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  Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 374 journals)
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SINET : Ethiopian Journal of Science
Number of Followers: 5  

  This is an Open Access Journal Open Access journal
ISSN (Print) 0379-2897
Published by African Journals Online Homepage  [261 journals]
  • Electric field induced and enhanced magnetic properties of multiferroic
           material (BiFeO3)

    • Authors: Abera Mebrahtu
      Pages: 125 - 131
      Abstract: In this research work, enhancement and induction of magnetization and other related properties of ferro-electromagnet is reported. The ascertained enhancement and induction is supported by the Hamiltonian composed of itinerant electrons, localized electrons, and their mutual interactions. Using double time temperature dependent Green’s function formalism and equation of motion, the study exhibited the effect of external electric field that can induce and enhance the magnetization and other related parameters of the material. The expressions for spin wave energy, magnetization, magnetic susceptibility, and heat capacity of the system have been obtained and influenced by the action of an external electric field. These enhanced and induced functional responses of this material will present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters. The results obtained in this work are in a good agreement with the previous theoretical and experimental findings.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.1
      Issue No: Vol. 45, No. 2 (2022)
       
  • The effect of surface plasmonic resonances on magneto-plasmonic spherical
           core-shell nanocomposites

    • Authors: Kinde Yeneayehu, Teshome Senbeta , Belayneh Mesfin
      Pages: 132 - 142
      Abstract:  In this study, the effect of plasmon resonance on magneto-plasmonic  spherical core-shell nanocomposite enclosed in a dielectric host medium is theoretically investigated by applying electrostatic approximation (esa) and Maxwell-Garnet effective medium theories to obtain magneto-optical parameters such as; effective electric permittivity and magnetic permeability as well as the corresponding extinction cross-sections. Likewise, for a fixed size of QDs (of radius  nm) numerical analysis was performed to determine the plasmonic resonance effect by varying the parameters such as the metal fraction (β) and the dielectrics (εh) of the host medium on the magneto-plasmonic nanostructures (nss). The results depict that graphs of absorption, scattering, and extinction cross-sections as a function of wavelength have two positions of resonance peaks. The first set of peaks are in the ultraviolet (uv) and the second located in visible regions. These peaks originated from the strong coupling between a regular periodic vibrations of surface plasmons of silver (Ag) with the excitonic state of the dielectric/semiconductor at the internal ( ) and external (Ag/host) interfaces. As β increases, the absorption and scattering cross-sections are blue-shifted in the first peak and red shifted the second set of peaks. Similarly, as εh increases or as β decreases, the sets of resonance peaks for extinction cross-section gets enhanced; while keeping one of these parametric quantities fixed at once. The resulting surface plasmon resonance effect might be utilized in a variety of applications that combines both the plasmonic and magnetic core-shell nanostructures ranging from UV to Visible spectral regions.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.2
      Issue No: Vol. 45, No. 2 (2022)
       
  • Petrology and geochemistry of bimodal volcanic rocks of Southern Lake Hayk
           area, northwestern Ethiopian plateau: implication for their petrogenesis

