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Search Results: 1 - 10 of 702 matches for " Rachid Ouifki "
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Modeling the Control of Trypanosomiasis Using Trypanocides or Insecticide-Treated Livestock
John W. Hargrove ,Rachid Ouifki,Damian Kajunguri,Glyn A. Vale,Stephen J. Torr
PLOS Neglected Tropical Diseases , 2012, DOI: 10.1371/journal.pntd.0001615
Abstract: Background In Uganda, Rhodesian sleeping sickness, caused by Trypanosoma brucei rhodesiense, and animal trypanosomiasis caused by T. vivax and T. congolense, are being controlled by treating cattle with trypanocides and/or insecticides. We used a mathematical model to identify treatment coverages required to break transmission when host populations consisted of various proportions of wild and domestic mammals, and reptiles. Methodology/Principal Findings An Ro model for trypanosomiasis was generalized to allow tsetse to feed off multiple host species. Assuming populations of cattle and humans only, pre-intervention Ro values for T. vivax, T. congolense, and T. brucei were 388, 64 and 3, respectively. Treating cattle with trypanocides reduced R0 for T. brucei to <1 if >65% of cattle were treated, vs 100% coverage necessary for T. vivax and T. congolense. The presence of wild mammalian hosts increased the coverage required and made control of T. vivax and T. congolense impossible. When tsetse fed only on cattle or humans, R0 for T. brucei was <1 if 20% of cattle were treated with insecticide, compared to 55% for T. congolense. If wild mammalian hosts were also present, control of the two species was impossible if proportions of non-human bloodmeals from cattle were <40% or <70%, respectively. R0 was <1 for T. vivax only when insecticide treatment led to reductions in the tsetse population. Under such circumstances R0<1 for T. brucei and T. congolense if cattle make up 30% and 55%, respectively of the non-human tsetse bloodmeals, as long as all cattle are treated with insecticide. Conclusions/Significance In settled areas of Uganda with few wild hosts, control of Rhodesian sleeping sickness is likely to be much more effectively controlled by treating cattle with insecticide than with trypanocides.
A General HIV Incidence Inference Scheme Based on Likelihood of Individual Level Data and a Population Renewal Equation
Guy Severin Mahiane, Rachid Ouifki, Hilmarie Brand, Wim Delva, Alex Welte
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044377
Abstract: We derive a new method to estimate the age specific incidence of an infection with a differential mortality, using individual level infection status data from successive surveys. The method consists of a) an SI-type model to express the incidence rate in terms of the prevalence and its derivatives as well as the difference in mortality rate, and b) a maximum likelihood approach to estimate the prevalence and its derivatives. Estimates can in principle be obtained for any chosen age and time, and no particular assumptions are made about the epidemiological or demographic context. This is in contrast with earlier methods for estimating incidence from prevalence data, which work with aggregated data, and the aggregated effect of demographic and epidemiological rates over the time interval between prevalence surveys. Numerical simulation of HIV epidemics, under the presumption of known excess mortality due to infection, shows improved control of bias and variance, compared to previous methods. Our analysis motivates for a) effort to be applied to obtain accurate estimates of excess mortality rates as a function of age and time among HIV infected individuals and b) use of individual level rather than aggregated data in order to estimate HIV incidence rates at times between two prevalence surveys.
Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a Semiarid Mediterranean Clay Soil  [PDF]
Rachid Mrabet
American Journal of Plant Sciences (AJPS) , 2011, DOI: 10.4236/ajps.2011.22022
Abstract: Agriculture is the single biggest user of land and water in Morocco; however its performances are still low due to high rainfall variation and rates of soil productivity depletion. Increasing concerns about soil and environment quality degradation have raised the need to review existing tillage management systems and develop new systems for seed-bed preparation. Consequently, No-tillage is found a promising practice of soil management to improve simultaneously soil quality and wheat production in semiarid Morocco. However, residue management under No-tillage was Not yet studied in conjunction with wheat rotation. Therefore, a field study was conducted in the semiarid Chaouia Plain of Morocco during the period from 1994 to 2003, in order to evaluate the impacts of different tillage practices (conventional tillage (CT), No-tillage (NT)); No-tillage wheat residue management scenarios (total NTr, partial NTp and No-removal of residues NTm) and crop rotations (continuous wheat (CW), Wheat-Fallow (WF), Wheat-Maize-Fallow (WMF), Wheat-Lentil-Fallow (WLF) and Wheat-Barley-Fallow (WBF)) on wheat production. Over-years, conventional tillage system permitted lower yield of wheat while NT maintenance of crop residue at the surface is needed to increase it. Basically, NTp could be adopted in mixed crop-livestock systems of semiarid areas for the purpose of guarantying grain and feed. Wheat yields were the lowest under continuous wheat for all years. Wheat-fallow rotation is an important option in dry years or areas, while wheat-fallow-lentil or barley rotations are recommended in better environments. Stability analysis indicated that yields in the No-tillage system were less influenced by adverse growing conditions than conventional tillage system, particularly under low rainfall. These results indicate that improved soil quality under No-tillage enhanced wheat yield stability by reducing the impact of adverse growing conditions.
