• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.11-16
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• 2002

In this paper, we present two successful results from active controls of flows over a circular cylinder and a sphere for drag reduction. The Reynolds number range considered for the flow over a circular cylinder is 40-3900 based on the free-stream velocity and cylinder diameter, whereas for the flow over a sphere it is $10^{5}$ based on the free-stream velocity and sphere diameter. The successful active control methods are a distributed (spatially periodic) forcing and a high-frequency (time periodic) forcing. With these control methods, the mean drag and lift fluctuations decrease and vortical structures are significantly modified. For example, the time-periodic forcing at a high frequency (larger than 20 times the vortex shedding frequency) produces $50{\%}$ drag reduction for the flow over a sphere at $Re=10^{5}$. The distributed forcing applied to the flow over a circular cylinder results in a significant drag reduction at all the Reynolds numbers investigated.

• 한국산림과학회지
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• 제96권5호
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• pp.572-579
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• 2007

Tree species diversity is an important aspect of forest ecosystem stability. Tree species inventories at defined sites and in minimum diameter classes give a reliable indicator of the diversity level as well as the structural stability level of a study site. This study was conducted to investigate the species composition and the stand structure of the natural forest, timber-harvested forest (logged-over forest) and degraded forest of the Oak-twin Township in the Bago Yoma Region of Myanmar. Natural forest showed the highest family and species richness in all the investigated forests. At the family level, Verbenaceae occupied the highest importance value index (IVI) in all the forest stands while teak (Tectona grandis Linn. f.) occupied the highest IVI at the species level. However, the small diameter classes of T. grandis and other commercial species were less than those of big diameter classes in all the investigated forests. This abnormal pattern of diameter distribution could be a problem for the sustainable production of commercial timber species in the near future.

• 한국자원식물학회지
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• 제10권3호
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• pp.271-273
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• 1997

This study was carried out to obtain basic envirinmental information of the native area and growth characteristics at different age of Dendropanax morbifera LEV. In the southern Korea. The Dendropanax morbifera LEV. Was grown naturally at Wando, Cheju(Mt. Halla), Yecheon(Kermoon island),Sinan(Hong isand), Jindo(Mt. Chermchill) and Haenam(Mt. Taeroon), all between 30 to 450m above the sea level. The soil characterisitics of the native area had a pH of 5.3 to 5.4 with 8.4 to 9.8% content of organic matter and 18.2 to 21.3% soil moisture. Flowering starting in the middle of July begun when the trees were 6 years old. Six year old trees are 129 cm in stem height, 34 mm in stem diameter,15.4 in number of leaves with petioles 12.9 cm long. Xylem sap can be obtained from over 10 year old trees that grew well and have over 10 cm stems in diameter.

• 대한치과기공학회지
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• 제26권1호
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• pp.69-76
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• 2004

The objective of this finite element method study was to analyze the stress distribution induced on a supporting bone by 3.75mm, 4.0mm, 5.0mm diameter of dental implant fixture(13mm length). 3-dimensional finite element models of simplified gold alloy crown(7mm height) and dental implant structures(gold cylinder screw, gold cylinder, abutment screw, abutment, fixture and supporting bone(cortical bone, cancellous bone) designs were subjected to a simulated biting force of 100 N which was forced over occlusal plane of gold alloy crown vertically. Maximum von Mises stresses(MPa) under vertical loading were 9.693(3.75mm diameter of fixture), 8.885(4.0mm diameter of fixture), 6.301(5.0mm diameter of fixture) and the highest von Mises stresses of all models were concentrated in the surrounding crestal cortical bone. The wide diameter implant was the good choice for minimizing cortical bone-fixture interface stress.