    • Authors: Getie Berlie , Dereje Dereje , Mohammed Assen
      Pages: 143 - 164
      Abstract: This study presents and integrates field, petrological, and whole-rock geochemical (major and trace elements) data of the volcanic rocks from the Lake Hayk area to understand their petrogenesis. The study area's major lithological components include lower and upper basalt, rhyolitic lava, rhyolitic tuff, rhyolitic ignimbrite, and unwelded tuff. Petrographic analysis suggests that felsic rocks are dominated by quartz and well-developed sanidine (K-feldspar) phenocrysts with glassy groundmass, whereas mafic volcanic products are characterized by aphyric to porphyritic textures with the olivine and plagioclase dominant phenocryst. The area constitutes bimodal composition of flood basaltic to rhyolitic rock with scarce intermediate composition. Basalts have low Rb/Nb = 0.5-0.58, La/Nb = 0.88-1.06 and high TiO2 = 2.08-3.04, basaltic andecite have higher Rb/Nb =2.7, La/Nb = 1.81 and low TiO2= 1.96 and rhyolite Rb/Nb = 0.97-1.69, La/Nb = 0.51-1.08 and lower TiO2 = 0.41- 0.71.The positive Ba and negative K anomalies testify amphibole mantle source. The basalts are characterized by low CaO/Al2O3 ratios (0.71–0.97) and relatively less fractionated and flat hree patterns with (TbN/YbN = 1.75-2.33) chondritic values. This suggests a mantle source mostly containing spinel rather than garnet. Rhyolites are characterized by a steep negative correlation in bivariate plots of MgO, Fe2O3, TiO, and CaO against SiO2 and positive anomaly of Ta with slight Nb trough.  This suggests that Fractional Crystallization is the major process for the genesis of rhyolitic rocks, rather than crustal contribution, partial melting, and assimilation, producing rhyolitic rocks.  
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.3
      Issue No: Vol. 45, No. 2 (2022)
       
  • Awareness of people living in Sagure District, Arsi, Ethiopia about ergot
           fungus (Claviceps purpurea) and ergotism

    • Authors: Asnake Desalegn, Dawit Abate , Birhanu Teshome
      Pages: 165 - 173
      Abstract: Ergot is a plant parasitic fungus that belongs to the genus Claviceps, and ergotism is a poisoning caused by secondary metabolites produced mainly by the ergot fungus (Claviceps purpurea). The presence of ergot fungi in the farmers’ field was surveyed, and ergot sclerotia were clearly observed in the farmers’ fields on wild oat plants. A cross-sectional study was therefore conducted in three Kebeles of the Sagure District (Kechema Murkicha, Digelu Kidame and Mankula Negele), near Asela town, Ethiopia, to assess awareness of the residents about ergot fungus and ergotism. From a total of 385 study participants only 100 (26%), knew what ergot and ergotism stand for. Thirty-one percent of the study participants described the most common symptoms of the ergot poisoning as ‘cutting off legs’ and removing wild oats (Avena abyssinica), the host for the ergot fungus, as the main method of prevention of the disease. Among the socio-demographic factors, education level was found to be significantly associated with the knowledge of ergot (p < 0.001), where participants from secondary education and above had better knowledge about ergot fungus and ergotism (cor: 2.5, 95% CI:1.34 – 6.22). From binary logistic regression model fitted, study site has statistically significant association with knowledge about ergot (AOR: 5.34, 95% CI:3.25 – 8.43, p< 0.001). In conclusion, though the fungus was prevalent in the farmers’ fields, majority of the study participants were not aware of ergot fungus and ergotism, thus there is a need to create awareness about the fungus and the disease in order to prevent possible future disease outbreaks.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.4
      Issue No: Vol. 45, No. 2 (2022)
       
  • Population dynamics of the Nile tilapia (Oreochromis niloticus L. 1758)
           stock in Lake Langeno, Ethiopia

    • Authors: Genanaw Tesfaye, Gashaw Tesfaye, Abebe Getahun, Zenebe Tadesse, Getinet Workiye
      Pages: 174 - 191
      Abstract: Nile tilapia, Oreochromis niloticus, is a widely distributed and economically most import fish species in Ethiopia. Effective management is essential to sustain their fisheries and the benefits for the local communities. However, little is known about the population dynamics of the Nile tilapia stock in Lake Langeno. Vital parameters of its population were determined using length frequency data collected from 5,949 specimens ranging from 8.5 to 35.7 cm total length (tl). These specimens were collected from August 2017to July 2018. The population parameters were determined using the elefan I routine in FiSAT software. Estimated von Bertalanffy growth parameters were asymptotic length (L∞) = 35.70 cm, growth curvature (K) = 0.32 yr-1, age at length zero (to) = -0.49, and growth performance index (Փ') = 2.61. Instantaneous total mortality (Z), natural mortality (M), and fishing mortality (F) rates were determined from length-converted catch curve and empirical models, respectively, and their values obtained were Z = 2.31 yr-1, M = 0.82 and F =1.56 yr-1, respectively. The exploitation rate (E) of Nile tilapia computed from its mortality rates was 0.67 yr-1, suggesting state of overfishing. The size at first capture (Lc) was estimated at 14.0 cm which is much lower than the size at first maturity (Lm=16.62 cm), which further substantiated the state of overfishing. The results of the study are very useful for fishery managers and scientists who wish to manage and further explore the Nile tilapia stock in Lake Langeno.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.5
      Issue No: Vol. 45, No. 2 (2022)
       
