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2002

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A New Petri-Net-Based Synthesis Technique For Supervisory Control Of Discrete Event Systems, Murat Uzam, Anthony H. Jones Jan 2002

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 …

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Approximations On The Aggregate Mpeg Video Traffic And Their Impact On Admission Control, Fati̇h Alagöz Jan 2002

Approximations On The Aggregate Mpeg Video Traffic And Their Impact On Admission Control, Fati̇h Alagöz

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, we investigate the aggregate traffic approximations for the Motion Pictures Expert Group (MPEG) coded variable bit rate (VBR) video traffic and their impact on admission control at a desired Quality of Service (QoS) level. In order to generate the MPEG coded VBR video traffic, we use a novel source model that employs a mixture of two first-order autoregressive processes with lognormally distributed residuals (2LAR). The model parameters are found based on least square estimates to capture the marginal distribution and autocorrelation function as well as the single server queuing behavior of an MPEG coded empirical bitstream. We …

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New Oscillator Topologies Using Inverting Second-Generation Current Conveyors, Ali̇ Toker, Hakan Kuntman, Oğüzhan Çi̇çekoğlu, Mehmet Di̇şçi̇gi̇l Jan 2002

New Oscillator Topologies Using Inverting Second-Generation Current Conveyors, Ali̇ Toker, Hakan Kuntman, Oğüzhan Çi̇çekoğlu, Mehmet Di̇şçi̇gi̇l

Turkish Journal of Electrical Engineering and Computer Sciences

In this work, new oscillator topologies based on a recently introduced active element, namely inverting second-generation current conveyor, are presented. This recently introduced unity gain based active element is suitable for integrated circuit realization and can easily be implemented with CMOS technology. Considering this fact, basic oscillator topologies employing a single, two and three conveyors are proposed. Several oscillator circuits based on these topologies are obtained. Expressions for oscillation conditions and frequencies are derived both for ideal and non-ideal cases. Some of them are single frequency and the others are variable frequency oscillators. The oscillators employing two and three active …

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Cover And Contents Jan 2002

Cover And Contents

Turkish Journal of Electrical Engineering and Computer Sciences

No abstract provided.

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Preface, Levent Sevgi̇ Jan 2002

Preface, Levent Sevgi̇

Turkish Journal of Electrical Engineering and Computer Sciences

No abstract provided.

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Electromagnetic Engineering In The 21^{St} Century: Challenges And Perspectives, Leopold B. Felsen, Levent Sevgi̇ Jan 2002

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.

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Time-Domain Simulation Of Thin Material Boundaries And Thin Panels Using Digital Filters In Tlm, J. Paul, V. Podlozny, Dave Thomas, C. Christopoulos Jan 2002

Time-Domain Simulation Of Thin Material Boundaries And Thin Panels Using Digital Filters In Tlm, J. Paul, V. Podlozny, Dave Thomas, C. Christopoulos

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the design and implementation of digital filters for the time-domain simulation of electromagnetic wave interaction with thin material boundaries and thin panels using the Transmission-Line Modelling (TLM) method are described. The technique is applied to the description of thin ferrite layers placed on the external boundaries of the modelled space and to plastic panels placed inside the modelled space. The approach is validated using one-dimensional examples having analytic solutions. Finally, the results obtained for the Shielding Effectiveness (SE) of a practical equipment enclosure are presented to demonstrate the utility of the method in Electromagnetic Compatibility (EMC) prediction.

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Aspects Of Radar Polarimetry, Ernst Luneburg Jan 2002

Aspects Of Radar Polarimetry, Ernst Luneburg

Turkish Journal of Electrical Engineering and Computer Sciences

This contribution is a tutorial introduction to the phenomenological theory of radar polarimetry for the coherent scatter case emphasizing monostatic backscattering and forward scattering (transmission). Characteristic similarities and differences between radar polarimetry and optical polarimetry and the role of linear and antilinear operators (time-reversal) are pointed out and typical polarimetric invariants are identified.

