• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.1
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• pp.15-20
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• 2014

In this research, the geopolymer was fabricated using municipal solid waste incineration ash (denoted as MSWIA) slag and alkali activator, NaOH and its properties were analyzed. Particularly, the effects of NaOH molarity, particle size of MSWIA, and liquid/solids ratio on the compressive strength of geopolymers were investigated. The compressive strength of geopolymers fabricated increased with finer grain size of MSWIA, and optimum value of the liquid/solids ratio was identified as 0.13. As the molarity of the NaOH increased, the compressive strength of geopolymers was increased. Even more the 20 M of NaOH, but the strength was not increased. The calcium aluminum silicate and calcium aluminum silicate hydrate zeolites were generated in the geopolymer fabricated with more than 20 M of NaOH, with some unreacted silica and unknown crystals remained. The highest compressive strength, 163 MPa, of geopolymer was appeared at conditions of curing temperature $70^{\circ}C$, and 20 M of NaOH, indicating that the high concentration of NaOH accelerates the geopolymer reaction and dense microstructure. The high-strength geopolymer fabricated in the present study is expected to contribute significantly to develop the field of cement alternative substances and to improve the recycling rate of MSWIA slag.

• Journal of Korea Water Resources Association
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• v.46 no.10
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• pp.977-987
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• 2013

This study aims to develop a multiple criteria decision making (MCDM) approach for flood vulnerability assessment which considers uncertainty. The flood vulnerability assessment procedure consists of three steps: (1) use the Delphi process to determine the criteria and their corresponding weights-the adopted criteria represent the social, economic, and environmental circumstances related to floods, (2) construct a fuzzy data matrix for the flood vulnerability criteria using fuzzification and standardization, and (3) set priorities based on the number of assessed vulnerabilities. This study uses a modified fuzzy TOPSIS method based on ${\alpha}$-level sets which considers various uncertainties related to weight derivation and crisp data aggregation. Further, Spearman's rank correlation analysis is used to compare the rankings obtained using the proposed method with those obtained using fuzzy TOPSIS with fuzzy data, TOPSIS, and WSM methods with crisp data. The fuzzy TOPSIS method based on ${\alpha}$-cut level sets is found to have a higher correlation rate than the other methods, and thus, it can reduce the difference of the rankings which uses crisp and fuzzy data. Thus, the proposed flood vulnerability assessment method can effectively support flood management policies.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.109-112
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• 2008

In this study, Assessment of bond property of HSC with the rate of Blust-furnace(0, 12, and 25 percent by weight cement) and Evaluation of the relationship of the compressive strength coefficient (${\beta}$) between compressive strength with 40${\sim}$120MPa were performed. Design and Test of Bond specimens were carried out based on the ASTM C-234. Test results are follows, most specimens showed that the splitting failure in all specimens, except for B-40 series which showed that the pull-out failure. For the B-40 Series, the relation of compressive strength versus bond stress has well converged that of the proposed equation with the variation(${\beta}$=2/3) in UCB/E.E.R.C-83. The crack strength of concrete in splitting was proportioned to the compressive strength of concrete, and was the highest on the contents of blast furnace slag to 12 percent by weight of cement in each series, except for B-60 series. In the relation of admixture replacement rate versus maximum bond stress, The maximum bond stress was the highest in 12 percent by weight of cement according to less than 40MPa, and was the highest in 25 percent by weight of cement according to 80MPa.

• Journal of Korean Association for Spatial Structures
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• v.6 no.4 s.22
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• pp.81-92
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• 2006

This paper presents exact solutions for the free vibrations and buckling of rectangular plates having two opposite, simply supported edges subjected to linearly varying normal stresses causing pure in-plane moments, the other two edges being free. Assuming displacement functions which are sinusoidal in the direction of loading (x), the simply supported edge conditions are satisfied exactly. With this the differential equation of motion for the plate is reduced to an ordinary one having variable coefficients (in y). This equation is solved exactly by assuming power series in y and obtaining its proper coefficients (the method of Frobenius). Applying the free edge boundary conditions at y=0, b yields a fourth order characteristic determinant for the critical buckling moments and vibration frequencies. Convergence of the series is studied carefully. Numerical results are obtained for the critical buckling moments and some of their associated mode shapes. Comparisons are made with known results from less accurate one-dimensional beam theory. Free vibration frequency and mode shape results are also presented. Because the buckling and frequency parameters depend upon Poisson's ratio ( V ), results are shown for $0{\leq}v{\leq}0.5$, valid for isotropic materials.

• Korean Journal of Social Welfare
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• v.61 no.2
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• pp.107-135
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• 2009

The purpose of this study is to develop and evaluate the Korean version of the SERVPERF which has been widely used in order to measure service quality in various kinds of fields including social work. A total of 328 adults using social welfare centers in Seoul and Gyeonggi-do participated in this study. Confirmatory factor analysis confirmed that the Korean version of the SERVPERF consists of 5 dimensions(tangibles, reliability, responsiveness, assurance, and empathy) like the original SERVPERF. 5 dimensions of the Korean version of the SERVPERF have acceptable levels of internal consistency. Its convergent validity and discriminant validity are satisfactory. Finally, weak or non-significant correlations between 5 dimensions of the Korean version of the SERVPERF and social desirability scale indicated that the participants' reponses to the Korean version of the SERVPERF were not affected by social desirability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1123-1129
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• 2015

