Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 6Citation - Scopus: 6Uncovering Nanoclusters in Amorphous AlN: An Ab Initio Study(Wiley, 2014-12-22) Durandurdu, MuratAmorphous AlN (a-AlN) is modeled by melt-and-quench technique using ab initio molecular dynamic simulations. For the first time, three-dimensional hexagonal-like nanoclusters embedded in amorphous matrix are proposed for a-AlN. The model is chemically ordered and dominantly fourfold coordinated, but its short-range order is partially different from the crystalline morphology due to the nanoclusters. The model is semiconducting with a theoretical band gap of 1.7eV.Article Citation - WoS: 6Citation - Scopus: 6Two Successive Amorphous-to Phase Transformations in TiO2(Wiley, 2017-05-22) Durandurdu, MuratBased on constant pressure ab initio simulations, we propose, for the first time, two successive amorphous-to-amorphous phase transformations for TiO2. The first one is a gradual phase transformation from a low-density amorphous phase to a high-density amorphous phase, whereas the second one is a first-order phase transformation from the high-density amorphous phase to a very high-density amorphous phase. The low-density amorphous to high-density amorphous phase change is irreversible, whereas the high-density amorphous to very high-density amorphous phase transformation is reversible. The high-density amorphous and very high-density amorphous phases consist of differently coordinated configurations. The sevenfold and ninefold-coordinated arrangements formed in amorphous TiO2 under pressure are similar to the main building motif of the baddeleyite and cotunnite polymorphs of TiO2, respectively, while the eightfold-coordinated configuration is different from the local structure of the cubic TiO2 phase. The electronic structure calculations suggest that both dense amorphous phases present a semiconducting character with a band gap energy less than that of the original low-density amorphous phase.Article Citation - WoS: 6Citation - Scopus: 6Tetrahedral Amorphous Boron Nitride: A Hard Material(Wiley, 2019-09-25) Durandurdu, MuratWe generate a tetrahedrally coordinated amorphous boron nitride (BN) model by means of first principles molecular dynamics calculations and report its mechanical and electrical properties in detail. The amorphous configuration is almost free from chemical disorder and consists of about 20% coordination defects, similar to tetrahedral (diamond-like) amorphous carbon. Its theoretical band gap energy is about 2.0 eV, less than 4.85 eV estimated for cubic BN. The bulk modulus and Vickers hardness of tetrahedral amorphous BN are computed as 206 GPa and 28-35 GPa, respectively. Based on these findings, we propose that tetrahedral noncrystalline BN can serve as electronic and hard materials as well.Article Citation - WoS: 29Citation - Scopus: 37Tactile Sensitivity and Capability of Soft-Solid Texture Discrimination(Wiley, 2015-08-09) Aktar, Tugba; Chen, Jianshe; Ettelaie, Rammile; Holmes, MelvinThe sensation and perception of food texture is regulated by tactile-dominated mechanisms and therefore, it is believed that one's capability in discriminating food textural properties could be related to one's tactile sensitivity. However, evidence to support this hypothesis is currently not available. This work aims to test this hypothesis by examining tactile sensitivity of individuals' (touch detection threshold and two-point discrimination threshold) and texture discrimination capability. A range of soft-solid food samples with controlled firmness and elastic moduli were designed for textural discrimination tests. A total of 32 healthy subjects threshold of touch detection was found to be 0.028 g for the fingertip and 0.013 g for the tongue. Similarly, the mean threshold of two-point discrimination was 1.42 mm and 0.62 mm for the fingertip and tongue, respectively. Threshold for firmness discrimination (compressing until yielding) of the gel samples was 13.3% for the fingertip and 11.1% for the tongue. However, the elasticity discrimination threshold (by gentle pressing) of the population was found to be much smaller at 2.3% and 1.2% for the fingertip and the tongue respectively. Results show that tongue is slightly more sensitive than the fingertip in discriminating food texture (P < 0.05). An expected correlation between individual's capability of texture discrimination and their tactile sensitivity was not observed. PRACTICAL APPLICATIONS Texture discrimination capability is a significant factor for food