• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.333-339
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• 1999

It is well recognized that ultrasonic technique is one of the most common and reliable nondestructive evaluation techniques for quantitative estimation of defects in structures. For the quantitative and accurate estimation of internal defects. the characteristics of scattered ultrasonic wavefields must be understood. In this study. the scattered near-field and far-field due to a circular cavity embedded in infinite media subjected to incident SH-waves were calculated by the boundary element method. The frequency response of the scattered ultrasonic far-field was transformed into the time-domain signal by obtaining its inverse Fourier transform. It was found that the amplitude of time-domain signal decreases and its time delay increases as the distance between the detecting point of ultrasonic scattered field and the center of internal cavity increases.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.2
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• pp.41-55
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• 1989

Successive iteration of geometrical optics(GO)is suggested to calculate wedge diffraction fields. For a wedge and given source, the GO field may be obtained when the fields by the half spaces are found and the shadow regions are determined. Furthermore, one may caluculate the sources which are equivalent to the discontinuities of the GO field along the shadow boundaries and form a new wedge problem with the equivalent sources instead of the original one. It is shown that the field by the wedge and the equivalent sources equals to the diffraction field which GO requires for the complete solution. Also, it is shown that the field generated by the equivalent sources in the unbounded space, or the incident field in the new wedge problem, equls to the diffraction field approximated by the physical optics. The new wedge problem is solved here by another application of the GO to approximate the diffraction field and the result is compared with that by the physical optics. For a validity of the successive iteration of GO , infinite iteration of GO is performed analytically and the convergence is examined ofr conducting wedges, of which the exact solution is available.

• Journal of the Korean Geotechnical Society
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• v.20 no.1
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• pp.61-73
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• 2004

Rayleigh wave and Love wave are the major elastic waves belonging to the category of the surface wave. The fact that Love wave is not contaminated by P-wave makes Love wave superior to Rayleish wave and other body waves. Therefore, the information that Love wave carries is more distinct and clearer than the information of Rayleigh wave. In this study, for the purpose of employing Love wave in the SASW method, the dispersion characteristics of the Love wave were extensively investigated by the theoretical, numerical and experimental approaches. The 2-D and 3-D finite element analyses for the half space and two-layer systems were performed to determine the phase velocities from Love wave as well as from both the vertical and the horizontal components of Rayleigh wave. Also, the SASW measurements were performed at the geotechnical sites to verify the results obtained by the numerical analysis. The results of the numerical analysis and the field testing indicated that the dispersion characteristics of Love wave can be an extended information to make better evaluation of the subsurface stiffness structure by SASW method.

• Journal of Plant Biotechnology
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• v.30 no.4
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• pp.375-380
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• 2003

This study was conducted to establish a practical masspropagation system of Phalaenopsis clones from basal shoot segments. The frequency of PLB (protocorm like body) induction was compared with various explants. Basal shoot segments showed the most successful result of 45％, while root tips, stalk node segments, stalk leaves and mature leaves represented low frequency (below 5％). The PLB induction ratio in the culture of basal shoot segments was examined with 11 different Phalaenopsis varieties, and the majority of varieties, including pink flower lines, showed an about 30％ rate of PLB formation. Especially, when whole basal shoot parts without cutting were inoculated onto PLB induction medium, giant PLB was induced from explant. This giant PLB was green color and big in size compared with normal PLB. When dissected giant PLB segments inoculated onto PLB multiplication medium, only normal size of PLBs were induced from them. PLBs induced by basal shoot culture were transferred onto proliferation medium and then shooting medium, from which normal plants were formed. Therefore, this culture method is considered as effective and practical protocol for Phalaenopsis mericlone production. In addition, it is suggested that clones of an infinite number can be produced consecutively by this culture system through repeated cycles of PLB induction and proliferation using the basal shoot segment of flask plant.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2328-2339
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• 1992

