İşletme Fakültesi

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Citation Count: 4
An Adaptive Affinity Matrix Optimization for Locality Preserving Projection Via Heuristic Methods for Hyperspectral Image Analysis
(IEEE-Inst Electrıcal Electronıcs Engıneers Inc, 2019) Taşkın, Gülşen; Ceylan, Oğuzhan
Locality preserving projection (LPP) has been often used as a dimensionality reduction tool for hyperspectral image analysis especially in the context of classification since it provides a projection matrix for embedding test samples to low dimensional space. However, the performance of LPP heavily depends on the optimization of two parameters of the graph affinity matrix: k-nearest neighbor and heat kernel width, when one considers an isotropic kernel. These two parameters might be optimally chosen simply based on a grid search. In case of using a generalized heat kernel where each feature is separately weighted by a kernel width, the number of parameters that need to be optimized is related to the number of features of the dataset, which might not be very easy to tune. Therefore, in this article, we propose to use heuristic methods, including genetic algorithm (GA), harmony search (HS), and particle swarm optimization (PSO), to explore the effects of the heat kernel parameters aiming to analyze the embedding quality of LPP's projection in terms of various aspects, including 1-NN classification accuracy, locality preserving power, and quality of the graph affinity matrix. The results obtained with the experiments on three hyperspectral datasets show that HS performs better than GA and PSO in optimizing the parameters of the affinity matrix, and the generalized heat kernel achieves better performance than the isotropic kernel. Additionally, a feature selection application is performed by using the kernel width of the generalized heat kernel for each heuristic method. The results show that very promising results are obtained in comparison with the state-of-the-art feature selection methods.
Citation Count: 6
Alone but Together Autonomous but Related: Self-Construal Effects on Happiness in Social Experiences
(Wiley, 2018) Merdin-Uygur, Ezgi; Hesapci, Ozlem
Communal tables and open workspaces have become popular servicescapes that is contemporary spaces for experiencing dining or working alone but together. Previous research demonstrates that experiencing with close others (e.g. with friends or family) increases happiness and satisfaction but experiences shared with strangers in contexts such as communal tables or workshops have not yet been thoroughly analyzed. Addressing this research gap from a social-psychological perspective we suggest that even though individuals are generally happier when they share experiences with loved ones self-construal plays a moderating role in the relationship. Individuals with high autonomy and high relatedness do not anticipate greater happiness from experiences shared with friends than with those shared with strangers. Three experimental studies (two online and one field) demonstrate this effect using different operationalizations of autonomy relatedness. Managerial implications are discussed and suggestions are made for future research.
Citation Count: 0
Analysis and Implications of the Giant Component for an Online Interactive Platform
(Int Business Information Management Assoc-IBIMA, 2016) Aydın, Mehmet Nafiz; Perdahci, N. Ziya
This research is concerned with practical and research challenges related to understanding the nature of online interactive platforms. So-called network science is adopted to investigate the very nature of these systems as complex systems. In this regard we examine an online interactive health network and show that the interactive platform examined exhibits essential structural properties that characterize most real complex networks. We basically look into the largest connected component so-called a giant component (GC) to better understand how the representative network has established. In particular we apply dynamic network analysis to investigate how the GC has evolved over time. We identify a particular pattern towards emerging a GC. Implications of the patterns have been elaborated from a management perspective. We recommend that the basic stages of the emergence of the GC might be of interest to platform managers while evaluating performance of online platforms.
Citation Count: 8
An Analysis of the Unemployment Selected Mena Countries and Turkey
(2008) Bilgin, Mehmet Hüseyin; Kilicarslan, Ismihan N, I. N.
One of the most important economic and social problems of the Middle East and North Africa (MENA) is the high rate of unemployment. Unemployment in the selected MENA countries like Egypt Israel Jordan and Turkey are examined as well as the relationship between growth and unemployment. For this reason active labor market policies should be designed to address job creation in addition to structural reform in labor markets.
Citation Count: 7
Anytime. Everywhere. Mobile Learning in Higher Education: Creating a Gis Course
(Springer-Verlag Berlin, 2012) Erkollar, Alptekin; Oberer, Birgit
The course concepts introduced in this contribution were implemented in 2011 in a university in Turkey and show an approach for integrating mobile learning modules in higher education. The results of the course show the advantages as well as potential for improvement of the system and the use of it in higher education.
