• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.17-19
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• 2002

Melt textured YBCO superconductors were fabricated by the top seeding method using Sml.8($Sm_{1.8}$ $Ba_{2.4}$ $Cu_{3.4}$$O_{7-Y}$) seed. We investigated the twin structures using the optical microscope, SEM and TEM. The twin structures formed during the tetragonal to orthorhombic transition which occurred at $450^{\circ}C$ in sample oxygen annealing. The twin structures were clearly observed by SEM due to the chemical etching effects. The lengths of twin structures were increased as the oxygenation heat treatment time increased from 1hr to 10hr. We investigated twin structure by TEM. The twin spaces were considered to be related to the oxygen contents. The results suggested an oxygen diffusion model for the formation of the twin lengths.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.155-158
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• 2002

Fabrication process of metal/intermetallic laminated composites by using self-propagating high temperature synthesis(SHS) reactions between Ni and Al elemental metal foils have been investigated. Al foils were sandwiched between Ni foils and heated in a vacuum hot press to the melting point of aluminium. SHS reaction kinetics was thermodynamically analyzed through the final volume fraction of the unreacted Al related with the initial thickness ratio of Ni:Al and diffusion bonding stage before SHS reaction. Thermal aging of laminated composites resulted in the formation of functionally gradient series of intermetallic phases. Microstructure showed that the main phases of intermetallics were NiAl and $Ni_3Al$ having higher strength at room and high temperatures. The volume fractions of intermetallic phases were measured as 82.4, 58.6, 38.4% in 1:1, 2:1, 4:1 initial thickness ratio of Ni:Al.

• 한국세라믹학회지
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• 제28권6호
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• pp.495-501
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• 1991

This study is intended to make defect-free region, denuded zone at the silicon wafer surface for semiconductor device substrates. In this experiment, initial oxygen concentration of starting material CZ-grown silicon wafer, various heat treatment combinations, denuding ambient and the amounts of oxygen reduction were measured, and then denuded zone (DZ) formation and depth were investigated. In Low/High anneal (DZ formation could be achieved), the optimum temperature for Low anneal was 700$^{\circ}C$∼750$^{\circ}C$. In case of High anneal, with the time increased, DZ depth was increased at 1000$^{\circ}C$, 1150$^{\circ}C$ respectively, but on the contrary, DZ depth was decreased at low temperature 900$^{\circ}C$. As well, out-diffusion time below 2 hours was unsuitable for effective Gettering technique even though the temperature was high, and DZ formation could be achieved when initial oxygen concentration was only above 14 ppm in silicon wafer.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.118.1-118.1
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• 2016

The laser surface modification has been reported for its functional applications for improving tribological performance, wear resistance, hardness, and corrosion property. In most of these applications, continuous wave lasers and pulsed lasers were used for surface melting, cladding, alloying. Since flexibility in processing, refinement of microstructure and controlling the surface properties, technology utilizing lasers has been used in a number of fields. Especially, femtosecond laser has great benefits compared with other lasers because its pulsed width is much shorter than characteristic time of thermal diffusion, which leads to diminish heat affected zone. Moreover, laser surface engineering has been highlighted as an effective tool for micro/nano structuring of materials in the bio application field. In this study, we applied femtosecond and nanosecond pulsed laser to treat biometals, such as Mg, Mg alloy, and NiTi alloy, by heating to improve corrosion properties and functionalize their surface controlling cell response as implantable biomedical devices.

• Journal of Korean Neurosurgical Society
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• 제55권2호
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• pp.99-102
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• 2014

A previously healthy 52-year-old man presented to the emergency room with acute onset left hemiparesis and dysarthria. Brain computed tomography and magnetic resonance examinations revealed acute cerebral infarction in the right middle cerebral artery territory and a sphenoid ridge meningioma encasing the right carotid artery terminus. Cerebral angiography demonstrated complete occlusion of the right proximal M1 portion. A computed tomography perfusion study showed a wide area of perfusion-diffusion mismatch. Over the ensuing 48 hours, left sided weakness deteriorated despite medical treatment. Emergency extracranial-intracranial bypass was performed using a double-barrel technique, leaving the tumor as it was, and subsequently his neurological function was improved dramatically. We present a rare case of sphenoid ridge meningioma causing acute cerebral infarction as a result of middle cerebral artery compression.

