• Journal of the Korean Chemical Society
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• v.40 no.8
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• pp.579-584
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• 1996

The HOMO-LUMO gap, and static and dynamic third-order polarizabilities for the polyenes are evaluated by means of the time-dependent Hartree Fock(TDHF) semiempirical PM3, AM1, MNDO, and MINDO/3 calculations. All calculations have performed on the series $C_2H_4$ to $C_{32}H_{34}$. The HOMO-LUMO gap increases in the order: MINDO/3> MNDO> PM3> AM1 levels. THG, DC-EFISHG, IDRI, and OKE for the various calculations show the order: AM1 > MNDO > PM3 levels. The various third-order effects for the polyenes have the following order: THG> DC-EFISHG> IDRI> OKE.

• Journal of the Korean Chemical Society
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• v.41 no.9
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• pp.449-459
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• 1997

The bonded state polarizabilities of ions in the alkali halides are estimated by using the Seitz and Ruffa (SR) energy level analysis relation. The effective number of electrons $(N_{eff})$ in the Slater-Kirkwood formula are used for all members of an isoelectronic sequence. The effective dispersion coefficients $(C_6^{eff})$ are calculated by the use of the empirical formula (J. Chem. Phys. 1991, 95, 1852) estimating $(N_{eff})$ values to reproduce the experimental $(C_6^{eff})$ for atom-atom (or molecule) interactions. In the framework of the T-Rittner model the model potential is constructed and used to calculate the values of dissociation energy and dipole moment. The results obtained in the present study are in good agreement with the experiment one.

• Journal of Astronomy and Space Sciences
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• v.16 no.1
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• pp.41-52
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• 1999

Near-earth space is composed of plasmas which embed a number of plasma waves. Space plasmas consist of electrons and multi-ion that determine local wave propagation characteristics. In multi-ion plasmas, it is difficult to find out analytic solutions from the dispersion relation in general. In this work, we have developed a model with an arbitrary magnetic field and density as well as multi-ion plasmas. This model allows us to investigate how plasma waves behave when they propagate along realistic magnetic field lines, which are assumed by IGRF(International Geomagnetic Reference Field). The results are found to be useful for the analysis of the in situ observational data in space. For instance, if waves are assumed to propagate into the polar region, from the equatorial region, our model quantitatively show how polarization is altered along earth travel path.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.210-214
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• 2007

Recent years have seen a rapid development of spintronics. One of the major achievements of this field is the understanding of spin dependent process in various physical systems, for example, metallic multilayers showing the giant magnetoresistance (GMR). Today devices based on the GMR are revolutionizing electronic data storage. In this paper, we review recent developments in the research on GMR of low dimensional structures. We describe the magnetoresistance properties of magnetic multilayers, multilayered nanowires and nonopillars, etc.

• Journal of the Korean Chemical Society
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• v.30 no.2
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• pp.172-180
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• 1986

The Hammett's substituent constants were analyzed for the substituted-benzoic acid, -benzene and -naphthalene by LCAO MO method. Hammett's ${\sigma}$-values have been theoretically proved to treat as the sum of independent contribution of inductive effect and resonance effect. That is, Is (static inductive effect) and Id (dynamic inductive effect) corresponding to inductive effect are chosen as net charge and approximate self atom polarizability indices respectively, and ${\Delta}E^{HOMO}$ which is the difference in HOMO energy level between substituted molecule and unsubstituted molecule as resonance effect. In conclusion, it has been found that the observed ${\sigma}$-values depend on the sum of Id, Is and ${\Delta}E^{HOMO}$.

• Polymer(Korea)
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• v.28 no.6
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• pp.545-550
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• 2004

The refractive index of thin copolymer film was controlled by photo-degradation of chromophores in the copolymer. FTIR and UV/Vis spectroscopy were employed to elucidate the effect of chemical structure on refractive index changes after photobleaching. The decrease of refractive index of the film by photobleaching can be ascribed to the decrease of polarizability of polymer molecules through breakage of C =C bond in the chromophore. Due to the selective photoreaction of the chromophores which align along the film plane, refractive index of the copolymer film measured in TE mode decreases faster than that in TM mode. Polarized ATR-FTIR spectroscopy was used to verify such a difference in refractive index of the film.

• The Journal of Natural Sciences
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• v.8 no.1
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• pp.23-26
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• 1995

Operating characteristics of a $Cr^3+$:LiASF laser pumped by 640 nm and pulsed DCM dye laser are observed. The laser consists of a 93% reflectivity of half mirror and a total reflector, and the length between two mirrors is 3cm. Maximum efficiency is 10% for 22 mJ of pumping energy and the maximum slope efficiency is 19%.

• Journal of the Korean Chemical Society
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• v.21 no.6
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• pp.434-439
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• 1977

The electronic structures of 4-pyridone and lutidone are studied by the SCF MO-CI PPP method and by the configuration analysis method. The spectral data are consistent with the values calculated by the method. The polarization of $S_1({\pi},{\pi}^*)$ state is along the long molecular axis in both compounds. The lowest $({\pi},{\pi}^*)$1 state shows significant charge transfer (16∼18%) from ${\pi}$ bonding orbital of C=O moiety to ${\pi}^*$ antibonding orbital of divinyl amine moiety. The lowest triplet state shows much larger charge transfer (24∼29 %) but in opposite direction compared to that of $S_1({\pi},{\pi}^*)$ state.

• Journal of the Korean Chemical Society
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• v.55 no.2
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• pp.268-278
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• 2011

Corrosion of aluminum in 0.1 M HCl solution in the absence and presence of ${\beta}$-blocker inhibitors (atenolol, propranolol, timolol and nadolol) was investigated using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increased with inhibitor concentration and decreased with rise of temperature. Potentiodynamic polarization curves revealed that they acted as cathodic inhibitors. Some thermodynamic parameters were calculated and discussed. All inhibitors were adsorbed on Al surface obeying Frumkin isotherm. All EIS tests exhibited one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. The inhibition efficiencies of all test methods were in good agreement.

• Journal of the Korean Chemical Society
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• v.28 no.5
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• pp.279-283
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• 1984

${\beta}$-Substituent effect on the reactivity of retro-ene decarboxylation of but-3-enoic acid was investigated theoretically. It was found that charge effect is important not only through ${\pi}$-electron transfer as has been claimed to rationalize experimental results but also through polarization as found for the $CH_3$ substituent. The reactivity was not determined by the charge effect alone but the HOMO-LUMO energy gap was also found to affect the reactivity. In general it was confirmed that the greater the ${\pi}$-electron donating power of the substituent, the greater is the reactivity.