• Journal of the Korean Chemical Society
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• v.50 no.4
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• pp.281-290
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• 2006

The electronic structure and properties of the 1H-indene and mono-sila-1H-indene series have been investigated using basis set of 6-31G(d, p) and hybrid density functional theory. Basic measures of aromatic character derived from structure, molecular orbitals, a variety of magnetic criteria (magnetic isotropic and anisotropic susceptibilities) are considered. Energetic criteria suggest that In(Si7) enjoy conspicuous stabilization. However, by magnetic susceptibility isotropic this system are among the least aromatic of the family: Within their isomer series, In(Si4) is the most aromatic using this criteria. Natural bond orbital (NBO) analysis method was performed for the investigation of the relative stability and the nature of the 8-9 bonds in 1H-indene and mono-sila-1H-indene compounds. The results explained that how the p character of natural atomic hybrid orbital on X8 and X9 (central bond) is increased by the substitution of the C8 and C9 by Si. Actually, the results suggested that in these compounds, the X8-X9 bond lengths are closely controlled by the p character of these hybrid orbitals and also by the nature of C-Si bonds. The magnitude of the molecular stabilization energy associated to delocalization from X8-X9 and to * X8-X9 bond orbital were also quantitatively determined. Molecular orbital (MO) analysis further reveal that all structure has three delocalized MOs and two delocalized MOs and therefore exhibit the aromaticity.

• Bulletin of the Korean Chemical Society
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• v.5 no.1
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• pp.37-41
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• 1984

The pseudolattice calculations in the CNDO/2 level of approximation are carried out for polymeric beryllium hydride, polyethylene and polymeric boron hydride. Since there is no evidence on the geometry for polymeric boron hydride, the two possible geometries are assumed. One is a polyethylene-type geometry and the other is a polymeric beryllium hydride-type geometry. In order to compare their relative stability, we calculate polyethylene and polymeric beryllium hydride and then compare with polymeric boron hydride having the assumed structures. The total energy calculation indicates that a polymeric beryllium bydride-type geometry is more stable than a polyethylene-type geometry. Our results obtained for polyethylene are in good agreement with those given by CNDO/2 crystal orbital. From the convergence problem with respect to the number of unit cells (M), the calculation with value of 4 for M can be considered to give the convergence limit results.

• Bulletin of the Korean Chemical Society
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• v.17 no.12
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• pp.1149-1153
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• 1996

Ab initio and extended Huckel calculations were carried out on the isomers of trans-RhCl(η2-C2H2)(PH3)2 (1). Due to π-back donation in 1 complex, the rotational energy barrier of alkyne ligand is computed to be in the range of 18.6-25.2 kcal/mol at MP4 levels. The optimized hydrido-alkynyl complex (2) at ab initio level has the distorted trigonal bipyramidal structure. Vinylidene complex (3) is computed to be more stable than 1 complex by 17.1 kcal/mol at MP4//MP2 level. The stabilities of isomers show similar trend at the various level calculations, that is, EHT, MP4//HF, and MP4//MP2 levels. The optimized geometries at ab initio level are in reasonable agreement with experimental data. A detailed account of the bonding in each isomers (1-3) have been carried out in terms of orbital analyses.

• 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.

• Journal of Aerospace System Engineering
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• v.14 no.1
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• pp.36-43
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• 2020

The start of satellite thermal design was to predict the worst operating environment through analysis of the thermal environment of the operation orbit. Because the satellites have different types of operating trajectories for their mission, the exposed thermal environment also varies. Thus, it is necessary to analyze in consideration of the orbital conditions, and a design was performed to guarantee thermal stability for the worst case defined through the analysis. The orbital thermal environmental analysis required an understanding of the basic orbit mechanics and the heat exchange relationship between the space environment and satellite. The purpose of this paper was to provide an understanding of the orbital thermal environment analysis by providing basic data on the space thermal environment in the earth-orbit and describing thermal relations that calculate the amount of space heat inflow into satellites. Additionally, an example of a virtual satellite shows the overall process of analyzing the orbital thermal environment during a mission lifetime.

