• Journal of Chest Surgery
• /
• v.26 no.9
• /
• pp.677-685
• /
• 1993

Experience with bileaflet mechanical valve replacement at the Inha Hospital in 192 patients, operated on from June 1986 until April 1993. Two hundred fourty-one prostheses [51 Duromedics, 79 St.Jude Medical, and 111 CafboMedics]were implanted during the total 195 operations. Mitral valve replacment[MVR]was done in 113 cases, aortic valve replacement[AVR]in 34, tricuspid valve replacement[TVR]in 2, and double valve replacement[DVR]in 46 cases.Of the total patients, 63.0% were women and 37.0% were men. The mean age of the patients was 40.8 years, ranged from 14 to 67years. Overall early mortality was 9.2\ulcorner%[18 out of 195]; 9.7%[11 out of 113]for MVR, 14,7% [5 out of 34]for AVR, and 4.3%[2 out of 46]for DVR. All of the operative survors were followed over a period of one to 83 months with a mean of 37 months, for total 543 patient-years. So far, eleven patients[6.7% of the long-term survivors]were lost to follov-up after a mean postoperative follow-up of 22.8 months. There were nine late deaths; three deaths due to prostetic valve endocarditis, two due to persistent heart failure, one due to cerebral hemorrhage, one due to aortic dissection after Bentall oreration, and two sudden deaths. Actuarial survival rate at 6.9 years was 94.8%, There were seventeen valve-related complications; three prosthetic valve thromboses, three thrombembolisms, three instances of prosthetic valve endocarditis, two paravalvular leakages, and six hemorrhagic complications related to anticoagulation. The actuarial rate of freedom from all valve-related complications at 6.9years was 91.3%. There were significant decreases in the heart size postoperatively that can be demonstrated by comparison of cardio-thoracic ratios on simple chest X-ray and left ventricle dimensions on echocardiography. We conclude that this midterm follow-up shows good results in terms of hemodynamics and durability although further long-term evaluations are mandatory.

• Journal of the Korean Institute of Gas
• /
• v.10 no.3 s.32
• /
• pp.20-26
• /
• 2006

The survey team has conducted the on-the-site inspection of 53 bridges to which LNG gas pipelines are attached, to ascertain their level of safety, durability and any defect by adapting a method of computer data input process and precision analysis. In this way, we could estimate an effective corrective action on the defective gas pipelines found through this survey. Our survey team has analyzed carefully these 2 defective lines selectively out of 10 lines, which are considered to be most seriously weak. According to our elaborate analysis these two pipelines go over 70% of the set standard stress based on our Safety Manual Scale. We have taken corrective actions on these lines by repairing/replacing/obsolete damaged lines to ensure the distress of the bridges involved with the pipelines and could secure safety.

• Computers and Concrete
• /
• v.18 no.5
• /
• pp.1041-1051
• /
• 2016

In this study, the construction of a reinforced concrete bridge pier was analyzed from durability point of view. The goal of the study is to analyze the crack iniation condition due to construction and present some recommendations for construction conditions of the reinforced concrete bridge pier. The bridge is located at the western port area of Shenzhen, where the climate is high temperature and humidity. To control the cracking of concrete, a construction simulation was carried out for a heat transfer problem as well as a thermal stress problem. A shrinkage model for heat produced due to cement hydration and a Burger constitutive model to simulate the creep effect are used. The modelling based on Femmasse(C) is verified by comparing with the testing results of a real underground abutment. For the bridge pier, the temperature and stress distribution, as well as their evolution with time are shown. To simulate the construction condition, four initial concrete temperatures ($5^{\circ}C$, $10^{\circ}C$, $15^{\circ}C$, $20^{\circ}C$) and three demoulding time tips (48h, 72h, 96h) are investigated. From the results, it is concluded that a high initial concrete temperature could result in a high extreme internal temperature, which causes the early peak temperature and the larger principle stresses. The demoulding time seems to be less important for the chosen study cases. Currently used 72 hours in the construction practice may be a reasonable choice.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.18 no.6
• /
• pp.525-533
• /
• 2016

The purpose of current tunnel maintenance system in South Korea is safety-based maintenance system for accident prevention, So it is difficult to conduct a strategic maintenance. The development of a new maintenance system can lead to effective investment of limited financial and it's effort is still in progress. In this study, to develop a performance-based assessment method, indexes for assessment are derived taking into account the safety, durability and serviceability. The indexes for performance-based assessment were selected by a literature analysis and a delphi survey. Then the importance among indexes were calculated by the AHP analysis.

