• Nuclear Engineering and Technology
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• 제31권6호
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• pp.572-585
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• 1999

The characteristics of two-phase flow instability in a vertical boiling channel connecting with an unheated riser are investigated through the linear stability analysis model. Various two-phase flow models, including thermal non-equilibrium effects, are taken into account for establishing a physical model in the time domain. A classical approach to the frequency response method is adopted for the stability analysis by employing the D-partition method. The adequacy of the linear model is verified by evaluating experimental data at high quality conditions. It reveals that the flow-pattern-dependent drift velocity model enhances the prediction accuracy while the homogeneous equilibrium model shows the most conservative predictions. The characteristics of density wave oscillations under low-power and low-quality conditions are investigated by devising a simple model which accounts for the gravitational and frictional pressure losses along the channel. The necessary conditions for the occurrences of type-I instability and flow excursion are deduced from the one-dimensional D-partition analysis. The parametric effects of some design variables on low quality oscillations are also investigated.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.434-442
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• 2015

The advanced passive pressurized water reactor (PWR) is being constructed in China and the passive residual heat removal (PRHR) system was designed to remove the decay heat. During accident scenarios with increase of heat removal from the primary coolant system, the actuation of the PRHR will enhance the cooldown of the primary coolant system. There is a risk of power excursion during the cooldown of the primary coolant system. Therefore, it is necessary to analyze the thermal hydraulic behavior of the reactor coolant system (RCS) at this condition. The advanced passive PWR model, including major components in the RCS, is built by SCDAP/RELAP5 code. The thermal hydraulic behavior of the core is studied for two typical accident sequences with PRHR actuation to investigate the core cooling capability with conservative assumptions, a main steam line break (MSLB) event and inadvertent opening of a steam generator (SG) safety valve event. The results show that the core is ultimately shut down by the boric acid solution delivered by Core Makeup Tank (CMT) injections. The effects of CMT boric acid concentration and the activation delay time on accident consequences are analyzed for MSLB, which shows that there is no consequential damage to the fuel or reactor coolant system in the selected conditions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.603-608
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• 1997

Studies on the second-order analysis of reinforced concrete columns have been chiefly dealt with symmetric section under uniaxial loading. In practical situations, however, columns are subjected to biaxial loadings. Therefore, for more accurate prediction of the behavior of concrete columns under biaxial loading, the interaction between bending moments of major and minor axes should be considered. Recently Kim & Lee proposed a numerical method of predicting the behavior of concrete columns under biaxial loading. In this paper, to investigate the behavior of concrete columns under biaxial loading and verify the validity of proposed method, a series of test were carried out for sixteen tied reinforced columns with 100${\times}$100mm square and 200${\times}$100mm rectangular sections under various loading conditions. The length of columns was 1,300mm and the concrete strength was 28MPa. The boundary conditions at the both ends were hinged and end eccentricities were equal(400mm). Proposed numerical analyses applied to the test piece were performed to predict behavior of concrete columns with square and rectangular sections under various loading conditions. Test results were also compared with those using the moment magnifier method in ACI code. The test results showed that the moment magnifier method is conservative.

• 에너지공학
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• 제13권3호
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• pp.181-190
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• 2004

Computational models for analyzing the in-reactor behavior of metallic fuel pins under transient conditions in liquid-metal reactors are developed and implemented in the TRAMAC (TRAnsient thermo-Mechanical Analysis Code) for a metal fuel rod under transient operation conditions. Not only the basic models for a fuel rod performance but also some sub-models used for transient condition are installed in TRAMAC. Among the models, a fission gas release model, which takes the multi-bubble size distribution into account to characterize the lenticular bubble shape and the saturation condition on the grain boundary and the cladding deformation model have been developed based mainly on the existing models in the MAC-SIS code. Finally, cladding strains are calculated from the amount of thermal creep, irradiation creep, and irradiation swelling. The cladding strain model in TRAMAC predicts well the absolute magnitudes and gen-eral trends of their predictions compared with those of experimental data. TRAMAC results for the FH-1,2,6 pins are more conservative than experimental data and relatively reasonable than those of FPIN2 code. From the calculation results of TRAMAC, it is apparent that the code is capable of predicting fission gas release, and cladding deformation for LMR metal fuel finder transient operation conditions. The results show that in general, the predictions of TRAMAC agree well with the available irradiation data.

