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Full-Text Articles in Physical Sciences and Mathematics

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 …


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 …


Preface, Levent Sevgi̇ Jan 2002

Preface, Levent Sevgi̇

Turkish Journal of Electrical Engineering and Computer Sciences

No abstract provided.


Network--Oriented Modeling Of Radiating Electromagnetic Structures, Peter Russer Jan 2002

Network--Oriented Modeling Of Radiating Electromagnetic Structures, Peter Russer

Turkish Journal of Electrical Engineering and Computer Sciences

The application of network-oriented modeling for radiating electromagnetic structures is investigated. Network methods are applied to the field problem using the segmentation technique and by specifying canonical Foster representations as compact models of reciprocal linear lossless electromagnetic structures. Connection between different subdomains is obtained via connection circuits exhibiting only ideal transformers. In the case of radiating structures, the complete structure is embedded into a sphere and the field outside the sphere is expanded into orthogonal spherical TM- and TE- waves. For each radiation mode a Cauer canonic circuit representation is given.


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.


Novel Time Domain Radiowave Propagators For Wireless Communication Systems, Funda Akleman, M. O. Özyalçin, Levent Sevgi̇ Jan 2002

Novel Time Domain Radiowave Propagators For Wireless Communication Systems, Funda Akleman, M. O. Özyalçin, Levent Sevgi̇

Turkish Journal of Electrical Engineering and Computer Sciences

In this study, novel time domain wave propagators are used in path loss calculations for macro and micro cell coverage planning in wireless communication systems. Both Transmission Line Matrix (TLM) and Finite-Difference Time-Domain (FDTD) based propagators, which were introduced recently and validated and verified on different canonical propagation scenarios, are used for this purpose. Examples are chosen both in rural and urban areas, where two propagators are compared with each other. Excellent agreement between the results obtained via two propagators is presented. The results presented here are very encouraging and these propagators are shown to be powerful tools for not …


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.


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.


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.


Floquet Wave Diffraction Theory For Tapered Planar Strip Array Green's Function, F. Capolino, F. Mariottini, S. Maci, L. B. Felsen Jan 2002

Floquet Wave Diffraction Theory For Tapered Planar Strip Array Green's Function, F. Capolino, F. Mariottini, S. Maci, L. B. Felsen

Turkish Journal of Electrical Engineering and Computer Sciences

This paper deals with the derivation and physical interpretation of a uniform high frequency representation of the Green's function for a planar phased array of dipoles. The asymptotic representation is based on Floquet wave edge diffraction theory herein extended to accommodate slowly varying tapered amplitude illumination with possible inclusion of dipole amplitudes that tend to zero at the edge. The phased array is assumed to be infinite with uniform amplitude excitation in the z-direction but finite and amplitude-tapered in the x-direction. This geometry permits study of diffraction phenomena occurring at the tapered edge of a rectangular array when the observation …


An Exact Line Integral Representation Of The Po Radiation Integral From A Flat Perfectly Conducting Surfaces Illuminated By Elementary Electric Or Magnetic Dipoles, Matteo Albani, Stefano Maci Jan 2002

An Exact Line Integral Representation Of The Po Radiation Integral From A Flat Perfectly Conducting Surfaces Illuminated By Elementary Electric Or Magnetic Dipoles, Matteo Albani, Stefano Maci

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, a line integral representation for the PO radiation integral from a flat perfectly conducting surface, illuminated by an arbitrary oriented elementary either electric or magnetic dipole, is presented. No restriction is imposed on the position of the source and of the observation point. The main application of this result is the acceleration of the numerical PO integration for electrically large surfaces. The formulation is based on the application of the equivalence principle to a projecting surface which allows the analytical evaluation in closed form of one of the two-fold surface integral which define the radiated field at …


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 …


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 …


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 …


Stability Analysis Of A Closed-Loop Control For A Pulse Width Modulated Dc Motor Drive, Fatma Gürbüz, Eyüp Akpinar Jan 2002

Stability Analysis Of A Closed-Loop Control For A Pulse Width Modulated Dc Motor Drive, Fatma Gürbüz, Eyüp Akpinar

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, the effect of the variation of amplitude and the chopping period of a PWM signal on the stability of a closed-loop control for a DC motor drive is investigated. First, the entire system is formulated as a Linear Quadratic (LQ) tracker with output feedback [1]. Then, stability analysis for the varying amplitude and the varying chopping period is carried out by the methods of root locus and the Jury test. Finally, stability limits obtained from a root locus and Jury test are checked by the simulation of the system in MATLAB.


