TOBB University of Economics and Technology
Recent publications
This paper offers a novel methodological perspective to public diplomacy studies discussing how to apply Qualitative Longitudinal Research (QLR) into public diplomacy. Accordingly, the paper first discusses the existing academic literature on longitudinal research in social sciences and highlights the necessity to use QLR in public diplomacy studies. Second, it offers a research design on how to conduct QLR in public diplomacy. Third, the paper discusses the historical evolution of German public diplomacy over a period of 70 years as viable case study comparing three global sports events, namely the 1936 Berlin Olympics, the 1972 Munich Olympics and the 2006 World Cup. Overall, the paper argues that QLR has an important potential to advance public diplomacy studies since it enables researcher to trace continuity and change in public engagement policies over extended periods and explain whether historical legacies are reproduced or erased over time and how this resonates with international audience.
Transition metal dichalcogenide (TMD) monolayers have recently garnered significant attention owing to their favorable electronic and optoelectronic properties. To date, chemical vapor deposition (CVD) growth of molybdenum di-sulfide, -selenide, and -telluride (MoS2, MoSe2, and MoTe2, respectively), and tungsten di-sulfide, -selenide, and -telluride (WS2, WSe2, and WTe2, respectively) has been widely investigated as the most promising two-dimensional (2D) TMDs. However, scalable and controllable growth of high-quality TMD monolayers remains a challenge. This review highlights the advances of CVD technique by focusing on the aspects of growth promoters, surface energy assistance and site selectivity, which are of great significance for the growth of monolayer TMDs. The challenges for high-performance applications are discussed at the end with a brief outlook on future work.
We evaluated the demographic features, etiologic risk factors, treatment strategies, and outcome of the infants and children with urolithiasis (UL). A retrospective multicenter study was conducted including 23 Pediatric Nephrology centers in Turkey. The medical records of 2513 children with UL were reviewed. One thousand, three hundred and four boys and 1209 girls (1.1:1) were reported. The mean age at diagnosis was 39.5 ± 35 months (0.4–231 months), and 1262 patients (50.2%) were in the first year of life (infants). Most of the cases with infantile UL were diagnosed incidentally. Microlithiasis (< 3 mm) was found in 794 patients (31.6%), and 64.5% of the patients with microlithiasis were infants. Stones were located in the pelvis-calyces in 63.2% (n: 1530) of the cases. The most common stone type was calcium oxalate (64.6%). Hypocitraturia was the most common metabolic risk factor (MRF) in children older than 12 months, but in infancy, hypercalciuria was more common. Fifty-five percent of the patients had received at least one medical treatment, mostly potassium citrate. At the end of a year’s follow-up, most of the patients with microlithiasis (85%) showed spontaneous remission. The rate of spontaneous stone resolution in infants was higher than in children. Spontaneous remission rate was higher in cases with MRF ( − ) stones than in MRF ( +) stones. However, remission rate with medical treatment was higher in cases with MRF ( +) stones. This study represents the results of a large series of infants and children with UL and showed that there are several differences such as underlying metabolic and anatomic abnormalities, clinical course, and stone remission rates between infants and children with urinary stone disease.
Psychogenic nonepileptic seizure (PNES) and epileptic seizure resemble each other, behaviorally. This similarity causes misdiagnosis of PNES and epilepsy patients, thus patients suffering from PNES may be treated with antiepileptic drugs which can have various side effects. Furthermore, seizure is diagnosed after time consuming examination of electroencephalography (EEG) recordings realized by the expert. In this study, automated temporal lobe epilepsy (TLE) patient, PNES patient and healthy subject discrimination method from EEG signals is proposed in order to eliminate the misdiagnosis and long inspection time of EEG recordings. Also, this study provides automated approach for TLE interictal and ictal epoch classification, and TLE, PNES and healthy epoch classification. For this purpose, subbands of EEG signals are determined from discrete wavelet transform (DWT), then classification is performed using ensemble classifiers fed with energy feature extracted from the subbands. Experiments are conducted by trying two approaches for TLE, PNES and healthy epoch classification and patient discrimination. Results show that in the TLE, PNES and healthy epoch classification the highest accuracy of 97.2%, sensitivity of 97.9% and specificity of 98.1% were achieved by applying adaptive boosting method, and the highest accuracy of 87.1%, sensitivity of 86.0% and specificity of 93.6% were attained using random under sampling (RUS) boosting method in the TLE patient, PNES patients and the healthy subject discrimination.
