• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.296-306
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• 1992

$^{13}C$ spin-lattice relaxation times were measured for n-alkanes of moderate chain length, ranging from n-octane to n-dodecane, under the condition of proton broad-band decoupling within the temperature range of 248-318 K in order to gain some insight into basic features of segmental motions occurring in long chain ploymeric molecules. The NOE data showed that except for methyl carbon-13 dipole-dipole interactions between $^{13}C$ and directly bonded $^1H$ provide the major relaxation pathway, and we have analyzed the observed $T_1data$ on the basis of the internal rotational diffusion theory by Wallach and the conformational jump theory by London and Avitabile. The results show that the internal rotational diffusion constants about C-C bonds in the alkane backbone are all within the range of $10^9\;-10^10\;sec^{-1}$ in magnitude while the mean lifetimes for rotational isomers are all of the order of $10^{-11}\;-10^{-10}$ sec. Analysis by the L-A theory predicts that activation energies for conformational interconversion between gauche and trans form gradually increase as we move from the chain end toward the central C-C bond and they are within the range of 2-4 kcal/mol for all the compounds investigated.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.203-211
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• 2009

In flows with deformation rates larger than the inverse Rouse time of the polymer chain, chains are stretched and their confining tubes become increasingly anisotropic. The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic and limit chain stretch. In the Molecular Stress Function (MSF) model, chain stretch is balanced by an interchain pressure term, which is inverse proportional to the $3^{rd}$ power of the tube diameter and is characterized by a tube diameter relaxation time. We show that the tube diameter relaxation time is equal to 3 times the Rouse time in the limit of small chain stretch. At larger deformations, we argue that chain stretch is balanced by two restoring tensions with weights of 1/3 in the longitudinal direction of the tube (due to a linear spring force) and 2/3 in the lateral direction (due to the nonlinear interchain pressure), both of which are characterized by the Rouse time. This approach is shown to be in quantitative agreement with transient and steady-state elongational viscosity data of two monodisperse polystyrene melts without using any nonlinear parameter, i.e. solely based on the linear-viscoelastic characterization of the melts. The same approach is extended to model experimental data of four styrene-butadiene random copolymer melts in shear flow. Thus for monodisperse linear polymer melts, for the first time a constitutive equation is presented which allows quantitative modeling of nonlinear extension and shear rheology on the basis of linear-viscoelastic data alone.

• The Journal of the Acoustical Society of Korea
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• v.17 no.6
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• pp.3-7
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• 1998

Methylcyclohexane의 초음파 흡수측정을 0.1-2MHz의 주파수 범위, 온도 30-60℃에 걸쳐 1MHz이하에서 정확한 초음파 흡수측정이 가능한 광 회절 초음파 공명법을 사용하여 행하였다. 그 결과, axial과 equatorial에 의한 완화는 단일 완화현상을 보였고 그 스펙트럼 으로부터 완화 주파수와 완화강도를 결정하였다. 완화 주파수의 온도 의존성으로부터 활성 화에너지(△H*)=10.0㎉/㏖을, 완화 강도의 온도 의존성에서 엔탈피 차(△H)=1.8㎉/㏖을 각각 구하였다.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.107-110
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• 2000

($^{11}$B NMR measurements have been performed on single crystals of LuNi$_2$B$_2$C superconductor to investigate vortex lattice structures and dynamical behavior. The spectrum in the superconducting state is significantly broadened by local field inhomogeneity due to the vortex lattice and the peak point of the spectrum shifts toward low magnetic field due to the imperfect field penetration. The linewidth of the spectrum reflecting local field variation is much smaller than expected for conventional vortex lattices and shows peculiar increase at low temperature. Furthermore, the transverse relaxation rate, 1/T$_2$, probing the slow motion of vortices, exhibits a single peak as temperature decreases. These prominent results highlight significant fluctuation of vortices even for this low T$_c$, and nearly isotropic 3D superconductor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.946-952
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• 2002

The electrical and dielectric characteristics of ZPCCY-based varistor ceramics were investigated in the sintering time range of 1∼3 h. Increasing sintering time deteriorated the nonlinearity, in which nonlinear exponent is decreased from 51.2 to 23.8 and leakage current is increased from 1.3 to 5.6 $\mu$A. As sintering time increases, the donor concentration was decreased in the range of (1.25∼l.73)$\times$10$\^$18/cm$\^$-3/ and the density of interface states is (3.64∼94.19)$\times$10$\^$12/cm$\^$-2/ with increasing sintering time. The increase in sintering time caused tan $\delta$ to increase in the range of 0.043 to 0.062 and relaxation time to increase in the range of 1.55 to 2.23 ㎲.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.121-124
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• 2000

