• 제목/요약/키워드: Critical size effect

검색결과 425건 처리시간 0.029초

Electrodeposited Tin Properties & Their Effect on Component Finish Reliability

  • Fusco Phil;Schetty Rob
    • 한국마이크로전자및패키징학회:학술대회논문집
    • /
    • 한국마이크로전자및패키징학회 2004년도 ISMP Pb-free solders and the PCB technologies related to Pb-free solders
    • /
    • pp.201-209
    • /
    • 2004
  • As the European Community's Directive on the Restriction of Hazardous Substances in Electrical and Electronic Equipment banning lead (Pb) in electronics products will take effect on July 1, 2006, most electronics manufacturers will be commencing with volume production of Pb-free components by the middle of 2004. Electrodeposited pure tin finishes on electronic components are a leading contender to replace the industry standard tin-lead. Commensurate with this shift will be a somewhat steep learning curve as manufacturers adapt a variety of equipment and processes to contend with the issues surrounding this critical, industry-wide material conversion. Since the electrodeposited finish directly influences the critical reliability characteristics of the component itself, the nature of the Pb-free component finish must be well characterized and understood. Only through a thorough examination of the attributes of the electroplated tin deposit can critical decisions be made regarding component finish reliability. This paper investigates the properties of electrodeposited tin that may have an effect on component reliability, namely, grain structure (size and shape), oxide formation, tin whisker formation, and solderability. Data will be presented from laboratory and production settings, with the objective being to enable manufacturers to draw their own conclusions regarding previously established perceptions and misconceptions about electrodeposited tin properties.

  • PDF

간소화 시스템적용을 위한 자기특성 (A Study on the Magnetic Properties of Ceramics Superconductors for Simpllified Testing System)

  • 이상헌
    • 전기학회논문지
    • /
    • 제61권2호
    • /
    • pp.339-341
    • /
    • 2012
  • The high Tc superconductor of YBCO system with the nominal composition of precursor was prepared from mixed powders of $Y_2O_3$, $BaCO_3$, CuO and $TiO_2$ by the thermal pyrolysis method. The effect of $TiO_2$ doping to Y based ceramics superconductors fabricated by the thermal pyrolysis reaction, to investigate the effect of the dopant on the superconductivity. The voltage appearing across the field-cooled HTS sample increased with external magnetic field. The improvement of critical current property as well as the mechanical property is important for the application. The improvement of the critical current can be achieved by forming the nano size defect working as a flux pining center inside the superconductor. We simply added $TiO_2$ to starting materials to dope $TiO_2$ and observed an increase in the trapped field and the critical current density up to at least 5 wt % $TiO_2$. The $TiO_2$ was converted to fine $BaTiO_3$ particles which were trapped in YBCO matrix during the sintering process. We observed a peak effect of Jc that can be attributed to $TiO_2$ doping and results suggest that introducing a proper amount of pinning centers can significantly enhance current density.

An investigation into the influence of thermal loading and surface effects on mechanical characteristics of nanotubes

  • Ebrahimi, Farzad;Shaghaghi, Gholam Reza;Boreiry, Mahya
    • Structural Engineering and Mechanics
    • /
    • 제57권1호
    • /
    • pp.179-200
    • /
    • 2016
  • In this paper the differential transformation method (DTM) is utilized for vibration and buckling analysis of nanotubes in thermal environment while considering the coupled surface and nonlocal effects. The Eringen's nonlocal elasticity theory takes into account the effect of small size while the Gurtin-Murdoch model is used to incorporate the surface effects (SE). The derived governing differential equations are solved by DTM which demonstrated to have high precision and computational efficiency in the vibration analysis of nanobeams. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of thermal loading, small scale and surface effects, mode number, thickness ratio and boundary conditions on the normalized natural frequencies and critical buckling loads of the nanobeams in detail. The results show that the surface effects lead to an increase in natural frequency and critical buckling load of nanotubes. It is explicitly shown that the vibration and buckling of a nanotube is significantly influenced by these effects and the influence of thermal loadings and nonlocal effects are minimal.