Citation Count: 0
Applications of Eigenvalue Counting and Inclusion Theorems in Model Order Reduction
(Springer-Verlag Berlin, 2010) Yetkin, E. Fatih; Dağ, Hasan
We suggest a simple and an efficient iterative method based on both the Gerschgorin eigenvalue inclusion theorem and the deflation methods to compute a Reduced Order Model (ROM) to lower greatly the order of a given state space system. This method is especially efficient in symmetric state-space systems but it works for the other cases with some modifications.
Citation Count: 5
Art Investment: Hedging or Safe Haven Through Financial Crises
(Springer, 2020) Öztürkkal, Belma; Toğan-Eğrican, Aslı
We analyze long-term art auction sales data focusing on and around financial crisis periods with other investment returns to understand whether art can be considered a safe haven during volatile times or a hedging option in general by analyzing art auction data in a volatile emerging market. Our findings suggest Turkish art returns are either negatively correlated or at low correlation with other investments, including the equity market. We have the view that art can be considered a hedging mechanism on average to enhance returns and to decrease the risk of portfolios and improve diversification. However, we do not discard the safe-haven hypothesis, either. Although the auction data on the crisis period is limited, results of and around crisis periods show art returns are positively correlated with various volatility indices. In addition, the number of art transactions also increases after the crisis years, which may be a sign of liquidity requirement of some investors and an opportunity for buyers. The benefit is visible especially during years of contractions, which do not end with a very severe crisis, since the art auction market liquidity dries if the crisis is severe.
Citation Count: 3
Assessment of Harmonic Distortion on Distribution Feeders With Electric Vehicles and Residential Pvs
(IEEE, 2017) Ceylan, Oğuzhan; Paudyal, Sumit; Dahal, Sudarshan; Karki, Nava R.
Power-electronic interfacing based devices such as photovoltaic (PV) panels and electric vehicles (EVs) cause voltage/current harmonic distortions on the power grid. The harmonic current profiles from EVs and PVs depend on the design of the controllers integrated to the PV inverters and EV chargers. Similarly the voltage and current harmonic distortions on a grid change throughout the day as the PV output power number of grid connected EVs and the other load pattern change. In this context we present harmonic assessment to demonstrate cumulative effect of large number of EVs and PVs on a medium voltage distribution grid. We will demonstrate the case studies on the IEEE 123-node distribution feeder with 20% 50% and 100% PV and EV penetrations based on time series simulations carried out for an entire day.
Citation Count: 0
Attitudes Towards Knowledge Management in Turkish Companies
(2002) Üçdal, Erol; Güzey, Yildiz Y.
Attitudes towards knowledge management in Turkish companies are discussed. More and more companies in Turkish economy are allocating responsibility and a budget for knowledge management. Analysis show that the acts of successful knowledge management strategies brings new types of working giving people the chance to invest in knowledge maintaining the culture change and rewarding employees with new incentive schemes.
Citation Count: 11
Behavioral Biases of Finance Professionals: Turkish Evidence
(Elsevier Science Bv, 2016) Kiymaz, Halil; Öztürkkal, Belma; Akkemik, K. Ali
This study extends the existing literature on the determinants of behavioral biases of Turkish finance sector professionals. It examines the impact of various personal and objective attributes of finance sector professionals on their risk choices derived from their portfolio allocation and personal wealth data. Utilizing survey data from 206 professionals we find that these professionals take higher risk in the form of investment in equities when investing in home country firms (geographic bias) and investing in firms headquartered in their home towns (home bias). Those relying on their own predictions when making investment decisions and those with emotional biases invest less in equities. Findings further show that younger professionals professional with less education with lower risk aversion and with single broker accounts are more likely to invest in equities. We also find that those with higher expected returns invest more in equities showing overconfidence. Subsample analysis results for finance professionals suggest that portfolio managers and brokerage company professionals display differing risk taking behavior. (C) 2016 Elsevier B.V. All rights reserved.
