Mühendislik Fakültesi

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Throughput maximisation of different signal shapes working on 802.16e mobile multihop network using novel cognitive methods
(Springer-Verlag Berlin, 2010) Preveze, Barbaros; Şafak, Aysel
This study proposes cognitive methods for managing the multimedia packet traffic of 802.16e system providing the dynamic spectrum sharing by TDM & OFDMA under heavy traffic conditions. The cognitive techniques are used in order to maximize the throughput of a system having different signal shapes such as video, voice or data packets. All real time voice and video packets transmissions have been provided with full success where the loss rate of data packets has been minimized using the cognitive methods. By these methods buffers are managed successfully for the given parameters, optimum buffer sizes have been formulized and it's shown that we brought the throughput up to its calculated theoretical limits for multi-hop mobile wimax (802.16e).
Citation - WoS: 3
Citation - Scopus: 6
A Novel Transformerless Single-Phase Three-Level Buck-Boost Inverter
(Ieee, 2023) Demirkutlu, Eyyup; Iskender, Ires
This paper proposes a novel transformerless, single-phase, three-level, buck-boost inverter. The proposed inverter can suppress the leakage current drawn from the input power source and provide a long-lasting solution for applications with a wide range and unregulated input voltage. Unlike similar topologies, in the proposed inverter there is no need to have a mid-point of DC sources or DC bus capacitors at the input side of the inverter. A single-phase, three-level, buck-boost inverter for realizing the power stage with 110-Vrms output AC voltage and a range of 100V-200V input DC voltage is investigated in this study. The proposed topology has been proven through theory, computer simulations, and experimental studies with SiC MOSFETs-based prototype of a 300-VA power supply. Theory, computer simulation, and experimental results are all correlated.
Citation - WoS: 6
Citation - Scopus: 4
Propagation of Cross Beams Through Atmospheric Turbulence
(Spie-int Soc Optical Engineering, 2005) Yenice, YE; Eyyuboglu, HT; Baykal, Y
Propagation properties of cross beam in turbulent medium are studied. A cross beam is constructed by the sum of two highly asymmetric Gaussian beams placed along transverse axes. It is known that such beams, when propagating in free space, will exhibit contrasting diffraction behaviours; they expand widely in one axis, while they are almost nondiffracting in the other axis within useful link lengths. This behaviour allows detecting the two components and a sum component if desired separately with a practical multiaperture receiver. Bearing in mind that this property can be exploited for a diversity scheme, our present work focuses on the propagation of such beams in turbulent atmosphere. To this end, starting with a source field expression of the cross beam, the second order mutual coherence function is formulated at the receiver plane. Intensity plots describing the dependence on the source and propagation parameters on the receiver plane are provided. The results tend to confirm the applicability of the concept provided the design parameters are appropriately chosen. For a decisive assessment, however, turbulence-induced beam wander must also be examined.
Broiler House Performance Analysis and Chick Entrance Planning for a Broiler Chicken Integration
(2012) Satır, Benhür; Yıldırım, Gonca; Kırca, Ömer
Increasing rates of chicken meat production has a substantial impact on the Turkish economy. Per capita production in Turkey is close to the average production of the top 20 countries in the world. The production is done by integrated organizations, incorporating an integrator chicken company affiliated with all aspects of the production in an organization. There are many complicated processes, stages and parties involved in a typical integration, bringing with them many interesting problems. In this paper, we focus on tactical and operational decisions required during the broiler growing stage, motivated by the requirements of a moderate-sized integrator in the Marmara Region of Turkey. We use analysis of variance to compare the performances of available broiler houses, and to find the factors effecting the performance measures. Then, we present a mixed-integer linear program which uses the results of our performance analysis to find the least costly set of broiler houses with which the integrator should work, and the chick entrance times into these houses over a planning period.
