Kayseri, Turkey
Kayseri, Turkey

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Guney K.,Nuh Naci Yazgan University | Onay M.,Erciyes University
Microwave and Optical Technology Letters | Year: 2011

In this article, we propose a method based on the bees algorithm (BA) to synthesize thinned linear antenna arrays with low sidelobe level.The BA is an optimization algorithm inspired by the behavior of the honey bees to find the optimal way of harvesting food resources around the hive. Several examples with different thinning percentages are given to show the effectiveness of the proposed method. The results of BA are compared with the results of real coded genetic algorithm, ant colony optimization, and iterative Fourier technique. © 2011 Wiley Periodicals, Inc.


Guney K.,Nuh Naci Yazgan University | Onay M.,Erciyes University
Expert Systems with Applications | Year: 2011

A method based on harmony search algorithm (HSA) for the pattern synthesis of linear antenna arrays with the prescribed nulls is presented. Nulling of the pattern is achieved by controlling the amplitude-only, the phase-only, and the position-only. The HSA is conceptualized using the musical process of searching for a perfect state of harmony. To show the effectiveness of the proposed HSA, several examples of linear antenna array patterns with the imposed single, multiple and broad nulls are given. It is found that the nulling method based on HSA is capable of steering the array nulls precisely to the undesired interference directions. The results of HSA are compared with the results of the modified touring ant colony optimization (MTACO), the bees algorithm (BA), the bacterial foraging algorithm (BFA), the plant growth simulation algorithm (PGSA), the clonal selection algorithm (CLONALG), the particle swarm optimization (PSO), the quadratic programming method (QPM), the tabu search algorithm (TSA), the genetic algorithm (GA), the memetic algorithm (MA), the nondominated sorting genetic algorithm 2 (NSGA-2), the multiobjective differential evolution (MODE), and the multiobjective evolutionary algorithms based on decomposition with differential evolution (MOEA/D-DE). © 2011 Elsevier Ltd. All rights reserved.


Bozer A.,Nuh Naci Yazgan University | Altay G.,Bogazici University
Structural Control and Health Monitoring | Year: 2013

The optimization of tuned mass damper (TMD) involves the attachment of a damper to a TMD unit. Although this supplementary damping renders TMD to be operational under broad bandwidth inputs (i.e., wind excitation), it also considerably decreases the efficiency. In this paper, an alternative approach is suggested to eliminate the requirement for supplementary damping, hence to utilize TMD in full efficiency. For this purpose, combined structure/undamped TMD system is equipped with an active controller to track the response of an oscillator with natural frequency set to the operating frequency of the TMD unit. In this case, a proposed controller does not aim returning a system to its zero state; instead, it supports the TMD unit to suppress vibration effectively. This tracking type controller is formulized by both linear quadratic regulator, and H∞ control schemes, and control performances of each system are evaluated through numerical simulations. © 2011 John Wiley & Sons, Ltd.


Gozbasi O.,Nuh Naci Yazgan University | Aslan A.,University of Nevsehir
International Journal of Economics and Financial Issues | Year: 2015

One of the main lacks of the profit persistence literature is the fact that it focuses on only manufacturing, banking and food industries. This study, for the first time, extends the literature by considering the intensity of competition in 13 energy companies from 1997 to 2011 in Turkey as an emerging market. The results show that the degree of persistence is higher in the energy industry mainly due to a low degree of market saturation, weak price competition and a lowly concentrated retailing industry, thus providing no support for the hypothesis that there is a lower persistence of profits in emerging markets due to more intense competition in Turkey. © 2015, International Journal of Economics and Financial Issues. All rights reserved.


Guney K.,Nuh Naci Yazgan University | Basbug S.,University of Nevsehir
International Journal of RF and Microwave Computer-Aided Engineering | Year: 2011

In this article, a stochastic search technique based on seeker optimization algorithm (SOA) is proposed for null steering of linear antenna arrays by controlling the position-only, phase-only, and amplitude-only. The SOA is relatively new optimization algorithm based on the concept of simulating the act of humans' intelligent search with their memory, experience, and uncertainty reasoning. Several numerical examples of Chebyshev pattern with the single, multiple, and broad nulls imposed at the directions of interference are given to illustrate the performance and flexibility of the proposed algorithm. For a comparison, the nulling patterns obtained by simulated annealing (SA) and tabu search (TS) algorithms are also given. Furthermore, the results of SOA are statistically compared with those of SA and TS algorithms. The statistical results of simulations show that SOA is superior to the other compared algorithms. © 2011 Wiley Periodicals, Inc.


