Mühendislik Fakültesi

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Citation - WoS: 15
Citation - Scopus: 16
Adaptive Optics Correction of Scintillation in Underwater Medium
(Taylor & Francis Ltd, 2020) Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Adaptive optics correction of the scintillation index of a Gaussian laser beam in underwater turbulence is studied. To introduce the adaptive optics correction, filter functions providing the piston, tilt and astigmatism effects are adapted to promote the spectrum of underwater turbulence. The reduction of the scintillation index due to the individual piston, tilt, astigmatism effects and their sum is examined versus the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean squared temperature, the rate of dissipation of kinetic energy per unit mass of fluid, receiving aperture diameter, source size, link length and the wavelength. For any value of underwater turbulence parameter, the most effective adaptive optics corrections are found to be the piston, tilt and astigmatism, respectively.
Citation - WoS: 22
Citation - Scopus: 23
Alternative Interpretation of the Edge-Diffraction Phenomenon
(Optical Soc Amer, 2008) Umul, Yusuf Z.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
An alternative interpretation of the phenomenon of edge diffraction is proposed according to a new separation of the Fresnel function. The subfields are investigated in the problem of diffraction of a plane wave by a perfectly conducting half-plane, and the results are compared numerically with other interpretations. (c) 2008 Optical Society of America.
Citation - WoS: 1
Citation - Scopus: 1
Analyses of Plate Perforation for Various Penetrator-Target Plate Combinations
(Korean Soc Mechanical Engineers, 2022) Akyurek, Turgut; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.06. Makine Mühendisliği
In this study, kinetics and kinematics of perforation process for various penetrator-target plate combinations is analyzed, a methodology in a flow chart format to decide on failure mode, and for each failure mode, an appropriate combined analytical model that requires only common test data is proposed. The proposed methodology and analytical models that are recommended for the related failure mode are assessed by using a huge amount of test data from the literature. The penetrator-target plate configurations cover the penetrators with ogive, conical, hemi-spherical and blunt noses, at different plate thicknesses, and plate thickness to penetrator diameter ratios, made of different metallic materials. Analyzed failure modes include ductile hole enlargement, plugging, dishing, and petal forming. Assessment is done for impact velocities ranging between 215-863 m/s. The estimations based on the proposed flow chart and recommended failure models are in good agreement with the related test data and numerical analysis results.
Analysing Iraqi Railways Network by Applying Specific Criteria Using the Gis Techniques
(Coll Science Women, Univ Baghdad, 2019) Naji, Hayder Fans; Maras, H. Hakan; 34410; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The railways network is one of the huge infrastructure projects. Therefore, dealing with these projects such as analyzing and developing should be done using appropriate tools, i.e. GIS tools. Because, traditional methods will consume resources, time, money and the results maybe not accurate. In this research, the train stations in all of Iraq's provinces were studied and analyzed using network analysis, which is one of the most powerful techniques within GIS. A free trial copy of ArcGIS (R) 10.2 software was used in this research in order to achieve the aim of this study. The analysis of current train stations has been done depending on the road network, because people used roads to reach those train stations. The data layers for this study were collected and prepared to meet the requirements of network analyses within GIS. In this study, the current train stations in Iraq were analyzed and studied depending on accessibility value for those stations. Also, to know the numbers of people who can reach those stations within a walking time of 20 minutes. So, this study aims to analyze the current train stations according to multiple criteria by using network analysis in order to find the serviced areas around those stations. Results will be presented as digital maps layers with their attribute tables that show the beneficiaries from those train stations and serviced areas around those stations depending on specific criteria, with a view to determine the size of this problem and to support the decision makers in case of locating new train stations within the best locations for it.
Citation - WoS: 4
Citation - Scopus: 4
The Analysis of Anisotropic the Non-Kolmogorov Turbulence Effect on Asymmetrical Gaussian Beam Propagation in a Marine Atmosphere
(Iop Publishing Ltd, 2019) Ata, Yalcin; Baykal, Yahya; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The variations of the scintillation index of an asymmetrical Gaussian beam are investigated when the beam propagates in anisotropic non-Kolmogorov marine atmospheric turbulence. The results indicate that the scintillation decreases when the anisotropy factors in both x and y directions increase. Increases in the beam asymmetry ratio and the inner scale length increase the scintillation index level. The scintillations are found to increase as the propagation distance and structure constant increase, and as the wavelength decreases. Being valid for any asymmetry and anisotropic factor, for small values of the power law exponent, alpha of non-Kolmogorov marine atmospheric turbulence, the scintillation index tends to increase proportionally with alpha. However, as alpha is further increased, the scintillation index starts to decrease after reaching a peak value. Larger anisotropy in the non-Kolmogorov marine turbulence is found to be preferable since the scintillation index is found to decrease at large anisotropic factors.
