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Acta polytechnica HungaricaVolume 8, Issue No. 4 (2011.)


  • Ákos Nemcsics :

    Abstract: In this work, we discuss the evolution of self-assembled III-V-based nanostructures. These nanostructures were prepared from Ga droplets during a crystallization process using a droplet epitaxy technique. Different nanostructures such as quantum dots, quantum rings, double quantum rings, and nano holes were formed from Ga droplets on a (001)-oriented AlGaAs surface, but at different substrate temperatures and various arsenic background pressures. We give a qualitative description of the elemental processes for the formation of all of these nanostructures. Our description is based on the size dependence of the key material properties (solubility, tension, etc.).

    Keywords: GaAs; droplet epitaxy; quantum dot; quantum ring; nano hole

  • Tobiáš Lazar ,
    Peter Pástor :
    Factors Limiting Controlling of an Inverted Pendulum23-34en [478.45 kB - PDF]EPA-02461-00030-0020

    Abstract: The aim of this paper is to show the limitation during an inverted pendulum control process. Assume the control signal and its derivate are limited. The goal is to find the maximum permissible value of the θ angle and state if this value can be determined only by symbolical calculation by using Maple software. This maximum value must guarantee the stability of whole system and the quality of the transient process. The nonlinear mathematical model of the inverted pendulum implemented in Simulink is utilized for result verification. A detailed description of these limitations is important for the application of advanced control methods based on expert knowledge to aircraft equipped with a thrust vectoring nozzles system.

    Keywords: inverted pendulum; transfer function; nonlinear analyses; maple

  • Mojtaba Ahmadieh Khanesar ,
    Mohammad Teshnehlab ,
    Okyay Kaynak :

    Abstract: This paper proposes a novel indirect model reference fuzzy control approach for nonlinear systems, expressed in the form of a Takagi Sugeno (TS) fuzzy model based on an optimal observer. In contrast to what is seen in the literature on adaptive observer-based TS fuzzy control systems, the proposed method is capable of tracking a reference signal rather than just regulation. Additionally the proposed algorithm benefits from an adaptation algorithm which estimates the parameters of observer optimally. The stability analysis of the adaptation law and the controller is done using an appropriate Lyapunov function. The proposed method is then simulated on the control of Chua's circuit and it is shown that it is capable of controlling this chaotic system with high performance.

    Keywords: fuzzy control; model reference fuzzy control; observer design

  • Alok Mishra ,
    Deepti Mishra :
    ERP Project Implementation: Evidence from the Oil and Gas Sector55-74en [96.33 kB - PDF]EPA-02461-00030-0040

    Abstract: Enterprise Resource Planning (ERP) systems provide integration and optimization of various business processes, which can lead to improved planning and decision quality, and a smoother coordination between business units, resulting in higher efficiency and a quicker response time to customer demands and inquiries. This paper reports the challenges and opportunities and the outcome of an ERP implementation process in the Oil & Gas exploration sector. This study will facilitate the understanding of the transition, constraints, and implementation process of ERP in this sector and will also provide guidelines from lessons learned in this regard.

    Keywords: case study; ERP; implementation; oil and gas exploration; SAP

  • Jozef Ban ,
    Matej Féder ,
    Miloš Oravec ,
    Jarmila Pavlovičová :

    Abstract: This paper deals with human face recognition based on the use of neural networks, such as MLP (multi-layer perceptron), RBF (radial basis function) network, and SVM (support vector machine) methods. The methods are tested on the MIT (Massachusetts Institute of Technology) face database. We use non-conventional methods of feature extraction for the MIT face images in order to improve the recognition results. These methods use so called HLO and INDEX images. HLO images are generated by feature extraction of the MLP neural network in auto-association mode, and INDEX images are formed by a self-organized map used for image vector quantization. We propose novel methods based on HLO and INDEX images with SVM classifier. We also analyze the impact of adding noise to the learning process.

    Keywords: human face recognition; feature extraction; multilayer perceptron; RBF networks; support vector machines

  • Hanifi Missoum ,
    Nadia Laredj ,
    Karim Bendani ,
    Mustapha Maliki :

    Abstract: Although many numerical models have been proposed for unsaturated porous media, unrealistic assumptions have been made, such as the non-deformable nature of media, constant material properties, the neglecting of convection heat flow transfer, and static air phase. Most of these conditions are not justifiable for porous media with low hydraulic permeability and high swelling activity. In the present article, a fully coupled thermo-hydro-mechanical model is proposed that takes into account nonlinear behavior, including both the effects of temperature on dynamic viscosity of liquid water and air phase, and the influence of temperature gradient on liquid and air flows. Fully coupled, nonlinear partial differential equations are established and then solved by using a Galerkin weighted residual approach in space domain and an implicit integrating scheme in time domain. The obtained model is finally validated by means of some case tests for the prediction of the thermo-hydro-mechanical behaviour of unsaturated swelling soils.

