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Articles 3001 - 3030 of 3096
Full-Text Articles in Physical Sciences and Mathematics
A Robustness Analysis Of Game-Theoretic Cdma Power Control, Xingzhe Fan, Murat Arcak, John T. Wen
A Robustness Analysis Of Game-Theoretic Cdma Power Control, Xingzhe Fan, Murat Arcak, John T. Wen
Turkish Journal of Electrical Engineering and Computer Sciences
This paper studies robustness of a gradient-type CDMA uplink power control algorithm with respect to disturbances and time-delays. This problem is of practical importance because unmodeled secondary interference effects from neighboring cells play the role of disturbances, and propagation delays are ubiquitous in wireless data networks. We first show L_p-stability, for p \in [1,\infity], with respect to additive disturbances. We pursue L_{\infity}-stability within the input-to-state stability (ISS) framework of Sontag [7], which makes explicit the vanishing effect of the initial conditions. Next, using the ISS property and a loop transformation, we prove that global asymptotic stability is preserved for sufficiently …
Parametrically Tunable Audio Shelving And Equalizing Ladder Wave Digital Filters, S. A. Samad
Parametrically Tunable Audio Shelving And Equalizing Ladder Wave Digital Filters, S. A. Samad
Turkish Journal of Electrical Engineering and Computer Sciences
Parametrically tunable audio equalizers are conventionally realized using allpass digital filter networks. They consist of first-order shelving filters and second-order equalizing filters. In this paper, ladder wave digital filters (WDFs) with parametrically tunable coefficients are proposed as shelving and equalizing filters. Similar to the allpass realization, the transfer function power complementary property of WDFs is used to obtain efficient shelving and equalizing filters. However, unlike the allpass structures, the transfer function and the tunable parameters of the ladder WDF are derived from the analog filter equivalent of the digital shelving and equalizing filters. For the shelving WDF, the cut-off frequency …
Improving The Security And Flexibility Of One-Time Passwords By Signature Chains, Kemal Biçakci, Nazi̇fe Baykal
Improving The Security And Flexibility Of One-Time Passwords By Signature Chains, Kemal Biçakci, Nazi̇fe Baykal
Turkish Journal of Electrical Engineering and Computer Sciences
While the classical attack of ``monitor the network and intercept the password'' can be avoided by advanced protocols like SSH, one-time passwords are still considered a viable alternative or a supplement for software authentication since they are the only ones that safeguard against attacks on insecure client machines. In this paper by using public-key techniques we present a method called signature chain alternative to Lamport's hash chain to improve security and flexibility of one-time passwords. Our proposition improves the security because first, like other public-key authentication protocols, the server and the user do not share a secret, thereby eliminating attacks …
New Approaches For On-Line Tuning Of The Linear Sliding Surface Slope In Sliding Mode Controllers, Sezai̇ Tokat, İbrahi̇m Eksi̇n, Müjde Güzelkaya
New Approaches For On-Line Tuning Of The Linear Sliding Surface Slope In Sliding Mode Controllers, Sezai̇ Tokat, İbrahi̇m Eksi̇n, Müjde Güzelkaya
Turkish Journal of Electrical Engineering and Computer Sciences
The main objective of this study is to propose new approaches for on-line tuning of the linear sliding surface slope in sliding mode controllers. The new approaches are developed for a class of second order systems on new coordinate axes, one of which is the classical sliding surface and the other one is naturally chosen to be orthogonal to it. The control input of the sliding mode control law is then modified accordingly by applying the Lyapunov stability condition. The adjustment of the linear sliding surface slope defined in the new coordinate axes is achieved by tuning a new parameter …
Resonant Demagnetization Pwm Forward Converter, B. Bi̇lgi̇n, Işik Çadirci, R. Ergül, M. Ermi̇ş
Resonant Demagnetization Pwm Forward Converter, B. Bi̇lgi̇n, Işik Çadirci, R. Ergül, M. Ermi̇ş
Turkish Journal of Electrical Engineering and Computer Sciences
In this paper, a new approach to demagnetization process of a PWM forward converter (FC) is proposed. According to this approach, the demagnetization winding and diode of a conventional FC are removed, and an external capacitor is added in parallel with the secondary diode. This replacement changes the linear demagnetization process of a conventional FC into a resonant demagnetization process. The theoretical performance results of the proposed resonant demagnetization forward converter (RDFC) are compared with those of a conventional FC. A side by side comparison made between the two types of demagnetization strategies has shown that RDFC has some advantages …
Initiatory Electrons In Compressed Gases In Positive Polarity, Mohammed Messaad, Mustapha Tioursi
Initiatory Electrons In Compressed Gases In Positive Polarity, Mohammed Messaad, Mustapha Tioursi
Turkish Journal of Electrical Engineering and Computer Sciences
This paper deals with the nature of seed electron sources in compressed N_2 for positive polarity. We present an experimental procedure that provides evidence of the fact that collisional detachment from negative ions plays the most important role in the supply of seed electrons. Conditioning phenomena in compressed SF_6, N_2 and air have been simulated under positive lightning impulses for point-plane geometry.
