• 소성∙가공
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• 제18권7호
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• pp.544-549
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• 2009

This study aimed to elucidate the deformation mechanism during low-temperature superplasticity of fine-grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy in the context of constitutive equation. For this purpose, initial coarse equiaxed microstructure was refined to $2.2{\mu}m$ via dynamic globularization. Globularized microstructure exhibited large superplastic elongations(434-826%) at temperatures of $650-750^{\circ}C$ and strain rate of $10^{-4}s^{-1}$. It was found that the main deformation mechanism of fine-grained material was grain boundary sliding accommodated by dislocation motion with both stress exponent (n) and grain size exponent (p) values of 2. When the alpha grain size, not sub-grain size, was considered to be an effective grain size, the apparent activation energy for low-temperature superplasticity of the present alloy(169kJ/mol) was closed to that of Ti-6Al-4V alloy(160kJ/mol).

• 한국응용곤충학회지
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• 제17권1호
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• pp.15-22
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• 1978

1. "Kresek" 유발균주(K균주)는 품종에 따라서 발현에 차이가 있었으며 지상부 또는 지하부에 접종하여도 "Kresek"을 유발시킬 수 있었으나 대조균주(N균주)는 전연 유발되지 않았다. 2. 엽백의 도관직경은 밀양 23이 유신이나 통일보다 현저히 작았으며 이들간에 고도의 통계적인 유의차가 인정되었다. 3. 밀양 23의 즙액에서 K균주들은 N균주들보다 세균의 증식이 왕성하였으며 통일에서는 균주들간에 증식의 차이가 없었다. 4. 밀양 23의 즙액친서는 K균주의 Dead phase가 정종 9일째부터 N균주는 4일째부터 시작되었으며 통일에서는 모두 3일째부터 시작되었다. 5. 밀양 23즙액의 경우 pH 3.0-4.0 범위에서 다량의 침전물이 형성되었으나 동일의 증액에서는 극히 소량의 침전물을 관찰할 수가 있었다.

• Bulletin of the Korean Chemical Society
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• 제16권10호
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• pp.977-980
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• 1995

A new chiral stationary phase (CSP 2) derived from cyclohexylamide of (S)-naproxen has been prepared. CSP 2 has shown greater enantioselectivities for the two enantiomers of N-(3,5-dinitrobenzoyl)-a-amino esters and amides than the CSP derived from 3,5-dimethylanilide of (S)-naproxen (CSP 1) as expected from the reciprocity conception of chiral recognition. However, CSP 2 has been found to be worse than CSP 1 in resolving N-(3,5-dinitrobenzoyl)-a-arylalkylamines, supporting the previously proposed chiral recognition mechanism which utilizes the 3,5-dimethylphenyl group of CSP 1 as an alternative π-basic interaction site. In addition, CSP 2 has been found to be reasonably good in resolving the two enantiomers of a variety of other π-acidic racemates.

• 한국진공학회지
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• 제6권S1호
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• pp.154-159
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• 1997

The crystal structure properties of TiN thin films deposited on SKD61 steel and Si(100) substrates by Ion Beam Assisted Deposition have been studied to clarify the thin film growth mechanism by using XRD, RBS, SEM, and AFM. The preferred orientation of TiN thin films changes from (111) to (100) as increasing the assisted energy. This tendency is independent of the substrate structure. The TiN thin film grow with (100) direction having surface free energy minimum as the assisted energy increases.

• Journal of Microbiology and Biotechnology
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• 제18권5호
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• pp.901-907
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• 2008

Thermotoga neapolitana $\beta$-glucosidase (BglA) was subjected to site-directed mutagenesis in an effort to increase its ability to synthesize arbutin derivatives by transglycosylation. The transglycosylation reaction of the wild-type enzyme displays major ${\beta}(1,6)$ and minor ${\beta}(1,3)$ or ${\beta}(1,4)$ regioselectivity. The three mutants, N291T, F412S, and N291T/F412S, increased the ratio of transglycosylation/hydrolysis compared with the wild-type enzyme when pNPG and arbutin were used as a substrate and an acceptor, respectively. N291T and N219T/F412S had transglycosylation/hydrolysis ratios about 3- and 8-fold higher, respectively, than that of the wild-type enzyme. This is due to the decreased hydrolytic activity of the mutant rather than increased transglycosylation activity. Interestingly, N291T showed altered regioselectivity, as well as increased transglycosylation products. TLC analysis of the transglycosylation products indicated that N291T retained its ${\beta}(1,3)$ regioselectivity, but lost its ${\beta}(1,4)$ and ${\beta}(1,6)$ regioselectivity. The altered regioselectivity of N291T using two other acceptors, esculin and salicin, was also confirmed by TLC. The major transglycosylation products of the wild type and N291T mutant were clearly different. This result suggests that Asn-291 is highly involved in the catalytic mechanism by controlling the transglycosylation reaction.

