African Journal of Science and Technology

Effect of heat treatment on wear resistance of a grinding plate

2017-05-15T11:41:42+00:00

The effects of heat treatment on the hardness and by extension the wear resistance of locally produced grinding plate of known composition were investigated. Specimens were prepared from the grinding plate and were heat treated at 840°C, 860°C and 880°C and quenched at different rate. Some of the specimens were quenched in water and palm oil, while some of the quenched specimens were tempered at 200°C. The results obtained were corroborated with the microstructure of the specimens examined under an optical microscope. The hardness values of the grinding plate specimens quenched in various media increased with increased heat treatment temperatures, and are higher than that of the as-cast specimen. Water quenched tempered specimens (WT) displayed higher hardness values than the as-cast, whereas oil quenched tempered specimens (OT) possessed lower hardness values. The presence of carbide was evident on the micrographs of the water quenched specimens at all the exposure temperatures, which corroborated the observed increased in the hardness values with increased heat treatment temperatures. However, there was significant reduction in the hardness value of the water quenched tempered specimens compared with the quenched specimens, which indicates a significant improvement in toughness. Thus, water quenched and tempered specimen with relatively high hardness value and improved toughness, will be suitable for use as grinding plate because of its relatively better wear resistance. The hardness of the specimens was found to depend on the formation of carbide precipitates within the matrix structure. There is also possibility of production of structure consisting of graphite embedded in a martensitic matrix through the heat treatment.

Keyword: carbide, heat treatment, hardness, microstructure, wear resistance

Determination of the parameters for design of flexible plastic tank

2017-05-15T11:41:47+00:00

The need to provide emergency water supplies in remote locations and to store water in small, irregular spaces was the main motivation for the research study. The flexible plastic tank provides a good solution to the challenges of efficient water supply to remote areas but has the disadvantage of creeping incessantly during use and does not recover its original dimensions after loading. This project sought to establish the limits within which the flexible HDPE tank may be used in hot tropical climates for water storage. The creep and recovery characteristics of the material were determined for the range of loads and temperatures at which the material is likely to be applied. A set of equations was developed from the creep and recovery curves to estimate the values of creep and recovery within the temperature range 30°C - 50°C and for stresses ranging from 0.781 to 1.563 MPa just by knowing only the applied stress and the operating temperature. Estimates were also provided for the expected permanent expansion of the material under load, when loaded once and when loaded and unloaded intermittently.

Use of limited hydrological data and mathematical parameters for catchment regionalization: a case study of the Osun Drainage Basin, Nigeria

2017-05-15T11:41:49+00:00

A protocol is proposed for the regionalization and subdivision of catchments based on hydrometric parameters. Such catchment regionalization may assist the development of appropriate catchment management strategies and policies. As a case study, the trends of variations in daily stage and discharge of seven gauging stations located in the 9,900 km² Osun Drainage Basin (South West Nigeria) were investigated. Linear regression models for all stations show the expected strong positive association of stage and discharge. The estimated daily changes explain only 1.44% of variations in stage, 0.25% variation in discharge and 99.5% in stage-discharge for station 5, 5.5% variation in stage, 0.7% variation in discharge and 99.7% in stage-discharge at station 25, and 10% variation in stage, 8.9% variation in discharge and 100% in stage-discharge at station 27. For the other studied stations, R² estimated from daily stage and daily discharge give widely varying patterns. R² estimated from daily stage and daily discharge is non-significant, but is significant for the daily stage-discharge relationship. The derived daily-stage and daily-discharge equations for the seven stations and their corresponding coefficients of determination can be used to classify the basin into three distinct zones. These are Zone I (coefficient of determination within the range of 0-6% for the daily-stage and daily-discharge), Zone II (coefficient of determination within the range of 7-10.5% for the daily-stage and daily-discharge), and Zone III (coefficient of determination within the range of 11-22% for the daily-stage and daily-discharge). The exponents of the stage-discharge equation can also be used for spatial classification. Zone A exponent is in the range of 1.3-1.7, Zone B exponent is in the range 2.2-2.3 and Zone C exponent is in the range 4.0-4.7. These can be combined to produce three hydrometric regions. It is proposed this regionalization protocol could be used as an initial step in dividing complex catchment systems into more homogeneous subunits, to assist subsequent catchment management and planning. The hydrometric regionalization protocol is now being evaluated on the Osun and other drainage basins in Nigeria.

