• 광물과 암석
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• 제34권2호
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• pp.121-131
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• 2021

마그네슘(magnesium; Mg)은 탄산염 광물이 침전된 과거의 환경 조건을 유추하기 위한 지화학 지시자로 활용되어오고 있다. Mg를 신뢰도 높은 지화학 지시자로 활용하기 위해서는 Mg의 화학종을 근거로 한 Mg의 광물 함유 기작이 반드시 규명되어야만 하며, 관련 실험 연구들은 주로 고해상도(high resolution)의 방사광가속기(synchrotron) X-선 흡수 분광(X-ray absorption spectroscopy; XAS) 기법을 통해 Mg의 화학종을 유추한다. 그러나, Mg가 미량 함유된 광물의 XAS 스펙트럼 해석의 높은 불확실성 때문에 화학종 유추가 어려운 경우가 많다. 양자역학 밀도범함수이론(density functional theory; DFT)은 결정구조에 대한 흡수 스펙트럼을 예측할 수 있기 때문에, XAS 스펙트럼 해석의 불확실성을 줄일 수 있다. 이번 논문에서는 DFT 기반의 제일원리 내각 준위 분광법(ab initio core-level spectroscopy method)을 통해 Mg 규산염 및 (수)산화광물에 대한 Mg K-edge 흡수 스펙트럼을 계산하여 Mg의 배위 결합 환경을 나타내는 구조 인자와의 상관관계를 분석하였다. 계산 결과, DFT 계산으로 얻은 Mg 규산염 및 (수)산화물의 이론 Mg K-edge 흡수 스펙트럼은 기존 XAS 실험으로 얻어진 스펙트럼의 주요 형태를 상당 부분 재현해낼 수 있었다. 계산으로 얻은 광물의 제일원리 Mg K-edge 흡수 스펙트럼의 흡수-끝(absorption edge)과 평균 Mg-O 결합거리 및 Mg 유효배위수를 비교 분석한 결과, 약한 양의 상관관계를 보여주었다. 이번 연구 결과는 DFT 계산이 다양한 광물 내 Mg의 화학종에 대한 표준 스펙트럼 세트를 제공할 수 있는 강력한 도구임을 보여주며, 추후 탄산염 광물에 함유된 정확한 Mg의 화학종을 동정하는데 DFT 계산이 큰 역할을 할 수 있음을 제시한다.

• 복식문화연구
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• 제17권5호
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• pp.819-833
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• 2009

The current research focused on exploration of a well known Korean fashion and clothing industry cluster, Dongdaemun Fashion Town(DFT). Many clothing and fashion wholesalers in DFT with various business formats are trying to obtain competitive advantages. For the empirical study, a questionnaire was developed. Items measuring descriptive statistics for each business and contractor selection criteria were included in the survey. 161 data from Employees of various wholesalers of DFT were used for statistical analysis. Majority of DFT customers were buyers of Internet shopping malls and street retail shops. 64% of them used domestic contractors for sourcing products. Most of them managed less than three contractors. Contractor selection criteria were factorized as flexibility, production ability, stability, fame and location. Wholesalers were segmented into three groups: product oriented, flexibility oriented and stability oriented groups. Group differences in terms of business practices were assessed and strategic implications were included.

• 정보교육학회논문지
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• 제15권3호
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• pp.517-524
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• 2011

어떠한 현상 혹은 사물의 이미지를 학생들에게 제공하는데 있어서 여러 가지 원인에 의해 초점이 흐리거나 혹은 흔들린 이미지들이 등장하여 학생들에게 보여주기가 힘든 경우가 빈번하게 발생한다. 특히, 이미지에 대한 구체적인 정보가 없는 경우에는 그 이미지는 쓸모가 없는 것이 된다. 본 연구는 무정보 블러링 이미지를 아주 빠른 시간 내에 복구할 수 있는 2차원 DFT 기반의 하나의 블러링 제거 알고리즘을 제안하는데 있다. 제안된 방법의 빠른 처리 속도는 이산 푸리에 변환, 변환의 필터링과 회선 관계 및 Moore-Penrose 역행렬의 효과적인 계산 방식을 바탕으로 한다. 특히, 필터의 주파수 응답에 관한 처리는 유용한 회선 공식을 유도한다. 제안된 방법의 구현은 보통 크기의 블러링 이미지에 적용했을 때, 아주 빠른 시간 내에 블러링 효과를 제거시킬 수 있고, 보다 선명한 이미지를 제공할 수 있음을 보인다.

• Bulletin of the Korean Chemical Society
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• 제32권2호
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• pp.673-680
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• 2011

The compound 3-(2-Mercaptopyridine)phthalonitrile has been synthesized and characterized by IR, UV-vis, and X-ray single-crystal determination. The molecular geometry from X-ray determination of the title compound in the ground state has been compared using the Hartree-Fock (HF) and density functional theory (DFT) with the 6-31G(d) basis set. The calculated results show that the DFT and HF can well reproduce the structure of the title compound. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6-31G(d) basis set by applying the Onsager and polarizable continuum model. Using the TD-DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and good agreement with the TD-DFT method and the experimental determination was found. The predicted nonlinear optical properties of the title compound are much greater than those of urea. Besides, molecular electrostatic potential of the title compound were investigated by theoretical calculations. The thermodynamic properties of the compound at different temperatures have been calculated and corresponding relations between the properties and temperature have also been obtained.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.193-193
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• 2013

Perfluorocarbons (PFCs) have been suggested as possible replacements for $SF_6$ and the fluorocarbons used in and emitted during technological plasma treatments because PFCs have significantly low greenhouse warming potentials. Of many PFCs, c-$C_4F_8$ and 2-$C_4F_8$ attract special attention because of their high CF2 radicallevels in commercial plasma treatments. Accordingly, several experimental and theoretical studies of these $C_4F_8$ species have been conducted, although only the geometries at their stationary states and their adiabatic electron affinities (EAs) have been determined. However, this information is not sufficient for a deep understanding of all the possible fates and roles of $C_4F_8$ species and their fragments in plasma phases. Although the performance and reliability ofeach DFT functional have been examined carefully by the development team of each functional form with respect to the training and test data sets of well-known molecular systems, no PFC was included in the data sets. So a careful additional assessment of the reliability of DFT functionals for the study of PFC systems is highly required. In order to find a DFT method appropriate to PFCs, the geometry, energy, and chemical reaction properties of $C_4F_8$ were calculated and compared with reference data.

