• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.1
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• pp.34-42
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• 2003

In this paper, the image restoration process is interpreted as a backward diffusion process and the restored image is given as the solution of the backward diffusion equation (BDF). The ill-posedness of the backward diffusion if subdued by manipulating the exponentially increasing coefficients of the eigenfunctions. In manipulating the coefficients the spectral characteristics of an image is taken into account. The proposed scheme uses an exponentially decreasing function of the coefficients of the eigenfunctions beyond a certain threshold which is optimal with respect to the observation accuracy. The use of decreasing functions also improves the result compared with the constant bounded algorithm since it can include more low frequency components.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.1
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• pp.1-5
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• 2004

A new method for the estimation of pitch-frequency contour of voiced speech is presented. The method is based on the double application of Kaiser's energy operator［1］, which has the capabilities of extracting amplitude and frequency of a sinusoidal waveform. According to the modulation model, a vowel can be represented by a combination of damped sinusoids representing formants, modulated by pitch pulses. Therefore, the amplitude envelope of each of the components will give a pitch-like waveform and the pitch can be obtained by averaging the frequencies of this waveform. The first part is the same as Gopalan's approach［9］, but by substituting the LPC based spectral analysis with the second application of energy operator, the algorithm becomes very simple and can be processed on-line. Although the estimation is rather coarse, the suggested algorithm can be useful for getting a general sketch of pitch contour on-line.

• Korean Journal of Optics and Photonics
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• v.3 no.2
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• pp.123-132
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• 1992

We designed and constructed the Cs beam tube which consists of a Ramsey cavity, four C-field rods, fluorescence detecting systems, and etc. for developing an optically pumped Cs atomic clock. A semiconductor laser was used for optical pumping and probing in the Cs beam. We observed Ramsey resonance signal by detecting the fluorescence signal in the probing region as the microwave frequency injected into the Ramsey cavity was scanned near 9192.6 MHz which corresponds to the "clock transition" of Cs atoms. We found that the linewidth of the Ramsey signal was 200 Hz, the magnetic field intensity was $8.61\muT$ when the current of 0.8A flowed in the C-field rods, and the second order Zeeman shift by the magnetic field was 3.17 Hz.s 3.17 Hz.

• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.457-467
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• 2018

This paper presents performance comparison of several high-resolution frequency estimation algorithms for pure real tone signal. Algorithms are DFT (Discrete Fourier Transform - for reference purpose), Jacobsen, Candan, reassignment and Cedron. Each algorithm is evaluated under various experimental conditions, e.g., different SNR (Signal to Noise Ratio), window function and window length and performance is compared in the perspective of bias, MSE (Mean Square-Error) and variance. Experimental results indicate that Cedron algorithms works well in the most cases. For actual usage in the engineering problem, each algorithm needs additional analysis and modification.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.203-209
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• 2010

In this study, the fatigue characteristics and life of a woven glass fabric/epoxy laminate composite applied to railway vehicles was evaluated. The fatigue test was conducted using a tension-tension load with a stress ratio R of 0.1 and frequency of 5 Hz. Two types of woven glass fabric/epoxy laminate composite was used in the fatigue test: with and without carbon/epoxy ply reinforcement. In addition, the fatigue life of the woven glass fabric/epoxy laminate composite was compared with that of aluminum 6005, which is used in the car body and underframe structures of railway vehicles. The test results showed that the failure strength and life of the woven glass fabric/epoxy laminate composite reinforced with three carbon/epoxy plies had a remarkable improvement compared with that of the bare specimen without reinforcement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.6
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• pp.904-908
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• 2002

In this paper, we propose a 4-coupled ferroelectric-based meander-type microstrip-line tunable phase shifter which has less than 2dB of insertion loss (IL) and larger than 10dB of return loss (RL)over 13~170Hz .Particularly at 15GHz, the differential phase shift (DPS) is observed to be $89{\circ}$ at zero bias and it increases up to $115{\circ}$ when 150V is applied. This indicates a DPS tunability of $26{\circ}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.123-129
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• 2010

In this paper, we analyze the code tracking biases of single and double early-minus-late processing schemes which are widely used code tracking method for global navigation satellite systems. The code tracking bias which results from the distortion in symmetry of correlation values is arisen in the presence of multipath signals. To analyze them, two civil signals which are spreading signals modulated by binary phase shift keying and binary offset carrier are considered.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.258-261
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• 2000

In this paper, the design of Binary FSK Using Cellular Oscillator Network architecture is newly introduced and analyzed. With its easy frequency controllability and MHz range of quadrature signals, the Cellular Oscillator Network can be used in RF communication systems. Binary Frequency Shift Keying can also be implemented through digital loop-path switching. This FSK model is simulated and proved with typical 3V, 0.5$\mu\textrm{m}$ CMOS N-well process parameters.

• Journal of Aerospace System Engineering
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• v.4 no.1
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• pp.19-22
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• 2010

The accuracy and integrity of global navigation satellite systems (GNSS) can be improved by using GNSS augmentation systems. Large ionospheric spatial gradient, during ionosphere storm, is a major threat for using GNSS augmentation systems by increasing the spatial decorrelation between a reference system and users. Ionosphere decorrelation behavior can be analyzed by using dual frequency GPS data. GNSS receivers have their own biases, called inter-frequency bias (IFB) between dual(P1 and P2) frequencies and they must be accurately estimated before computing ionosphere delays. GPS network data in Korea is used to compute each receiver's IFB, and their estimation accuracy and variability are analyzed. IFB estimation methodology to apply for ionosphere gradient analysis is discussed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.215-218
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• 2002

In this paper, we propose a microstrip line tunable phase shifter. If we vary the applied bias voltage, the relative dielectric constant of ferroelectrics also changes and we designed tunable phase shifter using Au/BSTO/MgO/Au structure. We also used a coupling structure to increase the amount of phase shift at certain frequency in a limited size and we could reduce the loss by reducing the line width.