Browsing Africa Centres of Excellence Scholarly Output by Issue Date
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ItemOn a certain family of quadratic Thue equations(GLASNIK MATEMATICKI, 2006) Ziegler, VolkerWe consider the parameterized Thue equation X^4 − 4sX^3Y − (2ab + 4(a + b)s)X^2Y^2 − 4absXY^3 + a^2b^2Y^4 = ±1, with a, b ∈ 1/4Z such that ab ∈ Z. By the hypergeometric method and a method of Tzanakis we find all solutions, if s is large with respect to |a| and |b|. ItemOn Biquadratic fields that admit unit power integral basis(Acta Mathematica Hungarica, 2011-04-07) Pethő, A.; Ziegler, V.We consider biquadratic number fields whose maximal orders have power integral bases consisting of units. We prove an effective and efficient criteria to decide whether the maximal order of a biquadratic field has a unit power integral basis or not. In particular we can determine all trivial biquadratic fields whose maximal orders have a unit power integral basis. Itemq-Hyperconvexity in Quasipseudometric Spaces and Fixed Point Theorems(Hindawi publishing Corporation, 2012-07-04) Künzi, Hans-Peter A.; Otafudu, Olivier OlelaIn a previous work, we started investigating the concept of hyperconvexity in quasipseudometric spaces which we called q-hyperconvexity or Isbell-convexity. In this paper, we continue our studies of this concept, generalizing further known results about hyperconvexity from the metric setting to our theory. In particular, in the present paper, we consider subspaces of q-hyperconvex spaces and also present some fixed point theorems for nonexpansive self-maps on a bounded q-hyperconvex quasipseudometric space. In analogy with a metric result, we show among other things that a set-valued mapping T* on a q-hyperconvex T0-quasimetric space (X, d) which takes values in the space of nonempty externally q-hyperconvex subsets of (X, d) always has a single-valued selection T which satisfies d(T(x), T(y)) ≤ dH(T*(x), T*(y)) whenever x, y ∈ X. (Here, dH denotes the usual (extended) Hausdorff quasipseudometric determined by d on the set P0(X) of nonempty subsets of X.) ItemA Survey on Fault Tolerance in Wireless Sensor Networks(American Society for Engineering Education, 2014) Alrajei, Nancy; Fu, HuirongWireless Sensor Networks (WSN) are useful for monitoring of physical conditions and passing the data gathered to the required location. They are like any other system prone to failure due to limitation of resources. In this paper we address fault tolerance concept in general, give analysis to the definition of fault tolerance and terms related to it based on the system requirements. We explored redundancy and touched upon fault tolerance in Wireless Sensor Networks. Topics covered include redundancy in hardware, N- Modules Redundancy (NMR), and software including N-version programming and check pointing. We also cover fault tolerance in Wireless sensor networks including connectivity and coverage and multipath. ItemAsymptotic behavior of neutral stochastic(Research Gate, 2014-12) Caraballo, Tom´as; Diop, Mamadou Abdoul; Ndiaye, Abdoul AzizThis paper deals with the existence, uniqueness and asymptotic behavior of mild solutions to neutral stochastic delay functional integro-differential equations perturbed by a fractional Brownian motion BH, with Hurst parameter H ∈ (12, 1). The main tools for the existence of solution is a fixed point theorem and the theory of resolvent operators developed in Grimmer [R. Grimmer, Trans. Amer. Math. Soc., 273 (1982), 333–349.], while a Gronwall-type lemma plays the key role for the asymptotic behavior. An example is provided to illustrate the results of this work. (c) 2014 All rights reserved. ItemA doubly stabilized bundle method for nonsmooth convex optimization(University of Wisconsin - Madison, 2016) de Oliveira, Welington; Solodov, MikhailWe propose a bundle method for minimizing non smooth convex functions that combines both the level and the proximal stabilizations. Most bundle algorithms use a cutting-plane model of the objective function to formulate a subproblem whose solution gives the next iterate. Proximal bundle methods employ the model in the objective function of the subproblem, while level methods put the model in the subproblem’s constraints. The proposed algorithm defines new iterates by solving a subproblem that employs the model in both the objective function and in the constraints. One advantage when compared to the proximal approach is that the level set constraint provides a certain Lagrange multiplier, which is used to update the proximal parameter in a novel manner. We also show that in the case of inexact function and subgradient evaluations, no