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- 저자 : Yunus Unal (검색결과 3 건)
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Ugur Kafkas,Yunus Unal,M. Ozgur Yayli,Busra Uzun Techno-Press 2023 Advances in nano research Vol.15 No.4
This work aims to present a solution for the buckling behavior of perforated nano/microbeams with deformable boundary conditions using nonlocal strain gradient theory (NLSGT). For the first time, a solution that can provide buckling loads based on the non-local and strain gradient effects of perforated nanostructures on an elastic foundation, while taking into account both deformable and rigid boundary conditions. Stokes' transformation and Fourier series are used to realize this aim and determine the buckling loads under various boundary conditions. We employ the NLSGT to account for size-dependent effects and utilize the Winkler model to formulate the elastic foundation. The buckling behavior of the perforated nano/microbeams restrained with lateral springs at both ends is studied for various parameters such as the number of holes, the length and filling ratio of the perforated beam, the internal length, the nonlocal parameter and the dimensionless foundation parameter. Our results indicate that the number of holes and filling ratio significantly affect the buckling response of perforated nano/microbeams. Increasing the filling ratio increases buckling loads, while increasing the number of holes decreases buckling loads. The effects of the non-local and internal length parameters on the buckling behavior of the perforated nano/microbeams are also discussed. These material length parameters have opposite effects on the variation of buckling loads. This study presents an effective eigenvalue solution based on Stokes' transformation and Fourier series of the restrained nano/microbeams under the effects of elastic medium, perforation parameters, deformable boundaries and nonlocal strain gradient elasticity for the first time.
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Deniz Begen,Gokce Calis-Ismetoglu,Omer Yunus Gumus,Halil Ibrahim Unal 대한환경공학회 2024 Environmental Engineering Research Vol.29 No.4
Coal is used in most of the power and chemical plants to meet energy needs which produce various waste ashes. Reuse of these ashes as electroactive materials has great importance for sustainable development. In this study, it was detected that the main components of coal fly (CFA) and bottom ashes (CBA) were oxides of silica (SiO₂), iron (Fe₂O₃), aluminium (Al₂O₃), and magnesium (MgO), besides carbon. These are well-known electrorheological (ER) active materials. The aim of this study is to reveal dielectric and electroactive vibration damping capabilities of CFA and CBA. According to the dielectric and ER flow tests carried out in insulating silicone oil (SO), the optimum concentration of particles was determined to be 35 wt.% for both ashes. Higher ER yield stress (τ<SUB>y </SUB>= 135 Pa), higher ER efficiency (32.8), and better viscoelastic properties (τ<SUB>c</SUB> = 128 Pa, G = 680 kPa) under 3.0 kV mm<SUP>-1</SUP> applied electric field were obtained for 35CFA/SO suspension system compared to 35CBA/SO (τ<SUB>y</SUB> = 125 Pa, ER<SUB>eff</SUB> = 24.0, τ<SUB>c</SUB> = 55 Pa, G = 260 kPa). Although it was concluded that both ashes can be upcycled to sustainable and smart vibration damping alternative materials, better performance was observed for CFA particles.
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Ahmet A. Kiykim,Ahmet Camsari,Serkan Kahraman,Mustafa Arici,Bulent Altun,Dilek Cicek,Yunus Erdem,Unal Yasavul,Cetin Turgan,Sali Caglar,Aytekin Oto 연세대학교의과대학 2004 Yonsei medical journal Vol.45 No.2
Cardiovascular disease (CVD) is still the major cause of the morbidity and mortality in hemodialysis (HD) patients. The characteristics of major arterial changes, atherosclerosis and related risk factors in HD patients remain unclear. We aimed to evaluate the atherosclerotic process in asymptomatic HD patients and healthy volunteers, and to determine the association between the risk factor(s) and the atherosclerotic process in these groups. 92 HD patients (female: 43, male: 49) and 62 age and sex matched healthy volunteers (female: 27, male: 35) were enrolled in this study. Diabetics, smokers, and patients with symptomatic CVD were excluded. The right and left carotid intima-media thicknesses (CIMTs) were measured and plaque structures were studied by B-mode ultrasound. The mean CIMT in patients and control group were 0.79±0.16 mm and 0.54±0.09mm, respectively. Mean CIMT in HD patients was thicker (p<0.001) and the presence ratio of plaque was higher in patients group (n=38, %61.2 vs n=9, %17.3) (p<0.001). Calcified type of plaque was more frequent in HD patients than control group. Age (r=0.48, p<0.001), left ventricular mass (r=0.42, p<0.05), and homocysteine (r=0.46, p<0.01), mean hematocrit (r=-0.36, p<0.05), plasma CRP (r=0.50, p<0.001), ESR (r=0.43, p<0.01) and albumin (r= -0.34, p<0.05) levels were correlated with the CIMT measurements and plaque presence, significantly. -CIMT as an atherosclerotic process indicator is thicker in asymptomatic HD patients than healthy subjects. We concluded that in addition to various classical risk factors, uremic environment may also contribute to acceleration of the atherosclerotic process.
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