• 한국세라믹학회지
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• 제53권3호
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• pp.312-316
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• 2016

The energetics of defects in the presence of domain walls in $LiNbO_3$ are characterized using density-functional theory calculations. Domain walls show stronger interactions with antisite defects than with interstitial defects or vacancies. As a result, antisite defects act as a strong pinning center for the domain wall in $LiNbO_3$. Analysis of migration behavior of the antisite defects across the domain wall shows that the migration barrier of the antisite defects is significantly high, such that the migration of antisite defects across the domain wall is energetically not preferable. However, further study on excess electrons shows that the migration barrier of antisite defects can be lowered by changing the charge states of the antisite defects. So, excess electrons can enhance the migration of antisite defects and thus facilitate domain wall movement by weakening the pinning effect.

• 한국인구학
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• 제23권2호
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• pp.5-37
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• 2000

이 글에서 저자는 국제이주과정에 대한 경험적 연구에 준거해 볼 수 있는 이론적 지침으로서 행위체계론적 접근을 제안하고 있다. 이 제안은 다음과 같이 일련의 이론적 검토와 평가를 통해서 이루어졌다. 먼저 국제이주과정의 국면별 연구, 즉 이주의 발생 과 영속화 및 이추자의 적응과 정착 연구에 적용되어 온 주요 이론적 관점들을 검토하였다. 그리고 이 검토를 통해서 이주의 각 국면에 영향을 주는 요인들은 상호배타적이 아니기 때문에 관련된 모든 주요 요인들을 총체적으로 파악할 수 있는 이론적 접근이 요구된다는 것이 주장되었다 국제이주 연구에서 행위론적 접근을 주도하여 온 신고전 경제학적 접근은 그 기본 가정 , 즉 합리적 행위 가정의 한정성 때문에 맑스주의 정치경제학에 뿌리를 둔 구조론적 접근에 의해서 강한 도전을 받았다. 그 도전을 주도하여 온 노동시장분절론과 세계체계론적 접근 등은 이주의 큰 흐름을 결정하는 거시구조적 요인을 구명하는 데에는 상당한 성공을 거두었다. 그러나 이주행위의 상황적 요인, 특히 사회문화적 요인을 탐구하는 데에는 한계가 있음이 지적되었다. 이에 따라 이 논문의 저자는 국제이주과정을 총체적으로 파악하기 위해서는 이주현상을 행위체계론적 관점에서, 즉 이주자의 지향 대상이 되는 모든 상황, 즉 경제적, 정치적, 사회적 및 문화적 상황을 상호연관해서 총체적으로 분석하는 것이 필요하다는 것을 제안하게 되었다.

• Advances in concrete construction
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• 제1권3호
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• pp.239-252
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• 2013

Mortar microstructure is considered as a three-phase composite material, which is cement paste, fine aggregate and interfacial transition zone. Interfacial transition zone is the weakest link between the cement paste and fine aggregate, so it has a significant role to determine the properties of cementitious composites. In this study, specimens (w/c = 0.35, 0.45, 0.55) with various volume fractions of fine aggregate ($V_f$ = 0, 0.1, 0.2, 0.3 and 0.4) were cast and tested. To predict the equivalent migration coefficient ($M_e$) and migration coefficient of interfacial transition zone ($M_{itz}$), double-inclusion method and Mori-Tanaka theory were used to estimate. There are two stages to estimate and calculate the thickness of interfacial transition zone (h) and migration coefficient of interfacial transition zone ($M_{itz}$). The first stage, the data of experimental chloride ion migration coefficient ($M_s$) was used to calculate the equivalent migration coefficient of fine aggregate with interfacial transition zone ($M_e$) by Mori-Tanaka theory. The second stage, the thickness of interfacial transition zone (h) and migration coefficient of interfacial transition zone ($M_{itz}$) was calculated by Hori and Nemat-Nasser's double inclusion model. Between the theoretical and experimental data a comparison was conducted to investigate the behavior of interfacial transition zone in mortar and the effect of interfacial transition zone on the chloride migration coefficient, the results indicated that the numerical simulations is derived to the $M_{itz}/M_m$ ratio is 2.11~8.28. Additionally, thickness of interfacial transition zone is predicted from $10{\mu}m$, 60 to $80{\mu}m$, 70 to $100{\mu}m$ and 90 to $130{\mu}m$ for SM30, M35, M45 and M55, respectively.

• 농촌계획
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• 제22권1호
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• pp.49-56
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• 2016

Throughout the economic development era of Korea, migration occurred within a spatial hierarchy, with upward flows from rural areas to urban. The concept of step migration is a typical theory to explain these upward migration flows. Recent migration data and trends, however, indicate that migration-pattern regime shows strongly opposite-direction flows, with many of the major migration flowing downward on this national-spatial hierarchy, away from urban areas. In this study, we examine the most recent structure of migration flows up and down within the national-spatial hierarchy. We define seven tiers to tabulate origin-destination migration flows from population density of local administrative districts for the period 2001-2014, and then analyze the migration patterns between the tiers over time. The results show differentiated patterns of migration within the national-spatial hierarchy over time including specific states of migrants' life cycles.