  • Distribution of benthic macroinvertebrates in relation to physicochemical
           parameters and macrophyte cover in the Ketar River, Ethiopia

    • Authors: Yadesa Chibsa, Seyoum Mengistou , Demeke Kifle
      Pages: 192 - 204
      Abstract: The aim of this study was to determine the effects of physicochemical parameters and macrophyte on the macroinvertebrate assemblages in the Ketar River, which drains into Lake Ziway. Six sampling sites were selected along the river stretch and samples were collected from December to April 2017/2018 based on the method outlined in Ontario Benthos Biomonitoring Network Protocol Manual. A total of 5,450 individuals comprised of one class, 7 orders, and 23 families were collected during the study period. Hemiptera families were the predominant taxa and contributed the largest percentage of the total samples followed by the Coleoptera. Notonectidae and Corixidae shared the highest total abundance. This study confirmed that the sites covered with macrophytes were significantly different from the substrate both in taxa richness and total abundance (P < 0.05). Redundancy Analysis revealed that pH, Temperature, electric conductivity, DO, NO2, NO3, NH4, SiO2 and TP were the most important variables explaining the variation in macroinvertebrate assemblage patterns. The mean Shannon diversity index also indicated that the sites covered by the macrophyte stand had a significantly higher value than the sites sampled from the substrate, which implies that macrophytes support abundant, and promoting the diversity of macroinvertebrates. Thus, the conservation of macrophytes can enhance the conservation of macroinvertebrates along the course of the river, besides the role of macrophyte in sediment trapping and reducing sedimentation buildup in Lake Ziway.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.6
      Issue No: Vol. 45, No. 2 (2022)
       
  • Optimization of Neochetina eichhorniae Warner and Neochetina bruchi
           Hustache for the management of water hyacinth, Eichhornia crassipes
           (Mart.) Solms in the Central Rift Valley lakes through the use of
           different nutrient levels in Ethiopia

    • Authors: Tatek Kassu, Emana Getu , Diriba Muleta
      Pages: 205 - 223
      Abstract: Water hyacinth, Eichhornia crassipes (Mart.) Solms, is an alien invasive weed in Ethiopia that has been established in freshwater bodies. Eichhornia crassipes negatively affects water transportation, fishing and biodiversity among others. Hence, implementation of eco-friendly management option such as biological control is a mandatory. The weevils, Neochetina eichhorniae Warner and N. bruchi Hustache, are the principal biocontrol agents against E. crassipes in their native ranges and have been introduced to Ethiopia for the management of the weed. The weevils and their host are affected by the nitrate and phosphate contents of the water body. Thus, this study was conducted to investigate the effect of N. bruchi and N. eichhorniae in relation to water nutrient contents in the management of E. crassipes. The experiment was conducted in a randomized complete block design with three replications in a 4x4x3 factorial arrangement. Eight weeks after the treatments’ application, the population of the weevils and E. crassipes growth parameters were recorded. The larval population was significantly (p < 0.05) affected only by the interaction effect of N. bruchi and the nutrient levels. Among the treatments, the highest mean number of larvae was found on the plants given high and medium nutrient levels. There was also a significant interaction (p < 0.05) between the two weevils adult density. The mean number of emerged adult density of the weevils increased with increasing nutrient levels. The nutrients and weevils exhibited a significant interaction effect on E. crassipes leaf scarring and petiole tunnel. Leaf scarring at the highest weevil density and nutrient level was sixfold greater than that at the lower nutrient level and weevil density. The tunnel length of the weed was threefold higher at the highest nutrient level regardless of the weevil density. The growth parameters of E. crassipes were found to be greater at high nutrient level, except for the mean number of flowers. Conversely, the growth parameters showed a non-uniform trend with the increasing density of the weevils. The current result suggests reduction in E. crassipes could be achieved by lowering the water nutrient levels and use of N. bruchi and N. eichhorniae.  
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.7
      Issue No: Vol. 45, No. 2 (2022)
       