Citation - Scopus: 4
Analysis of B2c Mobile Application Characteristics and Quality Factors Based on Iso 25010 Quality Model
(Springer Verlag, 2014) Tokdemir, G.; Cagiltay, N.E.; Erturan, Y.N.; Yildiz, E.; Bilgen, S.; 17411; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The number of mobile applications in mobile market has rapidly increased as new technology and new devices are emerging at remarkable speed which shows mobile applications have an important role in every field of our life. Among those, even some of the mobile applications have a long time life as end-users use those effectively, some of them fail to do so that prevents the companies to reach from their aim. The main reason of that problem results from the quality of the mobile applications. Although there are some methods and metrics to analyze the quality of mobile applications, they have lack of criteria since they are mostly based on ISO 9126 quality model factors which are invalid anymore. This study aims to analyze both mobile commerce applications' characteristics and quality factors and sub-factors based on ISO 25010 product quality model. Accordingly a quality model is proposed by analysis performed by a group of experts from the mobile software development area. The results of this study aims to help developing more qualified and effective mobile applications from developer perspective. © 2014 Springer International Publishing.
Citation - WoS: 26
Citation - Scopus: 28
Analysis of Flat-Topped Gaussian Vortex Beam Scintillation Properties in Atmospheric Turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2019) Elmabruk, Kholoud; Eyyuboglu, Halil T.; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
We analyze the scintillation properties of a flat-topped Gaussian vortex beam propagating in a weakly turbulent atmosphere. We utilize a random phase screen model to perform this analysis. We evaluate the scintillation against the changes of topological charge, beam order, operating wavelength, receiver aperture side length, and source size parameters. The results show that using a flat-topped Gaussian vortex beam with a high topological charge causes a reduction in scintillation. Increasing the receiver aperture side length reduces scintillation level. As the source size increases, scintillation decreases. Our results also indicate that a flat-topped Gaussian vortex beam with high topological charges has less scintillation than the fundamental Gaussian beam. We believe that our findings will be useful in improving the performance of next-generation optical communication links and networks. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 3
Citation - Scopus: 4
An Analytical Investigation of Rigid Plastic Beams Under Impact Loading
(Gazi Univ, Fac Engineering Architecture, 2015) Gultop, Tekin; Gültop, Tekin; Yilmaz, Mahmut Cem; Alyavuz, Bahadir; 5168; İnşaat Mühendisliği; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Beams might be subjected to impact loading which is a particular type of dynamic loading during their service lives. In this study the behaviour of beams under low speed impact loading has been investigated analytically. Simply supported and fixed ended beams have been analyzed with the assumption of rigid plastic behaviour. The collapse mechanism has been assumed to emerge by the instant formation of plastic hinges, hence, a limit analysis has been performed under dynamic loading considering the conservation principles of energy and momentum. The behaviour of rigid plastic beams under impact loading has been compared to the behaviour of elastic beams under similar loading conditions.
Citation - WoS: 12
Citation - Scopus: 12
Angle-Of Fluctuations for General-Type Beams
(Spie-soc Photo-optical instrumentation Engineers, 2007) Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Starting with the recently introduced phase correlation function of a general-type beam, the angle-of-arrival fluctuations are derived and evaluated in atmospheric turbulence for lowest-order Gaussian, cos-Gaussian, cosh-Gaussian, annular, and flat-topped beams. Our motivation is to examine the improvement in the performance of optical atmospheric links when such beams are employed. For these beams, the dependence of the angle-of-arrival fluctuations on the propagation length, displacement and focusing parameters, source size, inner and outer scales of turbulence, and receiver radius is investigated. It is found that in the majority of the cases examined, the angle- of- arrival fluctuations remain small and hence are not expected to adversely affect the operation of free-space atmospheric links. It is observed that amongst the beams considered, the cos-Gaussian beam offers the least amount of angle-of-arrival fluctuations, while the worst behavior is exhibited by the cosh-Gaussian beam. This situation is reversed, however, if focused beams are used. (C) 2007 Society of Photo-Optical Instrumentation Engineers.
Citation - WoS: 8
Citation - Scopus: 10
Anisotropy Effect on Performance of Subcarrier Intensity Modulated Binary Phase Shift Keying Optical Wireless Communication Links in Weakly Turbulent Underwater Channel
(Taylor & Francis Ltd, 2019) Gokce, Muhsin C.; Ata, Yalcin; Baykal, Yahya; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The effect of the anisotropy on the bit-error-rate (BER) performance of subcarrier intensity modulated (SIM) binary phase shift keying (BPSK) optical wireless communication (OWC) links operating in weakly turbulent underwater channels is examined. BER variations versus the anisotropic factor are examined when the bandwidth, photodetector responsivity, load resistor and the underwater turbulence parameters are varied. As anisotropy in the underwater channel becomes larger, SIM BPSK OWC links have better BER performance at any link and turbulence parameter.