• Journal of Advanced Marine Engineering and Technology
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• 제26권3호
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• pp.375-381
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• 2002

Measuring of the dissolved oxygen is widely used for the environmental control of natural waters, sewage waste treatment, medical and biochemical studies, soil husbandry, food and drug process control, and prevention of corrosion in boilers. Especially, a power plants need special management for preventing accidents from corrosion, therefore, it is essential to measure the concentration of dissolved oxygen in real-time. In this paper we present a method of measuring dissolved oxygen very accurately up to pub units. This method, called polarograph method, is based on the measures of the electric current generated by the oxidation process in cathode and de-oxidation process in anode, assuming that the amount of the current is proportional to the density of dissolved oxygen.

• 한국연소학회지
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• 제16권4호
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• pp.8-15
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• 2011

The present study investigates the combustion phenomena in a sludge incinerator using experimental and numerical method. The temperature and gas concentration were measured at 33 points during operation of the incinerator in order to assess the mixing and combustion characteristics. Numerical simulation was also carried out using a commercial CFD code. Simplified inlet conditions were introduced in oder to predict the bulk solid combustion and the diffusion of the volatile matter released by pyrolysis of sludge. The experimental results showed that the combustion process is extremely inhomogeneous. Large variations were observed in the temperature and gas concentrations in the freeboard of the incinerator due to poor mixing performance between the air and the combustibles, which is caused by massive and bulk generation of volatile matter by fast pyrolysis of sludge particles. The boundary condition of the CFD simulation was found effective in predicting the poor mixing and combustion performance of the reactor.

• 상하수도학회지
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• 제9권3호
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• pp.65-77
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• 1995

The kinetics of flocculation of heterodisperse suspension like those in water treatment plants and natural water system are usually described by the Smoluchowski equation, which incorporates collision frequency functions for particle collisions by Brownian motion, fluid shear, and differential sedimentation. These collisionfrequeney functions have been based on a rectilinear view of collisions, i.e., one that ignores short-range forces and changes in fluid motion as particles approach one another. In this research, a curvilinear approach, i.e., one that accounts for hydrodynamic forces and particle interaction in the collision of two different size particles is developed. Collision efficiency factors of each mechanism can be calculated by trajectory analysis (fluid shear and differential sedimentation) or the solution of diffusion equation (Brownian motion). The results are presented as a set of corrections to the rectilinear collision frequency functions for each mechanism.

• 전자공학회논문지A
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• 제33A권12호
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• pp.77-82
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• 1996

The breakdown characteristics of metal-oxide-semiconductor(MOS) capacitors fabricated by Al, polysilicon, and tungsten polycide gate electrodes onto gate oxide was evaluated by time zero dielectric breakdwon (TZDB). The average breakdown field of the gate oxide with tungsten polycide electride was lower than that of the polysilicon electrode. The B model (1~8MV/cm) failure of the gate oxide with tungsten polycide electrode was increased with increasing annealing temperature in the dry $O_{2}$ ambient. This is attributed ot fluorine and tungsten diffusion from thungsten silicide film into the gate oxide, and stress increase of tungsten polcide after annealing treatment.

• 한국정밀공학회지
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• 제15권2호
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• pp.28-34
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• 1998

Powder metallurgy processes are able to form Net-Shape products and have been widely used in the production of automobile parts to improve its productivity. However, because of pores in powder products, the toughness of powder products are generally poor. Therefore, forged products are used in parts which suffer severe fatigue loads. In this paper, the choice of powder materials and production processes such as mixing, compaction, sintering, heat treatment to produce automobile spline hub are studied. Three type of materials are selected and processed and its microstructure and properties are investigated by tensile test, compression ring test, and impact test. Materials and processing methods are selected from the results. Finally, experimental spline hubs are manufactured by selected processes from selected powders and proved by torsional durability test.