Bilgisayar Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://gcris.khas.edu.tr/handle/20.500.12469/45

Browse

Now showing 1 - 20 of 25

Citation Count: 0
Amplitude and Frequency Modulations with Cellular Neural Networks
(Springer, 2015) Tander, Baran; Özmen, Atilla
Amplitude and frequency modulations are still the most popular modulation techniques in data transmission at telecommunication systems such as radio and television broadcasting gsm etc. However the architectures of these individual systems are totally different. In this paper it is shown that a cellular neural network with an opposite-sign template can behave either as an amplitude or a frequency modulator. Firstly a brief information about these networks is given and then the amplitude and frequency surfaces of the generated quasi-sine oscillations are sketched with respect to various values of their cloning templates. Secondly it is proved that any of these types of modulations can be performed by only varying the template components without ever changing their structure. Finally a circuit is designed simulations are presented and performance of the proposed system is evaluated. The main contribution of this work is to show that both amplitude and frequency modulations can be realized under the same architecture with a simple technique specifically by treating the input signals as template components.
Citation Count: 5
Biclustering Expression Data Based on Expanding Localized Substructures
(Springer-Verlag Berlin, 2009) Erten, Cesim; Sözdinler, Melih
Biclustering gene expression data is the problem of extracting submatrices of genes and conditions exhibiting significant correlation across both the rows and the columns of a data matrix of expression values. We provide a method LEB (Localize-and-Extract Biclusters) which reduces the search space into local neighborhoods within the matrix by first localizing correlated structures. The localization procedure takes its roots from effective use of graph-theoretical methods applied to problems exhibiting a similar structure to that of biclustering. Once interesting structures are localized the search space reduces to small neighborhoods and the biclusters are extracted from these localities. We evaluate the effectiveness of our method with extensive experiments both using artificial and real datasets.
Citation Count: 4
Channel Estimation for Realistic Indoor Optical Wireless Communication in ACO-OFDM Systems
(Springer, 2018) Özmen, Atilla; Şenol, Habib
In this paper channel estimation problem in a visible light communication system is considered. The information data is transmitted using asymmetrical clipped optical orthogonal frequency division multiplexing. Channel estimation and symbol detection are performed by the Maximum Likelihood and the Linear Minimum Mean Square Error detection techniques respectively. The system performance is investigated in realistic environment that is simulated using an indoor channel model. Two different channels are produced using the indoor channel model. Symbol error rate (SER) performance of the system with estimated channels is presented for QPSK and 16-QAM digital modulation types and compared with the perfect channel state information. As a mean square error (MSE) performance benchmark for the channel estimator Cramer-Rao lower bound is also derived. MSE and SER performances of the simulation results are presented.
Citation Count: 10
Contraction and deletion blockers for perfect graphs and H-free graphs
(Elsevier Science, 2018) Diner, Öznur Yaşar; Paulusma, Daniel; Picouleau, Christophe; Ries, Bernard
We study the following problem: for given integers d k and graph G can we reduce some fixed graph parameter pi of G by at least d via at most k graph operations from some fixed set S? As parameters we take the chromatic number chi clique number omega and independence number alpha and as operations we choose edge contraction ec and vertex deletion vd. We determine the complexity of this problem for S = {ec} and S = {vd} and pi is an element of{chi omega alpha} for a number of subclasses of perfect graphs. We use these results to determine the complexity of the problem for S = {ec} and S = {vd} and pi is an element of{chi omega alpha} restricted to H-free graphs. (C) 2018 Elsevier B.V. All rights reserved.
Citation Count: 9
Contraction Blockers for Graphs with Forbidden Induced Paths
(Springer-Verlag Berlin, 2015) Diner, Öznur Yaşar; Paulusma, Daniel; Picouleau, Christophe; Ries, Bernard
We consider the following problem: can a certain graph parameter of some given graph be reduced by at least d for some integer d via at most k edge contractions for some given integer k? We examine three graph parameters: the chromatic number clique number and independence number. For each of these graph parameters we show that when d is part of the input this problem is polynomial-time solvable on P-4-free graphs and NP-complete as well as W[1]-hard with parameter d for split graphs. As split graphs form a subclass of P-5-free graphs both results together give a complete complexity classification for P-l-free graphs. The W[1]-hardness result implies that it is unlikely that the problem is fixed-parameter tractable for split graphs with parameter d. But we do show on the positive side that the problem is polynomial-time solvable for each parameter on split graphs if d is fixed i.e. not part of the input. We also initiate a study into other subclasses of perfect graphs namely cobipartite graphs and interval graphs.
