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OALib Journal期刊

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Assessment of the Levels of Brominated Flame Retardants in Computers and Televisions in Selected Regions of Eritrea  [PDF]
Afewerki Tesfagabr, Tesfamichael Haile, Mussie Sium, Teame Tekleab
Open Access Library Journal (OALib Journal) , 2018, DOI: 10.4236/oalib.1105061
Abstract:
During recent years, electronic waste (e-waste) around the world is growing at a fast rate and has become a matter of concern due to the presence of toxic brominated flame retardants (BFRs) and certain heavy metals. Currently, in Eritrea there is low awareness on the harmful effects of e-wastes, lack of proper storage facilities and no proper policy and legislative framework related to e-wastes. Thus, in most cases e-wastes still reside in homes, offices, and some are stored with other materials in different places. Therefore, the objective of the present study was to assess the levels of BFRs in obsolete as well as in lately imported computers and televisions using hand held hazardous substances analyzer—Genius 3000 XRF. The survey was done in selected regions of Eritrea and thus a total of 223 samples of computers and TVs from 78 different products were screened. Three readings at forty seconds were conducted for each sample and the average value was calculated. From 173 sampled computers, both oldest and lately imported products, different levels of Br were measured varying from the lowest detectable amount (0.3689 ppm) to the highest (87,821 ppm). Similarly, out of 50 screened old and new models of TVs various levels of Br were determined with minimum detectable level (1.5793 ppm) and highest level (80,916 ppm). The analysis displayed high levels of Br both in the obsolete and lately manufactured products. The concentration of Br didn’t show any consistency either to the product type or manufacturing time. This is a very first preliminary study conducted related to the levels of BFRs in electronic wastes in the country and thus in order to evaluate the environmental impacts and health hazards caused by BFRs and other toxic materials of e-wastes, further study using advanced analytical methods is mandatory.
Water balance modeling of Upper Blue Nile catchments using a top-down approach
S. Tekleab,S. Uhlenbrook,Y. Mohamed,H. H. G. Savenije
Hydrology and Earth System Sciences Discussions , 2010, DOI: 10.5194/hessd-7-6851-2010
Abstract: The hydrological behavior and functioning of twenty catchments in the Upper Blue Nile basin have been analyzed using a top-down modeling approach that is based on Budyko's hypotheses. The objective is to obtain better understanding of catchment response for prediction in ungauged catchments. The water balance analysis using Budyko-type curve at annual scale reveals that the aridity index does not exert a first order control in most of the catchments. This implies the need to increase model complexity to a monthly time scale to include the effects of seasonal soil moisture dynamics. The dynamic water balance model used in this study predicts the direct runoff and other processes based on limit concept. The uncertainty of model parameters has been assessed using the GLUE (Generalized Likelihood Uncertainty Estimation). The results show that the majority of the parameters are reasonably well identifiable. Moreover, a multi-objective model calibration strategy has been employed within the GLUE framework to emphasize the different aspects of the hydrographs on low and high flows. The model has been calibrated and validated against observed streamflow time series and it shows good performance for the twenty catchments of the upper Blue Nile. During the calibration period (1995–2000) the Nash and Sutcliffe coefficient of efficiency for monthly flow prediction varied between 0.52 to 0.93 during high flows, while it varied between 0.32 to 0.90 during low flows (logarithms of flow series). The model is parsimonious and it is suggested that the resulting parameters can be used to predict monthly stream flows in the ungauged catchments of the Upper Blue Nile basin, which accounts about 60% of total Nile basin flow.
Water balance modeling of Upper Blue Nile catchments using a top-down approach
S. Tekleab, S. Uhlenbrook, Y. Mohamed, H. H. G. Savenije, M. Temesgen,J. Wenninger
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2011,
Abstract: The water balances of twenty catchments in the Upper Blue Nile basin have been analyzed using a top-down modeling approach based on Budyko's hypotheses. The objective of this study is to obtain better understanding of water balance dynamics of upper Blue Nile catchments on annual and monthly time scales and on a spatial scale of meso scale to large scale. The water balance analysis using a Budyko-type curve at annual scale reveals that the aridity index does not exert a first order control in most of the catchments. This implies the need to increase model complexity to monthly time scale to include the effects of seasonal soil moisture dynamics. The dynamic water balance model used in this study predicts the direct runoff and other processes based on the limit concept; i.e. for dry environments since rainfall amount is small, the aridity index approaches to infinity or equivalently evaporation approaches rainfall and for wet environments where the rainfall amount is large, the aridity index approaches to zero and actual evaporation approaches the potential evaporation. The uncertainty of model parameters has been assessed using the GLUE (Generalized Likelihood Uncertainty Estimation) methodology. The results show that the majority of the parameters are reasonably well identifiable. However, the baseflow recession constant was poorly identifiable. Parameter uncertainty and model structural errors could be the reason for the poorly identifiable parameter. Moreover, a multi-objective model calibration strategy has been employed to emphasize the different aspects of the hydrographs on low and high flows. The model has been calibrated and validated against observed streamflow time series and it shows good performance for the twenty study catchments in the upper Blue Nile. During the calibration period (1995–2000) the Nash and Sutcliffe efficiency (E NS) for monthly flow prediction varied between 0.52 to 0.93 (dominated by high flows), while it varied between 0.32 to 0.90 using logarithms of flow series (indicating the goodness of low flow simulations). The model is parsimonious and it is suggested that the calibrated parameters could be used after some more regionalization efforts to predict monthly stream flows in ungauged catchments of the Upper Blue Nile basin, which is the vast majority of catchments in that region.
Substrate Interface Interactions
R. Czerw,B. Foley,D. Tekleab,A. Rubio,P. M. Ajayan,D. L. Carroll
Physics , 2001,
Abstract: By utilizing the current transients in scanning tunneling spectroscopy, the local interfacial electronics between multiwalled carbon nanotubes and several supporting substrates has been investigated. Voltage offsets in the tunneling spectra are directly correlated with the formation of a dipole layer at the nanotube-substrate interface strongly suggesting the formation of interface states. Further, a systematic variation in this local potential, as a function of tube diameter, is observed for both metallic substrates (Au) and semi-metallic substrates (graphite). In both cases, tubes with diameters between ~ 5 nm and 30 nm, the interfacial potential is nearly constant as a function of tube diameter. However, for tube diameters < 5 nm, a dramatic change in the local potential is observed. Using ab initio techniques, this diameter dependent electronic interaction is shown to derive from changes in the tube-substrate hybridization that results from the curvature of the nanotubes.
Identification of Electron Donor States in N-doped Carbon Nanotubes
R. Czerw,M. Terrones,J. -C. Charlier,X. Blase,B. Foley,R. Kamalakaran,N. Grobert,H. Terrones,P. M. Ajayan,W. Blau,D. Tekleab,M. Ruhle,D. L. Carroll
Physics , 2000, DOI: 10.1021/nl015549q
Abstract: Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and characterized by Scanning Tunneling Spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular hetero-junction devices.
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