Keyword: Derivation, Gauged and Ungauged Rivers, Drainage Basin, Power Equations

Solitary Rossby waves in the lower tropical troposphere

2017-05-15T11:41:52+00:00

Weakly nonlinear approximation is used to study the theoretical comportment of large-scale disturbances around the inter-tropical mid-tropospheric jet. We show here that the Korteweg de Vries (KdV) theory is appropriated to describe the structure of the streamlines around the African easterly jet (AEJ) region. The introduction of the additional velocity C1 permits to search the stage where the configuration of the wave will correspond in this zone to those of Rossby solitary waves. It was also shown that the configurations of disturbances can be influenced by this parameter so that we can look if the disturbances are in the control or not of their dispersive effects.

Keywords: Soliton; Rossby waves; KdV equation; African easterly waves

Transmission dynamics of HIV/AIDS with screening and non-linear incidence

2017-05-15T11:41:54+00:00

This paper examines the transmission dynamics of HIV/AIDS with screening using non-linear incidence. A nonlinear mathematical model for the problem is proposed and analysed qualitatively using the stability theory of the differential equations. The results show that the disease free equilibrium is locally stable at threshold parameter less than unity and unstable at threshold parameter greater than unity. Globally, the disease free equilibrium is not stable due existence of forward bifurcation at threshold parameter equal to unity. However numerical results suggest that screening of unaware infectives has the effect of reducing the transmission dynamics of HIV/AIDS. Also, the effect of non-linear incidence parameters showed that transmission dynamics of HIV/AIDS will be lowered when infectives after becoming aware of their infection, do not take part in sexual interaction or use preventive measures to prevent the spreading of the infection. Numerical simulation of the model is implemented to investigate the sensitivity of certain key parameters on the transmission dynamics of HIV/AIDS with screening using non-linear incidence.

Keywords: HIV/AIDS, Screening, Non-linear incidence, Reproduction number, Stability

Comparative study of the effects of treatment techniques on the thermal and frictional properties of Kenaf (Hibiscus canabinus) fibre reinforced brake pads

2017-05-15T11:41:56+00:00

Asbestos fibre has been used as the traditional base material in brake pads manufacture, but due to its health hazard, non-renewability, cost, non-biodegradability and difficulty in processing, its replacement has been sought. This paper reports the effects of some fibre treatment techniques namely: mercerization, acetylation and semi-carbonisation on the performance of Kenaf fibres. The treated kenaf fibres which are considered biodegradable, cost effective, renewable and user friendly have been used as a possible base friction material for brake pad production. Results indicated that the four kenaf brake pad samples behave differently during during performance evaluation. semi-carbonized samples had high thermal conductivity with an average value of 0.6215 W/m. K than all the samples investigated in this study.

Keywords: treatment techniques, kenaf fibre, comparative study, brake pads, thermal properties

On optimum dispatch of electric power generation via numerical method

2017-05-15T11:41:58+00:00

In this work we develop an optimum dispatch / generating strategy by presenting economically the best load flow configuration in supplying load demand among the generators. The main aim is to minimize the total production / generation costs, with minimum losses and at the same time satisfy the load flow equation without violating the inequality constraints.

Keywords: Generation, power flow, generator limits, power losses,Chironomidae, River Niger, Niamey, water quality

Additive main effects and multiplicative interactions analysis of harvest index performances in cassava (Manihot esculenta, Crantz) genotypes across 4 environments