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Two-Dimensional Photonic Crystal L-Shaped Bent Waveguide And Its Application To Wavelength Multi/Demultiplexer, Yoshihiro Naka, Hiroyoshi Ikuno Jan 2002

Two-Dimensional Photonic Crystal L-Shaped Bent Waveguide And Its Application To Wavelength Multi/Demultiplexer, Yoshihiro Naka, Hiroyoshi Ikuno

Turkish Journal of Electrical Engineering and Computer Sciences

The bent waveguide is a key element for integrated optical signal processing waveguide devices. We propose a new type of two-dimensional photonic crystal L-shaped bent waveguides with additional pillars at the corner. Using the FDTD method based on the principle of multidimensional wave digital filters we simulate its transmission characteristics and show an excellent transmission of light in L-shaped bent waveguide. As an application we design compact size multi/demultiplexer composed of the L-shaped bent waveguides and directional couplers and realize multi/demultiplexer with low-insertion loss and high extinction ratio device whose size is of the order of the wavelength of light.

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Discrete Array Representation Of Continuous Space-Time Source Distributions, Amir Shlivinski, Ehud Heyman Jan 2002

Discrete Array Representation Of Continuous Space-Time Source Distributions, Amir Shlivinski, Ehud Heyman

Turkish Journal of Electrical Engineering and Computer Sciences

We consider the realization of a continuous space-time source distributions using a sparse non-uniform point-source array. The construction determines the largest possible cells corresponding to the local source parameters in order to obtain a sparse array, while meeting an error criterion on the pulsed radiation pattern. The scheme is applied for the realization of collimated short-pulse beam fields. The error criterion is imposed within the main beam direction, while outside this region the relative realization error can be large but it is negligible since the field there is small compared to the main beam field.

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Development Of A Cylindrical Waveguide Antenna Array With A High Isolation Between Receive - Transmit Sub Arrays: Theory And Experiment, Vladimir I. Okhmatovsky, Konstantina S. Nikita, Stavros Koulouridis, Nikolaos K. Uzunoglu Jan 2002

Development Of A Cylindrical Waveguide Antenna Array With A High Isolation Between Receive - Transmit Sub Arrays: Theory And Experiment, Vladimir I. Okhmatovsky, Konstantina S. Nikita, Stavros Koulouridis, Nikolaos K. Uzunoglu

Turkish Journal of Electrical Engineering and Computer Sciences

The possibility of developing an antenna system consisting of transmit and receive arrays and being able to work simultaneously in full duplex mode at the same frequency is a very attractive task. This could only be achieved if the isolation between the transmit and receive arrays is sufficiently high not to cause a parasitic oscillation which will ruin the proper operation of a transponder system to which the arrays will be connected. Specifically, in this paper the operation of two peripheral open waveguide arrays placed on a cylindrical surface and being isolated with a radial line operating as a space …

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2d Complex Point Source Radiation Problem I. Complex Distances And Complex Angles, E. Gago-Ribas, M. J. Gonzalez Morales Jan 2002

2d Complex Point Source Radiation Problem I. Complex Distances And Complex Angles, E. Gago-Ribas, M. J. Gonzalez Morales

Turkish Journal of Electrical Engineering and Computer Sciences

A methodology based on the complex spaces analysis, which allows to generalize the study of wave radiation and scattering problems is presented in this paper. From the analytic continuation of functions defined in the real domain (real propagation or scattering spaces) into the complex space (space of complex coordinates), general non homogeneous phase field solutions are obtained for a particular wave problem. From these general solutions, other common solutions obtained under different approximations will arise. This procedure allows to obtain a complete classification of the solutions for the wave problem under analysis, and also to study both the ranges of …

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2d Complex Point Source Radiation Problem Ii.~Complex Beams, M. J. Gonzalez Morales, E. Gago-Ribas Jan 2002

2d Complex Point Source Radiation Problem Ii.~Complex Beams, M. J. Gonzalez Morales, E. Gago-Ribas

Turkish Journal of Electrical Engineering and Computer Sciences

The complex point source analytic continuation, and the analysis into the spaces of complex distances, angles, and other related magnitudes, may be applied to describe a wide variety of 2D wave propagation problems. This step will be essential in order to establish a complete complex methodology which may be applied to obtain general descriptions of more practical problems involving the scattering of waves under some kind of field incidence. A particular application of the methodology presented in Part I will be used in Part II. The specific problem under analysis in these papers will be the general complex beam solution …

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An Efficient Preconditioner For Iterative Solvers, V. V. S. Prakash, Raj Mittra Jan 2002

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 …

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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 Jan 2002

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.