We study quadratic payoff common-value sequential-move aggregative games with signaling. Applications include Stackelberg quantity-setting, public good contribution, common resource, gas emission, and manufacturer-retailer games. Whereas efficient aggregation of information occurs in large Stackelberg markets, it does not occur in the four remaining large markets. If all agents share their information with their followers, expected welfare increases in the Stackelberg and supply chain games and it decreases in the remaining three games. Finally, we characterize the conditions for payoffs and welfare to increase with more precise private or public information. We also provide robustness checks when the values are private. (JEL C70, D43, D82, D83, H41, Q21, Q54)
This study investigates the effects of bird strike on the wing leading edge of a trainer aircraft in accordance with the European Aviation Safety Agency’s CS-23 standards (“Normal, Utility, Aerobatic and Commuter Aeroplanes,” Certification Specifications, Part 23, Occupant Physical Environment), and it compares various options for the design of energy-absorbing support structures. In this study, the bird model with hemispherical-ended cylindrical geometry is simulated using the smoothed particle hydrodynamics finite element approach. After validating the impact of the bird model on a rigid plate, a bird strike on the wing leading edge is modeled; and the results are compared with the existing experimental and simulation data available in the literature. Finally, different design options for the support structure configurations of the wing leading edge (including traditional rib design, honeycomb sandwich, triangular reinforcement, and negative Poisson ratio structures) are evaluated, and the results are compared. It is found that a honeycomb sandwich panel support structure provides the best collision and weight performance.
Utilizing sunlight for energy conversion and storage through photoelectrochemical (PEC) water splitting has been regarded as one of the most featured ways in renewable energy applications. Herein, zinc oxide nanoflower (ZnONF) thin-film photoelectrodes have been prepared using different pH of the reaction solution. Additionally, gallium doping has been applied on the ZnONF thin-film having the highest performance to enhance the PEC efficiency. Consequently, ∼0.8−2 of photocurrent density generated on ZnONF photoanode has been enhanced to ∼1.3−2 (at 0.4 V vs. Ag/AgCl), while maximum IPCE% reached to 51% at 367 nm via gallium doping.
Ovarian cancer (OC) is clinically important because it is diagnosed late and has metastasis when it is diagnosed. Mortality risk increases 2.75 times in the presence of lymph node (LN) metastasis. During metastasis, many molecules including BMPs originated from stroma, and tumor cells participate through transcription factors and integrins for cytoskeleton regulation during cell migration. We hypothesized an inverse correlation between BMP2 and BMP7 along with changes in ZEB2, and integrin α5β1 in high-grade OCs in relation to LN metastasis. The BMP2 immunoreactivity was strong along with strong ZEB2 and weak integrins' immunoreactivity in samples with LN metastasis. Strong immunoreactivity of BMP7 was accompanied by strong immunoreactivity of integrins in the samples without LN metastasis. Study results showed BMP2's strong positive immunoreactivity and weak BMP7 immunoreactivity in tumor cells with a significantly weak inverse correlation. This inverse correlation should be considered as both BMPs have different effects in the window of cancer progression and invasion.
The rich multimedia-enhanced language content offered by modern commercial off-the-shelf games and students’ interest in playing such games has motivated efforts for seeking effective means to integrate them into the curriculum to enrich and enhance foreign language learning. Despite the general interest and appeal of game-enhanced learning in foreign language learning, there is a need for strategies for effective curriculum integration and empirical studies to test the effects of such interventions systematically. This study aims to contribute to this need by investigating the effectiveness of a ten-week-long game-enhanced language learning intervention on English foreign language learning. The study employed an embedded mixed methods design, including a controlled experiment and semi-structured interviews. The experiment group (n = 38) participated in a game-enhanced language learning program that was designed based on the Play Curricular activity Reflection Discussion (PCaRD) framework, whereas the control group (n = 38) received conventional instruction. Students took the TOEFL-ITP and L2 motivational self-system questionnaire before and after the intervention, whereas qualitative data were gathered via semi-structured interviews. The results indicated that both groups had significantly improved their scores, yet no significant differences were found in their post-test scores. The motivation questionnaire revealed a significant difference in cultural interest and attitudes to target community dimensions in favor of the game-enhanced condition. Moreover, the interview results indicated that participants had positive attitudes towards integrating commercial games into their language classrooms. Although the experimental group did not significantly outperform the control group, the game-enhanced intervention provided an equally effective learning experience with improved motivational attributes.
