• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.610-615
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• 2014

Filterbanks have been widely used in the field of multi-channel signal processing for their simple efficient implementation architectures. Especially, the polyphase DFT(Discrete Fourier Transform) filterbank is the most preferred filterbank for the uniform spaced multi-channel processing due to its simplicity. In frequency hopped communication systems, however, the use of the polyphase DFT filterbank is limited due to its undesirable transient response from hop-to-hop transitions. In this paper, the transient response of polyphase DFT filterbanks in the hop-to-hop transition was analyzed, and the efficient methods to overcome such a problem was proposed. Simulation results showed that the proposed schemes could resolve this issue efficiently.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.6
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• pp.531-536
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• 2002

This paper investigates the problem of the speed controller of conventional speed sensorless stator flux-oriented(SFO) induction motor drive, and proposes a robust speed controller to solve the conventional problem. In the proposed method, a robust speed controller for speed sensorless SFO system Is designed by taking advantage of disturbance torque observer and using feedforward.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.6
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• pp.554-562
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• 2002

This paper presents a new sensorless control scheme using simple duty signal feedback technique in DC/DC converters. The proposed Duty Feedback Control(DFC) has the characteristics that they show the same as operation performance of current mode control by using duty feedback technique without current sensor as well as present faster dynamic response performance than conventional Sensorless Current Mode(SCM) control in case that input source is perturbed by step change or DC input source includes the harmonics. Also, the proposed control scheme has good noise immunity and simple control circuits since they have one feedback loop, and can be applied to all DC/DC converters. The concept and control principles of the proposed control scheme are explained in detail and the validity of the proposed control scheme is verified through several interesting simulated and experimental results.

• Journal of IKEEE
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• v.24 no.4
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• pp.1074-1080
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• 2020

This paper proposes a digitally controlled buck converter insensitive to process, voltage and temperature and capable of three modes of operation depending on the state of the output voltage. Conventional digital-controlled buck converters utilized A/D converters, counters and delay line circuits for accurate output voltage control, resulting in increasing the number of counter and delay line bits. This problem can be resolved by employing the 8-bit and 16-bit bidirectional shift registers, and this design technique leads a buck converter to be able to control duty ratio up to 128-bit resolution. The proposed buck converter was designed and fabricated with a CMOS 180 nano-meter 1-poly 6-metal process, generating an output voltage of 0.9 to 1.8V with the input voltage range of 2.7V to 3.6V, a ripple voltage of 30mV, and a power efficiency of up to 92.3%. The transient response speed of the proposed circuit was measured to be 4us.

• Journal of the Korean Chemical Society
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• v.63 no.4
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• pp.280-288
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• 2019

The purpose of this study is to draw implication for scientific inquiry study by investigating level of understanding and actual state regarding the elementary school teachers' scientific inquiry. The survey was conducted toward 42 elementary school teachers who work at the D city by using questionnaire of Views About Scientific Inquiry. Actual state of understanding of scientific inquiry was investigated by categorized the responses to the level of understanding of the eight aspects of scientific inquiry in three levels (informed, mixed, naive) based on analysis criteria. And analyze whether the characteristic of the subjects affect to level of understanding about aspect of scientific inquiry. As a result of the analysis, the two aspects among the eights aspects of scientific inquiry; 'Inquiry procedures are guided by the question asked' and 'Research conclusions must be consistent with the data collected' were appeared to have high rates of informed level of understanding. In the remaining six perspectives, most of elementary school teachers had naive and mixed level of understanding, so informed level of understanding took a relatively low proportion. It implies that elementary school teachers who teach inquiry in the field have limit to understand about scientific inquiry. These results indicated that experiences that have taught students and science related training courses that open sofar have a little influence to increase comprehension about scientific inquiry. Therefore, it is required to reinforce the teachers' understanding about scientific inquiry and to formulate different form of plan unlike existing way of teaching for teaching scientific inquiry.

• Journal of the Korean Society of Clothing and Textiles
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• v.33 no.12
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• pp.1897-1909
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• 2009

This large-scale research project contributes to the theory development in the importance of clothing to the self and in the way that older persons might age successfully by fulfilling the need for self-actualization by incorporating a primary resource environment, such as clothing into their self-system. This paper presents one research objective from a lager project that explores the correlations among the Proximity of Clothing to Self (PCS), age identity (subjective or perceived age), and self-actualization (the highest level of human needs). A mail survey design was applied to this study. In November 2004, two questionnaires, Clothing: A Resource for Successful Aging? (to measure PCS, age identity, and demographic variables) and Personal Orientation Inventory (to measure self-actualization), were sent to 1,700 older persons in the U.S. and 195 completed usable questionnaires were returned (12% response rate). This research discovered that the age identity of older persons did not relate with PCS except for those 85 years and over. There were negative correlations among subscales of PCS and self-actualization. This result can be interpreted as that an older person who has not met the highest level of needs yet, can use clothing as a facilitator or need satisfier to meet a higher level of Self-Actualization (SA). Correlation analyses also revealed that older persons in the age category of 75 to 84 years were different from those in the category of 65 to 74 years and 85 years and over. This result implies that older persons in this age category are undergoing more psychological transitions than those in other categories. Further research is necessary to explore the relationship of several SA subscales with various clothing variables such as clothing interest, clothing involvement, or clothing satisfaction.