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Publication Metadata only EPR study of the structural phase transitions in Fe3+ doped TlInS2(WILEY-V C H VERLAG GMBH, 2006) Mikailov, F. A.; Kazan, S.; Rameev, B. Z.; Acikgoz, M.; Aktas, B.; Gebze Technical University; Azerbaijan National Academy of Sciences (ANAS); Institute of Physics of the Azerbaijan National Academy of Sciences; Russian Academy of Sciences; Kazan Scientific Centre of the Russian Academy of Sciences; Zavoisky Physical-Technical Institute; Bahcesehir UniversityThe results of low temperature EPR investigations of Fe doped TlInS2 single crystals in the temperature range 5-300 K are presented. The EPR signal due to Fe3+ centers located at the centers of InS4 tetrahedrons has been observed. It has been established that the resonance lines exhibit a slight shift and remarkable splitting at the temperatures lower than 200 K, which is attributed to the effect of the ferroelectric phase transition. The rotational patterns of the resonance fields reveal a doubling of the number of centers at low temperatures. The preliminary simulation indicates that the doubling is related to the rotation of the principal axis system of the centers, while the magnitude of fine structure splitting is nearly the same. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Publication Metadata only Sol-gel insulation coatings on Monel/Fe/MgB2 wires for coil development(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008) Arda, L.; Boyraz, C.; Sacli, O. A.; Tomsic, M.; Hascicek, Y. S.; Bahcesehir University; Marmara University; State University System of Florida; Florida State UniversityIn this study, preparation, structure, morphology and thermal properties of ceramic insulation coating on Monel/Fe/MgB2 wires, which were fabricated by Hyper Tech Research Inc., using Continuous Tube Forming and Filling (CTFF) process were studied for coil development. Ceramic insulation coatings were prepared by reel-to-reel sol-gel method using solutions of Y and Zr based organometallic compounds. The coating thickness was controlled by number of coating, withdrawal speed and solution chemistry. 29 meter of Monel/Fe/MgB2 wire was insulated by Y2O3-ZrO2 using sol-gel method. Monel/Fe/MgB2 coil was layer wounded and impregnated with stycast. Sister samples of coil were tested between 4.2 K and 30 K with a Variable Temperature Insert (VTI) in a 20 T superconducting magnet using the analog DC pulse four-wire method with 1 (mu V/cm) criterion. The sample had a J(c) of 0.16 x 10(5) (A/cm(2)) at 4 T at 21 K. The surface morphologies and microstructure of sister samples of coil were characterized by ESEM, EDS, DTA, TGA and XRD. Resistance was measured by using HP 4339A High Resistance Meter.Publication Metadata only Channel estimation and adaptive M-QAM in cognitive radio links(IEEE, 2008) Soysal, Alkan; Ulukus, Sennur; Clancy, Charles; Bahcesehir University; University System of Maryland; University of Maryland College Park; United States Department of DefenseCognitive radios have the ability to sense their RF environment and adapt their transmission parameters to perform optimally in any situation. Part of this involves selecting the best modulation type for a particular channel. In this paper we consider a variable-rate, variable-power, adaptive, M-ary Quadrature Amplitude Modulation (M-QAM) scheme in a single-user communication scenario. The channel between the transmitter and receiver is assumed to be a Rayleigh block-fading channel. Each block is divided into training and data phases. During the training phase, the receiver estimates the channel and feeds the estimate back to the transmitter. During the data phase, the transmitter sends its message by adapting the size of the M-QAM constellation. We first find a closed-form expression that relates the Bit Error Rate (BER) to the constellation size of the M-QAM, and therefore to the data rate of our system. Then, for a given target BER, we maximize the data rate over the training parameters, which are the training signal, the training duration, and the training power. When these optimum parameters are used in a MATLAB implementation, we find that the target BER is matched to within an order of magnitude, and the resulting data rate is close to the theoretical limit.Publication Metadata only MIMO Multiple Access Channels with Noisy Channel Estimation and Partial CSI Feedback(IEEE, 2008) Soysal, Alkan; Ulukus, Sennur; Bahcesehir University; University System of Maryland; University of Maryland College ParkWe consider correlated MIMO multiple access channels with block fading, where each block is divided into training and data transmission phases. We find the channel estimation and data transmission parameters that jointly optimize the achievable data rate of the system. Our results for the training phase are particularly interesting, where we show that the optimum training signals of the users should be non-overlapping in time. For the data transmission phase, we propose an iterative algorithm that updates the parameters of the users in a round-robin fashion. In particular, the algorithm updates the training and data transmission parameters of a user, when those of the rest of the users are fixed, in a way to maximize the achievable sum-rate in a multiple access channel, and iterates over users in a round-robin fashion.Publication Metadata only Optimizing the rate of a correlated MIMO link jointly over channel estimation and data transmission parameters(IEEE, 2008) Soysal, Alkan; Ulukus, Sennur; Bahcesehir University; University System of Maryland; University of Maryland College ParkWe consider a single-user correlated MIMO channel with block fading, where each block is divided