• Korean Journal of Materials Research
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• v.34 no.2
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• pp.116-124
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• 2024

In this study, we investigated the microstructure and piezoelectric properties of 0.96(K_0.456Na_0.536)Nb_0.95Sb_0.05-0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (KNNS-BNKZ) ceramics based on one-step and two-step sintering processes. One-step sintering led to significant abnormal grain (AG) growth at temperatures above 1,085 ℃. With increasing sintering temperature, piezoelectric and dielectric properties were enhanced, resulting in a high d₃₃ = 506 pC/N for one-step specimen sintered at 1,100 ℃ (one-step 1,100 ℃ specimen). However, for one-step 1,115 ℃ specimen, a slight decrease in d₃₃ was observed, emphasizing the importance of a high tetragonal (T) phase fraction for superior piezoelectric properties. Achieving a relative density above 84 % for samples sintered by the one-step sintering process was challenging. Conversely, two-step sintering significantly improved the relative density of KNNS-BNKZ ceramics up to 96 %, attributed to the control of AG nucleation in the first step and grain growth rate control in the second step. The quantity of AG nucleation was affected by the duration of the first step, determining the final microstructure. Despite having a lower T phase fraction than that of the one-step 1,100 ℃ specimen, the two-step specimen exhibited higher piezoelectric coefficients (d₃₃ = 574 pC/N and k_p = 0.5) than those of the one-step 1,100 ℃ specimen due to its higher relative density. Performance evaluation of magnetoelectric composite devices composed of one-step and two-step specimens showed that despite having a higher g₃₃, the magnetoelectric composite with the one-step 1,100 ℃ specimen exhibited the lowest magnetoelectric voltage coefficient, due to its lowest k_p. This study highlights the essential role of phase fraction and relative density in enhancing the performance of piezoelectric materials and devices, showcasing the effectiveness of the two-step sintering process for controlling the microstructure of ceramic materials containing volatile elements.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.781-789
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• 2009

The absorption coefficients of the materials used in a 1:50 scale model multipurpose hall were measured based on ISO 354 and related laws. The shape and materials for the scale model were evaluated based on reflective surfaces, variable acoustic elements and sound-absorbing quality (125Hz-1kHz average) of seats. The measured average absorption coefficients of audience seats, audience and orchestra were 0.64, 0.74 and 0,45, respectively, which were simulated with the combination of wood, absorption materials and foam board. Various mounting methods for absorption curtain and banner were considered according to the installation methods. The average absorption coefficient was measured as 0.42, 0.47 and 0.45 in the conditions of Type A mounting, E mounting with 0.9 m backing air cavity, and Type G mounting which is suspended at the ceiling, respectively. It was confirmed that the absorption coefficient was increased at low frequency by backing air gap. The finishing material of stage house was an absorption material covered with thin fabric, which aimed average absorption coefficient of 0.68 by using fiber glass board. Each part of the real materials was compared with those of 1:50 scale model and it was found that the absorption characteristics of both cases were similar.

• Quality Improvement in Health Care
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• v.30 no.1
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• pp.33-43
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• 2024

Purpose:The acute hospital accreditation program launched in South Korea has shown positive effects on safety culture and quality of care. However, relative weights have not yet been investigated for accreditation criteria with a hierarchical structure. This study aimed to derive the relative weights of acute-care hospital accreditation criteria. Methods: We conducted an online survey using the analytic hierarchy process (AHP) technique to assess the validity, importance, and urgency of acute hospital accreditation criteria. The AHP online survey link was distributed in November 2022 after obtaining informed consent from 10 experts in hospital accreditation. Results: 'Basic value system' ranked highest, while 'patient care system' ranked second in terms of validity, importance, and urgency. 'Performance management system' had the lowest validity and urgency, while 'organizational management system' carried the lowest importance. Within the 'patient care system' domain, 'surgery and anesthesia sedation management' scored highest in validity and importance, and 'patient care' scored highest in urgency. 'Care delivery system and evaluation' received the lowest scores for all three aspects. In the 'organizational management system' domain, infection control ranked highest in terms of validity, importance, and urgency. The lowest validity was observed for 'management and organizational operation' and the lowest importance and urgency were noted for 'human resource management'. Conclusion: The weights for validity, importance, and urgency, as shown in each domain and chapter, and the number of measurable elements included, are largely inconsistent. This study will contribute to the development of the structure and scientific improvement of accreditation standards.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.1-14
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• 2024

