• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.106-110
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• 1997

The binding energies of the ground state of both the heavy-hole and light-hole excitons in a GaAs(In\ulcornerGa\ulcornerAs) quantum well sandwiched between two semi-infinite Al\ulcornerGa\ulcornerAs(InP) layers are calculated as a function of well width in the presence of an arbitray magnetic field. A variational approach is followed using very simple trial wave function. The applied magnetic field is assumed to be parallel to the axis of growth and the binding energies are calculated for a finite value of the height of the potential barrier. The exciton binding energies for a given value of the magnetic field are found to be increased than their values in a zero magnetic field due to the compression of their wave functions within the well with the applied magnetic field.

• BMB Reports
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• v.33 no.1
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• pp.37-42
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• 2000

Based on the study by Leatham and Stabmann concerned with the rates (v) of amines and phenolic compounds oxidation catalyzed by laccase of basidiomycete Lentinus edodes (Berk.) Sing., as well as on the results of semiempirical quantum chemical computations using the PM3 method, the linear correlations of v and lnv values with first vertical ionization potentials of the substrates molecules and radicals derived from them, spin densities on N and O atoms of the above radicals, and with the radicals reorganization energies have been found.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.229-240
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• 2002

Quantum mechanical calculation is performed for the $O(^1D)$ + HCl ${\rightarrow}$OH + Cl reaction using Reactive Infinite Order Sudden Approximation. Shifting approximation is also employed for the l ${\neq}$ 0 partial wave contributions. Various dynamical quantities are calculated and compared with available experimental results and quasiclassical trajectory results. Vibrational distributions agree well with experimental results i.e. product states mostly populated at $v_f$ = 3, 4. Our results also show small peak at $v_f$ = 0, which indicates bimodal vibrational distribution. The results show two significant broad peaks in ${\gamma}_i$ dependence of the cross section, one is at ${\gamma}_i$ = $15^{\circ}-35^{\circ}$ and the another is at ${\gamma}_i$= $55^{\circ}-75^{\circ}$ which can be explained as steric effects. At smaller gi, the distribution is peaked only at higher state ($v_f$ = 3, 4) while at the larger gi, both lower state ($v_f$ = 0) and higher state ($v_f$ = 3, 4) are significantly populated. Such two competing contributions (smaller and larger ${\gamma}_i$) result in the bimodal distribution. From these points we suggest two mechanisms underlying in current reaction system: one is that reaction occurs in a direct way, while the another is that reaction occurs in a indirect way.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1218-1230
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• 2019

A sub-channel solver, named ${\underline{S}}teady$ and ${\underline{T}}ransient$ ${\underline{A}}nalyzer$ for ${\underline{R}}eactor$ ${\underline{T}}hermal$ hydraulics (START), has been developed using the homogenous model for two-phase conditions of light water reactors. The code is developed as a fast and accurate TH-solver for coupled and multi-physics calculations. START has been validated against the NUPEC PWR Sub-channel and Bundle Test (PSBT) database. Tests like single-channel quality and void-fraction for steady state, outlet fluid temperature for steady state, rod-bundle quality and void-fraction for both steady state and transient conditions have been analyzed and compared with experimental values. Results reveal a good accuracy of solution for both steady state and transient scenarios. Axially different values for turbulent mixing coefficient are used based on different grid-spacer types. This provides better results as compared to using a single value of turbulent mixing coefficient. Code-to-code evaluation of PSBT results by the START code compares well with other industrial codes. The START code has been parallelized with the OpenMP algorithm and its numerical performance is evaluated with a large whole PWR core. Scaling study of START shows a good parallel performance.

• Korean Journal of Optics and Photonics
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• v.3 no.3
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• pp.183-190
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• 1992

Luminescence properties of asymmetric double quantum well structure composed of $Al_x/Ga_{1-x}$ /As AIAs/GaAs have been studied by steady state and time-resolved photoluminescence and phtoluminescence excitation spectroscopy at low temperature. Two quantum well samples with different barrier thickness (15$\AA$ and 150$\AA$) were prepared to investigate the dependence of tunneling characteristics on barrier thickness. The abscence of excitonic recombination peak from $Al_x/Ga_{1-x}$As well for the 15$\AA$ barrier sample indicates a very fast electron tunneling to GaAs well. Meanwhile, T-X transition between well and barrier is supposed to be a major route for the fast decay of luminescence from $Al_x/Ga_{1-x}$As well in the 150$\AA$ barrier sample. Time-resolved photduminescence from GaAs well of 15$\AA$ sample shows the exsitence of the rise with 100 ps which is attributed to the hole tunneling.

