• Tribology and Lubricants
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• v.12 no.4
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• pp.7-12
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• 1996

Present study was undertaken to investigate the leakage and friction of self-lubricating piston seal rings. A crank-piston type gas leakage test set-up was constructed. The piston rings were made of PTFE-polyimide composite. The free gap configurations of the seal rings were butt and step types. Eccentric tension rings were used to give the seal rings prepressure between the seal rings and cylinder wall. Two sizes of the tension rings were installed to investigate their effect on the gas leakage and friction of the seal rings. The results showed that step type seal rings are superior than the butt types. High tension spring rings resulted in low leakage and high friction loss. In order to reduce the gas leakage and friction loss of the piston seal rings, there should be compromise between the number of ring stages and prepressure of the tension rings.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2783-2785
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• 1999

A fast switching gate driver suitable for high performance self resonant electronic ballasts is presented. The proposed gate driver has negligible switching loss and driving loss owing to pnpn structure and zero voltage switching( ZVS ); moreover, the gate driver has frequency control capability. Therefore, a self resonant inverter using proposed gate driver can operate as external exciting resonant inverters. The experiments confirm that the proposed gate driver perform the desired operations over full power control range for 40W fluorescent lamp electronic ballast.

• Progress in Superconductivity and Cryogenics
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• v.1 no.1
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• pp.38-41
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• 1999

Strands composing multistage superconducting cables for AC power applications have twisted structure in each stage for lower AC loss and higher stability. So, when transport currents flow in a cable, each strand is exposed to longitudinal and azimuthal magnetic fields produced by transport current flowing in strand itself and Iongitudinal and transverse magnetic fields by transport current flowing in twisted cable. In this paper. we study the influence on self field lesses generated in second stage superconducting cable for different twist direction of filaments in a strand considering twist of strands in cables.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.47-53
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• 2019

This study examined the effects of risk aversion on the Self-Insurance-cum-Protection activity (SICP) in a two period model, which is in contrast to existing studies that focused on an one period model. The assumption that there is a time difference between making an effort and incurring loss helps examine the effects of risk aversion in the long-term period. An increase in risk aversion always increases the efforts of SICP, whereas existing studies require additional restrictions to both the loss and cost function. Second, an increase in risk aversion always increases the efforts on self-insurance and self-protection. This result is in contrast to that of existing studies in that an increase in risk aversion increases the efforts of self-insurance, whereas the effects on the efforts of self-protection are unclear. Lastly, when there exists a background risk with zero mean and risk aversion increases in a two period model, the prudence condition of the utility function is a sufficient condition to increase the efforts of SICP.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.395-399
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• 1996

The Clamp Mode(CM) Forward Zero Voltage Switching Multi Resonant Converter(ZVS-MRC) with self-driven synchronous rectifier in studied. The loss at the synchronous rectification stage of the converter is analyzed using MOSFET linear model and is compared with the loss at the conventional schottky diode rectification stage of the converter. From the results of the analysis, it is known that the use of MOSFETs as a synchronous rectifier reduces the loss at the rectification stage over the whole load range comparing the use of schottky diodes as a conventional rectifier in the converter. In order to verify the validity of the analysis, we have built a 33W(3.3V/10A) CM Forward ZVS-MRC with self-driven synchronous rectifier, in which switching frequency is 1MHz, and tested. From the experimental results, it is known that the synchronous rectification achieved about 1W improvement in the loss at the rectification stage and about 3% in the efficiency at the converter as compared with the conventional schottky diode rectification.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1992.04b
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• pp.403-412
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• 1992

This note examines a situation where a risk-neutral insurer and a risk-averse individual (prospective insured) negotiate to reach an arbitration point of the price of insurance over the terms of an insurance contract in order to maximize their respective self-interests. The situation is modeled as a Nash bargaining problem. We analyze the dependence of the price of insurance, which is determined by the Nash solution, on the parameters such as the size of insured loss, the probability of a loss, the degree of risk-aversion of the insured, and the riskiness of loss distribution.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.69-72
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• 2007

