• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.214-219
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• 1997

The mechanical seals, which are installed in rotating machines like pump and compressor, are generally used as sealing devices in the many fields of industries. The failure of mechanical seals such as leakage, crack, breakage, fast and severe wear, excessive torque, and squeaking results in big problems. To identify abnormal phenomena on mechanical seals and to propose the proper monitoring parameter for the failure of mechanical seals, sliding wear experiments were conducted. Acoustic emission, torque, and temperature were measured during experiments. Optical microstructure was observed for the wear processing after every 10 minute sliding at rotation speed of 1750 rpm and scanning electron microscopy was also observed. Except for the initial part of every experiment, the variation of acoustic emission was well coincided with torque variation during the experiments. This study concludes that acoustic emission and torque are proper monitoring parameters for the failure of mechanical seals. The intensity of acoustic emission signals is measured in root mean square voltage. Temperature of sealing face will be used as a parallel parameter for increasing the reliability of monitoring system.

• Journal of the Korean GEO-environmental Society
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• v.11 no.8
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• pp.83-93
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• 2010

The purpose of this study is to present emergency rehabilitation, cause and the countermeasure of reinforcement about reinforced retaining wall and the slope collapse of the phyllite ground. The study area is broken easily because this area has rock mass discontinuity such as stratification, foliation, joint and fold. And this area consists of the ground where it happens easily to the failure of structure like reinforced retaining wall because of the phyllite ground sensitive to weathering. Counterweight fill in front of reinforced retaining wall was performed as emergency rehabilitation about displacement of reinforced retaining wall and the failure at the rear of slope on phyllite ground. After that, additional displacement didn't occur. Boring and geophysical exploration were launched to present emergency rehabilitation and develop the long-term method of reinforcement. This could grasp anticipated range of the failure section and identify internal and external factors of the cause of the slope collapse. Several methods of reinforcement were suggested by conducting the numerical analysis. When conducting design and construction of major structures at the ground which has complex discontinuities, the precise site investigation should be conducted. During construction, immediate action for over-displacement should be taken by performing the periodic measurement.

• Journal of the Korean Arthroscopy Society
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• v.6 no.1
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• pp.7-13
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• 2002

Purpose : Preliminary report of the technique and trial of double bundle PCL reconstruction using Achilles allograft. Materials and Methods : From May 1999 to July 2000, 8 cases of PCL insufficient patients were treated with Achilles allograft reconstruction using the double bundle and double femoral tunnel technique. The tibial tunnel was prepared anteromedially. All other combined injuries within the knees were treated accordingly. Minimal follow-up period was 1 year. The results was assessed from the point of function and stability using Lysholm knee score and KT-2000 arthrometer. Results : Up to present follow up. 8 patients showed good sign of recovery with no instability (translation less than 2 mm) except olio that has been grafted-ligament rupture. In addition, none showed any sign of infection nor ROM limitation. Two complications were seen, which one had grafted-bone fracture and the other grafted-ligament rupture. The former occurred during operation and the latter occurred due to improper protection. Conclusion : Presently the follow up period is too short to draw any conclusive opinion but it is essential to select healthy and well sterilized allografts fur successful outcome. Double femoral tunnel technique seems to be more physiologic in PCL reconstruction. With these prerequisites, it seems to be a good alternative to use Achilles allografts fur the reconstruction of PCL. However, a longer follow-up is needed.

• Journal of the Korean Geosynthetics Society
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• v.6 no.2
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• pp.1-8
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• 2007

Recently, the demand for industrial and residental land are increasing with economic growth, but it is difficult to acquire areas for development with good ground condition. For efficient and balanced development of land, new development projects are being carried out not only the areas with inland but those with the soft ground as well. As soft grounds have complex engineering properties and high variations such as ground subsidence especially when their strength is low and depth is deep, we need to accurately analyze the engineering properties of soft grounds and find general measures for stable and economic design and management. Vertical drain technology is widely used to accelerate the consolidation of soft clay deposits & dredged soil under pre-loading and various types of vertical drain are used with there discharge capacity. Under field conditions, discharge capacity is changed with various reason, such as soil condition, confinement pressure, long-term clogging and folding of vertical drains and so on. Therefore, many researcher and engineer recommend the use of required discharge capacity. In this paper, the experiment study were carried out to obtain the discharge capacity of four different types of vertical drains by utilizing the large-scale model tests and the required discharge capacity was calculated by several methods.

• Journal of Labour Economics
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• v.24 no.1
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• pp.35-66
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• 2001

This study first attempted to measure the job instability of Korean labor market by exploiting the data sets of 1998 and 1999 Korean Labor Panels. In order to compare the degrees of job instability of Korea with the one of U.S., we followed the same empirical methods used by Jaeger and Stevens(1999), Neumark et al.(1999), Bemhardt et al.(1999) recently published in the Journal of Labor Economics (vol. 17). Our empirical results suggest that the job retention rate of the Korean labor market during the IMF economic crisis was decreased to the level that the U.S. labor market has never experienced during the past two decades. One noticeable point regarding our estimated four year retention rate is that it takes a form of plateau peaked around 9 and 15 tenure year, which is in sharp contrast with the four year retention rate of u.S. showing a monotonically decreasing tendency over tenure periods. The comparison of 2-year retention rates before and after the economic crisis suggests that job stabilities has been conspicuously aggravated especially for cohorts of long tenure, irregular job, old age, service and sales jobs.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.281-292
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• 2008

