• 한국전자통신학회논문지
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• 제15권1호
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• pp.153-160
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• 2020

Brazil Alagoas 주의 동부 지역에서 우적 크기를 측정하는 디즈드로미터(disdrometer)로 산출한 강우량과 강우율의 관계로 우적의 역학 에너지가 예측되었다. 강우의 시작과 끝에서 측정되는 약한 강우 강도에서는 지수 형태의 방정식이 큰 우적의 영향을 억제하였다. 빗방울의 역학 에너지는 거의 모든 강우 강도 범위에서 과소평가 되었다. 결정 계수, 평균 절대 오차, 상대 오차 비율, 평균 절대 오차, 평균 제곱 오차, Willmott의 일치 지수 및 신뢰 지수와 같은 성과 지표에 기반을 두어 예측된 강우 역학 에너지가 유용한 결과로 평가되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.71-76
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• 1994

Recently, constructions of huge reinforced concrete structures such as nuclear power stations have been increased. When massive concrete is placed, cracking due to the hydration heat of cement is recognized as a major problem. The development of thermal stress is influenced by the structure shape and the constraint conditions, and cracks usually occure from tensile stresses which developed due to temperature drop. In this study a protocol specimen is made to examine the distribution of temperature and thermal stress of reaction wall of Daewoo Institute Construction Technology. The size of the specimen is made by considering minimum size of real structure. In this study, concrete strain gauge, concrete stress gauge, concrete non-stress gauge, and thermocouples, are instrumented to measure thermal stress in massive concrete structure. A new measuring technique is proposed to calculate thermal stress.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1451-1457
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• 2002

When an aqueous liquid such as water having high electric conductivity and high surface tension is discharged from a nozzle under a strong DC electric field, fine drops ranging from 30 to 450 microns can be obtained only through the spindle mode. In the present study, effects of the electric conductivity and the surface wettability of nozzle materials on formation of drops with this mode were investigated. For that, three nozzles with the same size but with different materials were prepared and tested; a stainless steel needle, and a plain and a metal (gold)-coated (except for the tip portion) silica needles. Uniform drops were obtained with the gold-coated silica nozzle over the wider range of the DC voltage input. That is, formation of the liquid cone and detachment of the liquid spindle (ligament) can be more stabilized and frequent with the needles having high electric conductivity but with low surface wettability at their tips.

• Journal of Mechanical Science and Technology
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• 제14권4호
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• pp.466-476
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• 2000

This paper presents atomization characteristics of a double impinging F -0-0- F type injector with four streams. A phase Doppler particle analyzer was employed to measure the droplet-size and water was used as the inert simulant liquid instead of reactive propellant liquids. The droplet mean diameter (SMD) and size distribution were measured to investigate the effects of the momentum ratio and pressure drop variations. This experimental results can be used during the preliminary design stage of a impinging stream type injector for liquid rockets.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.925-930
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• 2000

This paper is investigated the entrainment of air into sprays which has significant effects on the combustion efficiency, stability of flame using the air-assisted twin-fluid nozzle in non-burning. The factors which may be expected to affect the entrainment of air by a liquid spray are: Relative velocity of droplet and ambient gas; Drop size and size distribution; Density and other property of the liquid. Here, axial, radial velocity and turbulent kinetic energy of spray droplet was measured with the PIV(Particle Image Velocimetry). Spray characteristics were also visualized using CCD camera. The results indicate that the entrainment rate increases more or less non-linearly with the downstream region.

• 한국분무공학회지
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• 제11권3호
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• pp.131-139
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• 2006

An experimental study was performed to investigate the liquid breakup and atomization characteristics in electrohydrodynamic atomization according to the changing of experimental parameters such as nozzle size, fluid flow, and electrical intensity. An original electrohydrodynamic atomizer equipment was designed and manufactured for the analysis of spray visualization and the exploration of relationship between applied power and the behavior of liquid atomization. The image processing technique by using the back-illumination method was applied to visualize the distilled liquid breakup process and to examine the variation of the droplet size distribution. The results show that the spray modes of electrohydrodynamic atomization are closelyconnected by the strength of the electric stresses at the surface of the liquid film and the kinetic energy of the liquid jet leaving the needle tip.

