• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.498-505
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• 2020

Aggregate occupies about 70-85% of the concrete volume and is an important factor in reducing the drying shrinkage of concrete. However, when constructing high-rise buildings, it acts as a problem due to the high load of natural aggregates. If the load becomes large during the construction of a high-rise building, creep may occur and the ground may be eroded. Material costs increase and there are financial problems. In order to reduce the load on concrete, we are working to reduce the weight of aggregates. However, artificial lightweight aggregates affect the interface between the aggregate and the paste due to its higher absorption rate and lower adhesion strength than natural aggregates, affecting the overall strength of concrete. Therefore, in this study, in order to grasp the interface between natural aggregate and lightweight aggregate by type, we adopted a method of measuring electrical resistance using an EIS measuring device, which is a non-destructive test, and lightweight bone. The change in the state of the interface was tested on the outside of the material through a blast furnace slag coating. As a result of the experiment, it was confirmed that the electric resistance was about 90% lower than that in the air-dried state through the electrolyte immersion, and the electric resistance differs depending on the type of aggregate and the presence or absence of coating. As a result of the experiment, the difference in compressive strength depending on the type of aggregate and the presence or absence of coating was shown, and the difference in impedance value and phase angle for each type of lightweight aggregate was shown.

• The Journal of the Convergence on Culture Technology
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• v.8 no.2
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• pp.281-289
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• 2022

Our society is rapidly changing with the core technology of the 4th industrial revolution, the emergence of a generation with new characteristics, and the untact era following the With Corona policy. Although the transition to untact is accelerating in the field of performing arts, in the case of opera, face-to-face performances are mainly conducted by experts and enthusiasts through on-site performances. Therefore, it is necessary to consider the uncertainty of creating opportunities through the influx of new customers such as the MZ generation and the departure of existing experts and enthusiasts. In this study, in order to examine these existing problems, we conducted literature review and case analysis, compared the opera face-to-face/non-face-to-face performance characteristics, derived an activation plan, and conducted expert interviews to secure the coherence and validity of the plan. In conclusion, we thought that it was difficult to improve the sound and sound quality, impairing the sense of presence and emotion due to many shortcomings when operating non-face-to-face as a music genre with the characteristics of opera. Therefore, we established the direction of activating the opera mainly face-to-face, but making good use of the advantages of non-face-to-face, which is not limited by region and time, and promoting the direction of activating face-to-face and non-face-to-face performances complementary to each other through the concept of cultural enjoyment.

• The Journal of the Convergence on Culture Technology
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• v.7 no.4
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• pp.583-590
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• 2021

This study was attempted to identify the current status of education of gerontological nursing at nursing colleges across the country and to check whether 19 senior nursing competencies suggested by the American Association of Nursing Colleges are reflected in the courses. The subjects of this study were 198 nursing education institutions accredited by KABONE, and each university's website, department homepage, university handbook, admission-related information, curriculum table, and syllabus were collected and analyzed through an internet search engine. The collected syllabus and the most recent curriculum table of the elderly nursing course were checked and analyzed using SPSS 23.0. The current status of gerontological nursing management was presented by calculating the frequency and percentage, and the educational contents presented in the syllabus were analyzed based on 19 geriatric nursing competencies presented by AACN. 185 institutions (93.43%) operated the geriatric nursing subjects, 98 institutions (49.49%) offered theory subject, and 84 institutions (42.42%) offered both theory and practice. In the case of compulsory majors, 52.92% had the most, 27.84% for the first semester of the 4th year, and 53.54% for 2 credits. As a result of analyzing the lesson plan, communication-related educational competency was included in 40% of cases. As AACN gerontological nursing competency 'effective information provision ability for the elderly', 'ethical and non-coercive decision-making', 'care without restraint', 'safe and effective transition across levels of care' was not included in the education content. In conclusion, gerontological nursing education has been focused on disease, and effective information provision capabilities including communication with the elderly need to be reflected.

• Journal of the Society of Disaster Information
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• v.18 no.3
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• pp.622-635
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• 2022

Purpose: Due to the change of demography, the ratio of senior drivers has increased and the transition to a super-aged society is expected to make more seniors drive in the future. Method: In this research, we analyzed medical characteristics of the driver's age-specific decline in body function and saw that both the function of the physical as well as mental capacities deteriorates as people age. Among them, various functions are precipitously weakened after reaching 70, implying that those over the age of 70 are classified as seniors in a medical sense. In this context, we also could identify that based on such age criteria, various safety policies for senior drivers should be developed and set up in Korea. Result: We could find a steep fall in the physical function of body after reaching 70 from the chronological change of cognitive function and judgment ability. In particular, it is revealed that the driving license institution and aptitude test for drivers over 70 should be thoroughly examined, as physical functions necessary for driving such as eyesight and hearing ability is not strong enough in many drivers over 70. Conclusion: Focusing on the physical capacity to drive, we tried to find the hazardous age bracket of senior drivers which might influence driving behaviors. Going forward, we expect this work would help to understand the policies for senior drivers and drivers' physical differences.