• 대한화학회지
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• 제55권1호
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• pp.7-13
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• 2011

전자구조의 계산에서 교환과 상관 효과에 대한 기술을 개선하기 위해서는 교환-상관범함수에 대한 개념을 명확히 하는 것이 바람직하다. 이 목적을 성취하기 위해서는 많은 그룹의 물질에 대하여 다른 이론 방법을 적용할 필요가 있다. 본 연구에서는 탄소나노튜브의 고리와 바구니 내원자들의 밀도전하를 연구하기 위하여 혼성 밀도함수 이론(DFT) 계산을 수행하였다. 핵-핵 에너지, 전자-핵 에너지와 운동에너지에 대한 교환 및 상호작용을 관찰하였으며, B3P86, B3PW91, B1B96, BLYP와 B3LYP 수준에서 계산하였다.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1998-2004
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• 2012

We carried out DFT calculations for monohydrated sulfuric and phosphoric acids. We are interested in clusters which differ in orientation of hydrogen atoms only. Such molecular complexes are close in energy, since they lie in the vicinity of the global minimum energy structure on the flat potential energy surface. For monohydrated sulfuric acid we identified four different isomers. The monohydrated phosphoric acid forms five different conformers. These systems are difficult to study from the theoretical point of view, since binding energy differences in several cases are very small. For each structure, we calculated harmonic vibrational frequencies to be sure that if the optimized structures are at the local or global minima on the potential energy surface. The analysis of calculated -OH vibrational frequencies is useful in interpretation of infrared photodissociation spectroscopy experiments. We employed four different DFT functionals in our calculations. For each structure, we calculated binding energies, thermodynamic properties, and harmonic vibrational frequencies. Our analysis clearly shows that DFT approach is suitable for studying monohydrated inorganic acids with different hydrogen atom orientations. We carried out MP2 calculations with aug-cc-pVDZ basis set for both monohydrated acids. MP2 results serve as a benchmark for DFT calculations.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.67-76
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• 2009

The development of a variety of methods like AM1, PM3, PM5 and DFT now allows the calculation of atomic and molecular properties with high precision as well as the treatment of large molecules with predictive power. In this paper, these methods have been used to calculate a number of quantum chemical descriptors (like Klopman atomic softness in terms of $E_n^{\ddag}\;and\;E_m^{\ddag}$, chemical hardness, global softness, electronegativity, chemical potential, electrophilicity index, heat of formation, total energy etc.) for 75 alkanes to predict their boiling point values. The 3D modeling, geometry optimization and semiempirical & DFT calculations of all the alkanes have been made with the help of CAChe software. The calculated quantum chemical descriptors have been correlated with observed boiling point by using multiple linear regression (MLR) analysis. The predicted values of boiling point are very close to the observed values. The values of correlation coefficient ($r^2$) and cross validation coefficient ($r_{cv}^2$) also indicates the generated QSPR models are valuable and the comparison of all the methods indicate that the DFT method is most reliable while the addition of Klopman atomic softness $E_n^{\ddag}$ in DFT method improves the result and provides best correlation.

• 한국정보통신학회논문지
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• 제14권5호
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• pp.1078-1084
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• 2010

본 논문에서는 오차역전파알고리즘에 의한 신경회로망을 사용하여 이산푸리에변환에 의한 진폭성분과 위상 성분을 복원하는 음성강조 시스템을 제안한다. 먼저, 신경회로망이 잡음이 부가된 음성신호의 이산푸리에변환의 진폭성분과 위상성분을 사용하여 학습된 후, 제안한 시스템은 백색잡음에 의하여 열화된 잡음이 부가된 음성 신호를 강조한다. 백색잡음에 의하여 열화된 음성신호는 이산푸리에변환에 의한 진폭성분과 위상성분을 입력으로 하는 신경회로망을 사용하여 제안된 시스템에 의하여 강조되는 것을 실험결과로 증명한다. 제안한 시스템은 스펙트럼 왜곡율의 평가법을 사용하여 백색잡음에 의하여 열화된 음성신호에 대하여 효과적인 것을 실험으로 확인한다.

• Journal of Power Electronics
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• 제14권3호
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• pp.564-571
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• 2014

Rotor initial position is an important factor affecting the control performance of electrically excited synchronous motors. This study presents a novel method for estimating rotor initial position based on sliding discrete Fourier transform (sDFT). By injecting an ac excitation into the rotor winding, an induced voltage is generated in stator windings. Through this voltage, the stator flux can be obtained using a pure integral voltage model. Considering the influence from a dc bias and an integral initial value, we adopt the sDFT to extract the fundamental flux component. A quadrant identification model is designed to realize the accurate estimation of the rotor initial position. The sDFT and high-pass filter, DFT, are compared in detail, and the contrast between dc excitation and ac injection is determined. Simulation and experimental results verify that this type of novel method can eliminate the influence of dc bias and other adverse factors, as well as provide a basis for the control of motor drives.