• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.82-86
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• 1999

For nonconducting perovskite titanates ATiO3 and A'1/2A"1/2TiO3, 5 ferroelectric members were discriminated from 17 quantum paraelectric members via average mass of A ions m(A): ferroelectric for m(A)〉110 a.u. and quantum paraelectric for m(A)<100 a.u. An intuitive explanation of the origin of the discrimination is given concenrned with the ferroelectric soft modes in perovskite ATiO3. Based on the above discrimination, trial synthesis of ferroelectric candiate substances are presented.

• Laser Solutions
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• v.5 no.2
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• pp.31-38
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• 2002

This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ㎱, fluence 0.8∼2.0 J/㎠). Microparticles of mean diameter 18∼80 ㎛ are ablated in the ambient air The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

• Journal of Microbiology
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• v.38 no.3
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• pp.145-149
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• 2000

GroEL is a typical molecular chaperone. GroEL synthesis patterns at various culture temperatures in Escherichia coli were investigated in this study. No significant differences in the amount of GroEL produced from the chromosome were found at 30 and 37$^{\circ}C$. However, GroEL production increased 3.4-fold at 42$^{\circ}C$. GroEL synthesis was not transient but continuous at 42$^{\circ}C$, although most heat shock gene expression is known to be transient. To understand the role of the groEL structural gene, a groE promoter-lacZ fusion was constructed. Interestingly , while transcriptional fusion is not thermally inducible, it is inducible by ethanol, suggesting that the secondary structure of the groEL transcript is involved in thermal regulation of the groEL gene. Secondary structures of groE mRNA at 37 and 42$^{\circ}C$ were compared using the computer program RNAdraw. Distinct structures at the two temperatures were found, and these structures may be related to a high level of GroEL expression at 42$^{\circ}C$.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.249-254
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• 2014

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide($WO_3$) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the $WO_3$-Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of $WO_3$, Mg and $B_2O_3$. It was found that $WO_3$, Mg and $B_2O_3$ reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of $B_2O_3$ with B successfully solved the diffusion problem. From the optimum condition tungsten boride($W_2B$ and WB) powders which has 0.1~0.9 um particle size were synthesized.

• The Korean Journal of Zoology
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• v.36 no.3
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• pp.373-379
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• 1993

The heat shock protein (HSP) genes are expressed at various stages of the Drosophila life cycle even under non-heat-shock conditions. In the present study, developmental changes of HSP23 gene expression and the role of 20-hydroxyecdysone (2OHE) on the HSP23 gene expression were investigated in Drosophila melanogaster. The Northern blot and Western blot analyses showed that HSP23 gene expression occurred at the early third instar larval stage, reached the highest with a sharp peak in the white prepupa, and then decreased throughout the pupal period. When the HSP23 gene expression was compared with the secretion of 20HE, there is a slmiladty between 20HE synthesis and HSP23 gene expression during the third instar larval-prepupal period. It appears that 2OHE regulates expression of HSP23 gene at larva-pupa molting period, and that, 2OHE is also involved in the control the metamorphosis in some part through the HSP23.

• Korean Journal of Microbiology
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• v.35 no.2
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• pp.139-145
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• 1999

Aromatic hydrocarbons which are not easily degraded by microorganisms can be accumulated in the conlaminated environment for a long lime, producing toxic effects on wild lives and humans. However, the sublethal concentrations of the chemicals induce the synthesis of stress-shock proteins in the cells and increase the adaptability of the organisms to the environmental stresses. In this study, therefore, the cells of Psezido~nonus sp. DJ- 12 treated with catechol at various concentrations were inveshgated for their survival, biodegtadability of catechol, production of stress-shock proteins, and cytological changes. The organisms were capable of degrading catechol at the range of 0.5 to 1.0 mM concentration wilhin 6 hours incubation, but they were killed by $10^2$-10$^3$ celllinl at 3 mM or higel- concentration without any catechol degradation. These cells treated with catechol begm lo produce DnaK and GroEL at 1 mM and 0.5 mM. respectively. Pseudumonas sp. DJ-12 treated with 10 mM catechol for I hour exhihiled some punctuated pores on the cell wall and contortion of the rod shape. The cells treated with he sublethal concentration of catechol showed the increased tolerance for suvival when exposed to the lethal concentration, and such tolerant effects were functioned crossly among benzoate, 4-chlorobenzoate, 'and catechol.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.5
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• pp.430-436
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• 2014

