• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.618-622
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• 2017

Gasoline is a widely used product as a source for energy in homes, the automotive industry, and for industrial power generation, and it is also a product with a high risk of fire and explosion. In this study, to examine the risk for explosion for gasoline, PG, MG and RG, which are categorized according to octane number, were used as test specimens to measure their explosion limit according changes in oxygen concentration. The explosion limit for 21% oxygen concentration in air were confirmed to be 1.5~10.9%, 1.4~8.1%, and 1.3~7.6%, respectively, and the MOC for each of the test sample were confirmed to be 10.9%. The explosion limit measured in the test performed in this study confirmed between a 1.2%~7.6% wider explosion limit for the currently accepted MSDS for gasoline, and therefore it is considered that the results of this study can provide significant reference for preventing fires and explosions for process used gasoline.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.68-73
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• 2018

Substitution of hip and knee joints by CoCr alloys is in great demand due to their high wear resistance and good biocompatibility. Understanding of tribocorrosion in joint replacements requires study of variables such as coefficient of friction and the choice of a proper corrosive medium in wear-corrosion tests carried out in the lab. The objective of this study was to characterize tribocorrosion behaviour of CoCr alloy with low (LCCoCr) and high carbon (HCCoCr) contents in several corrosive media: NaCl, Phosphate Buffer Solution (PBS), and PBS with hyaluronic acid (PBS-HA). Tribocorrosion tests were carried out on a pin-on-disk tribometer with an integrated electrochemical cell. A normal load of 5N was applied on the alumina ball counterpart at a rotation rate of 120 rpm. Coefficient of friction (COF) was measured and tribocorrosion behaviour was characterized by in situ application of electrochemical techniques. HCCoCr alloy immersed in PBS-HA showed the best tribocorrosion behaviour with the lowest COF. In this case, in situ measurement of corrosion potential and the impedance data under wear corrosion process showed an active state while passive film was continuously destroyed without possibility of regeneration.

• Smart Structures and Systems
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• v.21 no.4
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• pp.435-448
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• 2018

This paper reports the development of a theoretically rigorous method for permanent way engineers to assess the condition of railway ballast under a concrete sleeper with the potential to be extended to a smart system for long-term health monitoring of railway ballast. Owing to the uncertainties induced by the problems of modeling error and measurement noise, the Bayesian approach was followed in the development. After the selection of the most plausible model class for describing the damage status of the rail-sleeper-ballast system, Bayesian model updating is adopted to calculate the posterior PDF of the ballast stiffness at various regions under the sleeper. An obvious drop in ballast stiffness at a region under the sleeper is an evidence of ballast damage. In model updating, the model that can minimize the discrepancy between the measured and model-predicted modal parameters can be considered as the most probable model for calculating the posterior PDF under the Bayesian framework. To address the problems of non-uniqueness and local minima in the model updating process, a two-stage hybrid optimization method was developed. The modified evolutionary algorithm was developed in the first stage to identify the important regions in the parameter space and resulting in a set of initial trials for deterministic optimization to locate all most probable models in the second stage. The proposed methodology was numerically and experimentally verified. Using the identified model, a series of comprehensive numerical case studies was carried out to investigate the effects of data quantity and quality on the results of ballast damage detection. Difficulties to be overcome before the proposed method can be extended to a long-term ballast monitoring system are discussed in the conclusion.

• Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.337-348
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• 2016