An Analytical Model For Calculating Bounds On Call Blocking Probabilities In Leo Satellite Networks, A. Hali̇m Zai̇m
An Analytical Model For Calculating Bounds On Call Blocking Probabilities In Leo Satellite Networks, A. Hali̇m Zai̇m
Turkish Journal of Electrical Engineering and Computer Sciences
We present an analytical model for calculating upper and lower bounds for call-blocking probabilities in a LEO satellite network that carries voice calls. The method is especially useful for large systems where calculation of call-blocking probabilities are too expensive. Our method calculates upper and lower bounds very easily and produces fairly accurate results.
Network Traffic Properties Of Bimodal Multicast Protocol, Öznur Özkasap, Mi̇ne Çağlar
Network Traffic Properties Of Bimodal Multicast Protocol, Öznur Özkasap, Mi̇ne Çağlar
Turkish Journal of Electrical Engineering and Computer Sciences
The popularity of large-scale distributed applications, such as videoconferencing, multimedia dissemination, electronic stock exchange and distributed cooperative work, has grown with the availability of high-speed networks and the expansion of the Internet. The key property of this type of applications is the need to distribute data among multiple participants together with an application-specific quality of service needs. This fact makes scalable multicast protocols an essential underlying communication structure. Although there exist several studies investigating the traffic characteristics of unicast communication, multicast traffic has not been examined extensively in previous studies. It is well known that the aggregate traffic properties of …
The \Mathcal{H}_\Infty Model Matching Problem With One Degree Of Freedom Static State Feedback, Murat Akin, Ati̇lla Bi̇r
The \Mathcal{H}_\Infty Model Matching Problem With One Degree Of Freedom Static State Feedback, Murat Akin, Ati̇lla Bi̇r
Turkish Journal of Electrical Engineering and Computer Sciences
The aim of this paper is to develop a new approach for a solution of the continuous-time model matching problem by a static state feedback in the sense of \mathcal{H}_\infty optimality criterion by using Linear Matrix Inequalities (LMIs). The main contribution could briefly be described as to reformulate the model matching problem in LMI formulation, to present the solvability conditions and to give a design procedure for the one degree of freedom static state feedback control law. Finally, the results are applied to an example system.