• 한국세라믹학회지
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• 제52권5호
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• pp.331-337
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• 2015

$LaBO_3$ (B = Cr, Mn, Fe, Co, and Ni) perovskites, the most common perovskite-type mixed ionic-electronic conductors (MIECs), are promising candidates for intermediate-temperature solid oxide fuel cell (IT-SOFC) cathodes. The catalytic activity on MIEC-based cathodes is closely related to the bulk ionic conductivity. Doping B-site cations with other metals may be one way to enhance the ionic conductivity, which would also be sensitively influenced by the chemical composition of the dopants. Here, using density functional theory (DFT) calculations, we quantitatively assess the activation energies of bulk oxide ion diffusion in $LaBO_3$ perovskites with a wide range of combinations of B-site cations by calculating the oxygen vacancy formation and migration energies. Our results show that bulk oxide ion diffusion dominantly depends on oxygen vacancy formation energy rather than on the migration energy. As a result, we suggest that the late transition metal-based perovskites have relatively low oxygen vacancy formation energies, and thereby exhibit low activation energy barriers. Our results will provide useful insight into the design of new cathode materials with better performance.

• 한국정보시스템학회지:정보시스템연구
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• 제30권4호
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• pp.43-69
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• 2021

Purpose Although companies occupied the network market take the advantageous position first and can be successful in securing users over a certain size, it is important to satisfy the customers' demand and prevent the outflow of users toward a new alternative SNS. What is more, there are frequent changes in the flow of users toward new SNSs. Despite these dynamic market circumstances, there is a lack of research to explain the switching behaviors of SNS users. Design/methodology/approach The objective of this study is to explain and verify a specified migration theory(Push-Pull-Mooring model) focused on SNS fatigue in the psychological point of view, as well as reviewing previous studies on functional and technical characteristics of SNSs themselves. Moreover, this study tried to highlight factors affecting users actual SNS switch rather than their switching intention. Findings According to the statistical analysis, the most influenced pull factor to switch SNS was the alternative attractiveness. On the other hand, undesired relationship burden, service innovation and important mooring factors to prevent users' SNS switch. This study has a significant contribution to the theory, which analyzed users' actual SNS switch, and examined SNS users' psychological factors(SNS fatigue), reviewing the characteristics of existing services. To secure more users and to keep them, companies providing social network service need to develop differentiated strategies by analyzing psychological characteristics of various users.

• Smart Structures and Systems
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• 제3권4호
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• pp.439-454
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• 2007

In this paper a damage imaging technique using pre-stack migration is developed using Lamb (guided) wave propagation in composite structures for imaging multi damages by both numerical simulations and experimental studies. In particular, the paper focuses on the experimental study using a finite number of sensors for future practical applications. A composite laminate with a surface-mounted linear piezoelectric ceramic (PZT) disk array is illustrated as an example. Two types of damages, one straight-crack damage and two simulated circular-shaped delamination damage, have been studied. First, Mindlin plate theory is used to model Lamb waves propagating in laminates. The group velocities of flexural waves in the composite laminate are also derived from dispersion relations and validated by experiments. Then the pre-stack migration technique is performed by using a two-dimensional explicit finite difference algorithm to back-propagate the scattered energy to the damages and damages are imaged together with the excitation-time imaging conditions. Stacking these images together deduces the resulting image of damages. Both simulations and experimental results show that the pre-stack migration method is a promising method for damage identification in composite structures.

• 한국인구학
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• 제23권2호
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• pp.39-77
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• 2000

본 논문에서는 1860년대에서 1930년대까지 비농업직을 중심으로 하여 러시아 극동지역의 한인 이주민의 직업에 관하여 고찰한다. 먼저 이주민의 직업선택과 노동시장에서의 위치에 관한 이론들 즉 문화이론, 분절노동시종이론, 인적자본론 및 인종적 특수시장이론 등을 살펴보고 이들 이론이 러시아 극동지역 이주한인의 직업들 중 농업을 제외한 여러 가지 직종에 어떻게 적용되는지를 검토한다. 이러한 과정을 통해서 기존 이론들에서는 이주민의 직업에 관한 공급적 측면과 수요적 측면을 모두 분리하여 고찰하고 있다는 한계성을 지적한다. 이러한 한계성을 극복하기 위하여 본 논문에서는 러시아 극동지역 한인 이주민의 사례를 들어 이주민의 직업에 관한 두 가지 측면을 모두 통합해야 할 필요성을 설명하고 이를 위해 공급적·수요적 측면을 모두 고려할 수 있는 통합적 모델을 제시한 후 이러한 모델에 따라 러시아 극동지역 한인이주민의 직업에 영향을 키친 요인들을 광업, 어업, 자영업종, 서비스직종, 기타 단순 노무직 등으로 나누어 고찰한다. 마지막으로 이주의 통합적 모형에서 공급적 측면에 포함되는 것으로서는 한인의 농업중심적 성격, 이민직전의 조선에서의 사회경제적 모순 및 한인의 자급자족적 성격 등과 수요적 측면에서는 러시아의 이민정책과 러시아 극동의 다양한 지역적 상황이 고려되어야 함을 지적하였다.

• 대한수학회보
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• 제50권2호
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• pp.353-373
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• 2013

In this paper, a class of delayed predator-prey models of prey migration and predator switching is considered. By analyzing the associated characteristic transcendental equation, its linear stability is investigated and Hopf bifurcation is demonstrated. Some explicit formulae for determining the stability and the direction of the Hopf bifurcation periodic solutions bifurcating from Hopf bifurcations are obtained by using the normal form theory and center manifold theory. Some numerical simulations for justifying the theoretical analysis are also provided. Finally, biological explanations and main conclusions are given.

• 한국세라믹학회지
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• 제48권2호
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• pp.195-199
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• 2011

The effect of copper oxide on migration and interaction of protons in barium zirconate was investigated using density functional theory. One copper atom was substituted for a zirconium atom site, and a proton was added to a $3{\times}3{\times}3$ barium zirconate superstructure. An energy barrier of 0.89 eV for proton migration was the highest among several energy barriers. To investigate the interaction between multiple protons and a copper atom, two protons were added to the superstructure. Various proton positions were determined by the interaction between the two protons and the copper atom.