• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2003년도 정기총회 및 학술발표회
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• pp.76-76
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• 2003

We report here the results on N-acetyl-N'-methylamide of 4-fluoroproline (Ac-Flp-NHMe) calculated using the ab initio molecular orbital method with the self-consistent reaction field (SCRF) theory at the HF level with the 6-31+G(d) basis set to investigate the stereoelectronic effects on the conformational preference of proline depending on the cis/trans peptide bonds and down/up puckerings along the backbone torsion angle $\square$ in the gas phase, chloroform, and water. In the gas phase, all potential energy surfaces for Ac-Flp-NHMe are quite similar to those of Ac-Pro-NHMe, except that up-puckered conformations are more stabilized than down-puckered ones. In chloroform and water, polyproline structures become dominant, whose populations are larger than those of Ac-Pro-NHMe. In chloroform and water, the populations of polyproline II (i.e., tF conformations) are quite similar to each other, but those of polyproline I (i.e., cF conformations) are larger by 5％ in water than in chloroform. In particular, all cis populations for Ac-Flp-NHMe in the gas phase, chloroform, and water are decreased than those of Ac-Pro-NHMe.

• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2069-2074
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• 2007

The 27Al multiple quantum magic angle spinning (MQMAS) nuclear magnetic resonance (NMR) spectra of mordenite zeolites were simulated using the point charge model (PCM). The spectra simulated by the PCM considering nearest neighbor atoms only (PCM-n) or including atoms up to the 3rd layer (PCM-m) were not different from those generated by the Hartree-Fock (HF) molecular orbital calculation method. In contrast to the HF and density functional theory methods, the PCM method is simple and convenient to use and does not require sophisticated and expensive computer programs along with specialists to run them. Thus, our results indicate that the spectral simulation of the 27Al MQMAS NMR spectra obtained with the PCM-n is useful, despite its simplicity, especially for porous samples like zeolites with large unit cells and a high volume density of pores. However, it should be pointed out that this conclusion might apply only for the atomic sites with small quadrupole coupling constants.

• Nuclear Engineering and Technology
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• 제9권1호
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• pp.39-44
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• 1977

N-methyl-C-phenylalkyl ketimine 이성질체, Ph-CR=N$CH_3$ (R=H, $CH_3$, $CH_3$CH$_2$)의 배치와 형태를 EHT 분자궤도함수법으로 연구하였다. 계산결과는 C=N 이중결함에 대하여 E-형의 배치가 Z-형의 배치보다 안전함을 나타내고 있다. N-methyl-C-phenylaldimine과 N-methyl-C-phenylmethylketimine에서는 phenyl 고러 회전자가 C=N 평면과 동일평면에 있는 형태가 안정하다. N-methyl-C-phenylethylketimine에서는 phenyl 고리와 C=N결합이 동일평면에 있고 회전자 $CH_3$CH$_2$-가 C=N 평면과 90$^{\circ}$인 gauche형이 가장 안정하다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.799-804
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• 2001

Nonlinear normal mode (NNM) vibration, in a nonlinear dual mass Hamiltonian system, which has 6th order homogeneous polynomial as a nonlinear term, is studied in this paper. The existence, bifurcation, and the orbital stability of periodic motions are to be studied in the phase space. In order to find the analytic expression of the invariant curves in the Poincare Map, which is a mapping of a phase trajectory onto 2 dimensional surface in 4 dimensional phase space, Whittaker's Adelphic Integral, instead of the direct integration of the equations of motion or the Birkhotf-Gustavson (B-G) canonical transformation, is derived for small value of energy. It is revealed that the integral of motion by Adelphic Integral is essentially consistent with the one obtained from the B-G transformation method. The resulting expression of the invariant curves can be used for analyzing the behavior of NNM vibration in the Poincare Map.

• Bulletin of the Korean Chemical Society
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• 제20권1호
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• pp.42-48
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• 1999

We have performed a quantum-chemical investigation on the conformations and electronic properties of a variety of methoxy-substituted poly(p-phenylenevinylenes) (PPVs) to elucidate the effects of alkoxy substitution. Geometrical parameters for the polymers were fully optimized through Austin Model I (AM I) semi-empirical Hartree-Fock (HF) band calculations. Electronic properties of the polymers were obtained by applying the AM I optimized structures to the modified extended Huckel method. To confirm validity of the AM I conformational results, we also carried out ab initio HF calculations with the 6-31G (d) basis set for a variety of methoxy-substituted divinylbenzenes. It is found that the potential energy surfaces of alkoxy-substituted PPVs are quite shallow around the planar conformations, suggesting that the prepared films possess a variety of conformations with different torsion angle in the solid state, depending on the synthetic conditions. When two alkoxy groups are concurrently substituted at the adjacent sites in the phenylene ring, these groups are subject to rotating around the C(sp2)-O bonds by 70-80° to avoid the strong steric repulsion between them. Consequently, the overlap between the π-type p orbital of oxygen and the π molecular orbitals of the polymer decreases. This leads to a wide gap and a high oxidation potential for tetramethoxy-substituted PPV, compared to those of dialkoxy-substituted PPV.

