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Botswana Journal of Technology

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Volume12, No.2, October 2003
ABSTRACTS

 

Pyroelectric ferroelectric and resistivity studies on samarium modified barium strontium sodium niobate ceramics

K.Sambasiva Rao, T.N.V.K.V.Prasad, N.Vallisnath and V.R.K.Murthy

Barium Strontium Sodium Niobate (Ba1-xSrx)2NaNb5O15 (BSNN) belongs to tungsten bronze ferroelectric morphotrophic phase boundary (MPB) system at x = 0.6, having  large spontaneous polarisation, pyroelectric coefficient and low dielectic constant and is expected to be applicable for piezoceramic filter and pyroelectic devices. Present communication illustrates preparative conditions and the influence of Sm2O3 on structure, ferroelectric, dielectric, pyroelectric and resistivity properties at and around MPB. Substitution of Sm2O3 decreased the cell volume and Curie temperature and enhance the room temperature dielectric constant. The pyroelectric coefficient at room temperature has been observed to be in the order of 10-9 C/cm2 0C.  The figure of merits FMRV, FMRN and FMRIhave been observed to be higher values of the order 10-14 CM/J, 10-12 CM/J, 10-11 CM/J, respectively on both pure and Sm: BSNN compositions. Resistivity studies indicated a PTCR response in the compositions.

 

 

Design and construction of variable direct current speed drive

H. M. Talukder, A. V. Gholap and P. Rugube

A direct current variable speed drive is designed and constructed using silicon-controlled rectifiers from the viewpoint of simplicity and cost effectiveness to act as power converter and controller. Design and construction of constituent circuits such as acceleration/deceleration, speed and current amplifier and the trigger circuit are presented together with their corresponding input and output waveforms.

 

 

Meson spectra: power law potential model in the dirac equation

L.K. Sharma  and J.O. Fiase

A single mass-spectra potential model has been used to predict the spectra of both light and heavy mesons (including leptonic decay-widths) in the Dirac equation.  In fact a power law potential has been proposed with effective power

where  is the mass of the constituent quarks (in GeV) of the mesons considered. The parameter  is chosen so as to make  dimensionless and this is accomplished by setting  = 1 GeV. Our results for both light and heavy mesons are in reasonably good agreement with the experimental results as well as with that of other authors.  The same model has also been applied to predict the mass-spectra for the toponium  system for which the experimental data is not yet available. It will therefore be interesting to watch the experimental evolution of this system to test the ideas developed in this paper regarding this meson structure.

 

Finite difference study of mhd stokes problem for a vertical infinite plate in a dissipative heat generating fluid with hall and ionslip currents

N. Chaturvedi

The explicit finite difference method is employed to study the effects of both the Hall and ionslip currents on a free convective flow of a viscous heat generating rotating fluid past an impulsively started infinite vertical plate, to which a strong magnetic field is applied perpendicularly.  The velocity (both primary and secondary) and temperature profiles are represented graphically and the results discussed in terms of the non-dimensional parameters m (Hall parameter),  (ionslip parameter), (heat source parameter), Gr(Grashof number), Er(the rotational paramenter) and Ec (the Eckert number).

 

 

A neuro-linguistic model for speech recognition in tone languages

O.A Odejobiand F. J Ogwu

The primary aim for this work is to develop a speech recognition system that exploits the computational paradigm with learning ability and the inherent robustness and parallelism in ANN coupled with the capability of fuzzy logic to model vagueness, handling uncertainness and support for human reasoning. This research made two unique contributions to the area of speech recognition. Firstly, we identified and specify entities in the speech recognition process using a neuro-linguistic approach.  This approach not only offers a non-conflict degree for different speech recognition situation, it also provide stable integration mechanism for various level of speech unit. Secondly, this work is the first to illustrate speech recognition model using an African language, in this case Yoruba language. It is important, however, to note that this approach can also be used for any tone language and with little modification for all languages as well.

 

 

On the scattering properties of urban and maritime aerosols and its humidity dependence

T. S. Verma and J. Prakash

The scattering properties of aerosols play a dominant role in radiative energy transfer and consequently influencing the visibility and turbidity in the atmosphere. In the present attempt, calculations for scattered intensity have been made in case of urban and maritime aerosols in the varying conditions of relative humidity. These theoretical findings suggest that asymmetry factor increases, in general, with an increase of relative humidity beyond 60 to 70% of RH for small particles, and with increase of aerosol size.

 

 

Deterrents on the over utilisation of stand alone photovoltaic (pv) systems: A case of the Botswana National Photovoltaic Rural Electrification Programme (NPVREP)

Ezekiel M. Chimbombi

The NPVREP is a national programme funded by the government of Botswana, through the Ministry of Minerals, Energy and Water Affairs with the overall goal of providing photovoltaic energy to rural households and institutions at affordable financial terms. The programme is implemented by Rural Industries Promotions Company, Botswana, through its operational arm, Rural Industries Innovation Centre (RIIC). At inception of the programme, systems were either undersized, or over utilised as clients did not reveal their usage needs in an attempt to reduce costs. This resulted in battery failures and other system breakdowns. The NPVREP categorised systems in order to alleviate the problem of under sizing and/or over utilization of systems. Categorised systems are pre-sized and users have to determine a category into which their needs fall. Statistical analysis at 5 % level of confidence show that the actual sizings of module array and battery bank are significantly different from the categorised system sizes for both the module array and the battery bank.

 

 

Behaviour and modelling of semi-rigid structural frame systems

M. A. Gizejowski, J. A. Karczewski, E. Postek, W. Sotomski, S. Wierzbickiand J. Witkowski

A computational finite element model is developed to predict the load-deflection characteristic of portal frames with semi-rigid welded and bolted joints. Plate components of frame members and joints are modelled by thin shell finite elements while bolt connectors by springs with the force-deformation characteristic evaluated from test results. The computer software ABAQUS is used. Experimental investigations were designed in order to evaluate frame load-deflection characteristics, joint local rotations, failure modes, and the contribution of end-plates and bolt connectors to the joint rotations. Theoretical results of frame load-deflection characteristics predicted with use of ABAQUS program are compared with the experimental results. The modelling of friction effect between the contact surfaces of bolted joints is verified to be the most important factor. The comparative analysis leads to the conclusion that the proposed advanced shell model can be very useful in the verification of simplified models being developed for practical applications.

 

 

The extent of variability of rates of building items in Botswana

J.K. Ssegawa and E. Motsipa

For any competitive tender for a construction project, the tender sums submitted by contractors are bound to vary considerably. Part of the reason for variation is the differences in rates of building items that make up the tender sum of entire project. The extent to which the rates vary and reasons for the variation constitute very important pieces of information for stakeholders of the construction industry, for example, contractors would know how far they could raise their rates without fear of failing to secure a contract or lower their rates without incurring a future loss.  Similarly, clients would be in a better position to evaluate the tender bids. This paper reports findings of a study carried out to investigate the variability of rates of common building items used in public building projects in Botswana. The paper concludes that tiling and glazing were found to have the highest rate of variability, while reinforcement and masonry had the lowest price variability

  

 

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