• 소성∙가공
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• 제17권8호
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• pp.586-593
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• 2008

In warm press forming of magnesium alloy sheet, it is important to control the sheet temperature by heating the sheet in closed die. When forming a commercial AZ31 magnesium alloy sheets which are 0.5mm and 1.0mm thick, respectively, time arriving at target temperature and temperature variation in magnesium alloy sheet have been investigated. The deep drawing process with rectangular shape alone at the first stage and with both circular and rectangular shapes at the second stage was employed. At the first stage, through deep drawing process with rectangular shape alone according to various forming temperature($150{\sim}350^{\circ}C$) and velocity($0.1{\sim}1.0mm/s$), optimum forming condition was obtained. At the second stage, deep drawing process with the circular and rectangular shapes were performed following deep drawn square cups with Limited Drawing Height(LDH) obtained at the first stage. Here, clearance which is defined a gap between the die and the punch including sheet was set to ratio of 20, 40 and 100% to thickness in sheet. Accordingly, temperature, velocities, and clearances suitable for forming were suggested through investigating the thickness variation of the product.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.3667-3671
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• 2015

PCB(Printed circuit board) 장착을 주목적으로 하는 포밍공정에서 주름을 발생시키지 않으면서, 실험을 통하여 재료의 두께 변화를 고찰하였다. 실험결과 제 1공정의 포밍 높이는 제 2공정에서의 재료두께 변화에 크게 영향을 미치는 것으로 나타났으며, 제 1공정에서 다이의 입구 모서리는 제품높이 50%정도의 라운드를 가져야 하며, 포밍의 높이는 원래의 제품보다 재료의 두께만큼 높게 하여야 한다. 또한 제 1공정에서 포밍형상을 구현하면 재료의 두께가 85%로 얇아지고 제 2공정에서 리스트라이킹시 재료의 두께가 80%로 얇아진다. 그러므로 정확한 형상을 구현하기 위해서는 재료가 얇아지는 것을 고려하여 다이는 원제품의 형상을 유지하고 펀치는 원제품의 깊이에 재료 두께의 20%이상 더한 값만큼 길이를 길게 하여야 압축의 효과를 얻을 수 있다.

• 해양환경안전학회지
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• 제29권3호
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• pp.255-269
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• 2023

Surface water temperature of a bay (from the south to the north) increases in spring and summer, but decreases in autumn and winter. Due to shallow water depth, freshwater outflow, and weak current, the water temperature in the central to northern part of the bay is greatly affected by the land coast and air temperature, with large fluctuations. Water temperature variations are large in the north-east coast of the bay, but small in the south-west coast. The difference between water temperature and air temperature is greater in winter and in the south-central part of the bay than that in the north to the eastern coast of the bay where sea dykes are located. As the bay goes from south to north, the range of water temperature fluctuation and the phase show increases. When fresh water is released from the sea dike, the surrounding water temperature decreases and then rises, or rises and then falls. The first mode of empirical orthogonal function (EOF) represents seasonal variation of water temperature. The second mode represents the variability of water temperature gradient in east-west and north-south directions of the bay. In the first mode, the maximum and the minimum are shown in autumn and summer, respectively, consistent with seasonal distribution of surface water temperature variance. In the second mode, phases of the coast of Seosan~Boryeong and the east coast of Anmyeon Island are opposite to each other, bordering the center of the deep bay. Periodic fluctuation of the first mode time coefficient dominates in the one-day and half-day cycle. Its daily fluctuation pattern is similar to air temperature variation. Sea conditions and topographical characteristics excluding air temperature are factors contributing to the variation of the second mode time coefficient.

