Assessment of solar and wind energy resources in Ethiopia. I. Solar energy

This paper describes how data from a variety of sources are merged to present new countrywide maps of the solar energy distribution over Ethiopia. The spatial coverage of stations with radiation data was found to be unsatisfactory for the purpose of a countrywide solar energy assessment exercise. Therefore, radiation had to be predicted from sunshine hours by employing empirical models. Using data from seven stations in Ethiopia, linear and quadratic correlation relationships between monthly mean daily solar radiation and sunshine hours per day have been developed. These regional models show a distinct improvement over previously employed countrywide models. To produce a national solar-energy distribution profile, a spatial extension of the radiation/sunshine relationships had to be carried out. To do this, the intercepts (a) and slopes (b) of each of the seven linear regression equations and another six from previous studies, completed in neighbouring Sudan, Kenya and Yemen, were used to interpolate the corresponding values to areas between them. Subsequent to these procedures, 142 stations providing only sunshine data were assigned their “appropriate” a and b values to estimate the amount of solar radiation received, which was then used to produce annual and monthly solar radiation distribution maps for Ethiopia. The results show that in all regions solar energy is an abundant resource.     

Activated extraction of coal using a hydrogen-donor solvent

The kinetics of the extraction of a high-volatile bituminous coal with 1,2,3,4-tetrahydronaphthalene (tetralin) under the influence of ultrasonic energy has been studied at five temperatures: from 47 to 87°C. The effects of intensity of ultrasonic energy, particle size, and hydrogen content of the coal were also recorded. Analysis of the results showed that a second-order reaction followed by a first-order reaction best describes the kinetics of the extraction process. The enthalpies of the second-order and first-order regions were respectively 8.7 and 2.5 kcal/mol, suggesting essentially physical control. The entropies were respectively ?44 and ?70 e.u. Auxiliary experiments and the kinetic data obtained suggest a model for the extraction process. The mechanism of the overall reaction is undoubtedly complex, but the data indicate that van der Waals and hydrogen-bonding forces are most affected by the ultrasonic energy, although stronger bonding is also affected giving much higher yields than would be expected. From the yields obtained in this study it is concluded that ultrasonic energy acts by rupturing bonds that are not affected by the solvent alone; the bonds affected are either strong hydrogen bonds or aliphatic covalent bonds, but not aromatic bonds.     

Genes Involved in the Endoplasmic Reticulum N-Glycosylation Pathway of the Red Microalga Porphyridium sp.: A Bioinformatic Study

N-glycosylation is one of the most important post-translational modifications that influence protein polymorphism, including protein structures and their functions. Although this important biological process has been extensively studied in mammals, only limited knowledge exists regarding glycosylation in algae. The current research is focused on the red microalga Porphyridium sp., which is a potentially valuable source for various applications, such as skin therapy, food, and pharmaceuticals. The enzymes involved in the biosynthesis and processing of N-glycans remain undefined in this species, and the mechanism(s) of their genetic regulation is completely unknown. In this study, we describe our pioneering attempt to understand the endoplasmic reticulum N-Glycosylation pathway in Porphyridium sp., using a bioinformatic approach. Homology searches, based on sequence similarities with genes encoding proteins involved in the ER N-glycosylation pathway (including their conserved parts) were conducted using the TBLASTN function on the algae DNA scaffold contigs database. This approach led to the identification of 24 encoded-genes implicated with the ER N-glycosylation pathway in Porphyridium sp. Homologs were found for almost all known N-glycosylation protein sequences in the ER pathway of Porphyridium sp.; thus, suggesting that the ER-pathway is conserved; as it is in other organisms (animals, plants, yeasts, etc.).     

Power generation scenarios for Nigeria: An environmental and cost assessment

Exploratory scenarios for the power sector in Nigeria are analysed in this paper using possible pathways within the Nigerian context and then compared against the Government's power expansion plan in the short to medium term. They include two fossil-fuel (FF and CCGT) and two sustainable-development-driven scenarios (SD1 and SD2). The results from the FF scenarios indicate this is the preferred outcome if the aim is to expand electricity access at the lowest capital costs. However, the annual costs and environmental impacts increase significantly as a consequence. The SD1 scenario, characterised by increased penetration of renewables, leads to a reduction of a wide range of environmental impacts while increasing the annual costs slightly. The SD2 scenario, also with an increased share of renewables, is preferred if the aim is to reduce GHG emissions; however, this comes at an increased annual cost. Both the SD1 and SD2 scenarios also show significant increases in the capital investment compared to the Government's plans. These results can be used to help inform future policy in the Nigerian electricity sector by showing explicitly the range of possible trade-offs between environmental impacts and economic costs both in the short and long terms.     

