Mühendislik ve Doğa Bilimleri Fakültesi

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Citation Count: 9
VLSI implementation of GRBF (Gaussian Radial Basis Function) networks
(IEEE, 2000) Çevikbaş, I. Can; Öğrenci, Arif Selçuk; Dündar, Günhan; Balkır, Sina
A GRBF network is designed for VLSI implementation. Building blocks of the network consist mainly of analog circuits: op-amp multiplier multiplying DAC (digital to analog converter) floating resistor summer and exponentiator. Parameters of the network (center width of the Gaussian function and output layer weights) are represented digitally for convenient interfacing. It is shown that individual GRBF units allow independent tuning of center width and amplitude. Several network structures are simulated as function approximation examples and the performance is verified to be satisfactory.
Citation Count: 0
A synthesis tool for the multiplierless realization of FIR-based multirate DSP systems
(IEEE, 2000) Yurdakul, Arda
In this study a synthesis tool using a novel multirate folding technique which handles each FIR filter in a multirate DSP system as a single node is developed. A new architecture is presented for the multiplierless realization of a fold of multirate FIR filters. This synthesizer fully exploits the redundancies (i.e. `idle' and `missing' cycles) and common terms in multirate systems without sacrificing from overall system quality to produce multiplierless multirate systems. It also enables the usage of a single clock for all parts of the circuit.
Citation Count: 0
The stability constants of the rare earth complexes with trimetaphosphoric acid
(Soc Chimica Italiana, 2001) Şungur, Şana Kutun
The stability constants of the complexes formed between the rare earth metal ions and the anion of trimetaphosphoric acid have been determined at a temperature of 20 degreesC and an ionic strength of mu =0.1 by the ion-exchange equilibrium method. The investigations indicate that stabilities of complexes increased from La to Lu.The highest and the lowest stability constant values (beta) were found to be 7.76 and 3.82 for Lu3+ and La3+ respectively.
Citation Count: 0
Parameter quantization effects in Gaussian potential function neural networks
(World Scientific and Engineering Academy and Society, 2001) Karakuş, Erkan; Öğrenci, Arif Selçuk; Dündar, Günhan
In hardware implementations of Gaussian Potential Function Neural Networks (GPFNN) deviation from ideal network parameters is inevitable because of the techniques used for parameter storage and implementation of the functions electronically resulting in loss of accuracy. This loss in accuracy can be represented by quantization of the network parameters. In order to predict this effect theoretical approaches are proposed. One-input one-output GPFNN with one hidden layer have been trained as function approximators using the Gradient Descent algorithm. After the training the network parameters (means and standard deviations of the hidden units and the connection weights) are quantized up to 16-bits in order to observe the percentage error on network output stemming from parameter quantization. Simulation results are compared with the predictions of the theoretical approach. Consequently the behaviour of the network output has been given with combined and separate parameter quantizations. Moreover given the allowed percentage error for the network a method is proposed where the minimum number of bits required for quantization of each parameter could be determined based on the theoretical predictions.
Citation Count: 10
Fault-tolerant training of neural networks in the presence of MOS transistor mismatches
(IEEE-INST Electrical Electronics Engineers Inc, 2001) Öğrenci, Arif Selçuk; Dündar, Günhan; Balkır, Sina
Analog techniques are desirable for hardware implementation of neural networks due to their numerous advantages such as small size low power and high speed. However these advantages are often offset by the difficulty in the training of analog neural network circuitry. In particular training of the circuitry by software based on hardware models is impaired by statistical variations in the integrated circuit production process resulting in performance degradation. In this paper a new paradigm of noise injection during training for the reduction of this degradation is presented. The variations at the outputs of analog neural network circuitry are modeled based on the transistor-level mismatches occurring between identically designed transistors Those variations are used as additive noise during training to increase the fault tolerance of the trained neural network. The results of this paradigm are confirmed via numerical experiments and physical measurements and are shown to be superior to the case of adding random noise during training.
Citation Count: 0
Chelate extraction of transition metal ions by ethylene diamine diacetic acid with n-substituted octadecyl groups
(Taylor & Francis Inc, 2002) Bıçak, Niyazi; Şungur, Şana Kutun; Tan, Nükhet; Gazi, Mustafa
An organic-soluble chelating agent NN'-di-n-octadecyl ethylenediamine-NN'-diacetic acid (DOED) has been synthesized in two steps by (i) condensation of dibromoethane with 1-amino octadecane (octadecylamine) and (ii) subsequent reaction with sodium chloro acetate in alcohol-water mixture. The chelating agent in 2-ethylhexanol-cyclohexanol (1:1) solutions shows extremely high chelating ability for Ni(II) Co(II) Cu(II) Fe(111) Cr(III) and Cd(II) ions in neutral aqueous solutions. Extractions take place by the formation of (1:1) ligand-to-metal complexes and extraction coefficients are in the range 0.74-0.99. The ligand can be regenerated almost quantitatively by washing its complexes with 1M HCl and 0.2 M NaOH solutions successively. In each extraction step the organic solution exhibits a clear-cut phase separation and does not need salting out. The chelating agent can be regenerated and recycled more than 24 times without losing its extracting ability due to nonhydrolyzability of linkages in its structure. Experiments indicate that in high metal concentrations (more than 1 M) the solvent mixture itself is able to extract appreciable amounts of metal ions (33-53%). The solubility in organic solvents induced by long aliphatic chains seems to be general and the method presented offers possibility of large scale chelate extraction of metal ions of relatively low concentrations.
