| 1. |
- Ek, Kristina, et al.
(author)
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- 2010
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In: Ecological Economics. - : Elsevier BV. - 0921-8009 .- 1873-6106. ; 69:12, s. 2356-2362
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Journal article (peer-reviewed)abstract
- The objective of this paper is to analyze the role of technology learning in European wind power generation in the presence of public R&D. A Cobb-Douglas cost function is employed to derive a learning curve model for wind power, thus illustrating how the investment costs for this technology are influenced by global learning-by-doing, scale effects, and a European R&D-based knowledge stock. We assume that public R&D expenses targeting wind power add to the above stock, and these R&D outlays are in turn hypothesized to be influenced by technology cost levels, the opportunity cost of public R&D as well as by government budget constraints. We estimate the learning and the R&D model, respectively, using a panel data set covering five European countries over the time period 1986-2002. The empirical results confirm the importance of both learning-by-doing and public R&D support in the cost reduction process, and governments' R&D expenses have declined in response to lowered investment costs. This is efficient in the sense that public funds are best targeted at technologies which are far from being commercial. The results also illustrate that governments in Europe have been sensitive to the opportunity cost of public R&D in the energy R&D budget process.
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| 2. |
- Özdogan, Özgecan, 1992-
(author)
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Analysis of Cellular and Cell-Free Massive MIMO with Rician Fading
- 2020
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Licentiate thesis (other academic/artistic)abstract
- The data traffic in cellular networks has grown at an exponential pace for decades. This trend will most probably continue in the future, driven by new innovative applications. One of the key enablers of future cellular networks is the massive MIMO technology. A massive MIMO base station is equipped with a massive number (e.g., a hundred) of individually steerable antennas, which can be effectively used to serve tens of user equipments simultaneously on the same time-frequency resource. It can provide a notable enhancement of both spectral efficiency and energy efficiency in comparison with conventional MIMO.In the literature, the achievable spectral efficiencies of massive MIMO systems with a practical number of antennas have been rigorously characterized and optimized when the channels are subject to either spatially uncorrelated or correlated Rayleigh fading. Typically, in massive MIMO research, i.i.d. Rayleigh fading or less frequently free-space line-of-sight (LoS) channel models are assumed since they simplify the analysis. Massive MIMO technology is able to support both rich scattering and LoS scenarios. However, practical channels can consist of a combination of an LoS path and a correlated small-scale fading component caused by a finite number of scattering clusters that can be modeled by spatially correlated Rician fading. In the first part of this thesis, we consider a multi-cell scenario with spatially correlated Rician fading channels and derive closed-form achievable spectral efficiency expressions for different signal processing techniques.Alternatively, a massive number of antennas can be spread over a large geographical area and this concept is called cell-free massive MIMO. In the canonical form of cell-free massive MIMO, the access points cooperate via a fronthaul network to spatially multiplex the users on the same time-frequency resource using network MIMO methods that only require locally obtained channel state information. Cellfree massive MIMO is a densely deployed system. Hence, the probability of having an LoS path between some access points and the users is quite high. In the second part of this thesis, we consider a practical scenario where the channels between the access points and the users are modeled with Rician fading.
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| 3. |
- Özel, Faith, et al.