into training and data transmission phases. The receiver has a noisy CSI that it obtains through a channel estimation process, while the transmitter has partial CSI in the form of covariance feedback. We optimize the achievable rate jointly over the parameters of the training and data transmission phases. In particular, we first choose the training signal to minimize the channel estimation error, and then, develop an iterative algorithm to solve for the optimum training duration, the optimum allocation of power between training and data transmission phases, and the optimum allocation of power over the antennas during the data transmission phase.Publication Metadata only Adjustable-Speed Drive Bearing-Fault Detection Via Wavelet Packet Decomposition(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009) Teotrakool, Kaptan; Devaney, Michael J.; Eren, Levent; University of Missouri System; University of Missouri Columbia; Bahcesehir UniversityAdjustable-speed drives perform many vital control functions in the industry, serving in such diverse applications as rolling mills, variable-speed compressors, fans, and pumps. When an adjustable-speed drive fails due to a bearing failure, it is usually catastrophic. Bearing defects introduce vibration anomalies that alter the current characteristic frequencies. This paper addresses the application of motor current signature analysis using wavelet packet decomposition to detect bearing faults in adjustable-speed drives.Publication Metadata only Bearing fault detection via wavelet packet decomposition with spectral post processing(IEEE, 2007) Eren, Levent; Teotrakool, Kaptan; Devaney, Michael J.; Bahcesehir University; University of Missouri System; University of Missouri ColumbiaWe present a method for detecting motor bearing fault conditions via wavelet packet decomposition (WPD) of induction motor current. This method involves the decomposition of motor current into equally spaced frequency bands by using all pass implementation of Elliptic IIR half-band filters in the filter bank structure to obtain wavelet packet coefficients (WPC). Then, the bias in WPCs for each frequency band is removed to suppress leakage from adjacent frequency bands. Fourier analysis is applied to wavelet packet coefficients to provide higher frequency resolution within each frequency band. The changes in the energy levels of frequency bands in which motor fault related current frequencies lie are monitored to detect motor fault conditions.Publication Metadata only Hyper-Spectral Image Segmentation Using Spectral Clustering With Covariance Descriptors(SPIE-INT SOC OPTICAL ENGINEERING, 2009) Kursun, Olcay; Karabiber, Fethullah; Koc, Cemalettin; Bal, Abdullah; Astola, JT; Egiazarian, KO; Nasrabadi, NM; Rizvi, SA; Bahcesehir University; Istanbul University; Gebze Technical University; Yildiz Technical UniversityImage segmentation is an important and difficult computer vision problem. Hyper-spectral images pose even more difficulty due to their high-dimensionality. Spectral clustering (SC) is a recently popular clustering/segmentation algorithm. In general, SC lifts the data to a high dimensional space, also known as the kernel trick, then derive eigenvectors in this new space, and finally using these new dimensions partition the data into clusters. We demonstrate that SC works efficiently when combined with covariance descriptors that can be used to assess pixelwise similarities rather than in the high-dimensional Euclidean space. We present the formulations and some preliminary results of the proposed hybrid image segmentation method for hyper-spectral images.Publication Metadata only Performance Comparison of Error Compensation Techniques with Multipath Transmission in Wireless Multimedia Sensor Networks(IEEE COMPUTER SOC, 2007) Sarisaray, Pinar; Gur, Gurkan; Baydere, Sebnem; Harmanci, Emre; Caglayan, MU; Field, AJ; Gelenbe, E; Bahcesehir University; Bogazici University; Yeditepe University; Istanbul Technical UniversityDue to the proliferation of the multimedia applications over unreliable medium like wireless networks, robust image and video communication have become more important. In this paper, we consider the transmission distortions on the multimedia data due to both channel impairments and instant node failures for Wireless Multimedia Sensor Networks (WMSN). Two techniques are investigated to compensate the multimedia distortions at the expense of incurring additional delays and/or wasting bandwidth resources. First technique is an error concealment technique utilizing discrete wavelet transform for embedding downsized replicas of original image into itself, thereby mitigating degradations in a backward-compatible scheme. The other is Reed-Solomon coding utilizing additional information bits to correct bit/symbol errors. Two techniques are also integrated with multipath transmission to provide fault tolerance. Performance results show that error concealment with multipath transmission technique (ECMF) is more promising to compensate for losses due to unreliable channels and instant node failures than Reed-Solomon coding with multipath transmission technique (RSMF) in WMSN.Publication Metadata only Emulsion polymerization of styrene and vinyl acetate with cationic surfactant(WILEY-V C H VERLAG GMBH, 2007) Erkal, Durdane; Senkal, B. Filiz; Sarac, Ayfer; Bahcesehir University; Istanbul Technical University; Yildiz Technical UniversityIn this study, the emulsion homopolymerization system containing vinyl acetate and styrene, potassium persulfate, and a new cationic surfactant was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate and styrene latex properties were investigated depending on surfactant percentage in homopolymerizations.