Browsing by Author "Bayri, A."
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Item Open Access Bilişsel algılamaya doğru: çok görevli öğrenme ile radar fonksiyon sınıflandırma(IEEE, 2019-04) Altıparmak, Fatih; Akyön, Fatih Çağatay; Özmen, E.; Çoğun, Fuat; Bayri, A.Elektronik Harp (EH) sistemleri için ortamda yayın yapan bir radarın tespiti ve ilgili radarın fonksiyonunun belirlenmesi, sistemin en önemli görevlerinden biridir. Bu çalışmada, EH sistemleri tarafından ölçülen radar parametreleri kullanılarak radarların Elektronik Karşı Tedbir (EKT) kullanım konseptine uygun olarak fonksiyonlarının belirlenmesi hedeflenmiştir. Çok Görevli Öğrenme ve Tek Görevli Öğrenme sinirağları probleme uyarlanmıştır. Sınıflandırıcı öncesinde aşırı örnekleme, aralık değerleri için nicemleme ve sınıf değerleri için gruplama ön işlemleri yapılmıştır. Çok Görevli Öğrenme tekniğinin performansının Tek Görevli Öğrenme tekniğininkinden daha iyi olduğu gözlenmiştir. Sınıflandırıcı öncesinde uygulanan aşırı örnekleme algoritmasının, ön işlemler neticesinde elde edilen verisetinin ve gruplandırılmış sınıfların bir veya daha fazlasının kullanımıyla her iki metodun performanslarının arttığı gözlenmiştir.Item Open Access High-power-high-repetition-rate-single-mode Er-Yb-doped fiber laser system(Optical Society of America, 2012) Pavlov, I.; Ilbey, E.; Dulgergil, E.; Bayri, A.; Ilday, F. O.We demonstrate an all-fiber-integrated, high-power chirped-pulse-amplification system operating at 1550 nm. The seed source is a soliton fiber laser with 156 MHz repetition rate. Two-stage single mode amplifier provides an amplification of more than 40 dB without significant spontaneous amplified emission. The power amplifier is based on cladding-pumped 10 mu m-core Er-Yb co-doped fiber, the output of which was spliced into standard singlemode fiber. We obtain 10 W average power in a strictly singlemode operation. After dechirping with a grating compressor, near transform-limited, 450 fs-long pulses are obtained. The laser source exhibits excellent short and long-term intensity stability, with relative intensity noise measurements characterizing the short-term stability. (C) 2012 Optical Society of AmericaItem Open Access Investigation of Ti‐substitution effects on structural and electrochemical properties of Na0.67Mn0.5Fe0.5O2 battery cells(Wiley, 2020) Altın, S.; Altundağ, S.; Altın, E.; Öz, Erdinç; Harfouche, M.; Bayri, A.Ti‐substituted Na0.67Mn0.5Fe0.5O2 powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X‐ray powder diffraction (XRD), and X‐ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X‐ray absorption near edge structure (XANES), and it was found that Ti‐substitution caused a decrease in the valance state of Fe in Na0.67Mn0.5Fe0.5O2. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti‐substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti‐substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10°C to 50°C, and it was found that the battery performance depends on the environmental temperatures.Item Open Access Magnetic Properties and Environmental Temperature Effects on Battery Performance of Na0.67Mn0.5Fe0.5O2(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-03-31) Altın, S.; Bayri, A.; Altın, E.; Öz, Erdinç; Yaşar, S.; Altundağ, S.; Harfouche, M.; Avcı, S.Herein, a modified solid state synthesis of Na0.67Mn0.5Fe0.5O2 and the results of a detailed investigation of the structural and magnetic properties via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis are reported. The magnetic properties of Na0.67Mn0.5Fe0.5O2 do not fit the Curie–Weiss law and a model regarding the spin configuration of the Mn and Fe ions and a possible ferrimagnetic order is suggested. Electrochemical measurements and ex situ structural analysis of the cathode material confirm the reversible structural transitions for the cells charged up to 4.0 V. Environmental temperature–dependent electrochemical measurements reveal a strong temperature dependence of both, the initial capacity and the capacity retention. Ex situ SEM, FTIR, and XRD studies on the battery membrane verify the formation of a Na2CO3 phase on the membrane, which blocks the Na ion diffusion through membrane pores and is responsible for the capacity fade for this compound.Item Open Access Phase-only beam synthesis by iterative semidefinite relaxations with rank refinement(IEEE, 2013) Alp, Yaşar Kemal; Arıkan, Orhan; Bayri, A.In phased array antennas, by varying the complex element weights beam patterns with desired shapes can be synthesized and/or steered to desired directions. These complex weights can be implemented by using amplitude controllers and phase shifters at the system level. Since controlling the phase of an RF signal is much easier than controlling its power, many systems do not have an individual amplitude controller for each element. Hence, beamshaping and steering are to be achieved by varying only the element phases. In this work, a new approach is proposed for phase-only beam synthesis problem. In this approach, the phase-only beam synthesis is formulated as a non-convex quadratically constrained quadratic problem (QCQP). Then, it is relaxed to a convex semidefinite problem (SDP), which generally provides an undesired high rank solution. An iterative technique is developed to obtain a rank-1 solution to the relaxed convex SDP. Conducted experiments show that, proposedmethod can successfully synthesize beam shapes with desired characteristics and steering directions by using only the element phases. © 2013 EURASIP.