EXPERIMENTAL AND NUMERICAL ANALYSIS OF FLOW OVER A PICKUP TRUCK
(2021) İnce, İbrahim Timuçin; Mercan, Hatice; Onur, Nevzat
The drag forces and the overall drag coefficient of a typical pickup truck are investigated experimentally and the 3D numerical analysis is performed. A detailed 1/4-scale model is constructed and experiments are performed at Reynolds numbers around 2 × 106in the Ankara Wind Tunnel (ART). The experimental study is divided into two stages: in the first stage the pressure distribution along the symmetry axis is measured and in the second stage the drag forces and overall drag coefficient are measured at five different wind speeds. The measured data are compared with the 3D numerical simulation performed in FLUENT. The turbulence standard, realizable, and RNG k-∈ models, the standard and SST k-ω models, and finally the RSM are compared for three near-wall treatments: standard wall function, nonequilibrium wall function, and enhanced wall function. The comparison revealed that for lower velocities the best turbulence model-wall treatment couple is the realizable k-∈ model with Reynolds stress model with standard wall function, whereas for higher velocities the standard k-∈ turbulence model is observed to be more compatible with experimental data. The highest pressure value is measured in front of the pickup truck and the lowest pressure value is evaluated at the rim where the windshield and the roof meet. © 2021 Begell House Inc.. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Development of Air-To Engagement Analysis Model of Fighter Aircrafts
(Gazi Univ, Fac Engineering Architecture, 2022) Bektas, Almila; Ergezer, Halit; Erdogan, Sinem
In operational analysis studies; it is possible to model and simulate at an engineering level, engagement level, task level and campaign forces level. In this study, modelling and simulation studies are performed in engagement-level allowing the analysis of air-to-ground engagement effectiveness of fighter aircraft according to the operational environment. The operating environment of the combat aircraft, which provides survivability analysis based on low visibility and electronic mixing capabilities, is created. The search radar and tracking radar models for ground-to-air threats have been designed in accordance with the engagement level. The dynamic model of the fighter aircraft and the ground-to-air missile have been modelled using pseudo 5 degree-of-freedom. Modelling has been carried out to allow the use of changes in the Radar Crosssectional Area (RCS), which is one of the most important factors affecting the survivability of the aircraft, with respect to azimuth and elevation angles. The Radio Frequency (RF) jamming capability of the fighter aircraft has also been modelled in accordance with the engagement level. The results of the generic scenarios for the analysis of the effect of these models' parameters on the survivability of fighter aircraft have been presented.
Citation - WoS: 11
Citation - Scopus: 11
Uniform Boundary Diffraction Wave Theory of Rubinowicz
(Optical Soc Amer, 2010) Umul, Yusuf Z.
Rubinowicz introduced a uniform asymptotic evaluation of the boundary diffraction wave at the transition region [Ann. Phys. (Leipzig) 378, 339 (1924)]. The uniform theory of Rubinowicz is generalized for the improved integrals of the boundary diffraction wave. The technique is applied to the scattering problem of plane waves by an impedance half-plane, and the diffracted waves are examined numerically. (C) 2010 Optical Society of America
Citation - WoS: 5
Citation - Scopus: 5
Optimal Supervisory Control of Discrete Event Systems: Cyclicity and Interleaving of Tasks
(Siam Publications, 2015) Schmidt, Klaus Werner
A substantial number of tasks in production systems are executed in a repetitive, cyclic fashion. Specifically, production systems run different production cycles of different products as well as different instances of the same production cycle. In this paper, we consider the optimal control and interleaving of such production cycles in a supervisory control framework for discrete event systems (DESs). That is, different from other approaches, our work is based on a behavioral specification of each production cycle. First, we adapt an optimal control approach for DESs, in order to optimize the operation of individual production cycles. Second, we employ the interleaving composition to design a supervisor that enables the simultaneous execution of different production cycles. Combining both results, we can further determine the maximum number of production cycles that can be executed simultaneously on a given production system.
