0.99±0.062 g/cm³. The use of binders has significantly improved the physical and combustion properties and thus the performance of the faecal sludge derived briquettes. It is recommended to use faecal sludge bond with sunflower cake binder.

Assessment of Onshore Wind Farm Performance to Geometric Layout Choices by Utilizing Mesoscale Modelling Techniques

2024-07-02T03:54:05+00:00

Previous studies have shown that the average losses of wind power production due to the wind turbine wake effect within operating wind farms is between 10% to 20% of the overall power output. Among other factors, it is reviled that, the wind farm array layout can contribute significantly to both wake effect and power loss at the wind farm site. This study employs mesoscale modelling techniques to assess the effect of geometric layout on the onshore wind farms performance. Geometric layout can be defined by the spacing and alignment (e.g. staggered or aligned) of the wind turbines with respect to the prevailing wind direction. The Weather Research and Forecasting (WRF) model in this study utilised Fitch’s wind farm parameterization to simulate the interaction between wind turbine blades rotation and the atmosphere. To examine a wide range of operating conditions observed within the real-world operating wind farms, two idealised numerical simulations are carried out for each designed wind farm geometric layout, one with the convective condition and another with stable condition. Among the four different designed wind farm geometric layouts, the triangular wind farm layout which offered staggering after every next row was noted to be the easiest method for improving the wind farm performance by increasing the capacity factor from 0.55 to 0.71 and decreasing array losses from 9.15 % to 4.63 %. Comparison between stable and convective regime indicates that the highest capacity factor was obtained during the stable case with the highest power loss owing to increased wake impacts downstream. The lowest value of the capacity factor was obtained during the convective case with the lowest power loss for both four designed wind farms.

Image Reconstruction Method Based on Iterative Linear Back Projection and Logistic Forward Solver for Electrical Capacitance Tomography Measurement System

2024-07-02T04:02:31+00:00

Image reconstruction is one of the important tasks in the application of electrical capacitance tomography (ECT) systems. Though numerous algorithms have been implemented, it is often challenging to obtain satisfactory images in all imaging regions by the use of a single algorithm due to the soft-field nature of ECT systems. The preferred iterative reconstruction algorithms are highly computationally inefficient. A new iterative reconstruction algorithm is proposed which combine iterative Linear Back Projection and Logistic Regression. In this method, the solution to the ECT forward problem is implemented using logistic regression, whereas the ECT inverse problem is solved using the algebraic reconstruction technique. By doing so, it is possible to obtain high quality images at relatively efficient computational cost. The simulated experimental results shows that the proposed algorithm outperforms the Projected Landweber and Iterative Linear Back Projection in terms of spatial similarity accuracy, quality of reconstruction images, and computational efficiency. There are improvements of 29 % spatial similarity accuracy and 58 % computational cost relative to Iterative Linear Back Projection algorithm. This is significant improvement toward using ECT system for online industrial operations.

Diffusion-Steered Algorithm for Improving Quality of Images Generated by Electrical Capacitance Tomography Measurement System

2024-07-02T04:25:47+00:00

Electrical Capacitance Tomography (ECT) is a non-invasive, non-intrusive, radiation-free, robust, and cost-efficient measurement system that generates cross-sectional images of industrial operations by measuring differences in dielectric properties within a container. Despite its advantages, the poor quality of reconstructed images limits its applicability. Researchers have explored both non-iterative and iterative methods to address this issue, yet the resulting image quality remains insufficient for high-stakes applications where accurate decision-making is critical. This study proposes a novel algorithm that integrates the ECT model with a diffusion-steered image denoising functional, enhancing the quality of ECT reconstructed images beyond existing methods. Empirical comparisons show that the proposed algorithm outperforms state-of-the-art techniques such as Linear Back Projection and Projected Landweber, with Distribution Error (DE) and Correlation Coefficient (CC) improvements of 62% and 19%, respectively. Qualitative assessments further indicate the superior performance of the proposed algorithm in reconstructing high-quality images.

