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Hailegiorgis D.,Aksum University | Mesfin M.,Aksum University | Genet T.,Bahir Dar University
Journal of Central European Agriculture | Year: 2011

An investigation was carried out with 49 bread wheat genotypes to assess the genetic diversity for yield and yield related traits. The Unweighted Pair Group Method using Arithmetic Averages (UPGMA) technique was used for the analysis. The genotypes were evaluated for 17 Characters and showed wide variability for the components studied. The cluster analysis grouped the 49 bread wheat genotypes into 22 different clusters. This indicates the presence of wide diversity among the tested genotypes. From cluster mean values, genotypes in cluster 9 and 13 deserve consideration for their direct use as parents in hybridization programs to develop high yielding wheat varieties. The genotypes in cluster 3 and 16 may be used for improvement of protein and gluten contents, early maturity-ness and other desirable characters other than grain yield. The result of the principal components analysis revealed that nine principal components (PC1 to PC9) accounted nearly 80% of the total variation. It was also noted that differentiation of genotypes into different clusters was because of the small contribution of few character rather than the cumulative effect of a number of characters. The information obtained from this study can be used to plan crosses and maximize the use of genetic diversity and expression of heterosis.

Mengistu E.,Aksum University | Kassa T.,Bahir Dar University
Advances in Space Research | Year: 2015

In this paper, we reported on a case study of the temporal characteristics of the Equatorial Electrojet (EEJ) and Counter Electrojet (CEJ) over Ethiopian sector during an interval on August 27, 2008 inferred from ground-based magnetometer observations. The EEJ is an intense eastward flowing electric current on the dayside along the dip equator in the equatorial ionospheric E-region between about 90-120 km. This intense current has an associated magnetic field ΔH which can produce a large enhancement on the horizontal component of the geomagnetic field. Calculating the difference between the horizontal components of magnetic perturbation (H) at the equator and off the equator, ΔH, yields information about the strength of the EEJ current. Simultaneously, the sign of the current provides us with information on the direction of current flow (when the normal eastward flow of the EEJ is reversed, the resulting current is known as the CEJ). By using data collected during an interval on August 27, 2008 from Addis Ababa, Ethiopia, observatory in conjunction with Adigrat, Ethiopia, observatory and applying the above mentioned technique, we have observed the electrojet as well as the CEJ in the sector. The electrojet has been observed between about 09:15-14:30 LT (LT: local time). The electrojet and CEJ are peaked at about 12:00 and 08:00 LT, respectively. In addition, we have also observed the CEJ between about 09:00-09:15 LT and in the afternoon about 14:00 LT. This study also presents the temporal and diurnal variations of the field on different quiet and disturbed days during an interval from September 01-19, 2008. Strongly perturbed, dimly perturbed, and almost smooth variations on the fields are observed. For example, strongly perturbed fields are observed on September 03-04, 2008 and September 15, 2008 days and smooth curves are observed between September 11-14, 2008 and September 17, 2008. © 2014 COSPAR.

Mohan A.,Aksum University
Advanced Materials Research | Year: 2014

Pressure vessels often have a combination of high pressure together with high temperature such as gun barrels and high pressure hydraulic rams. For high pressure application, the cylindrical vessels are made to withstand the working pressure. These types of pressure vessels are made by two techniques, one is shrink-fit cylinders and other one is autofrettage cylinders. Autofrettage technique is used to ensure the pressure vessel highly strengthened due to prestressed effect causing the internal portion of the part to yield and resulting in internal compressive residual stresses. The present work is concerned about the elastoplastic stress analysis of thick cylinders. The numerical analysis is carried out on four different materials which are widely used in pressure vessels by using finite element software ANSYS. The elastic breakdown pressure, overstrain pressure, and bursting pressure of the cylinder are found out and the results are compared with experimental results. © (2014) Trans Tech Publications, Switzerland.

