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Acta polytechnica HungaricaVolume 12, Issue No. 5. (2015.)


  • Chiu-Hsiung Chen ,
    Chang-Chih Chung ,
    Fei Chao ,
    Chih-Min Lin ,
    Imre Rudas J. :

    Abstract: This paper develops an intelligent robust control algorithm for a class of uncertain nonlinear multivariable systems by using a recurrent-cerebellar-modelarticulation-controller (RCMAC) and sliding mode technology. The proposed control algorithm consists of an adaptive RCMAC and a robust controller. The adaptive RCMAC is a main tracking controller utilized to mimic an ideal sliding mode controller, and the parameters of the adaptive RCMAC are on-line tuned by the derived adaptive laws from the Lyapunov function. Based on the  H control approach, the robust controller is employed to efficiently suppress the influence of residual approximation error between the ideal sliding mode controller and the adaptive RCMAC, so that the robust tracking performance of the system can be guaranteed. Finally, computer simulation results on a Chua’s chaotic circuit and a three-link robot manipulator are performed to verify the effectiveness and feasibility of the proposed control algorithm. The simulation results confirm that the developed control algorithm not only can guarantee the system stability but also achieve an excellent robust tracking performance.

    Keywords: recurrent-cerebellar-model-articulation-controller (RCMAC); sliding mode control; H control; nonlinear multivariable systems

  • Zoltán Fazekas ,
    Péter Gáspár :

    Abstract: Traffic signs setting out lane arrangements provide important and useful information for drivers, even when the road signs painted on the road surface are not visible for some reason. Though automatic traffic sign recognition systems are gaining real momentum and recent high-end cars are equipped with such systems, lane info traffic signs are often neglected by these systems. It is because of the high variability of the lane arrangements and their arrow-based representations. Herein, a syntactic approach is presented to describe lane info traffic signs and to decode and recognize their message in an automatic manner. The morphological features used for the purpose are kept intentionally simple at this stage of the research.

    Keywords: Traffic sign recognition; Syntactic pattern recognition; Morphological image processing

  • Jasenka Djikanovic ,
    Dusan Joksimovic ,
    Mirko Vujosevic :

    Abstract: A closed-loop problem in which vehicles deliver new products to the consumer and pick up products that have reached the end of their life is considered in this paper. It is assumed that capacities of vehicles and locations are limited. The aim is to minimize the total distances between locations in forward and reverse flow. A new mixed integer programming model (MILP) is presented. For its solution four variants of the variable neighbourhood search (VNS) method are proposed. The vehicle-routing search contains two steps, in which algorithms based on VNS are applied. Four VNS variants are also presented. The problems are solved optimally for a small number of nodes using MATLAB. The effectiveness of the presented model is evaluated with numerical examples.

    Keywords: supply chain; reverse logistics; vehicle-routing problem; variable neighbourhood search; closed-loop supply chain

  • Sucala, Ion Voicu ,
    Adriana Sava :

    Abstract: The paper presents the evolution of the market orientation of Romanian industrial companies in the first two decades of the post-communism period. While in the first decade of transition the market orientation was almost in-existent, at the end of the second decade a strong commitment towards marketing performance has been identified. The dimensions of marketing performance that emerged as most important were market performance, customer performance and marketing’s financial performance. However the companies’ average ability to measure marketing performance was slightly less than adequate.

    Keywords: industrial organizations; Romanian companies; market orientation; marketing performance measurement; post-communist transition

  • Roland Bérces :

    Abstract: In the article, I interpreted talent-nurturing as a key process of managing the quality of higher education and analyzed the Scientific Students' Association as a tool for successfully nurturing talents. By using analytical statistical methods, I showed which reasons motivate our students to join the Scientific Students' Association, and if those who participate in this particular form of university talent-nurturing share any common features or characteristics. Based on the results, I proposed quality improvement suggestions, which can increase the number of students that join formal talent-nurturing programs, thus, becoming more valuable for all higher education institutions.

