• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.103-106
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• 1989

A method of adaptive formation of the synthetic discriminant function(SDF) both in image plane and spatial frequency plane by using the Widrow-Hoff learning rule is proposed. The proposed method uses minimum number of interconnections between neurons so it can reduce the time for learning the neural net. Also complex valued interconnection weights are introduced for the purposes of handling the phase objects or Fourier transformed spatial frequency objects which usually have complex values for the representation of not only amplitude but also phase information. Also methods of optical implementation for the complex valued interconnection weights are discussed.

• Structural Engineering and Mechanics
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• v.8 no.2
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• pp.181-191
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• 1999

This paper presents an investigation of the mode localization and frequency loci veering phenomena in an aircraft with disordered external stores. Two theoretical analyses are carried out to study the occurring mechanism of the two phenomena: condensation technique in the subspace spanned by modes of interest and geometric mapping theory in the complex plane. Two simple criteria for predicting the occurrence of the mode localization and frequency loci veering are put forward. The prediction of the phenomena by our theoretically proposed criteria is in good agreement with that obtained through numerical calculations of characteristic solutions of the disordered system.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.493-498
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• 2015

Complex acoustic signals can be formed in a water-filled acoustic pulse tube under some exciting conditions. It makes difficult to measure plane-wave reflection coefficient with the pulse tube for low frequency bands. In this study, using COMSOL Multiphysics we show that the tube wall excitation generates complex acoustic field of nonplanar mode as well as planar one. From such field incident or reflected planar mode can be decomposed respectively with a modal decomposition method, two-dimensional Fourier filtering. It makes possible to more accurately determine the plane-wave reflection coefficient of acoustic specimen with time gating.

• Wind and Structures
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• v.20 no.5
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• pp.661-682
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• 2015

This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

• Journal of Power Electronics
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• v.17 no.2
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• pp.411-421
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• 2017

An approach based on a 2D lumped model is presented to quantify the voltage transfer gain (VTG) in power converter low power planes. The advantage of the modeling approach is the ease with which typical noise reduction devices such as decoupling capacitors or ferrite beads can be integrated into the model. This feature is enforced by a new modular approach based on effective matrix partitioning, which is presented in the paper. This partitioning is used to decouple power plane equations from external device impedance, which avoids the need for rewriting of a whole set of equation at every change. The model is quickly solved in the frequency domain, which is well suited for an automated layout optimization algorithm. Using frequency domain modeling also allows the integration of frequency-dependent devices such inductors and capacitors, which are required for realistic computation results. In order to check the precision of the modeling approach, VTGs for several layout configurations are computed and compared with experimental measurements based on scattering parameters.

• Korean Journal of Materials Research
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• v.32 no.4
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• pp.181-185
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• 2022

In this study, phase-pure titanium dioxide TiO₂ ceramics are sintered using standard high-temperature solid-state reaction technique at different temperatures (1,000, 1,100, 1,200, 1,300, 1,400 ℃). The effect of sintering temperature on the densification and impedance properties of TiO₂ ceramics is investigated. The bulk density and average grain size increase with the increase of sintering temperature. Impedance spectroscopy analysis (complex impedance Z^* and complex modulus M^*), performed in a broad frequency range from 100 Hz to 10 MHz, indicates that the TiO₂ ceramics are dielectrically heterogeneous, consisting of grains and grain boundaries. The complex impedance Z^* -plane indicates the resistance of grains of the TiO₂ ceramics increases with increasing sintering temperature, while that of grain boundaries develops in the opposing direction. The complex modulus M^*-plane shows a grain capacitance that seems to be independent of the sintering temperature, while that of the grain boundaries decreases with increasing sintering temperature. These results suggest that different sintering temperatures have effects on the microstructure, leading to changes in the impedance properties of TiO₂ ceramics.