Hybrids of nitrate-based molten salts (KNO3, NaNO3, and Solar Salt) and anodic aluminum oxide (AAO) with various pore sizes (between 25 and 380 nm) were designed for concentrated solar power (CSP) plants to achieve low melting point (<200 °C) and high thermal conductivity (>1 W m-1 K-1). AAO pore surfaces were passivated with octadecyl phosphonic acid (ODPA), and the results were compared with as-anodized AAO. The change in phase transition temperatures and melting temperatures of salts was investigated as a function of pore diameter. Melting temperatures decreased for all salts inside AAO with different pore sizes while the highest melting temperature decrease (ΔT = 173 ± 2 °C) was observed for KNO3 filled in AAO with a pore diameter of 380 nm. Another nanoconfinement effect was observed in the crystal phases of the salts. The ferroelectric phase of KNO3 (γ-phase) formed at room temperature for KNO3/AAO hybrids with pore size larger than 35 nm. Thermal conductivity values of molten salt (MS)/AAO hybrids were obtained by thermal property analysis (TPS) at room temperature and above melting temperatures of the salts. The highest increase in thermal conductivity was observed as 73% for KNO3/AAO-35 nm. For NaNO3/AAO-380 nm hybrids, the thermal conductivity coefficient was 1.224 ± 0.019 at room temperature. To determine the capacity and efficiency of MS/AAO hybrids during the heat transfer process, the energy storage density per unit volume (J m-3) was calculated. The highest energy storage capacity was calculated as 2390 MJ m-3 for KNO3/AAO with a pore diameter of 400 nm. This value is approximately five times higher than that of bulk salt.
In this study, zinc oxide (ZnO) powders in two different morphologies, nanowire (NW) and nanoflower (NF), have been synthesized by the hydrothermal method. The eligibility of the pristine ZnO nanopowders as a photo-active material has been revealed by designing P-SC devices via the facile drop-casting method on both glass and plastic substrates in large-area applications. The impact of physical properties and especially defect structures on photo-supercapacitor (P-SC) performance have been explored. Although the dark Coulombic efficiency (CE%) of both NW and NF-based P-SC were very close to each other, the CE% of NW P-SC increased 3 times, while the CE% of NF P-SC increased 1.7 times under the UV-light. This is because the charge carriers produced under light excitation, extend the discharge time, and as confirmed by electron paramagnetic resonance, photoluminescence, and transmission electron microscopy analyses, the performance of P-SCs made from NF powders was relatively low compared to those produced from NW due to the high core defects in NF powders. The energy density of 78.1 mWh kg−1 obtained for NF-based P-SCs is very promising, and the capacitance retention value of almost 100% for 3000 cycles showed that the P-SCs produced from these materials were entirely stable. Compared to the literature, the P-SCs we propose in this study are essential for new generation energy storage systems, thanks to their ease of design, adaptability to mass production for large-area applications, and their ability to store more energy under illumination.
Underwater wireless sensor networks (UWSNs) are utilized for a wide range of monitoring and surveillance applications. Lifetime maximization and maintenance of network reliability are among the most important considerations in the deployment of UWSNs. k-connectivity is a robust approach for reinforcing reliability. However, maintaining k disjoint paths from each sensor node to the BS, inevitably, results in extra energy dissipation, which reduces the network lifetime (NLT). Yet, there is no systematic exploration to determine the extent of lifetime reduction due to the increase in the k value, in the literature, to the best of our knowledge. In this study, we create an optimization framework to be able to explore the trade-off between NLT and k-connectivity based reliability in UWSNs. Through the optimal solutions of the proposed optimization model for a large set of salient parameters, we characterize the inter-play between lifetime and k-connectivity. Our analysis reveals that the k value to be maintained in a UWSN can affect the NLT significantly.