Effect of hydroxyapatite on critical-sized defect

  • Kim, Ryoe-Woon;Kim, Ji-Hyoung;Moon, Seong-Yong
    • Maxillofacial Plastic and Reconstructive Surgery
    • /
    • 제38권
    • /
    • pp.26.1-26.6
    • /
    • 2016
  • Background: Xenologous or synthetic graft materials are commonly used as an alternative for autografts for guided bone regeneration. The purpose of this study was to evaluate effectiveness of carbonate apatite on the critical-size bone defect of rat's calvarium. Methods: Thirty-six critical-size defects were created on 18 adult male Sprague-Dawley rat calvaria under general anesthesia. Calvarial bones were grinded with 8 mm in daimeter bilaterally and then filled with (1) no grafts (control, n = 10 defects), (2) bovine bone mineral (Bio-$Oss^{(R)}$, Geistlich Pharma Ag. Swiss, n = 11 defects), and (3) hydroxyapatite ($Bongros^{(R)}$, Bio@ Inc., Seongnam, Korea, n = 15 defects). At 4 and 8 weeks after surgery, the rats were sacrificed and all samples were processed for histological and histomorphometric analysis. Results: At 4 weeks after surgery, group 3 ($42.90{\pm}9.33%$) showed a significant difference (p < 0.05) compared to the control ($30.50{\pm}6.05%$) and group 2 ($28.53{\pm}8.62%$). At 8 weeks after surgery, group 1 ($50.21{\pm}6.23%$), group 2 ($54.12{\pm}10.54%$), and group 3 ($50.92{\pm}6.05%$) showed no significant difference in the new bone formation. Conclusions: $Bongros^{(R)}$-HA was thought to be the available material for regenerating the new bone formation.

BSCCO 2223선재의 임계전류밀도에 영향을 미치는 단계별 열처리의 효과 (The effect of step heat treatment in the critical current density of BSCCO 2223 tapes)

  • 박성창;유재무;고재웅;김영국;김철진
    • Progress in Superconductivity
    • /
    • 제4권1호
    • /
    • pp.90-93
    • /
    • 2002
  • The sintering process of BSCCO 2223 tapes is a complex process that is very sensitive to parameters, such as temperature, oxygen partial pressure, heating and cooling rate and holding time. During the first heat treatment, 2212 phase of precursor powder is partially transformed into 2223 phase and some residual secondary phases, such as $(Bi,Pb)_2$$Sr_2$CuO/sub y/(2201), $(Ca,Sr)_2$CuO/sub y/(2/1AEC), (Ca,Sr)/sub 14/Cu/sub 24/O/sub 41/(14/24 AEC) etc. The secondary phases are difficult to be removed from the BSCCO 2223 matrix on the heat treatment. These secondary phases degrade the critical current density. In order to minimize the amount and size of alkaline earth cuprate(AEC) particles step heat treatment is applied during the first heat treatment under the varying atmosphere. Experimental results showed that by adapting the step heat treatment process, the amount and particle size of the secondary phases in the final tapes are decreased. Consequently, the BSCCO 2223grain texture and Jc properties are improved.

  • PDF

나노유체의 임계열유속 및 비등특성에 미치는 나노입자 크기의 영향 (Effect of particle sizes on CHF enhancement and boiling characteristics of nano-fluids)

  • 조병남;강준원;유재석;김현정
    • 한국가시화정보학회:학술대회논문집
    • /
    • 한국가시화정보학회 2006년도 추계학술대회 논문집
    • /
    • pp.125-130
    • /
    • 2006
  • The characteristics of boiling heat transfer and critical heat flux (CHF) behavior of nano-fluids were studied by using various sized silver and alumina nanoparticles. The diameter of nanoparticles was from 2 nm to 250 nm for silver and from 20nm to 40nm for alumina. Pool boiling characteristics and CHF enhancement of nano-fluids with different sized nanoparticles were compared with those of pure water and each nano-fluids. The experiment was performed at atmospheric pressure and the temperature of the pool was maintained constantly by using a flat immersed heater. The concentration of nano-fluids was uniform in all experiments as 0.01g/liter. The results showed that the measured boiling curves were shifted to the right. It demonstrated that the occurrence of nucleate boiling regime in nano-fluids retarded, compared with that of pure water. Also, in nano-fluids, the boiling curves showed that CHF of nano-fluids is significantly enhanced and represented the effect of particle size on boiling characteristics.

  • PDF

전도냉각 고온초전도 SMES 시스템의 기초절연 특성 (Basic Insulation Characteristics of Conduction-Cooled HTS SMES System)

