p-TypeE InAs/GaAs Quantum Dot, Dot-In-Well, and Low-Frequency Noise Properties of Infrared Photodetectors

Several types of p-doped Infrared detectors were studied. These include InAs/GaAs quantum dot (QDIP), and dots-in-well (DWELL) and split off band-based heterojunction detectors. In these structures, IR absorption leading to detection is based on valence-band inter-sublevel hole transitions. For a QDIP and DWELL, at 80 K, two response bands observed at 1.5 – 3 and 3 – 10 µm were identified as due to optical transitions from the heavy hole to spin–orbit split-off QD level and from the heavy-hole to heavy/light-hole level, respectively. Unlike the n-type with bias dependent spectral response, the p-type hole response displays a well-preserved spectral profile (independent of the applied bias) observed in both QDIP and DWELL detectors. At a response peak of ~ 5.2 µm, QDIP and DWELL exhibit an external quantum efficiency of 17 % and 9 % respectively. At elevated temperatures between 100 and ~120 K (for QDIP), 130 K (for DWELL), both QDIP and DWELL detectors exhibit a strong far-infrared or terahertz (THz) response up to 70 µm which show promising potential of p-type QDs for developing THz infrared photodetectors. Based on the dark current and noise power spectral density analysis, structural parameters such as the numbers of active layers, the surface density of QDs, and the carrier capture or relaxation rate, type of material and electric field are some of the optimization parameters identified to improve the photoconductive and dark current gain of detectors. The capture probability of DWELL is found to be more than two times higher than the corresponding QDIP. Based on the noise analysis, QDs based structures suppressed phonon scattering and enhanced carrier life time or photoconductive gain. Furthermore, in a GaAs/AlxGa1-xAs heterostructure, for a given width of AxlGa1-xAs barrier, the barrier thickness can be varied by varying the Al mole fraction x, which is referred to as a graded barrier. Grading the barrier and optimizing the emitter thickness of GaAs/AlGaAs heterostructures enhance the absorption efficiency, the escape probability and lower the dark current; hence, enhances the responsivity and specific detectivity of detectors. The two important methods (Arrhenius plot and Temperature Dependent Internal photoemission (TDIPS)) of determining detectors threshold wavelengths or band offsets were compared. For detectors with long threshold wavelength (\u3e\u3e 9.3 μm), the Arrhenius plot used to extract activation energy leads to energy values with deviation higher than ~ 10 % from the corresponding TDIPS values and results from the temperature dependent Fermi distribution tailing effect and Fowler–Nordheim tunneling current. Therefore, TDIPS or other methods, that take the temperature effects on the band offset and Fowler–Nordheim tunneling current into account, are needed for a precise band offset characterization of a long threshold wavelength detectors

Rationalizing Historical Successes of Malaria Control in Africa in Terms of Mosquito Resource Availability Management.

Environmental management of mosquito resources is a promising approach with which to control malaria, but it has seen little application in Africa for more than half a century. Here we present a kinetic model of mosquito foraging for aquatic habitats and vertebrate hosts that allows estimation of malaria transmission intensity by defining the availability of these resources as the rate at which individual mosquitoes encounter and use them. The model captures historically observed responses of malaria transmission to environmental change, highlights important gaps in current understanding of vector ecology, and suggests convenient solutions. Resource availability is an intuitive concept that provides an adaptable framework for models of mosquito population dynamics, gene flow, and pathogen transmission that can be conveniently parameterized with direct field measurements. Furthermore, the model presented predicts that drastic reductions of malaria transmission are possible with environmental management and elucidates an ecologic basis for previous successes of integrated malaria control in Africa before the advent of DDT or chloroquine. Environmental management for malaria control requires specialist skills that are currently lacking in sub-Saharan Africa where they are needed most. Infrastructure and human capacity building in clinical, public health, and environmental disciplines should therefore be prioritized so that growing financial support for tackling malaria can be translated into truly integrated control programs

Investigation into the pressure-driven extension of the EPANET hydraulic simulation model for water distribution systems

Several hydraulic modelling approaches have been proposed previously to simulate pressure deficient operating conditions in water distribution networks more realistically. EPANET-PDX is an extension of EPANET 2 that has an embedded logistic nodal head-flow function. The EPANET-PDX algorithm was investigated to address the weaknesses uncovered under conditions of extremely low pressure. It was observed that, under certain circumstances, the norm of the system of equations increased from one iteration to the next. A criterion that detects false convergence was included. In general, in the examples considered, the formulation proposed had more consistent computational properties, required fewer iterations of the global gradient algorithm, and application of the line minimization procedure was frequent. The formulation proposed is significantly faster in conditions of extremely low pressure. The hydraulic and water quality modelling functionality of EPANET 2 was preserved. For the operating conditions with satisfactory pressure, where direct comparisons with EPANET 2 were possible, EPANET 2 was consistently faster

