• Bulletin of the Korean Chemical Society
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• 제16권2호
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• pp.126-129
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• 1995

Linear and nonlinear optical properties of CuCl nanocrystals in silica glass have been studied using low temperature absorption, degenerate four wave mixing (DFWM), and time-resolved photoluminescence spectroscopy. Assuming a spherical shape, effective radius of the CuCl quantum dots was estimated to be 2.5 nm, which is obtained from low temperature absorption data. The DFWM experiment was performed in 380-386 nm wavelength region, and the diffracted signal was measured as a function of wavelength with 1.0 nm interval. Time-resolved photoluminescence measurement was also carried out at 77 K to obtain the time response of CuCl nanocrystals. The experimental results on the large third order nonlinear optical of CuCl quantum dots are explained in terms of crystal size and oscillator strength of quantum spheres.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.136-146
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• 2021

This paper aims to numerically estimate the dynamic ice load on a conical structure. The Discrete Element Method (DEM) is employed to model the level ice as the assembly of numerous spherical particles. To mimic the realistic fracture mechanism of ice, the parallel bonding method is introduced. Cases with four different ice drifting velocities are considered in time domain. For validation, the statistics of time-varying ice forces and their frequencies obtained by numerical simulations are extensively compared against the physical model-test results. Ice properties are directly adopted from the targeted experimental test set up. The additional parameters for DEM simulations are systematically determined by a numerical three-point bending test. The findings reveal that the numerical simulation estimates the dynamic ice force in a reasonably acceptable range and its results agree well with experimental data.

• 대한설비공학회지:설비저널
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• 제7권3호
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• pp.151-159
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• 1978

A heat transfer model for the case of simultaneous vibration of both the heated surface and its surrounding medium is constructed and the dimensional analysis is applied to this model in order to and the governing dimensionless Parameters in which the vibration effects the heat transfer. In the second Part of this study, an experimental investigation of the effect of vibration on natural convective heal transfer from spheres has been performed for the case of the external oscillatory motion being imposed on the heated surface which is immersed in an otherwise undisturbed air, The ranges of the experimental variables were: temperature difference 10 to $120^{\circ}C$; vibration frequency 10 to 120Hz; displacement amplitude 1.3 to 12.5mm. Three different diameter aluminum were used as the experimental models. Improvements in heat transfer due to vibration were observed, with the maximum increase being 330 Percent. A dimensionless correlation describing the measured heat transfer data is given.

• 천문학회보
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• 제45권1호
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• pp.69.4-70
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• 2020

Raman-scattered He II features are known to be present in several young planetary nebulae (PNe) including NGC 7027, NGC 6302, IC 5117 and NGC 6790. These features provide a new spectroscopic window to probe both thick neutral regions and far UV regions near Lyman series. We carry out photoionization model calculations using 'CLOUDY' to explore He II emission strengths dependent on the physical conditions of the central star. The emission nebula is treated as a simple spherical shell with uniform density. It is found that detectable Raman-scattered He II are obtained for T∗ ~ 105 K in the presence of a thick neutral component. We present mock spectra exhibiting Raman He II features based on the photoionization calculations and compare them with observed data. We discuss effective strategies for searching young PNe with Raman-scattered He II emissivities.

• 제어로봇시스템학회논문지
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• 제22권8호
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• pp.597-602
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• 2016

In image guided surgery, a patient registration process is a critical process for the successful operation, which is required to use pre-operative images such as CT and MRI during operation. Though several patient registration methods have been studied, we concentrate on one method that utilizes 3D surface measurement data in this paper. First, a hand-held 3D surface measurement device measures the surface of the patient, and secondly this data is matched with CT or MRI data using optimization algorithms. However, generally used ICP algorithm is very slow without a proper initial location and also suffers from local minimum problem. Usually, this problem is solved by manually providing the proper initial location before performing ICP. But, it has a disadvantage that an experience user has to perform the method and also takes a long time. In this paper, we propose a method that can accurately find the proper initial location automatically. The proposed method finds the proper initial location for ICP by converting 3D data to 2D curvature images and performing image matching. Curvature features are robust to the rotation, translation, and even some deformation. Also, the proposed method is faster than traditional methods because it performs 2D image matching instead of 3D point cloud matching.