Citation Count: 0
BİRLEŞME VE SATIN ALMA İŞLEMLERİNİN ŞİRKET VE SEKTÖR DÜZEYİNDE ETKİLERİ
(2016) Akben Selçuk, Elif; Köksal, Emin; Altıok Yılmaz, Ayşe Dilara
[Abstract Not Available]
Citation Count: 37
Bitcoin Forecasting Using Arima and Prophet
(IEEE, 2018) Yenidoğan, Işıl; Çayır, Aykut; Kozan, Ozan; Dağ, Tugce; Arslan, Çiğdem
This paper presents all studies methodology and results about Bitcoin forecasting with PROPHET and ARIMA methods using R analytics platform. To find the most accurate forecast model the performance metrics of PROPHET and AMNIA methods are compared on the same dataset. The dataset selected 16r this study starts from May 2016 and ends in March 2018 which is the interval that Bitcoin values changing significantly against the other currencies. Data is prepared for time series analysis by performing data preprocessing steps such as time stamp conversion and feature selection. Although the time series analysis has a univariate characteristics it is aimed to include some additional variables to each model to improve the forecasting accuracy. Those additional variables are selected based on different correlation studies between cryptocurrencies and real currencies. The model selection for both ARIMA and PROPHET is done by using threefold splitting technique considering the time series characteristics of the dataset. The threefold splitting technique gave the optimum ratios for training validation and test sets. Filially two different models are created and compared in terms of performance metrics. Based on the extensive testing we see that PROPHET outperforms ARIMA by 0.94 to 0.68 in R-2 values.
Citation Count: 2
Branch Outage Simulation Based Contingency Screening by Gravitational Search Algorithm
(Praise Worthy Prize Srl, 2012) Ceylan, Oğuzhan; Özdemir, Aydoğan; Dağ, Hasan
Power systems contingency analysis is an important issue for electric power system operators. This paper performs branch outage simulation based contingency screening using a bounded network approach. Local constrained optimization problem representing the branch outage phenomena is solved by the gravitational search algorithm. The proposed method is applied to IEEE 14 30 57 and 118 Bus Test systems and its performance from the point of capturing violations is evaluated. In addition false alarms and the computational accuracy of the proposed method are also analyzed by using scattering diagrams. Finally the proposed gravitational search based contingency screening is compared with full AC load flow solutions from the point of computational speed. Copyright (C) 2012 Praise Worthy Prize S.r.l. - All rights reserved.
Citation Count: 1
Case Study 8: Igaranti: Expanding the Frontiers of Mobile Banking Innovation
(Springer International Publishing, 2016) Ozturkcan, Selcen; Tunçalp, Deniz
iGaranti have claimed many awards and recognitions in addition to the wide press coverage. Two years into its launch iGaranti counted for an active user base of 110 k. However the spread of its reach was only about 2?% of the active mobile banking users in the market. Mr. Yilmaz worried about the bottlenecks that had limited further user acceptance and engagement. © Springer International Publishing Switzerland 2017.
Citation Count: 2
Cash Holdings and Corporate Governance: Evidence From Turkey
(IGI Global, 2019) Akben Selçuk, Elif; Şener, Pınar
This chapter investigates the empirical factors affecting corporate cash holdings with special emphasis on corporate governance variables for a sample of Turkish-listed nonfinancial firms over the period 2006 to 2010. The findings reveal a significant non-linear relation between family ownership and cash holdings. In addition, while board structure does not significantly affect the level of cash holdings, tunneling increases cash reserves of firms. Furthermore, the results indicate that cash flow, leverage, other liquid assets that can be used as cash substitutes, the degree of tangibility of assets, and firm size are important in determining cash holdings among Turkish companies.
Citation Count: 0
Choice of Finance in an Emerging Market: the Impact of Independent Decisions Politics and Religion
(Springer International Publishing, 2017) Davutyan, Nurhan; Öztürkkal, Belma
This paper is based on a KONDA 1 Research and Consultancy 2 survey conducted in May 2014 on 2607 people forming a representative sample of the Turkish population. It focuses on how people’s religious and political characteristics impact the independence of their decision making regarding saving and borrowing. An earlier study by Davutyan and Ozturkkal (2016) reports saving and borrowing decisions strongly correlate with income, education, marital status and region within country. Furthermore, 54% of those surveyed did not save and the main motivation for those who saved was to finance children’s education or home purchase. Religious people and those with a conservative lifestyle are less likely to borrow from family and friends. Older, married and working individuals are more likely to have difficulty paying back loans. According to the results of this survey, religious individuals are less likely to independently decide on their investment choices. Thus, religious people tend to make investment decisions together with family, elderly and respected relatives.