  • Spectral problem for the Laplacian and a selfadjoint nonlinear elliptic
           boundary value problem

    • Authors: Natnael Gezahegn, Tadesse Abdi
      Pages: 224 - 234
      Abstract: In this paper, we present some connections between the spectral problem,
      −Δu(x) = λ1u(x) in Ω,
      u(x) = 0 on ∂Ω and selfadjoint boundary value problem,
      Δu(x) − λ1u(x) + g(x, u(x)) = h(x) in Ω,
      u(x) = 0 on ∂Ω, where λ1 is the smallest eigenvalue of −∆, Ω ⊆ Rn is a bounded domain, h ∈ L2(Ω) and the nonlinear function g is a Caratheodory function satisfying a growth condition. We initially investigate the existence of solutions for the spectral problem by considering the selfadjoint boundary value problem. The selfadjoint boundary value problem is then considered for both existence and estimation results. We use degree argument in order to show that the selfadjoint boundary value problem has a solution instead of the Landesman-Lazer condition or the monotonocity assumption on the second argument of the function g. In this paper, we present some connections between the spectral problem, and selfadjoint boundary value problem, where λ1 is the smallest eigenvalue of −∆, Ω ⊆ Rn is a bounded domain, h ∈ L2(Ω) and the nonlinear function g is a Caratheodory function satisfying a growth condition. We initially investigate the existence of solutions for the spectral problem by considering the selfadjoint boundary value problem. The selfadjoint boundary value problem is then considered for both existence and estimation results. We use degree argument in order to show that the selfadjoint boundary value problem has a solution instead of the Landesman-Lazer condition or the monotonocity assumption on the second argument of the function g.
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.8
      Issue No: Vol. 45, No. 2 (2022)
       
  • Geographical and population diversity of African honeybees, Apismellifera
           L. (Hymenoptera: Apidae): A review

    • Authors: Gemechis Legesse, Emana Getu
      Pages: 235 - 248
      Abstract: This review was prepared to summarize the information on geographic and genetic diversity of Apismellifera L. of African honeybees and the progresses made through time and applications of various advanced tools in their taxonomy at subspecies level. African honeybees have developed distinct morphology, behavior and physiology as they evolved in tropical favorable climate. The variations among the African honeybee populations have helped to produce geographic subspecies based on the morphological characteristics. However, the introduction of molecular taxonomic tools has come up with discrepancies in the number of subspecies and lineages, and subspecies composition of evolutionary lineages in Africa and other parts of the world. It has also brought up controversies in the evolutionary history of A. mellifera reporting different location as the center of origin of the species at different times: Asia, Africa and Europe. It is not only the tools that are used, but also the genetic variations within subspecies, within colonies in an apiary site and within individuals of the same colony temporally are the factors for continually appearing discrepancies. Natural hybridization between populations of adjacent subspecies along the geographic transition zones and introgression of genes through introduction of colonies that is mainly driven by human demand for desirable traits of honeybees have been among the challenges for discrimination of honeybee subspecies. Therefore, in future genetic diversity and taxonomic investigations, considering these natural variations at subspecies level and developing standardized and integrated procedures from sampling to analysis methods would help to produce generally recognized data base that is critically important to resolve the problem of inconsistencies in taxonomy and nomenclature of  honeybee subspecies of Arica and elsewhere.  
      PubDate: 2022-08-30
      DOI: 10.4314/sinet.v45i2.9
      Issue No: Vol. 45, No. 2 (2022)
       
 
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