• 대한치과기공학회지
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• 제6권1호
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• pp.19-26
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• 1984

This Experimental study was performed to study the effect of the heat soaking and the diameter of pattern on the casting ability of three nonprecious alloys manufactured for porcelain-metal restorations, with respect to their ability to reproduce test pieces by casting over a selected range of uniform diameters. Samples of total 60 were constructed and divided into 6 groups according to the two variables, the diameter and the heat soaking. The completed cast samples were examined visually and measured with a caliper calibrated to 0.05mm. The results obtained were as follows: 1. Length cast was significantly related to the diameter to be cast, especially in the case of the marrowest diameter of 230m. 2. Length cast not significantly related to the heat soaking. 3. The completeness of casting was significantly related to the diameter to be cast, particularly in the case of the narrowest diameter of 230m. 4. The completeness of casting was not significantly related to the heat soaking. 5. All of the three nonprecious alloys used for this experiment were significantly different from an ideal alloy in the completeness of casting.

• 대한핵의학회지
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• 제28권3호
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• pp.350-356
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• 1994

Purpose : Hepatic arterial perfusion scintigraphy with Tc-99m-macroggregated albumin (HAPS) study was carried out in 16 patients with hepatocellular carcinoma(HCC) and in six patients without liver tumor to evaluate HAPS findings of hepatocellular carcinoma and usefullness of HAPS. Materials and Methods : HAPS with planar and SPECT study were performed in 22 patients after conventional hepatic or celiac arteriography. For HAPS study, 4-5 mCi of MAA mixed with 2ml of saline was injected into proper hepatic artery or its distal branches at the rate of approximately 1ml/sec. We analysed 21 HCCs over 2cm in diameter(average diameter; 6.4cm) and 17 of 21 HCCs were over 4cm in diameter(Table 1). CT, sonography and angiography were performed within two week in all 16 patients and liver scan was performed in 12 patients. Results : Three different pattern of tumor perfusion were observed in 16 patients with HCC (Table 2). 1) diffuse increased perfusion in 16 of 21(76%)(Fig. 1) 2) increased peripheral perfusion in 4 of 21(19%) (Fig. 2) 3) diffuse decreased perfusion in 1 of 21 (5%) Arteriovenous shunt indicated by lung uptake of MAA were observed in 9 of 16(56%)(Fig. 4). In contrast, angiography demonstrates arteriovenous shunt in 2 of 16(13%). There was no accumulation of radioactivity on RBC-blood pool scan in all six patients with HCC examined (Fig. 1). Conclusion : HAPS is useful study in evaluation of perfusion pattern or vascularity of HCC and in detection of arteriovenous shunt.

• 임산에너지
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• 제20권1호
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• pp.62-72
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• 2001

목재의 알칼리 팽윤특성을ㄹ 해명하기 위해 국내산 주요 침·활엽수 4수종의 주요 구성요소의 알칼리 팽윤 거동을 횡단면 절편을 이용하여 조사하였다. 그 결과, 일본잎갈나무의 가도관 직경은 잣나무보다 크게 팽윤하였으며, 가도관의 벽두께는 10% 이상의 알칼리 수용액에 처리시 높은 팽윤율을 나타냈다. 알칼리 처리에 의해 도관의 직경은 방사방향으로 수축하였고, 접선방향으로 다소 팽윤하였다. 목섬유의 세코벽두께는 5%의 알칼리처리에서도 수분팽윤에 비해 3배 이상의 높은 팽윤성을 나타앴고, 알칼리 처리후 일본잎갈나무의 가도관 직경, 목섬유 직경 및 세포벽두께는 거의 등방적인 수축현상을 보여주었다. 또한 미처리 시료에 비해 머서화 처리 구성요소의 세포직경은 수축되었고, 세포벽은 팽윤되었다. 알칼리처리 과정에서 셀룰로오스 결정형의 변화는 없었지만 상대결정화도와 미결정의 폭이 다소 증가되었다. 결론적으로 알칼리의 농도, 수종, 세포의 종류가 목재의 알칼리 팽윤 특성에 크게 관여하는 것으로 생각되었다.

