Mühendislik ve Doğa Bilimleri Fakültesi

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Analysis and Optimization of Matching Networks-I Getting Started With Ads
(Springer-Verlag Berlin, 2008) Şengül, Metin Y.; Şengül, Metin
[Abstract Not Available]
Analysis and Optimization of Matching Networks-Ii Getting Started With Microwave Office
(Springer-Verlag Berlin, 2008) Şengül, Metin Y.; Şengül, Metin
[Abstract Not Available]
Channel Modeling for Visible Light Communications
(Springer-Verlag Berlin, 2016) Miramirkhani, Farshad; Panayırcı, Erdal; Uysal, Murat; Panayırcı, Erdal
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes the limitations of previous works. In our work, we consider wavelength dependency, effect of realistic light sources as well as different types of reflections such as specular and mixed cases of diffuse and specular. We use nonsequential ray tracing algorithms to calculate the detected power and path lengths from source to detector for each ray. These are then processed to yield the channel impulse responses for various indoor environments. We further present a channel characterization study where channel parameters such as channel DC gain, root mean square delay spread, coherence bandwidth, mean excess delay are calculated for different environments.
Conductivity Percolation of Carbon Nanotubes in Polyacrylamide Gels
(Intech Europe, 2011) Pekcan, Önder; Pekcan, Mehmet Önder; Evingür, Gülşen Akın
[Abstract Not Available]
Effect of Content and Temperature on the Phase Transitions of Polymer Composites Doped by Kappa Carrageenan and Alginate
(Elsevier Academic Press Inc, 2016) Evingür, Gülşen Akın; Pekcan, Mehmet Önder; Pekcan, Önder
[Abstract Not Available]
Effect of Inter-Block Region on Compressed Sensing Based Channel Estimation in Tds-Ofdm Systems
(Institute of Electrical and Electronics Engineers Inc., 2016) Başaran, Mehmet; Erküçük, Serhat; Erküçük, Serhat; Şenol, Habib; Şenol, Habib; Çırpan, Hakan Ali
Time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) is the basis technology for digital television standard (DTV) employed in some countries thanks to its high spectral efficiency when compared to traditional cyclic prefix OFDM. Moreover, it does not require pilot usage in frequency domain channel estimation. Instead of data usage as cyclic prefix, pseudo-noise (PN) sequences are transmitted in guard intervals. Due to interference from the previous OFDM data symbol, the received signal in guard interval can be decomposed into a small-sized signal that contains only PN sequences utilizing the inter-block-interference (IBI)-free region in the convolution matrix. Due to sparsity, multipath fading channel can be obtained by the application of compressed sensing (CS) technique to reconstruct the high-dimensional sparse channel from the decreased-size of received signal through the known PN sequence matrix. In this study, the effect of the size of IBI-free region on CS and Bayesian CS (BCS) based channel estimation is investigated. Accordingly, reconstruction error performances of basis pursuit (BP) and BCS are compared. Simulation results show that the channel estimation can be improved by trading-off the length of the IBI-free region. However, an increase in IBI-free region leads to decreased energy efficiency at both the transmitter and receiver side.
First Impressions on Social Network Sites: Impact of Self-Disclosure Breadth on Attraction
(Academic Conferences and Publishing International Limited, 2017) Baruh, Lemi; A. Bısson, Chrıstophe Louıs; Cemacılar, Zeynep; Bisson, Christophe; Chisik, Yoram I.
This paper reports the results of two experiments that investigate the relationship between the quantity of information disclosed on an SNS profile and profile viewers' first impressions of the profile owner. Both experiments utilized a 2 (low quantity of information vs. high quantity of information) by 2 (male vs. female profile) design. In the first experiment (n = 1059), the respondents were randomly assigned to the experimental conditions. The results showed that profile viewers were more favorable to profiles of women. Also, both for female and male SNS profiles, higher quantity of information led to more positive ratings of the profile owner. The second experiment expanded the findings from the first experiment in two ways. First, in the second experiment (n = 320), rather than being randomly assigned to the profile gender condition, the respondents could pick the gender of the profile they would review. Second, informed by previous research on face to face interactions which indicate that quantity of self-disclosure can increase interpersonal attraction by reducing the level of uncertainty about relational outcomes, we tested whether uncertainty reduction mediated the relationship between quantity of information presented in an SNS profile and interpersonal attraction. Female profiles were selected more often than male profiles by both female and male respondents; however, there was no difference in interpersonal attraction ratings that male and female profiles received. Higher quantity of information presented in an SNS profile had a significant impact on interpersonal attraction. The results from the second experiment also indicated that while quantity of information positively influenced profile viewers' perceptions regarding the agreeableness of the profile owner, it did not have an impact on viewers' perceptions regarding the dependability of the profile owner. As predicted, the impact of quantity of information on interpersonal attraction was mediated by a reduction in uncertainty levels.
