Agricultural-based commodity chains and development: the case of the tobacco sector in Zimbabwe

This thesis examines the nature of governance in the Zimbabwean tobacco value chain and what upgrading implications this has for participants at the lower end of the value chain, with a particular focus on smallholder tobacco growers. The nature of governance and upgrading opportunities will provide further implications for broader economic development in Zimbabwe. Value chain analysis was the over-arching method, adopting a mixed methods approach of both quantitative and qualitative data analysis. Data attained from the Tobacco and Industry Marketing Board (TIMB) was used to construct a Zimbabwean tobacco profile. This information was used to construct a simple Global Value Chain (GVC) framework in order to obtain an understanding of the Zimbabwean tobacco value chain. Information was gathered at the top end of the value chain via documents and data from British American Tobacco (BAT) and information was gathered at the middle and lower end of the value chain through interviews. It was found that the Zimbabwean tobacco value chain is characterised by two types of governance: modular and hierarchy. Modular governance existed where the value chain was disjointed by the leaf merchant and hierarchy governance existed where cigarette manufacturers have vertically integrated themselves backwards into the tobacco growing segment. It was found that contract lines offer smallholder tobacco growers’ financial and technical support that would otherwise be difficult to attain. This increased the likelihood for smallholder tobacco growers to produce a high quality crop that met Good Agricultural Practices (GAP) and other compliancy requirements; therefore achieving product and process upgrading. However, the environmental impact of tobacco growing through deforestation and the possibility of lead cigarette manufacturers relocating their operations to a different geographical location (as is the nature of GVCs) threatens the sustainability of Zimbabwe’s tobacco industry. Despite these issues it was argued that the tobacco value chain could assist Zimbabwe’s economy in diversifying away from simple tobacco production towards valueadding tobacco sectors, such as processing, by-product processing and cigarette manufacturing

Plasma simulation using the massively parallel processor

Two dimensional electrostatic simulation codes using the particle-in-cell model are developed on the Massively Parallel Processor (MPP). The conventional plasma simulation procedure that computes electric fields at particle positions by means of a gridded system is found inefficient on the MPP. The MPP simulation code is thus based on the gridless system in which particles are assigned to processing elements and electric fields are computed directly via Discrete Fourier Transform. Currently, the gridless model on the MPP in two dimensions is about nine times slower that the gridded system on the CRAY X-MP without considering I/O time. However, the gridless system on the MPP can be improved by incorporating a faster I/O between the staging memory and Array Unit and a more efficient procedure for taking floating point sums over processing elements. The initial results suggest that the parallel processors have the potential for performing large scale plasma simulations

Enhanced Surface Defect Detection Using Focused Electromagnetic Acoustic Transducers (EMATs)

Electromagnetic Acoustic Transducers (EMATs) are non-contact ultrasound transducers which function primarily via Lorentz force induction. Their non-contact nature allows for fast scanning, inspection of challenging surfaces, and performance in harsh environments. To meet industry demand, non-destructive evaluation (NDE) techniques need increasingly high resolution for the detection of smaller defects. For surface acoustic wave inspection of surface-breaking defects, using a higher frequency wave gives better depth resolution. However, the EMAT coil width has to decrease to increase the frequency, leading to a trade off with the signal strength. The use of geometric focusing is showing promise for increasing ultrasound strength and defect imaging precision, overcoming some of the issues associated with the use of higher frequency surface acoustic waves. Understanding and optimising transducer design is essential to obtain optimal signal strength, high frequency operation, and the ability to operate at stand-off from the sample. In this work multiple focused and unfocused EMAT coil configurations are presented. Focusing is seen to give significantly enhanced resolution for defects, with accurate detection of thin cracks, 0.2 wide, 2 mm length, 1.5 mm depth. The relationship between coil design and stand-off is investigated. Multiple phased coils are proposed to increase signal strength without lowering the frequency

A comparison of evaporative and liquid cooling methods for fuel cell vehicles

Despite having efficiencies higher than internal combustion engines, heat rejection from fuel cells remains challenging due to lower operating temperatures and reduced exhaust heat flow. This work details a full system simulation which is then used to compare a conventional liquid cooled fuel cell system to two types of evaporatively cooled fuel cell systems. Both steady state and transient operation are considered. Results show the radiator frontal area required to achieve thermal and water balance for an evaporatively cooled system with an aluminium condensing radiator is 27% less than a conventional liquid cooled system at 1.25 A/cm2 steady state operation. The primary reason for the reduction is higher heat transfer coefficients in the condensing radiator due to phase change. It is also shown that the liquid water separation efficiency has a significant influence on the required radiator frontal area of the evaporatively cooled system

Antimicrobial activities of four plant species from the Southern Overberg region of South Africa

