• Composites Research
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• 제36권3호
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• pp.141-153
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• 2023

본 리뷰 논문에서는 일반 접촉 역학 이론과 더불어 유기탄성체 마찰에 관한 이론 및 배경을 소개한다. 특히 Greenwood & Williamson 접촉 역학 이론을 확장하여 거친 표면을 자기-아핀(self-affine) 특성으로 고려한 접촉 역학 및 마찰의 수학적 모델을 제시한 Klüppel & Heinrich 이론을 중심으로 유기탄성체 복합재료의 마찰 거동에 대해 살펴본다. 자기-아핀 특성에 의한 노면의 멀티스케일 거칠기로 인해 미끄러짐 마찰 시 유기탄성체 복합재료는 다양한 주파수에 따른 동적 변형이 가해지며 이때 재료가 나타내는 점탄성이 마찰 거동에 주요한 영향을 미친다. 따라서 유기탄성체 복합재료의 비선형 점탄성을 고려하여 광범위한 주파수 영역에서의 점탄성 거동인 마스터커브를 구축하는 원리 및 방법을 제시하였다. 마지막으로 유기탄성체 복합재료 마찰 이론을 타이어 트레드 컴파운드와 노면 간의 마찰에 응용한 실험적 결과와 그 물리적 의미를 이론과 접목하여 설명하였다.

• 한국지반환경공학회 논문집
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• 제24권6호
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• pp.5-11
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• 2023

석탄 및 석유와 같은 전통적인 화석 연료는 연소 시 발생하는 열을 통해 에너지를 공급한다. 이러한 과정에서 대기 중에 이산화탄소를 배출하고 지구 온난화를 유발한다. 이산화탄소 저감을 위해 많은 연구들이 수행되고 있다. 이러한 방안 중 하나로, 이산화탄소 지중 저장 기술이 관심을 받고 있다. 이산화탄소 지중 저장은 플랜트 등에서 발생하는 이산화탄소를 포집하여 덮개암 하부 포화지반층에 이산화탄소를 주입하여 저장하는 방법을 일컫는다. 하지만, 제한된 공간에 더 많은 양의 이산화탄소 저장을 위해서는 저장 효율의 향상이 필요하다. 따라서, 본 연구에서는 계면활성제를 활용하여 이산화탄소 지중 저장의 효율을 향상하고자 한다. 또한, 지중저장소의 위치에 따라 압력 및 온도가 상이하기 때문에 이산화탄소는 기체, 액체 및 초임계 상태로 존재가능하다. 따라서, 이산화탄소 상태에 따른 저장 효율 특성을 평가하였다. 그 결과, 주입속도 및 계면활성제의 활용은 저장 효율의 향상을 기대할 수 있고, 그 효과는 기체, 액체 및 초임계 상태 이산화탄소에 발휘되는 것을 확인하였다.

• 대한토목학회논문집
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• 제26권6B호
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• pp.623-631
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• 2006

본 연구에서는 하상변화가 존재하는 자연하천에서의 물질거동을 해석하기 위한 주기적저장대모형을 개발하였다. 저장대 구조에 따른 저장효과를 살펴보기 위하여 자연하천의 특성을 고려한 4개의 주기적 여울-소 구조를 갖는 와 흐름에서 소금물과 염료를 이용하여 실험한 모형실험결과를 이용하였다. 염료실험 결과, 물질이동 및 혼합거동은 하상 및 하안의 구조에 영향을 받는 것으로 나타났다. 기존의 저장대분산모형이 주기적으로 변화하는 저장대 구조에 의한 이동 및 질량교환 효과를 정확히 재현하지 못하는 것에 비해서 경계변화에 따른 질량교환 효과를 보다 효과적으로 재현할 수 있는 주기적저장대모형은 모형 실험 결과를 잘 재현하는 것으로 나타났다. 새로운 저장대모형을 미국 텍사스주의 Sabin River에 적용하였으며, 그 결과는 실험을 통해서 수집된 농도분포를 잘 재현하는 것으로 나타났다.

• 한국자원식물학회:학술대회논문집
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• 한국자원식물학회 2020년도 춘계학술대회
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• pp.20-20
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• 2020

Eranthis stellata Maxim. is a perennial plant that grows around the valley. E. stellata is concerned about the decline in natural habitats due to climate change in KOREA, continues to be observed and protected as an endangered species (Least Concrned, LC). Nevertheless, studies on the characteristics of the seeds of E. stellata are insufficient. So, this study analyzed the morphological characteristics and dormancy types of seeds. Seeds of E. stellata was collected in April at Gyeongsangbuk-do Arboretum and kept at 5 ℃ until using. To investigate the morphology of seeds, an optical microscope and a scanning electron microscope (SEM) were used. GA3 treated or untreated seeds (4 replicates of 25 seeds each) were observed germination and embryo growth for 1 month at 5 ℃ and 25/15 ℃ (12h day/12h night). The seed surface of E. stellata, light brown, was observed as a common characteristic of Eranthis genus, reticulate. The short axis of seeds was 1.11~1.77mm (average 1.44mm), and the long axis was 1.27~1.91mm (average 1.63mm), which was investigated in a slightly round shape (subglose). While no germination was observed at all conditions, Embryo growth was observed at 5 ℃ both in the control group and with GA3treated groups. Thus, seeds of E. stellata are classified as morphological physiological dormancy (MDP), which requires embryonic development and dormant break at the same time. These results can be useful information for determining morphological physiological seed dormancy and germination, and will be an important basic data for seed propagation of E. stellata as a resource.

