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Permanent URI for this collectionhttps://ada.atilim.edu.tr/handle/123456789/19

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Citation Count: 102
A 1.6-mm, metal tube ultrasonic motor
(Ieee-inst Electrical Electronics Engineers inc, 2003) Cagatay, S; Koc, B; Uchino, K
A miniaturized metal tube ultrasonic motor, the dimensions of which are 1.6 mm in diameter and 6 rum in length, was developed. Two flattened surfaces with 90-degrees were ground on the outer surface of the stator. Two PZT-based piezoelectric ceramics were bonded onto these flat surfaces. The asymmetrical surface of the stator developed the split of the two degenerated orthogonal bending modes, resulting in a wobble motion. The working frequency of the 1.6-mm motor with 6 mm in length was 130 kHz. A torque of 0.5 mNm was reached at a maximum power of 45 mW with a speed of 45 rad/sec. The maximum efficiency was 16%.
Citation Count: 0
A 30-year journey of hospitality and tourism research: a comprehensive topic modeling analysis
(Emerald Group Publishing Ltd, 2024) Kurt, Senol; Assefa, Feven Zewdie; Tuzlukaya, Sule Erdem; Karatepe, Osman M.; Business
PurposeThe purpose of this study is to provide an overview of the research conducted on hospitality and tourism articles published in Q1 category journals from 1990 to 2023. This study also aims to measure the topic prevalence in selected journals throughout the years, their change over time and similarities of journals.Design/methodology/approachLatent dirichlet allocation algorithm is used as a topic modeling method to identify and analyze topics in hospitality and tourism research over the past 30 years.FindingsThe results of the study indicate that hospitality and tourism research has recently focused on topics such as employee behavior, customer satisfaction, online reviews, medical tourism and tourist experience. However, the results also indicate a negative trend in topics such as hotel management, sustainability, profession, economic growth and tourist destination.Practical implicationsThis study can be used to examine the evolution of research patterns over time, find hot and cold themes and uncover untapped or understudied areas. This can aid academics in their investigations and practitioners in making sound strategic decisions.Originality/valueThis study contributes to the existing literature by providing a new approach and comprehensive analysis of hospitality and tourism research topics. It delineates an overview of the progression of hospitality and tourism research over the past 30 years, identifies the trending topics and explores the potential impacts that these identified topics may have on future studies.
Citation Count: 4
3D Bioprinting tissue analogs: Current development and translational implications
(Sage Publications inc, 2023) Liu, Suihong; Cheng, Lijia; Liu, Yakui; Zhang, Haiguang; Song, Yongteng; Park, Jeong-Hui; Ramalingam, Murugan
Three-dimensional (3D) bioprinting is a promising and rapidly evolving technology in the field of additive manufacturing. It enables the fabrication of living cellular constructs with complex architectures that are suitable for various biomedical applications, such as tissue engineering, disease modeling, drug screening, and precision regenerative medicine. The ultimate goal of bioprinting is to produce stable, anatomically-shaped, human-scale functional organs or tissue substitutes that can be implanted. Although various bioprinting techniques have emerged to develop customized tissue-engineering substitutes over the past decade, several challenges remain in fabricating volumetric tissue constructs with complex shapes and sizes and translating the printed products into clinical practice. Thus, it is crucial to develop a successful strategy for translating research outputs into clinical practice to address the current organ and tissue crises and improve patients' quality of life. This review article discusses the challenges of the existing bioprinting processes in preparing clinically relevant tissue substitutes. It further reviews various strategies and technical feasibility to overcome the challenges that limit the fabrication of volumetric biological constructs and their translational implications. Additionally, the article highlights exciting technological advances in the 3D bioprinting of anatomically shaped tissue substitutes and suggests future research and development directions. This review aims to provide readers with insight into the state-of-the-art 3D bioprinting techniques as powerful tools in engineering functional tissues and organs.