Citation Count: 2
Cosmic ray intensity variation during a CME
(Pergamon-Elsevier Science Ltd, 2002) Kandemir, Gulcın; Geçkinli, Melih; Fırat, Coşkun; Yılmaz, Melek; Özuğur, B
The June 6 2000 coronal mass ejection was an exceptional full halo which made it possible to measure cosmic ray (CR) decrease with a simple experimental set-up. Variation in the local secondary cosmic ray density has been investigated by means of gamma rays. The experiment site was located in Istanbul (41.1N 29.0E). CR electrons and slow gamma rays have been eliminated. The CR density has dropped drastically starting on June 8 2000. The counts have been compared with the pre-shock levels and some other cases of CMEs. During strong solar modulation the local counts of secondary CR intensity values dropped down as much as 24%. (C) 2002 Elsevier Science Ltd. All rights reserved.
Citation Count: 11
Derivation of the optical constants of spin coated CeO2-TiO2-ZrO2 thin films prepared by sol-gel route
(Pergamon-Elsevier Science Ltd, 2011) Ghodsi, Farhad E.; Tepehan, Fatma Zehra; Tepehan, Galip Gültekin
Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate ce(NO3)(6)(NH4)(2) titanium butoxide Ti[O(CH2)(3)CH3](4) and zirconium propoxide Zr(OCH2CH2CH3)(4) were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO2-TiO2-ZrO2 gel to study the decomposition and phase transition of the gel. For molecular structural elemental and morphological characterization of the films Fourier Transform Infrared (FTIR) spectral analysis X-ray diffraction (XRD) energy dispersive X-ray spectroscopy (EDS) cross-sectional scanning electron microscopy (SEM) and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index extinction coefficient band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index extinction coefficient and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E-g approximate to 2.82 +/- 0.04 eV for indirect transition. (C) 2011 Published by Elsevier Ltd.
Citation Count: 2
Developing adaptive multi-device applications with the Heterogeneous Programming Library
(Springer, 2015) Bozkuş, Zeki; Bozkuş, Zeki; Fraguela, Basilio B.; Andrade, Diego; Doallo, Ramon
The usage of heterogeneous devices presents two main problems. One is their complex programming a problem that grows when multiple devices are used. The second issue is that even if the codes for these devices can be portable on top of OpenCL they lack performance portability effectively requiring specialized implementations for each device to get good performance. In this paper we extend the Heterogeneous Programming Library (HPL) which improves the usability of heterogeneous systems on top of OpenCL to better handle both issues. First we provide HPL with mechanisms to support the implementation of any multi-device application that requires arbitrary patterns of communication between several devices and a host memory. In a second stage HPL is improved with an adaptive scheme to optimize communications between devices depending on the execution environment. An evaluation using benchmarks with very different nature shows that HPL reduces the SLOCs and programming effort of OpenCL applications by 27 and 43 % respectively while improving the performance of applications that exchange data between devices by 28 % on average.
Citation Count: 1
A framework for combined recognition of actions and objects
(Springer-Verlag Berlin, 2012) Ar, İlktan; Akgül, Yusuf Sinan
This paper proposes a novel approach to recognize actions and objects within the context of each other. Assuming that the different actions involve different objects in image sequences and there is one-to-one relation between object and action type we present a Bayesian network based framework which combines motion patterns and object usage information to recognize actions/objects. More specifically our approach recognizes high-level actions and the related objects without any body-part segmentation hand tracking and temporal segmentation methods. Additionally we present a novel motion representation based on 3D Haar-like features which can be formed by depth color or both images. Our approach is also appropriate for object and action recognition where the involved object is partially or fully occluded. Finally experiments show that our approach improves the accuracy of both action and object recognition significantly.
Citation Count: 1
Fully Decentralized and Collaborative Multilateration Primitives for Uniquely Localizing WSNs
(Springer International Publishing Ag, 2010) Erten, Cesim; Erten, Cesim
We provide primitives for uniquely localizing WSN nodes. The goal is to maximize the number of uniquely localized nodes assuming a fully decentralized model of computation. Each node constructs a cluster of its own and applies unique localization primitives on it. These primitives are based on constructing a special order for multilaterating the nodes within the cluster. The proposed primitives are fully collaborative and thus the number of iterations required to compute the localization is fewer than that of the conventional iterative multilateration approaches. This further limits the messaging requirements. With relatively small clusters and iteration counts we can localize almost all the uniquely localizable nodes.
