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Acta polytechnica HungaricaVolume 12, Issue No. 2. (2015.)


  • Liberios Vokorokos ,
    Anton Baláž ,
    Norbert Ádám :
    Secure Web Server System Resources Utilization5-19en [577.25 kB - PDF]EPA-02461-00056-0010

    Abstract: One of the main goals of an operating system is the efficient usage of system resources and their management. Modern systems offer complex mechanisms for the management of these resources. Their system-wide use may be separated into multiple layers – from the lowest (the operating system kernel) to the highest (various virtualization techniques). Somewhere in the middle are the applications consuming these system resources. An example of such an application is the Apache web server. It implements some of the resource management mechanisms at application level. However, the system contains elements, the management of which is not possible at application level or its implementation has a significant overhead and may negatively affect the performance and secure usage of the server. The aim of the study is to create a more efficient resource management mechanism at the level of the Apache web server. The proposed architecture allows the treatment of possible security threats, such as DoS attacks, makes the use of system resources more efficient, thus – indirectly – it also addresses the environmental impacts of data centers. The reason for selecting the Apache web server as the referential implementation of the resource usage improvement are its market share and its open source nature, which renders making amendments to the server simple.

    Keywords: security; system resources; management; Apache; cgroups; CGI

  • József Bera ,
    László Pokorádi :
    Monte-Carlo Simulation of Helicopter Noise21-32en [680.76 kB - PDF]EPA-02461-00056-0020

    Abstract: Currently, applied flying noise investigation methods are done from energetic points of view, independent of other noise sources. These methods do not adequately accept the ground state of the environment and its changes. This paper proposes a new Monte-Carlo Simulation-based investigation method, to analyze changes of environment states when the number and characteristics of flying operations and noise levels fluctuate stochastically.

    Keywords: environment protection; noise; helicopter; Monte-Carlo Simulation

  • Aleksandar Rikalovic ,
    Ilija Cosic :
    A Fuzzy Expert System for Industrial Location Factor Analysis33-51en [731.11 kB - PDF]EPA-02461-00056-0030

    Abstract: The identification of a new industrial location requires consideration of a complex set of factors in the decision making process. These factors are generally described with a number of different indicators, expressed in quantitative and/or qualitative ways, thus resulting in a nonlinear optimization problem. Besides, some of the input data are imprecise, incomplete or not totally reliable. Therefore, it is necessary to interpret, standardize and fuse data in specific factors suitable for comparison. To take into account all of these aspects above and allow for identification of an optimal solution by reasoning on available information, this paper proposes the use of an expert system for industrial location factor analysis. Management of uncertainty is an important issue in the design of expert systems, since data maybe indefinite, inaccurate and ambiguous. Fuzzy logic provides an approach to data fusion and reasoning for uncertain data by using the human expert knowledge. The proposed expert system is based on Fuzzy Inference Systems (FIS), which solve the nonlinear optimization problem by using the available knowledge. Results show that the proposed approach obtains accurate results in industrial location factor analysis, similar to those devised by experts of the field.

    Keywords: expert system; fuzzy logic; fuzzy inference system (FIS); decision support system (DSS); industrial location; factor analysis

  • Vilmos Csala ,
    Tibor Szalay ,
    Balázs Farkas ,
    Sándor Markos :

    Abstract: Micro hole machining refers to the process of drilling holes with a diameter of less than 1 millimeter. This paper compares three commonly used technologies: mechanical drilling, laser machining and electrical discharge machining. All of these techniques were analyzed based on an experimental measurement of dimensional accuracy, circularity, burr formation and the image of the internal surface. The most significant criterion of analysis is surface quality, as the main purpose of the examination was to find the most precise process. In addition, a detailed cost analysis, pertaining to machining time, the tools and machines was performed. The experiment utilized a high precision lathe, an Nd:YAG laser and an electrical discharge machine. The final results revealed the micro drilling process as the one with the most promising parameters. Therefore, it was suggested for industrial applications. However, once the economic factors were not taken into account, the EDM also became a more attractive option, based on good technical and quality parameters.

    Keywords: micro manufacturing; drilling; EDM; laser machining

  • Abstract: In this paper analysis of the impact of front and back light on compression of static image necessary for realization of the chrome-key effect in virtual TV studio is presented. For image compression SPIHT method is used. The analysis is performed for the fixed value of front light and variable values of the back light. Compression is applied to different values of the bit per pixel (bpp). The quality of compressed images is rated based on the values MSE, SNR and PSNR. The obtained values are displayed in tables and graphics. Based on these graphics a comparison between compressed images with different levels of front and back lights was made and it is given a level of image brightness produces the best results. It was found how the quality of compression varies with the changing brightness of images at different bit per pixel.

