• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.29-36
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• 2006

Steel reinforced concrete(SRC) columns, which have been widely employed in high-rise buildings, exhibit a time-dependent behavior because of creep and shrinkage of concrete. This long-term behavior may cause a serious serviceability problem in structural systems, so it is very important to predict the deformation due to creep and shrinkage of concrete. However, it was found from the previous experimental studies that the long-term deformation of SRC columns was quite dissimilar from that of RC columns. A new method is required to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the discrepancy between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of reinforced concrete(RC) columns owing to the presence of a inner steel plate, which interferes with the moisture diffusion of concrete. This relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns. Therefore it is suggested that the differential moisture distribution should be taken into account in order to reasonably predict column shortening of SRC columns.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.239-248
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• 2006

Recently, a variety of researches has been carried out to obtain a more controlled durability and long-term performance of concrete structures under chloride attack environments. In particular, new procedures for probability-based durability analysis/design have been noticed to be very valuable for the enhancement of service life of concrete structures. Although there is still a lack of relevant data, this approach has been successfully applied to some new concrete structures. In this paper, the diffusion equation based on Fick's second law has been solved with a time dependent diffusion coefficient and the probabilistic analysis of the durability performance has been carried out by using a Monte Carlo Simulation. From the results, the influence of each parameter on the durability of concrete structures was investigated and the new procedure for durability analysis was demonstrated in terms of chloride penetration data from various concrete structures. The new procedure might be very useful in designing important concrete structures and help to predict the remaining service life of existing concrete structures under chloride attack environments.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2004.05a
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• pp.143-148
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• 2004

고로슬래그 미분말과 플라이 애쉬와 같은 재료들이 콘크리트의 내구성과 장기강도 증진을 목적으로 혼합재로서 사용되고 있다. 본 연구에서는 고로슬래그 사용 몰탈의 내구성 증진 특성을 활용하기 위하여 고로슬래그 미분말에 알칼리 자극제를 첨가한 알칼리 활성화 슬래그계 무기결합재 사용 몰탈의 내구성과 물리적 특성을 평가하였다. 실험결과, 몰탈의 초기 압축강도 발현에 알칼리 자극제가 큰 영향을 미치는 것을 확인하였다. 또한 알칼리 자극제가 첨가된 몰탈의 화학적 저항성을 평가하기 위하여 공시체를 재령 28 일 후, 5% 황산($H_2SO_4$) 용액에 침지하여 압축강도 및 질량 변화를 관찰하였다. 그 결과, 보통포틀랜드 시멘트로 제조한 몰탈의 경우, 황산용액 침지 후 압축강도가 54% 감소하였다. 반면 고로슬래그 미분말을 첨가한 몰탈의 경우, 약 10% 강도가 감소하였다. 질량변화의 경우, 보통포틀랜드 시멘트로 제조한 공시체는 17%, 고로슬래그 미분말을 첨가한 몰탈은 3%의 질량변화를 보였다. 이 결과로서 고로슬래그 미분말을 첨가한 몰탈의 경우, 화학적 저항성과 물리적 특성이 우수한 것을 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.44-48
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• 2003

할로겐 난연재료 및 고분자의 연소시 Dioxine의 문제점이 대두되고 있어 유럽국가를 중심으로 할로겐 난연제 사용을 규제하고 있다. 환경과 인체에 대한 안정성을 고려해서 저 유해 가스화, 저 발연화, 저 부식성, 리사이클링 등을 겸비한 제품의 개발로 관심이 모아지고 있는 실정이다. 본 연구에서는 환경친화적인 금속화합(수산화 알루미늄)을 사용하여 연소시 발생할 수 있는 난연성, 무독성, 소연성 등을 함량별로 확인하고 난연재가 증가할수록 취약한 기계적 물성 보완을 위해 moisture cure crosslikable 기술로 케이블절연 및 자켓 피복층 특성을 증가 시켰다. 그러나 수산화알루미늄 함량이 증가할수록 기계적 물성과 기타 특성도 감소하는 경향을 보이고 있어 최적의 난연제 조성함량이 약 130~150 phr정도에서 우수한 결과를 확인하였다. 또한 moisture cure agent는 전선압출 시 표면에 scorch 및 장기 압출에 영향을 주므로 약 1.5~2phr 범위에서 처방하는 것이 우수하다. 원료투입 후 mixing 공정 중에서는 온도관리가 매우 중요하므로 되도록 믹싱 온도를 $130^{\circ}C$ 이하를 유지해야한다. 온도는 수산화알루미늄의 분산성과 케이블 피복압출 시 표면에도 영향을 주기 때문이다 본 연구는 이런 작업방법을 통해 친환경 가교 난연콤파운드가 비(比) 가교된 제품에 비해 특성이 증가되는 것을 입증할 수 있었다.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.17-25
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• 2010

We studied on the watertightness improvement of cementitious material for durability enhancement of concrete. For improvement of watertightness of OPC and OPC with fly ash, we used various materials with watertightness properties to OPC and OPC with fly ash. The performance of watertightness improvement of cementitious materials closely related to formation of CSH by pozzolanic reaction and to reducing of size of contact angle in cement pore by using organic fatty acid. And volume of CSH formation at early hydration have an influence of watertightness improvement and reduction of long-term water absorption rate. In using of fly ash, improvement of workability by using the spherical fly ash caused to densify on the structures of cement material and CSH formation by pozzolanic reaction and cement using fly ash also caused watertightness improvement of cementitious materials. For improvement of concrete durability by watertightness, cementitious materials need using watertightness materials and at using fly ash, also it have to the effect of improvement of watertightness of cementitious materials by pozzolanic reaction.

