• Bulletin of the Korean Chemical Society
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• v.27 no.11
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• pp.1737-1740
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• 2006

The optimized structures and complexation energies of bis(18-crown-6-ether) analogue (2) of Trgers base (1) with a series of primary alkylbisammonium ions have been calculated by DFT B3LYP/6-31G(d,p) method. The calculated complexation efficiency (-142.84 kcal/mol) of 2 for butane-1,4-diylbisammonium guest is better than twice of the value (-61.40 kcal/mol) for butylammonium ion. The multiple hydrogen-bond abilities for the complexes are described as the function of the length of the alkyl substituents of the bisammonium guests with normal-alkyl chain [$-(CH_2)_{n-}$, n = 4-8]. The longer bisammonium guest shows the stronger hydrogen-bonding characterizations (the distance and the quasi-linear angle of the N-H…O) to the host 2 than the shorter bisammonium ions. These calculated results agree with the experimental data of the complexation of 2 with bisammonium salts ([$NH_3(CH_2)_nNH_3$] $Cl_2$).

• Journal of Communications and Networks
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• v.8 no.3
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• pp.323-329
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• 2006

For orthogonal frequency division multiplexing (OFDM), the discrete Fourier transform (DFT)-based processing at the receiver has been perceived equivalent to the matched filter (MF)-based processing. In this paper, we revisit the equivalence and mathematically show that when the guard interval is insufficient, the well-known DFT-based processing inherently causes more intersymbol and interchannel interference (ISI/ICI) than the MF-based processing. Then, with the adverse increase of interference, analytical expressions for the link performance are derived in terms of bit error rate (BER). Numerical results from computer simulation and analysis are presented to justify our claims.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.217-221
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• 2017

Improvement studies of existing phosphors are needed for use in light emitting diodes (LEDs). Among the phosphors discovered recently, the SLA ($SrLiAl_3N_4:Eu^{2+}$) is a phosphor that has a narrow width. It is now known as a good red phosphor that meets the industry's needs for warm white (color temperature ranging from 2700 to 4000 K) and high CRI (> 80). However, SLA phosphors are obtained from difficult synthetic methods. All commercially available phosphors should be derived from the general solid state synthesis method. The phosphors produced by difficult synthetic methods will inevitably fall out of price competitiveness and will be scrapped. This study succeeded in synthesizing SLA ($SrLiAl_3N_4:Eu^{2+}$) phosphors by using a general solid phase synthesis method based on the reaction energy obtained from DFT calculations. As a result, we found an optimal solid state synthesis method for SLA phosphors.

• Journal of Electrical Engineering and Technology
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• v.7 no.6
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• pp.1014-1022
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• 2012

This paper proposes a modified recursive sliding DFT to measure the phase of a single-tone. The modification is to provide a self error-cancelling mechanism so that it can significantly reduce the numerical error, which is generally introduced and accumulated when a recursive algorithm is implemented in finite wordlength arithmetic. The phase measurement error is analytically derived to suggest optimized distributions of quantization bits. The analytic derivation and the robustness of the algorithm are also verified by computer simulations. It shows that the maximum phase error of less than $5{\times}10^{-2}$ radian is obtained even when the algorithm is coarsely implemented with 4-bit wordlength twiddle factors.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.153-165
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• 2013

카이랄 ${\alpha},{\beta}$-불포화 N-Acyloxazolidinone은 Diels-Alder 반응의 친다이엔체로서 dialkylaluminium chloride 촉매하에서 높은 반응성과 부분입체선택성을 가지는 것이 이미 실험적으로 알려져 왔다. 제안된 Diels-Alder 반응의 메커니즘을 토대로 진행한 DFT 계산에서 dimethylaluminium chloride(이하 DMAC)는 $TiCl_4$에 비해 높은 endo 선택성을 띄는 반면, $TiCl_4$는 부분입체선택성에서 우세했다. 특히 DMAC는 현저히 낮은 활성화 에너지를 나타내어 이론적으로 반응속도의 측면에서 상당한 이득이 있음을 예측할 수 있다. 또한 chiral auxiliary로서 phenyl과 isopropyl은 구조적인 차이로 인해 선택성에서 역시 차이를 보였다. 계산화학적인 방법을 통한 입체선택적 Diels-Alder 반응의 분석은 알려진 메커니즘에 대한 명확한 증거를 제시할 뿐만 아니라 다른 유기합성 반응에 있어서 새로운 반응을 개발하는 데 이론적인 근거를 뒷받침 한다.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.4
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• pp.377-382
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• 2008

