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Search Results: 1 - 10 of 224276 matches for " R. Moussa "
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Comparison of different multi-objective calibration criteria using a conceptual rainfall-runoff model of flood events
R. Moussa,N. Chahinian
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2009,
Abstract: A conceptual lumped rainfall-runoff flood event model was developed and applied on the Gardon catchment located in Southern France and various single-objective and multi-objective functions were used for its calibration. The model was calibrated on 15 events and validated on 14 others. The results of both the calibration and validation phases are compared on the basis of their performance with regards to six criteria, three global criteria and three relative criteria representing volume, peakflow, and the root mean square error. The first type of criteria gives more weight to large events whereas the second considers all events to be of equal weight. The results show that the calibrated parameter values are dependent on the type of criteria used. Significant trade-offs are observed between the different objectives: no unique set of parameters is able to satisfy all objectives simultaneously. Instead, the solution to the calibration problem is given by a set of Pareto optimal solutions. From this set of optimal solutions, a balanced aggregated objective function is proposed, as a compromise between up to three objective functions. The single-objective and multi-objective calibration strategies are compared both in terms of parameter variation bounds and simulation quality. The results of this study indicate that two well chosen and non-redundant objective functions are sufficient to calibrate the model and that the use of three objective functions does not necessarily yield different results. The problems of non-uniqueness in model calibration, and the choice of the adequate objective functions for flood event models, emphasise the importance of the modeller's intervention. The recent advances in automatic optimisation techniques do not minimise the user's responsibility, who has to choose multiple criteria based on the aims of the study, his appreciation on the errors induced by data and model structure and his knowledge of the catchment's hydrology.
Comparison of different multi-objective calibration criteria of a conceptual rainfall-runoff model of flood events
N. Chahinian,R. Moussa
Hydrology and Earth System Sciences Discussions , 2007,
Abstract: A conceptual lumped rainfall-runoff flood event model was developed and applied on the Gardon catchment located in southern France and various mono-objective and multi-objective functions were used for its calibration. The model was calibrated on 15 events and validated on 14 others. The results of both the calibration and validation phases are compared on the basis of their performance with regards to six criteria, three global criteria and three relative criteria representing volume, peakflow, and the root mean square error. The first type of criteria gives more weight to strong events whereas the second considers all events to be of equal weight. The results show that the calibrated parameter values are dependent on the type of criteria used. Significant trade-offs are observed between the different objectives: no unique set of parameter is able to satisfy all objectives simultaneously. Instead, the solution to the calibration problem is given by a set of Pareto optimal solutions. From this set of optimal solutions, a balanced aggregated objective function is proposed, as a compromise between up to three objective functions. The mono-objective and multi-objective calibration strategies are compared both in terms of parameter variation bounds and simulation quality. The results of this study indicate that two well chosen and non-redundant objective functions are sufficient to calibrate the model and that the use of three objective functions does not necessarily yield different results. The problems of non-uniqueness in model calibration, and the choice of the adequate objective functions for flood event models, emphasise the importance of the modeller's intervention. The recent advances in automatic optimisation techniques do not minimise the user's responsibility, who has to chose multiple criteria based on the aims of the study, his appreciation on the errors induced by data and model structure and his knowledge of the catchment's hydrology.
