Mühendislik Fakültesi

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Citation - WoS: 110
Citation - Scopus: 112
Active Laser Radar Systems With Stochastic Electromagnetic Beams in Turbulent Atmosphere
(Optica Publishing Group, 2008) Cai, Yangjian; Korotkova, Olga; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam. (C) 2008 Optical Society of America
Citation - WoS: 7
Citation - Scopus: 6
Adaptive Optics Correction of Beam Spread in Biological Tissues
(Pergamon-elsevier Science Ltd, 2022) Baykal, Yahya; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Beam spread in turbulent biological tissues is examined when the tissue is excited with a collimated Gaussian laser beam. Adaptive optics correction is applied to the beam spread in the form of piston only (P Only), tilt only (T Only), piston + tilt (P + T), and the reduction in the beam spread is evaluated as com-pared to the no adaptive optics (No AO) corrected beam spread. No AO and adaptive optics corrected beam spread are expressed for various biological tissue types, against the variations in the strength co-efficient of the refractive-index fluctuations, source size, small length-scale factor of turbulence, tissue length, fractal dimension, characteristic lengths of heterogeneity and the wavelength. For the examined tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human) and deep dermis (mouse), No AO beam spread and the adaptive optics corrected beam spread are found to increase as the strength coefficient of the refractive-index fluctuations, tissue length, fractal dimension, the char-acteristic lengths of heterogeneity increase, and to decrease as the source size, small length-scale factor, wavelength increase. Reduction ratio of P + T correction is almost the same for all the evaluated cases which is 74%.(C) 2022 Elsevier Ltd. All rights reserved.
Citation - WoS: 14
Citation - Scopus: 16
Adaptive Optics Effect on Performance of Bpsk-Sim Oceanic Optical Wireless Communication Systems With Aperture Averaging in Weak Turbulence
(Pergamon-elsevier Science Ltd, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Turbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Airy-Type Relativistic Matter Wave
(Elsevier Gmbh, 2021) Umul, Yusuf Ziya; 4269; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A new relativistic Airy-type matter wave is introduced as a solution of the kinetic energy based wave equation. The parametric solution of the related differential equation is obtained. The total energy and momentum of the relativistic particle are derived by using a Bohmian type of decomposition of the kinetic energy based equation. The acceleration of the particle is also evaluated. The behavior of the matter wave is investigated numerically.
Citation - WoS: 4
Citation - Scopus: 5
Almost Autonomous Training of Mixtures of Principal Component Analyzers
(Elsevier Science Bv, 2004) Musa, MEM; de Ridder, D; Duin, RPW; Atalay, V; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In recent years, a number of mixtures of local PCA models have been proposed. Most of these models require the user to set the number of submodels (local models) in the mixture and the dimensionality of the submodels (i.e., number of PC's) as well. To make the model free of these parameters, we propose a greedy expectation-maximization algorithm to find a suboptimal number of submodels. For a given retained variance ratio, the proposed algorithm estimates for each submodel the dimensionality that retains this given variability ratio. We test the proposed method on two different classification problems: handwritten digit recognition and 2-class ionosphere data classification. The results show that the proposed method has a good performance. (C) 2004 Elsevier B.V. All rights reserved.
