• Restorative Dentistry and Endodontics
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• v.32 no.4
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• pp.385-396
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• 2007

The aims of this study were to compare the shaping effect and safety between single length technique recommended by manufacturer and crown-down technique using Mtwo rotary file and to present a modified method in use of Mtwo file. Sixty simulated root canal resin blocks were used. The canals were divided into three groups according to instrument and the manner of using methods. Each group had 20 specimens. Group MT was instrumented with single length technique of Mtwo, group MC was instrumented with crown-down technique of Mtwo and group PT was instrumented with crown-down technique of ProTaper. All of the rotary files used in this study were operated by an electric motor. The scanned canal images of before and after preparation were superimposed. These superimposed images were evaluated at apical 1 to 8 mm levels Angle changes were calculated. The preparation time, weight loss, instrument failure and binding, canal aberrations, and centering ratio were measured. Statistical analysis of the three experimental groups was performed with ANOVA and Duncan's multiple range tests for post-hoc comparison and Fisher's exact test was done for the frequency comparison. In total preparation time, group MT and group MC were less than group PT. In the aberrations, group MT had more elbows than those of group MC and group PT. The binding of group MC was least and group MT was less than group PT (P < 0.05). Under the condition of this study, crown-down technique using Mtwo rotary file is better and safer method than single length technique recommended by the manufacturer.

• The Journal of Fisheries Business Administration
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• v.35 no.1
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• pp.23-56
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• 2004

The offshore trawl fishery is seeking its survival way to overcome current management conditions in red, resulted from the bilateral agreement with China and Japan. However, this movement magnifies conflicts between fisheries on the contrary and it is thought to be impossible to get over current situations. For all that, this study is aimed at investigating how this current situations have occurred. The management freedom as response to the change in fishing conditions of a certain fishery, in case of Korea, is affected by institutional regulations. The example of this is controls on fishing gears, fishing vessels, and fishing grounds. The most exposure of this control is a segmentation of institutional fisheries. The initial segmentation of the offshore trawl fishery in Korea was occurred in the period of Japan's colonization when the degree of use of fishing grounds was limited geographically. At that time, fisheries were divided by fishing areas, but it did not divide the fishery itself. The large - sized fishing vessels were developed politically to be more competative to Japanese fishing vessels since 1950s. During this time, the trawl fishery was merged into current Eastern trawl fishery and South - Western trawl fishery. It was also inevitable to divide into the pair trawl and single trawl fishery as a result of the physical mergency between Western trawl and Southern trawl fishery. In order to develop the trawl fishery, new licenses were issued on the shrimp trawl fishery, through which it was expected to boost the trawl fishery. As opposed, the shrimp trawl fishery was changed into the mid - sized trawl fishery, targeting on the eastern fishing areas and the large - sized trawl fishery was developed since the late of 1970s with the development of filefish processing industry. The large trawl fishery that led in development of offshore trawl fishery since the late of 1950s was started to divide into a pair trawl and single trawl according to the fishing method and capital power. It finally became an institutionally independent fishery in 1980s, respectively. Looking into these historical process, the segmentation of the trawl fishery is thought as a result of the lack of long - term perspective and as a production of trial and error resulted by unprepared policy. As a result, these segmentation of fisheries roles as critical obstacles in harmonization of fisheries and in overcoming of current situations. Therefore, the review of this institutional segmentation of the offshore trawl fishery should be taken for an optimal redistribution of fishing grounds suits with business and fishing technology. For this, the fishery must be divided into large capitalized fishery and small - mid fishery with consideration of capital, fishing method, and the condition of use of fishing grounds. In addition to this, by limiting outline of fishing ground that the large fishery can harvest, it must allow for the small - mid fishery to catch with its own boundary. Furthermore, by launching buyback programs on the trawl, eastern trawl, pair trawl, it can provide broader fishing grounds where the fishery can harvest with management freedom.

