WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Integrated Quantitative Modelling for the Dimension Stone Quality Evaluation: Implications for Sustainable Resource Management(Springer Heidelberg, 2025-09-30) Koken, Ekin; Strzalkowski, Pawel; Strzałkowski, PawełThe growing demand for dimensional stones in construction and monument conservation requires fast, repeatable and scientifically valid quality assessment procedures. The present study, in this context, established a solid foundation for quantifying the quality of dimension stones by adopting two quantitative methods: the Suitability Index (SI) and Dimension Stone Field Performance Coefficient (DSFPC). Both methods were coded in the MATLAB environment and implemented for 20 different rock types used in various dimension stone applications in Turkey. Evaluations based on the above-mentioned methods demonstrate that the DSFPC provides a more conservative assessment than the SI method. Additionally, engineering interpretations derived from the SI and DSFPC approaches are compared with recently published classification systems developed for the dimension stone industry. Focusing on this comparison, it is concluded that the adopted methods offer a more holistic evaluation framework compared to the approaches based solely on a single input parameter, such as effective porosity (ne), uniaxial compressive strength (UCS), or B & ouml;hme abrasion value (BAV) of rocks. Furthermore, it is concluded that the adopted methods complement each other by yielding supportive outcomes. The coded methods can be adapted to other lithological series and integrated with spatial information systems to support decision-making in mining and construction sectors. From this point of view, the present study may be considered a case study supporting holistic approaches to sustainable resource management in the dimension stone industry.Article Citation - WoS: 3Citation - Scopus: 3RF MEMS Variable Attenuators With Improved dB-Linearity(Springer Heidelberg, 2023-02-22) Hah, DooyoungA variable attenuator is one of the essential components in radio frequency (RF) systems, such as automatic gain control amplifiers and full-duplex systems. Variable attenuators based on microelectromechanical systems (MEMS) technology have several advantages over the semiconductor counterparts, including low power consumption and suppressed harmonics. Attenuation can be realized by disruption of signal propagation, which is induced by moving electrodes placed next to a signal line. In this work, the effect of the moving electrodes on the RF characteristics of the variable attenuators is studied via numerical simulation. It is observed that 10 lm of moving electrode displacement can result in 18 dB of attenuation dynamic range at 20 GHz. The similar type of RF MEMS variable attenuators reported previously showed substantial nonlinearity in attenuation-voltage characteristics, which becomes a serious drawback for applications where high-precision attenuation management is required. The main objective of the current study is, therefore, to achieve high dB-linearity, by employing shaped-finger comb-drive actuators in the moving electrode displacement control. In addition, a nonlinear relationship between force and displacement in a clamped-clamped beam spring is taken into account for more accurate device modelling. Through finite element analysis, it is shown that an improvement by a factor of twelve can be obtained in dB-linearity by using a single-comb shaped-finger actuator, compared to standard straight-finger comb-drives. The study also shows that the dB-linearity can be further (2.2 times additionally) improved by utilizing dual-comb shaped finger actuators.Article Citation - WoS: 32Citation - Scopus: 33Naphthalene Diimide-Based Polymeric Semiconductors. Effect of Chlorine Incorporation and N-Channel Transistors Operating in Water(Springer Heidelberg, 2016-03) Ryu, Gi-Seong; Chen, Zhihua; Usta, Hakan; Noh, Yong-Young; Facchetti, AntonioWe demonstrate here the design, synthesis and characterization of two new chlorinated polymers, P(NDI2HD-T2Cl2) and P(NDI2OD-T2Cl2) based on N,N-difunctionalized naphthalene diimide (NDI) and 3,3-dichloro-2,2-bithiophene (T2Cl2) moieties. Our results indicate that organic thin-film transistors (OTFTs) based on these new chlorinated polymers exhibit electron mobilities approaching 0.1 cm(2)V(-1)s(-1) (I-on:I-off similar to 10(6)-10(7)), with far less ambipolarity due to their lower highest occupied molecular orbital energies, and they are more stable under deleterious high-humidity conditions (RH similar to 60%) and upon submersion in water, compared with those fabricated with the parent non-chlorinated polymers. In addition, OTFTs fabricated with the new chlorinated polymers exhibit excellent operational stabilities with <3% degradations upon bias-stress test.Article Citation - WoS: 1Citation - Scopus: 1Electret Vibration Energy Harvesters With Symmetrically Configured Curved-Beam Hinges(Springer Heidelberg, 2024-03) Hah, DooyoungFor vibration energy harvesters, broadband power spectral characteristics are often desirable. One way of achieving broadband spectrum is to employ curved-beam hinges, utilizing their nonlinear spring characteristics. In our previous study, electret-based vibration energy harvesters employing curved-beam hinges were investigated via numerical analysis based on stochastic differential equations and colored-noise inputs. It showed that the harvesters with curved-beam hinges can produce higher power than the ones with ordinary straight beams when the external acceleration is between 0.02g and 0.05g. It was also learned that the straight-beam device, a Duffing oscillator, performs better than the curved-beam device, a Duffing-Holmes oscillator, at higher acceleration (>= 0.1g\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\ge 0.1g$$\end{document}). Since the energy harvesting efficiency is one of the most important performance indicators, continuous search for novel configurations with