• Progress in Superconductivity
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• v.7 no.2
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• pp.140-144
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• 2006

We fabricated the YBCO films on single crystal $LaAlO_3$ substrates via a metal organic deposition (MOD) process. In the process, $Y_2Ba_1Cu_1O_x$ and $Ba_3Cu_5O_8$ powders were dissolved in trifluoroacetic acid (TFA) followed by calcining and firing heat treatments. To evaluate the effects of the firing temperature on YBCO phase formation and critical properties, the films were fired at $750^{\circ}C,\;775^{\circ}C\;and\;800^{\circ}C$ after calcining at $430^{\cric}C$. Microstructure observation indicated that a crack-free surface formed and a strong biaxial texture was developed. The FWHM of out-of-plane texture was measured to be in the range of $4.3^{\cric}-7.0^{\circ}$ for all the films. When the YBCO film was fired at $775^{\cric}C$, it had the highest critical properties: 88.5 K of critical temperature and 16 A/cm-width of critical current ($1MA/cm^2$ as critical current density). On the other hand, those properties were degraded as firing at $750^{\circ}C\;and\;800^{\circ}C$. It is considered that the improved critical values are partly owing to dense and homogeneous microstructure, strong texture, and high oxygen content.

• Korean Journal of Food Science and Technology
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• v.31 no.2
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• pp.482-487
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• 1999

Periodate-oxidized soluble starch and maltohexaose reacted with ${\alpha}-NH_2$ group of free amino acids and ${\varepsilon}-NH_2$ group of peptidyl lysine. The result shows that periodate-oxidized soluble starch and maltooligosaccharides reacted with protein and formed Schiff base between CHO group of oxidized sugar and ${\varepsilon}-NH_2$ group of surface lysine of protein molecule. Carbon and hydrogen composition of sweet potato ${\beta}-amylase$ modified with oxidized soluble starch increased and it's nitrogen composition decreased. Carbohydrate contents of sweet potato ${\beta}-amylase$ modified with oxidized soluble starch were 13.2% (pentamer), 13.4% (monomer), and with oxidized maltohexaose were 9.7% (pentamer), 9.3% (monomer) by $phenol-H_2SO_4$ method. Alpha-amino group of N-terminal, and ${\varepsilon}-NH_2$ group of lysine, of sweet potato ${\beta}-amylase$ were reacted with oxidized soluble starch by dinitrophenylation were 70% (pentamer), 73% (monomer) and 33% (pentamer), 26% (monomer), respectively, in comparison with native enzyme.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.431-431
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• 2011

Graphene, two dimensional sheet of sp2-hybridized carbon, has attracted an enormous amount of interest due to excellent electrical, chemical and mechanical properties for the application of transparent conducting films, clean energy devices, field-effect transistors, optoelectronic devices and chemical sensors. Especially, graphene is promising candidate to detect the gas molecules and biomolecules due to the large specific surface area and signal-to-noise ratios. Despite of importance to the disease diagnosis, there are a few reports to demonstrate the graphene- and rGO-FET for biological sensors and the sensing mechanism are not fully understood. Here we describe scalable and facile fabrication of rGO-FET with the capability of label-free, ultrasensitive electrical detection of a cancer biomarker, prostate specific antigen/${\alpha}1$-antichymotrypsin (PSA-ACT) complex, in which the ultrathin rGO sensing channel was simply formed by a uniform self-assembly of two-dimensional rGO nanosheets on aminated pattern generated by inkjet printing. Sensing characteristics of rGO-FET immunosensor showed the highly precise, reliable, and linear shift in the Dirac point with the analyte concentration of PSA-ACT complex and extremely low detection limit as low as 1 fg/ml. We further analyzed the charge doping mechanism, which is the change in the charge carrier in the rGO channel varying by the concentration of biomolecules. Amenability of solution-based scalable fabrication and extremely high performance may enable rGO-FET device as a versatile multiplexed diagnostic biosensor for disease biomarkers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1083-1091
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• 1988

Vacuum brazing is the most modern brazing process and is at present, far from being completely understood. By brazing under high vacuum, in an atmosphere free of oxidizing gases, a superior product with greater strength, ductility and uniformity can be obtained. In this study, the influence of brazing parameters such as base metal characteristics, joint clearance and brazing time were described in relation to the metallurgical phenomena and shear strength of vacuum-brazed joints between carbon steels and 304 stainless steel (SUS 304) brazed by copper filler metal. In copper brazing of SUS 304 to a medium carbon steel(M.C.S) the columnar Fe-Cr-Ni-Cu-C alloy structure was formed and grew from the M.C.S side and at the same time, the surface of M.C.S. was decarbonized. The driving force for the formation and growth of columnar structure was the difference of carbon content between base metals. As the joint clearance is narrower and brazing time is longer, the formation and growth of columnar phase and decarburization of carbon steels were more noticeable. Because of decarburization of carbon steels, the shear strength of brazed joints were reduced as the formation of columnar structure was increased.

