• Journal of Space Technology and Applications
• /
• v.1 no.1
• /
• pp.33-40
• /
• 2021

Based on the requirements of a total weight of 42 kg or less, the NEXTSat-2 SAR (synthetic aperture radar) system was developed. As the NEXTSat-2 is a small-sized satellite, the SAR system was designed to account for about 40% of the dry mass of the payload relative to the total mass. Among the major components of the SAR system - which are an antenna, an RF transceiver, a baseband signal processor, and a power unit - a part with a particularly large dry mass is the antenna, the core of the SAR system. Whereas various selections are possible in consideration of gain and efficiency when designing the antenna, the micro-strip patch array antenna was adopted by reflecting the dry mass, power, and resolution required by the NEXTSat-2 project. In order to meet the mission requirement of the NEXTSat-2, the antenna was developed with a frequency of 9.65 GHz, a gain of 42.7 dBi, and a return loss of -15 dB. The performance of the antenna was verified by conducting a field test onboard the vehicle.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.6
• /
• pp.167-174
• /
• 2022

The objective of this study is to evaluate the dynamic properties of DUS (damping-up system) composed of the materials with excellent damping capacity, and to compare with those of the conventional hangar bolt. The main parameters are the type and hardness (𝜂_H), of rubber and the prestress force (value converted from the compression strain (𝜂_R) in the stress-strain relationship of rubber). The dynamic properties were examined from the natural frequency (𝜔_n), maximum response acceleration (A_m), amplification coefficient (𝛼_p), maximum relative displacement (𝚫_m), and damping ratio (𝜉_D). The test results showed that the A_m, 𝛼_p, and 𝚫_m values of DUS were 46.3%, 46.6% and 62.9% lower, respectively, and the 𝜉_D value was 3.89 times higher, when compared to those of the conventional hangar bolt. In particular, the 𝛼_p value was 1.3 for DUS, and 2.45 for the conventional hanger bolt, which were similar to those of rigid and flexible components specified in KDS 41 17 00, respectively. Consequently, in the optimal details of DUS, the 𝜂_H values of 50 and 45 were required for the NR (natural rubber) and EPDM (ethylene propylene diene monomer), and the 𝜂_R value of 5% was also recommended.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.3
• /
• pp.29-38
• /
• 2022

In this study, the shaking table tests were carried out on six types of non-structural elements installed on a full-scale two-story steel structure. The shaking table tests were performed for non-structural elements with and without seismic isolators. In this study, the seismic performance of Uninterruptible Power Supply (UPS) specimens was tested and investigated. Non-seismic details were composed of conventional channel section steel beams, and the seismic isolators were composed of high damping rubber bearing (HDRB) and wire isolator. The input acceleration time histories were artificially generated to satisfy the requirements proposed by the ICC-ES AC156 code. Based on the test results, the damage and dynamic characteristics of the UPS with the seismic isolator were investigated in terms of the natural frequency, damping ratio, acceleration time history responses, dynamic amplification factors, and relative displacements. The results from the shaking table showed that the dynamic characteristics of the UPS including the acceleration response were significantly improved when using the seismic isolator.

• Journal of Korea Water Resources Association
• /
• v.54 no.11
• /
• pp.925-932
• /
• 2021

A drought-flood abrupt alternation event is an overlapping extreme event that is harder to cope with than a single event of drought and flood. It is also expected to have a significant adverse impact on ecosystems as well as industries and agriculture. However, there has not yet been a comprehensive study that characterizes the drought-flood abrupt alternation events in Korea. Therefore, this study employed a standard weighted average precipitation (SWAP) index, which is efficient to analyze not only individual events of drought and flood but also the drought-flood abrupt alternation events considering various time scales. The SWAP standardized the weighted average precipitation (WAP) by adding temporal weights to the precipitation. The SWAP indices were calculated for middle-sized watersheds of the Han River basin using the area average precipitation during 1966 and 2018. The severity K was calculated to represent the relative regional severity considering normal rainfalls, and used to characterize the drought-flood abrupt alternation in the study areas. The results indicated that 20 of the 30 middle-sized watersheds in the Han River basin were confirmed to increase the severity of drought-flood abrupt alternation over time. Considering the frequency and severity of drought-flood abrupt alternation events in each watershed, vulnerable areas and dangerous areas due to drought-flood abrupt alternation were identified, for example, the Upstream Namhan River (#1001).

