Ankara, Turkey
Ankara, Turkey

Çankaya University was established on July 9, 1997, by the Sıtkı Alp Education Foundation in Ankara, Turkey. The university began its teaching in the Fall 1997 semester. Sıtkı Alp is the Chairman of the Board of Trustees. Wikipedia.


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Baykal Y.,Cankaya University
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2015

In an oceanic optical communications link, the received intensity fluctuations, quantified by the scintillation index, are formulated and evaluated when a multimode laser is used. The variations of the scintillation index versus the oceanic turbulence parameters are examined for different multimode laser structures. Oceanic turbulence parameters used are the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, the Kolmogorov inner scale, and the parameter w that defines the ratio of temperature to salinity contributions to the refractive index spectrum. The results in this paper can be used to improve performance in the design of oceanic optical communications links. © 2015 Optical Society of America.


Baykal Y.,Cankaya University
Applied Optics | Year: 2014

Correlations of the fields at the receiver plane are evaluated after a symmetrical radial laser array beam incident field propagates in a turbulent atmosphere. The laser array configuration is composed of a number of the same size laser beamlets symmetrically located around a ring having a radius that determines the distance of the ring from the origin. The variations of the correlations of the received field originating from such laser array incidence versus the diagonal length starting from a receiver point are examined for various laser array parameters, turbulence parameters, and the locations of the reception points. Laser array parameters consist of the ring radius and the number and size of the beamlets. Structure constant, link length, and wavelength are the turbulence parameters whose effects on the field correlation of the laser arrays are also investigated. © 2014 Optical Society of America.


Baykal Y.,Cankaya University
Optics Letters | Year: 2014

In an atmospheric medium that shows a non-Kolmogorov turbulence behavior, the variation of the on-axis scintillation index is evaluated when higher-order laser modes are used as the excitation. The Rytov method is employed together with the equivalent structure constant, which makes our results valid in weak turbulence. In the limiting case, our solution correctly reduces to the known scintillation index of the Gaussian beam in Kolmogorov turbulence. For all the higher-order even modes, increase in the power law exponent, a of the non-Kolmogorov spectrum is found to increase the scintillations. When the source size of the higher-order modes is large, higher-order even modes attain almost the same scintillation index values for all a. However, for small source sizes, being valid for any realization of the non-Kolmogorov spectrum, the scintillations decrease as the mode order becomes large. The changes in the propagation distance, structure constant, and the wavelength do not vary these trends. © 2014 Optical Society of America.


Kucukali S.,Cankaya University
Renewable and Sustainable Energy Reviews | Year: 2014

This study aims to evaluate existing hydropower reservoirs for the development of pumped-storage schemes by using multi-criteria scoring technique. This method enables a screening of existing hydropower reservoirs, in order to assess and rank potential sites for pumped-storage development. This analysis is based on the documented evidence, measured data, and site surveys. The site assessments are categorized in 6 criteria namely geometrical conditions (maximum head, head to water way length ratio, distance to grid connection), geological conditions, environmental, and social conditions. In the context of the study, 7 existing hydropower reservoirs in Turkey, each with a catchment area of more than 50 km2, are evaluated in order to be utilized as the lower reservoirs of pumped-storage facilities. The overall score of each candidate site is obtained and, their performance is compared. The results indicate that Turkey have suitable existing hydropower reservoirs for the development of pumped-storage facilities. However, the country lacks from legal and market framework for the establishment of pumped-storage power plants. © 2014 Elsevier Ltd.


Eyyuboglu H.T.,Cankaya University
Applied Physics B: Lasers and Optics | Year: 2011

We study the scintillation aspects of partially coherent Lorentz Gaussian (LG) beams via numerically integrating the average and average squared intensity expressions. Within the examined range of input and propagation medium parameters, the LG beams are generally found to offer less and less scintillations against the pure Gaussian beam, particularly when the Lorentzian feature of the beam is emphasized more. This lower scintillation property is exhibited for collimated coherent beams with different Lorentz widths and at on-axis and off-axis positions of the receiver plane. When focusing is introduced, at shorter propagation distances the ordering of the beams remains as described above, but at longer propagations distances a complete reversing of the beam order is observed. Raising the turbulence levels by increasing the structure constant inevitably causes rises in scintillations, while preserving the advantage of LG beams over the pure Gaussian beam. Partial coherence reduces scintillations as expected, at the same time nearly eliminating the scintillation differences between the beam types. © 2011 Springer-Verlag.


Kucukali S.,Cankaya University
Energy for Sustainable Development | Year: 2014

A multi-criteria scoring tool is used to assess the environmental risk level of small hydropower plants on the basis of documented evidence, measured data, and on-site observations. The assessment is based on evaluating compliance with the standards of the European Bank for Reconstruction and Development (EBRD). The following environmental criteria are assessed: environmental flow, water quality, fish passage and protection, watershed protection, threatened and endangered species. I evaluated the Tefen hydropower plant, which has been in operation on the Filyos River in northwestern Turkey since 2011. The assessment showed that the plant failed all of the EBRD criteria. © 2013 International Energy Initiative.


Baykal Y.,Cankaya University
Applied Optics | Year: 2016

The parameters composing oceanic turbulence are the wavelength, link length, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum. The required physical entities such as the average intensity and the scintillation index in the oceanic medium are formulated by using the power spectrum of oceanic turbulence, which is described by oceanic turbulence parameters. On the other hand, there exists a rich archive of formulations and results for the above-mentioned physical entities in atmospheric turbulence, where the parameters describing the turbulence are the wavelength, the link length, and the structure constant. In this paper, by equating the spherical wave scintillation index solutions in the oceanic and atmospheric turbulences, we have expressed the oceanic turbulence parameters by an equivalent structure constant used in turbulent atmosphere. Such equivalent structure constant will help ease reaching solutions of similar entities in an oceanic turbulent medium by employing the corresponding existing solutions, which are valid in an atmospheric turbulent medium. © 2016 Optical Society of America.


Abdeljawad T.,Cankaya University
Mathematical and Computer Modelling | Year: 2011

Partial metric spaces were introduced by S. G. Matthews in 1994 as a part of the study of denotational semantics of dataflow networks. In this article, we prove fixed point theorems for generalized weakly contractive mappings on partial metric spaces. These theorems generalize many previously obtained results. An example is given to show that our generalization from metric spaces to partial metric spaces is real. © 2011 Elsevier Ltd.


Abdeljawad T.,Cankaya University
Computers and Mathematics with Applications | Year: 2011

In this paper, we define left and right Caputo fractional sums and differences, study some of their properties and then relate them to Riemann-Liouville ones studied before by Miller K. S. and Ross B., Atc F.M. and Eloe P. W., Abdeljawad T. and Baleanu D., and a few others. Also, the discrete version of the Q-operator is used to relate the left and right Caputo fractional differences. A Caputo fractional difference equation is solved. The solution proposes discrete versions of Mittag-Leffler functions. © 2011 Elsevier Ltd. All rights reserved.


Eyyuboglu H.T.,Cankaya University
Optics and Laser Technology | Year: 2013

We make an analysis on scintillation behavior of Airy beam using the Rytov method. To this end, scintillation index is formulated for a single receiver coordinate location. Area scintillation expressions are also derived. At peaks of receiver intensity, Airy beam is found to offer quite less scintillation at width values of around 1.6 cm. Furthermore, smaller values of the exponential truncation factor are also seen to cause less scintillation. When compared to Gaussian beam, on equal source and received power basis, it is observed that Airy beam will generally have less area scintillation. © 2012 Elsevier Ltd.

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