• Title/Summary/Keyword: dispersion phenomenon

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Preparation of a PVDF (Polyvinylidene Fluoride) Thin Film Grown by Using the Method of Electric Field Application (전계인가법을 이용한 PVDF 박막의 제작과 특성에 대한 연구)

  • 장동훈;강성준;윤영섭
    • Proceedings of the IEEK Conference
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    • 2000.06b
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    • pp.76-79
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    • 2000
  • The 3$\mu\textrm{m}$-thick PVDF (Polyvinyiidene fluoride) thin film have been prepared using physical vapor deposition with electric field, and its FT-IR specrum, dielectric property and electric conduction phenomenon have been investigated. Since the characteristic peaks ate detected at 509.45 and 1273.6〔cm〕 in the FT-IR spectrum, we are confirmed that the ${\beta}$ -phase is dominant in the PVDF thin film. In the results of dielectric properties, the PVDF thin film shows anomalous dispersion, i.e. gradual decrease of dielectric constant with increase of frequency, and also that the dielectric absorption point changes from 200Hz to 7000Hz with increasing temperature of thin film, which is consistent with the Debye's theory. The activation energy (ΔH) obtained from temperature dependence of dielectric loss is 21.64 ㎉/㏖. We confirm that the electric conduction mechanism of PVDF thin film is dominated by ionic conduction by investigating the dependence of the leakage current of the thin film on the temperature and the electric field.

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A Study on Fatigue Strength of Austenitic Stainless Steel for Centrifuge (원심분리기용 오스테나이트계 스테인리스강의 피로강도에 관한 연구)

  • Lee, Mee-Hae;Kim, Yong-Soo;Park, Joon-Woo
    • Journal of the Korean Society of Safety
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    • v.23 no.3
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    • pp.12-16
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    • 2008
  • For industrial centrifuges, the state of their welding areas, even with a naked-eye observation, offers potential safety problems such as inconsistent bead formation. STS304, which is used mainly in centrifuges, is made of metal alloys with chrome and nickel as the main ingredients, offering excellent corrosion resistance, thermal resistance, and high strength, and thus allowing it to be used for diverse purposes. This paper conducted tensile and fatigue tests of STS304 to improve the safety of centrifuges. In the findings, for the static behavior of the STS304 material, welded specimens increased their yield and tensile strength compared with the base test specimens, but decreased their elongation ratio. Also, the data dispersion phenomenon of welded specimens remarkably increased.

Contract Choice and Pricing of IPOs

  • Cho, Sung-Il
    • The Korean Journal of Financial Studies
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    • v.6 no.1
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    • pp.289-312
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    • 2000
  • This paper proposes a pricing model for IPOs which can reconcile the average underpricing phenomenon with the expected wealth maximizing behaviors of market participants. Under the usual informational asymmetry, the optimal offer price for best efforts IPOs is derived as a function of the uncertainty about market's valuation, the expected return on proposed projects and the size of offerings relative to the firm's market value. Depending on these firm-specific characteristics, best efforts IPOs can be underpriced, fairly priced, or overpriced. Introducing the investment banker as an outside information producer, the model is extended to provide empirical implications for pricing and underwriting contract choice decisions which are consistent with the existing empirical evidences. The model predicts that the issuers with greater uncertainty about market's valuation choose best efforts contract over firm commitment contract and the dispersion of initial returns would be greater for best efforts IPOs than for firm commitment IPOs.

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A study on nonlinear channel equalization using RBF network (RBF 네트워크를 이용한 비선형 채널 등화에 관한 연구)

  • 전선도;위진우;강철호
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.22 no.1
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    • pp.64-71
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    • 1997
  • Digital communication channels are imparied by linear effects such as dispersion, ISI(intersymbol Interference), fading phenomenon etc. But, the practical channel equalization system is required to design for compensating the nonlinear distortion caused by harmonic distortion etc. This paper is a study on the performance of nonlinear channel equalization using RBF(Radial Basis Funclion) network, which has the equivalent structure to the optimal Basian filter. Expecially, the variance of RBF network is modifiedby nonlinear polynomial filters to compare the convergence characteristic of nonlinear channel equalization. Experimental results show that the modified RBF network achieves the faster convergence property than conventional RBF network. Moreover, the RBF network ofhigher order variance modified represents the better performance than that of lower order variance in the bandpass channels and second/third order polynomial channels.

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Fast(submillisecond) Switching of Nematic Liquid Crystals and Effects of Dielectric Dispersion; Theory and Experiment

  • Shiyanovskii, Sergij V.;Golovin, Andrii B.;Yin, Ye;Lavrentovich, Oleg D.
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07a
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    • pp.181-186
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    • 2005
  • We demonstrate that the finite rate of dielectric relaxation in liquid crystals which has been ignored previously causes profound effects in the fast dielectric reorientation of the director. The phenomenon is relevant for submillisecond switching of the director when the switching rate approaches the rate of dielectric relaxation through the reorientation of the molecular dipoles. A submillisecond switching ($15-400\;{\mu}s$ for an optical retardation shift $0.3-2.2\;{\mu}m$ in $10-15\;{\mu}m$ thick cells) is demonstrated for dual frequency nematic cells with high pretilt that maximizes the dielectric torque acting on the director. We propose the theory of dielectric response in which the electric displacement depends not only on the present (as in the standard theory) but also on the past values of electric field and director. We design an experiment in which the standard "instantaneous" model and our model predict effects of opposite signs; the experimental data support the latter model.

