a borítólapra  Súgó epa Copyright 
Acta polytechnica HungaricaVolume 1, Issue No. 1. (2004 May)


  • András Farkas ,
    Pál Rózsa :

    Abstract: This paper develops the “best” rank one approximationmatrix to a general pairwise comparison matrix (PCM) in a least-squares sense. Such quadratic matrices occur in the multicriteria decision making method called the analytic hierarchy process (AHP). These matrices may have positive entries only. The lack of uniqueness of the stationary values of the associated nonlinear least-squares optimization problem is investigated. Sufficient conditions for the nonuniqueness of the solution to the derived system of nonlinear equations are given. Results are illustrated through a great number of numerical examples.

    Keywords: nonlinear optimization, least-squares method, multiple-criteria decision making

  • József K. Tar ,
    Imre J. Rudas ,
    János F. Bitó :

    Abstract: In this paper the applicability of an adaptive control based on a novel branch of Computational Cybernetics is illustrated for two different, imperfectly and inaccurately modeled particular physical sytems. One of them is a water tank stirring cold and hot water as input and releasing the mixture through a long pipe. The mass flow rate and the temperature are prescribed at the free end of the exit pipe while the taps at the input side can diretly be controlled. Due to the incompressibility of the fluid the variation of the mass flow rate of the output is immediately observableat the pipe’s end and is related to the control action at the input taps, while its effect on the temperature becomes measurable at the free end of the pipe only after a delay time needed for the fluid to flow through the pipe. This results in asymmetric and non-constant delay time. The other paradigm is the thermal decay of the molecular nitrogen during a throttling down process. As is well known chemical reactions hav very drastic non-linearities and it is not easy to construct their “exact” or satisfacorily avccurate model. The fundamental principles of this new branch of Computational Cybernetics are briefly presented in the paper. To some extent it is similar to the traditional Soft Computing, but by using a priori known, uniform, lucid structure of reduced size, it can evade the enormous structures so characteristic to the usual approach. Clumsy deterministic, semi-stochastic or stochastic machine learning is replaced by simple, short, explicit algebraic procedures especially fit to real time applications. The costs of these advantages may manifest themselves in the expected limitation of the applicabilityof this new approach. However, the simulation results exemplify the applicability of the new method in the control of systems of strong non-linearities and asymmetric delay time

  • László Horváth ,
    Imre J. Rudas :
    Modeling Course for Virtual University by Features 44-58en [66.05 kB - PDF]EPA-02461-00001-0030

    Abstract: Environments with large number of interrelated information uses several advanced concepts as computer description of different aspects of modeled objects in the form of feature based models. In this case a set of features is defined then used for the purpose of modification of an initial model to achieve a final model as a description of an instance of a well-defined complex object from a real world environment. Utilization this approach and some relevant methods have been investigated by the authors to establish course modeling in virtual university environments. The main objective is definition generic model entities for courses and instance model entities for student course profiles. Course model entities describe virtual university activities. The modeling can be applied generally but it is being developed for the domain of higher education in virtual technologies. The paper introduces some virtual university related concepts and the approach of the authors to virtual university. Following this feature driven associative model of virtual course developed by the authors is explained. Some issues about the conceptualized application oriented virtual course features are discussed as a contribution to implementation of a virtual classroom model proposed by the authors. Finally, possibilities of integration of the university model with engineering modeling systems are discussed taking into account present day virtual universities and possibilities to communicate with prospective students both in professional design and home computer environments

  • Tamás Réti ,
    Károly Böröczky :
    Topoligical Characterization of Cellular Structures59-85en [347.18 kB - PDF]EPA-02461-00001-0040