    Keywords: higher education; quality management; talent-nurturing; student motivation; statistical analysis

  • Mariana Dubravská ,
    Ladislav Mura ,
    Rastislav Kotulič ,
    Jaroslav Novotný :

    Abstract: The goal of this paper is to identify the factors motivating Slovak companies by the internationalization of their business activities. Based on methodology, we have searched the factors influencing specific Slovak companies operating in foreign markets and tested for statistically significant differences among the individual factors that motivate Slovak companies for the internationalization of their business activities. In the majority of factors, the influence was proven by the companies managers. The relationship between the examined factors and the level of foreign trade activities, expressed by foreign sales volume, was tested. Thru the foreign working experience of business management, the relationship was confirmed. At the same time, it is possible to identify that there is no statistically significant difference, among the individual factors, that motivate Slovak companies for the internationalization of their business activities.

    Keywords: internationalization; business; motivation factors; Slovak Republic

  • N. Muthukumar ,
    Seshadhri Srinivasan ,
    K. Ramkumar ,
    P. Kavitha ,
    Valentina Emilia Balas :

    Abstract: Web Transport Systems (WTS) are used in material processing industries to maintain constant tension on the transported material (web), that is required for assuring material integrity and to reduce production down-time. Maintaining constant web tension in the presence of disturbance is a challenging task. This investigation presents a cascade control design, with online supervisory web tension control using Generalized Predictive Controller (GPC) in major loop and offline evolutionary optimization based PI controller in the inner loop. Two algorithms are used to tune the inner PI controller: Real coded Genetic Algorithm (RGA) and Bacterial Foraging Particle Swarm Optimization (BF-PSO), due to their ability to solve non-linear optimization problems and convergence to global optimum. Our results indicate that the GPC –BF-PSO cascaded control design shows better performance by regulating tension without violating physical constraints in the presence of process and external disturbances, when compared to GPC – RGA cascaded control design.

    Keywords: Web Transport System (WTS); Multivariable system; Generalized Predictive Controller (GPC); real-coded genetic algorithm (RGA); Bacterial Foraying Particle Swarm Optimization (BF-PSO); constrained optimization; cascaded architecture

  • László Erdődi :

    Abstract: Memory corruption vulnerabilities are one of the most dangerous types of software errors. By exploiting such vulnerabilities the malicious attackers can force the operating system to run arbitrary code on the system. The understanding and the research of memory corruption exploitation methods are crucial in order to improve detection and promote protection techniques. This study analyses the return oriented and the jump oriented exploitation methods combined with heap spray payload delivery technique. According to our knowledge this combination of memory exploitation has never been analysed before. By creating proof of concept exploits for CVE-2007-0038 it is shown, that combining return oriented and jump oriented programming with heap spray payload delivery gives new perspectives to attackers. These unique exploitation techniques possess almost all favourable characteristics of the combined techniques together such as almost unlimited payload size or bypassing data execution prevention without changing memory page protections.

    Keywords: Return Oriented; Jump Oriented; Heap Spray

  • Nenad Vunjak ,
    Nada Milenković ,
    Jelena Andrašić ,
    Miloš Pjanić :

    Abstract: The world economic crisis has to a great extent, affected the financial flow of business entities; the impact of the crisis has primarily affected the financial solvency of business entities. The effect of late payments caused by the financial crisis has also changed the bank portfolio structure of the banks involved in the financing in the corporate sector. The aim of this paper is to point out to what extent the effects of the crisis in the banking sector of one country impacted banks’ portfolios, business stability and to identify sectors in which there was an increase of risk in loan offerings due to an increase in NPL. Moreover, the aim herein is to prove that regardless of banks’ size, by assets, banks with fewer assets are not the only ones to suffer the consequences of the recession. Stress testing is used in this work to measure the impact of the effective NPL on the bank equity. Bank portfolio analysis performed according to the methodology described in this paper served to determine the effective NPL. As a result, the analysis shows the impact of NPL on the capital adequacy ratio of the banks. Summing up the results of individual analysis provides an overview of sectors which had an increase in risk, due to the financial crisis. The paper is organized as follows: The first part explains the NPL term in order to argue its significance in the analysis of the effects of the recession. The second part explains the methodology, i.e. the process of analysis and investigation, and in the third part presents the results that are interpreted to finally reach the conclusions and give suggestions for further research.