• Knowledge Management Research
• /
• v.17 no.2
• /
• pp.27-50
• /
• 2016

Korean manufacturing industry have recently faced the catch-up of China in the mass commodity product, such as automotive, display, and smart phone in terms of market as well as technology. Accordingly, discussion on the importance of achieving catch-up in complex product systems (CoPS) has been increasing as a new innovation engine for the industry. In order to achieve successful catch-up of CoPS, we explored emerging technologies of CoPS, which are featured by the characteristics of radical novelty, relatively fast growth and self-sustaining, through the study of emerging technologies of gas turbine for power generation. We found that emerging technologies of the gas turbine are technologies for combustion nozzle and composition of electrical machine for increasing power efficiency, washing technology for particulate matter, cast and material processing technology for enhancing durability from fatigue, cooling technologies from extremely high temperature, interconnection operation technology between renewable energy and the gas turbine for flexibility in power generation, and big data technology for remote monitoring and diagnosis of the gas turbine. We also found that those emerging technologies resulted in technological progress of the gas turbine by converging with other conventional technologies in the gas turbine. It indicates that emerging technologies in CoPS can be appeared on various technological knowledge fields and have complementary relationship with conventional technologies for technology progress of CoPS. It also implies that latecomers need to pursue integrated learning that includes emerging technologies as well as conventional technologies rather than independent learning related to emerging technologies for successful catch-up of CoPS. Our findings provide an important initial theoretical ground for investigating the emerging technologies and their characteristics in CoPS as well as recognizing knowledge management strategy for successful catch-up of latecomers. Our findings also contribute to the policy development of the CoPS from the perspective of innovation strategy and knowledge management.

• Computers and Concrete
• /
• v.14 no.5
• /
• pp.577-597
• /
• 2014

This paper aims to develop a prediction model for the hardened properties of waste LCD glass that is used in concrete by analyzing a series of laboratory test results, which were obtained in our previous study. We also summarized the testing results of the hardened properties of a variety of waste LCD glass concretes and discussed the effect of factors such as the water-binder ratio (w/b), waste glass content (G) and age (t) on the concrete compressive strength, flexural strength and ultrasonic pulse velocity. This study also applied a hyperbolic function, an exponential function and a power function in a non-linear regression analysis of multiple variables and established the prediction model that could consider the effect of the water-binder ratio (w/b), waste glass content (G) and age (t) on the concrete compressive strength, flexural strength and ultrasonic pulse velocity. Compared with the testing results, the statistical analysis shows that the coefficient of determination $R^2$ and the mean absolute percentage error (MAPE) were 0.93-0.96 and 5.4-8.4% for the compressive strength, 0.83-0.89 and 8.9-12.2% for the flexural strength and 0.87-0.89 and 1.8-2.2% for the ultrasonic pulse velocity, respectively. The proposed models are highly accurate in predicting the compressive strength, flexural strength and ultrasonic pulse velocity of waste LCD glass concrete. However, with other ranges of mixture parameters, the predicted models must be further studied.