An image-reconstruction technology, involving the deployment of an unmanned mobility equipped with high-speed LiDAR (Light Detection And Ranging) has been proposed to reconstruct the shape of abandoned mine. Unmanned mobility operation is remarkably useful in abandoned mines fraught with operational difficulties including, but not limited to, obstacles, sludge, underwater and narrow tunnel with the diameter of 1.5 m or more. For cases of real abandoned mines, quadruped robots, quadcopter drones and underwater drones are respectively deployed on land, air, and water-filled sites. In addition to the advantage of scanning the abandoned mines with 2D solid-state lidar sensors, rotation of radiation at an inclination angle offers an increased efficiency for simultaneous reconstruction of mineshaft shapes and detecting obstacles. Sensor and robot posture were used for computing rotation matrices that helped compute geographical coordinates of the solid-state lidar data. Next, the quadruped robot scanned the actual site to reconstruct tunnel shape. Lastly, the optimal elements necessary to increase utility in actual fields were found and proposed.

• The Journal of the Convergence on Culture Technology
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• v.10 no.3
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• pp.839-844
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• 2024

This study analytically analyzed the impact of underground structure displacement behavior on track damage due to adjacent excavation work, ground deterioration, and changes in groundwater level. The concrete track that was the subject of the study was analyzed for sleeper floating track(STEDEF) and precast concrete slab track(B2S). Sleeper floating track is a track structure in which the concrete bed and sleepers are voided. precast concrete slab track is a track structure that induces the elastic behavior of the rail by assembling rails and fasteners using slabs. For numerical analysis, each concrete track, from rail to concrete bed, was modeled as three-dimensional elements. In addition, the displacement behavior of the underground structure was set as a variable to analyze the damage effect on the concrete bed. Using numerical analysis, the concrete bed stress due to uplift and subsidence was analyzed, and the level of crack effect was analyzed by comparing it to the tensile strength and shear strength. As a result of the analysis, it was found that the sleeper floating track was more vulnerable than the precast concrete slab track when the same uplift and subsidence occurred. In addition, uplift and subsidence, it was analyzed that the cracks range in the sleeper floating track was large.

• Resources Recycling
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• v.33 no.3
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• pp.48-56
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• 2024

In this study, physical property evaluation and physical separation of the target product were performed to investigate the possibility of using sewage sludge gasification solid residue (GSRs) as a circulating resource. Firstly, the GSRs used in this study was supplied by Sudokwon Landfill Management Corporation, and generally the GSRs was in the form of porous pellets with a particle size of several millimetres. In addition, the partially black areas were confirmed to be unburned and ungasified carbon, and the average carbon content was 5%. In addition, the content of silica, alumina and phosphorus oxide was more than 70% of the total content. It was confirmed that the metallic components of the wet grinding product were separated into individual elements. As a physical separation of metallic and non-metallic components was required, it was finally found that flotation screening was suitable. Accordingly, cationic and anionic surfactants were selected to separate metallic components in which a relatively large amount of non-metallic components were concentrated, and the separation characteristics were confirmed. As a result, it is expected that the concentration of non-metallic components such as silica, alumina and phosphorus will be easier than the separation of metallic components. Therefore, since it is possible to physically treat the gasified sludge residue, it is judged to have potential as a circular resource according to the proposed recycling method for the separated product.

• Journal of The Korean Association For Science Education
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• v.44 no.4
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• pp.313-323
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• 2024