Citation Count: 1
Acceptance of Educational Use of AI Chatbots in the Context of Self-Directed Learning with Technology and ICT Self-Efficacy of Undergraduate Students
(Taylor & Francis inc, 2024) Esiyok, Elif; Gokcearslan, Sahin; Kucukergin, Kemal Gurkan; Tourism Management; Public Relations and Advertising
For long now, the use of Artificial Intelligence (AI) chatbots in higher education to support and engage learners in classroom learning activities has been attracting the attention of researchers. The acceptance of this technology for learning purposes is indicative of learners' intentions and actual use in the future. Hence, this study aims to test the educational use of AI chatbots in the context of self-directed learning with technology (SDLT) along with information and communication technology (ICT) self-efficacy, using the extended Technology Acceptance Model (TAM). The study involved 414 undergraduate students, and the research model was tested by utilizing the Partial Least Square Structural Equation Model (PLS-SEM). The results indicate that ICT self-efficacy affects only the perceived ease of use (PEU), whereas PEU and perceived usefulness have a positive effect on the intention to use AI chatbots. Moreover, SDLT is shown to affect both the intention and the actual use of AI chatbots. As such, it is suggested - among other notes - that universities update their curricula and activities to support SDLT, and also organize activities in order to increase ICT self-efficacy among students.
Citation Count: 33
Accuracy assessment of temperature trends from ERA5 and ERA5-Land
(Elsevier, 2023) Yilmaz, Meric; Civil Engineering
Many environmental processes and ecological systems are being affected by the warming temperatures as a result of climate change. To correctly identify and attribute the uncertainty estimates in these systems, an investigation of tem-perature trend signal existing in the datasets that are used to study such systems is necessary. In this study, the trend of widely used ERA5 and ERA5-Land temperature estimates between 1951 and 2020 were validated using temperature trends from ground station-based observations in Turkey. The investigation included datasets obtained over 540 stations, and the seasonality and spatio-temporal variability of the trend accuracy was also investigated. On average, the trends of observations over all stations were 0.82 degrees C/decade and 0.30 degrees C/decade for the periods 2001-2020 and 1951-2020, respectively, indicating strong evidence of climate change. When the model datasets used spatially and temporally continuous datasets, the trends identified were 0.91 degrees C/decade and 0.21 degrees C/decade over the entire Turkey for the years 2001-2020 and 1951-2020, respectively. The difference in the 70-year trends of the two esti-mates was attributed to the missing datasets in observations. The differences between the trends of model estimates and observations were higher for the first decade than for the last two decades, stressing the impact of improved model estimates over time. All products showed heavy seasonality, suggesting that winter trends (1.3 degrees C/decade on average) are much higher than the summer (0.3 degrees C/decade) between 2001 and 2020. The results indicated a high degree of consistency between the trends of ERA5/ERA5-Land and observations, implying they may be used as a replacement to observations.
Citation Count: 5
Acoustic phonons scattering mobility and carrier effective mass in In₆S₇ crystals
(Elsevier Science Sa, 2006) Qasrawi, A. F.; Gasanly, N. M.; Department of Electrical & Electronics Engineering
Systematic dark electrical resistivity and Hall coefficient measurements have been carried out in the temperature range of 170-320 K on n-type In6S7 crystals. The analysis of the electrical resistivity and carrier concentration reveals the intrinsic type of conduction with an average energy band gap of similar to 0.75 eV The carrier effective masses of the conduction and valence bands were calculated from the intrinsic temperature-dependent carrier concentration data and were found to be 0.565m(0) and 2.020m(0), respectively. The temperature-dependent Hall mobility was observed to follow the mu alpha T-3/2 law and was analyzed assuming the domination of acoustic phonons scattering. The acoustic phonons scattering mobility was calculated from the crystal's structural data with no assumptions. The experimental Hall mobility data of In6S7 crystals coincides with the theoretical acoustic phonons scattering mobility data with acoustic deformation potential of 6.4 eV. (c) 2006 Elsevier B.V. All rights reserved.