additional procedure needs to be performed by our variant to deal with inexactness (as opposed to the proximal bundle methods that require special modifications). Numerical experiments on almost one thousand instances of different types of problems are presented. Our experiments show that the doubly stabilized bundle method inherits useful features of the level and the proximal versions, and compares favorably to both of them. ItemBiological effects of topical application of Moringa Oleifera extract versus Fluoride on Uremic patients extracted teeth(International Journal of Advanced Research, 2016-09) Khalaf, Eman A. S; Nagib, Ayman M.; Amin, Laila E.M.Chronic renal failure can elicit a wide spectrum of oral manifestations in the hard and soft tissues. Moringa oleifera leaves have been reported to be a rich source of β-carotene, protein, vitamin C, calcium and potassium. Many studies have demonstrated the efficacy of casein phosphopeptide amorphous calcium phosphate with fluoride paste in promoting remineralization of enamel and dentin in vitro. This study was designed to determine the effect of renal insufficiency on patients' teeth (enamel and dentin) and study biological effects of topical application of moringa extract versus fluoride on extracted teeth. Fifty sound posterior teeth were used, divided into 3 groups. Each group was subdivided into 2 subgroups; A (control) and B (uremic). Group I (control group).Group II (fluoride group). Group III (Moringa oleifera group).All the specimens were scanned by using scanning electron microscope and elemental analysis of enamel and dentin surfaces was tested using energy dispersive analytical x-ray. Enamel of uremic teeth showed irregular enamel surface with deep depressions and pitting. Also, dentinal tubules showed different shaped outlines and diameter. Increase in calcium and phosphorus levels was statistically significant with Moringa as same as CPP-ACPF groups. Conclusions: CRF leads to alteration in the structure of enamel and dentin of permanent teeth with significant increase in mineral content (Ca& P) of permanent enamel and dentin when compared with healthy controls. Moringa has a protective effect on enamel and dentin remineralization similar/or better than fluoridated pastes. ItemContribution of magnetic resonance soundings(HAL, 2016-12-08) Mazzilli, Naomi; Boucher, Marie; Chalikakis, Konstantinos; Legchenko, A.; Jourde, H.; Champollion, CUnderstanding the role of the unsaturated zone in aquifer recharge and contaminant attenuation processes is a major challenge for the protection and management of karstic water resources. We present the potential of the magnetic resonance soundings (MRS) geophysical method for characterizing the vadose zone of karst aquifers composed of epikarst and infiltration layers. To investigate the hydraulic functioning of the Durzon karst system located on the Larzac plateau (southern France), we used the MRS method at 16 sites. The MRS results have been compared with available geologic information and to core water content measurements. The remarkable spatial variability of the MRS response observed in the study area makes it possible to determine ranges of water storage properties in relation to the lithology of the investigated carbonate formations (dolomite, marly, and siliceous limestone). All soundings found either constant or increasing MRS water content with depth, which demonstrates that the infiltration zone might be the major water storage entity for permanent water storage, with important consequences for recharge quality and quantity. These results show the feasibility and potential of the MRS method for the characterization of the karst unsaturated zone and for understanding the vertical distribution of water content, which impacts the overall functioning of karst systems. ItemAsymptotic Behavior of Second-Order Impulsive Partial Stochastic Functional Neutral Integrodifferential Equations with Infinite Delay(University of Nis, Faculty of Sciences and Mathematics, 2017) Yan, Zuomao; Jia, XiumeiIn this paper, the existence and asymptotic stability in p-th moment of mild solutions to a class of second-order impulsive partial stochastic functional neutral integrodifferential equations with infinite delay in Hilbert spaces is considered. By using Hölder’s inequality, stochastic analysis, fixed point strategy and the theory of strongly continuous cosine families with the Hausdor measure of noncompactness, a new set of sufficient conditions is formulated which guarantees the asymptotic behavior of the nonlinear second-order stochastic system. These conditions do not require the the nonlinear terms are assumed to be Lipschitz