nigerian defence academy
journal of science and engineering (ajse)
TOPOLOGICAL ANALYSIS OF THYRISTOR CIRCUITS
Babatunde Araoye ADEGBOYE
The paper utilises the network topology in the analysis of a thyristor circuit – an oscillating chopper. The graph of the chopper was developed following which the complete incidence matrix was formed. The signal flow graph was also developed, which was reduced directly by the application of Mason’s Rule, this being the basis for the formulation of the state equations. For analytical reasons, the diodes and thyristors were classified along with the resistance branches because of their switching properties. The analysis concludes that the problem of varying time constants in the solution of state equations in the thyristor circuits is eliminated by opening the open circuit branches.
IDENTIFYING CABLE DISORDERS WITH ON-VOLTAGE TIME DOMAIN REFLECTOMETRY
Vincent Onotu FACHE
In this paper a diagnostics technique is presented for localization of degraded regions along a cross-linked polyethylene (XLPE) insulated power cable. The diagnostics would help to develop a strategy for condition based maintenance of old XLPE power cables. A design of the diagnostics system and results of measurements performed on two power cables are presented. The measurements data is processed in order to localize the degraded insulation regions. The sensitivity of the diagnostics is investigated in terms of signal attenuation along the cable.
TENSILE STRENGTH COMPARISON OF FOUNDRY SAND CORES BONDED WITH DIFFERENT GRADES OF NIGERIAN GUM ARABIC EXUDATES.
Nuhu A. ADEMOH & A.T ABDULLAHI
The empirical tensile strength values of baked sand cores bonded with each of the four commercial grades of exudates of Nigerian gum Arabic (acacia species) were experimentally measured using established standard procedures in foundry industry. The experimental test specimens which were shaped like the number 8 were made from silica sand bonded with different grades of gum Arabic exudates. The specimens were classified, oven baked at 1600C, 2000C, 2200C and 2500C for periods of 1-3 hours, oven cooled and then subjected to strength tests using a standard universal strength machine in foundry shop of Ajaokuta Steel Company Limited, Nigeria. The research result showed that expendable foundry sand cores bonded with Nigerian gum Arabic baked at 1600C for 1-3 hours didn’t reach optimum strength. Grades 1 and 2 acacia bonded cores gave peak tensile strength when baked at 2000C. Those bonded with grades 3 and 4 gum Arabic gave optimum tensile strength when baked at 2200C. At 2500C, cores were observed to burn and loose strength. For process economics gum Arabic grade 4 is best for foundry core application as it was cheapest in price and cores bonded with it attained required tensile strength at least baking temperature within the shortest baking time. This was followed by gum Arabic grade 3, grade 1 and gum Arabic grade 2 in that order.
GROWTH OF AFRICAN CATFISH, Clarias gariepinus (Teuglas).
EXPOSED TO DIFFERENT DIETS OF VARYING HORMONE TYPES
B. C. Onusiriuka
Replicates of Clarias gariepinus fingerlings were fed for 8 weeks on diet either treated with toad pituitary extract (TPE), synthetic hormone (SH), Clarias gariepinus pituitary extract (CGPE) or none (Control). Growth rate and food utilization in the different groups were compared. Results revealed that the best growth, parentage weight gain, specific growth rate, and apparent net protein utilization were obtained with the CGPE diet. The best food conversation ratio and protein efficiency ratio were obtained with TPE diet. There was no significant difference (P>0.05) in growth of all the treatments and within the weeks. The purchase of synthetic hormone just to accelerate growth rate and achieve greater increase in weight is ill-advised. The use of toad pituitary extract (TPE) is more economical than the use of C. gariepinus pituitary (CPE). It is also cheaper.
SOLID WASTE GENERATION AND CHARACTERIZATION IN KADUNA METROPOLIS, NIGERIA.
M.O. Nwude, S.B. Igboro, J.A. Otun and C.A. Okuofu
This study examined and characterized solid waste generated from forty-eight selected households in Kaduna metropolis. Four (4) households were randomly selected from low, medium and high-density areas of Kaduna North and South LGAs while, four (4) houses were also selected randomly from medium and high-density areas of Chikun and Igabi LGAs within the metropolis. The results show that the percentages of waste generated are 63.75% (Garbage), 5.28% (metals), 5.44% (Glass), 5.71%(rubber and Plastic), 5.55% (Paper/Cardboard), 2.19% (Textile) and 12.08% (Miscellaneous), while the mean per capita waste generation is 0.30 kg/day with a mean volume and mean density of 0.0029m3/day and 6.37kg/m3 respectively.
Apart from the amount of radiation, which may be encountered due to radioactive substances, individuals are also exposed to radiation because of the nature of the environment. This natural source of exposure is often referred to as background radiation and studies have revealed two main components, viz: radioactivity in the earth crust and extraterrestrial radiation called cosmic rays. The amount either of these radiation sources contributes varies with locations. To examine this, both LiF: Ti and CaSO4: Mn phosphor chips were investigated and the CaSO4 dosimeter chosen because of annealing and contamination problems associated with LiF. The CaSO4 TLD was calibrated using 90Sr beta source as standard. A low level standard deviation of 4% was recorded around 25mR region. It was established that among the sampled areas, the NNPC and Panteka recorded high radiation levels. Measurements of photoemission produced around these industrial areas of Kaduna were also determined and compared with standards. Results established that apart from NNPC and Panteka, other locations were uncontaminated. However, locations below ground level at various depths around metallic waste dumps of Panteka and NNPC recorded large exposure rate, which increased with depth until a plateau is attained.
