• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.224-234
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• 2008

Multi-phase machines can be used in variable speed drives. Their applications include electric ship propulsion, 'more-electric aircraft' and traction applications, electric vehicles, and hybrid electric vehicles. Multi-phase machines enable independent control of a few numbers of machines that are connected in series in a particular manner with their supply being fed from a single voltage source inverter(VSI). The idea was first implemented for a five-phase series-connected two-motor drive system, but is now applicable to any number of phases more than or equal to five-phase. The number of series-connected machines is a function of the phase number of VSI. Theoretical and simulation studies have already been reported for number of multi-phase multi-motor drive configurations of series-connection type. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information concerning the rotor speed is extracted from measured stator currents and voltages at motor terminals. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an MRAS estimator based sensorless control of a vector controlled series-connected two-motor five-phase drive system with current control in the stationary reference frame. Results, obtained with fixed-voltage, fixed-frequency supply, and hysteresis current control are presented for various operating conditions on the basis of simulation results. The purpose of this paper is to report the first ever simulation results on a sensorless control of a five-phase two-motor series-connected drive system. The operating principle is given followed by a description of the sensorless technique.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.685-688
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• 2005

An efficient sustain driver and a useful reset circuit composition technique are proposed for plasma display panel drive. The proposed sustain driver uses a series resonance between an external inductor and a panel to recover the energy dissipated by a capacitive displacement current of PDP. It consists of four switching devices, an inductor, and external capacitors, which supply sustain voltage sources. Although the amplitude of an input voltage source is twice as high as that of conventional sustain drivers, average voltage stress imposed on power switching devices is nearly same in their values. Moreover, the input voltage source can be directly applied for the use of a reset voltage source. Owing to this scheme, the proposed sustain driver and the embedded reset circuit have a simple configuration. The operational principle and design example are given with theoretical analyses. The validity of the proposed drive system is verified through experiments using a prototype equipped with a 7.5-inch-diagonal AC plasma display panel.

• Journal of Navigation and Port Research
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• v.26 no.2
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• pp.235-243
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• 2002

Theoretical analysis have been performed to design the high power semiconductor laser for an optical sensor at 1.55${\mu}{\textrm}{m}$ wavelength range which is the lowest loss wavelength in optical fiber. The materials of active region and SCH were $Ln_{1-x}Ga_xAs_yP_{1-y}$. In order to use the light source of optical sensors, it has to satisfy wide spectral width and short coherence length. Therefore, in order to suppress lasing oscillation, we proposed laterally tilted PBH type with a window region. Also, tapered stripe structure was applied for high coupling efficiency into a single mode fiber. From these analyses, the devices of laterally tilted angled and bending structure were fabricated and their characteristics were measured. In the results of the measurement, the fabricated devices have sufficient output power and wide FWHM to apply to the light source of optical fiber sensors.

• Journal of Korea Technology Innovation Society
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• v.20 no.4
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• pp.970-988
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• 2017

As an innovation cluster has become an important policy tool for attaining regional and national competitiveness, many nations and regions are making great efforts to foster innovation clusters. In the case of Korea also, many innovation clusters have been established and some of them are recently receiving a lot of attention due to their performance. In fact, there have been lots of investment by the central and regional governments. However, there have been no in-depth analyses on Korean successful innovation clusters. This study investigates some of the success factors of a Korean representative innovation cluster, Pangyo Techo Valley. We find out that the Pangyo Techno Valley has four groups of success factors: innovative environment, consistent policy support by regional government, knowledge networks, and good feed-back system of innovation. Our findings would have some theoretical and practical implications for innovation cluster research and policy practice.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1852-1865
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• 2017

The vibration of the structures with restrained motion has long been observed in various engineering fields. When the motion of vibrating structure is restrained due to the adjacent objects, the frequencies and the mode shapes of the structure change and its vibration characteristics becomes unpredictable, in general. Although the importance of the study on this type of vibration model increases in many engineering areas, most studies conducted so far are limited to the theoretical study on dynamic responses of the structure with stops, including some experimental works. Specially, the study on the nonlinear phenomena due to the impact between the structure and the stops have been mainly performed theoretically. In the paper, both numerical analyses and experiments are conducted to study the chaotic vibration characteristics of the nonlinear motion and the dynamic response of a cantilevered beam which has restrained motion at the free end by the stops. Results are presented for various magnetic forces and gaps between the beam and stops. The conclusions are as follows : Firstly, Numerical simulation results have a good agreement with experimental ones. Secondly, the effect of higher modes of beams are increased with increasing magnitude of exciting force, and displacement and velocity curves become more complicated shapes. Thirdly, nonlinear characteristics tend to appear greatly with increasing magnitude of exciting force, and fractal dimension is increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.875-882
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• 2014

The purpose of this study is to examine the effects of social capital on the life satisfaction of the community residents. For the research, social capital was consisted of participation, network, trust and norm. To achieve the purpose of this research, data were collected from 279 citizens of S-city in Gangwon-Do. The results of this study were summarized as follows: Mean analyses showed that social capital had $3.02{\pm}.52$. According to hierarchical multiple-regression, participation(${\beta}$=.26, p<.001), network(${\beta}$=.17, p<.01) and trust(${\beta}$=.16, p<.01) among social capital showed positive influence on life satisfaction of community residents(R2=.35). This study finally discussed theoretical implications for future study and practical implications on the results.

• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.463-472
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• 2007

This paper presents theoretical and finite element analysis results for the lateral-torsional buckling of I-girders with corrugated web under uniform bending. Lateral-torsional buckling is a major design aspect for flexural members composed of thin-walled I-section. However, torsional rigidities such as the warping constants of the I-girders with corrugated web are not fully understood yet. In this paper, bending and pure torsional rigidities of I-girders with corrugated web are first described using the results of previous researchers. Then, the location of the shear center and the warping constants are derived. Using the derived section properties of I-girders with corrugated web, the lateral-torsional buckling strength is determined. Finite element analyses are conducted and the proposed lateral-torsional buckling strength of I-girders with corrugated web is successfully verified. Finally, the effects of corrugation profiles of the web on the lateral-torsional buckling load of I-girders with corrugated web are discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.585-596
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• 2013

This study introduces a hybrid approach combining numerical results with pre-developed analytical calculations for the sound radiation from the modal vibration of a thick, finite length cylinder with various boundary conditions. Structural vibrations of the cylinder are numerically investigated with the finite element method, and distributions of vibratory displacements on the cylinder surface are idealized as simple mathematical expressions based on the numerical results. Sound radiations from the normal vibration of the cylinder are calculated based on idealized modal displacements using a previously introduced theoretical solution. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the solutions suggested in this study have good accuracies in calculating the vibro-acoustic properties of a thick, finite cylinder with various boundary conditions. Also, the sound radiation characteristics of many practical components such as brake drums and motor housings are expected to be investigated using the procedure proposed in this study.

• Journal of Community Nutrition
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• v.3 no.1
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• pp.21-29
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• 2001

This study was conducted to examine factors with attendance in hyperlipidemia nutrition eduction program among 101 hyperlipidemic outpatients (38 males 63 females) at Samsung Medical Center We employed the Health Belief Model (HBM) as the theoretical framework The individual nutrition education and counseling program was scheduled with 4- half hour session sin 2 to 4 weeks intervals. Upon initiation of the program a trained dietitian surveyed HBM constructs and psychosocial factors. The following were included perceived susceptibility to cardiovascular disease(CVD) perceived severity to CVD percieved benefits to diet modification perceived barriers to persistence in maintaining therapy and self efficicacy and social support from family Sociodemographic data health factors stress level nutrition knowledge, and 24-hour dietary recall behavior were also surveyed All these data was analyzed according to the number of nutrition sessions attended The subjects were 55.9$\pm$9.4 year old and 24.6$\pm$kg/㎡ Sociodemographic factors were not associated with the number of nutrition sessions attended HBM constructs and psychosocial factors were significantly associated with the number of nutrition sessions attended. According to Spearman correlation coefficients. From stepwis regression analyses using HBM constructs as independent variables perceive barriers to persistence in maintaining diet therapy (negative) proved to be the strongest predictors for the number of nutrition sessions attended (partial R$^2$= 72.3%) followed by perceived severity to CVD and self efficacy (model R$^2$=76.6% The findings indicate that HBM constructs and psychosocial factors were closely associated with patient attendance It suggests that information and guidance to minimize patients perceived barriers to diet therapy might help to improve patients to scheduled appointments in nutrition education programs.

• The Journal of the Korea Contents Association
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• v.17 no.5
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• pp.285-304
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• 2017

This paper introduces household's decision for schooling and firm's decision for technology-specific training together into the second generation model of endogenous innovation, and analyses how schooling and technology-specific training interact each other, how they respectively affect innovation and economic growth, and also how the portfolio mix of schooling and technology-specific training changes as economy becomes more innovative. Main results are as follows: First, schooling and technology-specific training both have "inverted-U"shape growth effects. Second, schooling investment per labor required for growth maximization is always greater than that for firm profit maximization. Third, the optimal schooling for growth maximization decreases with technology-specific training. Fourth, the schooling effect on technology-specific training is "U"shaped, so that for firm's profit maximization schooling is substitutable for technology-specific training at the relatively lower level of schooling but complementary at its relatively higher level. Fifth, as economy becomes more innovative, the portfolio mix of education changes in favor of schooling.