    Keywords: chroma key; front light; back light; SPIHT method; bit per pixel (bpp); mean square error (MSE); signal to noise ratio (SNR); peak signal to noise ratio (PSNR)

  • Ákos Oroszlány ,
    Péter Nagy ,
    József Gábor Kovács :

    Abstract: Compressive properties of three commercially available rigid polyvinyl chloride (PVC) foams intended for use as possible model material for human cancellous bone were investigated. Quasi-static compression tests were performed on PVC foam blocks of different densities (0.10, 0.13 and 0.20 g/cm3) with a crosshead speed of 0.15 mm/sec to determine the compressive Young’s modulus, the yield strength and the energy absorbed until yield. The results were compared with data obtained on human cancellous bone and polyurethane (PUR) foams. Results showed that according to their Young’s modulus and yield strength the investigated 0.1 and 0.13 g/cm3 PVC foams are suitable as mechanical model material for Osteoporotic cancellous bone, while 0.20 g/cm3 PVC foam is suitable as model material for normal bone. According to the energy absorbed until yield the 0.10 g/cm3 PVC foams are suitable as mechanical model material for Osteoporotic(OP) cancellous bone. For the modeling of normal bone both the 0.13 and 0.20 g/cm3 PVC foams are suitable. Based on these results, it can be concluded that the examined PVC foams may prove suitable as a model material for OP and normal cancellous bone.

    Keywords: PVC foam; compressive properties; synthetic bone; human cancellous bone; Osteoporotic bone; cross-linking

  • Abstract: At the outset, the design of an organization-based multiagent system is modeled according to the framework of Organization Model for Adaptive Complex Systems (OMACS). Subsequently, this design model is transformed into a process-network model. Eventually, the resultant process-network model in conjunction with the P-graph-based methodology give rise to: (i) the maximal structure of the process network, comprising all the feasible combinations of structures, i.e., OMACS-based design configurations, capable of yielding the specified products from the specified raw material; (ii) every feasible structure for the process of interest; and (iii) the optimal structure of the network, i.e., the optimal OMACS-based design configuration. Finally, in light of the tenet of a modeling-transformation-evaluation paradigm, an appraisal is made of the feasibility as well as the flexibility and cost of the optimal OMACS-based design configuration obtained.

    Keywords: Organization-based Multiagent System Design; Model Transformation; Process Synthesis; P-graph Framework; OMACS Framework

  • Károly Farkas :
    Placement Optimization of Reference Sensors for Indoor Tracking123-139en [648.51 kB - PDF]EPA-02461-00056-0080

    Abstract: Location-based applications and services are becoming widespread with the proliferation of smart mobile devices. They require position tracking which is still a challenge today in the indoor environment. Different wireless technologies and localization techniques can be used to obtain the position estimation. One possibility is deploying cheap ZigBee sensors as reference points and using triangulation to compute the position of the visiting node. This technique requires the reception of a wireless signal of at least three reference sensors with well-known positions everywhere within the covered area. In this paper, we propose OptiRef, our simulated annealing based method to find, in a given area, the optimal number and placement of the reference sensors to be used for indoor positioning. Our method has O(n) complexity and shows linear run-time behavior. We investigate the performance of OptiRef via simulations focusing on ZigBee technology, although our method is generic and can be used with any kind of wireless technologies. The resulted reference point setup(s) can be considered as a good starting point for real environment design.

    Keywords: Indoor localization; ZigBee; Triangulation; Simulated annealing; MATLAB

  • Michal Dorda ,
    Dusan Teichmann :
    On Two Modifications of Er/Es/1/m Queuing System Subject to Disasters141-158en [697.67 kB - PDF]EPA-02461-00056-0090

    Abstract: The paper deals with modelling a finite single-server queuing system with the server subject to disasters. Inter-arrival times and service times are assumed to follow the Erlang distribution defined by the shape parameter r or s and the scale parameter rλ or sμ respectively. We consider two modifications of the model − server failures are supposed to be operate-independent or operate-dependent. Server failures which have the character of so-called disasters cause interruption of customer service, emptying the system and balking incoming customers when the server is down. We assume that random variables relevant to server failures and repairs are exponentially distributed. The constructed mathematical model is solved using Matlab to obtain steady-state probabilities which we need to compute the performance measures. At the conclusion of the paper some results of executed experiments are shown.