• 천문학회보
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• 제46권1호
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• pp.28.1-28.1
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• 2021

We present a statistical analysis of dark matter halos with interacting neighbors using a set of cosmological simulations. We classify the neighbors into two groups based on the total energy (E₁₂) of the target-neighbor system; flybying neighbors (E₁₂ ≥ 0) and merging ones (E₁₂ < 0). First, we find a different trend between the flyby and merger fractions in terms of the halo mass and large-scale density. The flyby fraction highly depends on the halo mass and environment, while the merger fraction show little dependence. Second, we measure the spin-orbit alignment, which is the angular alignment between the spin of a target halo (${\vec{S}}$ ) and the orbital angular momentum of its neighbor (${\vec{L}}$). In the spin-orbit angle distribution, the flybying neighbors show a weaker prograde alignment with their target halos than the merging neighbors do. With respect to the nearest filament, the flybying neighbor has a behavior different from that of the merging neighbor. Finally, we discuss the physical origin of two interaction types.

• 천문학회보
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• 제46권1호
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• pp.28.3-29
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• 2021

Galaxies are not just randomly distributed in space; instead, a variety of galaxy alignments have been found over a wide range of scales. Such alignments are the outcome of the combined effect of interacting neighbors and the surrounding large-scale structure. Here, we focus on the spin-orbit alignment (SOA) of galaxy pairs, the dynamical coherence between the spin of a target galaxy and the orbital angular momentum of its neighbor. Based on a recent cosmological hydrodynamic simulation, the IllustrisTNG project, we identify paired galaxies with mass ratios from 1/10 to 10 at z = 0 and statistically analyze their spin-orbit angle distribution. We find a clear preference for prograde orientations (i.e., SOA), which is more prominent for closer pairs. The SOA is stronger for less massive targets in lower-density regions. The SOA witnessed at z = 0 has been developed progressively since z = 2. There is a clear positive correlation between the alignment strength and the interaction duration with its current neighbor. Our results suggest the scenario in which the SOA is developed mainly by interactions with a neighbor for an extended period of time, rather than by the primordial torque exerted by the large-scale structure.

• 천문학회지
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• 제56권2호
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.151-161
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• 2012

An intensive analysis of 148 timings of V700 Cyg was performed, including our new timings and 59 timings calculated from the super wide angle search for planets (SWASP) observations, and the dynamical evidence of the W UMa W subtype binary was examined. It was found that the orbital period of the system has varied over approximately $66^y$ in two complicated cyclical components superposed on a weak upward parabolic path. The orbital period secularly increased at a rate of $+8.7({\pm}3.4){\times}10^{-9}$ day/year, which is one order of magnitude lower than those obtained by previous investigators. The small secular period increase is interpreted as a combination of both angular momentum loss (due to magnetic braking) and mass-transfer from the less massive component to the more massive component. One cyclical component had a $20.^y3$ period with an amplitude of $0.^d0037$, and the other had a $62.^y8$ period with an amplitude of $0.^d0258$. The components had an approximate 1:3 relation between their periods and a 1:7 ratio between their amplitudes. Two plausible mechanisms (i.e., the light-time effects [LTEs] caused by the presence of additional bodies and the Applegate model) were considered as possible explanations for the cyclical components. Based on the LTE interpretation, the minimum masses of 0.29 $M_{\odot}$ for the shorter period and 0.50 $M_{\odot}$ for the longer one were calculated. The total light contributions were within 5%, which was in agreement with the 3% third-light obtained from the light curve synthesis performed by Yang & Dai (2009). The Applegate model parameters show that the root mean square luminosity variations (relative to the luminosities of the eclipsing components) are 3 times smaller than the nominal value (${\Delta}L/L_{p,s}{\approx}0.1$), indicating that the variations are hardly detectable from the light curves. Presently, the LTE interpretation (due to the third and fourth stars) is preferred as the possible cause of the two cycling period changes. A possible evolutionary implication for the V700 Cyg system is discussed.

• 한국항공우주학회지
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• 제50권3호
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• pp.203-214
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• 2022

세계적으로 500 kg 급 이하의 소형위성에 대한 수요가 늘어남에 따라 전용 소형발사체에 대한 개발과 운용이 크게 증가하고 있다. 소형위성을 원하는 시간에 목표로 하는 궤도에 투입하는 발사체의 신속한 대응성이 주목받고 있으며, 신속한 위성군 구축 측면에서 공중발사 방식에 대한 관심이 증대되고 있다. 본 연구에서는 국내 소형위성군의 수요가 증가함에 따라 우리나라 및 주변 지리적 환경을 고려하여 공중발사체의 활용가능성에 대한 분석을 수행하였다. 대응성 측면에서 공중발사체와 지상 소형 및 대형발사체에 대해 임무 대응시간을 비교, 분석하고, 발사체의 궤도투입 성능 측면에서 공중발사체와 지상 소형발사체를 정량적으로 비교, 분석하였다. 분석결과, 공중발사체는 신속한 위성군 구축 관점에서 우리나라의 경우 실질적인 대응성은 제한되나 상대적으로 빠른 턴어라운드 시간과 낮은 경사각의 궤도 투입 시 효과적인 대안이 될 수 있다. 또한, 궤도투입 성능은 지상 소형발사체의 성능에 근접할 뿐만 아니라 요구 추진제 질량 측면에서 높은 효율성을 나타내어 국내 소형위성군의 궤도투입에 효과적인 발사수단으로 평가된다.