• Current Applied Physics
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• 제18권12호
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• pp.1577-1582
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• 2018

While controlling the cation contents in perovskite rare-earth nickelate thin films, a metal-to-insulator phase transition is reported. Systematic control of cation stoichiometry has been achieved by manipulating the irradiation of excimer laser in pulsed laser deposition. Two rare-earth nickelate bilayer thin-film heterostructures with the controlled cation stoichiometry (i.e. stoichiometric and Ni-excessive) have been fabricated. It is found that the Ni-excessive nickelate film is structurally less dense than the stoichiometric film, albeit both of them are epitaxial and coherent with respect to the underlying substrate. More interestingly, as a temperature decreases, a metal-to-insulator transition is only observed in the Ni-excessive nickelate films, which can be associated with the enhanced disproportionation of the Ni charge valence. Based on our theoretical results, possible origins (e.g. anti-site defects) of the low-temperature insulating state are discussed with the need of future work for deeper understanding. Our work can be utilized to realize unusual physical phenomena (e.g. metal-to-insulator phase transitions) in complex oxide films by manipulating the chemical stoichiometry in pulsed laser deposition.

• 한국인구학
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• 제35권1호
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• pp.211-238
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• 2012

본 연구의 목적은 노년기 여성의 결혼지위가 신체 및 정신건강에 어떠한 영향을 미치며, 그러한 관련성이 연령 및 부모-자녀관계에 따라 달라지는가에 대해 시간의 변화를 고려하여 실증적으로 검증하는 것이다. 이러한 연구목적을 위해 한국노동연구원의 고령화연구패널조사 1차년도와 2차년도 자료를 이용하였으며, 65세 이상의 여성 노인 2046명을 분석하였다. 주요 분석결과는 다음과 같다. 첫째, 1, 2차년도 사이에 배우자를 상실한 여성 노인은 유배우 노인뿐만 아니라 이 기간 동안 지속적으로 배우자가 없는 노인에 비해서도 만성질환을 많이 앓고 있는 것으로 나타나 같은 무배우 상태임에도 불구하고 신체 건강 결과에서 차이를 보였다. 하지만 지속적 무배우 노인과 지속적 유배우 노인의 건강수준에는 유의한 차이가 없다. 둘째, 1, 2차년도에 배우자를 상실한 여성 노인은 유배우 노인보다 우울감 수준이 높은 것으로 나타나는데, 이러한 관련성이 65~74세의 젊은 노인 집단에서 강하게 나타났다. 셋째, 1, 2차년도에 배우자를 상실한 여성 노인은, 유배우 노인뿐만 아니라 이 기간 동안 지속적으로 배우자가 없는 노인에 비해서도 만성질환을 더 많이 앓고 있는 것으로 나타나는데, 이러한 관련성이 자녀만남빈도가 낮은 집단에서 강하게 나타났다. 하지만 결혼지위가 건강에 미치는 영향에서 자녀동거여부의 조절효과는 나타나지 않았다. 마지막으로, 건강의 하위차원에 따라 결혼지위가 건강에 영향을 미치는 과정에서 조절변인으로 작용하는 변수의 성격이 상이하였다. 본 연구는 전국 규모의 종단 자료의 분석을 통해 여성 노인의 결혼지위와 건강과의 인과관계에 대한 논리적인 검증을 시도하였고, 특히 결혼지위를 구분하는 기준과 연령 및 부모-자녀관계의 역할에 따라 건강에 미치는 영향이 상이하다는 것을 밝혔다는 점에서 의의가 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.268-271
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• 2004

The phase transition from amorphous to crystalline states, and vice versa, of $Ge_2Sb_2Te_5$ films by applying electrical pulses have been studied. This material can be used as nonvolatile memory. The reversible phase transition between the amorphous and crystalline states, which is accompanied by a considerable change in electrical resistivity, is exploited as means to store bits of information. The nonvolatile memory cells are composed of a simple sandwich (metal/chalcogenide/metal). It was formed that the threshold voltage depends on thickness, electrode distance, annealing time and temperature, respectively.

• 한국자기공명학회논문지
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• 제23권2호
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• pp.40-45
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• 2019

The phase transition temperatures and thermodynamic properties of $(NH_4)_2MnCl_4{\cdot}2H_2O$ grown by the slow evaporation method were studied using differential scanning calorimetry and thermogravimetric analysis. A structural phase transition occurred at temperature $T_{C1}$ (=264 K), whereas the changes at $T_{C2}$ (=460 K) and $T_{C3}$ (=475 K) seemed to be chemical changes caused by thermal decomposition. In addition, the chemical shift and the spin-lattice relaxation time $T_{1{\rho}}$ were investigated using $^1H$ magic-angle spinning nuclear magnetic resonance (MAS NMR), in order to understand the role of $NH_4{^+}$ and $H_2O$. The rise in $T_{1{\rho}}$ with temperature was related to variations in the symmetry of the surrounding $H_2O$ and $NH_4{^+}$.

