• 한국통신학회논문지
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• 제39C권11호
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• pp.1209-1215
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• 2014

기하학적 균일 회절 이론(UTD)은 특정 주파수에서 장애물에 의해 전파가 불연속적인 특성을 가질 때, 전자기학적으로 접근하여 회절 계수와 반사 계수 등을 계산하여 전파를 분석하는 기법이다. 본 논문에서는 실내 무선 채널 환경에서 사용자가 단말기 주변에 있을 때, 사용자에 의한 쉐도잉(Shadowing) 효과를 기하학적 UTD을 통하여 분석하였다. 사용자가 통화를 하고 있는 상황(Head Model)과 가슴 앞쪽에 단말기를 위치하여 사용하는 상황(Chest Model)으로 나누고, 각각에 대하여 복사 모델(Radiation Model)과 산란 모델(Scattering Model)에 적용하여 비교 및 분석하였다.

• Tribology and Lubricants
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• 제2권2호
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• pp.27-31
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• 1986

By Bong Goo Rhee, College of Engineering, The Univ. of Won Kwang (344-2, Sinyongdong, Iri-shi, 510 Chunpuk-do, Korea), Yoshitsugu Kimura and Kazumi Okada, Institute of Interdisciplinary Research, Faculty of Engineering, The Univ. of Tokyo(4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan), Katsuyuki Hashizume, Taiho Kogyo(2-47 Hosoya-Cho, Toyoda-Shi 471, Japan) and Chang Heon Chi, The G. S of Chon buk N. Unv. It is empirically known that, in concentrated conjunctions lubricated with O/W emulsions, only the oil is entrained to form elastohydrodynamic films. In the present work, this phenomenon is studied experimentally and the result is compared with a theory Which employes a starved lubrication concept. The experiment is conducted in a four roller machine with 0/W emulsions of varying concentration of oil, i.e. beef tallow, in which the film thickness is determined by detecting the rate of X-ray transmission through the conjunction. Excellent agreement is found between the experimental and the theoretical results.

• The Journal of Korean Physical Therapy
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• 제13권2호
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• pp.257-264
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• 2001

To take the Far-infrared(FIR) ray which is a optimized wavewlength and strength, at first, it is to be induced the characteristic algorithm and the computerized programing of FlR radiating materials. In this study, we induced that the formular of optimized FIR with physical, mathematical logic and theory, especially, Plank, Kirchhoff, Wien, Stefan-Boltzmann's logic and law. In the long run the formular was induced with mathematical integration. since we had to know the molecular wavelength. Base on the induced formular as above, we programmed the optimized FlR radiating computerized program, it would be useful to design semiconductor( VLSI) as the FlR instrument center control system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1307-1311
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• 2007

Three-dimensional transient keyhole profile is numerically analyzed for the case of stationary laser keyhole welding. Volume of fluid (VOF) method is adopted to track the free surface of molten metal based on the three governing equations which are continuity, momentum and energy equations. Multiple reflections of laser beam at the keyhole walls are also included in analysis through a real-time ray tracing technique. In this simulation, especially, polarization of laser is considered as an energy absorption mechanism following the Fresnel reflection theory. Both cases of linearly and circularly polarized beam are simulated and compared. The results show that the theoretically generated keyhole is asymmetrically stretched along the direction of polarization which is already observed experimentally before.

• 수산해양기술연구
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• 제32권4호
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• pp.395-401
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• 1996

In this paper, the propagation characteristics due to the horizontal water temperature variations in the sea such as thermal fronts is analyzed by the ray theory. Two models for the temperature anomaly layer are chosen. One is a plane type and the other is a cylindrical type. In the plane type, the temperature increases linearly from a isothermal region to 5km with the gradient of about $2^{\circ}C.$/km, and decreases with the same gradient in next 5km. In the cylindrical type, water temperature increases only with the same gradient from a half cylindrical thermal boundary surface. The result showed that the gradient of acoustic rays decreases in the temperature increasing region and vice versa in temperature decreasing region. And, the transmission loss due to the temperature variation was less than O.2dB in the plane type model as well as in the cylindrical one.