Four plant species used for medicinal purposes in the Bredasdorp/Elim (Southern Overberg) region of the Western Cape Province in South Africa, were screened for their antimicrobial activity. Theantimicrobial activity of aqueous, methanol, ethanol and ethyl-acetate leaf extracts of Bulbine lagopus (Asphodelaceae), Chironia baccifera (Gentianaceae), Conyza scabrida (Asteraceae) and Dodonaeaviscosa var. angustifolia (Sapindaceae), were tested against Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Mycobacterium smegmatis. In the disc-diffusion assay, 20 out of the 80 extracts showed activity. Better activity was observed in the liquid dilution assay with all extracts showing a degree of activity. The best activity was observed in the ethanol extract of B. lagopus and themethanol extract of C. scabrida both having an MIC value of 0.3125 mg/ml. In the bioautography, M. smegmatis was chosen as the test organism along with the ethanol, ethyl-acetate and methanolextracts of C. scabrida and D. viscosa var. angustifolia. All six extracts showed at least two zones of inhibition on the TLC plates overlaid with M. smegmatis

Focused Rayleigh wave EMAT for characterisation of surface-breaking defects

Developments towards higher resolution and the ability to detect small defects are bringing a step-change in non-destructive testing. This paper presents a new method for increasing resolution, using a focused electromagnetic acoustic transducer (EMAT) optimised to generate Rayleigh waves at 2 MHz. This high frequency allows detection of mm-depth defects, and the focusing allows sizing of much shorter defects than is possible when using standard EMATs. The focusing behaviour and the aperture angle effect are analysed using laser vibrometry and finite element modelling, showing that a reduced aperture shifts the focal point from the designed value and increases the focal depth. The dual-EMAT has excellent signal to noise ratio (up to 30 dB) and has been used in single shot mode to image a variety of surface-breaking defects, including detecting and positioning a pair of real defects in an aluminium billet sample, and a machined defect of 2 mm length, 0.2 mm width, and 1.5 mm depth, giving an upper limit on the defect length of 2.1 plus or minus 0.5 mm. The results can be used to design an EMAT with optimised focal behaviour for defect detection

Analysis of a 50 kWe indirect methanol proton exchange membrane fuel cell (PEMFC) system for transportation application

Steady state and dynamic models of proton exchange membrane fuel cell (PEMFC) or solid polymer fuel cell (SPFC) systems have been developed for transport and stationary applications. This paper reports the results of a steady state analysis of a methanol-fuelled PEMFC vehicle with a maximum (electrical) power output of 50 kW. The model incorporates a methanol steam reformer, gas clean-up unit, fuel cell stack, compressor, expander, battery pack, and heat exchangers as well as electrical power handling, motor, gearbox, and final drive. Results are given for the reformer as a function of steam–carbon ratio and reformer temperature. A degree of optimization of the system was conducted by (a) the addition of preheat to the reformer and burner reactants and (b) the addition of condensers for the fuel cell exhaust gases. The effect of operating pressure was also investigated. It was concluded that only by proper thermal integration could the target electrical system efficiency of better than 45 per cent at rated power be achieved

A comparison of evaporative and liquid cooling methods for fuel cell vehicles

Despite having efficiencies higher than internal combustion engines, heat rejection from fuel cells remains challenging due to lower operating temperatures and reduced exhaust heat flow. This work details a full system simulation which is then used to compare a conventional liquid cooled fuel cell system to two types of evaporatively cooled fuel cell systems. Both steady state and transient operation are considered. Results show the radiator frontal area required to achieve thermal and water balance for an evaporatively cooled system with an aluminium condensing radiator is 27% less than a conventional liquid cooled system at 1.25 A/cm2 steady state operation. The primary reason for the reduction is higher heat transfer coefficients in the condensing radiator due to phase change. It is also shown that the liquid water separation efficiency has a significant influence on the required radiator frontal area of the evaporatively cooled system

An electric vehicle model and validation using a Nissan Leaf: a Python-based object-oriented programming approach

Electric vehicles are becoming more and more prevalent, especially with major manufacturers announcing that they will be focusing on electric or hybrid vehicles in the future. This article describes an object-oriented approach to a vehicle model using Python 3. This approach allows for flexibility of vehicle design. The key parameters were input to define the specific vehicle for validation, in this case a Nissan Leaf. It is anticipated that this flexibility will lead to rapid exploratory design of vehicle variants, such as four-wheel drive, independent wheel drive and multiple electrical sources. The model had its objects individually validated before the whole vehicle was verified against common drive cycles and a real-world drive in the United Kingdom recorded using an On-board Diagnostics (OBD2) Bluetooth dongle

Energy economy analysis of the G-Wiz: a two-year case study based on two vehicles

This paper presents the data recorded from two G-Wiz Reva electric vehicles (EVs) over a period of two years and approximately 8000km on each vehicle. The analysis of the vehicle data demonstrates that the range of the vehicle obtained for a certain state-of-charge (SOC) drop was not consistent. The results show that the main factor affecting the available range was irregular vehicle usage. The recharge energy consumption patterns of the vehicle were identified and it was demonstrated that infrequent vehicle usage increased energy consumed by the vehicle. A maximum range of 66.8km was achieved when the vehicle was regularly used, but this fell to 42.8km when it was infrequently used. The energy economy when the vehicle was regularly used was 8.3 km/kWh. Additionally, the analysis results identify the need to determine discharge rate of the vehicle batteries to determine the precise effects on the available range and energy consumption of the vehicle