Mobile Assisted Language Learning: English Pronunciation at Learners' Fingertips
(Anı Yayıncılık, 2009) Saran, Murat; Seferoğlu, Gölge; Çağıltay, Kürşat
Problem Statement: The study of pronunciation had been a relatively neglected issue in the foreign/second language acquisition literature. Likewise, in classroom contexts, pronunciation has received less attention as compared to the other language components and skills with the belief that it is peripheral to successful communication. Yet, there is a recent revival of interest in pronunciation research. The literature on foreign/second language acquisition highlights that in general in-class activities are not sufficient for effective language learning and that learners should also have input and output opportunities outside the classroom. This holds true for learning pronunciation as the literature suggests that just classroom instruction has a negligible impact on oral production of learners. With their widespread use and their features such as mobility, localization, and personalization, mobile phones offer a great potential for out-of-class learning. Yet, there is scarce research on the use of mobile phones in language learning contexts nor any on using mobile phones to improve learners' pronunciation. This study is aimed to make a significant contribution to the literature in these respects. Purpose of the Study: The major aim of this study was to investigate the potentials and effectiveness of using mobile phones in foreign language education. In particular, the effects of using multimedia messages via mobile phones for improving language learners' pronunciation of words were explored. Methods: A mixed method approach involving both quantitative and qualitative components was employed in this study. The quantitative part of the study followed a pre-test/post-test quasi-experimental design. The qualitative part of the study included post-study semi-structured interviews with the students, and a questionnaire involving open ended items. The participants of this study were a group of students attending the English Preparatory School of an English-medium university in Turkey. There different groups were formed in order to investigate the comparative effectiveness of supplementary materials delivered through 3 different means: mobile phones, web pages, and handouts. Results: Analyses of the quantitative data showed that using mobile phones had positive effects on students' pronunciation learning. The qualitative data collected through the questionnaire and the interviews supported this finding. All participants provided positive feedback about the mobile learning application used in this study. Conclusions and Recommendations: This study extends the use of use mobile phones, which are already in use for communication and entertainment, to educational settings. The findings of the study pose crucial implications for foreign language teaching and learning
Citation - WoS: 10
Citation - Scopus: 12
Sparse Representations for Online-Learning Hyperspectral Image Compression
(Optical Soc Amer, 2015) Toreyin, Behcet Ugur; Ulku, Irem
Sparse models provide data representations in the fewest possible number of nonzero elements. This inherent characteristic enables sparse models to be utilized for data compression purposes. Hyperspectral data is large in size. In this paper, a framework for sparsity-based hyperspectral image compression methods using online learning is proposed. There are various sparse optimization models. A comparative analysis of sparse representations in terms of their hyperspectral image compression performance is presented. For this purpose, online-learning-based hyperspectral image compression methods are proposed using four different sparse representations. Results indicate that, independent of the sparsity models, online-learning-based hyperspectral data compression schemes yield the best compression performances for data rates of 0.1 and 0.3 bits per sample, compared to other state-of-the-art hyperspectral data compression techniques, in terms of image quality measured as average peak signal-to-noise ratio. (c) 2015 Optical Society of America
Simultaneous Detection of Two Different Bacteria Using QDs and MNPs
(2016) Doğan, Üzeyir; Kasap, Esin Nagihan; Çoğun, Ferah; Yıldırım, Ender; Çetin, Demet; Suludere, Zekiye; Boyacı, İsmail Hakkı; Ertaş, Nusret; Tamer, Uğur
Citation - WoS: 47
Citation - Scopus: 52
A Reliable and Competitive Mathematical Analysis of Ebola Epidemic Model
(Springer, 2020) Ahmad, Waheed; Abbas, Mujahid; Baleanu, Dumitru; Rafiq, Muhammad
The purpose of this article is to discuss the dynamics of the spread of Ebola virus disease (EVD), a kind of fever commonly known as Ebola hemorrhagic fever. It is rare but severe and is considered to be extremely dangerous. Ebola virus transmits to people through domestic and wild animals, called transmitting agents, and then spreads into the human population through close and direct contact among individuals. To study the dynamics and to illustrate the stability pattern of Ebola virus in human population, we have developed an SEIR type model consisting of coupled nonlinear differential equations. These equations provide a good tool to discuss the mode of impact of Ebola virus on the human population through domestic and wild animals. We first formulate the proposed model and obtain the value of threshold parameter R0 for the model. We then determine both the disease-free equilibrium (DFE) and endemic equilibrium (EE) and discuss the stability of the model. We show that both the equilibrium states are locally asymptotically stable. Employing Lyapunov functions theory, global stabilities at both the levels are carried out. We use the Runge-Kutta method of order 4 (RK4) and a non-standard finite difference (NSFD) scheme for the susceptible-exposed-infected-recovered (SEIR) model. In contrast to RK4, which fails for large time step size, it is found that the NSFD scheme preserves the dynamics of the proposed model for any step size used. Numerical results along with the comparison, using different values of step size h, are provided.