texture preference and appreciation. In order to understand texture perception, it is essential to identify the relevant factors and define characteristics that govern the processes involved. Having a meaningful and reliable texture discrimination indicator is critically important for the food industry in the development and optimization of new food products, and in particular for specific food design for individuals' with special needs, e.g., elderly, dysphagic patients, etc. With this study, we illustrate the differential threshold for soft-solid texture (firmness and elasticity) and also investigate the capabilities of tactile sensation (touch detection and two-point discrimination) and evaluate potential correlations. The results and correlations may provide information about texture sensitivity and also might provide useful information to R&D researchers. Methodologies could also be applied in general food sensory studies and also investigating relationships between sensory psychology and sensory physiology.Article Citation - WoS: 6Citation - Scopus: 6Surface Coating of Polyamide Reverse Osmosis Membranes With Zwitterionic 3-(3,4 (l-DOPA) for Forward Osmosis(Wiley, 2019-03-27) Saki, Seda; Uzal, NigmetTo overcome low permeability and fouling problems of membranes used in FO processes, modification is needed to improve the hydrophilicity, permeability and selectivity of membranes. In this work, thin film composite (TFC) commercial polyamide RO membranes (BW30-LE, SW30-HR, AG and AC) were functionalized with zwitterionicl-DOPA. The effect ofl-DOPA on the morphology of membranes was determined via SEM, FT-IR, AFM and contact angle analysis. Thel-DOPA modified BW30-LE membrane showed excellent properties with 46 degrees contact angle and 3.8 L/m(2)hbar water permeability and 0.83 L/m(2)h salt permeability. Although,l-DOPA modified BW30-LE membrane had the highest water flux and hydrophilicity,l-DOPA modified SW30-HR membrane showed higher FO flux with 9.38 L/m(2)h than BW 30 membrane with 3.5 L/m(2)h at 50 g/L NaCl draw solution. Introducing hydroxyl and carboxyl ionic groups on the membrane surface withl-DOPA coating enhanced the FO performance and water permeability which provide a new insight in FO applications.Conference Object Citation - WoS: 26Citation - Scopus: 26Semiconducting Copolymers Based on Meso-Substituted BODIPY for Inverted Organic Solar Cells and Field-Effect Transistors(Wiley, 2017-12-11) Ozdemir, Mehmet; Kim, Sang Woo; Kim, Hyungsug; Kim, Myung-Gil; Kim, Bumjoon J.; Kim, Choongik; Usta, HakanThe synthesis, physicochemical, and optoelectronic properties of a new class of low band-gap (approximate to 1.3 eV) donor-acceptor copolymers based on a highly electron-deficient meso-5-(2-octyldodecyl)thiophene-substituted BODIPY pi-unit are presented. The polymeric solutions exhibit strong aggregation-dependent excitonic properties indicating the presence of enhanced pi-coherence as a result of strong interchain interactions. The polymeric semiconductor thin films prepared by spin coating show isotropic nodule-like grains with essentially no ordering in the out-of-plane direction. Field-effect hole mobilities of 0.005 cm(2) V-1.s(-1) are observed in bottom-gate top-contact organic field-effect transistors, and inverted bulk-heterojunction organic photovoltaics employing the polymer:PC71BM active layer exhibit excellent power conversion efficiencies of 6.2% with a short-circuit current of 16.6 mA cm(-2). As far as it is known, this is a record high value achieved to date for a boron-containing donor polymer in the photovoltaic literature indicating a significant enhancement in power conversion efficiency (>3-4 times). The findings clearly present that rationally designed BODIPY-based donor-acceptor copolymers can be a key player in photovoltaic applications.Article Citation - WoS: 1Citation - Scopus: 1RF Phase Noise Filtering Properties of an Actively Mode-Locked Laser(Wiley, 2018-01-10) Mbonde, Hamidu; Ozharar, Sarper; Ozdur, IbrahimIn this article, we are presenting the experimental results and theoretical analysis of radio frequency (RF) phase noise filtering properties of a high Q cavity actively driven mode-locked laser. The experimental results show that, the phase noise of a 10 GHz RF tone can be filtered by at least 10 dB at 200 kHz offset frequency. A theoretical analysis on the limits of phase noise filtering due to the spontaneous emission and the frequency mismatch between the laser cavity modes and the synthesizer frequency is also included.Article Citation - WoS: 