(author)
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Associations of neuroimaging markers with depressive symptoms over time in middle-aged and elderly persons
- 2023
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In: Psychological Medicine. - : Cambridge University Press. - 0033-2917 .- 1469-8978. ; 53:10, s. 4355-4363
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Journal article (peer-reviewed)abstract
- Background Cerebrovascular disease is regarded as a potential cause of late-life depression. Yet, evidence for associations of neuroimaging markers of vascular brain disease with depressive symptoms is inconclusive. We examined the associations of neuroimaging markers and depressive symptoms in a large population-based study of middle-aged and elderly persons over time.Methods A total of 4943 participants (mean age = 64.6 +/- 11.1 years, 55.7% women) from the Rotterdam Study were included. At baseline, total brain volume, gray matter volume, white matter volume, white matter hyperintensities volume, cortical infarcts, lacunar infarcts, microbleeds, white matter fractional anisotropy, and mean diffusivity (MD) were measured with a brain MRI (1.5T). Depressive symptoms were assessed twice with the Center for Epidemiologic Studies Depression scale (median follow-up time: 5.5 years, IQR = 0.9). To assess temporal associations of neuroimaging markers and depressive symptoms, linear mixed models were used.Results A smaller total brain volume (beta = -0.107, 95% CI -0.192 to -0.022), larger white matter hyperintensities volume (beta = 0.047, 95% CI 0.010-0.084), presence of cortical infarcts (beta = 0.194, 95% CI 0.047-0.341), and higher MD levels (beta = 0.060, 95% CI 0.022-0.098) were cross-sectionally associated with more depressive symptoms. Longitudinal analyses showed that small total brain volume (beta = -0.091, 95% CI -0.167 to -0.015) and presence of cortical infarcts (beta = 0.168, 95% CI 0.022-0.314) were associated with increasing depressive symptoms over time. After stratification on age, effect sizes were more pronounced at older ages.Conclusions Neuroimaging markers of white matter microstructural damage were associated with depressive symptoms longitudinally in this study of middle-aged and elderly persons. These associations were more pronounced at older ages, providing evidence for the role of white matter structure in late-life depressive symptomatology.
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| 4. |
- ÖZEN, MUSTAFA, 1984, et al.
(author)
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Continuous Class-E Power Amplifier Modes
- 2012
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In: IEEE Transactions on Circuits and Systems II: Express Briefs. - 1549-7747 .- 1558-3791. ; 59:11, s. 731-735
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Journal article (peer-reviewed)abstract
- In this brief, a continuum of novel closed-form solutions is derived for class-E power amplifiers (PAs). It is analytically proven that the class-E zero voltage/zero voltage derivative switching conditions can be satisfied for an arbitrarily selected reactive second harmonic switch impedance (Z 2 S ). The higher order harmonic currents are terminated capacitively. The conventional class-E, class- E/F 2 , and class-EF 2 modes are thus subsets of the continuum. The arbitrary selection of Z 2 S enables robust waveform engineering for performance optimization in specific applications. Furthermore, the theoretical derivation provides important possibilities for wideband class-E PA synthesis. © 2004-2012 IEEE.
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| 5. |
- Özger, Mustafa, et al.
(author)
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Energy-Efficient Transmission Range and Duration for Cognitive Radio Sensor Networks
- 2021
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In: IEEE Transactions on Cognitive Communications and Networking. - : Institute of Electrical and Electronics Engineers (IEEE). - 2332-7731. ; , s. 1-1
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Journal article (peer-reviewed)abstract
- Cognitive Radio (CR) promises an efficient utilization of radio spectrum resources by enabling dynamic spectrum access to overcome the spectrum scarcity problem. Cognitive Radio Sensor Networks (CRSNs) are one type of Wireless Sensor Networks (WSNs) equipped with CR capabilities. CRSN nodes need to operate energy-efficiently to extend network lifetime due to their limited battery capacity. In this paper, for the first time in literature, we formulate the problem of finding a common energy-efficient transmission range and transmission duration for all CRSN nodes and network deployment that would minimize the energy consumed per goodput per meter toward the sink in a greedy forwarding scenario. Results reveal non-trivial relations for energy-efficient CRSN transmission range and duration as a function of nine critical network parameters such as primary user activity levels. These relations provide valuable insights for detailed CRSN designs prior to deployment.
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| 6. |
- Özkılıç, Yasin Onuralp, et al.