Citation Count: 16
ACPA decreases non-small cell lung cancer line growth through Akt/PI3K and JNK pathways in vitro
(Springernature, 2021) Boyacioglu, OEzge; Bilgic, Elif; Varan, Cem; Bilensoy, Erem; Nemutlu, Emirhan; Sevim, Duygu; Korkusuz, Petek; Basic Sciences
Therapeutic agents used for non-small cell lung cancer (NSCLC) have limited curative efficacy and may trigger serious adverse effects. Cannabinoid ligands exert antiproliferative effect and induce apoptosis on numerous epithelial cancers. We confirmed that CB1 receptor (CB1R) is expressed in NSCLC cells in this study. Arachidonoylcyclopropylamide (ACPA) as a synthetic, CB1R-specific ligand decreased proliferation rate in NSCLC cells by WST-1 analysis and real-time proliferation assay (RTCA). The half-maximal inhibitory concentration (IC50) dose of ACPA was calculated as 1.39x10(-12)M. CB1 antagonist AM281 inhibited the antiproliferative effect of ACPA. Flow cytometry and ultrastructural analyzes revealed significant early and late apoptosis with diminished cell viability. Nano-immunoassay and metabolomics data on activation status of CB1R-mediated pro-apoptotic pathways found that ACPA inhibited Akt/PI3K pathway, glycolysis, TCA cycle, amino acid biosynthesis, and urea cycle and activated JNK pathway. ACPA lost its chemical stability after 24hours tested by liquid chromatography-mass spectrometry (LC-MS/MS) assay. A novel ACPA-PCL nanoparticle system was developed by nanoprecipitation method and characterized. Sustained release of ACPA-PCL nanoparticles also reduced proliferation of NSCLC cells. Our results demonstrated that low dose ACPA and ACPA-PCL nanoparticle system harbor opportunities to be developed as a novel therapy in NSCLC patients that require further in vivo studies beforehand to validate its anticancer effect.
Citation Count: 2
Adaptation of Food Craving Inventory to Turkish culture: a validity and reliability study
(Bmc, 2022) Ozel, Irem Cagla; Yabanci Ayhan, Nurcan; Cetiner, Ozlem; Nutrition and Dietetics
Plain English Summary This study was carried out to adapt the Food Craving Inventory to Turkish. The English version of inventory consists of 4 sub-factors that measure cravings for high-fat foods, carbohydrates/starches, sweets, and fast food fats, and creates a total score. The sample of the study consists of 621 individuals between the ages of 19-50 who voluntarily agree to participate in an online survey. This study revealed that FCI-TR is a valid instrument of specific food cravings in the Turkish adult population. Turkish version of the FCI also consist of 4 sub-factors. Women experienced more food craving for sweets than men. While the most craved food by women was chocolate, men scored significantly higher on bread than women. In addition, a relationship was found between food craving and body weight. Introduction The Food Craving Inventory is a 28-item self-report measure of specific food cravings. The inventory consists of 4 factors: high fats, sweets, carbohydrates/starches and fast-food fats. Purpose This study was carried out to evaluate the Turkish validity and reliability of the Food Craving Inventory, and to determine the psychometric properties and factor structure of the Turkish version. Methods The sample of the study consists of 621 individuals between the ages of 19-50 who voluntarily agree to participate in online survey. Validity and reliability analyses were performed for the Turkish version of Food Craving Inventory (FCI-TR). Confirmatory factor analysis was performed to evaluate the factor structure of the Turkish version of FCI. Results Confirmatory factor analysis yielded a four-factor structure as "sweets," "high-fats," "carbohydrates/starches" and "fast food fats". The Cronbach-alpha coefficient for the total score was 0.84; subfactors were calculated as 0.74 for "sweets", 0.64 for "high-fat foods", 0.65 for "carbohydrates/starches", and 0.66 for "fast-food fats". The scores of the FCI-TR factors and its total score significantly correlated with the sub-factors of Three Factor Eating Questionnaire (TFEQ). A significant correlation was found between body mass index (BMI) and high fats and fast-food fats factor score. Also total and factor scores of the FCI-TR were different between BMI groups. Conclusions This study demonstrates that the Turkish version of the FCI is a valid and reliable tool to measure food cravings in the Turkish population. FCI is also correlated with sub-factors of TFEQ.
