Elektrik Elektronik Mühendisliği Bölümü

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Alternative Enhancement of Associativity Based Routing (Aeabr) for Mobile Networks
(Springer, 2010) Preveze, Barbaros; Safak, Aysel
This study proposes an alternative enhancement for the Enhanced Associativity Based Routing (EABR) method which is a derivation of ABR (Associativity Based Routing) by relative speed and relative distance estimation using the received power strength (RPS) of the nodes. In this study, it is shown that EABR outperforms some other well known protocols. The performance of EABR is improved in terms of number of route reconstructions (RRC) and connected status percentage (CSP). Message overhead and bandwidth utilization is also investigated.
Citation - WoS: 1
Citation - Scopus: 1
Calculation of the Spin-Lattice Relaxation Time and the Activation Energy Near the Iv-Iii Phase Transition in Pyridinium Fluorosulfonate (C5nh6)fso3
(Taylor & Francis Ltd, 2022) Kara, N.; Kiraci, A.; Yurtseven, Hamit
The spin-lattice relaxation time T-1(H) for protons nuclei is calculated in term of the pseudospin-phonon (PS) coupled and the energy fluctuation (EF) models close to the IV-III solid-solid phase transition of T-C = 235 K in (C5NH6)FSO3. This calculation was performed by associating the observed second moment of the H-1 as the order parameter below k and the disorder parameter above T-C. Values of the activation energy for the cation reorientation in this crystal are also deduced by using both models. In addition, the observed dielectric permittivity of this crystal is analyzed within the framework of the Landau theory and values of the spontaneous polarization (P-s) are determined as a function of temperature. The normalized values of P-s are used in the PS and EF models to extract the activation energy for the reorientation of the dipole moment of this compound arising from cation-anion interaction. Our results show that the PS and EF models can describe the observed behavior of the spin-lattice relaxation time adequately for the IV-III solid-solid transition in (C5NH6)FSO3.
Citation - WoS: 5
Citation - Scopus: 7
Comparison of Single Channel Indices for U-Net Based Segmentation of Vegetation in Satellite Images
(Spie-int Soc Optical Engineering, 2020) Ulku, Irem; Barmpoutis, Panagiotis; Stathaki, Tania; Akagunduz, Erdem
Hyper-spectral satellite imagery, consisting of multiple visible or infrared bands, is extremely dense and weighty for deep operations. Regarding problems related to vegetation as, more specifically, tree segmentation, it is difficult to train deep architectures due to lack of large-scale satellite imagery. In this paper, we compare the success of different single channel indices, which are constructed from multiple bands, for the purpose of tree segmentation in a deep convolutional neural network ( CNN) architecture. The utilized indices are either hand-crafted such as excess green index (ExG) and normalized difference vegetation index (NDVI) or reconstructed from the visible bands using feature space transformation methods such as principle component analysis (PCA). For comparison, these features are fed to an identical CNN architecture, which is a standard U-Net-based symmetric encoder-decoder design with hierarchical skip connections and the segmentation success for each single index is recorded. Experimental results show that single bands, which are constructed from the vegetation indices and space transformations, can achieve similar segmentation performances as compared to that of the original multi-channel case.
