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Istanbul, Turkey

Marmara University is a public university in the Fatih district of Istanbul, in Turkey. Marmara University has succeeded in becoming the second largest university in the country. The university's mission is to impart and promote knowledge and values consistent with universal standards; to meet the technological, social and cultural challenges of a global society; to contribute to the creation of an informed society, which learns about and shares this knowledge and values; and to emphasize the European dimension in the delivery of education opportunities. The rector of Marmara University is Prof. Dr. M. Zafer Gül who has held this position since July 2010. Wikipedia.

The weld strength of thermoplastics, such as high density polyethylene and polyprophylene sheets are influenced by friction stir welding parameters. The determination of the welding parameters plays an important role for the weld strength. For the influential use of the thermoplastics joints, the weld should have adequate strength. The quality of the joint was evaluated by examining the characteristics of the joint efficiency as a result of ultimate tensile strength. In this study, the Taguchi approach of parameter design was used as a statistical design of experiment technique to set the optimal welding parameters. The experiments were arranged by using Taguchi's L9 orthogonal array. The signal-to-noise ratio and the analysis of variance were utilized to obtain the influence of the friction stir welding parameters on the weld strength. Finally, the results were confirmed by further experiments. © 2011 Elsevier Ltd. Source

Yavuz I.,Marmara University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We theoretically investigate the boosts in high-order harmonic generation using fabricated nanostructures and determine that the distribution of an ensemble of gas atoms in the vicinity of nanostructures is substantial for the evaluation of harmonic emission. The distributional behavior is mimicked by a single-atom response as well as by allowing the target atoms to reside in different positions inside the nanogap. For a given population distribution, a maximum photon energy of ∼25 eV could be observed in qualitative agreement with experiment. © 2013 American Physical Society. Source

Yavuz I.,Marmara University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We address an efficient scheme to generate a broadband extreme-ultraviolet (xuv) continuum from high-order harmonic generation emerging from the concept of plasmonic field enhancement in the vicinity of metallic nanostructures. Based on the numerical solution of a time-dependent Schrödinger equation, for moderate field intensities and depending on the inhomogeneity of the field, we are able to increase the plateau region roughly by a factor of two and generate a broadband xuv continuum. The underlying physics of the plasmon enhancement in harmonic generation is investigated in terms of the semiclassical trajectories of strong field-electron dynamics, and perfect consistency is found between quantum mechanical simulations. It is found that the field inhomogeneity plays a critical role in quantum path selection. After a critical value, we observe a systematic suppression in the long trajectories, suggesting the generation of a single isolated attosecond pulse. Finally, we investigate the dependence of cutoff position on the order of field inhomogeneity and find a β2.3 0.2 scaling. © 2012 American Physical Society. Source

Kaynak Y.,Marmara University
International Journal of Advanced Manufacturing Technology | Year: 2014

There has been significant work on establishing relationships between machining performance and the cutting parameters for various work materials. Recent trends in machining research show that major efforts are being made to understand the impact of various cooling/lubrication methods on machining performance and surface integrity characteristics, all aimed at improving process and product performance. This study presents the experimental results of cryogenic machining of Inconel 718, a high-temperature aerospace alloy, and comparison of its performance in dry and minimum quantity lubrication machining. Experimental data on force components, progressive tool wear parameters such as flank wear, notch wear, crater wear, cutting temperature, chip morphology, and surface roughness/topography of machined samples are presented. New findings show that cryogenic machining is a promising research direction for machining of high-temperature aerospace alloy, Inconel 718, as it offers improved machining performance in terms of reduced tool wear, temperature, and improved surface quality. It was also found that the number of nozzles in cryogenic machining plays a vital role in controlling cutting forces and power consumption in cryogenic machining of Inconel 718. © 2014 Springer-Verlag London. Source

In the present study, hazelnut (Corylus avellana L.) kernel oil was transesterified with methanol using potassium hydroxide as catalyst to obtain biodiesel and a comprehensive experimental investigation of combustion (cylinder gas pressure, rate of pressure rise, ignition delay) and heat release (rate of heat release, cumulative heat release, combustion duration and center of heat release) parameters of a direct injection compression ignition engine running with biodiesel and its blends with diesel fuel was carried out. Experiment parameters included the percentage of biodiesel in the blend, engine load, injection timing, injection pressure, and compression ratio. Results showed that hazelnut kernel oil methyl ester and its blends with diesel fuel can be used in the engine without any modification and undesirable combustion and heat release characteristics were not observed. The modifications such as increasing of injection timing, compression ratio, and injection pressure provided significant improvement in combustion and heat release characteristics. © 2009 Elsevier Ltd. All rights reserved. Source

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