Zero-Crossing Based Demodulation Of Minimum Shift Keying, Mi̇ne Kalkan, Feza Keresteci̇oğlu
Zero-Crossing Based Demodulation Of Minimum Shift Keying, Mi̇ne Kalkan, Feza Keresteci̇oğlu
Turkish Journal of Electrical Engineering and Computer Sciences
Minimum shift keying (MSK) modulation has features such as constant envelope, compact spectrum and good error performance, which are all desirable in many digital applications including mobile radio. Numerous receiver structures to demodulate MSK have been suggested, such as correlation receivers, differential detectors and frequency discriminators. MSK is a form of biphase keying and can be detected by a zero-crossing based phase demodulator which gives near optimum performance. In this paper, the bit error performance of a zero-crossing based coherent MSK demodulator is theoretically investigated and a closed-form expression for the bit error rate is derived. The results indicate that …
Music, Cbf And Differential Algebraic Constant Modulus Algorithms For Direction Of Arrival Estimation In Passive Coherent Locators, Ahmet Özçeti̇n
Music, Cbf And Differential Algebraic Constant Modulus Algorithms For Direction Of Arrival Estimation In Passive Coherent Locators, Ahmet Özçeti̇n
Turkish Journal of Electrical Engineering and Computer Sciences
In passive coherent locators (PCL) systems, noise and the precision of direction of arrival (DOA) estimation are key issues. This paper addresses the implementation of high-resolution DOA estimation methods, in particular the multiple signal classification (MUSIC) algorithm, the conventional beam forming (CBF) algorithm, and the algebraic constant modulus algorithm (ACMA). The goal is to compare the ACMA to the MUSIC and CBF algorithms for application to PCL. The results and analysis presented here support the use of constant modulus information, where available, as an important addition to DOA estimation. The ACMA offers many simple solutions to noise and separation related …
A Full Adaptive Observer For Dc Servo Motors, Ata Sevi̇nç
A Full Adaptive Observer For Dc Servo Motors, Ata Sevi̇nç
Turkish Journal of Electrical Engineering and Computer Sciences
An adaptive observer estimating all parameters and load torque is proposed for DC servo motors. The observer uses no direct feedback but the adaptation schemes use current and speed measurements. Both the observer and adaptations are simple to implement for real-time applications. Simulation results are satisfactory for the full adaptive observer. If the observer works in parallel with only load torque and armature resistance adaptations, the results are very good even if very low-quality sensors are used. In this simulation, only a single hall sensor is used as a rotational transducer, which produces a single pulse per revolution, and very …
Design Of A Tem-Cell With Increased Usable Test Area, Kresimir Malaric, Juraj Bartolic
Design Of A Tem-Cell With Increased Usable Test Area, Kresimir Malaric, Juraj Bartolic
Turkish Journal of Electrical Engineering and Computer Sciences
Transversal electromagnetic mode cells (TEM-cells) are used for electromagnetic compatibility measurements (emission and immunity), and for biomedical applications. Over the years, higher and higher frequencies are being used, which demands smaller transmission structures in order to obtain the homogeneous field distribution due to resonance. Such resonance destroys the TEM field, introducing higher order modes. The goal was to design the TEM-cell for GSM frequencies that will have a larger area with a homogeneous field used for testing, while still obtaining the characteristic impedance. Commercial TEM-cells used for frequencies of 900 MHz have only 2 cm in height available for testing, …
New Infratechnologies In The Deregulated Power Sector, Jordan Shikoski, Vladimir Katic, Risto Rechkoski
New Infratechnologies In The Deregulated Power Sector, Jordan Shikoski, Vladimir Katic, Risto Rechkoski
Turkish Journal of Electrical Engineering and Computer Sciences
