• Journal of the Korean Society for Precision Engineering
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• v.23 no.6 s.183
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• pp.104-110
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• 2006

A design and control of electrostatic suspension system for flexible objects is presented. A number of electrode pairs of which the number depends on the object flexibility are positioned above the object and the voltages applied to each electrode pair are controlled, independently on the others, on the basis of the gap length. To implement the system with low cost and compactness, switched-voltage control scheme that is based on the relay feedback control is utilized. Relay feedback control method deploys only a single high-voltage power supply that can deliver a DC voltage of positive and/or negative polarity and thus high voltage amplifiers that are costly and bulky are not needed any more. It is shown that despite the inherent limit cycle property of the relay feedback based control, an excellent performance in vibration suppression is attained due to the presence of a relatively large squeeze film damping originating from the electrodes and levitated object. Employing fourteen electrode pairs, a thin aluminum plate with a thickness of 0.1 mm has been suspended at a gap length of 0.75mm.

• Korean System Dynamics Review
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• v.15 no.4
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• pp.101-127
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• 2014

This study aims to understand how and why each stage of capitalism grows and changes into the new direction in the moment of crisis, based on the systems thinking approach through the causal loop feedback structure. To achieve the research purpose, it classifies the evolution process of the capitalistic economic system into 4 types: Capitalism 1.0(Classical Laissez-Faire Capitalism), 2.0(Revised Capitalism), 3.0(Neo-liberalism), and 4.0(New Capitalism for the Future). This study focuses particularly on by which feedback structure the growth, crisis, and new transition of capitalism could be explained. The main research results are as follows. The intended positive feedback structure caused the growth at each early stage of capitalism. After that time, as a result of the uncontrolled growth, the negative feedback structure controlling its growth operated on the one hand, while the positive feedback structure amplifying the crisis did on the other hand. The study suggests the Resilient Capitalism as the new evolutional direction of Capitalism 4.0. It can contribute to strengthening its resilience by which all the economic players can recover promptly and flexibly from the crises such as the failure of competition and unemployment.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.6
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• pp.16-23
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• 2003

In this paper, we propose an efficient bias circuit of discrete BJT component for hearing aid. The collector feedback bias circuit, widely used for the hearing aid, has a resistor for negative feedback. As the resistor affects AC and DC simultaneously, it is quite difficult to adjust amplifier gain without changing DC bias point. The previous bias circuit also has weak point to be oscillated by the positive feedback of power noise if gain of hearing aid is high. In the proposed circuit, we can reduce the two weak points of the previous circuit by adding a resistor to the collector feedback bias circuit between base and power supply which is $\beta$ times target than the collector resistor. Thus. we can change amplifier gain without changing DC bias point, and reduce power noise gain about 18.5% compare to that of tile previous circuit in the simulation.

• Korean Journal of Child Studies
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• v.22 no.1
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• pp.147-162
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• 2001

This study examined the relation between mother-child verbal interaction strategies and children's narrative competence. Forty-eight 4-year-old middle class children(25 girls and 23 boys) and their mothers were observed in their homes. All the children were asked to produce a new story. Mothers used more descriptive statements and questions, more inferential questions and more evaluative questions than children. Children gave more answers and used more negative feedback than mothers. Mother's use of high-mental demanded question and positive feedback strategies were positively correlated with children's level of narrative structure. Mothers' use of inferential and evaluative questions were positively correlated with narrative length. Children's use of high-mental demanded statements and positive feedback strategies were positively correlated with their level of narrative structure and their use of descriptive and high-mental demanded strategies were positively correlated with narrative length.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.969-974
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• 2003

