• 전자공학회논문지
• /
• 제52권7호
• /
• pp.22-30
• /
• 2015

LTE (long-term evolution) MIMO 시스템에서는 제한된 피드백 환경 하에서 추정된 채널 정보를 활용하기 위한 코드북이 사용되고 있으며, 이와 관련된 연구도 활발히 진행되었다. 기존에 활용된 방식으로는 VQ (vector quantization) 기반 및 DFT(discrete fourier transform) 기반으로 생성된 코드벡터를 활용하는 코드북이 있으며, LTE 표준에서도 이를 변형한 방식을 최대 8개의 송신 안테나에 대해 적용할 수 있게 규정하고 있다. 그러나 안테나 개수가 추가적으로 증가하고, 공간 채널 모델이 LTE 시스템 전송 성능 평가에 기본적인 모델로 활용됨에 따라, 이에 따른 새로운 빔포밍 방안 및 코드북 설계가 필요하다. 본 논문에서는 LTE 전송 성능 평가에 활용되는 3차원 공간 채널 모델 (3D Spatial Channel Model; 3D-SCM)의 구현을 통해 생성된 채널의 핵심적인 통계적 특성을 분석하고, 이에 따른 코드북 설계의 방향성을 제시하고자 한다. 특히 DFT 기반 코드 북 활용 시, 기존의 균일위상 DFT 코드북을 개선한 비균일위상 DFT 코드북을 제안하고, 주어진 SCM 환경에서 성능을 평가한다. 코드벡터 설계에 필요한 인접한 안테나 원소 간의 위상차의 통계적 특성의 경우 SCM에서 뚜렷한 경향성이 존재하며, 이를 적절히 활용함으로써 기존 방식 대비 이득을 발생시킬 수 있다.

• 한국재료학회지
• /
• 제18권9호
• /
• pp.482-485
• /
• 2008

Tetragonal-$Ni_{1-x}Pd_x$Si/Si (001) structure was studied by using density functional theory (DFT). An epitaxial interface between $2{\times}2{\times}4$ (001) tetragonal-NiSi supercell and $1{\times}1{\times}2$ (001) Si supercell was first constructed by adjusting the lattice parameters of B2-NiSi structure to match those of the Si structure. We chose Ni atoms as a terminating layer of the B2-NiSi; the equilibrium gap between the tetragonal-NiSi and Si was calculated to be 1.1 ${\AA}$. The Ni atoms in the structure moved away from the original positions along the z-direction in a systematic way during the energy minimization. Two different Ni sites were identified at the interface and the bulk, respectively. The two Ni sites at the interface have 6 and 7 coordination numbers. The Ni sites with coordination number 6 at the interface were located farther away from the interface, and were more favorable for Pd substitution.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2010년도 제39회 하계학술대회 초록집
• /
• pp.78-78
• /
• 2010

The Adsorption structures of phenylalanine on Ge(100) surface have been investigated as a function of coverage using high-resolution photoemission spectroscopy (HRPES) and density functional (DFT) calculation. To converge these experimental and theoretical conclusion, we systematically performed HRCLPES measurements and DFT calculation for various coverage in the adsorption structures of phenylalanine molecules on the Ge(100) surface. In this study, we found two different adsorption structure as a function of coverage in phenylalanine on Ge(100), monitoring three core level spectra (Ge 3d, C 1s, N 1s, and O 1s) using HRPES Through analysis of the binding energies, we confirmed that O-H dissociated and N dative-bonded structure emerges at low coverage (0.10 ML), which is the same to the result of glycine and alanine on Ge(100) system, whereas O-H dissociation structure also appears at higher coverage. Moreover, we observed the shape of phenyl group being included in phenylalanine is changed from flat to tilting structure at final state using DFT calculation. Through the spectral analysis for phenylalanine, we will demonstrate variation of coverage dependent structural change for phenylalanine on Ge(100) surface using experimental (HRPES) and theoretical studies (DFT calculation).

• Bulletin of the Korean Chemical Society
• /
• 제34권11호
• /
• pp.3211-3217
• /
• 2013

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been employed to investigate the molecular structures and absorption spectra of three D-${\pi}$-A-type organic dyes (C1-1, D5 and TH208) containing identical ${\pi}$-spacers and electron acceptors, but different aromatic amine electron-donating groups (tetrahydroquinoline, triphenylamine and phenothiazine). The coplanar geometries indicate that the strong conjugation is formed in the dyes. The electronic structures suggest that the intramolecular charge transfer from the donor to the acceptor occurs, and the electron-donating ability of tetrahydroquinoline is stronger than those of triphenylamine and phenothiazine. The computed orbital energy levels of these dyes confirm that the electrons could be injected from the excited dyes to the semiconductor conduction band and the oxidized dyes could be reduced effectively by electrolyte. The TD-DFT results show that the CAM-B3LYP/6-31+G(d, p) is suitable for calculating the absorption spectra. The first absorption band for these dyes is assigned to the HOMO${\rightarrow}$LUMO and HOMO-1${\rightarrow}$LUMO transitions.