Citation Count: 1
Edge detection using steerable filters and CNN
(European Signal Processing Conference EUSIPCO, 2002) Özmen, Atilla; Akman, Emir Tufan
This paper proposes a new approach for edge detection using steerable filters and cellular neural networks (CNNs) where the former yields the local direction of dominant orientation and the latter provides iterative filtering. For this purpose steerable filter coefficients are used in CNN as a B template. The results are compared to the results where only CNN or steerable filters are used. As a result of this study the performance of the system can be improved since iterative filtering property of CNN and the ability of steerable filters for edge detection are used. © 2002 EUSIPCO.
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: 12
Metalization of polymer beads via polymer-supported hydrazines as reducing agents
(John Wiley & Sons Inc, 2002) Bıçak, Niyazi; Şungur, Şana Kutun; Tan, Nükhet; Bensebaa, Farid; Deslandes, Yves
A new method for depositing metal onto a polymer surface has been developed in which the metal coating of polymer beads is performed with hydrazine functions as reducing agents on the surface of the polymer itself. In this study glycidyl methacrylate-methyl methaerylate-divinyl benzene terpolymer was prepared as spherical beads with a suspension polymerization methodology. Beads of the polymer sample (210-420-mum fraction) containing 3.4 mmol g(-1) epoxy were treated with an excess of hydrazinium hydroxide to yield a polymer with 2.3 mmol g(-1) hydrazine functions. The hydrazine functions on the polymer surfaces were efficient in metal reductions. Therefore the modified bead polymer samples when soaked in aqueous ammonia solutions of Ni(II) Ag(I) and Cu(II) ions (0.1 M) were covered rapidly by the corresponding zero-valent metal ions. Metal deposition took place almost quantitatively (ca. 4.5 mmol/g of the polymer) within 60 min of the contact times. The accumulations of metal were followed visually and occurred only on the polymer beads. There was no evidence that the reaction occurred within the solution. (C) 2002 Wiley Periodicals Inc.
Citation Count: 5
A broadband microwave amplifier design by means of immittance based data modelling tool
(IEEE, 2002) Kilinç, Ali; Pinarbaşi, Haci; Şengül, Metin Y.; Yarman, Sıddık Binboğa
In this paper a practical broadband microwave amplifier design algorithm is introduced utilizing the immittance data-modelling tool. In the course of design first the optimum input and output terminations for the active device are produced employing the real frequency technique. Then these terminations are modelled utilizing the new immittance-modelling tool to synthesize the front-end and back-end matching networks. An example is included to exhibit the implementation of the proposed design algorithm to construct a single stage BJT amplifier over a wide frequency band. It is expected that the proposed design algorithm will find applications to realize wideband microwave amplifiers put on MMIC for mobile communication.
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: 5
Zero-crossing based demodulation of minimum shift keying
(2003) Kerestecioğlu, Feza; Kerestecioğlu, Feza
Minimum shift keying (MSK) modulation has features such as constant envelope compact spectrum and good error performance which are all desirable in many digital applications including mobile radio. Numerous receiver structures to demodulate MSK have been suggested such as correlation receivers differential detectors and frequency discriminators MSK is a form of biphase keying and can be detected by a zero-crossing based phase demodulator which gives near optimum performance. In this paper the bit error performance of a zero-crossing based coherent MSK demodulator is theoretically investigated and a closed-form expression for the bit error rate is derived. The results indicate that the demodulator performs within 0.8-1 dB of the theoratical optimum for MSK. Towards the goal of deriving probability of bit error it is also shown that under additive white Gaussian noise (AWGN) zero-crossing locations of MSK signals are Gaussian distributed except at very low signal-to-noise ratios.
Citation Count: 22
Selective liquid-liquid extraction of mercuric ions by octyl methane sulfonamide
(Marcel Dekker Inc, 2003) Bıçak, Niyazi; Sungur, Sana; Gazi, Mustafa; Tan, Nükhet
N-octyl methane sulfonamide (OMSA) has been demonstrated to be a very efficient reagent for selective extraction of Hg(II) ions from aqueous solutions. The extraction bases on rapid reaction of OMSA with Hg(II) ions yielding mono and disulfonamido mercury compounds in ordinary conditions. Solubility of OMSA and its mercury compounds in 2-ethyl hexanol provide a clear-cut phase separation in the extraction. The solution of OMSA in 2-ethyl hexanol (0.4 mol L-1) is able to extract 82.2% of mercuric-acetate (0.4 mol L-1) in non-buffered conditions. Although the process depends on the nature of accompanying anions the distribution coefficient is reasonably high (k(d) greater than or equal to 1.27) even in the presence of chloride ions. The extraction is strictly selective and the presence of Cd(II) Zn(II) Pb(II) do not bring any interference. The extraction system works in moderate concentrations. Extracted mercury in the organic phase can be recovered by back-extraction with concentrated HCl or H2SO4 solutions. After acid treatment the organic solution of OMSA becomes regenerated without losing its activity due to reasonable hydrolytic stability of the sulfonamide linkage and it can be recycled for further extractions.
