• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.234-236
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• 1994

We fabricated Au/PI/Pb and Au/PI/1-layer Arachidic acid/Pb structures in order to electron transport properties through the junctions. It was found that 9-layer PI LB films function as a good tunneling barrier from the I-V properties. And several peaks originating in the vibrational modes of the constituent molecules of 1-layer arachidicacid LB films were clearly observed in $d^2V/dI^2-V$ curves.

• Journal of Photoscience
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• v.9 no.3
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• pp.51-55
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• 2002

The 77 K emission and excitation spectra, and 298 K infrared and absorption spectra of [Cr(progly)(2,2-tri)]CIO$_4$[progly=prolylglycinate,2,2-tri=N-(2-aminoethyl)-1,2-ethanediamine] have been measured. The vibrational intervals of the electronic ground state are extracted from emission and infrared spectra. The twelve electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using the observed electronic transitions, a ligand field analysis was performed to determine the metaligand bonding properties for the coordinated atoms. It is found that the carboxylate oxygen of the progly is a strong $\sigma$-and $\pi$-donor while the peptide nitrogen has weak $\pi$-donor property toward chromium(III) ion.

• Bulletin of the Korean Chemical Society
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• v.20 no.1
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• pp.81-84
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• 1999

The emission and excitation spectra of [Cr(NH3)5(imH)](ClO4)3·H2O (imH=imidazole) taken at 77 K are reported. The 298 K visible and far-infrared spectra are also measured. The vibrational intervals of the electronic ground state are extracted from the far-infrared and emission spectra. The ten electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed transitions, a ligand field analysis has been performed to determine the bonding properties of coordinated imidazole in the title chromium(Ⅲ) complex. It is confirmed that nitrogen atom of the imidazole ligand has a medium it-acceptor property toward chromium(Ⅲ) ion. The zero-phonon line in the excitation spectrum splits into two components by 181 cm-1, and the large 2Eg splitting can be reproduced by the ligand field theory.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.613-620
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• 1992

The solvent-dependent photophysical properties of 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid(4BPCA), which have a pre-twisted conformation in the ground state, have been investigated. The fluorescence spectra of 4BPCA show vibrational structure with a non-mirror image to the absorption spectra in nonpolar solvent while those of 2BPCA show no structure even in nonpolar solvents. As the solvent polarity increases, the fluorescence spectra become diffuse and broad with a strong red shift resulting in the large Stokes shift. The large fluorescence Stokes shift of BPCA's in polar solvent is also partially due to an intramolecular charge transfer (ICT) interaction in the excited state, as demonstrated by the large dipole moment in the excited state (7.6-10.6 D). The fluorescence decay behaviors of BPCA's (decay-times and their pre-exponential factors) also depend on solvent polarity in agreement with the solvent-dependent properties of the steady-state fluorecence. The data have been discussed in terms of change in the excited-state potential energy surface with respect to change of the dihedral angle of biphenyl moiety.

• Structural Engineering and Mechanics
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• v.82 no.2
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• pp.151-161
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• 2022

In this study, the effect of porosity distribution pattern on the free vibration analysis of porous FG plates with various boundary conditions is studied. The material properties of the plate and the porosities within the plate are considered to vary continuously through the thickness direction according to the volume fraction of constituents defined by the modified rule of the mixture, this includes porosity volume fraction with four different types of porosity distribution over the cross-section. The governing partial differential equation of motion for the free vibration analysis is obtained using hyperbolic shear deformation theory. An analytical solution is presented for the governing PDEs for various boundary conditions. Results of the presented solution are compared and validated by the available results in the literature. Moreover, the effects of material and porosity distribution and geometrical parameters on vibrational properties are investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.1044-1048
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• 2002

The experimental modal testing has been carried out for the stator of a generator to confirm the vibrational mode shapes and the corresponding natural frequencies. The model of the stator for the vibration analysis was developed and a series of vibration analyses was carried out. And the properties of the solid element were updated to reduce the differences of the natural frequencies between the measured and the analysed. In the vibration anlyses, the axial, radial and circumferential properties of the solid element were separately varied to take into account the orthotropic effect of the laminated structure and to match the primary modes of the stator core which were extracted from the modal testing. After several attempts to match the measured natural frequencies and model shapes, the properties of the stator model were determined. Comparison of the vibration analyses results based on the determined properties showed fairly good coincidence with the measured data.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.4
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• pp.516-520
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• 2009

