• The Mathematical Education
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• v.47 no.1
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• pp.1-10
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• 2008

Some of school mathematics contents that have deep mathematical meanings are regarded as obvious and their importance is frequently overlooked. We first reexamined the mathematical meaning of pi as a constant. Then we indicated the educational implications of Archimedes' calculation method of pi and finally underlined the availability of pi as a valuable research topic in school mathematics.

• Bulletin of the Korean Chemical Society
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• v.6 no.5
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.385-397
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• 2014

신약을 개발하거나 단백질 구조를 예측하는데 Molecular Mechanics (MM)의 방법을 사용한다. 하지만, MM 만으로는 자연현상에서 일어나는 결과를 정확하게 기술하기 어렵다. 본 연구는 기존의 MM 방법으로는 정확히 예측이 불가능한 비 공유결합 중 하나인 ${\pi}-{\pi}$ interaction을 양자역학 계산을 통해 정확한 예측이 가능한지 보았다. ${\pi}-{\pi}$ interaction 이란 생체 내, 의약 화합물에서 발견되는 결합이기 때문에, 단백질과 결합하는 구조의 예측이 중요하다고 할 수 있다. 본 실험은 ${\pi}-{\pi}$ interaction을 갖는 Sandwich, T shape, 그리고 Parallel displaced 세 가지 모형을 가지고 양자역학 계산을 수행하였다. 양자역학 계산은 DFT의 세가지 함수 M06_2X, M05_2X, B3LYP를 이용하였다. 실험결과에서 세 가지 함수가 각기 다른 결과를 보였는데, M06_2X의 결과에서 ${\pi}-{\pi}$ interaction을 더 정확하게 계산하였다. 이러한 결과를 바탕으로, 양자역학의 방법을 통해 MM에서는 예측이 불가능한 ${\pi}-{\pi}$ interaction을 계산 할 수 있고 이 부분을 고려하여 화합물 간의 결합구조를 예측을 향상시킬 수 있다.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.5
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• pp.193-193
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• 2003

This Paper analyses several model-order reduction methods and then proposes an improved n model and a new delay calculation method to be used in analyzing RC-class interconnects, which does not involve moment calculation processes. The proposed delay calculation method has been derived by combining the unproved $\pi$ model, the concept of effective capacitance and Elmore delay. This method has an advantage in that it can be applied in the calculation of end-to-end delay as well as incremental delay.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.5
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• pp.193-200
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• 2003

This Paper analyses several model-order reduction methods and then proposes an improved n model and a new delay calculation method to be used in analyzing RC-class interconnects, which does not involve moment calculation processes. The proposed delay calculation method has been derived by combining the unproved $\pi$ model, the concept of effective capacitance and Elmore delay. This method has an advantage in that it can be applied in the calculation of end-to-end delay as well as incremental delay.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.91-93
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• 2004

정확한 $\pi$값의 계산은 자연과학의 여러 분야에 도움을 준다 이와 같이 $\pi$값을 계산하는 여러 가지 방법이 제안되어 있으며 널리 사용되고 있으나, 본 논문에서는 MPI 라이브러리를 활용한 $\pi$값 계산의 병렬화 알고리즘을 소개한다. tan$^{-1}$($\chi$)의 정의를 이용하는 $\pi$값 계산 방법은 다항식의 계산과정에서 각 항(term)들의 종속성으로 인하여 병렬화 수행이 힘든 단점이 있다. 본 논문에서는 tan$^{-1}$($\chi$)를 맥클로린 수열(Maclaurin Series)을 통하여 다항함수로 표현하고, 병렬화 수행에 적합한 적분형태로 변형한다. 따라서. MPI 환경에서 수행하기 적합한 $\pi$값 계산의 병렬화 알고리즘을 제안하고 8노드 클러스터 환경에서 성능을 비교해본다. 또한, 직렬화된 방법에 대한 성능향상(speedup)을 측정한다.

