• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.125-132
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• 2018

In this study, a direct tensile test was planned to identify the tensile performance of UHPC, and the irregularity of cracks, which is a problem of the direct tensile test, was complemented through the introduction of notches at the center of a specimen. In this regard, a number of specimens divided by batch to reduce the deviation of direct tensile test values were fabricated to present reference data with respect to highly reliable direct tensile strength values. In addition, the mechanical properties and reliability of the specimens were examined under the curing conditions of the specified design strength of 120MPa for the steel fiber reinforced concrete with 1.5% fiber volume fraction, which is most suitable for the field application. As a result, the deviation of averages by batch between compressive strength and direct tensile strength did not show a large difference, and all cracks occurred within 20mm in the direct tensile test. At the 95% confidence interval of the direct tensile strength, the range was considerably small in the mean and the standard deviation, and there was no significant difference depending on the curing conditions. The results confirmed that a stable direct tensile test was performed, and highly reliable results were obtained through the fabrication of specimens by batch and test progress.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.4
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• pp.54-63
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• 2017

With the aim of promoting the use of metropolitan railways, the present research developed a mode choice model for evaluating its competitiveness against passenger cars. A case study was carried out with Gyeongeui and Joongang line, and the area of interest was the direct operating railway between Ilsan and Guri station where the two lines intersect. The mode choice model was a disaggregate behavior model which used Stated Preference (SP) survey data, and the plot of competition was between private passenger cars and express trains. As a result, the mode choice model was established, and this model was used to analyze characteristics of passengers' time value and elasticity. It was shown that reducing travel time is more efficient than reducing travel cost when it comes to operating express trains in metropolitan railways. Therefore, policies designed for activating the use of metropolitan railways should expand direct operating service of individual lines and run more express trains in order to minimize transfer and in-vehicle time.

• International Commerce and Information Review
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• v.10 no.2
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• pp.411-432
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• 2008

This study presents the pattern and determinants of intra-industry trade in Korea's machinery and transport equipment industry focusing the influence of foreign direct investment on intra-industry trade. Using an OLS regression model the determinants of intra-industry trade are investigated. Results indicate that a statistically significant negative relationship is found between intra-industry trade and foreign direct investment, and show that intra-industry trade is positively affected by the degree of product differentiation and export structure similarity. Intra-industry trade is also positively associated with the economies of scale, the level of trade barrier, and transportation costs, although this is not statistically significant. The study found strong evidence that the propensity of foreign direct investment toward export specialized industry makes the negative relationship between intra-industry trade and foreign direct investment.

• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.139-144
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• 2023

In this study, carbon-coated porous nanofibers were prepared via electrospinning and the performance of Li[Ni_0.93Co_0.07]O₂ (NC) synthesized by electrospinning (E-NC) and co-precipitation (C-NC) was compared. E-NC had a discharge capacity of 206 mAh g^-1 at 0.1C (17 mA/g), which is 10% higher than that of C-NC (189.2 mAh g^-1). E-NC shows a high-rate performance of 118.32 mAh g^-1 (61.7%) at 5C (850 mA/g), which is 50% higher than that of C-NC (78.22 mAh g^-1 = 45.7%). Charge transfer of the carbon-coated porous nanofiber E-NC decreased by 35% compared to C-NC after 20 cycles as observed using electrochemical impedance spectroscopy. The results of this study show that the nanofiber structure with carbon coating shortens the Li-ion diffusion path, improves electrical conductivity, resulting in excellent rate performance.

• Journal of Korean Society of Transportation
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• v.20 no.7
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• pp.69-76
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• 2002

In conducting studies related to the national base networks, it is very important to construct a simulation network. This research provides an algorithm to construct the simulation network from the digital transportation map which is constructed based on the National Geographic Information System(NGIS). The algorithm consists of three functions(extraction of networks from transportation digital map, transform of the derived network into one suitable to transportation simulation model, and inspection of errors in the network). The direct derivation of a simulation network from GIS enables to enhance the reliability of an analysis related to a transportation facility investment as well as to reduce cost and time. In this research, Emme/2 which is generally accepted transportation planning fields is adapted for the target system. However, this algorithm will be extended to other simulation models such as Satong-Paldal which is the only transportation simulation model developed in Korea, and Tranplan in the near future.

