• Title/Summary/Keyword: physical transition

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Non-stoichiometry-induced metal-to-insulator transition in nickelate thin films grown by pulsed laser deposition

  • Lee, Jongmin;Choi, Kyoung Soon;Lee, Tae Kwon;Jeong, Il-Seok;Kim, Sangmo;Song, Jaesun;Bark, Chung Wung;Lee, Joo-Hyoung;Jung, Jong Hoon;Lee, Jouhahn;Kim, Tae Heon;Lee, Sanghan
    • Current Applied Physics
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    • v.18 no.12
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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.

The Effects of Marital Status on Health among Older Women: The Moderating Effects of Age and Parent-Adult Child Relationships (노년기 여성의 결혼지위와 건강에 관한 종단 연구: 연령 및 부모-자녀 관계의 조절효과를 중심으로)

  • Son, Jeong-Yeon;Han, Gyoung-Hae
    • Korea journal of population studies
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    • v.35 no.1
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    • pp.211-238
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    • 2012
  • Using data from Korean Longitudinal Study on Aging (KLoSA), this study examines how continuity and change of marital status is associated with health over time among older women, focusing on the moderating effects of age and parent-child relationships. KLoSA data set has two waves of interviews, and for this study, 2046 women aged 65 and over were selected. To analyze data, Structural Equation Modeling (SEM) was used. The major findings are as follows. First, there was no statistically significant difference in health between continuously married older women and continuously single older women. However, older women who had transition from being married to being single showed lower physical health than continuously married and continuously single older women. Second, there were statistically significant differences in the effect of marital status on mental health according to the age of older women. Older women who had transition from being married to being single showed lower mental health than continuously married elders when older women were younger. Third, contact with children moderated the effect of marital status on physical health. Older women who had transition from being married to being single showed lower physical health than continuously single and continuously married older women when older women had less contact with their children. The findings imply after the loss of marital role, older women's relationship with adult children plays a significant role in promoting health. In conclusion, the findings of this study show the different pathways through which marital status is associated with health for 3 different groups of older women, being continuously single, being continuously married, and making transition from being married to being single.

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The physical properties and switching characteristics of amorphous $Ge_2Sb_2Te_5$ thin film (비정질 $Ge_2Sb_2Te_5$ 박막의 물리적 성질 및 스위칭 특성)

  • Lee, Jae-Min;Yang, Sung-Jun;Shin, Kyung;Chung, Hong-Bay
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.11a
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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.

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Thermodynamic and Physical Properties of (NH4)2MnCl4·2H2O by Nuclear Magnetic Resonance Relaxation Times

  • Kim, Yoo Young
    • Journal of the Korean Magnetic Resonance Society
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    • v.23 no.2
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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 $NH_4{^+}$.

Low-energy band structure very sensitive to the interlayer distance in Bernal-stacked tetralayer graphene

  • Lee, Kyu Won;Lee, Cheol Eui
    • Current Applied Physics
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    • v.18 no.11
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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.

One-step synthesis of dual-transition metal substitution on ionic liquid based N-doped mesoporous carbon for oxygen reduction reaction

  • Byambasuren, Ulziidelger;Jeon, Yukwon;Altansukh, Dorjgotov;Ji, Yunseong;Shul, Yong-Gun
    • Carbon letters
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    • v.17 no.1
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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.

Optimization of Coaxial to Microstrip Transition (동축커넥터와 마이크로스트립의 전이구조 최적화)

  • 강경일;김진양;이해영
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.2
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    • pp.70-77
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    • 2003
  • In this paper, analysis and measurement on coaxial connecter designed for packaging of microwave and micro strip transition structure are carried out. Even though researches on optimization of various kinds of transition structures have been conducted actively; however, the range of the application was very limited since they have been focused mainly on improvement of specific transmission line. Therefore, in this paper, we tried to analyze three kinds of substrates of which dielectric constants are 2,5,10 and are commercially used nowadays. Besides, we have confirmed reliability of FEM analysis, extracted equivalent circuit of transition area, found out factors determining extracted physical values, and made proof of electromagnetic variations for optimum characteristics. In addition, transition structure showing optimized characteristics on the basis of dielectric and microstrip structure was proposed. We reckon that the result of this research will apply with effect to transition design in microwave packaging development.

DETERMINATION OF PHYSICAL QUANTITIES OF GLOBULAR CLUSTERS

  • Kim, Kang-Min;Lee, See-Woo
    • Journal of The Korean Astronomical Society
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    • v.22 no.2
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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.

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Role of Magnetism in the Volumic and the Elastic Anomalies in Ferromagnetic Materials

  • You, Sang-Koo;Kim, Chul-Koo;Nahm, Kyun
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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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.

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Effects of an Oral Stimulation Program on the Transition from Tube to Bottle Feeding in Premature Infants (미숙아에게 적용한 구강 자극 프로그램이 젖병 수유로의 이행에 미치는 효과)

  • Kim, Hee-Young;Bang, Kyung-Sook
    • Journal of Korean Academy of Fundamentals of Nursing
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    • v.18 no.2
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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.