• 한국전산구조공학회논문집
• /
• 제15권2호
• /
• pp.237-249
• /
• 2002

현재 국내에서는 벽과 슬래브으로만 이루어진 벽식 구조형식의 아파트 건물이 많이 사용되고 있다. 아파트 건물의 전단벽에는 기능적인 필요에 의하여 한 개 혹은 여러 개의 개구부가 존재할 수 있다. 이러한 개구부가 있는 전단벽의 해석에 대해서 기존에 많은 연구가 수행되어 왔으나, 적용하는데 많은 해석시간과 컴퓨터 메모리가 필요하는 등 여러 가지 제한점 때문에 실제 해석 및 설계에는 별로 적용되지 못하고 있다. 따라서, 본 논문에서는 기존 연구의 제한점들을 개선하여 개구부 크기, 위치 및 개수에 관계없이 적용할 수 있는 해석 방법을 제안하였다. 개구부가 있는 전단벽을 정확하게 해석하기 위해서는 전단벽을 평면응력요소로 세분화하여 모형화하는 것이 필요하다. 그러나 아파트 건물 전체를 평면응력요소로 세분하여 모형화하는 것은 상당한 해석시간과 컴퓨터 메모리가 소요되므로 실무에 적용하기에는 어려운 점이 많다. 따라서, 본 논문에서는 이러한 단점을 개선하고자 슈퍼요소와 행렬응축기법, 그리고 가상보를 사용한 해석기법을 제안하였다. 제안된 해석기법의 효용성을 검증하기 위하여 다양한 크기와 위치의 개구부가 있는 예제구조물을 선택하여 정적 및 동적해석을 수행하였다. 예제해석 결과 제안된 해석기법은 소요되는 해석시간과 컴퓨터 메모리를 대폭 줄이면서도 세분모델과 비슷한 정확성을 가지는 것을 확인할 수 있었다.

• Restorative Dentistry and Endodontics
• /
• 제22권2호
• /
• pp.596-608
• /
• 1997

The purpose of this study was to compare the apical leakage and adaptation to the dentinal wall of a glass ionomer root canal cement(Ketac-Endo) with those of AH-26 and Tubli-Seal. 102 single-rooted teeth were insrumented with step-back technique and randomly divided into four groups according to kinds of root canal cements: Ketac-Endo, AH-26, Tubli-Seal, and no root canal cement. Four experimental groups were as follows; Group 1 : Filling with gutta-percha and Ketac-Endo Group 2 : Filling with gutta-percha and AH-26 Group 3 : Filling with gutta-percha and Tubli-Seal Group 4 : Filling with gutta-percha without root canal cement All the specimens were obturated with lateral condensation technique, and stored in 100% humidity for 4 days. 20 teeth in each group were placed in centrifuge tube filled with India ink, and then centrifuged for 20 minutes at 3,000 rpm. And they were evaluated for linear dye leakage using a stereoscope and analyzed by one-way ANOVA. 22 teeth were split longitudinally and evaluated the adaptation to the dentinal wall using scanning electron microscope(4 teeth in each group) and stereoscope(2 teeth in 1, 2, 3 group). The obtained results were as follows ; 1. In case of not used root canal cement(Group 4), there was showed much degree of dye penetration comparerd with used root canal cements (Group 1, 2, 3)(P<0.01). 2. In the case of used root canal cements(Group 1, 2, 3), there was no significant difference in linear leakage in groups(P>0.01). 3. In the case of used root canal cements(Group 1, 2, 3), there was showed intimate adaptation to the dentinal wall independent on kinds of root canal cements. 4. Fractured surfaces indicated failure of cohesion in Ketac-Endo, and failure of adhesion to dentine in AH-26 and Tubli-Seal. 5. According to similar apical leakage and adaptability to the dentinal wall to another root canal cements, it is possible to be used glass-ionomer cement as root canal cement.