• 천문학회보
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• 제40권1호
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• pp.65.2-65.2
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• 2015

We developed a three-dimensional magnetohydrodynamic (MHD) code to reproduce the structure of a solar wind, the properties of a coronal mass ejection (CME) and the interaction between them. This MHD code is based on the finite volume method incorporating total variation diminishing (TVD) scheme with an unstructured grid system. In particular, this grid system can avoid the singularity at the north and south poles and relax tight CFL conditions around the poles, both of which would arise in a spherical coordinate system (Tanaka 1994). In this model, we first apply an MHD tomographic method (Hayashi et al. 2003) to interplanetary scintillation (IPS) observational data and derive a solar wind from the physical values obtained at 50 solar radii away from the Sun. By comparing the properties of this solar wind to observational data obtained near the Earth orbit, we confirmed that our model captures the velocity, temperature and density profiles of a solar wind near the Earth orbit. We then insert a spheromak-type CME (Kataoka et al. 2009) into the solar wind to reproduce an actual CME event. This has been done by introducing a time-dependent boundary condition to the inner boundary of our simulation domain. On the basis of a comparison between a simulated CME and observations near the Earth, we discuss the physics involved in an ICME interacting with a solar wind.

• 한국안광학회지
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• 제10권2호
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• pp.133-138
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• 2005

비구면렌즈는 구면렌즈계의 단점을 보완하여 결상 성능을 향상시키며, 렌즈의 사용매수를 경감시키고 이로 인하여 광학계의 무게와 부피를 줄이는 소형경량화를 목적으로 하여 사용되고 있다. 비구면 광학소자의 생산기술과 측정기술은 현대의 첨단기술로 부각되고 있다. 비구면으로 구성된 원광학계는 넓은 시야와 고성능, 양질의 상을 얻을 수 있고, 또한 소형, 경량화 시킬 수 있는 등 많은 장점을 가지고 있다. 이러한 비구면 소자의 급증하는 필요성에 부응하여 비구면 가공 기술과 측정 기술에 대하여 연구하고자 한다. 비구면 생산 기술과 측정 및 평가 기술은 끊임없이 발전하고 있음을 밝혀둔다.

• Korean Chemical Engineering Research
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• 제46권3호
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• pp.604-609
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• 2008

본 연구에서는 세계보건기구의 기준을 만족시키기 위한 포장재 개발을 목적으로 백신 수송용 장방형 포장재 내부열 전달에 대한 모델링 및 시뮬레이션을 수행하고 이를 실험결과와 비교하였다. 장방형의 박스를 구형 박스로 전환하여 구상한 1차원 모델은 냉각공정의 경우에는 실험 결과와 비교적 잘 일치하는 결과를 보였으나, 가열공정에서는 실험결과와 상당한 차이를 보여주었다. 이는 가열공정을 계산할 때, 포장재 외부에서의 경계조건을 적절히 고려해주지 못한 결과로 사료된다. 그러나, 본 연구를 통하여 상전이 물질을 함유한 다층 벽을 통한 열 전달의 문제를 전산 모사할 수 있는 기본적인 알고리즘을 성공적으로 개발할 수 있었다.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제23권1호
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• pp.1-11
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• 1995

Thermospheric neutral winds and temperatures have been collected from the ground-based Fabry-Perot interferometer (FPI) at Thule Air Base ($76.5^{\circ}N{\;}69.0^{\circ}W$), Greenland since 1985. The thermospheric observations are obtained by determining the Doppler characteristics f the [OI] 6300 ${\AA}$ emissions of atomic oxygen. The FPI operates routinely during the winter season, with a limitation in the observation by the existence of clouds. For this study, data acquired from 1985 to 1991 were analyzed. The neutral wind measurements from these long-term measurements are used to investigate the influence of solar cycle variation on the high-latitude thermospheric dynamics. These data provide experimental results of the geomagnetic polar cap are also compared with the predictions of two semiempirical models : the vector spherical harmonics (VSH) model of Killeen et al. (1987) and the horizontal wind model (HWM) of Hedin et al. (1991). The experimental results show a good positive correlation between solar activity and thermospheric wind speed over the geomagnetic polar cap. The calculated correlation coefficient indicates that an increase of 100 in F10.7 index corresponds to an increase in wind speed of about 100 m/s. The model predictions reveal similar trends of wind speed variation as a function of solar activity, with the VSH and HWM models tending to overestimate and underestimate the wind speed, respectively.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1802-1812
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• 2001

The purpose of this study is to analyze numerically the movement of particles included in turbulent fluid flow characteristics of metallic surfaces. To describe fluid flew, the incompressible Navier-Stokes equation discretized by the finite volume method were solved on the non-orthogonal coordinates with non-staggered variable arrangement, and the k-$\xi$ turbulence model was adapted. After fluid flow was calculated, particle movement was predicted from the Lagrangian approaches. Non-essential complexities were avoided by assuming that the particles had spherical shapes and the Stoke's drag formula only consisted of external farces acting upon them. In order to validate the numerical calculations, the results were compared with the experimental data reported in literature and agreed well with them. The drag force coefficient equation showed better agreement with the experimental data in the prediction of particle movement than the correction factor equation. Impact velocity and impact angle increased as inlet turbulence intensity decreased, relative jet height was lower. or the Reynolds number was larger.