Selection of a pull production control system in multi-stage production processes

In this paper, we conduct an analytical comparison of three pull production control systems: Kanban, CONWIP and Base-stock in multi-stage production processes. First, we compare the three control systems in a multi-stage serial production process. Then, we compare them in multi-stage assembly production processes, and present guidelines that allow us to select the best system. As a result, we show which structural parameters decide the superiority of one control scheme to the others, and how they are related. A key for superiority is a configuration of parameters, such as processing times and number of cards employed in the system. We show that there is no general superiority amongst the analysed concepts. Finally, we verify the effect of variability on the system performance, and generalise the analytical results of deterministic cases by conducting numerical experiments.     

MHD flow of a micropolar fluid towards a vertical permeable plate with prescribed surface heat flux

The problem of a steady mixed convection stagnation point flow towards a permeable vertical plate with prescribed surface heat flux immersed in an incompressible micropolar fluid is studied numerically. The governing partial differential equations are first transformed into a system of ordinary differential equations using a similarity transformation, before being solved numerically by a finite-difference scheme known as the Keller-box method and the Runge–Kutta–Fehlberg method with shooting technique. The effects of the material parameter, buoyancy parameter, suction/injection parameter and the Prandtl number on the fluid flow and heat transfer characteristics are discussed. It is found that dual solutions exist for both assisting and opposing flows. The skin friction coefficient and the local Nusselt number increase in the presence of suction and magnetic field. Moreover, suction as well as fluids with larger Prandtl number widens the range of the buoyancy parameter for which the solution exists.     

Evaluating the economics of biodiesel in Africa

Road transport in Sub-Saharan Africa is expected to rise in the coming years. Paradoxically, this expansion is occurring at a time when oil prices have reached new heights. Unstable oil prices do indeed increase the vulnerability of importers. However, it also presents them with a unique opportunity to explore promising technical options to help reduce their over-reliance on imported petroleum fuels. This paper takes a closer look at the potential for biodiesel, with an emphasis on fuels produced from oil palm, castor oil and jatropha in Ghana, Kenya and Tanzania, respectively. The paper provides an economic appraisal of biodiesels from these feedstocks, and sets the context for further discussions on biofuels in Africa.     

Power sector scenarios for Thailand: An exploratory analysis 2002–2022

Power sector scenarios for Thailand are constructed in this paper to represent the range of opportunities and constraints associated with divergent set of technical and policy options. They include Business-As-Usual (BAU), No-New-Coal (NNC), and Green Futures (GF) scenarios over a 20-year period (2002–2022). The results from the BAU scenario show that fossil fuels will continue to dominate electricity generation in Thailand during the study period. Similar results are obtained for the NNC option, although the dependence shifts from coal and oil towards natural gas-based power generation. This may represent a better environmental pathway but an all out shift from coal to natural gas is likely to increase Thailand's dependence on imported fuel, making it more vulnerable to unstable global oil and gas prices. The GF scenario offers a more optimistic route that allows the country to confront its energy security dilemma whilst fulfilling its environmental commitments by giving renewable energy technologies a prominent place in the country's power generation mix. Over the study period, our result showed little difference between the three scenarios in terms of financing new generation plants despite an early misgiving about the viability of an ambitious renewable energy programme. This paper also goes beyond the financial evaluation of each scenario to provide a comparison of the scenarios in terms of their greenhouse gas emissions together with the comparative costs of emissions reductions. Indeed, if such externalities are taken into account to determine ‘viability’, the GF scenario represents an attractive way forward for the Thai power sector.     

Deliberating on low carbon development

Low carbon development (LCD) is a much used word in development circles today. As such, governments are actively exploring how to achieve their growth targets through a low carbon trajectory or even through a ‘carbon neutral’ pathway. This is a new area that challenges how development has been done so far, calling for not only a serious rethink of old practices but also contesting entrenched value systems. In this viewpoint, we explore some of the underlying issues that are driving the process of mainstreaming climate change in development. Recognising that there are variations in LCD, we map out the diversity of understandings and interpretations with a view to lay out the range of possibilities that countries can consider. We argue that whilst countries should certainly draw lessons from the experiences of others on mainstreaming climate change in their policies and practices, the version of LCD that each country follows needs to emerge from within its own national reality, anchored in its development prospects, aspirations and capacities.