• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.861-864
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• 2002

Ferroelectric $Bi_{4-x}Nd_xTi_3O_{12}$(BNdT) thin films with the composition(x=0.75) were prepared on pt/Ti/$SiO_2$/Si(100) substrate by metal-organic deposition. The electrical and structural characteristics of BNdT thin films were investigated to develop ferroelectric thin films for capacitor layers of FRAM. After spin coating, thin films were annealed at $650^{\circ}C$ for 1hour in oxygen atmosphere. Scanning electron micrographs showed uniform surfaces composed of rod-like grains. The $Bi_{4-x}Nd_xTi_3O_{12}$(X=0.75) thin film capacitors with a Pt top electrode showed better ferroelectric properties. At the applied voltage of 5V, the dielectric constant$(\varepsilon_r)$, dissipation factor$(tan{\delta})$, remanent polarization(2Pr) and nonvolatile swiching charge of the $Bi_{4-x}Nd_xTi_3O_{12}$(x=0.75)thin films were about 346.7, 0.095, $56{\mu}C/cm^2$ and $38{\mu}C/cm^2$ respectively. Also the capacitor did not show any significant fatigue up to $8{\times}10^{10}$ read/write switching cycles at a frequency of 1MHz.

• Journal of Oral Medicine and Pain
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• v.22 no.2
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• pp.261-282
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• 1997

This study was undertaken to compare and investigate the wound healing process following Nd:YAG laser wounds and scalpel incisions of the rat tongue dorsal mucosa. Laser wounds were made parallel on the right side of tongue dorsum and scalpel incisions were made on the left side with 5mm length, respectively Visual inspection and immunohistochemistry with CD44 antibody after immediately, 6 hours, 1 day, 2, 4, 7, 11, 21 days after surgery were carried out. The results were as follows : 1. There was macroscopically no treat difference between laser wounds and scalpel incisions. 2. Laser wounds appeared as dry, bloodless and irregular grooves with carbonization and whitening of superficial tissues compared to sharp, straight and bleeding incisions using scalpel. 3. In the epithelium of rat tongue mucosa, CD44 expression in healing laser wounds and scalpel incisions were similar. 4. In the lamina propria and muscle layer, CD44 expression in healing laser wounds gradually increased earlier and decreased faster than scalpel incisions. Conclusively, it is suggested that pulsed Nd:YAG laser has more beneficial effect on the healing of wounded oral mucosa than scalpel in knew of CD44 expression.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.55-59
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• 1991

The temperature-dependent magnetization curves of amorphous Fe-Co-(Nd, Sm, Gd, Tb)-B alloys were measured using a vibrating sample magnetometer from 77 K up to 900 K. The spin wave stiffness constants and the range of the exchange interaction were calculated from the saturation magnetization values at 0 K. Curie temperatures and the Bloch coefficients estimated from the saturation magnetization curves. The low temperature dependence of magnetization is in good agreement with Bloch relation, $M_{s}(T)=M_{s}(O)(1-BT^{3/2}-CT^{5/2})$. The spin wave stiffness constant and the range of exchange interaction are decreased by substitution of heavy rare earth (Tb, Gd).

• Korean Journal of Health Education and Promotion
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• v.14 no.1
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• pp.11-21
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• 1997

We carried out this study to analyze the effectiveness through health education program in short term which was performed to use the special subject activities. This study was conducted on 63 students who were first grade in S Junior High School from Dec. 1995 to Feb. 1996. To analyze the effectiveness, we performed the Pretest, 1st Posttest, and 2nd Posttest for learned health knowledge. The results were as follows: 1. Most of the students(69.8%) responded that their health were good, and they got the information for health through Mass Com.. The students who had experience of health education were 15.9%, and the 77.8% of the respondents needed the health education. 2. The means of health knowledge on tests were 18.2(Pretest}, 21.5(1st Posttest), and 21.4(2nd Posttest). Increase of health knowledge between Pretest and 1st Posttest was 10.9%. 3. The mean of differences between Pretest and 1st Posttest was 3.26, it was significant(p〈0.01). And the mean of differences between Pretest and 2nd Posttest was 3.19, it was significant(p〈0.01);however, the mean of differences between 1st Posttest and 2nd Posttest was not significant(p=0.2514). 4. The significant main contents were Health Facilities(d=0.42), Pregnancy and Labor(d=0.39), Sex Education(d=0.29), Personal Hygiene(d=0.35), Safety Education (d=0.66), and Drug Abuse(d=0.60)(p〈0.01)

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.5
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• pp.636-644
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• 2006

Recently, there were some successful examples that the laser welding was introduced into production line. However, the spread of laser welding is not sufficient in many industries. There are several reasons why it is difficult to penetrate the laser welding into production lines. Because it is different from reflection, absorption and permeation of laser beam according to material and surface condition. Moreover, there are significant problems in processing such as absorption and scattering of beam by the induced plasma or plume. Therefore, understanding of mechanism on formation of weld defect in laser welding of the laminated core for motor is very important. In this paper, it was analyzed in terms of materials which was source of defect in laser welding and conventional arc welding. As a results of analysis, insulation coating film of the laminated core was judged to main factor of weld defect. it could be well aware as tracing carbon volume, and it was deduced that weld defect by insulation coating film was caused by difference of mechanism between the two heat sources.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.47.2-47.2
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• 2010

