• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.33-40
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• 2002

Vacuum concrete manufactured by vacuuming and decompressing fresh concrete. It is known to have improvement on abrasion and strength by making a structural confinement through elimination of internal gap. It has been implemented on buildings floors, concrete dam, etc. in developed countries. This study was aimed to monitor changes in physical characteristics such as strength and slump of concrete influenced by changes of vacuum, decompression level and combination condition during concrete manufacturing process. The results are as follows: It is indicated that decompressed concrete shoved increase in unit weight and compressive strength by compact compression phenomenon influenced by decrease in internal gap caused by diminishing oxygen. However, continuous research is necessary to resolve problems on construction, design and durability.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.743-746
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• 2004

This research investigates experimentally an effect on the properties of the high flowing concrete according to variations of concrete materials and site conditions. Variations of sensitivity test are selected items as followings; (1)Concrete temperature, (2)Unit water(Surface moisture of fine aggregate), (3)Fineness modulus of fine aggregate, (4)Addition ratio of high-range water reducing agent. And fresh conditions of the high flowing concrete should be satisfied with required range including slump flow$(65{\pm}5cm)$, 50cm reaching time of slump flow$(4\~10sec)$, V-box flowing time$(10\~20sec)$, U-box height(min.300mm) and air content$(4{\pm}1\%)$. As results of sensitivity test, material variations and site conditions should be satisfied with the range as followings; (1)Concrete temperature is $10\~20^{\circ}C$ (below $30^{\circ}C$), (2)Surface moisture of fine aggregate is within ${\pm}0.6\%$, (3)Fineness modulus of fine aggregate is $2.6{\pm}0.2$ and (4)addition ratio of high range water reducing agent is within $1\%$ considered flow-ability, self-compaction and segregation resistance of the high flowing concrete.

• The Korean Journal of Ecology
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• v.21 no.5_2
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• pp.501-518
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• 1998

Mt. Paektu(2,749.6m)m the biggest mountain in Northeast Asia, located on the border line of Korea and China is characterized as an aspite with broad gentle mountain area and rich biota. however, it seems that the study of forest vegetational feature or vegetation zones in the whole area of this mountain is not yet sufficient in spite of contribution by many investigators. in this paper thermal climatic approach was carried out for the determination of vegetation zones of the mountain with the meteorological data of four stations including Cheonjj and various vegetational data. the application of Warmth Index and/or coldness Index(Kira 1977) for the determination of forest vegetation boundary was useful also here, and their boundaries largely coincided with those of thermal indicies obtained in the Korean Peninsula(Yim and Kira, 1975), including the lapse rate of air temperature along increasing elevation. However, in the mountain the boundary of vegetation zones in not clear like those of mountains in Korea. It may be due so the topographic differences between this area and the Korean Peninsula. Besides, the broad ecotones between different vegetations in this area support the vegetation continum concept rather than the unit concept, and the limit of timber line or tree line reflects various hypothesis(Steven and fox 1991). Therefore, for the explantion of vegetation zone of this area should be considered topography or soil condition, for example, as known the hierachy of ecological units (zonobiomes, orobiomes and pedobiomes, Walter, 1973).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.113-117
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• 2009

Fly ash (called FA hereafter) that results from thermal power plants is a long-term strength improving substance with reactivity to pozzolan and has been used for long. However, large amount of FA shows many advantages such as reduction of hydratio energy, long-term improvement in strength and economic feasibility and also has difficulties from reduction in initial strength and durability. In a preceding study, fine particle cement was applied to test the effects on initial strength. Therefore in this study, the effects of fine particle cement on the quality of FA concrete were reviewed. The results can be summarized as follows. Liquidity was increased by the most at FC substitution ratio of 15%. Air capacity was reduced according to increasing substitution ratio of FA and FC. Compressive strength showed high strength expression at all ages when FC was substituted at 45%. Synthesizing the above results, appropriate mixing of FC in FA concrete can improve liquidity, reduce unit quantity and show improvement in strength. In particular, mixed use of FC seems effective in improving early quality of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.119-122
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• 2009

As architectures have recently become high-risers and mega-structured, stable high strength products have been ensured. Accordingly, use of precast concrete accouplement has been increased in order to facilitate air compression and rationalize construction. Since not only external heating but a1so internal temperature rise caused by the accumulation of cement hydration heat in manufacturing process, precast concrete members with large cross-section used for high-rise mega-structure's columns and beams may exhibit different temperature history compared to the precast concrete members for wall and sub-floor with relatively small cross-sections. Therefore, this study aims to elucidate the characteristics of temperature history of mass concrete members cast with high-strength concrete fur precast concrete application. In this study, large cross-sectional precast concrete mock-up, unit cement quantity, and temperature histories in manufacturing precast concrete member under different curing condition were inclusively investigated.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.60-67
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• 2018

