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Article Citation - WoS: 4Citation - Scopus: 6An Automata Networks Based Preprocessing Technique for Artificial Neural Network Modelling of Primary Production Levels in Reservoirs(Elsevier, 2007) Kilic, Hurevren; Soyupak, Selcuk; Tuzun, Ilhami; Ince, Ozlem; Basaran, GokbenPrimary production in lakes and reservoirs develops as a result of complex reactions and interactions. Artificial neural networks (ANN) emerges as an approach in quantification of primary productivity in reservoirs. Almost all of the past ANN applications employed input data matrices whose vectors represent either water quality parameters or environmental characteristics. Most of the time, the components of input matrices are determined using expert opinion that implies possible factors that affect output vector. Major disadvantage of this approach is the possibility of ending-up with an input matrix that may have high correlations between some of its components. In this paper, an automata networks (AN) based preprocessing technique was developed to select suitable and appropriate constituents of input matrix to eliminate redundancy and to enhance calculation efficiency. The proposed technique specifically provides an apriori rough behavioral modeling through identification of minimal AN interaction topology. Predictive ANN models of primary production levels were developed for a reservoir following AN based pre-modeling step. The achieved levels of model precisions and performances were acceptable: the calculated root mean square error values (RMSE) were low; a correlation coefficient (R) as high as 0.83 was achieved with an ANN model of a specific structure. (c) 2006 Elsevier B.V. All rights reserved.Conference Object Citation - Scopus: 2Comparison of Gross Calorific Value Estimation of Turkish Coals Using Regression and Neural Networks Techniques(2012) Ozbayoglu,A.M.; Ozbayoglu,M.E.; Ozbayoglu,G.Gross calorific value (GCV) of coals was estimated using artificial neural networks, linear and non-linear regression techniques. Proximate and ultimate analysis results were collected for 187 different coal samples. Different input data sets were compared, such as both proximate and ultimate analysis data, and only proximate analysis data and only ultimate analysis data. It was observed that the best results were obtained when both proximate analysis and ultimate analysis results were used for estimating the gross calorific value. When the performance of artificial neural networks and regression analysis techniques were compared, it was observed that both artificial neural networks and regression techniques were promisingly accurate in estimating gross calorific values. In general, most of the models estimated the gross calorific value within ±3% of the expected value.Review Citation - WoS: 67Citation - Scopus: 81Software Test Maturity Assessment and Test Process Improvement: a Multivocal Literature Review(Elsevier, 2017) Garousi, Vahid; Felderer, Michael; Hacaloglu, TunaContext: Software testing practices and processes in many companies are far from being mature and are usually conducted in ad-hoc fashions. Such immature practices lead to various negative outcomes, e.g., ineffectiveness of testing practices in detecting all the defects, and cost and schedule overruns of testing activities. To conduct test maturity assessment (TMA) and test process improvement (TPI) in a systematic manner, various TMA/TPI models and approaches have been proposed. Objective: It is important to identify the state-of-the-art and the-practice in this area to consolidate the list of all various test maturity models proposed by practitioners and researchers, the drivers of TMA/TPI, the associated challenges and the benefits and results of TMA/TPI. Our article aims to benefit the readers (both practitioners and researchers) by providing the most comprehensive survey of the area, to this date, in assessing and improving the maturity of test processes. Method: To achieve the above objective, we have performed a Multivocal Literature Review (MLR) study to find out what we know about TMA/TPI. A MLR is a form of a Systematic Literature Review (SLR) which includes the grey literature (e.g., blog posts and white papers) in addition to the published (formal) literature (e.g., journal and conference papers). We searched the academic literature using the Google Scholar and the grey literature using the regular Google search engine. Results: Our MLR and its results are based on 181 sources, 51 (29%) of which were grey literature and 130 (71%) were formally published sources. By summarizing what we know about TMA/TPI, our review identified 58 different test maturity models and a large number of sources with varying degrees of empirical evidence on this topic. We also conducted qualitative analysis (coding) to synthesize the drivers, challenges and benefits of TMA/TPI from the primary sources. Conclusion: We show that current maturity models and techniques in TMA/TPI provides reasonable advice for industry and the research community. We suggest directions for follow-up work, e.g., using the findings of this MLR in industry-academia collaborative projects and empirical evaluation of models and techniques in the area of TMA/TPI as reported in this article. (C) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Properties