• Restorative Dentistry and Endodontics
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• v.25 no.2
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• pp.180-192
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• 2000

One bottle system was recently developed in order to simplify the clinical skills and save chair time after continuous improvements on dentin bonding agents. There has been many studies to measure the bond strength of one bottle systems but no actual work has been done on micromorphologic study of resin-dentin interdiffusion zone after one bottle system application. To evaluate the bonding patterns of various commercially available one bottle systems to dentin, observation of resin-dentin interdiffusion zone under TEM was performed. Caries-free human third molars within one month of extractions were chosen for the experiments. The molars were sectioned 1mm above the cementoenamel junction and got rid of the root portions. Crown portions of the teeth were sectioned parallel to occlusal surface so that dentin discs of 1mm in thickness were remained. 7 one bottle systems and 1 two bottle system were applied according to manufacturer's instructions and followings were the results. 1. In every experimental groups, cross bandings of collagen fiber were distinguishable and tight bon dings between the bonding agents and dentin were observed. 2. Hybrid layer was clearly observed in ONE-STEP$^{(R)}$, Prime & Bond$^{(R)}$ 2.1, Syntac$^{(R)}$ SC, MAC-BOND II groups but it was not clear in Single Bond, D-Liner Dual PLUS, ONE COAT BOND groups. 3. Electron-density of hybrid layer was uniform in pattern in MAC-BOND II, Prime & Bond$^{(R)}$ 2.1 groups but not so uniform in ONE-STEP$^{(R)}$ group. 4. Electron-dense amorphous phase in most superior layer of the resin-dentin interdiffusion zone was characteristically observed in Single Bond, Syntac$^{(R)}$ SC, ONE COAT BOND groups. It can be concluded that bondings between the dentin bonding agents and dentin can be various in pattern according to their chemical compositions and the condition during applications.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.71-77
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• 2012

We studied the effect of heat treatment on the microstructures and mechanical strength of the solder joints in the Light Emitting Diode (LED) packages. The commercial LED packages were mounted on the a flame resistance-4 (FR4) Printed Circuit Board (PCB) in the reflow process, and then the joints were aged at $125^{\circ}C$ for 100, 200, 300, 500 and 1000 hours, respectively. After the heat treatment, we measured the shear strength of the solder joints between the PCB and the LED packages to evaluate their mechanical property. We used Pb-free Sn-3.0Ag-0.5Cu solder to bond between the LED packages and the PCBs using two different surface finishes, Electroless Nickel-Immersion Gold (ENIG) and Electroless Nickel-Electroless Palladium-Immersion Gold (ENEPIG). The microstructure of the solder joints was observed by a scanning electron microscope (SEM). (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed between the solder and the PCB, and the thickness of the IMCs was increased with increasing aging time. The shear strength for the ENIG finished LED package increased until aging for 300 h and then decreased with increasing aging time. On the other hand, in the case of an ENEPIG finished LED package, the shear strength decreased after aging for 500 h.

• Elastomers and Composites
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• v.39 no.3
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• pp.234-243
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• 2004

The elastomeric and conductive polyurethane (PU) films were prepared by poly(propylene glycol) (PPG), toluene 2,4-diisocyanate, 3-methylthiophene (3-MT) at various preparation conditions, such as the reaction time, the $FeCl_3$ concentration, the weight ratio of the 3-MT to PU and the reaction temperature for the diffusion-oxidative reaction. The conductive poly (3-methylthiophene) (PMT) layers via the diffusion-oxidative reaction of 3-MT and ferric chloride were formed by immersing the film in organic solution of $FeCl_3$/ethyl acetate. The preparation conditions greatly affected the electrical conductivity of the 3-MT/PU composite. The effects of the reaction time and temperature on morphology and surface free energy were investigated by scanning electron microscopy (SEM) analysis and contact angle measurement, respectively. The conductivity of the composite was as high as 42 S/cm.

• Applied Microscopy
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• v.18 no.2
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• pp.1-20
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• 1988

