• ETRI Journal
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• v.34 no.4
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• pp.536-541
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• 2012

This paper aims to extend the transmission line matrix method with a hybrid symmetrical condensed node (HSCN) to model ferrite media in the time domain. To take into account the anisotropy and dispersive properties of ferrite media, equivalent current sources are incorporated into supplementary stubs of the original HSCN. The scattering matrix of the proposed HSCN is provided, and the validity of this approach is demonstrated for both transversely and longitudinally magnetized ferrites. Agreement is achieved between the results of this approach and those of the theoretical and the finite-difference time-domain method.

• Journal of Technologic Dentistry
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• v.32 no.4
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• pp.307-315
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• 2010

Purpose: The purpose of this study was to investigate the change of microstructures and mechanical properties of pure titanium casting specimens as a function of mold temperatures. Methods: The pure titanium castings were fabricated using the centrifugal vacuum casting method with different mold temperatures of $200{\sim}500^{\circ}C$. The resulting castings were characterized by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and vicker,s hardness tester. Results: In case of the mold temperatures over $400^{\circ}C$, the porosity, surface crack and large grain size were observed in resulting castings. Conclusion: In this work, The most suitable mold temperature in casting of pure titanium was $300^{\circ}C$.

• Journal of Electrochemical Science and Technology
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• v.11 no.2
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• pp.165-171
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• 2020

The electrochemical preparation and spectroscopic characterisation of iridium-antimony (Ir-Sb) species is important owing to their potential applications as nanostructure materials. Nanostructures, i.e. nanoflower and nanodisk, of Ir-Sb were electrodeposited on conductive substrates using a practical electrochemical method based on the simultaneous underpotential deposition (UPD) of Ir and Sb from the IrCl₃ and Sb₂O₃ at a constant potential. Electrochemical UPD mechanism of Ir-Sb was studied using cyclic voltammetry and potential-controlled electrochemical deposition techniques. Herein, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron and Raman spectroscopy were used to determine the morphological and structural properties of the electrochemically-synthesised Ir-Sb nanostructures.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.3
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• pp.78-84
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• 1994

The location of periodic noises in phase of AC power wave reveals to be specific according to the noise kinds which can be generally classified into modulation and baseband types in DLC. The former noise type has constant noise phase which is originated from switching mode power supplies and the latter normally caused from thyristor circuit of low switching frequency is compared to be more dispersive than the other.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.3
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• pp.48-55
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• 2003

This study investigates the effect of temperature and electric field strength on the Bingham characteristics of Electro-Rheological(ER) fluids which change their Yield shear stress and viscosity by temperature and electric field strength. It is found that under constant temperature the Yield sheal stress and viscosity of ER fluids proportionally increase with the applied electric field strength, and under constant applied electric field strength the Yield shear stress and viscosity of ER fluids decrease with the increasing temperature. These results are considered to be applied to the fluid and pneumatic power industry.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1123-1126
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• 2003

In this research 4 plate type ER-Valves which have same surface but different width and length are designed and an experimental apparatus is constructed. With this experimental apparatus, flow rate and pressure drop of ER fluid flowing in ER-Valve are measured by varying electric field strength of ER-valve, and relation between valve types and pressure drop is also experimented. ER fluid is made silicon oil mixed with 40wt% starch having hydrous particles. The pressure drop according to the strength of electric field by differential pressure gauge in the present ER-Valve was used. This test reviewed experiment for the special changes of ER fluids in the steady flow condition.

• Korea-Australia Rheology Journal
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• v.18 no.3
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• pp.143-151
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• 2006

We analyzed the non-Newtonian and non-isothermal flow in a single screw extruder system and investigated the mixing performance with respect to the screw speed and the screw pitch. The viscosity of polymer melt was described with Carreau-Yasuda model. The mixing performance was computed numerically by tracking the motions of particles in the screw element system. The extent of mixing was characterized in terms of the deformation rate, the residence time distribution, and the strain. The results revealed that the high screw speed reduces the residence time but increases the deformation rate while the small screw pitch increases the residence time. It is concluded that the high screw speed increases the dispersive mixing performance and the small screw pitch increases the distributive mixing performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.266-271
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• 2005

Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the present method, the flexural wave signals measured in a plate were analyzed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.6
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• pp.399-405
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• 2015

In this work we use the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor. The mode decomposition technique is also used to estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize axial defects. The arrival times of the separated modes are calculated and the axial defect lengths can be evaluated by using the estimated arrival time. Results from an experiment on a carbon steel pipe are presented and it is shown that the accurate and quantitative defect characterization could become enabled using the proposed technique.

• Smart Structures and Systems
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• v.9 no.1
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• pp.21-33
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• 2012

In this study, a Lamb-wave based damage detection approach is proposed for damage localization in plate. A sensor network consisting of three PZT wafer type actuators/sensors is used to generate and detect Lamb waves. To minimize the complication resulted from the multimode and dispersive characteristics of Lamb waves, the fundamental symmetric Lamb mode, $S_0$ is selectively generated through designing the excitation frequency of the narrowband input signal. A damage localization algorithm based upon the configuration of the PZT sensor network is developed. Time-frequency analysis method is applied to purify the raw signal and extract damage features. Experimental result obtained from aluminum plate verified the proposed damage localization approach.