For stator winding protection of AC generator, KCL(Kirchhoff's Current Law) is widely applied. Actually a CRDR(Current Ratio Differential Relay) based on DFT(Discrete Fourier Transform) has been used for protecting generator. It has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. Wavelets techniques are proposed for the analysis of power system transients. This paper introduces an algorithm to choose a suitable Mother Wave1et for generator stator fault detection. For optimal selection, we analyzed db(Daubechies), sym(Symlets), and coif(Coiflects) of Mother Wavelet. And we compared with performance of the choice algorithm using detail coefficients energy and RMS(root mean square) error. It can be improved the reliability of the conventional DFT based CRDR. The feasibility and effectiveness of the proposed scheme is proved with simulation using collected data obtained from ATP (Alternative Transient Program) package.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.135-135
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• 2013

The electronic and adsorption structures of Mg and p-tert-butylcalix[4]arene (p-TBCA) adsorbed onto a Ge(100) surface under a variety of sample conditions were characterized using high-resolution photoemission spectroscopy (HRPES) and their corresponding DFT calculation results. Interestingly, after 0.10 ML p-TBCA molecules had been adsorbed onto a Ge(100) surface, subsequent adsorption of a small amount of metallic Mg (~0.10 ML) resulted in the formation of a capped structure inside the pre-adsorbed p-TBCA molecules. The adsorption structures resulting from further deposition of Mg (~0.50 ML) onto the Ge(100) surface were monitored based on the surface charge state and Mg 2s core level spectrum. Work function measurements clearly indicated the electronic structures of the Mg and p-TBCA adsorbed onto the Ge(100) surface. Moreover, we confirmed that three different adsorption structures are experimentally favorable at room temperature through DFT calculation results.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.280-287
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• 1998

In this paper, Dynamic Fault Tree algorithm(DFT algorithm) is presented. This new algorithm provides a concise representation of dynamic fault tolerance system structure with redundancy, dynamic redundancy management and complex fault ＆ error recovery techniques. And it allows the modeler to define a dynamic fault tree model with the relative advantages of both fault tree and Markov models that captures the system structure and dynamic behavior. This algorithm applies to TMR and Dual-Duplex systems with the dynamic behavior and show that this algorithm captured the dynamic behavior in these systems with fault ＆ error recovery technique, sequence-dependent failures and the use dynamic spare. The DFT algorithm for solving the problems of the systems is more effective than the Markov and Fault tree analysis model.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.7
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• pp.457-463
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• 2013

The removal of sulfonamide antibiotics (SAs) by activated carbon was investigated by using granular activated carbon (GAC) tests and density functional theory (DFT) simulations. The GAC absorption tests show the removal efficiency of 68.4~90.7% and 99.0~99.9% in 1 and 24 hours, respectively. In both GAC tests, the removal efficiency of sulfamethazine (SMZ) was the highest followed by those of sulfathiazole (STZ) and sulfamethoxazole (SMTZ): SMZ > STZ > SMTZ. In DFT adsorption simulations, we found that the 4-aminobenzenesulfonamide parts of SMZ and STZ and the 3-methyl-1,2-oxazol-5-amine part of SMTZ are preferentially adsorbed on the edges of graphene model, provided that the adsorbates keep their structures without dissociation upon adsorption process. The adsorption energies of SMZ, STZ, and SMTZ are -4.91, -4.64, and -4.62 eV, respectively. This adsorption strength (SMZ > STZ > STMZ) agrees with the trend of the removal efficiency of SAs by GAC. In addition, dissociative adsorption configurations of SAs are discussed.

• Journal of dental hygiene science
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• v.14 no.3
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• pp.371-378
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• 2014

This study aims to evaluate the influence of vitamin and mineral supplement intake, and degree of calcium and phosphorus intake on occurrence of dental caries in primary teeth. Research data was derived from the Fourth Korean National Health and Nutrition Examination Survey (KNHANES) and 1,139 Korean children of 3 to 6 years were selected as subject for this study. The dft index, nutrition factor including vitamin or mineral supplement intake and degree of intake for calcium (Ca) and phosphorus (P) were identified. Chi-square test was performed to assess the difference in socioeconomic status, oral health behavior and nutrition factor, including vitamin or mineral supplement intake and degree of intake for Ca and P. Linear regression analysis was performed to identify the relationship between the dft index and the related variables. As a result, the dft index was increased with the age. Significant differences in Ca intake was examined according to the sex, and P intake was different according to the sex in 3-year-old group. Among the 4-year-old children, the vitamin and mineral supplement takers had 1.206 less dft index than the non-takers. In conclusion, intake of Ca, P and vitamin/mineral supplement was not a pivotal factor to influence the incidence of primary teeth caries. However, significantly low dft index was observed from 4-year-old group who intake vitamin or mineral.