Sakarya University of Applied Sciences AXSIS
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Impact of Varying Storage Temperatures on Hazelnut (Corylus avellana L.) Pollen Quality
No full textThis study investigated the effect of pollen storage on viability and germination in ‘Foşa’, ‘Kara’, ‘Kalınkara’, ‘Mincane’ and ‘Palaz’ hazelnut cultivars (Corylus avellana L.). Pollen was kept at room temperature (22 °C), +4 °C and −18 °C, and on the 7th, 14th, 21st, 30th, 45th, 60th, 75th, 90th, 105th and 120th day, pollen viability was determined according to triphenyl tetrazolium chloride (TTC) and acetocarmine tests. Pollen germination was assessed at 15 and 20% sucrose according to the agar method. The highest viability at +4 °C was determined in ‘Mincane’ (64.67%) on the 7th day of storage, and the lowest was determined in ‘Palaz’ (11.50%) on the 120th day of storage in the TTC test. The highest pollen viability at −18 °C was determined on the 7th day in ‘Foşa’ (71%), and the lowest was determined on the 120th day in ‘Palaz’ (19%). Cultivar × temperature, cultivar × time and temperature × time interactions were found to be significant in the acetocarmine test. The highest germination was detected in ‘Kara’ (55.23%) with 15% sucrose and in ‘Mincane’ (73.8%) with 20% sucrose in pollen stored at −18 °C. Based on the analysis of pollen viability and germination during storage, it was determined that the ‘Foşa’ and ‘Mincane’ were among the most suitable cultivars. As the storage period rose, there were reductions in viability. However, it was found that pollen held at −18 °C had a longer viability compared to pollen stored at +4 °C. Pollen germination was found to be greater when exposed to 20% sucrose compared to 15% sucrose. © Der/die Autor(en), exklusiv lizenziert an Springer-Verlag GmbH Deutschland, ein Teil von Springer Nature 2024
Managing the surface piezoelectricity effect of the smart ZnO sandwich nanoplates using metal foam core layer and GPRL reinforced rim layers
No full textThis work examines the vibration characteristics of a sandwich nanosensor plate. The plate comprises a core material of nickel foams, with zinc oxide layers on the top and bottom and a rim layer reinforced with graphene. The study takes into account the surface effect. The study employed the innovative sinusoidal higher-order deformation theory and nonlocal strain gradient elasticity theory. Hamilton's principle obtained the equations governing the motion of a sandwich nanoplate. The Navier method was employed to solve these equations. The sandwich nanosensor plate consists of three different foam variants: a uniform foam model and two symmetric foam models. The work focused on analyzing the sandwich nanoplate's dimensionless fundamental natural frequencies. This investigation examined the impact of three different types of foam, the volumetric ratio of graphene, variations in temperature, nonlocal factors, the ratio of foam void, and electric potential. Additionally, the effect of the presence or absence of surface effects of the sandwich nanoplate on the non-dimensional fundamental natural frequencies was analyzed. Within this context, it was established that the buckling temperature of the nanoplate exhibited an estimated increase of 0.7% due to the surface effect. The research is expected to produce useful discoveries concerning developing and applying nanosensors, transducers, and nanoelectromechanical systems designed to function in high-temperature conditions. It has been noted that the surface impact can be diminished by increasing the stiffness of the foam core layer and supporting rim layers. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024
X-band microstrip antenna design with improved performance using electromagnetic band gap and defected ground structures
No full textMikroşerit yama antenler kablosuz iletişimde oldukça yaygın olarak kullanılmaktadır. Bu tez çalışmasında, mikroşerit yama antenin kendi yapısından kaynaklanan dar bant genişliği ve yüzey dalgalarından kaynaklanan düşük kazanç dezavantajlarına, Elektromanyetik Bant Aralığı (EBG) ve Kusurlu Toprak Yapıları (DGS) kullanılarak çözüm getirilmeye çalışılmıştır. EBG yapılar yalıtkan ve metal malzemelerin bir arada kullanılması ile oluşturulan birim hücrelerin genelde periyodik olarak sıralanması ile elde edilen yapılardır. Bu yapılar oluşturdukları yüksek empedanslı yüzeyleri ile belli frekans bant aralıklarında Elektromanyetik (EM) dalgaları kontrol etme özelliğine sahiptirler. Bu çalışmada gelenesel EBG yapıları yerine farklı pin konfigürasyonlarına ya da yama metal alanı azaltılmış özgün EBG yama geometrilerine sahip EBG yapılar referans antene uygulanmıştır. Anten tasarımlarında kullanılan EBG yapılar ile 4.86 dBi olan referans anten kazancı 8 dBi seviyesine çıkarılmıştır. Ayrıca referans antene EBG yama alanı azaltılmış birim hücrelere sahip bir EBG yapı uygulandığında geleneksel kare yamalı EBG yapı kullanılmasına oranla daha fazla kazanç artışı sağlandığı belirlenmiştir. Buna ek olarak tasarlanan antenlerin toprak tabakalarına farklı şekillerde yarıklar açılarak DGS uygulanması yapılmış ve referans anten empedans bant genişliğinde yaklaşık dört kat artma sağlanmıştır. Tasarlanan antenler için üretilen prototipler üzerinden yapılan ölçüm sonuçları ile elde edilen simülasyon sonuçları doğrulanmıştır. Çalışmada tasarlanan antenlerde standart EBG yamalar yerine metal kısmı azaltılmış daha hafif EBG yamalar kullanılarak yaklaşık %79, toprak tabakada yer alan DGS ile de %54 civarında hafifleme sağlanmıştır. Çalışmada iki farklı dielektrik malzeme (Rogers Ultralam 2000 ve FR4) kullanılarak hazırlanan 10 GHz merkez frekanslı referans antenler ile gerçekleştirilen tasarımlarda benzer sonuçlar elde edilmiştir