This experiment setup has been developed to elucidate the effect of different wave types (sinusoidal, triangle, square) of bi-directional magnetic field on hydrothermal characteristics of hybrid magnetite nanofluid flowing through a tube. The bi-directional magnetic field is not a novel method among active methods of heat transfer enhancements, yet the effects of different wave types have not been researched so far. In this study, the effects of different wave types of alternating magnetic fields with various frequencies (f) (2, 5, and 15 Hz) on flow and heat transfer characteristics of Fe3O4Cu/Water hybrid magnetic nanofluid flow have been investigated experimentally. The major findings have been discussed for different combinations of hybrid magnetite nanofluid, types of waves, values of Reynolds number (Re), and f. The hydrothermal characteristics and their effects on usability in the industry with high efficiency have been established in terms of average Nusselt number (Nu), average friction factor (f), and Performance Evaluation Criteria (PEC). It is concluded that the use of triangle wave type with f=15 Hz with 2% Fe3O4/water shows the highest enhancement in f by 500% compared to distilled water (DW) at Re=994 while the use of square wave type with f=5 Hz using the same Re and nanofluid presents the highest increase in Nu by 15.3% compared with DW. Above all, the triangular wave type is determined as an optimum wave type for f=15 Hz while the sinus and square wave types are realized as optimum ones for f=5 Hz.
In aerospace industry, optimizing designs has become inevitable in terms of weight and performance requirements. Topology optimization is the most suitable optimization type for use in the conceptual design phase. Even though academic topology optimization algorithms have a modular structure (open to development), they are often useable for a regular design domain. Alternatively, commercial topology optimization software products, on the other hand, are very useful in terms of their solution speed, accuracy, and ability to handle complex or irregular design domains. However, the user is restricted with the optimization algorithms available in the software, and these software do not usually have a modular structure. In this study, a modular topology optimization framework that combines useful features of the academic codes (e.g., modularity) and the commercial software tools (e.g., capability of easily handling complex design domains) is developed. The developed framework is tested on two popular academic topology optimization problems, followed by aerospace bracket design problem. It is observed that the proposed framework usually provides lower objective function values and converges to the optimum result in fewer iterations than the Altair Optistruct topology optimization software.
In this study, design optimization of the lower control arm, one of the main parts of double wishbone system widely used in the armored wheeled vehicles, is performed. The crucial factor in design is to keep the vehicle weight at a minimum especially for the amphibious vehicles that can operate in both the land and water. In this study, after the validation of the finite element (FE) analysis of suspension lower control arm with on-vehicle tests, weight optimization study is performed by using surrogate models. In FE model validation, strain values are collected with strain-gauge from the lower control arm of the 8 × 8 wheeled vehicle and the similar boundary conditions are applied to the FE model. A surrogate based approach is used in optimization. The training points for surrogate models are generated by using central composite design. Genetic aggregation surrogate modelling technique available in ANSYS Workbench. It is found that the weight of the control arm can be reduced from 25.2 to 21.8 kg, indicating a weight reduction of 13.3%. This leads to approximately 27 kg weight reduction in total for 8 × 8 vehicle. Finally, the performance of the optimized design is evaluated under two off-design quasi-static load scenarios (pothole strike and pavement crushing) that may be exposed on the suspension while the vehicle is in motion and preferred by vehicle manufacturers. It is observed that obtained stress values are below the yield strength of the material, and the off design performance of the control arm is verified with the safety factor of 1.46 for pothole strike scenario, and 1.08 for pavement crushing.
Light verb constructions (e.g., give a kiss to somebody) syntactically reflect typical ditransitive structures (e.g., give a violin to somebody) yet it is not clear whether these two structures thematically similar as well. We tested Turkish-speaking adults on their construal of light verb constructions with respect to the number of thematic roles1 they perceive in the event structure in a rating study. The light verb give with a different noun phrase was used in all critical utterances (e.g., give a response or give an assignment). The noun phrases of these constructions denominalized either by -lA or - lAn+dIr morpheme (e.g., response-lA and assignment-lAn+dIr) were also used as control items. The study concluded that the light verbs with their noun phrase complements contribute to the semantic construal of the event structure and the thematic role assignment processes for the denominalized versions of these structures reflect this meaning construal.
