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하태광 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.4
Zerodur, one of the optical materials, was used for large spherical mirrors in this study. For weight reduction, several types of honeycomb structures were investigated. The finite element simulation was used for deformation and mode analysis. It was revealed that the weight reduction rate and maximum deflection due to the gravity effect vary depending on the honeycomb structures. Additionally, this study highlights the potential of spline-shaped honeycomb structures as an alternative for weight reduction, and triangular honeycomb structures demonstrated the less deformation by the gravity effect. The findings from this study provide valuable insights for designing lightweight and high-performance spherical mirrors in optical systems.
구면 반사경의 측면 지지점을 이용한 반사경 경량화 설계: 허니컴 패턴 구조와의 비교 연구
하태광 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.5
In general, a large mirror without weight reduction in large optical or space telescope systems can increase the system’s weight or lead to significant deformation of the mirror surface. Thus, it is imperative to pursue lightweight design strategies. In this paper, the structure design of a spherical mirror, a diameter of 600mm and a mirror radius of 2,000mm, was investigated to reduce weight and minimize deformation. To establish load paths for internal and external loads, stiffeners were added across the lateral supports. This approach effectively reduced both weight and deformation caused by gravity. Weight reduction and reduction percentages were quantified, and the mirror deformation was evaluated by using finite element analysis (FEA). The proposed structures were compared with honeycomb structures for weight reduction. This evaluation allowed to assess the deformation characteristics and the potential advantages of the proposed structures for lightweight mirrors.
기하학적 형상을 응용한 구면 반사경 구조설계에 관한 연구
하태광 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.5
With the advancement of optical design and manufacturing technology, optical components have found diverse applications, spanning from semiconductors to the aerospace industry. A reflective mirror is a basic component in optics and plays a crucial role as the medium to reflect light. In this paper, a large mirror with a 700mm diameter was designed as a primary mirror using fused silica. The rear side of the mirror was subdivided into several equal angles, and neighboring vertices on the circumference were connected to establish a polygon. Accordingly, the geometric shapes of triangle, square, pentagon, and hexagon were formed. Furthermore, the mirror structure was strengthened by employing straight lines passing the vertices and the center of the circle. Based on the finite element analysis, deformations of the mirrors caused by the gravitational force were evaluated. Weight and deformation of the mirror structures were compared and analyzed to find a proper structure to reduce weight and deformation. This paper, therefore, presents a structural solution aimed at reducing the weight and deformation of a large aperture mirror induced by gravitational forces, thereby suggesting a geometric shape based structure to reduce surface deformation of a mirror.
2차원 튜브벤딩의 단면 변형에 관한 실험적 연구: 인장, 벤딩 시퀀스 및 벤딩 각도 중심으로
하태광 한국소성∙가공학회 2023 소성가공 : 한국소성가공학회지 Vol.32 No.4
While tube bending is a conventional forming technique, it is still used to make curved products for load-bearing members or aesthetically pleasing parts in various manufacturing industries such as automotive, aerospace, and others. Whole or local deformation of the final product such as springback, distortion, or local buckling are of interest in metal forming or precision manufacturing. In this paper, the factors affecting the cross-sectional deformation are explored. A 5-axis stretch bending machine was used for two-dimensional bending with extruded AA6082-T4 rectangular tubes. Three different bending sequences were employed: stretch before bending, stretch after bending, simultaneous bending and stretch. Furthermore, by considering both the stretch and bending angle, cross-sectional deformation was also analyzed. It was observed that employing stretch bending techniques can effectively reduce cross-sectional deformation and contribute to overall quality enhancement. Through this study, it was revealed that these factors have an impact on the cross-sectional deformation of the tubes.
하태광 한국기계기술학회 2024 한국기계기술학회지 Vol.26 No.2
The laser power has been continually increased since the laser was developed in the mid-20th century. Achieving higher laser power requires not only enhancing the cooling performance of laser systems but also addressing the potential degradation of optical characteristics due to thermal deformation induced by laser beam absorption in a mirror. This study delves into the thermal deformation characteristics of mirrors in high-power laser systems. To minimize thermal deformation by heat absorption, Zerodur, known for its low coefficient of thermal expansion, was employed as the mirror material. Various configurations including circular, rectangular, and spline shapes were implemented on a solid mirror structure. Furthermore, two different diameter of a mirror, 300mm and 400mm, were considered to investigate the size effect of the high-power laser beams. Also, three different transmitted beam power were adopted: 50W, 250W, and 500W. Based on the finite element analysis for the thermal deformation, the deformation characteristics of the different types of mirror structures were investigated and analyzed for high-power laser systems.
Chlorogenic acid 및 인동등 ethyl acetate 분획의 비장 및 흉선 세포에서의 유전자 발현 분석을 통한 면역조절효과
하태광 ( Tae Kwang Ha ),이영철 ( Young Cheol Lee ) 대한본초학회 2011 大韓本草學會誌 Vol.26 No.2
Objective: Lonicera japonica contains anti complementary polysaccharides and polyphenolic compound. Among these polyphenolic substances, chlorogenic acid is the major active component of this plant. However, the immunological mechanisms for these activities, have not been elucidated, nor the active components. To clarify immunomodulatory effects of those we examined the relationship between the activity of CD8+ T cell-mediated lysis and the frequency of cytokine profiles in spleen, thymus (especially IFN-γ, IL-4, GM-CSF etc.) expressing CD8+ T cells activated by IL-2. Methods: To study immunomodulatory effects ethyl acetate fraction from Lonicera japonica, chlorogenic acid on cytokine gene expression from spleen, thymus cells, RT-PCR was performed after quantitative normalization for each gene by a densitometry using β-actin gene expression. A modified standard 51Cr-release assay was used to measure cytotoxic activities of cytotoxic T cells. Spleen, thymus cells from NOD mice were stained with CD3, CD4, CD44, CD69 in staining buffer and analyzed by two color flow cytometry. Results: We showed that ethyl acetate fraction from Lonicera japonica in combination with IL-2 resulted in a significant enhancement of PCR products for IFN-γ, IL-4, IL-10, GM-CSF, IL-6 and cytotoxtic CD8+ T cell proportion in spleen and thymus T cells in NOD mice. This suggests that IFN-γ, IL-6 like IL-4 may be acting as a regulatory rather than proinflammatory cytokine. Conclusions: In conclusion, based on the results of the present study which showed that ethyl acetate fraction from Lonicera japonica and chlorogenic acid upregulating cytokine gene expression in spleen and thymus, we are tempted to speculate that some of the therapeutic efficacies such as anti-diabetic activity of Lonicera japonica are due to the immunomodulatory its ethylacetate fraction and chlorogenic acid.