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Article Citation - WoS: 6Citation - Scopus: 6Excessive Damage Increase in Dual Phase Steels Under High Strain Rates and Temperatures(Sage Publications Ltd, 2021) Cobanoglu, Merve; Ertan, Rasim K.; Simsir, Caner; Efe, MertDamage formation in dual phase steels is a complex process and it may be sensitive to the deformation conditions and mechanisms. In this study, the damage parameter is measured and compared under quasi-static and industrial forming conditions (temperatures: 25 vs 200, 300 degrees C and strain rates: 10(-3)vs 10 s(-1)) for DP590 and DP800 steels. Resonance frequency and ultrasonic sound velocity techniques are utilized for the measurements to test the effectiveness and validity of each technique. At a given strain, the damage values can be up to 700% higher at industrial forming conditions, under which dynamic strain aging (DSA) controls the deformation behavior. DSA results in lower formability and is the likely mechanism responsible from the abnormal damage evolution. Measured damage parameters are also confirmed with the void fraction characterization by microscopy, which also provided details on the void shape and distribution with respect to the deformation conditions.Article Citation - WoS: 19Citation - Scopus: 19Interaction Between Assembled 3d Honeycomb Cells Produced From High Density Polyethylene and a Cohesionless Soil(Sage Publications Ltd, 2012) Gurbuz, Ayhan; Mertol, Halit CenanAssembled 3D high-density polyethylene honeycomb cells, providing confinement to arrest spreading of the soil in cells and creating relatively stiff bed that redistributes footing pressure over wider area, were used in the present study to enhance load-carrying capacity and to reduce settlement of base materials under a foundation. The effects of various test parameters including width, height, number of layers of the 3D honeycomb cells, vertical distance between layers of the cells and depth of stress zone of the foundation were studied. The test results indicated that considerable improvement in the load-carrying capacity (congruent to 3.0) and reduction in settlement of the foundation (congruent to 62%) were obtained with the implementation of the single layer of the 3D cells into cohesionless soils. The optimum effective distance between two layers of the 3D cells was 0.142 times the width of foundation, the ratio of effective width of 3D cells to the foundation was about 4.2 and the depth of influence stress zone of the foundation was about two times the width of the foundation.Article Citation - WoS: 36Citation - Scopus: 42Modeling and Analysis of Weighted-k-out-of-n< G System Consisting of Two Different Types of Components(Sage Publications Ltd, 2014) Eryilmaz, Serkan; Sarikaya, KadirThis article is concerned with the reliability analysis of a weighted-k-out-of-n: G system consisting of two types of components. The system is assumed to have n components which are classified into two groups with respect to their weight and reliability, and it is assumed to operate if the total weight of all working components exceeds a prespecified threshold k. The reliability properties of such a system are studied. The optimal values of the number of components in each group are also determined under a minimum required reliability by minimizing the total acquisition cost.Article Citation - WoS: 7Citation - Scopus: 8Robust and Adaptive Control Design of a Drilling Rig During the Operating Modes(Sage Publications Ltd, 2019) Sadeghi, Amir Nobahar; Arikan, Kutluk Bilge; Ozbek, Mehmet Efe; Baranoglu, BesimOil well drilling towers have different operating modes during a real operation, like drilling, tripping, and reaming. Each mode involves certain external disturbances and uncertainties. In this study, using the nonlinear model for the modes of the operation, robust and/or adaptive control systems are designed based on the models. These control strategies include five types of controllers: cascaded proportional-integral-derivative, active disturbance rejection controller, loop shaping, feedback error learning, and sliding mode controller. The study presents the design process of these controllers and evaluates the performances of the proposed control systems to track the reference signal and reject the uncertain forces including the parametric uncertainties and the external disturbances. This comparison is based on the mathematical performance measures and energy consumption. In addition, three architectures are presented to control the weight on bit during drilling process, and also to maintain a preset constant weight on bit, two control approaches are designed and presented.Article Citation - WoS: 9Citation - Scopus: 11Reliability of the Two-Unit Priority Standby System Revisited(Sage Publications Ltd, 2022) Eryilmaz, Serkan; Finkelstein, MaximThis paper deals with reliability assessment of the repairable two-unit cold standby system when the first, main unit has the better performance level than the second one. Therefore, after its repair, the main unit is always switched into operation. The new Laplace transform representation for the system's lifetime is obtained for arbitrary operation and repair time distributions of the units. For