Citation Count: 2
Cloud Elearning: Transforming Education Through Cloud Technology: Preliminaries for Generation C
(ACAD Conferences Ltd, 2012) Oberer, Birgit; Erkollar, Alptekin
Cloud computing is a buzz word that is also spilling over into the education industry which enables access to software applications hardware data and computer processing power on the Web rather than installing software onto one's computer or server. For education it offers new possibilities to structure and perform learning processes. In this study the potential impact of cloud computing on education is analyzed showing what it means for educators and students as well as institutions and summarized under the heading 'Generation C' where C stands for cloud. The results of the study revealed that cloud computing can be used by educators institutions and individual students as well as by jurisdiction to support particular teaching and learning experiences and to organize software availability. Challenges for educators and institutions using cloud computing in teaching could be summarized under the following keywords: interoperability and transferability terms and conditions security and privacy issues backup and perpetuity denial of service and content issues. On a whole some implications of using cloud computing need to be kept in mind good understanding of the applications in use development of guidelines for use and migration strategies as well as the implementation of risk management could allow educators and institutions to take advantage of cloud computing in turn offering rich online learning experiences for students.
Citation Count: 6
Comparative Study of Active Power Curtailment Methods of Pvs for Preventing Overvoltage on Distribution Feeders
(IEEE, 2018) Paudyal, Sumit; Bhattarai, Bishnu P.; Tonkoski, Reinaldo; Dahal, Sudarshan; Ceylan, Oğuzhan
Overvoltage is one of the major issues on distribution grids with high penetration of photovoltaic (PV) generation. Overvoltage could be prevented through the control of active/reactive power of PVs. However given the high R/X ratio of low voltage feeders voltage control by using reactive power would not be as effective as using active power. Therefore active power curtailment (APC) of PVs though not desirable becomes necessary at times to prevent the overvoltage issues. Existing literature is rich in centralized and droop-based methods for APC and/or reactive power control of PVs to prevent overvoltage issues. In this context this paper revisits the most popular existing methods and evaluates the performance of droop-based and centralized methods using a typical North American 240 V low voltage feeder with 24 residential homes. In this work our key findings are: a) droop-based methods provided conservative solutions or did not eliminate the overvoltages completely b) power flow sensitivity based droop approach led to 13% more curtailment than the centralized approaches c) centralized approach had 40% less energy curtailed compared with standard droop while no overvoltages were observed and d) operating PVs at non-unity power factor in centralized approach led to 5% less energy curtailment.
Citation Count: 0
Comparison of Cost-Free Computational Tools for Teaching Physics
(IEEE, 2010) Er, Neslihan Fatma; Dağ, Hasan
It is widely accepted that it is quite difficult to engage today's students, from high schools to university, both in educational activities in class and "teaching" them physics due to their prejudices about the complexity of physics. The difficulty in capturing students' attention in class for a long time also plays a role in less effective teaching during learning activities. Research shows that students learn little from traditional lectures. According to constructivist learning theories, visual aids and hands-on activities play a major role in learning physics. In addition to laboratory work there are many computational tools for teaching physics, which help teachers and students in constructing a conceptual framework. With this in mind, this paper compares freeware and open source computational tools for teaching physics.
Citation Count: 12
Comparison of Post Outage Bus Voltage Magnitudes Estimated by Harmony Search and Differential Evolution Methods
(2009) Ceylan, Oğuzhan; Özdemir, Aydoğan; Dağ, Hasan
Contingency studies are indispensable tools of both the power system planning and operational studies. Real time implementation of operational problems makes necessary the use of high speed computational methods while requiring reasonable accuracies. On the other hand, accuracy of the results and the speed of calculation depend on branch outage modeling as well as solution algorithm used. This paper presents a comparison of post outage bus voltage magnitudes calculated by two meta-heuristic approaches; namely differential evolution (DE) and harmony search (HS) methods. The methods are tested on IEEE 14, IEEE 30, IEEE 57, and IEEE 118 bus test systems and the results are compared both in terms of accuracy and calculation speed.

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