This study aims to explore educational methods to help students and citizens, who are exposed to numerous manufactured risks, better understand the nature of science and technology. It also seeks to develop their ability to identify, analyze, and evaluate the risks associated with science and technology, ultimately enabling them to live safer lives in society. To achieve this, through an extensive literature review, we explored the definition of risk, the necessity of risk education, and the relationship between SSI (Socioscientific Issues) education and risk education. Based on the results, we proposed the SSI-CURE (Socioscientific Issues Centered on the Understanding of Risk and its Evaluation) model, which can systematically educate about risks in the context of SSI. The SSI-CURE model proceeds through the following four steps: 1) Confrontation of SSI, 2) Understanding the Nature of Science and Technology with SSI, 3) Risk Assessment in SSI, and 4) Enactment of Countermeasures for SSI. These steps represent the key elements for education on risks in the context of SSI: Conceptual understanding of risks (risk knowledge), competencies necessary for discussing or addressing risk situations (risk competency), scientific content knowledge needed to understand risks (knowledge in science), and knowledge required to understand the causes of risks and their impacts (knowledge about science). We expect that the SSI-CURE model can be used not only as a guide for instruction but also as a representative framework for developing programs to educate about risks in the SSI context.

• Explosives and Blasting
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• v.42 no.3
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• pp.38-48
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• 2024

This study is to evaluate the applicability of high-speed, high-pressure dynamic compression technology for the powder molding of talc. To achieve this, powder molding test was conducted using a self-developed high-speed, high-pressure dynamic compression device, and the results were analyzed. Additionally, the behavior characteristics of pyrophyllite powder particles under dynamic compression were analyzed using the PFC2D. Quantitative analyses, as well as mapping and point analyses, were conducted using the SEM on pyrophyllite from the Naju ceramic Mine and the Bugok mine. The results showed that the weight ratio of composed elements in both mines was in the order of oxygen > silicon > aluminum. A pyrophyllite powder solid with a diameter of 14.5 mm and a thickness of 3 mm was successfully produced using a high-speed, high-pressure dynamic compression device capable of generating an instantaneous compressive force with a 30 kgf projectile dropped from a height of 1.5 m in about 0.4 seconds. Numerical analysis of pyrophyllite powder using PFC2D analyzed that in the numerical model, the compression ratio was approximately 56%, and the porosity decreased from 16.0% to 1.0%, indicating almost no remaining pores.

• Journal of the Korean Society of Earth Science Education
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• v.17 no.2
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• pp.181-193
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• 2024

Summative assessment provides information on how well students have achieved learning objectives, making the development of high-quality assessment items essential for accurate evaluation. This is one of the competencies that teachers must possess. This study aims to analyze summative assessment items created by pre-service elementary teachers, examining their intentions and the difficulties encountered in the item development process. The study involved 45 second-year students enrolled in an elementary teacher training university. They were grouped into teams of three and tasked with developing ten items, documenting the purpose of each item, the answer key, and the challenges faced during item creation. The collected summative assessment items were analyzed using a two-dimensional purpose classification table that includes Klopfer's taxonomy of educational objectives. The intentions behind the summative assessments and the difficulties faced during item development were inductively organized and analyzed through qualitative data analysis. The results revealed that pre-service elementary teachers adequately reflected scientific content elements but did not evenly cover assessment domains. The most challenging aspect for them was adjusting the difficulty level. Although they considered most factors that should be taken into account during item development, these considerations were not reflected in the actual items. These findings suggest that knowledge and experience are crucial in developing summative assessment items, and systematic lectures are necessary for pre-service elementary teachers.

• Korean Journal of Agricultural and Forest Meteorology
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• v.26 no.3
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• pp.209-218
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• 2024

The National Institute of Agricultural Sciences (NAS) operates in-house long-range climate forecasting system to support the agricultural use of climate forecast data. This system, developed through collaborative research with Pusan National University, is based on the PNU/RDA Coupled General Circulation Model (CGCM) and includes the regional climate model WRF (Weather Research and Forecasting). It generates detailed climate forecast data for periods ranging from 1 to 6 months, covering 20 key variables such as daily maximum, minimum, and average temperatures, precipitation, and agricultural meteorological elements like solar radiation, soil moisture, and ground temperature-factors essential for agricultural forecasting. The data are provided at a daily temporal resolution with a spatial resolution of a 5km grid, which can be used in point form (interpolated) or averaged across administrative regions. The system's seasonal temperature and precipitation forecasts align closely with observed climatological data, accurately reflecting spatial and topographical influences, confirming its reliability. These long-range forecasts from NAS are expected to offer valuable insights for agricultural planning and decision-making. The detailed forecast data can be accessed through the Climate Change Assessment Division of NAS.