• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.125-126
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• 2007

In this paper, we analyze the channel estimation performances associated with the interpolation order for OFDM systems. We first analyze the time varying channel and frequency selective channel, and then we derive the channel Index which indicates the ratio of time axis variation and frequency axis variation. The analyzed results show that time interpolation followed by a frequency interpolation is adequate for the channel with a channel index larger than a certain threshold value and vice versa. Computer simulation explains that the method which decides Interpolation order outperforms fixed order estimation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.4
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• pp.1059-1067
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• 1996

A 128/129 dual-modulus prescalar IC is designed for application to frequency synthesizers in high frequency communication systems. The FET logic used in this design is SCFL(Source Coupled FET Logic), employing depletion-mode 1.mu.m gate length GaAs MESFETs with the threshold voltage of -1.5V. This circuit consists of 8 flip-flops, 3 OR gates, 2 NOR gates, a modulus control buffer and I/O buffers, which are integrated with about 440 GaAs MESFETs on dimensions of 1.8mm. For $V_{DD}$ and $V_{SS}$ power supply voltages 5V and -3.3V Commonly used in TTL and ECL circuits are determined, respectively. The simulation results taking into account the threshold voltage variation of .+-.0.2V and the power supply variation of .+-.1V demonstrate that the designed prescalar can operate up to 2GHz. This prescalar is fabricated using the ETRI MMIC foundary process and the measured maximum operating frquency is 621MHz.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1000-1002
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• 2003

The characteristics of eddy current sensor has been analyzed by using numerical analysis which is performed by modeling eddy current sensor and analytic object into three-dimension axis-symmetry in this paper. The eddy current sensor is modeled as cylindrical shape with variation of inside and outside diameter and frequency range between 1[kHz] and 1[MHa] for numerical analysis. The value of impendence on eddy current sensor depending on frequency variation was calculated through numerical analysis. The characteristics of eddy current sensor can be studied by normalized impendence which is gained from the calculated impendence. Therefore, sensitivity of eddy current sensor depending on frequency, inside and outside diameter can be known by investigating diameter of half circle impendence and its locus.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1303-1305
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• 2005

This paper deals with the impedance modeling and frequency response of moving-magnet linear actuator considering mass/spring system. By expressing mechanical components as electrical components such as impedance from the motion equation, this paper investigates not only the variation of system impedance according to system parameters such as moving mass, thrust constant, the coefficient of elasticity for spring and damping coefficient but also the variation of power vs. frequency for moving-magnet linear actuator with spring.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.349-354
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• 2001

A structure which is accelerated in the chordwise direction induces variation of the bending stiffness due to inertia force. Thus, the characteristic of natural vibration is also changed. This paper presents a modeling method for the vibration analysis of translationally accelerated cantilever plates. The dependence of natural frequencies and modes on the acceleration changes of the plate is investigated. Particularly, a natural frequency loci veering is observed and discussed in the present study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.338-344
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• 1996

In this paper, a semi-active suspension adapting to road variation which also considers the frequency snesitivity of human is proposed. First, a road adapting controller composed of system identification and LQG control is designed. Using the extended least squares method, the road property is estimated by system identification as it varies, and the LQG controller considering the estimated road property and the frequency sensitivity of human is designed. Next, the semi-active suspension is made, which tracks the performance of the active suspension with the road adapting controller. Through numerical simulation, the performance of the proposed semi-active suspension is compared with that of a non-adaptive semi-active suspension with frequency-shaped performance index. As a result, we see that the road adapting semi-active suspension has better performance.

• Journal of the Korea Furniture Society
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• v.16 no.1
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• pp.17-23
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• 2005

European maple is famous for the optimum solid wood for making bridge which is the most important part in violin acoustics. This study was carried out to investigate the variation of main features, i. e. annual ring width and cutting direction of costly imported violin bridge blanks and to examine the effect of these features of the blanks on the vibrational characteristics of bridge blanks. Imported violin bridge blanks had somewhat large variation in major macroscopical and physical properties and there was little relationship between annual ring density and weight of maple blanks. Resonant frequency of violin bridge blanks had some positive correlation with weight, however, damping having negative relationship with frequency was seldom affected by any physical properties of the maple blanks. Deviation from the radial cutting of tail side(ray direction from top toward feet on the edge of bridge blank) lowered the resonant frequency. Consequently, weight and ray direction should be taken for the critical quality decisive factors(QDF) of incoming bridge blanks by not only inspectors also luthiers who tune the bridge by shaping and are responsible for the final timbre quality of this complicate instrument.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.46-51
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• 2004

The cause for the variation of the initial permeability according to the Co substitution of Ni-Zn ferrite used in the LC resonance filter for the power line communication is studied. The initial permeability decreases as the quantity of Co diminishes, and the saturation magnetization increases as the quantity increases. Because the sintering density and the microstructure of ferrite show little change, the variation of the initial permeability can't be explained by the density, microstructure nor the saturation magnetization factor. The magnetocrystalline anisotropy increases, similar with the saturation magnetization, as the quantity of Co increases. The increase of magnetocrystalline anisotropy value makes the domain wall energy grow, which leads to the decrease of the initial permeability, because there's linear law between the magnetocrystalline anisotropy and the domain wall energy. The resonance frequency to Co substitution moved to high frequency band, due to the close relationship with domain wall energy, Initial permeability decreaed a little with an increase of Co contents, but resonace frequency moved to high frequency band. as a result of that, when Co was added 0.05 mol, initial permeability and resonace frequency was 75 and 25 MHz respectively.

• Journal of computational fluids engineering
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• v.20 no.1
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• pp.16-25
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• 2015

The present study investigates the sloshing phenomena in a two-dimensional rectangular tank at a low filling level by using a level set method based on finite volume method. The code validations are performed by comparing between the present results and previous numerical and experimental results, which gives a good agreement. Various excitation frequencies and excitation amplitude of the 30% filling height tank have been considered in order to observe the dependence of the sloshing behavior on the excitation frequency and amplitude. Regardless of excitation amplitude, the maximum value of wall pressure occurs when the excitation frequency reaches the natural frequency. The time sequence of free surface and corresponding streamlines for excitation frequencies have been presented to analysis the variation of wall pressure according to time, which contributes to explain the double peaks in the time variation of wall pressure.

• The Journal of the Acoustical Society of Korea
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• v.15 no.5
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• pp.118-124
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• 1996

Signal frequency lines generated from the acoustic targets are of particular importance for target detection and classification in passive sonar systems. The underwater noise consists of a mixture of ambient noise and radiated noise of targets. Detction of exact signal frequency lines depends on signal detection threshold and variation of ambient noise. In this paper, a detection method of signal frequency lines for acoustic targets using autoassociative memory (ASM) neural network, which is not sensitive to variation of signal detection threshold and ambient noise, is proposed. It is confirmed by simulation and application of real acoustic targets that the proposed method shows good performance for detection of signal frequency lines.