• 한국레이저가공학회지
• /
• 제6권1호
• /
• pp.33-40
• /
• 2003

The ablative decomposition mechanism of PMMA(polymethyl methacrylate) and PET(polyethylene terephthalate) with KrF excimer laser(λ : 248nm, pulse duration: 5㎱) is investigated. The UV/Vis spectrometer analysis showed that PMMA is a weak absorber and PET is a strong absorber at the wavelength of 248nm. The results(surface debris, melt, etch depth, etching shape) from drilling and direct writing experiments imply that ablation mechanism of PMMA is dominated by photothermal process, while that of PET is dominated by photochemical process.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.55-59
• /
• 2004

Recently, life cycle and lead-time of products have been shortened with the demand of customers. Therefore, it is important to reduce time and cost at the step of manufacturing trial molds. In order to realize three dimensional shape on CAD, the machining process has been widely used because it offers practical advantages such as precision and versatility. However, traditional machining process spends a lot of time in cutting product and the remained material causes trouble such as inconvenience for clean. In this work, a new machining process using the hot tool has been proposed to overcome those limitations. In the process, the hot tool moves the predetermined path and the heat of the tool decomposes the remained material. In order to set up the process, the hot tool to satisfy requirements is designed and the material thermal properties are obtained using the DSC and TGA machine. The relationships between process parameters and thermal radius of the tool are obtained through experiment.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.565-569
• /
• 2011

고체추진기관의 연소 환경에서 노즐 조립체의 온도, 삭마두께를 고려한 2차원 축대칭 열구조 해석을 하였다. 복합재료의 내부 열반응은 Arrhenius 모델을 이용하였으며, 표면 삭마반응은 Zvyagin 이론을 사용하였다. 표면 삭마에 의한 경계조건 및 격자 이동은 상용해석 코드에서 활용되는 Rezoning-remeshing 기법을 사용하였다. 형상이 복잡한 부품으로 이루어진 2차원 축대칭 노즐 조립체에 적용된 방법은 향후 3차원 FEM 열구조 해석에 활용을 목표로 발전될 것이다.

• 한국세라믹학회지
• /
• 제47권2호
• /
• pp.177-182
• /
• 2010

To synthesize $Gd_2O_3:Eu^{3+}$ phosphor, gadolinium-europium oxalate precursors were prepared from oxalic acid, NaOH or aqueous ammonia via coprecipitation method. The obtained precursors were heat-treated and then characterized by XRD, SEM and PL. The kinds and amounts of coprecipitant (NaOH or aqueous ammonia) were found to affect the powder morphology and properties of gadolinium-europium oxalate precursors. Two crystalline precursors and one amorphous precursor were synthesized. The nanometer-sized amorphous gadolinium-europium oxalate precursor was first prepared using the oxalate coprecipitation technique. The calcined powders obtained from the amorphous precursor were nearly spherical in shape, and a narrow size distribution was obtained. The NaOH coprecipitant was more effective in the preparation of nanometer-sized spherical powders. A thermal decomposition process was conducted for the three kinds of precursors. The photoluminescence property was also measured as a function of europium content, and concentration quenching occurred for samples with europium concentrations of over 10 mol%.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.1857-1860
• /
• 2003

The ablative decomposition mechanism of PMMA(polymethyt methacrylate), PET(polyethylene terephthalate) and PC(polycarbonate) with KrF excimer laser(λ: 248nm, pulse duration: 5ns) is investigated. The UV/Vis spectrometer analysis showed that PMMA is a weak absorber and PET, PC are a strong absorber at the wavelength of 248nm. The results(surface debris, melt, etch depth, etching shape) from drilling and direct writing experiments imply that ablation mechanism of PMMA is dominated by photothermal process, while that of PET, PC are dominated by photochemical process.

• 한국멀티미디어학회:학술대회논문집
• /
• 한국멀티미디어학회 2000년도 추계학술발표논문집
• /
• pp.239-244
• /
• 2000

영상공간에서의 역 해프토닝 성능을 향상시키기 위해서는 정확한 해프톤 셀 정보를 기반으로 최적의 평활화 마스크가 생성되어야 한다. 이에 본 논문에서는, 퓨리에 공간에서 피크형태와 영상공간에서의 해프토닝 특성을 이용해서 정확한 해프톤 셀 정보를 추출하는 새로운 방법을 제안한다. 제안한 방법은 차원분해(dimension decomposition)와 제한된 구간의 자동 탐색에 의해 정확한 해프톤 셀 정보를 효율적으로 추출하므로 역 해프토닝의 성능을 향상 시키며, 전체 영상에서 오차의 누적없이 셀 중심(seed pixel)을 정확하게 찾는 것을 실험을 통해 확인하였다. 정확한 해프톤 셀 정보는 셀 단위의 연산이나 해프톤 영상의 채널 분리 및 모아레 패턴의 존재 여부 판정 시 활용할 수 있다.

• 대한기계학회논문집A
• /
• 제27권4호
• /
• pp.593-600
• /
• 2003

Structural optimization often requires the evaluation of design sensitivities. The Semi Analytic Method(SAM) fur computing sensitivity is popular in shape optimization because this method has several advantages. But when relatively large rigid body motions are identified for individual elements. the SAM shows severe inaccuracy. In this study, the improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes. Moreover. the error of the SAM caused by numerical difference scheme is alleviated by using a series approximation for the sensitivity derivatives and considering the higher order terms. Finally the present study shows that the refined SAM including the iterative method improves the results of sensitivity analysis in dynamic problems.

• 동력기계공학회지
• /
• 제9권4호
• /
• pp.124-129
• /
• 2005

Copper oxide, CuO, are very important components include of high temperature super- conductors, and widely used. The properties of sintered materials were affected by the size and shape of copper oxide with starting materials in the solid-phase reaction. A homogeneous and fine CuO powder was prepared by thermal decomposition of the copper oxalate precursor. Copper oxalate was precipitated by the addition of copper nitrate solution to an oxalic acid solution. The influence of various factors such as temperature, pH, concentration as well as ultrasonic irradiation in the solution were investigated.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
• /
• pp.143-144
• /
• 2000

The aerosol pyrolysis technique was introduced to prepare the spherical phosphors for enhancing low-voltage phosphor efficiency. The density, the shape, and the crystallinity of phosphors were controlled by thermal decomposition temperature and phosphor annealing condition. The particle size was adjusted by the precursor concentration and reactor pressure. It was fond that the efficiency of phosphors synthesized in this work was superior to the commercial products at the low-voltage excitation by 1.5 times and the screen efficiency was also higher than that of any value reported in literature.

• 한국세라믹학회지
• /
• 제35권3호
• /
• pp.239-244
• /
• 1998

출발원료인 ferric nitrate와 ethylene glycol를 사용하여 iron complex를 제조하였으며 이를 $350^{\circ}C$ 이상의 온도에서 열처리하여 200nm 이하의 미세한 입자 크기를 갖는 ${\alpha}-Fe_2O_3$ 분말을 얻었다. 또한 열분석 X-선 회절 분석 및 적외선 분광 분석을 통하여 제조된 iron complex의 분해 mechanism에 대하여 조사하였고, 출발원료의 조성비 및 반응온도에 따른 입자 크기 및 형상의 변화 양상을 전자현미경 분석과 비표면적 분석을 통하여 조사하였다.