continuous. An example is also discussed to illustrate the efficiency of the obtained results. ItemSynchrony in the phenologies of fine roots and leaves of Vitellaria paradoxa in different land uses of Burkina Faso(Springer Science + Business Media B.V, 2017-09-27) Bazie, Paulin; Ky-Dembele, Catherine; Jourdan, Christophe; Roupsard, Olivier; Zombre, Gerard; Bayala, JulesThis study focused on leaf and root density dynamics of the most dominant tree species (Vitellaria paradoxa) of West African savannas in two land use types (farmed land and forest). Ten trees located at least 100 m from each other were selected, with five trees each located in the field and in the forest. Five of the trees were of small-diameter [two in the fields (diameter at breast height or DBH 20.1–20.7 cm) and three in the forest (DBH 7.0–8.0–10.8 cm)] and five others were of large-diameter [three in the fields (DBH 38.2–81.8–81.9 cm) and two in the forest (DBH 20.1–20.7 cm)]. One near-vertical rhizotron was installed under each tree to evaluate root density while canopy openness, diffuse and directly transmitted light were monitored by taking hemispheric photograph monthly. After a two-year period of monitoring, the results revealed a strong seasonality in root density with peak root density observed during the rainy season in August and the lowest production during the dry season in April. Significant lowest canopy openness was observed from August to September while the highest occurred from March to May, which was found to be synchronous with fine root dynamics. The light interception followed the same trends as the leaf production. Furthermore, both mature and young trees showed significant higher root density in the fields compared to the forest while the mean values of all the parameters of canopy openness and light transmittance were higher in the forest than the fields. ItemHydrogeochemical Model and Water Quality(Scientific Research, 2018) Akoachere, R.A.; Eyong, T. A.; Eduvie, M. O.; Egbe, S.E.; Yaya, O.O.; Nwude, M.O.This study determined the hydrogeochemical model of groundwater and groundwater domestic-agro-industrial quality in Bafoussam using hydrogeochemical tools and physicochemical parameters: Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters; pH ranged from, 4.47 - 7.84; EC, 10 - 820 μS/cm; Temperature, 22.3°C - 29.5°C and TDS, 6.7 - 549.4 mg/L. The major ions fell below WHO acceptable limits. The sequences of major ionic abundance are: Ca2+ > Mg2+ > K+ > Na+ > NH+4, HCO-3 > Cl- > SO2-4 > NO3 > HPO2-4. Recharge by atmospheric precipitation, ion-exchange and simple dissolution processes are responsible for groundwater character, ionic content resulted from ion exchange and rock-weathering. Water types are Ca-HCO3 and Ca-Cl Hydrogeochemical facies are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3. Domestic water quality was determined by use of pH, electrical Conductivity EC, total dissolved solids TDS, total Hardness HT and water quality index WQI. WQI values ranged from 0 - 42.09 and HT 67.89 - 339.01 indicating that water is of good domestic quality. Agro-industrial suitability of groundwater was determined using, sodium adsorption ratio SAR, permeability index PI, Magnesium adsorption ratio MAR, percent sodium %Na, Kelly’s ratio KR and Residual sodium carbonate RSC and Wilcox diagram; From irrigational water suitability parameters, SAR values ranged from 0.01 - 0 05; %Na 3.69 - 15.50; KR 0.005 - 0.023; PI 1.04 - 67.98; MAR 2.89 - 55.27; RSC -5.22 to -0.44 and Wilcox diagram indicate that inorganic groundwater content in the study area is excellent-good for irrigation; this is of significance since Bafoussam a major agroindustrial zone in Cameroon and Central Africa is in the process of developing large scaled irrigation based agricultural projects dependent on use of surface and groundwater. Recharge from precipitation exchanges ions with the weathered country rocks and mixes with regional flow in a generally south-east north-westerly direction by piston flow in the granito-basaltic aquiferous formations in Bafoussam. There is need for detailed studies to determine aquifer characteristics: permeability, transmissivity and storativity, vertical-lateral regional extent of aquifer boundaries, groundwater pollution potentials for biological, organic and trace metals. ItemImpact of mycorrhiza-based inoculation strategies on Ziziphus mauritiana Lam. and its native mycorrhizal communities on the route of the Great Green Wall (Senegal)(Elsevier, 2018) Thioye, Babacar; Sanguin, Hervé; Kane, Aboubacry; De Faria, Sergio Mania; Fall, Dioumacor; Prin, Yves; Sanogo, Diaminatou; Ndiaye, Cheikh; Duponnois, Robin; Sylla, Samba