African
Journals Online
Tanzania Journal of Science
Volume
28, Number 1, June 2002
Abstracts
A simple method for indexing powder
diffraction patterns of cubic materials:(1) using the θ-values of reference
ME Kamwaya
Department of Chemistry, University of Dar
es Salaam, P O Box 35061, Dar es Salaam, Tanzania
ABSTRACT:
From the values of sin2θ taken from powder photographs of the cubic crystal system, a
variable constant, K, which is a multiple of (h2 + k2
+ l2) can be determined. The smallest value of sin2θ1 gives rise to a multiple of one, two, or three which corresponds
to the smallest value of Σhl2 for the
primitive, bcc and fcc crystals, respectively. The old assumption that
when indexing, the occurrence of numbers of the form (h2 +
k2 + l2) = 8n + 7, where n = 0.1.2.3… should
cause each of (h2 + k2 + l2) to be
multiplied first by two before indexing, is disapproved.
Optimization of EDXRF for the study of
heavy metal pollution of Lake Victoria
NK Mahommed and IN Makundi
Department of Physics, University of Dar
es Salaam, P O Box 35063, Dar es Salaam, Tanzania
ABSTRACT:
This study reports on the optimisation and
calibration of the Energy Dispersive X-ray Fluorescence (EDXRF)
spectrometer installed in the Department of Physics, University of Dar
es Salaam. The spectrometer was subsequently utilized to determine
concentrations of heavy metals in water hyacinth (Eichhornia
crassipes (Mart) Solms.) found growing along the shore of
Lake Victoria. The optimal conditions and detection limits were
determined experimentally by variation of the excitation parameters.
The study found that the use of a collimator with two apertures of
diameter 4 mm each placed 8 mm apart and made of materials that do not
interfere with elements to be determined from the samples, gave lowest
detection limits. The optimal pairing of voltage and current was found
to be 40 kV and 30 mA while measuring time was 2000 seconds.
Roots of the water hyacinth were used in
experiments to check the validity and sensitivity of the equipment.
The water plants were collected from areas influenced by industrial
and domestic seqage around Mwanza town, namely Mwanza South, Mwanza
Central and Mwanza North. Mwanza North had quite a few industries and
human settlements. The samples were each oven-dried, ground into a
fine powder and pressed into a pellet. Water hyacinth from the
industrial area and those from sewage discharge points were found to
have higher concentrations of heavy metals (K, Ca, Sc, Ti, Mn, Fe, Co,
Ni, Zn and Pb) than those from non polluted area. A more detailed
study, involving more samples, is needed in order to be able to
statistically quantify the differences.
Speciation of cadmium, copper, lead and
zinc in the waters of River Mzimbazi Dar es Salaam, Tanzania
OC Othman
Chemistry Department, University of Dar es Salaam, P O Box
35061, Dar es Salaam, Tanzania
ABSTRACT:
The water of river Mzimbazi and its
attributaries are known to contain heavy metals originating from
industry and the water is used for domestic and vegetable irrigation
purposes. The present study describes chemical forms of some of the
heavy metals found in the water. Water samples from different
locations along river Msimbazi were analysed by Differential Pulse
Anodic Stripping Voltammetry (DPSAV) based on an operational scheme
for the determination of the chemical forms of dissolved copper, lead,
cadmium and zinc. Zinc (82%), cadmium (73%) and copper (93%) were
found to exist mainly as soluble metal ions while lead existed as
moderately soluble ions (<60%). On the average, 40% of the lead was
found complexed to the filterable contents of the water as compared to
only 6.6% of the copper, 17.5% of the zinc and 26.3% of the cadmium.
Thus membrane filtration was able to remove quite a large amount of
pollutants.
The lability of the lead (52.6%) in raw
river water, was lower than that of zinc (61.6%), copper (65.4%) and
cadmium (61%). The lability of the lead (38%) in filtered water, was
also lower than that of zinc (51.9%), copper (63.7%) and cadmium
(48.8%). In raw river water, cadmium had the lowest ASV lability
(42.0%) as compared to zinc (48.4%), copper (50.7%) and lead (47.4%)
whereas in filtered water the ASV lability of lead (29.3%) was the
lowest; those of zinc (37.6%), copper (45.4%) and cadmium (40.8%) were
much higher. A high percent of the labile trace lead (27.8%), cadmium
(20%) and zinc (15.7%) and only 2.6% of the labile copper adhere to
the filterable content of the water thus may be filtered off.