Citation - WoS: 36
Citation - Scopus: 43
Annular Beam Scintillations in Strong Turbulence
(Optical Soc Amer, 2010) Gercekcioglu, Hamza; Baykal, Yahya; Nakiboglu, Cem; 7812; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
A scintillation index formulation for annular beams in strong turbulence is developed that is also valid in moderate and weak turbulence. In our derivation, a modified Rytov solution is employed to obtain the small-scale and large-scale scintillation indices of annular beams by utilizing the amplitude spatial filtering of the atmospheric spectrum. Our solution yields only the on-axis scintillation index for the annular beam and correctly reduces to the existing strong turbulence results for the Gaussian beam-thus plane and spherical wave scintillation indices-and also correctly yields the existing weak turbulence annular beam scintillations. Compared to collimated Gaussian beam, plane, and spherical wave scintillations, collimated annular beams seem to be advantageous in the weak regime but lose this advantage in strongly turbulent atmosphere. It is observed that the contribution of annular beam scintillations comes mainly from the small-scale effects. At a fixed primary beam size, the scintillations of thinner collimated annular beams compared to thicker collimated annular beams are smaller in moderate turbulence but larger in strong turbulence; however, thinner annular beams of finite focal length have a smaller scintillation index than the thicker annular beams in strong turbulence. Decrease in the focal length decreases the annular beam scintillations in strong turbulence. Examining constant area annular beams, smaller primary sized annular structures have larger scintillations in moderate but smaller scintillations in strong turbulence. (C) 2010 Optical Society of America
Citation - WoS: 1
Citation - Scopus: 1
Antenna Synthesis by Levin's Method Using a Novel Optimization Algorithm for Knot Placement
(Applied Computational Electromagnetics Soc, 2023) Sener, Goker; 17740; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
- Antenna synthesis refers to determining the antenna current distribution by evaluating the inverse Fourier integral of its radiation pattern. Since this inte-gral is highly oscillatory, Levin's method can be used for the solution, providing high accuracy. In Levin's method, the integration domain is divided into equally spaced sub-intervals, and the integrals are solved by transfer-ring them into differential equations. This article uses a new optimization algorithm to determine the location of these interval points (knots) to improve the method's accuracy. Two different antenna design examples are pre-sented to validate the accuracy and efficiency of the pro-posed method for antenna synthesis applications.
Antenna Synthesis by Levin's Method Using Reproducing Kernel Functions
(Applied Computational Electromagnetics Soc, 2023) Sener, Goker; 17740; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
An antenna synthesis application is presented by solving a highly oscillatory Fourier integral using a stable and accurate Levin's algorithm. In antenna synthesis, the current distribution is obtained by the inverse Fourier integral of the antenna radiation pattern. Since this integral is highly oscillatory, the Levin method can be used for its solution. However, when the number of nodes or the frequency increases, the Levin method becomes unstable and ineffective due to the large condition number of the interpolation matrix. Thus, an improved scheme of the method is used in an antenna synthesis application in which reproducing kernel functions are used as the basis of the approximation function. The accuracy of the new method is verified by a log-periodic antenna example. The error and stability analysis results show that the new method is more stable and accurate than other well-known kernels, especially for a large number of nodes.
Citation - WoS: 8
Citation - Scopus: 9
Aperture Averaging in Multiple-Input Single-Output Free-Space Optical Systems
(Spie-soc Photo-optical instrumentation Engineers, 2015) Baykal, Yahya; Kamacioglu, Canan; Uysal, Murat; Gokce, Muhsin C.; 28643; 7812; 124615; 06.03. Elektrik-Elektronik Mühendisliği; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens Fresnel principle. Then the effect of the receiver aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 25
Citation - Scopus: 25
Aperture Averaging in Multiple-Input Single-Output Free-Space Optical Systems Using Partially Coherent Radial Array Beams
(Optical Soc Amer, 2016) Baykal, Yahya; Uysal, Murat; Gokce, Muhsin Caner; 28643; 7812; 124615; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Multiple-input single-output (MISO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, for the MISO FSO system, a partially coherent radial array and a finite-sized receiver aperture are used at the transmitter and the receiver, respectively. Using the extended Huygens - Fresnel principle, we formulate the average power and the power correlation at the finite-sized slow detector in weak atmospheric turbulence. System performance indicators such as the power scintillation index and the aperture averaging factor are determined. Effects of the source size, ring radius, receiver aperture radius, link distance, and structure constant and the degree of source coherence are analyzed on the performance of the MISO FSO system. In the limiting cases, the numerical results are found to be the same when compared to the existing coherent and partially coherent Gaussian beam scintillation indices. (C) 2016 Optical Society of America
Citation - WoS: 7
Citation - Scopus: 8
Apertured Paraxial Bessel Beams
(Optical Soc Amer, 2010) Umul, Yusuf Z.; 42699; 06.02. Elektronik ve Haberleşme Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The paraxial Bessel beam is obtained by applying an approximation in the wavenumbers. The scattering of the beams by a circular aperture in an absorbing screen is investigated. The scattered fields are expressed in terms of the Fresnel integrals by evaluating the Kirchhoff diffraction integral in the paraxial approximation. The results are examined numerically. (C) 2010 Optical Society of America
Citation - WoS: 6
Citation - Scopus: 10
Application of Adaptive Optics on Bit Error Rate of M-Ary Pulse-Position Oceanic Optical Wireless Communication Systems
(Iop Publishing Ltd, 2020) Gokce, Muhsin C.; Ata, Yalcin; Baykal, Yahya; 7812; 06.02. Elektronik ve Haberleşme Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.