some particular cases, the Laplace transform of the system is shown to be rational, which enables the use of the matrix-exponential distributions for obtaining relevant reliability indices. The discrete setup of the model is also considered through the corresponding matrix-geometric distributions, which are the discrete analogs of the matrix-exponential distributions.Article Citation - WoS: 2Citation - Scopus: 3Change of Frontal Sinus in Age of According To the International Frontal Sinus Anatomy Classification(Sage Publications Ltd, 2023) Koksal, Ali; Demir, Berin Tugtag; Cankal, FatihBackground The radiological and surgical anatomy of the frontal sinus should be well-known in all age groups to successfully manage frontal sinus diseases and reduce the risk of complications in sinus surgery. Purpose To define frontal sinus and frontal cells according to the International Frontal Sinus Anatomy Classification (IFAC) criteria in pediatrics and adults. Material and Methods A total of 320 frontal recess regions of 160 individuals (80 pediatric, 80 adults) who underwent a computed tomography (CT) scan of the paranasal sinus (PNS) were included in the study. Agger nasi cells, supra agger cells, supra agger frontal cells, suprabullar cells, suprabullar frontal cells, supraorbital ethmoid cells, and frontal septal cells were evaluated in the CT analysis. Results The incidence rates of the investigated cells were determined to be 93.1%, 41.9%, 60.0%, 76.3%, 58.5%, 18.8%, and 0% in the pediatric group, respectively, and 86.3%, 35.0%, 44.4%, 54.4%, 46.9%, 19.4%, and 3.4% in the adult group, respectively. Considering the unilateral and bilateral incidence of the cells, agger nasi cells were highly observed bilaterally in both the pediatric group (89.87%) and the adult group (86.48%). Conclusion Our study results show that IFAC can be used as a guide to increase the chance of surgical treatment in the pediatric and adult groups and that the prevalence of frontal cells can be determined radiologically and contributes to the generation of estimations of the prevalence of frontal cells.Article Citation - WoS: 4Citation - Scopus: 4Multiloop State-Dependent Nonlinear Time-Varying Sliding Mode Control of Unmanned Small-Scale Helicopter(Sage Publications Ltd, 2020) Ozcan, Sinan; Salamci, Metin U.; Nalbantoglu, VolkanTime delays, parameter uncertainties, and disturbances are the fundamental problems that hinder the stability and reduce dramatically the tracking performance of dynamical systems. In this paper, a new state-dependent nonlinear time-varying sliding mode control autopilot structure is proposed to cope with these dynamical and environmental complexities for an unmanned helicopter. The presented technique is based on freezing the nonlinear system equations on each time step and designing a controller using the frozen system model at this time step. The proposed method offers an improved performance in the presence of major disturbances and parameter uncertainties by adapting itself to possible dynamical varieties without a need of trimming the system on different operating conditions. Unlike the existing linear cascade autopilot structure, this study also proposes a nonlinear cascade state-dependent coefficient helicopter autopilot structure consisting of four separate nonlinear sub-systems. The proposed method is tested through the real time and PC-based simulations. To show the performance of the proposed robust method, it is also bench-marked against a linear sliding control control in PC-based simulations.Article Citation - WoS: 66Citation - Scopus: 75Production and Characterization of Poly (lactic Acid)-Based Biocomposites Filled With Basalt Fiber and Flax Fiber Hybrid(Sage Publications Ltd, 2020) Eselini, Najah; Tirkes, Seha; Akar, Alinda Oyku; Tayfun, UmitPoly (lactic acid) (PLA)-based biocomposites containing flax fiber (FF) and basalt fiber (BF) both separately and together were prepared by melt blending method at the total constant ratio of 30 wt%. Mechanical properties, thermo-mechanical characteristics, thermal stability, flow behaviors, water uptake, and morphology of composites were investigated by tensile, hardness and impact tests, dynamic mechanical analysis (DMA), thermal gravimetric analysis, melt flow index (MFI) test, water absorption, and scanning electron microscopy, respectively. Mechanical test results show that tensile strength, elongation, elastic modulus, and impact strength are extended up to higher values with increase in BF content in hybrid composites. Conversely, the presence of FF displays a negative effect in which these values drop down drastically as the FF concentration increases. On the other hand, slightly higher hardness values are obtained by the addition of FF at higher loadings. DMA analysis reveals that BF inclusion leads glass transition temperature of PLA to one point higher, but hybrid and FF containing composites shift that temperature to lower values. Storage moduli of composites are enhanced with the increase in BF concentration and remarkable decreases are observed for FF-filled composites. Hybrid composites exhibit average MFI values between PLA/FF and PLA/BF composites.Article Citation - WoS: 6Citation - Scopus: 4Latent Dynamics of Movement