Atmosphere Plasmas of Gas Discharge (APGD) have been used in plasma sources for material processing such as etching, deposition, surface modification, etc. This study is to investigate and understand the fundamental plasma discharge properties. Especially, $SF_6/N_2$ mixed gas would be used in power transformer, GIS (Gas insulated switchgear) and so on. In this paper, we developed a one dimensional fluid simulation model with capacitively coupled plasma chamber at the atmosphere pressure (760 [Torr]). 38 kinds of $SF_6/N_2$ plasma particles which are an electron, two positive ions (${SF_5}^+$, ${N_2}^+$), five negative ions (${SF_6}^-$, ${SF_5}^-$, ${SF_4}^-$, ${F_2}^-$, ${F_1}^-$), thirty excitation and vibrational particles for $N_2$ were considered in this computation. The $N_2$ gases of 20%, 50%, 80% were mixed in $SF_6$ gas. As the amount of $N_2$ gas was increased, the properties of electro-negative plasma moved toward the electro-positive plasma.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.611-633
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• 2020

In this paper, a comprehensive review of nanostructures that exhibit piezoelectric behavior on all mechanical, buckling, vibrational, thermal and electrical properties is presented. It is firstly explained vast application of materials with their piezoelectric property and also introduction of other properties. Initially, more application of material which have piezoelectric property is introduced. Zinc oxide (ZnO), boron nitride (BN) and gallium nitride (GaN) respectively, are more application of piezoelectric materials. The nonlocal elasticity theory and piezoelectric constitutive relations are demonstrated to evaluate problems and analyses. Three different approaches consisting of atomistic modeling, continuum modeling and nano-scale continuum modeling in the investigation atomistic simulation of piezoelectric nanostructures are explained. Focusing on piezoelectric behavior, investigation of analyses is performed on fields of surface and small scale effects, buckling, vibration and wave propagation. Different investigations are available in literature focusing on the synthesis, applications and mechanical behaviors of piezoelectric nanostructures. In the study of vibration behavior, researches are studied on fields of linear and nonlinear, longitudinal and transverse, free and forced vibrations. This paper is intended to provide an introduction of the development of the piezoelectric nanostructures. The key issue is a very good understanding of mechanical and electrical behaviors and characteristics of piezoelectric structures to employ in electromechanical systems.

• Steel and Composite Structures
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• v.43 no.5
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• pp.603-623
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• 2022

This article is dedicated to predict the natural frequencies of joined conical shell structures made of Functionally Graded Material (FGM). The structure includes two conical segments. The equivalent material properties are found by using the rule of mixture based on Voigt model. In addition, three well-known patterns are employed for distribution of material properties throughout the thickness of the structure. The main objective of the present research is to propose a novel exponential pattern and obtain the related equivalent material properties. Furthermore, the Donnell type shell theory is used to obtain the governing equations of motion. Note that these equations are obtained by employing First-order Shear Deformation Theory (FSDT). In order to discretize the governing system of differential equations, well-known and efficient semi-analytical scheme, namely Generalized Differential Quadrature Method (GDQM), is utilized. Different boundary conditions are considered for various types of single and joined conical shell structures. Moreover, an applicable modification is considered for the continuity conditions at intersection position. In the first step, the proposed formulation is verified by solving some well-known benchmark problems. Besides, some new numerical examples are analyzed to show the accuracy and high capability of the suggested technique. Additionally, several geometric and material parameters are studied numerically.

• Korean Journal of Materials Research
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• v.33 no.3
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• pp.95-100
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• 2023

This research examines the effect of adding aluminum on the structural, phasic, and magnetic properties of CoCrFe NiMnAl_x high-entropy alloys. To this aim, the arc-melt process was used under an argon atmosphere for preparing cast samples. The phasic, structural, and magnetic properties of the samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrational magnetometry (VSM) analyses. Based on the results, the addition of aluminum to the compound caused changes in the crystalline structure, from FCC solid solution in the CoCrFeNiMn sample to CoCrFeNiMnAl BBC solid solution. It was associated with changes in the magnetic property of CoCrFeNiMnAl_x high-entropy alloys, from paramagnetic to ferromagnetic. The maximum saturation magnetization for the CoCrFeNiMnAl casting sample was estimated to be around 79 emu/g. Despite the phase stability of the FCC solid solution with temperature, the solid solution phase formed in the CrCrFeNiMnAl high-entropy compound was not stable, and changed into FCC solid solution with temperature elevation, causing a reduction in saturation magnetization to about 7 emu/g.