• Macromolecular Research
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• 제17권10호
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• pp.785-790
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• 2009

In this paper, the relaxation behavior of the regenerated silk fibroin (SF) films was investigated using dielectric thermal analysis (DETA), and compared with the dynamic mechanical behavior obtained from dynamic mechanical thermal analysis (DMTA), in order to gain a better understanding of the characteristics of dielectric behavior of SF film and identify the differences between the two analyses. Compared to DMTA, DETA exhibited a higher sensitivity on the molecular relaxation behaviors at low temperature ranges that showed a high $\gamma$-relaxation peak intensity without noise. However, it was not effective to examine the relaxation behaviors at high temperatures such as $\alpha-$ and ${\alpha}_c$-relaxations that showed a shoulder peak shape. On the contrary, DMTA provided more information regarding the relaxation behaviors at high temperatures, by exhibiting the changes in width, intensity and temperature shift of the $\alpha$-relaxation peak according to various crystallinities. Conclusively, DETA and DMTA can be utilized in a complementary manner to study the relaxation behavior of SF over a wide temperature range, due to the different sensitivity of each technique at different temperatures.

• Korean Journal of Veterinary Research
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• 제34권3호
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• pp.479-486
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• 1994

Effects of catecholamines and the site of receptor of catecholamines were investigated in the longitudinal muscle of the rumen. In order to this experiment, specimens were obtained from 35 Korean Native Cattles, 2-3 years old, in the Kwang-ju area slaughterhouse. Longitudinal muscle strips of rumen were made from sample, and then measured the isometric contraction with physiograph in $37{^{\circ}C}$ organ bath. The results were summarized as follows. 1. 30% of all strips showed rhythmic contraction after short incubation time. 2. Relaxation produced by catecholamines in this preparations increased in a dose-dependant manner. 3. Isoproterenol(${\beta}$-agonist) caused relaxation, but phenylephrine(${\alpha}_1$-agonist) and xylazine(${\alpha}_2$-agonist) were unaffected. 4. The relaxation induced by epinephrine and norepinephrine were not affected by phentolamine(${\alpha}$-blocker) and prazosin(${\alpha}_1$-blocker), yohimbine(${\alpha}_2$-blocker). But propranolol(${\beta}$-antagonist) abolished the effect of catecholamines on relaxation. 5. It is concluded that catecholamines produced relaxation in the longitudinal muscle of rumen via the ${\beta}$-adrenoceptor.

• Journal of Nutrition and Health
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• 제36권9호
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• pp.918-923
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• 2003

L-theanine Is an amino acid in green tea and has been known to decrease serotonin and increase norepinephrine in rat brains, and also reported to produce mental relaxation, lower blood pressure and improve learning ability in human beings. But, few studies on these effects for human beings have been conducted so far. This study was conducted to evaluate the effect of L-theanine on the release of brain alpha waves known to be related with mental relaxation and concentration. Twenty healthy male volunteers aged 18 to 30 years without any Physical and Psychological diseases were recruited through written advertisement. Alpha power values of EEG as a surrogate marker of mental relaxation and concentration were measured in frontal and occipital regions for 40 minutes after administration of four placebo or test tablets and 20 minute resting period. The same procedure crossed over at 7-day intervals. We analyzed average alpha power values in frontal and occipital regions at 10 minute intervals. Repeated ANOVA revealed that there were significant differences of occipital alpha power values between placebo and test groups with high anxiety (p < 0.05). The mean values at 20,30,40,50 and 60 minute intervals were 0.23, 024, 0.28, 0.25 and 0.34 in placebo, respectively and 0.23, 0.29, 0.40, 0.34, and 0.45 in test, respectively. But there were no significant differences of frontal and occipital alpha power values between placebo and test groups with low anxiety (p > 0.05) . The results of this study suggest that L-theanine containing tablets promote the release of alpha waves related to mental relaxation and concentration in young adult males.

• Macromolecular Research
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• 제14권4호
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• pp.416-423
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• 2006

The dynamic mechanical thermal properties of poly(hexamethylene terephthalate) (PHT), poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) and their P(HT-co-CT) random copolymers in the amorphous state were examined as a function of temperature and frequency. All the samples exhibited two main relaxation processes in the plot of tan ${\delta}$ versus temperature: the primary ${\alpha}$-relaxation associated with the glass transition and the secondary ${\beta}$-relaxation attributed to the local segmental motions of mostly cyclohexylene rings for PCT and to cooperative motions of methylene, carboxyl, and phenylene groups for PHT. Both ${\alpha}$- and ${\beta}$-relaxation temperatures increased with increasing CT content. The activation energy of the ${\alpha}$-relaxation increased with increasing CT content, whereas that of the ${\beta}$-relaxation decreased. The sub-glassy secondary ${\beta}$-relaxation processes of PCT and PHT were investigated in terms of the cooperativity of main-chain segmental motions.

