• The Journal of Industrial Distribution & Business
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• v.9 no.1
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• pp.39-49
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• 2018

Purpose - This present aims to analyze the effect of export modes on initial export amount and time to export by selecting export modes among various success strategies and factors. Research design, data, and methodology - It surveyed 980 small and mid-sized venture enterprises across Korea. The export modes and its impact on exports through frequency analysis and cross analysis, and validated through a PPML(regression analysis applied the enterprise growth model) analysis. Results - Five export modes were investigated : direct export, indirect export, transfer from direct export to indirect export, transfer from direct export to indirect export, and parallel export to indirect export. It was found that SMVEs that exported directly from establishment to initial export had the shortest period, and also had the highest export price Conclusions - From a marketing point of view, it took an average of 1.6 years to switch from export directly to indirect export or directly export, and the reason for the export modes conversion was to supplement export specialists and improve export competitiveness. And the export amount and time period that SMVEs establishes and export is a significant factor in export success strategy and there has been few prior study in export modes.

• Journal of the Korean Solar Energy Society
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• v.28 no.5
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• pp.85-95
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• 2008

Photovoltaic conditioning systems normally use a maximum power point tracking (MPPT) technique to deliver the highest possible power to the load continuously when variations occur in the insolation and temperature. A unique method of tracking the maximum power points (MPPs) and forcing the boost converter system to operate close to these points is presented through deriving small-signal model and transfer function of boost converter considering input capacitor. This paper aims at modeling boost converter including fairly large equivalent series resistance(ESR) of input reservoir capacitor by state-space-averaging method and PWM switch model. In the future, properly designed controller for compensation will be constructed in 3kw real system for maximum photovoltaic power tracking control.

• International Journal of Computer Science & Network Security
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• v.21 no.12spc
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• pp.483-490
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• 2021

The COVID-19 pandemic has posed significant community challenges towards higher education around the world. The urgent and unexpected request for full-time university courses to switch over to online teaching was a particular challenge. Online learning and learning imply a certain pedagogical knowledge content (PKC), mainly related to the design and organization for better learning and the creation of unique learning environments using digital technologies. With the help of the present academic paper, we provide some expert opinion on the PKC connected with online learning with the aim of helping non-university professionals (that is, those with lack of online learning experience) navigate these challenging times. Our findings point to the planning of learning activities with certain features, a combination of three types of presence (social, cognitive and facilitative) and the need to adapt the assessment system to new learning requirements. We will conclude by contemplating on how responding to a crisis can improve teaching and learning practices in the post-digital era.

• Journal of Power Electronics
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• v.19 no.4
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• pp.1011-1019
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• 2019

In this paper, a buck-flyback (fly-buck) stand-alone photovoltaic (PV) system for charge balancing with a differential power processor (DPP) circuit is proposed. Conventional feed-back DPP converters draw differential feed-back power from the output of a string converter. Therefore, the power is always through the switches and diodes of the string converter. Because of the returning conduction path, there are always power losses due to the resistance of the switch and the forward voltage of the diode. Meanwhile, the proposed feed-back DPP converter draws power from the magnetically-coupled inductor in a string converter. This shortens the power path of the DPP converter, which reduces the power losses. In addition, the extra winding in the magnetically-coupled inductor works as a charge balancer for battery-stacked stand-alone PV systems. The proposed system, which uses a single magnetically-coupled inductor, can control each of the PV modules independently to track the maximum power point. Thus, it can overcome the power loss due to the power path. It can also achieve charge balancing for each of the battery modules. The proposed topology is analyzed and verified using 120W hardware experiments.

• Journal of Power Electronics
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• v.19 no.1
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• pp.146-157
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• 2019

The inverter is an essential part of permanent magnet synchronous motor (PMSM) drive systems. The performance of an inverter is greatly influenced by its modulation strategy. Using a proper management of modulation strategies can guarantee high performance from a PMSM under various speed conditions. Switching between modulations is a pivotal technique that determines the performance of a PMSM. Most works on hybrid methods focus on two-level induction motors drive systems. In this paper, in order to improve the performance of PMSMs under various speed conditions, a hybrid method of a pulse width modulation (PWM) control scheme based on a neutral-point-clamped (NPC) three level topology was proposed. This hybrid PWM modulation comprised space vector PWM (SVPWM) and selective harmonic elimination PWM (SHEPWM). Under low speed conditions, the SVPWM is employed to cause the PMSM to start smoothly, and to obtain a rapid response from the control system. Under high speed conditions, the SHEPWM is employed to reduce the switching frequency and to eliminate particular current harmonics. Moreover, the harmonic characteristics of different modulations are analyzed to obtain a smooth transition between the SHEPWM and the SVPWM. Experimental and simulation results indicated the effectiveness of the proposed control method.