Citation Count: 92
Adaptive dimensional search: A new metaheuristic algorithm for discrete truss sizing optimization
(Pergamon-elsevier Science Ltd, 2015) Hasancebi, Oguzhan; Azad, Saeid Kazemzadeh; Department of Civil Engineering
In the present study a new metaheuristic algorithm called adaptive dimensional search (ADS) is proposed for discrete truss sizing optimization problems. The robustness of the ADS lies in the idea of updating search dimensionality ratio (SDR) parameter online during the search for a rapid and reliable convergence towards the optimum. In addition, several alternative stagnation-control strategies are integrated with the algorithm to escape from local optima, in which a limited uphill (non-improving) move is permitted when a stagnation state is detected in the course of optimization. Besides a remarkable computational efficiency, the ease of implementation and capability of locating promising solutions for challenging instances of practical design optimization are amongst the remarkable features of the proposed algorithm. The efficiency of the ADS is investigated and verified using two benchmark examples as well as three real-world problems of discrete sizing truss optimization. A comparison of the numerical results obtained using the ADS with those of other metaheuristic techniques indicates that the proposed algorithm is capable of locating improved solutions using much lesser computational effort. (C) 2015 Elsevier Ltd. All rights reserved.
Citation Count: 5
The adhesion and tribological properties of c-BN films deposited by high power impulse magnetron sputtering
(Elsevier Sci Ltd, 2019) Efeoglu, Ihsan; Totik, Yasar; Keles, Aysenur; Gulten, Gokhan; Ersoy, Kivilcim; Durkaya, Goksel; Department of Metallurgical and Materials Engineering
Nitride based films are very important for industrial applications due to their mechanical and tribological properties. Among the nitride based films, c-BN films have superior properties. But, the adhesion properties of c-BN films deposited using magnetron sputtering with different power sources are inadequate generally. Recently, High Power Impulse Magnetron Sputtering (HiPIMS) power sources have been used to increase the adhesion of coatings and there is no open literature about c-BN deposited using HiPIMS. From this point, c-BN films were coated on 4140 steels using HiPIMS with closed-field unbalanced magnetron sputtering (CFUBMS). In the process, two B4C, two Ti targets and Ar + N-2 gas mixture were used to synthesize c-BN films. The amount of N-2 was altered as 2.5, 3.5 and 4.5sccm. The characteristic properties of c-BN films were analyzed using SEM, XRD and FT-IR. The mechanical properties were tested using a microhardness and scratch testers. The tribological properties were performed by a pin-on-disc tribotester under atmosphere, argon, and oil test conditions. The results showed that the properties of c-BN films deposited by HiPIMS are interesting. The hardness values were obtained above 36 GPa and the maximum critical load was reached to 80 N. Also, the minimum CoFs were observed as expected from the oil condition, in that case, the lowest CoF (mu congruent to 0.06) was noted from the hardest coating.
Citation Count: 31
Adoption of mobile applications for teaching-learning process in rural girls' schools in India: an empirical study
(Springer, 2020) Chatterjee, Sheshadri; Majumdar, Dipasree; Misra, Sanjay; Damasevicius, Robertas; Computer Engineering
The purpose of this study is to identify the factors that can impact the adoption of mobile apps for teaching-learning process focusing on the girls' school in rural India. The hypotheses were proposed and a conceptual model has been developed. There is a survey work conducted to collect the data from different respondents using a convenience sampling method. The model has been validated statistically through PLS-SEM analysis covering feedbacks of 271 effective respondents. The study highlights the impact of different antecedents of the behavioural intention of the students of using mobile applications for teaching-learning process. The results also show that among other issues, price value has insignificant influence on the intention of the girl students of the rural India. During survey feedbacks have been obtained from the 271 respondents, which is meagre compared to vastness of the population and school of rural India. Only few predictors have been considered leaving possibilities of inclusion of other boundary conditions to enhance the explanative power more than that has been achieved in the proposed model with the explanative power of 81%. The model has provided laudable inputs to the educational policy makers and technology enablers and administrators to understand the impact of the mobile applications on the rural girls' school of India and facilitate the development of m-learning. Very few studies been conducted to explore the impact of mobile applications on the school education of rural India especially focusing on the girls' schools.
