• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.4
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• pp.20-30
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• 2001

A novel 200 MHz CMOS transconductor using translinear cells is proposed. The proposed transconductor consists of voltage followers and current followers based on translinear cells and a resistor. For wide applications, a single-input single-output, a single-Input differential-output, and a fully-differential transconductor are systematically designed, respectively. The theory of operation is described and computer simulation results are used to verify theoretical predictions. The results show that the fully-differential transconductor has a linear input voltage range of ${\pm}2.7$ V, a 3 dB frequency of 200 MHz, and a temperature coefficient of less than 41 $ppm/^{\circ}C$ at supply voltages of ${\pm}3$ V. In order to certify the applicability of the fully-differential transconductor, A ladder-type 3th-order cllitic low pass filter is also designed based on the inductance simulation method. The filter has a ripple bandwidth of 22 MHz, a pass-band ripple of 0.36 dB, and a cutoff frequency of 26 MHz.

• Korean Journal of Plant Taxonomy
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• v.38 no.4
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• pp.459-476
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• 2008

Taxonomic characteristics of spores of 17 species belonging to 6 genera of the Korean Thelypteridaceae are examined. Description of each species and key to the species are provided. Spores of Korean Thelypteridaceae are monad and monolete with bilateral symmetry. Perispore, the sporoderm of spore, was found in all the species examined. The perispores and exospores of Thelypteris japonica var. japonica, T. japonica var. glabrata and Pseudocyclosorus subochthodes are much similar to each other, but the rest of taxa examined shows diverse patterns of the surface ornamentation of perispores and exopores enough to distinguish genera and sometimes to distinguish species in some genera. Previous study reported that perispore is not easily distinguished from exospore in Cyclosorus and Leptogramma. However, three species of Cyclosorus examined here show different pattern having scabrate or verrucate exospores and cristate or echinate perispores. Leptogramma pozoi ssp. mollisima also have echinate perispore and fossulate exospore. Macrothelypteris oligophlebia var. elegans and M. viridifrons have scabrate exospore which is contrast to previous report of reticulate exospore. Thelypteris glanduligera, T. angustifrons and T. laxa show same patterns of perispore and exospore with reticulate perispore and fossulate exospore and hence cannot be distinguished by spores only.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.3
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• pp.221-233
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• 2007

In this paper, a simple but effective position profile generation algorithm for single axis high dynamic linear machine drive system is presented. In the recent industrial application fields like as LCD/PDP and semiconductor factory, requirements for the high performance positioning system with optimal position profile generator are highly increased to reduce the overall processing time. There might be various solutions for position profile generating algorithm according to the application type. A square-wave Impact quantity(Jerk) based algorithm with minimal locomotion time is argued in this paper to minimize the total time of one movement under some specific constrains such as maximum speed limit and maximum acceleration limit. In order to reduce the calculation efforts and satisfy the minimal locomotion time condition, the time variants representing each profile sector and a simple condition comparison algorithm are adopted. Also, the actual implementation method for profile generation algorithm and it's real performance results are presented through commercial linear machine drive system.

• Journal of Digital Convergence
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• v.19 no.8
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• pp.75-88
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• 2021

Along with the advent of the Fourth Industrial Revolution, fostering young talents with convergent mind is getting important. Moreover pre-service teachers' ability to design proper convergent classes can be a meaningful issue for high quality future education. This study proposes the role of professors' exquisite feedback is so significant for developing their competence in STEAM education, It analyzed how various theories regarding feedback support them to enhance convergent knowledge with e-learning. They participated in the 5 step group and individual activities for creating STEAM lesson plan and received suitable feedback. Lastly a survey was performed. The researchers did modeling how integrative feedback was applied to the procedure step by step according to the 'Ladder of Inference' theory. This strategic model contributed to elevating the participants' convergent knowledge, competence, achievement and satisfaction.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.467-471
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• 2021

A ladder-like polysilsesquioxane (LPMA64) functionalized with a crosslinkable group was synthesized and used for the preparation of organic-inorganic hybrid gel polymer electrolytes through a thermal crosslinking process of the liquid electrolytes. A small weight percent of LPMA64 polymer crosslinker (5 wt%) was able to form a well-developed network structure, resulting in good dimensional stability with high ionic conductivity. The lithium-sulfur batteries fabricated with organic-inorganic hybrid gel polymer electrolytes exhibited stable C-rate and cycling performance with excellent Coulombic efficiency due to the alleviated lithium polysulfide shuttling effect during prolonged cycling. The result demonstrates that the organic-inorganic hybrid gel polymer electrolytes could be a promising candidate electrolyte for application in lithium-sulfur batteries.

