• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.149-149
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• 2018

Prediction on initial motion of sediment is crucial to evaluate sediment transport and channel stability. The condition of incipient movement of sediment is characterized by bed shear stress, which is generated from force of moving water against the bed of the channel, and by critical shear stress, which depends on force resisting motion of sediment due to the submerged weight of the grains. When the bed shear stress exceeds the critical shear stress, sediment particles begin rolling and sliding at isolated and random locations. In Mountain River, debris flow frequently occurs due to heavy rainfall and can lead some natural stones from mountain slope into the bed river. This phenomenon could add additional forces to sediment transport system in the bed of river and also affect or change direction and magnitude of sediment movement. In this paper, evaluations on incipient motion of uniform coarse gravel under falling spheres impacts using small scale flume channel were conducted. The drag force of falling spheres due to water flow and length movement of falling spheres were investigated. The experiments were carried out in flume channel made by glass wall and steel floor with 12 m long, 0.6 m wide, and 0.6 m deep. The bed slopes were selected with the range from 0.7% to 1.5%. The thickness of granular layer was at least 3 times of diameter of granular particle to meet grain placement condition. The sphere diameters were chosen to be 4cm, 6 cm, 8 cm, 10 cm. The spheres were fallen in to the bed channel for critical condition and under critical condition of motion particle. Based on the experimental results, the Shields curve of particles Reynold number and dimensionless critical shear stress were plotted. The relationship between with drag force and the length movement of spheres were plotted. The pathways of the bed material Under the impact of spheres falling were analyzed.

• 한국수소및신에너지학회논문집
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• 제17권1호
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• pp.39-46
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• 2006

Highly ordered Li dispersed nickel oxide nanotubes were prepared with anodic aluminum oxide (AAO) template for hydrogen storage. Electron microscope results showed that uniform length and diameter of nickel oxide nanotubes were obtained. The wall thickness and outer diameter of nickel oxide nanotubes are about 40 - 50 nm and 200 - 400 nm, respectively. It was observed that the diameter of nickel oxide nanotubes is bigger than the pore diameter of AAO template. Li dispersed nickel oxide were consisted of nanoflakes and had structures of nanotubes and nanorods. For increasing the hydrogen adsorption and desorption capacity, the Li dispersed nickel oxide nanotubes were fluorinated. The fluorinated Li dispersed nickel oxide nanotubes showed 1.65 wt% of the hydrogen adsorption capacities at 77 K under 47 atm.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1077-1084
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• 2002

Optimum tool design is carried out fur a multi-stage rectangular cup deep-drawing and ironing process with the large aspect ratio. Finite element simulation is carried out to investigate deformation mechanisms with the initial design made by an expert. The analysis considers the deep drawing process with ironing for the thickness control in the cup wall. The analysis reveals that the difference of the drawing ratio within the cross section and the irregular contact condition produce non-uniform metal flow to cause wrinkling and severe extension. For remedy, the modification guideline is proposed in the design of the tool and the process. Analysis results confirm that the modified tool design not only improves the quality of a deep-drawn product but also reduces the possibility of failure. The numerical result shows fair coincidence with the experimental one. After tryouts of the tool shape, the rectangular cup has been produced in the transfer press.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1478-1485
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• 2000

An experimental study has been performed to investigated the forced convection heat transfer characteristics of 6 circular cylinders in staggered arrangement in a cross flow of air. The water scale deposited on condenser wall of power plant was used to investigate the effect of roughness of scaled surfaces. The relative roughness*average diameter of scale/cylinder diameter) was in a range of k/d=0.0066, 0.0111, 0.0167, 0.0222 and 0.0278. The cylinder spacings(L/d) varies from 1.5 to 4.0 where L denote the cylinder spacings along and normal to the upstream uniform flow direction. The Reynolds number was varied in a range of 10, 000$\leq$ Re $\leq$ 50,000. The local and mean Nusselt numbers were investigated as a function of scale roughness, the cylinder spacing and Reynolds number. The results are compared with those of clean cylinder and inline tube bank, subsequently the mean fouling resistance over the entire circumference was estimated from those results as a function of scale roughness, the cylinder spacing and Reynolds number.

