Browsing by Author "Getachew, Samuel"

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    Allelopathic Effects of the Invasive Prosopis juliflora (Sw.) DC. on Selected Native Plant Species at Middle Awash, Southern Afar Rift of Ethiopia.
    (Addis Ababa University, 2010-01) Getachew, Samuel; Demissew, Sebsebe (Professor); Wolde, Tadessse {PhD)
    The allelopathic effect of aqueous extracts of leaf, bark and root of Prosopis juliflora was studied on germination percentage, germination rate and seedling growth of Acacia nilotica, Acacia tortilis (both members of the legume Family, Fabaceae), Cenchrus cillaris and Enteropogon rupestris (both members of the grass Family, Poaceae). Effects of soil amended with decaying plant parts of P. juliflora and it’s under canopy soil were analyzed on germination percentage of the above selected plants to observe the field situation. Vegetation sampling in different habitat types in the area was made to identify the target plant species. Comparison of canopy characteristics among P. juliflora, A. nilotica and A. tortilis was also made to observe differences if any in canopy closure. P. juliflora was recorded in all habitat types in the study area: open Acacia woodland, riverine and swamp vegetation types. P. juliflora was observed invading the different habitats and affecting the plant diversity there in. Low plant diversity was recorded in P. juliflora dominated fields. Even if the canopy closure of P. juliflora was not significantly different from other trees, its growth characteristics and dense thickets formation restrict light to the ground flora and block winds. This results in the death of under canopy vegetation and hence low plant diversity. Leaf, bark and root aqueous extract of P. juliflora at 0, 0.5, 0.8, 1, 2 and 6% were prepared and their effect studied on germination percent, germination rate and seedling growth of the selected plant species in the study. Germination of A. nilotica and A. tortilis was not affected by all treatment types. Leaf and root extracts at higher concentrations inhibited germination of C. cillaris and E. rupestris. Bark extract facilitated germination of C. cillaris at lower concentrations. In general all treatment types speeded up the germination rate for A. nilotica and A. tortilis at the beginning, while these slow down the germination rate of C. cillaris and E. rupesteris. Shoot and root growth of the study species was inhibited by leaf extracts. Bark extracts were stimulatory to shoot and root growth of the species under study at lower concentrations except for C. cillaris. C. cillaris root growth was not affected by bark extracts at lower concentrations. Root extracts were stimulatory at lower concentrations while it was inhibitory at higher concentrations to shoot and root growth of the study species except for C. cillaris. C. cillaris shoot growth was not affected by root extracts at lower concentrations. Seed germination of all study species except A. nilotica was inhibited by the amended and under canopy soil. The effect was high on the grasses than on the tree species studied and root growth was more inhibited than shoot growth. Suppression of seed germination, facilitation or retardation of the germination speed and seedling growth of the study species suggests that these responses are attributed to an allelopathic effect of P. juliflora on the test species. These results indicate that the effect is species specific and leaf seems to contain greater number / amount of inhibitors than does bark and root. Bark seems to contain the least. Heavy accumulations of leaf litter under P. juliflora result in accumulation of toxic substances in soil layers, inhibiting growth of other species. This may be one of the main reasons for its invasiveness and low plant diversity seen under its canopy. Keywords: Allelopathy, aqueous extract, canopy closure, germination percentage, germination rate, habitat, plant diversity, P. juliflora, seedling growth
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    Determinants of Dividend Policy: Evidence from Ethiopian Insurance Companies
    (Addis Ababa University, 2017-06) Getachew, Samuel; Berhanu, Habtamu (PhD)
    The purpose of this study was to examine the determinants of dividend policy in Ethiopian insurance companies. For this purpose, samples of nine Ethiopian insurance companies were selected. Ordinary Least Squares (OLS) Regression was used to examine the impact of profitability, liquidity, leverage, firm size, growth opportunity, previous year dividend and asset structure on dividend policy in the insurance sector over a period of nine years from 2007/08 to 2015/16. The empirical results of this study showed that profitability, leverage, liquidity, previous year dividend and asset structure have a positive relationship with dividend payout. Meanwhile, firm size and growth opportunities have a negative relationship with dividend payout. Furthermore, the results of the analysis indicated that profitability, liquidity, growth opportunities, previous year dividend and asset structure were the major factors that affected dividend policies of Ethiopian insurance companies and mangers of Ethiopian insurance companies need to consider these factors while setting/revising their dividend payout policy; on the same token investors need to consider these factors in their investment decisions when they want to make an investment in Ethiopian insurance companies.Moreover, further investigations including different company selected factors like firm’s age, business risk, insider ownership, corporate tax and capital structure would provide better insight for determinants of dividend policy in Ethiopian insurance Companies. Keyword: Dividend policy; Dividend payout; Insurance Companies
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    Layer Based Log Analysis for Enhancing Security of Enterprise Data Center: The Case of Ethiopian Education and Research Network
    (Addis Ababa University, 2015-02) Getachew, Samuel; Ejigu, Dejene (PhD)