COMPARISON OF LONG SHORT-TERM MEMORY NETWORKS FOR DAILY AHEAD-FLOW PREDICTIONS ON A RIVER
No full textPrediction of peak river flows is an important problem for the design, management, and safety of hydraulic structures. The aim of the present study was to investigate the prediction capabilities of Long Short-Term Memory (LSTM) networks in predicting daily river flows of the Lüleburgaz stream-flow gauging station (SGS) for the observation period of 1987-2015. The Lüleburgaz SGS is on the Ergene River in the Meriç Ergene Basin in Turkey. Daily measured values of river flow at times seven-days (T-6 to T), two-days (T-1 to T), and one-day (T) were used as input to predict the univariate output of one day ahead flow for an acceptable estimation pattern. The dataset was divided into 75% for the training set and 25% for the test set, and then LSTM, Stacked LSTM, Bidirectional LSTM (BiLSTM), Convolutional LSTM (Conv-LSTM) and Convolutional Neural Network and Long Short-Term Memory (CNN-LSTM) were implemented. The river flow predictions were evaluated by using root mean square error (RMSE), mean absolute error (MAE), regression accuracy (R2) and Nash–Sutcliffe efficiency (NSE). The calculated performance metrics during the test phase showed that, predictions using only one-day of historical data provided the highest performance compared with two-days and seven-days. It is concluded that the river flow predictions would be accurate, especially when using BiLSTM as this was superior to the other models with RMSE of 20.76 m3/s and MAE of 5.33 m3/s. Our comparisons show that LSTM networks can be a viable alternative for estimating future river flows. © 2024 Gheorghe Asachi Technical University of Iasi, Romania. All rights reserved
Relationship between Financial Services Confidence Index and Stock Market Returns: Toda-Yamamoto and Asymmetric Causality Analysis
No full textThe management of expectations is a critical factor in shaping the dynamics of financial markets. Therefore, changes in confidence indices, which reflect the expectations of economic agents, are closely monitored by economists. This study examines the sectoral relationships between the Financial Services Confidence Index and stock market returns in Turkey for the period from June 2012 to May 2024. To compare the causality results, the relationships between the variables were analysed using the Toda-Yamamoto (1995) and Hatemi-J (2012) causality tests. According to the results of the Toda-Yamamoto (1995) causality test, no causality relationship was found between the Financial Services Confidence Index and the Borsa Istanbul (BIST) sector index returns. However, an asymmetric causality relationship was identified between the variables. Thus, it is observed that hidden relationships, which could not be detected by the Toda-Yamamoto (1995) causality test, were revealed through the asymmetric causality test. According to the results of the asymmetric causality test, a causality relationship from the Financial Services Confidence Index to the BIST Financial index returns was found for negative shocks. There is a causality relationship from the BIST Electricity index and the BIST Financial Leasing and Factoring index returns to the Financial Services Confidence Index in both positive and negative shocks. A causality relationship from the BIST Information Technology index and the BIST Technology index returns to the Financial Services Confidence Index was found in positive components. A causality relationship from the BIST Services index and BIST Industrial index returns to the Financial Services Confidence Index was also found among the negative shocks. Considering the results obtained from the study, it can be stated that the Financial Services Confidence Index is a variable that should be considered in terms of changes in financial markets
Understanding the Effects of Reservation Systems and Online Transaction Capacity on the Competitiveness of Travel Agencies
