Browsing by Author "Taha, Osman"

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    Development of A Stemmer for Afaraf Text Retrieval
    (Addis Ababa University, 2015-11) Taha, Osman; Abebe, Ermias (PhD)
    This study describes the design of a stemming algorithm for Afaraf text retrieval system. Nowadays, a considerable amount of electronical information has produced in Afaraf. Information retrieval system is a mechanism that enables users to retrieve relevant unstructured information material from large collection. The Afaraf morphology leterature reviewed in order to develop the rule-based stemmer. Each natural language has words structure in its own forms, that are different prefixes and suffixes, which need special handling of affixes with specific rules. The rule based stemmer proposed based on grammar and dictionary of Afaraf, included Numbers (singular and plural), personal pronoun, adjectives, adverbs, verbal-noun, strong and weak verb, indefinite pronoun, conditional and subjunctive mood, linkage to remove suffixes and prefixes from the word and produce stem word. For this study text document corpus are prepared by the researcher used 300 text files of Afaraf documents, which collected from different school text books, Samara university modules, Qusebaa Maca magazines and other online and experiment is made by using eight different queries. Data pre-processing techniques of VSM involved for both document indexing and query text. The evaluation conducted on the stemmer shows that the accuracy is 65.65 % with error rate of 4.50% for over-stemming and 29.85% for under-stemming. The information retrieval system registered effective performance of 0.785 precision and 0.233 recall. It has been witnessed that the challenging task in developing a full-fledged Afaraf text retrieval system is handling morpholoical word variations. The performance of the system may increase if the performance of the stemming algorithm is improved and if standard test corpus is used.
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    Magnetized Plasma with Ferromagnetic Grains as a Tunable Left Handed Medium
    (Addis Ababa University, 2016-11) Taha, Osman; Mesfin, Belayneh (PhD)
    The propagation of electromagnetic waves in a cold magnetized plasma with ferromagnetic grains (MPFG) in the high frequency domain is studied. The MPFG medium that consists of magnetized electron-ion plasma and ferromagnetic grains is assumed to be a homogeneous anisotropic medium. Its dispersion properties which is controlled by the simultaneous characterization of the permittivity and permeability tensors is investigated theoretically and numerically near the resonance frequency. It is found that MPFG becomes transparent for the waves that cannot propagate in conventional magnetized electron-ion plasma. The refractive index of the waves propagating parallel to the applied magnetic field is found to be negative for the extraordinary wave in certain frequency domain. Moreover, by varying the parameters of the electric subsystem (electron-ion plasma), the nontransparent region for electromagnetic wave propagation can be eliminated. The results obtained show that in a narrow band of the super-high-frequency range near the electron cyclotron frequency, the MPFG medium possesses all the known characteristics of negative refractive index media, which would make it as a viable alternative medium to demonstrate the known and predicted peculiar properties of media having negative index of refraction