• Title, Summary, Keyword: relaxation mechanism

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Dielectric Relaxation and Electrical Conduction Properties of La2NiO4+δ Ceramics (La2NiO4+δ세라믹스의 유전이완 및 전기전도특성)

  • Jung, Woo-Hwan
    • Korean Journal of Materials Research
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    • v.21 no.7
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    • pp.377-383
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    • 2011
  • Thermoelectric power, dc conductivity, and the dielectric relaxation properties of $La_2NiO_{4.03}$ are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of $La_2NiO_{4.03}$ decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in $La_2NiO_{4.03}$ was analyzed using Mott's approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for $La_2NiO_{4.03}$ are consistent with the polaronic nature of the charge carriers.

A Study on Weld Residual Stress Relaxation by furnaced and local PWHT Procedures (노내 및 국부 후열처리에 의한 잔류응력 완화 거동 평가)

  • Lee, Seung-Gun;Kim, Jong-Sung;Jin, Tae-Eun;Dong, P.
    • Proceedings of the KSME Conference
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    • pp.250-255
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    • 2004
  • In this paper, we established baseline information and insight on residual stress relief mechanism associated with furnaced and local PWHT(post weld heat treatment) operation. Based on FEM analysis results, we suggested that furnaced PWHT stress relief mechanism was based on creep relaxation and local PWHT stress relief mechanism involved complicated interactions between plasticity and creep. In case of furnaced PWHT, significant stress relaxation was occurred in the early stage of PWHT. In case of local PWHT, stress relaxation magnitude was increased as PWHT time increased. Finally, We have proposed that detailed furnaced and local PWHT procedure, and qualification criteria to support current codes of practices.

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Viscoelastic behavior of aqueous surfactant micellar solutions

  • Toshiyuki Shikata;Mamoru Shiokawa;Shyuji Itatani;Imai, Shin-ichiro
    • Korea-Australia Rheology Journal
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    • v.14 no.3
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    • pp.129-138
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    • 2002
  • A cationic surfactant, cetyltrimethylammonium $\rho$-toluenesufonate (CTA$\rho$TS), forms long threadlike micelles in aqueous solution. The threadlike micelles make concentrated entanglement networks, so that the solution shows pronounced viscoelastic behavior as concentrated polymer systems do. However, a mechanism for a process responsible for the longest relaxation time of the threadlike micellar system is different from that of semi-dilute to concentrated polymer systems. The threadlike micellar system exhibits unique viscoelasticity described by a Maxwell model. The longest relaxation time of the threadlike micellar system is not a function of the concentration of CTA$\rho$TS, but changes with that of $\rho$-toluenesufonate ($\rho$$TS^{-}$) ions in the bulk aqueous phase supplied by adding sodium $\rho$-toluenesulfonate (NapTS). The rates of molecular motions in the threadlike micelles are not influenced by the concentration of $\rho$$TS^{-}$ anions, therefore, molecular motions in the threadlike micelles (micro-dynamics) are independent of the longest relaxation mechanism (macro-dynamics). A nonionic surfactant, oleyldimethylamineoxide (ODAO), forms long threadlike micelles in aqueous solution without any additives. The aqueous threadlike micellar system of ODAO also shows Maxwell type viscoelastic behavior. However, the relaxation mechanism for the longest relaxation process in the system should be different from that in the threadlike micellar systems of CTA$\rho$TS, since the system of ODAO does not contain additive anions. Because increase in the average degree of protonation of head groups of ODAO molecules in micelles due to adding hydrogen bromide causes the relaxation time remarkably longer, changes in micro-structure and micro-dynamics in the threadlike micelle are closely related to macro-dynamics in contrast with the threadlike micellar system of CTA$\rho$TS.

A Study on Spin-Lattice Relaxation of Methyl Protons in 2,6-Dichlorotoluene and N-Methyl Phthalimide

  • Lee, Jo-Woong;Lim, Man-Ho;Rho, Jung-Rae
    • Bulletin of the Korean Chemical Society
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    • v.12 no.1
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    • pp.47-51
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    • 1991
  • Spin-lattice relaxation of methyl protons in 2,6-dichlorotoluene and N-methyl phthalimide, each dissolved in CDCl$_3$, has been studied at 34$^{\circ}$C and the contribution from spin-rotation interaction to the relaxation process has been separated from that due to dipole-dipole interactions among methyl protons. The results show that the spin-rotational contributions to the initial rate of relaxation in 2,6-dichlorotoluene and N-methyl phthalimide amount to 18 and 31%, respectively, of the total relaxation rate at 34$^{\circ}$C. The method of separating the spin-rotational contribution from that of dipolar interactions adopted in this paper is based on the well known fact that in an A$_3$ spin system such as methyl protons in liquid phase dipolar relaxation mechanism gives non-exponential decay of the z-component of total magnetization of protons while the random field fluctuation such as spin-rotational mechanism causes exponential decay.