A pair of two-way valves typically is used in automotive washing machines, where the water flow direction is frequently reversed and highly pressurized clean water is sprayed to remove the oil and dirt remaining on machined engine and transmission blocks. Although this valve system has been widely used because of its competitive price, its application is sometimes restricted by surging effects, such as pressure ripples occurring in rapid changes in water flow caused by inaccurate valve control. As an alternative, one three-way reversing valve can replace the valve system because it provides rapid and accurate changes to the water flow direction without any precise control device. However, a cavitation effect occurs because of the complicated bottom plug shape of the valve. In this study, the cavitation index and percent of cavitation (POC) were introduced to numerically evaluate fluid flows via computational fluid dynamics (CFD) analysis. To reduce the cavitation effect generated by the bottom plug, the optimal shape design was carried out through a parametric study, in which a simple computer-aided engineering (CAE) model was applied to avoid time-consuming CFD analysis and difficulties in achieving convergence. The optimal shape design process using full factorial design of experiments (DOEs) and an artificial neural network meta-model yielded the optimal waist and tail length of the bottom plug with a POC value of less than 30%, which meets the requirement of no cavitation occurrence. The optimal waist length, tail length and POC value were found to 6.42 mm, 6.96 mm and 27%, respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.4
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• pp.17-24
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• 2009

This paper deals with the cancellation performance of loop back interference signal in the case of multihop relay of 16-QAM received signal at the USN radio network. For this, it is necessary to the exchange of information with long distance located station by means of the relay function between the node in the USN environment. In the relay node, the loop-back interference signal which the retransmitting signal is feedback to the receiver side due to the antenna of transmitter and receiver are co-used or very colsely located or using the nonlinear device. Due to this signal, the performance of USN system are degraded which are using the limited resource of frequency and power. For improve this, it is necessary to applying the adaptive signal processing algorithm in order to cancellating the unwanted loop-back interference signal at the frontend of receiver in relaying node, we can get the better system and multi hop performance. In the adaptive signal processing, we considered the 16-QAM signal which has a good spectral efficiency, firstly, than, the QR-Array RLS algorithm was used that has a fairly good convergence property and the solving the finite length problem in the H/W implementation. Finaly, we confirmed that the good elimination performanc was confirmed by computer simulation in the learing cuved and received signal constellation compared to the conventional RLS.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.363-376
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• 2011

1-D hydrodynamic numerical models have been most widely used in the field of flood analysis. The model's input data are upstream/downstream boundaries, roughness coefficients, cross-sections, and so on, and computational distance step and time step are the most important factors in order to guarantee the computational accuracy, stability, and efficiency. In this study, a theoretical explanation is presented for the basis of the previous empirical selection criteria of cross-section's location; also, the estimation technique of computationally variable distance step is proposed to reflect the properties of flow at every computational time step. Combining this technique with 1-D unsteady numerical model, it was applied to two events of Teton dam failure flood and the Han River flood. The numerical experimental results demonstrate that the accuracy and stability is increased when used more interpolated cross-sections and show that the proposed technique of computationally variable distance step has the same order of accuracy with smaller numbers of cross-section than previous empirical selection criteria. The practical use of this technique will be possible to analyze the river floods with high efficiency as well as accuracy and stability.

• Journal of Gifted/Talented Education
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• v.22 no.2
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• pp.427-450
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• 2012

This study was intended to develop a self-report wisdom scale for the elementary gifted students. For this, related literature was reviewed in depth and open ended questionnaire about the wisdom qualities was conducted. Based on these, a self-report wisdom scale, which was comprised of 42 items in 4 factors such as the situation judgment and problem-solving ability, the communication ability and skills, the emotional stability, the insight and adaptation, was developed. For this preliminary scale, 215 elementary gifted students were surveyed. And for the confirmatory factor analysis, 256 elementary gifted students participated. The results of the study were as follows. The fit of measurement model was found to be ${\chi}^2$=1596.46 (df=813, p=.00), TLI .90, CFI .91, RMSEA .046, indicating most of fit indexes were acceptable. The reliability for each of 42-item by the sub-factors also appeared to be good, showing that internal consistency reliability by the configuration factors was 0.86, .87, .89, .87 each relatively. In addition, to verify the validity of the wisdom scale, the convergent and discriminate validities were obtained through the correlation analysis among the psychological characteristics which were considered to be related to the wisdom. Finally, practical implications of the study were discussed in depth.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.3
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• pp.211-222
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• 2020

The purpose of this study is to derive a plan to improve the standard of survey cost, which is a system for estimating survey cost operated by the National Geographic Information Institute. The current standard has not been revised significantly since the initial enactment. However, in the situation where the survey industry is getting worse, the actualization of the standard is an urgent task for training engineers and industrial development. In this study, in order to break the problems of the standard and to derive improvement plan, we analyzed the outline, basic characteristics, and history of the standard and compared it with similar domestic ones. We collected opinions from the government and the industry through a survey, and verified labor cost and overhead rates. The conclusions are as follows. First, it is necessary to complement standard for production rate that directly affects direct cost, and to compensate for the missing items in the direct cost. Second, when compared with cost standards in foreign countries and cadastre field, the labor cost in survey field was found to be very low and improvement is needed. Third, the overhead rates were assessed to be appropriate, and the problem of improper overhead design should be coped with by strengthening education and promotion. Fourth, it is necessary to consider the introduction of deliberation committee or standard market price system for rapid response to new technologies.