• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.89-95
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• 2003

Propulsion system of the current developing satellite is roughly composed of propellant tank and four major modules. Each module prevides the pulse momentum for spacecraft attitude control, filling/draining of propellant and pressurant, propellant filtering, and the change of flow passage in the spacecraft emergency situation, respectively. These modules will be fixed on the propulsion platform with their suitable mounting brackers, so the brackets shall be designed sufficiently to support a function of the modules under launch environment and on-orbit condition. The purpose of this article is to check if all the bracket designs satisfy the defined structural requirements through finite element analysis, and then to verify structural safety.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.30.3-30.3
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• 2008

In this study, we investigate the magnetic latitude of phase reversal on the sudden commencement (SC)-associated preliminary impulse with 267 SC events using the ground magnetometer data of the IMAGE from 1997 to 2005. During SC event, geomagnetic fields are affected by various currents flowing in the magnetosphere and/or ionosphere. In particular, high-latitude geomagnetic field variations are significantly dominated by the change of SC-associated field aligned current (FAC). Until now, however, there are few studies to examine where the location of the FAC in the ionosphere is and what determines the location of the FAC. The location of the SC-associated FAC can be examined by using magnetometer data obtained from high-latitude stations distributed along the same magnetic meridian. The phase reversal locations are concentrated two regions, ~62 deg (L~4.5) and ~70 deg (L~8.5) in magnetic latitude. If FAC is a result of a mode conversion from fast mode to Alfven mode, then the FAC location could be determine by the duration time of the input energy. When we use the rise time, dT, as the input energy, there is no relationship between dT and the location where the first pulse of SC is reversed. We consider other factors such as local time and solar wind condition.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.4 no.1
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• pp.1-6
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• 1971

In order to study the catching efficiency of shrimp trawl equipped with electrodes around the net mouth and stimulant devices attached to the ground rope, an experimental operation was carried out at Oma-Island Shrimp Farm from October 3rd to November 5th, 1970. Many studies have been made on the shrimp trawl with electric stimulant devices, but few can be found for detailed scientific catching methods. Electric power consumption was so excessive that electric stimulant devices could not be developed for commercial purposes. As a first step toward the successive operations of the electric stimulant devices in the field, it is necessary to study fundamental principles, such as electric current, voltage, electric potential, potential difference, electric field and suitable pulse. The behaviour response of the common shrimp, Penaeus japonicus BATE to moving nets and electric stimulant devices were reported in the preceding papers based on the water tank experiments (Ko and Kim, 1970). Through comparative fishing tests the rate of catching efficiency during daylight time was confirmed to be from 89 to 96 per cent of the night catch efficiency, and with 30 V. 1.5 A. electric power was sufficent for practical sea operation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.7
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• pp.7-15
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• 2008

A single active capacitor snubber-assisted soft-switching sinewave pulse modulation utility-interactive power conditioner with a three-winding flyback high frequency transformer link and a bidirectional active power switch in its secondary side has been proposed. With the aid of the switched-capacitor quasi-resonant snubber cell, the high frequency switching devices in the primary side of the proposed DC-to-AC sinewave power inverter can be turned-off with ZVS commutation. In addition to this, the proposed power conditioner in the DCM can effectively take the advantages of ZCS turn-on commutation. Its output port is connected directly to the utility AC power source grid. At the end, the prototype of the proposed HF-UPC is built and tested in experiment. Its power conversion conditioning and processing circuit with a high frequency flyback transformer link is verified and the output sinewave current is qualified in accordance with the power quality guidelines of the utility AC interactive power systems.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1456-1467
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• 2015

