Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Article Citation - WoS: 4Citation - Scopus: 5Beyond Trans-Dimensional Rjmcmc With a Case Study in Impulsive Data Modeling(Elsevier Ltd., 2018) Karakuş, Oktay; Kuruoğlu, Ercan Engin; Altınkaya, Mustafa AzizReversible jump Markov chain Monte Carlo (RJMCMC) is a Bayesian model estimation method, which has been generally used for trans-dimensional sampling and model order selection studies in the literature. In this study, we draw attention to unexplored potentials of RJMCMC beyond trans-dimensional sampling. the proposed usage, which we call trans-space RJMCMC exploits the original formulation to explore spaces of different classes or structures. This provides flexibility in using different types of candidate classes in the combined model space such as spaces of linear and nonlinear models or of various distribution families. As an application, we looked into a special case of trans-space sampling, namely trans-distributional RJMCMC in impulsive data modeling. In many areas such as seismology, radar, image, using Gaussian models is a common practice due to analytical ease. However, many noise processes do not follow a Gaussian character and generally exhibit events too impulsive to be successfully described by the Gaussian model. We test the proposed usage of RJMCMC to choose between various impulsive distribution families to model both synthetically generated noise processes and real-life measurements on power line communications impulsive noises and 2-D discrete wavelet transform coefficients.Article Citation - WoS: 11Citation - Scopus: 10Bayesian Volterra System Identification Using Reversible Jump Mcmc Algorithm(Elsevier Ltd., 2017) Karakuş, Oktay; Kuruoğlu, Ercan Engin; Altınkaya, Mustafa AzizVolterra systems have had significant success in modelling nonlinear systems in various real-world applications. However, it is generally assumed that the nonlinearity degree of the system is known beforehand. In this paper, we contribute to the literature on Volterra system identification (VSI) with a numerical Bayesian approach which identifies model coefficients and the nonlinearity degree concurrently. Although this numerical Bayesian method, namely reversible jump Markov chain Monte Carlo (RJMCMC) algorithm has been used with success in various model selection problems, our use is in a novel context in the sense that both memory size and nonlinearity degree are estimated. The aforementioned study ensures an anomalous approach to RJMCMC and provides a new understanding on its flexible use which enables trans-structural transitions between different classes of models in addition to transdimensional transitions for which it is classically used. We study the performance of the method on synthetically generated data including OFDM communications over a nonlinear channel.Article Citation - WoS: 14Citation - Scopus: 15Compensating of Added Mass Terms in Dynamically Positioned Surface Vehicles: a Continuous Robust Control Approach(Elsevier Ltd., 2017) Bıdıklı, Barış; Tatlıcıoğlu, Enver; Zergeroğlu, ErkanIn this work, we provide a tracking controller formulation for dynamically positioned surface vessels with an asymmetric added mass terms that affects the overall system dynamics at the acceleration level. Specifically a novel continuous robust controller is proposed for surface vessels that in addition to unstructured uncertainties in its dynamics, contains added mass effects in its inertia matrix. The proposed controller compensates the overall system uncertainties while ensuring asymptotic tracking by utilizing the knowledge of the leading principal minors of the input gain matrix. Stability of the closed–loop system and asymptotic convergence are proven via Lyapunov based approaches. Simulation studies are also presented to illustrate the viability of the proposed methodArticle Citation - WoS: 19Citation - Scopus: 20Numerical Analysis of a Near-Room Magnetic Cooling System(Elsevier Ltd., 2017) Ezan, Mehmet Akif; Ekren, Orhan; Metin, Çağrı; Yılancı, Ahmet; Bıyık, Emrah; Kara, Salih MuratIn this study, for a near-room-temperature magnetic cooling system, a decoupled multi-physics numerical approach (Magnetism, Fluid Flow, and Heat Transfer) is developed using a commercial CFD solver, ANSYS-FLUENT, as a design tool. User defined functions are incorporated into the software in order to take into account the magnetocaloric effect. Magnetic flux density is assumed to be linear during the magnetization and demagnetization