    Keywords: Stress test; NPL; capital adequacy ratio; economic crisis

  • Marko Đuković ,
    Ervin Varga :
    Load Profile-based Efficiency Metrics for Code Obfuscators191-212en [493.75 kB - PDF]EPA-02461-00059-0110

    Abstract: Code obfuscation techniques are gaining more attention and importance as ubiquitous computing becomes commonplace. The necessity to protect intellectual property rights as well as the need to prevent tampering with code running on all sorts of autonomous devices increases the demand for high quality code obfuscator tools. Currently, the principal quality metrics for evaluating code obfuscators mostly revolve around aspects such as security and functional correctness of the generated code. Nevertheless, power consumption plays a central role in handheld devices, as battery life and endurance is usually the bottleneck in achieving an acceptable level of user satisfaction with the system. Consequently, the criteria for choosing the right code obfuscator should be extended to also take into account the impact of obfuscation on the overall power consumption. This paper presents one viable approach for evaluating code obfuscators in regard to a power consumption level of the obfuscated code. The methodology is based upon load profiles. The performance of the solution has been tested using various commercial code obfuscators. The results show that there are significant differences in power consumption levels between original and obfuscated code. In order to select an obfuscation tool it is not enough to rely solely on non-power related attributes. High increase in a power consumption level may be totally inappropriate on mobile devices, despite the best obfuscation achieved with that particular tool. Accordingly, power consumption level should be incorporated into a set of quality metrics for code obfuscator

    Keywords: Energy-aware system; measurement techniques; protection mechanisms; obfuscation

  • Balázs Farkas ,
    ERnő Paál ,
    Károly Veszprémi :
    Low Power Photovoltaic Inverters Built up with SiC JFETs213-224en [330.33 kB - PDF]EPA-02461-00059-0120

    Abstract: The new generation of semiconductor switching devices based on silicon carbide makes higher efficiency and power density possible in photovoltaic (PV) inverters among many applications. The new type of JFET requires new driver circuits and a more careful arrangement of them. The main circuit arrangement has to have low stray inductance to ensure low overvoltage spikes and switching losses. It is well known that converter efficiency is an important parameter in the PV industry. SiC devices offer a good possibility to achieve 99% efficiency. This paper approaches the topic from the application point of view.

    Keywords: SiC JFET; Gate driver circuit; Photovoltaic Inverter

  • Karolina Kaszás-Lažetić ,
    Dejana Herceg ,
    Nikola Djurić ,
    Miroslav Prša :

    Abstract: In this paper, we present a new method for determining the earth return impedance. The proposed method, based on electromagnetic field theory, is very accurate and convenient for the analysis of earth behavior over a wide range of low frequencies. It takes into account all crucial physical events, including an exact treatment of the skin and proximity effects within the earth. Combining analytical and numerical procedures for finding the exact current distribution and the earth return impedance per unit length, we have developed an efficient and powerful tool that is described in this paper. In all calculations, real situations were considered, consisting of various soil resistivity values, overhead conductor heights, and combinations of parameters at various frequencies. Although most commonly applied simplified formulas give accurate results at industrial frequencies, significantly worse results are obtained in the presence of higher harmonics. Hence, verification of the developed method was achieved by comparing obtained results with the results of the Carson-Clem simplified formula and the FEM-based calculations. The generality of the developed program indicates that it may also be applied for calculating the earth return impedance in the presence of higher current harmonics.

    Keywords: Applied electromagnetic approach; Bessel functions; current distribution; earth return impedance; Poynting vector flux