Citation - WoS: 203
Citation - Scopus: 231
Ammonia Removal From Anaerobically Digested Dairy Manure by Struvite Precipitation
(Elsevier Sci Ltd, 2005) Uludag-Demirer, S; Demirer, GN; Chen, S; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.04. Endüstri Mühendisliği
Ammonia is one of the most important contaminants impairing the quality of water resources. When this is considered along with the fact that the global demand for nitrogenous fertilizers is in constant rise, the need for recovery as well as removal of nitrogen is well justified. Crystallization of N and P in the form of struvite (MgNH4PO4 center dot 6H(2)O), which is a slow releasing and valuable fertilizer, is one possible technique for this purpose. This study investigated the removal of NR4+ through struvite precipitation from the effluents of one- (R1) and two-phase (R2) anaerobic reactors digesting dairy manure. To force the formation of struvite in the anaerobic reactor effluents, Ma(2+) ion was added by using both Mg(OH)(2) and MgCl2 center dot 6H(2)O. To prevent the effect of different total phosphorus (TP) concentration in the effluents of RI and R2, as well as to not limit the formation of struvite, an excess amount Of PO43- (0.14 M) was added in the form of NaHPO4. Different stoichiometric Mg2+:NH4+:PO43- ratios were tested to determine the required Mg2+ concentrations for maximum NH4+ removal by keeping NH4+:PO43- ratio constant for the effluents of reactors RI and R2. The results revealed that very high NH4+ removal efficiencies (above 95%) were possible by adding Mg 21 ions higher than 0.06 M concentration in the effluents from reactors RI and R2. It was also observed that the initial pH adjustment to 8.50 using NaOH did not result in any significant increase in the removal of NH4+ and the removal of NH4+ in the reactors treated with MgCl2 center dot 6H(2)O was higher than those treated with Mg(OH)(2) for the same Mg2+ concentration. (c) 2005 Published by Elsevier Ltd.
Citation - WoS: 9
Citation - Scopus: 10
Analysis of Exergy and Energy of Sugar Production Process in Sugar Plant
(Maney Publishing, 2010) Acir, A.; Altunok, T.; Baysal, E.; Kocyigit, E.; Sahin, H. M.; 40424; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.06. Makine Mühendisliği
In this paper, the energy and exergy analysis results of sugar production processes were presented by using operational system data from the Kayseri sugar plant, Turkey. All sugar production processes were thought as a steady state open thermodynamics system and employed the energy and exergy analyses, based on the first and second laws of thermodynamics. The best values of the energy and exergy efficiencies were obtained as 95.1% for the juice production process and 74.3% for the juice concentration process respectively. Moreover, the location of the energy degradation and the irreversibility were determined during the whole sugar production processes. Consequently, it has been pointed out that the energy and exergy efficiencies can be improved if the rates of the energy degradation and irreversibility in the sugar production processes are reduced.
Citation - WoS: 8
Citation - Scopus: 8
Analysis of Quantum Radar Cross-Section by Canonical Quantization Method (Full Quantum Theory)
(Ieee-inst Electrical Electronics Engineers inc, 2020) Salmanogli, Ahmad; Gokcen, Dincer; 01. Çankaya Üniversitesi
This article investigates the difference between two quantum-based theories to calculate the radar cross-section (RCS). Quantum radar cross-section (QRCS) has been commonly analyzed using the dipole approximation method, and the related results show that it can improve the sidelobe of the interference pattern in contrast to the classical methods. This study, on the other hand, utilizes the canonical quantization (or microscopic) method, which is a more comprehensive theory than the dipole approximation method to calculate the radar cross-section. It is shown that there are some similarities between two methods; nonetheless, there are some crucial quantities and factors that have been ignored in the dipole approximation methods. The main difference arises due to the interaction Hamiltonian that two methods relied on. The theoretical calculation shows some critical points suggesting that the dipole approximation method cannot cover all aspects of the radar cross-section calculation. To verify the mentioned point, we establish a new method in which the radar cross-section is calculated by merging the quantum approach with the method of moment (MoM), called quantum-method of moment (QMoM). The simulation results show that the newly established method is in harmony with the canonical quantization method.
Citation - WoS: 183
Citation - Scopus: 193
Analysis of Reciprocity of Cos-Gaussian and Cosh-Gaussian Laser Beams in a Turbulent Atmosphere
(Optical Soc Amer, 2004) Eyyuboglu, HT; Baykal, Y; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In a turbulent atmosphere, starting with a cos-Gaussian excitation at the source plane, the average intensity profile at the receiver plane is formulated. This average intensity profile is evaluated against the variations of link lengths, turbulence levels, two frequently used free-space optics wavelengths, and beam displacement parameters. We show that a cos-Gaussian beam, following a natural diffraction, is eventually transformed into a cosh-Gaussian beam. Combining our earlier results with the current findings, we conclude that cos-Gaussian and cosh-Gaussian beams act in a reciprocal manner after propagation in turbulence. The rates (paces) of conversion in the two directions are not the same. Although the conversion of cos-Gaussian beams to cosh-Gaussian beams can happen over a wide range of turbulence levels (low to moderate to high), the conversion of cosh-Gaussian beams to cos-Gaussian beams is pronounced under relatively stronger turbulence conditions. Source and propagation parameters that affect this reciprocity have been analyzed. (C) 2004 Optical Society of America.