• Korean journal of applied entomology
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• v.24 no.4 s.65
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• pp.231-238
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• 1986

Molecular orbital theoretical study on the stability of conformations and chemical reactivity of 0,0-diethylphenylphosphate derivatives were carried out by EHT and CNDO/2 molecular orbital calculation method. The results shown that the dipole moment(${\mu}$) and total energies of the ${\theta}=90^{\circ}$ conformer were ${\mu}=3.185D\;&\;E_t=-162.6479(au)$ and also that of the ${\theta}=0^{\circ}$ conformer were ${\mu}=5.596D\;&\;E_t=-162.4013(au)$, respectively. Therefore, the values of ${\mu}\;&\;E_t$ of the ${\theta}=90^{\circ}$ conformer were much smaller than that of the ${\theta}=0^{\circ}$ conformer. The form with angle of rotation ${\theta}=90^{\circ}$ of phenyl ring was shown to be most stable and this was interpreted in terms of electrostatic and steric effect. 0,0-diethylphenylphosphate derivatives are predicted to increase both charge and orbital controlled $SN_2$ reactivity of the electron withdrawing substituent reduces the HOMO & LUMO energy, while the electron withdrawing substituent due to increase in positive charge of phosphorus atom of phosphate molecule.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.67.5-67
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• 2001

A closed loop system with a linear plant and nonlinearity in the feedback connection is analyzed for its quasi-static orbital stability by a state-space approach. First a periodic orbit is assumed to exist in the loop which is determined by describing function method for the given nonlinearity. This is possible by selecting a proper nonlinearity and a rigorous justification of the describing function method.[1-3, 18, 20]. Then by introducing residual operator, a linear perturbed model can be formulated. Using various transformations like a modified eigenstructure decomposition, periodic-averaging, charge of variables and coordinate transformation, the stability of the periodic orbit, as a solution of harmonic balance, can be shown by investigating a simple scalar function and result of linear algebra. This is ...

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1911-1916
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• 2004

The conformational preference of tetrahomodioxacalix[4]arenes with three different para substituents on the phenolic ring has been investigated by using ab initio molecular orbital theory (RHF/6-31$G^{\ast}$) and density functional theory (B3LYP/6-31$G^{\ast}$). The stability order is predicted to be cone > C-1,2-alternate > partial cone > 1,3-alternate > COC-1,2-alternate. The distorted cone conformation is found to be most stable in a gas phase and the calculated results are in agreement with the reported $^1$H NMR and X-ray experimental observations. The substitution of methylene with dimethyleneoxa bridges increases the size of the annulus of the molecule, its conformational mobility, and the number of hydrogen bonding patterns. The thermodynamic stability and the conformational characteristics of tetrahomodioxacalix[4]arenes are discussed in regards of the number of phenolic hydrogen bonding patterns and the polarity of a molecule. The substituent effects on the para position of the phenolic ring are also introduced.

• Journal of Electrical Engineering and Technology
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• v.6 no.5
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• pp.697-705
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• 2011

In this paper, a closed-loop system constructed with a linear plant and nonlinearity in the feedback connection is considered to argue against its planar orbital stability. Through a state space approach, a main result that presents a sufficient stability criterion of the limit cycle predicted by solving the harmonic balance equation is given. Preliminarily, the harmonic balance of the nonlinear feedback loop is assumed to have a solution that determines the characteristics of the limit cycle. Using a state-space approach, the nonlinear loop equation is reformulated into a linear perturbed model through the introduction of a residual operator. By considering a series of transformations, such as a modified eigenstructure decomposition, periodic averaging, change of variables, and coordinate transformation, the stability of the limit cycle can be simply tested via a scalar function and matrix. Finally, the stability criterion is addressed by constructing a composite Lyapunov function of the transformed system.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.269-277
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• 2013

In this study, we present results of precise orbital geodetic parameter estimation using satellite laser ranging (SLR) observations for the International Laser Ranging Service (ILRS) associate analysis center (AAC). Using normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 in SLR consolidated laser ranging data format, the NASA/GSFC GEODYN II and SOLVE software programs were utilized for precise orbit determination (POD) and finding solutions of a terrestrial reference frame (TRF) and Earth orientation parameters (EOPs). For POD, a weekly-based orbit determination strategy was employed to process SLR observations taken from 20 weeks in 2013. For solutions of TRF and EOPs, loosely constrained scheme was used to integrate POD results of four geodetic SLR satellites. The coordinates of 11 ILRS core sites were determined and daily polar motion and polar motion rates were estimated. The root mean square (RMS) value of post-fit residuals was used for orbit quality assessment, and both the stability of TRF and the precision of EOPs by external comparison were analyzed for verification of our solutions. Results of post-fit residuals show that the RMS of the orbits of LAGEOS-1 and LAGEOS-2 are 1.20 and 1.12 cm, and those of ETALON-1 and ETALON-2 are 1.02 and 1.11 cm, respectively. The stability analysis of TRF shows that the mean value of 3D stability of the coordinates of 11 ILRS core sites is 7.0 mm. An external comparison, with respect to International Earth rotation and Reference systems Service (IERS) 08 C04 results, shows that standard deviations of polar motion $X_P$ and $Y_P$ are 0.754 milliarcseconds (mas) and 0.576 mas, respectively. Our results of precise orbital and geodetic parameter estimation are reasonable and help advance research at ILRS AAC.