This paper presents a novel close-loop control scheme based on small signal modeling and weighted composite voltage feedback for a three-phase input and single-phase output Matrix Converter (3-1MC). A small non-polar capacitor is employed as the decoupling unit. The composite voltage weighted by the load voltage and the decoupling unit voltage is used as the feedback value for the voltage controller. Together with the current loop, the dual-loop control is implemented in the 3-1MC. In this paper, the weighted composite voltage expression is derived based on the sinusoidal pulse-width modulation (SPWM) strategy. The switch functions of the 3-1MC are deduced, and the average signal model and small signal model are built. Furthermore, the stability and dynamic performance of the 3-1MC are studied, and simulation and experiment studies are executed. The results show that the control method is effective and feasible. They also show that the design is reasonable and that the operating performance of the 3-1MC is good.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1119-1129
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• 2014

This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.58-61
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• 2001

Metal-insulator-semiconductor (MIS) C-V properties with high dielectric AIN thin films showed no hysteresis and good interface properties. The dielectric constant of the AIN film calculated from the capacitance at the accumulation region in the capacitance-voltage(C-V) characteristics was about 8. The C-V characteristics of MFIS capacitor showed a hysteresis loop due to the ferroelectric nature of the LiNbO$_3$ thin films. Typical dielectric constant value of LiNbO$_3$ film of MFIS device was about 23. The memory window width was about 1.2V at the gate voltage of $\pm$5 V ranges. Typical gate leakage current density of the MFIS structure was the order of 10$^{-9}$ A/cm$^2$ at the range of within $\pm$500 kV/cm. The ferroelectric capacitors showed no polarization degradation up to about 10$^{11}$ switching cycles when subjected to symmetric bipolar voltage pulse(peak-to-peak 8V, 50% duty cycle) in the 500kHz.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.1
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• pp.44-51
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• 2000

In this paper, using a wide-band AE sensor with the frequency range from 100[kHz] to 1.5[kHz], the frequency spectra of AE signals generated from the corona discharges of the needle-plane gap and from the partial discharges of an epoxy void were analyzed to determine the proper ultrasonic sensor with optimum frequency range according to the patterns of corona discharges. We also examined the propagation characteristics of AE signals in oil and the relationship between the magnitude of corona discharge and the magnitude of AE signals in peak-to-peak value under the application of 60[Hz] ac high-voltage. From these results, the main frequency spectra of AE signals emitted from the corona discharges of the needle-plane gap were about 130[kHz] by the fast fourier transform, but the main frequency spectra appeared to be 230[kHz] in the partial discharges of an epoxy void. The magnitude of AE signals was proportional to the magnitude of corona discharge and discharge current pulse with increasing the applied voltages.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.27-30
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• 2013

Catalyst-free graphene nano-sheets without substrates have been synthesized using fullerene and a high direct current (dc) pulse in the spark plasma sintering (SPS) process. Graphene nano-sheets were synthesized directly in the gas phase of carbon atoms which are generated from fullerene at a temperature of $600^{\circ}C$. Characterization has been carried out by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).

• Korean Journal of Adult Nursing
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• v.18 no.5
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• pp.691-698
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• 2006

Purpose: This research was conducted to evaluate, analyze, and determine the limitation of the anesthesia that is used in there covery room in order to provide the foundation for developing the effectiveness of it. Method: There covery records of this study were collected from 41 hospitals in Seoul, Kyung Kii-Do, and Inchon province. The post anesthetic recovery records consisted of the evaluation of type, evaluative items, frequency, time, score and $SaO_2$. These records were collected from September to December of 2005. Results: The most commonly used post anesthetic evaluation tool was Alderete Score, which was used in 73% of hospitals. The second was Aldrete Score with $SaO_2$(17%). Also, 5% of the hospitals used the modified AS form. There were 2.5% of the hospitals applying the adult and child in the evaluation separately. Also, the last 2.5% of the hospitals did not use AS but measured BP, pulse, respiration, temperature, and $SaO_2$ with observing nausea, vomiting, urinary retention, backache, laryngitis, shock, and neurologic assessment. Conclusion: It is necessary to develop a post-anesthetic recovery evaluation tool including the application of $SaO_2$, so that the early-diagnosis of hypoxia can be possible. In addition, it is necessary to develop a post- anesthetic recovery evaluating method that can distinguish a difference between adults and children.