• Progress in Superconductivity
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• 제11권2호
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• pp.87-91
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• 2010

We fabricated the polyacrylic acid (PAA)-doped $MgB_2$ bulks and characterized their lattice parameters, actual C substitutions, microstructures, and critical properties. The boron (B) powder was mixed with PAA using N,N-dimethylformamide as solvent and then the solution was dried out at $200^{\circ}C$ and crushed. The C treated B powder and magnesium powder were mixed and compacted by uniaxial pressing at 500 MPa, followed by sintering at $900^{\circ}C$ for 1 h in high purity Ar atmosphere. We observed that the PAA doping increased the MgO amount but decreased the grain size, a-axis lattice constant, and critical temperature ($T_c$), which is indicative of the C substitution for B sites in $MgB_2$. In addition, the critical current density ($J_c$) at high magnetic field was significantly improved with increasing PAA addition: at 5 K and 6.6 T, the $J_c$ of 7 wt% PAA-doped sample was $6.39\;{\times}\;10^3\;A/cm^2$ which was approximately 6-fold higher than that of the pure sample ($1.04\;{\times}\;10^3\;A/cm^2$). This improvement was probably due to the C substitution and the refinement of grain size by PAA doping, suggesting that PAA is an effective dopant in improving $J_c$(B) performance of $MgB_2$.

• 간호행정학회지
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• 제6권2호
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• pp.211-225
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• 2000

With the drastically changing healthcare market, the adoption of DRG system and the use of Critical Pathway will be increased gradually in order to care hospitalized patients qualitatively and manage cost-effectively in Korea. The purpose of this quasi-experimental research is to apply and analyze the developed critical pathway to the patients with Cesarean section. 35 eligible subjects for the control group were chosen from postpartum patients who has delivered at H-hospital in Kwang-ju, and were questioned after appling previous care plan from May to December, 1998. For the experimental group, 37 subjects were chosen and questioned after applying Critical Pathway service from January to June, 1999. The instruments are a critical pathway for the patients with Cesarean section developed by chung(1998) and a questionnaire that evaluate patients and family members' satisfaction level. Also, educational materials were used to inform them in the process of Critical Pathway application. As a result of chi-square test on general characteristics, there is significant difference between control group and experimental group only in terms of room size(p= .010). There are no significant differences in the average length of stay in the hospital between control group and experimental group(t=.078). Also, the average medical consult fee has no difference significantly between two groups(t= .105). The findings showed that the experimental group with critical pathway service scored significantly higher than control group on the satisfaction level toward care services(p=.000). The items are post-operative care, postpartum exercise technique, breast feeding and breast manage through educational materials. In conclusion, the research indicates that the application of planned Critical Pathway can have a positive impact on satisfaction level of inpatients with Cesarian section.

• Progress in Superconductivity
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• 제3권1호
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• pp.5-12
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• 2001

Our experimental research focuses on manipulating pinning deflects to alter the phase diagram of vortex matter, creating new vortex phases. Vortex matter offers a unique opportunity for creating and studying these novel phase transitions through precise control of thermal, pinning and elastic energies. The vortex melting transition in untwinned YB $a_2$C $u_3$ $O_{7-}$ $\delta$/ crystals is investigated in the presence of disorder induced by particle irradiation. We focus on the low disorder regime, where a glassy state and a lattice state can be realized in the same phase diagram. We follow the evolution of the first order vortex melting transition line into a continuous transition line as disorder is increased by irradiation. The transformation is marked by an upward shift in the lower critical point on the melting line. With columnar deflects induced by heavy ion irradiation, we find a second order Bose glass transition line separating the vortex liquid from a Bose glass below the lower critical point. Furthermore, we find an upper threshold of columnar defect concentration beyond which the lower critical point and the first order melting line disappear together. With point deflect clusters induced by proton irradiation, we find evidence for a continuous thermodynamic transition below the lower critical point..

• 한국재료학회지
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• 제25권8호
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• pp.365-369
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• 2015

This paper investigates the dependency of the critical content for electrical conductivity of carbon powder-filled polymer matrix composites with different matrixes as a function of the carbon powder content (volume fraction) to find the break point of the relationships between the carbon powder content and the electrical conductivity. The electrical conductivity jumps by as much as ten orders of magnitude at the break point. The critical carbon powder content corresponding to the break point in electrical conductivity varies according to the matrix species and tends to increase with an increase in the surface tension of the matrix. In order to explain the dependency of the critical carbon content on the matrix species, a simple equation (${V_c}^*=[1+ 3({{\gamma}_c}^{1/2}-{{\gamma}_m}^{1/2})^2/({\Delta}q_cR]^{-1}$) was derived under some assumptions, the most important of which was that when the interfacial excess energy introduced by particles of carbon powder into the matrix reaches a universal value (${\Delta}q_c$), the particles of carbon powder begin to coagulate so as to avoid any further increase in the energy and to form networks that facilitate electrical conduction. The equation well explains the dependency through surface tension, surface tensions between the particles of carbon powder.