MODELING VARIATION IN SEASONAL WATER LEVELS OF BAUCHI TOWNSHIP RESERVOIR
Abdullahi IBRAHIM & O.I NDUBUBA
ABSTRACTInadequate of potable water and its likely poor quality have been man’s age big problem. In Bauchi Township the main source of water supply is through Gubi dam, though the available water in the dam varies in quantity and quality due to seasonal changes. This research was carried out to establish the relationship between reservoir water level in Gubi dam and rainfall, temperature, evaporation, relative humidity and wind speed in Bauchi., using data from meteorological records in Bauchi and Gubi dam water supply from the period 1997 to 2003. The study was carried out using software package known as Polymath Polynomial, statistica and Mini-Tab R14, employing multiple regression analysis.. The result of the analysis gave high value of the multiple regressions coefficient R of 0.827377 for the dependent variable Y with the independent variable X close to 1. This shows that the relationship is positively significant between the dependent variable Y with the independent variable X. Similarly this high value of R also indicated that the dependent variable Y with the independent variable X are correlated.
CHARACTERIZATION OF NON-METALLIC INCLUTIONS IN HOT ROLLED CALCIUM TREATED STEEL
A study of the relationship between inclusions’ shape and composition in hot-rolled calcium treated industrial steel was undertaken in this work. Scanning electron microscope equipped with an energy dispersive X-ray (EDX) analyzer was used to analyze the elemental composition of the inclusions. The analyzed elemental compositions were converted into their respective thermodynamically most stable oxides and sulphides, and appropriate phase diagrams were used to determine their formulae. Results obtained reveal that complex oxysulphides and CaO.Al2O3 compound of very small sizes remain undeformed. 12CaO.7Al2O3 compound deformed and fractured into strings. 12CaO.7Al2O3 containing small amount of CaO.Al2O3 deformed plastically. While inclusions that deform into short plastic threads and brittle strings mixed together are made up of small amounts of 3CaO.Al2O3 compound in the core of 12CaO.7Al2O3. The undeformed (irregular shaped) parts of some of the inclusions were found to contain CaO.Al2O3, Al2O3.MgO and 2Al2O3.3CaO.MgO compounds.
ACUTE TOXICITY OF A NIGERIAN ARMAMENT FACTORY EFFLUENT ON OREOCHROMIS NILOTICUS (LINNAEUS+)
Effluents from a Nigerian armament factory were characterized using standard methods. The acute toxicity of this effluent on Oreochromis niloticus was determined in a 96h static bioassay under laboratory conditions, in 3%, 6%, 9%, 12% and 15% effluent concentrations. The effluent was generally acidic. Fourteen parameters had values above the Federal Environmental Protection Agency (FEPA) limit. The values for ammonia (x=3.0. mg/l), cyanide (x=2.27mg/l), sulphide (x=2.8 mg/l), and total alkalinity (x=403.0 mg/l) were consistently higher than FEPA approved limits in all batches of effluent investigated. Some heavy metals such as Nickel and chromium and also ammonia were consistently high in all the three batches of effluents analysed. The Effluent caused mortality to Oreochromis niloticus. This mortality was dose – dependent and occurred in all effluent concentration used. The 96h LC50 was 4.16% while the lethal time (LT) was 21 hours for the 15% effluent concentration and 84 hours for the 6% effluent concentration. Hyperactivity and disorientation were observed in all fish before death and dead fish was observed to have oedematous gills and copious mucus deposition on the gills and body.
EFFECT OF WATER QUALITY ON THE COMPRESSIVE STRENGTH OF CONCRETE (A case study of well, stream and tap water in Kaduna State)
Water forms the basic constituents in concrete work. It is the principal hydrating agent that initiates the chemical reaction; other constituent materials are cement, fine and coarse aggregates. Water is the most important and least expensive ingredient of concrete as it actively participates in the chemical reaction with the content. A part of mixing water is utilized in the hydration of cement to form the binding matrix in which the inert aggregate are held in suspension until the matrix has hardening. The remaining water serves as a lubricant between the fine and coarse aggregate and makes concrete workable. The quality of water used in mixing concrete plays an important role in the resulting compressive strength of the concrete. The water used for the mixing and curing of concrete should be free from injurious amounts of deleterious materials. Hence the need to investigate the effect of water quality on the compressive strength of concrete is of paramount importance. A visit to most construction sites in Northern Nigeria shows that the common sources of water used are well, stream/river and treated water from the public system which is seldomly available due to epileptic supply. A close examination of these water show different shades of colours and impurities. This paper presents the results of water samples obtained from the various sources mentioned above and their suitability for concrete production. The water samples were analyzed to determine the level of impurities in terms of solid suspension/dissolved and their corresponding pH values. Compressive strength tests were carried out on concrete cubes cured at 28days. In addition the fresh concrete was subjected to relevant tests in order to establish their conformity with established standards as in BS 1881part 102 to 104, 1983.