A Modified Real-Time Fault-Tolerant Task Allocation Scheme for Wireless Sensor Networks

In WSNs, the sensor nodes are at risk of failure and malicious attacks (selective forwarding). This may have a profound negative effect when you consider real-time WSNs, making them challenging to deploy. When there is a delay in tasks allocation execution processes in real-time WSNs because of sensor nodes failures, this will cause disastrous consequences if the systems are safety-critical, e.g. aircraft, nuclear power plant, forest fire detection, battlefield monitoring, thus the need to developed a real-time system that is fault-tolerable. This paper developed a modified real-time fault-tolerant task allocation scheme (mRFTAS) for WSNs (wireless sensor networks), using active replication techniques. mRFTAS and RFTAS performance were compared using time of execution of the task, network lifetime and reliability cost. The mRFTAS performance showed an improvement over that of RFTAS when it comes to reducing the time it takes for task execution by 45.56% and reliability cost of 7.99% while prolonging the network lifetime by 36.35%

Long-Term Reliability of a Hard-Switched Boost Power Processing Unit Utilizing SiC Power MOSFETs

Silicon carbide (SiC) power devices have demonstrated many performance advantages over their silicon (Si) counterparts. As the inherent material limitations of Si devices are being swiftly realized, wide-band-gap (WBG) materials such as SiC have become increasingly attractive for high power applications. In particular, SiC power metal oxide semiconductor field effect transistors' (MOSFETs) high breakdown field tolerance, superior thermal conductivity and low-resistivity drift regions make these devices an excellent candidate for power dense, low loss, high frequency switching applications in extreme environment conditions. In this paper, a novel power processing unit (PPU) architecture is proposed utilizing commercially available 4H-SiC power MOSFETs from CREE Inc. A multiphase straight boost converter topology is implemented to supply up to 10 kilowatts full-scale. High Temperature Gate Bias (HTGB) and High Temperature Reverse Bias (HTRB) characterization is performed to evaluate the long-term reliability of both the gate oxide and the body diode of the SiC components. Finally, susceptibility of the CREE SiC MOSFETs to damaging effects from heavy-ion radiation representative of the on-orbit galactic cosmic ray environment are explored. The results provide the baseline performance metrics of operation as well as demonstrate the feasibility of a hard-switched PPU in harsh environments

Compendium of Single Event Effect Results from NASA Goddard Space Flight Center

We present the results of single event effects (SEE) testing and analysis investigating the effects of radiation on electronics.This paper is a summary of test results

Single-Event Effects in Silicon Carbide Power Devices

This report summarizes the NASA Electronic Parts and Packaging Program Silicon Carbide Power Device Subtask efforts in FY15. Benefits of SiC are described and example NASA Programs and Projects desiring this technology are given. The current status of the radiation tolerance of silicon carbide power devices is given and paths forward in the effort to develop heavy-ion single-event effect hardened devices indicated

From cassava to gari: Mapping of quality characteristics and end-user preferences in Cameroon and Nigeria

User's preferences of cassava and cassava products along the value chain are supported by specific root quality characteristics that can be linked to root traits. Therefore, providing an evidence base of user preferred characteristics along the value chain, can help in the functional choice of cassava varieties. In this respect, the present paper presents the results from focus group discussions and individual interviews on user preferred quality characteristics of raw cassava roots and the derived product, gari, ‐ one of the major cassava products in Sub Saharan Africa ‐ in major production and consumption areas of Cameroon and Nigeria. Choice of cassava varieties for farming is mainly determined by the multiple end‐uses of the roots, their agricultural yield and the processing determinants of roots that support their major high‐quality characteristics: size, density, low water content, maturity, colour and safety. Processing of cassava roots into gari goes through different technological variants leading to a gari whose high‐quality characteristics are: dryness, colour, shiny/attractive appearance, uniform granules and taste. Eba, the major consumption form of gari in Cameroon and Nigeria is mainly characterized by its textural properties: smoothness, firmness, stickiness, elasticity, mouldability. Recommendations are made, suggesting that breeding will have to start evaluating cassava clones for brightness/shininess, as well as textural properties such as mouldability and elasticity of cassava food products, for the purpose of supporting decision‐making by breeders and the development of high‐throughput selection methods of cassava varieties. Women are identified as important beneficiaries of such initiatives giving their disadvantaged position and their prominent role in cassava processing and marketing of gari

