Autotransformer fed traction power supply system: analysis,modeling and simulation

For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer(AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profiles of both power supply configurations on the basis of BS EN 50163:2004 international standard.     

Estimating sediment yield risk of reservoirs in northern Ethiopia using expert knowledge and semi‐quantitative approaches

Reservoir siltation is a serious problem that threatens the productivity and sustainability of water‐harvesting schemes. Quantification of sediment deposition in reservoirs and understanding of its major drivers are needed to apply targeted management interventions. Most of the techniques used to estimate sediment deposition in reservoirs require extensive measurements on a frequent time basis, as well as being costly and time‐consuming. Thus, a rapid and relatively economical means of assessing the erosion susceptibility of catchments and predicting their sediment yield potential is necessary. In this study, expert‐based rankings and semi‐quantitative factorial scoring approaches were applied to assess the siltation severity of 25 reservoirs in the Tigray region of northern Ethiopia. The results were then correlated with quantitative sediment yield estimates acquired for representative sites, and a sediment yield predication model was developed for the region. The calibrated model has an efficiency and relative root mean square error (RRMSE) of 79 and 36%, respectively, which is considered adequate to assess erosion susceptibility and siltation risk of reservoirs in similar environments. The study demonstrates that expert knowledge and rapid characterization of catchments, in terms of susceptibility to erosion, are viable options for assessing siltation risks and for analysing controlling factors at a larger number of sites, with minimum costs and acceptable accuracy.     

Chelating agent-free solid phase extraction (CAF-SPE) of uranium,cadmium and lead by Fe-Al-Mn nanocomposite from aqueous solution

Fe-Al-Mn nanocomposite has been synthesized by impregnating MnO₂ with Fe and Al nitrate aqueous solution for preconcentration and determination of Pb (II), Cd (II) and U (VI) ions from aqueous solution. Fourier Transform Infrared spectroscopy (FTIR), X-Ray-diffraction (XRD) and Scanning electron microscopy coupled with energy dispersive X-ray detector (SEM–EDX) were employed to characterize the as-synthesized nanocomposite. The XRD result indicates that the as-synthesized nanocomposite had a crystal size with rhombohedral structure and size of 30.81 nm. FTIR results confirmed the presence of hydroxyl group and Metal–Oxygen vibration in the adsorbent. A sensitive and simple solid-phase preconcentration procedure for the determination of trace amounts of Pb(II) and Cd(II) ions by FAAS and U(VI) ions by Uv–Vis was developed. The adsorption isotherm was formally described by both Langmuir and Freundlich equation with a maximum adsorption capacity of 12.5 (Pb), 12.8(Cd) and 14.9(U) mg g^?1 respectively with preconcentration factor of 15. The limits of detection were 0.09, 0.05 and 0.0097 mg L^?1 and the relative standard deviation for ten replicate measurements were 2.47, 0.979 and 2.04%, for Pb (II), Cd(II) and U(VI) ions, respectively. The recovery of Pb(II), Cd(II) and U(VI) ions were found to be 92.7, 91.3, and 81.76%, respectively. On the basis of these findings, the as-synthesized Fe-Al-Mn nanocomposite was successfully applied as a solid phase extraction for preconcentration and determination of Pb(II), Cd(II) and U(VI) ions in aqueous solution.

     

Effects of excessive speeding and falling asleep while driving on crash injury severity in Ethiopia: A generalized ordered logit model analysis

The severity of injury from vehicle crash is a result of a complex interaction of factors related to drivers’ behavior, vehicle characteristics, road geometric and environmental conditions. Knowing to what extent each factor contributes to the severity of an injury is very important. The objective of the study was to assess factors that contribute to crash injury severity in Ethiopia. Data was collected from June 2012 to July 2013 on one of the main and busiest highway of Ethiopia, which extends from the capital Addis Ababa to Hawassa. During the study period a total of 819 road crashes was recorded and investigated by trained crash detectors. A generalized ordered logit/partial proportional odds model was used to examine factors that might influence the severity of crash injury. Model estimation result suggested that, alcohol use (Coef. = 0.5565; p-value = 0.017), falling asleep while driving (Coef. = 1.3102; p-value = 0.000), driving at night time in the absence of street light (Coef. = 0.3920; p-value = 0.033), rainfall (Coef. = 0.9164; p-value = 0.000) and being a minibus or vans (Coef. = 0.5065; p-value = 0.013) were found to be increased crash injury severity. On the other hand, speeding was identified to have varying coefficients for different injury levels, its highest effects on sever and fatal crashes. In this study risky driving behaviors (speeding, alcohol use and sleep/fatigue) were a powerful predictor of crash injury severity. Therefore, better driver licensing and road safety awareness campaign complimented with strict police enforcement can play a pivotal role to improve road safety. Further effort needed as well to monitor speed control strategies like; using the radar control and physical speed restraint measures (i.e., rumble strips).     

A review of prospects and challenges of photocatalytic decomposition of volatile organic compounds (VOCs) under humid environment

Volatile organic compounds (VOCs) are harmful for humans and the surrounding ecosystem. Emissions from these pollutants have caused a significant reduction in air quality, which has an effect on people's health. Alkanes, alkenes, alcohols, aromatics, and other VOC pollutants have all been broken down by TiO₂ photocatalytic processes. Due to several operating inefficiencies and deactivation issues in humid environments, the practical application of photocatalysis has not been realized on a broader scale. The effectiveness of photo-oxidation of VOCs is impacted by a variety of environmental conditions. In the photocatalytic oxidation of the VOCs, relative humidity (RH) is critical. Therefore, it is important to review the recent findings on how humidity affects the photocatalytic breakdown of VOCs in air. To satisfy this need, this work provides a critical review of the related literature with focus on the fundamentals of photocatalysis, photocatalytic degradation of air pollutants, and the influence of humidity on the photocatalytic process degradation for selected air pollutants. It also highlights the kinetic models and typical photocatalytic reactor and supports for VOC removal.     

Comparative Analysis of Dielectric Engineered Tunnel FET for Biosensing Applications

Silicon - Among several types of innovative bio-sensing technologies, label free dielectric modulated field-effect transistor (DM-FET) based biosensors, stand out because of their appealing...