Citation Count: 73
Adsorption properties of a natural zeolite-water pair for use in adsorption cooling cycles
(Elsevier Sci Ltd, 2010) Solmus, Ismail; Yamali, Cemil; Kaftanoglu, Bilgin; Baker, Derek; Caglar, Ahmet; Manufacturing Engineering
The equilibrium adsorption capacity of water on a natural zeolite has been experimentally determined at different zeolite temperatures and water vapor pressures for use in an adsorption cooling system. The Dubinin-Astakhov adsorption equilibrium model is fitted to experimental data with an acceptable error limit. Separate correlations are obtained for adsorption and desorption processes as well as a single correlation to model both processes. The isosteric heat of adsorption of water on zeolite has been calculated using the Clausius-Clapeyron equation as a function of adsorption capacity. The cyclic adsorption capacity swing for different condenser, evaporator and adsorbent temperatures is compared with that for the following adsorbent-refrigerant pairs: activated carbon-methanol; silica gel-water; and, zeolite 13X-water. Experimental results show that the maximum adsorption capacity of natural zeolite is nearly 0.12 kg(w)/kg(ad) for zeolite temperatures and water vapor pressures in the range 40-150 degrees C and 0.87-738 kPa. (C) 2009 Elsevier Ltd. All rights reserved.
Citation Count: 0
Advanced 3D printed bone scaffolds with sodium alginate/Tri-calcium phosphate/probiotic bacterial hydroxyapatite: Enhanced mechanical and biocompatible properties for bone tissue engineering
(Elsevier Sci Ltd, 2024) Nouri, Sabereh; Emtiazi, Giti; Ulag, Songul; Gunduz, Oguzhan; Koyuncu, Ayse Ceren Calikoglu; Roghanian, Rasoul; Sasmazel, Hilal Turkoglu; Metallurgical and Materials Engineering
Introduction: The increasing prevalence of severe bone diseases, such as osteoporosis and critical bone defects, necessitates the development of more effective bone substitutes. This study addresses this need by investigating 3D-printed bone scaffolds composed of sodium alginate and tricalcium phosphate, enhanced with three distinct types of hydroxyapatite (HA): bovine-derived HA, commercially available HA, and HA enriched with probiotic bacteria. We aim to evaluate the performance of these scaffolds in terms of mechanical strength, biocompatibility, and their ability to support bone regeneration. Methods: The scaffolds were analyzed through various tests, including X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) to characterization. Scanning Electron Microscopy (SEM) was used to examine pore structure, while swelling and degradation tests evaluated the scaffold's stability. Compression testing determined mechanical strength, and in vitro cell culture assays assessed cell proliferation, osteogenic differentiation, and biomineralization. Results: SEM results indicated that 3D scaffolds with probiotic bacterial HA had the desired 472 mu m pore size. These scaffolds demonstrated a strain of 29.26 % and a compressive strength of 10 MPa, meeting the mechanical standards of human trabecular bone. Cell culture studies revealed enhanced cell proliferation by 50 %, osteogenic differentiation with 15.3 U/mg ALP activity, and 1.22-fold biomineralization, suggesting they are highly biocompatible and promote bone growth. Conclusion: Probiotic bacterial HA scaffolds exhibit ideal properties and biocompatibility, enhancing bone regeneration and serving as an ideal alternative to chemical types.
Citation Count: 4
Age based preventive replacement policy for discrete time coherent systems with independent and identical components
(Elsevier Sci Ltd, 2023) Eryilmaz, Serkan; Industrial Engineering
The paper is concerned with an age based preventive replacement policy for an arbitrary coherent system that consists of components that are independent and have common discrete lifetime distribution. The system having an arbitrary structure is replaced preventively after a specific number of cycles or correctively at its failure time. The necessary conditions for the unique and finite replacement cycle that minimize the expected cost per unit of time are obtained. The policy is studied for some particular system models including the well-known k-out-of -n structure. The findings of the paper extend the results in the literature from single unit and parallel systems to an arbitrary coherent system. Numerical results are presented for particular discrete component lifetime distributions.
