• Journal of Power Electronics
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• v.18 no.1
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• pp.81-91
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• 2018

This paper proposes a double line voltage synthesis (DLVS) strategy for three-to-five phase direct matrix converters. In the proposed strategy, the input and expected output voltages are divided into 6 segments and 10 segments, respectively. In addition, in order to obtain the maximum voltage transfer ratio (VTR), the input line voltages and "source key" should be selected reasonably according to different combinations of input and output segments. Then, the corresponding duty ratios are calculated to determine the switch sequences in different segment combinations. The output voltages and currents are still sinusoidal and symmetrical with little lower order harmonics under unbalanced or distorted input voltages by using this strategy. In addition, the common mode voltage (CMV) can be suppressed by rearranging some of the switching states. This strategy is analyzed and studied by a simulation model established in MATLAB/Simulink and an experimental platform, which is controlled by a DSP and FPGA. Simulation and experimental results verify the feasibility and validity of the proposed DLVS strategy.

• Journal of Educational Research in Mathematics
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• v.25 no.2
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• pp.189-206
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• 2015

There has been a recurring call for using visual representations in textbooks to improve the teaching and learning of proportional reasoning. However, the quantity as well as quality of visual representations used in textbooks is still very limited. In this article, we analyzed visual representations presented in a Grade 6 textbook from two perspectives of proportional reasoning, multiple-batches perspective and variable-parts perspective, and discussed the potential of the double number line and the double tape diagram to help develop the idea 'things covary while something stays the same', which is critical to reason proportionally. We also classified situations that require proportional reasoning into five categories and provided ways of using the double number line and the double tape diagram for each category.

• Journal of Educational Research in Mathematics
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• v.27 no.4
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• pp.791-810
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• 2017

This study explored the possibility of using visual models in teaching proportional reasoning based on the review of previous studies. Many studies on proportional reasoning emphasize that students tend to simply apply formal procedures without understanding the meaning behind them and that using visual models may be an alternative to help students develop informal strategies and proportional reasoning. Given these, we re-constructed and implemented the unit of a textbook to teach sixth graders proportional reasoning with ratio table, double number line, and double tape diagram. The results of this study showed that such visual models helped students understand the meaning of proportion, explore the properties of proportion, and solve proportional problems. However, several difficulties that students experienced in using the visual models led us to suggest cautionary notes when to teach proportional reasoning with visual models. As such, this study is expected to provide empirical information for textbook developers and teachers who teach proportional reasoning with visual models.

• Education of Primary School Mathematics
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• v.22 no.1
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• pp.29-48
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• 2019

Previous studies on double scale models, visual models with two different scales (Chong, 2015), have focused on double number line and little research has been conducted on how to employ double scale models in the elementary mathematics textbooks series. Given this, we analyzed the characteristics of double scale models in the Japanese elementary mathematics textbooks in the following aspects: (a) the contents of units where double scale models were used; (b) the purposes of using such models; (c) the types of such models tailored to the contents and grade levels; and (d) the characteristics of problem contexts dealing with the models. The results of this study showed that double scale models were effectively used to connect the contents related to multiplication, specifically for the contexts of ratio. Such models were addressed for students in a systematic and gradual way as the grade levels went up. Based on these results, this paper describes implications on how to use double scale models in mathematics textbooks.

• Archives of Plastic Surgery
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• v.50 no.2
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• pp.142-147
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• 2023

Some of Asian eyelids have double fold and some do not. Many people tend to prefer double eyelid in aesthetic and functional reasons. Since the mechanism of double eyelid is bonding the eyelid skin to the eye-opening tissue, the principle of double eyelid surgery is also connecting the eyelid skin to levator component. Double eyelids are differentiated by their shape according to the height and curvature. The double eyelid surgery procedure is divided into incision method and nonincision method. And the incision method is subdivided into double fold line design, skin and oculi muscle incision or excision, pretarsal or preaponeurotic soft tissue excision, fixation of posterior lamella to anterior lamella, and skin suture. The nonincision method is to connect the posterior lamella and the anterior lamella as a thread only without an incision. A successful double eyelid surgery creates a fold well-balanced in height, curvature, and depth of the fold based on patient's preference. In this article, the author's own methods of performing surgery are described, with a step-by-step guide and surgical tips.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.7
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• pp.1033-1037
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• 2013