Gebru B.,Aksum University | Bezu S.,Norwegian University of Life Sciences
Environment and Development Economics | Year: 2014

This paper examines the adverse effect of natural resources scarcity on children's schooling and the possible gender bias of resource collection work against girls' schooling. It uses cross-sectional data on 316 children aged 7-18 years collected from 120 rural households in Tigray, northern Ethiopia. The two-stage conditional maximum likelihood estimation technique is employed to take care of endogeneity between schooling and collection intensity decisions. The results revealed that a 50 per cent increase in collection intensity reduces the likelihood of child schooling by approximately 11 per cent. However, we find no evidence of gender bias against girls' schooling. Copyright © Cambridge University Press 2013.

Gebrelibanos T.,Aksum University | Assen M.,Addis Ababa Institute of Technology
African Journal of Ecology | Year: 2014

This study aimed to determine the spatial variation of topsoil properties as influenced by slope aspects and vegetation types. Three vegetation types and two slope aspects were considered. Disturbed and undisturbed samples were taken from the top soils. A two-way analysis of variance was used to test significant mean differences (α = 0.05). Results showed that contents of bulk density, total porosity, organic matter and exchangeable magnesium were significantly different with changes in slope aspect (P < 0.05). Textural classes, organic matter, available phosphorus, carbon-to-nitrogen ratio, cation-exchange capacity, per cent base saturation and exchangeable bases demonstrated significant variation among vegetation types (P < 0.05). The south-facing aspect and the grass vegetation showed higher bulk density but lower organic matter and total porosity. As a remedy for the identified problems, there is a need to undertake plantation of indigenous trees. © 2013 John Wiley & Sons Ltd.

Mulugeta Y.,Aksum University | Woldeghebriel H.,Mekelle University
Computational and Theoretical Chemistry | Year: 2014

The geometric and electronic structures of lead telluride clusters are investigated numerically. The result provided both vertical and adiabatic electron affinities (VEAs and AEAs) for this clusters, revealing a pattern of alternating values in which even n clusters exhibited lower values than odd n clusters up until Computations found lead telluride clusters with even n to be thermodynamically more stable than their immediate odd n neighbors, with a consistent pattern also being found in their HOMO-LUMO gaps. Analysis of cluster dissociation energies found at cube to be the preferred product of the queried fragmentation processes, consistent with our finding that cluster exhibits enhanced stability; it is a magic number species. Beyond, prefer two dimensional stacking of face-sharing lead telluride cubical units, where lead and tellurium atoms possess a maximum of fivefold coordination. The preference for sixfold coordination, which is observed in the bulk, was not observed at these cluster sizes. © 2014 Elsevier B.V.

Mulugeta Y.,Aksum University | Woldeghebriel H.,Mekelle University
Structural Chemistry | Year: 2015

Density functional theory calculations are performed to investigate tin content effect on the structural and energetic properties of lead telluride clusters. Tin atoms prefer to be doped on the exterior sites rather than the interior sites of lead telluride clusters. The geometry of the clusters is not affected due to the amount of tin content except for a slight distortion observed by changes in bond length. A considerable change has been observed in the HOMO-LUMO gap of the clusters with increasing number of tin atoms for corresponding size, but the band inversion which is observed in the bulk is not observed on the clusters in these size ranges. The change in binding energy between doped clusters is almost negligible for the same number of tellurium atoms, it is observed to be constant or there is a change of up to 0.02 eV with each successive doping of tin atoms. Both adiabatic and vertical detachment energies are observed to increase with increasing number of doping tin atoms. The fragmentation energy of losing PbTe dimer changes with an even-odd alternation, clusters with even number of Te atoms are more stable because they need higher energy to dissociate as compared to the other clusters. Some clusters are found to be magic (more stable) because of their enhanced binding, HOMO-LUMO gap, and fragmentation energies, typical examples are Pb4-m Sn m Te4 (m = 1-4) clusters. © 2014 Springer Science+Business Media New York.

