• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.318-319
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• 2008

In this article, magnetic properties of multiferroic bi-layer $BiFeO_3$ (BFO)/$BaTiO_3$ (BTO) thin films were studied. It was found that the magnetization increased by the insertion of BTO buffer layer even though the interfacial stress was slightly relaxed, which indicated a coupling between the ferroelectric and ferromagnetic orders. Furthermore, with slightly increase of BFO film thickness, both BFO and BFO/BTO bi-layer films showed anisotropic magnetic properties with higher in-plane magnetization than the values measured out-of-plane. These are attributable to strain constraint effect at the interface.

• Geomechanics and Engineering
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• v.6 no.3
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• pp.277-292
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• 2014

Soil nailing, as an effective stabilizing method for slopes and excavations, has been widely used worldwide. However, the interaction mechanism of a soil nail and the surrounding soil and its influential factors are not well understood. A pullout model using a hyperbolic shear stress-shear strain relationship is proposed to describe the load-deformation behavior of a cement grouted soil nail. Numerical analysis has been conducted to solve the governing equation and the distribution of tensile force along the nail length is investigated through a parametric study. The simulation results are highly consistent with laboratory soil nail pullout test results in the literature, indicating that the proposed model is efficient and accurate. Furthermore, the effects of key parameters, including normal stress, degree of saturation of soil, and surface roughness of soil nail, on the model parameters are studied in detail.

• Journal of Ship and Ocean Technology
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• v.12 no.4
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• pp.1-6
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• 2008

Nowadays, the computational capability and graphical power based on PCs increase very rapidly every year. As a result, the complicated engineering or scientific problems that could have only been handled by supercomputers a couple of decades ago can now be routinely run on PCs. Besides, the PCs can be assembled in parallel to increase its computational capability theoretically without limitation. The Web-based interface and communication tools are also being enhanced very rapidly and the real-time distance learning (E-Learning) and project cooperation on web get increasing attention. Using the-state-of-the-art computational method, a number of complicated and computationally intensive problems are being solved by PCs. The results can be well demonstrated on screen by graphics and animation tools. Those examples include the simulations of fully nonlinear waves, their interactions with floating bodies, global-motion analysis of multi-unit floating production system including complicated mooring lines and risers. Several examples will be presented in this regard. Also, Web and java-applet based educational tools have been developed at Texas A&M University for better understanding of waves and wave-body interactions. The background and examples of such Web-based educational tools published in Kim et al. (2003) are briefly introduced here.

• Journal of the Semiconductor & Display Technology
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• v.10 no.1
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• pp.57-61
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• 2011

To develop high efficiency crystalline solar cells, the rear surface passivation is very important. In this paper, $Al_2O_3$ films deposited by thermal ALD(atomic layer deposition) method were studied for rear surface passivation of crystalline solar cells and their passivation properties were evaluated. After the deposition of $Al_2O_3$ films on p-type Si wafers, the lifetime was increased very much due to the reduction of interface state density and the field effects of the negative fixed charge in the films. Also, optimum annealing condition and effects of SiNx capping layer were investigated. The best lifetime was obtained when the films were annealed at $400^{\circ}C$ for 15min. And the lifetime degradation of the $Al_2O_3$ films with SiNx capping layers was improved compared to those without the capping layers.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.5
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• pp.505-511
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• 2011

In this paper, we have developed an automatic velocity control system of a small-sized commercial treadmill (belt length of 1.2 m and width of 0.5 m) which is widely used at home and health centers. The control objective is to automatically adjust the treadmill velocity so that the subject's position is maintained within the track when the subject walks at a variable velocity. The subject's position with respect to a reference point is measured by a low-cost sonar sensor located on the back of the subject. Based on an encoder sensor measurement at the treadmill motor, a state feedback control algorithm with Kalman filter was implemented to determine the velocity of the treadmill. In order to reduce the unnatural inertia force felt by the subject, a predefined acceleration limit was applied, which generated smooth velocity trajectories. The experimental results demonstrate the effectiveness of the proposed method in providing successful velocity changes in response to variable velocity walking without causing significant inertia force to the subject. In the pilot study with three subjects, users could change their walking velocity easily and naturally with small deviations during slow, medium, and fast walking. The proposed automatic velocity control algorithm can potentially be applied to any locomotion interface in an economical way without having to use sophisticated and expensive sensors and larger treadmills.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.3
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• pp.130-136
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• 1989

