• Journal of Forest and Environmental Science
• /
• 제30권2호
• /
• pp.226-232
• /
• 2014

To understand transition characteristics from wood to charcoal the dimensional changes of carbonized woods at low temperature from $300^{\circ}C$ to $350^{\circ}C$ at the intervals of $10^{\circ}C$ were investigated. Three species of hardwoods and two species of softwoods were used in this study. Measurements of dimensional changes of cells were observed by stereoscopic microscope and an image analyzer. The apparent volume of each specimen decreased greatly with increasing temperature. Severe cracks and collapse were observed frequently in hardwoods and hardly in softwoods. Vessel diameter and tracheid cell wall thickness of the wood samples were decreased with increasing carbonization temperature. Contraction of vessel diameter in tangential direction was greater than that in radial direction. Cell wall thickness of tracheids decreased with increasing carbonization temperature. Consequently, even though it was small range of carbonization temperature, dimensions of wood components were changed considerably.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.545-550
• /
• 2004

KSTAR cryostat is a 8.8 m diameter vacuum vessel that provides the necessary thermal barrier between the ambient temperature test cell and the supercritical helium cooled superconducting magnet providing the base pressure of 1 ${\times}$ $10^{-3}Pa$. The cryostat is a single walled vessel consisting of central cylindrical section and two end closures, a flat base structure with external reinforcements and a dome-shaped lid structure. The base structure has 8 equally spaced support legs anchored on the concrete base. The cryostat vessel design was executed to satisfy the performance and operation requirements. The major loads considered in the structural analysis were vacuum pressure, dead weight, electromagnetic load driven by plasma disruption, and seismic load. Based on the fabrication and inspection procedures for the vessel, cryostat vessel was fabricated and inspected. It was confirmed that the inspection results were acceptable.

• Nuclear Engineering and Technology
• /
• 제55권1호
• /
• pp.180-189
• /
• 2023

We measured the heat load to a reactor vessel with and without the in-vessel debris bed under an IVR-ERVC condition. Mass transfer methodology was adopted based on heat and mass transfer analogy to achieve high Ra'_H of order ~10¹⁵ with compact test rigs. We postulated the in-vessel debris bed has a flat top and particulate debris was simulated as an identical diameter spheres. We conducted experiments varying the height of the debris bed and the results showed that Nusselt numbers decreased in both uppermost and curved surfaces with the increasing bed height. Once the debris bed is formed, it acts as an obstacle to the natural convective flow, which reduces the buoyancy. The reduction of driving force results in the impaired heat transfer in both upward and downward heat transfers.

• Journal of Chest Surgery
• /
• 제37권3호
• /
• pp.220-227
• /
• 2004

관상동맥 질환과 말초혈관 질환의 증가에 따라 직경 6 mm 이하의 소구경 혈관의 필요성이 증가하고 있다. 저자들은 조직공학적 방법을 이용하여 소구경 인공혈관을 제작하여 생체 실험을 시행하였다. 동종 판막을 얻어 이를 탈세포화시킨 후 피실험동물의 골수를 채취하여 탈세포화시킨 혈관용 지지체(scaffold) 위에 이식하였다. 이와 같이 하여 제작된 인공 혈관을 잡견의 양측 경동맥에 이식한 후 혈관이 막히거나, 8주가 되었을 때 이를 제거하여 조직학적 검사를 시행하였다. 자가 세포를 이식하지 않고 지지체만을 이식하였던 대조군 4마리 중 3마리의 혈관은 2주 이내에 모두 막힌 것을 확인하였고 나머지 한 마리의 혈관은 혈관류(aneurysm)가 발생하였다. 그러나 자가 세포를 이식한 실험군 4마리 중 2마리는 각각 4주와 6주까지 혈관의 개통성을 유지하였고, 나머지 2마리는 8주까지 혈관의 개통성을 유지하였다. 조직학적 검사 결과, 8주까지 개통성을 유지하였던 혈관은 정상의 혈관과 거의 유사한 조직학적 구조를 나타내었다. 자가 세포와 탈세포화된 지지체를 이용하여 제작한 인공혈관은 조직학적 검사 결과 정상과 유사한 구조로 재생이 가능함을 보여주었다.

• Macromolecular Research
• /
• 제16권4호
• /
• pp.345-352
• /
• 2008

Poly(lactic-co-glycolic acid) (PLGA) tubes (5 mm in diameter) were fabricated using an electro spinning method and used as a scaffold for artificial blood vessels through the hybridization of smooth muscle cells (SMCs) and endothelial cells (ECs) differentiated from canine bone marrow under previously reported conditions. The potential clinical applications of these artificial blood vessels were investigated using a canine model. From the results, the tubular-type PLGA scaffolds for artificial blood vessels showed good mechanical strength, and the dual-layered blood vessels showed acceptable hybridization behavior with ECs and SMCs. The artificial blood vessels were implanted and substituted for an artery in an adult dog over a 3-week period. The hybridized blood vessels showed neointimal formation with good patency. However, the control vessel (unhybridized vessel) was occluded during the early stages of implantation. These results suggest a shortcut for the development of small diameter, tubular-type, nanofiber blood vessels using a biodegradable material (PLGA).

