L’évaluation du succès de l’EDI dans lesPME: un modèle intégrateur

EDI is by far the Information Technology (IT) that has aroused, these last ten years, many interesting works in the field of theSME organizational development. The absence of federative conceptual framework is probably behind the great diversity of results, especially in the area of the prediction of its adoption and the evaluation of its success. These observations are behind a five years field research carried by an objective ofEDI success evaluation by end users. This article contributes to validate an “abductive” approach. To be made, it summarizes and classifies theoretical foundations of an analysis of thisIT impacts, and formulate an evaluation model using a system approach. Each of the three levels of the studied system (processing factor keys of success, quality of theEDI acceptance process, and success or internal performance) fact thus the object of premises allowing to confront observations of the four field enterprises to the conceptual framework and concepts identified in the review of the literature. Results of this approach using an appropriate qualitative methodology on cases of enterprises users ofEDI have allowed to validate the structure of the model and to refine the constructs of the different variables, that, so as to commit ulterior empirical works destined for validate the aimed explanatory of the model.     

Utilisation de la théorie géométrique de la diffraction pour l’étude du rayonnement des ouvertures circulaires dans leur zone de champ proche

The aim of this article is to evaluate the precision which can be given by the geometrical theory of diffraction (GTD)when it is used to calculate the field radiated by a circular aperture in its near zone. Both versions of the GTD are used, that due to Keller (classical GTD)and that due to Kouyoumjian (modified GTD).The results obtained with the latter are far better than those obtained with the first one, since the divergence disappears in the neighborhood of the shadow boundary. Moreover, with times of calculation shorter by several tens of times, they can well be compared to the reference results obtained with Kottler’s formulas.     

Potentialités des séquences d’étalement chaotiques pour l’amélioration duTEEB d’un systèmeDS-CDMA asynchrone

The use of chaotic sequences as spectral spreading sequences in a Direct Sequence-Code Division Multiple Access is proposed in this paper. The simulation of the system is performed with the system simulator Omnisys. The chaotic spreading sequences are generated from a non-linear recursive equation. The Bit Error Rate of this system is compared with theBER of the same system using binary Gold sequences. The results show that chaotic sequences can improve performances in terms of allowable number of users.     

Synthèse optimale d’un réseau de télécommunication avec contraintes de sécurité

A commonly used method for achieving a prescribed security level in a telecommunication network is to manage extra capacities all over the network. This paper describes a number of computational methods, both exact and approximate, for determining a minimum cost network of extra capacities needed to achieve security under any given trunk dimensioning, routing and grouping policy. From a mathematical point of view, it is shown that the problem reduces to the determination of a minimum cost network subject to a number of non simultaneous multicommodity flow requirements. Since real life instances of such problems commonly result in very large linear programs of many thousands of variables and constraints, the techniques of linear programming would be unacceptably time and space-consuming. Instead, it is shown how the use of Lagrangean relaxation in conjunction with sub-gradient optimization schemes can lead to efficient and easy-to-implement solution methods. The various procedures described in this paper form the heart of a general software product for long and medium term planning applications (Supersec program) which has already been used to investigate the economical implications of security requirements in telecommunication networks.     

Mécanisme de l’évolution des champs électromagnétiques dans un simulateur de grandes dimensions. Projet d’un simulateur semi-rhombique

The purpose of this paper is to evaluate theoretically and experimentally the transient electric field in anemp simulator. Using a time domain analysis, the mechanism of the field deformation can be analysed and consequently modifications can be introduced in the conception of new simulators (for example: rhombic simulator).     

Étude de la génération d’impulsions brèves d’un laser DFB à trois contrôles de phases (3QWS-DFB)

The purpose of this paper is to study the generation of short pulses of the three quarter wave shift distributed feedback (3Qws-dfb) laser by using switching gain technique. We have used the temporal domain model (Tdm) which is a multimode spatio-temporal model that considers simultaneously all the modes of the overall intra-cavity field as well as the two following nonlinear effects, the spectral hole burning (Shb) and the gain saturation. Obtained results showed that a 3Qws-dfb laser can generate short pulses in accordance with Fourier criteria. These results show that 3Qws-dfb lasers are potential candidates as monomode optical sources for long distance high bit rate telecommunications.