An experimental approach is presented for the measurement of wear that is common in the threading of cold-forged steel. In this work, the first objective is to measure wear on various types of roll taps manufactured to tapping holes in microalloyed HR45 steel. Different geometries and levels of wear are tested and measured. Taking their geometry as the critical factor, the types of forming tap with the least wear and the best performance are identified. Abrasive wear was observed on the forming lobes. A higher number of lobes in the chamber zone and around the nominal diameter meant a more uniform load distribution and a more gradual forming process. A second objective is to identify the most accurate data-mining technique for the prediction of form-tap wear. Different data-mining techniques are tested to select the most accurate one: from standard versions such as Multilayer Perceptrons, Support Vector Machines and Regression Trees to the most recent ones such as Rotation Forest ensembles and Iterated Bagging ensembles. The best results were obtained with ensembles of Rotation Forest with unpruned Regression Trees as base regressors that reduced the RMS error of the best-tested baseline technique for the lower length output by 33%, and Additive Regression with unpruned M5P as base regressors that reduced the RMS errors of the linear fit for the upper and total lengths by 25% and 39%, respectively. However, the lower length was statistically more difficult to model in Additive Regression than in Rotation Forest. Rotation Forest with unpruned Regression Trees as base regressors therefore appeared to be the most suitable regressor for the modeling of this industrial problem.

• Atmosphere
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• v.25 no.1
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• pp.19-30
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• 2015

The Ka-band cloud radar (KCR) has been operated by the National Institute of Meteorological Research (NIMR) of Korea Meteorological Administration (KMA) at Boseong National Center for Intensive Observation of severe weather since 2013. Evaluation of data quality is an essential process to further analyze cloud information. In this study, we estimate the measurement error and the sampling uncertainty to evaluate data quality. By using vertically pointing data, the statistical uncertainty is obtained by calculating the standard deviation of each radar parameter. The statistical uncertainties decrease as functions of sampling number. The statistical uncertainties of horizontal and vertical reflectivities are identical (0.28 dB). On the other hand, the statistical uncertainties of Doppler velocity (spectrum width) are 2.2 times (1.6 times) larger at the vertical channel. The reflectivity calibration of KCR is also performed using X-band vertically pointing radar (VertiX) and 2-dimensional video disdrometer (2DVD). Since the monitoring of calibration values is useful to evaluate radar condition, the variation of calibration is monitored for five rain events. The average of calibration bias is 10.77 dBZ and standard deviation is 3.69 dB. Finally, the statistical characteristics of cloud properties have been investigated during two months in autumn using calibrated reflectivity. The percentage of clouds is about 26% and 16% on September to October. However, further analyses are required to derive general characteristics of autumn cloud in Korea.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.9
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• pp.1837-1845
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• 2015

The longitudinal velocity is necessary for accurate vehicular positioning in urban environment. The pitch angle, which is a road slope, should be calculated to acquire the longitudinal velocity. However, it is impossible to consider very accurate pitch, when using a sensor and an algorithm. That's why process noise and positioning stimation error of IMU should be adjusted to the driving environment and fuse GPS, OBD data with ACF which consist of AKF, CF in this paper. Then, final pitch angle which is appropriate for driving environment is estimated by IMMKF in order to optimize the system model according to road slope models.

• Journal of Information Technology Services
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• v.17 no.3
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• pp.117-138
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• 2018

The purpose of this study is to empirically analyze the relationships between the Boundary Spanning Activities (BSA) of project team and system performance in ERP system development projects. We could theoretically classify the BSA in the ERP development projects into five categories on the basis of existing studies on the BSA in the research fields of organization theory, new product development, and information systems development. These five categories are 'Ambassador' activities, 'Task-coordinator' activities, 'Scout' activities, 'Sentry' activities and 'Guard' activities. And the relationship between the implementation level of activities included in each category and the project performance (system usage and users' satisfaction) was hypothesized with respect to five BSA categories. In order to test the hypotheses, we conducted on/offline survey of the participants who were involved in the ERP system development projects, and received 345 valid responses. The unit of analysis was the project team, and the total number of teams that survey participants belonged to were 103 ones. The Structural Equation Model Analysis using the SMART PLS 3.0 was applied to statistically testing the hypotheses. The results showed that 10 hypotheses among 12 hypotheses could be supported. The theoretical implications of this study can be summarized as following; first, redefining and categorizing the BSA (Boundary Spanning Activities) in the ERP system development projects, secondly, deriving measurement indicators of the implementation level for each BSA category and statistically proving the validity and the reliability of them, and finally, suggesting the theoretical background of expanding the management area of ERP systems development projects. Furthermore, the practical implication of this study is that concrete BSA items which are empirically derived can be utilized as effective guidelines for successfully implementing the BSA in the process of managing the ERP system development projects.

