• 폴리머
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• 제37권4호
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• pp.518-525
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• 2013

폴리프로필렌(PP)을 매트릭스로, 황산처리된 녹조류(SGA)를 보강재로 사용한 바이오복합재료(biocomposites)의 기계적 특성을 향상시키기 위해 그래핀(GNP)의 평균입자크기와 첨가량에 따른 SGA/GNP/PP 복합재료를 제조하고 그 특성을 분석하였다. GNP의 첨가량에 의해 굴곡강도 및 충격강도는 점차 감소하는 경향을 나타내었다. 반면에, SGA와 GNP의 영향으로 인해 굴곡탄성률 및 저장탄성률은 크게 증가하였다. 평균입자크기가 $5{\mu}m$(GNP5)인 크기가 작은 GNP를 보강재로 사용하였을 경우 평균입자크기가 $15{\mu}m$(GNP15)인 GNP를 보강재로 사용한 복합재료와 비교하여 상대적으로 우수한 기계적 특성을 보였다. 이는 상대적으로 GNP5의 효과적인 분산에 기인한 것이다. 반면에, GNP5를 보강재로 사용한 복합재료의 열팽창에 대한 저항 특성은 GNP15와 비교하여 상대적으로 감소한 결과를 나타내었으며, 이는 열전도 특성이 우수한 GNP5가 상대적으로 넓고 고르게 분포되어있기 때문에 복합재료 전체에 열이 쉽게 전달되었기 때문으로 해석할 수 있었다. 결과적으로 SGA/GNP/PP 복합소재는 굴곡저항, 저장탄성률, 댐핑특성 등은 충분히 향상되어 범용 바이오컴포지트로 적용가능하였다.

• Journal of Animal Science and Technology
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• 제65권1호
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• pp.244-257
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• 2023

The study aimed to investigate the effect of low-frequency oscillations on the cow udder, milk parameters, and animal welfare during the automated milking process. The study's objective was to investigate the impact of low-frequency oscillations on the udder and teats' blood circulation by creating a mathematical model of mammary glands, using milkers and vibrators to analyze the theoretical dynamics of oscillations. The mechanical vibration device developed and tested in the study was mounted on a DeLaval automatic milking machine, which excited the udder with low-frequency oscillations, allowing the analysis of input parameters (temperature, oscillation amplitude) and using feedback data, changing the device parameters such as vibration frequency and duration. The experimental study was performed using an artificial cow's udder model with and without milk and a DeLaval milking machine, exciting the model with low-frequency harmonic oscillations (frequency range 15-60 Hz, vibration amplitude 2-5 mm). The investigation in vitro applying low-frequency of the vibration system's first-order frequencies in lateral (X) direction showed the low-frequency values of 23.5-26.5 Hz (effective frequency of the simulation analysis was 25.0 Hz). The tested values of the first-order frequency of the vibration system in the vertical (Y) direction were 37.5-41.5 Hz (effective frequency of the simulation analysis was 41.0 Hz), with higher amplitude and lower vibration damping. During in vivo experiments, while milking, the vibrator was inducing mechanical milking-similar vibrations in the udder. The vibrations were spreading to the entire udder and caused physiotherapeutic effects such as activated physiological processes and increased udder base temperature by 0.57℃ (p < 0.001), thus increasing blood flow in the udder. Used low-frequency vibrations did not significantly affect milk yield, milk composition, milk quality indicators, and animal welfare. The investigation results showed that applying low-frequency vibration on a cow udder during automatic milking is a non-invasive, efficient method to stimulate blood circulation in the udder and improve teat and udder health without changing milk quality and production. Further studies will be carried out in the following research phase on clinical and subclinical mastitis cows.

• Earthquakes and Structures
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• 제26권6호
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• pp.417-431
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• 2024

The fundamental period of vibration is one of the most critical parameters in the analysis and design of structures, as it depends on the distribution of stiffness and mass within the structure. Therefore, building codes propose empirical equations based on the observed periods of actual buildings during seismic events and ambient vibration tests. However, despite the fact that infill walls increase the stiffness and mass of the structure, causing significant changes in the fundamental period, most of these equations do not account for the presence of infills walls in the structure. Typically, these equations are dependent on both the structural system type and building height. The different values between the empirical and analytical periods are due to the elimination of non-structural effects in the analytical methods. Therefore, the presence of non-structural elements, such as infill panels, should be carefully considered. Another critical factor influencing the fundamental period is the effect of Soil-Structure Interaction (SSI). Most seismic building design codes generally consider SSI to be beneficial to the structural system under seismic loading, as it increases the fundamental period and leads to higher damping of the system. Recent case studies and postseismic observations suggest that SSI can have detrimental effects, and neglecting its impact could lead to unsafe design, especially for structures located on soft soil. The current research focuses on investigating the effect of infill panels on the fundamental period of moment-resisting and eccentrically braced steel frames while considering the influence of soil-structure interaction. To achieve this, the effects of building height, infill wall stiffness, infill openings and soil structure interactions were studied using 3, 6, 9, 12, 15 and 18-story 3-D frames. These frames were modeled and analyzed using SeismoStruct software. The calculated values of the fundamental period were then compared with those obtained from the proposed equation in the seismic code. The results indicate that changing the number of stories and the soil type significantly affects the fundamental period of structures. Moreover, as the percentage of infill openings increases, the fundamental period of the structure increases almost linearly. Additionally, soil-structure interaction strongly affects the fundamental periods of structures, especially for more flexible soils. This effect is more pronounced when the infill wall stiffness is higher. In conclusion, new equations are proposed for predicting the fundamental periods of Moment Resisting Frame (MRF) and Eccentrically Braced Frame (EBF) buildings. These equations are functions of various parameters, including building height, modulus of elasticity, infill wall thickness, infill wall percentage, and soil types.