• Journal of the Korean Institute of Gas
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• v.26 no.4
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• pp.58-63
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• 2022

With the emergence of environmental problems caused by fine dust worldwide, LNG, which is cheaper and less pollution than diesel, is attracting attention as the next generation energy of automobiles and is expanding its supply. However, it is difficult to operate smoothly due to the lack of infrastructure for LNG charging stations in Korea and the limited size of containers that can be installed according to regulations. In Korea, research and development on the contents of containers for the smooth operation of natural gas vehicles are underway, but there is a problem that the container directly receives the impact of the vehicle collision and explodes, causing a major disaster. Therefore, in this study, the safety of the container was verified by deriving the strain and stress values through ANSYS Explicit Dynamics analysis. As a result, a maximum stress of 565.37MPa occurred in the container, and it is expected that plastic deformation will occur as it exceeds the yield stress of STS304 used as a material for the container, which is beyond 505MPa. When an impact caused by a collision between a vehicle and a container is applied, it is considered necessary to design a support or reinforcement because the container may be damaged or defective.

• Journal of the Korean Society of Radiology
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• v.16 no.1
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• pp.15-23
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• 2022

3D printing technology is being used in various fields such as medicine and biotechnology, and materials containing metal powder are being commercialized through recent material development. Therefore, this study intends to analyze the photon spectrum during added filtration using 3D printing material during diagnostic X-ray examination through simulation. Among the Monte Carlo techniques, MCNPX (ver. 2.5.0) was used. First, the appropriateness of the photon spectrum generated in the simulation was evaluated through SRS-78 and SpekCalc, which are X-ray spectrum generation programs in the diagnostic field. Second, photon spectrum the same thickness of Al and Cu filters were obtained for characterization of 3D printing materials containing metal powder. In addition, the total photon fluence and average energy according to changes in tube voltage were compared and analyzed. As a result, it was analyzed that PLA-Al required about 1.2 ~ 1.4 times the thickness of the existing Al filter, and PLA-Cu required about 1.4 ~ 1.7 times the thickness of the Cu filter to show the same degree of filtration. Based on this study in the future, it is judged that it can be utilized as basic data for manufacturing 3D printing additional filters in medical fields.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1074-1081
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• 2021

Nitrous oxide (N₂O) is one of the six major greenhouse gases and is known to produce a greenhouse ef ect by absorbing infrared radiation in the atmosphere. In particular, its global warming potential (GWP) is 310 times higher than that of CO₂, making N₂O a global concern. Accordingly, strong environmental regulations are being proposed. N₂O reduction technology can be classified into concentration recovery, catalytic decomposition, and pyrolysis according to physical methods. This study intends to provide information on temperature conditions and reaction time required to reduce nitrogen oxides with cost. The high-temperature ranges selected for pyrolysis conditions were calculated at intervals of 100 K from 1073 K to 1373 K. Under temperatures of 1073 K and 1173 K, the N₂O reduction rate and nitrogen monoxide concentration were observed to be proportional to the residence time, and for 1273 K, the N₂O reduction rate decreased due to generation of the reverse reaction as the residence time increased. Particularly for 1373 K, the positive and reverse reactions for all residence times reached chemical equilibrium, resulting in a rather reduced reaction progression to N₂O reduction.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1201-1208
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• 2022

In general, to maximize the supply and efficiency of floating offshore wind power generation energy, the motion caused by wave attenuation of the substructure must be reduced. According to previous studies, the motion response was reduced due to the vortex viscosity generated by the damping plate installed in the lower structure among the waves. In this study, a 5 MW semi-submersible OC5 platform and two platforms with attenuation plates were designed, and free decay experiments and numerical calculations were performed to confirm the effect of reducing motion due to vortex viscosity. As a result of the model test, when the heave free decay tests were conducted at drop heights of 30 mm, 40 mm, and 50 mm, compared with the OC5 platform, the platform with two types of damping plates attached had relatively improved motion damping performance. In the model test and numerical calculation results, the damping plate models, KSNU Plate 1 and KSNU Plate 2, were 1.1 times and 1.3 times lower than OC5, respectively, and the KSNU Plate 2 platform showed about two times better damping performance than OC5. This study shows that the area of the damping plate and the vortex viscosity are closely related to the damping rate of the heave motion.

