• 한국음향학회지
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• 제31권4호
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• pp.214-224
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• 2012

The objective of this paper is to design multichannel spherical loudspeaker array by considering various positioning methods such as Gaussian grid, Lebedev grid and packing method. For the spatial sound manipulation, which is to make desired sound field by controling multiple sound sources, the Kirchhoff-Helmholtz integral states that sound fields can be reproduced in terms of infinite control sources on the integral surface. But since we cannot control infinite number of sources for the implementation, we have to allocate finite number of sound sources which can approximately act as infinite number of sources. To manipulate sound field inside of a sphere (which is typical example of three dimensional array) by controlling sound sources on the surface, three methods of allocating sound sources, which are Gaussian grid, Lebedev grid and packing method, are reviewed. For each geometry, the performances of manipulation rendered by time-reversal operator and higher-order ambisonics are compared.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.381-382
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• 2002

The Fluid film between the valve plate and the cylinder block was measured by use of a gap sensor and the mercury-cell slip ring unit under real working conditions. During the operating periods, experiments with discharge pressure, revolution speed, and valve geometry was carried out for the fluid film on the valve plate. To investigate the effect of the valve shape, we designed two valve plates each having a different shape; the first valve plate was a plane valve plate. while the second valve plate was a spherical valve plate. It was noted that these two valve plates observed different aspects of the fluid film characteristics between the cylinder block and the valve plate. The leakage flow rate and the shan torque were also investigated in order to clarify the difference between these two types of valve plates. From the results of this study. we found that the spherical valve plate estimated good fluid film patterns and performance more than the other valve plate in oil hydraulic axial piston pumps.

• 한국국방경영분석학회지
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• 제3권1호
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• pp.83-96
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• 1977

The combustion chamber and nozzle of an end burning, small spherical rocket is designed. A spherical external shape has a number of advantages such as fixed center-of-gravity and minimum aerodynamic precession torques during flight and a better mass distribution for gyro-stabilization as contrasted to a conventional ogive rocket shape. It is shown that the cross-sectional variation of the end burning solid propellant with length is an exponential geometry to provide a constant thrust-weight ratio of the rocket device during the propellant burning period, and that the factors which affect the attainment of the constant relationship of thrust to weight in the design are the initial propellant area, initial weight of the rocket and propellant density. The measurement of the transient thrust in the ground static test using black powder propellant supports the predicted results. A wind tunnel having a $30{\times}30{\times}75cm$ test section and Mach number 0.11 is constructed, and a simple balance-type device is designed for the measurement of the drag of a spinning sphere. The experimental results indicate that the. spinning has no effect on the magnitude of the drag up to the Reynolds number $3{\times}10^5$. Numerical computation of the flight trajectories for various launching angles is presented, and the gyro-stabilization of spinning sphere is discussed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.33-37
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• 2009

Finite-element methods are used to study non-adhesive, frictionless rough contact of elastic and plastic solids. Roughness on spherical surfaces is realized by self-affine fractal. True contact area between the rough surfaces and flat rigid surfaces increases with power law under external normal loads. The power exponent is sensitive to surface roughness as well as the curvature of spherical geometry. Surface contact pressures are analyzed and compared for the elastic and plastic solids. Distributions of local contact pressure are shown dependent on the surface roughness and the yield stress of plastic solids.

• 한국산업융합학회 논문집
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• 제6권1호
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• pp.49-56
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• 2003

Based on the flow patterns of cylindrical vessel, the flow patterns of conical vessel, spherical vessel, rectangular vessel and cylindrical vessel with baffles were visualized by a trace method using aluminum powder. In addition, the correlations of the critical circulating frequency for mixing were derived from the experimental results. The conical and spherical vessels which have circular cross sections were same effective as cylindrical vessel for the shake mixing due to developing the rotational flow. Both a rectangular vessel and a cylindrical vessel with baffles should not be adapted for shake mixing because of not developing rotational flows in these type of vessels.