• 보건행정학회지
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• 제22권3호
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• pp.427-450
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• 2012

Objectives : This study examined the factors influencing variation by local areas of antibiotics prescription rate in upper respiratory infections (URI) according to the public reporting. Methods : We used the National Health Insurance Claims Data which the clinics claimed for URI (Korean Standard Classification of Disease, J00 ~ J06) in ambulatory care. The period of analysis was from the first quarter (from January to March) of 2005 to the first quarter of 2007. The number of samples was total 242 local areas that included all clinics (N = 7,942), which prescribed antibiotics for URI in ambulatory care. Results : None of the demographic and socioeconomic characteristic indicators was statistically significant. Among the provider factors, An increase in number of doctors and the average annual antibiotics prescription rate (from 2003 to 2004) for URI by local area were significantly related to an increase of antibiotics prescription rate according to the public reporting. And an increase in number of pediatric clinics, the proportion of clinics less than 5 years since has opened and the average annual fluctuation of antibiotics prescription rate (from 2003 to 2005) were significantly related to a decrease in antibiotics prescription rate by local area according to the disclosure of information. Conclusions : According to the public reporting, the antibiotics prescription rate in clinics had decreased sharply. However, the reduction of antibiotic prescription rate varied in different local areas. The factors influencing variation by local areas in antibiotics prescription rate can be used for establishing effective strategies to reduce variation by region in antibiotics prescription rate.

• 국토계획
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• 제54권2호
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• pp.54-66
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• 2019

This study analyzed whether a subway accessibility impact on house price is constant since its operation over time or not. The study was approached specifically to answer two research questions. One is "Are there significant temporal variations in the relationship between subway accessibility and housing price transacted after its opening?" The other one is "How the pattern of its temporal variation in housing price is formed as a function of the distance from the nearest station?" The study area is the subway station areas in the Daejeon metropolitan city, South Korea. Its first subway line has started to be opened in 2006 with 12 stations and then opened its additional 10 stations in 2007. It can be more appropriate to observe its impacts of subway accessibility on housing price because it has only one transit line with more than 10-year reaction term to its operation. The study employed alternative models to estimate yearly variation of subway accessibility on house price for the station areas with 500-meter and 1-kilometer radius respectively. While the study originally considered both a hedonic price model with interaction terms of its access distance to yearly transacted housing and a time-variant random coefficient model, the former model was finally selected because it is better fitted. Based on our analysis results, the reaction of house price to its transit line had significant temporal variation over time after opening. In addition, the pattern in its variation from our analysis results indicates that its capitalization impact on house price is over-estimated in its first several years after the opening. In addition, its positive capitalization impact is more effective in the 1000-meter station area than in the 500-meter one.

• 한국해양환경ㆍ에너지학회지
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• 제14권1호
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• pp.1-10
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• 2011

전남 서해 갯벌 연안경계부 수질특성을 파악하기 위하여 5개 해역(무안만, 탄도만, 함평만, 신안지도 및 영광해역)을 대상으로 2008년에서 2009년까지 2년 동안 한 달에 두 번씩 현장조사를 실시하였다. 수온은 $1.3{\sim}31.1^{\circ}C$로 연교차가 컸다. 염분은 비교적 32 내외로 균일하였으나 강우가 집중되는 시기에 염분 함량이 20 이하로 저염화가 나타났으며, 수온 변화에 따라 용존산소는 하계에 낮고 동계에 높았다. 수소이온농도는 용존산소와 비슷한 분포경향을 보였다. 부유물질의 경우 영광해역에서 100 mg/l 이상으로 높은 함량을 보였다. 화학적 산소요구량은 1 mg/l 내외로 큰 변화가 없었으며, 용존무기질소와 용존무기인은 담수유입이 증가하는 시기에 높은 함량을 보였다. 용존무기질소는 겨울과 초봄에 낮은 반면에 용존 무기인은 월별 변화 없이 균일한 분포를 보이다가 2009년 7월 이후 다소 증가하는 경향을 보였다. 엽록소a는 봄철에 $10\;{\mu}g/l$내외로 나타났으며 이후 대부분 비슷한 분포 경향을 보이나 특히 타 해역에 비하여 여름철에 영광해역에서 높게 나타났다. 해역별 수질특성을 비교하기 위하여 실시한 주성분분석 결과는 다음과 같이 뚜렷한 특징을 보였다. 무안만과 탄도만에서 제 1 주성분 요인은 담수유입 변동이었으며, 신안지도 해역과 영광해역에서는 수온의 변화로 나타났다. 함평만에서는 담수유입 변동과 수온변화의 영향이 제 1 주성분 요인으로 복합되어 나타났다.