• Structural Engineering and Mechanics
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• 제67권2호
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• pp.115-123
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• 2018

By using the first order shear deformation plate theory (FSDT) in the present paper, the effect of porosity on the buckling behavior of carbon nanotube-reinforced composite porous plates has been investigated analytically. Two types of distributions of uniaxially aligned reinforcement material are utilized which uniformly (UD-CNT) and functionally graded (FG-CNT) of plates. The analytical equations of the model are derived and the exact solutions for critical buckling load of such type's plates are obtained. The convergence of the method is demonstrated and the present solutions are numerically validated by comparison with some available solutions in the literature. The central thesis studied and discussed in this paper is the Influence of Various parameters on the buckling of carbon nanotube-reinforced porous plate such as aspect ratios, volume fraction, types of reinforcement, the degree of porosity and plate thickness. On the question of porosity, this study found that there is a great influence of their variation on the critical buckling load. It is revealed that the critical buckling load decreases as increasing coefficients of porosity.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2012년도 자성 및 자성재료 국제학술대회
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• pp.90-90
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• 2012

• 한국화재소방학회논문지
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• 제33권4호
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• pp.70-76
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• 2019

본 연구에서는 임계온도스위치를 이용하여 저전력 단독경보형 정온식 감지기를 개발하였다. 임계온도스위치는 70 ℃에서 저항이 급격하게 감소하는 특성을 나타내는 소자로, 금속-절연체 전이 현상을 이용함으로써 온도 측정에 대한 높은 신뢰성을 보장한다. 또한 임계온도스위치의 금속에서 절연체로 변하는 디지털적인 특성을 이용하여 마이크로컨트롤러 사용 없이 화재를 감지함으로써 단독경보형 정온식 감지기의 소비 전력을 최소화하였다. 시험결과 임계온도스위치를 이용한 단독경보형 정온식 감지기는 소방청 고시 단독경보형 정온식 감지기 시험 조건을 만족했으며, 소비 전력을 측정한 결과 기존 제품 대비 70%의 전력만으로 화재를 감지함을 확인하였다.

• 한국분말재료학회지
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• 제26권5호
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• pp.432-436
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• 2019

This study demonstrates the effect of addition of Fe particles of different sizes on the critical properties of the superconductor $MgB_2$. Bulk $MgB_2$ is synthesized by ball milling Mg and B powders with Fe particles at $900^{\circ}C$. When Fe particles with size less than $10{\mu}m$ are added in $MgB_2$, they easily react with B and form the FeB phase, resulting in a reduction in the amount of the $MgB_2$ phase and deterioration of the crystallinity. Accordingly, both the critical temperature and the critical current density are significantly reduced. On the other hand, when larger Fe particles are added, the $Fe_2B$ phase forms instead of FeB due to the lower reactivity of Fe toward B. Accordingly, negligible loss of B occurs, and the critical properties are found to be similar to those of the intact $MgB_2$.

• 한국초전도ㆍ저온공학회논문지
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• 제10권2호
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• pp.16-19
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• 2008

Angular dependence of critical current density of SmBCO coated conductor fabricated by co-evaporation method was investigated. For comparison, three samples were fabricated by a co-evaporation method and one sample was fabricated by a pulsed laser deposition process. The deposition system, named EDDC (Evaporation using Drum in Dual Chambers), is a batch type co-evaporation system, which is composed of reaction chamber and evaporation chamber. The normalized critical current density ratio ($I_c/I_c$(H//ab-plane)) of EDDC-SmBCO samples was found to be higher than that of PLD-YBCO sample in the whole range of angle. While the EDDC-SmBCO samples evidently had a peak at the angle of H//c-axis in the plot of the angular dependence of critical current, the normalized critical current of PLD-YBCO sample decreased monotonically without any peak as angle increased. The field dependence of critical current under the magnetic field parallel to the normal direction of those samples showed similar aspect in the range of $0\;G{\sim}5000\;G$.

• 한국화재소방학회논문지
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• 제22권2호
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• pp.30-37
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• 2008

건축용 바닥재의 화재예방을 위하여 국제규격으로 정해져 있는 바닥재 시험평가 방법인 KSISO 9239-1을 이용하여 각종 바닥재에 대한 연소성 시험을 복사열 판넬 시험기를 사용하여 실시하였다. 복사열 판넬 시험기를 이용하여 각종 바닥재에 대한 화염 전파거리, 임계 열류량 그리고 연기 발생농도 측정하였다. 측정결과 바닥재의 구성 물질 별로 서로 다른 연소특성을 나타내었으며, 바닥재의 표면 재질 및 구성성분이 열 방출과 연기 발생량에 있어 중요한 영향을 미치게 된다는 것을 확인할 수 있었다. 위의 평가방법은 화재위험성을 연구하는데 중요한 인자인 임계 열류량, 연기 발생량 및 화염 전파거리를 정량적으로 평가하는 중요한 시험방법임을 알 수 있었고 국내 건축용 바닥재 화재평가 방법을 국내실정에 맞게 제정 및 적용하는 것이 적합할 것으로 판단되었다.