This paper discusses new infratechnologies in the deregulated power sector. Most measurement and standardization techniques can be viewed as infratechnology. Infratechnologies are technical tools, including the measurement of data, test methods, and practices and technique. Standardization requirements are related to the measurement requirement. Although the system operation and market transactions concern many import aspects, they are insupportable and often complementary. This distinction between the technical and market information is important because the characteristics of information needs and the impact on economic efficiency and clean power are generally different. The present paper focuses on infratechnologies that can potentially increase the benefits …
A Digitally Controlled Drive System For Travelling-Wave Ultrasonic Motor, Güngör Bal
A Digitally Controlled Drive System For Travelling-Wave Ultrasonic Motor, Güngör Bal
Turkish Journal of Electrical Engineering and Computer Sciences
A digitally controlled drive system was implemented in this study to control the speed and direction of a travelling-wave ultrasonic motor. The drive system, based on a 2-phase voltage-fed high-frequency serial-resonant inverter, uses the mechanical resonant frequency of an ultrasonic motor. A TMS320F243 digital signal processor was used to control an ultrasonic motor drive system. The speed control of the ultrasonic motor was achieved with a driving frequency in the 41.3-43.3 kHz frequency range. The feasible evaluations of the proposed drive and control system were tested by experiments. Experimental results demonstrated that the proposed drive and control system is flexible …
A New Simulator For Hvdc/Ac Systems-Part I, Baktiar Zangeneh, Abbas Shoulaie
A New Simulator For Hvdc/Ac Systems-Part I, Baktiar Zangeneh, Abbas Shoulaie
Turkish Journal of Electrical Engineering and Computer Sciences
A simulator with optimal step time (SOST) has been designed to investigate Large HVdc/ac systems. The adequacy and robustness of the simulator will be demonstrated by showing some important applications relevant to operation, operational planning and medium-term planing. Some of the features of our SOST simulator are optimal step time algorithm, interpolation, chatter removal, MATLAB interface, unlimited size of ac system, and Farsi command that help model complex power electronic circuits, provide fast and accurate results. On account of its reduced calculation effort and deterministic execution time, optimal-step simulation is a prerequisite for real-time performance. However, when simulating electromagnetic-transients behavior, …
A New Simulator For Hvdc/Ac Systems-Part Ii, Baktiar Zangeneh, Abbas Shoulaie
A New Simulator For Hvdc/Ac Systems-Part Ii, Baktiar Zangeneh, Abbas Shoulaie
Turkish Journal of Electrical Engineering and Computer Sciences
This paper presents a performance comparison (the focus of numerical simulation) of traditional simulation (TCS,TSE) with an optimal step time simulator (SOST) for large HVdc systems.In SOST, a Detailed simulation of HVdc converter behavior has been modified to include the automatic selection of optimal integration steps, frequency-dependent effects of an ac system, ac system phase and magnitude dynamics of voltage (particularly weak ac systems), control assessment and temporary over-voltage consequences. SOST, via graphical interfaces,provides fast and accurate information of electromechanical and the electromagnetic-transients behavior of a large HVdc/HVac system.
Sar Simulations In Wireless Communication And Safety Discussions In The Society, M. O. Özyalçin, Funda Akleman, Levent Sevgi̇
Sar Simulations In Wireless Communication And Safety Discussions In The Society, M. O. Özyalçin, Funda Akleman, Levent Sevgi̇
Turkish Journal of Electrical Engineering and Computer Sciences
Numerical simulation in cellular phone - human tissue interaction is discussed in this paper. The powerful time domain (TD) techniques, the transmission line matrix (TLM) and the finite-difference time-domain (FDTD) methods, are used to model mutual effects. The purpose is to calculate specific absorption rate (SAR; defined as the power absorbed by the unit mass of the tissue), validate the codes and verify the results. Also, effectiveness of the SAR parameter in determination of the exposure limits for human health and environmental pollution is discussed.
