• Applied Microscopy
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• v.7 no.1
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• pp.45-49
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• 1977

For obtaining high manganese steel plates, the study has been made on the optimum conditions in melting, forging, rolling and water toughning treatment practices. The optimum water toughning temperature and time was found to be $1030^{\circ}C$ and 30 min. respectively for the plates of 1 mm thickness. The argon atmosphere is very effective for the prevention of decarburization which can be easily occured in open air. There is a close relation between the degree of c 이 d working and the hardess. The greater the cold reduction ratio is, the smaller the grain size is and it results in the increase of hardness. The improvement of tensile and bending properties can be made by the addition of small amount of nickel, chromium and vanadium.

• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.53-59
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• 2012

Adiabatic demagnetization refrigerator (ADR) for hydrogen re-liquefaction operating between 24 K and 20 K has been designed. $Dy_{0.9}Gd_{0.1}Ni_2$, whose Curie temperature is 24 K, is selected as a magnetic refrigerant. The magnetic refrigerant powder is sintered with oxygen-free high purity copper (OFHC) powder to enhance its effective thermal conductivity as well as to achieve relatively high frequency. A perforated plate heat exchanger (PPHE) operated with forced convection is utilized as a heat switch. The forced convection heat switch is expected to have fast response relative to a conventional gas-gap heat switch. A conduction-cooled high Tc superconducting (HTS) magnet is employed to apply external magnetic field variation on a magnetic refrigerant. $2^{nd}$ generation GdBCO coated conductor HTS tape with Kapton$^{(R)}$ insulation (SUNAM Inc.) will be utilized for the HTS magnet. The magnetization and demagnetization processes are to be achieved by the AC operation of the HTS magnet. The designed magnetic field and target ramp rate of the HTS magnet are over 4 T with 180 A and 0.4 T/s, respectively. AC loss distribution on HTS magnet is theoretically estimated.

• YAKHAK HOEJI
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• v.47 no.3
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• pp.184-189
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• 2003

Peptide deformylase (PDF) is essential and unique to bacteria, thus making it an attractive target for the discovery of novel antibacterial drugs. PDF deformylates the N-formylmethionine of newly synthesized polypeptides in prokaryotes. In this study, a pdf gene from Staphylococcus aureus 6538p was cloned in pET-14b vector and PDF protein was over-produced in Escherichia coli BL21 (DE3). NH$_2$-terminal His-tagged PDF protein was purified by nickel-nitrilotriacetic acid (Ni-NTA) metal-affinity chromatography. Enzymatic activity of purified 6xHis-tagged PDF was tested on the substrate (formyl-Methionine-Alanine-Serine) by formate dehydrogenase-coupled spectrometric assay of peptide deformylase. For the discovery of new PDF inhibitors from chemical libraries and culture broths of soil bacteria, a target-oriented screening system using a 96-well plate was developed. About 3,000 commercial chemical libraries were tested in this screening system, and 2 chemicals (0.07％) among them showed an inhibitory activity against PDF enzyme. This result showed that a new screening system can be used for the discovery of new PDF inhibitors.

• Journal of the Korean Institute of Navigation
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• v.22 no.4
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• pp.51-57
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• 1998

According to the rapid development of the electric industry, the demand of the frequency allocation and the usage of electromagnetic wave are increased due to automation of modem society. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the effective frequency bandwidth by the way of forming air layer(practically in urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. In this paper, a broadband electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 8,000 MHz in the bandwidth. A super broadband electromagnetic wave absorber is achieved by inserting square Ferrite Cylinders Type with the thickness less than 23.5 mm and with the frequency band from 30 MHz to 8,000 MHz under the above tolerance limits. The purpose of this research is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell and also a wall material for preventing TV ghost, etc.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.1
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• pp.43-50
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• 1999

Electromagnetic wave absorbers for anechoic chamber are needed to broaden the useful frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the useful frequency bandwidth by the way of forming air layer. Therefore, an air layer is formed absorber between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 450 MHz in frequency band, far narrower than the aimed bandwidth. The purpose of this paper is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell, wall material for prevention of TV ghost, etc. Accordingly, in this paper, a broadened electromagnetic wave absorber is designed, which has the reflection characteristics less than -20 dB from 30 MHz to 5,430 or 8,000 MHz in the bandwidth. Then we will design a super broadband electromagnetic wave absorber by inserting square Ferrite Cylinders Type with the thickness less than 23.5 m in three-layed type and with the frequency band from 30 MHz to 5,430-8,000 MHz under the above tolerance limits.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.523-527
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• 2000

Vanadate glasses in the Li$_2$O-P$_2$O$_{5}$-V$_2$O$_{5}$ system containing 10mo1% glass former, P$_2$O$_{5}$ were prepared by melting the batch in pt. crucib1e followed by quenching on the copper plate. We found that Li$_2$O-P$_2$O$_{5}$-V$_2$O$_{5}$ glass-ceramics obtained from nucleation of glass showed significantly higher capacity and longer cycle life than conventionally made crystalline LiCoO$_2$, LiNiO$_2$and LiV$_3$O$_{8}$. In the present paper, We describe electro-chemical properties during crystallization process and find the best crystallization condition of Li$_2$O-P$_2$O$_{5}$-V$_2$O$_{5}$ g1ass as cathod material. Li$_2$O-P$_2$O$_{5}$-V$_2$O$_{5}$ glass-ceramics shows superior rechargeable capacity of 220 mAh/g in the cycling between 2.0 and 3.9V.etween 2.0 and 3.9V.