The presence of induction motor loads in a power system may cause the phenomenon of delayed voltage recovery after the occurrence of a severe fault. A high proportion of induction motor loads in the power system can be a significant influence on the voltage stability of the system. This problem referred to as FIDVR(Fault Induced Delayed Voltage Recovery) is commonly caused by stall of small HVAC unit(Heating, Ventilation, and Air Conditioner) after transmission or distribution system failure. This delayed voltage recovery arises from the dynamic characteristics associated with the kinetic energy of the induction motor load. This paper proposes the UVLS (Under Voltage Load Shedding) control strategy for dealing with FIDVR. UVLS based schemes prevent voltage instability by shedding the load and can help avoid major economic losses due to wide-ranging cascading outages. This paper review recent topic about under voltage load shedding and compare decentralized load shedding scheme with conventional load shedding scheme. The load shedding strategy is applied to an actual system in order to verify the proposed FIDVR mitigation solution. Simulations demonstrate the effectiveness of the proposed method in resolving the problem of delayed voltage recovery in the Korean Power System.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.22-26
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• 1996

In this paper, we designed 4-channel electrolyte analyzer that can measure simultaneousely the 4 electrolytes - pH, $pNa^{+}$, $pCa^{2+}$, and $pK^{+}-$ using 2-point calibration and implemented it. Developed electrolyte analyzer consists of singal processing part, actuator part and control unit for sample flow system. To implement reliable instrument, design considerations are emphasized on flow system and sample chamber that requires small sample volume and prevent air contact with sample solution. In addition to the hardware design, we developed system software which controls full measuring process. After system developed, we verified the system performance by the test measurement for pH, $pNa^{+}$, $pCa^{2+}$, and $pK^{+}$ value.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.952-961
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• 1989

The purpose of this study is to investigate the behavior of operational and design factors on the performance characteristics of a horizontal fin-tube heat exchanger under phase change conditions for refrigerant. The flow and heat transfer in the heat exchanger are simulated numerically taking into account the variations of heat transfer coefficients, thermodynamic and flow properties of refrigerant, and the axial heat conduction in the tube wall. As the results of this study, it was found that the annular flow model was more reasonable physically than the homogeneous one for the two phase flow of refrigerant and axial heat conduction of tube wall did not have a great influence on the analysis. The effects of refrigerant pressure, mass flow rate of air, diameter of tube and the number of fins per unit length of tube were also discussed.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.252-259
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• 1997

A method to automate hazard analysis of chemical plants is proposed in this paper. The proposed system is composed of three knowledge bases - unit knowledge base, organizational knowledge base and material knowledge base, and three hazard analysis algorithms - deviation, malfunction and accident analysis algorithm. Hazard analysis inference procedure is developed based on the actual hazard analysis procedures and accident development sequence. The proposed algorithm can perform hazard analysis in two methods and represent all conceivable types of accidents using accident analysis algorithm. In addition, it provides intermediate steps in the accident propagation, and enables the analysis result to give a useful information to hazard assessment. The proposed method is successfully demonstrated by being applied to diammonium phosphate manufacturing process. A system to automate hazard analysis is developed by using the suggested method. The developed system is expected to be useful in finding the propagation path of a fault or the cause of a malfunction as it is capable to approach causes of faults and malfunctions simultaneously.

• Restorative Dentistry and Endodontics
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• v.25 no.2
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• pp.219-224
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• 2000

The purpose of this study is for evaluating the effect of MS Coat desensitizing agent in clinical situation. In this study total 60 teeth of 30 patients who is feeling hypersensitivity after periodontal surgery were treated with MS Coat desensitizing agent, and 20 teeth with saline solution for placebo effects and evaluated. All teeth were cleaned with rubber cup and pumice, after then the antibacterial agent was applied for 20 seconds and simply isolated using cotton roll Desensitizing agent was applied with a specific instrument in the manufacturers package by abrading motion for 10 seconds and re-done 8 times. Tactile stimulus with sharp explorer, air stimulus with syringe of dental unit, $7^{\circ}C$ cold water stimulus using micropipette applicator was done to evaluate hypersensitivity before apply test agent, immediate after application, 1 week after, and 3 month after application. The degree of hypersensitivity was recorded using 100mm Visual Analogue Scale and compared between group and evaluation times. From this clinical study sensitivity to the stimulus was significantly induced in both groups and MS Coat made a significant reduction in VAS score than placebo group did(p<.01). The results of this study could demonstrate that MS Coat desensitizing agent can use effectively to heat dentinal hypersensitivity.