• Journal of Educational Research in Mathematics
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• v.23 no.2
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• pp.253-267
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• 2013

The newly revised mathematics curriculum of 2007 speaks of ultimate goal to develop ability to think and communicate mathematically, in order to develop ability to rationally deal with problems arising from the life around, which puts emphasize on mathematical communication. In this study, analysis on mathematical communication and analogical thinking process of group of students with similar level of academic achievement and that with different level, and thus analyzed if such communication has affected analogical thinking process in any way. This study contains following subjects: 1. Forms of mathematical communication took placed at the two groups based on achievement level were analyzed. 2. Analogical thinking process was observed through trapezoid's area obtaining activity and analyzed if communication within groups has affected such process anyhow. A framework to analyze analogical thinking process was developed with reference of problem solving procedure based on analogy, suggested by Rattermann(1997). 15 from 24 students of year 5 form of N elementary school at Gunpo Uiwang, Syeonggi-do, were selected and 3 groups (group A, B and C) of students sharing the same achievement level and 2 groups (group D and E) of different level were made. The students were led to obtain areas of parallelogram and trapezoid for twice, and communication process and analogical thinking process was observed, recorded and analyzed. The results of this study are as follow: 1. The more significant mathematical communication was observed at groups sharing medium and low level of achievement than other groups. 2. Despite of individual and group differences, there is overall improvement in students' analogical thinking: activities of obtaining areas of parallelogram and trapezoid showed that discussion within subgroups could induce analogical thinking thus expand students' analogical thinking stage.

• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.443-453
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• 2017

In this study, a trapezoidal hollow ball is used, instead of a spherical hollow ball commonly used in void slab, to secure the high hollow ratio in the deck type void slab. The bending and shear performance was measured with consideration for the shape change of the hollow ball. And to confirm the effect of deck plate and truss wire on shear performance, experiments were performed depending on the installation directions of the one-way deck plate. As a result, the bending performance of the deck type void slab with a trapezoidal hollow ball was similar to that of the void slab with a spherical hollow ball. However, according to the data of shear strength examined, the contribution of shear performance enhancement of the truss wire had a more effect on the shear performance of deck type void slab, rather than the influence by changing of the shape of hollow ball. In the previous studies, the shear strength is reduced to about 60%, due to the reduction of the effective section of concrete by installation of hollow ball. But in this experiment, the maximum load of specimen, in which the deck was installed in horizontal direction, so expected to have no influence on the shear performance, was only reduced to about 87%, due to the truss framework of truss wire.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.5
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• pp.62-70
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• 2007

In this paper, the boost Power Factor Correction(PFC) technique for Direct Torque Control(DTC) of brushless DC motor drive in the constant torque region is implemented on a TMS320F2812DSP. Unlike conventional six-step PWM current control, by properly selecting the inverter voltage space vectors of the two-phase conduction mode from a simple look-up table at a predefined sampling time, the desired quasi-square wave current is obtained, therefore a much faster torque response is achieved compared to conventional current control. Furthermore, to eliminate the low-frequency torque oscillations caused by the non-ideal trapezoidal shape of the actual back-EMF waveform of the BLDC motor, a pre-stored back-EMF versus position look-up table is designed. The duty cycle of the boost converter is determined by a control algorithm based on the input voltage, output voltage which is the dc-link of the BLDC motor drive, and inductor current using average current control method with input voltage feed-forward compensation during each sampling period of the drive system. With the emergence of high-speed digital signal processors(DSPs), both PFC and simple DTC algorithms can be executed during a single sampling period of the BLDC motor drive. In the proposed method, since no PWM algorithm is required for DTC or BLDC motor drive, only one PWM output for the boost converter with 80 kHz switching frequency is used in a TMS320F2812 DSP. The validity and effectiveness of the proposed DTC of BLDC motor drive scheme with PFC are verified through the experimental results. The test results verify that the proposed PFC for DTC of BLDC motor drive improves power factor considerably from 0.77 to as close as 0.9997 with and without load conditions.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.360-364
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• 2001

Numerical Aanlysis is made on the thermal performance of micro heat pipe in a axial flat grooved channel. The flow of liquid and vapor is investigated in trapezoidal grooves and the effect of variable shear stress along the interface of the liquid and vapor considered. The results from this study are obtained in the axial variation of pressure difference between vapor and liquid, contact angle, velocity of liquid and vapor and so forth. In addition, maximum heat transport capacity of micro-heat pipe is provided by varying the operation temperature, and compared with that from Schneider and Devos's model in which the interfacial shear stress is neglected.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.143-151
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• 1999

The twisting and extrusion process of the product with trapezoidal helical fin from the round billet is developed by the upper bound analysis. The twisting of extruded product is caused by the twisted die surface connecting the die entrance section and the die exit section linearly. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is increased linearly by axial distance from the die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increases with the die twisting angle, the reduction of area, and decreases with the die length, the friction condition.