• Structural Engineering and Mechanics
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• 제76권4호
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• pp.451-463
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• 2020

In this paper, a new semi-analytical solution for estimating the pull-in parameters of electrically actuated functionally graded (FG) nanobeams is proposed. All the bulk and surface material properties of the FG nanoactuator vary continuously in thickness direction according to power law distribution. Here, the modified couple stress theory (MCST) and Gurtin-Murdoch surface elasticity theory (SET) are jointly employed to capture the size effects of the nanoscale beam in the context of Euler-Bernoulli beam theory. According to the MCST and SET and accounting for the mid-plane stretching, axial residual stress, electrostatic actuation, fringing field, and dispersion (Casimir or/and van der Waals) forces, the nonlinear nonclassical equation of motion and boundary conditions are obtained derived using Hamilton principle. The proposed semi-analytical solution is derived by employing Galerkin method in conjunction with the Particle Swarm Optimization (PSO) method. The proposed solution approach is validated with the available literature. The freestanding behavior of nanoactuators is also investigated. A parametric study is conducted to illustrate the effects of different material and geometrical parameters on the pull-in response of cantilever and doubly-clamped FG nanoactuators. This model and proposed solution are helpful especially in mechanical design of micro/nanoactuators made of FGMs.

• Current Optics and Photonics
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• 제2권2호
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• pp.147-152
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• 2018

We propose a novel bi-focal metallic Fresnel zone plate (MFZP) with shallow depth-of-field (DOF) characteristics. We design the specific annular slit patterns, exploiting the phase-selection-rule method along with the particle swarm optimization algorithm, which we have recently proposed. We numerically investigate the novel characteristics of the bi-focal MFZP in comparison with those of another bi-focal MFZP having equivalent functionality but designed by the conventional multi-zone method. We verify that whilst both bi-focal MFZPs can produce dual focal spots at $15{\mu}m$ and $25{\mu}m$ away from the MFZP plane, the former exhibits characteristics superior to those of the latter from the viewpoint of axial resolution, including the axial side lobe suppression and axial DOF shallowness. We expect the proposed bi-focal MFZP can readily be fabricated with electron-beam evaporation and focused-ion-beam processes and further be exploited for various applications, such as laser micro-machining, optical trapping, biochemical sensing, confocal sensing, etc.

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1860-1865
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• 2019

The confinement degradation of the energetic particles during RMP would be a key issue in success of realizing the successful energy production using fusion plasma, because a 3.5 MeV energetic alpha particle should be able to sustain the burning plasma after the ignition. As KSTAR recent results indicate the generation of high-performance plasma(${\beta}_p{\sim}3$), the confinement of the energetic particles is also an important key aspect in neutral beam driven plasma. In general, the measured absolute value of the neutron intensity is generally used for to estimating the confinement time of energetic particles by comparing it with the theoretical value based on transport calculations. However, the availability of, but for its calculation process, many accurate diagnostic data of plasma parameters such as thermal and incident fast ion density, are essential to the calculation process. In this paper, the time evolution of the neutron signal from an He3 counter during the beam blank has permitted to facilitate the estimation of the slowing down time of energetic particles and the method is applied to investigate the fast ion effect on ELM suppressed KSTAR plasma which is heated by high energy deuterium neutral beams.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.942-948
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• 2021

The aim of this work is to help inform the decision for choosing a convenient material for the PGAA (Prompt Gamma Activation Analysis) collimator plug to be installed at the tangential channel of the Moroccan Triga Mark II Research Reactor. Two families of materials are usually used for collimator construction: a mixture of high-density polyethylene (HDPE) with boron, which is commonly used to moderate and absorb neutrons, and heavy materials, either for gamma absorption or for fast neutron absorption. An investigation of two different collimator designs was performed using N-Particle Monte Carlo MCNP6.2 code with the ENDF/B-VII.1 and MCLIP84 libraries. For each design, carbon steel and lead materials were used separately as collimator heavy materials. The performed study focused on both the impact on neutron beam quality and the neutron-gamma background at the exit of the collimator beam tube. An analysis and assessment of the principal findings is presented in this paper, as well as recommendations.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.91-91
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• 2015