• Plant Biotechnology Reports
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• 제5권4호
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• pp.309-315
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• 2011

Rice grown in anaerobic waterlogged soil accumulates ammonium as a major source of nitrogen (N). We have compared the physiological symptoms of rice seedlings subjected to N-starvation stress with those receiving sufficient N, based on measurements of shoot/root length and weight and an analysis of protein expression patterns. N starvation marginally increased root growth but notably decreased shoot biomass. N uptake was reduced by >50% in the roots and shoots of N-starved seedlings. To better understand the mechanism of N starvation in rice, we performed a comparative proteome analysis of proteins isolated from rice leaves. Twenty-five differentially expressed proteins were analyzed by matrixassisted laser desorption/ionization time-of-flight (TOF) mass spectrometry and electron spray ionization quadrupole TOF. Functional analysis of the N-starvation response proteins suggested their involvement in protein synthesis and fate, metabolism, and defense. These results indicate that these proteins may play important roles in regulating the plant's complex adaptation responses for N use during N starvation. The proteins may be useful for further characterization of protein function in plant N nutrition.

• 대한화학회지
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• 제30권3호
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• pp.296-300
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• 1986

MeOH-$H_2O$, EtOH-$H_2O$, MeOH-MeCN and MeOH-$(Me)_2$CO 혼합용매계에서 pseudo-saccharinechloride의 가용매분해반응에 대한 유사일차 반응속도상수를 여러 온도에서 구하였다. Kivinen식의 n값과 Grunwald-Winstein식의 m값을 구하고 분광용매화 관계식의 파라메타들을 결정하였다. 이들 용매효과 파라메타와 활성화 파라메타들을 종합하여 볼때 Pseudo saccharinechloride의 가용매 분해반응은 $S_N2$ 반응으로 진행됨을 알았다.

• Journal of Electrochemical Science and Technology
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• 제7권2호
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• pp.153-160
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• 2016

The inhibition ability of N,N-bis(2,4-dihydroxyhydroxybenzaldehyde)-1,3-Propandiimine (DHBP) as a schiff base against the corrosion of API-5L-X65 steel in 1 M HCl solution was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization and scanning electron microscopy. Electrochemical impedance studies indicated that DHBP inhibited corrosion by blocking the active corrosion sites. The inhibition efficiency increased with increasing inhibitor concentrations. EIS data was analysed to equivalent circuit model and showed that the charge transfer resistance of steel increased with increasing inhibitor concentration whilst the double layer capacitance decreased. The adsorption of this compound obeyed the Langmuir adsorption isotherm. Gibbs free energy of adsorption was calculated and indicated that adsorption occurred through physical and spontaneous process. The corrosion inhibition mechanism was studied by potential of zero charge. Polarization studies indicated that DHBP retards both the cathodic and anodic reactions through adsorption on steel surface. Scanning electron microscopy was used to study the steel surface with and without inhibitor.

• Annals of Clinical Neurophysiology
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• 제8권1호
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• pp.63-70
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• 2006

Background: Testosterone is reported to have neuroprotective effect in various neurological diseases. Recently, the mechanism involved in nitric oxide (NO)-mediated motor neuron death is under extensive investigation. The Cu/Zn-superoxide dismutase (SOD1) mutations has been implicated in selective motor neuron death of amyotrophic lateral sclerosis (ALS) and it is said to play an important role in NO-mediated motor neuron death. However, neuroprotective effect of testosterone on motor neuron exposed to NO has rarely been studied. Methods: Motor neuron-neuroblastoma hybrid cells expressing wild-type or mutant (G93A or A4V) SOD gene were treated with $200{\mu}M$ S-nitrosoglutathione. After 24 hr, cell viability was measured by MTT assay. To see the neuroprotective effect of testosterone, pretreatment with 1 nM testosterone was done 1 hr before S-nitroglutathione treatment. To study the mechanism of protective effect, $20{\mu}M$ flutamide (androgen receptor antagonist) was also pretreated with testosterone 1 hr before S-nitroglutathione treatment. Results: S-nitrosoglutathione showed significant neurotoxic effect in all three cell lines. Percentage of cell death was somewhat different in each cell line. 1 nM testosterone showed neuroprotective effect in G93A and wild-type cell line. In A4V cell line, testosterone did not showed neuroprotective effect. The neuroprotective effect of testosterone was reversed by $20{\mu}M$ flutamide. Conclusions: These results indicate that testosterone induces neuroprotection in NO-mediated motor neuron death directly through the androgen receptor. This neuroprotective effect of testosterone varies according to the types of SOD1 gene mutation. These data suggest that testosterone may be of therapeutic value against ALS.

• 전자공학회논문지
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• 제53권2호
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• pp.36-44
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• 2016

본 논문에서는 $0.18{\mu}m$ CMOS 공정을 이용하여 WBAN(Wireless Body Area Network)용 IR-UWB(Impulse Radio Ultra Wide Band) RF 송수신기를 제안한다. 설계된 송수신기는 3-5GHz UWB low band를 지원하며 OOK(On-Off Keying) 변조 방식을 사용한다. 수신기는 복잡도와 소모 전력을 줄이기 위해서 비동기식 에너지 검출 방식을 사용하였다. 원하지 않는 잡음을 제거하고 감도를 개선하기 위하여 RF active notch filter가 내장되어 있다. VCO 기반의 수신기는 switch mechanism을 사용하였다. 사용된 switch mechanism은 소모 전력을 줄이고 VCO leakage를 최소화 할 수 있다. 또한, 중심주파수가 변해도 항상 동일한 spectrum mask를 가진다. 측정된 수신기의 감도는 3.5 GHz의 중심주파수에서 1.579 Mbps의 전송 속도를 가질 때 -84.1 dBm을 가진다. 송신기와 수신기는 각각 0.3 nJ/bit, 41 mW의 소모 전력을 사용한다.