Browsing by Author "Girma, Mekonnen"

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    Computational Modeling of ZnO/WSSe van Der Waals Heterostructures for Solar Cell Applications
    (Addis Ababa University, 2020-09) Girma, Mekonnen; Georgies, Alene (PhD)
    Stacking of two-dimensional materials into layered Van der Waals heterostructures are recently considered as a promising candidate for applications on photovoltaic devices because they can combine advantages of individual‟s 2D materials. Janus transition metals dichalcogenides (WSSe) have emerged because of favorable electronic properties as an attractive absorbing material. We therefore systematically examine the geometric features, electronic properties, work function, and density of states, band alignment of monolayer ZnO and WSSe and their heterostructures in this work using density functional theory methods (DFT) with PBE calculations as implemented in the Quantum ESPRESSO and VASP codes. It was found that, the negative binding energies indicate all the four configurations of ZnO-WSSe heterostructures are stable and feasible. Moreover, three configurations B, C and D exhibit indirect band gaps of 1.6248 eV, 1.6319 eV and 1.3126 eV, respectively. But the other configuration A has direct band gap of 1.7106 eV. In addition, it is found that all four configurations show band alignment type-II. In type-II alignment, donor-acceptor interface band heterojunctions can easily promote electron and hole carrier transfer and separation at interface, which can significantly enhance the efficiency of photovoltaic solar cells. With direct band gap, configuration A is the preferred heterostructure for photovoltaic devices applications.
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    Major Challenges of Medical Laboratories for ISO 15189 Accreditation in Selected Government Hospitals of Addis Ababa, Debrebrhan, and Bishoftu, Ethiopia
    (Addis Ababa University, 2017-06) Girma, Mekonnen; Tsegaye, Aster (PhD)
    Background: Numerous global initiatives in Africa have focused on clinical laboratory harmonization and standardization, and accreditation. Though accreditation has many advantages and advocated largely, it is still challenging for the laboratories to fulfill all requirements and the criteria of accrediting bodies. So identifying the different challenges faced by the laboratories during the process of accreditation is important for proper planning and action to resolve those challenges. Objective: To assess the major challenges of Medical Laboratories for ISO 15189 accreditation in selected government hospitals of Addis Ababa, Debrebrhan, and Bishoftu, Ethiopia. Method: Cross sectional study design using qualitative and quantitative data collection approach was used from March to May 2017. The data for this study was gathered using structured questionnaire and in-depth interview. Stratified-proportional sampling technique was used. Data was entered, cleaned using EPI-Data 3.1 and exported to SPSS version 20 software for further processing and analysis. Simple descriptive statistics like percentages and frequency was used. The qualitative data from in-depth interview were categorized and discussed. Result: In this research 175 questionnaire respondents and 24 key informants from 12 hospitals were included to identify the major challenges facing medical laboratory’s accreditation process. All respondents had awareness about the accreditation process but only 79% of them have involved in the process in one or more ways. More than half of the respondents (51%) had training experience related to either laboratory LQMS or ISO accreditation. High turnover of trained and experienced laboratory professionals for better job opportunity and education was reported to mainly affect the accreditation process. Routine work load, poor equipment quality, shortage and quality of laboratory supplies, inconsistent mentorship and training, strict assessment process and low attention and commitment from top management were among the major challenges identified. Conclusion: Even though there exists an effort to fulfil accreditation requirements, achieving and maintaining accreditation was still challenging for many facilities due to; trained staff turnover, training and mentorship inadequacy, low staff satisfaction, low quality and quantity of equipments, low top management support, and poor quality laboratory facility. This study highlights the need for stronger engagement, commitment and advocacy with all stakeholders to harmonize and lead accreditation program effectively. Keywords: LQMS, accreditation, challenge, ISO 15189, SLMTA/SLIPTA, Medical laboratory