Geopolitics and Gas-Transit Security Through Pipelines
(Springer International Publishing, 2020) Ediger, Volkan S.; Aydın, Mustafa; Bowlus, John V.; Ediger, Şevket Volkan; Aydın, Mustafa
Hydrocarbons are valuable only if they can be transited from where they are produced to where they are consumed. Despite the enduring importance of transit to the global energy system, the topic did not begin to be extensively analyzed until contentious relations between Russia and Ukraine disrupted natural gas flows to Europe in 2006. This chapter examines the geopolitics and security of transiting gas through pipelines by exploring the connection between geography, global energy strategies, and natural gas markets. Gas has grown in recent years as a percentage of global energy consumption and is helping the world transition to a cleaner energy regime. At the same time, it is intensifying the contest for and control of gas-transit routes. Russia, the world’s second-largest producer, has built new pipelines to Europe since 2006 in order to diversify its flow from relying on Ukraine, while the USA, the world’s largest gas producer, is increasingly exporting liquefied natural gas (LNG) through sea routes mostly controlled by the US navy. We argue that geostrategic calculations will more profoundly affect gas transit in the future and that countries that rely solely on market or commercial factors for their gas-transit security will become increasingly vulnerable to geopolitical volatility.
Geostrategic Challenges in the Oil and Gas Sectors
(Springer International Publishing, 2018) Ediger, Volkan S.; Ediger, Şevket Volkan; Berk, Istemi
This chapter identifies the major geostrategic challenges that have emerged during the last two decades and assesses their implications for the global oil and gas sectors. The historical development of oil prices shows that there have been two major periods of volatility 1973-1986 and 1998-present each of which was preceded by two relatively stable periods. The two oil price shocks of the 1970s that were triggered by geopolitical events had long-term effects on global politics and economics. Major oil and gas producers faced the challenges of declining consumption on the demand side as consumers turned to alternative energies energy efficiency improved and non-Organization of Petroleum Exporting Countries (OPEC) oil supplies increased. The crisis in the 2000s on the other hand had similar but more intense consequences deeply altering the structure of oil and gas markets. We identify two major challenges facing the oil and gas industry: energy substitution and resource scarcity. While the substitution of coal and renewables threatens to reduce oil and gas demand resource scarcity is expected to promote the development of unconventional hydrocarbon resources such as shale oil and gas and heavy oil. Unlike in the 1970s oil consumption did not decline when oil prices peaked in the 2000s. Moreover the recent fall in oil and gas prices created a fiscal challenge for conventional producers such as OPEC countries and non-OPEC countries like Russia and Mexico whose governmental budgets depend on export revenues. These fiscal challenges are expected to increase competition between national oil companies (NOCs) and international oil companies (IOCs) necessitating structural change in the governance of the industry. The NOCs are expected to continue dominating the industry and due to the increasing intervention of the corresponding governments the next decades could experience a rise in state capitalism not only in major oil and gas producing countries but also in the global energy business. © Springer International Publishing AG part of Springer Nature 2018.
Introduction: Energy Economics Finance and Geostrategy
(Springer International Publishing, 2018) Dorsman, Andre B.; Ediger, Şevket Volkan; Ediger, Volkan S.; Karan, Mehmet Baha
Since countries’ economic independence is based on energy security decisions on energy economy and financing are assessed mainly by geostrategic considerations. Economically optimal decisions are not enough regarding geostrategy. This situation makes it difficult to make decisions in energy markets and it creates considerable controversy. The role of financial markets is to measure the risk of this complex structure or energy projects and price them in financial basis. Understanding behavior of energy markets it is necessary to look at them on an event basis. The limited availability and unequal distribution of energy sources and different pricing and cost mechanism of energy supplies are hardening to arrive a simple solution. Therefore the research articles of this book are aimed to open new perspectives for the reader and researchers. © Springer International Publishing AG part of Springer Nature 2018.
Minimum Length Scheduling for Discrete Rate Based Full Duplex Wireless Powered Communication Networks
(Springer, 2019) Iqbal, Muhammad Shahid; Şadi, Yalçın; Şadı, Yalçın; Ergen, Sinem Coleri
In this study, we consider a wireless powered communication network where multiple users with radio frequency energy harvesting capabilities communicate to a hybrid energy and information access point in full duplex mode. We characterize an optimization framework for minimum length scheduling to determine the optimal rate adaptation and transmission scheduling subject to energy causality and traffic demand constraints of the users considering discrete-rate transmission model. We first formulate the problem as a mixed integer nonlinear programming problem which is hard to solve for a global optimum in polynomial-time. Then, based on an analysis on the characteristics of the optimal solution, we derive optimality conditions for rate adaptation and scheduling using which we propose a fast polynomial-time complexity heuristic algorithm. We illustrate through numerical analysis that the proposed algorithm performs very close to optimal for various network scenarios.

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