• Current Optics and Photonics
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• 제4권1호
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• pp.9-15
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• 2020

Fresnel zone plates have been widely used in many applications, such as x-ray telescopes, microfluorescence, and microimaging. To obtain an x-ray Fresnel zone plate, many fabrication methods, such as electron-beam etching, ion-beam etching and chemical etching, have been developed. Fresnel zone plates fabricated by these methods will inevitably lead to some nonideal factors, which have an impact on the focusing characteristics of the zone plate. In this paper, the influences of these nonideal factors on the focusing characteristics of the zone plate are studied systematically, by numerical simulations based on scalar diffraction theory. The influence of the thickness of a Fresnel zone plate on the absolute focusing efficiency is calculated for a given incident x-ray's wavelength. The diffraction efficiency and size of the focal spot are calculated for different incline angles of the groove. The simulations of zone plates without struts, with regular struts, and with random struts are carried out, to study the effects of struts on the focusing characteristics of a zone plate. When a Fresnel zone plate is used to focus an ultrashort x-ray pulse, the effect of zone-plate structure on the final pulse duration is also discussed.

• 한국방사선학회논문지
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• 제15권7호
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• pp.949-956
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• 2021

본 연구의 목적은 전자빔 치료에서 산란선을 차폐하는 데 사용되는 납의 단점을 극복하기 위한 대체 재료로 텅스텐 나노입자를 선택하여 고선량에서 발생하는 산란선에 차폐 효과가 있는지 여부를 평가하는 것이다. 선량계의 위치와 조사야의 크기를 일정하게 설정하기 위해 판을 자체 제작하였다. 유리 선량계는 10 × 10 cm² 크기의 조사야의 중앙에서 십자로 1, 2, 4 cm 떨어진 지점에 위치하여 12곳의 지점에 위치시켰다. 10 × 10 cm² 크기의 텅스텐 나노입자 차폐체를 0.4, 0.75, 1 mm의 소재로 두께 0.75 mm에서 최대 두께 4.0 mm의 총 12가지 유형의 차폐가 적용되었다. 선형가속기를 사용해서 6 MeV에서 4회, 12 MeV에서 4회 측정하였고 선량의 세기는 100 MU로 조사하였다. 실험 결과 조사야로부터 1 cm 거리에서 4 mm 차폐판이 가장 높은 차폐 효과를 보였다. 조사야로부터 2 cm 거리에 적용된 1 mm 차폐판이 차폐 효과가 가장 낮았다. 텅스텐 차폐판의 두께가 두꺼워짐에 따라 전자선 차폐 효과는 급격히 증가하였다. 결론적으로 텅스텐 나노입자는 전자빔 치료에서 납의 대체 재료로 사용이 가능함을 확인하였다.

• Advances in materials Research
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• 제5권4호
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• pp.279-298
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• 2016

Present disquisition proposes an analytical solution method for exploring the buckling characteristics of porous magneto-electro-elastic functionally graded (MEE-FG) plates with various boundary conditions for the first time. Magneto electro mechanical properties of FGM plate are supposed to change through the thickness direction of plate. The rule of power-law is modified to consider influence of porosity according to two types of distribution namely even and uneven. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM plate under magneto-electrical field via Hamilton's principle. An analytical solution procedure is exploited to achieve the non-dimensional buckling load of porous FG plate exposed to magneto-electrical field with various boundary condition. A parametric study is led to assess the efficacy of material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage, boundary conditions, aspect ratio and side-to-thickness ratio on the non-dimensional buckling load of the plate made of magneto electro elastic FG materials with porosities. It is concluded that these parameters play remarkable roles on the dynamic behavior of porous MEE-FG plates. The results for simpler states are confirmed with known data in the literature. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• 산업경영시스템학회지
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• 제41권3호
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• pp.186-193
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• 2018