Comparison of Single Channel Indices for U-Net Based Segmentation of Vegetation in Satellite Images
(SPIE, 2020) Ülkü, İrem; Barmpoutis, P.; Stathaki, T.; Akagündüz, Erdem
Hyper-spectral satellite imagery, consisting of multiple visible or infrared bands, is extremely dense and weighty for deep operations. Regarding problems related to vegetation as, more specifically, tree segmentation, it is difficult to train deep architectures due to lack of large-scale satellite imagery. In this paper, we compare the success of different single channel indices, which are constructed from multiple bands, for the purpose of tree segmentation in a deep convolutional neural network (CNN) architecture. The utilized indices are either hand-crafted such as excess green index (ExG) and normalized difference vegetation index (NDVI) or reconstructed from the visible bands using feature space transformation methods such as principle component analysis (PCA). For comparison, these features are fed to an identical CNN architecture, which is a standard U-Net-based symmetric encoder-decoder design with hierarchical skip connections and the segmentation success for each single index is recorded. Experimental results show that single bands, which are constructed from the vegetation indices and space transformations, can achieve similar segmentation performances as compared to that of the original multi-channel case
Citation - WoS: 1
Citation - Scopus: 1
Effects of Laser Multimode Content on the Angle-Of Fluctuations in Free Space Optics Access Systems
(Spie-int Soc Optical Engineering, 2004) Eyyuboglu, HT; Baykal, Y
The effects of the multimode content in a laser beam on the angle-of-arrival fluctuations are examined for free space optics (FSO) access systems. Multimode excitation is represented by coherent addition of Hermite-Gaussian higher order modes. Root mean square angle-of-arrival fluctuations are formulated using the previously reported multimode phase structure function, which is valid in weak atmospheric turbulence. Results are found for practical FSO links operating at 1550 nm and 850 nm wavelengths and for link spans of up to 5 km. In choosing the mode content, various sequential grouping of all possible mode combinations are used up to a certain order (n,m) mode. We start with the single fundamental mode (TEM00) and span up to the highest order (n = 10, m = 10) mode. In this manner, different degrees of source coherence are also taken into account. Angle-of-arrival fluctuations are found to be in the range of several tens of muradians and almost insensitive to the mode content except for the cases when the mode group terminates with an odd mode. In such instances, the fluctuations rise to a few hundreds of murad. Comparing our results with the field of view of a practical FSO receiver, which is several mrad, we conclude that the-angle-of arrival fluctuations due to multimode excitation will not influence the FSO link performance to a major extent.
Citation - WoS: 1
Citation - Scopus: 3
Hyperspectral Image Compression Using an Online Learning Method
(Spie-int Soc Optical Engineering, 2015) Ulku, Irem; Toreyin, B. Ugur
A hyperspectral image compression method is proposed using an online dictionary learning approach. The online learning mechanism is aimed at utilizing least number of dictionary elements for each hyperspectral image under consideration. In order to meet this "sparsity constraint", basis pursuit algorithm is used. Hyperspectral imagery from AVIRIS datasets are used for testing purposes. Effects of non-zero dictionary elements on the compression performance are analyzed. Results indicate that, the proposed online dictionary learning algorithm may be utilized for higher data rates, as it performs better in terms of PSNR values, as compared with the state-of-the-art predictive lossy compression schemes.
Influence of Atmospheric Turbulence on Quality of Multichannel Laser Radiation and Correction for Distortion
(Spie-int Soc Optical Engineering, 2016) Kanev, F. Yu.; Lukin, V. P.; Makenova, N. A.; Antipov, O. L.; Eyyuboglu, Halil Tanyer
In this paper the results of simulation are presented of multichannel radiation propagation in the atmosphere, and correction for turbulent distortion on the base of the beam phase control is considered. The results demonstrate dependence of correction effectiveness on number of channels and on precision of a reference beam phase reconstruction. Additionally increase of effectiveness is possible with adjustment of amplification in the channels of the optical system, i.e., with the use of amplitude-phase control of radiation.
Citation - Scopus: 1
Intensity Fluctuations of Incoherently Superposed Gaussian Beams in Atmospheric Turbulence
(Spie-int Soc Optical Engineering, 2010) Baykal, Yahya
Intensity fluctuations of incoherently superposed Gaussian beams are formulated in weak turbulence by employing the extended Huygens-Fresnel principle. Each individual beam superposed is taken to be fully incoherent. The scintillation index evaluated for different number of beams indicates that as the number of beams increase, scintillations decrease. Incoherent superposition of smaller sized Gaussian sources exhibits smaller fluctuations. Comparing the scintillation index arising from incoherently superposed Gaussian beams to the scintillation index of coherently superposed Gaussian beams of the same structure shows that incoherent superposition yields lower intensity fluctuations, thus can be advantageous in atmospheric optical communication links.