• 보험의학회지
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• 제9권
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• pp.122-129
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• 1990

Authors analyzed sonographic findings of 59 cases of hepatic hemangioma, with had been diagnosed through examination in our Medical. dept, from Januray, 1985 to December 1989. The results of the analysis are as follows: 1) The hepatic hemangioma was found in 59 cases(0.33%) among the 17,714 insureds. 2) In all 59 cases who have hemangioma, hemangioma was found in 37 cases(0.35%) among the 10,724 insureds of male, and in 22 cases(0.31%) among the 6,990 insureds of female. 3) The possessing rate of hemangioma in male was increased by age regardless of sex-5/2,120 cases(0.24%) in $21{\sim}30$ years, 25/8,122 cases(0.31%) in $31{\sim}40$ years, 16/4,997 cases(0.32%) in $41{\sim}50$ years, 8/1,775 cases(0.45%) in $51{\sim}60$ years, and 5/359 cases(1.39%) in over 61 years. 4) The tumor involved right lobe of the liver in majority(71.4%) 5) The size of tumor was 10 lesions in under 10 mm, 58 lesions in $31{\sim}50$ mm, and 6 lesions in over 51 mm. The smallest tumor was 8 mm in diameter and the largest was 72 mm in diameter and 78 lesion(92.8%) were less than 50 mm in size. 6) Posterior acoustic enhancement was noted in 4 lesions among 68 lesions of less than 30 mm in long diameter, and in 4 lesions among 16 lesions more than 30 mm in long diameter. 7) Echographically most of the lesions presented as a round or oval high homogeneous echogenic mass, although a few mass appeared to be hypoechoic or Mixed echogenic. Finally a small round echogenic, sharply-marginated and internally homogeneous lesion is highly suggestive of hemangioma. If the hypoechoic lesion has homogeneous internal echoes and/or strong marginal echoes, it is also suggestive of hemangioma.

• 한국광학회지
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• 제18권4호
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• pp.256-263
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• 2007

SELFOC 소재를 사용하여 높은 수치구경을 가지는 광픽업용 대물렌즈를 설계하였다. SELFOC 소재는 radial gradient-index 분포를 가지며, 이것은 설계에 추가적인 자유도를 제공하므로, 비구면이 아닌 구면만으로 높은 수치구경의 대물렌즈의 설계가 가능하다. 이 연구에서는 quadratic constant와 광축의 굴절률, 광축 두께, 입사동 직경을 변화시키며 rms 스폿 직경 변화를 조사하였으며, Code V를 사용하여 대물렌즈의 최적화와 결상특성을 평가하였다. 이 분석에서는 quadratic constant와 광축의 굴절률이 클수록, 렌즈가 두꺼워질수록, 입사동 직경은 작을수록 더 좋은 특성을 보임을 알 수 있었다. 이 결과를 바탕으로 2매의 구면 SELFOC 렌즈로 구성된 높은 NA의 DVR용 대물렌즈를 설계하였으며, 2가지 형태의 해 Solution I, II가 존재하였다 Solution I은 두 매 모두 양의 굴절능을 가지며 compact한 광학계를 구성하지만, 비축 수차 보정이 Solution II에 비해 부족하였다. Solution II는 음-양의 굴절능으로 조합된 광학계로 비축 수차가 비교적 잘 보정되었지만, 광학계의 전장길이가 길고 렌즈의 직경이 커지는 문제점이 있었다.

• 한국정보과학회논문지:시스템및이론
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• 제30권5_6호
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• pp.319-323
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• 2003

이차원 평면에 주어진 n개의 점 집합 P에 대한, 최소 신장 트리(minimum spanning tree, MST)는 P의 점들을 연결한 신장 트리 중에서 에지 길이의 총합이 최소가 되는 트리로 정의된다. P에 대한 신장 트리의 지름(diameter)은 트리의 두 점을 연결한 트리 경로 중에서 최장 경로의 길이로 정의되며, 최소 지름 신장 트리(minimum-diameter spanning tree, MDST)는 P에 대한 신장 트리 중에서 지름이 가장 작은 트리를 의미한다. 현재까지 알려진 가장 좋은 알고리즘[3]은 MDST를 O(n$^3$) 시간에 구한다. 본 논문에서는 MDST의 지름보다 최대 5/4배 이내의 지름을 보장하는 신장 트리를 구하는 $O(n^2)$ 시간 근사 알고리즘(approximation algorithm)을 제시한다. 이것은 MDST 문제에 관한 첫 번째 근사 알고리즘이다.