A simple and cost-effective method for the electrostatic suspension of thin plates like silicon wafers is proposed which is based on a switched voltage control scheme. It operates according to a relay feedback control and deploys only a single high-voltage power supply that can deliver a dc voltage of positive and/or negative polarity. This method possesses the unique feature that no high-voltage amplifiers are needed which leads to a remarkable system simplification relative to conventional methods. It is shown that despite the inherent limit cycle property of the relay feedback based control, an excellent performance in vibration suppression is attained due to the presence of a relatively large squeeze film damping origination from the air between the electrodes and levitated object. Using this scheme, a 4-inch silicon wafer was levitated stably with airgap variation decreasing down to 1 $\mu\textrm{m}$ at an airgap of 100 $\mu\textrm{m}$

• Korean Journal of Child Studies
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• v.22 no.2
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• pp.77-90
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• 2001

This study used 2 coordination tasks to examine the strategy and quality of interactions between mothers and their children. Results were: (1) Most frequently employed strategies of mothers were feedback, orders, explanations followed by questions and opinions. Most frequently employed strategies of children were offering opinions followed by recognition and explanation. (2) In mother-initiated interactions, the mother's-question/child's-opinion sequence was most frequent, and child's acceptance of mother's order, explanation, suggestion, or opinion; child's question to mother's order, and child's explanation were also frequent. In child-initiated interactions, child's-opinion/mother's-feedback occurred most frequently. Mothers' feedback to child's explanation, acceptance, and question was also observed. (3) When mothers and children used strategies of low quality, such as rejection or reprimand, the interactions tended to be negative.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.231-234
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• 2002

In this paper, we propose an efficient bias circuit for hearing aid using discrete BJT. The collector feedback bias circuit, widely used for the hearing aid, has a resister for negative feedback. As the resistor affects AC and DC simultaneously, it is quite difficult to adjust amplifier gain without changing DC bias point. The previous bias circuit also has weak point to be oscillated by the positive feedback of power noise if gain of hearing aid is high. In the proposed circuit, we can reduce the two weak points of the previous circuit by adding a resistor which is ${\beta}$ times larger than collector resistor between base of BJT and power supply.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1696-1701
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• 2003

This paper deals with a vibration control analysis of a rotating composite blade, modeled as a tapered thinwalled beam induced by heat flux. The displayed results reveal that the thermally induced vibration yields a detrimental repercussions upon their dynamic responses. The blade consists of host graphite epoxy laminate with surface and spanwise distributed transversely isotropic (PZT-4) sensors and actuators. The controller is implemented via the negative velocity and displacement feedback control methodology, which prove to overcome the deleterious effect associated with the thermally induced vibration. The structure is modeled as a composite thin-walled beam incorporating a number of nonclassical features such as transverse shear, secondary warping, anisotropy of constituent materials, and rotary inertias.

• Korean System Dynamics Review
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• v.10 no.1
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• pp.97-107
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• 2009

In this paper, a structural similarity between traditional oriental philosophy and systems thinking is discussed. The polarity of causal relationship and feedback loops can be interpreted in terms of yin and yang of oriental philosophy. A positive feedback loop which is linked to the yang is a force or mechanism that accelerates changes in systems. A negative feedback loop which is linked to the yin can be interpreted as a force oppressing any changes. In this sense, systems thinking can be related to the oriental philosophy. With this linking pin between them, systems thinking can be introduced and educated more friendly in oriental society. Furthermore, systems thinking can get a set of rich insights from the oriental philosophy. This paper suggests a linking leverage between systems thinking and oriental philosophy.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.56-64
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• 2005

A simple and cost-effective method for the electrostatic suspension of thin plates like silicon wafers is proposed which is based on a switched voltage control scheme. It operates according to a relay feedback control and deploys only a single high-voltage power supply that can deliver a DC voltage of positive and/or negative polarity. This method possesses the unique feature that no high-voltage amplifiers are needed which leads to a remarkable system simplification relative to conventional methods. It is shown that despite the inherent limit cycle property of the relay feedback based control, an excellent performance in vibration suppression is attained due to the presence of a relatively large squeeze film damping origination from the air between the electrodes and levitated object. Using this scheme, a 4-inch silicon wafer was levitated stably with airgap variation decreasing down to $1 {\mu}m$ at an airgap of $100{\mu}m$.