• Bulletin of the Korean Chemical Society
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• v.22 no.7
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• pp.703-708
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• 2001

K2NiF4-type organic-based perovskites of the (C4H9NH3)2FexPb1-xCl4 (x=0.00, 0.25, 0.50, and 0.75) system have been synthesized using a low-temperatu re solution method under a flowing argon gas. When stoichiometric butylamine, iron chloride, and lead chloride are mixed, a yellow solution are obtained from slow cooling of 90 to -10 $^{\circ}C.$ The final product is a plate-like yellow crystal. The X-ray crystallographic analysis has been carried out using XRD in the range of $5^{\circ}{\leq}$ 2${\theta}$ ${\leq}80^{\circ}.$ The local symmetry around the absorbing Pb atom of the samples has been determined by the EXAFS spectroscopic study. The crystals assign to orthorhombic system by the XRD analysis. The FT-IR spectra are analyzed in the range of 600 to 3300 cm-1 . DSC and TGA are measured to detect thermal stability between 30 and 300 $^{\circ}C.$ Two endothermic peaks are detected in all samples. The electrical conductivity has been measured using the four-probes technique for the (C4H9NH3)2FexPb1-xCl4 system in 300-460 K. Photoluminescence phenomenon was also investigated at room-temperature.

• Bulletin of the Korean Chemical Society
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• v.16 no.5
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• pp.401-406
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• 1995

The P. fragi lipase overexpressed in E. coli as a fusion protein of 57 kilodalton (kDa) has been purified through glutathione-agarose affinity chromatography by elution with free glutathione. The general properties of the purified GST-fusion protein were characterized by observing absorbance of released p-nitrophenoxide at 400 nm which was hydrolyzed from the substrate p-nitrophenyl palmitate. The optimum condition was observed at 25 $^{\circ}C$, pH 7.8 with 0.4 ${\mu}g$ of protein and 1.0 mM substrate in 0.6% (v/v) TritonX-100 solution. Also the lipase was activated by Ca+2, Mg+2, Ba+2 and Na+ but it was inhibited by Co+2 and Ni+2. pGEX-2T containing P. fragi lipase gene as expression vector was named pGL191 and used as a template for the site-directed mutagenesis by sequential PCR steps. A Ser-His-Asp catalytic triad similar to that present in serine proteases may be present in Pseudomonas lipase. Therefore, the PCR fragments replacing Asp217 to Arg and His260 to Arg were synthesized, and substituted for original fragment in pGL19. The ligated products were transformed into E. coli NM522, and pGEX-2T harboring mutant lipase genes were screened through digestion with XbaI and StuI sites created by mutagenic primers, respectively. No activity of mutant lipases was observed on the plate containing tributyrin. The purified mutant lipases were not activated on the substrate and affected at pH variation. These results demonstrate that Asp217 and His260 are involved in the catalytic site of Pseudomonas lipase.

• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.374-379
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• 2006

In this study, carbon nanotubes (CNTs) were grown on glass substrates coated with Ni/Cr by an atmospheric pressure plasma enhanced chemical vapor deposition(AP-PECVD) and their structural and electrical characteristics were investigated as a possible application to the field emitter of field emission display (FED) devices. The substrate temperature ($400{\sim}500^{\circ}C$) were varied and the grown CNTs were multi wall CNTs (at $500^{\circ}C$, 15 - 20 layers of graphene sheets, distance of each layer : 0.3nm, inner diameter: 10 - 15nm, outer diameter: 30 - 40nm). The ratio of defective carbon peak to graphite carbon peak of the CNTs grown at $500^{\circ}C$ (C measured by fourier transform(FT)-Raman was 0.772 $I_D / I_G$ ratio. When field emission properties were measured, the turn-on field was $2.92V/{\mu}m$ and the emission field at $1mA/cm^2$ was $5.325V /{\mu}m$.

• Economic and Environmental Geology
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• v.38 no.2 s.171
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• pp.113-127
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• 2005

Cretaceous intrusive and extrusive rocks are widely distributed in the southwestern part of the Korean peninsula, possibly the result of intensive magmatism which occurred in response to subduction of the western proto-Pacific plate beneath the north-eastern part of the Eurasian plate. Geochemical and petrological study on the Cretaceous granitic rocks were carried out in order to constrain the petrogenesis of the granitic magma and to establish the paleotectonic environment of the area. Whole rock chemical data of the granitic rocks from the study area indicate that the all the rocks have characteristics of calc-alkaline series in the subalkaline field. The overall geochemical features show systematic variations in each granitic body, but the source materials of each granitic body are thought to have been different in their chemical composition. Higher values of $Fe_2O_3/FeO$ of the granitic rocks in the western area suggest that the granitoids had been solidified under highly oxidizing environment. The granitic bodies in the eastern area also show higher contents of Li, Ni, Co, Sr, Cr, Sc and lower Rb and Nb compared to the those of the western area. Chondrite normalized REE patterns show generally enriched LREE and strong negative Eu anomalies in the western wet while slight to flat Eu anomalies in the east-ern area. The REE and $(La/Lu)_{CN}$ of the granites are $60{\~}499ppm$ and $8.9{\~}66$ correspond to the range of the continental margin granite. On the ANK vs. ACNK and tectonic discrimination diagrams, parental magma type of the granites corresponds to I-type, VAG and syn-collision granite. Interpretations of the chemical characteristics of the granitic rocks favor their emplacement in a compressional tectonic regime at continental margin during the subduction of proto-Pacific plate.