improved efficiency is needed. For that purpose, a symmetric configuration of curved-beam hinges (a Duffing oscillator) is proposed in this work, in contrast to the previously reported one with an asymmetric configuration (a Duffing-Holmes oscillator). This study shows, via numerical analysis, that the symmetric configuration can produce higher (up to 7.3% more) power outputs for the external acceleration magnitude higher than 0.1g, when compared to an asymmetric configuration. The study results also show that it can produce higher power outputs (up to 4.5 times) than the harvesters employing ordinary straight-beam hinges.Conference Object Citation - WoS: 3Citation - Scopus: 3Analytical Design of MEMS Variable Capacitors Based on Shaped-Finger Comb-Drives(Springer Heidelberg, 2019-02-23) Hah, DooyoungA variable capacitor is one of the widely used components in radio frequency (RF) circuits. Variable capacitors can benefit from the microelectromechanical systems (MEMS) technology, to be equipped with attractive characteristics such as high quality factor and wide tuning range. One of the design goals for MEMS varactors has been to realize linear capacitance-voltage (C-V) characteristics, for which a design method is proposed in this paper, based on shaped-finger comb-drive actuators. The shaped-finger design method, originally developed for a tunable optical filter application by the author, is redeveloped in this work for a linear C-V varactor. Moreover, the conformal mapping method is employed in calculation of capacitances, making the whole design process more time-efficient, being almost all-analytical with the minimum usage of numerical analysis methods. Effects of sense capacitor finger shapes to the optimized drive capacitor finger shapes and the corresponding C-V characteristics are investigated as well. Variable capacitors with the shaped-finger design show linearity factor (LF)-defined as the maximum deviation from the perfect linear relationship-as good as 0.4%, enormously improved from that of the conventional constant-finger-gap devices (LF: 49.9%). Further probed by 3-D numerical analysis, the C-V characteristics of the designed variable capacitor show LF better than 2.62% in the case of constant-gap sense capacitors, and as good as 0.77% in the case of shaped-finger sense capacitors. Versatility of the design method is further demonstrated by presenting a varactor for linear resonant frequency-voltage (f-V) characteristics in voltage-controlled oscillator (VCO) applications. Finally, effects of etch bias, one of common fabrication imperfections, to the linearity of C-V characteristics are studied. The developed analytical design method with shaped fingers can find a wide range of applications where comb-drive actuators are used.Article Citation - WoS: 6Citation - Scopus: 6Admissible Invariants of Genus 3 Curves(Springer Heidelberg, 2015-06-03) Cinkir, ZubeyirSeveral invariants of polarized metrized graphs and their applications in Arithmetic Geometry are studied recently. In this paper, we explicitly calculated these admissible invariants for all curves of genus 3. We find the sharp lower bound for the invariants phi, lambda and epsilon for all polarized metrized graphs of genus 3. This improves the lower bound given for Effective Bogomolov Conjecture for such curves.Article Citation - WoS: 4Citation - Scopus: 4Advanced Hybrid Machine Learning Methods for Predicting Rainfall Time Series: The Situation at the Kütahya Station in Türkiye(Springer Heidelberg, 2025-07-22) Ilkentapar, Mucella; Citakoglu, Hatice; Talebi, Hamed; Akturk, Gaye; Spor, Pinar; Caglar, Yasin; Aksit, SerhatLong-term variations in rainfall patterns, known as rainfall variability, have increasingly impacted ecological and socioeconomic systems, particularly in regions with high sensitivity. Consequently, accurate forecasting of rainfall at both short- and long-term time scales is essential, necessitating a comprehensive analysis of historical rainfall time series data collected from meteorological stations. In this study, K & uuml;tahya Province was selected as the study area, utilizing monthly rainfall data from its sole meteorological station spanning the period from 1960 to 2023. The dataset was partitioned into a training set (January 1960-March 2008) and a test set (April 2008-December 2023). Lagged rainfall values at t-1, t-2, and t-3 were used as input variables to predict rainfall at time t. The primary objective of this research is to assess the effectiveness of various preprocessing techniques in developing hybrid machine learning models for rainfall prediction. Gaussian Process Regression (GPR), Support Vector Machines, and Adaptive Neuro-Fuzzy Inference System were employed as machine learning methods. Furthermore, multiple signal decomposition techniques, including Complete Ensemble Empirical Mode Decomposition (CEEMD), Tunable Q-Factor Wavelet Transform, Empirical Mode Decomposition, Robust Empirical Mode Decomposition, Variational Mode Decomposition, Empirical Wavelet Transform, and Ensemble Empirical Mode Decomposition (EEMD), were utilized as preprocessing steps to enhance model performance. The predictive performance of the developed hybrid models was evaluated using various statistical measures. Among the evaluated models, the CEEMD-GPR hybrid model exhibited the best prediction performance with Coefficient of Determination (R2 = 0.998) and Nash-Sutcliffe Efficiency (NSE = 0.998) values close to 1, Mean Absolute Error (MAE = 1.42) and Mean Squared Error (RMSE = 1.79) values close to zero. These findings indicate that CEEMD demonstrated superior decomposition efficiency compared to the other six decomposition techniques. Additionally, the Kruskal-Wallis test conducted during the analysis phase yielded a statistical significance level of p > 0.05, confirming that the observed and predicted rainfall data originated from the same distribution. Consequently, the effectiveness and reliability of the proposed hybrid models for rainfall prediction were validated.