processes. Furthermore, the minimum and maximum magnetic flux densities (Bmin and Bmax) are defined as 0.27 and 0.98, respectively. Two different sets of analyses are conducted by assuming an insulated cold heat exchanger (CHEX) and by defining an artificial cooling load in the CHEX. As a validation case, experimental work from the literature is reproduced numerically, and the results show that the current methodology is fairly accurate. Moreover, parametric analyses are conducted to investigate the effect of the velocity of heat transfer fluid (HTF) and types of HTF on the performance of the magnetic cooling system. Also, the performance metrics of the magnetic cooling system are investigated with regards to the temperature span of the magnetic cooling unit, and the cooling load. It is concluded that reducing the cycle duration ensures reaching lower temperature values. Similarly, reducing the velocity of the HTF allows reducing the outlet temperature of the HTF. In the current system, the highest temperature spans are obtained numerically as around 6 K, 5.2 K and 4.1 K for the cycle durations of 4.2 s, 6.2 s and 8.2 s, respectively.Article Citation - WoS: 30Citation - Scopus: 35Robust Dynamic Positioning of Surface Vessels Via Multiple Unidirectional Tugboats(Elsevier Ltd., 2016) Bıdıklı, Barış; Tatlıcıoğlu, Enver; Zergeroğlu, ErkanIn this paper, the problem of accurate positioning of an unactuated surface vessel by using multiple uni-directional tugboats is investigated. Specifically a robust controller that ensures asymptotic position tracking is designed. The control design procedure is implemented in two steps: Initially by locating opposing tugboats to specific configurations, the overall problem is transformed into a second order system with an uncertain non-symmetric input gain matrix. Then via a matrix decomposition, a novel robust controller methodology is proposed. The stability of the overall system is ensured via rigorous stability analysis where asymptotic position tracking is ensured. Numerical simulation results are presented to demonstrate the efficiency of the proposed controller.Article Citation - WoS: 1Citation - Scopus: 2Joint Effect of Data Rate and Routing Strategy on Energy-Efficiency of Ieee 802.11 Dcf Based Multi-Hop Wireless Networks Under Hidden Terminal Existence(Elsevier Ltd., 2015) Aydoğdu, Canan; Sancaklı, SibelWe investigate the joint effect of data rate and routing strategy on energy-efficiency of multi-hop wireless networks incorporating a comprehensive behavior of the IEEE 802.11 DCF under the presence of hidden terminals. Two basic routing strategies, direct transmission versus multi-hop routing, are considered over a large range of traffic loads. The goal of this study is to layout guidelines for a cross-layer energy-efficient rate adaptation algorithm, which takes medium access control and network layer dynamics into account together with the hidden terminal effect. Our results show that, for the low-power wireless IEEE 802.11g standard considered in this article, the highest data rate consumes the least power in multi-hop wireless networks when hidden terminals mostly constitute the reason of collisions. In case of channel impairments, adapting the rate jointly with the routing strategy can save the energy consumed per bit by up to 250% under moderate traffic loads and much more under heavy traffic loads. © 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3Inhomogeneity Reconstructions in Tendon Ducts Via Boundary Integral Equations(Elsevier Ltd., 2014) Yaman, Fatih; Weiland, Thomas W.In this study, as an alternative to the formerly presented investigations, Newton-type numerical algorithms are proposed to find location and shape of an air void inside of a tendon duct and to identify gathered metallic bars in a concrete column. The simulated structures are illuminated by four acoustic sources at a fixed frequency such that the scattered field is measured in a near-field region at 128 points. According to the nature of physical problems, the Dirichlet boundary condition is employed to model air-filled cavities and transmission conditions are assumed for metallic objects. Additionally, conductive boundary conditions are suggested for a more realistic representation of the inhomogeneities for the rusty metallic skin of the duct. Potential approaches are used to derive boundary integral equations. The proper treatment of the ill-conditioned equations is established via Tikhonov regularization. Applicability of the proposed inversion