• Journal of Biomedical Engineering Research
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• v.44 no.1
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• pp.73-79
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• 2023

The purpose of this study is to derive medical devices with different management systems through comparison of domestic and overseas medical device product classification systems and to propose management conversion measures for the products. The definitions of medical devices were compared and the scope of medical devices defined by each country was confirmed through surveys of the Medical Device Act, Federal Food, Drug & Cosmetics Act (FD&C) in the U.S., and Medical Device Regulations (MDR) in Europe. Using the Ministry of Food and Drug Safety's regulations on medical device products and grades, 21 CFR part 860-892 and product code classification files in U.S., and EMDN in Europe as basic data to compare medical device products and derive medical devices with different management systems. As a result of comparing the definition and product classification systems of medical devices in Korea, the U.S. and Europe, medical device accessories, prosthetic limbs and aids among assistive devices for persons with disabilities, drugs, quasi-drugs and industrial products that are not managed by medical devices in Korea are managed as medical devices in the U.S. and Europe. This study aims to improve public health by securing systematic product safety management and essential performance under medical device regulations. Management within a single medical device system will increase the efficiency of licensing work of domestic medical device manufacturers and related organizations. It is also expected to help advance the system according to the international harmony of the item classification system and enhance smooth import and export competitiveness.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.5
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• pp.191-202
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• 2022

Markov envelope as a theoretical solution of the parabolic wave equation with Markov approximation for the von Kármán type random medium is studied and approximated with the convolution of two probability density functions (pdf) of normal and gamma distributions considering the previous studies on the applications of Radiative Transfer Theory (RTT) and the analysis results of earthquake records. Through the approximation with gamma pdf, the constant shape parameter of 2 was determined regardless of the source distance r_o. This finding means that the scattering process has the property of an inhomogeneous single-scattering Poisson process, unlike the previous studies, which resulted in a homogeneous multiple-scattering Poisson process. Approximated Markov envelope can be treated as the normalized mean square (MS) envelope for ground acceleration because of the flat source Fourier spectrum. Based on such characteristics, the path duration is estimated from the approximated MS envelope and compared to the empirical formula derived by Boore and Thompson. The results clearly show that the path duration increases proportionately to r_o^1/2-r_o², and the peak value of the RMS envelope is attenuated by exp (-0.0033r_o), excluding the geometrical attenuation. The attenuation slope for r_o≤100 km is quite similar to that of effective attenuation for shallow crustal earthquakes, and it may be difficult to distinguish the contribution of intrinsic attenuation from effective attenuation. Slowly varying dispersive delay, also called the medium effect, represented by regular pdf, governs the path duration for the source distance shorter than 100 km. Moreover, the diffraction term, also called the distance effect because of scattering, fully controls the path duration beyond the source distance of 300 km and has a steep gradient compared to the medium effect. Source distance 100-300 km is a transition range of the path duration governing effect from random medium to distance. This means that the scattering may not be the prime cause of peak attenuation and envelope broadening for the source distance of less than 200 km. Furthermore, it is also shown that normal distribution is appropriate for the probability distribution of phase difference, as asserted in the previous studies.

• Journal of the Korean Association of Geographic Information Studies
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• v.25 no.3
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• pp.29-58
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• 2022

Recently, Korea has been experiencing a problem of population decline, therefore the transition to a compact spatial structure is being urged. However, what is required is not just physical compression, but a compact city that also considers connectivity, in view of the changes in today's demographic and industrial structure. From this point of view, this study measures the compressibility of domestic cities suffering from extinction risk due to low birth rates, aging population, and population decline, and examined the spatial structure characteristics. In addition to the compressibility evaluation index used in previous studies, the compressibility of six indicators (population, land use, service accessibility, transport accessibility, connectivity, and concentration) was compared and analyzed, and a comprehensive compression index was calculated. The analysis results, based on the comprehensive compression index, classified 2.3% cities in the first grade, 4.6% in the second grade, 16.09% in the third grade, 43.68% in the fourth grade, and 33.33% in the fifth grade areas. Currently, the urban characteristics affecting the compactness index differ from region to region. Therefore, it is necessary to establish measures and policies for extinction risk considering the influence of each region's compactness index. This study is meaningful in that connectivity was considered using spatial syntax, and the compactness of cities at risk of extinction was compared and analyzed quantitatively. It is expected that this study will be used as basic data to establish the direction and action strategy for extinction risk cities.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.189-207
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• 2023