Approximation zones of the Saint-Venant equations f flood routing with overbank flow
R. Moussa,C. Bocquillon
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2000,
Abstract: The classification of river waves as gravity, diffusion or kinematic waves, corresponds to different forms of the momentum equation in the Saint-Venant system. This paper aims to define approximation zones of the Saint-Venant equations for flood routing in natural channels with overbank flow in the flooded area. Using linear perturbation theory, the different terms in the Saint-equations were analysed as a function of the balance between friction and inertia. Then, using non-dimensionalised variables, flood waves were expressed as a function of three parameters: the Froude number of the steady uniform flow, a dimensionless wave, number of the unsteady component of the motion and the ratio between the flooded area zone width and the main channel width. Finally, different theoretical cases, corresponding to different flooded area zone widths were analysed and compared. Results show that, when the width of the flooded area increases, the domain of application of the diffusive wave and the inematic wave models is restricted. Keywords: Saint-Venant equations; river waves; overbank flow
Production of Corundum-Mullite Mixture with High Added Value from Raw Materials of Morocco  [PDF]
S. El Kalakhi, A. Samdi, R. Moussa, M. Gomina
New Journal of Glass and Ceramics (NJGC) , 2016, DOI: 10.4236/njgc.2016.63004
Abstract: In search of new mineral raw materials with industrial potential, we identified a deposit located in the southwest of Oujda (in the Northeastern Morocco). The physicochemical analyses indicate that the ore consists mainly of diaspore, topaz and quartz, and also secondary minerals. The presence of topaz in the ore is explained by hydrothermal action on the structure of diaspore. The investigation of structural transformations reveals complex reaction mechanisms that result in a mixture of corundum-mullite at 1200℃, which is of great industrial interest. Thus, the peculiarity of this ore is the presence of fluorine and secondary minerals.
A Generalization of Ince’s Equation  [PDF]
Ridha Moussa
Journal of Applied Mathematics and Physics (JAMP) , 2014, DOI: 10.4236/jamp.2014.213137
Abstract: We investigate the Hill differential equation \"\" where A(t), B(t), and D(t) are trigonometric polynomials. We are interested in solutions that are even or odd, and have period π or semi-period π. The above equation with one of the above conditions constitutes a regular Sturm-Liouville eigenvalue problem. We investigate the representation of the four Sturm-Liouville operators by infinite banded matrices.
Limits on the amplification of evanescent waves of left-handed materials
Th. Koschny,R. Moussa,C. M. Soukoulis
Physics , 2005, DOI: 10.1364/JOSAB.23.000485
Abstract: We investigate the transfer function of the discretized perfect lens in finite-difference time-domain (FDTD) and transfer matrix (TMM) simulations; the latter allow to eliminate the problems associated with the explicit time dependence in FDTD simulations. We argue that the peak observed in the FDTD transfer function near the maximum parallel momentum $k_{\|,\mathrm{max}}$ is due to finite time artifacts. We also find the finite discretization mesh acts like imaginary deviations from $\mu=\epsilon=-1$ and leads to a cross-over in the transfer function from constance to exponential decay around $k_{\|,\mathrm{max}}$ limiting the attainable super-resolution. We propose a simple qualitative model to describe the impact of the discretization. $k_{\|,\mathrm{max}}$ is found to depend logarithmically on the mesh constant in qualitative agreement with the TMM simulations.
Fabrication and Characterization of PZN-4.5PT Inorganic Perovskites Nanoparticles Thin Films Deposited on P-Type Silicon Substrate  [PDF]
Rémi Ndioukane, Moussa Touré, Diouma Kobor, Laurence Motte, Marcel Pasquinelli, Jeanne Solard
Journal of Modern Physics (JMP) , 2018, DOI: 10.4236/jmp.2018.92018
Abstract: This work involves an investigation of nanostructures, microelectronic properties and domain engineering of nanoparticles thin layers of Pb(Zn1/ 3Nb2/3)O3-PbTiO3 (PZN-PT) ferroelectric single crystals deposited on nanostructured silicon substrate. In this study, devices made from PZN-4.5PT nanoparticles thin films successfully deposited on silicon substrate have been studied and discussed. SEM images show the formation of local black circles and hexagonal shapes probably due to the nucleation of a new Si-gel component or phase induced by annealing. Micro Xray Fluorescence mapping shows that the high values of Si and B atoms (7 and 4 normalized unit respectively) can be explained by the fact that the substrate is p-type silicon. The most interesting result of optical measurements is the very good absorption for all the thin films in UV, Visible and NIR regions with values from 70% to 90% in UV, from 75% to 93% in Visible and NIR. Tauc plots present particularities (rarely encountered behavior) with different segments or absorption changes showing the presence of multiple band gaps coming from the heterogeneity of the thin films (nanowires, gel and nanoparticles). Their values are 1.9 and 2.8 eV for DKRN-Gel, 2.1 and 3.1 eV for DKRN-UD and 2.1 and 3.2 eV for DKRN-D) corresponding respectively to the band gap of nanowires and that of the gel while the last ones correspond to the undoped and doped nanoparticles (3.1 and 3.2 eV respectively).
