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Investigation of Transition Possibilities between Drought Classifications Using Standardized Precipitation Index for Wet and Dry Periods-Lower Seyhan Plain, T?rkiye Case
No full textIn this study, the Karaisali region of Turkiye, which has a semi-arid climate and is known to contain the exten-sive plains and rich water resources of the Seyhan Basin, was preferred as a study area for investigating wet and drought periods for a long timescale. Forty-one years of total precipitation data, between 1980 and 2020, belonging to the closest precipitation observation station located in the Karaisali region were used. By using the Standardized Precipitation Index (SPI), which is one of the frequently used meteorological drought indices, drought classifica-tion probabilities, expected first transition period and residence time in each drought severity class values were calculated for the 12-month time scale. As a result of the study, it was determined that the most drought period took place in 2012 according to the examined time duration. In addition, the most wet period was observed in 2001. When various time scales were considered, SPI-3 and SPI-6 have Near Normal Wet periods, while SPI-9 and SPI-12 have Near Normal Drought periods. Extremely Wet periods were more numerous, while Extremely Drought periods lasted longer. In addition, 3 months after the end of the drought categories, it can be seen that the Wet and Drought periods change into Near Normal Wet and Near Normal Drought periods
Investigation of the Effect of Different Parameters of Phase Change Materials on Heat Exchanger Performance
No full textTechnological improvements and increasing energy demand necessitate energy efficient designs for heat transfer systems. The storage and reuse of heat energy plays an important role in the development of energy-efficient systems. Phase change materials (PCMs) are crucial components which increase energy efficiency in heat exchangers as can be applied to many systems. In this study, the heat transfer performance of different types of phase change materials in a regenerative heat exchanger was investigated according to different parameters. Reynolds number depending on the hot fluid velocity (Re=400, 800, 1200, 1600), hot fluid inlet temperature (Tsıcak,giriş=40, 60, 70, 80?), and different types of phase change materials (RT60, RT100, and SP70) are the parameters used in this study. ANSYS Fluent software was used for computational fluid dynamics analysis. As a result, it has been determined that when the Reynolds number of the hot fluid in the heat exchanger was increased in the range of Re=400-1600, the heat transfer effectiveness increase of 17%; when the hot fluid inlet temperature was increased in the range of Thot,inlet=40-80?, the heat transfer effectiveness increase of 21%. As regards the effect of different types of phase change materials, the heat transfer effectiveness was 81% for RT60, 79% for SP70 and 76% for RT100. It has been evaluated that, with the results obtained from this study, heat exchangers with higher heat transfer effectiveness and higher energy storage capacity can be designed
THE EFFECTS OF NEW EQUITY ANNOUNCEMENTS ON STOCK RETURNS: AN EXAMINATION ON BIST*
No full textThe aim of this study is to examine the effect of rights and bonus issue announcements on stock returns. The study analyzes the companies included in the BIST-30 and BIST-50 indices between 2010 and 2022 and the companies that made capital increase announcements while they were included in these indices. In total, 84 different capital increase announcements of 35 companies were included in the study. In the study, the event study method was used and two different event windows were created as (-10, +10) and (-5, +5). At the end of the analysis, it was observed that new equity announcements affected stock returns. The study revealed that this effect was statistically significant negative. According to this situation, it can be said that the return expectations of the investors from the companies that announce the new equity issue should be negative and they should arrange their portfolios according to this result. According to the results of the research, it has been revealed that Borsa Istanbul is an inefficient market in semi-strong form
Broadband electromagnetic wave absorbing via PANI coated Fe3O4 decorated MoS2 hybrid nanocomposite
No full textHigh performance electromagnetic wave (EMW) absorbing material systems are required for stealth applications and sensitive electronic devices. Absorbing of an incident EMW in a wide band range still has limitations in terms of materials system and engineering. It is required to extend the bandwidth and minimize the reflection from the material system for the next level stealth technologies. In this work, hybrid nanocomposite structures are developed by semiconductor flower-like MoS2 nanosheets, Fe3O4 magnetic nanoparticles and conductive poly aniline. A systematic study is presented by investigation the structural, magnetic, morphological, thermal, electronic and electromagnetic characteristic of hybrid nanocomposites (Fe3O4:MoS2, PANI@Fe3O4, PANI@MoS2 and PANI@Fe3O4:MoS2). EMW absorption characteristics results showed that Fe3O4:MoS2 and PANI@Fe3O4:MoS2 hybrid nanocomposites exhibit excellent EMW absorption characteristics. While the minimum reflection loss (RL) value was found as 54.97 dB at 15.99 GHz for the Fe3O4:MoS2 nanocomposite, the broad bandwidth (7.65 GHz) was observed in PANI@Fe3O4:MoS2 hybrid nanocomposite having 39.96 dB RL. According to the experimental results, a lightweight and high temperature resistance PANI@Fe3O4:MoS2 like hybrid nanocomposite can absorb almost 90% of incident EMW in a wide bandwidth.Scientific and Technological Research Council of Turkiye [121F367]This work is supported by The Scientific and Technological Research Council of Turkiye under Project Number: 121F367
Feeling In-Between Experienced by Tertiary-Level English Preparatory Students: An Investigation of Two Turkish EMI Universities