In the present study, the thermoshearing experiment on a rough rock fracture were modeled using a three-dimensional grain-based distinct element model (GBDEM). The experiment was conducted by the Korea Institute of Construction Technology to investigate the progressive shear failure of fracture under the influence of thermal stress in a critical stress state. The numerical model employs an assembly of multiple polyhedral grains and their interfaces to represent the rock sample, and calculates the coupled thermo-mechanical behavior of the grains (blocks) and the interfaces (contacts) using 3DEC, a DEM code. The primary focus was on simulating the temperature evolution, generation of thermal stress, and shear and normal displacements of the fracture. Two fracture models, namely the mated fracture model and the unmated fracture model, were constructed based on the degree of surface matedness, and their respective behaviors were compared and analyzed. By leveraging the advantage of the DEM, the contact area between the fracture surfaces was continuously monitored during the simulation, enabling an examination of its influence on shear behavior. The numerical results demonstrated distinct differences depending on the degree of the surface matedness at the initial stage. In the mated fracture model, where the surfaces were in almost full contact, the characteristic stages of peak stress and residual stress commonly observed in shear behavior of natural rock joints were reasonably replicated, despite exhibiting discrepancies with the experimental results. The analysis of contact area variation over time confirmed that our numerical model effectively simulated the abrupt normal dilation and shear slip, stress softening phenomenon, and transition to the residual state that occur during the peak stress stage. The unmated fracture model, which closely resembled the experimental specimen, showed qualitative agreement with the experimental observations, including heat transfer characteristics, the progressive shear failure process induced by heating, and the increase in thermal stress. However, there were some mismatches between the numerical and experimental results regarding the onset of fracture slip and the magnitudes of fracture stress and displacement. This research was conducted as part of DECOVALEX-2023 Task G, and we expect the numerical model to be enhanced through continued collaboration with other research teams and validated in further studies.

• Journal of Space Technology and Applications
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• v.3 no.2
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• pp.101-117
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• 2023

Active debris removal, a technology that approaches and removes space debris in orbit, and the on-orbit service, a technology for extending the mission life of satellites by fuel charging or by exchanging the battery, are gaining interest with the growth of the space community. SaTReC plans to develop a satellite capable of capturing and removing Korean satellites orbiting in space after the end of their missions. In contrast to the previously launched satellites by Korea, which were mainly intended to observe Earth and the space environment, rendezvous/docking technologies, as required in the future during, for instance, space exploration missions, will be implemented and demonstrated. In this paper, an orbital transition method for next-generation small satellites that will capture and remove space debris will be introduced. It is assumed that a small satellite with a mass of approximately 200 kg will be injected into the mission orbit through Korea Space Launch Vehicle-II in 2027. Because the satellite must access the target using a minimum amount of fuel, an approaching technology using Earth's J2 perturbation force has been developed. This method is expected to enable space debris removal missions for relatively lightweight satellites and to serve as the basis for carrying out a new type of space exploration in what is termed the 'Newspace' era.

• Clean Technology
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• v.28 no.3
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• pp.238-248
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• 2022

The world is striving to transition to a carbon-neutral society. It is expected that using hydrogen instead of hydrocarbon fuel will contribute to this carbon neutrality. However, there is a need for combustion technology that controls the increased NOx emissions caused by hydrogen co-firing. Flameless combustion is one of the alternative technologies that resolves this problem. In this study, a numerical analysis was performed using the 1D opposed-flow diffusion flame model of Chemkin to analyze the characteristics of flameless combustion and the chemical reaction of methane-hydrogen fuel according to its hydrogen content and flue gas recirculation rate. In methane combustion, as the recirculation rate (K_v) increased, the temperature and heat release rate decreased due to an increase in inert gases. Also, increasing K_v from 2 to 3 achieved flameless combustion in which there was no endothermic region of heat release and the region of maximum heat release rate merged into one. In H₂ 100% at K_v 3, flameless combustion was achieved in terms of heat release, but it was difficult to determine whether flameless combustion was achieved in terms of flame structure. However, since the NOx formation of hydrogen flameless combustion was predicted to be similar to that of methane flameless combustion, complex considerations of flame structure, heat release, and NOx formation are needed to define hydrogen flameless combustion.