of Tl4se3< Single Crystals and Characterization of Ag/Tl4< Schottky Barrier Diodes(Elsevier Science Bv, 2010) Qasrawi, A. F.; Gasanly, N. M.The main physical properties of Tl4Se3S single crystals were investigated for the first time. Particularly, the crystal data, Debye temperature, dark electrical resistivity and Hall effect in addition to the temperature dependent current-voltage characteristics and photosensitivity of the Ag/Tl4Se3S Schottky barrier diode were studied. The X-ray diffraction patterns have revealed that the crystal exhibited a single phase of tetragonal structure belonging to the D-4h(18) - 14mcm space group. A Debye temperature of 100 K was calculated using the results of the X-ray diffraction analysis. The dark electrical resistivity and Hall-effect measurements indicated that the samples exhibits p-type conduction with an electrical resistivity, carrier concentration and Hall mobility of 6.20 x 10(3) Omega cm, 1.16 x 10(12) cm(-3) and 873 cm(2) V-1 s(-1), respectively. The crystals were observed to have Schottky diode properties. The Ag/Tl4Se3S Schottky barrier device bias voltage was observed to depend on the crystal direction and on temperature. It was found that the calculated energy barrier height decreased and the diode ideality factor increased with temperature decreasing. The photosensitivity-light intensity dependence of this device was found to be linear reflecting the ability of using it in optoelectronics. (C) 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 10Combined Use of Ultrasonic-Assisted Drilling and Minimum Quantity Lubrication for Drilling of Niti Shape Memory Alloy(Taylor & Francis inc, 2023) Namlu, Ramazan Hakki; Lotfi, Bahram; Kilic, S. Engin; Yilmaz, Okan Deniz; Akar, SametThe drilling of shape-memory alloys based on nickel-titanium (Nitinol) is challenging due to their unique properties, such as high strength, high hardness and strong work hardening, which results in excessive tool wear and damage to the material. In this study, an attempt has been made to characterize the drillability of Nitinol by investigating the process/cooling interaction. Four different combinations of process/cooling have been studied as conventional drilling with flood cooling (CD-Wet) and with minimum quantity lubrication (CD-MQL), ultrasonic-assisted drilling with flood cooling (UAD-Wet) and with MQL (UAD-MQL). The drill bit wear, drilling forces, chip morphology and drilled hole quality are used as the performance measures. The results show that UAD conditions result in lower feed forces than CD conditions, with a 31.2% reduction in wet and a 15.3% reduction in MQL on average. The lowest feed forces are observed in UAD-Wet conditions due to better coolant penetration in the cutting zone. The UAD-Wet yielded the lowest tool wear, while CD-MQL exhibited the most severe. UAD demonstrated a & SIM;50% lower tool wear in the wet condition than CD and a 38.7% in the MQL condition. UAD is shown to outperform the CD process in terms of drilled-hole accuracy.Article Mathematical Modeling of a Direct Dimethyl Ether Fuel Cell(Wiley-hindawi, 2022) Alpaydin, Guvenc Umur; Durmus, Gizem Nur Bulanik; Colpan, C. Ozgur; Devrim, Yilser; Bulanik Durmuş, Gizem NurIn this study, a mathematical model of a direct dimethyl ether fuel cell (DDMEFC) is developed to examine the effect of operating conditions on voltage losses and cell performance. In modeling, the electrochemical relations and mass balances are used to find the cell voltage for the given conditions. The values of some modeling parameters are determined using experimental data through curve fitting. For validation purposes, in-house experimental studies are conducted. For this purpose, Pt50Ru25Pd25/C, Pt40Ru40Pd20/C, and Pt50Pd50/C anode catalysts are synthesized by the microwave method. The effects of these synthesized catalysts and the operating conditions (cell temperature, the molar ratio of dimethyl ether, and water) on the DDMEFC performance are discussed by comparing the activation and ohmic polarization as well as the polarization curves using the model developed. This cell-level modeling approach could be considered as a preliminary step in the design process of a DDMEFC stack.Article Citation - WoS: 40Citation - Scopus: 42Illumination and Voltage Effects on the Forward and Reverse Bias Current-Voltage (i-V) Characteristics in In/In2< Photodiodes(Springer, 2021) Yukselturk, Esra; Surucu, Ozge; Terlemezoglu, Makbule; Parlak, Mehmet; Altindal, SemsettinThe illumination and voltage effects on the I-V measurements of the fabricated In/In2S3/p-Si photodiode were investigated in dark and under various illumination intensities (20-100 mW/cm(2)) between +/- 2 V. Two linear regions in the forward-bias ln(I)-V plots were observed. The value of diode ideality factor (n) had an increasing trend with increasing illumination intensity while the barrier height (phi(Bo)) had a decreasing trend due to the increase of photocurrent. The photodiode properties were also investigated, and the value of linear-dynamic value range (LDR) was found to be 20.56 dB. The photoresponse (I-ph/I-dark), the photoresponsivity (R), and specific detectivity (D*) of the photodiode were calculated as a function of the illumination. The open-circuit voltage (V-oc) and short-current (I-sc) were