Coercion transformer is commonly used in the electrical grid which in three phase of distribution system. The accident of the electrical grid is divided into a single, a double, a third line-to-ground faults and a double, a third line-to-line faults. A single line-to-ground fault accounts for nearly 75[%] among them. In this research, when a Superconducting Fault Current Limiters (SFCL) was applied to the three phase power system, operation in a single line-to-ground fault and limiting characteristics of fault current according to turns ratio of third winding were analyzed. When a single line-to-ground fault happened, secondary winding's circuit was open. Then third winding's circuit with a SFCL was closed. So fault current was limited by diverted circuit. At this time, we could find out that size of the limited fault current could be changed according to third winding rate. We confirmed that limiting operation of the fault current was carried out within one-period. These results will be utilized in adjusting the size of the SFCL.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.335-336
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• 2008

Overhead transmission lines are mainly crossing mountainous area. They are easily affected in weathers like typhoon, strong wind, lightning, heavy rain, or heavy snow. Sometimes these weathers cause transmission line faults. A lightning flashover is most often fault. Nowadays lightning density in KOREA is growing high and lightning flashovers occur more often. A lightning flashover on transmission line is mostly cleared by momentary operation of a circuit breaker, so power failure happens rarely. However, when both circuits trip simultaneously due to the lightning flashovers on double circuit transmission line, short time power failure and voltage drop happen. KEPCO has used transmission line arresters to avoid double circuit simultaneous trip out since 2003. And transmission line arresters cannot be installed with KEPCO's present metal fittings, so various fittings have been used for each transmission line arrester manufacturer. This paper introduces development and standardization of arc-horn and metal fittings for transmission line arrester which can be used for both existing lines and new lines in KEPCO.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.2
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• pp.101-107
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• 2009

This paper deal with development of on-line type voltage sag compensation system using supercapacitor EDLC to solve the voltage sag problems which are considered to be dominant disturbances affecting the power quality. With the wide use of semiconductor devices in electrical equipment, modem-type loads are becoming increasingly sensitive to the voltage sags and the disturbances prove to be costly to industries. Supercapacitor EDLC is employed to compensate dynamically for the voltage sag of system with sensitive loads. This capacitor has higher energy density than the electrolytic capacitor. Also, this capacitor has a lot of advantage such as no maintenance, longer life cycle and faster charge-discharge time than the battery system. Therefore, in this paper, the energy design scheme of supercapacitor and the configuration technique of on-line type voltage sag compensation systems are newly introduced. According to the results of experimental of prototype 5[kVA] system, it is verified that the developed system has effectiveness of voltage sag compensation by using a supercapacitor EDLC.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.451-455
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• 1996

This paper specified the measurement results conducted by the Korea Electric Power Research Institute (KEPRI) 765kV double circuit transmission test line that measured the audible noise, hum noise, radio interference, electric field and aeolian measurement. This test line consists of 6-480mm$^{2}$ conductors per phase. The analysis of the test results shows that this 6-Rail conductor bundle satisfies the audible noise criterion under the stable rainy weather condition and the radio interference level under the fair weather. And the other items are also agreed with the design level criterion. (author). 9 refs., 7 figs., 2 tabs.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.23-31
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• 2015

This paper proposes an advanced distance relaying based on the DC offset removal filter to minimize the effects of DC offset on a double circuit transmission line. The proposed DC offset removal filter uses only one cycle of data for phasor extraction computation, which does not need to preset the time constant of the DC offset component. This proposed distance relaying uses not only the residual current of the faulted circuit but also mutual current of the healthy adjacent circuit. A series of off-line test results using ATP simulation data show the effectiveness of the an advanced distance relaying.