Electrical transport and thermally induced metastability in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) using boron-doped amorphous silicon as an active layer have been studied. The device characteristics n-channel and p-channel operations. The thermal quenching experiments on amorphous silicon-silicon nitride ambipolar TFT give clear evidence for the co-existence of two distinct metastable changes. The densities of metastable active dopants and dangling bonds increase with the quenching temperature. On the other hand, the interface state density appears to decrease with increasing quenching temperature.

• Journal of Magnetics
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• v.2 no.3
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• pp.86-92
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media in the wavelength of a blue laser beam, due to large Kerr rotation angle. However, since the Co/Pd multilayer is a non-equilibrium state in terms of free energy and MO recording is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, the assessment of the thermal stability in the Co/Pd multilayer is crucially important both for basic research and applications. As the parameter of the thermal stability in this research, effective interdiffusion coefficients (Deff) perpendicular to the interface of the Co/Pd multilayers are measured in terms of Ar sputtering pressure and heat treatment temperature. From the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects Deff of the Co/Pd multilayers. This discovery will provide the understanding of the magnetic exchange energy in the effective interdiffusion process of a magnetic multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• Structural Engineering and Mechanics
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• v.58 no.4
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• pp.731-743
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• 2016

Plastic behaviors, based on the von Mises yield criterion, of circular discs containing a purely elastic, circular inclusion under uniform temperature loading are studied with the finite element analysis. Temperature-dependent mechanical properties are considered for the matrix material only. In addition to analyzing the plane stress and plane strain disc, a 3D thin disc and cylinder are also analyzed to compare the plane problems. We determined the elastic irreversible temperature and global plastic collapse temperature by the finite element calculations for the plane and 3D problem. In addition to the global plastic collapse, for the elastically hard case, the plane stress problem and 3D thin disc may exhibit a local plastic collapse, i.e. significant pile up along the thickness direction, near the inclusion-matrix interface. The pileup cannot be correctly modeled by the plane stress analysis. Furthermore, due to numerical difficulties originated from large deformation, only the lower bound of global plastic collapse temperature of the plane stress problem can be identified. Without considerations of temperature-dependent mechanical properties, the von Mises stress in the matrix would be largely overestimated.

• Structural Engineering and Mechanics
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• v.39 no.1
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• pp.77-91
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• 2011

A simply structural damage detection software is developed to identification damage in beams. According to linear fracture mechanics theory, the localized additional flexibility in damage vicinity can be represented by a lumped parameter element. The damaged beam is modeled by wavelet-based elements to gain the first three frequencies precisely. The first three frequencies influencing functions of damage location and depth are approximated by means of surface-fitting techniques to gain damage detection database of forward problem. Then the first three measured natural frequencies are employed as inputs to solve inverse problem and the intersection of the three frequencies contour lines predict the damage location and depth. The DLL (Dynamic Linkable Library) file of damage detection method is coded by C++ and the corresponding interface of software is coded by virtual instrument software LabVIEW. Finally, the software is tested on beams and shafts in engineering. It is shown that the presented software can be used in actual engineering structures.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.2
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• pp.79-86
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• 2004

An analytical and experimental study has been conducted to determine the optimal charging mass of working fluid for the maximum heat transport capacity of heat pipe with axially grooved wick. When the heat pipe is operated in a steady state, the liquid-vapor meniscus recession of working fluid to the bottom of groove is occurred in the evaporator region. In this work, the optimal charging mass of working fluid was obtained by considering the meniscus recession from the axial variation of capillary pressure, the radius of curvature and wetting angle of meniscus of liquid-vapor interface. Experimental results were also obtained by varying the charging mass of working fluid within a heat pipe, and presented for the trend of maximum heat transport capacity corresponding to the operating temperature and the elevation of heat pipe. Finally, the analytical results of the optimal charging mass of working fluid were compared with those from the experiment, both of which were in good agreement with each other.