• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.322-326
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• 2014

Recently, the LOE(loss of excitation) incidents are occurred in domestic synchronous generator frequently, the synchronous generator protection system has been much attention for the LOE protection of the incidents that threats synchronous generators and power systems. This paper was showed the characteristics and practices of distance relay that widely used LOE protection relaying in generator. Firstly, the operating characteristics and the impedance locus for LOE of the generator protection were introduced. Even if the conventional simulation program is used for modeling, but it is difficult to implement a LOE modeling and simulation of synchronous generator. So, the LOE relay operation data collected from thermal power plant and nuclear power plant in real fields were analyzed. By reviewing the applications of GE Mho relays, the reliability of LOE for synchronous generator protection in domestic were improved.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1453-1459
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• 2015

Loss of excitation (LOE) relay is prevalently used to protect synchronous generator. The widely used method for synchronous generator LOE protection is a negative offset mho relay with two zones. The basis of this relay is identical to mho impedance relay. In other words, this relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of series compensation, changes measured voltage and current signals during loss of excitation. This paper reveals that the presence of series compensators such as fixed series capacitors (FSCs) and static synchronous series compensator (SSSC) causes a significant delay on the performance of generator LOE relay. It is also shown that the presence of SSSC causes the LOE relay to be under-reached. Different operating modes of the power system, the SSSC and also different percentages of series capacitive compensations have been considered in the modeling. All the detailed simulations are carried out in the MATLAB/Simulink environment using the SimPowerSystems toolbox.

• Resources Recycling
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• v.14 no.3
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• pp.63-67
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• 2005

As there are recent tendencies to raise horizontal frequencies so as to improve screen definition for high-quality TV and high definition display, ferrite core for deflective yokes requires materials with low coreloss in the areas of high frequencies. The researcher added CuO to low-loss Mg-Zn ferrite. After choosing MgO, ZnO, Fe$_2O_3$ and CuO, the researcher changed a ratio of composition, substituting MgO for CuO. These samples were sintered for three hours up to 980$^{\circ}C$~1350$^{\circ}C$. Measure magnetic permeability, electric loss, core loss and a rate of contraction.

• Journal of Korean Dental Science
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• v.3 no.2
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• pp.20-25
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• 2010

Aim : This study was conducted to assess the oral health status of deaf and mute children attending special school. Materials and Methods : A cross-sectional descriptive survey was conducted among 137 deaf and mute children with ages ranging from 7 to 18 years. A total of 76 males (55.47%) with mean age of $14.2{\pm}4.5$ and 61 females (44.53%) with mean age of $13.8{\pm}4.2$ years and studying in a school for deaf and mute children in Warora were considered. Data were collected using a standard method recommended by WHO for the oral health survey in 1977. Oral health status was assessed using OHIS, Loe and Sinless, and CPI Index along with DMFT and DMFS Index. Gingival position was considered for measuring attachment loss. Statistical analysis was performed using the SPSS software package (version 17.0). Results : The mean DMFT was found to be $2.53{\pm}1.72$, and mean DMFS, $3.37{\pm}3.16$. The prevalence of dental caries was pegged at 35.32%, with mean OHIS score at $1.49{\pm}0.76$. Overall gingival index among deaf and mute children was $0.81{\pm}1.4$, whereas that for the upper arch and lower arch was $0.92{\pm}0.84$ and $1.19{\pm}0.95$, respectively. The mean score for the CPI Index among deaf and mute children was found to be $0.42{\pm}0.32$. Gingival clinical attachment loss was found to be $0.26{\pm}0.15mm$. Conclusion : These findings suggest that children with hearing disabilities can also have good oral hygiene comparable to normal individuals of the same age group. These results may be attributed to the fact that the study sample was taken from a single school of a private organization with a well-equipped dental setup.

• Journal of Periodontal and Implant Science
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• v.23 no.2
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• pp.345-351
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• 1993

Various alloplastic materials have been used on the periodontally diseased ossous defects. Hydroxyapatite, which is used the most common alloplastic material is a non-resorbable form of calcium phosphate and natural coral which is a biodegradable by carbonic anhydrase in osteoclast was introduced recently. The purpose of the present study was to evaluate the clinical effects of porous hydoxyapatite and natural coral on the human periodontal defects. Four males and three females who had adult periodontitis were selected for this study. The teeth that had similar bone loss radiographically and periodontal pocket deeper than 5mm were selected. Gingival recession, pocket depth, plaque index(Silness & Loe), sulcus bleeding index and tooth mobility (measured by Periotest$^{(r)}$) were examined before graft. Before insertion of alloplastic materials, the depth from CEJ to bone crest and from CEJ to base of the osseous defect was recorded. Porous particulate hydroxyapatite(Interpore 200$^{(r)}$, A group) was place on the defect and natural coral(Biocoral$^{(r)}$, B group) was placed on the defect of the opposing tooth. Six months post-surgically the same parameters were recorded by reentry procedures. A and B group showed 0.6mm of mean recession. Mean reduction of pocket depth were 5mm for A group and 4.9mm of B group. Reduced SBI and tooth mobility were recorded. Osseous defect fills of the original defects were 2.9mm for A and 3mm for B group. Percentage defect fills were 71% for A and 59% for B group. The difference of defect fill between pre- and post-insertion was statstically significant(p<0.05). But the difference between the two groups was not significant statistically(p<0.05). The clinical impression at 6 month re-entry and the numerical date indicate that natural coral as well as porous particulate hydoxyapatite has a definite potential as an alloplastic implant in the treatment of periodontal osseous defects.

• Journal of dental hygiene science
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• v.8 no.4
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• pp.395-401
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• 2008

This study was carried out in order to offer basic data available for being helpful to promoting periodontal health, by analyzing effects in socio-demographical and health-behavior characteristics on index of evaluating periodontal status. The study conducted a survey for the 151 adults aged 30 to 59 from October. 1, 2006 to March. 30, in 2007. The collected data were analyzed with t-test and one-way of variance using SPSS 12.0. Then, the following result were obtain. 1. sociodemographic and health-behavior characteristics is not related to O'Leary plaque index, Loe & Silness gingival index. 2. The number of sextants possessing periodontal pocket was higher in men(3.34) than women(2.43), also statistically significant difference in the occupational fields. Smoker(3.38) was higher than non-smoker(2.72), and it was higher over 3 times a week than almost no drinking as for frequence alcohol intake. 3. The amount of loss for inter-dental alveolar crest was higher in men(71.79) than women(42.24), was highest of the 'professional' in the occupational fields, and smoker(67.23) was higher than non-smoker(48.22). 4. There was significantly difference in the number of missing tooth between age and frequence of alcohol intake. These results that occupational fields, smoking and alcohol intake were related to the number of sextants possessing periodontal pocket and amount of loss for inter-dental alveolar crest.