• Journal of Power Electronics
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• v.18 no.5
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• pp.1336-1346
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• 2018

Wide band gap semiconductor devices such as SiC MOSFETs are becoming the preferred devices for high frequency and high power density converters due to their excellent performances. However, the proportion of the switching loss that accounts for the whole inverter loss is growing along with an increase of the switching frequency. In view of the third quadrant working characteristics of a SiC MOSFET, synchronous rectification discontinuous pulse-width modulation is proposed (SRDPWM) to further reduce system losses. The SRDPWM has been analyzed in detail. Based on a frequency domain mathematical model, a quantitative mathematical analysis of the harmonic characteristic is conducted by double Fourier transform. Meanwhile, a switching loss model and a conduction loss model of inverter for SRDPWM have been built. Simulation and experimental results verify the result of the harmonic analysis of the double Fourier analysis and the accuracy of the loss models. The efficiencies of the SRDPWM and the SVPWM are compared. The result indicates that the SRDPWM has fewer losses and a higher efficiency than the SVPWM under high switching frequency and light load conditions as a result of the reduced number of switching transitions. In addition, the SRDPWM is more suitable for SiC MOSFET converters.

• The Journal of the Korea Contents Association
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• v.11 no.4
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• pp.448-457
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• 2011

A wetting and drying(WAD) scheme was introduced in KU-RLMS which is a two-dimensional depth-averaged unsteady model, and applicability tests for wetting and drying were performed in this study. WAD scheme in the model uses a mathematically less elegant but numerically easier method to test for dry or wet cells at each time step, then to apply blocking conditions for fluxes at cells' interfaces. WAD scheme introduced in the model was verified against an analytical solution in a frictionless parabolic basin. It was found that there occurs a little phase difference between analytical and numerical solution and little decrease of amplitude of numerical result. I used three test channels having a linear sloping bottom topography, a stepwise bottom topography, and a stepwise, a bumpy and bowl-shaped bottom topography. It could be found that numerical simulation results in test channels have similar shapes of Balzano[4] and Oey[15].

• Journal of Microbiology and Biotechnology
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• v.7 no.4
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• pp.215-222
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• 1997

The regulatory mechanism of the flux of acetyl-CoA in Alcaligenes eutrophus in unbalanced growth conditions was investigated using a PHB-negative mutant and transformants reintroduced PHB-biosynthesis enzymes through the transformation of cloned phbCAB genes. The PHB-negative mutant was defected absolutly in PHB synthase but partially in ${\beta}$-ketothiolase and acetoacetyl-CoA reductase, and excreted substantial amount of pyruvate to culture broth at late growth phase. The excretion was due to the inhibitory effect of acetyl-CoA on the activity of pyruvate dehydrogenase. The cloned phbC and phbCAB genes were transformed to the PHB-negative mutant strain to reintroduce PHB biosythesis enzymes. Pyruvate excretion could be decreased substantially but not completely by transformation of PHB synthase alone, while pyruvate excretion was ceased by transformation of all three PHB biosynthesis enzymes. To identify the most critical PHB biosynthesis enzyme influencing on the flux of acetyl-CoA, the effect of the variation of PHB biosynthesis enzymes on pyruvate dehydrogenase was investigated. ${\beta}$-Ketothiolase influenced the activity of pyruvate dehydrogenase more sensitively than PHB synthase. ${\beta}$-Ketothiolase, the first step enzyme of PHB biosynthesis that condense acetyl-CoA to acetoacetyl-CoA, seems to be the major enzyme determining the flux of acetyl-CoA to PHB biosynthesis or TCA cycle, and the rate of PHB biosynthesis in A. eutrophus.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.1-7
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• 2007

