• Journal of Welding and Joining
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• 제31권3호
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• pp.17-21
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• 2013

Sn whiskers are one of the serious causes of the failure of electronics. Sn whiskers grow spontaneously from Sn-based, lead-free finished surfaces, even at room temperature. A primary factor of these Sn whiskers growth is compressive stress, which enhances the diffusion of Sn or other elements. The sources of compressive stress are the growth of non-uniform large intermetallic compounds along the interface between the Sn grain boundary and Cu substrate. Recent studies revealed the methods for reducing Sn whisker growth. This paper gives an overview about recent researches for mitigation methods of Sn whisker growth during nearly room temperature storage.

• 한국레이저가공학회지
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• 제18권3호
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• pp.6-8
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• 2015

Finishing process includes deburring, polishing and edge radiusing. It improves the surface profile of specimen and eliminates the alien substance on surface. Deburring is the elimination process for debris of edges. Polishing lubricates surfaces by rubbing or chemical treatment. There are two types for electron finishing. The one is using pulse beam. The other is using the convergent and scanning electron beam. Pulse type device appropriates the large area process. But it does not control the beam dosage. Scanning type device has advantages for dosage control and edge deburring. We design the convergence and scan type. It has magnetic lenses for convergence and scan device for scanning beam. Magnetic lenses consist of convergent and objective lens. The lenses are designed by the specification(beam size and working distance). In this paper, we evaluate the convergence performance by pattern process. Also, we analysis the results and important factors for process. The important factors for process are beam size, pressure, stage speed and vacuum. These results will be utilized into systematizing pattern shape and the factors.

• 정보저장시스템학회논문집
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• 제5권2호
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• pp.58-63
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• 2009

This paper describes the effects of slider behavior over patterned media. The flying characteristics of a slider over patterned media are different from slider flying behavior over conventional plane disk. In order to perform the most realistic simulation of slider flying characteristics over patterned disk surfaces, our simulation approach virtually distributes the grooves on the slider ABS instead of on the disk surface. Also, we define SSFA which is steady-state slider flying attitude. The results show that the more patterned size is small and height is large, the more increased SSFA is. Also if patterned distance is small, then SSFA is increased. In addition, we analyzed the effects of patterned shapes.

• Restorative Dentistry and Endodontics
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• 제8권1호
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• pp.147-153
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• 1982

The purpose of this study is to observe the effect of cleansing action of irrigation solutions which are 3% hydrogen peroxide, 5% sodium hypochlorite and 15% EDTA solution on the root canal wall. After the root canal wall is enlarged with K-file in distilled water, the canal wall which is irrigated with each irrigant for 2 minutes, is compared with the. control group without using any irrigants. Each sample is dehydrated, and coated with 200-250${\AA}$ of gold, and observations are made with the use of scanning electron microscope. The results are as follows: 1. The canal walls irrigated with 3% hydrogen peroxide, 5% sodium hypochlorite and 15% EDTA solution are cleaner than the walls without using irrigants. 2. There are no significant difference of cleansing effect among 3% hydrogen peroxide, 5% sodium hypochlorite and 15% EDTA. 3. After using 3% hydrogen peroxide and 5% sodium hypochlorite solution, large debris are removed on root canal walls, but micro debris remain on the canal walls. 4. The root canal walls irrigated with 15% EDTA solution are decalcifed slightly and show clean surfaces.

• 한국측량학회지
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• 제7권1호
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• pp.49-57
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• 1989

본 연구에서는 Landsat데이타를 이용하여 간척전후의 토지이용분류를 하였으며, 열적외선 Band(TM Band6)데이타로부터 지표면온도를 추출하였다. 인공위성데이타를 이용함으로서 간척에 따른 토지이용의 변화를 효과적으로 추출할 수 있었으며, 열적외선 데이타값을 지표면 및 수표면온도로 변환함으로서 간척지주변지역의 열특성을 파악할 수 있었다. 이러한 분석결과는 향후의 인공위성데이타 및 관련정보와 결합되어 대규모간척지의 효율적 국토관리에 이용될 수 있으리라 생각된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.288-298
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• 2009

It is well known that the peak strength envelope of geomaterials with no cohesion, such as sand, gravel and rockfill, exhibits significant curvature over a range of stresses. In a practical design of slope, however, the linear Mohr-Coulomb's failure envelope is used as a failure criterion and consequently gives inaccurate safety factors, especially for some ranges of small normal stresses on shallow failure surfaces. Necessity of a nonlinear shear strength envelope in slope stability analysis is on this point. Hence, this study describes how to evaluate nonlinear shear strength of gravel fill materials using the results of large triaxial tests under consolidated-drained condition, and compares the safety factors from slope stability analyses for a homogeneous gravel fill or rockfill embankment incorporating the non-linearity of strength, so as to show its effects on safety factors.

• Journal of the Optical Society of Korea
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• 제9권2호
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• pp.68-73
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• 2005

When aligning catoptric or catadioptric telescopes for space cameras, it is difficult to align precisely if the field of view is large or there are several reflective surfaces. The quantitative knowledge of mirror misalignments greatly helps align a misaligned telescope precisely, and also reduce the alignment time. This paper describes a generalized reverse-optimization alignment solution algorithm using Zernike sensitivity, and proposes the minimum number of fields to take interferograms. This method was successfully applied on a Cassegrain telescope design for Earth observation from space with arbitrary misalignments and a model including some primary mirror deformation.

• Journal of the Optical Society of Korea
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• 제10권1호
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• pp.48-54
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• 2006

White-light scanning interferometry (WLI) and phase shifting interferometry (PSI) are increasingly used for surface topography measurements, particularly for areal measurements. In this paper, we compare surface profiling results obtained from above two optical methods with those obtained from stylus instruments. For moderately rough surfaces ($Ra{\approx}500\;nm$), roughness measurements obtained with WLI and the stylus method seem to provide close agreement on the same roughness samples. For surface roughness measurements in the 50 nm to 300 nm range of Ra, discrepancies between WLI and the stylus method are observed. In some cases the discrepancy is as large as 109% of the value obtained with the stylus method. By contrast, the PSI results are in good agreement with those of the stylus technique.

• 소성∙가공
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• 제9권2호
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• pp.193-202
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• 2000

The influence of rolling draughts on the formation of through-thickness textures in aluminum 5000X sheet was investigated by X-ray texture measurements and microstructure observations. In order to intensify the deformation inhomogeneities, cold rolling was performed without lubrication. Applying a large draught gave rise to the formation of the shear texture at the surface, whereas a normal plane strain testure formed at the surface after deformation with a small draught. The orientation density along the $\beta$-fiber orientations which developed in the center layer of the rolled specimen was also dependent on the strain gradients in a roll gap. Upon annealing, the deformed substructure of sample surfaces was transformed into a fine grained recrystallized microsturcture through extended recovery reaction. However, coarse grains developed after the discontinuous recrystallization which gave rise to the development of the Cube-texture.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.164-167
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• 2003

열충격은 재료가 갑작스런 온도나 압력변화 혹은 급냉 조건하에 있을때 발생하는 물리적 현상이다. 본 논문에서는 레이저 조사를 이용하여 열충격 강도와 열충격 파괴인성을 평가하였다. 시험편의 온도 분포는 타입 K와 C 열전대를 이용하여 측정하였다. 조사된 표면은 SEM을 이용하여 관찰하였다. 파괴에 필요한 임계 레이저 파워가 재료의 열충격 강도와 열충격 파괴인성을 결정짓는 주요한 요소라고 할 수 있다.