• Journal of Family Resource Management and Policy Review
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• v.25 no.3
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• pp.103-120
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• 2021

Recently, the importance of the fathers role in the care of young children has been emphasized in Korea for the balance of childcare responsibilities between mothers and fathers. This study investigates the trends in paternal childcare in Korea over the last 15 years. Childcare is divided into primary and developmental care and fathers's Childcare time and participation rates are inverstigated for dual- and single-income households. Data are collected from the four waves of the five-yearly Statistics of Korea Life Time Surveys between 2004(t₁) and 2019(t₄) including the workday time diaries of fathers with preschool children(n₁=2,264, n₂=1,242, n₃=959, n₄=952). Three major results are identified. First, paternal childcare time and participation rates have increased with dual-income fathers spending 24 more minutes a day with their young child(ren) in 2019 than in 2004, which is nearly double. Second, in the analysis of fathers' childcare time use and participation rates comparing primary and developmental care, primary care is found to have increased more than developmental care, especially among dual income fathers: this further exhibits a reversed relation between primary and developmental care over time. Third, the determinants of paternal childcare time are fathers' age, market labor time, commuting time, gender equality consciousness, and education. In particular, market labor time was significant in all four waves, while gender equality consciousness is only significant for single-income fathers. Based on these results, a specific agenda is provided for family-friendly policies to improve the balance of childcare roles between fathers and mothers, especially encouraging increased(significant and sufficient) participation of fathers in primary care activities.

• Atmosphere
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• v.28 no.3
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• pp.291-303
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• 2018

In this study, a new consensus technique for predicting tropical cyclone (TC) intensity in the western North Pacific was developed. The most important feature of the present consensus model is to select and combine the guidance numerical models with the best performance in the previous years based on various evaluation criteria and averaging methods. Specifically, the performance of the guidance models was evaluated using both the mean absolute error and the correlation coefficient for each forecast lead time, and the number of the numerical models used for the consensus model was not fixed. In averaging multiple models, both simple and weighted methods are used. These approaches are important because that the performance of the available guidance models differs according to forecast lead time and is changing every year. In particular, this study develops both a multi-consensus model (M-CON), which constructs the best consensus models with the lowest error for each forecast lead time, and a single best consensus model (S-CON) having the lowest 72-hour cumulative mean error, through on training process. The evaluation results of the selected consensus models for the training and forecast periods reveal that the M-CON and S-CON outperform the individual best-performance guidance models. In particular, the M-CON showed the best overall performance, having advantages in the early stages of prediction. This study finally suggests that forecaster needs to use the latest evaluation results of the guidance models every year rather than rely on the well-known accuracy of models for a long time to reduce prediction error.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1215-1220
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• 2004

Reactive distillation (RD) is a combination process where both separation and reaction are considered simultaneously in a single vessel. This kind of combination to enhance the overall performance is not a new attempt in the chemical engineering areas. The recovery of ammonia in the classic Solvay process for soda ash of the 1860s may be cited as probably the first commercial application of RD. The RD system has been used for a long time as a useful process and recently the importance of the RD is enlarged more and more. In addition to that, the application fields of RD are diversely diverged. To make the most of the characteristic of RD system, we must decide the best operating condition under which the process shows the most effective productivity and should decide the best control algorithm which satisfies an optimal operating condition. Phosgene which is a highly reactive chemical is used for the production of isocyanates and polycarbonates. Because it has high reactivity and toxicity, its utilization is increasingly burdened by growing safety measures to be adopted during its production. Dimethyl Carbonate (DMC) was proposed as a substitute of phosgene because it is non-toxic and environmentally benign chemical. In this study, RD is used for DMC production process and the transesterification is performed inside of column to produce DMC. In transesterification, the methanol and ethylene carbonate (EC) are used as the reactants. This process use homogeneous catalyst and the azeotrope exists between the reactant and product. Owing to azeotrope, we should use two distillation columns. For this DMC production process, we can suggest two configurations. One is EC excess process and the other is methanol excess process. From the comparison of steady state simulation results where the Naphtali-Sandholm algorithm is used, it showed the better performance to use the methanol excess process configuration than EC excess process. Then, the dynamic simulation was performed to be based on the steady state simulation results and the optimal control system was designed. In addition to that, the optimal operating condition was suggested from previous results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.11
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• pp.28-33
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• 2002

In this paper, the impedance-tuned monopole microstrip antenna designed for PCS is analyzed using finite difference time domain(FDTD) method. The perfectly matched layer(PML) absorbing material condition proposed by Berenger is used for the truncation of finite difference time domain lattice. A Gaussian pulse is selected as an excitation signal and a resistive voltage source model is used to reduce the error caused by the reflection waves. The FDTD method is inherently a near field technique. Therefore, the near field to far field transformation is need to compute far field antenna parameters such as radiation patterns and gain. The near field to far field transformation can be done both in the time domain and the frequency domain. We use the frequency domain transformation to compute the far field radiation patterns at single frequency. All the numerical results obtained by the FDTD method are compared with simulation results using the HFSS software. Good agreements are obtained in all cases.