• 한국분말재료학회지
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• 제19권4호
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• pp.271-277
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• 2012

$SnO_2$ nanotubes were successfully synthesized using an electrospinning technique followed by calcination in air. The nanotubes were the single phase nature of $SnO_2$ and consisted of approximately 14 nm nanocrystals. SEM and TEM characterizations demonstrated that uniform hollow fibers with an average outer diameter of around 124 nm and wall thickness of around 25 nm were successfully obtained. As anode materials for lithium ion batteries, the $SnO_2$ nanotubes exhibited excellent cyclability and reversible capacity of $580mAhg^{-1}$ up to 25 cycles at $100mAg^{-1}$ as compared to $SnO_2$ nanoparticles with a capacity of ${\sim}200mAhg^{-1}$. Such excellent performance of the $SnO_2$ nanotube was related to the one-dimensional hollow structure which acted as a buffer zone during the volume contraction and expansion of Sn.

• 한국재료학회지
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• 제16권11호
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• pp.715-718
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• 2006

Porous hydroxyapatite (HAp) scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of MgO content in slurry on the pore morphology and size, density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 mm had open, relatively uniform, and interconnected porous structure regardless of MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds prepared by the sponge method were significantly affected by the addition of MgO.

• 한국전산구조공학회논문집
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• 제16권2호
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• pp.197-206
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• 2003

임의의 경계조건과 변두께를 갖는 축대칭 반구형 쉘과 반구형체의 진동수와 모우드형상을 결정하는 3차원적 해석법이 소개되었다. 수학적으로 2차원적인 전통적인 쉘이론과는 달리 본 연구의 해석법은 3차원 동적 탄성방정식을 사용하였다 자오선방향 (Φ), 법선방향(z), 원주방향(θ)으로의 변위성분인 μ/sub Φ/, μ/sub z/, μ/sub θ/는 시간에 대해서는 정현적으로, θ에 대해서는 주기적으로, 와 z 방향에 대해서는 대수다항식으로 표현될 수 있다. 축대칭 반구형 쉘의 변형률 에너지와 운동 에너지를 정식화하고, 리츠법으로 고유치문제를 계산하였다. 진동수의 최소화과정을 통해 엄밀해의 상위 경계치 진동수를 구하였으며, 이 때, 다항식의 차수를 증가시키면 진동수는 엄밀해에 수렴하게 된다. 자오선방향으로 선형적으로 꿩 두께가 변하는 반구형 쉘과 반구형체치 3차원적 진동수를 최초로 계산하였으며, 축방향으로 난 조그만 원추형 구멍이 진동수에 미치는 영향도 분석하였다. 상두께와 자유경계조건을 갖는 두꺼운 축대칭 반구형 쉘에 대한 3차원적 리츠해와 3차원적 유한요소법에 의한 진동수를 서로 비교하였다.

• 한국임상수의학회지
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• 제18권2호
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• pp.139-145
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• 2001