• 구강회복응용과학지
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• 제31권1호
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• pp.1-9
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• 2015

목적: 중합방법 및 측정시기에 따른 여러 이중중합 레진 시멘트의 기계적 성질인 압축강도와 간접인장강도를 비교 평가하는 것이다. 연구 재료 및 방법: 1개의 레진강화형 글래스아이오노머 시멘트인 FujiCEM 2, 2개의 전통적인 이중중합 레진 시멘트인 RelyX ARC와 Multilink N, 2개의 이중중합 자가접착 레진 시멘트인 RelyX U200과 G-CEM LinkAce를 사용하였다. 제조사의 지시에 따라 시멘트를 혼합하여 압축강도와 간접인장강도 측정을 위한 시편을 제작하였다. 중합방법 및 측정시기의 영향을 평가하기 위해 시멘트에 따라 4가지 실험 조건으로 나눴고, 만능시험기로 압축강도와 간접인장강도 측정하였다. 각각의 강도 값을 계산 후 통계처리 하였다. 결과: 압축강도에서는 RelyX ARC의 광중합과 Multilink N의 광중합, 간접인장강도에서는 RelyX ARC의 광중합을 제외하고 모든 중합방법에서 24시간 뒤 측정된 강도가 즉시 측정한 강도보다 더 높은 값을 보여주었다. FujiCEM 2는 시멘트간 비교에서 가장 낮은 강도 값을 보였다(P < 0.05). 결론: 치과용 시멘트 중에서 최근 출시된 이중중합 자가접착 레진 시멘트는 기존의 레진 시멘트와 비교시 제품별로 차이가 있었으나, 압축강도와 간접인장강도에서는 유의한 차이를 보이지 않았다.

• Restorative Dentistry and Endodontics
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• 제36권3호
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• pp.211-218
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• 2011

연구목적: 의도적 재식술은 재근관치료와 치근단 수술이 곤란하거나 실패한 경우 치아를 유지하기 위한 치료 방법이다. 성공적인 의도적 재식술을 위해서 파절 없는 안전한 발치는 필수적인 과정이다. 이를 위해 최근 의도적 재식술을 위한 비외상성 안전 발치법이 소개되었다. 환자 및 방법: 분당서울대학교 병원 치과 보존과에서 의도적 재식술을 시행한 96명의 환자를 대상으로 하였다. 재근관 치료가 실패하였거나 해부학적 접근의 어려움 등으로 치근단 수술이 곤란한 경우나 환자가 거부한 경우를 대상으로 하였다. 술전교정적 정출술을 약 2-3주간 시행하여 치아의 동요도를 증가시키고 동시에 치주인대의 양을 증가시켰다. 이후 Physics Forceps를 이용하여 발치하였으며 결과에 대해 분석하였다. 결과: 96개의 치아는 상,하악 소구치 또는 대구치였다. 완전한 발치 성공은 93% (n = 89)였으며 제한적인 성공(치근의 일부가 부러짐)은 2% (n = 2), 골절제술을 동반하여 발치한 경우가 5% (n = 5)였다. 임상적인 성공률은 95%였으며 전체적인 발치 성공률은 100% 였다. 결론: 비외상성 안전 발치법은 의도적 재식술을 위해 재현성 있고 예측가능한 발치방법으로 볼 수 있다.

• Restorative Dentistry and Endodontics
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• 제30권5호
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• pp.385-392
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• 2005

목적은 근관충전이 상아세관 내에 남아있는 세균에 미치는 영향을 알아보고 가터퍼차와 resilon의 밀폐 능력을 상아 세관 내에 남아있는 세균의 생존 여부를 통하여 비교하는 것이다. 발치된 우전치로 치아시편에 E. faecalis를 접종하고 제 1군은 음성대조군, 제 2군은 양성대조군, 제 3군은 ZOE 계통의 근관전색제와 가터퍼차, 제 4군은 레진 계통의 근관전색제와 가터퍼차 제 5군은 레진 계통의 근관전색제와 resilon으로 근관 충전하였다. 각 시편은 1, 2, 3주 및 4주간 보관한 뒤 round bur로 근관 내를 삭제하여 얻은 상아질을 배양하고 혼탁도를 측정하였다. 1. Nail varnish로 상아세관을 완전히 밀폐한 경우, 상아세관 내의 E. faecalis의 수는 가터퍼차 및 resilon으로 근관 충전 한 경우보다 통계적으로 유의차 있게 감소하였다 (p < 0.05) .2. 레진 계통의 근관전색제와 resilon으로 근관충전 한 군에서는 시간의 흐름에 따라 상아세관 내의 E. faecalis의 수가 유의차 있게 감소하였다 (p < 0.05) 3. 가터퍼차와 resilon으로 근관충전한 군 사이에 상아세관 내에 남아있는 E. faecalis의 생존 정도는 통계학적 유의차가 없었다 (p > 0.05).

• Restorative Dentistry and Endodontics
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• 제27권3호
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• pp.249-256
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• 2002