    Keywords: Er/Es/1/m; queuing; disasters; method of stages; balking; Matlab

  • Edit Tóth-Laufer ,
    Márta Takács ,
    Imre J. Rudas :

    Abstract: Nowadays the patient monitoring systems are more and more widely used due to the advances in the technical background. These systems can improve the quality of life and by using them, several complications can be avoided in emergency situations. Nevertheless, the proper evaluation of the measured factors is a highly problematic task. The medicine uses a number of parameters, which are difficult to quantify, the boundaries of the examined risk factors cannot be given in a general form, the realistic result is only available from personalized thresholds. For these reasons, user-specific evaluation is required as much as possible, which uses individual characteristics, also the living conditions, habits and the medical recommendations taken into account during the risk calculation. In addition, the complex interactions between the input factors, which are often opaque, can be better handled in a patient-specific way based on the medical history of the patient or previous measurements. We developed a risk assessment framework to meet the above mentioned requirements. This system is flexible with a high degree of adaptive capacity. For the sake of ease of extensibility, and in order to achieve transparency, a generalized, modular system structure is implemented, which is joined with a database to specify the parameters of the configurable subsystems.

    Keywords: risk assessment; fuzzy logic; relational database

  • Hung Linh Le ,
    Thuong Cat Pham ,
    Minh Tuan Pham :

    Abstract: This paper proposes a speed and flux control method of three-phase AC motors using an artificial neural network (ANN) to compensate for uncertain parameters in the motor’s dynamic model such as rotor resistance, moment of inertia, friction coefficients, and load changes during system operation. Global asymptotic stability of the overall system is proved by Lyapunov’s theory. Matlab simulation results are given to demonstrate the validity of the proposed control method.

    Keywords: three-phase AC motor; artificial neural network; speed and flux control; uncertain dynamics

  • Abstract: Public procurement is one of the most significant activities within the sphere of public administration, whose primary purpose is to achieve maximized cost effectiveness and efficiency for the expenditure of public money. This principle is also known as the principle of "value for money" - meaning to achieve the best possible ratio between the amount paid and the value received. The selection of a suitable bidder within the public procurement procedure assists in our achievement of the aforementioned purpose. In this paper an integrated approach based on the fuzzy Technique for Order Preference by Similarity to Ideal Solution (fuzzy TOPSIS) method and the fuzzy Extent Analysis Method is proposed for utilization within the evaluation and bidder selection processes associated with the process of public procurement. The proposed method objectively allows for the evaluation of bidders without the setting of weights by public procurement committees and in so doing helps to avoid subjectivity in respect to the setting of weights for criteria and or sub-criteria. In order to demonstrate the effectiveness and feasibility of the proposed method and its application in public procurement, a real-life case scenario from the Government of Serbia will be presented in this paper.

    Keywords: public procurement; bidder selection; fuzzy extent analysis method; fuzzy TOPSIS

  • Abdülkadir Çakir ,
    Seyit Akpancar :

    Abstract: Resistivity-induced polarization is a method that is used to identify underground layers by resistivity. In this study, a resistivity induced polarization receiver/transmitter device was designed using the CCS C programming language and tested. The most outstanding feature of the implemented system is that the connection between the receiver and the transmitter were enabled by wireless bluetooth. The data obtained by this system were sent to a PC via wireless bluetooth connection and the data were analyzed after being processed by a program in C# language. The system has 55 volt, 110 volt, 220 volt output amplitudes, as direct or alternating current. The frequency of the current used in the system is 0.1 Hz, 0.3 Hz, 1 Hz, and 3 Hz, and the signals follow the square wave amplitude form. The system was designed to be user-friendly by LCD monitors, which were used to detect the amplitude and frequency of the current sent to the underground.

    Keywords: Resistivity IP; geological structge; resistivity; bluetooth

  • Dragana Jankov Masirevic :
    Sturm–Liouville problem and I–Bessel sampling231-246en [197.10 kB - PDF]EPA-02461-00056-0140

    Abstract: The main aim of this article is to establish summation formulae in form of the sampling expansion series building the kernel function by the samples of the modified Bessel function of the first kind In , and to obtain a sharp truncation error upper bound occurring in the derived sampling series approximation. Summation formulae for functions Iv+1=Iv ;1=Iv ; I2v and the generalized hypergeometric function 2F3 are derived as a by–product of these results. The main derivation tools are the Sturm–Liouville boundary value problem and various properties of Bessel and modified Bessel functions.

    Keywords: Bessel function of the first kind Jn , modified Bessel function of the first kind In , sampling series expansions, Sturm–Liouville boundary value problems, generalized hypergeometric function 2F3, Fox-Wright generalized hypergeometric function pYq , sampling series truncation error upper bound