• Journal of Korean Society of Transportation
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• v.17 no.1
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• pp.41-52
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• 1999

Recently, much literature has surveyed the economic effects of transportation investment, focusing on the relationship between transportation infrastructure investment and economic development. Although the conventional views assume that transportation investment stimulates economic growth, the results of recent studies are not conclusive and in some cases reject the conventional views. The contradictory results are linked with double counting Problem and Keynesian/Neo-classical economics theory. This article investigates the economic effects of road transportation with regard to freight transport using Stated Preference technique. This study examines, in particular, the value of time saving for freight which has been rarely studied in this area. In the first part, the value of time saving, excluding the value for driver and operating cost, is theoretically investigated through the model of continuous review system and periodic review system. At last, the empirical study using the Seated Preference technique shows the value of time saving for freight and the value of reliability, compared with other studies and the value of those in COBA. The result makes us conclude that road investment produces the secondary effects as well as the direct benefit such as time saving for passengers, operating cost saving. and accident cost reduction. The secondary effect includes the contribution to economic development.

• Journal of the Korean Society for Railway
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• v.20 no.4
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• pp.558-567
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• 2017

This study was conducted to analyze the turnover intentions of railway traffic controllers among employees of a domestic railway corporation. Variables influencing job turnover intention included exploited variables (empowerment, job stress, job satisfaction, organizational commitment, exhaustion) that have been actively studied in other fields. The results showed that the empowerment of railway traffic controllers did not directly affect job stress and turnover intention, but had a direct effect on job satisfaction, organizational commitment, and exhaustion. Job stress did not directly affect job satisfaction, organizational commitment, and exhaustion, and job satisfaction did not directly affect organizational commitment, burnout, and turnover intentions. Burnout has a direct effect on turnover intention, indicating that exhaustion of railroad traffic controllers has an effect on turnover intentions. In conclusion, empowerment has a direct effect on burnout and exhaustion has a direct effect on turnover intention. This study suggests that management of empowerment and exhaustion is important for the prevention of turnover of railway traffic controllers.

• Architectural research
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• v.16 no.4
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• pp.149-156
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• 2014

This research is designed to identify factors that affect life satisfaction of the Korean elderly by studying residential environments and individual personalities as independent variables, and life satisfaction of the elderly as a dependent variable. It also includes emotional and instrumental support to describe relations between variables as mediating variables. It utilizes a questionnaire survey as its research method and studies those aged 65 and over living in urban, suburban and rural areas. In addition, regression and path analysis is used to identify casual links between different variables. The results are as follows: (1) Direct factors that impact emotional support are home ownership (direct effect= -.18) and transportation services (.15). That is, those who own their home and have easy access to public transpiration show increased levels of emotional support. (2) Direct factors that affect instrumental support are economic status (direct effect= .311) and living arrangement (.17). In other words, those who are financially stable and live with their children have more instrumental support. (3) Factors linked directly to life satisfaction of the elderly are their age (direct effect= -.10), health status (.19), economic status (.25), region of living (.22) and housing type (.19). (4) Among the mediating variables, emotional support has direct effect (.45) while instrumental support has indirect effect (.16).

• Proceedings of the KOR-KST Conference
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• 2007.11a
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• pp.404-411
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• 2007

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.37-40
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• 2015

Recently, the electrical insulation design for electrical apparatuses is important to cope with the tendency of high voltage. The degradation characteristics of a superconducting coil due to an electrical breakdown should be considered to design a high voltage superconducting coil. In this paper, the degradation characteristics of 2G high temperature superconducting (HTS) wires are studied with respect to electrical breakdown tests. To analyze the dependency of the degradation characteristics of 2G HTS wires, the electrical breakdown tests are performed with AC(alternating current) and DC(direct current) voltage. All tests are performed by applying various magnitudes of AC and DC breakdown voltages. To verify the degradation characteristics of 2G HTS wires, the tests are performed with various 2G HTS wires with respect to stabilizer materials. The degradation characteristics of 2G HTS wires, such as Ic(critical current) and index number are measured by performing electrical breakdown tests. It is found that the characteristics such as Ic and index number can be degraded by an electrical breakdown. Moreover, it is concluded that the degradation characteristics of 2G HTS wires are affected by the stabilizer material and applied voltages. The cross-sectional view of 2G HTS wires is observed by using a scanning electron microscope (SEM). As results, it is found that the degradation characteristics of 2G HTS wires are concerned with hardness and electrical conductivity of stabilizer layers.