Citation Count: 0
Age replacement policy for heterogeneous parallel systems
(Elsevier, 2024) Ozdemir, Irem Bulanik; Kilicoglu, Sevval; Eryilmaz, Serkan; Industrial Engineering
The optimization policy on age replacement mostly focuses on systems comprised of identical components. In this paper, both discrete and continuous time age replacement policies are considered by relaxing the assumption of identical components and working with heterogeneous parallel system, i.e. system with not necessarily identical components. In particular, necessary conditions are obtained for the existence and uniqueness of optimal replacement cycle/time for the parallel system with two nonidentical components under the proposed policy. The extension of the results to a system with more than two components is also presented.(c) 2023 Elsevier B.V. All rights reserved.
Citation Count: 37
Age-based preventive maintenance for coherent systems with applications to consecutive-k-out-of-n and related systems
(Elsevier Sci Ltd, 2020) Eryilmaz, Serkan; Industrial Engineering
This article presents a signature-based representation for the expected cost rate of age-based preventive maintenance policy for a binary coherent system consisting of independent exponential components, and then specializes the method to consecutive k-out-of-n system and its generalizations. According to the age-based preventive maintenance policy, the system is replaced at failure or before failure. For an arbitrary coherent system, the number of failed components at replacement time is a random variable. Thus, the expected cost per unit of time involves the mean number of failed components at replacement time. This mean is represented in terms of signature. Extensive numerical and graphical examples are presented for m-consecutive k-out-of-n:F and consecuthre-k-within-m-out-of-n:F systems.
Citation Count: 4
'Aid with Chinese characteristics': competitive and/or complementary?
(Routledge Journals, Taylor & Francis Ltd, 2021) Gulseven, Yahya
China's growing foreign aid program in recent years has sparked many debates on alternative development cooperation approaches and practices. 'Aid with Chinese characteristics' is often approached with skepticism in the West and considered as posing challenges to the traditional aid architecture. The more optimistic perspectives see China's emergence as a major donor in a more positive light because it offers an alternative development cooperation model for aid recipient countries, contesting the hegemony of the neoliberal development model. While analysts have mostly focused on whether 'aid with Chinese characteristics' is a good or bad alternative, few have questioned its novelty and its actual potential as an alternative development cooperation model. From a neo-Gramscian perspective, this study investigates to what extend China, as a major donor, differs from the traditional donors and in how far that its aid model can be understood as representing a counter-hegemonic alternative. The core argument of this study is that 'aid with Chinese characteristics' serves the overall objectives and interests of the neoliberal historical bloc, while at the same time it also plays a role in the increasing tensions and competitions within it, between China and the Western countries in the context of the global financial crisis.
Citation Count: 35
An algorithmic approach for the dynamic reliability analysis of non-repairable multi-state weighted k-out-of-n:G system
(Elsevier Sci Ltd, 2014) Eryilmaz, Serkan; Bozbulut, Ali Riza; Industrial Engineering
In this paper, we study a multi-state weighted k-out-of-n:G system model in a dynamic setup. In particular, we study the random time spent by the system with a minimum performance level of k. Our method is based on ordering the lifetimes of the system's components in different state subsets. Using this ordering along with the Monte-Carlo simulation algorithm, we obtain estimates of the mean and survival function of the time spent by the system in state k or above. We present illustrative computational results when the degradation in the components follows a Markov process. (C) 2014 Elsevier Ltd. All rights reserved.
Citation Count: 18
alpha-psi-Geraghty contractions on generalized metric spaces
(Springer, 2014) Asadi, Mehdi; Karapinar, Erdal; Kumar, Anil; Mathematics
In this work, we introduce the class of alpha-psi-Geraghty contraction as well as generalized alpha-psi-Geraghty contraction mappings in the context of generalized metric spaces where psi is an auxiliary function which does not require the subadditive property and set up some fixed point results for both classes individually. Our results will extend, improve and generalize several existing results in the literature.
Citation Count: 0
Amendments on "Application of Mises yield criterion to rotating solid disk problem" by N. Aleksandrova [Int. J. Eng. Sci. 51 (2012) 333-337]
(Pergamon-elsevier Science Ltd, 2012) Eraslan, Ahmet N.; Akis, Tolga; Civil Engineering
[No Abstract Available]

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