Citation Count: 0
Design of low-pass ladder networks with mixed lumped and distributed elements by means of artificial neural networks
(AVES YAYINCILIK, 2003) Özmen, Atilla; Özmen, Atilla; Yılmaz, Melek
In this paper, calculation of parameters of low-pass ladder networks with mixed lumped and distributed elements by means of artificial neural networks is given. The results of ANN are compared with the values that are desired. It has been observed that the calculated and the desired values are extremely close to each other. So this algorith can be used to obtain the parameters that will be used to synthesize such circuits.
Citation Count: 2
Active reconfigurable control of a submarine with indirect adaptive control
(2003) Kerestecioğlu, Feza; Kerestecioğlu, Feza
An indirect adaptive controller is designed for submersibles. The design is developed using a linearized MIMO model of a submarine. Standard recursive least squares estimation method is used to estimate the parameters. Depth and pitch angle of the submarine is controlled by means of the well-known indirect self-tuning method. In case of a system fault estimated parameters of the submarine model have been used to update the controller coefficients.
Citation Count: 0
Yönlendirmeli Filtreler Yardımıyla Konya Bölgesi Civarındaki Gömülü Fayların Tespiti
(Doğuş Üniversitesi, 2003) Özmen, Atilla; Uçan, Osman N.; Albora, A. Muhittin
Bu makalede, yönlendirmeli filtreler jeofizik verilerin değerlendirilmesinde kullanılmışlardır. Yönlendirmeli filtreler belirli bir doğrultuda band geçiren filtrelerdir. Yönlendirmeli filtreler de, giriş görüntüsündeki farklı yönlerdeki kenarların elde edilmesi için, görüntü ilk önce farklı yönlere sahip temel filtrelerden geçirilir ve daha sonra yönelim alt bandlarına ayrılır. Bu çalışmada, yönlendirmeli filtrelerin başarımını görebilmek için, çeşitli açılara sahip sentetik datalar ele alınmış ve kenar belirlemesi yapılmıştır. Arazi çalışması olarak, Konya bölgesinin gravite anomali haritasını kullandık. Gömülü durumda bulunan fayların oluşturduğu anomaliler farklı yönler için incelenmiş ve bölgenin oluşturulan fay haritası jeolojik bilgilerle karşılaştırılmıştır.
Citation Count: 0
Sliding mode controller solution for the shallow submerged operation ok a submarine
(IFAC Secretariat, 2003) Kerestecioğlu, Feza; Kerestecioğlu, Feza
In this paper a submarine controller is presented which can accommodate the sea wave effects on a submarine a(shallow water operation. Sliding mode method is implemented in a way that the robustness of the controller increased with respect to disturbance distribution vector in order to perform the depth control of a shallow submerged submarine under sea wave disturbances. Designed controller kept the submarine performance within acceptable limits. Copyright © 2003 IFAC.
Citation Count: 15
A re-configuring sliding-mode controller with a ustable robustness
(Pergamon-Elsevier Science Ltd, 2004) Kerestecioğlu, Feza; Kerestecioğlu, Feza
In this paper a controller design method for underwater vehicles is presented which is based on re-configuration of a sliding-mode controller in case of disturbances caused by shallow water conditions. The disturbance distribution information can be obtained and used to update the corrective gain vector of the sliding-mode controller. This increases the robustness of the controller and hence keeps the system performance within acceptable limits. Proposed method is validated with simulations on a submarine model. (C) 2003 Published by Elsevier Ltd.
Citation Count: 1
An open software architecture of neural networks: Neurosoft
(2004) Arsan, Taner; Arsan, Taner; Saydam, Tuncay
Software architecture of generic distributed neural networks and its relevant information model have been developed. Principles of on-line architecture building training controlling (managing) and topological optimization guidelines are provided and extensively discussed.
Citation Count: 12
Optimal input design for the detection of changes towards unknown hypotheses
(Taylor & Francis Ltd, 2004) Kerestecioğlu, Feza; Cetin, I
The effects of auxiliary input signals on detecting changes in ARMAX processes via statistical tests are discussed. Two extensions to the Cumulative Sum Test are considered. The first is applicable when the direction of the change in the parameter space is known but its magnitude is unknown. The second is applicable when neither is known. The performance criteria for the design of stationary stochastic inputs are based on the asymptotic properties of the tests. It is shown that power-constrained optimal inputs have discrete spectra and a suitably chosen input can greatly improve the detection performance.

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