• 한국세라믹학회지
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• 제47권5호
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• pp.474-478
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• 2010

We studied the energy barrier for proton conduction with volume variation in $BaZrO_3$ using a first principles study to investigate an optimum volume for the proton conduction. The volume increase of $BaZrO_3$ was expected to decrease the energy barrier for proton rotation and to increase that for proton transfer, and these trends could be extrapolated when the volume was decreased. However, the energy barriers for the proton transfer with the volume decrease were increased, while all the other energy barriers varied as expected. We could explain this unexpected behavior by the bent Zr-O-Zr structure, when the volume was decreased.

• Coupled systems mechanics
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• 제6권1호
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• pp.29-40
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• 2017

This work employed density functional theory to investigate the structural and ferroelectric properties of the Ruddlesden-Popper (RP) phase of lead titanate, $Pb_2TiO_4$, as well as its phase transitions with epitaxial strain. A wealth of novel structural instabilities, which are absent in the host $PbTiO_3$ material, were identified in the RP phase through phonon soft-mode analysis. Our calculations showed that the ground state of $Pb_2TiO_4$ is antiferroelectric, distinct from the dominant ferroelectric phase in the corresponding host material. In addition, applied epitaxial strain was found to play a key role in the interactions among the instabilities. The induction of a sequence of antiferroelectric and antiferrodistortive (AFD) phase transitions by epitaxial strain was demonstrated, in which the ferroic instability and AFD distortion were cooperative rather than competitive, as is the case in the host $PbTiO_3$. The RP phase in conjunction with strain engineering thus represents a new approach to creating ferroic orders and modifying the interplay among structural instabilities in the same constituent materials, enabling us to tailor the functionality of perovskite oxides for novel device applications.

• 한국자기학회지
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• 제17권3호
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• pp.109-113
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• 2007

CsCl 구조를 가진 VRu(001) 표면의 자기적 성질을 일반기울기근사(GGA)를 채택한 총퍼텐셜선형보강평면파(FLAPW) 에너지 띠 계산 방법을 이용하여 이론적으로 연구하였다. 이를 위해 각기 V 및 Ru 원자층으로 끝나는 두 개의 (001) 표면을 고려하였다. 계산된 머핀-틴 구 내의 다수 및 소수 전자의 수로부터 V로 끝나는 표면의 자기모멘트는 $1.71_{{\mu}_B}$로 매우 큰 값을 가졌으며, Ru로 끝나는 표면은 자성이 거의 없는 것으로 계산되었다. 이러한 자성을 계산된 스핀분극상태밀도와 스핀전하밀도와 연관지어 설명하였다.

• 한국재료학회지
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• 제30권12호
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• pp.666-671
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• 2020

The electronic structure and magnetic properties of chalcopyrite (CH) AlGaAs2 with dopant Mn at 3.125 and 6.25 % concentrations are investigated using first-principles calculations. The CH AlGaAs2 alloy is a p-type semiconductor with a small band-gap. The AlGaAs2:Mn shows that the ferromagnetic (FM) state is the most energetically favorable one. The Mn-doped AlGaAs2 exhibits FM and strong half-metallic ground states.The spin polarized Al(Ga,Mn)As2 state (Al-rich system) is more stable than the (Al,Mn)GaAs2 state (Ga-rich system), which has a magnetic moment of 3.82mB/Mn. The interaction between Mn-3d and As-4p states at the Fermi level dominates the other states.The states at the Fermi level are mainlyAs-4p electrons, which mediate strong interaction between the Mn-3d and As-4p states. It is noticeable that the FM ordering of dopant Mn with high magnetic moment originates from the As(4p)-Mn(3d)-As(4p) hybridization, which is attributed to the partially unfilled As-4pbands. The high FM moment of Mn is due to the double-exchange mechanism mediated by valence-band holes.

• 반도체디스플레이기술학회지
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• 제20권4호
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• pp.125-129
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• 2021

We investigated the electronic property and atomic structure for chalcopyrite (CH) Al_xGa_1-xAs semiconductor by using first-principles FPLMTO method. The CH-Al_xGa_1-xAs exhibits a p-type semiconductor with a direct band-gap. For low Al concentration unoccupied hole-carriers are induced, but for high Al concentration it is formed a localized bonding or anti-bonding state below Fermi level. The hybridization of Al(3s)-Ga(4s, or 4p) is larger than that of Al(3s)-As(4s, or 4p). And the Al film on As-terminated surface, Al/AsGa(001), is more energetically favorable one than that on Ga-terminated (001) surface. Consequently, the band-gap of CH-Al_xGa_1-xAs system increases exponentially with increasing Al concentration. The change of lattice parameter is shown two different configurations with increasing Al concentration. The calculated lattice parameters for CH-Al_xGa_1-xAs system are compared to the experimental ones of zinc-blend GaAs and AlAs.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.895-901
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• 2023