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Electrical Transport Properties of La0.5Sr0.5CrO3 Ceramics (La0.5Sr0.5CrO3 세라믹스의 전기전도특성)

  • Jung, Woo-Hwan
    • Korean Journal of Materials Research
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    • v.26 no.1
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    • pp.35-41
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    • 2016
  • The electrical transport properties of $La_{0.5}Sr_{0.5}CrO_3$ below room temperatures were investigated by dielectric, dc resistivity, magnetic properties and thermoelectric power. Below $T_c$, $La_{0.5}Sr_{0.5}CrO_3$ contains a dielectric relaxation process in the tangent loss and electric modulus. The $La_{0.5}Sr_{0.5}CrO_3$ involves the transition from high temperature thermal activated conduction process to low temperature one. The transition temperature corresponds well to the Curie point. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The low temperature conduction and relaxation takes place in the ferromagnetic phase. The ferromagnetic state in $La_{0.5}Sr_{0.5}CrO_3$ indicates that the electron - magnon interaction occurs, and drives the carriers towards localization in tandem with the electron - lattice interaction even at temperature above the Curie temperature.

The Effects of Siegesbeckiae Herba on EDRF in the Carotid Artery of the Rabbit (희렴이 가토(家兎)의 혈관내피세포성(血管內皮細胞性) 이완인자(弛緩因子)에 미치는 영향(影響))

  • Kim, Ho-Hyun;Kim, Gil-Whon
    • The Journal of Korean Medicine
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    • v.18 no.2
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    • pp.15-32
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    • 1997
  • This study was undertaken to define the mechanism of Siegesbeckiae Herba-induced relaxation in rabbit common carotid artery contracted by agonists. In order to investigate the effect of Siegesbeckiae Herba on contracted rabbit carotid arterial strips, transverse strips with intact or damaged endothelium were used for the experiment using organ bath. To analyze the mechanism of Siegesbeckiae Herba-induced relaxation, Siegesbeckiae Herba extract infused into contracted arterial strips induced by agonists after treatment of lanthanum chloride, indomethacin, atropine, $N\omega-nitro-{_L}-arginine$, cobalt chloride or methylene blue. The relaxation effect of Siegesbeckiae Herba was dependent on the presence of endothelium, showing that Siegesbeckiae Herba-induced relaxation was not observed in the strips without endothelium. The endothelium-dependent relaxation induced by Siegesbeckiae Herba was suppressed by the pretreatment of lanthanum chloride, $N\omega-nitro-{_L}-arginine$, cobalt chloride or methylene blue, but it was not observed in the strips pretreated with indomethacin or atropine. These results demonstrated that Siegesbeckiae Herba may inhibit agonist-induced contraction through an increase in the cyclic GMP by the production of nitric oxide in the vascular endothelial cells.

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Studies on the Effect and Mechanism of Geupoongjibo-dan's Relaxation on a Blood Vessel (거풍지보단(祛風至寶丹)의 혈관이완 효능과 기전에 관한 연구)

  • Kim, Dong-Eun;Park, Dong-Wan;Jeong, Sung-Hyun;Shin, Gil-Cho;Lee, Won-Chul;Han, Sung-Ho
    • The Journal of Internal Korean Medicine
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    • v.22 no.2
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    • pp.119-125
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    • 2001
  • Objectives : This study was conducted to evaluate the effect and mechanism of Geupoongjibo-dan's relaxation of the tension of the blood vessel caused by Phenylephrine and KCI. Methods : In order to study the effect of Geupoongjibo-dan's relaxation of the blood vessel tension, Geupoongjibo-dan extract was infused into Phenylephrine and KCI-induced contracted rabbit aorta strips. To analyze the mechanism of Geupoongjibo-dan's effect on the blood vessel, Geupoongjibo-dan extract infused into Phenylephrine and KCI-induced contracted strips induced by agonists after treatment of N${\omega}$-nitro-L-arginine, Methylene Blue. Results : 1. Geupoongjibo-dan was very effective in relaxing the blood vessels contracted by Phenylephrine. 2. Geupoongjibo-dan was effective against Phenylephrine, than against KCI. 3. Geupoongjibo-dan's more relaxation effect on a blood vessel was terminated by N${\omega}$-nitro-L-arginine and methylene treatment. Conclusion : THis study showed that Geupoongjibo-dan's relaxation effect on a blood vessel is irrelevant to ${\alpha}$-adrenalin receptor, and it relaxes contracted vessels through cGMP channel.

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