DSpace@ATÜ (Adana Alparslan Türkeş Bilim ve Teknoloji Universiti)
Not a member yet
3463 research outputs found
Sort by
Failure of surface modification 3D printed polymer materials by UV/ozone irradiation
No full textIn today's technology, AM processes are widely adopted in the aerospace, energy, automotive, medicine, and agriculture industries. Fused Deposition Modeling (FDM) is one of the most remarkable methods in the AM family because of its superiorities. Besides the advantages pro-vided, the mechanical strength of the printed parts is still not at a satisfactory level. Here, there are various secondary processes applied to polymer materials to improve both the mechanical properties and functionality of the printed part. Among these processes, the UV/O3 surface treatment method stands out as the most suitable one in terms of ease of application. In this study, two different infill orientation angles were applied to two standard test models. The fabrication process was initiated using suitable process parameters for filaments made of Polylactic Acid (PLA) and Thermoplastic Polyurethane (TPU) materials. The purpose of this investigation was to examine the mechanical strength of 3D printed polymer structures. For the same purpose, the UV/O3 (UV/Ozone) process was applied to the manufactured samples. The samples are then subjected to tensile and compression tests, Shore surface hardness measurements and Scanning Electron Microscopy (SEM) analyze for both the evaluation of mechanical properties and the examination of fracture surface structures. Consequently, significant increases of 28.33%, 25.21%, 27.90%, and 32.92% were observed in material surface hardness levels. This study is important in terms of presenting that the mechanical properties of 3D printed parts can be significantly improved with UV/O3 application, which is an effective and a practical process
COVID-19 enfeksiyon tespiti için yeni bir ince ayar mekanizmasına sahip mobilenet tabanlı CNN modeli
No full textLisansüstü Eğitim Enstitüsü, Bilgisayar Mühendisliği Ana Bilim DalıAralık 2019'da Çin'in Wuhan kentinde ortaya çıkan COVID-19 adlı yeni bir koronavirüs, dünya çapında hızla yayılması ve ciddi akut solunum sendromuna neden olması nedeniyle çok tehlikeli bir hal aldı. Ocak 2022'de bildirildiği üzere, virüs dünya çapında 349.641.119 kişiye bulaştı ve 5.592.266'dan fazla ölüme neden oldu. Birkaç farklı teşhis yöntemi olmasına rağmen, polimeraz zincir reaksiyonu (PCR), COVID-19 patojeninin laboratuvar teşhisi için ana standart olarak kabul edilir. Ancak test sonuçları birkaç saat ile iki gün arasında elde edilmesi erken müdahalenin önündeki en büyük engeldir. Bu yüzden araştırmacılar, hastalığı teşhis etme süresini kısaltmak için röntgen görüntülerini kullanan alternatif yöntemlere odaklandılar. Bu çalışma, göğüs röntgeni görüntülerini kullanarak COVID-19 hastalığını saptamak için yeni ince ayar mekanizmalarına sahip bir derin aktarım öğrenme yaklaşımı önermektedir. Model, MobileNetV2 mimarisine dayanmaktadır. Önerilen modeli değerlendirmek için, üç sınıf içeren halka açık iki veritabanından birleştirilmiş bir veri seti kullandık: normal, COVID-19 ve pnömoni X-ray görüntüleri. Yaklaşımımızda, sınıflandırma doğruluğunu artırmak için bir klasik ve iki yeni ince ayar mekanizması önerdik ve beş kat çapraz doğrulama ile 3 sınıflı sınıflandırmada ortalama %95.62, %96.10 ve %97.61 doğruluk oranlarına ulaştık. Ayrıca üçüncü modelimiz, toplam ince ayar işlemlerinin %81.92'sini azalttı ve daha iyi sonuçlar elde etti. Sayısal sonuçlar, önerilen yaklaşımın, karmaşık ön işleme adımları olmaksızın ham veriler kullanıldığında umut verici sonuçlar elde ettiğini göstermektedir.A new coronavirus called COVID-19, which emerged in Wuhan, China, in December 2019, is very dangerous because of its rapid global spread worldwide, causing severe acute respiratory syndrome. It has infected 349.641.119 people worldwide and caused over 5.592.266 deaths, as reported in January 2022. Although there are several different diagnostic methods, polymerase chain reaction (PCR) is considered the gold standard for laboratory diagnosis of the COVID-19 pathogen. However, test results are obtained within a few hours to two days, and this relatively late response is the main barrier to early intervention. Researchers have focused on alternative methods that use x-ray imaging to shorten the time to diagnose the disease. This study proposes a deep-transfer learning approach with novel fine-tuning mechanisms for detecting COVID-19 disease using chest X-ray images. The model is based on the MobileNetV2 architecture. To evaluate the proposed model, we used a combined dataset from two publicly available databases containing three classes: normal, COVID-19, and pneumonia X-ray images. In our approach, we proposed one classical and two new fine-tuning mechanisms to increase classification accuracy and achieved average accuracy rates of 95.62%, 96.10%, and 97.61% for 3-class cases with five-fold cross-validation. In addition, our third model reduced 81.92% of the total fine-tuning operations and achieved better results. The numerical results show that the proposed approach achieves promising results when raw data without complex preprocessing steps are used
