Browsing by Author "Tesfaye, Debela"

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    Designing a Stemmer for Afaan Oromo Text: A Hybrid Approach
    (Addis Ababa University, 2010-06) Tesfaye, Debela; Abebe, Ermias (PhD)
    Most natural language processing systems use stemmer as a separate module in their architecture. Specially, it is very significant for developing, machine translator, speech recognizer and search engines. In linguistic morphology, stemming is the process for reducing inflected (or sometimes derived) words to their stem, base or root form. In this thesis work, a stemming system for Afan Oromo is presented. This system takes as input a word and removes its affixes according to a rule based algorithm. This stemmer is not enough to define every rule applied in Afan Oromo word formation. Therefore, N-gram is integrated with the rule to handle cases that are not covered by rule in the hybrid version of this stemmer. The algorithm follows the known Porter algorithm for the English language and it is developed according to the grammatical rules of the Afan Oromo, as they are described in a Grammatical sketch of Written Oromo (Mewis, 2001) and Caasluga Afaan Oromoo, Jildii-1 (Oromo, 1995). Afan Oromo morphology was studied and described in order to model the language and develop an automatic procedure for conflation. The inflectional and derivational morphologies of the language are discussed. The result of the study is a prototype context sensitive iterative stemmer for Afan Oromo. Error counting technique was employed to evaluate the performance of this stemmer. For testing purpose 198 sentences (with a total of 2458 words) is collected from different public Afaan Oromo newspapers and bulletins to make the testing set address variety of issues. An evaluation of the system shows that the algorithms accuracy works with better performance than other past stemming algorithms for Afan Oromo giving 95.73 percent correct results. Finally, possible extensions of the proposed system and further evaluation methods are briefly reviewed.
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    ―Removal of Lead from Waste Water Using Corn Cob Activated Carbon as An Adsorbent
    (Addis Ababa University, 2016-07) Tesfaye, Debela; Yimam, Abubeker (PhD)
    Industrial development has caused the release of various pollutants including heavy metals into the environment. These toxic compounds are extremely dangerous to living beings and the environment due to their non-biodegradability, severe toxicity, carcinogenicity, the ability to be accumulated in nature and the ability to contaminate groundwater and surface water. The aim of the present research was to provide an appropriate and cost-effective adsorbent to remove one of these heavy metals namely lead from waste water. The activated carbon was produced from the dried corn cob. Batch experiments were performed on synthetic samples at room temperature. The effect of pH, adsorbent dose, initial concentration, and contact time were studied, and the adsorption isotherms of heavy metals were determined. The optimum conditions for corn cobs activated carbon preparation were determined as impregnation ratio of 1.5, carbonization temperature of 450oC, activation time of 120min, and acid concentration 60% by weigh. The result of the characterization showed that the corn cob activated carbon has good properties as compared with other reference activated carbons. The maximum removal efficiency of heavy Pb2+ions by activated carbon adsorbent prepared from corn cobs was obtained optimum pH 5, optimum adsorbent dose of 3g, and the optimum contact time of 120 min; in these optimum conditions the removal efficiency was 96.8%. Greater adsorption amount of 10.7mg/g occurs at smaller adsorbent dose of 1g. The results were also confirmed that the adsorption process follows Langmuir isotherm model with a better sorption fit and supported for the monolayer adsorption of Pb+2ions on corn cobs activated carbon. The kinetic model of this study shows a pseudo-second order kinetic model with good correlation coefficient. Based on the results obtained, the activated carbon produced from corn cob has a good capability in removal of the lead ions from the aqueous solutions. Key words: corn cobs activated carbon; adsorption of lead (Pb2+); optimal conditions.