• 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.

• Applied Chemistry for Engineering
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• v.34 no.5
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• pp.534-540
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• 2023

The high-rate performance is limited by several factors, such as polarization generation, low electrical conductivity, low surface energy, and low electrolyte permeability of CF_X, which is widely used as a cathode active material in the lithium primary battery. Therefore, in this study, we aimed to improve the battery performance by using carbon fluoride modified by surface treatment using oxygen plasma as a cathode for lithium primary batteries. Through XPS and XRD analysis, changes in the surface chemical characteristics and crystal structure of CF_X modified by oxygen plasma treatment were analyzed, and accordingly, the electrochemical characteristics of lithium-ion primary batteries were analyzed and discussed. As a result, the highest number of semi-ionic C-F bonds were formed under the oxygen plasma treatment condition (7.5 minutes) with the lowest fluorine to carbon (F/C) ratio. In addition, the primary cell prepared under this condition using carbon fluoride as the active material of the cathode showed the highest 3 F/C(3 C rate-performance) rate-performance and maintained a relatively high capacity (550 mAh/g) even at high rates. In this study, it was possible to produce lithium primary batteries with high-rate performance by adjusting the fluorine contents of carbon fluoride and the type of carbon-fluorine bonding through oxygen plasma treatment.

• Clean Technology
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• v.30 no.2
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• pp.105-112
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• 2024

Globally, the demand for electric vehicles has surged due to greenhouse gas regulations related to climate change, leading to an increase in the production of used batteries as a consequence of the battery life issue. This study aims to selectively leach and recover valuable metal lithium from the cathode material of spent LFP (LiFePO₄) batteries among lithium-ion batteries. Generally, the use of inorganic acids results in the emission of toxic gases or the generation of large quantities of wastewater, causing environmental issues. To address this, research is being conducted to leach lithium using organic acids and other leaching agents. In this study, selective leaching was performed using the organic acid methane sulfonic acid (MSA, CH₃SO₃H). Experiments were conducted to determine the optimal conditions for selectively leaching lithium by varying the MSA concentration, pulp density, and hydrogen peroxide dosage. The results of this study showed that lithium was leached at approximately 100%, while iron and phosphorus components were leached at about 1%, verifying the leaching efficiency and the leaching rates of the main components under different variables.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.28-53
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• 2024

In general, high-level radioactive waste (HLW) generated as a result of nuclear power generation should be disposed within the country. Determination of the disposal site and host rock for HLW deep geological repository is an important issue not only scientifically but also politically, economically, and socially. Considered host rock types worldwide for geological disposal include crystalline rocks, sedimentary rocks, volcanic rocks, and salt dome. However, South Korea consists of various rock types except salt dome. This paper not only analyzed the geological and rock mechanical characteristics on a nationwide scale with the preliminary results on various rock type studies for the disposal host rock, but also reviewed the characteristics and possibility of various rock types as a host rock through deep drilling surveys. Based on the nationwide screening for host rock types resulted from literature review, rock distributions, and detailed case studies, Jurassic granites and Cretaceous sedimentary rocks (Jinju and Jindong formations) were derived as a possible candidate host rock types for the geological disposal. However, since the analyzed data for candidate rock types from this study is not enough, it is suggested that the disposal rock type should be carefully determined from additional and detailed analysis on disposal depth, regional characteristics, multidisciplinary investigations, etc.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.69 no.2
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• pp.88-96
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• 2024

Recently, interest in renewable energy development has been increasing to promote carbon-neutral policies. Agrivoltaic is a solar power generation facility with the potential to aid in meeting carbon-neutral policies. It has the advantage of generating electricity while farming takes place, but it also has the disadvantage of reducing crop yield and cultivation safety. We analyzed the rice yield, quality, and stem growth characteristics according to different transplanting densities under agrivoltaics. Under agrivoltaics, the number of rice panicles was reduced by the shading effect, but the reduction was lower under 60 hills than under 80 and 100 hills. Brown rice perfect ratio was increased under 60 hills under agrivoltaics. Brown rice yield did not differ significantly between 60 and 80 hills under agrivoltaics. However, stem dry weight by unit(mg/cm) in each internode showed highest under 60 hills compared to 80 and 100 hills under agrivoltaics. Therefore, 60 hill density was considered appropriate to ensure cultivation safety and yield when cultivated rice under agrivoltaics.