• Transactions on Electrical and Electronic Materials
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• 제18권4호
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• pp.211-216
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• 2017

The dielectric properties of two polyurethanes (PUs) with different hard segments, i.e., aromatic methylene di-p-phenyl diisocyanate (MDI) and aliphatic hexamethylene diisocyanate (HDI), were investigated in the temperature range of -100 to $100^{\circ}C$ and in the frequency range of 1 Hz to 3 kHz. The ${\alpha}$-relaxations induced by the glass transition of the equivalent soft segments in the two PUs occurred at relaxation times of ${\tau}=3.46{\times}10^{-3}s$ for MDI-PU and ${\tau}=3.39{\times}10^{-2}s$ for HDI-PU at $-20^{\circ}C$, in accord with the temperature-frequency superposition principle, resulting in similar shifting factors. However, different I-relaxations were observed for the two PUs. The I-relaxation of MDI-PU occurred due to the mobility of the chain extenders near $80^{\circ}C$ with a slower shifting rate than the ${\alpha}$-relaxation. On the other hand, I-relaxation arising from both the extender and the unconstrained hard segments of HDI-PU occurred at $70{\sim}100^{\circ}C$, indicating complicated dielectric behavior due to partial interaction with the ${\alpha}$-relaxation at high frequencies. Thus, the I-relaxation of HDI-PU did not follow the superposition principle. The dielectric behaviors of the PUs were mainly influenced by their phase transitions, which were affected by the structure and components of the materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.470-473
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• 2001

In this study, 70/30 mol% P(VDF-TrFE) copolymer thin films were prepared by physical vapor deposition, and dielectric properties with frequency were investigated. From results of TA(Thermal Analysis), the Curie transition temperature and melting temperature were observed at 118.8$^{\circ}C$ and 146$^{\circ}C$, respectively. Therefore, while thin films were prepared, the substrate temperature was varied from 30$^{\circ}C$ to 90$^{\circ}C$. The dielectric constant decreased with increasing frequency. At measuring frequency of 1kHz, the relative dielectric constant increased from 3.643 to 23.998 with increasing substrate temperature from 30$^{\circ}C$ to 90$^{\circ}C$. As a result of dielectric loss factor, ${\alpha}$-relaxation and ${\beta}$-relaxation were observed near at 100Hz and 1MHz, respectively. And the magnitude of ${\alpha}$-relaxation decreased and that of ${\beta}$-relaxation increased with increasing substrate temperature.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.468-473
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• 1991

Viscoelastic properties of PET filament fibers on stress relaxation were investigated in the solvents of $H_2$O, 0.05% NaOH and 50% DMF using an Instron (UTM4-100 Tensilon) with solvent chamber. The theoretical stress relaxation equation derived by applying the Ree-Eyring's hyperbolic sine law to dashpot of three element non-Newtonian model was applied to the experimental stress relaxation curves, and the model parameters $G_1,G_2$, ${\alpha}$ and ${\beta}$ were obtained. By analyzing temperature dependency of the relaxation time, the values of activation entropy, activation enthalpy and activation free energy for flow in PET filament fiber were evaluated, the activation free energy being about 25.7 kcal/mol. The self diffusion coefficient and hole distance were obtained from parameters ${\alpha}$, ${\beta}$ and crystallite size in order to study the self diffusion and the orientation of crystallites in amorphous region and the effect of solvent.

• Advances in Traditional Medicine
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• 제2권2호
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• pp.87-93
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• 2002

The present study was aimed to examine the role of endothelium in the relaxant effect of hawthorn fruit extract of Crataegus pinnatifida in four different types of rat arteries, posterior cerebral communicating artery, right descending coronary artery, common carotid artery, and aorta. In $9,11-dideoxy-11{\alpha}$, $9{\alpha}-epoxy-methanoprostaglandin$ $F_{2{\alpha}}$ (U46619)-preconstricted arterial rings except for aorta, the extract produced endothelium-independent relaxations with similar potency. This relaxation was unaffected by pretreatment with $100\;{\mu}M\;N^G-nitro-L-arginine$ methylester (L-NAME, the nitric oxide synthase inhibitor), $3\;{\mu}M$ 1H-[l,2,4]oxadiazolo$[4,2-{\alpha}]$quinoxalin-1-one (ODQ, the guanylate cyclase inhibitor), or $10\;{\mu}M$ indomethacin (the cyclooxygenase inhibitor). Putative $K^+$ channel blockers (charybdotoxin plus apamin or glibenclamide) did not affect the extract-induced relaxation in cerebral or coronary artery rings. In contrast, in rat aortic rings the extract produced significantly smaller relaxant response in endothelium-denuded rings than that in endothelium-intact rings. Pretreatment with L-NAME or ODQ abolished the extractinduced endothelium-dependent aortic relaxation, whilst indomethacin $(3\;{\mu}M)$ had no effect. The present results indicate that hawthorn fruit extract possesses a vasorelaxing effect in cerebral, coronary and carotid arteries and this effect is independent of the presence of a functional endothelium. However, the extract-induced endothelium-dependent relaxation in rat aorta was mediated through endothelial nitric oxide and cyclic GMP-dependent mechanisms, suggesting that active components in the extract may act on endothelium to stimulate release of nitric oxide in large conduit arteries of the rats.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.822-825
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• 2003

Maxwell displacement current (MDC) measurement has been employed to study the dielectric property of Langmuir-films. A method for determining the dielectric relaxation time $\tau$ of floating monolayers on water surface is presented. WC flowing across monolayers is analyzed using a rod-like molecular model. It is revealed that the dielectric relaxation time $\tau$ of monolayers in the isotropic polar orientational phase is determined using a liner relationship between the monolayer compression speed ${\alpha}$ and the molecular area Am. Compression speed ${\alpha}$ was about 30, 40, 50mm/min.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.279-282
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• 2000

The displacement current measurement has been employed to study the dielectric properties of Langmuir films. A method for determining the dielectric relaxation time $\tau$ of floating monolayers on water surface is presented. The displacement current flowing across monolayers is analyzed using a rod-like molecular model. It's revealed that the dielectric relaxation time $\tau$ of monolayers in the isotropic polar orientational phase is determined using a liner relationship between the monolayers compression speed $\alpha$ and the molecular maximum area $A_{m}$. The compression speed $\alpha$ was about 30, 40, 50mm/minmm/min