• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.245-255
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• 2023

Time comparison techniques are necessary for generating and keeping Coordinated Universal Time (UTC) and distributing standard time clocks. Global Navigation Satellite System (GNSS) Common View, GNSS All-in-View, Two-Way Satellite Time and Frequency Transfer (TWSTFT), Very Long Baseline Interferometry (VLBI), optical fiber, and Network Time Protocol (NTP) based methods have been used for time comparison. In these methods, GNSS based time comparison techniques are widely used for time synchronization in critical national infrastructures and in common areas of application such as finance, military, and wireless communication. However, GNSS-based time comparison techniques are vulnerable to jamming or interference environments and it is difficult to respond to GNSS signal disconnection according to the international situation. In response, in this paper, Code-Division Multiple Access (CDMA) based All-to-All TWSTFT operation method is proposed. A software-based simulation platform also was designed for performance analysis in multi-TWSTFT signal environments. Furthermore, code and carrier measurement jitters were calculated in multi-signal environments using the designed simulation platform. By using the technique proposed in this paper, it is anticipated that the TWSTFT-based time comparison method will be used in various fields and satisfy high-performance requirements such as those of a GNSS master station and power plant network reference station.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.09a
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• pp.109-109
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• 1995

• Journal of the military operations research society of Korea
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• v.33 no.1
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• pp.1-18
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• 2007

In the early stage of weapon system acquisition process, acquisition policy is necessarily established to acquire weapon system in a faster, better, cheaper way. Several alternatives, such as "buy", "domestic research and development", and "technical corporative production", can be considered for the best acquisition policy making. However, the comparison factors for those alternatives have different metrics and values. Therefore, the aim of this paper is to suggest KAAM(Knowledge-based Alternatives Analysis Model) as a scientific method to compare the alternatives having such different metrics and values and giving a weighted and normalized single measurement for the easy comparison. KAAM is a hybrid model incorporating Satty technique, Delphi/Shang method, Consensus method, and SAW method. KAAM is implemented on Microsoft Excel environment and provided tabular form user interface. Finally, an illustrative example is shown using KAAM.

• Journal of Sensor Science and Technology
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• v.31 no.6
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• pp.448-454
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• 2022

An intralaboratory comparison of the realization of the triple-point temperature of mercury, which is defined as -38.8344℃ on the international temperature scale of 1990 (ITS-90), was conducted at the Korea Research Institute of Standards and Science (KRISS), the national metrology institute of Korea. To this end, four triple-point-of-mercury cells were compared using the resistance ratio measurement of a standard platinum resistance thermometer to validate the calibration results obtained using the triple-point-of-mercury cells at KRISS. The triple-point temperatures of all the four cells, one of which is designated as the national standard cell, were within 0.3 mK of the national standard. Based on 13 experiments on the four triple-point-of-mercury cells, the uncertainty in the comparison of the triple-point-of-mercury cells was 0.08 mK, and the uncertainty in the realization of the triple-point temperature of mercury was 0.19 mK. The results of the intralaboratory comparison validated that utilizing any of the four triple-point-of-mercury cells would result in the realization of a temperature within 0.3 mK of the average value determined by two key international comparisons for the realization of -38.3844℃ following the ITS-90.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.468-473
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• 2010

We confirmed that the dismantling of two research reactors with thermal power of $2MW_{th}$ and $100kW_{th}$, respectively, reveals no significant difference between the radiation levels of the research reactor site and the surrounding environment far away from it, from the radiation level aspect. Radiation dose and radioactivity were measured at monitoring points around the research reactor site of the Korea Atomic Energy Research Institute (KAERI) in Seoul and comparison points 0.5 km to 3.3 km from the site. To grasp trends in the radiation levels during dismantling from the end of 2002 to the end of 2007, the gamma radiation dose rate, the accumulated dose, and the radioactivity of the strontium, tritium, and gamma isotopes were statistically treated and estimated. The averages of these items between the two groups, the research reactor site and comparison points, were assessed by applying a T-test with a significance level of 0.05. P-values found by using the T-test were from 0.12 to 0.83 where the values were much higher than the significance level. As a result, no difference was observed between the radiation levels at the research reactor site and at the comparison points by this T-test. This study showed that dismantling activity of the Korea Research Reactor of the Seoul site did not expose the public or the environment to harmful levels of radiation.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.315-322
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• 2015

