Hauptfleisch M.L.,Polytechnic of Namibia |
Avenant N.L.,University of the Free State
Integrative Zoology | Year: 2015
Understanding ecosystems within and around airports can help to determine the causes and possible mitigation measures for collisions between aircraft and wildlife. Small mammal communities are an important component of the semi-arid savanna ecosystems of Namibia, its productivity and its ecosystem integrity. They are also a major direct attractant for raptors at airports. The present study compared the abundance and diversity of small mammals between Namibia's 2 main airport properties (Hosea Kutako International Airport and Eros Airport), and among areas of land used for various purposes surrounding the airports. A total of 2150 small mammals (3 orders, 11 species) were captured over 4 trapping seasons. Small mammal abundance was significantly higher at the end of the growing season than during the non-growing season. The grass mowing regimen in current management plans at the airports resulted in a significant reduction of small mammal abundance at Hosea Kutako during the non-growing season only, thus indicating that annual mowing is effective but insufficient to reduce the overall abundance of mammal prey species for raptors. Small mammal numbers were significantly higher at Hosea Kutako Airport compared to the cattle and game farming land surrounding the airport, while no differences in small mammal densities or diversity were found for areas with different land uses at and surrounding Eros. The study suggests that the fence around Hosea Kutako provides a refuge for small mammals, resulting in higher densities. It also indicates that different surrounding land use practices result in altered ecosystem function and productivity, an important consideration when identifying wildlife attractants at airports. © 2015 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and Wiley Publishing Asia Pty Ltd.
Joubert D.F.,Polytechnic of Namibia |
Smit G.N.,University of the Free State |
Hoffman M.T.,University of Cape Town
Journal of Arid Environments | Year: 2013
Seed production and seedling survival are under-researched in savannas. We investigated these in a population of a major thickening species, Acacia mellifera, in an arid Namibian savanna over a nine year period (late 1998-early 2007) We asked the following questions: (i) How does viable seed production vary with rainfall and tree size, (ii) when does seed germination occur, (iii) is the seed bank of A. mellifera persistent, and (iv) how do competitive interactions with established trees influence recruitment of A. mellifera seedlings? Seed production was highly correlated with annual rainfall. In dry years, there was no viable seed production. En masse seed production only occurred in exceptionally high rainfall years, and was strongly correlated with size among trees >2 m tall. Seed predation was low. Seedlings only emerged directly after en masse seed production, suggesting ephemeral seed banks. Three times more seedlings emerged per m2, but seedling survival was five times less, under trees than away from trees, indicating strong competition for water with established trees. Seed production is a recruitment bottleneck in this species. Recruitment requires at least two consecutive seasons of favourable rainfall, and is highly episodic in arid savannas. © 2012 Elsevier Ltd.
Nggada S.H.,Polytechnic of Namibia
International Journal of Control and Automation | Year: 2014
The improvement of system reliability can be achieved by improving the reliabilities of its constituent components. This could be done through maintenance actions that are performed on the components. There are two extreme states in which a component could assume following a maintenance stage; bad-as-old (BAO) or good-as-new (GAN). For some components of the system, the maintenance actions may bring them to an in-between state. This in-between state is achieved under the assumptions of imperfect maintenance. This paper investigates the improvement in reliability of a component and system in the in-between state through imperfect preventive maintenance policy. Thus, it establishes a mathematical model for component reliability evaluation under assumptions of imperfect preventive maintenance. © 2014 SERSC.
John S.,Polytechnic of Namibia |
Pedro J.O.,University of Witwatersrand
International Journal of Artificial Intelligence | Year: 2013
Safety systems in road vehicles are categorised into two main types: passive and active systems. The antilock braking system (ABS) is an active safety system in road vehicles, which senses the slip value between the tyre and the road and uses these values to determine the optimum braking force. Due to the high non-linearity of the tyre and road interaction, and uncertainties from vehicle dynamics, standard control methods: like PID, sliding mode control and feedback linearization will not suffice. This paper, therefore proposes a neural network-based feedback linearization control design method. The experimental results reveal that slip regulation using neural network-based control scheme is feasible for different slip values (road conditions) and robust to external disturbances. © 2013 by IJAI (CESER Publications).
Iyamu T.,Polytechnic of Namibia
Journal of Systems and Information Technology | Year: 2013
Purpose: The paper was intended to demonstrate the use and order of a combined lenses of two theories in IS research. It helps to understand how theories could be adopted in the order of methodological value. The way data are collected, organised and analysed is influenced and shaped by the order of use of the underpinning theories. The importance of the order is to create consistency, predictability, and uniformity of analysis, which have impact on the findings. Design/methodology/approach: Review of literature, and teaching and supervision experiences were used in the approach. Findings: The result of a combined use of both ST and ANT in the same study has been less than expected. The application of theories helps exhume findings. This makes the order-of-use of application of the theories significant. Some studies applied ST before ANT, and vice versa. There has never been a model or framework which defines the order-of-use of the theories. It could be argued that it depend on the nature and objectives of the study. This paper focuses on order-of-use of combined theories in information systems studies. No organisation has total power to determine what the choice(s) of an actor will be in a particular situation. Actor and structure by virtue of their interaction recursively produces and reproduces, on the one hand and on another, the actor and structure enable and at the same time there are constraints. Originality/value: Both theories can be used as a way of thinking and speaking about the phenomena being studied and also, as a "lens" through which the data is viewed and interpreted. © Emerald Group Publishing Limited.