Walkthrough In Complex Environments At Interactive Rates Using Level-Of-Detail, Alper Selçuk, Uğur Güdükbay, Bülent Özgüç
Walkthrough In Complex Environments At Interactive Rates Using Level-Of-Detail, Alper Selçuk, Uğur Güdükbay, Bülent Özgüç
Turkish Journal of Electrical Engineering and Computer Sciences
One of the biggest problems in computer graphics is displaying huge geometric models at interactive rates. A lot of work has been done to achieve the required frame-rates in architecture, simulation, computer-aided design and entertainment applications. In this paper, a system that enables walkthrough in complex environments using level-of-detail approximations is explained. The system uses hierarchical triangulated models as input. In the preprocessing phase, multiresolution models of objects are created using polygonal simplification techniques. During walkthrough, fast frustum culling based on bounding boxes is performed to eliminate branches of hierarchy that are not visible. An appropriate level for detail of …
A New Petri-Net-Based Synthesis Technique For Supervisory Control Of Discrete Event Systems, Murat Uzam, Anthony H. Jones
A New Petri-Net-Based Synthesis Technique For Supervisory Control Of Discrete Event Systems, Murat Uzam, Anthony H. Jones
Turkish Journal of Electrical Engineering and Computer Sciences
A new Petri-net-based top-down synthesis technique for supervisory control of Discrete Event Systems (DES) is proposed to solve the forbidden state problem. The supervisors obtained are compiled supervisors, whose control policy is represented as a net structure, as opposed to mapping supervisors, whose control policy is computed as a feedback function of the marking of the system. The compiled supervisors obtained by using the technique proposed in this paper are both nonblocking and maximally permissive. The supervisors to be synthesised consist of a controlled Automation Petri Net model of the system. Automation Petri Nets (APN) include the following extensions to …
A Note On The Poisson Summation Formula And Its Application To Electromagnetic Problems Involving Cylindrical Coordinates, Anastassios H. Panaretos, Hristos T. Anastassiu, Dimitra I. Kaklamani
A Note On The Poisson Summation Formula And Its Application To Electromagnetic Problems Involving Cylindrical Coordinates, Anastassios H. Panaretos, Hristos T. Anastassiu, Dimitra I. Kaklamani
Turkish Journal of Electrical Engineering and Computer Sciences
A modified version of the Poisson Summation Formula is derived,involving the Fourier-Bessel Transform of the kernel function, as opposed to the conventional Fourier Transform engaged in the standard formula. This novel form can be applied to problems employing cylindrical coordinates, such as the fast evaluation of the dyadic Green's function in a waveguide or cavity of circular cross-section.
A Time Domain Uniform Geometrical Theory Of Slope Diffraction For A Curved Wedge, Prabhakar H. Pathak, Paul R. Rousseau
A Time Domain Uniform Geometrical Theory Of Slope Diffraction For A Curved Wedge, Prabhakar H. Pathak, Paul R. Rousseau
Turkish Journal of Electrical Engineering and Computer Sciences
A time domain version of the uniform geometrical theory of diffraction (TD-UTD) is developed to describe, in essentially closed form, the field which is produced via slope diffraction at a perfectly conducting, arbitrarily curved wedge excited by a time impulsive wave that exhibits a rapid spatial variation near the edge of the wedge. This TD-UTD slope diffracted field for a curved wedge is obtained by a Fourier inversion of the corresponding frequency domain UTD expression. An analytical signal representation of the transient fields is used since it is convenient, and because it circumvents some of the difficulties, which especially arise …
A Novel Mom Approach For Obtaining Accurate And Efficient Solutions In Optical Rib Waveguide, Namik Yener, Ercan Topuz
A Novel Mom Approach For Obtaining Accurate And Efficient Solutions In Optical Rib Waveguide, Namik Yener, Ercan Topuz
Turkish Journal of Electrical Engineering and Computer Sciences
The optical rib waveguide (ORW) plays an important role in the design of several integrated optical devices. Various methods have been proposed for obtaining the modal field solutions in ORW. However, to the best of our knowledge none of them is capable of providing accurate full-wave benchmark solutions. Here we present a novel MoM approach wherein the modes of a loaded rectangular waveguide are utilized as basis functions and demonstrate that this approach is very efficient and yields highly accurate full-wave results which can serve as benchmark solutions in assessing the quality of the data reported in the literature.
A Personel Note, Leopold B. Felsen
A Personel Note, Leopold B. Felsen
Turkish Journal of Electrical Engineering and Computer Sciences
No abstract provided.