No full textThe purpose of this study is to determine the effect of travel agencies’ reservation systems and online transaction capacities on their competitiveness. With the developments in technology and the integration of these developments in all business areas, travel agencies have also had to benefit from information and communication technologies. In the research, the primary data were used, and the data were collected by the questionnaire method. The convenience sampling method was used, and data were collected from a total of 566 travel agency managers in Istanbul. According to the results of the research, reservation systems and online transactions capacities of travel agencies affect their competitiveness. Reservation systems and online transactions capacities of travel agencies affect their competitiveness in specific issues such as cost, service quality and market share. Although appropriate and enlightening results were obtained regarding travel agencies technological capacity and competitiveness, research was carried out on the perceptions and evaluations of the managers in this study. In this context, in future studies, studies can be conducted on the relationships between measurable quantitative variables such as the online transactions of travel agencies and the capacity and transaction volume of reservation systems and competition structures. The study reveals that the traditional office travel agencies should be more successful than their competitors in terms of reservation systems and online transaction capacities to gain affordable cost, quality service and more market share
INVESTIGATION OF THE BENDING BEHAVIOR OF INC625/SUS316L LASER-CLADDING LAYERS APPLIED TO GGG40
No full textLaser cladding is a multi -purpose thermal coating technology whose application area has increased rapidly in recent years. It can be used for the purposes of obtaining a thick (mm to cm) layer on surfaces by the interaction of different materials in powder form (especially metallic and metal -matrix composite) with the laser beam, thus repairing, restoring, improving and protecting the surface resistance of various industrial metallic parts. It is normally used to refurbishment, create and repair metallic components, hydraulic mills, gears, shafts, turbine blades, drilling tools, and other static or dynamically loaded mechanical parts. The benefits of laser cladding over alternative technologies include better metallurgy (bonding, hardness or lower porosity) as well as reduced part deformation and stress due to lower overall heat input. The melting of substrate material ensures a good metallurgical bond between the cladding layer and the substrate material. However, the melting of the substrate material causes dilution. Therefore, the melting of the substrate material should be controlled and kept to a minimum because high substrate melting causes an increase in the dilution, which may degrade the mechanical and corrosion properties of the clad layer. The laser beam over the substrate materials creates temperature gradients in the thickness direction that can lead to mechanical deformation (such as bending) and changes in the microstructural and interface properties. Depending on the substrate type and production history, as well as the laser -clad powder properties and process parameters (power, feed rate, clad speed etc.) used in the application, the deformation properties of the cladded part and its bending behavior can change. In this study, INC625 and SUS 316L+INC625 clad layers were applied on a GGG40 substrate with optimized parameters and then subjected to bending tests. Bending -test results were examined comparatively and their microstructural properties were examined. Cladding powder feedstock material properties, substrate type and its thermo-physical properties, clad process parameters and surface preparation conditions, number and thickness of layers are the most important factors affecting the bending behaviour in laser -cladding applications and require optimization studies. The INC625 clad layer on the SUS316L bond layer has reduced the diffusional effects, and the hardness distribution has a more homogeneous profile. In this way, an increase in bending angles was observed. The highest bending angle of 32 degrees was measured with dublex-clad layered samples
Impact of global capabilities on performance in international logistics companies
No full textPurpose: In order to make a difference in a globally competitive environment, companies should analyze their competitors, which is one of the factors around them, well, do research, observe the environment and know how to adapt. For this purpose, the research examines the effects of competitive intensity and marketing and sales capabilities, together with the global capabilities of logistics companies operating internationally (third-party logistics companies (3PL)), which are examined. Design/methodology/approach: To establish and test the model, a sample of 504 participants working at senior levels in internationally operating logistics companies (third-party logistics companies (3PL)) with their headquarters in Istanbul was taken and a scale consisting of a total of 32 statements was presented to them. Analyses were performed using Jamovi and SmartPLS 3.3.5. This program was used because, in addition to estimating path models with latent variables, it also calculated standard results evaluation criteria. First, the results