• Advances in nano research
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• 제13권1호
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• pp.47-61
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• 2022

The present research investigates the dynamic behavior of a rotating functionally graded (FG) nonlocal cylindrical beam. The cylindrical beam is mathematically modeled via third-order beam theory linked with nonlocal strain gradient theory. The tube structure is made of functionally graded materials composed of Aluminum oxide coated on the Nickel, which the mechanical properties vary in the tube radius direction according to the power law. The bending harmonic force is applied in the tube length middle. The nonlocal spinning equations of the tube are derived via the energy method of the Hamilton principle, and they are solved via a robust numerical procedure for different boundary conditions. The main application of the rotating nanostructures is for the production of small-scale motors and devices and the drug-delivery application, the presented results can help the researcher have a better view regarding the different conditions.

• 대한방사선기술학회지:방사선기술과학
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• 제19권2호
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• pp.71-77
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• 1996

Studies were conducted to determine the clinical application of photodiode. We compared photodiode with ion-chamber as to change of tube potential, tube current, mAs and measured decreasing rate of penetration dose. When tube potential was changed from 60 kVp to 120 kVp, output of photodiode and ion-chamber were changed from 0.4 to 1.625, and 1.018 to 4.268, respectively. This was a good agreement to theory that $I=Kv^2it$(I is intensity, K is constant, v is tube potential, i is tube current, t is time). Characteristics for change of tube current and mAs were also a good agreement to theory. And comparison in decreasing rate of penetration dose was similar except above 6 cm in depth. Our results indicated that photodiode was a good instrument for relative measurement of radiation exposure, but we can not use the photodiode for absolute radiation dose.

• Steel and Composite Structures
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• 제42권5호
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• pp.599-615
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• 2022

In the present paper, the numerical dynamic analysis of a functionally graded nano-scale nonuniform tube was investigated according to the high-order beam theory coupled with the nonlocal gradient strain theory. The supposed cross-section is changed along the pipe length, and the material distribution, which combines both metal and ceramics, is smoothly changed in the pipe length direction, which is called axially functionally graded (AFG) pipe. Moreover, the porosity voids are dispersed in the cross-section and the radial pattern that the existence of both material distribution along the tube length and porosity voids make a two-dimensional functionally graded (2D-FG) truncated conical pipe. On the basis of the Hamilton principle, the governing equations and the associated boundary conditions equations are derived, and then a numerical approach is applied to solve the obtained equations.

• International Journal of Air-Conditioning and Refrigeration
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• 제11권3호
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• pp.105-113
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• 2003

This study developed a practical two-microphone impedance tube method to measure the sound transmission loss of sound isolation materials without the use of an expensive reverberation room or an acoustic intensity probe. In order to evaluate the validation and applicability of the two-microphone impedance tube method, sound transmission losses for several sound isolation materials with different surface density and bending stiffness were measured, and the measured values were compared with the results from the reverberation room method and the theory. From the experimental results, it was found that the accuracy of sound transmission loss obtained by the impedance tube method depends upon the diameter size of the impedance tube (i.e., tested sample size). For sound isolation materials having relatively large bending stiffness such as acryl, wood, and aluminum plates, it was found that the impedance tube method proposed by this study was not valid to measure the sound transmission loss. On the other hand, for sound isolation materials having relatively small bending stiffness such as rubber, polyvinyl, and asphalt sheets, the comparisons of transmission loss between the results from the impedance tube method and the theory showed a good agreement within the range of the frequencies satisfying the normal incidence mass law. Therefore, the two-microphone impedance tube method proposed by this study can be an effective measurement method to evaluate the sound transmission loss for soft sound isolation sheets having relatively small bending stiffness.

• 한국자동차공학회논문집
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• 제3권3호
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• pp.29-36
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• 1995

The present paper deals with the crushing characteristics of double hatted-section tube used in body structure of passenger car. Being crushed, a double hatted-section tube shows symmetric or antisymmetric buckling mode according to section aspect ratio and flange size. Zone of buckling mode is shown by numerical methods. It is supposed that crippling behavior of double hatted-section tube corresponds with rectangular tube without flange. Crippling plate coefficient is also calculated when section aspect ratio of tube is higher than one.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1925-1928
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• 2012

Adsorption of alkali metals (Li, Na, and K) on the surface of magnesium oxide nanotubes (MgONTs) with different diameters was investigated using density functional theory. According to the obtained results, the most stable adsorption site was found to be atop the oxygen atom of the tube surface with adsorption energies in the range of -0.25 to -0.74 eV. HOMO-LUMO gap ($E_g$) of the tubes dramatically decreases upon the adsorption of the alkali metals, resulting in enhancement of their electrical conductivity enhancement. The order of $E_g$ decrement caused by the metal adsorption is as follows: K > Na > Li. The results suggest that the MgONTs were transformed from semi-insulator to semiconductor upon the alkali metal adsorption. Increasing the tube diameter, the HOMO/LUMO gap of the pristine tube is enhanced and adsorption energies of the alkali metals are decreased.

