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Acta polytechnica HungaricaVolume 7, Issue No. 2 (2010.)


Tematikus cím:
  • Anna Černá ,
    Jan Černý :
    Position Identification of Moving Agents in Networks5-23en [296.08 kB - PDF]EPA-02461-00023-0010

    Abstract: The paper introduces a group of problems connected with the position identification of an agent moving through a given network and starting in an unknown vertex or edge (arrow). It presents a classification of the problems, describes the application fields and outlines further possible developments of the theory.

    Keywords: Agent; position; identification; network

  • Tamás Szakács :

    Abstract: The design and management of agricultural transport systems is facing a series of challenges. The goals of increasing vehicle mobility and reducing soil stress have always been in the center of attention. Involving trailer wheels in the production of pulling force could be beneficial in both cases. In this way, the mobility of the transport system could be secured even in heavy soil conditions, and the soil damage could be reduced as well. Despite the potential advantages, trailer protrusion is not currently practical. The reason for this is the lack of proper safety measures. The origin of this problem is the force generated by the trailer protrusionacting on the drawbar, which can bring the tractor into an unstable state, causing the tractor to roll over or the vehicle train to jack-knife. To avoid such accidents, a control system must be developed which can recognize the beginning of unstable vehicle behavior and either by warning or intervention help to maintain the stable state of the vehicle.

    The goals of this paper can be summarized as follows:
    – To introduce a computer simulation model of an agricultural transport vehicle-park consisting of different dynamical models of tractors and trailers. The aim of this modelpark is to perform stability analysis of tractor – propelled axle trailer vehicle combinations.
    – To introduce stability criteria equations for future stability control programs which can determine different unstable states, and by interaction can re-stabilize the vehicle combinations.

    Keywords: Vehicle-train; stability; agricultural transport systems

  • Tiberiu Tudorache ,
    Cristian Roman :

    Abstract: This paper deals with the numerical modeling of a diesel generator set used as a main energy source in isolated areas and as a back-up energy source in the case of renewable energy systems. The numerical models are developed using a Matlab/Simulink software package and they prove to be a powerful tool for the computer aided design of complex hybrid power systems. Several operation regimes of the equipment are studied. The numerical study is completed with experimental measurements on a Kipor type dieselelectric generator set.

    Keywords: Diesel generator set; numerical models; experimental analysis

  • Fatima Zohra Zerhouni ,
    M’hamed Houari Zerhouni ,
    Mansour Zegrar ,
    M. Tarik Benmessaoud ,
    Amine Boudghene Stambouli ,
    Abdelhamid Midoun :

    Abstract: Lately, the use of solar energy has seen considerable development. Transformation in electric energy is one of its applications which attracts considerable interest, owing to the fact that it makes it possible to solve a major problem in isolated cities that lack electrical supply networks. For solar energy use, the current drawback remains its high cost. This problem can be resolved through different improvements in terms of power production. For that, different axis of research can be explored [1-3].

    Over the past few years, solar cells arrays (SCA) have been connected to various loads in a direct coupled method. A PV module can produce the power at a point, called an operating point, anywhere on the current- voltage (I-V) curve. The coordinates of the Operating point are the operating voltage and current. There is a unique point near the knee of the I-V curve, called a maximum power point (MPP), at which the module operates with the maximum efficiency and produces the maximum output power. The point of maximum power is the desired operating point for a PV array to obtain maximum efficiency. A PV array is usually oversized to compensate for a low power yield during winter months. This mismatching between a PV module and a load requires further over-sizing of the PV array and thus increases the overall system cost [3-5]. To mitigate this problem, different methods have been developed [6-12]. A maximum power point tracker (MPPT) can be used to maintain the PV module’s operating point at the MPP. The system in a direct coupled method cannot always operate at maximum power point (MPP) of the solar array when the load, irradiance or temperature changes. A PV-load coupling system should be able to maximize the energy output of the PV generator, which should operate always at its maximum power point (MPP) in order to achieve maximum global efficiency. Some authors have supported the direct coupling between the PV generator and the load [2-3]. Several methods and algorithms to track the maximum power point have been developed [2-12].

    We focused our effort on improving the matching between PV sources and loads through the development of new performing methods. In this paper, a rapid approach for peak power tracking is proposed. The system PV generator - load is optimized, when the working point in direct coupling is quite near the MPP of the PV generator, so that the global efficiency of the system is acceptable. Another method is proposed. It is based on reconfiguring on-line the SCA by changing the connections between different modules in order to minimize the losses due to load and operation conditions. Two strategies for improvements are chosen for testing in this study, whatever the loads and operating conditions.

    The experimental system used a microcontroller. It is robust when undergoing environment changes and load variations. The performance of the methods is verified through simulations and experiments.

    Keywords: photovoltaic; MPPT; configuration; optimum power; switching

  • Dániel Mihályi ,
    Valerie Novitzká :
    A Coalgebra as an Intrusion Detection System71-79en [233.62 kB - PDF]EPA-02461-00023-0050

    Abstract: In this paper we construct a coalgebra for an intrusion detection system to describe the behaviour of a packet stream together with selected actions in the case of intrusions. We start with an extension of the notion of the many-typed signature to the generalised signature and we construct the category of packets as a basic structure of our approach. A defined endofunctor captures the expected behaviour of the packet stream. The constructed coalgebra enables the description of the behaviour of the packet stream together with the reaction to intrusions.

