Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
Browse
609 results
Search Results
Article Numerical and Experimental Investigation of Effects of Porous Layer on Cooling of Electronic Components(American Society of Mechanical Engineers (ASME), 2026) Kocak, E.; Türkoǧlu, H.In this study, heat transfer and temperature distribution characteristics of an electronic component covered with a porous medium were investigated both experimentally and numerically. An experimental setup was designed and constructed to conduct the experiments. For the numerical analysis, a computational fluid dynamics (CFD) software was developed on the OPENFOAM platform. The experimental results were used to validate the mathematical model and the computer program developed. The validated computer program was used to investigate the effects of Reynolds number, porosity, Darcy number, porous layer sizes, and the channel height on the heat transfer rate from the heat dissipating elements (electronic component) to the flow in wider ranges of the parameters. Using the Nusselt number values obtained both experimentally and numerically, a correlation equation was developed, and an artificial neural network architecture was trained for the Nusselt number. Results show that the Nusselt number increases with increasing Reynolds number, porosity, and the ratio of the height of the porous layer to the channel height. It was observed that the width of the porous medium has no noticeable effect on the Nusselt number. The correlation equation developed with four independent parameters predicts the Nusselt number with an average error of 7.59%. The artificial neural network architecture developed prevails as a more accurate tool, with a maximum error of 1%, for the prediction of the Nusselt number in the range of the parameters considered. © © 2026 by ASME.Article Propagation Characteristics of Higher-Order Annular Gaussian Beams in Oceanic Turbulence(Institute of Physics, 2025) Arpali, S.A.; Arpali, Ç.; Baykal, Y.This study aims to explore the propagation characteristics of higher-order annular Gaussian (HOAG) beams in oceanic turbulence. We provide an analytical derivation of the average intensity at the receiver plane based on excitation from a HOAG source field. Additionally, we conduct a detailed analyses of various beam intensity moments including kurtosis parameter, power-in-the-bucket (PIB) and the beam size variation. As oceanic turbulence strength increases, the HOAG beam gradually transforms into a pure Gaussian beam. As the strength of turbulence increases, PIB values for all modes of HOAG beams gradually decrease in an exponential manner until they stabilize, exhibiting behavior similar to that of Gaussian beams. It is also observed that modes of HOAG beams having larger mode numbers carry less energy to the receiver compared to lower-order modes as turbulence strength increases. Analyses of the kurtosis parameter for HOAG beams indicate that during propagation over intermediate distances, there is a tendency for more beam energy to be distributed toward the wings rather than to the center. In contrast, at longer distances, the beam redistributes its energy, resulting in a lower energy concentration in the wings compared to the center. This research can enhance our understanding of the effects of higher-order laser beams, thereby potentially facilitating longer communication distances in underwater wireless optical communication technologies. © 2025 IOP Publishing Ltd.Article Citation - WoS: 2Citation - Scopus: 2An Investigation of the Performance of Equal Channel Angular Pressed Copper Electrodes in Electric Discharge Machining(MDPI, 2025) Simsek, Ulke; Cogun, CanThis study examines the mechanical, thermal, and electrical properties of copper tool electrodes processed via Equal Channel Angular Pressing (ECAP), with a specific focus on their performance in Electrical Discharge Machining (EDM) applications. A novel Crystal Plasticity Finite Element Method (CPFEM) framework is employed to model anisotropic slip behavior and microscale deformation mechanisms. The primary objective is to elucidate how initial crystallographic orientation influences hardness, thermal conductivity, and electrical conductivity. Simulations are performed on single-crystal copper for three representative Face Centered Cubic (FCC) orientations. Using an explicit CPFEM model, the study examines texture evolution and deformation heterogeneity during the ECAP process of single-crystal copper. The results indicate that the <100> single-crystal orientation exhibits the highest Taylor factor and the most homogeneous distribution of plastic equivalent strain (PEEQ), suggesting enhanced resistance to plastic flow. In contrast, the <111> single-crystal orientation displays localized deformation and reduced hardening. A decreasing Taylor factor correlates with more uniform slip, which improves both electrical and thermal conductivity, as well as machinability, by minimizing dislocation-related resistance. These findings make a novel contribution to the field by highlighting the critical role of crystallographic orientation in governing slip activity and deformation pathways, which directly impact thermal wear resistance and the fabrication efficiency of ECAP-processed copper electrodes in EDM.Article Stylometric Analysis of Sustainable Central Bank Communications: Revealing Authorial Signatures in Monetary Policy Statements(MDPI, 