Oxide-dispersion- strengthened nickel alloys with Hf additions are expected to present high temperature mechanical properties and durable helium resistance based on first-principles density functional theory (DFT) calculations. Energetic and charge density evaluations of the helium behaviors were performed in Ni matrix, Y₂Hf₂O₇ oxide and the oxide/matrix interface. With the presence of coherent Y₂Hf₂O₇ in Ni matrix, chances of helium bubbles in Ni can be greatly diminished. The helium atoms shall occupy the interfacial site initially, then diffuse into in the octahedral sites of Y₂Hf₂O₇, and these oxide-captured He atoms prefer to separate individually. Much higher diffusion barrier of He in Y₂Hf₂O₇ than in nickel is related to the strong hybridization between interstitial He-1s and nearest-neighboring O-2p orbitals.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.27-28
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• 2021

The search for new corrosion inhibitors for different corrosive mediums is a never-ending task. In the present work, the corrosion inhibition behavior and adsorption mechanism of two novel synthetic thiazolidinedione derivatives noted MTZD and ATZD in 3.5 wt.% NaCl solution on copper were investigated. Electrochemical, scanning electron microscope (SEM), atomic force microscopy (AFM) techniques were used along with first-principles DFT calculations. At maximum inhibitor concentration i.e., 300 ppm corrosion inhibition efficiency reached maximum up to 90% and 96% for MTZD and ATZD, respectively, and thereby followed the order of ATZD > MTZD. The inhibition efficiency increased up to 24 h of immersion, and then decreased after 48h immersion. The potentiodynamic curves suggested that the inhibition action of tested compounds is a mixed type of inhibitor. The first-principles DFT calculations suggested that compounds under investigation formed covalent bonds with Cu(111) surface via reactive sites. SEM and AFM results confirmed the formation of protective barrier that prevent corrosion attack.

• 수산해양교육연구
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• 제23권1호
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• pp.75-91
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• 2011

The purposes of this study were to compare and analyze the local primary textbooks for the subject of 'We are the First Graders'. This study analyzed the common points and the differences among three textbooks developed by the three educational bureaus of Seoul, Daegu and Busan. The criterion of analysis were scope, sequence and integration of curriculum representing the principles for developing curriculum. The results were as follows: First, the scopes of topics included in 2007 National Curriculum of 'We are the First Graders' were faithfully reflected in the three local textbooks. Second, the sequences of textbooks were generally arranged according to the order of curriculum content except for some contents. As for 'Wise School Life', some contents were presented at the first unit of the three textbooks and the others were gradually expanded at the latter of the textbooks. Third, the integration of curriculum appeared meaningfully in the three textbooks. Based on these results, this study suggested some recommendations on the activites for the adaptation at the early stage in the primary school under 2009 National Curriculum.

• 한국실내디자인학회논문집
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• 제23권6호
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• pp.150-159
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• 2014

Recently, violent crimes against the socially disadvantaged have become more frequent and became serious social issues. In addition, compared to the past, the crime methods have become more diverse and intricate, which results in larger damages. For those reasons, the public are increasingly concerned about crimes and it is detrimental to the quality of life in general. Currently, safety in alleys and other residential spaces is protected only by mechanical and managerial functions such as CCTV and police patrol. Safe environment from crimes can be achieved only if there are environmental and spatial plans such as CPTED (Crime Prevention through Environmental Design) principles. The purpose of this study is to propose a direction for spatial planning that can prevent crimes through environmental elements, by researching the spatial planning and current status of alleys and residential spaces from the viewpoint of CPTED. To do so, first, a review checklist was created based on five principles of CPTED and field surveys were conducted on the northern districts of Busan with high crime rates. Second, the problems were analyzed through the field surveys and checklist was classified based on five principles of CPTED to propose improvements for each item. Also, a computer graphic simulation was used to suggest a design proposal. We expect that the application of the basic environmental design principles and guidelines for CPTED will have the effect of creating crime-free and safe spaces in alleys and residential environment.

• 무역상무연구
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• 제17권
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• pp.71-91
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• 2002

The purpose of this paper is to examine the viewpoints of the different legal systems for the validity of LD Clause and the possibility of gap-filling function of UNIDROIT Principles in International Sales Contract. The results of comparative study between common law system and civil law system, and between CISG and UNCDROIT Principles is as follows: First, common law system distinguishes LD Clause and Penalty Clause, but civil law system including Korean law does not strictly distinguish the difference between them, provided that the liquidated damages are not grossly excessive. Second, CISG does not concerned with the validity of LD Clause but entrust this matter to the law applicable by virtue of the rules of private international law; conversely the Principles follow similar position of civil law system. The possibility of gap-filling of the Principles is more positive in the case of arbitration than in the case of litigation. On the basis of above study, I also checked the LD Clauses of ICC Model International Sales and the Model Contracts of Korean Commercial Arbitration Board. The LD Clauses of there two Model Contract seem very appropriate and reasonable for the reference in practical application. The appropriate, not excessive, LD Clause will contribute not only to eliminate the burden of proof for the actual damages, but also to enforce both parties to perform their obligations in their contracts. Therefore, When we make contract, we should keep in our mind to insert the reasonable and appropriate LD Clause in the sales contract. If not, so to speak, litigated damages are grossly excessive, the Clause may be invalid in some legal system.