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 …


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 …


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 …


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, …


Hybrid Sr Arq Scheme Using Trellis Coded Modulation For Point-To-Multipoint Communication Over Nonstationary Channels, Necmi̇ Taşpinar Jan 2002

Hybrid Sr Arq Scheme Using Trellis Coded Modulation For Point-To-Multipoint Communication Over Nonstationary Channels, Necmi̇ Taşpinar

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, a type-I hybrid SR ARQ scheme using trellis coded modulation (TCM) for point-to-multipoint communication was analyzed on nonstationary broadcast channels where the channel bit error rate (BER) varies over time. A nonstationary channel is modelled as a two-state Markov chain. In the numerical calculations, it is found that, for a given p_{1} and \bar \varepsilon , the values of the average burst length \bar b have a very small influence on the throughput. Numerical results show that the throughput is better for values between 10 ^{-6} and 10 ^{-4}of average bit error rate \bar \varepsilon if the …


Meta-Genetic Programming: Co-Evolving The Operators Of Variation, Bruce Edmonds Jan 2001

Meta-Genetic Programming: Co-Evolving The Operators Of Variation, Bruce Edmonds

Turkish Journal of Electrical Engineering and Computer Sciences

The standard Genetic Programming approach is augmented by co-evolving the genetic operators. To do this the operators are coded as trees of indefinite length. In order for this technique to work, the language that the operators are defined in must be such that it preserves the variation in the base population. This technique can varied by adding further populations of operators and changing which populations act as operators for others, including itself, thus to provide a framework for a whole set of augmented GP techniques. The technique is tested on the parity problem. The pros and cons of the technique …


All-Optical Networking, Altan Koçyi̇ği̇t, Demeter Gökişik, Semi̇h Bi̇lgen Jan 2001

All-Optical Networking, Altan Koçyi̇ği̇t, Demeter Gökişik, Semi̇h Bi̇lgen

Turkish Journal of Electrical Engineering and Computer Sciences

A survey of recent literature on all optical networking is presented. Starting from multiplexing techniques and topological features, network design and performance issues are reviewed. Particular attention is devoted to Wavelength Division Multiplexing (WDM) networks. Static and dynamic solutions of the routing and wavelength assignment (RWA) problem are considered. Issues of current research are summarized.


An Integrated Design-Object Modeling Environment -- Pluggable Metamodel Mechanism --, Masaharu Yoshioka, Takayuki Sekiya, Tetsuo Tomiyama Jan 2001

An Integrated Design-Object Modeling Environment -- Pluggable Metamodel Mechanism --, Masaharu Yoshioka, Takayuki Sekiya, Tetsuo Tomiyama

Turkish Journal of Electrical Engineering and Computer Sciences

We propose a new integrated computational environment to support design object modeling, during engineering design process that requires a variety of design object models, such as a geometric model, a control model, and a finite element model. To integrate multiple design object models, we have developed a mechanism called a metamodel mechanism that maintains consistency among various models. The metamodel mechanism represents relationships among concepts used in these models and is useful, for example, to conduct concurrent engineering practices. In this framework, we formalize a design process as operations to the metamodel. This paper expands the concept of the metamodel …


Accurate Parameter Estimation For An Articulatory Speech Synthesizer With An Improved Neural Network Mapping, Hali̇s Altun, Tankut Yalçinöz, K. Mervyn Curtis Jan 2001

Accurate Parameter Estimation For An Articulatory Speech Synthesizer With An Improved Neural Network Mapping, Hali̇s Altun, Tankut Yalçinöz, K. Mervyn Curtis

Turkish Journal of Electrical Engineering and Computer Sciences

Neural network (NN) applications have recently been employed to extract the parameters of an articulatory speech synthesizer from a given speech signal. Results from these attempts showed that a single NN is insufficient to cover all of the possible configurations uniquely. Moreover, apart from their computational advantages, NN mapping is so far not superior to the other mapping techniques [1]. Thus there is a clear need to improve NN solution to the inverse problem. Results from our earlier experiments with an articulatory speech synthesizer have shown that the statistical characteristic of the articulatory target pattern vectors can be exploited for …


Combining Multiple Representations For Pen-Based Handwritten Digit Recognition, Fevzi̇ Ali̇moğlu, Ethem Alpaydin Jan 2001

Combining Multiple Representations For Pen-Based Handwritten Digit Recognition, Fevzi̇ Ali̇moğlu, Ethem Alpaydin

