• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.574-585
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• 2015

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.

• Journal of fish pathology
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• v.21 no.3
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• pp.241-246
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• 2008

The effects of temperatures on pearl oyster, Pincdata fucata were studied by evaluating some functional immune responses of the haemocytes. Water temperature is one of the most important factors in bivalve immune defense. Haemocytes comprise a primary line by inflammation, encapsulation and phagocytosis. These phagocytic abilities of haemocytes were observed in different temperatures. The number of the circulating haemocytes by migratory assay, phagocytic activities by MTT assay and reactive oxygen species production of haemocytes by CL assay were measured at different temperatures. Results showed that pearl oyster maintained at 20℃ and 25℃ displayed significantly higher values for all the measured immune parameters in comparison to maintained at 10, 15, and 30℃.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.8
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• pp.764-768
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• 2006

For the possible application of pearl pigment, multi-layered $TiO_2/Al,\;Cr/TiO_2$ thin film were deposited on $SiO_2$ substrate by using sputtering method, $TiO_2$ and Al or Cr was selected as a possible high and low refraction material at the film interface respectively. Optical properties including color effect were systematically studied in terms of different film thickness and film layers by using spectrometer. In order to expect the experimental results, the simulation program, the Essential Macleod Program(EMP) was adopted and compared with the experimental data. The film consisting of $TiO_2/Al,\;Cr/TiO_2$ layers shows a wavelength range of $430{\sim}760nm$, typically color ranges between bluish purple and red. It was confirmed that this experimental result was quite well consistent with the experimental one.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.550-558
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• 2014

Direct Torque controlled induction motor (DTC-IM) drives use stator resistance of the motor for stator flux estimation. So, stator resistance estimation properly is very important for a stable and effective operation of the induction motor. Stator resistance variations because of changing in temperature make DTC operation difficult mainly at low speed. A method based on artificial neural network (ANN) to estimate the stator resistance online of IM for DTC drive is modeled and verified in this paper. To train the neural network a back propagation algorithm is used. Weight adjustment of neural network is done by back propagating the error signal between measured and estimated stator current. An extensive simulation has been carried out in MATLAB/SIMULINK to prove the efficacy of the proposed stator resistance estimator. The simulation & experimental result reveals that proposed method is able to obtain precise torque and flux control at low speed.

• Advances in environmental research
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• v.3 no.3
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• pp.199-206
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• 2014

Dewatering is an extremely important step in wastewater treatment process to reduce the final sludge volume in order to minimize the cost of sludge transportation and disposal. In the present study, the effect of different sludge solids content (1, 2 and 3.8%) on the dewaterability of anaerobically digested sludge using Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was studied. The pH reduction rate was higher during initial process in the sludge having low solids content, but after 48 h of bioleaching, similar pH of below 3 was observed with all the different solids content. Bio-oxidation rate of $Fe^{2+}$ was initially higher in sludge with low solids content, but 100% $Fe^{2+}$ was oxidized within 60 h in all the three treatment levels. Compared to the control, specific resistance to filtration was reduced by 75, 78 and 80% in the sludge with a solids content of 1, 2 and 3.8% respectively, showing improvement in dewaterability with an increase in sludge solids content. Sludge effluent quality and sludge settling rate were also improved in treatments with higher solids content after the bioleaching process.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.308-308
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• 2022

β-glucan, a nonstarch polysaccharide, is one of the main functional component in the cell wall of barley. This study was quality characteristics to use a korean variety with a high β-glucan as an original material for developing functional food. The high β-glucan 'Jeonju528, and 'Betaone' were compared with 'Hyeyang', 'Dahyang', 'Hwanggeumchal' and 'Glacier AC38' total 6 varieties. Seed section dyed to classify of Waxy/non-waxy type, starch granule was tested and moisture, protein, amylose, and β-glucan of whole grains and pearl barleys were experiment. Whole grains were the average protein of 13.2% and were the average starch 50.1%. β-glucan of whole grains were 5.3-10.0%, and amylose were 3.0-23.4%. Pearl barleys were the average protein of 11.7% and were the average starch of 65.0%. β-glucan of pearl barleys were 6.5-12.3%, and amylose were 3.6-31.1%. As a results of the correlation analysis were recognized significance among varieties for protein, starch and β-glucan but there was no difference in other traits. It was concluded that amylose showed a positive correlation with starch and β-glucan showed a negative correlation with amylose.

