• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 추계학술대회 논문집 전문대학교육위원 P
• /
• pp.4-6
• /
• 1999

We have performed spin-spray ferrite plating of $Fe_{3-x}Zn_xO_4$($X=0.47{\sim}0.97$) films in the temperature region T=85[$^{\circ}C$]. A reaction solution and an oxidizing solution were supplied to a reaction chamber by supply pumps. The Zn composition X in the $Fe_{3-x}Zn_xO_4$ Film increases as the content of $ZnCl_2$ increase, from X=0.47 at O.05[g/l] to X=0.97 at 0.15[g/l]. All the films are polycrystalline with no preferential orientation, and the magnetization exhibits no definite anisotropy. Grain size in the films increases as X increases, reaching 0.98[${\mu}m$] at X=0.97.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.469-474
• /
• 2002

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bumps reflowed by laser was superior than the solder bumps reflowed by hot air, and the microstructure inside the solder bumps reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn$_4$ layer and remnant Au element. Needle-like AuSn$_4$ grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni$_3$Sn$_4$ intermetallic compound was found at the interface of solder bump reflowed by hot air, AuSn$_4$ particles distributed inside the whole solder bump randomly. It is the combination effect of the continuous AuSn$_4$ layer and finer eutectic microstructure inside the solder bump reflowed by laser that resulted in higher shear strength.

• KSTLE International Journal
• /
• 제4권2호
• /
• pp.66-72
• /
• 2003

This paper presents the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existing investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal choices of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high-speed spindle. In this paper, The pressure behavior in theory of air film in high speed region of journal according to the eccentricity of journal and the source positions analyzed. The theoretical analysis has been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high-speed milling.

• Steel and Composite Structures
• /
• 제6권2호
• /
• pp.103-122
• /
• 2006

The capacity of tubular truss chords subjected to concentrated reaction forces in the vicinity of the open end (i.e., the bearing region) is not directly treated by existing design specifications; although capacity equations are promulgated for related tubular joint configurations. The lack of direct treatment of bearing capacity in existing design specifications seems to represent an unsatisfactory situation given the fact that connections very often control the design of long-span tubular structures comprised of members with slender cross-sections. The case of the simple-span overhead highway sign truss is studied, in which the bearing reaction is applied near the chord end. The present research is aimed at assessing the validity of adapting existing specifications' capacity equations from related cases so as to be applicable in determining design capacity in tubular truss bearing regions. These modified capacity equations are subsequently used in comparisons with full-scale experimental results obtained from testing carried out at the University of Pittsburgh.

• Journal of Electrochemical Science and Technology
• /
• 제11권4호
• /
• pp.379-383
• /
• 2020

The novel voltammetry using a semi-circular potential wave for quasi-reversible charge transfer system on electrode is theoretically investigated. Compared with conventional voltammetry based on linear sweep such as linear sweep voltammetry (LSV), semi-circular potential sweep voltammetry (SCV) may decrease the charging current outside the center of potential range and increase the faradaic current at the midpoint due to variable scan rate. In this paper, we investigate the system based on macroelectrode where simple 1 dimensional (1 D) diffusion system is valid with various charge transfer rate constant (k₀). In order to observe the amplification at midpoint, voltammetric response with different midpoint ranging from -200 mV to 200 mV are studied. SCVs shows both the shift of peak potential and the amplification of peak current for quasi-reversible electrode reaction while only higher peak current is observed for reversible reaction. Moreover, the higher current at midpoint enable the amplification of current at low overpotential region which may assist the determination of onset potential as a figure-of-merit in electrocatalyst.

• 한국결정학회지
• /
• 제12권3호
• /
• pp.166-170
• /
• 2001

실리콘 기판에 도핑되어 있는 도판트는 종류에 따라 코발트와 실리콘 기판과의 반응에 영향을 준다. 인은 붕소나 비소에 비해 코발트와 실리콘과의 반응을 억제하여 저온 열처리 동안에 CoSi₂대신에 CoSi가 형성되도록 한다. CoSi층 내에서의 확산원소는 Si으로, CoSi 층은 Co/CoSi 계면에서 성장하며 반응에 참여하는Si 소모에 의해 생기는 기판의 빈 공간을 태우기 위해 Si 기판쪽으로 이동한다. 게이트 측벽에서는 접촉되어 있는 게이트 산화막과의 결합에 의해 CoSi층의 이동이 억제된다. 따라서 기판의 빈 공간을 태우지 못하게 되어 게이트 측벽 아래에 기공이 형성된다.

• 연구논문집
• /
• 통권25호
• /
• pp.163-168
• /
• 1995

The intermetallic compound $Ni_3Al$ causes a peritectic reaction at the composition and temperature very close to the eutectic reaction in Ni-Al system. Although the phase diagram accepted for this system by ASM Handbook has the eutectic forming between the $\gamma$ and $\gamma$ phases, directional solidification study has shown that the eutectic occurs between $\beta$ and $\gamma$. This work examines the liquidus region using quenched, directional solidification experiments that preserve the microstructrues formed at the solidification front. It is also shown that under certain composition and growth conditions a metastable eutectic between the $\beta$ and $\gamma$ phases forms in this system. Finding of the metastable eutectic provided an important information to understand the phase equilibria near the $Ni_3Al$ composition.

• 한국식물병리학회지
• /
• 제14권6호
• /
• pp.589-593
• /
• 1998

DNA amplification by polymerase chain reaction (PCR) was used to specifically detect Plasmodiophora brassicae, causing clubroot of crucifers. On the basis of DNA sequence informations, an oligonucleotide primer set specific for the pathogen was designed form small subunit gene (18S-like) and internal transcribed spacer (ITS) region of ribosomal DNA. Primer ITS 5/PB-C produced an amplification product of approximately 520 bp in length with DNA from P. brassicae. However, no amplification product was produced with DNAs from several soil-borne fungi, Didymella bryoniae and Rhizopus stolonifer. Using these primers, the clubroot pathogen was readily detected from infected roots of crucifers, but not from healthy roots. Southern hybridization analysis further confirmed that the amplification product was originated from P. brassicae.

• 반도체디스플레이기술학회지
• /
• 제6권2호
• /
• pp.65-68
• /
• 2007

High brightness and long persistent luminescence phosphor $CaAl_2O_4:Eu^{2+}$ was prepared with varying $Eu^{2+}$ concentration by solid state reaction technique. Synthesized materials were investigated by powder X-ray diffractometer (XRD), SEM, TEM, photoluminescence excitation and emission spectra. Broad band UV excited luminescence of the $CaAl_2O_4:Eu^{2+}$ was observed in the blue region (${\lambda}_{max}\;=\;440\;nm$) due to transitions from the $4f^65d^1$ to the $4f^7$ configuration of the $Eu^{2+}$ ion. The decay time of the persistence indicated that the persistent luminescence phosphor has bright phosphorescence and maintains a long duration. These materials have great potential for outdoor night time displays.

• Bulletin of the Korean Chemical Society
• /
• 제32권3호
• /
• pp.961-963
• /
• 2011

Spin-coated waterborne polyurethane to protect glass surface from environmental attacks was cured by using microwave heating. The effect of microwave heating on the reaction kinetics, chemical durability, and transmittance of polyurethane was investigated. In comparison to the conventional heating the results show that the microwave heating substantially accelerates the curing process of waterborne polyurethane and the total time for the completion of the reaction is only 1/7 of that in the conventional process. The microwave cured sample showed an excellent caustic resistance compared to conventional cured one. It means that microwave heating produces dense structure during curing process. The dense structure does not affect to the transmittance in the visible region.