• Corrosion Science and Technology
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• v.3 no.1
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• pp.1-5
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• 2004

A polarization resistance is generally used to estimate the corrosion rate in the corrosion monitoring by an electrochemical impedance method. When the Faradaic impedance has a time constant due to the reaction intermediate, the electrochemical impedance describes more than one loop on the complex plane. For example, the electrochemical impedance of iron in acidic solution shows capacitive and inductive loops on the complex plane. In this case, the charge transfer resistance and the polarization resistance are determined at middle and low frequency ranges, respectively. Which should be selected for corrosion resistance in corrosion monitoring, the charge transfer resistance or the polarization resistance'? In the present paper, the above-mentioned question is examined theoretically and experimentally.

• Restorative Dentistry and Endodontics
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• v.25 no.3
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• pp.359-370
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• 2000

The purpose of this investigation was to observe the viscoelastic properties of five commercial flowable(Aeliteflo, Flow it, Revolution, Tetric flow, Compoglass flow), three conventional hybrid(Z-100, Z-250, P-60) and two condensable(Synergy compact, SureFil) resin composites. A dynamic oscillatory shear test was done to evaluate the storage shear modulus (G'), loss shear modulus(G"), loss tangent(tan ${\delta}$) and complex viscosity(${\eta}^*$) of the resin composites as a function of frequency - dynamic frequency sweep test from 0.01 to 100 rad/s at $25^{\circ}C$ - by using Advanced Rheometric Expansion System(ARES). To investigate the effect on the viscosity of resin composites of filler volume fraction, the filler weight % and volume % were measured by means of Archimedes' principle using a pyknometer. The results were as follows 1. The complex viscosity ${\eta}^*$ of flowable resins was lower than that of hybrid resins and significant differences were observed between brands. The complex viscosity ${\eta}^*$ of condensable resins was higher than that of hybrid resins. The order of complex viscosity ${\eta}^*$ at ${\omega}$=10 rad/s was as follows, Surefil, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it, Revolution. The relative complex viscosity of flowable resins compared to Z-100 was 0.04~0.56 but Surefil was 30.4 times higher than that of Z-100. 2. The storage shear modulus G' and the loss shear modulus G" of flowable resins were lower than those of hybrid resins but those of condensable resins were higher. The patterns of the change of loss tangent, tan ${\delta}$, of resin composites with increasing frequency were significantly different between brands. The phase angles, ${\delta}$, ranged from $30.2{\sim}78.1^{\circ}$ at ${\omega}$=10 rad/s. 3. All composite resins represent pseudoplastic nature with increasing shear rate. 4. The complex shear modulus $G^*$ and the phase angle ${\delta}$ was represented by the frequency domain phasor form, $G^*({\omega})=G^*e^{i{\delta}}=G^*{\angle}{\delta}$. The locus of frequency domain phasor plots in a complex plane was a valuable method that represent the viscoelastic properties of composite resins. 5. There was no direct linear correlationship but a weak positive relation was observed between filler volume % or weight % and the viscosity of the resin composites.

• Journal of the Korean housing association
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• v.8 no.1
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• pp.77-85
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• 1997

The purpose of this study was to estimate the quality if New Town housing environment, and to present the direction of design policy to elevate it. For this study questionnaires were administrated to 272 homemakers living in apartment in Bundang. From 1st of May to 31st of May in 1995. Used statistical method was Frequency. Percentage. Mean, Factor Analysis, Correlation, Multiple Regression. The major finding is as follows : 1) Housing values were classified into five types : convenience, beauty, sociality, education, and economy, Resident ranked first economy among housing values the second is convenience, the third beauty, the forth education, while the most unimportant value is sociality. 2) House satisfaction was classified into four types : house size and plane structure, environment and facilities, interior decoration materials and facilities and building design. Residents were found to show the middle degree satisfaction on their house. 3) Housing complex satisfaction was ciassified four types : community facilities, management stage, neighborhood connection and complex facilities. Resident showed dissatisfaction on their apartment complex relatively. 4) Residents showed dissatisfaction on the interior decoration materials and facilities, local facilities and management attitude relatively.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.134-143
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• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.