• 한국통신학회논문지
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• 제35권12C호
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• pp.984-994
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• 2010

Pose variation is a critical problem in face recognition. Three-dimensional(3D) face recognition techniques have been proposed, as 3D data contains depth information that may allow problems of pose variation to be handled more effectively than with 2D face recognition methods. This paper proposes a pose-normalized 3D face modeling method that translates and rotates any pose angle to a frontal pose using a plane fitting method by Singular Value Decomposition(SVD). First, we reconstruct 3D face data with stereo vision method. Second, nose peak point is estimated by depth information and then the angle of pose is estimated by a facial plane fitting algorithm using four facial features. Next, using the estimated pose angle, the 3D face is translated and rotated to a frontal pose. To demonstrate the effectiveness of the proposed method, we designed 2D and 3D face recognition experiments. The experimental results show that the performance of the normalized 3D face recognition method is superior to that of an un-normalized 3D face recognition method for overcoming the problems of pose variation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.504-507
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• 1997

It is well known that Variable Structure Controller(VSC) is robust to parameters variation and disturbance but its performance depends on the design parameters such as switching gain and slope of sliding surface. This paper proposes a more robust VSC that is composed of local VSC's. Each local VSC considers the local system dynamics with narrow parameter variation and disturbance. First we optimize the local VSC's by use of Evolution Strategy, and next we use Artificial Neural Network to generalize the local VSC's and construct the overall VSC in order to cover the whole range of parameter variation and disturbance. Simulation on BLDC motor current control shows that the proposed VSC is superior to the conventional VSC.

• Structural Engineering and Mechanics
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• 제32권1호
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• pp.167-178
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• 2009

Initial imperfections, such as initial deflection or remaining stress, cause deterioration of buckling strength of structures. The Koiter imperfection sensitivity law has been extended to describe the mechanism of reduction for structures. The extension is twofold: (1) a number of imperfections are considered, and (2) the second order (minor) imperfections are implemented, in addition to the first order (major) imperfections considered in the Koiter law. Yet, in reality, the variation of external loads is dominant over that of imperfection. In this research, probabilistic evaluation of buckling loads against external loads subjected to probabilistic variation is conducted by extending the concept of imperfection sensitivity. A truss arch subjected to dead and live loads is considered as a numerical example. The mechanism of probabilistic variation of buckling strength of this arch is described by the proposed method, and its reliability is evaluated.

• The Korean Journal of Ecology
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• 제21권3호
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• pp.301-307
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• 1998

Intraspecific and interspecific isozyme variations and their relationship of 16 local populations in 3 species of Phyllostachys, that is, P. bambusoides, P. nigra var. henonis and P. pubescens were investigated by multi-variate analysis. Leaf isozymes of Phyllostachys such as 6-PGD (6-phosphogluconate dehydrogenase), MDH (malate dehydrogenase), PGI (phosphoglucoisomerase), PRX (peroxidase), PGM (phosphoglutamase), IDH (isocitrate dehydrogenase) showed electrophoretic variations in the number of zymotypes (7, 6, 6, 9, 3 and 5, respectively). In the cluster analysis on the isozymic characteristics, 16 populations were classified into 3 species at the euclid genetic distance of 2.041. P. nigra var. henonis and P. bambusoides were clustered first at 2.813 and then P. pubescens at 3.001. So far, 3 local types of intraspecific ariation were found in P. nigra var. henonis and P. bambusoides.