• 대한기계학회논문집A
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• 제27권1호
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• pp.77-87
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• 2003

The residual stress and birefringence in injection-molded plastic parts can be divided into the flow-induced residual stress and birefringence produced in flowing stage, the thermally-induced residual stress and birefringence produced in cooling stage. However, the physics involved in the generation of the thermally-induced residual stress and birefringence still remains to be understood. Because polymer experiences viscoelastic history near the glass-transition temperature it is hard to model the entire process. Volume relaxation phenomenon was included to predict the final thermally-induced residual stress and birefringence in quenched plastic parts more accurately. The present study focused on comparing the predicted values far thermally-induced residual stress and birefringence with and without volume relaxation behavior (or free volume theory) under free and constrained quenching conditions. As a result, tile residual stress remained as a tensile stress at the center and as a compressible stress near the surface for the free quenching cases. In contract the residual stress remained as a compressible stress at the center and as a tensile stress near the surface fur the constrained quenching cases. The residual birefringence remained as minus values at the center and as plus values near the surface for the free quenching cases. Interestingly the residual birefringence showed minus values in entire zone for the constrained quenching cases. In the prediction of birefringence only the case including free volume theory showed the correct result for the distribution of birefringence in thickness direction.

• 한국안전학회지
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• 제12권3호
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• pp.83-89
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• 1997

The behaviors of flame propagation and quenching ability in a pipe were investigated to make a design criteria of flame arrester. The effects of the number of wire gauzes and free area on the quenching ability were discussed. Experimental results showed that the flame velocity was important factor of the quenching ability. The flame velocity in case of closed pipe was increased about twenty times faster then that of opened. The quenching ability was increased about 10% with 3% decrease of free area and it was changed significantly by the sealing condition of the pipe end. The quenching flame velocity can be estimated by using experimental equations.

• 한국정밀공학회지
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• 제14권11호
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• pp.58-68
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• 1997

The residual stresses in injection-molded plastic parts can be divided into two, i.e., the flow-induced residual stress produced in flowing stage and the thermally-induced residual stress produced in cooling stage. Especially, the main source for the defect in the final parts, such as warpage, is known to be the thermally-induced stresses. For the freely quenched samples the structures of residual stresses and bire-fringence have been investigated by many researchers extensively. However, the boundary condition for free quenching was found to be improper to study actual injection molding process. In the present study a datailed structure of the residual stresses and birefringence produced under constrained quenching has been investigated experimentally. In constrained quenched samples a similar pattern but much less stress values than that for the freely quenched samples has been found in the case of the thickness of 1.0 mm. Howvere, in the case of the thickness of 4.0mm, totally different stress profile has been found experimentally. Suprisingly uniform birefringence throughout whole thickness has been found for all the cases of constrained quenching. Finally, to explain the mechanism to produce the final residual stresses and bire-fringence some preliminary numerical results including free volume theory have been introduced briefly.

• 한국재료학회지
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• 제10권8호
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• pp.581-588
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• 2000

Free surface를 가진 레나트-존스 이원계의 가열, 냉각에 따른 상전이를 molecular dynamics simulation을 이용하여 연구하였다. 용매-용질우너자간의 size misfit과 용질우너자의 농도변화에 따른 상전이 거동을 살펴본 결과 size misfit과 용질원자의 농도가 증가함에 따라 가열시 용융시 낮은 온도에서 쉽게 발생하였고, 냉각시 임계냉각속도가 감소하여 결정화는 어려워졌다.

• 한국염색가공학회지
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• 제26권4호
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• pp.277-282
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• 2014

Two tert-butyl substituted phthalocyanines(Pcs), in metal-free and metallated forms, were synthesized and the fluorescence responses toward various nitro derivatives, including picric acid(PA), 2,4-dinitrotoluene(DNT), 1,4-dinitrobenzene(DNB), 4-nitrotoluene(NT), nitrobenzene(NB), 1,4-benzoquinone(BQ), and nitromethane(NM) were investigated. Among the various nitro derivatives, current Pc derivatives exhibited efficient and exclusive fluorescence quenching in the presence of picric acid, which was readily observed by a naked eye. Quenching efficiency was estimated by the Stern-Volmer relationship, in which quenching constant, KSV, was calculated to be in the range of $10^4M^{-1}$. It was also found out that the aggregational behaviors of these Pcs are heavily dependent on the nature of solvent systems, subsequently affecting the quenching efficiency.