• Journal of the Korean Geosynthetics Society
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• v.9 no.4
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• pp.75-84
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• 2010

In this study, the long-term performance tests, which have extensibility, creep deformation, installation resistance and durability characteristic, is conducted to apply geosynthetic strip in field. The strength reduction factors using the test results are evaluated in order to calculate long-term design tensile strength. First, the creep deformation was evaluated by both the stepped isothermal method(SIM) and the time-temperature superposition(TTS) method. The creep reduction factor is reasonable to apply 1.6. Second, the result of installation damage test had little damage of yarn, which affected strength of reinforcement. Therefore, it can be analyzed that the installation damage of geosynthetic strip has little effect of long-term design tensile strength. Finally, the durability reduction factor considering chemical, biological and outdoor exposure resistance is reasonable to apply 1.1, which is considered the stability and economic efficiency of reinforced earth wall using geosynthetic strip.

• Journal of the Korean GEO-environmental Society
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• v.24 no.8
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• pp.13-20
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• 2023

Tunnelling through the geological anomalies has widely known to have many difficulties such as bottom heave, crack of lining, squeezing and so on. To stabilize the tunnel during the construction or after construction, various reinforcing methods have been introduced and applied such as micropiling at the bottom of tunnel to prevent the bottom heave. In this study, long-term behavior of tunnel in the presence of geological anomalies was predicted using numerical analyses. To this end, material properties for swelling rock model capable of representing the rock swelling behavior was obtained using matching process with measured data to validate the adopted model. After the model validation, simulations were performed to predict the long-term behavior of tunnel in the geological anomalies.

• Journal of Chest Surgery
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• v.30 no.9
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• pp.876-884
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• 1997

Fourteen patients underwent orthotopic heart transplantation between March 1994 and May 1996 in Seoul National University Hospital. There were 9 male and 5 female patients, and the mean age was 40.8 $\pm$ 12.4 years ranged from 12 to 56 years. All patient were in NYHA Fc III or IV preoperatively. The underlying heart diseases were dilated cardiomyopathy in 11 and restrictive cardiomyopathy in 3. The mean age of donors was 24.9$\pm$ 10.2 years and the causes of the brain death were head trauma by traffic accidents in 8, subarachnoid hemorrhage in 2, 1 asphyxia, 1 fall down injury, 1 brain tumo , and 1 drowning, respectively The blood type was identical in 11, compatible in 2, and incompatible in 1 patient. The direct bicaval anastomosis technique was used in 11 cases, and standard right atrial anastomosis was done in the remaining 3 cases. The graft ischemic time was 158$\pm$44 minutes ranged 94 to 220 minutes. There were two hospital deaths(14.3%). The causes of deaths were 1 right ventricular failure followed by suspected cyclosporine induced hemolytic uremic syndrome and rejection, and 1 delayed massive bleeding, probably from rupture of the anastomotic pseudoaneurysm, respectively. The follow-up duration was 16$\pm$9 months(3 to 28 months). There was one late death(8.3%). All the other patients were in NYHA Fc I except one patient who was in hospital because of the acute rejection. The actuarial survival rates including hospital deaths were 93.7% at 1 month, 86.9% at 6 months, and 77$\pm$12% at 2 years. Conclusively, heart transplantation is the good strategy for the management of end stage heart disease with acceptable operative mortality and early follow-up results.

• The Korean Journal of Applied Statistics
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• v.28 no.3
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• pp.429-442
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• 2015

Volatility forecasting in financial markets is an important issue because it is directly related to the profit of return. The volatility is generally modeled as time-varying conditional heteroskedasticity. A generalized autoregressive conditional heteroskedastic (GARCH) model is often used for modeling; however, it is not suitable to reflect structural changes (such as a financial crisis or debt crisis) into the volatility. As a remedy, we introduce the Markov regime switching GARCH (MRS-GARCH) model. For the empirical example, we analyze and forecast the volatility of the daily Korea Composite Stock Price Index (KOSPI) data from January 4, 2000 to October 30, 2014. The result shows that the regime of low volatility persists with a leverage effect. We also observe that the performance of MRS-GARCH is superior to other GARCH models for in-sample fitting; in addition, it is also superior to other models for long-term forecasting in out-of-sample fitting. The MRS-GARCH model can be a good alternative to GARCH-type models because it can reflect financial market structural changes into modeling and volatility forecasting.

• Korean Journal of Clinical Laboratory Science
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• v.51 no.1
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• pp.119-123
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• 2019

Obstructive sleep apnea (OSA) is a sleep disorder with no breathing symptoms due to repetitive upper airway resistance. OSA is a disease that can have significant effects on the cerebral cardiovascular system. Active treatment is needed to prevent these complications. The use of continuous positive airway pressure (CPAP), the standard therapy of OSA, has comparative therapeutic effects. On the other hand, there is no comparison report of the polysomnography (PSG) results before and after CPAP therapy without using a mask. This paper reports a patient who was diagnosed as OSA and used CPAP every night for more than 2 years. The patient showed a decrease in the apnea-hypopnea index from 64.7/h to 12.9/h. In addition, other sleep-related indicators improved significantly. The daily use of CPAP as a treatment for OSA for more than 2 years may improve the PSG results. Constant follow up of PSG will be needed to adjust the appropriate CPAP pressure to patients because there might be a change in the Apnea-Hypopnea Index and other sleep-related indicators for constant CPAP users for at least 2 years.