of factor analysis are given. After these analyses were completed, the hypotheses were tested. Findings: This research is supported by hypotheses as a result of the analysis that global capabilities are an important factor for logistics companies at the international level, and that the competitive intensity also affects the performance outputs and that marketing and sales capabilities also have an impact. Research limitations/implications: Since data are collected from logistics companies operating globally, it is necessary to pay attention when the analysis results are compared with different sectors. Because the intensity of competition may vary depending on the sector and market in which companies operate. At the same time, the data were collected from authorized white-collar employees working at a senior level in logistics companies. Because, in terms of the level of being able to answer the questions about the variables examined in the research model, data were collected from high-level officials. Practical implications: It is getting harder and harder to compete on a global scale by going beyond national borders. The results of the analysis show how important the global capabilities of logistics companies are, especially the increasing importance of logistics activities for countries. For this reason, logistics companies operating on an international scale need to attach importance to the competitive intensity and develop their marketing and sales capabilities. Originality/value: The research is original in that it examines the global capabilities of logistics companies in their international activities and the effects of competition intensity. In addition, it is important for companies in this sector to examine the effects of marketing and sales capabilities so that logistics companies can reach more customers in their international activities and be more effective in the market compared to their competitors. © 2024, Emerald Publishing Limited
CAM ELYAF TAKVİYESİNİN POLİ-ETER-İMİD NUMUNELERİN KURU KAYMA AŞINMA DAVRANIŞINA ETKİSİ
No full textEndüstrinin değişik sektörlerinde kullanılan makinaların bazı aksamlarında plastik esaslı burç ve yataklar kullanılmaktadır. Yüksek sıcaklık, korozyon, kimyasal direnç ve aşınma direnci istenen uygulamalarda doğru malzeme seçimi, makina elemanının çalışma ömrü açısından oldukça önemlidir. Bu çalışmada, saf poli-eter-eter-keton (PEEK) polimeri ile ağırlık olarak %30 oranında cam elyaf (CE) takviyeli poli-eter-eter-keton (PEEK-30CE) kompozitin tribolojik performansları araştırılmıştır. Deneylerde kullanılan malzemeler, ekstrüzyon yöntemiyle endüstriyel amacıyla üretilmiş çubuk formunda malzemelerdir. Tribolojik deneyler disk üzerinde pim cihazı kullanılarak oda sıcaklığında 2000 m kuru kayma şartlarında gerçekleştirilmiştir. Deneylerde iki farklı yük (30 N ve 60 N) ve dört farklı hız (1, 2, 3 ve 4 m s-1) kullanılmıştır. Deneyler sonucunda saf PEEK polimer ve %30 oranında cam elyaf takviyeli PEEK kompozitinin sürtünme katsayısı, pim sıcaklığı ve spesifik aşınma oranı belirlenmiştir. Deneyler sonucunda kayma hızının artması ile hem saf PEEK hem de cam elyaf takviyeli PEEK kompozitin aşınma oranı artarken sürtünme katsayısı değerleri ise azalmıştır. Düşük yük (30 N) ve hızda (1 m s-1) PEEK kompoziti saf PEEK polimerine göre 2.46 kez daha aşınma dirençli olduğu tespit edilmiştir. Ayrıca optik mikroskop kullanılarak deney malzemelerinin aşınma yüzeyi mikroyapı incelemeleri gerçekleştirilmiştir. Her iki deney malzemesi için düşük yük ve hızlarda adhezif aşınma, yüksek hız ve yüklerde ise abrazif aşınma mekanizması gözlenmiştir
Investigation of tribological behavior of poly(methyl methacrylate) biocomposite containing hydroxyapatite
No full textPoly(methyl methacrylate) (PMMA), is widely used in biomedical applications such as bone cement. However, it is known to have low wear resistance. To enhance its tribological behavior, a reinforcement phase is necessary. For this purpose, in this study, homemade hydroxyapatite (HAp) was utilized to enhance the mechanical properties and wear resistance of PMMA while also increasing its biocompatibility. Using the thermal extraction method, natural raw materials were used to synthesize homemade HAp powder successfully. The d(0.5) of HAp powders in particle size analysis was 7.464 mu m. Hot isostatic pressing (HIP) was used to create PMMA-HAp biocomposites with various HAp ratios (5, 10 and 15wt%) in PMMA. The wear morphology was characterized by scanning electron microscopy (SEM). The SEM images showed a severe abrasive wear mechanism, but a relatively stable wear surface was observed that indicated slight abrasion during the wear tests with the increase in HAp ratio. The highest wear rate was obtained in 15% HAp-reinforced PMMA at a sliding speed of 1.0m/s and had value of 4.72 x 10(-4)mm(3)/(N m) under a 20N load. The HIP'ed densities of the samples increased from 1.15 to 1.31g/cm(3) with increasing amount of HAp. Similarly, the Vickers test results showed that the hardness values increased from 14.76 to 22.03HV