• Journal of Power Electronics
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• v.15 no.1
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• pp.177-189
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• 2015

The output of the controller is said to exceed the input limits of the plant being controlled when a control system operates in a non-linear region. This process is called the windup phenomenon. The windup phenomenon is not preferable in the control system because it leads to performance degradation, such as overshoot and system instability. Many anti-windup strategies involve switching, where the integral component differently operates between the linear and the non-linear states. The range of state for the non-overshoot performance is better illustrated by the boundary integral error plane than the proportional-integral (PI) plane in windup inspection. This study proposes a PI controller with a separate closed-loop integral controller and reference value set with respect to the input command and external torque. The PI controller is compared with existing conventional proportional integral, conditional integration, tracking back calculation, and integral state prediction schemes by using ScicosLab simulations. The controller is also experimentally verified on a direct current motor under no-load and loading conditions. The proposed controller shows a promising potential with its ability to eliminate overshoot with short settling time using the decoupling mode in both conditions.

• Progress in Superconductivity
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• v.13 no.3
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• pp.146-150
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• 2012

We solve the momentum resolved d-wave Eliashberg equation employing the magnetic excitation spectrum from the inelastic neutron scattering on the LSCO superconductors reported by Vignolle et al. The magnetic excitation spectrum exhibits 2 peaks: a sharp incommensurate peak at 18 meV at momentum (${\pi}$, ${\pi}{\pm}{\delta}$) and (${\pi}{\pm}{\delta}$, ${\pi}$) and another broad peak near 40~70 meV at momentum (${\pi}$, ${\pi}$). Above 70 meV, the magnetic excitation spectrum has a long tail that is shaped into a circle centered at (${\pi}$, ${\pi}$) with ${\delta}$. The sign of the real part of the self-energy is determined by the momentum position of the peaks of the magnetic excitation spectrum and bare dispersion. We will discuss the effects of the each component of the magnetic excitation spectrum on the self-energy, the pairing self-energy.

• Journal of the Korean Chemical Society
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• v.29 no.1
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• pp.23-30
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• 1985

PMO expressions for ${\pi}^{\ast}$-${\pi}^{\ast}$ orbital interaction have been derived. Important differences between ${\pi}$-${\pi}$ and ${\pi}^{\ast}$-${\pi}^{\ast}$ interactions predicted by PMO expressions are : (ⅰ) energy splitting in ${\pi}^{\ast}$-${\pi}^{\ast}$ interaction will be greater than that in ${\pi}$-${\pi}$ interaction, (ⅱ) energy change due to interaction will be more destabilizing in ${\pi}^{\ast}$-${\pi}^{\ast}$ than in ${\pi}$-${\pi}$ interaction. These predictions were borne out in experimental data and in results of MO theoretical computations. It was pointed out that both STeO-3G and INDO-LCBO methods underestimate ${\pi}^{\ast}$-${\pi}^{\ast}$ orbital interaction and in order to estimate properly with MO theoretical calculation, use of split valence basis set is required.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.5
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• pp.109-119
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• 1993

To improve limitations of fuzzy PI controllers especially when applied to systems of order higher than one, we propose a fuzzy PI controller that takes out appropriate amounts of accumulated control input according to fuzzily described situations in addition to the calculation of incremental control input as in the case of conventional fuzzy PI controllers. The structure of the proposed controller was motivated by the characteristics of fuzzy PI controller that it generally gives inevitable overshoot when one tries to reduce rise time of the response especially when a system of order higher than one is under consideration. Since the undesirable characteristics of the fuzzy PI controller is caused by integrator of the controller, even though the integrator is introduced to overcome steady state error of response, we propose a controller that fuzzily clears out integrated quantities according to situation to give reduced rise time as well as small overshoots. To show the usefulness of the proposed controller, it is applied in simulations to such systems as are difficult to stabilize or difficult to get satisfactory responses by conventional fuzzy PI controllers.