• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.31-40
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• 2000

This paper describes the numerical computations of the interaction between the streamwise vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of the streamwise vortices introduced in turbulent boundary layers. The flow behind a vortex generator is modeled by the information that is avilable from studies on the dalta winglet. An algorithm of the solution of the incompressible Navier-Stokes equations for three-dimensional turbulent flows, together with a two layer turbulent model to resolve the near-wall flow, is based on the method of artificial compressibility. The present results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary thinning, and have a good agreement with the experimental data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.11a
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• pp.167-176
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• 1996

Flaw classification and sizing are very essential issues in quantitative ultrasonic nondestructive evaluation of various materials and structures including weldments. For performing of these tasks in an automated fashion, we are developing an intelligent ultrasonic evaluation system with a multi-axis portable scanner which can do consistent and efficient acquisition and processing of ultrasonic flaw signals. Here we present our efforts to develop of this intelligent system including design of the portable scanner, acquisition and processing of ultrasonic flaw signals, display of pseudo 3-D image of flaws, and classification and sizing of flaws in weldments.

• The Journal of the Acoustical Society of Korea
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• v.25 no.1E
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• pp.1-7
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• 2006

This study examines the reflection characteristic of a thin transition layer of the ocean bottom showing variability with respect to depth. In order to model the surficial sediment simply, we reduce the Biot model to the depth dependent wave equation for the pseudo fluid using the fluid approximation (weak frame approximation). From the reduced equation, the difference between the inherent frequency dependency of the reflection and the frequency dependency resulting from a thin transition layer is investigated. Using Tang's depth porosity profile model of the surficial sediment [D. Tang et al., IEEE J. Oceanic Eng., vol.27(3), 546-560(2002)], we numerically simulated the reflection loss and investigated the contribution from both frequency dependencies. In addition, the effects of different sediment type and varying depth structure of the sediment are discussed.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.872-875
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• 2002

A digital watermarking technique applying psychoacoustic model for audio signal is proposed in this paper. In the watermarking scheme, the pseudo-random bit stream used as a watermark signal is embedded into the audio signal in both speech and music. The strength of the embedded signal is subject to the human auditory system in such a way that the disturbances on host audio signal are beyond the sensing of human ears. The experimental results show that the quality of the watermarked audio signal, in term of signal to noise ratio, can be improved up to 3.2 dB.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.348-355
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• 2001

A computer program named \"NLDA-BIS\", which runs under the MATLAB environment, is developed fur seismic response analysis of base isolated structures. This program can explicitly model the various nonlinear isolation elements such as elastomeric bearings, sliding bearings and general viscous dampers, and so on. Newmark'\`s constant average acceleration method fur calculating the responses in time domain and the iterative pseudo-force method for treating the nonlinear isolation forces are adopted. For capturing the hysteretic behavior of isolation elements, the modified Wen's equations are adopted and solved by the numerical differentiation formula method. To verify the validity of the developed program, the seismic responses of a six-story reinforced concrete base isolated structure are calculated and compared with results obtained by the program \"3D-BASIS\" developed at the State University of New York at Buffalo which is the most widely used code far analyzing isolated structures today.ed structures today.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2002.11a
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• pp.169-172
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• 2002

Embedding information into video data is a topic that recently gained increasing attention. This paper proposes a new approach for digital watermarking and secure copyright protection of video, the principal aim being to discourage illicit copying and distribution of copyrighted material. The method presented here is based on the three dimensional discrete cosine transform of video scene, in contrast with previous works on video watermarking where each video frame was marked separately, or where only intra-frame or motion compensation parameters were marked in MPEG compressed videos. The watermark sequence used is encrypted, pseudo-noise signal to the video. The performance of the presented technique is evaluated experimentally

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.137-140
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• 2011

