Open Access. Powered by Scholars. Published by Universities.®

Computer Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Electrical and Computer Engineering

2002

Institution
Keyword
Publication
Publication Type

Articles 61 - 77 of 77

Full-Text Articles in Computer Engineering

Maximum-Likelihood Image Estimation Using Photon-Correlated Beams, Majeed M. Hayat, Muhammad Sajjad Abdullah, Adel Joobeur, Bahaa E.A. Saleh Jan 2002

Maximum-Likelihood Image Estimation Using Photon-Correlated Beams, Majeed M. Hayat, Muhammad Sajjad Abdullah, Adel Joobeur, Bahaa E.A. Saleh

Electrical and Computer Engineering Faculty Research and Publications

A theory is presented addressing the fundamental limits of image estimation in a setup that uses two photon-correlated beams. These beams have the property that their photon arrivals, as a point process, are ideally synchronized in time and space. The true image represents the spatial distribution of the optical transmittance (or reflectance) of an object. In this setup, one beam is used to probe the image while the other is used as a reference providing additional information on the actual number of photons impinging on the object. This additional information is exploited to reduce the effect of quantum noise associated …

Go to article

Cpl: A Language For Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan Jan 2002

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 …

Go to article

An Efficient Middleware Architecture Supporting Real-Time Distributed Object Programming, Erhan Saridoğan, Nadi̇a Erdoğan Jan 2002

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.

Go to article

Walkthrough In Complex Environments At Interactive Rates Using Level-Of-Detail, Alper Selçuk, Uğur Güdükbay, Bülent Özgüç Jan 2002

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

Iterative Solution Of Field Problems With A Varying Physical Parameter, Anton G. Tijhuis, Martijn C. Van Beurden, A. Peter M. Zwamborn Jan 2002

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 …

Go to article

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 …

Go to article

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 …

Go to article

A Personel Note, Leopold B. Felsen Jan 2002

A Personel Note, Leopold B. Felsen

Turkish Journal of Electrical Engineering and Computer Sciences

No abstract provided.

Go to article

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.

Go to article

Sar Simulations In Wireless Communication And Safety Discussions In The Society, M. O. Özyalçin, Funda Akleman, Levent Sevgi̇ Jan 2002

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.

Go to article

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.

Go to article

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 …

Go to article

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 …

Go to article

Adaptive Radio Resource Management For 2.5g Cellular Networks, Ken Murray Jan 2002

Adaptive Radio Resource Management For 2.5g Cellular Networks, Ken Murray

Theses

Recent years have seen a dramatic increase in demand for mobile communication services and with the introduction of 2.5G services such as general packet radio service, this trend is expected to increase further. These new services will introduce highly dynamic tele-traffic variations due to the inherent variability in resource usage of the new data services. The net effect will be considerable increase in load on the available radio resources. The currently employed fixed channel allocation scheme lacks the flexibility to support such traffic variations. A plethora of dynamic channel allocation schemes have been proposed in the past in an effort …

Go to article

First Prev