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Acta polytechnica HungaricaVolume 7, Issue No. 3 (2010.)


  • Dusan Kocur ,
    Jan Gamec ,
    Maria ©vecová ,
    Maria Gamcová ,
    Jana Rovňáková :

    Abstract: This paper presents the imaging method applied for moving target tracking by a multistatic ultra-wideband radar system. The imaging method consists of such signal processing phases as raw radar data pre-processing, background subtraction, the fusion of the data obtained by the particular receiving channels of a radar, detection, localization and the tracking itself. In this paper, the particular phases of the imaging method are described. Firstly, the theoretical base of the particular phases is denoted and then an overview of the signal processing methods which can be applied within corresponding phase is given. Here, we will also outline that a signal cross-talk, exponential averaging, 2D double-stage (N,k) detector, a target gravity center estimation and a low-complex nonlinear two-stage tracking filter can be used within the mentioned radar signal processing phases as convenient signal processing methods. The good performance of the imaging method presented in this contribution is illustrated by processing signals obtained by the ultra-wideband radar for a scenario represented by through wall tracking of a single moving target.

  • Andrew Rusinko :

    Abstract: The paper is concerned with the generalization of the synthetic theory to the modeling of both plastic and creep deformation. Non-classical problems such as creep delay, the Bauschinger negative effect and reverse creep have been analytically described; the calculated results show satisfactory agreement with experiments. These problems cannot be modeled in terms of classical creep/plasticity theories. The main peculiarity of the generalized synthetic theory consists in the fact that the macro-deformation is highly associated with processes occurring on the micro-level of material.

    Keywords: plastic deformation; primary creep; steady-state creep; the Bauschinger negative effect; creep delay; reverse creep

  • R. M. Patel ,
    G. M. Deheri ,
    Pragna A. Vadher :
    Performance of a Magnetic Fluid-based Short Bearing 63-78en [159.46 kB - PDF]EPA-02461-00024-0030

    Abstract: An effort has been made to study and analyze the performance of a magnetic fluid based infinitely short hydrodynamic slider bearing. The Reynolds’ equation is solved with appropriate boundary conditions. The expressions for various performance characteristics such as pressure, load carrying capacity and friction are obtained. Results are presented graphically. It is clearly seen that the load carrying capacity increases considerably due to the magnetic fluid lubricant. Further, the film thickness ratio increases the load carrying capacity. It is found that the load carrying capacity increases as the ratio of the length to outlet film thickness increases while it decreases with respect to the increasing values of the ratio of the width to the outlet film thickness. In addition, it is investigated that the magnetic fluid lubricant unalters the friction. Lastly, this article makes it clear that the negative effect induced by the ratio of the width to the outlet film thickness can be neutralized up to a considerably large extent by the combined positive effect of the magnetization parameter, the film thickness ratio and the ratio of the length to outlet film thickness. This study provides ample scope for extending the life period of the bearing system.

    Keywords: short bearing; magnetic fluid; Reynolds’ equation; pressure; load carrying capacity

  • Magda Komorníková ,
    Jozef Komorník :

    Abstract: The currencies of the Visegrád countries (Poland, the Czech Republic, Hungary, and Slovakia) have been considered by the international financial community as a basket of currencies which are closely related, especially in times of their depreciations. On July 1, 2008 the official terminal exchange rate SKK/EUR was fixed. During the following 8 months, the remaining three currencies (PLN, CZK, HUF) changed their long-term behaviour to one of strong parallel depreciation. On the other hand, in the first selected long-term period (January 4, 1999 – June 30, 2008), a relatively mixed development of HUF seemed to exhibit a rather low degree of interdependence with CZK (that had been appreciating very intensively). The values of the Kendall’s correlation coefficient calculated for all 3 remaining couples of returns substantially rose in the second period (indicating that similarities between the returns of these exchange rates are stronger in the times of crises). We have performed modeling and fitting of the dependencies of the above mentioned couples of returns of currencies in both the mentioned time periods by several classes of bivariate copulas, as well as by (optimized) convex combinations of their elements.

    Keywords: bivariate copula; return of exchange rates; Kendall’s tau; convex combinations of copulas; goodness of fit (GOF) test

  • Lóránt Szabó ,
    István Patkó ,
    Gabriella Oroszlány :
    The Dynamic Study of the Weft Insertion of Air Jet Weaving Machines93-107en [374.72 kB - PDF]EPA-02461-00024-0050

    Abstract: The application of the air jet loom is widespread in the textile industry because of its high productivity, convenient controllability, high filling insertion rate, low noise and low vibration levels. Air stream in confusor guides can be classified into two types. A weft yarn ejected with high speed air flow is given the drag force caused by friction between the weft yarn and the air flow. In this article we show the study of the dynamics of the type P air jet weaving machines and the definition of the skin friction coefficient for multifilament weft. We have given a calculation procedure for the dynamic description of the insertion process of weaving machines marked P.