The research carried out on thorium-based fuels indicates that these fuels can be considered as economic alternatives with improved physical properties and proliferation resistance issues. In the current study, neutronic assessment of $UO_2$ in comparison with two $(Th-^{233}U)O_2$, and $(Th-^{235}U)O_2$ thorium-based fuel loads in a heavy water research reactor has been proposed. The obtained computational data showed both thorium-based fuels caused less negative temperature reactivity coefficients for the modeled research reactor in comparison with $UO_2$ fuel loading. By contrast, $^{235}U$-containing thorium-based fuel and $^{235}U$-containing thorium-based fuel loadings in the thermal core did not drastically reduce the effective delayed neutron fractions and delayed neutron fractions compared to $UO_2$ fuel. A provided higher conversion factor and lower transuranic production in the research core fed by the thorium-based fuels make the fuel favorable in achieving higher cycle length and less dangerous and costly nuclear disposals.

• Journal of Sensor Science and Technology
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• v.13 no.2
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• pp.114-120
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• 2004

The $Comet{\acute{e}}$ Consultatif de $Thermom{\acute{e}}trie$ (CCT) under the Comete International des Poids et Measures (CIPM) has decided to perform the Key Comparison (KC) for triple point of water cells used as a reference fixed point of thermometry at the 21st meeting held at November 2001, and the Bureau International des Poids et Measures (BIPM) has been nominated as a KC coordinator. According to the KC protocol prepared by BIPM, KRISS performed the KC experiments and evaluate a uncertainty. The temperature difference between two reference cells for the Korea Research Institute of Standards and Science (KRISS) and a test cell for the transfer standard, which is moved to BIPM was 0.024 mK and the combined standard uncertainty evaluated 0.055 mK.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1895-1897
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• 1996

Lightning impulse voltage is essential to evaluate the insulation performance of electric power apparatus. Recently international standard (IEC-60) on high voltage measurement techniques are being revised. In the draft of this standard, a new calibration method is introduced and the accuracy of most industrial measuring systems is maintained by means of comparison test against the reference measuring systems. Comparison tests of dividers for chopped lightning impulse measurement were rallied out by KERI. The 700kV shielded resisitive divider with and without compensation element were done comparison test with 300kV PTB divider which have the similar charateristics as that were circulated among the laboratories. This paper reports on the calculation results of response charateristics obtained by EMTP and the comparison test results with chopped lightning impulse voltages from 150kV to 250kV. It is demonstrated that KERI are capable of realizing the idea in the revision of the IEC standand, that is, to establish traceability.

• Asian Journal for Public Opinion Research
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• v.11 no.1
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• pp.4-30
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• 2023

Previous research has empirically demonstrated the negative effects of social media use on young people's psychological well-being. Unlike most previous studies that focused on either Facebook or Instagram, this study comparatively examined the differences in upward comparison and its effects on self-esteem, life satisfaction, and depression between Facebook and Instagram. An analysis of survey data from 641 Korean college students, who reportedly use these two social media more actively than any other age group, found that college students experience more upward comparisons on Instagram than on Facebook. Upward comparisons on both Facebook and Instagram increased by college students' age and weekly usage time. Upward comparisons on Instagram increased by the additional factors of gender (females more than males) and number of "followings." Subsequently, the effects of upward comparison on psychological well-being were found to differ by social media platform. Upward comparisons were found to negatively impact all determinants of psychological well-being only on Instagram, but not on Facebook. The differences in upward comparison and its impact on young users' psychological well-being found in this study were discussed in terms of the different functional characteristics of the two social media platforms, which provides direction for further research needed to establish guidelines for healthy social media use by young people.

• Journal of the Korean Operations Research and Management Science Society
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• v.30 no.2
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• pp.185-199
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• 2005

With the growth of internet shopping malls, there is increasing interest in comparison shopping mall. However most comparison sites compare only book prices by collecting simple XML data and do not provide .the exact comparison Including precise shipping costs. Shipping costs vary depending on each customer's address, the delivery method, and the category of selected goods, so rule based system is required in order to calculate exact shipping costs. Therefore, we designed and implemented comparison shopping mall which compares not only book prices but also shipping costs using rule based inference. By adopting the extensible Rule Markup language (XRML) approach, we proposed the methodology of extracting delivery rules from Web pages of each shopping mall. The XRML approach can facilitate nearly automatic rule extraction from Web pages and consistency maintenance between Web pages and rule base. We developed a ConsiderD system which applies our rule acquisition methodology based on XRML. The objective of the ConsiderD system is to compare the exact total cost of books including the delivery cost over Amazon.com, BarnesandNoble.com, and Powells.com. With this prototype, we conducted an experiment to show the potential of automatic rule acquisition from Web pages and illustrate the effect of delivery cost.