• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.218-219
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• 2000

공동광자감쇠 분광학(Cavity Ringdown Spectroscopy, CRDS)은 고감도의 흡수분광법으로 미량기체의 농도나 흡수분광선의 연구에 사용되어 왔으며 화염이나 플라스마에도 응용되고 있다. 이 분광법은 시간에 따라 지수함수로 감쇠하는 공동광자감쇠신호의 감쇠상수를 측정하는 기술인데, 레이저의 밴드폭이 흡수선폭보다 넓으면 감쇠신호가 지수함수에서 벗어나 오차를 발생하게 된다. 그러므로 오차를 줄이려면 좁은선폭의 레이저를 사용하거나 공동광자감쇠신호의 주파수를 분리하여야 한다. 분광선폭보다 매우 넓은 선폭의 레이저를 사용하고 분광기를 이용하여 공동광자감쇠신호를 분리하는 방법들이 제안되었다. (중략)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.629-640
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• 2007

In this paper an analytical study is carried out to improve the capacity of absorbing boundary using dashpot, one of the most widely used absorbing boundaries in FEM. Using 2-D harmonic plane wave equation, absorbing boundary condition is modified to maximize its capacity according to the incident angle. Validity of the absorbing boundary conditions which is modified is investigated by adopting the solution of Miller and Pursey. The Miller and Pursey's problem is then numerically simulated using the finite element method. The absorption ratios are calculated by comparing the displacements at the absorbing boundary to those at the free field without the absorbing boundary. The numerical study is carried out through comparison of displacement at the interior region and the boundary of the numerical model.

• Journal of the Korean Society of Radiology
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• v.16 no.1
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• pp.61-66
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• 2022

The purpose of this study is to derive photon energy fluence and mass energy absorption coefficient for 1 Gy of absorbed dose of water in brachytherapy using an Ir¹⁹² source. From the radiotherapy physics written by Khan, the half-value of lead for the gamma ray beam of the Ir¹⁹² source was obtained. The linear attenuation coefficient and the mass attenuation coefficient were calculated from the obtained half-value layer of lead. By matching the calculated lead mass attenuation coefficient with the NIST mass attenuation coefficient data, the photon energy of the matching mass attenuation coefficient was determined as the effective energy. By matching the determined effective energy with the photon energy of the NIST data on the mass energy absorption coefficient of water, the mass energy absorption coefficient of water was obtained as 0.03273 cm²/g(32.73 cm²/kg). The photon energy fluence was calculated as 0.03055 J/cm² by dividing the obtained mass energy absorption coefficient (32.73 cm²/kg) by the absorbed dose of water 1 Gy.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.9-15
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• 2005

A linear acoustic analysis is performed to explore the characteristics of acoustic damping by a gas-liquid scheme coaxial injector in a liquid rocket engine. The injector can play a role of acoustic resonator. Acoustic-damping characteristics of half-wave resonator are compared with those of quarter-wave resonator. Various effects of the boundary absorption coefficient, injector length and sound speed in combustion chamber and resonator are investigated. As a result, short tuning length of resonator and low sound speed of the medium have a favorable effect on acoustic damping. As the boundary absorption coefficient decreases, the tuning range of the resonator length becomes narrower.

• Journal of Navigation and Port Research
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• v.26 no.1
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• pp.101-105
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• 2002

Many malfunction take place in container crane spreader due to impact. So we designed a 2 DOF hydraulic impact absorbing equipment to absorb the impact and we studied the change of damping coefficient with respect to the variation of dimensions of oil-Cylinder wail. When we design the dimension of hydraulic cylinder wall considering the displacement on the wall, the value of it over 20m didn't affect the damping coefficient.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.49-54
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• 1991

In this study the correlation between material constants and microwave absorbing characteristics of ferroxplana composite microwave absorber used in X-band was investigated. The real part of permeability(${\mu}_{r}'$) was decreased and the imaginary part of permeability(${\mu}_{r}"$) of ferroxplana composite was increased with increaing ferroxplana loading ratio(F/R). The frequency showing maximum attenuation was shifted to lower frequency with increasing absorber thickness. The absorber 2.6 mm thick showed good band width property and 3.2 mm thick showed good attenuation property. From the apphcation of ferroxplana composite's material constants to the region of material constants which satisfy broad band width, it is found that the absorbing characteristics were estimated quantitatively. Estabhshment of material constants' region which satisfies broad band width can make practical application to design of high performance ferrite microwave absorber.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.93-99
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• 2003

In this study, new shock absorbing system is proposed by using nano-technology based on the theoretical analysis. The new shock absorbing system is complementary to the hydraulic damper, having a cylinder-piston-orifice construction. Particularly for new shock absorbing system, the hydraulic oil is replaced by a colloidal suspension, which is composed of a porous matrix and a lyophobic fluid. The matrix of the suspension is consisted of porous micro-grains with a special architecture: they present nano-pores serially connected to micro-cavities. Until now, only experimentally qualitative studies of new shock absorbing system have been performed, but the mechanism of energy dissipation has not been clarified. This paper presents a modeling and theoretical analysis of the new shock absorbing system thermodynamics, nono-flows and energy dissipation. Compared with hydraulic system, the new shock absorbing system behaves more efficiently, which absorb a large amount of mechanical energy, without heating. The theoretical computations agree reasonably well with the experimental results. As a result. the proposed new shock absorbing system was proved to be an effective one, which can replace with the conventional one.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.942-946
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• 1995

Using database obtained by means of experiments, or using the synamic behaviour analysis program of automotive shock absorber, database system is constructed within the limits of adequate reliability. Thus constructed data base can be used to find out corresponding specification of shock absorber design parameters to the required damping ability and tolerance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.227-231
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• 1995

This paper describes a basic programming and interfacing modele which can link DataBase form experiments and dynamic analysis program of chock absorber within the limit of adequate reliability. The system developed can provid a user specific Database of shock absorber within the required damping performance and endurable tolerance, thus show a good application possibilities in commercial vehicle design.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1991.07a
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• pp.11-17
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• 1991

현재 사용중인 대부분의 항만부진동 예측을 위한 수치모형은 Lee(1969), Chen and Mei(1974)의 경우와 같이 Helmholtz 방정식을 사용하고 있으나 여기에는 경계면에서의 에너지 흡수 및 해저면 마찰에 의한 에너지 감쇠가 제외되었다. 그러나, 항내 파랑응답 문제에서는 경계면에서의 흡수와 해저면 마찰에 의한 에너지 감쇠가 중요한 역할을 하는 것으로 보고되고 있다(Ganaba et al., 1982).(중략)