Citation - WoS: 4
Citation - Scopus: 4
An Analytical Solution for the Plane Wave Diffraction by a Resistive Half-Plane Residing at the Interface of Left and Right Handed Media
(Elsevier Gmbh, 2019) Basdemir, Husnu Deniz; 20399; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The diffraction of waves by a resistive half-plane lying on the interface of left and right handed media is investigated in this study. Because of the anomalous refraction property of left handed media, shadow boundary shifts toward to the lower surface of the half-plane. In order to obtain the shifted boundary, diffracted waves are divided to subfields. Thus, obtained diffracted waves compensates the deficiency of geometries optics fields at the transition regions. The uniform version of waves is obtained by using the uniform theory of diffraction. The wave behaviors are examined numerically.
Citation - WoS: 8
Citation - Scopus: 9
Anisotropy Effect on Multi-Gaussian Beam Propagation in Turbulent Ocean
(Osa-optical Soc, 2018) Ata, Yalcin; Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Average transmittance of multi-Gaussian (flat-topped and annular) optical beams in an anisotropic turbulent ocean is examined analytically based on the extended Huygens-Fresnel principle. Transmittance variations depending on the link length, anisotropy factor, salinity and temperature contribution factor, source size, beam flatness order of flat-topped beam, Kolmogorov microscale length, rate of dissipation of turbulent kinetic energy, rate of dissipation of the mean squared temperature, and thickness of annular beam are examined. Results show that all these parameters have effects in various forms on the average transmittance in an anisotropic turbulent ocean. Hence, the performance of optical wireless communication systems can be improved by taking into account the variation of average transmittance versus the above parameters.
Citation - WoS: 11
Citation - Scopus: 12
Anisotropy Effect on Performance of Ppm Optical Wireless Oceanic Communication Links
(Pergamon-elsevier Science Ltd, 2019) Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The performance, quantified by the bit-error-rate (BER), of M-ary pulse position modulated (PPM) optical wireless oceanic communication (OWOC) link is investigated when such a link operates in anisotropic weak oceanic turbulence. For this purpose, formulations of the average received power and the scintillation index of collimated Gaussian optical beam detected by a point detector are developed for anisotropic weak oceanic turbulence, which in turn are employed in the BER expression of the PPM OWOC links. BER is evaluated under various turbulence parameters of anisotropic oceanic turbulence, M of M-ary PPM, data bit rate, average current gain of avalanche photodiode (APD). For any investigated parameter, it is found that the BER performance of M-ary PPM OWOC links is improved as the ocean becomes more anisotropic. (C) 2019 Elsevier Ltd. All rights reserved.
Citation - WoS: 3
Antibacterial Behavior of Oxynitride Glasses as a Glassy Grain Boundary Phase for Silicon Nitride-Based Ceramics
(Wiley Periodicals, inc, 2021) Kushan Akin, Seniz R.; Dolekcekic, Emrah; Webster, Thomas J.; 224219; 01. Çankaya Üniversitesi
Silicon nitride-based ceramics have provided significant advantages due to their high chemical resistance, high elastic modulus, and combination of hardness and fracture toughness (depending on self-reinforcement). Over the past two decades, a significant amount of interest has been generated for the bio-applications of these materials. However, the effect of the grain boundary phase on such applications is still not very well understood. In this study, the effect of different cations on biological (such as antibacterial and cytocompatibilty) and material properties (like wetting angles and isoelectric points [IEP]) of oxynitride glasses, mimicking the grain boundary phase in Si3N4 and SiAlON ceramics, were investigated. Results revealed that the antibacterial behavior and mammalian cell viability were inversely correlated in glasses with rare-earth cation additions. Ca was the best cation when the two properties (bacterial response and cell proliferation) were considered together, and, thus should be further studied for a wide range of applications.