Citation - Scopus: 4
Applications and Design for a Cloud of Virtual Sensors
(Institute of Advanced Engineering and Science, 2016) Hussein, A.J.; Riadh, A.; Alsultan, M.; Tareq, A.A.-R.; 01. Çankaya Üniversitesi
The use of sensors in our daily lives is a growing demand with the large number of electronic devices around us. These sensors will be included in our daily life requirements soon and they will affect our lives in both positive and negative ways. In this paper, we discuss the manner, applications and design issues for a cloud of virtual sensors, and we introduce a distributed system design to deal with physical sensors that reside in diverse locations and operate in different environments. This design operates in a cloud computing vision and can make virtual sensors in upper of physical one available from anywhere using ICT structure. Then, we negotiated the future of this technology, i.e., the Internet of Things (IoT). Additionally, we go over the strengths and weaknesses of using this technology. Our test lab shows high performance and good total cost of ownership and effective response time. © 2016 Institute of Advanced Engineering and Science. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 4
Automatic Coastline Detection Using Image Enhancement and Segmentation Algorithms
(Hard, 2016) Caniberk, Mustafa; Maras, Hadi Hakan; Maras, Erdem Emin; 34410; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Coastlines have hosted numerous civilizations since the earliest times of mankind due to the advantages they offer such as natural resources, transportation, arable areas, seafood, trade, and biodiversity. Coastal regions should be monitored vigilantly by planners and control mechanisms, and any changes in these regions should be detected with its human or natural origin, and future plans and possible interventions should be formed in these aspects to maintain ecological balance, sustainable development, and planned urbanization. Integrated coastal zone management (ICZM) provides an important tool to reach that goal. One of the important elements of ICZM is the detection of coastlines. While there are several methods to detect coastlines, remote sensing methods provide the fastest and the most efficient solutions. In this study, color infrared, grayscale, RGB, and fake infrared images were processed with the median filtering and segmentation software developed within the study, and coastal lines were detected by the edge detection method. The results show that segmentation with fake infrared images derived from RGB images give the best results.
Citation - Scopus: 2
Automatic Detection of Spina Bifida Occulta With Deep Learning Methods From Plain Pelvic Radiographs
(Springer Science and Business Media Deutschland GmbH, 2023) Üreten, K.; Maraş, Y.; Maraş, H.H.; Gök, K.; Atalar, E.; Çayhan, V.; Duran, S.; 34410; 06.01. Bilgisayar Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Purpose: Spina bifida occulta (SBO), which is the most common congenital spinal deformity, is often seen in the lower lumbar spine and sacrum. In this study, it is aimed to develop a computer-aided diagnosis method that will help clinicians in the diagnosis of spina bifida occulta from plain pelvic radiographs with deep learning methods and transfer learning method. Materials and methods: The You Only Look Once (YOLO) algorithm was used for object detection, and classification was made by applying transfer learning with a pre-trained VGG-19, ResNet-101, MobileNetV2, and GoogLeNet networks. Our dataset consisted of 206 normal lumbosacral radiographs and 160 SBO lumbosacral radiographs. The performance of the models was evaluated by metrics such as accuracy, sensitivity, specificity, precision, F1 score, and area under the ROC curve (AUC) results. Results: In the detection of SBO, 85.5%, 80.8%, 89.7%, 87.5%, 84%, and 0.92 accuracy, sensitivity, specificity, precision, F1 score, and AUC results were obtained with the pre-trained VGG-19 model, respectively. The pre-trained VGG-19 model performed better than the others. Conclusion: Successful results were obtained in this study performed to the diagnosis of SBO with deep learning methods. A model that will assist physicians in the diagnosis of SBO can be developed with new studies to be conducted with a large number of spinal radiographs. © 2023, The Author(s), under exclusive licence to The Brazilian Society of Biomedical Engineering.

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