Generally, an electric railroad feeding system has many problems due to the different characteristics in contrast with a load of general three-phase AC electric power system. One of them is harmonics problem caused by the switching device existing in the feeding system, and moreover, the time-varying dynamic loads of rail way is inherently another cause to increase this harmonics problem. In Korea power systems, the electric railroad feeding system is directly supplied from the substation of KEPCO. Therefore, if voltages fluctuation or unbalanced voltages are created by the voltage and current distortion or voltage drop during operation, it affects directly the source of supply. The trainloads of electric railway system have non-periodic but iterative harmonic characteristics as operating condition, because the electric characteristic of the electric railroad feeding system is changed by physical conditions of the each trainload. According to the traditional study, the estimation of harmonics has been performed by deterministic way using the steady state data at the specific time. This method is easy to analyze harmonics, but it has limits in some cases which needs an assessment of dynamic load and reliability. Therefore, this paper proposes the probabilistic estimation method, moments matching method(MW) in order to overcome the drawback of deterministic method. In this paper, distributions for each harmonics are convolved to obtain the moments and cumulants of TDD(Total Demand Distortion), and this can be generalized for any number of trains. For the case study, the electric railway system of LAT(Intra Airport Transit) in Incheon International Airport is modeled using PSCAD/EMTDC dynamic simulator. The raw data of harmonics for the moments matching method is acquired from simulation of the LAT model.

• Analytical Science and Technology
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• v.9 no.2
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• pp.123-133
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• 1996

The optimum conditions for the analysis of the difenoconazole fungicide on soil and crops were investigated and the residues of that in apple and soil were identified by using the gas chromatography. The extract with acetonitrile was separated with saturated NaCl and n-hexane solution after filtered, and concentrated. Obtained fungicide residues were transfered to the florisil column and eluted with acetone and n-hexane mixed solution for the analysis by GLC(ECD). From the standard addition experiments with 0.20 and 1.0ppm, the average recoveries were 86~92% and the detection limit was 0.01 ppm. It seems to be safely used when difenoconazole is treated three times until 15 days before harvest of apple. In this case residual amounts of difenoconazole in apple was from 0.037ppm to 0.044ppm. The soil samples extracted with methanol and ammonium hydroxide mixed solution were partitioned with dichloromethane and saturated sodium chloride solution. The organic phase was concentrated and redissolved with toluene and analyzed with GLC(FID) after cleaned with Sep-Pak column. From the standard addition experiments with 0.10, 0.50 and 1.0ppm, the average recoveries were 101.2~103.7% and the detection limit was 0.025ppm.

• Journal of Biomedical Engineering Research
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• v.32 no.1
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• pp.61-73
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• 2011

The purpose of this study was to investigate changes in the center of pressure (COP), ground reaction force (GRF) and joint angles of elderly people and young people while stair-descent. The participants in this experiment were 5 elderly people and 5 young people, each of which was asked to descend stairs of three different heights (8 cm, 16 cm, and 32 cm). As they climbed down the stairs, they received vibration stimulation on the lower limb. The change of COP, GRF and joint angles were analyzed during the standing phase. COP decreased as the Achilles tendon and tibialis anterior tendon were vibrated. Vertical GRF increased as the Achilles tendon was vibrated, and the joint angle differed according to vibration stimulation conditions. These results mean that ankle joint, knee joint and hip joint were influenced by the vibrations on the lower limb as the participants descended the stairs. It was concluded that the vibration stimulation on the lower limb allowed the participants to efficiently climb down the stairs.

• Mycobiology
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• v.44 no.3
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• pp.162-170
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• 2016