반도체 공정의 발전에 의해 최근 생산되는 메모리 등은 십 수 나노미터까지 좁아진 선 폭을 갖게 되었다. 이러한 이유로, 기존에는 큰 문제를 발생시키지 않던 나노미터 영역의 입자들이 박막 증착 공정과 같은 반도체 제조공정 수율을 저감시키게 되었다. 따라서 오염입자의 유입을 막거나 제어하기 위해 transmission electron microscopy (TEM)나 scanning electron microscopy (SEM)과 같은 전자현미경을 활용한 비 실시간 입자 측정 방법 및 광원을 이용하는 in-situ particle monitor (ISPM) 및 전기적 이동도를 이용한 scanning mobility particle sizer (SMPS) 등 다양한 원리를 이용한 실시간 입자 측정방법이 현재 사용중에 있다. 이 중 진공 내 입자의 수농도를 측정하기 위해 개발된 particle beam mass spectrometer (PBMS) 기술은 박막 증착 공정 등 chemical vapor deposition (CVD) 방법을 이용하는 진공공정에서 활용 가능하여 개발이 진행되어 왔다. 본 연구에서는 PBMS의 한계점인 입자 밀도, 형상 등의 특성분석이 용이하도록 PBMS와 scanning electron microscopy (SEM), 그리고 energy dispersive spectroscopy (EDS) 기술을 결합하여 입자의 직경별 개수농도, 각 입자의 형상 및 성분을 함께 측정 가능하도록 하였다. 협소한 반도체 제조공정 내부 공간에 적용 가능하도록 기존 PBMS 대비 크기 또한 소형화 하였다. 각 구성요소인 공기역학 집속렌즈, electron gun, 편향판, 그리고 패러데이 컵의 설치 및 물리적인 교정을 진행한 후 입자발생장치를 통해 발생시킨 sodium chloride 입자를 상압 입자 측정 및 분류장치인 SMPS 장치를 이용하여 크기별로 분류시켜 압력차를 통해 PBMS로 유입시켜 측정을 진행하였다. 나노입자의 입경분포, 형상 및 성분을 측정결과를 토대로 장치의 측정정확도를 교정하였다. 교정된 장치를 이용하여 실제 박막 증착공정 챔버의 배기라인에서 발생하는 입자의 수농도, 형상 및 성분의 복합특성 측정이 가능하였으며, 최종적으로 실제 공정에 적용가능하도록 장치 교정을 완료하였다.

• 대한치과기공학회지
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• 제37권1호
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• pp.23-29
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• 2015

Purpose: The selective laser melting (SLM) process for dentistry, which is one of the additive manufacturing technologies (AM) allows for rapid production of a three-dimensional model with complex shape by directly melting metal powder. This process generates detailed items of a three-dimensional model shape through consolidation of a thin powder layer by utilizing both selective melting and laser beam simultaneously. In regard to SLM process, Fe-base powder, Ti-6AI-4V powder, AI-base powder, etc. have been researched. It is believed that the aforementioned technologies will be widely utilized in manufacturing metal parts using metal powder of raw material. This study chose Ni-Cr-Mo metal powder in order to manufacture metal powder materials that would be used in the selective laser melting for dentistry. Methods: This study manufactured metal powder using mechanical alloying technique (MA) among those metal powder manufacturing techniques. Moreover, this study aimed to utilize the metal powder manufactured after observing the characteristics of powder as preliminary data of Ni-Cr-Mo metal powder. This study could obtain the following conclusions within the experimental limitations. Results: As a result of mechanically alloying Ni-Cr-Mo powder over time, its mean particle size was $66.93{\mu}m$ $54.4{\mu}m$ and $45.39{\mu}m$ at 10h, 20h and 30h, respectively. The gtain form of metal powder by mechanical alloying technique was a sponge-like shape of irregular plate; however, the gtain form manufactured by high-pressure water aromization process had the following three types: globular type, chain type and oval type. Conclusion: This study found $37.65{\mu}m$ as the mean particle size of Ni-Cr-Mo metal powder, which was manufactured using water atomization technique under the following conditions: water atomization flux of 300 liter/min, hydraulic pressure of $400kgf/cm^2$ and injection angle of $45^{\circ}$. This study confirmed that the grain form of powder (solid particle form) would vary depending on the manufacturing process.

• 한국진공학회지
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• 제10권3호
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• pp.380-386
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• 2001

정밀가변슬릿과 자기사중극렌즈로 구성된 핵 마이크로프로브 (nuclear microprobe) 시스템을 일차행렬법을 이용한 빔광학 전산모사를 통해 설계하였으며, 제작된 시스템을 KIGAM 1.7 MV 탄뎀 반데그라프 가속기의 $30^{\circ}$ 빔라인에 설치하였다. X 및 Y축에 대한 역배율은 각각 25와 4.9로 계산되며, 3 MeV 양성자빔의 경우 최소 빔크기는 약 5 미크론, 빔전류는 약 1 nA 정도로 추산된다. PIXE, RBS, ERDA등 MeV 이온빔분석법과 이온빔 미세가공을 위해 다목적 8각형 표적함을 제작하였으며, 표적함은 X-선 및 하전입자검출기, 줌현미경, 파라데이컵, 4축 시료이송계 및 고진공계로 구성되어 있다. 현재 핵 마이크로프로브 시스템 성능 조사가 이루어지고 있으며, 자동화된 시료 이송 및 자료 처리 시스템이 설치되면 일상적인 마이크로 이온빔 분석이 가능해 질 것으로 예상된다.