• Current Applied Physics
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• 제18권11호
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• pp.1393-1398
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• 2018

We have investigated Bernal-stacked tetralayer graphene as a function of interlayer distance and perpendicular electric field by using density functional theory calculations. The low-energy band structure was found to be very sensitive to the interlayer distance, undergoing a metal-insulator transition. It can be attributed to the nearest-layer coupling that is more sensitive to the interlayer distance than are the next-nearest-layer couplings. Under a perpendicular electric field above a critical field, six electric-field-induced Dirac cones with mass gaps predicted in tight-binding models were confirmed, however, our density functional theory calculations demonstrate a phase transition to a quantum valley Hall insulator, contrasting to the tight-binding model prediction of an ordinary insulator.

• Carbon letters
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• 제17권1호
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• pp.53-64
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• 2016

Nitrogen (N)-doped ordered mesoporous carbons (OMCs) with a dual transition metal system were synthesized as non-Pt catalysts for the ORR. The highly nitrogen doped OMCs were prepared by the precursor of ionic liquid (3-methyl-1-butylpyridine dicyanamide) for N/C species and a mesoporous silica template for the physical structure. Mostly, N-doped carbons are promoted by a single transition metal to improve catalytic activity for ORR in PEMFCs. In this study, our N-doped mesoporous carbons were promoted by the dual transition metals of iron and cobalt (Fe, Co), which were incorporated into the N-doped carbons lattice by subsequently heat treatments. All the prepared carbons were characterized by via transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To evaluate the activities of synthesized doped carbons, linear sweep was recorded in an acidic solution to compare the ORR catalytic activities values for the use in the PEMFC system. The dual transition metal promotion improved the ORR activity compared with the single transition metal promotion, due to the increase in the quaternary nitrogen species from the structural change by the dual metals. The effect of different ratio of the dual metals into the N doped carbon were examined to evaluate the activities of the oxygen reduction reaction.

• 대한전자공학회논문지TC
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• 제40권2호
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• pp.70-77
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• 2003

본 논문에서는 초고주파 대역의 패키징을 위한 동축커넥터와 마이크로스트립의 전이 구조를 해석하고 측정하였다. 현재까지 여러 가지 전이구조의 최적화에 대한 연구는 활발히 이루어졌다. 하지만 주로 특정 전송 선로에 대해서만 개선되어져 왔기 때문에 그 적용범위가 매우 좁다. 따라서 본 논문에서는 상용화되고 있는 비유전율이 2, 5, 10인 세 종류의 기판을 모델로 해석하였다. 또한 FEM 해석의 신뢰성을 확인 후 전이부 분의 등가회로 모델을 추출하고, 추출된 물리적인 값들을 결정 하는 요인을 찾아내고 최적의 전이 특성을 위한 전자기적 변수들을 확인하였다. 더불어 기판 유전율과 마이크로스트림 구조를 기준으로 최적의 전이특성을 내는 전이구조를 제시하였다. 본 논문의 결과는 마이크로파 패키징 개발에서 동축커넥터와 마이크로스트립 최적의 전이구조 설계에 효과적으로 활용 될 수 있으리라 기대된다.

• 천문학회지
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• 제22권2호
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• pp.81-99
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• 1989

Applying five morphological parameters defined along the main sequence (MS), red giant branch (RGB) and horizontal branch (HB) in the C-M diagram (CMD), and the transition period-luminosity relation for RR Lyrae variables, some basic physical quantities such as helium abundance, age, mass and luminosity are determined for 21 well observed globular clusters with combination of evolutionary models and atmospheric models properly chosen by the numerical test. The dependences of these quantities on the age and chemical abundance are investigated.

• 한국자기학회지
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• 제5권5호
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• pp.351-353
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• 1995

The physical origins of anomalous volume effect (Invar effect) and elastic effect (Elinvar effect) are critically examined. We found that, unlike the volume effect, the shear elastic properties are not much influenced by the ferromagnetic transition. This finding shows that the two anomalies originate from different physical origins, thus contradicting the conventional wisdom. We discuss the consequences of this finding in the light of recent experiments.

• 기본간호학회지
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• 제18권2호
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• pp.160-167
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• 2011

Purpose: The purpose of this study was to identify the effects of an oral stimulation program on premature infant's transition from tube feeding to bottle feeding, decrease in desaturation during feeding, and early discharge. Methods: This quasi-experimental study was performed in one neonatal intensive care unit (NICU) of an university hospital. The control group data (n=69) were obtained from June 2008 to May 2009, and the experimental group data (n=67), from June 2009 to May 2010. The oral stimulation program (OSP) was provided daily before feeding for the experimental group until transition to bottle feeding was completed. Results: The OSP group began bottle feeding earlier and were on complete bottle feeding earlier than control group. Discharge delay due to feeding desaturation was lower than for the control group. Conclusion: The results indicate that OSP for premature infants was helpful in transition from tube feeding to bottle feeding and early discharge and thus can contribute health and development in premature infants.