Citation Count: 0
Fully decentralized, collaborative multilateration primitives for uniquely localizing WSNs
(Springer, 2009) Erten, Cesim; Erten, Cesim
We provide primitives for uniquely localizing WSN nodes. The goal is to maximize the number of uniquely localized nodes assuming a fully decentralized model of computation. Each node constructs a cluster of its own and applies unique localization primitives on it. These primitives are based on constructing a special order for multilaterating the nodes within the cluster. The proposed primitives are fully collaborative and thus the number of iterations required to compute the localization is fewer than that of the conventional iterative multilateration approaches. This further limits the messaging requirements. With relatively small clusters and iteration counts we can localize almost all the uniquely localizable nodes. © 2009 Springer Berlin Heidelberg.
Citation Count: 5
GPU Accelerated Molecular Docking Simulation with Genetic Algorithms
(Springer International Publishing Ag, 2016) Bozkuş, Zeki; Bozkuş, Zeki; Fraguela, Basilio B.
Receptor-Ligand Molecular Docking is a very computationally expensive process used to predict possible drug candidates for many diseases. A faster docking technique would help life scientists to discover better therapeutics with less effort and time. The requirement of long execution times may mean using a less accurate evaluation of drug candidates potentially increasing the number of false-positive solutions which require expensive chemical and biological procedures to be discarded. Thus the development of fast and accurate enough docking algorithms greatly reduces wasted drug development resources helping life scientists discover better therapeutics with less effort and time. In this article we present the GPU-based acceleration of our recently developed molecular docking code. We focus on offloading the most computationally intensive part of any docking simulation which is the genetic algorithm to accelerators as it is very well suited to them. We show how the main functions of the genetic algorithm can be mapped to the GPU. The GPU-accelerated system achieves a speedup of around similar to 14x with respect to a single CPU core. This makes it very productive to use GPU for small molecule docking cases.
Citation Count: 5
Information theoretical performance limits of single-carrier underwater acoustic systems
(Inst Engineering Technology-IET, 2014) Şenol, Habib; Uysal, Murat; Panayırcı, Erdal; Şenol, Habib
In this study the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number location and power delay profile of significant taps as well as environmental parameters such as distance temperature salinity pressure and depth. Then the authors use this expression to determine the optimal carrier frequency input signalling and bandwidth for capacity maximisation.
Citation Count: 14
Joint Channel Estimation and Symbol Detection for OFDM Systems in Rapidly Time-Varying Sparse Multipath Channels
(Springer, 2015) Şenol, Habib
In this paper we propose a space-alternating generalized expectation maximization (SAGE) based joint channel estimation and data detection algorithm in compressive sensing (CS) framework for orthogonal frequency-division multiplexing (OFDM) systems in rapidly time-varying sparse multipath channels. Using dynamic parametric channel model the sparse multipath channel is parameterized by a small number of distinct paths each represented by the path delays and path gains. In our model we assume that the path gains rapidly vary within the OFDM symbol duration while the number of paths and path delays vary symbol by symbol. Since the convergency of the SAGE algorithm needs statistically independent parameter set of interest to be estimated we specifically choose the discrete orthonormal Karhunen-Loeve basis expansion model (DKL-BEM) to provide statistically independent BEM coefficients within one OFDM symbol duration and use just a few significant BEM coefficients to represent the rapidly time-varying path gains. The resulting SAGE algorithm that also incorporates inter-channel interference cancellation updates the data sequences and the channel parameters serially. The computer simulations show that our proposed algorithm has better channel estimation and symbol error rate performance than that of the orthogonal matching pursuit algorithm that is commonly proposed in the CS literature.
Citation Count: 2
Linear expansions for frequency selective channels in OFDM
(Elsevier GMBH Urban & Fischer Verlag, 2006) Şenol, Hande; Çırpan, Hakan Ali; Panayırcı, Erdal
Modeling the frequency selective fading channels as random processes we employ a linear expansion based on the Karhumen-Loeve (KL) series representation involving a complete set of orthogonal deterministic vectors with a corresponding uncorrelated random coefficients. Focusing on OFDM transmissions through frequency selective fading this paper pursues a computationally efficient pilot-aided linear minimum mean square error (MMSE) uncorrelated KL series expansion coefficients estimation algorithm. Based on such an expansion no matrix inversion is required in the proposed MMSE estimator. Moreover truncation in the linear expansion of channel is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We first exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also provide performance analysis results studying the influence of the effect of SNR and correlation mismatch on the estimator performance. Simulation results confirm our theoretical results and illustrate that the proposed algorithm is capable of tracking fast fading and improving performance. (c) 2005 Elsevier GmbH. All rights reserved.