This study was undertaken to determine the normal serial ultrasonographic appearance of the postpartum uterine involution in small pet dogs (Yorkshire terrier and Maltese). Postpartum changes in uterine shape, architecture, echogenicity and diameter were monitored by ultrasonography in 12 small pet dogs. Serial ultrasonographic examinations were done daily during the first week, 3 days interval from 8 to 30 days, and weekly from 31 to 100 days postpartum. The excretory period of vaginal discharge in 12 normal bitches of uterine involution was finished completely within 3 weeks postpartum. The short axis shape of the uterus was initially often flaccid-appearing. It varied from circular to polygonal. This lasted until 15.75$\pm$3.84 days postpartum, during which time the short axis uterine shape gradually changed to circular. Also, the long axis shape of the uterus was a beaded appearance until 30.89$\pm$4.25 days postpartum. After 30 days, it was appeared as tubular shape between placental and interplacental sites. The ultrasonographic image of the postpartum uterus consisted of four echogenicity distinct layers. Uterine wall was represented as very hyperechoic serosa, hypoechoic myometrium, hyperechoic endometrium and anechoic structures of fluid in the uterine cavity until 7 days postpartum. The individual uterine layers were most prominent during the first week postpartum, and they became progressively less distinct throughout the course of uterine involution. The thickness of myometrium was decreased rapidly in the placental sites from 4.47$\pm$1.42 mm at 1 day to 1.92$\pm$0.26 mm at 16 day, and in the interplacental sites from 3.19$\pm$0.61 mm at 1 day to 1.39$\pm$0.61 mm at 16 day. And it was decreased slowly until 94 day and was been minimum thickness at 94 day. The thickness of endometrium was also decreased like that of myometrium. The uterine diameter in the placental sites was decreased from 22.28$\pm$3.01 mm at 1 day to 16.11$\pm$1.46 mm at 7 day, and in the interplacental sites was decreased from 13.65$\pm$2.34 mm at 1 day to 9.41$\pm$1.59 mm at 7 day postpartum. From 7 day to 93 day, the change of diameter was more and more slow. At 94 days postpartum, the uterine diameter was 5~6 mm both placental and interplacental sites, and the uterine horns were uniform hypoechoic, tubular structures without enlargement. Therefore, complete involution of the uterus occurred at 94 days. It was concluded that normal post partum uterine involution in small pet dogs appeared to be completed 94 days postpartum by gross findings such as vaginal discharges, and by ultrasonographic findings, uterine shape and echogenicity.

• Parasites, Hosts and Diseases
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• 제48권3호
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• pp.213-217
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• 2010

Sarcocystis sp. infection was investigated in 20 necropsied captive wild mammals and 20 birds in 2 petting zoos in Malaysia. The gross post-mortem lesions in mammals showed marbling of the liver with uniform congestion of the intestine, and for birds, there was atrophy of the sternal muscles with hemorrhage and edema of the lungs in 2 birds. Naked eye examination was used for detection of macroscopic sarcocysts, and muscle squash for microscopic type. Only microscopically visible cysts were detected in 8 animals and species identification was not possible. Histological examination of the sections of infected skeletal muscles showed more than 5 sarcocysts in each specimen. No leukocytic infiltration was seen in affected organs. The shape of the cysts was elongated or Circular, and the mean size reached $254{\times}24.5{\mu}m$ and the thickness of the wall up to $2.5{\mu}m$. Two stages were recognized in the cysts, the peripheral metrocytes and large numbers of crescent shaped merozoites. Out of 40 animals examined, 3 mammals and 5 birds were positive (20%). The infection rate was 15% and 25% in mammals and birds, respectively. Regarding the organs, the infection rate was 50% in the skeletal muscles followed by tongue and heart (37.5%), diaphragm (25%), and esophagus (12.5%). Further ultrastructural studies are required to identify the species of Sarcocystis that infect captive wild animals and their possible role in zoonosis.

• Tuberculosis and Respiratory Diseases
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• 제49권2호
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• pp.246-252
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• 2000

저자들은 양측성 신혈관근지방종, 경련, 지능저하 및 피지선종을 동반한 결절성 경화증으로 진단된 26세 여자 환자에서 객혈을 주증상으로 하여 흉부 X-선 및 고해상도 흉부전산화단층 촬영상 폐림프관평활근종증이 의심되었던 1예와 분만후 호흡곤란과 객혈을 주소로 내원한 30세 여자 환자에서 흉부 X-선 촬영, 고해상도 흉부전산화단층 촬영 및 폐생검을 통해 확진한 폐임파관 평활근종증 1예를 경험하였기에 문헌고찰과 함께 보고하는 바이다.