In Korea-LTPP(Long Tenn Pavement Performance) project, the full depth asphalt pavement test sections are constructed on the national highway to evaluate the structural capacity of asphalt pavement reinforced with glass fiber. Truck loading test and FWD test were performed to measure the structural capacity of test sections. Test results showed that the reinforcement of glass fiber installed at between surface and intermediate asphalt layer decreased the strain at the bottom of surface layer and moved up the stress neutral axis in asphalt layer. As a result, the tensile stress was developed at the bottom of intermediate asphalt layer of reinforced asphalt pavement, while the compressive stress was developed at the bottom of intermediate asphalt layer of unreinforced asphalt pavement. On the other hand, the tensile strain at the bottom of asphalt base layer didn't show a difference between glass fiber reinforced and unreinforced pavements. From the FWD test, it was shown that the surface deflection of asphalt pavement reinforced with glass fiber decreased 24 percents comparing to that of unreinforced asphalt pavement. This shows that the reinforcement with glass fiber appears to improve the rutting resistance of asphalt pavement.

• Radiation Oncology Journal
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• v.11 no.2
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• pp.439-448
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• 1993

The B-type gamma knife unit was installed at Kyung-Hee University Hospital in March 1992. The selective beam plugging method can be used to reduce the low percentage isodose profiles of normal sensitive organ and to modify the isodose curves of treatment volume for better shaping of the target volume. For representing the changes of the low percentage isodose profiles, the variations of dose distribution for several cases were discussed in this paper. The film dosimetry was peformed for the evaluation of calculated isodose profiles predicted by KULA dose planning system. The results were verified by RFA-3 automatic densitometry. The clinical application of selective beam shielding method was peformed in 17 patients in 100 patients who have undergone gamma knife radiosurgery for a year. The calculated and the measured isodose profiles for the high percentage regions were well consistent with each other. When the target of pituitary tumor is macro-size, the selective beam shielding method is the most applicable method. When the target size, however, is small, the correct selection of the proper helmet size is very important. All patients were exposed almost about 3~12 Gy for brain stem, and 3~11.2 Gy for optic apparatus. It is recommended that the same or other plugging patterns with multiple isocenters should be used for protection of the radiosensitive normal structures with precise treatment of CNS lesions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.129-136
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• 2012

Temperature of fresh concrete can be effectively used to predict the strength of concrete being cured and make an informed decision for stripping the molds. A hygrothermograph and thermo-couple sensors that require an extensive wiring have been applied to measure a temperature of concrete at the early stage of the curing process on site. However, these methods have limits to provide the temperature data in real time due to harsh working environment including frequent cutting of wires. Therefore, this study is aiming at developing a device based on wireless sensor network to measure the temperature of concrete being cured in formwork. The result showed that the wireless sensor with probe type thermistor which is developed had the same temperature data compared to the existed wire type thermistor, and we confirmed the temperature history of concrete in real time for 28 days throughout the gateway by wireless network that collects the temperature data measured from specimens in laboratory. Also, the network device for transmission can be easily separated from the probe sensor part and reused consistently. If the wireless sensor network device developed uses in the field, the temperature management of concrete will be systematically conducted from at the early stage of the curing, and especially be effective for cold weather concrete construction. In addition, it will contribute to the establishment of advanced quality control system for concrete and productivity of supervisors on site will be increased in the future.

• Journal of Korea Water Resources Association
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• v.38 no.4 s.153
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• pp.271-280
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• 2005

The goal of this study is to recommend a new type of stage-discharge rating curve ($Q=p(h-e)^{\beta}-{\gamma}$) useful for satisfying divergence, and one other seemingly irresolvable problem related to exited rating curves, while also extending this rating curve model. The problem of divergence is that during the finding of the CZF (cease-to-zero flow) parameter e and while minimizing the sum of total errors of the estimated curve, the exponential parameter ${\beta}$ become an abnormally large value. The insoluble problem is that when the value e is greater then the recorded minimum at the gauged stage, it is impossible to have a negative logarithm value (h-e). The two problems above can be satisfied by adapting the control value ${\gamma}$, which affects the reduction of ${\gamma}$ and gives us the possibility of controlling (h-e) over zero. The study results show that the effects of parameter ${\gamma}$ are very similar to that of e when conducting physical and sensitivity analyses. This system can be used towards developing a new stage-discharge rating curve for river discharge, for use in evaluating the acceptability of existing stage-discharge rating curves generated by using hydrologic analyses at all stations.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.41-50
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• 2010

Long-term floor deflection caused by excessive construction load became a critical issue for the design of concrete slabs, as a flat plate is becoming popular for tall buildings. To estimate the concrete cracking and deflection of an early age slab, the construction load should be accurately evaluated. The magnitude of construction load acting on a slab is affected by various design parameters. Most of existing methods for estimating construction load addressed only the effects of the construction period per story, material properties of early age concrete, and the number of shored floors. In the present study, in addition to these parameter, the effects of shore stiffness and concrete cracking on construction load were numerically studied. Based on the result, a simplified method for estimating construction load was developed. In the proposed method, the calculation of construction load is divided to two steps: 1)Onset of concrete placement at a top slab. 2)Removal of shoring. At each step, the construction load increment is distributed to the floor slabs according to the ratio of slab stiffness to shore stiffness. The proposed method was compared with existing methods. In a companion paper, the proposed method will be verified by the comparison with the measurements of actual construction loads.