algorithms is tested with realistic parameters for different scenarios using noisy scattered field data and accurate numerical results are presented at 10 kHz for the unknown physical properties of the duct's skin.Article Citation - WoS: 2Citation - Scopus: 4Constraint Removal for Sparse Signal Recovery(Elsevier Ltd., 2012) Şahin, Ahmet; Özen, SerdarThis paper presents a new iterative algorithm called constraint removal (CR) for the recovery of a sparse signal x from an incomplete number of linear measurements y such that ym× 1= Am× nxn× 1 and m<n. It is empirically demonstrated that the CR algorithm has a recovery performance which is between basis pursuit linear programming (BP-LP) and subspace pursuit (SP) for both zero-one and Gaussian type signals.Article Citation - WoS: 86Citation - Scopus: 101A Comparative Study of Glottal Source Estimation Techniques(Elsevier Ltd., 2012) Drugman, Thomas; Bozkurt, Barış; Dutoit, ThierryAbstract: Source-tract decomposition (or glottal flow estimation) is one of the basic problems of speech processing. For this, several techniques have been proposed in the literature. However, studies comparing different approaches are almost nonexistent. Besides, experiments have been systematically performed either on synthetic speech or on sustained vowels. In this study we compare three of the main representative state-of-the-art methods of glottal flow estimation: closed-phase inverse filtering, iterative and adaptive inverse filtering, and mixed-phase decomposition. These techniques are first submitted to an objective assessment test on synthetic speech signals. Their sensitivity to various factors affecting the estimation quality, as well as their robustness to noise are studied. In a second experiment, their ability to label voice quality (tensed, modal, soft) is studied on a large corpus of real connected speech. It is shown that changes of voice quality are reflected by significant modifications in glottal feature distributions. Techniques based on the mixed-phase decomposition and on a closed-phase inverse filtering process turn out to give the best results on both clean synthetic and real speech signals. On the other hand, iterative and adaptive inverse filtering is recommended in noisy environments for its high robustness. © 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 26Computerized Method for Nonrigid Mr-To Breast-Image Registration(Elsevier Ltd., 2010) Ünlü, Mehmet Zübeyir; Krol, A.; Magri, A.; Mandel, J. A.; Lee, W.; Baum, K. G.; Lipson, E. D.; Coman, I. L.; Feiglin, D. H.We have developed and tested a new simple computerized finite element method (FEM) approach to MR-to-PET nonrigid breast-image registration. The method requires five-nine fiducial skin markers (FSMs) visible in MRI and PET that need to be located in the same spots on the breast and two on the flanks during both scans. Patients need to be similarly positioned prone during MRI and PET scans. This is accomplished by means of a low gamma-ray attenuation breast coil replica used as the breast support during the PET scan. We demonstrate that, under such conditions, the observed FSM displacement vectors between MR and PET images, distributed piecewise linearly over the breast volume, produce a deformed FEM mesh that reasonably approximates nonrigid deformation of the breast tissue between the MRI and PET scans. This method, which does not require a biomechanical breast tissue model, is robust and fast. Contrary to other approaches utilizing voxel intensity-based similarity measures or surface matching, our method works for matching MR with pure molecular images (i.e. PET or SPECT only). Our method does not require a good initialization and would not be trapped by local minima during registration process. All processing including FSMs detection and matching, and mesh generation can be fully automated. We tested our method on MR and PET breast images acquired for 15 subjects. The procedure yielded good quality images with an average target registration error below 4 mm (i.e. well below PET spatial resolution of 6-7 mm). Based on the results obtained for 15 subjects studied to date, we conclude that this is a very fast and a well-performing method for MR-to-PET breast-image nonrigid registration. Therefore, it is a promising approach in clinical practice. This method can be easily applied to nonrigid registration of MRI or CT of any type of soft-tissue images to their molecular counterparts such as obtained using PET and SPECT. © 2009 Elsevier Ltd. All rights reserved.