Browsing by Author "Beyene, Gashaw"

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    The Condition factor, Feeding and Reproductive Biology of Oreochromis niloticus L. (Pisces: Cichlidae) in Lake Beseka (Metehara) , Ethiopia.
    (Addis Ababa University, 2005-06) Beyene, Gashaw; Admassu, Demeke (PhD)
    The condition factor , feeding and reproductive biology of O. niloticus from L. Beseka , Ethiopia , were studied from samples taken during November 2003 to November 2004. The length - weight relationship of 1028 fish ranging in size from 4 cm to 24 cm TL and from 6 g to 140 g TW was computed . The 2 g relationship was curvilinear, and described by TW = 0.0546 X TL ! the regression equation for females was TW = 0.1005 X TL2'3 and that of males was TW = 0.0742 X TL2'7. Fulton’s condition factor (FCF) was calculated for the total sample as well as for both sexes separately . The mean monthly FCF was highly significantly different between sampling months and sexes and the sex by month interaction was insignificant . The mean . i SE ranged from 1.2 ± 0.06 to 2.0 ± 0.04 for females whereas from 1.3 ± 0.01 to 2.6 ± 0.04 for males. The stomach contents of 690 fish ( 200 males and 490 females ) were examined . The stomach contents were found to be composed of diverse items. A total of 22 algal genera belonging to three families! Cyanophyceae ( blue greens), Chlorophyceae (green algae ), Bacillariophyceae (diatoms) , were identified . Among the diatoms Navicula, Cyclotella, Cymbella and Thallasiossira, from the blue greens Microcysts, Osciiiatoria and Anabena and from the green algae Cosmarium, Botryococcus and Scendsmus were the most frequently encountered algal genera in the stomach of the fish. In addition , foods of animal origin , zooplankton, macrophytes, sand grains and detritus were found in the stomach of the fish. Generally, diatoms and blue greens as a group contributed the bulk of the diet. Considering the average importance of algal genera, Microcysts and Navicula are the most important in the diet of the fish in L. Beseka. The smallest sexually mature female was 6 cm TL whereas the male was 10 cm TL. However, the 50% maturity length (Lso) was 12cm TL for females and 14cm TL for males, and all fish above 20cm TL were sexually mature. The average ± SE fecundity of O, niloticus ranging in length from 10 to 23cm TL and in weight from 14 to 81g TW was 154 ± 2.8. The smallest count was 110 eggs and the largest was 235 eggs. In general, fecundity of O. niloticus in L. Beseka was linearly related to total length, total weight and gonad weight. The mean monthly gonadosomatic index (GSI) of females ranged from 0.7 to 3.5 and that of males from 0.6 to 2.1. There was biannual cycle in which GSI increased from February peaking in April and from August peaking in September. Ripe females and males also occurred at high frequencies in April and September. Hence, it was found that the fish in L. Beseka spawned throughout the year, with a peak of activity between March and April and also between August and September. Key words/ phrases: Breeding season, fecundity, Fulton’s condition factor, L. Beseka, Oreochromis niloticus, stomach contents.
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    Investigation of Plasmon Enhanced Optical Properties and Photocatalytic Applications of Composite Nanostructures
    (Addis Ababa University, 2021-03-07) Beyene, Gashaw; Senbeta, Teshome (PhD); Mesfi n, Belyaneh (PhD); Zhang, Qinfang (Professor)
    In this dissertation, we investigated plasmon enhanced optical properties and photocatalytic applications of composite nanostructures by using noble materials from theoretical and experimental perspectives. The theoretical investigation mainly focused on the optical and plasmonic properties of spherical and spheroidal ZnO@Ag core-shell nanocomposite embedded in nonabsorptive medium. The e_ective dielectrics function, polarizability, refractive index and optical absorbance for spherical as well as absorption cross-section and radiation e_ciency for spheroidal nanocomposite are studied. These optical and plasmonic properties are tuned when size of core and/or composite, shell thickness, shape of core and/or shell, and refractive index of the host-medium is changed. In spherical nanocomposite, there are two resonances associated with interfaces while in spheroidal nanocomposite four plasmonic resonances are appeared that correspond to interfaces and the bonding/antibonding pairs. The tunable of plasmonic resonances from UV to infrared spectral regions of such composite enables it to exhibit very interesting material properties in a variety of applications. Experimentally, we emphasized the optical properties and photocatalytic applications of ZnO nanoparticles, triple layered ZnO@SiO2@Ag core-shell composite nanostructures and Bi doped/undoped TiO2 nanostructures. In particular, we synthesized ZnO nanoparticles using three di_erent methods as presented in the experimental section of the study. Due to di_erent synthesis methods and procedures as well as di_erent surfactant/stablizing agent, the synthesized ZnO nanoparticles have di_erent morphology, band gap energy, varying quantum size e_ect and photocatalytic responses. The photocatalytic performance of ZnO nanoparticles were evaluated by using methyl orange dye as a pollutant under UV-light irradiation. Triple layered ZnO@SiO2@Ag core-shell nanocomposites are also fabricated at 400 oC for di_erent calcination time. The photocatalytic activity and stability of the as-synthesized samples were evaluated by photo-degradation of organic methylene blue under ultraviolet light irradiation. When ZnO@SiO2 is coated with Ag, the stability and photocatalytic performance of the composite ZnO@SiO2@Ag photocatalysts were highly enhanced. In addition, Bi- doped/undoped TiO2 nanoparticles are synthesized by green synthesis method using zingiber o_cinale extract solution. After doping Bi, the band gap energy is decreased from 3:00 eV to 2:76 eV , absorption region is shifted to visible range of solar spectrum, and surface function is modi_ed. The photocatalytic activity of the sample is analyzed by UV-Vis spectroscopy using trypan blue dye. The photo-degradation e_ciency of chemical synthesis TiO2 nanoparticles is enhanced to 98:34 % by doping basic metal Bi and using ginger extraction solution. The synthesized samples were analyzed using a characterization techniques such as X-ray di_raction (XRD) spectroscopy, scanning electron microscope (SEM), Transmission electron microscope (TEM), Ultraviolet visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS).