• Korea-Australia Rheology Journal
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• v.19 no.1
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• pp.43-47
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• 2007

The polydiacethylene (PDA) is known to change its color by mechanical shear. The shear-induced color transition has been reported with elastomer or film type of PDA. In this paper, we newly investigated the transition with liposome type of PDAs in polymeric solutions. The liposomes were dispersed in Poly(vinyl alcohol) 2% + Sodium borate 1%, Poly(vinyl alcohol) 15% and Hyaluronic acid 1% (PVA/B, PVA, HA). The shear stress was continuously imposed to each solution by stress control type rheometer with coni-cylinder fixture. The degree of color transition was quantified with the characteristic absorbance peak at 540 nm (blue) and 640 nm (red). As a result, PDA liposome in PVA/B solution changed the color from blue to red upon increasing the magnitude of shear (from 0 to 100 Pa) and the duration of shear-imposed time (from 0 to 5400 sec). Meanwhile, PDA liposome in HA or PVA solution did not noticeably change the color, even though the low shear viscosities of the solutions were kept almost constant. This color transition of PDA liposome is expected to measure the magnitude of shear, and to distinguish different responses of polymeric solutions to the applied shear.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.22 no.2
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• pp.167-173
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• 1996

The stability of gel structured emulsion and the effect of polyols on it have been studied by rheological property and interfacial tension. In this paper, three types of gel structured emulsions were prepared by using three polyols respectively(glycerine for sample 1, 1.3 BG for sample 2, PG for sample 3). And both complex modulus($G^*$) and loss angle[$\delta$ = tan-1(G"/G')] of samples were investigated against oscillating shear stress and frequency($\omega$). The results show sample 1 is most highly consistent with oscillating shear stress. And the results were compared with those of accelerated tests concerning storage stability of gel structured emulsion. To correlate consistency of rheological property with storage stability, interfacial tension from which adsorption efficiency of surfactant(Octyldodecyl Ether) could be known was measured. Sample 1 showed the largest value of [$d{\gamma}/dIn_{Cconc. of surfactant}$] in Gibbs equation. In summary, the prediction of stability could be correctly made by the consistency of rheological property(G*,$\gamma$) of gel structured emulsion against oscillating shear stress and it could be supported by measuring interfacial tension. And polyol affected the value of [$d{\gamma}/dIn_{Cconc. of surfactant}$], consequently affected the stability.lity.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2290-2295
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• 2018

An acceleration stress test (AST) was performed to evaluate the durability of a polymer membrane in a polymer electrolyte membrane fuel cell (PEMFC) for 500 hours. Previous studies have shown that hydrogen crossover measured by linear sweep voltammetry (LSV) increases when the polymer membrane deteriorates in the AST process. On the other hand, hydrogen crossover of the membrane often decreases in the early stages of the AST test. To investigate the cause of this phenomenon, we analyzed the MEA operated for 50 hours using the AST method (OCV, RH 30% and $90^{\circ}C$). Cyclic voltammetry and transmission electron showed that the electrochemical surface area (ECSA) decreased due to the growth of electrode catalyst particles and that the hydrogen crossover current density measured by LSV could be reduced. Fourier transform infrared spectroscopy and thermogravimetric/differential thermal analysis showed that -S-O-S- crosslinking occurred in the polymer after the 50 hour AST. Gas chromatography showed that the hydrogen permeability was decreased by -S-O-S- crosslinking. The reduction of the hydrogen crossover current density measured by LSV in the early stages of AST could be caused by both reduction of the electrochemical surface area of the electrode catalyst and -S-O-S- crosslinking.

• Archives of Pharmacal Research
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• v.28 no.12
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• pp.1358-1364
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• 2005

In this study, we investigated whether a novel anti-ischemic $K_{ATP}$ opener KR-31378 [(2S,3S,4R)­N'-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2 -methly-2-dimethoxymethly-2H-benzopyran-4-yl)­N'-benzylguanidine] has protective effect against oxidative stress-induced death in heart-derived H9c2 cells. Cell death was induced by BSO, butionine sulfoximine, which inhibits GSH synthesis and subsequently increases reactive oxygen species (ROS) level. Cell death was quantitatively determined by measuring lactate dehydrogenase (LDH) activity and stained by Hoechst 33258. BSO-induced ROS production and mitochondrial membrane potential (MMP) were measured using 2',7'-dichlorofluorescein diacetate oxidation and rhodamine 123, respectively. Both the LDH release and the ROS elevation induced by treatment of H9c2 cells with 10 mM BSO, were significantly decreased by KR-31378. These protective effect and antioxidant effect of KR-31378 appeared to be independent on $K_{ATP}$ channel opening. Cells exposed to BSO showed an early reduction in MMP, and this reduction in MMP was significantly reversed by treatment with KR-31378. Caspase-3 activity in BSO treated H9c2 cells was remarkably increased, and this increased caspase-3 activity was significantly reversed by KR-31378. In conclusion, our results suggest that KR-31378 can produce cardioprotective effect against oxidative stress-induced cell death through antioxidant mechanism.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.7 no.4
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• pp.234-237
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• 1974

Electro-chemical aspects of stress corrosion on the mild steels when immersed in the $5\%\;H_2SO_4$ solution and charged with 100mV and 100mA were discussed. The main results of the experiment are follows; 1. The weight loss by corrosion was concerned with the applied stress. and the larger the applied stress, the greater the weight loss. 2. Reduction of corrosion stress was a factor of inverse proportion to the applied stress. 3. Corrosion began at first on the parts of impurities concentrated and the grain boundaries, and gradually developed and spreaded out. 4. The materials of unsteady structure deformed of space lattice by the high stress or work-hardening showed less reduction of corrosion stress.

• Korean Journal of Agricultural Science
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• v.42 no.1
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• pp.1-5
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• 2015

Drought is one of the major abiotic constraints limiting quantity and quality of rice grain. In order to elucidate the effects of drought on chemical compositions of rice grain, seedlings were cultivated in a rainout shelter controlled with well-watered or water-deficit conditions. After harvesting, the key components including proximates, amino acids, fatty acids, minerals, and vitamins of rice grains were analyzed. Drought stress increased the amounts of methionine, phenylalanine, linoleic acid, linolenic acid, calcium, potassium, vitamin B1, and vitamin E in rice grains, whereas it decreased the contents of lignoceric acid. Particularly, drought stress caused a marked increase in vitamin E content. These results indicate drought significantly influence the chemical compositions of rice grains.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.293-303
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• 1971

The theological properties of aqueous suspensions of Black Hills bentonite were measured by using a Couette-type viscometer. Three kinds of flow units in aqueous bentonite suspension were postulated. Each has a different average relaxation time, one Newtonian. One of the non-Newtonian types is thixotropic, and the other is non-thixotropic. The thixotropic non-Newtonian unit is transformed to a Newtonian unit by shear stress. If the stress is relieved, the transformed unit returns to its original state. Two flow equations were derived by introducing chemical kinetics consideration for such a transition into the generalized theory of viscous flow. One equation describes the "upcurve," a diagram of rate of sheat versus shear stress, obtained by increasing the rate of shear, and the other relates to the "downcurve" obtained by decreasing the shear rate. The equations satisfactorilly describe the experimental thixotropic hysteresis of bentonite suspensions. The equations also were successfully applied to the flow curves of the suspensions containing various amounts of monovalent electrolyte (KCI).

• Anxiety and mood
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• v.13 no.1
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• pp.1-9
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• 2017

We reviewed the scientific literature on psychological effects of Chemical, Biological, Radiological, Nuclear, Explosive (CBRNE) disaster, which is one of the biggest threat to modern society. CBRNE disaster has the potential to cause specific physical symptoms and psychological distress in victims ; moreover, various toxic symptoms and carcinogenesis/mutation would be an important issue. Bioterrorism can cause localized outbreaks of infectious disease or pandemic disaster. Somatization as well as posttraumatic stress symptoms and depression are the characteristic psychological symptoms in CBRNE disaster's victims. CBRNE disasters could lead to large-scale public fear and social chaos due to the difficulties involved in verifying the extent of exposure and unfamiliar area to the common people. In the evacuation process, problems associated with adjustment and conflict between victims and residents should be considered.

• Bulletin of the Korean Chemical Society
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• v.20 no.6
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• pp.753-756
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• 1999

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.249-251
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• 2003

The effects of fermentor types on biopolymer production with Cordyceps militaris has been studied in this articles. Since the shear stresses of stirred tank ferementor and bubble column fermentor were different, the mycelium growth and biopolymer production were different. The mycerial growth was high with the bubble column fermentor for the early stage but biopolymer production was lower than that with stirred tank fermentor. The production of biopolymer was closely related to shear stress to the cells and biopolymer production was increased with increased shear stress.