No full textEnglish preparatory programs at English medium instruction (EMI) universities aim to help students gain the necessary competence in English so that they can fulfil their academic and communicative goals at the international level. Preparatory students may experience different psychological situations including feeling in-between. Being neither a high school nor a bachelor student, they may experience difficulties likely to stem from the uncertainty regarding their status and environment and this could have adverse effects on the quality of their language learning including distraction and demotivation. This study is the first of its kind investigating English preparatory students’ feeling in-between by exploring their descriptions, reasons, and suggested solutions. The data were collected from 238 students at two Turkish EMI universities through a questionnaire and interviews and thematically analysed. Findings show feeling in-between was defined as “not feeling like a real university student”. The participants likened their environment to high school and complained about lack of activities and contents not related to their majors. The suggestions included content-based instruction and social, psychological, and academic support. The study implies preparatory students be fully included in educational life and have a say in relevant policies. The research also has implications for tertiary-level EFL instruction worldwide. © 2023 Language Institute, Thammasat University. All rights reserved
Experimental study and hybrid optimization of material extrusion process parameters for enhancement of fracture resistance of biodegradable nanocomposites
No full textAmong the additive manufacturing processes, the material extrusion (ME) is the most popular and affordable technique in production of a wide range of products, from prototypes to the final products, for different industrial sectors. The most popular raw material in this process is the biodegradable polylactic acid (PLA) polymer that offers ease of production in relatively low price and wide applications in synthesis of medical proteases. However, the mechanical strength of fabricated samples and their resistance against the fracture loadings, which are critical for components synthesized for medical applications, are strongly dependent on the ME process parameters and the composition of the base material. Therefore, this study is aimed to address both the strengthening mechanisms of inorganic CaCO3 nanoadditives in the PLA matrix and the influence of ME process parameters on the fracture resistance of fabricated samples. To this aim, the PLA/CaCO3 nanocomposite filaments have been produced by mix-blending/extrusion tech-nique and were employed to fabricate tensile and fracture test samples in ME process under different sets of parameters, including printing speed, layer thickness, filling ratio and printing pattern, determined by Taguchi L27 orthogonal array. The fracture experiments were conducted on a uniaxial tensile test machine using a specially designed fixture that makes the application of mixed-mode loading on fracture samples possible. The results of fracture toughness of specimens were employed as input data to model the response of fabricated samples and to determine the ME parameter levels and nanoparticle concentrations for maximum fracture resistance of fabri-cated samples based on a hybrid algorithm of artificial neural network and ant colony optimi-zation (ANN/ACO). Differential scanning calorimetry was used to characterize the thermal features (i.e. glass transition, crystallization and melting temperatures) as well as the degree of crystallization of ME samples. Scanning electron microscopy of fracture surfaces were employed to study the influence of ME parameters and CaCO3 nanoadditives on the characteristics of fracture of 3D printed specimens under various modes of loading. Overall, the results showed that the effects of ME parameters on the fracture behavior of 3D printed samples are highly inter-connected and, in the case of a semicrystalline polymer, are highly dependent on the physical characteristics of the fabrication process, including the heat transfer and crystallization rate of the matrix.[22303001]Acknowledgment This work was supported by Scientific Research Coordination Unit of Adana Alparslan Turkes, Science and Technology University with project number of 22303001
Increasing the Robustness of i-vectors with Model Compensated First Order Statistics
No full textSpeaker recognition systems achieved significant improvements over the last decade, especially due to the performance of the i-vectors. Despite the achievements, mismatch between training and test data affects the recognition performance considerably. In this paper, a solution is offered to increase robustness against additive noises by inserting model compensation techniques within the i-vector extraction scheme. For stationary noises, the model compensation techniques produce highly robust systems. Parallel Model Compensation and Vector Taylor Series are considered as state-of-the-art model compensation techniques. Applying these methods to the first order statistics, a noisy total variability space training is aimed, which will reduce the mismatch resulted by additive noises. All other parts of the conventional i-vector scheme remain unchanged, such as total variability matrix training, reducing the i-vector dimensionality, scoring the i-vectors. The proposed method was tested with four different noise types with several signal to noise ratios (SNR) from -6 dB to 18 dB with 6 dB steps. High reductions in equal error rates were achieved with both methods, even at the lowest SNR levels. On average, the proposed approach produced more than 50% relative reduction in equal error rate
CURRENT STATUS AND ENVIRONMENTAL IMPACTS OF COAL-FIRED POWER PLANTS IN TURKEY: AN OVERVIEW