• Membrane and Water Treatment
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• v.11 no.3
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• pp.207-215
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• 2020

Vivianite (Fe₃²⁺(PO₄)2·8H₂O) and green rust ([Fe₄²⁺Fe₂³⁺(OH)^-₁₂][SO₄^2-·2H₂O]^2-), ferrous containing minerals, could remove aqueous U(VI) in 5 min. and the efficiencies of green rust were roughly 2 times higher than that of vivianite. The zeta potential measurement results implies that the better performance of green rust might be attributed to the favorable surface charge toward uranyl phosphate species. The removal behaviors of the minerals were well fitted by pseudo-second order kinetic model (R² > 0.990) indicating the dominant removal process was chemical adsorption. Effects of Ca²⁺ and CO₃^2- at pH 7 were examined in terms of removal kinetic and capacity. The kinetic constants of aqueous U(VI) were 8 and 13 times lower (0.492 × 10^-3 g/(mg·min); 0.305 × 10^-3 g/(mg·min)) compared to the value in the absence of the ions. The thermodynamic equilibrium calculation showed that the stable uranyl species (uranyl tri-carbonate) were newly formed at the condition. Surface investigation on the reacted mineral with uranyl phosphates species were carried out by XPS. Ferrous iron and U(VI) on the green rust surface were completely oxidized and reduced into Fe(III) and U(IV) after 7 d. It suggests that the ferrous minerals can retard U(VI) migration in phosphate-rich groundwater through the adsorption and subsequent reduction processes.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.672-676
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• 1999

Adsorption isotherm is the most fundamental information in adsorption separation-process. Directly from the elution profile of a peak, the elution-curve method and frontal analysis(FA) were utilized to measure the adsorption isotherm in this work. Using RP-HPLC, sample and the buffer added in mobile phase were 5'-GMP and sodium phosphate, respectively. In this experimental condition, the retention time was decreased with increase in the injected mass of sample. And the front part of a peak was very stiff, so Langmuir adsorption isotherm might be applied. By the elution-curve method, the parameters used in the isotherm were obtained by optimization method, while by the FA, the concentrations of stationary phase were measured from the elution curve and the isotherm was determined by regression analysis. Compared to FA, the consumption of sample was less, and only one or two injections were needed by the elution-curve method. Finally, the effect of concentration of sodium phosphate in mobile phase on the parameters of the isotherm was investigated.

• Journal of architectural history
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• v.24 no.6
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• pp.45-55
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• 2015

After the Korean war, two major attempts were made to reconstruct Gwanghwamun Gate as an important part of Korea's lost cultural heritage. In December 2006, the Korean government replaced the concrete gate with a wooden one, yet traces of the attempts made in the 1960s to transform Gwanghwamun Gate and the main road remain to this day. At the time, the Third Republic of Korea, sought to legitimize itself in the name of modernity, and went on to modernize the architecture and urban landscape of Seoul. The location and design selected for the rebuilt Gwanghwamun illustrated the symbolic relationship between historic heritage and urban development. The reconstruction of the gate began as part of the Third Republic's project to restore the Central Administration Building and culminated in the transformation of the main road in front of the gate. By reconstructing the traditional gate using concrete, the military government intended to convey the message that we could inherit our proud tradition using modern materials, and that we should actively adopt the new technologies of the modern era. This study begins with the premise that the Gwanghwamun reconstruction project of 1968 represents the application of new technological thinking to Korea's architectural style, and has two objectives. The first is to summarize the reconstruction process and method using the records and drawings from the 1968 project, which was then under the leadership of architect Kang Bong-jin. The second is to analyze the characteristics of the architectural style and structure of the reconstructed Gwanghwamun so as to reinterpret the relationship between Korean tradition and modern technology.