• Journal of the Korea Convergence Society
• /
• v.6 no.6
• /
• pp.241-246
• /
• 2015

In cold winter season, the apparatuses of heating and heater which warm up the interior of a room are necessary element and the used amount of these apparatuses from the year 2000 has been increased abruptly. But, the fire accident and the danger of fire are also increased. Therefore, 3D modelling is done by referring three kinds of the electric heaters as the heaters of ceramic, carbon and near infrared ray sold in the city for the design of more safe heating apparatuses in this study. The thermal analyses with these models are carried out and the durabilities due to the thermal deformation and stress are studied. By the background of the study results derived in this study ultimately, the durabilities of electric heater models due to each shape can be anticipated and contributed to the development of new heating apparatus with more safe resistance to fire. And it is possible to be grafted onto the convergence technique at design and show the esthetic sense.

• Journal of the Korean Geotechnical Society
• /
• v.16 no.1
• /
• pp.227-234
• /
• 2000

Soilcrete has been a traditional material for pavement and soft ground improvement techniques. However, since the durability is not excellent and the quality is not consistent, it has not been used for various purposes up to date. However, with the increase of naturally oriented needs for light traffic roads such as pedestrian roads of garden, golf courses and sidewalks, the cases of the high strength soilcrete paving have been increased lately. This study aims at making a reference table of mix design in accordance with the required design specifications fur the high strength soilcrete admixtured with the pozzolanic cement by using a statistical experimental method. The treated soil is the clay which is widely found in Korea. As the results of this study, we could derive an effective reference mix design table for the clay treated with the pozzolanic cement stabilizer in accordance with the compressive strength of $50~150kg/cm^2$ soilcrete.

• Journal of Hydrogen and New Energy
• /
• v.10 no.4
• /
• pp.197-210
• /
• 1999

The hydrogen storage performance and electrochemical properties of $Zr_{1-X}Ti_X(Mn_{0.2}V_{0.2}Ni_{0.6})_{1.8}$(X=0.0, 0.2, 0.4, 0.6) alloys are investigated. The relationship between discharge performance and alloy characteristics such as P-C-T characteristics and crystallographic parameters is also discussed. All of these alloys are found to have mainly a C14-type Laves phase structure by X-ray diffraction analysis. As the mole fraction of Ti in the alloy increases, the reversible hydrogen storage capacity decreases while the equilibrium hydrogen pressure of alloy increases. Furthermore, the discharge capacity shows a maxima behavior and the rate-capability is increased, but the cycling durability is rapidly degraded with increasing Ti content in the alloy. In order to analyze the above phenomena, the phase distribution, surface composition, and dissolution amount of alloy constituting elements are examined by S.E.M., A.E.S. and I.C.P. respectively. The decrease of secondary phase amount with increasing Ti content in the alloy explains that the micro-galvanic corrosion by multiphase formation is little related with the degradation of the alloys. The analysis of surface composition shows that the rapid degradation of Ti-substituted Zr base alloy electrode is due to the growth of oxygen penetration layer. After comparing the radii of atoms and ions in the electrolyte, it is clear that the electrode surface becomes more porous, and that is the source of growth of oxygen penetration layer while accelerating the dissolution of alloy constituting elements with increasing Ti content. Consequently, the rapid degradation (fast growth of the oxygen-penetrated layer) with increasing Ti substitution in Zr-based alloy is ascribed to the formation of porous surface oxide through which the oxygen atom and hydroxyl ion with relatively large radius can easily transport into the electrode surface.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.8 no.4
• /
• pp.11-21
• /
• 1988

In twentieth century, a rigid pavement composed of a series of thin Portland Cement Concrete has been accepted due to the desirable structural strength of concrete, durability and economy. However, despite of precise design and construction of concrete highway pavements, some of concrete pavements (example : Interstate-l0 and 75 in U.S.A, 88 Olympic express highway and Jung-bu express highway in Korea) has already shown severe signs of longitudinal and transverse cracking, faulting, and pumping before the end of their intended service life. This highlights the need for better understanding of concrete pavement behavior using structural analysis program. For these reasons, this research was performed to study an analytical behavior of concrete pavements, especially for the effects of skewed joints on concrete pavements. Subsequently, this research should give better understanding of concrete pavement behavior to the highway engineers and provide effective remedies to the concrete highway pavements.