• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.477-483
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• 2016

Velocity profiles of laminar, transition and turbulent boundary layers were investigated by using Particle Image Velocimetry(PIV) measurements on the flat plate at Mach 2.96. The Schlieren visualization and PIV measurements are also used to confirm whether the oblique shock wave generated from the leading edge affects the flow field over the flat plate. The laminar velocity profile measured from the experiment was well matched with the compressible Blasius solution. The velocity profile of the transition boundary layer was well correlated with the theoretical turbulent velocity profile from near the wall and the transition began from Re = $1.41{\times}106$. For the turbulent boundary layer, considering compressibility effects, the Van Driest-transformed velocity satisfies the incompressible log-law. It is found that the log region is extended farther in the wall-normal direction compared to the log region in incompressible boundary layer.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2020.08a
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• pp.3-3
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• 2020

최근 지구온난화로 인한 기후변화로 인해 지리적 분포가 한정적인 한반도 구과식물들은 점점 서식지 내 생육에 위협을 받고 있다. 이러한 구과식물의 지속이용가능한 보전을 위해서는 각 종별 형질 특성 및 분포, 생육정보 등의 기초정보 구축이 필요할 것이다. 구과식물(Pinidae, Conifers)은 전 세계적으로 나자식물(Gymnosperms)의 3/5정도인 630여분류군이 분포하는 것으로 알려져 있다(Farjon, 2008). 은행나무나 소철나무류 등 다른 나자식물과 비교하여 여러 복잡한 구조로 이루어진 구과(웅성, 자성 구과)를 형성하고, 잎은 대부분 바늘형으로 단순하며, 상록성인 특징 등으로 구분된다. 우리나라에 분포 및 식재되고 있는 나자식물 중 은행나무와 소철나무를 제외한 모든 나자식물이 구과식물에 속한다. 구과식물이 전 세계적으로 넓은 분포역을 갖지만, 종별로는 제한적인 분포를 갖는 것들이 많이 나타난다. 우리나라에 자생하는 구과식물 대부분도 동북아시아에만 분포하는 종들이 대다수이다. 한반도 구과식물은 총 5과 12속 23종 5변종 총 28분류군으로 확인되었다. 소나무과는 5속 12분류군으로 구상나무와 분비나무의 형태적 중복형질이 확인되었으며, 측백나무과는 3속 9분류군으로 눈향나무를 변종에서 종 수준으로 적용하였고, 어청도에서 해변노간주의 분포를 확인하였다. 개비자나무과는 1속 3분류군으로 수형에 따라 큰개비자나무, 눈개비자나무, 개비자나무로 구분하였다. 주목과는 비자나무속을 포함하여 2속 3분류군으로 설악눈주목에 대한 세부적인 분류학적 재검토가 필요할 것으로 판단한다. 나한송과는 1속 1분류군으로 신안군 가거도에서 나한송의 자생지를 확인하였다. 구상나무와 분비나무의 형태적 구분형질이 모호함에 따라 집단별 유전정보 분석을 통한 계통지리학적 연구를 수행하였다. 분석을 통해 구상나무는 빙하기에 북부지역의 조상종이 남하하여 분화되고, 후빙기에 중부지역까지 분포확장이 이루어진 것으로 판단된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.837-847
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• 2020

A velocity profile for flapping flight is optimized to increase the power efficiency of 20g weighted flapping wing micro air vehicle in hover. The experimental optimization of flapping velocity profile is carried out with a real sized flapper, and various velocity profiles are realized by non-circular gear. Kriging with noise is adopted as a meta model of the profile optimization to reflect the data noise by uncertainty. The optimization results confirm that the flapping efficiency (thrust-to-power ratio) is substantially improved (11.3%) through the elastic deformation that carries the angular kinetic energy from previous stroke.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.4
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• pp.135-141
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• 1993

고속으로 변형을 받는 재료의 변형 강도는 정적인 부하를 받는 경우와는 다르며 이 고속 현상을 해석하기 위해서는 시간적, 공간적 변화를 조사할 필요가 있다. 일반적으로 스트레인 속도를 구하는 데는 스트레인 게이지를 이용하고 있지만, 고무와 같은 대변형을 하는 물체에서는 정확한 데이터를 얻기가 곤란 하므로 스플라인 함수를 이용해서 보간 작업을 해야 한다. 그래서, 최근에는 스트레인 속도를 구하는 방법 으로 격자법, 모아레법, 광탄성법 등이 이용되고 있다. 재료의 변위 분포를 구하는 데는 격자법이 잘 이용 되어지고 있지만 스트레인 속도 분포의 해석의 정도에 문제가 되고 있다. 이러한 문제를 해결하기 위하여 본 논문에서는, 고속으로 변형하는 물체의 형상을 역학적으로 해석하기 위해 고속도 카메라로 촬영을 하고 그 때 얻어진 격자 화상을 퓨리에 변환 격자법을 이용해서 위상을 구하고 스트레인 속도 분포를 해석했다.

• Journal of Korean Society of Transportation
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• v.24 no.4 s.90
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• pp.43-53
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• 2006

Pedestrian countdown signals were newly introduced to make Pedestrians feel more comfortable and safer in crossing the streets This Paper analysed pedestrian walking-speed through a before-after behavior study Data was collected from 22 sites. and the total number of pedestrians was 19,800. The results showed that the average Pedestrian walking-speed of existing pedestrian signal, an inverted triangle countdown signal and a numeric countdown signal were 1.44, 1.39 and 1.42m/sec. The difference between the three methods was statistically significant. The results showed that the distribution of the walking-speed of existing signal. an inverted triangle countdown signal and a numeric countdown signal were statistically Erlang(0.117, 10) distribution. Weibull(1.17, 3.72) distribution and Gamma(0.137, 8.18) distribution at 95% confidence level.

