• Tunnel and Underground Space
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• v.16 no.1 s.60
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• pp.58-72
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• 2006

In recent years, not only the occurrences but the magnitude of earthquakes in Korea are on an increasing trend and other sources of dynamic events including large-scale construction, operation of hi띤-speed railway and explosives blasting have been increasing. Besides, the probability of exposure fir rock joints to free faces gets higher as the scale of rock mass structures becomes larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, a shaking table test system was set up and a series of dynamic test was carried out to examine the dynamic frictional behavior of rock joints. In addition, a computer program was developed, which calculated the acceleration and deformation of the sliding block theoretically based on Newmark sliding block procedure. The static friction angle was back-calculated by measuring yield acceleration at the onset of slide. The dynamic friction angle was estimated by closely approximating the experimental results to the program-simulated responses. As a result of dynamic testing, the static friction angle at the onset of slide as well as the dynamic friction angle during sliding were estimated to be significantly lower than tilt angle. The difference between the tilt angle and the static friction angle was $4.5\~8.2^{\circ}$ and the difference between the tilt angle and the dynamic friction angle was $2.0\~7.5^{\circ}$. The decreasing trend was influenced by the magnitude of the base acceleration and inclination angle. A DEM program was used to simulate the shaking table test and the result well simulated the experimental behavior. Friction angles obtained by shaking table test were significantly lower than basic friction angle by direct shear test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.109-118
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• 2005

A concrete shear wall system is commonly adopted in high-rise residential apartment buildings. In the construction stage, a rectangular opening is often made for the convenience of horizontal movement of workers, and construction materials and equipment. In the case of safety or stability assessment of a shear wall, the cutout part can be a critical factor. Finite element method is adopted to investigate the elastic stability behavior of the perforated unit shear wall. The key analysis parameters are the cutout location and its size. The effect of out-of-plane bending and horizontal shear are also examined in the stability analysis.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.39-48
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• 2004

Turbo codes, whose performance in bit error rate is close to the Shannon limit, have been adopted as a part of standard for the third-generation high-speed wireless data services. Iterative Turbo decoding results in decoding delay and high power consumption. As wireless communication systems can only use limited power supply, low power design techniques are essential for mobile device implementation. This paper proposes new effective criteria for stopping the iteration process in turbo decoding to reduce power consumption. By setting two stopping criteria, decodable threshold and undecodable threshold, we can effectively reduce the number of decoding iterations with only negligible error-correcting performance degradation. Simulation results show that the number of unsuccessful error-correction can be reduced by 89% and the number of decoding iterations can be reduced by 29% on the average among 12500 simulations when compared with those of an existing typical method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.10
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• pp.653-658
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• 2016

A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.1-11
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• 2018

Sound propagation in shallow water changes from spherical spreading to cylindrical spreading, depending on boundary conditions, and this point is defined as a transition point of the sound propagation condition. Theoretically, the transition point can be estimated using the transmission loss as a function of source-receiver range. In this paper, the transmission loss curve in a Pekeris waveguide is predicted using a parabolic-equation based acoustic propagation model and using this transmission loss curve, the range from the source of the transition point is estimated, which is compared to the critical distance calculated using the sound speed ratio of water to sediment. In addition, the effects of the sound speed profile and source depth change on the transition point are investigated. Finally, the transition point is estimated using the transmission loss data measured during the period of the SAVEX15 (Shallow Water Acoustic Variability EXperiment 2015) conducted 65 km southwest of Jeju Island in May 2015, and it is compared to the ocean environmental parameters to understand the properties of sound propagation in the experimental area.

• Journal of Korea Multimedia Society
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• v.11 no.1
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• pp.13-22
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• 2008

This paper proposes an efficient ROI code block discrimination algorithm for dynamic ROI coding. The proposed algorithm calculates the girth of the ROI only with some mask information in consideration of the characteristics of the shape of the ROI for reducing a ROI code block discrimination time, and this proposed algorithm discriminates whether there is a ROI code block by the girth and the critical value of the ROI. Also, this discrimination algorithm is capable of treating the coefficients of the background within a ROI code block preferentially and controlling a loss by controlling the threshold value of the ROI. In order to demonstrate the utility of the proposed method, this paper conducted a comparative experiment of the proposed method with the existing methods. As a result of this experiment, it was confirmed that the proposed method was superior to the conventional methods in terms of quality and speed.

• Nuclear Engineering and Technology
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• v.18 no.1
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• pp.17-26
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• 1986

A test is made for a method to determine reliable bias in the criticality safety analysis of spent fuel storage pool with turnup credit between the reference and rack criticality calculation methods. The spent fuel pool of Kori Unit 1 is conceptually redesigned to the most compact rack with turnup credit, and its multiplication factors are calculated depending on fuel enrichment and burnup, by the Monte Carlo code KENO-IV as a reference and by a two-dimensional collision probability code FATAC as a practical method. Then, the computed values with the help of the above two computer codes are compared to evaluate the bias and its trend in terms of multiplication factor on fuel enrichment and turnup. The result indicates that the bias can be determined with reliability basis but without any disadvantage in criticality safety margin compared with the conventional method.

• Geophysics and Geophysical Exploration
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• v.10 no.2
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• pp.124-130
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• 2007

Least squares ($l^2$ norm) solutions of seismic inversion tend to be very sensitive to data points with large errors. The $l^1$ norm minimization gives more robust solutions, but usually with higher computational cost. Iteratively reweighted least squares (IRLS) method gives efficient approximate solutions of these $l^1$ norm problems. I propose an efficient implementation of the IRLS method for a hybrid $l^1/l^2$ minimization problem that behaves as $l^2$ norm fit for small residual and $l^1$ norm fit for large residuals. The proposed algorithm shows more robust characteristics to the decision of the threshold value than the l1 norm IRLS inversion does with respect to the threshold value to avoid singularity.

• Journal of the Korea Society of Computer and Information
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• v.12 no.5
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• pp.39-47
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• 2007

In this thesis, a method of generating an adaptable Region-Of-Interest(ROI) Mask for the Region-Of-Interest coding is suggested. In the method, an ROI Mask is generated using the information of the ROI designated by a user. In the existed method of ROI coding, after scanning all the pixels in order and discriminating an ROI, an ROI Mask is generated. But, in our method, after scanning a part of pixels based on the shape pattern of an ROI and discriminating a ROI by one code block unit, an ROI Mask is generated. Moreover, from the method, a pattern number, threshold of a ROI and background threshold parameter are provided. According to the result of its comparing test with the existed methods to show the usability, it is proved that our method is superior in speed to the existed ones.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.151-157
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• 1993

Abstract We have fabricated Y-Ba-Cu-O superconducting thin films by in-situ on-axis rf magnetron sputtering method using $Y_1$B$a_2$C${u_4}\;{_2O_x}$ nonstoichiometric target. Reactive ion etching (RIE) method was used in patterning the films. We have investigated the properties of patterned films, and compared the properties of the films before and after patterning. As the line width of the pattern decreases from 5${\mu}$m to 2${\mu}$m, a slight but not significant degradation in superconducting properties of the patterned films is observed. The bridge patterns are found to have clean edges and good electrical properties enough to be applied in device applications. From the result of this research, the possibility of submicron patterning by RlE is confirmed.