• Computers and Concrete
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• 제30권3호
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• pp.185-196
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• 2022

In this paper, the dynamic characteristics of a composite cylindrical beam made of a mechanism of carbon dioxide absorption coated on the tube core are investigated based on the classical beam theory coupled with the modified couple stress theory. The composite tube structures are assumed to be uniform along the tube length, and the energy method regarding the Hamilton principle is utilized for generating the governing equations. A powerful numerical solution, the generalized differential quadrature method (GDQM), is employed to solve the differential equations. The carbon dioxide trapping mechanism is a composite consisting of a polyacrylonitrile substrate and a cross-link polydimethylsiloxane gutter layer. Methacrylate, poly (ethylene glycol), methyl ether methacrylate, and three pedant methacrylates are all taken into account as potential mechanisms for capturing carbon dioxide. The application of the present study is helpful in the design and production of microelectromechanical systems (MEMS) and the different valuable parameters, such as the length-scale parameter, rate of section change, aspect ratio, etc., are presented in detail.

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.654-659
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• 2020

The reliability of the spent fuel pool instrument is very important for the security of nuclear power plant, especially during the earthquake. The effect of the fluid force on the vibration characteristics of the flexible tube of the spent fuel pool instrument needs comprehensive analysis. In this paper, based on the potential flow theory, the hydrodynamic pressures acting on the flexible tube were obtained. A mathematical model of a flexible tube was constructed to obtain the dynamic response considering the effects of seismic load and fluid force, and a computer code was written. Based on the mathematical model and computer code, the maximum stresses of the flexible tube in both safe shutdown earthquake and operating basis earthquake events on the spent fuel pool with three typical water levels were calculated, respectively. The results show that the fluid force has an obvious effect on the stress and strain of the flexible tube in both safe shutdown earthquake and operating basis earthquake events.

• 한국항공우주학회지
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• 제46권9호
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• pp.703-711
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• 2018

본 연구에서는 실기체 환경 모사(고도 모사)가 가능한 극초음속 Ludwieg tube 개념설계 도구를 개발하고, 전산유체해석을 통해 Ludwieg tube 개념설계 도구의 성능을 검증하였다. 극초음속 Ludwieg tube 개념설계 도구를 개발하기 위해 Ludwieg tube의 작동원리를 연구하였고, 도구를 활용하여 목표 성능을 만족하기 위한 Ludwieg tube의 제원을 결정하였다. 마하수 4에서 10의 유동을 모사할 수 있고, 특히 마하수 4 유동은 고도 모사가 가능하다.

• 한국콘텐츠학회논문지
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• 제20권9호
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• pp.29-42
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• 2020

본 연구의 목적은 소셜미디어 중 하나인 YouTube 동영상 사용자들이 남긴 의견을 추출하여 분석하는 질적연구방법을 제시한다. 이를 위해서 YouTube 동영상 사용자의견을 사용하여 사용과 충족 이론의 쾌락적 충족, 사회적 충족, 그리고 실용적 충족을 빈도분석과 토픽모델링을 통해 측정하였다. 측정결과, YouTube KBS 한국방송 채널 중 트로트 가수 조명섭 동영상을 사용자들이 시청하는 이유는 첫 번째로 높은 빈도를 보이는 것이 쾌락적 충족을 위해서였다. 다음 순으로 사회적 충족과 실용적 충족으로 나타났다. 단어-문서 네트워크 분석에서 연결정도중심성은 '응원', '감사', '화이팅', '최고' 등이 높게 나타났고, 매개중심은'감사', '응원', '화이팅'등의 단어가 높게 나타나 연결정도 중심성과 유사함을 보였다. 아이겐벡터중심성은 '사랑', '마음', '감사' 등의 단어가 높게 나타나 사용자들의 의견들에 가장 영향력이 높은 단어들임을 알 수 있다. 이는 YouTube의 트로트 가수 조명섭 동영상 시청자들 중 대다수가 동영상에 대해 사랑과 감사의 마음을 보이고 있음을 알 수 있다. 위의 세 가지 중심성 분석결과는 동영상을 시청하는 동기로 사용충족 이론의 쾌락적 충족과 사회적 충족 관련 단어들이 높은 값을 보이고 있다. 본 연구는 설문조사 기반의 구조방정식 모형을 따르지 않고, 질적분석연구를 자동화한 텍스트마이닝 기법을 사용하여 YouTube동영상을 사용하는 동기를 사용 및 충족 이론에 의해 밝혀냈다는 것에서 연구 함의를 찾을 수 있다.