• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.3
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• pp.132-138
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• 2003

We investigated the polarization retention characteristics of ferroelectric capacitors with $Pb(Zr,Ti)O_3$ (PZT) thin films which were fabricated by different deposition methods. In thermally-accelerated retention tests, PZT films which were prepared by a chemical solution deposition (CSD) method showed rapid decay of retained polarization charges as the thickness of the films decreased down to 100 nm, while the films which were grown by metal organic chemical vapor deposition (MOCVD) retained relatively large non-volatile charges at the corresponding thickness. We concluded that in the CSD-grown films, the thicker interfacial passive layer compared with the MOCVD-grown films had an unfavorable effect on retention behavior. We observed the existence of such interfacial layers by extrapolation of the total capacitance with thickness of the films and the capacitance of these layers was larger in MOCVD-grown films than in CSD-grown films. Due to incomplete compensation of surface polarization charges by the free charges in the metal electrodes, the interfacial field activated the space charges inside the interfacial layers and deposited them at the boundary between the ferroelectric layer and the interfacial layer. Such space charges built up an internal field inside the films, which interfered with domain wall motion, so that retention property at last became degraded. We observed less imprint which was a result of less internal field in MOCVD-grown films while large imprint was observed in CSD-grown films.

• Journal of the Korean earth science society
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• v.26 no.6
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• pp.560-572
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• 2005

This study investigates the characteristics of atmospheric circulation and the heat source $(Q_1)$ related to the winter cold surge in Korea from 1979 to 1999. The occurrence frequency of cold surge is about one event per year and $60\%$ of the total events occurred during the former period, before 1989. During the cold surge, the pressure pattern shows more dominant east-west dipole circulation pattern in the lower troposphere and the effect of upper level trough is stronger than normal cases. Temperature falling pattern over Korea shows that the pattern opposite to the temperature structure over Lake Baikal and temperature change has opposite signs between the low-middle level and upper level, with the boundary at 400 hPa. The analysis of heat source shows that atmospheric cooling by cold advection during the cold surge is balanced by adiabatic warming due to downward motion, indicating that the movement path of cold core is associated with that of heat sink. Therefore, the movement mechanism of the heat source and sink should be well known for understanding the maintenance mechanism of cold surge and predicting cold surges.

• Journal of Environmental Science International
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• v.22 no.5
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• pp.571-580
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• 2013

In this study, compared with the result of water surface elevation and water velocity on the establishment of river maintenance basic plan and result of HEC-GeoRAS based GIS, and after use the result of water surface elevation and velocity were observed in the Han stream on Jeju island, analysis 2 dimensional stream flow. the lateral hydraulic characteristics and curved channel of the stream were analyzed by applying SMS-RMA2 a 2 dimensional model. The results of the analysis using HEC-RAS model and HEC-GeoRAS model indicated that the distribution ranges of water surface elevation and water velocity were similar, but the water surface elevation by section showed a difference of 0.7~2.18 EL.m and 0.63~1.16 EL.m respectively, and water velocity also showed differences of maximum 1.58m/sec and 2.67m/sec. SMS-RMA2 analysis was done with the sphere of Muifa the typhoon as a boundary condition, and as a result, water velocity distribution was found to be 1.19 through 3.91 m/sec, and the difference of lateral water velocity in No. 97 through 99 the curved channel of the stream was analyzed to be 1.59 through 2.36 m/sec. In conclusion it is anticipated that the flow analysis of 2 dimension model of stream can reflect the hydraulic characteristics of the stream curved channel or width and shape, and can be applied effectively in the establishment of river maintenance basic plan or management and designing of stream.

• 대한공업교육학회지
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• v.34 no.1
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• pp.238-251
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• 2009

The noise itself that affects the sensor array is defined as the noise which happens in the place where the system is installed and the circumference noise which comes from the ocean. The array structure for detecting acoustic signal in the underwater effected turbulent layer flow noise. In this paper to design the conformal array spectral density function was introduced and several cases of flow induced noise which affect transfer function were simulated. Modified Corcos wall pressure model was used as turbulent boundary layer flow noise. The effect of noise has been reduced as integrated sum of transfer function has been reduced by decreasing elastomer thickness and density when kx is in low wave number area. Also the characteristics of transfer function by Corcos wall pressure displayed the product of frequency density function. This simulation results can be applied to the conformal array design in unmmaned underwater vehicle in the near future.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.957-964
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• 2011

This investigation presents a finite element method to obtain the transmission properties of bulk elastic waves in piezoelectric band gap structures(phonon crystals) for varying frequencies and modes. To this end, periodic boundary conditions are imposed on a three-dimensional model while both in-plane and out-of-plane modes are included. In particular, the mode decoupling characteristics between in-plane and out-of-plane modes are identified for each electric poling direction and the results are incorporated in the finite element modeling. Through numerical simulations, the proposed modeling method was found to be a useful, effective one for analyzing the wave characteristics of various types of piezoelectric phononic band gap structures.