Multiobjective evolutionary optimization of water distribution systems : exploiting diversity with infeasible solutions

This article investigates the computational efficiency of constraint handling in multi-objective evolutionary optimization algorithms for water distribution systems. The methodology investigated here encourages the co-existence and simultaneous development including crossbreeding of subpopulations of cost-effective feasible and infeasible solutions based on Pareto dominance. This yields a boundary search approach that also promotes diversity in the gene pool throughout the progress of the optimization by exploiting the full spectrum of non-dominated infeasible solutions. The relative effectiveness of small and moderate population sizes with respect to the number of decision variables is investigated also. The results reveal the optimization algorithm to be efficient, stable and robust. It found optimal and near-optimal solutions reliably and efficiently. The real-world system based optimisation problem involved multiple variable head supply nodes, 29 fire-fighting flows, extended period simulation and multiple demand categories including water loss. The least cost solutions found satisfied the flow and pressure requirements consistently. The cheapest feasible solutions achieved represent savings of 48.1% and 48.2%, for populations of 200 and 1000, respectively, and the population of 1000 achieved slightly better results overall

Integration of hydraulic and water quality modelling in distribution networks : EPANET-PMX

Simulation models for water distribution networks are used routinely for many purposes. Some examples are planning, design, monitoring and control. However, under conditions of low pressure, the conventional models that employ demand-driven analysis often provide misleading results. On the other hand, almost all the models that employ pressure-driven analysis do not perform dynamic and/or water quality simulations seamlessly. Typically, they exclude key elements such as pumps, control devices and tanks. EPANET-PDX is a pressure-driven extension of the EPANET 2 simulation model that preserved the capabilities of EPANET 2 including water quality modelling. However, it cannot simulate multiple chemical substances at once. The single-species approach to water quality modelling is inefficient and somewhat unrealistic. The reason is that different chemical substances may co-exist in water distribution networks. This article proposes a fully integrated network analysis model (EPANET-PMX) (pressure-dependent multi-species extension) that addresses these weaknesses. The model performs both steady state and dynamic simulations. It is applicable to any network with various combinations of chemical reactions and reaction kinetics. Examples that demonstrate its effectiveness are included

Practical Application Of Pressure-Dependent EPANET Extension

Hydraulic models have been widely used in the design and operation of water distribution system (WDSs). The models enable planning for possible changes in the system under a wide range of conditions. Under abnormal operating condition, for instance, WDSs become pressure deficient and unable to satisfy demand fully. In such circumstances, pressure dependent models are suitable to quantify the shortfall in flow and pressure accurately for crucial decision-making. Most recently, a pressure dependent extension of the renowned EPANET hydraulic simulator was developed to enable modelling of pressure deficient networks. The model has an integrated pressure dependent demand (i.e. nodal flow) function coupled with a line search and backtracking procedure to facilitate convergence. Extensive verifications were conducted on the model using benchmark and real life networks and good modelling performances were accomplished. The model was combined with multi-objective genetic algorithm for optimisation of design, rehabilitation and operation of WDSs. It generated superior results for benchmark as well as real life networks in terms of cost, hydraulic performance and computational time in reference to previous solutions. It has also been utilised for water quality modelling of real life networks. Overall, the model has not experienced convergence problems when executing the various simulations. Having demonstrated the robustness and benefits of the model previously including seamless integration in genetic algorithms, it would be greatly beneficial on investigating ways of improving the algorithm further. In this work, the line search and backtracking procedure of the algorithm has been improved. This has improved the robustness further by enhancing greatly the computational properties for low flow conditions and increasing the algorithm’s consistency over a wider range of operating conditions. Extended period simulations were executed on real life network considering source head variations and pipe closure conditions

Influencing preventive behavior with regard to HIV/AIDS among the Police Force of Harari Region, Eastern Ethiopia, 2011