    The development of various Internet technologies recently leads many organizations to connect their data center with the global networking infrastructure for communication and sharing of resources. This proves the concept of “global village” that can foster corporation among organizations. However, the issues of security are becoming important as society is moving to the digital information age. For enterprises to evaluate, know data center health as well as conduct their business in a secured manner they must incorporate security. Though, existing security systems use limited log files type and formats for analysis, lead to unclear picture for administrators to decide the existence of attacks in their data center infrastructure. In this thesis, log analysis technique was used to identify intrusions found at different layers of organizations data center through scrutinizing log events recorded by various network devices, applications and others. Log analysis is an approach that provides valuable information by utilizing various collections of log files gathered from critical data center devices. Thus, to discover a wide range of anomalies (attacks) the considerations of heterogeneous log files are basis for analysis and provides surplus amount of information about the health status of the data center. In our work, central engine is composed of two major components to perform log analysis tasks. Those are clustering module and correlation process which is core of the log analyzer and work together with attack knowledge base to identify attacks. The collected log files are well organized together into common format and analyzed based on their features to identify anomalies. Clustering algorithms such as Expectation Maximization, K-means were used to determine the number of clusters and filter events based on filtering threshold respectively. On the other hand, correlation finds a relationship among log events and investigates new attack definitions. We have evaluated the prototype of our proposed system and obtained an encouraging result. Further study and implementation of log analysis like we developed can significantly enhance data center security of an organization. Key words: Log analysis, Data center security, Layered security, Attack identification.
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    Layer Based Log Analysis for Enhancing Security of Enterprise Data Center: The Case of Ethiopian Education and Research Network
    (Addis Ababa University, 2015-02) Getachew, Samuel; Ejigu, Dejene (PhD)
    The development of various Internet technologies recently leads many organizations to connect their data center with the global networking infrastructure for communication and sharing of resources. This proves the concept of “global village” that can foster corporation among organizations. However, the issues of security are becoming important as society is moving to the digital information age. For enterprises to evaluate, know data center health as well as conduct their business in a secured manner they must incorporate security. Though, existing security systems use limited log files type and formats for analysis, lead to unclear picture for administrators to decide the existence of attacks in their data center infrastructure. In this thesis, log analysis technique was used to identify intrusions found at different layers of organizations data center through scrutinizing log events recorded by various network devices, applications and others. Log analysis is an approach that provides valuable information by utilizing various collections of log files gathered from critical data center devices. Thus, to discover a wide range of anomalies (attacks) the considerations of heterogeneous log files are basis for analysis and provides surplus amount of information about the health status of the data center. In our work, central engine is composed of two major components to perform log analysis tasks. Those are clustering module and correlation process which is core of the log analyzer and work together with attack knowledge base to identify attacks. The collected log files are well organized together into common format and analyzed based on their features to identify anomalies. Clustering algorithms such as Expectation Maximization, K-means were used to determine the number of clusters and filter events based on filtering threshold respectively. On the other hand, correlation finds a relationship among log events and investigates new attack definitions. We have evaluated the prototype of our proposed system and obtained an encouraging result. Further study and implementation of log analysis like we developed can significantly enhance data center security of an organization. Key words: Log analysis, Data center security, Layered security, Attack identification.
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    Stratigraphic, Petrographic and Geochemical Characteristics of the Gohatsion Formation in the Blue Nile Basin, Central Ethiopia: Implications for Paleoenviroment Reconstruction
    (Addis Ababa University, 2018-06-02) Getachew, Samuel; Atnafu, Balemwal (PhD)
    This thesis investigates the stratigraphic, petrographic and geochemical characteristics of the Gohatsion Formation in the Blue Nile Basin, central Ethiopia. In addition to detailed geological mapping and stratigraphic logging in the field, petrographic, mineralogical and major/trace element chemical analysis was performed on 27 samples by means of XRD, ICP-MS/AES analysis. The Formation consists cyclic intercalation of fine siliciclastic and evaporite beds and has been classified into 3 informal members namely, the Upper Mudrock Member, Gypsum Member and the Lower Mudrock Member. Four lithostratigraphic sections were constructed at the Gohatsion-Dejen, Mugher and Jemma localities. Lithofacies at an outcrop and petrographic scale indicates the presence of complex geological history. The Lower and Upper Mudrock Members were formed under tidal influenced environments such as intertidal, supratidal, lagoonal, back-barrier mudflats and tide dominated estuary. The Gypsum Member shows both subaqueous and subaerial facies formed under holomictic brine flux with both continental and marine influences. Geochemistry of mudrock samples showed lower compositional maturity and low weathering index (CIA and PIA values) which is indicative of first cycle deposition. Trace element analysis showed that the provenance composition for such rocks are felsic to intermediate metamorphic to plutonic rocks formed under an active continental arc setting. Diagenetic evolution of sandstone and dolomitic packstone rocks seem to be influenced by meteoric and late stage diagenetic processes whereas the gypsum recorded much of telogenetic processes.