Aksaray University Institutional Repository
Not a member yet
8503 research outputs found
Sort by
Underpricing and aftermarket performance of IPOs during the Covid-19 period: Evidence from Istanbul stock exchange
Get PDFThe effect of uncertainty on IPO underpricing, short-term performance after IPO, and hot-and-cold-IPO market cycles have received a great deal of attention in the literature. This study revisits these issues of IPO activities under the Covid-19 pandemic with a focus on the Turkish IPO market. Measuring the underpricing and aftermarket performance of IPOs based on the cumulative abnormal returns of the first, second, third, fourth, fifth, tenth, and twenty-first days, we examine how underpricing and aftermarket performances are influenced by Covid-19 and some uncertainty proxies, such as some company characteristics (age, total assets), offering characteristics (gross proceeds, IPO price risk), and aftermarket variables (first-day trading volume, standard deviation of stock prices after the IPO) after controlling for firm, industry and market level variables (first-day trading value, the portion of the firm offered to public, price-earnings ratio, dummy variables for technology, manufacturing, and financial institutions sectors, standard deviation of a market index, moving average return of a market index). The study documents that while an IPO launched during the Covid-19 period has larger underpricing, an average IPO firm that is older, has more assets, generates larger proceeds, trades more on its first day of trading, is expected to fluctuate less after the IPO has a smaller underpricing at its initial public offering. Empirical results show that short-term market-adjusted abnormal returns of IPO firms during the pandemic are much larger than those before the pandemic. Copyright (c) 2023 Borsa.Istanbul Anonim Sirketi. Published by Elsevier B.V
Functional Role of Macrofungi as Prebiotics and Health Perspectives
No full textMushrooms have been used since centuries as source of food and also as important part of folk medicine in many ancient cultures. Nowadays, with the increased awareness’s of the importance of healthy food, mushrooms become one of the main components of healthy food food and food supplements. In addition to the known functional role in prevention and treatment of many diseases, recent research find also that it includes also many nutrients which can act as prebiotic. This plays crucial role as natural supplement to provide healthy growth of human and animal through supporting the growth of microbiome and thus, increase the functional role of probiotics. This chapter will highlight the recent development of mushroom research as functional prebiotic source for both human and animal health
Plasma Apelin Levels and Thiol/Disulfide Balance in Patients with Type 2 Diabetes Mellitus
Get PDFThe main objective of this research is to investigate the relationship between the plasma apelin concentrations, oxidative stress biomarkers (dynamic thiol/disulfide balance), and albuminuria in patients with type 2 diabetes mellitus. Methods: The study was carried out with 87 patients with type 2 diabetes mellitus and 24 age- and sex-matched healthy control group. Serum apelin concentrations were studied using the enzyme-linked immunosorbent assay method. Colorimetric method was used to determine native and total thiol levels. Concentrations of spot urine albumin and creatinine were measured to calculate the albumin creatinine ratio (mg/g). Results: Serum apelin concentrations were significantly lower in patients with type 2 diabetes mellitus compared to the control group (P < .001). Native and total thiol ratios were also significantly lower in diabetic patients compared to healthy patients (P < .001). The calculated disulfide levels of the patients and control groups were similar (P = .182). A negative and significant correlation was detected between serum apelin concentrations, and glucose and hemoglobin A1c levels in diabetic patients (r = −0.272, P = .004, r = −0.280, P = .003, respectively). A negative and significant correlation was also observed between native and total thiol levels and albumin (r = −0.338, P = .001, r = −0.328, P = .001, respectively). Conclusion: We found significantly lowered serum apelin concentrations and native and total thiol levels in patients with type 2 diabetes mellitus. An association was also observed between serum apelin concentrations and glycemic control. The role of apelin and thiol/disulfide balance in diabetic kidney disease requires more detailed studies
Activation of NO2 by Modifying the Porphyrin Unit with Oxygen in a MnN4 Graphene Layer
