Browsing by Author "Getachew, Melese"

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    Isolation and Characterization of Native Cellulose and Microcrystalline Cellulose from Teff Straw, and Evaluation of Microcrystalline Cellulose as Directly Compressible Pharmaceutical Excipient
    (Addis Ababa University, 2019-07) Getachew, Melese; Prof.Gebre-Mariam, Tsige; Dr.Belete, Anteneh
    Cellulose is one of the major components of agricultural byproducts. Teff is the most widely cultivated cereal crop in Ethiopia covering 22.95% of the cultivated land from which about 7.46 million tons of Teff straw is produced as a byproduct each year. The aim of this study was to isolate and characterize native cellulose and microcrystalline cellulose (MCC) from Teff straw, and evaluate MCC as directly compressible pharmaceutical excipient. Cellulose was isolated from Teff straw with formic/ acetic acid-based treatments and MCC was prepared through HCl catalyzed hydrolysis of cellulose. The isolated cellulose and MCC were characterized through scanning electron microscope (SEM), infrared spectroscopy (FTIR), differential thermal analysis (DTA), thermogravimetric analysis (TGA) and x-ray diffraction (XRD). Powder property, compressibility and tablet properties of MCC were also studied. Yields of cellulose and MCC powder from the raw material were 35.2% and 27.2%, respectively. Cellulose displayed rod-shaped fibers whereas MCC showed irregularly shaped aggregated particles. The IR spectra of both cellulose and MCC, and thermogram of MCC showed similarity with that of Avicel PH-101. The degree of polymerization (DP) and crystallinity index of cellulose were 594.51 and 72.26%, respectively. Whereas, MCC powders showed DP of 241.09–257.38 and crystallinity index of 76.45–84.52%. Spray dried MCC (MCC-SD) exhibited poor flow while oven dried MCC (MCC-OD) showed passable flow property. Both MCC-SD and MCC-OD displayed lower mean particle size and wider particle size distribution than Avicel PH-101. At all compression forces studied, MCC-SD showed superior compactibility than MCC-OD. Both MCC-OD & MCC-SD showed lower lubricant sensitivity and compressibility than Avicel PH-101. Paracetamol loaded tablets of MCC-SD and Avicel PH-101 powders exhibited comparable tensile strength. Disintegration and dissolution profiles of all tablets fall within acceptable limits set for conventional tablets. Based on the results of this study, MCC powder could be prepared from locally available alternative source (Teff straw) for pharmaceutical applications. But, critical variables of MCC preparation should be optimized in order to improve its powder and compaction properties.
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    Study on the Façade Detailing for Wind Load
    (Addis Ababa University, 2020-07) Getachew, Melese; Shifferaw, Taye (PhD)
    Building facades are the first aesthetic characteristic that distinguishes one structure from another. Its unique appearance is frequently the subject of trouble attracting. Façade systems are now widely used for new high-rise buildings, and they represent a significant investment in both the building's construction and long-term success. Even the simplest types of façade systems are far more sophisticated than their earlier equivalents, though many of the earliest walls are still performing admirably. More than fifty years of research and development have eliminated the major drawbacks of the original designs, resulting in improved products. Some people think that a façade system is just an assemblage of glass, aluminum, steel, screws, and sealant. Its construction is not just a combination of various components, but also a sophisticated technology involving complex calculations. Some architects are confused by the relationship between sealant and glass size and wind load, as well as the strength of the glass to withstand the loads. Beginning in the early 1950s, a series of window units and panels joined and supported by simple framing components was a relatively simple but creative concept. Façade system technology has progressed over time to include a wide range of highly engineered designs. This dissertation will focus on the façade details for wind load using sealant bite for glass, limit state design for glass pane, and finite element analysis methods. Finally, the results were discussed and a conclusion and recommendation on façade details were provided.