Modern manufacturing industries is to produce both precise and robust mechanical parts without failure while they are in service. In order to prevent a part failure for its lifetime, a mechanical design for a part should be examined on a basis of mechanical simulation. A nozzle plate, being a key part in steam engines, changes flow directions of steam in a turbine used in power plant. This paper is to the design and test for part safety and durability. Currently, nozzle plates are fabricated by welding nozzles to their plates. Welding causes some defects on the used materials while they are being manufactured. Another major defect is un-even pitches between welded nozzles. Welding causes phase changes because of high melting temperature of metal. This leads to decay on the welding spots, which weakens their structural strength and then, may lead to early damages on mechanical structures. This research proposes assembly-typed nozzle plate without welding. From the beginning, nozzle and plate are designed for insertion-typed assembly. Nozzle head and foot are designed in accordance with the grooves on outer ring and inner ring of a plate to make mating surfaces. Then the nozzle plate should be proved for structural and fatigue safety before they are put in manufacturing. This research adopts commercial softwares for modeling and mechanical simulation. The test result shows that the design with smaller mating area and deeper insertion produces higher safety in terms of structure and durability. From the conclusion, this paper proposes the assembly-typed nozzle plate to replace the welding typed.

• 대한의용생체공학회:의공학회지
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• 제19권2호
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• pp.133-142
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• 1998

Bayesian SPECT 영상재구성에 있어서 정교한 형태의 사전정보를 사용할 경우 bias 및 variance와 같은 통계적 차원에서의 정량적 성능을 향상시킬 수 있다. 특히, "thin plate" 와 같은 고차의 smoothing 사전정보는 "membrane"과 같은 일반적인 다른 사전 정보에 비해 bias를 개선시키는 것으로 알려져 있다. 그러나, 이와 같은 장점은 영상재구성 알고리즘에 내재하는 hyperparameters의 값을 최적으로 선택하였을 경우에만 적용된다. 본 연구에서는 thin plate와 membrane의 두가지 대표적인 사전정보를 포함하는 영상재구성 알고리즘의 정량적 성능에 대해 집중 고찰한다. 즉, 알고리즘에 내재하는 hyperparameters 가 통계적 차원에서 bias와 variance에 어떠한 영향을 미치는지 관찰한다. 실험에서 Monte Carlo noise trials를 사용하여 bias와 variance를 계산하며, 각 결과를 ML-EM 및 filtered backprojection으로부터 얻어진 bias 및 variance와 비교한다. 결론적으로 thin plate와 같은 고차의 사전정보는 hyperparameters의 선택에 민감하지 않으며, hyperparameters 값의 전 범위에 걸쳐 bias를 개선시킴을 보인다. 걸쳐 bias를 개선시킴을 보인다.

• Structural Engineering and Mechanics
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• 제72권1호
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• pp.113-129
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• 2019

A four-variable shear deformation refined plate theory has been proposed for dynamic characteristics of smart plates made of porous magneto-electro-elastic functionally graded (MEE-FG) materials with various boundary conditions by using an analytical method. Magneto-electro-elastic properties of FGM plate are supposed to vary through the thickness direction and are estimated through the modified power-law rule in which the porosities with even and uneven type are approximated. Pores possibly occur inside functionally graded materials (FGMs) due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical properties. The governing differential equations and boundary conditions of embedded porous FGM plate under magneto-electrical field are derived through Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factors. An analytical solution procedure is used to achieve the natural frequencies of embedded porous FG plate supposed to magneto-electrical field with various boundary condition. A parametric study is led to carry out the effects of material graduation exponent, coefficient of porosity, magnetic potential, electric voltage, elastic foundation parameters, various boundary conditions and plate side-to-thickness ratio on natural frequencies of the porous MEE-FG plate. It is concluded that these parameters play significant roles on the dynamic behavior of porous MEE-FG plates. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• Earthquakes and Structures
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• 제26권3호
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• pp.203-218
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• 2024

