Browsing by Author "Hailu, Girma"

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    Collisional Radiative Models for Hydrogen Atoms and for Hydrogen Molecules In a Tokamak Plasma
    (Addis Ababa University, 1992-06) Hailu, Girma
    A collisional radiative model is applied to study the ionization, recombination, and energy loss rates of an optically thin hydrogen plasma in a Tokamak thermonuclear fusion reactor. The effective ionization and recombination coefficients are found to be increasing functions of electron density, the increase being bigger when the temprature is low. The rate of radiative energy loss is significant only in low density plasmas; and the estimate that has been used by most plasma modelers is pretty big that it cannot be applied for dense plasmas. Edge plasma cooling due to the interaction of recycling neutral particles near diverter targets with the scrape off layer is an important effect to reduce the heat load on Tokamak vessel components. The relevant atomic data for hydrogenic atoms are well established, whereas the data base for molecules is less complete. Collisional radiative processes are considered to study the effects of hydrogen molecules in the edge plasma boundary. Effective dissociation and dissociative ionization rate coefficients are calculated. Rate coefficients for the production of neutral atoms from hydrogen molecules are also evaluated. Finally the rate of electron energy loss per dissociation of molecules into atoms and/or ions is calculated. The rate of this energy loss is significant and the dissociation of the molecules may account for the missing heating power in the divertor region
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    Geochemical and Petrographic Characteristics of Crystal Rich Volcanic Rocks From Lalibela Area, Northwestern Ethiopia.
    (Addis Ababa University, 2018-06-03) Hailu, Girma; Ayalew, Dereje (Professer)
    The Bilbala magmatic complex is situated in northwestern Ethiopian plateau near to northern main Ethiopia rift. The aim of this work was to investigate and identify the sources involved in the petrogenesis of the pre –rift basalts of the Bilbala area around Lalibela wich located with approximate distance of 730 Km from Addis Ababa. Field observation, ptrographic analysis and geochemical data analysis are the main method used to meet the aim or objective of this study. Based on field observation and description the study area is covered by basaltic rocks. The paper presents the results of a comprehensive major element, trace element, and petrographic study of Oligocene volcanic sequences from the northwestern Ethiopian flood basalt province around Lalibela. A petrographic analysis result with field observation indicates the presence of clinopyroxene, olivine and plagioclase as phenocrysts and groundmass with Fe-Ti oxides, opaque minerals and volcanic glass. The major and trace element compositions with mineral assemblage of crystal rich basaltic rocks in the area show the HT basalts characteristics of the Ethiopian continental flood basalt. The analyzed samples result displays high contents of TiO2 (3.36-6.87%), FeO* (11.59-15.71%), CaO/Al2O3 (0.89-1.989%) and enrichment of incompatible trace elements and LREE. On primitive mantle normalized diagram of the studied samples there is positive Ta and Nb anomalies, but Sr with Pb shows negative anomalies.Enrichment of LREE and a relative depletion of HREE in the studied samplesis observed and this suggest the presence of residual garnet in the source, and from trace elements concentration and ratios there is little evidence for contamination during the magmatic ascent.The Ce/Pb, Nb/Th and Nb /U ratios of the study area basaltic rocks display 21.3-51.7, 9.5-13.8 and 33.1-45.2 respectively. These elemental ratios have nearly OIB type character. The studied samples have low Zr/Nb ratios (< 10). The low Zr/Nb value of this mafic lava might imply a dominant mantle plum contribution during the genesis of the study area lavas. .
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    The Study of Porphyrins Confinement in Nafion Membrane and Photovoltaic Properties of a Bulk Heterojunction Solar Cell
    (Addis Ababa University, 2007-03) Hailu, Girma; Tessema, Genene (PhD)
    With the development of strong laser sources for different applications which in some instances has extremely high intensity, optical power limiters are needed to provide human eye and optical detector protection. So, a smart ultra fast optical power limiter that is transparent for low incident intensities and blocks the output at high input intensities is required. The operation of optical power limiters is based on the phenomena of nonlinear absorption (NLA). Different Porphyrins have been reported to have NLA property which put them as potential candidate for application as optical power limiters. In this paper, we have investigated NLA and optical limiting properties of five different types of Porphyrins by using the Z-scanning technique. The Porphyrins were confined into Nafion membrane in order to protect them from possible degradation. The results of the experiments clearly show the fascinating NLA and optical power limiting properties of the Porphyrins under investigation. By fitting the Z-scan results with the theoretical fitting function, the nonlinear absorption coefficients (¯) of all the Porphyrins with different concentrations for each of them is determined. Besides, their linear absorption coefficients are obtained by considering low intensity regimes from the data and applying Beer’s low of linear absorption