• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2310-2314
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• 2007

Stable molecular conformations were calculated for the p-tert-butylcalix[4]arene crown ether bridged at the lower rim with pyridyl unit (1) in the various conformers and their potassium-ion complexes. The structures of three distinct conformations have been optimized using DFT B3LYP/6-31G(d,p) method. Relative stability of free host 1 is in following order: cone (most stable) > partial-cone > 1,3-alternate conformer. For two different kinds of complexation mode, the potassium cation in the crown-ether moiety (cr) has much better complexation efficiency than in the benzene-rings (bz) pocket for all three kinds of conformation of host molecule 1. The relative stability of complex (1+K+) in the cr-binding mode is in following order: partial-cone (most stable) ~ cone > 1,3-alternate conformer.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1893-1897
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• 2008

We have performed DFT calculations to investigate the conformational characteristics and hydrogen bonds of the p-tert-butylcalix[5]arene (1) and p-tert-butylcalix[4]arene (2). The structures of different conformers of 1 were optimized by using B3LYP/6-31+G(d,p) method. The relative stability of the various conformers of 1 is in the following order: cone (most stable) > 1,2-alternate > partial-cone > 1,3-alternate. The relative stability of four conformers of 2 is in the following order: cone (most stable) > partial-cone > 1,2-alternate > 1,3-alternate. The primary factor affecting the relative stabilities of the various conformers of the 1 and 2 are the number and strength of the intramolecular hydrogen bonds. The hydrogen-bond distances are discussed based on different calculation methods.

• Bulletin of the Korean Chemical Society
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• v.29 no.3
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• pp.541-545
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• 2008

Stable molecular isomers were calculated for the azobenzene crown ether p-tert-butylcalix[4]arene (1) in the host and their alkali-metal-ion complexes. The structures of two distinct isomers (cis and trans) have been optimized using DFT B3LYP/6-31G(d,p) method. Trans isomer of 1 is found to be 11.69 kcal/mol more stable than cis analogue. For two different kinds of complexation mode, the alkali-metal-cation in the crown-ether moiety (exo) has much better complexation efficiency than in the benzene-rings (endo) pocket for both isomers of 1. Sodium ion has much better complexation efficiency than potassium ion in all kinds of complexation mode with host 1. The Na+ complexation efficiency of the trans-complex (1) in the exo-binding mode is 8.24 kcal/mol better than cis-exo analogue.

• 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 ([$NH_3(CH_2)_nNH_3$] $Cl_2$).

• Proceedings of the IEEK Conference
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• 2002.06d
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• pp.171-174
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• 2002

This paper presents an implementation method of phasor measurement device, which is based on the FPGA implementation of the sliding-DFT The design is verified by the timing simulation of its operation. The error effect of coefficient approximation and frequency deviation in the recursive implementation of the sliding-DFT is analytically derived and verified with the computer simulations.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2001.05a
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• pp.237-240
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• 2001

In this work, we will present an iris pattern recognition method as a biometrically based technology for personal identification and authentication. For this, we propose a new algorithm for extraction unique feature from images of the iris of the human eye and representing these feature using the discrete fourier transform. From the computational simplicity of the adopted transform, we can obtain more fast and efficient results than previous ones.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3514-3520
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• 2014

Molecular structures of the various conformers of para-bromocalix[4]aryl derivatives 1-4 were optimized using the DFT B3LYP calculation method. The total electronic and Gibbs free energies and normal vibrational frequencies of the different structures (CONE, partial cone (PACO), 1,2-Alternate(1,2-A) and 1,3-Alternate(1,3-A)) were calculated from the four kinds of para-bromocalix[4]aryl derivatives. The B3LYP/6-31G(d,p) calculations suggested the following: 1(PACO) is the most stable among four conformers of 1; 2(CONE) is the most stable among five conformers of 2; 3(PACO) is the most stable among four conformers of 3; 4(1,3-A) is the most stable among four conformers of 4. All the most stable structures optimized by the B3LYP calculation method were in accordance with the experimental crystal structures of 1-4. The calculated IR spectra of the various conformers (CONE, PACO, 1,2-A and 1,3-A) of 1-4 were compared.

• The Journal of the Korea institute of electronic communication sciences
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• v.3 no.4
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• pp.260-265
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• 2008

The arc-fault occurring in the customer system becomes the direct cause of electric fire. However, it is very difficult to identify the arc-fault using the existing fault detection mechanism because the magnitude of the fault current is very small. Accordingly, this paper analyzes the causes of arc fault and designs the basic detection mechanism of arc fault. And then, it proposes an signal processing-based arc-fault determination methodology which can enhance the of accuracy of the arc-fault determination by applying DFT/DWT to the voltage and current waveform. Finally, this paper showed the application methodology of the proposed signal processing based fault determination method by applying and analyzing DFT/DWT to an high voltage in-rush current waveform.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.9
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• pp.1485-1490
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• 2008

This paper proposes a new Fourier transform-based phasor estimation method to eliminate the adverse influence of the exponentially decaying dc offsets when Discrete Fourier Transform (DFT) is used to calculate the phasor of the fundamental frequency component in a relaying signal. By subtracting the result of odd-sample-set DFT from the result of even-sample-set DFT, the information of dc offsets can be obtained. Two dc offsets in a relaying signal are treated as one dc offset which is piecewise approximated in one cycle data window. The effect of the dc offsets can be eliminated by the approximated dc offset. The performance of the proposed algorithm is evaluated by using computer-simulated signals and EMTP-generated signals. The algorithm is also tested on a hardware board with TMS320C32 microprocessor. The evaluation results indicate that the proposed algorithm has the stable and accurate eliminating performance even if the input signal contains two decaying dc components having different time constants.

• Bulletin of the Korean Chemical Society
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• v.29 no.7
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• pp.1374-1378
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• 2008

Using DFT B3LYP/6-31+G(d,p)//B3LYP/6-31G(d,p) calculation method, stable molecular structures were optimized for the p-tert-butylcalix[4]arene functionalized at lower rim by cage-annulated crown ether (1) in two different conformers and their potassium-ion complexes. Cone conformer of free host 1 was slightly more stable than partial-cone conformer. For two different kinds of complexation mode, the potassium ion in benzene-rings (bz) pocket showed comparable complexation efficiency with the cation in cage-annulated crown-ether (cr) for the cone and partial-cone conformers of 1. The complex (1${\bullet}K^+$) in the cr-binding mode for the partial-cone conformer was more stable than the cone conformer for B3LYP/6-31G(d,p) geometry optimization. However, $1_{(cone)}{\bullet}K^+$(cr) showed lower single-point energy than the $1_{(pc)}{\bullet}K^+$(cr) for B3LYP/6- 31+G(d,p) calculation method.