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A Time Domain Uniform Geometrical Theory Of Slope Diffraction For A Curved Wedge, Prabhakar H. Pathak, Paul R. Rousseau Jan 2002

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 …

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A Novel Mom Approach For Obtaining Accurate And Efficient Solutions In Optical Rib Waveguide, Namik Yener, Ercan Topuz Jan 2002

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.

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Cover And Contents Jan 2002

Cover And Contents

Turkish Journal of Zoology

No abstract provided.

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Cover And Contents Jan 2002

Cover And Contents

Turkish Journal of Zoology

No abstract provided.

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Effects Of Substrate Temperature On Properties Of A-Sin_X:H Films, Tayyar Güngör, Hüseyi̇n Tolunay Jan 2002

Effects Of Substrate Temperature On Properties Of A-Sin_X:H Films, Tayyar Güngör, Hüseyi̇n Tolunay

Turkish Journal of Physics

Hydrogenated amorphous silicon nitride films were prepared in an rf glow-discharge system by the decomposition of silane + nitrogen gas mixture at various substrate temperatures. The effects of substrate temperature on the electrical and optical properties of the films have been studied.

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The Temperature Dependence Of The Electronic Structure Of Si \Delta-Doped Gaas, Emi̇ne Öztürk Jan 2002

The Temperature Dependence Of The Electronic Structure Of Si \Delta-Doped Gaas, Emi̇ne Öztürk

Turkish Journal of Physics

We investigated theoretically the change of electronic properties of Si \delta-doped GaAs layer as a function of temperature. We studied the influence of temperature on the donor concentration for a nonuniform distribution, which is taken as different from the known Gaussian distribution. In order to obtain the electronic structure we have calculated self-consistent Schrödinger - Poisson equations. We have seen that the change of the electronic properties as dependent on temperature is less pronounced at higher doping concentration.

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Defect Structure Of Glow Peak 1 In Lif:Mg,Ti (Tld-100), A. Necmeddi̇n Yazici Jan 2002

Defect Structure Of Glow Peak 1 In Lif:Mg,Ti (Tld-100), A. Necmeddi̇n Yazici

Turkish Journal of Physics

The possible defect structure of peak 1 of LiF:Mg,Ti (TLD-100) was studied in the present work after different pre-irradiation heat treatments between 80°C and 150°C using the computer glow curve deconvolution (CGCD) method. It was shown that the defect structure of peak 1 is based on colloid centers, Ti^{+4}-3O_{2}^{-}-mixed centers and U_{1}-centers.

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Cover And Contents Jan 2002

Cover And Contents

Turkish Journal of Veterinary & Animal Sciences

No abstract provided.

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Effect Of Rf Power On The Electrical Properties Of Glow-Discharge A-Si:H, Hüseyi̇n Tolunay Jan 2002

Effect Of Rf Power On The Electrical Properties Of Glow-Discharge A-Si:H, Hüseyi̇n Tolunay

Turkish Journal of Physics

Hydrogenated amorphous silicon films were prepared in an rf glow-discharge system by decomposing undiluted silane at various rf power densities. Dark conductivity and photoconductivity of the films have been measured in the temperature range 420K-100K at four different photon fluxes. It was observed that both dark conductivity and photoconductivity increase with increasing rf power density.

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Plane Wave Diffraction By A Dielectric Loaded Open Parallel Thick Plate Waveguide, Bahatti̇n Türetken, Ali̇ Alkumru Jan 2002

Plane Wave Diffraction By A Dielectric Loaded Open Parallel Thick Plate Waveguide, Bahatti̇n Türetken, Ali̇ Alkumru

Turkish Journal of Electrical Engineering and Computer Sciences

A uniform asymptotic high-frequency solution for a two-dimensional diffraction problem of plane electromagnetic waves by a dielectric loaded open parallel thick plate waveguide is investigated rigorously using the Fourier transform technique in conjunction with the mode matching method. This mixed method of formulation gives rise to scalar modified Wiener-Hopf equations of the second kind for which the solution contains a set of infinitely many constants satisfying an infinite system of linear algebraic equations. A numerical solution of this system is obtained for various values of plate thickness, incidence angle and permittivity, and the effect of these parameters on the diffraction …

