African
Journals On-line
Botswana Journal of Technology
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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