• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1753-1755
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• 2005

This paper deals with the dynamic analysis of doubly-fed induction generators for wind power system. The 3-phase voltage equations for stator and rotor of doubly-fed induction generator (DFIG) are derived and then, the equivalent circuit and mechanical output power of induction generators are obtained by converting the 3-phase voltage into do voltage equation. Finally, the dynamic characteristics such as torque, speed and voltage for rotor of DFIG are presented, for the case when wind is considered.

• Macromolecular Research
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• v.17 no.3
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• pp.168-173
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• 2009

This study reports the preparation and characterization of nanohydrogels by using sodium alginate as a model material. Alginate nanohydrogels (ANH) were prepared by emulsification-diffusion method in a w/o system with 1,2-diacyl-sn-glycero- 3-phosphocholin as the lipophilic surfactant. The effects of the alginate to surfactant ratio and the remaining water contents on the mean particle size and swellability of ANHs were investigated in terms of the concentration, agitation speed, and agitation time. The feasibility of using nanohydrogels and their controllability were proved by the water the absorbency of ANHs during a 7-day evaluation by dynamic light scattering. In this work, the mean particle sizes of ANHs could be controlled from 49.2 nm (measured in ethanol phase) to $1.9{\mu}m$ (measured in water phase, after 7 days of water absorption).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.377-383
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• 1997

Yttria-stabilized TZP alloyed with pentavalent oxides $(Ta_2O_5,\;Nb_2O_5)$ were fabricated by the conventional sintering method at $1500^{\circ}C$ in air to construct the simplified ternary phase diagram. The phase stability of tetragonal -$ZrO_2$ from the quasi-binary system $ZrO_2-YTa(Nb)O_4$, which do not transform to monoclinic-$ZrO_2$ even for a wide range of grain size and annealing temperature, was investigated to determine composition region of the non-transformable $t-ZrO_2$ solid solution$(NT_{ss})$. Phase stability of $NT_{ss}$ was probably due to the enhanced stability of $_YTa(Nb)O4$ having the tetragonal fergusonite structure. It was experimentally found that mixtures having $NT_{ss}$ alloyed with $T_{ss}$ by weight%% showed both excellent phase stability of $t-ZrO_2$ and fracture toughness even though the calculated composition of the mixture /was located outside $NT_{ss}$ composition region.

• Journal of the Korean Society for information Management
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• v.28 no.3
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• pp.295-312
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• 2011

This study conducted time-series analysis on domestic studies related to entrepreneurship for more than last 50 years by integrating the co-word analysis method of intellectual structure analysis into the study of entrepreneurship. The co-word analysis method is a quantitative analysis method to analyze the overall trend of the study and further study topics by visualizing the information between study topics and arranging the topics on two-dimensional plane and the study result showed largely four phases and the direction of the study path. According to the analysis, the study is started at embryonic study phase(third quadrant), the study topic of independent study phase(second quadrant) is a phase to be a settled independent area as a study and the topics of the study include topics of the study reflecting the situation of the times. At growing study phase(first quadrant) study topics which are closely related to the study topic are arranged, and the topics, the center of the study, are positioned at the study topics of maturity phase(4th quadrant).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.266-273
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• 2020