    Keywords: multiphase flow; water transfer; unsaturated porous media; finite element; conservation; simulation

  • Aleksander Rodić ,
    Gyula Mester :

    Abstract: This paper presents the modeling and simulation of an autonomous quad-rotor microcopter in a virtual outdoor scenario. The main contribution of this paper focuses on the development of a flight simulator to provide an advanced R/D tool suitable for control design and model evaluation of a quad-rotor systems to be used for control algorithm development and verification, before working with a real experimental system. The main aspects of modeling of rotorcraft kinematics and rigid body dynamics, spatial system localization and navigation in a virtual outdoor scenario are considered in the paper. Some high-level control aspects are considered, as well. Finally, several basic maneuvers (examples) are investigated and simulated in the paper to verify the simulation software capabilities and engineering capabilities.

    Keywords: modeling; simulation; autonomous quad-rotor microcopter; Xaircraft X 650; rotorcraft; virtual outdoor scenario; quad-rotor dynamics; spatial navigation; GPS coordinates; GPS navigation, simulation example

  • L. V. Zaitseva ,
    Boris I. Koval'chuk :

    Abstract: The experimental investigation of the influence of time-dependent, thermal and mechanical factors on the kinetics of martensite transformation has been performed in the austenitic chromium-nickel steels. Additionally, the effects of martensite transformation on the mechanical properties are studied and the nature of strengthening is analyzed during low-temperature deformation in the linear and two-dimensional stress states. The equation is evaluated which describes the kinetics of martensitic transformation in the stress strain states. A variant of the deformation theory of plasticity for metastable materials under proportional loading is considered.

    Keywords: metastable austenitic steels; plastic deformation; tensile; torsion; compression; biaxial tension; low temperatures; phase (γ →α ) -transformations; plasticity theory

  • Redouane Belbachir ,
    Zoulikha M. Mekkakia ,
    Ali Kies :

    Abstract: Given the development of multimedia applications with intensive consumption of network resources by the traffic generated, and the emergent use of mobile ad hoc networks, the guarantee of the quality of service (QoS) has become essential. The available bandwidth is the crucial resource, particularly in mobile ad hoc networks, since it is very limited; this is why it must be optimally managed and accurately estimated. Several projects have been conducted to provide new techniques for measuring the available bandwidth in mobile ad hoc networks. But mobility, which is the basic criterion of this type of network, is neglected and isn't processed by any measurement technique proposed. In this paper we disclose the importance of the taking into account this criterion and we will unveil a novel measurement technique ABE_MM (Available Bandwidth Estimation with Mobility Management) which is an extension of other robust existing measurement methods and which treats mobility in a specific manner.

    Keywords: ad hoc networks; mobility; estimation; bandwidth; ABE_MM

  • Dorina Fechete :
    Some Categorial Aspects of the Dorroh Extensions149-160en [158.90 kB - PDF]EPA-02461-00030-0100

    Abstract: Given two associative rings R and D, we say that D is a Dorroh extension of the ring R, if R is a subring of D and D = R ⊕ M for some ideal M ⊆ D. In this paper, we present some categorial aspects of the Dorroh extensions and we describe the group of units of this ring.

    Keywords: bimodule; category; functor; adjoint functors; exact sequence of groups; (group) semidirect product

  • TianZhi Shin :
    Definite Integral and the Gibbs Paradox161-170en [143.15 kB - PDF]EPA-02461-00030-0110

    Abstract: The Gibbs paradox does not exist at all. Entropy is an additive quantity but not an extensive quantity. Neither entropy nor the increment of entropy is an extensive quantity. When T denotes thermodynamic temperature, lnT does not make sense. The correctness of dimension is a necessary condition for proper formulas. The definite integral is preferable to the indefinite integral; it should be used in science instead of the latter. The Gibbs correction factor is not only cumbersome but also erroneous; it causes some contradictions in statistical mechanics. Entropy is not a quantity that can be measured, but the increment of entropy can be measured. So what the experiment can check is not entropy but the increment of entropy.

    Keywords: Gibbs paradox; entropy; extensive; additive; definite integral

  • Young-gang Wang ,
    Shen-sen Huang ,
    Wen-sen Xiang ,
    Yu-long Pei :

    Abstract: Many studies focused on the development of crash analysis approaches have resulted in aggregate practices and experiences to quantify the safety effects of human, geometric, traffic and environmental factors on the expected number of deaths, injuries, and/or property damage crashes at specific locations. Traffic crashes on roads are a major cause of road crashes in the metropolitan area of Xi’an. In an attempt to identify causes and consequences, reported traffic crashes for six years in Xi’an were analyzed using a sample of 2038 reports. The main types of information from such reports were extracted, coded, and statistically analyzed. Important results were obtained from frequency analyses as well as multiple contributory factors related to traffic crashes, including crash severity, time and location of occurrence, geometry of the road, AADT and v/c. This paper presents the results of such analyses and provides some recommendations to improve traffic safety and further studies to analyze potential crash locations.

    Keywords: traffic accidents; crash features; contributory factor; crash type; v/c