• 한국지하수토양환경학회지:지하수토양환경
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• 제28권6호
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• pp.58-70
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• 2023

The improper management of radioactive waste or accidents caused by natural disasters can result in the release of radioactive materials into the surrounding environment, potentially leading to soil and groundwater contamination by radionuclides. In this study, adsorption-desorption behaviors of the radionuclides (cobalt and strontium) in natural soil, montmorillonite, Mn-PILC, Fe-PILC, and fishbone were investigated. Several models were used to predict adsorption isotherms of radionuclides on various absorbents. Adsorption isotherms of cobalt and strontium in several adsorbents were examined at pH 5.5. The amount of sorbed cobalt and strontium were represented fishbone > natural soil > Mn-PILC > Fe-PILC > montmorillonite and natural soil > Mn-PILC > fishbone > Fe-PILC > montmorillonite, respectively. Adsorption datas were fitted with several models such as Freundlich, Langmuir, Sips, Redlich-Peterson, Khan, and Generalized model. The results of curve fitting showed R²> 0.98 in all of adsorption models, except Sr²⁺ adsorption onto montmorillonite. For modified clays (Mn-PILC, Fe-PILC), it is suggested that, unlike natural soils and fish bones, there are not only single adsorption mechanisms but also adsorption mechanisms based on chemical adsorption and surface charge. In the case of fish bones, due to the relatively higher adsorption capacity than modified clays and its characteristic of significant desorption, it is expected more suitable for the removal of radionuclides in aquatic environments than for the immobilization of radionuclides in soil.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• 제4권4호
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• pp.159-176
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• 2023

The conservation of the raccoon dog (Nyctereutes procyonoides) in South Korea requires the protection and preservation of natural habitats while additionally ensuring coexistence with human activities. Applying habitat map modeling techniques provides information regarding the distributional patterns of raccoon dogs and assists in the development of future conservation strategies. The purpose of this study is to generate potential habitat distribution maps for the raccoon dog in South Korea using geospatial technology-based models. These models include the frequency ratio (FR) as a bivariate statistical approach, the group method of data handling (GMDH) as a machine learning algorithm, and convolutional neural network (CNN) and long short-term memory (LSTM) as deep learning algorithms. Moreover, the imperialist competitive algorithm (ICA) is used to fine-tune the hyperparameters of the machine learning and deep learning models. Moreover, there are 14 habitat characteristics used for developing the models: elevation, slope, valley depth, topographic wetness index, terrain roughness index, slope height, surface area, slope length and steepness factor (LS factor), normalized difference vegetation index, normalized difference water index, distance to drainage, distance to roads, drainage density, and morphometric features. The accuracy of prediction is evaluated using the area under the receiver operating characteristic curve. The results indicate comparable performances of all models. However, the CNN demonstrates superior capacity for prediction, achieving accuracies of 76.3% and 75.7% for the training and validation processes, respectively. The maps of potential habitat distribution are generated for five different levels of potentiality: very low, low, moderate, high, and very high.

• 한국정보전자통신기술학회논문지
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• 제17권1호
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• pp.67-75
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• 2024

복잡한 도시 환경에서 횡단보도는 보행자의 안전한 이동을 위해 중요한 역할을 한다. 하지만 시각 장애인에게는 횡단보도가 큰 위험 요소가 될 수 있다. 안전한 보행을 위한 점자 블록이나 음향 신호등과 같은 보조 시설들이 존재하지만, 부실한 관리로 인하여 때로는 오히려 안전을 저해하는 요소로 작용할 수 있다. 본 논문에서는 시각 장애인의 보행 보조를 위한 애플리케이션에 활용할 수 있는 딥러닝 기반 실시간 횡단보도 탐지 모델에 정확도 향상을 위한 방법을 제안한다. 횡단보도 이미지의 흰색 줄이 도로 표면과 대조를 이루는 특성을 활용하여 이미지를 이진화하고, 이를 통해 횡단보도를 더 잘 인식할 수 있게 하고 횡단보도 전체와 중간 부분을 각각 학습한 두 가지 모델을 활용하여 횡단보도의 위치를 더 정확하게 파악할 수 있도록 하였다. 또한 횡단보도를 인식하는 경계 상자를 전체와 부분의 두 단계로 생성하여 정확도를 높이고자 하였다. 이러한 방법을 통해 횡단보도 횡단 영상에서 RGB 이미지 학습에서 탐지 모델이 탐지하지 못한 프레임들을 추가로 탐지할 수 있었다.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4642-4646
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• 2023