  • 최재형;곽동순;천현권;김상현
    • 대한전기학회논문지:전기물성ㆍ응용부문C
    • /
    • 제55권8호
    • /
    • pp.404-410
    • /
    • 2006
  • Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 40[K] should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. In order to take advantage of a greater critical current density of high temperature superconducting (HTS) and considerably reduce the size and weight of the system, conduction-cooled HTS superconducting magnetic energy storage (SMES) at temperatures well below 40[K] should be investigated. This work focuses on the breakdown and flashover phenomenology of dielectrics exposed in air and/or vacuum for temperatures ranging from room temperature to cryogenic temperature. Firstly, we summarize the insulation factors of the magnet for the conduction cooled HTS SMES. And Secondly a surface flashover as well as volume breakdown in air and/or vacuum with two kind insulators has been investigated. Finally, we will discuss applications for the HTS SMES including aging studies on model coils exposed in vacuum at cryogenic temperature. The commercial application of many conduction-cooled HTS magnets, however, requires refrigeration at temperatures below 40[K], in order to take advantage of a greater critical current density of HTS and reduce considerably the size and weight of the system. The magnet is driven in vacuum condition. The need to reduce the size and weight of the system has led to the consideration of the vacuum as insulating media. We are studying on the insulation factors of the magnet for HTS SMES. And we experiment the spacer configure effect in the dielectric flashover characteristics. From the results, we confirm that our research established basic information in the insulation design of the magnet.

플랜트 및 선박의 액체용 우량제어밸브 설계에 관한 연구(II) (A Study on the Design of Liquid Flow Control Valves for the Pants and Ships(II))

  • 최순호;배윤영;김태한;한기남;주경인
    • Journal of Advanced Marine Engineering and Technology
    • /
    • 제19권2호
    • /
    • pp.1-9
    • /
    • 1995
  • The processing paper has devoted to the theory of the flow equations, the basic derivative procedure, the meaning of a valve flow coefficient $C_v$, the valve Reynolds R$R_{ev}$ and its application for liquid control valves, which applicable under the condition of a non-critical flow and the case of piping geometry factor $F_p$=1.0. However there is no information on the effects of fittings, a critical flow and the flow resistance coefficient of a valve equivalent to that of pipe which is conveniently used in the piping design. Since the piping systems of plants or ships generally contain various fittings such as expanders and reducers due to different size between pipes and valves and there may occur a critical flow, that a mass flowrate is maintained to be constant, due to the pressure drop in a piping when a liquid is initially maintainder ar a saturated temperature or at nearby corresponding to upstream pressure, system designer should have a knowledge of the effect to flow due to fittings and the critical flow phenomenon of a liquid. This study is performed to inform system designers with the critical flow phenomenon of a liquid, a valve resistance coefficient, a valve geometry factor and their applications.

  • PDF

도로터널 임계풍속 산정에 격자개수 및 화원의 크기와 위치가 미치는 영향 (The effect of grid number and the location and size of the fire source on the critical velocity in a road tunnel fire)

  • 이승철;김상일
    • 한국터널지하공간학회 논문집
    • /
    • 제14권3호
    • /
    • pp.183-195
    • /
    • 2012
  • 본 연구에서는 도로터널 내 화재 시 임계풍속 산정을 위해 3차원 전산유체역학 기법을 이용하여 격자수, 그리고 화원의 크기와 위치에 따라 그 결과를 비교 분석하였다. 본 대상터널에서 1차원 식으로 산출된 임계풍속은 터널 높이 대신 수력지름을 적용한 경우 2.22 m/s로 산정되었다. 임계풍속 2.25 m/s를 적용하여 격자수에 따른 6가지 수치해석 결과, 격자수에 따라 역류의 위치와 온도, CO 농도 값이 상이하게 나타났으며, 본 대상터널의 경우는 약 84만개 격자수를 사용한 case 1이 적절한 격자임을 알 수 있었다. 또한 화원의 크기와 위치에 따른 수치해석 결과, 화원의 크기와 위치에 따라 상이한 기류분포, 온도분포 및 CO농도분포를 나타내어 임계풍속에 영향을 미친다는 것을 확인했다. 이것은 열교환 면적과 위치에 기인된다고 판단된다. 향후 실제 실험결과와 상세히 비교하여 3차원 수치해석의 격자 의존성과 화원의 위치 및 크기를 반드시 확인해야 할 것으로 판단된다.

2안식 입체TV 주시전후의 동공면적의 변화 (The change of pupil size after viewing three dimensional TV)

  • 조암
    • 대한인간공학회지
    • /
    • 제14권2호
    • /
    • pp.25-32
    • /
    • 1995
  • The physiological change of eyes while viewing 3D TV was investigated. The change of pupil size was used as the measure of evaluation. The results are as follows : (1) The pupil size decreases after viewing 2D and 3D image and the the tendency is more critical with 3D images. (2) The indoor illumination has a significant effect on the pupil size in both 2D and 3D cases. (3) Less chage of pupil size were observed under the indoor illumination. Thus, if we only focus on the visual load on the eye, for viewing 3D image, it will be better to use indoor illumination.

  • PDF