• 한국전자파학회논문지
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• 제7권3호
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• pp.263-271
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• 1996

20GHz 이상 주파수대역은 아직까지 사용하고 있지 않는 넓은 대역의 전파자원이지만 대기에 의한 전파감쇠가 심해 중계거리에 제약을 받게 되므로 단거리통신에 사용되고 있다. 그러나 현재 국내에서는 20 GHz 이상의 주파수대역에서 어느정도의 거리에서 무선시스템의 선뢰도를보장할수있는지 연구된 적이 없는 실정이다. 본 논문은 20GHz 이상 대역에서 대가중의 전파특성을 분석하고 그 중 무선 경로 길이에 가장 많은 영향을 미치는 강우감쇠를 추정할 수 있는 계산식을 분석하였다. 그리고, 강우감쇠 계산에 가장 기본적인 요소인 강우강도를 국내 측후소에서 측정된 강우 자료를 이용하여 서울등 대 도시에서의 시간별 강우강도 데이터로 제시하고 이를 기 본 데이터로 하여 대도시에서의 무선 중계시스템의 최적 중계거리를 제시하였다.

• 한국분무공학회지
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• 제19권4호
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• pp.188-196
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• 2014

The spray and combustion characteristics of n-dodecane fuel were investigated in a CVCC (constant volume combustion chamber). The selection of ambient conditions for the spray followed ECN (engine combustion network) guidelines, which simulates the ambient condition of diesel engines at start of fuel injection. ECN is a collaboration network whose main objective is to establish an internet library of well-documented experiments that are appropriate for model validation and the advancement of scientific understanding of combustion at conditions specific to engines. Therefore repeatability of the experiments with high accuracy was important. The ambient temperature was varied from 750 to 930 K while the density was fixed at around $23kg/m^3$. The injection pressure of the fuel was varied from 500 to 1500 bar. The spray was injected in both non-reacting ($O_2$ concentration of 0%) and reacting conditions ($O_2$ concentration of 15%) to examine the spray and the combustion characteristics. Direct imaging with Mie Scattering was used to obtain the liquid penetration length. Shadowgraph was implemented to observe vapor length and lift-off length at non-reacting and reacting conditions, respectively. Pressure data was analyzed to determine the ignition delay with respect to the spray and ambient conditions.

• 한국항공우주학회지
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• 제39권9호
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• pp.871-876
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• 2011

본 논문에서는 작은 가로세로비를 가진 전통 방패연의 풍동실험 공력자료를 이용하여 평형 비행 성능을 분석하였다. 공력 및 압력 중심 위치로부터 전통 방패연의 정적 평형비행조건을 충족시키는데 필요한 목줄과 공수줄의 상대적 길이를 산출하였다. 연을 띄우기에 적합한 연실-지평각 ${\theta}=30^{\circ}{\sim}60^{\circ}$에서 고정된 목줄 길이 0.88c에 대해 공수줄의 길이는 ($0.88{\pm}0.02$)c 범위 내에 있었다. 이러한 전통 방패연의 평형 비행 성능 분석을 통해 얻은 목줄과 공수줄의 상대적 길이는 전통적 벌잇줄 매기법에 의한 길이와 정확히 일치하였다.

• 설비공학논문집
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• 제7권3호
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• pp.528-537
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• 1995

Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.

• Journal of the Optical Society of Korea
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• 제18권2호
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• pp.162-166
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• 2014

The impact of booster section length made from passive erbium-doped fiber (EDF) on the L-band multiwavelength Brillouin-Erbium fiber laser (MBEFL) is studied experimentally in this paper. The influence on the performance of MBEFL in term of number of generated Stokes lines, tuning range and lasing threshold were investigated. A comparison was made between MBEFL without a booster section and with booster sections of different lengths. Through comparative study and at fixed BP power and 100mW of 1480 pump power, longer passive EDF length of 5m exhibits the highest average number of Stokes lines of 23 with tuning range of 14nm. In contrast, shorter passive EDF length of 1m shows the highest tuning range of 17nm and an average number of 21 Stokes lines.