The use of flowable composite resins as liners in class II packable composite restoration has been suggested by some manufacturers. However, the contributions of this technique are unproven. The purpose of this study was to compare the gingival microleakage in class II packable composite restorations with or without the use of flowable composite resins as liners. Slot cavities were prepared on both proximals of 80 extracted human molars and randomly assigned to 8 groups of 20 each. The gingival margins were located at 1mm above CEJ in 80 cavities (group1-4) and 1mm below CEJ in 80 cavities (group5-8). The prepared teeth were mounted in the customized tray with adjacent teeth to simulate clinical conditions and metallic matrix band (Sectional matrix) and wooden wedges were applied. After acid etching and application of Single Bond, each group was restored with the following materials using incremental placement technique: Group 1,5 (Filtek P60), group 2, 3, 4 and group 6, 7, 8 (AeliteFlo, TetricFlow, Revolution/ Filtek P60). All specimens were thermocycled 500 times between 5$^{\circ}C$ and 55$^{\circ}C$ with 1 mimute dwell time, immersed 2% methylene blue dye for 24 hours and then rinsed with tab water. The specimens were embedded in clear resin and sectioned longitudinally through the center of restoration with a low speed diamond saw. Dye penetration at gingival margin was viewed at 20 magnification and analyzed on a scale of 0 to 4. Kruscal-Wallis One way analysis and Mann-Whitney Rank sum test were used to analyze the results. The results of this study were as follows. 1. The leakage values seen at the enamel margin were significantly lower than those seen at the dentin margin(P<0.05). 2. On the enamel margin, packable composite resins with flowable liners showed lower leakage than those without flowable liners, but there were no significant differences among the four groups(P>0.05). 3. On the dentin margin, four groups demonstrated moderate to severe leakage, and there were no significant differences in leakage values(P>0.05).

• Restorative Dentistry and Endodontics
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• 제20권2호
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• pp.432-461
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• 1995

The basic principles in the design of Class II amalgam cavity preparations have been modified but not changed in essence over the last 90 years. The early essential principle was "extension for prevention". Most of the modifications have served to reduce the extent of preparation and, thus, increase the conservation of sound tooth structure. A more recent concept relating to conservative Class II cavity preparations involves elimination of occlusal preparation if no carious lesion exists in this area. To evaluate the ideal ClassII cavity preparation design, if carious lesion exists only in the interproximal area, three cavity design conditions were studied: Rodda's conventional cavity, simple proximal box cavity and proximal box cavity with retention grooves. In this study, MO amalgam cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method. Linear, eight and six-nodal, isoparametric brick elements were used for the three dimensional finite element model. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. Three types model(B option, Gap option and R option model) were developed. B option model was assumed perfect bonding between the restoration and cavty wall. Gap option model(Gap distance: $2{\mu}m$) was assumed the possibility of play at the interface simulated the lack of real bonding between the amalgam and cavity wall (enamel and dentin). R option model was assumed non-connection between the restoration and cavty wall. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as followed. 1. Rodda's cavity form model showed greater amount of displacement with other two models. 2. The stress and strain were increased on the distal marginal ridge and buccopulpal line angle in Rodda's cavity form model. 3. The stress and strain were increased on the central groove and a part of distal marginal ridge in simple proximal box model and proximal box model with retention grooves. 4. With Gap option, Rodda's cavity form model showed the greatest amount of the stress on distal marginal ridge followed by proximal box model with retention grooves and simple proximal box model in descending order. 5. With Gap option, simple proximal box model showed greater amount of stress on the central groove with proximal box model with retention grooves. 6. Retention grooves in the proximal box played the role of supporting the restorations opposing to loads.

• Restorative Dentistry and Endodontics
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• 제17권1호
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• pp.104-114
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• 1992

The purpose of this study was to evaluate the shear bond strength of glass ionomer cement(Ketacfil, ESPE, Co.) against dentin surface which had been treated with surface conditioning agents(distilled water, 5% sodium hypochlorite solution, Ketac - conditioner, 40% polyacrylic acid). In this study, 60 human molars with sound and healthy crown portion which were previously extracted for orthodontic or periodontal problem. The dentin surfaces of these teeth were exposed with wet trimmer and polished with 150 - grit and 600 - grit silicon carbide paper and the teeth were divided into four groups(15 teeth per group) according to the following surface conditioning methods. Group I : Surface treatment with distilled water as control group. Group II : Surface conditioning with 5% sodium hypochlorite solution. Group III : Surface conditioning with Ketac conditioner. Group IV : Surface conditioning with 40% polyacrylic acid. The shear bond strengths were measured by Autograph(Shimatzu Co. Japan). The result of the evaluations were then subjected to statistical analysis using one - way analysis of variance and Duncan test and the results were as follows : 1. The shear bond strength accrding to the dentin surface conditioning conditions was highest in Ketac conditioner group, with measurements of $44.44{\pm}0.74(kg/cm^2)$ and lowest in the distilled water group, with measurements of $28.84{\pm}0.88(kg/cm^2)$. 2. Statistically significant differences were found between surface conditioning with 5% sodium hypochlorite solution group or Ketac conditioner group and distilled water group(P<0.01). 3. Also, statistically significant difference was found between surface conditioning with distilled water group and 40% polyacrylic acid group(P<0.05). 4. Overall difference in statistical significance between the groups was not found (P<0.05). 5. Fractured dentin surface treated with conditioning solutions showed cohesive fracture. 6. Distilled water group and 5% sodium hypochlorite solution group removed the smear layer less effectively. 7. Conditioning dentin with Ketac conditioner and 40% polyacrylic acid resulted in the removal of a significant amount of the smear layer without removing the tubular plugs and dissolving the peritubular dentin.