Browsing by Author "Hailemariam, Solomon"

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    Extraction and Characterization of Essential Oil from Rosemary Leaves
    (Addis Ababa University, 2016-10) Hailemariam, Solomon; Worku, Teshome (Ass.Professor)
    Rosemary (Rosmarinus officinalis L.) extracts enriched in phenolic compounds are effective antioxidants due to their phenolic hydroxyl groups and they also possess innumerable applications starting from markers for plant identifications to bases for semi-synthesis of highly complex molecules. Therefore, the aim of this research is extraction and characterization of rosemary essential oil (Rosmarinus officinalis) using steam distillation method. In this research, rosemary leaves were collected from Sebeta region (town and separate wereda in central Ethiopia). An integrated procedure for steam distillation extraction followed by volatiles sampling and characterization from the leaves of the rosemary was implored. The effect of different process parameters, such as pre-distillation drying conditions and extraction time on the extraction yield was investigated. The parameters taken up for the study like the pre-distillation drying conditions and extraction time were found to significantly affect the extraction yield and quality of the essential oil. Increase in yield was observed when increase the extraction time and pre-distillation drying conditions. The essential oil yield was found to vary from 0.378 to 1.137% under different method of drying and extraction time. Maximum yield was observed from sun dried rosemary leaves at 120 min of extraction time. The volatiles rosemary essential oil in vapour form released from the leaves were condensed and characterized their physical and chemical properties and found within the recommended range. The components of rosemary essential oil was determined using Gas Chromatography-Mass Spectroscopy, and eight major components were identified. Monoterpene hydrocarbons were found to be predominant. The major components were α-pinene (12.08 %), camphor (9.14 %), camphene (2.14 %), bornyl acetate (6.79 %), borneol (5.07%), and α‐terpineol (3.08%). Therefore, pre-distillation drying and extraction time have greater effect on the quality and quantity of rosemary essential oils. Key words: Rosmarinus officinalis L; rosemary; essential oil composition; extraction; steam distillation.
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    Mechanisms for Formations of Photoluminescience from Silicon and Germanium Nanostructures and Formulating Models
    (Addis Ababa University, 2011-06) Hailemariam, Solomon; Bedassa, Tesgera (PhD)
    Bulk silicon (Si) and germanium (Ge) have an indirect band gap transitions however when they are miniaturized to nanometer scale, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases, and hence the transition changes to direct due to confinement. The HOMO-LUMO gap determines the excitation of electrons so that the nanostructures will emit light. In this work,quantum confinement effects for Si and Ge,some methods to calculate band structures and formation mechanisms of photoluminescence from Si and Ge nanostructures are presented. We presented the parameters that influence the photoluminescence intensity of Si and Ge nanostructures. Finally we developed a model that could explain experimental results of Si nanocrystal photoluminescence versus size and wavelength by using Matlab program