Citation - WoS: 14
Citation - Scopus: 18
Application of Bilstm-Crf Model With Different Embeddings for Product Name Extraction in Unstructured Turkish Text
(Springer London Ltd, 2024) Arslan, Serdar; 325411; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Named entity recognition (NER) plays a pivotal role in Natural Language Processing by identifying and classifying entities within textual data. While NER methodologies have seen significant advancements, driven by pretrained word embeddings and deep neural networks, the majority of these studies have focused on text with well-defined grammar and structure. A significant research gap exists concerning NER in informal or unstructured text, where traditional grammar rules and sentence structure are absent. This research addresses this crucial gap by focusing on the detection of product names within unstructured Turkish text. To accomplish this, we propose a deep learning-based NER model which combines a Bidirectional Long Short-Term Memory (BiLSTM) architecture with a Conditional Random Field (CRF) layer, further enhanced by FastText embeddings. To comprehensively evaluate and compare our model's performance, we explore different embedding approaches, including Word2Vec and Glove, in conjunction with the Bidirectional Long Short-Term Memory and Conditional Random Field (BiLSTM-CRF) model. Furthermore, we conduct comparisons against BERT to assess the efficacy of our approach. Our experimentation utilizes a Turkish e-commerce dataset gathered from the internet, where traditional grammatical and structural rules may not apply. The BiLSTM-CRF model with FastText embeddings achieved an F1 score value of 57.40%, a precision value of 55.78%, and a recall value of 59.12%. These results indicate promising performance in outperforming other baseline techniques. This research contributes to the field of NER by addressing the unique challenges posed by unstructured Turkish text and opens avenues for improved entity recognition in informal language settings, with potential applications across various domains.
Citation - WoS: 1
Citation - Scopus: 1
Application of the Method of Transition Boundary To the Half-Planes With Mixed Boundary Conditions
(Elsevier Gmbh, 2020) Umul, Yusuf Ziya; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The scattering problems of waves by soft-hard and hard-soft half-planes are investigated by the method of transition boundary. The functional values at the transition boundaries are found to be identical to the ones for the soft and hard half-screens. It is shown that the factorization process should be applied by also taking into account the boundary conditions besides the principle of reciprocity. The exact diffracted field expressions are obtained for both of the half-planes.
Citation - WoS: 53
Citation - Scopus: 58
Average Intensity and Spreading of an Elegant Hermite-Gaussian Beam in Turbulent Atmosphere
(Optical Soc Amer, 2009) Yuan, Yangsheng; Cai, Yangjian; Qu, Jun; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The propagation of an elegant Hermite-Gaussian beam (EHGB) in turbulent atmosphere is investigated. Analytical propagation formulae for the average intensity and effective beam size of an EHGB in turbulent atmosphere are derived based on the extended Huygens-Fresnel integral. The corresponding results of a standard Hermite-Gaussian beam (SHGB) in turbulent atmosphere are also derived for the convenience of comparison. The intensity and spreading properties of EHGBs and SHGBs in turbulent atmosphere are studied numerically and comparatively. It is found that the propagation properties of EHGBs and SHGBs are much different from their properties in free space, and the EHGB and SHGB with higher orders are less affected by the turbulence. What's more, the SHGB spreads more rapidly than the EHGB in turbulent atmosphere under the same conditions. Our results will be useful in long-distance free-space optical communications. (C) 2009 Optical Society of America
Citation - WoS: 113
Citation - Scopus: 115
Average Irradiance and Polarization Properties of a Radially or Azimuthally Polarized Beam in a Turbulent Atmosphere
(Optical Soc Amer, 2008) Cai, Yangjian; Lin, Qiang; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Analytical formulas are derived for the average irradiance and the degree of polarization of a radially or azimuthally polarized doughnut beam (PDB) propagating in a turbulent atmosphere by adopting a beam coherence-polarization matrix. It is found that the radial or azimuthal polarization structure of a radially or azimuthally PDB will be destroyed (i.e., a radially or azimuthally PDB is depolarized and becomes a partially polarized beam) and the doughnut beam spot becomes a circularly Gaussian beam spot during propagation in a turbulent atmosphere. The propagation properties are closely related to the parameters of the beam and the structure constant of the atmospheric turbulence. (C) 2008 Optical Society of America.