    Abstract: In order to characterize quantitatively the local topological structure of cellular systems a new method has been developed. First, we analyzed the topological properties of infinite periodic cellular structures, and then the general theoretical results obtained have been adapted to the local topological characterization of 2-dimensional finite cellular surface systems. The concept of this new approach is based on the use of the so-called double toroidal embedding (DT embedding) by which a finite cellular system defined on a torus can be generated from an infinite periodic cellular system. The DT embedding is a special mapping, which enables to preserve all the local topological properties of the original infinite periodic cellular system. As a result of performing a DT embedding, socalled neighborhood coefficients can be generated. The neighborhood coefficients are scalar topological invariants, by which the local topological structure of cellular systems can be quantitatively evaluated and compared. Moreover, by investigating the relationship between the neighborhood coefficients and other local topological quantities, we verify that the validity of the Weaire-Fortes identity can be extended to a broad class of infinite periodic cellular systems and 2-d finite cellular surface systems (i.e. generalized fullerenelike surface structures). Finally, it has been shown that the traditional definition of fullerenes can be generalized by introducing the notion of the cellular fullerene, which is considered as a finite cellular system defined on a 2-d unbounded, closed and orientable surface.

    Keywords: cell, embedding, toroidal graphs, Weaire-Fortes identity, corona, fullerene

  • Éva Borbély ,
    József Erdélyi :

    Abstract: The Ce4+/ Ce3+ redox system was studied to initiate the grafting of idustrial cellulose pulp with vinyl acetate monomer. The parameters of the copolymerization reaction (reaction time, temperature, monomer and initiator contentration, freeness, chemical composition of the cellulose) were investigated and their effects are discussed

    Keywords: cellulose, copolymerization, vinyl acetate, ceric ion redox system, parameters

  • András I. Bakó ,
    Zoltán Horváth :
    Decision Supporting Model for Highway Maintenance 96-107en [60.96 kB - PDF]EPA-02461-00001-0060

    Abstract: A decision model for pavement management has been developed herein based on linear programming formulation. Markov transition probability matrices are introduced to model the deterioration process of the road sections. To every type of road surfaces and class of traffic amount belongs a certain Markov matrix. The presented model and methodology is used to determine the optimal rehabilitation and maintenance policy in network level. Depending on the objective function two types of problems could be solved by the model : the necessary funds calculation and the optimal budget allocation for the entire network. We have developed the computer program on microcomputer and it has been used by the Ministry of Transport who is responsible for the 30000 km road network of Hungary.

    Keywords: Markov process, Decision Support System, Pavement Management System, Network - Level Model, Linear Programming

  • Béla Palásti-Kovács ,
    Zoltán Néder ,
    Árpád Czifra ,
    Károly Váradi :
    Microtopography Changes in Wear Process 108-112en [478.16 kB - PDF]EPA-02461-00001-0070

    Abstract: Wear experiments and measurements were performed to study surface microtopography changes. Investigations extended to wear in the course of the non-lubricated sliding friction of ground bronze-steel sliding pairs. In the knowledge of 3D microtopography, asperities were statistically processed. Asperities were replaced by paraboloid and pyramidal surfaces, in order to determine the distribution of the direction angle of asperities, the height distribution of the peak points, the radius distribution of the peak curvatures, and slope angle distribution. These can be properly used for characterizing microtopography changes in the course of the wear process. It was also examined what additional information was provided by SEM recordings of surfaces on surface structure, with particular regard to tribological phenomena.

    Keywords: microtopography, asperities, wear, statistical analysis

  • István Szűts :
    Measurement Methods in the field of benchmarking 120-129en [63.27 kB - PDF]EPA-02461-00001-0080

    Abstract: In benchmarking1 we often come across with parameters being difficult to measure while executing comparisons or analyzing performance, yet they have to be compared and measured so as to be able to choose the best practices. The situation is similar in the case of complex, multidimensional evaluation as well, when the relative importance and order of different dimensions, parameters to be evaluated have to be determined or when the range of similar performance indicators have to be decreased with regard to simpler comparisons. In such cases we can use the ordinal or interval scales of measurement elaborated by S.S. Stevens.