found to be 0.36 V and 2.87 mA under 100 mW.cm(-2) illumination intensity, respectively. The possible conduction mechanisms (CMs) were investigated using the forward ln(I)-V and reverse ln(I)-V-0.5 plots. The energy-dependent surface states (N-ss) profile was extracted from the positive I-V data by considering voltage-dependent barrier height (BH) and ideality factor (n) in dark and illumination at 100 mW/cm(2).Article Citation - WoS: 25Citation - Scopus: 34Modelling and Controlling of Drill String Stick Slip Vibrations in an Oil Well Drilling Rig(Elsevier, 2022) Sadeghi, Amir Noabahar; Arikan, Kutluk Bilge; Ozbek, Mehmet Efe; Noabahar Sadeghi, AmirMitigating of drill string vibrations, plays a distinctive role in increase of rate of penetration and consequently decrease of the operation costs, prevent of severe damages to drill string and bit, increase of drilling operation quality and safety, and enhance the performances of the controllers. This study deals with modelling and controlling of drill string vibrations with focus on stick slip vibrations in vertical wells. The approach taken to subdivide the drill string into smaller torsional sections and model the complete system dynamically and employ the extracted torsional model to model the stick slip vibrations mathematically. To mitigate and or active control of stick slip vibrations, three architectures are developed and proposed, manipulation of the rotational speed, manipulation of the weight on bit, and increasing of the damping in the bottom of the drill string. The performance of each strategy is analysed individually as well as relative to each other, using a mathematical measure when the drill string length is divided into smaller torsional sections. By the aid of the simulations and mathematical measures, it is shown that manipulation of rotational speeds at the surface may not be an effective solution to reduce the stick slip vibrations, however manipulation of weight on bit and increasing of damping at the bottom of string can be two effective solutions to mitigate these kinds of vibrations. As a general conclusion, it is proved that the manipulation of bottom side drilling parameters is more effective than the manipulation of surface drilling parameters.Article Citation - Scopus: 10The Effects of Text Density Levels and the Cognitive Style of Field Dependence on Learning From a Cbi Tutorial(2011) Ipek,I.The purpose of this study was to investigate the effects of variations in text density levels and the cognitive style of field dependence on learning from a CBI tutorial, based on the dependent measures of achievement, reading comprehension, and reading rate, and of lesson completion time. Eighty college undergraduate students were randomly assigned to text density levels, after being assigned to three cognitive style groups: Field dependent, field neutral, and field independent, based on their Group Embedded Figure Test scores. Instruction was delivered by means of two versions of a CBI tutorial: Low density text and high density text. A two-way analysis of covariance was used to investigate whether there are main effects and interactions between the cognitive style of field dependence and text density levels. In order to control statistical power and to equate the treatment groups, Nelson-Denny Reading Comprehension Test scores were used as a covariate. The analysis of regression coefficients between text density type and dependent variables and between field dependence and dependent variables were shown in tables. Although the findings show non-significance in formal tests of hypotheses, a preference for the high-density level was found. Then, the interaction effects between field dependence and tex density levels on dependent measures were clarified. Six research questions converted to statistical hypotheses were tested according to the factorial design model. Specifically, the tests of hypotheses generated discussion and conclusions were given at the end of the study. © The Turkish Online Journal of Educational Technology.Article Citation - WoS: 4Citation - Scopus: 5Space Efficiency in Tall Hotel Towers(Mdpi, 2024) Aslantamer, Ozlem Nur; Ilgin, Huseyin EmreMaximizing spatial utilization within tall buildings stands as a paramount planning consideration for ensuring project feasibility, particularly accentuated ins the context of hotel constructions. To date, no comprehensive study has addressed this issue while considering crucial architectural and structural planning factors. This article fills this gap by using a case study method based on data from 31 contemporary tall hotel towers. The findings revealed several key points: (i) central core typology was mostly utilized; (ii) prismatic buildings were the most prevalent forms; (iii) shear-walled frame systems were predominantly employed; (iv) concrete was the preferred choice for hotel construction; (v) the average space efficiency and the ratio of core area to gross floor area (GFA) averaged 81.2% and 16%, respectively; (vi) the range changed from a minimum of 70% to 4% to a maximum of 94% to 28%; and (vii) space efficiency showed an inverse relationship with the height of the building. It is anticipated that this paper will assist architects and structural engineers as well as builders involved in the planning of hotel developments.