    Keywords: Coalgebra; Category theory; Intrusion detection system

  • Asim Egemen Yilmaz :

    Abstract: Recently, swarm intelligence and its applications have gained much popularity among researchers of various disciplines. The main aim of this study is to investigate the situation for the electromagnetic theory and microwave technology practitioners and try to point to an interesting analogy.

    Keywords: Swarm intelligence; ant colony optimization; particle swarm optimization; electromagnetic theory; microwave theory

  • Petár Čisar ,
    Sanja Maravić Čisar :

    Abstract: The available literature is not completely certain what type(s) of probability distribution best models network traffic. Thus, for example, the uniform, Poisson, lognormal, Pareto and Rayleigh distributions were used in different applications. Statistical analysis presented in this paper aims to show how skewness and kurtosis of network traffic samples in a certain time interval may be criterions for selection of appropriate distribution type. The creation of histogram and probability distribution of network traffic samples is also discussed and demonstrated on a real case.

    Keywords: skewness; kurtosis; network traffic; histogram; probability distribution

  • Bülent Oral ,
    Ferdun Dönmez :

    Abstract: An earthquake is an instantly occurring and unpredictable natural event. The potential and effects of earthquakes and other natural disasters on power systems are system faults. The faults are not only limited to the physical damage of power systems, but power quality disturbances may also take place. The Marmara Earthquake, which occurred in Turkey on Aug 17, 1999, caused death and catastrophe. After the earthquake, the Turkish Power System collapsed. This is the largest power blackout in Turkey in last twenty years. In this study, the impact of the Marmara earthquake on the Turkish power system are described and the Marmara Earthquake Blackout is examined in detail as regards the qualitative behavior of the power system.

    Keywords: Power System Blackouts; Power System Disturbances; Overvoltages in Power Systems

  • Mostefa Belkhatir ,
    Ahmed Arab ,
    Noureddine Della ,
    Hanifi Missoun ,
    Tom Schanz :

    Abstract: Silty sands are the most common type of soil that could be involved in both static and earthquake-induced liquefaction. Most of the recent earthquakes have revealed the liquefaction of silty sands. Therefore, the selection of the appropriate undrained residual shear strength of liquefied soils to be used in the assessment of the post-liquefaction stability of earth dams and other earth structures is becoming a major challenge. A series of undrained monotonic and cyclic triaxial tests were carried out on reconstituted saturated samples of sand with variation in the fines content ranging from 0 to 50% for the monotonic tests and from 0 to 40% for the cyclic ones, in order to study the influence of fines fraction and other parameters on the undrained residual shear strength and liquefaction potential of loose, medium dense and dense silty sand samples (Dr = 12%, 50%, 60% and 90%). The results of the monotonic tests show that the stress-strain response and shear strength behaviour is controlled by the percentage of fines fraction and the samples become contractive for the studied relative densities (Dr = 12% and 90%). The undrained residual shear strength decreases as the global void ratio decreases and the fines content increases up to 30% fines content. Beyond that, it decreases with increasing the global void ratio and the fines content. Moreover, the undrained residual strength decreases linearly as the fines content and the inter-granular void ratio increase. Cyclic test results show that the increase of the fines fraction accelerates the liquefaction phenomenon for the studied amplitude and the liquefaction resistance decreases with the increase of the global void ratio and the loading amplitude. We notice that the reduction in the liquefaction resistance of Chlef sand-silt mixtures becomes very marked for the smaller cyclic stress ratios CSR = 0.15 and 0.25.

    Keywords: silty sand; residual strength; fines content; undrained tests; liquefaction

  • Deepti Mishra ,
    Alok Mishra :

    Abstract: Radio frequency identification (RFID) has been identified as one of the ten greatest contributory technologies of the 21st Century. This technology has found a rapidly growing market, and an increasing variety of enterprises are employing RFID to improve the efficiency of their operations and to gain competitive advantage. In the aviation industry, major airports/airlines have been looking for the opportunity to adopt RFID in the area of baggage handling for a long time. Many pilot tests have been done at numerous U.S., European, and Hong Kong airports. RFID tags were found to be far more accurate than bar codes, and their performance was also measured to be well above that of bar codes. This paper presents the state of RFID adoption planning, architecture and implementation at a major airline, with a special focus on improved services due to improved baggage handling, on increased airport/airline security and on frequent flier program services. This is accomplished by integrating RFID technology together with networking and database technologies.

    Keywords: Radio Frequency Identification; RFID; baggage handling/tracking; airline industry; customer-service

  • Lívia Szedmina :
    Could You Check This, Please? Experiences in a Bilingual Environment155-162en [121.58 kB - PDF]EPA-02461-00023-0110

    Abstract: This paper describes some experiences of a proof reader and translator working in a very specific bilingual linguistic environment. Bilingualism has a peculiar effect on the use of technical English, as seen with language users at Subotica Tech. Vajdaság is a unique location in terms of language composition. While for many, Hungarian is the first language, there is some language transfer from Serbian, especially concerning the use of English technical terminology in native language texts. A number of examples are offered to show different patterns that may be explained by the overwhelming influence of the first language.

    Keywords: technical English; bilingualism; Vajdaság; proofreading; correction