Citation - WoS: 2
Citation - Scopus: 3
Method of Evaluation of the Mutual Coherence Function of Laser Beams and Its Application for Symmetric Dark Hollow Beams
(Spie-int Soc Optical Engineering, 2011) Banakh, V. A.; Marakasov, D. A.; Rytchkov, D. S.; Baykal, Y. K.; Eyyuboglu, T.
In our report, a method of evaluation of the mutual coherence function (MCF) of optical wave propagating in turbulent atmosphere is proposed. The method is based on using inverse Fresnel transform and 2-D Fast Fourier Transformation procedure (FFT) and provides a high accuracy in various propagation conditions from weak up to strong optical turbulence regime. This technique allows significantly reducing the evaluation time of MCF. The proposed method is suitable for optical waves with arbitrary initial distribution of amplitude and phase. Results of investigations on the degradation of coherence of symmetric dark hollow beams (DHB) propagating in turbulent atmosphere are presented. Analysis of evolution of MCF is brought up, and some characteristics of DHB, such as mean intensity distribution, and moments of Wigner distribution are calculated for various kinds of profiles of structural characteristic of refractive index. All of the evaluations for DHB are fulfilled for Kolmogorov spectrum of correlation function of refractive index fluctuations. The comparison between mean intensity calculations within the proposed method and method based on semi-analytical approach using of quadratic approximation of spherical wave structure function, is presented.
Citation - WoS: 3
Optical Propagation in Unguided Media
(Springer-verlag Berlin, 2016) Baykal, Yahya Kemal
This chapter provides fundamentals of light propagation in unguided media and particularly discusses turbulence of transmission environment. The degradation effects of turbulence in the received signal of an OWC system are presented. The turbulence power spectra used in the formulation of various entities are given in various links operating in different environments such as atmosphere, space and underwater. The Rytov method and the extended Huygens-Fresnel principle are employed in the evaluation of the average intensity and the scintillation index. Effects of different optical beam profiles in the average received intensity and the scintillation index are further examined. Finally, some mitigation methods, such as the transmitter and the receiver aperture averaging, to reduce the turbulence degradation are given.
Citation - WoS: 5
Citation - Scopus: 7
Performance Analysis of Mimo Fso Systems With Radial Array Beams and Finite Sized Detectors
(Spie-int Soc Optical Engineering, 2014) Kamacioglu, Canan; Uysal, Murat; Baykal, Yahya; Gokce, Muhsin C.
Multiple-input multiple-output (MIMO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MIMO FSO system with practical transmitter and receiver configurations that consists of a radial laser array with Gaussian beams and finite sized detectors. We formulate the average received intensity and the power scinitillation as a function of the receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens-Fresnel principle. Then, integrations over the finite sized multiple detectors are performed and the effect of the receiver aperture averaging is quantified. We further derive an outage probability expression of this MIMO system in the presence of turbulence-induced fading channels. Using the derived expressions, we demonstrate the effect of several practical system parameters such as the ring radius, the number of array beamlets, the source size, the link length, structure constant and the receiver aperture radius on the system performance.
Silicon-Based Core-Shell Nanoparticle's Nanobiomedical Characterisation
(Inderscience Publishers, 2019) Sana, F.A.; Farhadnia, F.; Salmanogli, A.
Using functionalised nanoparticles in nanobiomedical applications cause to raise questions about unintentional effect of such powerful agents on the human body. In other words, the study of nanoparticle toxicity can be considered as a curtail key for the biological applications. In this study, the core/shell nanoparticles such as Si/Au and SiO2/Au were synthesised and functionalised with some biological elements. For satisfying some medical standards and biomedical critical test conditions, a few in-vitro assays as cytotoxicity and haemolysis should be done. For this reason, cytotoxicity and haemolytic effects of the functionalised nanoparticles such as Si/Au/biotin and SiO2/Au/biotin and their derivatives were evaluated on Hep-G2 cells and humane red blood samples. It is shown that cytotoxicity and haemolysis effects of the all synthesised nanoparticles are concentration-dependent. Also, the results are shown that most cytotoxicity and haemolytic effects are observed for Si/Au and SiO2/Au without biotin groups after 48 hours and 30 minutes, respectively. © 2019 Inderscience Enterprises Ltd.

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