• The Journal of the Acoustical Society of Korea
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• v.6 no.4
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• pp.5-11
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• 1987

In this paper, the measurement of SAW velocity on piezoelectric ceramic is studied. It can be done by using oscilloscope and pulse generator, and measure the velocity especially when feed-through is appeared. The propagating distance was exactly calculated considering that IDT responses are obtained by convolution theory, therefore the velocity was measured by the above simple method. As the results, the measurement velocity at room temperature was 3480 m/sec for $YZ-LiNbO_3$ single crystal and 2770 m/sec for a family of $PbTiO_3$ceramics with feed-through signal.

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.74-79
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• 2005

The tribrachial flame in laminar coflow jet has been investigated experimentally with unsteady propagating condition. With adopting various visualization techniques, including OH-PLIF, Rayleigh Scattering technique, it was confirmed that the location of tribrachial point is on the inclined surface of flame and the propagation speed of tribrachial flame was significantly affected by the velocity gradient.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.38-41
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• 2001

The combustion characteristics of the disilicides molybdenum system have been studied experimentally. The pertinent reaction parameters that control self-propagating high temperature synthesis reactions have been examined. These include reactant particle size, powder mixing and compaction, reaction stoichiometry, diluents. The influence of experimental variables on integrity, uniformity, structure, and related material properties will be discussed. Formation mechanism of $MoSi_2$ during SHS might be different and depending on experimental conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.303-308
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• 1994

The finite element method has been used to model and analyze the heat transfer phenomena during manufacturing process of MoSi $_{2}$ by SHS. For this urpose nonlinear transient heat transfer analyses by using ANSYS have been performed to compute the temperature distributiuon and the peak temperature in the test specimen. The effects of manufacturing process parameters such as a pre-heating temperature, the velocity of reaction zone have also been investigated. The results of the analysis have been compared with the experimental results.

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1201-1214
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• 2015

This paper introduces the combined effect of electric field, magnetic field and thermal field on edge wave propagating in a homogeneous isotropic prestressed plate of finite thickness and infinite length. The dispersion relation of edge wave has been obtained by using classical dynamical theory of thermoelasticity. The phase velocity has been computed and shown graphically for various initial stress parameter, electro-magneto parameter, electric parameter and thermoelastic coupling parameter.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.38-41
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• 2001

The combustion characteristics of the disilicides molybdenum system have been studied experimentally. The pertinent reaction parameters that control self-propagating high temperature synthesis reactions have been examined. These include reactant particle size, powder mixing and compaction, reaction stoichiometry, diluents. The inf1uence of experimental variables on integrity, uniformity, structure, and related material properties will be discussed. Formation mechanism of MoSi$_2$ during SHS might be different and depending on experimental conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.578-586
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• 2010

This paper describes a theoretical model and acoustic analysis of hysteresis of contacting surfaces subject to compression pressure. Contacting surfaces known to be nonlinear and hysteretic is considered as a simple spring that has a complex stiffness connecting discontinuous displacements between two solid contact boundaries. Mathematical formulation for 1-D interfacial wave propagation between two contacting solids is developed using the complex spring model to derive the dispersion relation between the interface wave speed and the complex interfacial stiffness. Existence of the interface wave propagating along the hysteretic interface is studied in theory and discussed by investigating the solution to the dispersion equation. Unlike the linear interface without hysteresis, there can exist only one distinct mode of interface waves for the hysteretic interface, which is anti-symmetric motion. The anti-symmetric mode of interface wave propagates with the velocity faster than the Rayleigh surface wave but less than the shear wave depending on the interfacial stiffness. If the contacting surfaces are compressed so much that the linear interfacial stiffness is very high, the hysteretic stiffness does not affect the interface wave velocity. However, it has an effect on the speed of interface wave for a loosely contact surfaces with a relatively low linear stiffness. It is also found that the phase velocity of anti-symmetric wave mode converges to the shear wave velocity in despite of the linear stiffness value if the hysteretic stiffness approaches 0.5.

• Nuclear Engineering and Technology
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• v.41 no.3
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• pp.327-334
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• 2009

Elastic wave is one of the most useful tools for non-destructive tests in nuclear power plants. Since the elastic properties are indispensable for analyzing the behaviors of elastic waves, they should be predetermined within an acceptable accuracy. Nuclear power plants are exposed to harsh environmental conditions and hence the structures are degraded. It means that the Young's modulus becomes unreliable and in-situ measurement of Young's modulus is required from an engineering point of view. Young's modulus is estimated from the group velocity of propagating waves. Because the flexural wave of a plate is inherently dispersive, the group velocity is not clearly evaluated in temporal signal analysis. In order to overcome such ambiguity in estimation of group velocity, Wigner-Ville distribution as the time-frequency analysis technique was proposed and utilized. To verify the proposed method, experiments for steel and acryl plates were performed with accelerometers. The results show good estimation of the Young's modulus of two plates.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.366-371
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• 1997

We performed the velocity selective optical pumping(VSOP) spectroscopy using the rubidium atomic vapor in the room temperature. This spectroscopic technique removes the Doppler broadening by both optical pumping effect and the selection of atoms with a particular velocity. In this experiment, we used two independent lasers; one was a locked laser whose frequency was fixed and the other was a sweep laser whose frequency was tunable. The two beams were passing through the sample in the same direction unlike the conventional VSOP spectroscopy using two counter-propagating beams. We could make the velocity selective range of atoms much wider with this method than the old one.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.6
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• pp.428-436
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• 1991

Double shelf topography allows the existence of two sets of waves propagating in opposite directons. In the case that two shelves are apart sufficiently enough, the solutions show two independent sets of waves which recover the single shelf waves. However, if the distance between two shelves is less than the Rossby deformation radius, the waves become dependent on the geometry of both shelves. Even over a double shelf topography, shelf waves propagate with the shallow water to the right in the Northern Hemisphere. The group velocity of shelf wave has the same direction as phase velocity in the long wave case, but the opposite direction in the short wave case. Each shelf mode has a zero group velocity at some intermediate value of wave length.