Get PDFIn this article, the activation of N−O bonds in NO2 molecules has been investigated by Density Functional Theory (DFT) calculations. Considering the graphene-based MnN4 layer, nitrogen atoms in the porphyrin unit were sequentially replaced with oxygen atoms to create different MnNmOn/G (m+n=4 and 1<m≤4) layers. As more oxygen atoms are incorporated in porphyrin units for bare layers, the covalent character of the Mn−O bonds is switched to the transit nature with respect to Mn−N bonds. Moreover, the trend in bond strength decreasing in all oxygen-containing bonds is in line with the formation energy trends of bare layers. The same situation is also valid for the bonds between Mn−N/O. For NO2 adsorption configurations on all MnNmOn/G layers, N−O bonds in NO2 are weakened by populating/depopulating antibonding/bonding orbitals, respectively. Even if the MnN2O2(hex)/G layer has a moderate NO2 adsorption energy among the other layers, this layer provided the most significant activation over N−O bonds based on crystal orbital Hamilton population (COHP), crystal orbital bond index (COBI), and Atoms in Molecules (AIM) Bader Topological Analysis. Our results show that integrated COHP and integrated COBI values show a remarkable correlation with AIM-Bader parameters for the specific bonds which have descriptive capability over NO2 molecule activation
Measurement and optimization of cutting forces, surface roughness and temperature in turning of AZ91 Mg alloy
No full textThis study presents the experimental and statistical examination of machinability of AZ91 alloy, in terms of cutting forces (Fc, Ff, and Fp), surface roughness (Ra) and cutting temperature (T). In the first step, test samples have been produced using the casting method and the microstructures of these samples have been characterized by SEM and EDS. Secondly, the turning tests have been performed in CNC turning at three different cutting speeds (200, 300, and 400 m/min), three different feed rates (0.1, 0.2, and 0.3 mm/rev), and three different depths of cut (1, 1.5, and 2 mm). Thereafter, the turning simulations have been performed by Deform 3D software. Finally, experiment results were statistically analyzed using Taguchi, Anova, and regression analysis. The outcomes of this study show that the feed rate is the most significant parameter with 69.43, 90.04, 88.53, and 96.22% effect rates on the cutting force components (Fc, Ff, and Fp) and surface roughness (Ra) respectively, while the cutting speed is the most significant parameter with 70.83% effect rates on the cutting temperature. There is an average of 4.5% deviation between the experimental and simulation results of Fc. The results also stated that the microstructure of the samples consisted of α-Mg phase and β-intermetallic (Mg17Al12) phase, and the built-up edge (BUE) formation was the dominant wear mode for all the cutting tools
Öykü temelli öğrenme yaklaşımı ile bütünleştirilmiş yaratıcı yazma uygulamalarının ortaokul öğrencilerinin yazma tutumlarına ve yaratıcı yazma becerilerinin gelişimine etkisi
Get PDFBu araştırmanın temel amacı, öykü temelli öğrenme yaklaşımı ile bütünleştirilmiş yaratıcı yazma uygulamalarının ortaokul 6. sınıf öğrencilerinin yazma tutumları ve yaratıcı yazma becerileri üzerine etkisini incelemektir. Araştırma, karma yöntem araştırma desenlerinden yakınsayan paralel desen yaklaşımıyla gerçekleştirilmiştir. Araştırmanın nicel boyutunda yarı-deneysel modellerden biri olan ön test-son test eşleştirilmiş kontrol gruplu modelden, nitel boyutunda ise nitel araştırma yöntemlerinden biri olan durum çalışmasından yararlanılmıştır. Araştırmanın çalışma grubunu 2021-2022 eğitim-öğretim yılının güz döneminde Aksaray ilinde iki farklı devlet okulunda 6. sınıfa devam eden öğrenciler oluşturmuştur. Araştırma deney grubunda 27, kontrol grubunda 27 öğrenci olmak üzere toplam 54 öğrenciyle yürütülmüştür. Eğitim süreci boyunca deney grubunda yer alan öğrencilerle öykü temelli öğrenme yaklaşımı ile bütünleştirilmiş yaratıcı yazma uygulamaları yapılırken kontrol grubundaki öğrencilerle mevcut ders kitabındaki yazma etkinlikleri ile öğretim sürdürülmüştür. Uygulama 8 hafta sürmüştür. Deney ve kontrol grubunda yer alan öğrencilerin yaratıcı yazma başarılarını ölçen ön test ve son testler “Yaratıcı Yazma Değerlendirme Ölçeği”, yazmaya yönelik tutumları ise “Yazma Tutum Ölçeği” ile değerlendirilmiştir. Araştırmada nicel olarak elde edilen veriler betimsel istatistiklerin yanı sıra (Bağımsız) Örneklemler t-testi, Mann Whitney U, Wilcoxon Sıralı İlişkiler Testi, Kovaryans Analizi (ANCOVA); yarı yapılandırılmış görüşme formları ile elde edilen nitel veriler ise içerik analizi tekniği ile incelenmiştir. Araştırma sonucunda öykü temelli öğrenme yaklaşımı ile bütünleştirilmiş yaratıcı yazma uygulamalarının öğrencilerin yaratıcı yazma becerilerini geliştirdiği sonucuna ulaşılmıştır
Chemische und biologische Charakterisierung von 3D-Keratinfaser-Chitosan-basierenden Folien aus Gänsefedern