Turkish Journal of Electrical Engineering and Computer Sciences

We investigate techniques to combine multiple representations of a handwritten digit to increase classification accuracy without significantly increasing system complexity or recognition time. In pen-based recognition, the input is the dynamic movement of the pentip over the pressure sensitive tablet. There is also the image formed as a result of this movement. On a real-world database of handwritten digits containing more than 11,000 handwritten digits, we notice that the two multi-layer perceptron (MLP) based classifiers using these representations make errors on different patterns implying that a suitable combination of the two would lead to higher accuracy. We implement and compare …


Fuzzy Modeling Approach For Integrated Assessments Using Cultural Theory, Adnan Yazici, Fred E. Petry, Curt Pendergraft Jan 2001

Fuzzy Modeling Approach For Integrated Assessments Using Cultural Theory, Adnan Yazici, Fred E. Petry, Curt Pendergraft

Turkish Journal of Electrical Engineering and Computer Sciences

It has already been noted that the accurate prediction of societal responses requires the use of a formal model based on some social or cultural taxonomy. One such taxonomic candidate is Cultural Theory (CT). CT argues that all societies, irrespective of time or place, are informed by their underlying worldviews, which must be more or less Hierarchic, more or less Individualistic, more or less Egalitarian, and more or less Fatalistic. This approach appears to have a potential for cross-temporal and spatial comparisons that makes it a particularly attractive instrument for a study of the human dimensions of global climate change. …


Advances In Computer And Information Sciences: From Abacus To Holonic Agents, Tuncer Ören Jan 2001

Advances In Computer And Information Sciences: From Abacus To Holonic Agents, Tuncer Ören

Turkish Journal of Electrical Engineering and Computer Sciences

The shift of paradigm emphasizing the importance of the ability to process knowledge rather then being knowledgeable is stressed. A taxonomy of knowledge processing tools, machines, or systems is offered. Major possibilities for future achievements that the author would like to underline are listed with emphasis on agent technology, agent-directed simulation, holonic agents, holonic-agent simulation, and contribution of system theories for cognitive abilities such as understanding, learning, adaptation, and anticipation in computerization.


Bag Distributed Real-Time Operating System And Task Migration, Beki̇r Tevfi̇k Akgün Jan 2001

Bag Distributed Real-Time Operating System And Task Migration, Beki̇r Tevfi̇k Akgün

Turkish Journal of Electrical Engineering and Computer Sciences

BAG is a distributed operating system designed for real-time applications which is run on a distributed real-time system. The heterogeneously distributed BAG system consists of nodes which have VME-bus chassis, different types of processor modules, and an interconnection network. The operating system has three main parts having distributed properties: task migration, load balancing and a distributed file system. Heterogeneous task migration is based on the extended finite state machine (EFSM) programming model. The EFMS model has also eased the implementation of the migration mechanism. The load balancing algorithm is centralized in one node. But the overall system will be a …


Avalanche And Bit Independence Properties For The Ensembles Of Randomly Chosen N \Times N S-Boxes, Işil Vergi̇li̇, Melek D. Yücel Jan 2001

Avalanche And Bit Independence Properties For The Ensembles Of Randomly Chosen N \Times N S-Boxes, Işil Vergi̇li̇, Melek D. Yücel

Turkish Journal of Electrical Engineering and Computer Sciences

Cryptographic test methods such as avalanche, strict avalanche and bit independence criteria, which measure the degree of security of the s-boxes of substitution-permutation networks, are applied to randomly generated ensembles of ( n \times n \) s-boxes. Statistical analysis of experimental data directs the work towards defining ``relative errors'' and examining the avalanche and strict avalanche criteria within ``relative error ranges''. Histograms of relative errors in each ensemble are evaluated, and combining the results of different ensembles corresponding to different values of the s-box size, variations of maximum relative errors versus the size of the s-box are depicted. Some predictions …


Performance Evaluation Of Safer K-64 And S-Boxes Of The Safer Family, Ekrem Aras, Melek D. Yücel Jan 2001

Performance Evaluation Of Safer K-64 And S-Boxes Of The Safer Family, Ekrem Aras, Melek D. Yücel

Turkish Journal of Electrical Engineering and Computer Sciences

If the characteristics of s-boxes of the SAFER family of ciphers are examined for the criteria of strict avalanche, bit independence, and XOR table distribution, experiments show that the ``exponentiating'' s-box has a weakness for an input difference of 128 (=10000000_{2}) and the ``logarithm-taking'' s-box has a weakness for an input difference of 253 (=11111101_{2}). However, since these experiments are performed by isolating the s-boxes from the general structure, they do not necessarily indicate a weakness in the overall algorithm. We propose a quick and rough test method, called the avalanche weight distribution criterion, to evaluate the overall performance of …