• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.1
• /
• pp.9-17
• /
• 2013

In this study, an efficient analytical model for the dynamic analysis of tall buildings with a shear wall-frame structural system has been proposed. A shear wall-frame structural system usually consists of a core wall showing flexural behavior and a frame presenting shear behavior. Therefore, the deformed shape of the shear wall-frame structural system is shown by the combination of flexural mode and shear mode. These characteristics should be considered when an efficient analytical model is developed. To this end, the effect of shear wall and frame on the dynamic behavior of a tall building with a dual system has been separately investigated. In this study, the structural characteristics of a separated individual shear wall model and the frame model without shear wall has been evaluated. In order to consider the effect of the shear wall in the frame model without shear wall, a rigid body was used instead of the shear wall. Each equivalent model for the separated shear wall part and frame part has been independently developed and two equivalent models were then combined to create an efficient analytical model for tall buildings with a shear wall-frame structural system. In order to verify the efficiency and accuracy of the proposed method, time history analyses of tall buildings with a shear wall-frame system were performed. Based on analytical results, it has been confirmed that the proposed method can provide accurate results, requiring significantly reduced computational time and memory.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.32 no.3
• /
• pp.569-575
• /
• 2005

The aim of this study was to compare the efficiency of sonic and manual toothbrush in decreasing plaque accumulation in young orthodontic patients. Twenty one healthy orthodontic patients attending department of pediatric dentistry at Samsung Medical Center were chosen for the study. The subjects were randomly assigned to either sonic or manual toothbrush and instructed to brush for 2 minutes. Plaque score was assessed with the modified Visible Plaque Index (VPI) before and after brushing. Each brush was repeated twice. A mean plaque reduction of sonic toothbrush was 61.79%(${\pm}7.95$) compared to 69.19%(${\pm}10.08$) of manual toothbrush(p<0.05). With the sonic toothbrush, male presented a mean plaque reduction of 63.07%(${\pm}8.64$) while female presented 60.39%(${\pm}7.30$). For manual toothbrush, male presented 69.33%(${\pm}10.14$) and female presented 69.03%(${\pm}10.55$) reduction of plaque accumulation(p>0.05). There was no statistically significant correlation between age and plaque removal efficacy in this study(p>0.05). Manual toothbrush was significantly more efficient in removing plaque than the sonic toothbrush in young fixed orthodontic patients.

• Clinical and Experimental Reproductive Medicine
• /
• v.30 no.4
• /
• pp.293-298
• /
• 2003

목 적: 인간의 배아줄기세포는 전분화능과 영속성을 가지고 있어 발생 및 분화에 관련된 기초 연구 뿐 만 아니라 재생의학, 약물검색 등에서도 매우 유용한 재료로 이용될 수 있다.본 연구에서는 유전체의 변형이 배아줄기세포주의 확립 효율에 미치는 영향을 살펴보고자 비정상적인 포배기 배아에서 내세포괴를 분리하여 배양하였다. 연구 방법: 인간의 체외수정 및 배아이식술에서 공여 받은1개 또는3개의 전핵이 관찰되는 비정상 수정란 (n=20)과 착상전 유전진단에서 이수성이 확인된 배아 (n=27)를 대상으로 하였다. 일반적인 immunosurgery 방법으로 영양배엽세포들을 제거하고 내세포괴를 분리한 후 PMEF 혹은 STO feeder 세포위에서 배양하였다. 배아줄기세포의 배양시스템을 검증하기 위해서 이미 확립된 Miz-hES1 cell line을 동시에 같은 조건 하에서 계대배양하였다. 결 과: 비정상 수정란에서 발생된 포배기 배아에서 분리한 1개의 내세포괴가 배아줄기세포와 유사한 colony를 형성하였으나, 계대배양에는 실패하였다. 이수성 배아에서 발생된 포배기 배아의 내세포괴 배양에서는 두개의 colony가 계대배양 중에 영양배엽세포의 형태로 분화되어 미분화 상태를 유지하지 못하였다. 동일한 시기와 조건 하에서 계대배양된 Miz-hES1 cell line이 미분화상태로 유지됨을 karyotyping (46, XY)과 immunophenotyping (positive in SSEA-3 and -4)으로 확인하였다. 결 론: 본 연구의 결과에서 비정상 수정란과 이수성 배아에서 발생된 포배기 배아에서 유래한 내세포괴는 배아줄기세포주 확립 및 미분화 상태 유지 능력이 매우 저조한 것으로 여겨진다. 따라서, 인간의 배아줄기세포주를 확립하는데 있어 배아의 정상여부가 중요한 요소로 작용할 것으로 생각된다.