Stability of Thermochromic Vanadium Dioxide Thin Films in Harsh Environments of Temperature and Humidity

2024-07-02T04:40:51+00:00

Stability of thermochromic VO₂ thin films against harsh environmental conditions, which is important if the films are to be used in practical smart windows, was investigated. The films were prepared on normal soda-lime glass substrates by reactive radio frequency magnetron sputtering of metallic vanadium target (99.95% purity) at a working pressure of mbar, argon and oxygen flow rates of 76 and 1.4 – 3.0 ml/min, respectively, substrate temperature of 400 ^°C and sputtering power of 150 watts. After deposition, the films were exposed to extreme temperatures and relative humidity at 100 °C, 400 °C and 89%, respectively, for different time durations. Upon exposure, the films structural properties were investigated using the transmission electron microscope and the atomic force microscope, whereas the UV/VIS/NIR spectrophotometer was used to investigate the films’ optical properties. The results showed some degradation in the first high-temperature exposure cycle (at t = ~ 100 ^°C) but were quite stable, and with sufficient thermochromism, after the subsequent cycles. Exposure of the films to extreme temperatures at 400 ^°C, resulted in complete loss of thermochromism. Exposure of the films to extreme humidity (RH ~ 89%) displayed a gradual increase in degradation with exposure time; however, the films retained sufficient thermochromism even after 3 weeks of exposure. Possible explanations for the degradation mechanism are discussed by correlating the observed effects in the structural and optical properties of the films.

The Analysis of a Co-Dynamic Ebola and Malaria Transmission Model Using the Laplace Adomian Decomposition Method with Caputo Fractional-Order

2024-07-02T02:46:38+00:00

The study presents a novel mathematical framework for addressing Ebola and malaria concerns in Sub-Saharan Africa that combines Laplace transformation with Caputo fractional order derivative. It takes into account socioeconomic aspects that influence disease dynamics and uses the basic reproduction number to quantify transmission dynamics. Extensive numerical simulations using Maple 18 software are used to investigate the effect of fractional order derivatives on disease dynamics. It shows how the Laplace-Adomian decomposition approach simplifies nonlinear equations and generates control solutions. It emphasizes the necessity of turning discoveries into concrete plans and encourages stakeholders to be proactive in implementing them. Overall, the study emphasizes the importance of proactive disease management measures and the promise of novel approaches to treating infectious diseases. Stakeholders may create a more resilient response to these health emergencies by working together to adopt these measures.

Application of Time-Varying Mortality Rate Model in Pension System: A case of Tanzania

2024-07-02T02:52:55+00:00

The current increase in the ageing population, driven by a decrease in mortality rates, has impacted most pay-as-you-go defined benefit pension schemes. The resulting increase in the dependency ratio places a greater burden on these schemes. Many pension funds currently use static lifetables to project future obligations, overlooking the gradual decline in mortality rates. This study explores the application of a time-varying mortality rate model to forecast Tanzanian mortality rates. The time-varying model was successfully employed together with multi state method to project and analyse the funding ratio and cashflow to asset value ratio of the mandatory Tanzania Public Service Social Security Fund for the years 2020–2070. Numerical results indicate a decreasing trend in mortality rates over time, leading to a decline in the funding ratio from 92.92% in 2020 to 21.12% in 2070. Additionally, a decrease in cash flow will result in a 0.25% depletion of assets by 2060. Therefore time-varying mortality rate model is an effective tool for pension systems to forecast mortality rates and project their future financial obligations.

Performance Comparison of Deep Learning Models in Predicting HIV Incidences in Tanzania