The time dependence of irreversible magnetization of grain aligned infinite layer superconductor Sr$_{0.9}$La$_{0.1}$CuO$_2$ was measured in temperature range of 2 K < T < 30 K for H= 0.5 T, 1.0 T and 1.5 T parallel to c-axis. From this, we calculated normalized flux creep rate S(T) ${\equiv}$ dlnM/dlnt and found that the temperature independent region in S(T) is significantly wide in comparision with other cuprate superconductors. Using the method of Maley et al., we also deduce the current density dependence of pinning potential and glassy exponent ${\mu}$.

• Elastomers and Composites
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• v.43 no.4
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• pp.259-263
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• 2008

An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.

• Journal of Physiology & Pathology in Korean Medicine
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• v.22 no.1
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• pp.148-154
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• 2008

The butanol extract of Euonymus alatus (BEA) induced dose-dependent relaxation of phenylephrine-precontracted aorta, which was abolished by removal of functional endothelium. Pre-treatment of the endothelium-intact aortic tissues with $N^G-nitro-L-arginine methylester$ (L-NAME), and 1 H-[1,2,4]-oxadiazole- [$4,3-{\alpha}$]-quinoxalin-1-one (ODQ) inhibited the relaxation induced by BEA, respectively. BEA-induced vascular relaxation was not blocked by glibenclamide, tetraethylammonium (TEA), indomethacin, atropine, propranolol, verapamil, and diltiazem, respectively. Moreover, BEA inhibits phenylephrine-induced vascular constriction in a dose-dependent manner. These results suggest that BEA relaxes vascular smooth muscle via endothelium-dependent nitric oxide/cGMP signaling.

• Journal of Physiology & Pathology in Korean Medicine
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• v.18 no.4
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• pp.1078-1082
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• 2004

The purpose of this study was to investigate the possibility of medicinal plants application as an edible functional food resources. We carried out to develop a traditional functional beverage by using hot-water extraction of 4 medicinal plants(Polygonatun sibiricum, Ophiopogonis radix, Lycii fructus, Schizandriae fructus) and we examined the effects of drink on physiological function in aorta relaxation. Thus, the effect of developed beverage on phenylephrine induced contraction of isolated rat thoracic aorta. Contractile force was measured with force displacement transducer under 1.5g loading tension. Brix, pH and titratable acidity of developed drink were 9.5%, 3.3 and 0.22%. The approximate nutritional composition of beverage was carbohydrate, 5.98%, crude protein, 0.70%, crude fat, 0.20% and crude ash, 0.20%. Developed beverage contained K(4.00 ㎎%), Na(3.68 ㎎%), Ca(2.54 ㎎%), Mg(1.60 ㎎%) and Fe(0.29㎎%). The contraction forces by injection of phenylephrine in isolated thoracic aorta were significantly low in each experimental groups compared with control groups, These results that developed drink with medicinal plants can be used as a functional material to decrease aorta contraction.

• Bulletin of the Korean Chemical Society
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• v.15 no.7
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• pp.553-559
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• 1994

Dynamics of $CH_2CI$ group in ${\alpha},2,6$-trichlorotoluene dissolved in $CDCl_3$ was studied by observing various relaxation modes for $^{13}C$ under proton undecoupled condition. Partially relaxed $^{13}C$ spectra were obtained at $34^{\circ}C$ as a function of evolution time after applying various designed pulse sequences to this $AX_2$ spin system. It was found that nonlinear regression analysis of the relaxation data for these magnetization modes could provide the information about dipolar and spin-rotational auto-correlation and cross-correlation spectral densities for fluctuation of the $^{13}C-^1H$ internuclear vector in $CH_2Cl$ group. The results show that the effect of cross-correlation is comparable in magnitude to that of auto-correlation and the relaxation in this spin system is dominated by dipolar mechanism rather than spin-rotational one. From the resulting spectral density data we could calculate the bond angle ${\angle}HCH\;(105.1$^{\circ}$) and elements of the rotational diffusion tensor for $CH_2Cl$ group.