In this paper, we describe the analysis of interior noise for tilting train that is being developed in Korea. Tilting train is made of composite material to reduce the car body's weight and attached a self-steering system on bogie to improve curving performance. However, the acoustic performance (Transmission Loss) of such material is worse than the materials of conventional train, such as aluminum, steel and so on. Therefore, we measure the transmission loss of side wall / floor of tiling train and predict the interior noise for tilting train using its measuring results

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.45-48
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• 2005

Self compacting concrete has the strong point in capability of concrete to be uniformly filled and compacted in every corners of formwork by its self-weight without vibration during placing. However, powder type self compacting concrete has the weak point in the heat of hydration, the drying shrinkage and the elastic property of concrete etc. Recently viscosity agent has been developed in order to overcome these weaknesses. In this study, self compacting concrete is made with viscosity agent based on polysaccharide derivative in order to develope the normal strength self compacting concrete. Slump flow, loss of slump flow and setting time are measured for comparison with normal concrete. Compressive strength, freezing and thawing test and carbonation test are conducted on normal and self compacting concrete using viscosity agent. In the experiment, we acquired good results in fresh and hardened self compacting concrete using viscosity agent based on polysaccharide derivative.

• The Journal of Korea Robotics Society
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• v.6 no.3
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• pp.230-236
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• 2011

In previous researches, the self-stability was studied for the spring-mass model and the two segment leg model. In these researches, it was presented that the spring-mass model has the self-stable region at relatively high speed running and the two segment leg model has the self-stable region at relatively low speed running. If the model was run in the self-stable region, the cost of transport is zero ideally. That is, actually, only the energy loss is needed to compensate for running. This means that the energy efficiency is high, running in the self-stable region. We want to have high energy efficiency at low and high speed running. So, in this paper, we propose the design direction of the three segment leg having the self-stable region at low and high speed running. And we prove the self-stable region of the three segment leg designed by the proposed design direction.

• Journal of Korean Academy of Nursing
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• v.22 no.2
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• pp.157-173
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• 1992

The purposes of study were to investigate the prenatal psychological adaptation and the perception of birth experience, and to identify the relationship between them. The subjects consisted of 162 women who visited the obstetrical outpatient clinic for prenatal examinations and who delivered the in babies at SNUH during the period from June 20 to August 10, 1990. The tools used for measurement were Lederman's Prenatal Self Evaluation Questionnaire and Marut & Mercer's scale of the Perception of Birth. The results are summarized as follows : 1. The orders and item means of psychosocial adaptation in pregnancy were the Acceptance of pregnancy(1.58). Identification of motherhood role(1.63). Relationship with husband(1.65) and Relationship with mother(1.67). The preparation for labor, concern for wellbeing of self and baby, and fear of pain, helplessness and loss of control were found to be less adaptive. 2. The level of the perception of the birth experience was mid-range(item mean : 3.22). The score of the perception of birth experience for primiparas was higher than for multiparas. However there was not a significant difference the groups. There were significant differences in the perception of the birth experience between certain general characteristics, namely, sex of the baby(p＜0.05), type of delivery(p＜0.005), and type of anesthesia(p＜0.005). 3. There were significant differences in the perception of the birth experience between the groups below the mean and above the mean of concerti for wellbeing of self and baby, Fear of pain, Helplessness and loss of control, Relationship with husband and Identification of motherhood role (p＜0.05). The perception of the birth experience was predicted by Fear of pain, Helplessness and loss of control (11%), Type of Delivery(6%), Concern for wellbeing of self and baby(3%), Preparation for labor(1%), sex of baby(1%), Relationship with mother(1%), Parity(1%) and Identification of motherhood role(1%). The Childbirth education should be revised to improve the psychosocial adaptation in pregnancy.