The propagation of coherent time-harmonic elastic L-and SV-waves is studied in a medium with random distribution of cylindrical inclusions. The purpose of the research is to characterize the dynamic elastic moduli and the attenuation properties of fiber-reinforced composite materials. The cylindes representing the fibers are assumed to be distributed in parallel with each other and the direction of incident waves are normal to the cylinder axes. A multiple scattering formula using the single scattering coefficients in conjunction with the Lax's quasicrystalline approximation is derived from which the dispersion relation for such medium is obtained. In order to formulate the multiple scattering interaction between cylinders, the pair correlation functions are generated by the Monte Carlo simulation technique. From the numerically evaluated complex wavenumbers, the propagation speed of the average wave, the coherent attenuation and the effective elastic moduli are presented as functions of frequency and fiber volume fraction.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.915-918
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• 2008

Hydration heat and autogenous shrinkage are generated essentially by the same hydration. Many researchers have studied the close relationship between hydration temperature and autogenous shrinkage but hardly any research has been undertaken to explain the specific numerical relation. In this study, early age properties of hydration heat and autogenous shrinkage of specimen whose section size was changed were analyzed, and relationship between hydration heat and autogenous shrinkage was investigated. In the results of the study, inner temperature and autogenous shrinkage increased as the section size increased. And rise and rise ratio of hydration temperature and autogenous shrinkage in hydration heating section and autogenous shrinking section are increased too. Temperature rise and autogenous shrinkage rise increased respectively, as hydration heating velocity and autogenous shrinking velocity increased. And autogenous shrinkage rise and autogenous shrinking velocity increased as hydration heating velocity increased.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.3
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• pp.193-200
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• 1996

In this paper, Strip Halo Antenna used for the proximity sensor in 800 MHz band was fabricated by using a dielectric board with the relative dielectric constant of 6.15. Dimensions of the strip halo antenna were optimized by the theoretical simulation and many experiments. The impedance of the strip halo antenna mounted on the proximity sensor with the finite circular groud plane was measured as 16.5 + j1.1[$\Omega$]. The matching characteristic of the strip halo antenna was greatly improved by attaching the matching section designed through experiments to the rear side of dielectric board. The impedance of the strip halo antenna with the matching section was measured as 43.79-j0.04[$\Omega$], and the 3 dB beam width of its radiation pattern was measured about $90^{\circ}$.

• The KIPS Transactions:PartB
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• v.12B no.5 s.101
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• pp.567-576
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• 2005

This paper proposes an image-based modeling method which recovers 3D models using projected line segments in multiple images. Using the method, a user obtains accurate 3D model data via several steps of simple manual works. The embedded nonlinear minimization technique in the model parameter estimation stage is based on the distances between the user provided image line segments and the projected line segments of primitives. We define an error using a finite line segment and thus increase accuracy in the model parameter estimation. The error is defined as the sum of differences between the observed image line segments provided by the user and the predicted image line segments which are computed using the current model parameters and camera parameters. The method is robust in a sense that it recovers 3D structures even from partially occluded objects and it does not be seriously affected by small measurement errors in the reconstruction process. This paper also describesexperimental results from real images and difficulties and tricks that are found while implementing the image-based modeler.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.761-764
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• 2008

The present study is aimed to study the effect of elevated temperatures ranging from 20 to $700^{\circ}C$ on the strain properties of high-strength concrete of 40, 60, 80MPa grade. In this study, the types of test were the stressed test and stressed residual test that the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating and when target temperature is reached, the specimens are loaded to failure. Or specimens are loaded to failure after 24hour cooling time. tests were conducted at various temperatures ($20{\sim}700^{\circ}C$) for concretes made with W/B ratios 46%, 32% and 25%. Test results showed that the relative values of elastic modulus decreased with increasing compressive strength grade of specimen and the axial strain at peak stress were influenced by the load before heating. thermal strain of concrete at high temperature was affected by the preload as well as the compressive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.821-824
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• 2008

In this study, it is willing to present that fundamental data for proposing quantitatively shrinkage cracking evaluation method such as plat-ring type restrained test method. It is possible to decide that specimen diameter is s 150mm with evaluating restrained shrinkage crack properties of concrete according to change of ring diameter in specimen. Also, effectiveness of test method according to mixing of PVA fiber is evaluated as part of a repeatability verification experiment of plat-ring type restrained test method using ring which diameter is 150mm. As a result, it is possible to measure the crack due to the plastic shrinkage which was occurred within 48hours at early age with plat-ring type restrained test method. Hereafter, it is considered that the study concerning environmental condition and mixing factor in plat-ring type restrained test method is need.