Sınıflandırmada Küçük ve Dengesiz Veri Kümesi Problemi
(2019) Par, Öznur Esra; Akçapınar Sezer, Ebru; Sever, Hayri
Verilerinin sınıflandırılması, veri kümesinin küçük ve dengesiz olması durumunda zorlaşmakta ve sınıflama performansını direkt etkilemektedir. Veri setinin küçük olması ve/veya sınıflar arasında dengesizlik olması veri madenciliğinde büyük bir sorun haline gelmiştir. Sınıflama algoritmaları, veri setlerinin yeterli büyüklüğe sahip, dengeli olduğu varsayımı üzerine geliştirilmiştir. Bu algoritmaların çoğu, azınlık sınıfındaki örnekleri göz ardı ederken veya yanlış sınıflandırırken, çoğunluk sınıfa odaklanır. Medikal veri madenciliğinde bazı kısıtlardan dolayı küçük ve dengesiz veri seti problemi ile sıklıkla karşılaşılmaktadır. Çalışma kapsamında erişime açık hepatit veri seti, küçük veri setlerine bölünmüş, oluşturulan her bir veri seti uzaklık tabanlı yöntemlerle çoğaltılmıştır. Çoğaltılan veri setleri dört farklı makine öğrenmesi algoritması (Yapay Sinir Ağları, Destek Vektör Makineleri, Naive Bayes ve Karar Ağacı) kullanılarak sınıflandırılmış, elde edilen sınıflama sonuçları karşılaştırılmıştır.
Citation - WoS: 18
Citation - Scopus: 19
Scattering by an Impedance Half-Plane: Comparison of the Solutions of Raman/Krishnan and Maliuzhinets/Senior
(Electromagnetics Acad, 2009) Umul, Y. Z.
There are three approaches for the solution of the diffraction problem of plane waves by an impedance half-plane in the literature. The diffracted field expressions, obtained by the related methods, are compared numerically. The examination of the scattered field shows that the most reliable solution is the field representation of Raman and Krishnan. Since the diffracted fields of Senior and Maliuzhinets do not compensate the discontinuities of the geometrical optics waves at the transition regions.
Entropy Functional Based Adaptive Decision Fusion Framework
(2012) Günay, O.; Töreyin, B.U.; Köse, K.; Çetin, A.E.
In this paper, an entropy functional based online adaptive decision fusion framework is developed for image analysis and computer vision applications. In this framework, it is assumed that the compound algorithm consists of several sub-algorithms, each of which yields its own decision as a real number centered around zero, representing the confidence level of that particular sub-algorithm. Decision values are linearly combined with weights which are updated online according to an active fusion method based on performing entropic projections onto convex sets describing sub-algorithms. It is assumed that there is an oracle, who is usually a human operator, providing feedback to the decision fusion method. A video based wildfire detection system was developed to evaluate the performance of the decision fusion algorithm. © 2012 IEEE.
Citation - Scopus: 23
Using Announcement Options in the Bid Construction Phase for Disaster Relief Procurement
(2012) Ertem, M.A.; Buyurgan, N.; Pohl, E.A.