No full text28th International Mining Congress and Exhibition of Turkiye, IMCET 2023 -- 28 November 2023 through 1 December 2023 -- Antalya -- 202125Literature research indicates that there are several social reports and superficial information related to coal-fired power plants (CFPPs) in Turkey, whereas a collective and comprehensive study on the issue is scarce in the related literature. In this study, the current status and environmental impacts of CFPPs in Turkey are comprehensively and critically overviewed. With the fast growth of Turkey's economy, population, and energy demand CFPPs have largely increased in the last fifteen years. Turkey's energy policy has consistently developed to support its growing economy and population, reduce the increasing import dependence and reach the country's aims, and meet international standards. Fossil fuel reserves are highly restricted when compared to the country's demands, thus the majority of the energy demand is provided by imports. Turkey's top priority is to decrease its import dependency and current account deficit using domestic coal and renewable energy potential. Coal mining operations and CFPPs are substantially subsidised by the government including research and development support, coal exploration, and extraction. CFPPs contribute to greenhouse gas emissions and air pollution which harm human health and the environment. This will be prevented by adopting a policy of high-efficiency and low emissions, using clean coal technologies, by installing a flue-gas desulphurisation system on the power plant. Finally, this review could help global researchers, energy investors, and Turkish Authorities to design the country's coal-based sustainable energy future. © 2023 IMCET 2023 - Proceedings of the 28th International Mining Congress and Exhibition of Turkey. All rights reserved
Analysis of Current Limiting Algorithm with Anti-Windup Control for Transient Stability of Grid-Forming Converters
No full textIn modern power grids, renewable energy sources (RESs) are integrated to the grid through voltage source converters (VSCs) with grid-forming capabilities. Grid forming VSCs’ weak overcurrent capability revealed the need for current limiting techniques under large disturbances like short-circuit faults. However, current saturation algorithms induce transient instabilities due to the AC voltage controller windup issue when the current is saturated. Therefore, analyzing the transient stability of the grid-forming units in case of fault conditions is crucial for ensuring the reliable and secure operation of the grid. This paper investigates the effects of the current limiting algorithm with anti-windup control to handle transient instabilities during fault conditions. An elaborated theoretical analysis of the presented system is performed by considering different case studies. The simulations are conducted by using Matlab/Simulink software to test the validity of the presented system. The obtained results highlight the advantages of an anti-windup controller during current saturation mode
Kararlı hipotez testi ile görüntü bölütleme teknikleri
No full textLisansüstü Eğitim Enstitüsü, Elektrik-Elektronik Mühendisliği Ana Bilim DalıBu tezde, kararlı hipotez testine dayalı yöntem kullanılarak renkli görüntülerin çoklu kesimlenmesi incelenmiştir. Kararlı hipotez testi, birkaç farklı yöntemle görüntü bölütlendirmeye uyarlanmıştır. İlk yaklaşımda, NP-zorluğa sahip bu problemin çözümü için kullanıcı yardımıyla farklı etiketlerden gelen piksellerin kabaca seçildiğini farz ettik. Önerilen algoritma bu seçimle başlatılır ve piksel yoğunluklarının ampirik histogramları daha sonra kararlı bir hipotez testinde nominal yoğunluklar olarak kullanılır. Test çerçevesini çok boyutlu renkli görüntü üzerinden elde edilen hassas ölçümleri içerecek şekilde değiştirerek, DGL testini uyguluyoruz. Sonraki yöntemlerimize süperpikselleri dahil ettik. Ancak temel yöntem olan süperpikselleri eklemek, kullanıcı girişinin uzamsal bilgisinden yararlanmaz ve yalnızca renk alanında çalışır. Süperpiksellere ek olarak, karmaşıklığı artırmadan geliştirilmiş performans için sınırlayıcı kutuların uzamsal bilgilerinin teste dahil edildiği uzamsal-zamansal dağılıma dayalı DGL testini uyguladık. Ayrıca Berkeley'in BSDS500 görüntü veri seti üzerinde simülasyonlar sağladık ve uygulanan son yöntem, ilk yönteme göre segmentasyon doğruluğunda \%10'luk bir iyileşmeyle sonuçlandı. Geliştirdiğimiz yöntemler, düşük karmaşıklığa sahip renkli görüntüleri çoklu segmentasyon haline getirebilir. Bu performans avantajı simülasyonlarla da doğrulanmıştır.In this thesis, the multiple segmentation of color images is examined using the method based on robust hypothesis testing. The robust hypothesis test has been adapted to image segmentation by several different methods. In the first approach, to ease this NP-hard problem, we provide the user to choose certain areas over the image whose pixels are regarded as candidates from different labels. The suggested algorithm is started through this selection process, and the empirical histograms of the pixel densities are then employed as nominal densities in a reliable hypothesis test. By modifying the test framework to include soft metrics obtained over the multi-dimensional color image, we specifically apply the DGL test. In other ways, we included superpixels in our test. But just adding superpixels, the baseline method, does not take advantage of the spatial information of user input, and only works in the color domain. In addition to superpixels, we have applied the DGL test based on spatial-temporal distribution, where the spatial information of bounding boxes is included in the test for improved performance without increasing the complexity. We also provided simulations on Berkeley's BSDS500 image dataset and showed that the last method applied could result in a 10\% improvement in segmentation accuracy to the first method. The methods we develop can multiple segmentation color images with low complexity. This performance advantage has also been verified by simulations