• Wind and Structures
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• v.31 no.4
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• pp.373-380
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• 2020

For large-scale 5MW offshore wind turbines, the discrete equation of fluid domain and the motion equation of structural domain with geometric nonlinearity were built, the three-dimensional modeling of the blade considering fluid-structure interaction (FSI) was achieved by using Unigraphics (UG) and Geometry modules, and the numerical simulation and the analysis of the vibration characteristics for wind turbine structure under rotating effect were carried out based on ANSYS software. The results indicate that the rotating effect has an apparent effect on displacement and Von Mises stress, and the response and the distribution of displacement and Von Mises stress for the blade in direction of wingspan increase nonlinearly with the equal increase of rotational speeds. Compared with the single blade model, the blade vibration period of the whole machine model is much longer. The structural coupling effect reduces the response peak value of the blade displacement and Von Mises stress, and the increase of rotational speed enhances this coupling effect. The maximum displacement difference between two models decreases first and then increases along wingspan direction, the trend is more visible with the equal increase of rotational speed, and the boundary point with zero displacement difference moves towards the blade root. Furthermore, the Von Mises stress difference increases gradually with the increase of rotational speed and decreases nonlinearly from the blade middle to both sides. The results can provide technical reference for the safe operation and optimal design of offshore wind turbines.

• Journal of the Korean Society of Costume
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• v.54 no.6
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• pp.119-130
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• 2004

The purpose of this study was to analyze the characteristics of 1980s' oversize fashion. Especially in 1980s, there were some characteristics that the leading style did not exist as the other decades, but instead of that, various styles coexisted and the existing traditional rule of fashion was destroyed. On the basis of such background, the moulding nature resident in oversize fashion is considered and analyzed as follows. Firstly, 1980s is the time of power suit booming and through such clothes, women disclosed their consciousness that they want to be equal with men. Secondly, In contrast to that a shoulder pad was the trademark of 1980s' clothes, the social aspect that Japanese designers' clothes of layered look and them of grunge look coexisted is directly expressed through these oversize clothes. Thirdly, In 1980s of the time that people's interest to health risen, sports wear was developed to be everyday wear and furthermore, it had variously influences on high fashion so that developed to big look. Fourthly, when it comes to 1980s' clothes, the atmosphere of society denying apparent boundary between sex at that time was resident in androgynous look and the folklore image of sexless style by their appearance in oversize fashion. What is this situation that the style of the past time is popular in the 21st century even such intentional spirit of challenge already passed？ Maybe for women, the one way of expressing themselves is through their clothes, and for such reason, it can be considered that the social meaning resident in 1980s' clothes is re-examined in the present age.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.606-612
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• 1985

On the stability of the Beck's column with a tip mass, the influence of the characteristics of the springs at the fixed end of the column are studied. The equations of motion and boundary conditions of this system are established by using the Hamiton's principle. On the evaluation of the stability of the column, t he effect of the shear deformation and rotatory inertial is considered in calculation. For the maintenance of the stability of the column, it is proved that the constant of the translational spring at the fixed end must be very large while th magnitude of the constant of the rotational spring at the fixed end has no effect. When the constants of the springs at the fixed end are small, it is also proved that the influence of the moment of inertial of the tip mass on the stability of the column are decreased and for the translational spring the degree of the decrease is more and more. Therefore it is found that the characteristics of the springs at the fixed end are very effective elements for the stability of the column when the columns subjected to a compressive follower force are designed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1335-1341
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• 2011

The purpose of this research is to investigate how separated and reattached flow affects mass transfer, by comparing the local mass transfer characteristics on an inclined flat plate with those on a parallel flat plate. The local mass transfer coefficients for the flat plate were measured using the naphthalene sublimation technique; the inclined angle of the flat plate was varied from $-10^{\circ}$ to $10^{\circ}$ at $5^{\circ}$ intervals, and the free-stream velocity was varied from 2m/s to 15m/s. At positive inclined angles, the local Sherwood numbers decreased gradually because the boundary-layer thickness increased. On the other hand, for negative inclined angles, the local Sherwood numbers assumed the minimum value at the separation point of the recirculation flow and the maximum value at the reattachment point. The average Sherwood numbers for both positive and negative inclined angles were lower than those in the case of the parallel plate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.1
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• pp.30-37
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• 2005

The microwave dielectric properties and their related structural characteristics in solid solutions of (1-$\chi$) Ba($Mg_{1/3}$Nb$_{2/3}$) $O_3$-$\chi$La(Mg$_{2/3}$Nb$_{1}$3) $O_3$(BLMN) have been investigated by measuring the dielectric constant($\varepsilon$r), Q value and temperature coefficient of resonant frequency($\tau$f) and by observing the crystal structure using high resolution transmission electron microscopy (HRTEM). Microwave dielectric properties showed characteristic features for specific composition. Dielectric constant($\varepsilon$$_{r}$) showed maximum value at the composition which corresponds to the phase boundary between 1 : 2 ordered and 1 : 1 ordered structure. The increase in $\varepsilon$$_{r}$ may be caused by the rattling of ions by incorporating smaller ions and the disordered structure. The variation of temperature coefficient of resonant frequency($\tau$$_{f}$) was investigated in terms of oxygen octahedra tilting.dra tilting.