Citation - WoS: 6
Citation - Scopus: 8
Babinet's Principle in the Fraunhofer Diffraction by a Finite Thin Wire
(Elsevier Gmbh, Urban & Fischer verlag, 2011) Umul, Yusuf Ziya; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The scattered waves by a thin finite wire are evaluated by using the Rayleigh-Sommerfeld integral in the Fraunhofer approximation. The scattered fields by the complementary thin wire are also obtained with the aid of the Babinet's principle. The scattering integrals are evaluated directly. It is shown that Babinet's principle holds excellently for this problem. The scattered fields are examined numerically. (C) 2010 Elsevier GmbH. All rights reserved.
Citation - WoS: 21
Citation - Scopus: 24
Behavior of Glulam Timber Beam Strengthened With Carbon Fiber Reinforced Polymer Strip for Flexural Loading
(Sage Publications Ltd, 2021) Isleyen, ummu K.; Ghoroubi, Rahim; Mercimek, Omer; Anil, Ozgur; Erdem, Recep Tugrul; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In the last 20 years, the use of wooden structures and their dimensions have gradually increased. The wood application has increased in different structures such as multistory buildings, sports, industrial facilities, road and railway bridges, power transmission lines, and towers. The widespread use and size of wood structures have increased the research on developing special types of wood products supported by composite materials. Laminated wood elements are the leading composite wood materials. Laminated wooden beams allow making much larger openings than standard solid wood structural elements. The development of the sizes and usage areas of wooden structures has increased the capacity of glulam structural elements and reveals the need to improve their performance. Carbon fiber reinforced polymers (CFRPs) are the most suitable options for increasing the bearing capacity values of glulam beams and improving general load-displacement behaviors. In this study, the use of CFRP strips in different layouts to increase glulam wooden beams and the application of CFRP fan-type anchors in the CFRP strip endpoints are the studied variables. Anchored and non-anchored glulam wooden beams reinforced with CFRP strips with different layouts were tested using a three-point bending test. The ultimate load capacity, initial stiffness, displacement ductility ratio, energy dissipation capacity, failure mechanisms, and general load-displacement behavior of wooden beam test specimens were obtained and interpreted as a result of the experiments.
Citation - WoS: 23
Citation - Scopus: 26
Bi-Objective Adaptive Large Neighborhood Search Algorithm for the Healthcare Waste Periodic Location Inventory Routing Problem
(Springer Heidelberg, 2022) Aydemir-Karadag, Ayyuce; 116059; 01. Çankaya Üniversitesi
There has been an unexpected increase in the amount of healthcare waste during the COVID-19 pandemic. Managing healthcare waste is vital, as improper practices in the waste system can lead to the further spread of the virus. To develop effective and sustainable waste management systems, decisions in all processes from the source of the waste to its disposal should be evaluated together. Strategic decisions involve locating waste processing centers, while operational decisions deal with waste collection. Although the periodic collection of waste is used in practice, it has not been studied in the relevant literature. This paper integrates the periodic inventory routing problem with location decisions for designing healthcare waste management systems and presents a bi-objective mixed-integer nonlinear programming model that minimizes operating costs and risk simultaneously. Due to the complexity of the problem, a two-step approach is proposed. The first stage provides a mixed-integer linear model that generates visiting schedules to source nodes. The second stage offers a Bi-Objective Adaptive Large Neighborhood Search Algorithm (BOALNS) that processes the remaining decisions considered in the problem. The performance of the algorithm is tested on several hypothetical problem instances. Computational analyses are conducted by comparing BOALNS with its other two versions, Adaptive Large Neighborhood Search Algorithm and Bi-Objective Large Neighborhood Search Algorithm (BOLNS). The computational experiments demonstrate that our proposed algorithm is superior to these algorithms in several performance evaluation metrics. Also, it is observed that the adaptive search engine increases the capability of BOALNS to achieve high-quality Pareto-optimal solutions.

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