• Bulletin of the Korean Chemical Society
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• 제16권12호
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• pp.1184-1189
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• 1995

The rapid quenching dynamics of F center excitation by OH- defects in KCl crystals are investigated by monitoring ground state absorption bleach recovery, using a picosecond streak camera absorption spectrometer. F center absorption bleach in OH--doped crystals shows three distinguishable recovery components with the current temporal resolution, designated as slow, medium and fast components. The slow one is due to the normal relaxation process of F* centers as found in OH--free crystals. The others are consequent on energy transfer from electronically excited F centers to OH--vibrational levels. The fast component is a minor energy transfer process and resulting from the relaxation of somewhat distant, not the closest, associated pairs of F* and OH- defects. The energy transfer between widely separated F* and OH- defects opens up a recovery process via the medium component which is assisted by OH- librations, lattice vibrations and OH- dipole reorientations. The quenching behaviors of F* luminescence and photoionization by OH- are explained well by the relaxation process of the medium component.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1999년도 추계학술발표강연 및 논문개요집
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• pp.42-42
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• 1999

• 생약학회지
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• 제43권4호
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• pp.274-278
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• 2012

As part of ongoing study focused on the discovery of natural antioxidants from Korean plants by measuring the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging effect and superoxide quenching activity, ethanol extract of the aerial parts of Curcuma longa (Zingiberaceae) was found to show potent antioxidant activities. Subsequent activity-guided fractionation of the ethanol extract led to the isolation of two phenolic compounds, 1,2,3,4,6-penta-O-galloyl-${\beta}$-D-glucopyranoside (1) and gallic acid (2), as antioxidant compounds. Their structures were elucidated by spectroscopic studies. Compounds 1 and 2 were isolated for the first time from this plant. These compounds showed the significant antioxidative effects during the DPPH free radical scavenging test, and the riboflavin- and xanthine-originated superoxide quenching activity tests.

• Biomolecules & Therapeutics
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• 제17권4호
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• pp.412-417
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• 2009

In the course of screening for antioxidant compounds by measuring the radical scavenging effect on DPPH (1,1-diphenyl- 2-picrylhydrazyl), a total extract of the twigs of Vitex rotundifolia (Verbenaceae) was found to show potent antioxidant activity. Subsequent activity-guided fractionation of the methanolic extract led to the isolation of three iridoid compounds, 10-O-vanilloylaucubin (1), 10-O-p-hydroxybenzoylaucubin (2) and aucubin (3), two C-glycoside flavones, vitexin (4) and orientin (5), and a quinic acid derivative, 3,4-di-O-caffeoylquinic acid (6). Their structures were elucidated by spectroscopic studies. Among them, compounds 5 and 6 showed the significant antioxidative effects on DPPH free radical scavenging test. In riboflavin-NBT-light and xanthine-NBT-xanthine oxidase systems, compounds 5 and 6 exhibited the formation of the blue formazan in a dose-dependent manner. Compounds 5 and 6 showed better superoxide quenching activities than vitamin C.

• Journal of Microbiology and Biotechnology
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• 제7권4호
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• pp.242-249
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• 1997

Stability of bioluminescence was investigated with Photobacterium phosphoreum immobilized on the strontium alginate in order to develope continuous real time monitoring of pollutants. The stability of bioluminescence emission was improved by prolonged aging time. The aging time of ${\geq}40$ min and the cell concentration of ${\leq}0.6\;of\;OD_660$ were selected for the immobilization of P. phosphoreum to give linearity between cell concentrations and bioluminescence intensity. In sensitivity tests using phenol, it was found that this compound quenched bioluminescence proportional to the concentration without lowering of cell growth. The lower value for maximum quenching ($q_s$) and higher dissociation constant ($K_s$) were observed with strontium-alginate immobilized cells compared to free cells. The response of bioluminescence to toxicants was evaluated with the immobilized luminescent bacteria. The sensitivity of the immobilized cells was found to be good in response to toxicants, 4-nitrophenol, salicylate and cadmium, when evaluated with a specific rate of bioluminescence quenching.