Citation Count: 0
Machine Learning Approaches for Predicting Protein Complex Similarity
(Mary Ann Liebert Inc Publ, 2017) Farhoodi, Roshanak; Akbal-Delibas, Bahar; Haspel, Nurit
Discriminating native-like structures from false positives with high accuracy is one of the biggest challenges in protein-protein docking. While there is an agreement on the existence of a relationship between various favorable intermolecular interactions (e.g. Van der Waals electrostatic and desolvation forces) and the similarity of a conformation to its native structure the precise nature of this relationship is not known. Existing protein-protein docking methods typically formulate this relationship as a weighted sum of selected terms and calibrate their weights by using a training set to evaluate and rank candidate complexes. Despite improvements in the predictive power of recent docking methods producing a large number of false positives by even state-of-the-art methods often leads to failure in predicting the correct binding of many complexes. With the aid of machine learning methods we tested several approaches that not only rank candidate structures relative to each other but also predict how similar each candidate is to the native conformation. We trained a two-layer neural network a multilayer neural network and a network of Restricted Boltzmann Machines against extensive data sets of unbound complexes generated by RosettaDock and PyDock. We validated these methods with a set of refinement candidate structures. We were able to predict the root mean squared deviations (RMSDs) of protein complexes with a very small often less than 1.5 angstrom error margin when trained with structures that have RMSD values of up to 7 angstrom. In our most recent experiments with the protein samples having RMSD values up to 27 angstrom the average prediction error was still relatively small attesting to the potential of our approach in predicting the correct binding of protein-protein complexes.
Citation Count: 9
Navigation of non-communicating autonomous mobile robots with guaranteed connectivity
(Cambridge Univ Press, 2013) Kerestecioğlu, Feza; Kerestecioğlu, Feza
We consider the connectivity of autonomous mobile robots. The robots navigate using simple local steering rules without requiring explicit communication among themselves. We show that using only position information of neighbors the group connectivity can be sustained even in the case of bounded position measurement errors and the occlusion of robots by other robots in the group. In implementing the proposed scheme sub-optimal solutions are invoked to avoid an excessive computational burden. We also discuss the possibility of deadlock which may bring the group to a standstill and show that the proposed methodology avoids such a scenario in real-life settings.
Citation Count: 2
Nonuniform sampling for detection of abrupt changes
(Birkhauser Boston Inc, 2003) Kerestecioğlu, Feza; Tokat, Sezai
In this work detection of abrupt changes in continuous-time linear stochastic systems and selection of the sampling interval to improve the detection performance are considered. Cost functions are proposed to optimize both uniform and nonuniform sampling intervals for the well-known cumulative sum algorithm. Some iterative techniques are presented to make online optimization computationally feasible. It is shown that considerable improvement in the detection performance can be obtained by using nonuniform sampling intervals.
Citation Count: 11
Peer-to-peer live video streaming with rateless codes for massively multiplayer online games
(Springer, 2018) Büyükkaya, Eliya; Bouras, Christos; Büyükkaya, Eliya; Dawood, Muneeb; Hamzaoui, Raouf; Kapoulas, Vaggelis; Papazois, Andreas; Simon, Gwendal
We present a multi-level multi-overlay hybrid peer-to-peer live video system that enables players of Massively Multiplayer Online Games to simultaneously stream the video of their game and watch the game videos of other players. Each live video bitstream is encoded with rateless codes and multiple trees are used to transmit the encoded symbols. Trees are constructed dynamically with the aim to minimize the transmission rate at the source while maximizing the number of served peers and guaranteeing on-time delivery and reliability. ns-2 simulations and real measurements on the Internet show competitive performance in terms of start-up delay playback lag rejection rate used bandwidth continuity index and video quality.
Citation Count: 22
A review on the recent energy-efficient approaches for the Internet protocol stack
(Springeropen, 2015) Dağ, Tamer; Dağ, Tamer
The reduction of energy consumption has become a key research area for the information and communication technology (ICT) industry due to economical environmental and marketing reasons. While the environmental direction aims at minimization of greenhouse gas emissions by enforcing the usage of renewable energy in the ICT industry economical and marketing directions lead researchers to design low-power components or develop and enhance energy-saving protocols without an impact on the level of the performance. With the steady increase in the cost of energy the expanding number of energy-hungry components and widespread usage of ICT industry most of the protocols that have become an integral part of our lives but are yet developed without any energy constraints in mind in the past will need to be restructured or developed again. For this reason researchers are studying on all layers of the Internet protocol stack to develop energy-efficient protocols and algorithms. This paper reviews recent approaches for energy efficiency studies for each layer in the Internet protocol stack from the physical layer to the application layer. It is expected that with the deployment of current research output the studies performed at each layer will result in significant energy savings for the ICT industry which in turn will have a positive impact on our lives for their economical and environmental results.

Browse

Browsing Bilgisayar Mühendisliği Bölümü Koleksiyonu by Scopus Q "Q2"