This paper presents an analysis of the bid construction phase of procurement auctions in disaster relief and humanitarian logistics. Substitution and partial fulfillment options are presented in formulations to allow bidders with fewer inventories to offer substitute item types and partial bids in auctions. During the auction announcement phase, a coordinating platform for disaster locations (i.e., auctioneer) allows substitution and partial fulfillment options to the relief suppliers (i.e., bidders) when acceptable. Thus, suppliers with fewer inventories can offer substitute item types and participate in more auctions by partially bidding. A genetic algorithm, a simulated annealing algorithm and an integer program are used for the analysis of the bid construction phase with different announcement options. Heuristic solution techniques and an IP formulation help understand the dynamics of the bid construction problem. It is shown that the addition of substitution and partial fulfillment options is essential to diversify and increase the usable capacity of the supplier base. Additionally, the partial fulfillment option enables better usage of supplier inventories in an environment with scarce supplies. © 2012 Elsevier Ltd.
Effects of Type of Incidence on the Second and Fourth Order Moment Parameters Evaluated in Turbulent Atmosphere
(2010) Baykal, Y.; Baykal, Yahya Kemal; Elektrik-Elektronik Mühendisliği
Using a general type incidence, the second and fourth order moments are formulated in atmospheric turbulence. Received field and intensity correlations are evaluated and the behaviour of these correlations are compared for different beam types. © 2010 OSA/FiO/LS.
Citation - WoS: 11
Citation - Scopus: 11
Effects of Extremely Strong Turbulent Medium on Scintillations of Partially Coherent Annular and Flat-Topped Gaussian Beams
(Elsevier Science Bv, 2012) Oztan, Mehmet A.; Baykal, Yahya; Nakiboglu, Cem
Scintillation index of partially coherent annular and partially coherent flat-topped Gaussian beams propagating in horizontal links is found at the receiver origin when these beams propagate in extremely strong atmospheric turbulence. Scintillation index of coherent versions of such beams attain unity saturation value whereas the decrease in the degree of source coherence results in the decrease of the scintillations. At a fixed degree of partial coherence, thin ring sized annular beams possess smaller scintillations than thick ones. For partially coherent Flat-topped Gaussian beams, higher flatness yields smaller intensity fluctuations. In extremely strong turbulence, partially coherent annular and partially coherent flat-topped Gaussian beams have smaller scintillations when compared to partially coherent single Gaussian beam scintillations. (C) 2011 Elsevier B.V. All rights reserved.
Citation - WoS: 43
Citation - Scopus: 54
A Normally Closed Electrostatic Parylene Microvalve for Micro Total Analysis Systems
(Elsevier Science Sa, 2012) Arikan, M. A. Sahir; Kulah, Haluk; Yildirim, Ender
This paper presents an electrostatically actuated, normally closed microvalve for parylene microfluidics. The proposed valve structure isolates the fluid from the electric field, and hence results in relatively low actuation potentials (<60 V) irrespective of the working fluid. Hereby, the microvalve solves electrolysis or electrode shielding problems observed in electrostatic actuation in micro total analysis systems. To investigate leakage properties, microvalves were tested under pressurized flow with de-ionized (DI) water. No detectable leakage ratio was observed up to 20 kPa inlet pressure, due to the unique semicircular valve seat design. It was shown that the valve seat could be reconfigured to enable sealing at various pressure levels for different applications. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 28
Citation - Scopus: 30
Effect of Anisotropy on Intensity Fluctuations in Oceanic Turbulence
(Taylor & Francis Ltd, 2018) Baykal, Yahya
For an optical spherical wave propagating in an oceanic turbulent medium, the effect of anisotropy on the received intensity fluctuations is investigated. For different anisotropy factors, the variations of the scintillation index vs. the ratio that determines the relative strength of temperature and salinity in the index fluctuations, the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, viscosity, link length and the wavelength are plotted. It is found that, for all the oceanic turbulence and the link parameters of interest, as the medium becomes more anisotropic, the intensity of the optical spherical wave fluctuates less. It is concluded that the performance of an optical wireless communication systems (OWCS) operating in anisotropic oceanic turbulence is better than the performance of OWCS operating in isotropic oceanic turbulence.

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