• 대한방사선기술학회지:방사선기술과학
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• 제21권2호
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• pp.57-63
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• 1998

AEC was designed to assist in the production of radiographs of equal density and to aid in the production f consistently high quality radiographs. Many improvements have been made in the AEC and these have helped to increase it's acceptance. Newer system (Falling load) control kVp and mA as well as exposure time. Authors have had experiments about the characteristics of AEC by Zone System. Zone System is the method to detection of photographic image qualify by control the photo print from Fred Archer and Ansel Adams. With the Zone System theory the experiments of density control, characteristics of phantom thickness and reproducibility of occupation rate of contrast media could make quality control of X-ray photography effectively in falling load system.

• Structural Engineering and Mechanics
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• 제52권1호
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• pp.137-147
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• 2014

The present paper deals with the first ply failure analysis of the laminated composite plates under various static and dynamic loading conditions. Static analysis has been carried out under patch load and triangular load. The dynamic failure analysis has been carried out under triangular pulse load. The formulation has been carried out using the finite element method and a computer code has been developed. The first order shear deformation theory has been applied in the present formulation. The displacement time history analysis of laminated composite plate has been carried out and the results are compared with those published in literature to validate the formulation. The first ply failure load for laminated composite plates with various lamination schemes under static and dynamic loading conditions has been calculated using various failure criteria. The failure index-time history analysis has also been carried out and presented in this paper.

• 전자공학회논문지B
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• 제31B권5호
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• pp.26-33
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• 1994

Phase retrieval is concerned with the reconstruction of a signal from its Fourier transform magnitude (or intensity), which arises in many areas such as X-ray crystallography, optics, astronomy, or digital signal processing. In such areas, the Fourier transform phase of the desired signal is lost while measuring Fourier transform magnitude (F.T.M.). However, if a reference 'signal is added to the desired signal, then, in the Fourier trans form magnitude of the added signal, the Fourier transform phase of the desired signal is encoded. This paper addresses uniqueness and retrieval of the encoded Fourier phase of a multidimensional signal from the Fourier transform magnitude of the added signal along with the Fourier transform magnitude of the desired signal and the information of the additive reference signal. In Part I, several conditions under which the desired signal can be uniquely specified from the two Fourier transform magnitudes and the additive reference signal are presented. In Part II, the development of non-iterative algorithms and an iterative algorithm that may be used to reconstruct the desired signal(s) is considered.

• Journal of the Optical Society of Korea
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• 제4권2호
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• pp.79-85
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• 2000

The main purpose of this paper is to present the potential of photovoltaic systems using holographic solar concentrators. A hologram used here focuses light, spectrally splits it and diverts unwanted infrared heat away from the solar cell. The output of the hologram appears as a perpendicular thin spectral line and is displaced to solar cells on both sides. To obtain optimum design conditions we used the coupled wave theory and the vector ray tracing method. The measured data showed that the diffraction efficiency was 75 ％ and the spectral bandwidth was 350 nm.

• 한국생산제조학회지
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• 제24권1호
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• pp.15-22
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• 2015

In the present paper we report the results of a study into Friction Stir Welds (FSWs) made in 13 mm-thick 12%-Cr steel plates. Based on residual strains obtained by diffraction techniques, eigenstrain analysis was performed using the Eigenstrain Reconstruction Method (ERM), which is a novel methodology for the reconstruction of full-field residual strain and stress distributions within engineering components. Significant eigenstrain distributions were found at around Thermo-Mechanically Affected Zone (TMAZ) where the most severe plastic deformation was occurred. Microstructure analysis was used to elucidate this phenomenon showing that the grain structure in TMAZ was bent and not successfully recrystallised, resulting in severe deformation behaviour. The reconstructed residual strain distributions by the ERM agree well with the experimental results. It was found that the approach based on theory of eigenstrain is a powerful basis for reconstructing the full-field residual strain/stress distributions in engineering components and structures.