Background: Water pipe smoking has become a global public health problem as its popularity increased over time, especially among youth. The objective of our study was to estimate water pipe tobacco smoking prevalence and to assess socioeconomic factors associated with ever water pipe smoking by public and private university students in Ankara, Turkey. Methods: This descriptive study was based on a survey conducted among public (n=2685) and private (n=2485) university students via an online questionnaire on demographics and water pipe consumption patterns. For every student in the sample, a socioeconomic status index was calculated using principal component analysis. Binary logistic regressions for the outcome variable of ever-using water pipe yielded estimates of adjusted odds ratios (aORs) for the associated factors such as the respondent's age, gender, university type, and socioeconomic status. Results: The prevalence of ever use of water pipe was 69.1% (95% CI: 67.2-70.9%) among private and 59.1% (95% CI: 57.2-60.9%) among public university students. A substantial share of ever users were current users (25.5% in private versus 21.6% in public, p=0.008). On average, private university students had higher socioeconomic status than public university students (for example, access to a car (51.7% versus 35.8%, p=0.008), financial support from family (71.5% versus 65.1%, p<0.001)), also demonstrated by a higher socioeconomic status index. Being a private university student (aOR 1.57, 95% CI: 1.38-1.79), older (aORs 1.50 to 2.39, p<0.001), male (aOR 2.36, 95% CI:2.06-2.70), as well as having greater financial resources, such as having access to a car (aOR 1.24, 95% CI:1.07-1.42), or having income support from family (aOR 1.32, 95% CI:1.13-1.54), were associated with ever-using water pipe. A higher SES index was significantly associated with higher odds of ever using water pipe among both private (aOR 1.13, 95% CI:1.06,1.20) and public university (aOR 1.12, 95% CI:1.06,1.19) students. Conclusions: Water pipe smoking was common in both public and private universities; however, private university students had higher odds of ever using water pipe. There is an urgent need to implement evidence-based interventions, taking into account the socioeconomic status of young adults, to prevent them from water pipe smoking.
Aim: To assess the correlation between the ratio of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and slow coronary flow (SCF). Methods: A total of 119 patients with SCF and 121 age- and sex-matched patients with normal coronary flow were included in this retrospective cross-sectional study. Thrombolysis in myocardial infarction frame count of angiography images was marked by two interventionalists. In addition to AST and ALT levels, complete blood count; kidney, liver and thyroid function tests; age; sex; medication and medical history were recorded. Results: Significant spikes in AST/ALT ratio were discovered in the SCF group compared with the normal coronary flow group (p < 0.001). Thrombolysis in myocardial infarction frame count values were significantly higher in all coronaries for the SCF group compared with the normal coronary flow group (p < 0.001). Thrombolysis in myocardial infarction frame count values of the left anterior descending artery (r = 0.258; p < 0.001), left circumflex artery (r = 0.297; p < 0.001) and right coronary artery (r = 0.195; p = 0.002) were positively correlated with AST/ALT ratio. Conclusion: AST/ALT ratio is significantly correlated with SCF; therefore, this ratio may have predictive value.
A new method to classify electronic devices using a Frequency-Swept Harmonic Radar (FSHR) approach is proposed in this paper. The FSHR approach enables us to utilize the frequency diversity of the harmonic responses of the electronic circuits. Unlike previous studies, a frequency-swept signal with a constant power is transmitted to Electronic Circuits Under Test (ECUTs). The harmonic response to a frequency-swept transmitted signal is found to be distinguishable for different types of ECUTs. Statistical and Fourier features of the harmonic responses are derived for classification. Later, the harmonic characteristics of the ECUTs are depicted in 3D harmonic and feature spaces for classification. Three-dimensional harmonic and feature spaces are composed of the first three harmonics of the re-radiated signal and the statistical or Fourier features, respectively. We extensively evaluate the performance of our novel method through Monte Carlo simulations in the presence of noise.
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2,196 members
Erdem Acar
  • Department of Mechanical Engineering
Bulent Tavli
  • Department of Electrical and Electronics Engineering
Hüseyin Merdan
  • Department of Mathematics
Ersin Emre Oren
  • Deparment of Biomedical Engineering
Nart Bedin Atalay
  • Department of Psychology
Söğütözü cad. No:43, 06560, Ankara, Turkey
Head of institution
Yusuf Sarınay
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