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Array Pattern Nulling By Phase And Position Perturbations With The Use Of A Modified Tabu Search Algorithm, Ali̇ Akdağli, Keri̇m Güney Jan 2002

Array Pattern Nulling By Phase And Position Perturbations With The Use Of A Modified Tabu Search Algorithm, Ali̇ Akdağli, Keri̇m Güney

Turkish Journal of Electrical Engineering and Computer Sciences

A useful and flexible method based on the tabu search algorithm for the pattern synthesis of linear antenna arrays with the prescribed nulls is presented. Nulling of the pattern is achieved by controlling both the phase and the position of each array element. To show the versatility of the present method, some design specifications such as the maximum sidelobe level and the null depth level are considered by introducing a set of weighting factors in the cost function constructed for the tabu search algorithm. Several illustrative examples of a Chebyshev pattern with the imposed single, multiple and broad nulls are …

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Scalar Wave Diffraction By Perfectly Soft Thin Circular Cylinder Of Finite Length; Analytical Regularization Method, Eylem Özkan, Fati̇h Di̇kmen, Yury Alexanderovich Tuchkin Jan 2002

Scalar Wave Diffraction By Perfectly Soft Thin Circular Cylinder Of Finite Length; Analytical Regularization Method, Eylem Özkan, Fati̇h Di̇kmen, Yury Alexanderovich Tuchkin

Turkish Journal of Electrical Engineering and Computer Sciences

A new mathematically rigorous and numerically effective method for solving the boundary value problem of scalar wave diffraction by an infinitely thin circular cylindrical screen of finite length is proposed. The method is based on the combination of the Orthogonal Polynomials Approach, and on the ideas of the methods of analytical regularization. As a result of the suggested regularization procedure, the initial boundary value problem is equivalently reduced to the infinite system of the linear algebraic equations of the second kind, i.e. to an equation of the type (I + H)x = b in the space \ell _{2} of square …

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Active Clamped Zvs Forward Converter With Soft-Switched Synchronous Rectifier, A. Açik, Işik Çadirci Jan 2002

Active Clamped Zvs Forward Converter With Soft-Switched Synchronous Rectifier, A. Açik, Işik Çadirci

Turkish Journal of Electrical Engineering and Computer Sciences

This paper presents the analysis, design and implementation of an active-clamped, ZVS forward converter equipped with a soft-switched synchronous rectifier (ACFC-SR) proposed for high-efficiency, low output voltage dc-dc converter applications. The converter efficiency is maximized due to the soft-switching of the main, active clamp, synchronous rectifier and freewheeling MOSFET switches. The operating principles of the ACFC-SR are analyzed in detail and the converter performance is compared with the alternative forward converter schemes employed in low output voltage dc-dc converters. Experimental results are presented for a converter with a dc input voltage of 48 V, an output voltage of 5 V, …

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C-Closed Sets In L-Fuzzy Topological Spaces And Some Of Its Applications, Ali̇ Ahmed Nouh Jan 2002

C-Closed Sets In L-Fuzzy Topological Spaces And Some Of Its Applications, Ali̇ Ahmed Nouh

Turkish Journal of Mathematics

We introduce and study the notion of C-closed sets in L-fuzzy topological spaces. Then, C-convergence theory for nets and ideals is established in terms of C-closedness. Finally, we give a new concept of C-continuity on L-fuzzy topological space by means of L-fuzzy C-closedness and investigate some of its properties and its relationships with other L-fuzzy mappings introduced previously. Then we systematically study the characterizations of this notion with the aid of the C-convergence of L-fuzzy nets and L-fuzzy ideals.

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On Locally Pre-C^{*}-Algebra Structures In Locally M-Convex H^{*}-Algebras, A. El-Kinani Jan 2002

On Locally Pre-C^{*}-Algebra Structures In Locally M-Convex H^{*}-Algebras, A. El-Kinani

Turkish Journal of Mathematics

We endow any locally m-convex H^{*}-algebra \left( E,\tau \right) with a locally pre-C^{*}-topology weaker than \tau. Examples and applications are provided.

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