2025) Emekci, Hakan; Ozkan, IbrahimSustainable economic development requires transparent and consistent institutional communication from monetary authorities to maintain long-term financial stability and public trust. This study investigates the latent authorial structure and stylistic heterogeneity of central bank communications by applying stylometric analysis and unsupervised machine learning to official announcements of the Central Bank of the Republic of Turkey (CBRT). Using a dataset of 557 press releases from 2006 to 2017, we extract a range of linguistic features at both sentence and document levels-including sentence length, punctuation density, word length, and type-token ratios. These features are reduced using Principal Component Analysis (PCA) and clustered via Hierarchical Clustering on Principal Components (HCPC), revealing three distinct authorial groups within the CBRT's communications. The robustness of these clusters is validated using multidimensional scaling (MDS) on character-level and word-level n-gram distances. The analysis finds consistent stylistic differences between clusters, with implications for authorship attribution, tone variation, and communication strategy. Notably, sentiment analysis indicates that one authorial cluster tends to exhibit more negative tonal features, suggesting potential bias or divergence in internal communication style. These findings challenge the conventional assumption of institutional homogeneity and highlight the presence of distinct communicative voices within the central bank. Furthermore, the results suggest that stylistic variation-though often subtle-may convey unintended policy signals to markets, especially in contexts where linguistic shifts are closely scrutinized. This research contributes to the emerging intersection of natural language processing, monetary economics, and institutional transparency. It demonstrates the efficacy of stylometric techniques in revealing the hidden structure of policy discourse and suggests that linguistic analytics can offer valuable insights into the internal dynamics, credibility, and effectiveness of monetary authorities. These findings contribute to sustainable financial governance by demonstrating how AI-driven analysis can enhance institutional transparency, promote consistent policy communication, and support long-term economic stability-key pillars of sustainable development.Article Dielectric and Thermal Properties of the Ferroelectric NH4HSO4 Close to Phase Transitions(Elsevier, 2025) Kiraci, A.; Yurtseven, H.This work gives the analysis of the dielectric and thermal properties close to the second order and first order types of ferroelectric-paraelectric phase transitions in ferroelectrics, in particular, NH4HSO4. The power-law formula is used by adapting the Kouvel-Fisher (KF) method describing the magnetization (M) and magnetic susceptibility (chi M) in the case of the spontaneous polarization (PS) and the dielectric constant (& varepsilon;), respectively, in ferroelectric systems. Similar treatment is performed to describe the heat capacity (CP) and the thermal expansivity (proportional to P) close to the phase transitions in NH4HSO4. We show that the variations of PS and & varepsilon; with the temperature near the upper Curie point (TC1 = 270 K) exhibit linearity for the second order transition in NH4HSO4. A linear variation is also obtained between the CP and proportional to P with the temperature close to the lower Curie point (TC2 = 160 K) for the first order transition in this crystal. Experimental data are used from the literature for our analysis. Our approach given here to describe dielectric and thermal properties of NH4HSO4 close to the Curie points, can be applied to some other ferroelectric materials.Article Scintillation Characteristics of Annular Beam Array in Underwater Optical Links(IOP Publishing Ltd, 2025) Erdogdu, Ekin; Gokce, Muhsin Caner; Baykal, YahyaUnderwater optical wireless communication systems offer a promising alternative to traditional acoustic methods for achieving high data rate transmission. However, the propagation of optical waves in underwater environments is severely impacted by oceanic turbulence, leading to intensity fluctuations and consequent performance degradation. In this work, we employ a laser beam array to model transmit spatial diversity for suppressing these fluctuations. The model uses annular-shaped lasers at the transmitter as a representation of beam shaping for turbulence mitigation, with a point detector assumed at the receiver. Through the use of the Huygens-Fresnel principle, we derive two key optical parameters: the average received intensity and the average of the intensity squared. We subsequently determine the scintillation index for this model. Our findings demonstrate reductions in scintillation under varying system parameters. For instance, increasing the number of beams in the array, the ring radius, and the secondary field amplitude of the annular beam leads to a lower scintillation index.Article Unit Root Testing in the Presence of Mean Reverting Jumps: Evidence From US T-Bond Yields(Walter de Gruyter GmbH, 2019) Ilalan, Deniz; Ozel, OzgurMean reversion of financial data, especially interest rates is often tested by linear unit root tests. However, there are times where linear unit root test results can be misleading especially when mean reverting jump formations are at stage. Considering this framework, we provide a new unit root