2017-05-15T11:42:00+00:00

Eight cassava genotypes were evaluated for harvest index performance across four environments. Data analysis was performed using MATMODEL and GGEbiplot. AMMI analysis of variance showed that 10.02% of the total sum of squares was attributable to environmental effects, 3.99% to genotypic effects and 50.13% to GEI effects. The GEI sum of squares contained approximately 76.52% (0.30709) pattern and 23.48% (0.09442) noise of the total GEI. The mean squares for IPCA 1 and IPCA 2 were significant at P = 0.000 and 0.002 respectively; all together they contributed 94.18% of the total GEI. Therefore, the post-dictive evaluation using an F-test at 0.000 and 0.002 suggested that two principal axes of the interaction were significant for the model with 16 degrees of freedom. The predictive assessment measured by the average root mean square predictive difference (RMS PD), selected AMMI1 with the first interaction PCA axis as the most predictively accurate. The AMMI1 model had the lowest average RMS PD (9.996). Mean performance and stability of the genotypes assessed by biplot analysis showed that the most stable genotypes were G2, G1 and G7. However G5 was highly unstable followed by G8 and G3. Two mega-environments were defined namely: G5-winning niche and G3-winning niche. The current study has demonstrated that the GGE biplot is a useful tool for the analysis of multi-environment trial (MET) data.

Keywords: AMMI, GGEbiplot, stability, harvest index, mega-environment

Etude phenomenologique sur la convection naturelle au dessus d’un disque rainure par voie optique

2017-05-15T11:42:03+00:00

Parmi toutes les méthodes expérimentales, l’optique a toujours occupé une place de choix grâce à son caractère non intrusif : la traversée d’un écoulement par un faisceau lumineux n’entraine pas de perturbation dans les conditions requises par la visualisation ou la mesure. C’est ce qui explique l’importance de la technique que nous allons décrire. Cette étude vise la mise en place d'un banc d'essai en vue de visualiser et traiter numériquement la convection naturelle induite par un disque rainuré et chauffée par le bas dans un système ouvert. La méthode de visualisation choisie est l'ombroscopie comme méthode non intrusive afin de ne pas perturber la convection. Il est utile aussi de rappeler que cette dernière technique délivre en fait des images qu'il faudra lire et éventuellement traiter. Ainsi, dans pratiquement tous les cas de contrôle optique, il faut, pour obtenir des images reconstituées de bonne qualité et envisager une vision nette, mettre en oeuvre un système élaboré de traitement d'images. Ce système a pour premier but d'améliorer la qualité de l'image sur le plan du contraste et du niveau de bruit; il doit en seconde lieu très souvent prendre en compte la morphologie des objectifs recherchés afin de rendre l'image reconstituée parfaitement exploitable.

Mots clés: Convection naturelle, Disque rainuré, Ombroscopie, Traitement d’image, thermographie

Etude bathymetrique, sedimentologique et environnement de depots des sables superficiels de la lagune de fresco (zone ouest du littoral Ivoirien)

2017-05-15T11:42:06+00:00

Les études granulométriques et les levés bathymétriques effectués en lagune de Fresco, ont permis de caractériser les sédiments et la morphologie du fond de cette lagune. Sur le fond, les sédiments sont constitués de vases localisées dans les bras de la lagune alors que dans la lagune de Fresco proprement dite, on rencontre essentiellement des sables. Les galets et les graviers se localisent par endroit, sur la rive Nord de la lagune, au Sud-Est de la ville de Fresco. L’essentiel des sables de la lagune de Fresco provient d’un environnement de type continental fluviatile. La majorité des sables se déplace par saltation. Le mode de transport des silts, des argiles et des sables très fins est exclusivement par suspension. Les sables fins ont un mode de transport dominé par le transport par suspension. Les sables moyens se déplacent exclusivement par saltation. Le transport par roulement est le mode de transport dominant des sables grossiers. Cette étude a permis de réaliser les cartes bathymétriques et de répartition des sédiments, ainsi que la détermination de l’environnement de dépôts des sables.

Mots clés: Morphologie, Sédimentologie, Environnement de dépôts, Lagune de Fresco, Côte d’Ivoire

Èvaluation de la virose du jaunissement et de l’enroulement en cuillere des feuilles de tomate (Lycopersicon esculentum Mill) sur divers cultivars au Senegal