The crowding-out effect of shareholder value-based CEO compensation on R&D investment in the European context: a new interpretation
No full textPurpose In the present study, using a novel fractional logit model, the link between R&D (Research & Development) investment and shareholder value-based CEO (Chief Executive Officer) compensation has been examined within the non-financial sector in the Euro area economies using a firm-level dataset for 2002-2019. Design/methodology/approach The fractional logit model is utilized to examine the effects of corporate payment on R&D investment. The fractional logit model can be considered the empirical approach that takes into account R&D non-performer firms to avoid reducing the sample size. The fractional logit model is superior to the censored or truncated models, like Tobit, since the fractional logit model is useful to address the econometric limitations that are found in the censored and truncated models in the non-linear models. Findings The findings obtained in this study showed a significant and negative effect of short-term aim-based CEO payment on R&D expenditures in the Euro area economies using firm-level data. These findings are robust to different robustness checks and modeling alternatives. Originality/value To the author's knowledge, there is no study that examines the effects of short-term shareholder value maximization-based CEO compensation on R&D in the European context in the literature
Supplementing Missing Data Using the Drainage-Area Ratio Method and Evaluating the Streamflow Drought Index with the Corrected Data Set
No full textIn water resources management, it is essential to have a full and complete set of hydrological parameters to create accurate models. Especially for long-term data, any shortcomings may need to be filled using the appropriate methods. Moving the recorded observed data using the drainage-area ratio (DAR) method to different points is considered one of these methods. The present study used data from six different flow observation stations in the Asi River sub-basin, known as the fertile agricultural areas in Turkey, and transferred the data to various other locations that already have existing observations. This study tested how close the values this method produced were to the actual values and investigated the question how is missing data imputation improved by the determination of method bias coefficients? to analyze the method's accuracy, the streamflow drought index (SDI)-a hydrological drought index-was applied over a 12 month timescale. Contour maps were formed according to both the obtained index results by using the original data from the target station and the transferred streamflow data. As a result of this study, a severe divergence from the actual values was observed in the data directly transferred to the target stations in proportion to their area. The distance of the existing stations between each other produced a very high correlation coefficient, both in the direct transfer process and after the correction was applied. Similarly, in terms of drought index calculations, values close to 97% were seen in the original and transferred flow rates. Consequently, from the perspective of the effective management processes of water resources, the transportation of the data from basin-based observation stations corrected according to the drainage areas can be thought to positively affect the design stages and cost calculations for future water structures
Chemical and physical characterization of microencapsulated Spirulina fermented with Lactobacillus plantarum
No full textSpirulina fermented by lactic acid bacteria (LAB) stands out among innovative fermented products with bioactive properties. In addition, the fermentation of algae with LAB has a significant effect on protein, essential amino acid content, essential fatty acid, etc. Changes in nutritional components, colour and morphological appearances of unfermented and fermented Spirulina as a result of microencapsulation with different ratios of coating material were investigated. The fermentation of wet Spirulina was carried out with Lactobacillus plantarum FI 8595 at 37 degrees C for 72 h under anaerobic condition. Microencapsulation of unfermented (USp) and fermented Spirulina (FSp) was performed by spray drying using 170 degrees C air inlet temperature, 20 mL/min feed