Electromagnetic Engineering In The 21^{St} Century: Challenges And Perspectives, Leopold B. Felsen, Levent Sevgi̇
Electromagnetic Engineering In The 21^{St} Century: Challenges And Perspectives, Leopold B. Felsen, Levent Sevgi̇
Turkish Journal of Electrical Engineering and Computer Sciences
This paper aims at a broad-brush look at certain technological and educational challenges that confront wave-oriented electromagnetic (EM) engineering in the 21^{st} century, in a complex computer and technology-driven world with rapidly shifting societal and technical priorities. Simulation strategies for complex EM systems, both analytic and numerical, are reviewed and categorized, and are illustrated on selected practical complex multicomponent system scenarios currently under investigation in Turkey. Educational issues to ensure proper multidisciplinary exposure of new generations of computer-weaned students, who will have to deal with these problems, are touched upon as well.
Iterative Solution Of Field Problems With A Varying Physical Parameter, Anton G. Tijhuis, Martijn C. Van Beurden, A. Peter M. Zwamborn
Iterative Solution Of Field Problems With A Varying Physical Parameter, Anton G. Tijhuis, Martijn C. Van Beurden, A. Peter M. Zwamborn
Turkish Journal of Electrical Engineering and Computer Sciences
In this paper, linear field problems with a varying physical parameter are solved with the conjugate-gradient FFT method and a dedicated extrapolation procedure for generating the initial estimate. The scheme is formulated and illustrated for two simple example problems. The importance of the choice of the stop criterion and the step size are demonstrated for the case of a straight thin-wire segment. A brief summary is given of the applications that have appeared in the open literature until now, and actual three-dimensional scattering problems for a rectangular conducting plate and an inhomogeneous, dispersive dielectric body are discussed. Finally, the case …
An Efficient Preconditioner For Iterative Solvers, V. V. S. Prakash, Raj Mittra
An Efficient Preconditioner For Iterative Solvers, V. V. S. Prakash, Raj Mittra
Turkish Journal of Electrical Engineering and Computer Sciences
The method of moments solution of the Maxwell's equations leads to a dense system of complex equations. Direct solution of these equations using LU factorization becomes unwieldy as the size of the scatterer increase in terms of wavelength. Iterative solvers, such as those based on Krylov projection methods, offer an alternative approach for solving large system of equations. Most often, the iterative methods are used in combination with some kind of preconditioning to improve the condition number of the system matrix A in order to acheive accelerated convergence [1-2]. This paper discusses the application of Multi-Frontal Preconditioners (MFPs) for the …
Cpl: A Language For Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan
Cpl: A Language For Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan
Turkish Journal of Electrical Engineering and Computer Sciences
As processing and time requirements of computer systems increase over the borders of single processor architectures, it is becoming more and more attractive to use distributed computing with additional real-time capabilities. In several cases, traditional programming languages have become insufficient to build distributed systems easily, especially when real-time issues and basic software quality factors are concerned. In this paper, a concurrent, object-oriented, distributed real-time programming language, CPL, with a supportive run-time system, namely the CORD-RTS, is introduced and new language features are described. The new language provides an efficient solution for command and control systems by embedding distribution and real-time …
An Efficient Middleware Architecture Supporting Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan
An Efficient Middleware Architecture Supporting Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan
Turkish Journal of Electrical Engineering and Computer Sciences
With the increasing demand for distributed real-time systems, the need for programming tools and execution platforms useful in development of such application systems is widely recognized. This paper presents CORD-RTS, an efficient middleware architecture that provides support for real-time distributed object programming. The communication infrastructure and various components of the middleware, which support several modes of interactions among distributed real-time objects, along with its real-time features and services, are discussed in detail.
A New Congestion Control Mechanism Proposed For The Sscop Protocol, A. Hali̇m Zai̇m
A New Congestion Control Mechanism Proposed For The Sscop Protocol, A. Hali̇m Zai̇m
Turkish Journal of Electrical Engineering and Computer Sciences
International Telecommunication Union, Telecommunications Sector (ITU-T) Recommendation Q.2110 states that the update of a granted credit window to the transmitter (VR(MR)) is implementation dependent. In this paper, a new algorithm is designed to control the traffic flow coming from malfunctioning users. The VR(MR) parameter is controlled for that purpose. The simulation results show that this new technique nearly doubles the system performance.