• Bulletin of the Korean Chemical Society
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• v.22 no.4
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• pp.337-348
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• 2001

This article gives an overview of a recently developed channel system, frit-inlet asymmetrical flow field-flow fractionation (FI-AFlFFF), which can be applied for the separation of nanoparticles, proteins, and water soluble polymers. A conventiona l asymmetrical flow FFF channel has been modified into a frit-inlet asymmetrical type by introducing a small inlet frit near the injection point and the system operation of the FI-AFlFFF channel can be made with a great convenience. Since sample components injected into the FI-AFlFFF channel are hydrodynamically relaxed, sample injection and separation processes proceed without interruption of the migration flow. Therefore in FI-AFlFFF, there is no requirement for a valve operation to switch the direction of the migration flow that is normally achieved during the focusing/relaxation process in a conventional asymmetrical channel. In this report, principles of the hydrodynamic relaxation in FI-AFlFFF channel are described with equations to predict the retention time and to calculate the complicated flow variations in the developed channel. The retention and resolving power of FI-AFlFFF system are demonstrated with standard nanospheres and protreins. An attempt to elucidate the capability of FI-AFlFFF system for the separation and size characterization of nanoparticles is made with a fumed silica particle sample. In FI-AFlFFF, field programming can be easily applied to improve separation speed and resolution for a highly retaining component (very large MW) by using flow circulation method. Programmed FI-AFlFFF separations are demonstrated with polystyrene sulfonate standards and pululans and the dynamic separation range of molecular weight is successfully expanded.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.2
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• pp.83-89
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• 2022

For precise GNSS applications, the antenna phase center correction (PCC) is absolutely required. The PCC magnitude can reach the centimeter level with the antenna structure. In the present study, we first investigate the phase center offset (PCO) and phase center variation (PCO) of three different antenna models in two different reference frames, IGS08/igs08.atx and IGS14/igs14.atx. Clear L1 and L2 PCO differences were found between IGS08 and IGS14. In addition, the PCV showed characteristics that is dependent upon the signal direction (azimuth and elevation angle). The remarkable thing is that the changes of a Dorne Margolin choke-ring antenna model (AOAD/MT DOME) was very small in two reference frames. In order to analyze changes in positions according to different reference systems, GNSS data obtained from DAEJ, SUWN, and TSKB stations were processed by the precise point positioning (PPP) method. We suggest that an antenna PCO/PCV can affect the precise GNSS positioning on the order of several millimeters in two different reference frames.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.175-179
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• 2022

Magnetic arc extinguishing technology is effective as an extinguishing device for low-voltage direct current (DC) circuit breakers with a resistive load of ≤4 kW. The separation distance between the magnet and the electrical contact must be shortened to increase the magnetic arc extinguishing force. However, if the magnet is installed too close to the electrical contact points, the magnet is exposed to high temperatures due to the arc current generated when the load current is cut off and the magnetism is lost. To solve this problem, the effective magnetic flux density at the electrical contact can be maintained high by placing the arc extinguishing magnet in a tandem structure with the electrical contact point between them, and the proper separation distance between the contact points and the magnet can be maintained. In addition, an electric arc extinguishing technology that emits arc energy using a series circuit of diode and resistor is used to suppress the continuous arc voltage generated by the inductive load. For the proposed circuit breaker, the breaking characteristics are analyzed through the breaking test for the DC load of the 760 V level, the load power of 4 kW, and the time constant of 5 ms, and an appropriate arc extinguishing design guideline is proposed.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.3
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• pp.455-462
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• 2023

In this study, an automatic spraying lubrication system was developed to maintain the cleanliness of the switchgear when detecting the movement of the track through the switchgear. To develop this system, an air tank, valve block, and spray nozzle were designed, and the safety was secured through the pressure test of the prototype after designing the air tank. Furthermore, the environmental aspect was considered by minimizing the use of lubricant by enabling the mixing of air and lubricant through the production of a valve using the Venturi principle. The performance evaluation was conducted by implementing (producing) the injection system, and the product developed in this study was deemed installable in actual switchgear. It is expected that the proposed system will enable the maintenance of the cleanliness of the track during switching and reduce faults and malfunctions caused by switchgear defects.

• Journal of Korean Society of Transportation
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• v.31 no.2
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• pp.45-59
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• 2013

This study deals with the comparative analysis between two freight demand estimation methods : Unimodal O/D based method and P/C based method. The data of access/egress truck trips has been omitted from the Korean freight unimodal O/D of KTDB. This is because KTDB's unimodal O/D has not marked the series of unlinked trips down as the whole freight intermodal transport and surveyed only the main-haul trips of them. For these reasons, freight intermodal transport mechanism has not been analysed perfectly with Korean unimodal O/D data. This study tries to estimate P/C table of Korean Import/Export container freight and develop the MCC(Multimodal Channel Choice) model. Then, comparing unimodal O/D based method and P/C based method in terms of the switch commodities between production point(the initial point of freight transport) and consumption point(the terminal point of freight transport), unimodal commodities, and commodities on links is conducted. The results show that the P/C based method is able to simulate the freight intermodal transport.