In this paper, we demonstrate the ability of Arabidopsis thaliana to detect different mixtures of volatile organic compounds (VOCs) emitted by the common indoor fungus, Aspergillus versicolor, and demonstrate the potential usage of the plant as a bioindicator to monitor fungal VOCs in indoor air. We evaluated the volatile production of Aspergillus versicolor strains SRRC 108 (NRRL 3449) and SRRC 2559 (ATCC 32662) grown on nutrient rich fungal medium, and grown under conditions to mimic the substrate encountered in the built environment where fungi would typically grow indoors (moist wallboard and ceiling tiles). Using headspace solid phase microextraction/gas chromatography-mass spectrometry, we analyzed VOC profiles of the two strains. The most abundant compound produced by both strains on all three media was 1-octen-3-ol. Strain SRRC 2559 made several terpenes not detected from strain SRRC 108. Using a split-plate bioassay, we grew Arabidopsis thaliana in a shared atmosphere with VOCs from the two strains of Aspergillus versicolor grown on yeast extract sucrose medium. The VOCs emitted by SRRC 2559 had an adverse impact on seed germination and plant growth. Chemical standards of individual VOCs from the Aspergillus versicolor mixture (2-methyl-1-butanol, 3-methyl-1-butanol, 1-octen-3-ol, limonene, and ${\beta}-farnesene$), and ${\beta}-caryophyllene$ were tested one by one in seed germination and vegetative plant growth assays. The most inhibitory compound to both seed germination and plant growth was 1-octen-3-ol. Our data suggest that Arabidopsis is a useful model for monitoring indoor air quality as it is sensitive to naturally emitted fungal volatile mixtures as well as to chemical standards of individual compounds, and it exhibits relatively quick concentration- and duration-dependent responses.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.39-45
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• 2004

A computer simulation about removal of the 0-th order diffraction is achieved by using numerical reconstruction in digital holography and the Fourier transform method. A light intensity distribution hologram is generated through numerical calculation of the interference pattern. Additionally a phase hologram without the 0-th order diffraction is generated. The removal function for elimination of the 0-the order diffraction is introduced and the numerical reconstructions with several conditions for the removal of the 0-th order diffraction and the production of high quality numerically reconstructed images are tested and compared. The removal function is proven to be more effective at the suppression of the 0-th order diffraction compared with the DC suppression method.

• Physical Therapy Korea
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• v.27 no.4
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• pp.227-232
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• 2020

Background: Hallux valgus (HV) is a foot deformity developed by mediolateral deviation of the first metatarsophalangeal joint. Although various foot-toe orthoses were used to correct the HV angle, verification of the effects of kinetics variables such as ground reaction force (GRF) through three-dimensional (3D) gait analysis according to the various type of orthoses for HV is insufficient. Objects: This study aimed to investigate the effect of soft and hard types of foot and toe orthoses to correct HV deformity on the GRF in individuals with HV using 3D motion analysis system during walking. Methods: Twenty-six subjects participated in the experiment. Participants had HV angle of more than 15° in both feet. Two force platforms were used to obtain 3D GRF data for both feet and a 3D motion capture system with six infrared cameras was used to measure exact stance phase point such as heel strike or toe off period. Total walk trials of each participant were 8 to 10, the walkway length was 6 m. Two-way repeated measures ANOVA was used to determine the effects of each orthosis condition on the various GRF values. Results: The late anteroposterior maximal force and a first vertical peak force of the GRF showed that the hard type orthosis condition significantly increased GRF compared to the other orthosis conditions (p < 0.05). Conclusion: There were significant effects in GRF values when wearing the hard type foot orthosis. However, the hard type foot orthosis was uncomfortable to wear during walking. Therefore, it is necessary to develop a new foot-toe orthosis that can compensate for these disadvantages.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.49 no.2
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• pp.109-115
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• 2016

The efficacy of depuration following growing area translocation for the defecation of norovirus was evaluated under experimental conditions using oysters Crassostrea gigas previously subjected to bioaccumulation of this virus at a waste treatment plant discharge site. Three trials were assayed in an open experimental system with a commercial oyster farm located in a shellfish growing area approved by the Korean Shellfish Sanitation Program. Real-time reverse-transcription polymerase chain reaction (RT-PCR) was used to quantify viruses in the digestive glands of oysters. The final viral loads in oysters after 12 days remained under the detection limit (10 copies/g digestive gland) of the real-time RT-PCR. This reduction trend showed two-phase removal kinetics, with an initial slow reduction or slight increase in viruses during the first 2 days of depuration and subsequent stabilization with 0.12 to 2.64 log unit norovirus copies/g digestive gland per 2 days of depuration for the remaining time.