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Capillary Electrophoresis of Microbes

  • Moon, Byoung-Geoun;Lee, Yong-Ill;Kang, Seong-Ho;Kim, Yong-seong
    • Bulletin of the Korean Chemical Society
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    • v.24 no.1
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    • pp.81-85
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    • 2003
  • Direct analysis of microbes such as either gram-positive or gram-negative bacteria without cell lysis was investigated using capillary electrophoresis. Bacteria cells were directly introduced into the microbore fusedsilica capillary, then separated under high electric field in less than 15 min. It was found that a proper dispersion of bacteria cells was important for reproducible results. Migration behavior of bacteria at different storage condition was investigated and many unexpected peaks were observed from bacteria stored at room temperature due to the distortion of cells. This phenomenon was attributed to the change of size and shape of the same bacterium and confirmed by the scanning electron microscopic images.

Analysis of Hydrodynamic Dispersion in Contaminated Soil based on Mobile-Immobile Model (Mobile-Immobile 모델을 활용한 유류오염토양 내 수리분산 특성 연구)

  • Kim, Yong-Sung;Woo, Hee-Soo;Park, Jun-Boum
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.1512-1517
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    • 2008
  • Laboratory column tests were conducted in this study using $Cl^-$ tracers on Jumunjin sand to analyze contaminant transport in mixed contaminated soils. Results obtained from clean soils and soils containing residual diesel verified heterogeneous distribution of residual diesel, and clear acceleration of solute movement. In addition, asymmetric breakthrough curves indicated development of immobile region where solute movement becomes stagnant and creates tailing phenomenon.

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Permittivity of Semiconductive Shield Materials in Power Cables by Frequency, Temperature (주파수, 온도에 따른 전력케이블용 반도전 재료의 유전올)

  • Yang, Hoon;Park, Dae-Hee
    • Proceedings of the KIEE Conference
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    • 2007.11a
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    • pp.218-219
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    • 2007
  • This paper researched permittivity of carbon nanotube reinforced semiconductive shield materials for power cable in accordance with carbon nanotube content. Permittivity measured 1[Hz], 1[kHz], 1[Mhz] in frequency range, and range of temperature measured to 100$[^{\circ}C]$ from -50$[^{\circ}C]$. It is stable to 100$[^{\circ}C]$ from -50$[^{\circ}C]$ without different gap. But, in case of CNT:CB=100:0, permittivity decreased by temperature increment. Also, in case of CNT:CB=100:0, it shows highest permittivity. Permittivity of change have little no the power of influence by frequency, but in case of 1[Mhz], CNT:CB=100:0 of specimen decreased more than other frequency. This influence thinks phenomenon of induced electricity dispersion.

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Homogeneous Dual Composite Right/Left-Handed Metamaterial Using Subwavelength Defected Ground Structure(DGS) (Subwavelength 결함접지구조(defected grounded structure : DGS)를 이용한 Homogeneous Dual Composite Right/Left-Handed 메타물질 구현)

  • Park, Woo-Young;Lim, Sung-Joon
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.11
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    • pp.2242-2246
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    • 2009
  • In this paper, a homogeneous dual composite right/left-handed (D-CRLH) transmission line (TL) is proposed by using a defected ground structure (DGS) on the ground plane. In order to satisfy a homogeneity condition of metamaterial, a subwavelength unit cell is designed by way of a spiral DGS and a meander stub. From a dispersion diagram, it is expected that the frequency bands for the left-handed (LH) property is 3.5 - 4.4 GHz. At 3.8 GHz in the LH band, backward propagating phenomenon is observed from full-wave analysis. The experimental results show that the proposed TL has a stop-band in 1.75 - 3.6 GHz.

Solvolyses of N-Methyl-N-phenylcarbamoyl Chlorides with Electron Acceptor Substituents in A Queous Binary Mixtures

  • Gu, In Seon;An, Seon Gyeong;Yang, Yeol;Go, Han Jung;Choe, Mun Ho;Lee, Ik Chun
    • Bulletin of the Korean Chemical Society
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    • v.22 no.8
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    • pp.842-846
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    • 2001
  • Solvolyses of N-methyl-N-phenylcarbamoyl chlorides in aqueous binary mixtures of acetone, ethanol, methanol and in water, D2O, and 50% D2O-CH3OD are investigated at 25.0 $^{\circ}C.$ The Grunwald-Winstein plots of first-ord er rate constants for N-methyl-N-phenylcarbamoyl chlorides with YCl (based on 2-adamantyl chloride) show a dispersion phenomenon. The ring parameter (I) has been shown to give considerable improvement when it is added as an hI term to the original Grunwald-Winstein and extended Grunwald-Winstein correlations for the solvolyses of N-methyl-N-phenylcarbamoyl chlorides. This study has shown that the magnitude of l, m and h values associated with a change of solvent composition is able to predict the dissociative SN2 transition state. The kinetic solvent isotope effects determined in deuterated water are consistent with the proposed mechanism of the general base catalyzed and/or a dissociative SN2 mechanism channel for N-methyl-N-phenylcarbamoyl chlorides solvolyses.