1980년대 이후로 등장한 Nd-Fe-B 소결자석은 뛰어난 자성특성을 나타내며, 원재료도 풍부하기 때문에 단위 자기 에너지당 가격은 비교적 저가이다. 따라서 대부분의 기존 Sm-Co와 주조 Al-Ni-Co 자석재료를 대체하며 다양한 첨단사업의 핵심소재로 적용되며, 자동차 및 의료기기 등 산업 전반에 사용되고 있다. 이러한 응용 중에서도 향후 녹색성장을 위한 신성장동력 산업인 하이브리드 자동차의 구동 모터로서 사용되는 대표적인 영구자석이다. 현재 개발된 Nd계 영구자석은 큐리온도가 낮고 높은 온도에서 자기적 성능의 열화가 심하게 진행된다는 단점이 있기 새로운 합금 설계 및 공정의 최적화를 통해 보자력을 향상 시킴으로써 사용온도를 $200^{\circ}C$ 정도로 높이는 연구가 활발히 진행되고 있다. 본 연구에서는 일반적인 제조공정을 통해 제조된 소결체의 미세구조에 변화시키기 위하여 약 $10^{-5}$ Torr의 진공분위기에서 $10^{\circ}C/min$의 승온/냉각속도로 $350^{\circ}C$부터 $450^{\circ}C$ 구간에서 2 사이클부터 8 사이클까지 승온과 냉각을 반복하는 열처리를 수행하였다. Nd-Fe-B 소결자석을 $350^{\circ}C{\sim}450^{\circ}C$ 온도구간에서 반복적인 열처리를 수행한 결과 열처리 사이클에 따라 보자력 특성이 다르게 나타내었다. 이에 승온과 냉각을 반복하며 나타난 미세구조의 변화가 자성특성에 어떠한 영향을 미쳤는지에 대해 고찰하였다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.988-997
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• 2012

Laser surface hardening is one of core technologies to enhance various characteristics such as the strength, hardness, toughness, abrasion resistance, and fatigue resistance for the mold material. This paper focuses on testing characteristics of the laser heat treatment according to the preheating parameters in case of the SM45C medium carbon steel. In this paper, we assume that the power and travel speed of the laser are 1,800W and 0.5m/min, respectively, and the range of the preheating temperature is $50^{\circ}C{\sim}300^{\circ}C$. From the result of the test, we observed that the hardness width and depth are enhanced as the temperature is increased. Also, the best average hardness was 751.7Hv for the temperature of $100^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.346-349
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• 2002

Ferroelectric $Bi_{4-x}Nd_{x}Ti_{3}O_{12}(BNdT)$ thin films with the composition(x=0.75) were prepared on $Pt/Ti/SiO_{2}/Si(100)$ substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to $650^{\circ}C$ and then the electrical and structural characteristics of BNdT films were investigated for the application of FRAM. Electrical properties such as dielectirc constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at $650^{\circ}C$ was $56{\mu}C/cm^{2}$ at an applied voltage of 5V. In fatigue characteristics value remained costant up to $8{\times}10^{10}$ read/write switching cycles at a frequency of 1Mhz regardless of annealing temperatures.

• Journal of Magnetics
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• v.9 no.4
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• pp.105-108
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• 2004

The attempt for the addition of double-phase nanocomposite $Nd_2Fe_{14}BFe_3B$ powders, respectively, into several $RE_2Fe_{14}B$(RE=Pr, Nd) powders with high magnetic properties was carried out. The powders were compounded and compressed to take shape bonded magnets. By means of investigating the variation of compound magnet $B_r$, the interaction between magnetic powders was revealed. The result shows that not chemical just but physical interaction exists between elements. The compound effect of $Nd_2Fe_{14}BFe_3B$-ferrite bonded magnets was detailed studied. The functional relation was revealed between magnetic properties and ferrite content. That is $Y = 5.42 x^2 -11.34x + 6.62$. The variation of $_iH_c$ temperature coefficient ${\beta}_{iHc}$ with ferrite content was investigated. Following the ferrite content increased, ${\beta}_{iHc}$ and $h_{irr}$ were obviously decreased, compression-resistant strength was enhanced.

• Journal of Oral Medicine and Pain
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• v.18 no.1
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• pp.107-117
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• 1993

The author has taken intraoral standard films by the paralleling technique of 6414 teeth in 838 patients ranged from early twenties to early sixties and analysed the change of pulp cavity in the mandibular posterior teeth by ageing. The obtined results were as follows : 1. There was no significant difference between the right and left teeth. 2. The degree of change of pulp cavity in female was higher than that in male. 3. The change of pulp cavity was increased by ageing. 4. The correlation between the degree of change of pulp cavity inmandibular posterior teeth (X) and age (Y) were : Male 1st premolar Y=13.22X3.37+ r=0.79 2nd premolar Y=12.09X+3.65 r=0.79 1st molar Y=11.90X+1.25 r=0.78 2nd molar Y=10.51X+10.43 r=0.83 Female 1st premolar Y=13.66X-2.49 r=0.86 2nd premolar Y=13.63X-2.42 r=0.86 1st molar Y=12.42X-1.44 r=0.79 2nd molar Y=11.42X+5.91 r=0.84