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Kayseri, Turkey

Durandurdu M.,Abdullah Gul University
Journal of the American Ceramic Society | Year: 2016

The high-pressure behavior of amorphous aluminum nitride is investigated for the first time by means of ab initio molecular dynamics simulations. It is found to undergo two successive first-order phase transformations with the application of pressure. The first one is a polyamorphic phase transition in which the low-density amorphous phase transforms into a high-density amorphous phase having an average coordination number of about 4.6. The high-density amorphous structure transforms back to a low-coordinated amorphous network upon pressure release but its density is higher than that of the original low-density amorphous phase. The second phase change is the crystallization of the high-density amorphous state into a rocksalt structure. A careful analysis suggests that the hexagonal-like nanoclusters presented in amorphous aluminum nitride prevent the formation of a very dense amorphous phase (about sixfold coordinated) during the first phase transition and they act as a nucleation center for the crystallization process. © 2016 American Ceramic Society. Source

Ablay G.,Abdullah Gul University
Transactions of the Institute of Measurement and Control | Year: 2015

U-tube steam generator level control systems are used to maintain the water level within prescribed narrow limits and to provide constant supply of high-quality steam during power demand variations. Traditional level control systems are often found to be unsatisfactory during low power operations and start-up conditions. Robust non-linear estimator-based optimal control systems are proposed for steam generator level control systems to solve the water level tracking problem during power (or steam) demand variations. It is shown that the proposed control strategies provide optimal and robust water level tracking with a single controller over the complete range of power operation with model and parameter uncertainties and noisy measurements. © The Author(s) 2014. Source

Dogan E.,Abdullah Gul University
Renewable and Sustainable Energy Reviews | Year: 2015

The main objective of this study is to analyze the short and long run estimates as well as the causality relationships between economic growth (GR), electricity consumption from renewable sources (RELC) and electricity consumption from non-renewable sources (NRELC) for Turkey in a multivariate model wherein capital (K) and labor (L) are included as additional variables. Using the autoregressive distributed lag (ARDL) approach to cointegration, the Johansen cointegration test and the Gregory-Hansen cointegration test with structural break, we show that GR, RELC, NRELC, K and L are cointegrated. Although NRELC has a long run positive effect on GR, the long run estimate of RELC is negative but insignificant at 5% level of significance. The Granger causality test based on the vector error correction model reveals the evidence of neutrality hypothesis between RELC and GR, and between NRELC and GR in Turkey in the short run. In addition, the Granger causality runs from RELC, NRELC, K and L to GR as well as from GR, RELC, K and L to NRELC in the long run, which supports the existence of growth hypothesis between RELC and GR, and feedback hypothesis between NRELC and GR in the long run. It is advised that policy makers in the Turkish government should continue to reduce the share of electricity consumption from renewable sources and encourage the usage of electricity from non-renewable sources to have sustainable long run growth rates. It is also essential to promote the investment projects to increase the efficiency of electricity generation from non-renewable sources. © 2015 Elsevier Ltd. All rights reserved. Source

Bilim C.,Mersin University | Ati C.D.,Abdullah Gul University | Ati C.D.,Erciyes University
Construction and Building Materials | Year: 2012

The aim of the present study is to investigate some properties of alkali-activated mortars containing slag at different replacement levels. Ground granulated blast furnace slag was used at 0%, 20%, 40%, 60%, 80% and 100% replacement by weight of cement, and liquid sodium silicate having three different Na dosages was chosen as the alkaline activator. In this research, carbonation resistance measurements and compressive and flexural strength tests were performed on the mortar specimens with size of 40 × 40 × 160 mm. The findings obtained from the tests showed that carbonation depth values of the mortars decreased with the increase of activator dosage. Additionally, compressive and flexural strength values increased with the increase in activator concentration and slag replacement level. Portland cement/slag mortars activated by liquid sodium silicate exhibited lower strength than the slag alone activated by the same activator. © 2011 Elsevier Ltd. All rights reserved. Source

Ablay G.,Abdullah Gul University
Energy Conversion and Management | Year: 2013

Advanced nuclear power plants are currently being proposed with a number of various designs. However, there is a lack of modeling and control strategies to deal with load following operations. This research investigates a possible modeling approach and load following control strategy for gas turbine nuclear power plants in order to provide an assessment way to the concept designs. A load frequency control strategy and average temperature control mechanism are studied to get load following nuclear power plants. The suitability of the control strategies and concept designs are assessed through linear stability analysis methods. Numerical results are presented on an advanced molten salt reactor concept as an example nuclear power plant system to demonstrate the validity and effectiveness of the proposed modeling and load following control strategies. © 2013 Elsevier Ltd. All rights reserved. Source

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