Beam-column joints in the frame structure are at high risk of brittle shear failure which would lead to significant residual deformation and even the collapse of the structure during an earthquake. In order to improve the damage issue and enhance the recoverability of the beam-column joints, a sector lead rubber damper (SLRD) has been developed. The SLRD can increase the bearing capacity and energy dissipation capacity, and also demonstrating recoverability of seismic performance following cyclic loading. In this paper, the hysteretic behavior of SLRD was experimentally investigated in terms of the regular hysteretic behavior, large deformation behavior and fatigue behavior. Furthermore, a parametric analysis was performed to study the influence of the primary design parameters on the hysteretic behavior of SLRD. The results show that SLRD resist the exerted loading through the shear capacity of both rubber parts coupled with the lead cores in the pre-yielding stage of lead cores. In the post-yielding phase, it is only the rubber parts of the SLRD that provide the shear capacity while the lead cores primarily dissipate the energy through shear deformation. The SLRD possesses a robust capacity for large deformation and can sustain hysteretic behavior when subjected to a loading rotation angle of 1/7 (equivalent to 200% shear strain of the rubber component). Furthermore, it demonstrates excellent fatigue resistance, with a degradation of critical behavior indices by no more than 15% in comparison to initial values even after 30 cycles. As for the designing practice of SLRD, it is recommended to adopt the double lead core scheme, along with a rubber material having the lowest possible shear modulus while meeting the desired bearing capacity and a thickness ratio of 0.4 to 0.5 for the thin steel plate.

• Steel and Composite Structures
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• 제5권2_3호
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• pp.235-246
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• 2005

Local buckling is a major consideration in the design of thin-walled cold-formed steel sections. The main effect of local buckling in plate elements under longitudinal compressive stresses is to cause a redistribution of the stresses in which the greatest portion of the load is carried near the supporting edges of the plate junctions. The redistribution produces increased stresses near the plate junctions and high bending stresses as a result of plate flexure, leading to ultimate loads below the squash load of the section. In singly symmetric cross-sections, the redistribution of longitudinal stress caused by local buckling also produces a shift of the line of action of internal force (shift of effective centroid). The fundamentally different effects of local buckling on the behaviour of pin-ended and fixed-ended singly symmetric columns lead to inconsistencies in traditional design approaches. The paper describes local buckling and shift of effective centroid of thin-walled cold-formed steel channel columns. Tests of channel columns have been described. The experimental local buckling loads were compared with the theoretical local buckling loads obtained using an elastic finite strip buckling analysis. The shift of the effective centroid was also compared with the shift predicted using the Australian/New Zealand and American specifications for cold-formed steel structures.

• 대한치과교정학회지
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• 제47권5호
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• pp.289-297
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• 2017

Objective: The objective of this study was to analyze the patterns of tooth movements when distalization of mandibular molars using a mini-plate took place. A finite element analysis was applied to analyze patterns of tooth movements. Methods: The model of the mandible and teeth were used to build a finite element analysis model, and a mini-plate was inserted in the mandibular ramus. Two different orthodontic forces were established for displacement of mandibular molars. Orthodontic forces were applied at the level of the bracket and at the level of the cemento-enamel junction in the mandibular canine respectively. Results: Applying orthodontic forces at the level of the cemento-enamel junction resulted in a greater biomechanical bodily movement in distalization of the mandibular molars compared to when the orthodontic forces were applied at the level of the bracket. Applying orthodontic forces to the cemento-enamel junction also resulted in unwanted greater extrusive movements in distalization of the mandibular molars compared to the bracket level. Conclusions: With considering the mode of orthodontic teeth movement, applying different vertical orthodontic forces for distalization of mandibular molars can lead to more effective distalization of teeth.

• 한국세라믹학회지
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• 제47권6호
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• pp.503-508
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• 2010

$Eu^{2+}$-doped $\beta$-SiAlONs ($Si_{6-z}Al_zO_zN_{8-z}:Eu_y$) are recognized as promising phosphor materials to build an white LED for lighting application due to its excellent absorption/emission efficiency in the long wave length region. In this research, the fabrication of $\beta$-SiAlON:Eu plate phosphor by sintering was investigated with fixed Eu content(y) and varied composition of the host lattice(z). The addition of the activator $Eu_2O_3$ lead to enhanced densification by forming the transient liquid phase. The refinement of a composition by the calculated lattice parameter indicated that the measured composition of the fabricated specimens is nearly same to that of designed one. The single phase $\beta$-SiAlON:Eu plate with relative density of 96.4% was achieved by addition of 2 wt% CaO, which implies the possibility of full densification by adjusting the processing variables.