1Citation - Scopus: 4QoS-Aware MAC Protocols Utilizing Sectored Antenna for Wireless Sensor Networks-Based Smart Grid Applications(Wiley, 2016-07-25) Yigit, Melike; Incel, Ozlem Durmaz; Baktir, Selcuk; Gungor, V. Cagri; Durmaz Incel, OzlemWireless sensor networks (WSNs) are the most commonly deployed technology in smart grid environments owing to their advantages including low cost and successful adoption in various harsh smart grid environments. However, providing the quality of service (QoS) requirements of smart grid applications with WSNs is difficult because of the power constraints of sensor nodes and unreliable wireless links. In order to meet the QoS requirements of smart grid applications usingWSNs, in this paper, we first propose a QoS-aware omnidirectional antenna-based medium access control (QODA-MAC). Then, in order to investigate the impact of using sectored antennas on meeting QoS requirements, we also propose another QoS-aware four-sectored antenna-based MAC protocol (QFSA-MAC). The aim of the proposed approaches is to increase channel utilization with efficient service differentiation considering traffic flows with different requirements as well as providing reliable and fast delivery of data. We measure the performance of QODA-MAC and QFSA-MAC by making extensive simulations and compare them with each other. The results show that QFSA-MAC outperforms the QODA-MAC protocol and satisfies QoS requirements of smart grid applications by achieving significant improvement in terms of latency, energy consumption and data delivery. Copyright (C) 2016 John Wiley & Sons, Ltd.Article Citation - WoS: 8Citation - Scopus: 16QoS-Aware LTE-A Downlink Scheduling Algorithm: A Case Study on Edge Users(Wiley, 2019-07-31) Uyan, Osman Gokhan; Gungor, Vehbi Cagri4G/LTE-A (Long-Term Evolution-Advanced) is the state of the art wireless mobile broadband technology. It allows users to take advantage of high Internet speeds. It makes use of the OFDM technology to offer high speed and provides the system resources both in time and frequency domain. A scheduling algorithm running on the base station holds the allocation of these resources. In this paper, we investigate the performance of existing downlink scheduling algorithms in two ways. First, we look at the performance of the algorithms in terms of throughput and fairness metrics. Second, we suggest a new QoS-aware fairness criterion, which accepts that the system is fair if it can provide the users with the network traffic speeds that they demand and evaluate the performance of the algorithms according to this metric. We also propose a new QoS-aware downlink scheduling algorithm (QuAS) according to these two metrics, which increases the QoS-fairness and overall throughput of the edge users without causing a significant degradation in overall system throughput when compared with other schedulers in the literature.Article Citation - WoS: 5Citation - Scopus: 6Predicting Potential of Pressure Retarded Osmosis Power for Different Estuaries in Turkey(Wiley, 2018-11-29) Saki, Seda; Uzal, Nigmet; Gokcek, Murat; Ates, NurayPressure retarded osmosis (PRO) is an alternative renewable energy source recovered from the salinity gradient between the fresh water (feed solution) and salty water (draw solution). In order to implement osmotic power, the site-specific characteristics including the river and sea salinity, annual flow rates, ecological restrictions were taken into account. This study revealed a comprehensive analysis for a theoretical potential of PRO process for different estuaries in Turkey. In this study, the power potential prediction of PRO process for the Ceyhan, Sakarya, and Meric Rivers were analyzed via Gibbs free energy calculations. The net annual energy production is projected to be 167, 164, and 208 GWh/y for Ceyhan, Sakarya, and Meric Rivers, respectively. Meric River has the highest energy production of 208 GWh/yr with 186 m(3)/s mean flow rate and 245 mg/L salinity. These results clearly show that Turkey's rivers having high salinity and flow rate are feasible and applicable for making the osmotic power plant economically. Thereby, it is providing essential direction to the improvement of its design, installation, and operation. The developed methodology for the evaluation of the osmotic power potential of other rivers can be considered as a basis to assess the whole potential on a worldwide level. (c) 2018 American Institute of Chemical Engineers Environ Prog, 38:e13085, 2019
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