• 한국전기전자재료학회논문지
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• 제23권2호
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• pp.137-142
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• 2010

A plane wave expansion method (PWEM) was applied for photonic band structure calculation. We examined zero group velocity modes in photonic crystal. The zero group velocity modes were obtained at the second band along F-K direction. We expanded higher order Brillouin zone (BZ) to find the locations of zero group velocity modes and to investicate their properties. We found twelve locations, inside the first Brillouin zone, where the group velocities became zero. Also, we calculated band structure and group velocity in off-plane configuration.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.52-54
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• 2009

A plane wave expansion method(PWEM) was applied for photonic band structure calculation. We examined zero group velocity modes in photonic crystals. The zero group velocity was obtained in second band along G-K direction. We expanded Brillouin zone, and investigated on zero group velocity.

• Journal of Magnetics
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• 제11권1호
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• pp.20-24
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• 2006

Very recently, it was presented that the one dimensional (1D) CuO atomic chains can maintain large magnetic moments. In this work, we analyzed m-resolved density of states (DOS) to understand the peculiar spin polarization occurred in Cu atoms. It was found that the $\mid{m}\mid=1$ states play an essential role in the spin polarization of Cu atoms. In addition, we calculated magnetic anisotropy energy (MAE) and observed that the distribution of MAE is strongly sensitive to the interatomic distance between Cu and O atoms. Besides, it was revealed that the contribution to MAE comes for the second half of Brillouin zone (BZ).

• Nuclear Engineering and Technology
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• 제38권5호
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• pp.433-436
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• 2006

The implementation of multiplexing techniques combined with advances in neutron optics make the neutron three-axis spectrometers (TAS) an efficient tool to map inelastic response from single crystals over momentum transfer ranges comparable to the size of a single Brillouin zone. Thanks to recent progress in polarization techniques such experiments can be combined relatively easily with neutron polarization analysis, which does not only provide unambiguous separation of response corresponding to structural and magnetic degrees of freedom, but permits a quantitative analysis of the magnetic response anisotropy, often of crucial importance to test theoretical predictions. In the forthcoming decade we therefore expect a further development of the complementary use, rather than competition, of the reactor-based TAS's with time-of-flight (TOF) instruments for single crystal spectroscopy at the existing (ISIS) as well as at the newly built (SNS, J-PARK) pulsed sources.

• 전자공학회논문지A
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• 제33A권11호
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• pp.112-119
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• 1996

Impact ionization model in GaAs has been presented by modified keldysh formula with two sets of power exponent of 7.8 and 5.6 in study. Impact ionization rate is derived from fermil's golden rule and ful lenergy band stucture based on empirical pseudopotential method. Impact ionization rates show anisotropic property in low energy region (<3eV), but isotropic in high energy region (3>eV). Full band monte calo simulator is coded for investigating the validity of the GaAs impact ionization model, and validity is checked by comparing impact ionization coefficients with experimental values and ones in anisotropic model. Valley transitions to energy alteration are explained by investigating electron motion in brillouin zone for full band model to electric field variation.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.341-344
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• 2001

제일원리 슈도퍼텐셜 계산을 통해 강유전성 격자 불안정성의 미시적 기원과 페로브스카이트 PbTiO$_3$의 전자구조를 연구했다. 의사 얀-텔러 효과를 이용해서 격자 불안정성을 논의한다. 얀-텔러 효과의 원인은 O 원자의 p 궤도함수와 Ti 원자의 d 궤도함수의 혼성결합이다. 얀-텔러 효과는 브릴루앙 영역의 중심에서 가장 중요해진다는 것을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제73권1호
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• pp.37-52
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• 2020

This paper investigates the free and forced longitudinal vibration of a double nanorod system using doublet mechanics theory. The doublet mechanics theory is a multiscale theory spanning between lattice dynamics and continuum mechanics. Equations of motion and boundary conditions for the double nanorod system are obtained using Hamilton's principle. Clamped-clamped and clamped-free boundary conditions are considered. Frequencies and dynamic displacements are determined to demonstrate the effects of length scale parameter of considered material and geometry of the nanorods. It is shown that frequencies obtained by the doublet mechanics theory are bounded from above (van Hove singularity) and unlike classical elasticity theory doublet mechanics theory predicts finite number of modes depending on the length of the nanotube. The present doublet mechanics results have been compared to molecular dynamics, experimental and nonlocal theory results and good agreement is observed between the present and other mentioned results. The difference between wave frequencies of graphite is less than 10% between doublet mechanics and experimental results near to the end of the first Brillouin zone.

• Journal of the Optical Society of Korea
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• 제7권1호
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• pp.38-41
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• 2003

We present an analysis of highly-dispersive guided modes of two-dimensional photonic crystal waveguides. By the plane ave expansion method, band structures and mode profiles of two-dimensional photonic crystal waveguides are obtained. It is found that guided modes have very small group velocities and very large group velocity dispersions in the region near the f-point and in the region near the Brillouin zone edge. Especially, the group velocity dispersions are found to be millions of times larger than that of a conventional optical fiber. The contributions of the transverse resonance formed by two photonic band gap reflectors and the standing wave mode formed by periodic structures are discussed. We conclude that the highly-dispersive characteristics originate from the resonator-like aspect of the photonic crystal waveguide.

• Bulletin of the Korean Chemical Society
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• 제16권2호
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• pp.164-168
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• 1995

The band structure of nickel monoxide having a cation defect rock salt structure is calculated by means of the tight-binding extended Huckel method. The calculation is also made for the net charge, the DOS, the COOP, the electron density of the constituent atoms, and the O 1s binding energy shift when one of the adjacent nickel atoms is defected. It is found that the band gap near the Γ direction on the Brillouin zone is about 0.2 eV, and that all of the properties calculated including the electronic structure of the oxygen atom are more effectively affected by the surface defect than the inside one. The core O 1s binding energy shift is calculated by the use of valence potential method and the results are very satisfactory in comparison with the XPS experimental findings.

• 한국정보통신학회논문지
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• 제3권4호
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• pp.915-922
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• 1999

본 논문에서는 GaAs 풀밴드 E-k관계를 이용하여 전계방향에 따라 임팩트이온화가 전자전송에 미치는 영향을 분석하였다. E-k관계를 구하기 위하여 페르미황금법칙과 local form factor를 이용하는 의사포텐셜방법을 사용하였으며 임팩트이온화율을 구하기 위하여 브릴로우인영역을 사면체로 분할하여 각 사면체마다 적분하는 사면체방법을 이용하였다. 임팩트이온화의 이방성분석을 위하여 Monte Carlo시뮬레이션을 수행하였다. 특히 임팩트이온화의 과도상태분석을 수행한 결과, 이방성은 과도상태에서만 발생하는 것으로 나타났으며 정상상태에서는 등방성 특성을 보이는 것으로 나타났다. 본 연구에서 제시한 GaAs 임팩트이온화의 이방성특성은 GaAs 소자의 과도응답특성분석에 사용될 수 있으리라 사료된다.