Background: HIV/AIDS has emerged as one of the serious public health challenges in Ethiopia. This disease has individual and institutional impacts, making difficult for the police services to act effectively in protecting the public from crime.Objective: To assess factors that influence HIV/AIDS prevention among police personnel in Harari Region, Ethiopia, 2010.Methodology: A cross-sectional study was conducted in January 2010 involving 310 out of the 790 police personnel found in the Region. A simple random sampling technique was used to select study participants by using their identification numbers as sampling frame from registration books of the Personnel Department of the Regional Police Commission. Both bivariate and multivariate analyses were used to identify  determinants of sexual behavior.Results: Attitudes and perceptions of study participants showed significant association with their sexual behavior. Fifty two percent of the respondents were engaged in risky sexual practices and believed that they are susceptible to HIV infection. Twenty-nine percent had multiple sexual partners of which 60% did not use condom consistently. Overall, the study participants were of young age group and have habits of consuming alcohol. Almost all have access to VCT services and opportunities for peer education.Conclusion: The study participants were at risk of HIV because of their sexual behavior and misconceptions related to the risk factors and means of prevention. Hence, basic police training should include BCC on HIV/AIDS, expansion of HIV counseling and testing services, strengthening of peer education and establishing anti-AIDS clubs.[Ethiop. J.Health Dev. 2012;26(1):3-8

Pattern of Vascular Diseases at Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia

BACKGROUND: Vascular diseases are evolving fast in sub-Saharan Africa, but its management is challenged by lack of expertise and infrastructure. In the light of the prevailing challenge, this study was done to see the pattern of vascular disease and its treatment in a tertiary referral hospital.METHODS: A prospective cross-sectional study was done over a period of one year (February 9, 2016 to February 8, 2017) at Tikur Anbessa specialized hospital (TASH) at Addis Ababa, Ethiopia.RESULTS: A total of 386 patients were seen at the surgical OPD. Of these, 78(20.2%) were admitted and operate on. The male to female ratio was 1.3:1. The mean age affected was 39 +/- 10 (Range 12-91 years). On the other hand, 132 (34.2%) patients came with PAD. Of them, 46(34.8%) presented with either frank Gangrene or pre-gangrene stage. The rest 86(65.1%) had claudication pain. The other diseases seen are Varicose Vein, 100(25.9%), Carotid body tumors, 60(15.4%), Aneurysmal diseases, 36(9.1%), Vascular malformations, 34(8.7%), and Vascular injuries, 22(5.6%). During the study period, 28(35.9%) PAD, 22(28.2%) trauma patients, 8(10.2%) Chemodectomas, 8(10.2%) aneurysms, 6(7.7%) hemangiomas, 4(5.1%) varicose vein and 2(2.6%) AV fistula patients were operated.CONCLUSION: The pattern of vascular disease in Ethiopia is becoming a challenge. The gap created due to limited vascular surgeons, poor infrastructure and absent supply chain system has significantly compromised the number and type of operated-on patients. These challenges result in preventable morbidity and mortality

Assessment of water quality modelling capabilities of EPANET multi-species and pressure dependent extension models

The need for accurately predicting water quality through models has increasingly been crucial in meeting rigorous standards and customer expectations. There are several endeavours on developing robust water quality models for water distribution systems. In this paper, two variants of the EPANET 2 water quality model have been assessed to inform future research. The models are the multiple species extension EPANET-MSX and the pressure-dependent extension EPANET-PDX. Water quality analysis was conducted on a hypothetical network considering various operating pressure conditions. Different kinetic models were employed to simulate water quality. First order, limited first order and zero order models were used for predicting chlorine residual, disinfection by-products (DBPs) and water age respectively. Generally, EPANET-MSX and EPANET-PDX provided identical water quality results for normal operating conditions with adequate pressure but different results for pressure-deficient networks. Also, a parallel first order model with fast and slow reacting components was used for chlorine decay and DBPs using the EPANET-MSX model for a network operating under normal pressure conditions

Penalty-free multi-objective evolutionary approach to optimization of anytown water distribution network

This paper describes the development and application of a new multi-objective evolutionary optimization approach for the design and upgrading of water distribution systems with multiple pumps and service reservoirs. The optimization model employs a pressure-driven analysis simulator that accounts for the minimum node pressure constraints and conservation of mass and energy. Pump scheduling, tank siting and tank design are integrated seamlessly in the optimization without introducing additional heuristic procedures. The computational solution of the optimization problem is entirely penalty-free, thanks to pressure-driven analysis and the inclusion of explicit criteria for tank depletion and replenishment. The model was applied to the Anytown network that is a benchmark optimization problem. Many new solutions were achieved that are cheaper and offer superior performance compared to previous solutions in the literature. Detailed and extensive simulations of the solutions achieved were carried out. Spatial and temporal variations in water quality were investigated by simulating the chlorine residual and disinfection by-products in addition to water age. The hydraulic requirements were satisfied; efficiency of pumps was consistently high; effective operation of the new and existing tanks was achieved; water quality was improved; and overall computational efficiency was high. The formulation is entirely generic