• Interaction and multiscale mechanics
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• v.1 no.4
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• pp.467-476
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• 2008

In this work, a nano-size rocksalt crystal (magnesium oxide) is considered as a continuous collection of unit cells, while each unit cell consists of discrete atoms; and modeled by a multiscale concurrent atomic/continuum field theory. The response of the crystal to an electromagnetic (EM) wave is studied. Finite element analysis is performed by solving the governing equations of the multiscale theory. Due to the applied EM field, the inhomogeneous motions of discrete atoms in the polarizable crystal give rise to the change of microstructure and the polarization wave. The relation between the natural frequency of this system and the driving frequency of the applied EM field is found and discussed.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.976-981
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• 1997

The magnetic susceptibilities of molybdenum ions with 4d1 electronic configuration in the octahedral crystal field were calculated on the basis of ligand field theory. The experimental magnetic susceptibilities for molybdenum ions, which are stabilized at the octahedral site in the perovskite lattice of Ba2ScMoⅤO6 and Sr2YMoⅤO6, were compared with the theoretical ones. We have tried to fit their temperature dependence of magnetic susceptibility with ligand field parameters, spin-orbit coupling constant ζSO, and orbital reduction parameter κ according to intermediate field coupling and strong field theory. Strong field coupling theory could not explain experimental curves without unrealistically large axial ligand field, since it ignores the mixing up between different state via spin-orbit interaction and ligand field. On the other hand, the intermediate field coupling theory could successfully reproduce experimental data in octahedral and trigonal ligand field. The fitting result demonstrates not only the fact that spin-orbit interaction is primarily responsible for the variation of magnetic behavior but also the fact that effective orbital overlap, enhanced by cubic crystal structure, reduces significantly orbital angular momentum as indicated by κ parameter.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.1-14
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• 2009

This paper proposes an interaction field concept based on the field theory of plasticity. Relative deformation between two arbitrary scales, e.g., macro and micro fields, is defined which can be implemented in the crystal plasticity-based constitutive framework. Differential geometrical quantities responsible for describing dislocations and defects in the interaction field are obtained, based on which dislocation density and incompatibility tensors are further derived. It is shown that the explicit interaction exists in the curvature or incompatibility tensor field, whereas no interaction in the torsion or dislocation density tensor field. General expressions of the interaction fields over multiple scales with more than three scale levels are derived and implemented into the present constitutive equation.

• Journal of the Korean Chemical Society
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• v.20 no.3
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• pp.198-205
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• 1976

The integral Hellmann-Feynman Theorem of Parr is generalized to give a full significance to the off-diagonal form, and certain aspects of it are discussed. By use of the generalized form of the theorem, effects of configuration interaction to the crystal field theory are examined, taking perturbation energies of all order collectively into account. Thus, it is shown that there do not exist, especially when the field is strong, the radial integral which is common to all states characterized by ${\Gamma}$, S and m, and could be parametrized. If, however, one restricts the perturbing excited states only to those angularly undistorted and radially equally distorted, there results simple scaling of the crystal field parameter 10 Dq and Condon-Slater parameter $F^n$ defined within the framework of the classical crystal field theory.

• Journal of the Korean Chemical Society
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• v.17 no.5
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• pp.332-336
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• 1973

Integral Hellmann-Feynman Theorem is extended to degenerate case. The characteristics of the extended formula are studied and an approximation is suggested. The possibility of higher order perturbation energy correction to the conventional crystal field theory is discussed.

• Bulletin of the Korean Chemical Society
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• v.18 no.8
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• pp.861-864
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• 1997

Luminescence spectrum of Na3[Eu(ODA)3]·7H2O (ODA≡oxydiacetato) was measured at various temperatures. The characteristic band splitting within 5D0→7FJ (J = 1, 2, 3 and 4) were phenomenologically simulated by using crystal field theory. The set of crystal field parameters reproduces the emission lines in a satisfactory manner with a rms deviation of 21.4 cm-1. It leads the reliable assignment of the luminescence bands and the energy level scheme of 7FJ (J = 1, 2, 3 and 4) multiplets.

• Journal of the Korean Magnetics Society
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• v.18 no.4
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• pp.159-162
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• 2008

The phenomenon of magnetostriction occurs in magnetic systems when the temperature is changed or the external magnetic field is applied. It is known that the magnetostriction observed in rare-earth elements and compounds is well described by the crystal-field striction and the exchange striction. In this review paper, we discuss the standard theory for the magnetostriction which includes the crystal-field and the exchange interaction.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.181-186
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• 2005

We demonstrate that the finite rate of dielectric relaxation in liquid crystals which has been ignored previously causes profound effects in the fast dielectric reorientation of the director. The phenomenon is relevant for submillisecond switching of the director when the switching rate approaches the rate of dielectric relaxation through the reorientation of the molecular dipoles. A submillisecond switching ($15-400\;{\mu}s$ for an optical retardation shift $0.3-2.2\;{\mu}m$ in $10-15\;{\mu}m$ thick cells) is demonstrated for dual frequency nematic cells with high pretilt that maximizes the dielectric torque acting on the director. We propose the theory of dielectric response in which the electric displacement depends not only on the present (as in the standard theory) but also on the past values of electric field and director. We design an experiment in which the standard "instantaneous" model and our model predict effects of opposite signs; the experimental data support the latter model.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.15-30
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• 2009

The theoretical framework of the interaction fields for multiple scales based on field theory is applied to one-dimensional problem mimicking dislocation substructure sensitive intra-granular inhomogeneity evolution under fatigue of Cu-added steels. Three distinct scale levels corresponding respectively to the orders of (A)dislocation substructures, (B)grain size and (C)grain aggregates are set-up based on FE-RKPM (reproducing kernel particle method) based interpolated strain distribution to obtain the incompatibility term in the interaction field. Comparisons between analytical conditions with and without the interaction, and that among different cell size in the scale A are simulated. The effect of interaction field on the B-scale field evolution is extensively examined. Finer and larger fluctuation is demonstrated to be obtained by taking account of the field interactions. Finer cell size exhibits larger field fluctuation whereas the coarse cell size yields negligible interaction effects.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.1
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• pp.17-20
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• 2004

We derive specific heat gap at the critical temperature as an exact anylitical function of applied magnetic field by using the thermodynamics. And we calculate numerical value of specific heat gap for some superconductors with the derived results and discuss the physical meaning. And it will be discussed that gap of specific heat discontinuity under certain magnetic field intensity become zero at the critical temperature.