Mobility and immobility of mid-ocean
ridges and their implications to mantle dynamics
ME Kamwaya
Department of Chemistry, University of Dar
es Salaam, P O Box 35061, Dar es Salaam, Tanzania
ABSTRACT:
In
the past two decades, the mobility of mid-ocean ridges relative to the
mantle (absolute migration) have been correlated with major observable
features, such as, spreading asymmetry and asymmetry in the abundance
of seamounts. The mobility of mid-ocean ridges is also thought to be
an important factor that influences the diversity of ridge-crest
basalts. However, the mobility of mid-ocean ridges have not yet been
defined and mapped. The absolute migration of global mid-ocean ridges
since 85 Ma has been computed and mapped. Global mid-ocean ridges have
migrated extensively at varying velocities during that period.
Presently, the fast-migrating ridges are the Pacific-Antarctic ridges,
migrating at velocities between 3.3 and 5.5 cm/yr. The slow-migrating
ridges are the Mid-Atlantic and the southwest Indian ridges migrating
at velocities between 0.3 and 2.0 cm/yr. Comparison of these results
with mantle tomography results shows that the slow-migrating ridges
have deeper depth of origin than the fast-migrating suggesting a
correlation between the absolute migration velocity and the depth of
origin of ridges. Furthermore, the southwest Indian ridge appears to
be tapping the same portion of mantle as did the Central Indian ridge.
These results have important thermo-chemical implications, such as
variations in the extent of melting and mineralogical composition of
the mantle beneath different ridges, which may influence mantle
dynamics.
Comparison of various methods for
estimating wave incident angles in the nearshore zone
AS Ngusaru
Institute of Marine Sciences, University
of Dar es Salaam, P O Box 668, Zanzibar
ABSTRACT:
Five
different methods were examined for their suitability in estimating
the inshore wave incident angles on a nearshore zone with a complex
topography. Visual observation provided preliminary estimates. Two
frequency independent methods and one frequency dependent method based
on current meter measurements were examined. Another frequency
dependent method based on collocated bottom pressure and current meter
measurements was also examined. The results from all the methods
provided a reasonably consistent estimate of the inshore wave incident
angles. The frequency independent methods gave exactly the same
results while the frequency dependent methods had a 5% relative error
among themselves. Between frequency independent and frequency
dependent methods, the relative error was 11%. However, since the
frequency dependent methods involve smoothing of the velocity spectra,
this method was found to be rather subjective. The frequency
independent method based on high passed velocity vectors seems to be
easy to apply and to provide unambiguous estimate of inshore wave
incident angles.
The polarising effects in sintered kaolin
FM D’ujanga, Y Kaahwa
Physics Department, Makerere University, P
O Box 7062, Kampala, Uganda
And
L Atteraas
Department of Physics, University of
Bergen
ABSTRACT:
The
polarizing effects in sintered kaolin samples were analysed in terms
of the sample density (or porosity) using direct current (dc)
techniques. More porous samples exhibited higher polarizing effects
than the less porous ones. The conduction carriers in kaolin samples
at room temperature were found to be mainly electrons, with ionic
conduction being enhanced by the moisture content with the pores. The
influence of the uniaxial pressure and particle-size on the compacted
and sintered density of the ceramic have been studied, and a
density-pressure relationship before- and after-sintering conditions
obtained.
Studies on benthic denitrification in the
Chwaka Bay mangrove sediments, Zanzibar
SM Mahommed1 and RW Johnstone2
1Institute of Marine Sciences, University of Dar es Salaam, P O Box 668,
Zanzibar
2Formerly of Stockholm University, S-106 91 Stockholm, Sweden
ABSTRACT:
Denitrification
was measured at three sites in a narrow tidal creek in the Chwaka
mangrove ecosystem. Denitrification arising from water column nitrate
(Dw) was low (< 0.1μM Nm-2h-1)
and there was little spatial and seasonal variation in Dw
rates in the creek. Coupled nitrification-denitrification (Dn) was
found to be low, but within the range measured in other mangrove
sediments. Average values ranged from 0.01 to 0.45 μM Nm-2h-1
and showed strong spatial variations. The low denitrifcation rates
observed in the creek were possibly as a result of the low
availability of NO3 and high C:N values of the organic
matter in the sediment. Spatial variations in denitrification rates
were due to variations in concentration levels of organic matter and
possibly to disproportionate competition for inorganic nitrogen
between denitrifiers and benthic autotrophs among sites. There were no
seasonal differences in denitrification rates. Results from the
present study suggest that sediment denitrification does not play a
major role as a sink for N in this ecosystem
Interpretation of refelction seismic data
from the Usangu Basin, East African Rift System
EI Mbede
Department of Geology, University of Dar
es Salaam, P O Box 35052, Dar es Salaam, Tanzania
ABSTRACT:
Reflection
seismic data collected by AMOCO Tanzania Oil Company in the 80s, are
herin used to correlate the main Usangu Basin parameters to those
estimated from outcrop, gravity and aeromagnetic data. The seismic
data are further used to constrain the geometry of crustal extension
in this south-western sector of the East African Rift System (EARS) in
Tanzania. Three distinct sedimentary packages on top of the basement
reflector are interpreted and correlated to the Permo-Carboniferous
Karoo rocks, the Jurassic/Cretaceous and Miocene Red Sandstone Group
and Miocene to recent Lake Beds in the adjacent Rukwa basin, where the
ages of the sedimentary sequences have been established on the basis
of drill hole data.