Formation: the Kurdish Case in Turkey (1940s-1960s)(Sage Publications Ltd, 2015) Ozen, HayriyeThe attention of social movement studies has so far tended to focus on visible phases of movements, neglecting latent ones. This study argues that invisible mobilizations may be critical in preparing the groundwork of public mobilizations, particularly in authoritarian contexts. Using a process-oriented constructivist account of mobilization which incorporates insights from resistance studies, this article analyzes the Kurdish case in Turkey in the authoritarian 1940s and semi-authoritarian 1950s. Based on in-depth interviews, memoirs, newspaper reports, and official documents, it is demonstrated that a latent Kurdish dissent emerged in this period through the constitution of a sense of shared grievance and common identity both in hidden ways within the submerged networks of Kurdish students and professionals, and in public and visible, yet disguised, ways. Incubating the movement out of the gaze of the authorities within the authoritarian context, this latent dissent formed the groundwork of public acts of defiance and mobilization which emerged towards the end of the 1950s as the political changes encouraged Kurdish dissenters to publicly declare their opposition, and expanded in the more liberal context of the 1960s. Resume Les etudes des mouvements sociaux ont eu tendance jusqu'a present a privilegier les phases visibles de ces mouvements, negligeant les stades latents. Cette etude soutient que les mobilisations invisibles peuvent etre essentielles pour preparer le terrain des mobilisations publiques, en particulier dans un contexte autoritaire. En s'appuyant sur une interpretation constructiviste, axee sur le processus de mobilisation et reunissant des idees tirees des etudes des mouvements de resistance, cet article analyse le cas kurde dans la Turquie autoritaire des annees quarante et semi-autoritaire des annees cinquante. Fonde sur des entretiens approfondis, des biographies, des articles de journaux et des documents officiels, ce travail met en evidence l'apparition au cours de cette periode d'une dissidence kurde latente grace a la constitution d'un sentiment partage de mecontentement et d'identite commune au sein des reseaux secrets des etudiants et professionnels kurdes, de facon a la fois invisible et publique, mais dissimulee. Couvant a l'abri des regards des gouvernements autoritaires, cette dissidence latente a pose les bases des manifestations publiques de defiance et de mobilisation qui sont apparues a la fin des annees cinquante a l'occasion des changements politiques ayant encourage les dissidents kurdes a declarer publiquement leur opposition et favorise les mouvements sociaux dans le contexte plus liberal des annees soixante. Resumen La atencion de los estudios sobre movimientos sociales hasta ahora ha tendido a centrarse en las fases visibles de los movimientos, dejando de lado los latentes. Este estudio sostiene que las movilizaciones invisibles pueden ser centrales para la preparacion de las bases de movilizaciones publicas, en particular en contextos autoritarios. A partir de un relato constructivista orientado a los procesos de movilizacion que incorpora perspectivas de estudios de resistencia, este trabajo analiza el caso kurdo en Turquia en la decada autoritaria de 1940 y semi-autoritaria de 1950. Sobre la base de entrevistas en profundidad, memorias, informes de prensa y documentos oficiales, se demuestra que una disidencia kurda latente surgio en este periodo a traves de la constitucion de un sentimiento de agravio compartida y de identidad comun tanto en formas ocultas dentro de las redes sumergidas de estudiantes y profesionales kurdos, asi como de maneras publicos y visibles, aunque disfrazadas. Incubando el movimiento fuera de la mirada de las autoridades en el contexto autoritario, esta disidencia latente formo las bases del acto publico de rebeldia y movilizacion que surgio a finales de la decada de 1950 como los cambios politicos alentados disidentes kurdos para declarar publicamente su oposicion, y ampliado en el contexto mas liberal de la decada de 1960.Article Citation - WoS: 83Citation - Scopus: 116Effect of Social Media Sharing on Destination Brand Awareness and Destination Quality(Sage Publications Ltd, 2020) Dedeoglu, Bekir Bora; van Niekerk, Mathilda; Kucukergin, Kemal Gurkan; De Martino, Marcella; Okumus, FevziThis study examines the effect of social media sharing on tourism destination brand awareness and destination natural and service quality and also examines the moderating roles of country of origin (COI; macro and micro) image on destination natural and service quality. Data were collected from 568 domestic and international tourists who have visited Alanya, Turkey. Relationships in the study were examined through structural equation modeling. As one of the components of social media sharing, participant sharing positively affects destination brand awareness, whereas any significant effect of nonparticipant sharing on destination brand awareness was not found. Destination brand awareness positively influences tourist perceptions of both destination service quality and destination natural quality. COI image moderates most of the relationships.