• The Journal of the Korean Society for Microbiology
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• v.21 no.3
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• pp.311-329
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• 1986

The experimental exposure of animals to sources of ultraviolet radiation (UVR) which emit their energy primarily in the UVB region (280-320nm) is known to result in a number of well-described changes in the recipient's immune competence. Two such changes include a depressed capacity to effectively respond immunologically to transplants of syngeneic UVR tumors and a markedly reduced responsiveness to known inducers of delayedtype (DTH) and contact hypersensitivity (CH) reactions. The results of experiments that were designed to elucidate the mechanisms responsible for UVR-induced immunomodulation have implicated: 1) an altered pattern of lymphocyte recirculation, 2) suppressor T cells(Ts), 3) deviations in systemic antigen presenting cell (APC) potential. 4) changes in the production of interleukin-1-like molecules, and 5) the functional inactivation of epidermal Langerhans cells in this process. The exposure of skin to UVR, therefore, causes a number of both local and systemic alterations to the normal host immune system. In spite of this seeming complexity and diversity of responses, our recent studies have established that each of the UVR-mediated changes is probably of equal importance to creating the UVR-induced immunocompromised state. Normal animals were exposed to low dose UVR radiation on their dorsal surfaces under conditions where a $3.0\;cm^2$ area of skin was physically protected from the light energy. Contact sensitization of these animals with DNFB, to either the irradiated or protected back skin, resulted in markedly reduced CH responses. This was observed in spite of a normal responsiveness following the skin sensitization to ventral surfaces of the UVR-exposed animals. Systemic treatment of the low dose UVR recipients with the drug indomethacin (1-3 micrograms/day) during the UVR exposures resulted in a complete reversal of the depressions observed following DNFB sensitization to "protected" dorsal skin while the altered responsiveness found in the group exposed to the skin reactive chemical through directly UVR-exposed sites was maintained. These studies implicate the importance of EC as effective APC in the skin and also suggest that some of the systemic influences caused by UVR exposure involve the production of prostaglandins. This concept was further supported by finding that indomethacin treatment was also capable of totally reversing the systemic depressions in CH responsiveness caused by high dose UVR exposure (30K joules/$m^2$) of mice. Attempts to analyze the cellular mechanisms responsible established that the spleens of all animals which demonstrated altered CH responses, regardless of whether sensitization was through a normal or an irradiated skin site, contained suppressor cells. Interestingly, we also found normal levels of T effector cells in the peripheral lymph nodes of the UVR-exposed mice that were contact sensitized through normal skin. No effector cells were found when skin sensitization took place through irradiated skin sites. In spite of such an apparent paradox, insight into the probable mechanisms responsible for these observations was provided by establishing that UVR exposure of skin results in a striking and dose-dependent blockade of the efferent lymphatic vessels in all peripheral lymph nodes. Therefore, the afferent phases of immune responses can apparently take place normally in UVR exposed animals when antigen is applied to normal skin. The final effector responses, however, appear to be inhibited in the UVR-exposed animals by an apparent block of effector cell mobility. This contrasts with findings in the normal animals. Following contact sensitization, normal animals were also found to simultaneously contain both antigen specific suppressor T cells and lymph node effector cells. However, these normal animals were fully capable of mobilizing their effector cells into the systemic circulation, thereby allowing a localization of these cells to peripheral sites of antigen challenge. Our results suggest that UVR is probably not a significant inducer of suppressor T-cell activity to topically applied antigens. Rather, UVR exposure appears to modify the normal relationship which exists between effector and regulatory immune responses in vivo. It does so by either causing a direct reduction in the skin's APC function, a situation which results in an absence of effector cell generation to antigens applied to UVR-exposed skin sites, inhibiting the capacity of effector cells to gain access to skin sites of antigen challenge or by sequestering the lymphocytes with effector cell potential into the draining peripheral lymph nodes. Each of these situations result in a similar effect on the UVR-exposed host, that being a reduced capacity to elicit a CH response. We hypothesize that altered DTH responses, altered alloresponses, and altered graft-versus-host responses, all of which have been observed in UVR exposed animals, may result from similar mechanisms.