    Keywords: air jet weft insertion; confusor air guides; maintained air jet; fiction force; skin friction coefficient; friction force measurement; momentum; multifilament weft yarn

  • Ján Vaącák ,
    Ladislav Madarász :
    Adaptation of Fuzzy Cognitive Maps – a Comparison Study109-122en [499.79 kB - PDF]EPA-02461-00024-0060

    Abstract: This paper deals with the experimental study and comparison of various adaptation methods for setting-up parameters of fuzzy cognitive maps (FCMs). A survey is given of the best known methods, which are mostly based on unsupervised learning. The authors show better performance using supervised learning, namely least mean square approaches. Experiments were done on a simulation example of autonomous vehicle navigation. The paper is concluded by comparing their efficacy and properties.

    Keywords: adaptation methods; fuzzy cognitive learning; Hebbian learning; supervised learning

  • Tamás Szádeczky :
    Problems of Digital Sustainability123-136en [137.91 kB - PDF]EPA-02461-00024-0070

    Abstract: The article introduces digital communication by drawing comparisons between the histories of digital and conventional written communication. It also shows the technical and legal bases and the currently reached achievements. In relation to the technical elements, it acquaints the reader with the development and current effects of computer technology, especially cryptography. In connection with the legal basis, the work presents the regulations which have emerged and made possible the legal acceptance of the digital signature and electronic documents in the United States of America, in the European Union and among certain of its member countries, including Hungary. The article reviews the regulations and the developed practices in the fields of e-commerce, electronic invoices, electronic records management and certain e-government functions in Hungary which are necessary for digital communication. The work draws attention to the importance of secure keeping and processing of electronic documents, which is also enforced by the legal environment. The author points to the technical requirements and practical troubles of digital communication, called digital sustainability.

    Keywords: electronic archive; digital sustainability; preservation; electronic signature; data security

  • Monika Michalíková ,
    Lucia Bednarcíková ,
    Martin Petrík ,
    Jozef ®ivcák ,
    Richard Raąi :
    The Digital Pre-Operative Planning of Total Hip Arthroplasty 137-152en [785.87 kB - PDF]EPA-02461-00024-0080

    Abstract: Pre-operative planning is a very important part of hip arthroplasty (especially reimplantation of total hip and hip joint). Conventional pre-operative planning is realized with caliper, protractor, plastic transparent templates and x-ray images. This conventional templating technique is time consuming with many errors and impractical. This paper presents the current applications of computer technology in the field of surgery and preoperative planning of total hip implantation. At the present time, orthopaedic surgeons use transparent template radiographs as part of pre-operative planning in order to gauge the suitability and correct size of an implant. The newly developed CoXaM software offers a simple solution to the problems by using digital x-ray images and handmade transparent plastic templates. The utilization of developed software has many advantages in the hospital unit (the elimination of storing large inventories of implants, the minimalization of errors from the magnification of templates and x-ray images, etc.). The proposed methodology provides the opportunity for comfortable, user-friendly and dimensionally accurate computer programming surgical operation. The technique is reliable, cost effective and acceptable to patients and radiographers.

    Keywords: digital pre-operative planning; software; x-ray image; hip joint replacement; template

  • András Keszthelyi :
    Remarks on the Efficiency of Information Systems153-161en [52.78 kB - PDF]EPA-02461-00024-0090

    Abstract: In Hungary there exist two big and well-known scholar information systems (SIS). Both of them have become part of everyday life in the administration of higher education. These SISes have made quite a long journey during their evolution. Even so, they have some annoying disadvantages even today; e.g. they serve too few users at a time too slowly in the case of critical activities, such as during registration for courses or for examinations. There are many circumstances which can result in such poor efficiency. In this paper I try to investigate the role of three-level data modelling in an indirect way. I, with a colleague of mine at Budapest Tech, planned and executed a measurement which shows that (much) better performance can be reached based on a 'good' data model, even in a poorer environment.

    Keywords: database efficiency; scholar information system

  • Bachir Ghalem ,
    Bendiabdellah Azeddine :
    Six-Phase Matrix Converter Fed Double Star Induction Motor163-176en [375.49 kB - PDF]EPA-02461-00024-0100

    Abstract: two different control strategies applied to a direct AC-AC six-phase matrix converter are investigated in the present paper. The first strategy is derived from the Venturini method, and the second approach is practically an extension of the scalar strategy control. Both strategies were originally applied to the three-phase matrix converter.

    The current investigation deals with a comparative performance study of a double star induction motor fed from a six-phase matrix converter using the two above control strategies.

    After a theoretical introduction of the six-phase matrix converter, a detailed description of the strategies implementation is presented followed by a discussion of results obtained from simulation results.

    Keywords: six-phase; matrix converter; modulation coefficients; double star induction motor