2024-07-02T04:09:37+00:00

Human immunodeficiency virus infection/acquired immune deficiency syndrome (HIV/AIDS) is a global pandemic that has claimed more than 40 million lives since it was discovered in the late 1970s. In sub-Saharan Africa, including Tanzania. Different measures to combat the diseases have failed to be attained, like the UNAIDS 90-90-90 target, which aimed to reduce HIV by 2020, and it was moved to 2030. The availability of proper tools to control and monitor diseases and ensure proper early intervention is very important. Prediction of disease trends using Machine Learning (ML) models can improve speed towards attaining the UNAIDS targets by providing accurate insights into the disease trends. The performance of ML models depends on many factors, including datasets that influence the generalization of models. This study aims to suggest the best deep-learning model to predict HIV incidences in Tanzania. Four deep learning models, recurrent neural network (RNN), Gated Recurrent unit (GRU), Long Short-Term Memory (LSTM), and 2D convolution layer (CONV2D), have been studied. HIV data is collected from District Health Information System 2 (DHIS2), the national Health Management Information System (HMIS). The HIV data collected is for 26 regions in Mainland Tanzania, recorded from January 2015 to October 2022. The accuracy of the models was evaluated using three metrics: Mean absolute error (MAE), Mean absolute Percentage Error (MAPE), and mean square error (MSE). The results show that Conv2D achieved the lowest average training time for short-term predictions, while RNN records the highest accuracy with the lowest MAE for all considered cases. The GRU was the fastest for the long-term predictions, and the LSTM reported the best accuracy.

Effect of Post-harvest Handling Conditions on Polyphenol Content and Ferric Reducing Antioxidant Properties of Selected Ugandan Sweet Potato Varieties

2024-06-30T20:30:26+00:00

Sweet potatoes are rich in nutrients, including bioactive compounds like carotenoids and polyphenols. This study provided information on the effect of postharvest handling conditions; curing (direct sunshine) and ambient storage on the total carotenoids, total polyphenols and antioxidant activity of five Ugandan sweet potato varieties. The total carotenoid content was determined following Rodriguez and Kimura's method, while total polyphenol content and antioxidant activity were assessed using Folin-Ciocalteu’s reagent and the FRAP assay, respectively. Findings showed significant variation in total carotenoids, total polyphenol content and antioxidant activity of the different sweet potato varieties. There was an increase in total carotenoids in both cured (322 to 391 µg/100g) and non-cured roots (325 to 366 µg/100g), on average during storage. The total polyphenol content declined from 1.04 mg GAE/g (at harvest) to (0.42 and 0.47 mg GAE/g) in cured and non-cured roots, respectively, on average. The antioxidant activity was reduced from 8.74 µmol/g (at harvest), to 3.40 and 3.73 µmol/g in cured and non-cured roots respectively, on average. This study concluded that curing under direct sunshine decreases the polyphenols and antioxidant activities in all varieties but increases total carotenoid content, suggesting careful consideration of postharvest handling procedure before storage, for nutrient maximization.

Acute Toxicity Assessment of Centella asiatica and Bidens pilosa Aqueous Crude Leaf Extracts in Pregnant Rat Model

2024-06-30T20:50:15+00:00

There is little information on the safety of using traditional medicines during pregnancy. The current study assessed the safety of aqueous crude leaf extracts from two medicinal plants; Centella asiatica L. and Bidens pilosa L. in pregnant rats. Acute toxicity was evaluated by administering a single dose of plant extracts to pregnant rats at three standard doses of 1000, 2000 and 5000 mg/kg for 14 days. Distilled water was used as a negative control. Physiological and behavioural responses were assessed at 30 minutes, 1 hour, 4 hours, 12 hours and every other day until gestation day 22. The pregnant rats were humanely sacrificed at term after anaesthesia using CO₂. Blood was collected for haematological analysis and tissues (liver, kidney and gravid uterus) were for histopathological examination. The findings showed that the plants extracts are non-toxic at low studied dose of 1000 mg/kg when taken only once. However, C. asiatica and B. pilosa aqueous crude leaf extracts at higher doses (5000 mg/kg) caused a significant increase (p < 0.05) of platelets, and biochemical parameters, Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) resulting in severe histopathological effects to the liver, kidney and gravid uterus. These findings provide baseline data on the safety of studied plant crude leaf extracts and exposure time to pregnant rats, as well as indications for future preclinical and clinical studies on the formulation of the plant extracts. Furthermore, the results give insights to the current users of the plant extracts to avoid their maximum consumption during pregnancy.

