• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.419-425
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• 2014

The current work investigated the variation of numerical solutions according to the grid number, the distance of the first grid point off the ship surface, turbulence modeling and discretization. The subject vessel is KVLCC. A commercial code, Gridgen V15 and FLUENT were used the generation of the ship hull surface and spatial system and flow computation. The first part of examination, the effect of solutions were accessed depending on the grid number, turbulence modeling and discretization. The second part was focus on the suitable selection of the distance of the first grid point off the ship surface: $Y_P+$. When grid number and discretization were fixed the same value, the friction resistance showed differences within 1 % but the pressure resistance showed big differences 9 % depending on the turbulence modeling. When $Y_P+$ were set 30 and 50 for the same discretization, friction resistance showed almost same results within 1 % according to the turbulence modeling. However, when $Y_P+$ were fixed 100, friction resistance showed more differences of 3 % compared to $Y_P+$ of 30 and 50. Whereas pressure resistance showed big differences of 10 % regardless of turbulence modeling. When turbulence modeling and discretization were set the same value, friction, pressure and total resistance showed almost same result within 0.3 % depending on the grid number. Lastly, When turbulence modeling and discretization were fixed the same value, the friction resistance showed differences within 5~8 % but the pressure resistance showed small differences depending on the $Y_P+$.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.41-45
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• 2000

The purpose of this study was to evaluate the microleakage of compomers. In this in vitro study, class V cavities were prepared on buccal and lingual surfaces of thirty extracted human premolars and molars on cementum cervical margin. The experimental teeth were randomly divided into five groups of six samples (12 surfaces) each, Group 1 : Dyract AP, Group 2 : F2000 compomer(non-etch), Group 3 : F2000 compomer(etch), Group 4 : Elan, Group 5 : Compoglass. The bonding agents and compomer were applied for each group following the manufacturer's instructions. After 500 thermocycling between $5^{\circ}C$ and $55^{\circ}C$, the 30 teeth were placed 1% methylene blue dye for 24 hours then rinsed with tab water. The specimens were embedded in clear resin, then sectioned buccolingually through the center of the restoration with a low speed diamond saw. The dye penetration on each of the specimen was observed with a stereomicroscope. The results of study were statistically analyzed using the Student-Newmann-Kaul' s Test. The results were obtained as follows. 1. All compomer restoration systems did not completely prevent marginal leakage. 2. In enamel margin, F2000 compomer(etch) group showed lower leakage value than other systems. Elan and Compoglass groups showed lower leakage value than Dyract AP and F2000 compomer(non-etch) groups (p<0.05). 3. In cementum margin, F2000 compomer(etch) and F2000 compomer (non-etch) groups showed lower leakage value than other systems. Dyract AP and Elan groups showed lower leakage value than Compoglass group (p<0.05).

• Journal of the Korean Society of Food Science and Nutrition
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• v.28 no.6
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• pp.1316-1320
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• 1999

Antioxidative effect of ethanolic extracts of various tea materials(Camellia sinensis, Cassia tora, Lyc ium chinense, Polygonatum odoratum, Schizandrae chinensis) on red pepper seed oil was investigated. Ethanolic extracts were added to red pepper seed oil at a concentration of 0.05%(w/v). Two experimental conditions were employed : 50$\pm$0.1oC for 45 days and 150$\pm$3oC for 24 hours. Oxidation of red pepper seed oil was determined by measuring peroxide value and acid value. Electron donating ability(EDA) and total phenolic contents of each extract were also determined. The result showed that the extracts possess an antioxidative activities. The effectiveness of them was in the following order: C. sinensis>C. tora>P. odoratum>S. chinensis >L. chinense. Ethanolic extracts of C. sinensis showed substantially higher EDA value and total phenol contents than other tea materials. These results indicate that the antioxidative effect was strongly related with EDA and total phenol contents.

• Journal of the Korean Society for Precision Engineering
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• v.3 no.2
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• pp.62-75
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• 1986

An experimental investigation of the machining characteristics such as cutt- ing resistance, surface roughness and tool wear in turning the test pieces of SM45C steel with both coated and uncoated carbide tool tips under various cutting conditions was conducted. Also a specially designed simple vibration damping device was experimentally evaluated for its effectiveness on machined surface roughness and a vibration test was conducted to confirm its ability to reduce the amplitude. Based on these tests finding, the following conclusions are made; 1. The cutting resistance($\textrm{p}_{1}$) increases as the depth of cut(d) increases at fixed feed rate(f) over the cutting speed(v) range of 43-226 m/min and p decreses about 18% average when V is increased for fixed d and f. At V= 226m/min, $\textrm{p}_{1}$/for A, C tips are about the same level but $\textrm{p}_{1}$ for B tip is 15% less than A, C tips. 2. The specific cutting resistance(Ks) at V=226 m/min was derived for A, B, C tips respectively and the value of Ks for B rip is about 20% less than A, C tips. 3. The surface roughness(Ra) improves significantly as the cutting speed(V) is increased and this effect was greater when V>100 m/min. On the other hand, Ra deteriorates as the feed rate(f) is increased and this trend was accelerated when f>0.3 mm/rev. With regard to the difference of Ra values among A, B, C tips, at V=226m/min, d=0.4mm, and f=0.31-0.61mm/rev, Ra values for B.C tips are about 17% less than tip A. 4. The experimental tool wear equations were derived for A, B, C tips and from these equations, the tool life($\textrm{T}_{\textrm{L}}$) baced on the I.S.O. criteria was calculated to be $\textrm{T}_{\textrm{L}}$<$\textrm{T}_{\textrm{LB}}$<$\textrm{T}_{\textrm{LC}}$ for both flank wear($\textrm{V}_{\textrm{B}}$) and boundary wear($\textrm{V}_{\textrm{N}}$). Hence, the coated tips are superior to the uncoated tip and tip C is considered to be the best. 5. The cutting resistance may be slightly reduced and the surface rounghness improved when the damper is used especially when V>100 m/min. Therefore this damping device is considered to be effective and practical. The experimental surface roughness equations were also derived. Based on the vibration test, it is established that the surface roughness improvement was the result of amplitude reduction made possible by the damper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.182-186
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• 1995