• Restorative Dentistry and Endodontics
• /
• 제20권2호
• /
• pp.549-576
• /
• 1995

Bacteria are one of the most important causative agents of the pulpal and periapical diseases. Streptococci are one of the most frequently isolated facultative anarerobic bacteria in the infected root canals. Bacterial cell wall components have a direct effect in the pathogenesis of the pulpal and periapical infections. Hyaluronidase produced by bacteria has been implicated in dissemination of the diseases. The purpose of this study was to evaluate the effect of cell wall extract of streptococci on the L929 cells using inverted microscope and the transmission electron microscopy (TEM). Hyaluronidase production of streptococcal strains were investigated to determine the correlation between the severity of cell damage and the activity of enzymes. Bacterial cell wall extracts of S. sanguis, S. mitis and S. uberis isolated from infected root canals and ATCC type strains of S. mutans (ATCC 10449) and E. faecalis (ATCC 19433) were prepared by sonication and confirmed with SDS-PAGE. Silver stain of SDS-PAGE of sonic extract was efficient at $100{\mu}g$/ml concentration of cell wall protein, while Coomasie blue stain was efficient at $100{\mu}g$/ml concentration. Inverted microscope showed that sonic extract-treated L929 cells were round and detached from the substratum while others lost their fibroblastic shapes. Transmission electron microscopic examination revealed that streptococcal extracts induced death of L929 cells. Sonic extracts of streptococci had variable effect on microstructure of L929 cells. significant chromatin condensation was observed in the nucleus of the cells. Disappearance of cell surface microvilli and nuclear fragments with dense chromatin were observed. The cell nucleus had an irregular shape and numerous large vacuoles were seen in the cytoplasm and some breaks of the cell membrane could be seen. Cell organelles were in various stages of destruction and cristae of mitochondria were disoriented or disappeared. Eighteen strains of streptococci did not produce hyaluronidase.

• Restorative Dentistry and Endodontics
• /
• 제17권2호
• /
• pp.365-382
• /
• 1992

The purpose of this study was to evaluate the adaptation of filling material to the dentinal walls of root canals with and without smear layer. Fifty extracted upper and lower anterior teeth were selected, and the root canals were instrumented with K - files 1mm short of the apical foramen by step - back method. The teeth were randomly divided into two groups of 25 each : in the group I, smear layers were not removed, and in the group II, smear layers were removed by 15% EDTA solution. Again the two groups 25 teeth were randomly divided into unfilled contol group and filling groups(lateral, ultrasonic, ULTRAFIL, McSpadden compaction group). Upon completion of root canal filling, the teeth were grooved on the both the labial and lingual surfaces and then split with mallet and chisel. Each specimens were examined with JSM - 840 Scanning Electron Microscope (JEOL., Japan). The results were as follows : 1. In the contol group, dentinal tubules of group I couldn't be distinguished in the canal wall, but those of group II appeared to be open and patent. 2. In the filling groups of group I, the tubular penetration of the sealer or gutta percha couldn't be seen, but in the filling groups of group II, it could be seen except McSpadden compaction group. 3. In the filling groups, ULTRAFIL group showed the best adaptation of filling material to root canal wall among the group I, and lateral and ultrasonic condensation group showed the best adaptation of filling material among the group II. McSpadden compaction group showed the worst adaptation in group I, II. 4. Generally, the group II showed better adapation of filling material to root canal wall than the group I.

• 한국마린엔지니어링학회:학술대회논문집
• /
• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
• /
• pp.1143-1148
• /
• 2005

Experimental results for heat transfer characteristic and pressure gradient of HCs refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 during condensing inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.86 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than those of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than those of R-22 in 12.7 mm and 9.52 mm. This results from the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• 한국농촌건축학회논문집
• /
• 제23권4호
• /
• pp.63-71
• /
• 2021

The purpose of this study was to investigate whether the standard models for rural housing and wooden housing model have performance for hygrothermal and to propose a way of improvement relevant to hygrothermal performance for those models. All of the models to be analyzed were found to have some parts that were absent of stability in terms of performance for hygrothermal. In the process of analyzing the causes and proposing improvement measures, the following conclusions were derived. Fist, The exterior surface of the structure should be composed of a structure with good moisture permeability, and for the interior surface, a variable vapor retarder paper should be applied in consideration of the reverse condensation phenomenon in summer. Second, in terms of performance for hygrothermal, applications of external insulation plaster finish to the exterior wall or of ventilation method using a rafter vent on the roof should be avoided. Third, a rain screen method with a ventilation layer should be applied to the exterior wall, and a method of constructing ventilation layer separated from the insulation layer with a vapor retarder paper should be applied to the roof. Fourth, the application of insulation materials having capillary action, such as wood fiber insulation board or cellulose insulation board, contributes to more stable performance for hygrothermal.