Mulugeta Y.,Aksum University | Woldeghebriel H.,Mekelle University
International Journal of Quantum Chemistry | Year: 2015

Theoretical computations of (PbTe)n (n = 21-45)clusters based on density functional theory have demonstrated that at cluster size of (PbTe)22 there is a transition from the strong preference of fivefold coordination to sixfold coordination of lead and tellurium atoms. (PbTe)24 cluster is the smallest tetragonal structure in which its central atoms have bulk-like coordination. This quantum dot (QD)contains a single-unit cell of lead telluride crystal, thus can be considered as an "infant crystal." (PbTe)32 cluster is a perfectly cubic cluster for which its inner (PbTe)4 core enjoys bulk-like coordination. This (PbTe)4 core unit of (PbTe)32 cubic cluster has exactly the same environment as a primitive cell of lead telluride crystal. The (PbTe)8n, (n ≥ 3)clusters are the magic number species with bulk-like structure such that (n = 3-5)the nanoblocks considered here (PbTe)24, (PbTe)32, and (PbTe)40 clusters exhibiting bulk-like structure that can be replicated to obtain the bulk crystal. The calculated dimensions of this special clusters provided a rubric for understanding the pattern of aggregation, that is, the creation of defined nanoblocks [(PbTe)8n, (n ≥ 6)], when they were accumulated on an appropriate surface. It is evident that the QDs (PbTe)8n, (n = 3-5)clusters show high stability compared to their neighboring clusters. This can also be seen from the second-order energy difference, binding, and fragmentation energy graphs. © 2014 Wiley Periodicals, Inc.

Gebrelibanos T.,Aksum University | Assen M.,Addis Ababa Institute of Technology
Journal of Land Use Science | Year: 2015

This study analysed long-term land use/land cover (LULC) dynamics and their underlying causes and implications for land resources management in a dryland watershed of Hirmi and its adjacent agro-ecosystem, northern highlands of Ethiopia. Two sets of aerial photographs (1964 and 1994) and 2006 Spot 5 satellite images were utilised in the study. These derived data were complemented with the help of focus group discussions and personal interview methods. The study identified five LULC types: cultivated and rural settlement, forest, grassland, town and a small artificial pond. Expansions of cultivated and rural settlement and forestland use/land cover and a reduction of grassland and shrubland use/cover types were observed throughout the analysis period. Over the 42-year period, cultivated and rural settlement land increased by 24.6%. Grassland declined sharply from 20% in 1964 to 11.3% in 2006. The area under forest cover expanded from 0.9% in 1964 to 1.8% in 2006. The town of Indaselassie increased at a rate of 8.95 hectare (8.1%) per annum. An artificial pond covering 6 ha emerged between 1994 and 2006. Combinations of proximate and underlying causes such as poverty, demographic pressure, institutional and policy factors have influenced LULC dynamics in the Hirmi watershed and the adjacent agro-ecosystem. The LULC dynamics resulted in the degradation of land resources. There is a need to control the immediate causes of LULC dynamics by limiting cropland expansion via increasing land productivity and devising strategies to regulate urban land expansion. Long range strategies such as methods of easing population growth and ways of alleviating rural poverty need to be devised to bring about sustainable land resources management practices in the study site. © 2013 Taylor & Francis.

Bakrudeen A. S.B.,Aksum University
Proceedings of the International Conference on "Advanced Nanomaterials and Emerging Engineering Technologies", ICANMEET 2013 | Year: 2013

In the last decade, as demand for high quality materials are increased, the development of lightweight aluminum (Al) also increased especially in aerospace and automotive industries. It has been well known that Al based metal matrix composites (MMCs) offers a very low thermal expansion coefficient, high specific strengths, wear and heat resistance as compared to conventional Al alloys. In order to combine all these properties, MMCs have become a very attractive method for various industrial applications. The interest in Carbon Nano Tube (CNT) as reinforcements for aluminum (Al) has been growing considerably. Efforts have been largely focused on investigating their contribution to the enhancement of the mechanical performance of the composites. The uniform dispersion of Carbon Nano Tube in the Al matrix has been identified as being critical to the pursuit of enhanced properties. In this present research paper emphasis, the effect of Carbon Nano Tube content on the Mechanical properties of the composites like Tensile strength, Percentage of Elongation was investigated. The improvement of mechanical properties for composites of Al/CNT has been compared with pure aluminum. © 2013 IEEE.

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