2017-05-15T11:42:09+00:00

La tomate est le second plus important légume après l’oignon au Sénégal. Elle est très sensible au virus du TYLC (Tomato Yellow Leaf Curl). Douze variétés issues d’un criblage de résistance au TYLC et deux témoins sensibles (Roma VF et Xina) ont été testés pour confirmer cette résistance. L’incidence, la sévérité de la maladie et les variables de rendement ont été évaluées aux stades de floraison, fructification et après la première récolte. Les résultats ont confirmé ceux du criblage chez toutes les variétés. Les témoins ont fortement été attaqués par le virus. Lety F1 a produit plus de fruits. Le nombre de fruits/grappe a varié entre les variétés. La masse unitaire des fruits a été plus élevée pour Bybal, Roma VF et Lety F1. La longueur des fruits de Thoriya et Lety F1 a été plus importante. Roma VF et Bybal ont présenté les plus gros diamètres des fruits. TY75 et Ponchita ont produit les rendements consommables les plus élevés. Roma VF et Lety F1 ont produit les rendements non consommables les plus élevés. Globalement, les plus fortes productions ont été obtenues par TY75 et Roma VF. Ces résultats pourraient aider à faire le bon choix des variétés à cultiver dans des conditions similaires à celles des Niayes.

Mots-clés: Tomate, variétés, Lycopersicon esculentum, virus, résistance, TYLC, Xina, Roma VF, Sénégal

English Title: Effect of Yellow Leaf Curl Disease (TYLC) on different tomato cultivars (Lycopersicon esculentum Mill) in Senegal

English Abstract

Tomato is the second most important vegetable, after onion, in Senegal. The species is very sensible to the TYLC virus. Twelve promising varieties of tomato, from a resistance to the Tomato Yellow Leaf Curl (TYLC) screening and two susceptible checks (Roma VF and Xina) were tested to confirm their resistance to the virus. The variables measured were: incidence and severity of the disease and yield variables. Observations were made during the flowering, fruiting and at first harvest stages. Our results confirmed the screening results. The susceptible checks were strongly attacked by the virus. Lety F1 has produced more fruits per plant. Fruits number per cluster showed significant differences between varieties. Bybal, Roma VF and Lety F1 recorded the highest fruit weight. Mean fruit length was higher with Thoriya and Lety F1. Roma VF and Bybal exhibited the largest fruit diameter. TY75 and Ponchita have produced the highest consumable yields while Roma VF and Lety F1 produced the highest non consumable yield. The largest overall yields were obtained by TY75 and Roma VF. These results could be used to make the best variety choice for areas that have similar conditions to those of the Niayes region.

Keywords: Tomato, Lycopersicon esculentum Mill., virus, resistance, TYLCV, Xina, Roma VF, Senegal

On the pressure velocity and temperature factors and the effect of viscosity on the arterial blood flow in relation to the hypertension patient, Part 1 – flow without outflow

2017-05-15T11:42:11+00:00

In this paper, we examine the effects of viscosity on the blood pressure, velocity and temperature distributions in the arterial blood flow in the absence of outflows. The governing continuity, momentum and energy equations are solved analytically by method of characteristics. Using the wavefront expansions, an equation of the form of the Riccatti equation is derived. By this, explicit results about the pressure, velocity and temperature distributions are obtained. It is observed that viscosity reduces the pressure, hence, the velocity and temperature distributions. Our results may find relevance in the medical treatment of high blood-pressure problem

Keywords: Viscosity pressure, velocity, temperature, arterial blood flow, hypertension

Analysis of the weld strength of the High Density Polyethylene (HDPE) dam liner

2017-05-15T11:42:13+00:00

An analysis was carried out to determine the strength of welded joints in High Density Polyethylene (HDPE) dam liners. Samples were collected of welded joints and subjected to tensile tests and creep test. It was observed that the welded joints from field welded samples were much weaker and had a very low straining capacity than the un-welded material. The field welded specimens registered average strengths of 5 MPa as compared to 12 MPa of un-welded specimens and a maximum strain at fracture of 0.5 as compared to 3.5 of un-welded specimens. As a result of the weak welds it was found necessary to conduct further research into the best welds possible and a protocol for hot air and hot knife welding was developed. It was shown that for hot air welding while holding the width of the weld, applied pressure and dwell time of the pressure constant at 2.6cm, 0.3 MPa and 60 s, the recommended temperature of the hot air to achieve the strongest weld was 176 and for hot knife welding the recommended temperature of the knife was 400°C.