In this pacer, it is examined and confirmed that the R factor which is compensated after analyzing the characteristics of superconductor resulted from this experimented theory with the computer simulation, is refined to R$\sub$WP/=8.83[%], R$\sub$P/=6.47[%], R$\sub$I/=10.08[%], RF=7.19[%], R/eub E/=3.76(%), and on the basis of these experimental data, the significant parameter such as the scale factor(s) and the zero point shift(Z) and FWHM value(U,V,W) are optimized as follows; S =72.0827E-3, Z=0.2146, U=4.2761E-2, V=1.7983E-2, and W=2.6768E-2

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.8
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• pp.27-34
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• 2012

This paper proposes variable incremental conductance(IC) algorithm for maximum power point tracking(MPPT) control of photovoltaic. The conventional perturbation & observation(PO) and IC MPPT control algorithm generally uses fixed step size. A small step size reduces a tracking error in the steady state but slows a tracking speed in the transient state. Also, a large step size is fast a tracking speed but increases a tracking error. Therefore, this paper proposes variable IC MPPT algorithm that adjust automatically step size according to operating conditions. To improve a tracking speed and accuracy, when operating point is far from the maximum power point(MPP), the step size uses maximum value and when a operating point is near from the MPP, the step size uses variable step size that adjust according to slope of P-V curve. The validity of MPPT algorithm proposed in this paper prove through compare with conventional PO and IC MPPT algorithm.

• Journal of the korean Society of Automotive Engineers
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• v.9 no.4
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• pp.50-60
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• 1987

Combustion characteristics of opposed-jet-flames spouting out from dual prechambers of a divided combustion chamber were investigated by using high speed schilieren photography and chamber pressure measurement. Result shows that opposed-jet-flames are characterized by the parameter ( $A_{ori}$/ $V_{p}$) and there exists a certain critical value of ( $A_{ori}$/ $V_{p}$)c which distinguishes flame propagation patterns in the main chamber. Also higher chamber pressure and shorter total burning time can be derived by adopting this dual prechamber divided combustion chamber, which would lead a possibility of an appropriate combustion method of high load and low emissions.ons.ons.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.1
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• pp.50-55
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• 1992

Piezoelectric Buzzer which has been generally used requires about 30kV/cm poling process and has the aging effects. In this study, 0.85 PZN - 0.10 BT - 0.05 PT system ceramics with additives of 0 - 2 wt% YS12TOS13T were fabricated and investigated on electromechanical coupling coefficient(kS1pT), electric field induced charge coefficient(dS131T), and sound level. As the results, in the 0.4 wt% YS12TOS13T added composition ceramics compared with the basic, kS1pT was increased from 0.355 to 0.39 and induced piezoelectric d constant increased from 204 to 220 x 10S0-12T (C/N) and sound level of electrostrictive Buzzer has the highest value of 71.5 dB under 8kV/cm bias electric field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.678-682
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• 2004

Generally Bi-2223/Ag tapes have a broad S/N transition region and their sheath is a good electric conductor. In this study, the current distribution between superconductor and metal sheath in HTS tapes were investigated. AC with its peak value above 10 times $I_{c}$ was applied to HTS tapes for around 6 cycles and V-I characteristics were measured. Using the resistance of the sheath and V-I curves, the current distribution between superconductor and metal sheath was calculated. When 150 $A_{p}$ was applied, more than 2/3 of the current flows through superconductor. However, in the case of 304 $A_{p}$, most of the applied current came to flow through the metal sheath at the 6th cycle.e.e.e.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.255-258
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• 2003

In this paper there are different methods used to study the voltage stability, such as the P-V curve method. Jacobian method and the voltage collapse proximity indicator(L-index) method. The P-V curve method is to check operating margin from the maximum operating point. The Jacobian method is to check the eigenvalue or the minimum singular value of the load flow Jacobian matrix. If the power system is unstable, one of the eigenvalues, at least, has crossed the imaginary axis. The L-index method is to quantify how to close a particular operating point. This paper describes these methods to select the best location of FACTS and demonstrate the effectiveness of STATCOM of voltage stability on the IEEE 9-bus system.