• Journal of the Korean Geographical Society
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• v.30 no.1
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• pp.1-13
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• 1995

One of the oldest fossil of conifers and taxads in the Korean peninsula includes Elatocladus, Ullmannia, Walchia and dates back to the Permian period of the Palaeozoic era. The only conifer which successfully survived since the Cretaceous period is Pinus and still thrives in Korea. The extinction of Miocene conifers, such as Sciadopitys, Taxodiaceae, Metasequoia and Cryptomeria may due to the climatic deteriorations during the late Pleistocene period. However, the cryophilous conifers and taxads, e.g..Pinus, Juniperus, Abies, Picea, Cupressaceae, Larix and Taxus continued to exist from the Miocene to the late Pleistocene and became major vegetational elements in the mountainous areas of Korea. As the temperature ameliorates in the late Holocene period, thermophilous Pinus (Diploxylon) gradually had increased in numbers and became a dominant vegetation in the lowland and montane areas since 2,000 years B.P. in korea. Out of various Korean conifers and taxads, Pinus which surviving since the Cretaceous period of Mesozoic era, ranges spatially from southern coastal area to northern alpine belt of the Korean peninsula. Pinus which contains largest species number in conifers is one of the most well-adapted genus to the Korean environment. The next important conifer Juniperus dates back to the Miocene period of Cenozoic era and continuously maintains speciation and expansion of distributional range. Other major conifers and taxads of Korea include Picea, Abies, Lorix and Taxus. The restriction of distributional range of Cephralotaxus and Tsuga may due to the climatic deterioration during the Pleistocene period of Cenozoic era. The patterns of the temporal and spatial distribution of Korean conifers and taxads may provide invaluable informations for the better understanding of present-day distributional range and ecology.

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.17-24
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• 2014

This paper determines 1D shear wave velocity (Vs) distribution of rockfill zone of CFRD using Vs profile determined by the surface wave test. There exists uncertainty in the field test result because of a spatial variation of material property. The harmonic wavelet transform is used to evaluate the uncertainty of test result and generate random 1D Vs distributions which may exist in the rock fill zone. Through the statistical analysis of generated random Vs distributions, the representative 1D Vs distribution considering the uncertainty of test results is proposed for the rockfill zone of CFRD in Korea.

• Korean Journal of Plant Taxonomy
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• v.39 no.1
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• pp.35-41
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• 2009

Astilbe (Saxifragaceae) is a genus well known for its disjunctive distribution in Asia and eastern North America. In this study, we reconstructed a molecular phylogeny of the genus using the sequences of ITS regions of nuclear ribosomal DNA. A total of 17 species representing major lineage of Astilbe and closely related taxa were included in the phylogenetic analyses. We obtained a Bayesian phylogenetic tree in which Saxifragopsis was positioned as a sister group to Astilbe. The Japanese endemic species, A.platyphylla was the most basal lineage within the genus. This species is well known for its distinct morphological features such as unisexual flowers, apetaly, and calyx with 7-11 lobes. Two species, A. biternata, a New World representative of the genus, and A. rivularis widely distributed in S. Asia, branched off early in the evolution of Astilbe. The remaining species formed a strongly supported core clade, which diverged into two robust geographical lineages: the first ("Japonica" clade) of species distributed in Japan, Taiwan, and Philippines and the other ("Rubra" clade), of taxa in China and Korea. The ITS phylogeny indicates that the Bering land bridges were the major route for the origin and dispersal of A. biternata. The two Taiwanese taxa and A. philippinensis were found to derive from the Japanese member, as the genus advanced southwards. The ITS phylogeny suggests that apetaly originated independently at least two times within the genus. Our results do not support Engler's classification system of the genus based on the leaf type (simple vs. compound), but reaffirm Hara's taxonomic idea which primarily considered the features of calyx.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2D
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• pp.251-258
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• 2006

This study is to develop an estimation method of freeway design capacity through the analysis of time headway distribution in continuum flow. Traffic flow-speed diagram and time headway distribution plotted from individual vehicle data shows: a) a road capacity is not deterministic but stochastic, b) time headway distribution for each vehicle speed group follows pearson type V distribution. The freeway design capacity estimation model is developed by determining a minimum time headway for capacity with stochastic method. The estimated capacity values for each design speed are lower when design speed ${\leq}80km/h$, and higher when design speed ${\geq}106km/h$ in comparison with HCM(2000)'s values. In addition, The distinguish difference is that this model leads flexible application in planning level by defining the capacity as stochastic distribution. In detail, this model could prevent a disutility to add a lane for only one excess demand in a road planning level.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.11a
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• pp.1092-1095
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• 2013

오늘날 모바일 스마트 기기의 발전은 위치기반의 새로운 기술을 이끌었다. 현재 위치 데이터를 사용하는 많은 응용프로그램들이 소개되었고, 또한 널리 사용되고 있다. 하지만 아직 이러한 위치 데이터들은 환경적인 요소 등으로 인해 오류가 많다. 우리는 이전 연구에서 위치 데이터의 오류 검출 및 교정 알고리즘을 제안하였다. 또 다른 연구에선 인간의 이동속도가 어떠한 확률분포모델을 따르는지 연구하였다. 그리하여 본 논문에서는 인간의 이동속도의 분포로서 적합하다고 판명된 확률분포모델 중 Lognormal 분포, Gamma 분포, Weibull분포를 선택하여 위치데이터 오류 검출 및 교정 알고리즘에 적용하기 위한 확률분포 계산을 제안한다. 그 중 일부는 계산의 복잡도를 낮추기 위해 확률분포표를 제공할 것이다.