testing methodology and compute its asymptotic critical values via Monte Carlo simulation. Moreover, we numerically compare the power of this generalized mean reversion test with the pioneering linear unit root test in the literature namely the Augmented Dickey Fuller (ADF) test. We deduce that our test is a refinement of ADF test with a higher power. Weapply our findings to US 10-year Treasury bond yields. We aim to shed light to the discussion among researchers whether interest rates can sometimes revert to a long-term constant mean or not from an unorthodox point of view.Article Citation - WoS: 23Citation - Scopus: 31An Integrated Framework on Soundscape Perception and Spatial Experience by Adapting Post-Occupancy Evaluation Methodology(Sage Publications Inc, 2018) Aburawis, Ayad A. Mohamed; Yorukoglu, Papatya Nur Dokmeci; Dokmeci Yorukoglu, Papatya NurThe effecting factors of soundscape perception and space experience have a very close relationship. This study aims to synthesize the diversity of soundscape classifications and schemes and unify such factorial variations in order to develop an integrated framework for soundscape perception and spatial experience within a systematic review of recent progress and by adapting post-occupancy evaluation methodology. First, factors under soundscape perception and space experience are reviewed in detail and merged to form conceptual classification models. Six soundscape perception factors are formed as (1) sonic, (2) spatial, (3) temporal, (4) psychological, (5) behavioural and (6) personal. Similarly, five space experience factors are formed as (1) user, (2) usage, (3) architectural design, (4) social context and (5) physical environment. All related items in the literature are presented and the sub-items under each factor are exemplified. Second, factors under the merged conceptual models are integrated by considering occupants' experience of space regarding their variance in perception of soundscapes through acoustical post-occupancy evaluation. An adapted study design is proposed under indicative, investigative and diagnostic stages of the post-occupancy evaluation by presenting the methods, data types and factorial correlations for each stage.Article Enhancing Content-Based Retrieval Through an End-to-End Approach Utilizing Deep Learning and Multidimensional Indexing(Springer London Ltd, 2025) Uzel, Omer; Arslan, SerdarRecent advancements in technology, coupled with reductions in hardware and software costs, have propelled visual search applications into the spotlight, making them both popular and indispensable. Consequently, the rapid and precise retrieval of images from vast databases through image queries has become a critical task. We introduce a novel end-to-end retrieval architecture that significantly enhances retrieval performance when compared to a baseline system that conducts database searches at the video frame level. Leveraging a pre-trained convolutional neural network model, we employ unsupervised image retrieval processes to extract and store low-level features for efficient indexing. To facilitate swift and effective access, we implement a tree-based indexing structure known as VP-Tree. This structure utilizes the extracted low-level features. To make these features compatible with our system, we employ dimension reduction techniques to represent them in a lower-dimensional space. Our experiments, conducted on three benchmark datasets, demonstrate that VP-Tree consistently outperforms k-nearest neighbor (KNN) search in terms of retrieval accuracy and efficiency. Specifically, for image data set, VP-Tree achieves a precision of 56.3903, an F1-score of 68.703, and an area under the curve (AUC) of 93.518719, all slightly surpassing KNN. Similarly, for news video data set, VP-Tree attains a precision of 38.704011, an F1-score of 55.029674, and an AUC of 64.6412, again outperforming KNN. For documentary data set, VP-Tree achieves a notable improvement with a precision of 73.511723, an F1-score of 84.734013, and an AUC of 80.981328, demonstrating superior performance over KNN. In addition to accuracy, we evaluated retrieval time across different dataset sizes. While KNN performs slightly faster on smaller datasets, VP-Tree scales significantly better as dataset size increases. For 100,000 images, VP-Tree reduces retrieval time from 79.77 to 54.34 ms, and for 200,000 images, it improves performance from 108.75 to 44.63 ms, confirming its efficiency in large-scale retrieval scenarios. These results highlight VP-Tree as a robust and scalable alternative to traditional KNN-based methods, ensuring both accuracy and efficiency in large-scale image retrieval tasks.Article Citation - WoS: 46Citation - Scopus: 48Solutions of the Fractional Davey-Stewartson Equations With Variational Iteration Method(Editura Acad Romane, 2012) Baleanu, Dumitru; Jafari, Hossain; Kadem, Abdelouahab; Yılmaz, Tuğba; Baleanu, Dumitru; Yilmaz, Tugba; Matematik; PsikolojiThis paper presents approximate analytical solutions for the fractional Davey-Stewartson equations using the Variational iteration method. The fractional derivatives are described in the Caputo sense. This method is based on the incorporation of the correction functional for the equation. The results obtained by this method have been compared with the exact solutions and show that the introduced approach is a promising tool for solving many linear and nonlinear fractional differential equations.