• 펄프종이기술
• /
• 제42권1호
• /
• pp.7-12
• /
• 2010

Morphological characteristics of hemp fiber were investigated using a light microscope in order to provide fundamental data for the use of hemp as a papermaking law material. Phloem of hemp is composed of cortical parenchyma cells and bast fiber with thick walls while xylem is composed of vessel, wood fiber and ray parenchyma cells. Also there are solitary pore and radial pore multiple which exist in diffuse porous pattern. Ray cells consist of uniseriate rays and thin walled ray parenchyma cells. Wood fibers are composed of three types: a large diameter fiber with longer length; a large diameter fiber with shorter length; a small diameter fiber with medium length. Vessel elements are composed of: a medium length one; a longer length one; the one whose both end walls have ligules or tails. Parenchyma cells in xylem and pit parenchyma cells have completely different size and shape. For bast fiber, the average length is about 4.4 mm and the width is about $30.5\;{\mu}m$; for vessel element, $600.0\;{\mu}m$ in length and $493.6\;{\mu}m$ in width; for wood fiber, $1000\;{\mu}m$ and $38.9\;{\mu}m$; for parenchyma cell, $50\;{\mu}m$ and $26.4\;{\mu}m$.

• 대한의용생체공학회:의공학회지
• /
• 제23권3호
• /
• pp.181-187
• /
• 2002

일정한 주기를 갖는 맥동유동에 대하여 혈관이 확장될 때 나타나는 동맥류 내부에서의 유동 및 벽면전단응력의 특성을 2차원적으로 고찰하였다. 상용 소프트웨어를 이용하여 직경비 1.5. 2.0 및 2.5 그리고 Womersley 수 15.47에 대한 복부대동맥내의 유동 현상을 수치해석하였다. 해석결과 동맥류 상단부에서 형성된 재순환유동은 시간의 흐름에 따라 생성과 소멸을 반복하였고. 시간이 3.19초인 경우, 동맥류 입구부 상단 근처에서 매우 미약한 재순환유동이 발달하고 있음을 예상할 수 있었다. 그리고 직경비가 증가할수록 동맥류 말단부에서 전단응력의 변화의 폭이 증가하였고 최대 전단응력의 값도 증가하는 것을 알 수 있었다. 그러나 최대 벽면전단응력의 발생 위치는 직경비의 변화와 거의 무관하였으며 동맥류 말단부 근처 (z : 35mm)에서 발생하였다

• 한국정밀공학회지
• /
• 제16권7호
• /
• pp.24-31
• /
• 1999

Bulging is a forming method to shape of die cavity by using hydraulic pressure in tube or vessel. Bulging machine and die were developed in order to produce vessel for keeping warm. Bulging machine is a double type with two horizontal cylinders for bulging of two pieces at the same time. The developed die system has one bulging die and two drawing dies for necking at the both ends of tube. The diameter of tube expands by hydraulic pressure in tube. at the same time, thrust at the both ends of tube. pushes tube in the direction of expansion to obtain high expanding rate with no crack. In this study, the bulging properties were investigated to solve tube crack and necking in manufacturing vessel by the combination method of bulging and drawing. As a result, high expanding rate of tube radius without crack, precision necking and high productivity were obtained.

• International Journal of Precision Engineering and Manufacturing
• /
• 제2권4호
• /
• pp.40-46
• /
• 2001

Bulging is a forming method to shape die cavity by using hydraulic pressure in tube or vessel. Bulging machine and die were developed in order to produce vessel for keeping warm. Bulging machine is a double type with two horizontal cylinders for bulging of two pieces at the same time. The developed die system has one bulging die and two drawing dies for necking at both ends of the tube. The diameter of tube expands by hydraulic pressure in tube. At the same time, thrust at both ends of the tube pushes tube in the direction of expansion to obtain high expansion rate with no crack. In this study, the bulging properties were investigated to solve tube crack and necking in manufacturing vessel by combining bulging and drawing. As a result, high expanding rate of tube radius without crack, precision necking and high productivity were obtained.

• Journal of Plant Biology
• /
• 제26권1호
• /
• pp.7-16
• /
• 1983

Internodal vessel elements are studied in 20 genera, 75 species and 33 cultivars of Hibiscus rosa-sinensis belong to the Malvaceae. The minimum and maximum length and diameter range from 79~466 and 14~88 ${\mu}{\textrm}{m}$, respectively. The vessel elements are either cylindrical, fusiform, conical, clavate, oval, column-, drum-, fish and cup-like or erratic. Perforation plates are exclusively simple in all the species investigated, except occasionally scalariform in varieties of Hibiscus rosa-sinensis. In most of the species studied vessel elements have predominantly two perforation plates or occasionally one and three. Adjacen side wall thickening is commonly simple and border pitted, mixed, scalariform, helical and reticulate. The vessel elements vary in their size, shape, number and inclination of perforation plates and adjacent wall thickening.