(author)
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Influence of ceramic waste powder on shear performance of environmentally friendly reinforced concrete beams
- 2024
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In: Scientific Reports. - : Springer. - 2045-2322. ; 14
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Journal article (peer-reviewed)abstract
- This investigation considered the usability of ceramic waste powder (CWP) in altered quantities in reinforced concrete beams (RCBs). In this way, it was aimed to reduce the environmental impacts of concrete by using CWP as a raw material in RCBs. 12 small-scale shear RCBs with the dimensions of 100 × 150 × 1000 mm were tested in this study. The variations of stirrups spacing and CWP ratio were examined in these specimens. The percentages of CWP by weight utilized in RCBs were 10%, 20%, and 30%, and stirrups spacings were adopted as 270 mm, 200 mm, and 160 mm. At the end of the study, it was determined that more than 10% CWP additive negatively affected the RCBs’ compressive strength. The load-carrying capacity reduced between 30.3% and 59.4% when CWP increased from 0% to 30% as compared to RCB with stirrups spacing of 270 mm without CWP. However, compared to RCB with stirrups spacings of 200 mm and 160 mm without CWP, there were decreases in the load-carrying capacity as 21.4%–54.3% and 18.6%–54.6%, respectively. While the CWP ratio increased, the specimens with 160 mm, 200 mm, and 270 mm stirrups spacings obtained a lower maximum load value. However, with the increase of the CWP ratio in the specimens with 160 mm stirrups spacing, RCBs reached the maximum load-carrying capacity at an earlier displacement value. When stirrups spacing was selected as 270 mm, it was observed that the maximum load-carrying capacity of RCBs reached at a similar displacement value as the CWP ratio increased. Besides, it was resulted that the bending stiffness of RCBs reduced as the quantity of CWP enhanced. The bending stiffness decreased by 29.1% to 66.4% in the specimens with 270 mm stirrups spacing, 36.3% to 20.2% with 200 mm stirrups spacing, and 10.3% to 36.9% with 160 mm stirrups spacing. As an implication of the experiments, the use of CWP up to 10% in RCBs was realized as an economical and environmental approach and is suggested. There is some evidence to report that making use of CWP may be considered to be ecologically benign. This is due to the fact that reusing CWP may significantly reduce CO2 emissions, save energy, and reduce total power consumption. Furthermore, the experimental results were compared to the analytical calculations.
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| 7. |
- Özkirimli, Umut, et al.
(author)
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Nationalism (Transcendence of)
- 2016
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In: The Wiley-Blackwell Encyclopedia of Race, Ethnicity and Nationalism. - Oxford, UK : John Wiley & Sons, Ltd. - 9781405189781 - 9781118663202
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Book chapter (peer-reviewed)abstract
- The future of nations and nationalism appears to many to be more uncertain than ever in view of the growing interdependence of the planet. The question of whether globalization heralds the end of nationalism cannot be answered properly without distinguishing between nation and state. In the case of the state, the question is whether states can preserve their sovereignty intact in an age when politics is conducted at a supranational and subnational level. In the case of the nation, the question is whether there are forms of community that offer alternative foci of belonging. Even though the nation continues to be an important source of political and cultural identity, it can be argued that globalization has increased people's reflexiveness with regard to their identity and facilitated the emergence of new forms of belonging that are deterritorial, plural, and hybrid.
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| 8. |
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| 9. |
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| 10. |
- Öztayşi, Başar, et al.
(author)
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Fuzzy Analytic Hierarchy Process with Interval Type-2 Fuzzy Sets
- 2014
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In: Knowledge-Based Systems. - : Elsevier BV. - 0950-7051. ; 59, s. 48-57
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Journal article (peer-reviewed)abstract
- The membership functions of type-1 fuzzy sets have no uncertainty associated with it. While excessive arithmetic operations are needed with type-2 fuzzy sets with respect to type-1’s, type-2 fuzzy sets generalize type-1 fuzzy sets and systems so that more uncertainty for defining membership functions can be handled. A type-2 fuzzy set lets us incorporate the uncertainty of membership functions into the fuzzy set theory. Some fuzzy multicriteria methods have recently been extended by using type-2 fuzzy sets. Analytic Hierarchy Process (AHP) is a widely used multicriteria method that can take into account various and conflicting criteria at the same time. Our objective is to develop an interval type-2 fuzzy AHP method together with a new ranking method for type-2 fuzzy sets. We apply the proposed method to a supplier selection problem.
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