The mission objective of STEP Cube Lab. (Cube Laboratory for Space Technology Experimental Project) classified as a pico-class satellite is to verify the technical effectiveness of payloads such as variable emittance radiator, SMA washer, oscillating heat pipe and MEMS based solid propellant thruster researched at domestic universities. In addition, the MEMS concentrating photovoltaic power system and the non-explosive holding and separation mechanism with the advantages of high constraint force and low shock level will be developed as the primary payloads for on-orbit verification. In this study, the feasibility of the mission actualization has been confirmed by the preliminary system design.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.784-794
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• 1994

Though spodumene have a law theraml expension and good thermal shock resistance, its sintering temperature is too close to its melting point in the application for industral purpose. Solving the problems, impurities within the silicate minerals act as a frit during firing, so its densification is expected through enlargement of sintering temperature range. By the heat treatment of starting materials, mixtures of silicate mineral, lithium carbonate, if necessary SiO2 or Al2O3 were added for stoichiometric correction, in the range of 1000~125$0^{\circ}C$ for 10 hrs, $\beta$-spodumene single phase was synthesized. Mixtures with sillimanite group minerals, $\beta$-spodumene was formed at 120$0^{\circ}C$ or 125$0^{\circ}C$ via intermediate phases of petalite, Li2SiO3 and LiAlO2. For the case of kaolin group minerals, synthesis were completed at 110$0^{\circ}C$ for Hadon pink kaolin, 120$0^{\circ}C$ for New Zealand white kaolin, When pyrophyllite group minerals were used, those were at the range of 1000~125$0^{\circ}C$. Spodumene was completed at lowest temperature, 100$0^{\circ}C$ from the mixture of Wando pyrophyllite among them. Microstructure of synthesized powders showed the inrregular lump shape such as densed crystallines.

• Journal of the Korean Ceramic Society
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• v.28 no.2
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• pp.130-140
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• 1991

The powders of the system Si3N4-Y2O3-AlN were prepared using Si(OC2H5)4 and YCl3.6H2O together with commercial AlN powder. $\alpha$-Si3N4 was prepared by the carbothermal reduction and nitridation of the hydrolyzed gel at 135$0^{\circ}C$ for 10h in N2 atmosphere. YCl3.6H2O was observed to be changed to Y2O3 during the reaction. $\alpha$-Sialon(X=0.2, 0.4, 0.6) ceramics were obtained by hot-pressing the Si3N4-Y2O3-AlN mixture at 178$0^{\circ}C$ for 1h under 30 MPa. The content of $\alpha$-Sialon increased with increasing metal solubility(x value) and $\alpha$-Sialon single phase was obtained at the metal solubility of 0.6. With increasing metal solubility, flexural strength, fracture toughness and thermal shock resistence were decreased, while the microhardness was increased. Large elongated $\beta$-Si3N4 grains were mainly observed at lower metal solubility. Mechanical prorerties of the sintered ceramics with X=0.2 were measured as follows : flexural strength ; 650 MPa, fracture toughness ; 3.63 MN/m3/2, hardness ; 14.7 GPa, thermal shock resistence temperature ; 58$0^{\circ}C$.

• Korean Journal of Microbiology
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• v.34 no.1_2
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• pp.43-50
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• 1998

Induction and purification of the GroEL homolog from Streptococcus pneumolliae were characterized. The stress conditions were determined by temperature, ethanol, NaCI, $H_2O_2$ methyl methanesulfonate, and ethyl methanesulfonate. And stress induced proteins were analyzed using [$^{35}S$]-methionine labeling method. Heat shock induced the synthesis of a set of about 3 heat shock proteins (hsps) (65, 73, and 84-kDa). Of those 3 hsps, a 65 kDa protein, hsp65, was purified by DEAE-Sephacel and ATP-agarose column chromatography, and used for antibody preparation. Immunoblot analysis employing antisera raised against pneumococcus hsp65 demonstrated cross-reactivity with a 60 kDa protein in Eschericha coli. Also cross reaction of the purified p65 with anti-Escherichia coli GroEL monoclonal antibody demonstrated that pneumococcal hsp65 is the GroEL homolog.