The species of the slug used in the experiment is Limax flavus L. For identifying the chemical characteristics of the epidermis, granules and mucus-producing cell of this animal is examined with methylene blue-basic fuchsin double stain and PAS-alcian blue reagent. For the ultrastructural research of the epidermal free surface, the epitheial cell and the parenchymal cell are used with scanning electron microscope and transmission elec-tron microscope respectively. I . Epidermal tissue The epidermal tissue of the slug is observed being divided into the dorsal and the ventral side(toot pad) respectively. 1) Dorsal epidermal tissue The dorsal epidermis of the slug is constituted with the simple columnar epithelium and the microvilli are compacted on the epidermal free surface. Two different types of the secretory granules of the neutral and the acid mucus are observed between the epithelial cells, and the neutral mucous granules are highest electron-dense but the acid mucous granules are observed to be electron-lucent. 2) Foot epidermal tissue The Foot epidermis is formed with the taller simple columnar epithelium than the dorsal epidermis and these cells have both a large number of the microvilli and a few number of the large villi. The secretory granules of three different types, which are acid, neutral and mixed mucous granule of two different types are observed between the epithelial cells. The neutral mucous granules are highest electron dense but the acid mucous granules are observed to be electron-lucent. II . Mucous granule-producing cell and mucus-producing cells Seven different types of the granules-producing cell and the mucus-producing cells are observed between the parenchyma. 1) A-type of acid mucous granule-producing cell The electron-lucent granules are largely occupied in the cytoplasm of these cells and then the granules are surrounded by irregular membrane. These electron-lucent granules exhibit alcianophilia with PAS-alcian blue reaction, so these granules are certified to be acid mucopolysaccharide. 2) B-type of acid mucus-producing cell The nucleus and the cytoplasm of these cells are pushed by the acid mucus of the electron-lucent toward the cell membrane. This mucus has been confirmed to be the acid mucopolysaccharide with PAS-alcian blue reagent. 3) A-type of neutral mucous granule-producing cell These cells contain the electron-dense round granules with approximately $1{\mu}m$ in diameter, which exhibit strongly PAS-positive reaction. These granules are confirmed to be the neutral mucoplysaccharide. 4) B-type of neutral mucous granule-producing cell These cells contain two different types of electron dense granules and electron-lucent granules; The former exhibits to be strongly PAS-positive and the latter to have alcianophilia reaction respectively. 5) C-type of neutral mucus-producing cell These cells are similar to the shape and the size of the B-type of mucus-producing cell but these two different types of cells are stained with reversing properties to each other. The mucus of the C-type cell that electron-lucent is largely occupied in the cytoplasm that exhibits strongly PAS-positive reaction. 6) D-type of neutral mucous granule-producing cell These cells contain round granules about $1{\mu}m$ in size which are observed to be medium electron-dense granules and those granules are stained brightly red with PAS-weak positive reaction. The granules are certified to be neutral mucopolysaccharide. 7) E-type of neutral mucous granule-producing cell These cells are similar to the shape and the size of the D-type of neutral mucous granule-producing cell. These cells contain a large number of granules with about $1{\mu}m$ in diameter showing electron-lucent and then granules are seen to be PAS-weak positive reaction. III. Parenchyma The clear cell and dark cell are found in the parenchyma of the Limax flavus L. 1) Clear cell These cells are round formed and the nucleus of the cells are larger than cytoplasm. These cells which have the electron-lucent cytosol possess poorly developed organelles. 2) Dark cell These cells are found to be dark cells due to high electron-density, which exhibit strongly methylene-blue reaction from double stain of methylene blue-basic fuchsin.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.3 s.32
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• pp.37-45
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• 2004

Electroless Ni(P) has been widely used for under bump metallization (UBM) of flip chip and surface finish layer in microelectronic packaging because of its excellent solderability, corrosion resistance, uniformity, selective deposition without photo-lithography, and also good diffusion barrier. However, the brittle fracture at solder joints and the spatting of intermetallic compound (IMC) associated with electroless Ni(P) are critical issues for its successful applications. In the present study, the mechanism of IMC spatting and microstructure change of the Ni(P) film were investigated with varying P content in the Ni(P) film (4.6,9, and $13 wt.\%$P). A reaction between Sn penetrated through the channels among $Ni_3Sn_4$ IMCs and the P-rich layer ($Ni_3P$) of the Ni(P) film formed a $Ni_3SnP$ layer. Thickening of the $Ni_3SnP$ layer led to $Ni_3Sn_4$ spatting. After $Ni_3Sn_4$ spatting, the Ni(P) film directly contacted the molten solder and the $Ni_3P$ phase further transformed into a $Ni_2P$ phase. During the crystallization process, some cracks formed in the Ni(P) film to release tensile stress accumulated from volume shrinkage of the film.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.289-297
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• 1999

Concentrations of total dissolved free amino acids (DFAAs) in the northeast Pacific Ocean $9^{\circ}54'-10^{\circ}27'N$, $131^{\circ}43'-131^{\circ}53'W$) ranged from 15.9 to 1778.2 17M, and the average was 407.2 nM. Concentrations of DFAAs in surface mixed layers, ranged from 60.1 to 1411.9 nM, and the average was 535.2 nM. Seasonal thermoclines with maxima were formed between the depth of 50 to 150 m. DFAAs in this layer were varied in concentrations from 91.7 to 1778.2 nM, and the average was 588.5 nM. DFAAs below the seasonal thermoclines fluctuated from 15.9 to 384.2 nM, and the average was 175.1 nM. Consequently, in average relatively abundant DFAAs were observed in the subsurface layer than the deeper layer. DFAA vertical profiles and compositions of station A showed similar to station Band C. Glycine, alanine, glutamic acid, serine and valine were predominant accounting for more than 60% of total amino acids. Isoleucine, tyrosine, methionine and phenylalanine comprised only few percents of total DFAAs in the study area. In mole % of amino acid, according to characteristics of functional group of amino acid, aliphatic neutral accounted for 59% and aliphatic hydroxy 16%, acidic 12%, respectively. Although differences in DFAA concentrations with depth were observed, the amino acid composition and mole % of deeper layers in all stations were similar to those of subsurface layers. The results indicate that individual DtAAs remains invariably in water columns relative to the compositions and distributions of DFAAs in the study area, which may be the result of close coupling between microbial activity and their water solubility.