A Markov Model for Human Resources Supply Forecast Dividing the HR System into Subgroups  [PDF]
Rachid Belhaj, Mohamed Tkiouat
Journal of Service Science and Management (JSSM) , 2013, DOI: 10.4236/jssm.2013.63023

Modeling the manpower management mainly concerns the prediction of future behavior of employees. The paper presents a predictive model of numbers of employees in a hierarchical dependent-time system of human resources, incorporating subsystems that each contains grades of the same family. The proposed model is motivated by the reality of staff development which confirms that the path evolution of each employee is usually in his family of grades. That is the reason of dividing the system into subgroups and the choice of the superdiagonal transition matrix.

Which Yields with Wastes? Study on Pilot of the Efficiency of Water Treatment Plant— Case of the Sector of Algerian Tanning  [PDF]
Mohamed Necer, Rachid Smail
Journal of Water Resource and Protection (JWARP) , 2014, DOI: 10.4236/jwarp.2014.615134
Abstract: Tannery industries generate wastewater containing high concentrations of sulfur. Most of wastes are liquid (effluent). The river section and tanning are the source of most tannery waste. Dehairing is a process of separation of hair and epidermis. Lime and sulfides are used for this process. Thus, sulfur in wastewater dehairing occurs as sulfide. Today, catalysis is at the centre of major societal concerns about energy, environment and sustainable development. The discovery of new catalytic processes and the improvement of existing ones are also critically important for improving the quality of life while simultaneously reducing the adverse impact of human activities on the environment. With a substitution approach of a catalyst MnSO4 by multiple wastes from tannery and the metallurgical sector, this study investigated the recycle of waste from dehairing process and waste from metallurgical industry. The results indicated 32% of oxidized sulfur for the first waste derived from process of depilation and 30% for the second waste from metallurgical process industry. A preliminary cost analysis demonstrated that the proposed solution is much cheaper than the discharging of waste and wastewater in a WWTP; however, the sustainability of the proposed solution provided a second alternative, to alleviate the operational costs of installations wastewater from tanneries, without significantly impacting the environment.
Analytical Approach for the Systematic Research of the Periodic Ferroresonant Solutions in the Power Networks  [PDF]
Fathi Ben Amar, Rachid Dhifaoui
Energy and Power Engineering (EPE) , 2011, DOI: 10.4236/epe.2011.34056
Abstract: Ferroresonance is a complex and little known electrotechnical phenomenon. This lack of knowledge means that it is voluntarily considered responsible for a number of unexplained destructions or malfunctioning of equipment. The mathematical framework most suited to the general study of this phenomenon is the bifurcation theory, the main tool of which is the continuation method. Nevertheless, the use of a continuation process is not devoid of difficulties. In fact, to continue the solutions isolats which are closed curves, it is necessary to know a solution belonging to this isolated curve (isolat) to initialise the continuation method. The principal contribution of this article is to develop an analytical method allowing systematic calculation of this initial solution for various periodic ferroresonant modes (fundamental, harmonic and subharmonic) appearing on nonlinear electric system. The approach proposed uses a problem formulation in the frequency domain. This method enables to directly determine the solution in steady state without computing of the transient state. When we apply this method to the single-phase ferroresonant circuits (series and parallels configurations), we could easily calculate an initial solution for each ferroresonant mode that can be established. Knowing this first solution, we show how to use this analytical approach in a continuation technique to find the other solutions. The totality of the obtained solutions is represented in a plane where the abscissa is the amplitude of the supply voltage and the ordinate the amplitude of the system’s state variable (flux or voltage). The curve thus obtained is called “bifurcation diagram”. We will be able to then obtain a synthetic knowledge of the possible behaviors of the two circuits and particularly the limits of the dangerous zones of the various periodic ferroresonant modes that may appear. General results related to the series ferroresonance and parallel ferroresonance, obtained numerically starting from the theoretical and real cases, are illustrated and discussed.