Saatci M.,Nuh Naci Yazgan University | Dumrul Y.,Usak University
International Journal of Energy Economics and Policy | Year: 2013

In this study the aim was to investigate empirically the role of energy consumption in economic growth for the Turkish economy. The data used include annual energy consumption and economic growth series from 1960 to 2008. We used aggregate as well as various disaggregate data on energy consumption, including, oil, electricity, coal and renewable energy. Our contribution is that we take a structural breaks modeling approach in this paper. In the literature, the Kejriwal cointegration test has not been applied to date. The main conclusion of the study was that Turkey's energy consumption and economic growth has a positive relationship varying quantity with structural breaks.


Yamacli S.,Nuh Naci Yazgan University
Computational Materials Science | Year: 2014

Investigation of the conductance properties of metal-graphene contacts is essential for the future nanoelectronics technology. In this study, we focus on the conductance mechanism and the voltage-dependent transport properties of both p-type and n-type graphene-metal contacts. Copper and gold are chosen as the contact metal for n-type and p-type doped graphene-metal interface, respectively. Utilizing first principles quantum mechanical calculations with density functional theory in conjunction with Green's function formalism, transmission spectra of graphene-metal contacts and the voltage-dependent variations of the current and the resistance are obtained. Finally, it is shown that obtained resistance-voltage behaviours of graphene-metal contacts are in consistent with the results reported in the literature and the voltage-dependency of the contact resistance has to be taken into consideration for the nanoscale circuit design process. © 2013 Elsevier B.V. All rights reserved.


Yamacli S.,Nuh Naci Yazgan University
Computational Materials Science | Year: 2014

Considering that the current microelectronics technology is built upon silicon, various nanoscale silicon structures are being investigated. In this study, voltage-dependent transmission characteristics of short silicon nanotubes (SiNTs) are investigated using first-principles methods. Density functional theory in conjunction with non-equilibrium Green's function formalism is utilized to simulate metallic (5, 5) and (8, 8) SiNTs in order to obtain their current-voltage characteristics. The variation of the SiNT resistance with the applied voltage is also given and discussed together with the change in the transmission spectra. It is shown that current-voltage characteristics of short metallic SiNTs show nonlinear behaviour due to the changes in their transmission spectra. Obtained results and characteristics have implications on nanoscale SiNT interconnect design. © 2014 Elsevier B.V. All rights reserved.


Yamacli S.,Nuh Naci Yazgan University
Journal of Nanoparticle Research | Year: 2014

Carbon-based materials such as carbon nanotubes and graphene nanoribbons are investigated extensively for the near future nanoelectronics technology. Considering the expertise on the processing of silicon, various implementations of silicon counterparts of these nanoscale components such as silicon nanotubes and silicene nanoribbons have also been reported recently. In this work, electronic transport properties of metallic graphene and silicene nanoribbons (GNRs and SiNRs) are compared. Ab initio simulations based on density functional theory combined with non-equilibrium Green's function formalism are used to obtain the voltage-dependent transmission spectra, resistance-voltage variations and the potential profiles of realistic metallic GNR and SiNR samples. The investigation of the variations of the transmission characteristics of the GNRs and SiNRs exposes that both nano structures show voltage-dependent resistances due to elastic potential scattering compliant with Büttiker formalism. However, the variation of the transmission spectra of GNRs by the applied voltage is lower than that of SiNRs indicating that metallic GNRs seem to be better candidates compared to their silicon counterparts for use as metallic interconnects. © 2014 Springer Science+Business Media.


Yamacli S.,Nuh Naci Yazgan University
Journal of Computational Electronics | Year: 2016

Although silicon and similar bulk materials are widely used in today’s integrated circuits, the transition to lower dimensional structures such as two-dimensional graphene, one-dimensional graphene nanoribbons (GNRs) and silicene nanoribbons (SiNRs) seems inescapable due to the increment of inelastic scattering and related performance degrading effects in bulk circuit components. In this context, GNRs and SiNRs provide advantages such as low area consumption and the adjustment of their electronic behaviours by edge states and widths. On the other hand, rectifiers together with their static and dynamic behaviours constitute the basics of the electronics technology. In this paper, rectifier characteristics of bare-dihydrogenated junctions of GNR and SiNR structures are investigated and compared utilizing first-principles approach. Density functional theory in combination with non-equilibrium Green’s function formalism are used to obtain current–voltage characteristics, transmission eigenstates and dynamic electron densities of the considered GNR and SiNR rectifiers and then these quantities are processed to obtain the dynamical resistance, junction capacitance and time constants of these structures, which is essential for graphene and silicene based electronics design. The paper is concluded with the discussion of the large-signal and small-signal performances of the considered GNR and SiNR rectifiers for commercial integrated circuit applications. © 2016 Springer Science+Business Media New York

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