Browsing by Subject "International conferences"
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Item Open Access Analysis of an arbitrary profile reflector antenna having resistive-type surface-H-polarization case(IEEE, 2008-06-07) Oǧuzer, T.; Altıntaş, Ayhan; Nosich, A. I.A regularization-based numerical solution is obtained for arbitrary-shape conic section profile reflector antenna in 2-D, for the H-polarization case. New point is that the reflector surface is assumed a resistive-type material. The problem is treated by reducing the singular integral equation obtained from the boundary condition to the dual series equations and application of the Riemann Hilbert Problem (RHP) technique. The resulting matrix equation has regularized form. Sample numerical results are obtained for various values of the eccentricity of the conic section contour of reflector and the resistivity of its surface. © 2008 IEEE.Item Open Access Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires(IEEE, 2008-06) Byelobrov, V. O.; Benson, T. M.; Altıntaş, Ayhan; Nosich, A.I.In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE.Item Open Access Distance laboratory applications ERRL: A study on radio communication in electronic field(IEEE, 2008-05) Aydın, C. Ç.; Türkmen, G.; Özyurt, E.; Aydın, E. U.; Çaǧıltay, N. E.; Özbek, M. E.; Alparslan, N. Ceren; Kara, A.In the last decade, the effect of internet usage in education is gradually increased. When we look from academic perspective, the new technologies provided alternatives for students learning. As distance education becomes important everyday, the indispensable elements of teaching and education, laboratories must be reachable via remote connection. Consequently, the education that is going to be given to the students will be more flexible with respect to place and time constraints and students can reach laboratory facilities at any time and anywhere not only in lectures and practical hours. In this study, European Remote Radio Laboratory (ERRL) which is a distance remote Radio Frequency (RF) laboratory designed for electrical-electronics students, is described generally. The software architecture, infrastructure and experiment that can be done with a remote connection have been described.Item Open Access Dynamics of commitment and contribution quality in collaborative communities(IEEE, 2007-11) Schaal, Markus; Eren, Y.It is well-known that commitment is an important ingredient for contributions of high quality. With the internet heading towards being an actionable social space, rather than a collection of web-sites, the issue of quality becomes crucial for sharing knowledge and action in collaborative scenarios. We propose a case study for the investigation of the influence of time, user feedback and interface complexity on contribution quality. We plan to exploit different online user groups across two different temporal phases for the evaluation.Item Open Access Generation of new frequencies in toroid microcavities(IEEE, 2008) Akbulut, Duygu; Tülek, Abdullah; Bayındır, MehmetMicrotoroid cavities with ultra high Q-factor have been fabricated using a combined process of photolithography and reflow technique for observing non-linear effects such as generation of new frequency components. For this purpose SiO2 material was used to form the toroidal cavity shape, and chalcogenide material of As2S3 maintaining very high nonlinear refractive index was thermally evaporated on top with varying thicknesses. Simulation results of the fabricated structure have exhibited new frequency components around the excitation window of 1520 nm produced by non-linear interactions.Item Open Access Lexical cohesion based topic modeling for summarization(Springer, 2008-02) Ercan, Gönenç; Çiçekli, İlyasIn this paper, we attack the problem of forming extracts for text summarization. Forming extracts involves selecting the most representative and significant sentences from the text. Our method takes advantage of the lexical cohesion structure in the text in order to evaluate significance of sentences. Lexical chains have been used in summarization research to analyze the lexical cohesion structure and represent topics in a text. Our algorithm represents topics by sets of co-located lexical chains to take advantage of more lexical cohesion clues. Our algorithm segments the text with respect to each topic and finds the most important topic segments. Our summarization algorithm has achieved better results, compared to some other lexical chain based algorithms. © 2008 Springer-Verlag Berlin Heidelberg.Item Open Access Motion control for realistic walking behavior using inverse kinematics(IEEE, 2007-05) Memişoǧlu, Aydemir; Güdükbay,Uğur; Özgüç, BülentThis study presents an interactive hierarchical motion control system for the animation of human figure locomotion. The articulated figure animation system creates movements using motion control techniques at different levels, like goal-directed motion and walking. Inverse Kinematics using Analytical Methods (IKAN) software, developed at the University of Pennsylvania, is utilized for controlling the motion of the articulated body. © 2007 IEEE.Item Open Access Numerical modeling of electromagnetic scattering by perfectly conducting surfaces of revolution(IEEE, 2008-06-07) Nechitaylo, S.; Sukharevsky, I.; Altıntaş, Ayhan; Sukharevsky, O.The integro-differential equation (IDE) of a three-dimensional (3-D) electromagnetic excitation problem of unclosed surfaces is numerically treated by means of the novel direct solver. © 2008 IEEE.Item Open Access On the performance of linear least-squares estimation in wireless positioning systems(IEEE, 2008-05) Gezici, Sinan; Güvenç, İ.; Sahinoğlu, Z.A common technique for wireless positioning is to estimate time-of-arrivals (TOAs) of signals traveling between a target node and a number of reference nodes, and then to determine the position of the target node based on those TOA parameters. In determining the position of the target node from TOA parameters, linear or nonlinear least-squares (LS) estimation techniques can be employed. Although the linear LS techniques are suboptimal in general, they facilitate low-complexity position estimation. In this paper, performance of various linear LS techniques are compared, and suboptimality of the linear approach is quantified in terms of the Cramer-Rao lower bound (CRLB). Simulations are performed to compare the performance of the linear LS approaches versus the CRLBs for linear and nonlinear techniques. ©2008 IEEE.Item Open Access Performance analysis of turbo codes over Rician fading channels with impulsive noise(IEEE, 2007) Ali, Syed Amjad; Ince, E.A.The statistical characteristics of impulsive noise differ greatly from those of Gaussian noise. Hence, the performance of conventional decoders, optimized for additive white Gaussian noise (AWGN) channels is not promising in non-Gaussian environments. In order to achieve improved performance in impulsive environments the decoder structure needs to be modified in accordance with the impulsive noise model. This paper provides performance analysis of turbo codes over fully interleaved Rician fading channels with Middleton's additive white Class-A impulsive noise (MAWCAIN). Simulation results for the memoryless Rician fading channels using coherent BPSK signaling for both the cases of ideal channel state information (ICSI) and no channel state information (NCSI) at the decoder are provided. An eight state turbo encoder having (1, 13/15, 13/15) generator polynomial is used throughout the analysis. The novelty of this work lies in the fact that this is an initial attempt to provide a detailed analysis of turbo codes over Rician fading channels with impulsive noise rather than AWGN. ©2007 IEEE.Item Open Access Robust threshold schemes based on the Chinese remainder theorem(Springer, 2008-06) Kaya, Kamer; Selçuk, Ali AydınRecently, Chinese Remainder Theorem (CRT) based function sharing schemes are proposed in the literature. In this paper, we investigate how a CRT-based threshold scheme can be enhanced with the robustness property. To the best of our knowledge, these are the first robust threshold cryptosystems based on a CRT-based secret sharing. © 2008 Springer-Verlag Berlin Heidelberg.Item Open Access Solution of extremely large integral-equation problems(IEEE, 2007) Ergül, Özgür; Malas, Tahir; Gürel, LeventWe report the solution of extremely large integral-equation problems involving electromagnetic scattering from conducting bodies. By orchestrating diverse activities, such as the multilevel fast multipole algorithm, iterative methods, preconditioning techniques, and parallelization, we are able to solve scattering problems that are discretized with tens of millions of unknowns. Specifically, we report the solution of a closed geometry containing 42 million unknowns and an open geometry containing 20 million unknowns, which are the largest problems of their classes, to the best of our knowledge.