flow rate and different ratios of maltodextrin. After fermentation, there was an increase in dry matter and crude ash contents unlike the protein content. Aspartic acid, histidine and lysine concentrations were found to be significantly higher in FSp compared to USp. The main fatty acids in USp and FSp were palmitic (27.39-31.11 %), gamma linolenic (17.41-18.93 %), linoleic (8.11-10.45 %) and palmitoleic acids (4.36-5.05 %). A significant decrease was observed in the phycocyanin content of Spirulina after fermentation. However, the highest total organic acid content was observed in spray dried fermented Spirulina groups (9-22 g/100 g). Increasing maltodextrin (MD) concentrations caused a significant reduction in moisture content of USp and FSp and provided more effective drying. In addition, with the increase of MD addition, the essential/nonessential amino acid ratio raised from 0.83 to 1.26 and from 0.72 to 0.76 in USp and FSp, respectively. According to the SEM results, it was observed that the fermented Spirulina were coated more effectively with the coating material. In addition, fermentation and microencapsulation revealed positive effects on colour properties of Spirulina. Therefore, it can be concluded that microencapsulation of fermented Spirulina has significant potential for the production of new functional foods.Scientific Research Projects of Cukurova University, Turkey [FYL2022-15423]This work was financially supported by the Scientific Research Pro- jects of Cukurova University (FYL2022-15423) , Turkey
GC-MS-Olfactometric Characterization of Volatile and Key Odorants in Moringa (Moringa oleifera) and Kinkeliba (Combretum micranthum G. Don) Herbal Tea Infusions Prepared from Cold and Hot Brewing
No full textHerbal teas are a popular global drink and are widely used in many traditional medicines. Key odorants are one of the main parameters to elucidate the final herbal tea's overall quality and consumer acceptance. In the present study, for the first time, the brewing effect on volatile, key odorants, total phenolic contents, and antioxidant potential of Moringa (Moringa oleifera) and Kinkeliba (Combretum micranthum G. Don) herbal teas was comprehensively investigated. Two different infusions were studied and labeled as 25 degrees C/24 h (room temperature) and 98 degrees C/10 min (hot temperature). A total of 45 and 44 aroma compounds were detected in Moringa cold and hot teas, respectively, whereas 39 volatiles were determined in both infusion techniques for Kinkeliba herbal teas. The total amount of volatile compounds in both cold-infused herbal teas was higher than those in the hot-infused ones. Based on GC-MS-Olfactometry results, 19 and 21 key odorants in total were found in Moringa and Kinkeliba teas, respectively. The principal key odorants in Moringa teas with the highest flavor dilution (FD) factors were (E)-2-hexen-1-ol (herbal/fresh aroma), 3-hexanol (green/grassy), 2-phenyl ethanol (floral/rose), while in Kinkeliba teas they were 2-hexanol (herbal/green) and 3-penten-2-ol (green/fresh). The total phenolic content and antioxidant potential in Moringa and Kinkeliba teas increased using hot infusion. Principal component analysis showed that each tea infusion was clearly discriminated in terms of its volatile profiles. Our findings demonstrated that the brewing procedures had a significant impact on the key odorants of Moringa and Kinkeliba infusions
Effect of Encapsulation Techniques on Aroma Retention of Pistacia terebinthus L. Fruit Oil: Spray Drying, Spray Freeze Drying, and Freeze Drying
No full textThe primary aim of this investigation was to assess the impact of varying the ratio of gum arabic to maltodextrin and employing diverse encapsulation techniques on the properties of the powdered substance and the capacity to retain the aromatic attributes of terebinth fruit oil. Distinct ratios of gum arabic to maltodextrin (75:25, 50:50, and 25:75) were employed to fabricate oil-in-water emulsions. The utmost stability of the emulsion was realized at a gum arabic to maltodextrin ratio of 75:25, characterized by a minimal creaming index and an even and small-scale dispersion. The encapsulation techniques employed included spray drying (SD), spray freeze-drying (SFD), and freeze-drying (FD). These methodologies were compared based on encapsulation efficiency, desiccation yield, powder attributes, and the capacity to retain aroma. The encapsulation efficiencies were notably higher (>90%) in SD, particularly with the application of an ultrasonic nozzle and a two-fluidized nozzle (2FN), in contrast to those obtained through SFD and FD. Notably, SD employing an ultrasonic nozzle exhibited superior preservation of volatiles (73.19%) compared to FD (24.45%), SD-2FN (62.34%), and SFD (14.23%). Among the various components, ?-pinene and linalool stood out with near-perfect retention rates, close to 100%. © 2023 by the authors