The
Karoo beds, deposited on an undulating weathered basement surface are
relatively thin (~ 200m). The Red Sandstone Group reach a maximum
thickness of up to 420 m while the Lake Beds are up to 289 m thick.
Beneath the Karoo, seismic reflections show interval velocities of
3.22 km/s, which are less than typical crystalline basement velocities
of 4.2 km/s in the adjacent Rukwa Rift. These “sub-basement”
velocities are attributed to the slightly metamorphosed sediments of
Upper Proterozoic, Buanji Group that crop out extensively on top of
the Chimala scarp. Previous estimate of the thicknesses of Buanji
sediments from outcrop data has been up to 1.086 km. The present
study, however, suggests a thickness of more than 2 km for the Buanji
sediments beneath the Mesozoic to recent sediments in the Usangu
Basin. Age wise the Usangu Basin, which has always been considered to
be much younger than its south-western continuation, the Luangwa
valley, is here suggested to be an old structure in which
sedimentation has been going on since Karoo time. Recent faulting
mechanism inferred from recent earthquake data and the present
interpretation of seismic sections suggest that deformation in the
Usangu Basin has been predominantly strike slip. Thus, the Usangu
Basin is best interpreted as a transfer fault, accommodating the
relative movement between the southern-most sub-basin of the Rukwa
Rift and the northernmost sub-basin of the Malawi Rift.
Tectonic setting of gabbroic rocks in the
western part of the Lupa Gold Field, south-west Tanzania
SR Mnali
Department of Geology, University of Dar
es Salaam, P O Box 35053, Dar es Salaam, Tanzania
ABSTRACT:
There
is a pronounced occurrence of gabbroic rocks in the western part of
the Lupa gold field, SW Tanzania. These rocks occur in the peripheral
part around the Saza-Chuya granodiorite with which it makes a
gradiational, unchilled contact. The rocks have been altered or
metamorphosed to low-grade greenschist facies as indicated by the
presence of secondary epidote, penninite, chlorite, sericite and
calcite. The majority of major-element oxides show scattered variation
trends against immobile elements such as Zr, indicating some degree of
element mobility during post-crystallization processes of alteration
or metamorphism. Major-trace-element data show that the gabbroic rocks
in the study area are calc-alkaline. REE patterns show that the rocks
are highly evolved with a high (La/Yb)N ratio of about 30
and (La/Sm)N ratios of between 18-40. The highly evolved
nature of the studied rocks is shown also by low values of magnesium
between 56-62%. The gabbroic rocks in the western part of the Lupa
gold field seem to have been formed in the continental arc setting.
Identification of mushroom mycelia using
DNA techniques
MHS Muruke, AK Kivaisi, FSS Magingo
Applied Microbiology Unit, Department of
Botany, University of Dar es Salaam, P O Box 35060, Dar es Salaam,
Tanzania
And
E Danell
Department of Forest Mycology and
Pathology, Swedish University of Agricultural Sciences (SLU), Uppsala,
Sweden
ABSTRACT:
The
suitability of using DNA techniques in the determination of
relatedness of mushroom fruiting bodies to isolated mycelia was
examined. Nine isolates of edible mushroom mycelia of general Oudemansiella,
Coprinus and Pleurotus were identified using fruiting
bodies as references. Polymerase Chain Reaction (PCR) in conbination
with Restriction Fragment Length Polymorphism (RLFP) analyses were
carried out on fruiting bodies and mycelia of the isolates. The
internally transcribed spacer region (ITS) and ribosomal RNA gene
(rDNA) was amplified using ITS1 and ITS4 primers. The RLFP analysis
was carried out on the regions amplified by PCR from fruiting bodies
and the mycelia was established by looking at DNA fragment band sizes
and patterns. Banding patterns and fragment sizes of DNA obtained from
mycelia and their corresponding fruiting bodies were identical and
characteristic for the species. Using this technique, it was possible
to sort out a case of mistaken identity of Oudemansiella
fruiting bodies, which were interchanged with another mushroom
specimen during packing. The method is fast, accurate, and could be
used for routine screening of edible mushrooms of Tanzania for
taxonomical purposes. For the latter purpose, it is required that the
RFLP database of taxonomically known species is in place.
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