Ndao; Bâ, Amadou MustaphaA wide program of fruit tree planting, notably jujube trees, has been implemented in the framework of the pan-African Great Green Wall (GGW) project to improve food security in arid and semiarid regions. However, the success of such initiatives is highly limited by a low tree growth and high tree mortality rates due to transplant shocks from tree nursery to field. The positive impact of mycorrhiza-based ecological engineering strategies on jujube trees were previously demonstrated in nursery conditions, but field monitoring is necessary to evaluate their sustainability in terms of plant growth and survival. In the current study, local (Tasset) and exotic (Gola) jujube cultivars were tested for their response to mycorrhizal inoculation with the non-native arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis IR 27 and fertilization with rock phosphate. The environmental impacts of both treatments were assessed by characterizing the native AM fungal community in a 13-month-old jujube orchard. Field results demonstrated higher rates of survival and a relative stability of nursery driven plant benefits of inoculated jujube trees, as well as a potential higher persistence of AM fungal inoculum for the exotic cultivar. The native AM fungal community associated with the local cultivar was the most diverse, but Glomeraceae was predominant in both cultivars. The mycorrhiza-based ecological engineering strategies proposed in this work affected both AM fungal communities, notably Glomeraceae and Gigasporaceae members, but in a higher extent for the local jujube cultivar. Results highlight the strong benefits of mycorrhizal inoculation at the very early stages of tree seedling growth in nursery and their stability in the first year of plantation. Nevertheless, a deeper assessment of mycorrhizal inoculum persistence and spread, and a wider characterization of soil and root microbiome need to be implemented in further field monitoring to better evaluate the environmental impacts. ItemEffects of Passive Hydrodynamics Force(Elsevier, 2018) Olabodé, D.L.; Miwadinou, C.H.; Monwanou, V.A.; Orou, Chabi J.B.This work studies the nonlinear dynamics and passive control of chemical oscillations governed by a forced modified Van der Pol-Duffing oscillator. We considered the dynamics of nonlinear chemical systems subjected to fluctuating hydrodynamic drag forces. The computation of fixed points of the nonlinear chemical system is made in detail by utilizing Cardan’s method. The harmonic balance method is used to find the amplitudes of the oscillatory states. The Floquet theory and the Whittaker method are utilized to analyze and analytically determine the stability boundaries of oscillations. The influences of system parameters in general and in particular the effect of the parameter K and the constraint parameter β which shows the difference between a nonlinear chemical dynamics order two differential equation and ordinary Van der Pol-Duffing equation are observed on the state of the second stability criterion. The effects of the control process on chaotic dynamics states are investigated through bifurcations structures, Lyapunov exponent, phase portraits and Poincar´e section. The results obtained by the analytical methods are validated and complemented by the results of numerical simulations. ItemCosmological Study of Autonomous Dynamical Systems(Research Gate, 2018-04-25) Ganiou, M.G; Logbo, P.H; Houndjo, M.J.S; Tossa, J.Cosmological approaches of autonomous dynamical system in the framework of f(T ) gravity are investigated in this paper. Our methods applied to flat Friedmann-Robertson Walker equations in f(T ) gravity, consist to extract dynamical systems whose time-dependence is contained in a single parameter m depending on the Hubble rate of Universe and its second derivative. In our attempt to investigate the autonomous aspect of the dynamical systems reconstructed in both vacuum and non-vacuum f(T ) gravities, two values of the parameter m have been considered for our present analysis. In the so-called quasi-de Sitter inflationary era (m ≃ 0), the corresponding autonomous dynamical systems provide stable de Sitter attractors and unstable de Sitter fixed points. Especially in the vacuum f(T ) gravity, the approximate form of the f(T ) gravity near the stable and the unstable de Sitter fixed points has been performed. The matter dominated era case (m = −9/2) leads to unstable fixed points confirming matter dominated era or not, and stable attractor fixed point describing dark energy dominated era. Another subtlety around the stable fixed point obtained at matter dominated case in the non-vacuum