• Nuclear Engineering and Technology
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• 제22권2호
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• pp.108-115
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• 1990

0.5~l.2-MeV 양성자빔에 대한 X-선 발생단면적의 측정을 Cu와 Au에 대해 수행하였다. 이 실험에서는 SNU 1.5-MV 탄뎀 반데그라프 가속기에서 얻은 양성자빔을 표적에 입사시켰다. 여기서 방출된 X-선과 후방산란된 양성자는 Si(Li) X-선 검출기와 SSB(Silicone Surface Barrier) 하전입자 검출기를 이용해 동시 측정하였다. 그리하여 측정된 X-선 발생단면적은 다른 실험치들 및 PWBA(Plane Wave Born Approximation)와 ECPSSR(Perturbed Stationary State corrected Energy loss, Coulomb deflection, Relativistic effects)인 이론치들과 비교하였다. 1.0-MeV근처의 양성자에너지에 대해 측정치는 PWBA 값보다는 ECPSSR(D.D. Cohen et al., 1985) 값에 더 잘 일치함을 보였다. 특히, Au의 측정치는 1.2-MeV 양성자빔에 대해 9.69$\pm$0.39 bams이었고, ECPSSR 이론치와는 5% 이내로 일치했으며, 0.5~l.2-MeV 양성자에 대한 실험치는 대부분의 다른 실험치들과 30% 이내로 일치했다.

• Applied Science and Convergence Technology
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• 제23권6호
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• pp.309-316
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• 2014

A large particle accelerator requires an ultrahigh vacuum (UHV) system of average pressure under $1{\times}10^{-7}$ Pa for mitigating the impact of beam scattering from the residual gas molecules. The surface inside the beam ducts should be controlled with an extremely low thermal outgassing rate under $1{\times}10^{-9}Pa{\cdot}m^3/(s{\cdot}m^2)$ for the sake of the insufficient pumping speed. To fulfil the requirements, the aluminum alloys were adopted as the materials of the beam ducts for large accelerator that thanks to the good features of higher thermal conductivity, non-radioactivity, non-magnetism, precise machining capability, et al. To put the aluminum into the large accelerator vacuum systems, several key technologies have been developed will be introduced. The concepts contain the precise computer numerical control (CNC) machining process for the large aluminum ducts and parts in pure alcohol and in an oil-free environment, surface cleaning with ozonized water, stringent welding process control manually or automatically to form a large sector of aluminum ducts, ex-situ baking process to reach UHV and sealed for transportation and installation, UHV pumping with the sputtering ion pumps and the non-evaporable getters (NEG), et al. The developed UHV technologies have been applied to the 3 GeV Taiwan Photon Source (TPS) and revealed good results as the expectation. The problems of leakage encountered during the assembling were most associated with the vacuum baking which result in the consequent trouble shootings and more times of baking. Then the installation of the well-sealed UHV systems is recommended.

• Composites Research
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• 제16권1호
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• pp.19-25
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• 2003

본 연구에서는 나노구조를 갖는 카본블랙이 충전된 CB/HDPE 복합재료를 용융 혼합법으로 제조한 후 온도변화에 따른 전기적 특성을 고찰하였다. 복합재료의 전기적 재현성 향상과 negative temperature coefficient (NTC) 현상의 제거를 위하여 전자선을 30-150 kGy로 조사하였으며, 조사된 복합재료의 가교함량 분석은 용매 추출법을 이용하였다. 실험결과, CB/HDPE 복합재료의 PTC 세기는 카본블랙의 함량과 입자크기에 크게 영향을 받으며. 가교함량의 급격한 증가에 따른 NTC 현상의 제거는 전자선 흡수선량이 60 kGy일 때였다. 또한 전자선 조사를 통하여 전기적 재현성이 향상되었는데, 이는 복합재료의 가교도 증가에 따른 수지의 용융온도 근처에서의 카본블랙 유동성의 감소 때문이라 사료된다.