This study was undertaken to determine the effects of diet supplementation with complex probiotics (CPB), on growth performance, nutrient digestibility, blood metabolites, noxious gas, and fecal microflora in weaning pigs. On the basis of body weight, a total of 234 weaned pigs (Landrace×Yorkshire×Duroc, 6.14±0.78kg) were randomly allotted to 3 treatments and 6 replicates (13 pigs per pen). The experimental diets were fed in a meal form for 28 days (days 0-14, PhaseI, and days 15-28, PhaseII). The dietary treatment groups were as follows: T1 (basal diet), T2 (T1+0.13% CPB) and T3 (T1+0.25% CPB). The CPB supplement contained Bacillus subtilis 1.0×10⁶ CFU/g, Enterococcus faecium 1.0×10⁶ CFU/g, Saccharomyces cerevisiae 1.0×10⁶ CFU/g, Bacillus licheniformis 3.0×10⁸ CFU/g, and Bacillus polyfermenticus 3.0×10⁸ CFU/g. Pigs fed the T3 diet showed an increase (p<0.05) in the overall average daily gain and average daily feed intake, increased (p<0.05) crude protein digestibility in PhaseI, and greater (p<0.05) dry matter and gross energy digestibility in PhaseII. Supplementation of CPB had no effect on the blood profile. Furthermore, pigs fed the T3 diet had lower (p<0.05) NH₃ emission and overall count of fecal Clostridium spp. In conclusion, we believe that CPB supplementation has a beneficial effect on growth performance, nutrient digestibility, noxious gas, and fecal microflora in weaning pigs.

• Asian-Australasian Journal of Animal Sciences
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• v.13 no.8
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• pp.1137-1146
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• 2000

This study was carried out to establish an optimum number of phase feeding regimen which enable to reduce nutrients excretion without affecting growth performance and to investigate the effects of different feeding regimens on growth performance, nutrients excretion and carcass characteristics in finishing pigs. A total of 120 finishing pigs (an average initial body weight of 54.3 kg) were assigned to the feeding trial and 12 pigs were assigned to the metabolic trial. Treatments included one phase (54 to 104 kg), two phase (54 to 80 and 80 to 104 kg), three phase (54 to 70, 70 to 90 and 90 to 104 kg) and four phase (54 to 65, 65 to 80, 80 to 95, 95 to 104 kg) feeding regimens. Experimental diets were formulated to contain 16% crude protein for one phase feeding regimen, 16% and 12% crude protein for two phase feeding regimen, 16%, 14% and 12% crude protein for three phase feeding regimen, and 16%, 14.7%, 13.4% and 12% crude protein for four phase feeding regimen, respectively. Although there were no significant differences in any criteria measured during the entire experimental period, pigs reared in three phase feeding regimen grew slightly faster than those reared in other feeding regimens and showed a tendency to increase ADFI during the whole experimental period. The metabolic trial indicated that there were no significant differences in DM (dry matter), CP (crude protein) and P (phosphorus) digestibilities. However, fecal nutrient excretion except P was significantly influenced by feeding regimens. DM excretion of one phase feeding group was significantly higher than that of three phase feeding group and daily fecal N (nitrogen) excretion of one phase feeding group was higher than that of other phase feeding groups (p<0.05). Three and four phase feeding regimens resulted in 12% lower fecal N and DM excretion than one phase feeding regimen. Blood urea concentrations were lower for pigs reared in two, three and four phase feeding regimens than for those reared in one phase feeding regimen (p<0.05). Three phase feeding regimen for the finishing period showed better carcass grade than one phase feeding regimen, though the difference was not significant. The tenth rib fat thickness of pigs fed on four phase feeding regimen was reduced most and there was a trend that backfat thickness decreased as the number of phases increased. Feed cost per kg weight gain was significantly low in four phase feeding group than one phase feeding group (p<0.05). In summary, it seemed that producers generally oversupply the expensive nutrients for the finishing pigs. High nutrient diets do not always guarantee high growth rate of pigs and cause more unwanted nutrient excretion. It rather seems that meeting nutrient requirements for the each growth phase is more important for the reduction of pollutants and economical pork production.