The aminolysis reactions of phenyl N-benzyl thiocarbamate with benzylamines in acetonitrile at $50.0^{\circ}C$ are investigated. The reactions are first order in both the amine and the substrate. Under amine excess, pseudo-first coefficient ($k_{obs}$) are obtained, plot of $k_{obs}$ vs free amine concentration are linear. The signs of ${\rho}_{XZ}$ (< 0) are consistent with concerted mechanism. Moreover, the variations of $\rho_X$ and $\rho_Z$ with respect to the sustituent in the substrate and large ${\rho}_{XZ}$ value indicate that the reactions proceed concerted mechanism. The normal kinetic isotope effects ($k_H/k_D$ = 1.3 ~ 1.5) involving deuterated benzylamine nucleophiles suggest a hydrogen-bonded, four-centered-type transition state. The activation parameters, ${\Delta}H^\ddagger$ and ${\Delta}S^\ddagger$, are consistent with this transition state structure.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.376-379
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• 1995

Employing the muffin-tin-orbital theory combined with pseudo-potential concepts, we have evaluated hybridization matrix elements between R and T sites in $RT_{2}$ compounds. The matrix elements are calculated with two parameters, the interatomic distance between R and T atoms from the crystal structure data, and the expectation values of the radial distances for the radial wave functions of the ground state charge densities, which are obtained from the linearized muffin-tin orbital band method within the local density approximation. It is found that the R 4f/T 3d hybridization matrix elements decrease with an increasing atomic number from R=Ce to Gd, and that they are smaller in $RNi_{2}$ than in $RCo_{2}$, which are consistent with trends observed in recent photoemission spectroscopy experiments. It is also found that the magnitudes of the hybridization matrix elements in $RFe_{2}$ are comparable to those in $RNi_{2}$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.532-543
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• 2003

In this paper, we proposed structure of a reversible discrete-time cellular neural network (DTCNN) for labeling digital images to protect copylight. First, we present the concept and the structure of reversible DTCNN, which can be used to generate 2D binary pseudo-random images sequences. We presented some, output examples of different kinds of reversible DTCNNs to show their complex behaviors. Then both the original image and the copyright label, which is often another binary image, are used to generate a binary random key image. The key image is then used to scramble the original image. Since the reversibility of a reversible DTCNN, the same reversible DTCNN can recover the copyright label from a labeled image. Due to the high speed of a DTCNN chip, our method can be used to label image sequences, e.g., video sequences, in real time. Computer simulation results are presented.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.4
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• pp.145-149
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• 2008

Purpose: To study the difference between refractive errors obtained from manifest refraction (MR) and cycloplegic refraction (CR) in first-time spectacle wearers. To study the difference between manifest refractive errors and cycloplegic refractive errors in first-time spectacle wearers. Methods: From January 2002 to December 2002, manifest and cycloplegic refractions were carried out on the patients who visited an ophthalmology clinic for a spectacle prescription for the first-time. The patients were 509 male and 499 female patients aged between from 3 to 15 years old. Results: The cycloplegic refraction showed a less myopia and a more hyperopia compared with the non-cycloplegic refraction. The differences were more in female patients. The CR showed a less myopic and a more hyperopic refractive errors than the MR. The differences were more in female patients. The average results from a pre- and a post-cycloplegic refraction showed a reduction of -0.22D in male, and -0.20D in female for the myopic group. For the myopic group, the myopic refractive errors by MR were -0.22D in male and -0.20D in female higher than the refractive errors by CR. Hyperopic group showed an increase of +0.37D in male, and +0.56D in female. For hyperopic group the hypropic refractive errors by CR were +0.37D in male and +0.56D in female higher than the refractive errors by CR. This difference between the results of a preand a post-cycloplegic refraction was more if the patients were younger. This difference between refractive errors by MR and by CR showed the younger the more and the proportions of pseudo-myopia and or latent hyperopia were also higher with younger patents age. The amounts of with-the-rule astigmatism and the oblique astigmatism were increased for the post-cycloplegic refraction in the CR refraction. Simple astigmatism reduced, but there was no difference found in the amount of astigmatism. The prevalence of simple astigmatism reduced, but there was no difference in the amount of astigmatism. Conclusions: The difference between manifest refraction and cycloplegic refraction was more in younger group. The difference of refrative error between by MR and CR increases with ageing decrease. Pseudo-myopia and latent hyperopia was also found in the younger group. Simple astigmatism reduced after cycloplegic refraction, there was no difference found in the amount of astigmatism. The prevalence of simple astigmatism reduced, but there was no difference in the amount of astigmatism.