Language and Gender: Communication in the Professional Setting

Differences in the linguistic styles of male and female doctors engaged in professional interaction as a form of public communication were examined in the work setting. Linguistic and non-linguistic styles of subjects were observed through overt video recording in their roles as participants, both as leaders and as members of the audience, in seminar and lecture settings. It was found that female doctors tended to be more detailed, elaborate and conversational in their presentations than males, who focused more on the cogency of the facts they were presenting; question consistently ranked highest among the linguistic features employed both by male and by female doctors; only female doctors engaged in collaborative efforts to build another female speakers presentation, and adopted a conversational tone as a part of their rhetorical style. Although these gender-linked patterns emerged, professionalism appeared to be a more influential factor in determining the linguistic choices of the group of professionals studied.LWATI: A Journal of Contemporary Research Vol. 5 2008: pp. 165-18

Effect of improved fallow systems on soil chemical properties and crop yield in the rain forest of southeastern Nigeria

In most of sub-Saharan Africa, there has been shortening of fallow periods to less than 10 years by farmers. In southeastern Nigeria, fallow periods have been reduced to less than 5 years due to population pressure. Marginal lands are being brought under cultivation. Under these circumstances, there is need for soil and crop management options to improve productivity. The study site is in the humid forest zone with an average elevation of 10m a. s. l. and receives a mean annual rainfall of 2400 mm, usually in a monomodal distribution lasting from March to November. The soils are highly weathered and acidic with Ultisols of pH ranging from 3.5 to 6.0 and mineralogy dominated by low activity clays with low cation exchange capacity (CEC) and low base saturation. The soils have a low organic matter (0.5-3%) and consequently low nutrient reserve. Two experiments were conducted between 1996 and 2000 with improved fallow systems. Soil chemical properties under the improved fallow systems, were significantly improved within a short period of time while cassava and maize yields were greatly increased. Although the Tephrosia mulch showed a tendency of soil acidification in the present study, the lab lab fallow either with or without sheep grazing, led to increases in soil pH, organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K). The adoption of these fallow systems by farmers will depend on their profitability and sustainability in these fragile tropical ecosystems.Dans la majorité des zones subsahariennes d’Afrique, les paysans ont réduit la durée de la jachère à moins de dix années. Mais dans le SE du Nigeria, la pression démographique est telle que la jachère a été réduite à moins de 5 ans. Des terres marginales ont été mises en culture: d’où la nécessité de définir des techniques de production capables d’améliorer la productivité des sols. L’étude eut lieu dans une zone de forêts humides, à 10 m d’altitude et 2400 mm de pluie monomodale, entre mars et novembre. Les sols sont des ultisols très acides, profondément altérés, à argile kaolinitique à faible capacité d’échange de cations et faible saturation en bases. Ces sols sont pauvres en matières organiques (0,5 à 3 % de MO) et ont par conséquent peu de réserve de nutriments. Deux essais ont été conduits de 1996 à 2000 comparant divers systèmes de jachères. Sous les jachères améliorées, les propriétés chimiques des sols ont été significativement améliorées en une courte période et les rendements en manioc et maïs largement augmentés. Bien que le paillage de Tephrosia a entrainé une tendance à l’acidification dans cet essais, la jachère à Lablab, avec ou sans pâturage par les moutons, a amené une augmentation du pH, du taux de MO, de l’azote, du P et K. L’adoption par les paysans de ces techniques va dépendre de la rentabilité et de la durabilité de ces techniques dans ces écosystèmes tropicaux très fragiles

Chapitre 5. Influences de jachères améliorées et pâturées sur le rendement des cultures et les propriétés chimiques de sols ferrallitiques acides dans la région des forêts humides du Sud-Est du Nigéria