Effects of Urea Fertilizer on Yield and Water Productivity of Amaranthus viridis in the Tropical Rainforest and the Derived Savanna of Nigeria

2024-07-02T03:39:28+00:00

The experiment was conducted using a lysimeter in June, 2014 in Saki (Derived Savanna) and Ile-Ife (Tropical Rainforest) to determine the crop coefficients and the effects of Urea fertilizer on the yield and water productivity of Amaranthus viridis in Nigeria. The loamy sandy soil in the top 15 cm was sampled, air-dried and analysed. Eighteen (18) kg of the air-dried and sieved soils were weighed into the thirty-two (32) lysimeters. Drill method was used for the sowing and the seeds were spread within 2 cm in the lysimeter. Urea fertilizer was applied at 0, 40, 80 and 160 kg N/ha twice during the growing season. The crop coefficients at the initial, mid, and late stages ranged from 0.15 to 0.41 in Ile-Ife, while in Saki, they ranged from 0.29 to 1.15 under Urea fertilizer. In Saki, the peak crop evapotranspiration was 1.21 mm/day for 0 kg N/ha of Urea while in the Ile-Ife, the crop evapotranspiration was 1.83 mm/day for 160 Kg N/ha of Urea. Water productivity in Saki and Ile-Ife were 45.47 kg/ha mm and 18.58 kg/ha mm respectively for 160 kg N/ha. This implies that Amaranthus viridis required more water during canopy expansion and flowering in Ile-Ife than in Saki.

Assessment of Bottled Drinking Water Quality, Safety and Community Perceptions in Dodoma City, Tanzania

2024-07-02T04:19:09+00:00

The popularity of bottled drinking water stems from its convenience and purity, driving its rapid growth, but concerns about safety and quality persist. Physicochemical and microbiological parameters of bottled drinking in Dodoma City were evaluated from September to December 2023. Additionally, key informant interviews and questionnaire surveys were conducted with government regulators, producers, and consumers on regulatory frameworks, production processes, and consumer perceptions. Overall, all brands tested were suitable for drinking and met World Health Organization and Tanzania Bureau of Standards guidelines. The total dissolved solids (F = 0.86, p < 0.05), calcium (F = 5.26, p < 0.05) and chloride (F = 0.32, p < 0.05) were significantly different, while other parameters were not (p > 0.05) between measured and labelled values. The total viable and coliform counts in two brands (10%) of water were higher than the suggested levels of 100 cfu/ml and 0 cfu/ml, respectively. Bottling companies reported observance of quality control measures (93%), adherence to regulations (91%), transparency in production processes (86%), and consumer awareness of labels, expiration dates, and trust in the bottled water industry (95%). Public awareness, inspection, and testing of bottled water, as well as strengthening the existing framework, are recommended.

Prevalent Chronic Infections Modulate T-Cell Phenotypes and Functions Enhancing HIV Susceptibility, Dissemination, and Persistence in African Population

2024-07-02T07:27:07+00:00

While many studies have associated HIV prevalence with socio-economic status, few have explored the host's immunity status prior to HIV infection. High HIV prevalence in Africa may in part be contributed by a high prevalence of other persistent infections that modulate the host immunity towards phenotypes that promote HIV acquisition. In this narrative review, we examined how four most prevalent pathogens in Africa (human papillomavirus, herpesviruses, Mycobacterium tuberculosis, and helminth infections) modulate immunity to favor their survival and in turn, also influence HIV acquisition. We have described how these pathogens expand the number of memory and activated T cells, increase the expression of HIV entry receptors leading to an increased HIV susceptibility, and show how these pathogens' immunoevasive strategies may favor HIV persistence. A better understanding of the association between immunomodulation caused by other prevalent infections and HIV/AIDS prevalence may improve HIV/AIDS preventive strategies in Africa. We suggest intensifying efforts to control these chronic infections by making drugs or vaccines available in endemic regions. This may act as another indirect strategy to complement current HIV/AIDS interventions in Africa. We also call for more research to understand better the relationship between immunomodulation by other prevalent infections and HIV incidence.