• Korean Journal of Materials Research
• /
• v.33 no.8
• /
• pp.330-336
• /
• 2023

The effects of Ni²⁺ substitution for Mg²⁺-sites on the microwave dielectric properties of (Mg_1-xNi_x)(Ti_0.95(Mg_1/3Ta_2/3)_0.05)O₃ (0.01 ≤ x ≤ 0.05) (MNTMT) ceramics were investigated. MNTMT ceramics were prepared by conventional solid-state reaction. When the MgO / TiO₂ ratio was changed from 1.00 to 1.02, MgTi₂O₅ was detected as a secondary phase along with the MgTiO₃ main phase in the MNTMT specimens sintered at 1,400 ℃ for 4h. For the MNTMT specimens with MgO / TiO₂ = 1.07 sintered at 1,400 ℃ for 4h, a single phase of MgTiO₃ with an ilmenite structure was obtained from the entire range of compositions. The relative density of all the specimens sintered at 1,400 ℃ for 4h was higher than 95 %. The quality factor (Qf) of the sintered specimens depended strongly on the degree of covalency of the specimens, and the sintered specimens with x = 0.01 showed the maximum Qf value of 489,400 GHz. The dielectric constant (K) decreased with increasing Ni²⁺ content because Ni²⁺ had a lower dielectric polarizability (1.23ų) than Mg²⁺ (1.32ų). As Ni²⁺ content increased, the temperature coefficient of resonant frequency (TCF) improved, from -55.56 to -21.85 ppm/℃, due to the increase in tolerance factor (t) and the lower dielectric constant (K).

• Journal of Korea Entertainment Industry Association
• /
• v.13 no.1
• /
• pp.185-197
• /
• 2019

This study intended to analyze the early childhood education freshmen's academic interest. For this study relationship among academic self-efficacy, character strength and learning motivation. The study subjects were 144 early childhood education freshmen at K-college in Deagu. They answered the survey regarding academic self-efficacy scale, VIA-IS(Values in action inventory of strength) short form scale, school learning motivation scale. The collected data were analyzed by frequency analysis, descriptive statistics, pearson correlation and multiple regression analysis using SPSS 18.0 program. The study finding are as follows. First, the average of academic self-efficacy, character strength and learning motivation of students were near at the intermediate-level. Second, academic self-efficacy, character strength and learning motivation were significantly positive correlated. Third, when examining the relative effect of early childhood education freshmen's academic self-efficacy and character strength on learning motivation, self regulatory efficacy among the sub-factors for academic self-efficacy and courage among the sub-factors for character strengths.

• Journal of the Korean Society for information Management
• /
• v.40 no.1
• /
• pp.121-148
• /
• 2023

The purpose of this study is to propose a scholarly paper recommendation system based on metadata attribute similarity with excellent performance. This study suggests a scholarly paper recommendation method that combines techniques from two sub-fields of Library and Information Science, namely metadata use in Information Organization and co-citation analysis, author bibliographic coupling, co-occurrence frequency, and cosine similarity in Bibliometrics. To conduct experiments, a total of 9,643 paper metadata related to "inequality" and "divide" were collected and refined to derive relative coordinate values between author, keyword, and title attributes using cosine similarity. The study then conducted experiments to select weight conditions and dimension numbers that resulted in a good performance. The results were presented and evaluated by users, and based on this, the study conducted discussions centered on the research questions through reference node and recommendation combination characteristic analysis, conjoint analysis, and results from comparative analysis. Overall, the study showed that the performance was excellent when author-related attributes were used alone or in combination with title-related attributes. If the technique proposed in this study is utilized and a wide range of samples are secured, it could help improve the performance of recommendation techniques not only in the field of literature recommendation in information services but also in various other fields in society.