• Bulletin of the Korean Chemical Society
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• v.16 no.5
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• pp.449-453
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• 1995

An exact quantum mechanical theory is employed to treat predissociation process of the $A^2{\Sigma}^+$ state of OH. The widths and positions of the lower (v= 2 and v= 3) rovibrational levels are calculated. Energy shifts of the resonances from the zeroth order (pure Hund'scase (b)) positions are shown to be small for N $\leq$ 10, indicating that the $A^2{\Sigma}^+$ state can be described as case (b) very well for low N. Due to the differential interactions of the $A^2{\Sigma}^+_{1/2}$ and $A^2{\Sigma}^+_{-1/2}$ states with $X^2II$and $2^2II$ states, small splittings between the $F_1$ and $F_2$ levels are predicted. Calculated lifetimes of the resonances agree with experimental results reasonably well.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.973-980
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• 1998

The fluorescence spectroscopic properties of both trans and cis forms of 9-anthryiethylene derivatives such as 9-AnthCH=$CHCO_2CH_3$ [Ⅰ] and 9-AnthCH=CHCN [Ⅱ] as well as 9-AnthCH=>TEX>$CHCH_2O_2CCH_3$ [Ⅲ] and 9-AnthCH=$CHCH_2OH$ [Ⅳ] have been measured in various solvents. In nonpolar solvent, the trans-I and trans-Ⅱ show dual emission spectral bands at 340 nm and 460 nm when exciting with 270 nm while the other trans derivatives show single emission band at 430 or 460 nm. The dual emissions exhibit different excitation spectra, indicating that two emissive states are different from each other. It is interesting to note that the 340 nm emission of both trans-Ⅰ and trans-Ⅱ is enhanced at the expense of the drastic quenching of the 460 nm emission as the solvent polarity increases. The dual emissions are also observed for both cis-Ⅰ and cis-Ⅱ. The solvent dependence of the fluorescence decay times and quantum yields can be correlated with the solvent and excitation wavelength dependences of the trans→cis photoisomerization quantum yields. These results indicate that the 340 nm emission is originated from the $S_2$ state of the cis-form, and the $S_1$ state is the only singlet excited state presenting a large CT (charge transfer) character to facilitate the photoisomerization.

• Bulletin of the Korean Chemical Society
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• v.20 no.11
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• pp.1281-1287
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• 1999

The low-lying electronic states of diazirine and 3,3'-dimethyldiazirine have been studied by high level ab initio quantum chemical methods. The equilibrium geometries of the ground state and the first excited singlet and triplet states have been optimized using the Hartree-Fock (HF) and complete active space SCF (CASSCF) methods, as well as using the Møller-Plesset second order perturbation (MP2) theory and the single configuration interaction (CIS) theory. It was found that the first excited singlet state is of 1 B1 symmetry resulting from the n- π* transition, while the first excited triplet state is of 3 B2 symmetry resulting from the π- π* transition. The harmonic vibrational frequencies have been calculated at the optimized geometry of each electronic state, and the scaled frequencies have been compared with the experimental frequencies available. The adiabatic and vertical transition energies from the ground electronic state to the low-lying electronic states have been estimated by means of multireference methods based on the CASSCF wavefunctions, i.e., the multiconfigurational quasidegenerate second order perturbation (MCQDPT2) theory and the CASSCF second-order configuration interaction (CASSCF-SOCI) theory. The vertical transition energies have also been calculated by the CIS method for comparison. The computed transition energies, particularly by MCQDPT2, agree well with the experimental observations, and the electronic structures of the molecules have been discussed, particularly in light of the controversy over the existence of the so-called second electronic state.

• Bulletin of the Korean Chemical Society
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• v.16 no.5
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• pp.436-438
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• 1995

Based on the collisional time-correlation function approach a general analytical expression has been derived for the double differential cross-section with respect to the scattering angle and the final rotational energy, which can be applied to molecules with non-zero electronic orbital angular momentum after collision with fast hydrogen atoms. By integrating this expression another very simple expression, which gives the final rotational distribution as a function of the rotational quantum number, has also been derived. When this expression is applied to NO(2Π1/2, v'=1) and NO(2Π3/2, v'=1, 2, 3), it can reproduce the experimental rotational distribution after collision with fast H atom very well. The average rotational quantum number and average rotational energy using this expression are also in good agreement with those deduced from the experimental distributions.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.22-22
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• 2002

It is well known that nanoscale magnetic materials can exhibit significantly different magnetic properties than the corresponding bulk materials. In present work, we summarized the preparation, microstructure, Mossbauer study and magnetic properties of nanocomposites. It was found that both grain size and the amount of magnetically soft phase ${\alpha}$-Fe play a very important role in determining the magnetic properties. (omitted)