• Journal of Astronomy and Space Sciences
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• 제25권4호
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• pp.329-334
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• 2008

We investigate the spectral energy distributions (SEDs) of Massive Young Stellar Objects (MYSOs) using the various infrared observational data including the Infrared Space Observatory (ISO) data. We model the dust envelopes around the stars using a radiative transfer model for spherically symmetric geometry. Comparing the model results with the observed SEDs of the two MYSOs (AFGL 4176 and AFGL 2591), we derive the relevant dust shell parameters including the dust opacity, the dust density distribution, and dust temperature distribution. We find that the spherical model can produce the SEDs roughly similar to the observations. We expect that the results would be helpful for making more realistic non-spherical dust envelope models for MYSOs.

• 한국안광학회지
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• 제15권2호
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• pp.145-150
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• 2010

목적: 본 연구에서는 역기하렌즈(Reverse Geometry Lens;RGL)의 근시교정효과와 각막편심률 변화의 상관관계를 알아보고자 하였다. 방법: 3개월 이상 역기하렌즈를 지속적으로 착용한 학령기 아동 23명(46안) 중, 렌즈의 파라미터(parameter)가 다른 두 종류의 렌즈를 착용한 학령기 아동을 각각 Group I과 Group II로 나누고, 각각의 그룹에서 역기하렌즈의 착용 전, 착용 1주일, 착용 1개월, 착용 3개월 시점에서 각막정점으로 부터 $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ 범위의 편심률을 측정하였다. 역기하렌즈 교정 이후의 나안시력, 등가구면 굴절력, 각막 굴절력을 측정하여 각막의 편심률의 변화와의 상관관계를 조사하고 이에 대한 통계학적 유의성을 조사하였다. 결과: Group I과 Group II의 각막정점으로부터 $10^{\circ}$ 범위에서 착용 후 1주일에서 통계학적 유의성(p=0.03, t=-.2.29)이 있었으나, $20^{\circ}$, $30^{\circ}$ 범위에서는 통계학적 유의성이 없었다(p>0.05). 각막편심률의 변동에 대한 교정시력과의 상관관계는 Group II의 착용 후 1주일에서 비교적 크게 나타났다(r=-0.36, p=0.00, t=6.5). Group II의 착용 1주일에서 편심률과 각막곡률반경의 변화에 대한 상관관계는 r=-0.36, p=0.00, t=6.5이며, 편심률과 등가구면 굴절력의 변화에서는 r=-0.72, p=0.00, t=-.70.5로 높은 상관관계를 보였다. 결론: 각막편심률의 변화로 본 각막교정굴절효과는 착용 후 1주일에서 상관관계가 높았으며, 단기효과증진에 대한 원인을 규명하는 연구가 필요할 것으로 사료된다.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.409-414
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• 2010

This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the $2\pi$ ambiguity. The unwrapped phase map is converted to height and the 3D surface height of the surface object is reconstructed. The results extracted from the single shot off-axis geometry are compared with the results extracted from four-frame phase shifting in-line interferometry, and the results are in excellent agreement.

• 천문학회보
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• 제36권1호
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• pp.53.2-53.2
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• 2011

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles indicating the presence of a relativistic accretion disk model. Using a Monte Carlo technique, we compute the linear polarization of a double peaked broad emission line. A Keplerian accretion disk is adopted for the double peak emission line region and the Schwarzschild geometry is assumed in the emission region. Far from the accretion disk where flat Minkowski geometry is appropriate, we place a scattering region in the shape of a spherical shell sliced. We generate a line photon in the accretion disk in an arbitraray direction in the local rest frame and follow the geodesic of the photon until it hits the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the linear degree of polarization also shows a double peak structure. Under a favorable condition we show that up to 1% of linear degree of polarization may be obtained.

• 호남수학학술지
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• 제34권1호
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• pp.103-111
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• 2012

Wetzel[5] proved if ${\Gamma}$ is a closed curve of length L in $E^n$, then ${\Gamma}$ lies in some ball of radius [L/4]. In this paper, we generalize Wetzel's result to the non-Euclidean plane with much stronger version. That is to develop a lower bound of length of a triangle inscribed in a circle in non-Euclidean plane in terms of a chord of the circle.