• Journal of Oriental Neuropsychiatry
• /
• v.34 no.2
• /
• pp.71-82
• /
• 2023

Objectives: The existing reductionist approach has not reached complete understanding of the cause of schizophrenia. The objective of this study was to investigate yin-yang and five-element characteristics reflected on four time pillars of birth of patients with schizophrenia through comparison with the general population in the perspective of consilience-based holistic approach. Methods: This study was conducted using a random sequential recruitment method for the general population and individuals with schizophrenia aged 18 to 64 based on the exact date and time of birth using structured questionnaires. Relative positional relations of yin-yang and five-element with day master were primarily examined. In addition, the strength of day master with a score range of 0~100 points was assessed through operational score allocation. Results: Of 591 participants, 576 (346: general population, 230: individuals with schizophrenia) were analyzed. Between-group analyses showed no significant difference in the distribution of types of day master (χ²=10.41, df=9, p=0.318). However, significant between-group differences were shown in the distribution of the strength of day master (t=2.14, p=0.032) and frequency of restraining month branch (χ²=5.23, df=1, p=0.022). In logistic regression analysis, 10-point increase on the strength of day master decreased the probability of onset of schizophrenia over the age of 30 by 29.6% (p=0.002; 95% confidence interval, 0.566~0.876). Conclusions: Findings in this study suggest that four time pillars of birth might be associated with schizophrenia through yin-yang and five-element theory and synchronicity principle, implicating the plausibility of consilience-based holistic approach in the determination of risk factors or cause of schizophrenia.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.2
• /
• pp.238-247
• /
• 2023

Liquefied petroleum gas (LPG) is an attractive fuel for ships considering its current technology and economic viability. However, safety guidelines for LPG-fueled ships are still under development, and there have been no cases of applying LPG propulsion systems to small and medium-sized ships in Korea. The purpose of this study was to perform an objective risk assessment for the first marine LPG engine system and propose safe operational standards. First, hazard and operability (HAZOP) analysis was used to divide the engine system into five nodes, and 58 hazards were identified. To compensate for the subjectivity of qualitative evaluation using HAZOP analysis, fuzzy set theory was used, and additional risk factors, such as detectability and sensitivity, were included to compare the relative weights of the risk factors using a fuzzy analytical hierarchy process. As a result, among the five risk factors, those with a major impact on risk were determined to be the frequency and severity. Finally, the fuzzy technique for order of preference by similarity to ideal solution (TOPSIS) was applied to select the risk rank more precisely by considering the weights of the risk factors. The risk level was divided into 47 groups, and the major hazard during the operation of the engine system was found through the analysis to be gas leakage during maintenance of the LPG supply line. The technique proposed can be applied to various facilities, such as LPG supply systems, and can be utilized as a standard procedure for risk assessment in developing safety standards for LPG-powered ships.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.25 no.4
• /
• pp.446-454
• /
• 2023

The impact of climate change on agriculture is substantial, especially as global warming is projected to lead to varying temperature and humidity patterns in the future. These changes pose a higher risk for both crops and livestock, exposing them to environmental stressors under altered climatic conditions. Specifically, as temperatures are expected to rise, the risk of heat stress is assessable through the Temperature-Humidity Index (THI), derived from temperature and relative humidity data. This study involved the comparison of THI collected from 10 Korea Meteorological Administration ASOS stations spanning a 60-year period from 1961 to 2020. Moreover, high-resolution temperature and humidity distribution data from 1981 to 2020 were employed to generate high-resolution TH I distributions, analyzing temporal changes. Additionally, the number of days characterized by heat stress, derived from TH I, was compared over different time periods. Generally, TH I showed an upward trend over the past, albeit with varying rates across different locations. As TH I increased, the frequency of heat stress days also rose, indicating potential future cost increases in the livestock industry due to heat-related challenges. The findings emphasize the feasibility of evaluating heat stress risk in livestock using THI and underscore the need for research analyzing THI under future climate change scenarios.