• 전기학회논문지P
• /
• 제57권2호
• /
• pp.91-95
• /
• 2008

The large AC generator fault may lead to large impacts or perturbations in power system. The generator protection control systems in Korea have been imported and operated through a turn-key from overseas entirely. Therefore a study of the generator protection field has in urgent need for a stable operation of the imported goods. In present, the algorithm using the current ratio differential relaying based DFT for stator winding protection or a fault detection had been applied that of internal fault protection of a generator. the DFT used for the analysis of transient state signal conventionally had defects losing a time information in the course of transforming a target signal to frequency domain. In this paper, the discrete wavelet transform (DWT) was applied a fault detection of the generator being superior to a transient state signal analysis and being easy to real time realization. The fault signals after executing a terminal fault modeling collect using a MATLAB package, and calculate the wavelet coefficients through the process of a muiti-level decomposition (MLD). The proposed algorithm for a fault detection using the Daubechies WT (wavelet transform) was executed with a C language and the commend line function for the real time realization after analyzing MATLAB's graphical interface. The advanced technique had improved faster a speed of fault discrimination than a conventional DFR based on DFT.

• 반도체디스플레이기술학회지
• /
• 제7권2호
• /
• pp.45-48
• /
• 2008

An epitaxial $\beta-FeSi_2$ structure on Si (001) substrate was calculated by using density functional theory (DFT). Unit cell of orthorhombic $\beta-FeSi_2$ and $\sqrt{2}\times\sqrt{2}\times2$ supercell were calculated to find the energetically favorable structures first. The $\chi$- and y-direction axes of $\beta-FeSi_2$ were changed into y- and z-direction axes to match its structure with that of Si, to minimize the lattice mismatch between $\beta-FeSi_2$ and Si. Distance between the Si (001) surface and the $\beta-FeSi_2$ surface was varied to find an optimum distance between them, resulting in 0.825 $\AA$.

• 대한소아치과학회지
• /
• 제26권1호
• /
• pp.25-31
• /
• 1999

The purpose of study was to test the hypothesis that preschool children who experienced nursing caries have high dft index and caries activity in primary dentition. One thousand and seventy-five preschool children from 4 to 6 years old were examined for their caries experience and salivary invertase activity by Resazurin Disc Test. Nursing caries group was identified by the criteria of having more decayed and filled teeth among the upper incisors than among the upper molars. The prevalence of nursing caries was 15.8%. The dft index of nursing caries group was significantly higher than that of the other groups except the rampant caries group(P<0.01). The Resazurin Disc Test score of nursing caries group was significantly higher than that of the other groups(P<0.01) and there was no difference between nursing caries group and rampant caries group. Therefore, it is recommended that children who experienced nursing caries should be incorporated in the caries prevention program through the primary and mixed dentition.

• 한국보건간호학회지
• /
• 제13권2호
• /
• pp.59-69
• /
• 1999

This study was conducted to investigate dental caries according to obesity in order to provide basic data for efficient dental health program for elementary school students. Data were obtained from a health record book of 668 elementary school students in Chun Cheon city in 1998. Obesity was categorized into overweight. normal and under weight groups by Rohrer index. Dental caries was classified into decayed. filled and missed teeth. The result were as follow: 1. Prevalence rate of dental caries(dft) was $78.7\%$ and mean dft was 2.96; decayed and filled teeth was 1.01 and 1.95. respectively. As for mean dft. a siginificant difference were shown according to obesity and age. while no siginificant difference was shown between boys and girls. 2. Prevalence rate of dental caries including missed teeth (dmft) rate was $83.9\%$ and mean dmft was 3.64. As for mean dmft. a siginificant difference were shown according to obesity and age. while no siginificant difference was shown between boys and girls.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2011년도 전력전자학술대회
• /
• pp.477-478
• /
• 2011

본 논문에서는 신재생 에너지를 전력 계통에 효율적으로 연계시키기 위한 요소 기술로 Filter 대신 DFT 기법을 사용한 고정밀 계측에 대해 제안한다. 일반적으로 Filter를 사용할 경우 원신호의 위상 지연, 크기 감소 같은 신호 왜곡으로 정확한 제어가 어려우나, 제안된 DFT 기법을 사용하면 기존 문제점을 해결 가능하다. 따라서 본 논문에서 제안된 DFT 기법은 PSIM을 이용한 시뮬레이션과 실험을 통해 제안된 알고리즘의 타당성과 우수성을 검증하였다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.647-647
• /
• 2013

We apply a density functional theory (DFT) and DFT-based non-equilibrium Green's function approach to study the structures, energetics and charge transport characteristics of nitrogen-doped graphene and graphene nanoribbons (GNRs) with additional doping of phosphorus or boron atoms. Considering graphitic, pyridinic, and porphrin-like N doping sites and increasing N-doping concentration, we analyze the structures of N-P and N-B doped graphene and particularly focus on how they affect the charge transport along the lateral direction. For the GNRs, we also consider the differences between defects formed at the edge and bulk regions. Implications of our findings in the context of electronic and energy device applications will be also discussed.