No full textThe rapid increase in the world's population leads to increased consumption of animal products. Its impact on the environment is also an increase in the amount of solid waste such as feathers of poultry after processing. Feathers arise as a by-product of poultry farming, which makes them a sustainable resource in areas where feathers can be used as raw materials. The need for biopolymers alternative to synthetic ones which are not biocompatible and/or environmentally harmful, is increasing in various fields. With more than 90% keratin content, the feathers are a durable reinforcement product. Herein, it is aimed to produce 3D keratin-fibre chitosan-based film obtained from goose feathers for the first time. The method of this research involves Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) to characterise and compare the structure of films. Additionally, thickness and antioxidant activity tests were performed. The result obtained from SEM images showed that feather films (100, 200 and 300 mg 3D keratin-fibre) have the roughest surface compared to the control (only chitosan solution and glycerol). Keratin-fibre blending with chitosan showed structural changes, especially at the absorption bands of 3272–2961 cm–1 as well as the amide I, II and III regions. Moreover, thermal properties of the 3D keratin-fibres were increased by increasing the amount of feathers. The present study suggests a new natural material from goose feathers, e.g., for medical applications and reduces the problem of environmentally sensitive waste disposal of feathers. Thus, biological recycling of feathers will provide benefits to the poultry industry and ecosystem
Sodium Pentaborate Prevents Acetaminophen-Induced Hepatorenal Injury by Suppressing Oxidative Stress, Lipid Peroxidation, Apoptosis, and Inflammatory Cytokines in Rats
No full textAcetaminophen (N-acetyl-p-aminophenol, APAP, or paracetamol) is one of the drugs that may be damaging to the kidneys and liver when used in excess. In this context, it is vital to treat these side effects on the liver and kidneys with various antioxidants. Diseases have been treated using herbal and mineral remedies since ancient times. The mineral boron, found in rocks and water, is a crucial ingredient with multiple positive biological effects. The primary objective of this research is to determine whether or not boron has a protective effect against the toxicity generated by APAP in rats. Male Sprague-Dawley rats were pretreated orally with boron-source sodium pentaborate (B50 and B100 mg/kg) for 6 days by gastric gavage in order to counteract the toxicity caused by a single dose of APAP (1g/kg). APAP increased lipid peroxidation as well as serum BUN, creatinine concentrations, and serum activities of AST, ALP, and ALT by consuming GSH in liver and kidney tissues. In addition, the activity of antioxidative enzymes, including SOD, CAT, and GPx, was diminished. Inflammatory indicators such as TNF-α, IL-1β, and IL-33 were elevated in conjunction with APAP toxicity. In kidney and liver tissues, APAP dramatically increased the activity of caspase-3 and triggered apoptosis. Sodium pentaborate therapy on a short-term basis reduced biochemical levels despite these effects of APAP
Apriori Algorithm in Market Basket Analysis: A Retailer Example in Turkey
No full textIn recent years, along with the technological improvements and data volume increase, data mining in CRM and marketing’s common strategical issues became more popular. There is an increasing trend that data mining can help customer relations and the research of these analyses’ is directly related to consumers. In this study, the management of customer relations and the timeline of customer's life cycle research models were explained along with the theory of togetherness apriori algorithm. The authors collected the data via a Turkish company's retail sales verification in the Istanbul airport. The sales data for two months of this company has been analyzed. From the total number of 1650 transactions, 1550 customer transactions were found who pick more than one product. In this two-month dataset, 42 groups of product associations were examined using SPSS 15.0 module program. The research showed that the products displayed together and which one can display separately from other products have emerged. This study also provided a general insight into the efficient demand number of the goods to be evaluated for the customers’ needs and demands
Solubility of Salicylic Acid in Some (Ethanol + Water) Mixtures at Different Temperatures: Determination, Correlation, Thermodynamics and Preferential Solvation
Get PDFEquilibrium mole fraction solubility of salicylic acid in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from T = (293.15 to 323.15) K. Salicylic acid solubility in these mixtures was adequately correlated with well-known correlation/prediction methods based on Jouyban-Acree model. Apparent thermodynamic quantities, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution and mixing processes, were computed by means of the van’t Hoff and Gibbs equations. The enthalpy–entropy compensation plot of enthalpy vs. Gibbs energy of dissolution was not linear exhibiting positive slopes from neat water to the mixture of w 1 = 0.30 and from the mixture of w 1 = 0.50 to neat ethanol indicating enthalpy-driven drug transfer processes but negative in the interval of 0.30 < w 1 < 0.50 indicating entropy-driven drug transfer processes from more polar to less polar solvent systems. Moreover, by using the inverse Kirkwood–Buff integrals it is observed that salicylic acid is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in those mixtures of 0.24 < x 1 < 1.00