• Analytical Science and Technology
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• v.33 no.6
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• pp.252-261
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• 2020

Currently, the potentiometric titration and the high pressure liquid chromatography (HPLC) method were utilized in Korean Pharmacopoeia XII (KP XII) as well as other pharmacopoeias (USP, EP, BP) for determination of loperamide hydrochloride in raw materials and capsules, respectively. The research objective is to overcome the remaining drawbacks from current methods such as solubility of mobile phase (KP XII), less scientific approach (USP 43) or using paired-ion chromatography reagent which shows some limitations (BP2017 and other formulation monographs). The proposed method was optimized by Design of Experiment (DoE) tool to obtain the satisfied method for determination of loperamide hydrochloride. The optimal condition was performed on the common C18 column (150 mm × 4.6 mm; 5 ㎛) using isocratic elution with the mobile phase containing 40 mM of potassium phosphate monobasic (pH 3.0) and acetonitrile (56:44), at a flow rate of 0.7 mL/min. The optimized method was validated and met the requirements of the International Conference on Harmonization. The developed method was applied to determine loperamide hydrochloride in capsules and can be used to update the current monograph in KP XII.

• Journal of Korea Foundry Society
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• v.40 no.2
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• pp.7-15
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• 2020

The high-temperature stability of Mg-8.0Zn-1.6Y (wt.%) alloys upon the addition of Ca has been investigated by characterizing the ignition temperature, microstructure, tensile and creep properties. The ignition temperature increases with an increase in the Ca content, indicating that an addition of Ca enhances the ignition resistance of the Mg-Zn-Y alloy. The as-cast microstructures of all tested alloys mainly consisted of the dendritic α-Mg matrix and I-phase (Mg₃Zn₆Y) at the grain boundaries. In the Ca-added Mg-8.0Zn-1.6Y alloys, the Ca₂Mg₆Zn₃ phase forms, with this phase fraction increasing with an increase in the Ca contents. However, a high volume fraction of the Ca₂Mg₆Zn₃ phase rather deteriorates the mechanical properties. Therefore, a moderate amount of Ca element in Mg-8.0Zn-1.6Y alloys is effective for improving the tensile and creep properties of the Mg-Zn-Y alloy. The Mg-8.0Zn-1.6Y-0.3Ca alloy exhibits the highest tensile strength and the lowest creep strain among the alloys investigated in the present study. The creep resistance of Mg-Zn-Y-Ca alloys depends on the selection of the secondary solidification phase; i.e., when Ca₂Mg₆Zn₃ forms in an alloy containing a high level of Ca, the creep resistance deteriorates because Ca₂Mg₆Zn₃ is less stable than the I-phase at a high temperature.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.137-144
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• 2009

This paper deals with the performance comparison of jammer signal's angle spreading in the beamforming after the estimation of direction of arrival using 3D array antenna basis of the GPS signal. After the estimation of direction of arrival using array antenna, the beamforming is need for the direction of arrival by spatial filtering and the other direction are nulling for reducing intererence signal, it is possible to improving the received signal strength and quality. But we obtains the degraded performance by the angle spreading due to the multi-jammer signal in this process. In this paper, the MUSIC and LCMV algorithms are applied for the estimating the direction of arrival and for beamforming using the 5 types of 3D array antenna. we performs the comparison of performance by calculating the bit error rate applying the BPSK modem and the varying the azimuth and elevation angle of incoming jammer signal. As a result of simulation, the Curved (B) type 3D array antenna has a more better performance compared to the other type antenna.

• Journal of Power Electronics
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• v.9 no.5
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• pp.691-699
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• 2009

This paper presents the analysis of series active power filter for reactive power compensation, load balancing, harmonic elimination, and neutral current eradication in three-phase four-wire power systems. Generally, the three-phase four-wire system is widely employed in distributing electric energy to several office building and manufacturing plants. In such systems, the third harmonic and its 3rd harmonics are termed as triple and zero sequence components that do not cancel each other in the system neutral. Consequently, the triple harmonics add together creating a primary source of excessive neutral current. Regarding this concern, this paper presents a new control algorithm for a series hybrid active system, whereas the control approach it adopts directly influence its compensation characteristics. Hence, the advantage of this control algorithm is the direct extraction of compensation voltage reference without phase transformations and multiplying harmonic current value by gain and the required rating of the series active filter is much smaller than that of a conventional shunt active power filter. In order to show the effectiveness of the proposed control algorithm, experiments have been carried out.