• Geophysics and Geophysical Exploration
• /
• v.5 no.4
• /
• pp.257-261
• /
• 2002

We have carried out integrated research including field survey and numerical modeling to appraise the applicability of SP method to the leakage problems of irrigation facilities. The leakage pattern of the dike studied here can be classified into the three categories: leakage through the abutment, leakage by piping through dike, and leakage due to the composite effects of landslide and distortion of the dike structure. for the numerical modeling to interpret quantitatively SP survey results acquired at dike, we have modified the computer code proposed by Sill (1983) to apply to the leakage problems. The numerical studies match the characteristic patterns of SP anomalies according to the leakage types and appear to be very useful to interpret the leakage zone and path. The SP monitoring results were also well coincided with tidal variations observed at every embankment so we found the SP method is quite effective not only to detect the leakage zone but also to determine the leakage trend. The numerical modeling results also reproduced the SP anomalies due to seawater leakage in the embankment.

• Korean Journal of Materials Research
• /
• v.10 no.4
• /
• pp.312-316
• /
• 2000

A study has been made to investigate the effects of hot isostatic pressing(HIP ping) on bond strength and elevated temperature characteristics of thermal barrier coating(TBC). The specimens were prepared by HIPping of TBC which is composed of the ceramic top coat(8wt%$Y_2$$O_3$-$ZrO_2$) and the metallic bond coat on the matrix of IN738LC superalloy. The results showed that the porosity and microcracks in the ceramic top coat of TBC were significantly decreased by HIP. As a result, the bond strength of the HIPped coating was increased above 48% compared to that of as-coated specimen and microstructure was homogenized. It was found that the thermal cycle resistance of HIPped coating was inferior to that of as-coated specimen. It was considered that this result was mainly caused by the reduction of internal defects in the top coat layer which could play a role in relaxing the thermal stress due to a large difference in thermal expansion between TBC and matrix.

• Journal of the Korea Concrete Institute
• /
• v.17 no.4 s.88
• /
• pp.505-511
• /
• 2005

This experimental investigation was conducted to examine the seismic performance of reinforced concrete bridge columns. The columns were subjected to a constant axial load and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research were the volumetric ratios of transverse reinforcement (ps=0.96, 1.44 percent) and axial load ratios (P/Po=0.05, 0.1, 0.2) and concrete strengths (35, 60MPa). Test results showed that bridge columns with $44\%$ higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behavior. For bridge columns with axial load ratio(P/Po) less than 0.2, the ratio of $M_{max}\;over\;M_{ACI}$, nominal moment capacity predicted by ACI 318-02 provisions, was consistently greater than 1 with approximately a $20\%$ margin of safety.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.4
• /
• pp.113-124
• /
• 1998

Numerical study using nonlinear finite element analysis is done for investigating behavior of isolated reinforced concrete walls subject to combined in-plane and out-of-plane bending moments and axial force. A method for estimating the ultimate strength of wall is developed, based on the analytical results. For the nonlinear finite element analysis, a computer program addressing material and geometric nonlinearities is developed. An existing unified method combining plasticity theory and damage model is used for material model of reinforced concrete. By numerical studies, the internal force distribution in the cross section is idealized, and a new method for estimating the ultimate strength of wall is developed. According to the proposed method, variation of the interaction curve of in-plane bending moment and axial force depends on the range of the permissible axial force per unit length that is determined by the given amount of out-of-plane bending moment. As the out-of-plane bending moment increases, the interaction curve shrinks, which indicates a decrease in the ultimate strength. The proposed method is compared with an existing method using the general assumption that strain shall be directly proportional to the distance from the neutral axis. Compared with the proposed method, the existing method overestimates the ultimate strength for walls subject to low out-of-plane bending moments, and it underestimates the ultimate strength for walls subject to high out-of-plane bending moments.