A Multiresolution Channel Decomposition for H.264/AVC Unequal Error Protection  [PDF]
Rachid Abbadi, Jamal El Abbadi
Journal of Signal and Information Processing (JSIP) , 2012, DOI: 10.4236/jsip.2012.31001
Abstract: The most commonly used transmission channel in nowadays provides the same level of protection for all the information symbols. As the level of protection should be adequate to the importance of the information set, it is justified to use UEP channels in order to protect information of variable importance. Multiresolution channel decomposition has emerged as a strong concept and when combined with H.264/AVC layered multiresolution source it leads to outstanding results especially for mobile TV applications. Our approach is a double multiresolution scheme with embedded constellation modulations on its baseband channels followed by OFDM time/frequency multiresolution passband modulation. The aim is to protect The NAL units carrying the most valuable information by the coarse constellations into coarse sub-channels, and the NAL units that contain residual data by fined constellations and transposed into the fined OFDM sub-channels. In the multiresolution protection coding, our approach is a multiresolution decomposition of the core convolutional constituent of the PCCC where the NAL units carrying the most valuable information are coded by the rugged coefficient of the multiresolution code and the NAL units that contains residual data are coded by refined less secure coding coefficients.
Numerical Study of Natural Convection in a Two-Dimensional Enclosure with a Sinusoidal Boundary Thermal Condition Utilizing Nanofluid  [PDF]
Ibtissam El Bouihi, Rachid Sehaqui
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.48058
Abstract: Nanofluids are considered to offer important advantages over conventional heat transfer fluids. A model is developed to analyze the behavior of nanofluids taking into account the solid fraction χ. The Navier-Stokes equations are solved numerically with Alternating Direct Implicit method (ADI method) for various Grashof numbers 104 and 105; we have an excellent agreement between our numerical code and previously published works. Copper-Water nanofluid is used with Pr = 6.2 and solid volume fraction χ is varied as 0%; 5%; 10%; 15% and 20%. The problem considered is a two-dimensional heat transfer in a square cavity. The vertical walls are differentially heated, the left is maintained at hot con- dition (sinusoidal) when the right one is cold. The horizontal walls are assumed to be insulated, non conducting and impermeable to mass transfer. The nanofluid in the enclosure is Newtonian, incompressible and laminar. The nanopar- ticles are assumed to have a uniform shape and size. Moreover, it is assumed that both the fluid phase and nanoparticles are in thermal equilibrium state and they flow at the same velocity. The thermophysical properties of the nanofluid are assumed to be constant except for the density variation in the buoyancy force, which is based on the Boussinesq approximation. Different correlations are proposed for predicting heat transfer for uniform and sinusoidal boundary thermal conditions.
Development of Coatings Marine Antifouling Based on Perfluorinated Surfactants Synthesis and Physicochemical Study  [PDF]
Abdelkader Bacha, Rachid Méghabar
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2014, DOI: 10.4236/jsemat.2014.42012

The fight against dirt settling on the hulls of ships and more generally on all underwater structures is more than 2000 years. The need for effective antifouling paints, which prevents the establishment and growth of marine organisms on submerged structures, is universally recognized. In this work, we synthesize two perfluorinated surfactants from simple monomers. After describing the reactions, we discuss the different analyzes of the proton nuclear magnetic resonance (1H NMR), the fluorine nuclear magnetic resonance (NMR I9F), gel permeation chromatography (GPC) and the light scattering (LS) at a fixed angle 90. The glass transition temperature of the two surfactants diethylallylphosphonate and allylamine are obtained by Differential Scanning Calorimetry (DSC). Antifouling paint properties were followed by exposure of the plates to the marine environment by visual observation.

On chains of centered valuations
Rachid Chibloun
International Journal of Mathematics and Mathematical Sciences , 2003, DOI: 10.1155/s0161171203206360
Abstract: We study chains of centered valuations of a domain A and chains of centered valuations of A [X1,…,Xn] corresponding to valuations of A. Finally, we make some applications to chains of valuations centered on the same ideal of A [X1,…,Xn] and extending the same valuation of A.
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