f(T ) gravity is when the dark energy dominated era is reached, at the same time, the radiation perfect fluid dominated succumbs. ItemAphrodisiac Effect of Aqueous Stem Bark Extract of Ficus Sycomorus on Female Wistar Rats(Nigerian Journal of Basic and Applied Science, 2018-06) Tijjan, U.; Mabrouk, M. I.; Yarube, I. U.In the present study, the effect of aqueous stem bark extract of Ficus sycomorus was evaluated on female sex hormones and sexual behavior in female Wistar rats. Adult female rats having regular estrous cycle confirmed by daily cytology of the vaginal smear analysis were used. Rats were andomly divided into 3 groups (n=10): Group I served as a control; while group II, and III received 40 mg/kg and 80 mg/kg of the extracts respectively. The results revealed significant increase (p<0.5) in serum concentration of the estradiol in group II and a significant decrease (p<0.5) in serum concentration of estradiol in group III in comparison with the control. There was also significant decrease (p<0.5) in serum level of progesterone in group II and no significant effect in group III in comparison with the control. The result also indicated no significant effect (p>0.5) of the extract on female sexual behavior, which may suggest no scientific basis for the use of the extract as an aphrodisiac in females. ItemApplying machine learning methods in managing urban concentrations of traffic-related particulate matter(t: https://www.researchgate.net/publication/326242401, 2018-07) Suleiman, .A; Tight, M.R.; Quinn, A.DThis study presents a new method for evaluating the effectiveness of roadside PM10 and PM2.5 reduction scenarios using Machine Learning (ML) based models. The ML methods include Artificial Neural Networks (ANN), Boosted Regression Trees (BRT) and Support Vector Machines (SVM). Traffic, meteorological and pollutant data collected at nineteen Air Quality Monitoring (AQM) sites in London for a period between 2007 and 2012 was used. The ML models performed very well in predicting the concentrations of PM10 and PM2.5 with around 95% of their predictions falling within the factor of two of the observed concentrations at the roadsides. The prediction errors observed were very small as indicated by the average normalised mean gross errors of 0.2. Also, the predictions of the models correlated well with the observed concentrations as shown by the average values of R (0.8) and index of agreement (0.74). Additionally, when some PM10 and PM2.5 reduction scenarios were modelled, the ML models predicted various degree of reductions in the roadside concentrations. In conclusion, well trained ANN and BRT models can be successfully applied in predictions of roadside PM10 and PM2.5 concentrations. Moreover, they can be applied in measuring the effectiveness of roadside particle reduction scenarios. ItemType IV singular bouncing cosmology from f ( T ) Gravity(arXiv, 2018-07-14) Logbo, P.H.; Houndjo, M.J.S.We investigate bouncing scenario in the modified f(T ) gravity, T being the torsion scalar. Attention is attached to the reconstruction of f(T ) able to describe type IV singular bouncing evolution, where we adopt as assumption that the bouncing and type IV singularity points coincide. In the context of the reconstructed f(T ) model we calculate the Hubble slow-roll parameters in order to determine the dynamical evolution of the cosmological system under study. The results show that the Hubble slow-roll parameters become singular at the type IV singularity indicating a dynamical instability. Moreover we perform the stability analysis of the f(T ) gravity solution where, according to the obtained result, the type IV singularity point is a saddle point in agreement with the bounce scenario. ItemExperiment-based Methodology of Kinetic Battery Modeling for Energy Storage(Research Gate, 2018-08) Bako, Zeinabou Nouhou; Tankari, Mahamadou Abdou; Lefebvre, Gilles; Maiga, Amadou SeidouThis paper presents a methodology of the battery modeling based on experimental tests results. As main contribution, authors conducted an analysis of the main constraints and effects of each parameter of the batteries model on its behavior and lifetime. This can help to improve the accuracy of the model. Due to its capability to model the recovery effect and the rate-capacity one, the Kinetic Battery Model serves as basis of the study. Results of experimental tests are used to realize the analysis and to define the suitable methodology of batteries parameters identification. These last can serve for prediction and estimation of the battery lifetime according to the actual operating conditions, particularly in microgrid and distributed systems.