• Journal of the Mineralogical Society of Korea
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• v.28 no.1
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• pp.9-16
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• 2015

A mineralogical analysis on the factors affecting the luster of pearls was carried out using gravity measurement, optical microscope observation, X-ray diffraction analysis, and scanning electron microscopy. We divided the seawater cultured pearls from Tongyeong into the following four types based on luster and shape; good luster and round (LR), lackluster and round (LLR), lackluster and baroque (LLB), and lackluster and two nucleus (LTN) pearls. Pearls with high-quality luster had slightly lower specific gravity as compared to pearls with low-quality luster, but both these types of pearls are within the specific gravity range of commercial pearls. Regarding the cross-sectional thickness of the mother-of-pearl layer, LR pearls showed a uniform thickness of about 0.3 mm in average. On the other hand, LLR pearls were characterized by relatively thinner, but uniform thickness. LTN and LLB pearls showed a tendency of significantly large variation in thickness even within a single pearl. For the surface of pearls, pearls with high-quality luster showed narrower and clearer growth lines of aragonite crystals as compared to pearls with low-quality luster. Pearls with high-quality luster were characterized by fewer aragonite crystal lattice defects as compared to pearls with low-quality luster, and the former showed parallel arrangement, thinner thickness, and less difference in thickness on the surface and inside. If a pearl has a prismatic layer, it is composed of aragonite with calcite in the prismatic and nacreous layer, and calcite content is very high in the lackluster pearl. Pearls without a prismatic layer were devoid of calcite irrespective of their quality of luster, and were composed of aragonite.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.4 s.48
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• pp.543-548
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• 2004

For pearl pigments used for splendor or gloss effect of make-up products, especiallv point make-up products like eye-shadow and blusher, we studied the variation of particle size distribution by the grinding time and by the binder used as a binding agent. In this study. high speed mixer was used and the particle sire distribution was measured by using the light scattering method. In case of pearl pigments, its median diameter of $5{\;}{\mu}m$, the particle size was reduced to 4.6 um when it was ground for 120 s. When it was applied for the pearl pigment of $45{\;}{\mu}m$, the particle size was reduced to $27{\;}{\mu}m$. We confirmed that the latter was reduced more largely and the original gloss was reduced too. For the binder, we studied the correlation between particle size of raw material and grinding time. We also investigated the effects of the binder contents on the variation of particle size distribution of products by aggregation of particles.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.35 no.2
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• pp.122-125
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• 1990

Pearl millet (Pennisetum americanum (L.) Leeke) has been detected as an excellent and new forage crop in Korea. Thus the objective of the study was to determine optimum planting season, growing degree days and productivity by shifting the planting season of pearl millet. Days to emergence of Australia pearl millet inbred line were shortened from 12 days to 3 days by delaying planting season from April 15 to July 15 in Suwon, 1986, but their growing degree days remained relatively constant 32.1$^{\circ}C$ in average. Days to heading also were shortened from 96 days to 54 days by shifting the planting season, but their growing degree days varied little being 697$^{\circ}C$ in average. For grain crop, economic planting season was from early May to late June, and their harvest index also did not varied much, but suddenly reduced in the July 15 planting plot. For forage crop, economic planting season was from mid-May to mid-June with optimum planting time of mid-May. Particularly, when planted in early July, 1987 and 1988, green fodder yields of Suwon 1 pearl millet hybrid were very low being 54 percent as compared with optimum planting season's yield 10.8t/10a.

• Korean Journal of Weed Science
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• v.10 no.2
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• pp.99-102
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• 1990

Pearl millet (Pennisetum americanum (L.) Leeke) has been found as a promising new forage crop of higher quality and yield in Korea since 1985. The objective of the study was to select preemergence herbicides for weed control in growing pearl millet in order to reduce production cost and with increased yields. Propazine (Milogard 4L) was the best in controlling weeds without its phytotoxicity at the standard application rate, and with the highest survival rate of seedlings of peal millet "Suwon 1" hybrid. Sprayings with Atrazine and Simazine caused lower survival rate of peal millet and with their light phytotoxicity as compared with manual weeding and Propazine spraying. Alachlor killed pearl millet seedlings almost completely. Pendimethalin also was not good for weed control of peal millet due to its severe phytotoxicity and with very low survival rate of pearl millet seedlings.