• 전기의세계
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• 제24권5호
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• pp.107-110
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• 1975

This paper describes computational algorithms and a computer program for optimum determinations of wire conductor sizes of radial or tree-type distibution lones with given constraints. Here, The objective function is defined as the total summation of the volume or weight of respective conductor materials required for buildingup the entire distributing system. Four categories of constraints are applied to the obiective function. That is, on the respective load points constraint is imposed by a specified voltage drop limit, and the respective line elements are capable of carrying the current safely(safety current) and also must maintain the minimum thickness in viewpoint of mechanical strength and legal requirements. And finally, the conductor sizes have to be selected among the standardized size levels of the products. These kinds of optimization problems cannot be solved by the ordinary optimization tediniques such as the Linear Programming Method, SUMT Technique, etc. This paper, therefore, successfully devised the powerful alorithms to solve the problem, using the particular properties or characteristics ingerent to the radial or tree-type distribution system. The computer program developed from the algorithms was applied to several sample systems and shown to be exact and very efficient.

• 대기
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• 제20권4호
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• pp.519-530
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• 2010

In this paper we review current research on Atmospheric Brown Clouds (ABCs) with lightweight Unmanned Aerial Vehicles (UAVs) and miniaturized instruments. The UAV technology for in-situ measurements, including aerosol concentration, aerosol size distribution, aerosol absorption, cloud drop size distribution, solar radiation fluxes (visible and broadband), and spectral radiative fluxes, is a leading-edge technology for cost-effective atmospheric sounding, which can fill the gap between the ground measurement and satellite observation. The first experimental observation with UAVs in Korea, Cheju ABC Plume Monsoon Experiment (CAPMEX), conducted during summer 2008 revealed that the Beijing plumes exerted a strong positive influence on the net warming and fossil-fuel-dominated black-carbon plumes were approximately 100% more efficient warming agents than biomass-burning-dominated plumes. Long-term sustainable routine UAV measurements will eventually provide truly three-dimensional data of ABCs, which is necessary for the better understanding of their climate impacts and for the improvement of numerical models for air pollution, weather forecast and climate change.

• 산경연구논집
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• 제9권1호
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• pp.9-23
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• 2018

Purpose - The purpose of this paper is to investigate the potential benefits or detriments of team management on fund performance in the mutual fund market. An additional purpose of this study is to examine the optimal number of managers in a fund industry for superior performance. Research design, data, and methodology - This paper investigates the effect of managerial structure on fund performance in the Korean active mutual fund market between 2001 and 2008. For this, we analyze two risk-adjusted performances measures- the capital asset pricing model (CAPM) and the three-factor model of Fama & French (1993). Results - First, we found that single-managed funds exhibited superior performance. Second major finding was that as the number of managers in a fund increases, the fund performance deteriorates. Finally, the results reveal that the sharpest performance drop occurs when team size increases from a 5-person team to a 6-person team. Conclusions - The results suggest that the management structure can be a source of competitive advantage for fund performance. As considering fund performance is the outcome of managers' decision-making, this study contributes to not only the financial literature but also the literature in other areas, such as management and general business.

• 동국한의학연구소논문집
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• 제7권2호
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• pp.97-105
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• 1999

본 연구는 긴볼레기말 추출물의 항고지혈증 효과를 조사하기 위해 ICR 생쥐에 Triton WR-1339(TX) 복강주사로 인위적인 고지혈증을 유발시킨 후 긴볼레기말 추출물(30mg/kg)를 복강주사하여 시간의 경과에 따른 간세포내에서의 지방 축적 변화를 조직화학적으로 관찰하였다. TX 주사후 그물구조의 세포질을 가진 간세포가 간엽 전체에서 관찰되었고, 일부 간소엽에서는 간세포 손상으로 인한 간세포판 소실이 나타났다. 또한 간세포내 지방축적도 증가하여 전체 간소엽의 간세포에서 지방의 과출현을 확인 할 수 있었고, 지방의 크기도 대조군에 비해 증가된 것으로 관찰되었다. 그러나 긴볼레기말 추출물 주사군에서는 그물구조의 세포질을 가진 간세포의 수가 TX 주사군에 비해 감소되었고, 대부분의 간소엽에서 정상적인 간세포판의 배열을 확인할 수 있었다. 간세포내의 지방 축적과 크기도 감소된 경향으로 관찰되었다. 이상의 결과로 볼 때 해조류 긴볼레기말 추출물은 고지혈증이 유발된 생쥐 간세포 내에서의 과도한 지방축적을 감소시키는 항고지혈증 효과을 하는 것으로 사료된다.