• 대한미생물학회지
• /
• 제11권1호
• /
• pp.1-11
• /
• 1976

Escherichia coli(ATCC 11115)에 실험실등에서 상용하는 여러가지 항균제를 시간별로 처리, 그 변화양상을 전자현미경으로 관찰한 바 그 결과를 요약하면 다음과 같다. 1) 대조군은 3층의 단일막으로 형성된 세포벽에 둘러쌓여 있으며 세포질은 전자밀도가 낮은 nucleoid와 ribosme들이 산재하여 있음을 관찰할 수 있었다. 2) 70% ethanol용액 처리군은 핵물질을 관찰할 수 없었고 세포질은 세포 중앙부로 응집되어 있었으며 세포벽의 외부에서는 bleb 들을 관찰 할 수 있었다. 3) 3% $H_2O_2$ 용액 처리군은 세포내용물의 변화는 70% ethanol 처리군과 대동소이(大同小異)하였으나 세포벽에서는 심한 굴곡현상이 관찰되었다. 4) 5% lysol 용액처리군은 세포질 및 핵물질 부위가 완전히 구분되어 나타났으며 세포질내의 ribosome과립들은 시간이 경과할수록 그 응집현상이 심하였고 세포 외부에는 ribosome 양 과립들이 부착하고 있음이 관찰되었다. 5) 1% DDEGH 용액 처리군은 세포질의 응집 및 세포막과 세포벽이 뚜렷이 관찰되지 않았으며 세포외부에 세포내용물과 동일한 물질로 생각되는 물질이 부착되어 있음을 관찰할 수 있었다. 6) 고압멸균 처리군은 세포막 및 세포벽의 파괴, 탈락 및 세포내용물의 유출현상이 관찰되었다.

• Nuclear Engineering and Technology
• /
• 제56권6호
• /
• pp.2029-2038
• /
• 2024

A deep understanding of the characteristics and mechanism of geyser boiling and capillary pumping is necessary to optimize a high-temperature sodium heat pipe. In this work, the Volume of Fluid (VOF) two-phase model and the capillary force model in the mesh wick were used to model the complex phase change and fluid flow in the heat pipe. Computational Fluid Dynamics (CFD) simulations successfully predicted the process of bubble nucleation, growth, aggregation, and detachment from the wall in the liquid pool of the evaporation section of the heat pipe in horizontal and tilted states, as well as the reflux phenomenon of capillary suction within the wick. The accuracy and stability of the capillary force model within the wick were verified. In addition, the causes of geyser boiling in heat pipes were analyzed by extracting the oscillation distribution of heat pipe wall temperature. The results show that adding the capillary force model within the wick structure can reasonably simulate the liquid backflow phenomenon at the condensation; Under the horizontal and inclined operating conditions of the heat pipe, the phenomenon of local dry-out will occur, resulting in a sharp increase in local temperature. The speed of bubble detachment and the timely reflux of liquid sodium (condensate) replenishment in the wick play a vital role in the geyser temperature oscillation of the tube wall. The numerical simulation method and the results of this study are anticipated to provide a good reference for the investigation of geyser boiling in high-temperature heat pipes.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2113-2118
• /
• 2007

In this study, a mathematical model for a thermal analysis of a flat heat pipe with a grooved wick structure is presented. The effects of the liquid-vapor interfacial shear stress, the contact angle, and the amount of liquid charge have been included in the proposed model. In particular, the axial variations of the wall temperature and the evaporation/condensation rates are considered by solving the one-dimensional conduction and the augmented Young-Laplace equations, respectively. In order to verify the model, the results obtained from the model are compared to existing experimental data.

• Bulletin of the Korean Chemical Society
• /
• 제33권8호
• /
• pp.2553-2559
• /
• 2012

The adsorption properties of benzene, toluene, p-xylene in MCM-41 with heterogeneous and cylindrical pore were studied using grand canonical ensemble Monte Carlo simulation. The simulated isotherms were compared with experimental ones, and the different adsorption behaviors in MCM-41 with pore diameters of 2.2 and 3.2 nm were investigated. The simulated adsorption amounts above the capillary-condensation pressure agreed with the experimental ones. The simulation results showed that most molecular planes were nearly parallel to the pore axis. This orientation was not affected by the molecular position in the pore. The molecular planes were nearly parallel to the pore surface for the adsorbate molecules close to the pore wall, and the molecules in the MCM-41 with the pore diameter of 3.2 nm were ordered along the pore axis.