Dielectric and Ferroelectric Properties of PZN-4.5PT Nanoparticles Thin Films on Nanostructured Silicon Substrate for Ferrophotovoltaic and Energy Storage Application  [PDF]
Rémi Ndioukane, Moussa Touré, Diouma Kobor, Laurence Motte, Jeanne Solard, Laurent Lebrun
Journal of Modern Physics (JMP) , 2019, DOI: 10.4236/jmp.2019.106043
Abstract: The integration of ferroelectric materials as thin films has attracted considerable attention these last years thanks to their outstanding performances that allow considering new features for the realization of photovoltaic devices. Our study focuses on investigating structural, dielectric and ferroelectric properties of undoped and Mn doped PZN-4.5PT nanoparticles thin films on Silicon substrate. We fabricate very stable PZN-4.5PT nanoparticles thin films deposited on nanostructured silicon substrate with giant relative dielectric permittivity of 2.76 × 104 and 17.7 × 104 for respectively the undoped and Mn doped thin films. These values are very large compared to those found in single crystals and might be explained by the influence of the gel in which nanoparticles were dispersed. The SEM images show the crystallization of new hexagonal phases on the film surface probably coming from interaction between Si and the gel. The hysteresis loops permitted to determine the spontaneous polarization (Ps), remnant polarization (Pr) and coercive field Ec which are equal to 11.73 μC/cm2, 10.20 μC/cm2 and 20 V/cm, respectively for the undoped nanoparticles thin film and 22.22 μC/cm2, 19.32 μC/cm2 and 20 V/cm respectively for the Mn doped one. These values are high and correspond to the best ones found in literature compared to typical ferroelectric thin films.
Electrochemical Self-Assembly of Nanoporous Alumina Templates Title  [PDF]
Muna Moussa Abbas
Advances in Materials Physics and Chemistry (AMPC) , 2013, DOI: 10.4236/ampc.2013.35035
Abstract: Porous alumina was fabricated electrochemically through anodic oxidation of aluminum by means of such a self-organized method. Anodic aluminium oxide (AAO) template with nanopores was grown by two-steps anodization processes from a high purity aluminium foil. The anodization process was carried out in a phosphoric acid electrolyte at ambient temperature with a different duration of anodization. The analysis observation by Atomic Force Microscopy (AFM) showed that nanopore size increased with anodization time. The nanopore sizes of porous alumina were (16.04, 26.19 and 37.39 nm) for (1, 2 and 3 hour) respectively.
Effect of Hydrochloric Acid on the Structural of Sodic-Bentonite Clay  [PDF]
Samira Bendou, Moussa Amrani
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2014, DOI: 10.4236/jmmce.2014.25045
Abstract: The objective of this work is to determine changes of surface properties of a bentonite after acid activation, using hydrochloric acid solutions (HCl) at room temperature. XRD, FX, FTIR, MEB, and BET analyses of the samples have been carried out to examine the structure of bentonite before and after acid activation. It is found that the raw bentonite is composed of dioctahedral montmorillonite with predominant quantity and certain amounts of quartz, albite and illite, etc. It has an cation exchange capacity (CEC) of 74.32 meq/g which allows it to be characterized as typical sodium bentonite. The changes, at low acid concentrations, are the result from from cation exchange (exchangeable cations with H+ ions). Differences of surface area at high acid concentrations (0.25 - 0.4 M) were caused by structural changes and partial decomposition of the samples. Data of surface area measurements have showed that with increase of concentration of hydrochloric acid, the surface area increased. The maximum value (837.11 m2/g) was reached by the sample activated with 0.4 M HCl. By against, activation with higher concentration (0.6 M) caused a decrease in the surface area.
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