Au sud-est du Nigeria, la durée de la jachère a été réduite à moins de 5 ans et les terres marginales ont été mises en culture à cause de la pression démographique. Il fallait donc trouver des techniques culturales capables d’améliorer la productivité des terres. Les recherches ont été conduites en zone de forêt humide, à 10 m d’altitude, avec une pluviosité monomodale moyenne de 2 400 mm. Le sol (Ultisol) est très acide (pH = 3,5 à 6,0), à argile kaolinitique à faible capacité d’échange de cations (CEC) et faible taux de saturation. Le taux de matières organiques (0,5-3 %) et la réserve en nutriments sont très faibles. Deux essais de jachère améliorée (Tephrosia et Lablab, pâturées ou non) ont été conduits entre 1996 et 2000. Les propriétés chimiques du sol et les rendements en manioc et maïs ont été améliorés en peu de temps. Le mulch de Tephrosia a entraîné une baisse du pH, mais la jachère de Lablab, pâturée ou non, a amélioré le pH, le carbone organique, l’azote, le phosphore et le potassium. Cependant, l’adoption de ce nouveau système par les paysans dépend du bilan économique et de la durabilité du système.In southeastern Nigeria, fallow periods have been reduced to less than 5 years. Marginal lands are being brought under cultivation due to population pressure. Under these circumstances, there is need for soil and crop management options to improve productivity. The study site is in the humid forest zone with an altitude of 10 m, a mean annual rainfall of 2,400 mm, with a monomodal distribution. The soils are highly weathered and acidic with Ultisols of pH ranging from 3.5 to 6.0 and mineralogy dominated by low activity clays with low cation exchange capacity (CEC) and low base saturation, a low organic matter (0.5-3 %) and a low nutrient reserve. Two trials of improved short fallow were conducted between 1996 and 2000. Soil chemical properties under the improved fallow systems were significantly improved within a short period of time while cassava and maize yields were greatly increased. Although the Tephrosia mulch showed a tendency of soil acidification in the present study, the Lablab fallow either with or without sheep grazing, led to increases in soil pH, organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K). The adoption of these fallow systems by farmers will depend on their profitability and sustainability in these fragile tropical ecosystems

Fate of Nitrogen-Fixing Bacteria in Crude Oil Contaminated Wetland Ultisol

The effect of crude oil on the growth of legumes (Calopogonium muconoides and Centrosema pubescens) and fate of nitrogen-fixing bacteria in wetland ultisol was investigated using standard cultural techniques. The results revealed observable effects of oil on soil physico-chemistry, plant growth and nodulation as well as on densities of heterotrophic, hydrocarbonoclastic and nitrogen fixing bacteria. The effects however varied with different levels (0.5%, 1%, 5%, 10%, 15% and 20%) of pollution. Ammonium and nitrate levels were high in the unpolluted soil but decreased with increase in pollution levels. Nitrite was not detected in contaminated soil probably due to the reduction in numbers of nitrogen fixers, from 5.26 ± 0.23 × l06cfu/g in unpolluted soil to 9.0 ± 0.12 × 105 and 2.2 ± 0.08 × l05 cfu/g in soils with 5% and 20% levels of pollution respectively. The contaminated soil also exhibited gross reduction in the nodulation of legumes. A range of 13–57 nodules was observed in legumes from polluted soil against 476 nodules recorded for plants cultured on unpolluted soil. The heterogeneity of the microbial loads between oil-polluted and unpolluted soil were statistically significant (p < 0.05, ANOVA). Positive significant relationships were observed between the levels of hydrocarbons and the densities of heterotrophic bacteria (r = 0.91) and that of hydrocarbon utilizing bacteria (r = 0.86). On the other hand, relationships between the densities of nitrogen fixing bacteria and total hydrocarbons content was negative (r = −0.30) while positive relationships were recorded between the densities of different microbial groups and treatment periods except at 15% and 20% pollution levels. The LSD tests revealed highly significant differences (p < 0.001) in the physiological groups of soil microorganisms at all levels of pollution. The results imply that crude oil seriously affects rhizosphere microbial growth in legumes. Among the bacterial species isolated, Clostridium pasteurianum, Bacillus polymyxa and Pseudomonas aeruginosa exhibited greater ability to degrade hydrocarbons than Azotobacter sp, Klebsiella pneumoniae and Derxia gummusa while Nitrosomonas and Nitrobacter had the least degradability. A continuous monitoring of the environment is advocated to prevent extinction of nitrogen-fixing bacteria and total loss of soil fertility attributable to petroleum hydrocarbon contamination in the Niger Delta ultisol