• Journal of the Korea Concrete Institute
• /
• v.20 no.2
• /
• pp.239-247
• /
• 2008

Use of both carbon fiber (CF) and glass fiber (GF) at the same time to strengthen existing flexural members was exploited. Using a proper volumetric GF / CF ratio, the CF can rupture first followed by subsequent rupture of GF at higher stress and strain showing a pseudo-ductile behavior. A theoretical study indicated that the ratio is 4.62 : 1 and higher where the pseudoductile effect can be shown. Flexural tests of plain concrete beams strengthened using fibers were first carried out. Hybrid FRP sheet using 8.8 : 1 ratio was then fabricated and the sheet was used to strengthen reinforced concrete beams. The RC beams strengthened using 1-ply and 2-ply hybrid sheets both revealed increased strength over a non-strengthened beam and ductile flexural behavior. A comparable beam strengthened using CF also showed increased strength but with limited ductility.

• Journal of Korean Foot and Ankle Society
• /
• v.18 no.3
• /
• pp.108-114
• /
• 2014

Purpose: Ligament reattachment technique using a suture anchor appears to show satisfactory functional outcomes and mechanical stability compared with conventional bone tunnel technique. This study was prospectively conducted in order to evaluate functional outcomes of modified Brostrom procedures using the suture bridge technique for chronic ankle instability in athletes. Materials and Methods: Twenty eight athletes under 30 years of age were followed for more than two years after undergoing the modified Brostrom procedure using the suture bridge technique. Functional evaluation consisted of the foot and ankle outcome score (FAOS), foot and ankle ability measure (FAAM) score. Range of motion and time to return to exercise were evaluated using a periodic questionnaire. Talar tilt angle and anterior talar translation were measured through stress radiographs for evaluation of mechanical stability. Results: FAOS improved significantly from preoperative mean 59.4 points to 91.4 points (p<0.001). Daily living and sport activity scores of FAAM improved significantly from preoperative mean 50.5, 32.5 points to 94.8, 87.3 points, respectively (p<0.001). Talar tilt angle and anterior talar translation improved significantly from preoperative mean $16.8^{\circ}$, 13.5 mm to $4.2^{\circ}$, 4.1 mm at final follow-up (p<0.001). Times to return to exercise were as follows: mean 10.2 weeks in jogging, 15.4 weeks in spurt running, 13.1 weeks in jumping, 11.5 weeks in walking on uneven ground, 9.1 weeks in standing on one leg, 7.2 weeks in tip-toeing gait, 8.4 weeks in squatting, and 10.6 weeks in descending stairs. Conclusion: Modified Brostrom procedure using the suture bridge technique showed satisfactory functional outcomes for chronic ankle instability in athletes. Optimal indication and cost-effectiveness of the suture bridge technique will be studied in the future.

• Journal of the Korean Ceramic Society
• /
• v.39 no.9
• /
• pp.871-877
• /
• 2002

Alumina slurriers, having various amount of alumina and ratio of organic additives, were prepared for tape casting. The relative viscosities were compared to investigate influence of composition on stability of the slurry and plotted as a function of powder fraction. They raised with increasing powder fraction of slurries, revealing a exponential function curve, which means that stability of slurry was not affected by amount and composition of organic additives. Cast green tapes were tested under tensile condition at room temperature. The increase in alumina ratio and binder ratio was found to decrease strain to failure of green tapes from 363% to 45% and from 68% to 25%, respectively. Tensile strength of green tapes increased abruptly with increasing alumina ratio, which showed its maximum at 1 MPa. On other hand, Tensile strength increased continuously from 0.5 MPa to 4 MPa with increasing binder ratio. Mechanical properties of them were affected seriously and lost their properties by elevating temperature from 20$^{\circ}C$ to 80$^{\circ}C$.