• Journal of Broadcast Engineering
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• v.14 no.6
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• pp.807-810
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• 2009

This paper deals with a real-time image based relighting system for tangible video teleconference. The proposed image based relighting system renders the extracted human object using the virtual environmental images. The proposed system can homogenize virtually the lighting environments of remote users on the video teleconference, or render the humans like they are in the virtual places. To realize the video teleconference, the paper obtains the 3D object models of users in real-time using the controlled lighting system. In this paper, we use single color camera and synchronized two directional flash lights. Proposed system generates pure shading images using on and off flash images subtraction. One pure shading reflectance map generates a directional normal map from multiplication of each reflectance map and basic normal vector map. Each directional basic normal map is generated by inner vector calculation of incident light vector and camera viewing vector. And the basic normal vector means a basis component of real surface normal vector. The proposed system enables the users to immerse video teleconference just as they are in the virtual environments.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.75.2-76
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• 2021

MESSIER is a science satellite project to observe the Low Surface Brightness (LSB) sky at UV and optical wavelengths. The wide-field, optical system of MESSIER is optimized minimizing optical aberrations through the use of a Linear Astigmatism Free - Three Mirror System (LAF-TMS) combined with freeform mirrors. One of the key factors in observations of the LSB is the shape and spatial variability of the Point Spread Function (PSF) produced by scatterings and diffraction effects within the optical system and beyond (baffle). To assess the various factors affecting the PSF in this design, we use PhoSim, the Photon simulator, which is a fast photon Monte Carlo code designed to include all these effects, and also atmospheric effects (for ground-based telescopes) and phenomena occurring inside of the sensor. PhoSim provides very realistic simulations results and is suitable for simulations of very weak signals. Before the application to the MESSIER optics system, PhoSim had not been validated for confocal off-axis reflective optics (LAF-TMS). As a verification study for the LAF-TMS design, we apply Phosim sequentially. First, we use a single parabolic mirror system and compare the PSF results of the central field with the results from Zemax, CODE V, and the theoretical Airy pattern. We then test a confocal off-axis Cassegrain system and check PhoSim through cross-validation with CODE V. At the same time, we describe the shapes of the freeform mirrors with XY and Zernike polynomials. Finally, we will analyze the LAF-TMS design for the MESSIER optical system.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.10
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• pp.47-53
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• 2012

Time-reversal (TR) precoding focuses the energy of the effective channel in time and improves receive performance of a single tap receiver. Frequency-domain equal-gain-combining (FD-EGC) TR scheme, which works in linear block precoding fashion, has better temporal focusing performance than the traditional TR. Also, the FD-EGC improves receive performance of minimum mean square error receiver with distributed antenna systems (DAS). The detailed receive performance of the FD-EGC was analyzed in our previous work. In this paper, we focused on capacity analysis of the FD-EGC in DAS. We derived a scaling law which shows how the use of multiple antenna can increase the capacity of the FD-EGC precoding compared with that of no precoding. In addition, we analyze the secrecy rate of the FD-EGC which shows how high-rate messages can be transmitted towards an intended user without being decoded by the other users from the view point of information theoretic security.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.43-50
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• 2020

We have developed an algorithm for tracking coronal mass ejection (CME) propagation that allows us to estimate CME speed and its arrival time at Earth. The algorithm may be used either to forecast the CME's arrival on the day of the forecast or to update the CME tracking information for the next day's forecast. In our case study, we successfully tracked CME propagation using the algorithm based on g-values of interplanetary scintillation (IPS) observation provided by the Institute for Space-Earth Environmental Research (ISEE). We were able to forecast the arrival time (Δt = 0.30 h) and speed (Δv = 20 km/s) of a CME event on October 2, 2000. From the CME-interplanetary CME (ICME) pairs provided by Cane & Richardson (2003), we selected 50 events to evaluate the algorithm's forecast capability. Average errors for arrival time and speed were 11.14 h and 310 km/s, respectively. Results demonstrated that g-values obtained continuously from any single station observation were able to be used as a proxy for CME speed. Therefore, our algorithm may give stable daily forecasts of CME position and speed during propagation in the region of 0.2-1 AU using the IPS g-values, even if IPS velocity observations are insufficient. We expect that this algorithm may be widely accepted for use in space weather forecasting in the near future.