The Tb³⁺ or Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor were fabricated by funace at 1500 ℃ for 12 h using a solid state reaction. The XRD (X-ray diffraction_Panalytical X'Pert Pro) and FE-SEM (field emission scanning electron microscope) are measured to confirm the crystalline structure and surface morphology of the phosphor. The Tb³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor emits the lights in 470~650 nm wavelength range due to transitions from ⁵D₄ to ⁷F_j. Therefore, it shows the green region in the CIE chromaticity diagram under both UV and X-rays excitations. The Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor emits the lights in 550~750 nm wavelength range because of ⁵D_i to ⁷F_j. The emission is confirmed to be in the red region using the CIE chromaticity diagram. The Tb³⁺ or Eu³⁺-doped Lu₂Gd₁Ga₂Al₃O₁₂ phosphor shows the characteristic f-f transition with a long decay time, which is about several milliseconds. They have the high efficiency of light emission for X-ray because of their high effective Z number (Z_eff = 58.5) and density. Therefore, they are very much promising phosphors for X-ray imaging application in medical fields.

• The Journal of Advanced Prosthodontics
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• 제16권1호
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• pp.12-24
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• 2024

PURPOSE. This study aimed to evaluate the maximum vertical wear, volume wear, and surface characteristic of antagonist enamel, opposing monolithic zirconia or lithium disilicate crowns. MATERIALS AND METHODS. The study comprised 24 participants (n = 12), who were randomly allocated to receive either a 5 mol% Y-TZP or a lithium disilicate crown in positions which would oppose the natural first molar tooth. The contralateral first molar along with its antagonist was considered as the enamel opposing natural enamel control. Data collection was performed using an intraoral scanner and polyvinylsiloxane impression. The means of the maximum vertical loss and the volume loss at the occlusal contact areas of the crowns and the various natural antagonists were measured by 3D comparison software. A scanning electron microscope was subsequently used to assess the wear characteristics. RESULTS. The one-year results from 22 participants (n = 11) indicated no significant differences when comparing the zirconia crown's antagonist enamel (40.28 ± 9.11 ㎛, 0.04 ± 0.02 mm³) and the natural enamel wear (38.91 ± 7.09 ㎛, 0.04 ± 0.02 mm³) (P > .05). Also, there is no significant differences between lithium disilicate crown's antagonist enamel (47.81 ± 9.41 ㎛, 0.04 ± 0.02 mm³) and the natural enamel wear (39.11 ± 7.90 ㎛, 0.04 ± 0.02 mm³) (P > .05). CONCLUSION. While some studies suggested that monolithic zirconia caused less wear on opposing enamel than lithium disilicate, this study found similar wear levels to enamel for both materials compared to natural teeth.

• Korean Journal of Radiology
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• 제20권4호
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• pp.589-598
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• 2019

Objective: To evaluate whether data acquired from perfusion computed tomography (PCT) parameters can aid in the prediction of treatment outcome after palliative chemotherapy in patients with unresectable advanced gastric cancer (AGC). Materials and Methods: Twenty-one patients with unresectable AGCs, who underwent both PCT and palliative chemotherapy, were prospectively included. Treatment response was assessed according to Response Evaluation Criteria in Solid Tumors version 1.1 (i.e., patients who achieved complete or partial response were classified as responders). The relationship between tumor response and PCT parameters was evaluated using the Mann-Whitney test and receiver operating characteristic analysis. One-year survival was estimated using the Kaplan-Meier method. Results: After chemotherapy, six patients exhibited partial response and were allocated to the responder group while the remaining 15 patients were allocated to the non-responder group. Permeability surface (PS) value was shown to be significantly different between the responder and non-responder groups (51.0 mL/100 g/min vs. 23.4 mL/100 g/min, respectively; p = 0.002), whereas other PCT parameters did not demonstrate a significant difference. The area under the curve for prediction in responders was 0.911 (p = 0.004) for PS value, with a sensitivity of 100% (6/6) and specificity of 80% (12/15) at a cut-off value of 29.7 mL/100 g/min. One-year survival in nine patients with PS value > 29.7 mL/100 g/min was 66.7%, which was significantly higher than that in the 12 patients (33.3%) with PS value ≤ 29.7 mL/100 g/min (p = 0.019). Conclusion: Perfusion parameter data acquired from PCT demonstrated predictive value for treatment outcome after palliative chemotherapy, reflected by the significantly higher PS value in the responder group compared with the non-responder group.