Numerical Investigation of Flow Structure around NACA 0018 with slot
No full textWe numerically investigated NACA 0018 airfoil with slot at various angles of attack. The computational fluid dynamics (CFD) results were compared with the base airfoil to show the effectiveness of the airfoil. Reynolds number was kept constant as Re=3x105 to thoroughly understand how different locations of slot would provide passive flow control from aerodynamic perspective. We have used three different slot locations to reveal the effectiveness of the slot compared to the base airfoil for higher angles of attack. Our results show that the slotted design would yield to increase the lift and to delay the stall angle of base airfoil
A hybrid ANN/PSO optimization of material composition and process parameters for enhancement of mechanical characteristics of 3D-printed sample
No full textPurposeThis paper aims to study the effects of inorganic CaCO3 nanoadditives in the polylactic acid (PLA) matrix and fused filament fabrication (FFF) process parameters on the mechanical characteristics of 3D-printed components. Design/methodology/approachThe PLA filaments containing different levels of CaCO3 nanoparticles have been produced by mix-blending/extrusion process and were used to fabricate tensile and three-point bending test samples in FFF process under various sets of printing speed (PS), layer thickness (LT), filling ratio (FR) and printing pattern (PP) under a Taguchi L27 orthogonal array design. The quantified values of mechanical characteristics of 3D-printed samples in the uniaxial and the three-point bending experiments were modeled and optimized using a hybrid neural network/particle swarm optimization algorithm. The results of this hybrid scheme were used to specify the FFF process parameters and the concentration of nanoadditive in the matrix that result in the maximum mechanical properties of fabricated samples, individually and also in an accumulative response scheme. Diffraction scanning calorimetry (DSC) tests were conducted on a number of samples and the results were used to interpret the variations observed in the response variables of fabricated components against the FFF parameters and concentration of CaCO3 nanoadditives. FindingsThe results of optimization in an accumulative scheme showed that the samples of linear PP, fabricated at high PS, low LT and at 100% FR, while containing 0.64% of CaCO3 nanoadditives in the matrix, would possess the highest mechanical characteristics of 3D-printed PLA components. Originality/valueFFF is a widely accepted additive manufacturing technique in production of different samples, from prototypes to the final products, in various sectors of industry. The incorporation of chopped fibers and nanoparticles has been introduced recently in a few articles to improve the mechanical characteristics of produced components in FFF technique. However, the effectiveness of such practice is strongly dependent on the extrusion parameters and composition of polymer matrix.Scientific Research Coordination Unit of Adana Alparslan Tuuml;rkes Science and Technology University [22303004]This work was supported by Scientific Research Coordination Unit of Adana Alparslan Turkes Science and Technology University with project number of 22303004
Optimization of spray drying conditions for improved physical properties in the production of enzyme-modified cheese powder
No full textEnzyme-modified cheese (EMC), a cheese flavor additive with high-fat content, is preferably produced in powder form because of its long shelf-life and high industrial applicability. The physical properties of additives, especially with high-fat contents, are very important for their industrial usage, and the spray drying process conditions substantially determine the physical properties of powders. In this study, optimization of the spray drying process during the production of EMC powder was performed to improve the powder physical properties. The process factors were inlet temperature, feed flow rate, and aspiration rate, while the responses were selected as drying yield, Carr index (CI), wettability, surface fat content, and browning index (BI). The optimum spray drying conditions were calculated as 150 degrees C, 9.1 mL/min, and 28.4 m(3)/h for inlet temperature, feed flow rate, and aspiration rate, respectively. It has been determined that the spray drying conditions at low inlet temperature, medium feed flow, and aspiration rates in order to obtain improved powder physical properties should be preferred.Scientific and Technological Research Council of Turkey (TUBITAK); [115O229]ACKNOWLEDGMENTS This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) [project no: 115O229]