Browsing by Author "Demissie, Tesfaye"

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    Calculation of Stability Ranges of Charged Alkali Halide Clusters
    (Addis Ababa Universty, 1996-06) Demissie, Tesfaye; Marx, V. (PhD)
    The critical Coulomb explosion number, i.e., the lower bounds of particle size required to stabilize a multiply charged alkali halide cluster against Coulomb explosion were calculated using a simple Coulomb potential. The magnitude of the charge ranges from 2 to 10. The influence of sign and position of the charges were assessed . The critical Coulomb explosion number increases with increasing number of charges on the clusters. The critical coulomb explosion number and the charge of the clusters are linearly related with a good correlation . The binding energies of the most tightly bound neutral isomers of (NaCl) n, n=2- 12, were calculated using a simple Coulomb potential. The stability order of the various isomers of a given cluster size is predicted using binding energy as a criteria. These results are compared with other works which employ refined but computationally expensive potential models . The agreement is good
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    Pejrology, Geochemistry and Mineral Occurrences of the Big Dubicha Metaultramafic Rocks, Northeast of Kibremengist, Southern Ethiopia
    (Addis Ababa Universty, 1999-11) Demissie, Tesfaye; Ayalew, Tekiewold (PhD)
    The Big Dubicha metauitramafic mass is part of thy, east;,:l'n belt (Kenticha belt)Of, Adola area. Lithologic units in the area include; biotite - muscovite - quartz schist, chlorite schist, taic schist and tremolite - actinolite - talc - serpentine schist. Mineral assemblages of the Big Dubicha altered ultramafic rocks are characteristic of lower greenschist facies, representing serpentinization, chloritization and carbonation reactions among others. These reactions are the result of low temperature water-rock interactions. The metamorphic mineral assemblages of the enveloping metamorphosed sedimentary rock fall within lower to middle amphibolite facies, suggesting the presence of allofacial relationship between the Big Dubicha altered ultramafic rocks versus the enveloping rock. In addition shallow angle westward dipping foliation is related to the thrusting event. Whole rock geochemical data examined in the system CaO - MgO - Si02 - H20 - CO2 for" tremolite - actinolite - talc - serpentine schist and chlorite schist suggest harzburgitic and dunitic anhydrous mineralogy, together with the limited metamorphic and structural observations, the Big Dubicha altered uitramafic rocks represent a slice or fragmcnt 01 subcontinental mantle lithosphere, From the geochemical maps of soil samples, anomalous zones of Ni, Cr, Co, Mn, and Zn are observed along the strongly deformed and serpentinized tremolite - actinolite - talc -serpentine schist, indicating insitu weathering (lateritization) of the bedrock was responsible for the' observed mineral occurrences.