• 한국정보통신학회논문지
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• 제26권3호
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• pp.449-455
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• 2022

본 논문에서는 발광 다이오드(LED)의 조도를 기반으로 삼각측량법을 사용한 위치 계측 시스템을 제안한다. 세 개의 LED는 가상공간의 천장에 위치하고 각각의 고정 좌표는 모니터링 프로그램에 입력하여, 조도 값과 길이의 관계식을 통해 각각 LED로부터 조도 센서까지의 길이를 도출하였다. 도출된 길이를 바탕으로 삼각측량법을 사용해 가상공간의 물체 위치 정보를 검출하였다. 삼각측량법으로 도출된 길이의 오차를 최소화하기 위해 최소자승식을 이용하여 오차를 최대한으로 줄였다. 기존의 가시광통신(VLC)을 이용한 실내 위치 측정시스템과는 달리, 제안된 시스템은 송신기와 수신기 사이의 동기화가 필요치 않으므로 시스템을 간결하게 구성할 수 있다.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2020년도 춘계학술대회
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• pp.120-120
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• 2020

Based on the simple sequence repeat (SSR) marker, a Korean wheat core collection were established with 616 wheat accessions. Among them, the SNP genotyping for the entire genome was performed using DNA chip array to clarify the whole genome SNP profiles. Consequently, a total of 35,143 SNPs were found and we re-established a mini-core collection with 247 accessions. Population diversity and phylogenetic analysis revealed genetic diversity and relationships from the mini core set. In addition, genome-wide association study (GWAS) was performed on 19 phenotypic traits; ear type, awn length, culm length, ear length, awn color, seed coat color, culm color, ear color, loading, leaf length, leaf width, seeding stand, cold damage, weight, auricle, plant type, heading stage, maturation period, upright habit, and degree of flag leaf. The GWAS was performed using the fixed and random model circulating probability unification (FarmCPU), which identified 14 to 258 SNP loci related to 19 phenotypic traits. Our study indicates that this Korean wheat mini-core collection is a set of germplasm useful for basic and applied research with the aim of understanding and exploiting the genetic diversity of Korean wheat varieties.

• 보건의료산업학회지
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• 제11권3호
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• pp.51-64
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• 2017

Objectives : This study examined the effect of private health insurance on medical care utilization by subscription type. Methods : The data used were the six waves of the Korea Health Panel (2009-2014), and 16,187 persons were the subjects of the analysis. We performed a panel regression with a fixed effects model. Results : Indemnity private health insurance was positively related to the number of physician visits, number of admissions, and total length of stays. However, fixed-benefit private health insurance was not related to medical care utilization. Conclusions : The result of this study, which shows the difference by subscription type in the effect of private health insurance on medical care utilization, suggests that continuous monitoring of indemnity private health insurance is needed in the future.

• Tribology and Lubricants
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• 제22권5호
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• pp.252-259
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• 2006

Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performances, stiffness, damping coefficient and load capacity, depend on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1 mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권2호
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• pp.188-197
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• 2016

Offshore substructures have been developed to support structures against complex offshore environments. The load at offshore substructures is dominated by waves, and deformation of waves caused by interactions with the current is an important phenomena. Wave load simulation of fixed offshore substructures in waves with the presence of uniform current was carried out by numerical wave tank technique using the commercial software, FLUENT. The continuity and Navier-Stokes equations were applied as the governing equations for incompressible fluid motion, and numerical wavemaker was employed to reproduce offshore wave environment. Convergence test against grids number was carried out to investigate grid dependency and optimized conditions for numerical wave generation were derived including investigation of the damping effect against length of the damping domain. Numerical simulation of wave and current interactions with fixed offshore substructure was carried out by computational fluid dynamics, and comparison with other experiments and simulations results was conducted.