• Title, Summary, Keyword: odd-even effect

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Odd-Even Effects of the Anchoring Strength for Nematic Liquid Crystal on Rubbed Polyimide LB Surfaces (러빙처리된 폴리이미드막 LB막에 있어서 네마틱액정의 결합강도의 홀수짝수 효과)

  • Seo, Dae-Shik
    • Proceedings of the KIEE Conference
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    • pp.1453-1455
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    • 1996
  • The odd-even effect of the alkyl chain length of rubbed polyimide Langmuir-Blodgett (LB) surfaces on the extrapolation length of 5CB has been successfully evaluated for the first time by measuring polar anchoring strength. The extrapolation length of 5CB for rubbed PI-LB surfaces with even-numbers is small compared with odd-numbers for alkyl chain lengths of greater than 7 carbons. The extrapolation length of 5CB on rubbed PI-LB surfaces with odd-numbers increases gradually as the temperature increases but tends to diverge near the clearing temperature (Tc=$35.3^{\circ}C$). The extrapolation length diverges because of rapidly decreasing surface order near $T_c$. We suggest that the polar anchoring strength on rubbed PI-LB surfaces with even-number is strong because of relatively high surface ordering caused by more crystalline surfaces. Finally, we conclude that the odd-even effects of the polar anchoring strength in NLCs are strongly related to the character of the polymer and observed clearly for long alkyl chain lengths.

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Odd-even Effects on the Surface Anchoring Strength and the Pretilt Angle Generation in NLC on Rubbed Polythiophene Surfaces with Alkyl Chain Lengths

  • Seo, Dae-Shik
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.12 no.1
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    • pp.69-74
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    • 1999
  • We have investigated that the high pretilt angle of the NLC, 4-n-pentyl-4-cyanobiphenyl (5CB), was observed on rubbed polythiophene (PTP) surfaces with alkyl chains with more than 10 carbon atoms; it is attributed to the surface-excluded volume effect by the alkyl chain lengths between the LCs and the PTP surfaces. Next, we investigated that the odd-even effect of the polar anchoring strength in 5CB on rubbed PTP surfaces with alkyl chain lengths has been successfully evaluated. The anchoring strength of 5CB for rubbed PTP surfaces with odd-number is weak compared with even-number up to the 6 carbon atoms in the alkyl chain; however, odd-number is strong compared with even-number above 7 carbon atoms. The weak anchoring strength of 5CB is approximately $1\times10^{-3} (J/m^2$) on rubbed PTP surface with 7 carbon atoms; it is relatively strong anchoring strength. Consequently, we conclude that the odd-even effects of the polar anchoring strength in NLCs are strongly related to the characteristics of the polymer and observed clearly for short alkyl chain lengths.

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Poly(ether-ester) Multiblock Copolymers Based on Poly(oxymethylene-alt-oxyalkylene) Glycols

  • Kim, Jin-Bong;Chun, Jae-Hwan;Kim, Dong-Hee;Park, Yun-Hee;Lee, Moo-Sung
    • Macromolecular research
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    • v.10 no.4
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    • pp.230-235
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    • 2002
  • Alternating polyols of oxymethylene and oxyalkylene were synthesized and used as precursors for thermoplastic poly(ether-ester) elastomers (TPEs). The polyols were synthesized by reacting diols having different methylene units with dichloromethane in the presence of a phase transfer catalyst. The number of methylene units in the alkylene oxides was varied from 3 to 6. TPEs were prepared using the polyols as soft segments and poly(butylene terephthalate) units as hard segments. The polyols and TPEs synthesized were characterized using FTIR, NMR, GPC, DSC, and polarized optical microscopy. The polyols showed a profound odd-even effect on the melting (T$_{m}$) and glass transition temperatures (T$_{g}$). Polyols with odd numbers of methylene groups in the alkylene units have higher transition temperatures than polyols with odd number of methylene groups. The tendency is still kept in TPEs, even though the T$_{g}$ of soft segment in TPEs are slightly higher than those of corresponding neat polyols. The T$_{m}$ and T$_{g}$ of soft segments are almost constant in the range of 20 to 60 wt % contents of soft segments. On the other hand, the normalized heat of fusion of hard segment decreased with increasing the content of loft segment.ent.t.ent.

Nuclear Charge Distribution in Fission Products

  • Baik, Joo-Hyun;Bak, Hae-Ill
    • Nuclear Engineering and Technology
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    • v.11 no.4
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    • pp.295-301
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    • 1979
  • For thermal-neutron-induced fission of $U^{235}$, nuclear charge distribution in the light part of the primary products has been calculated by using several postulates of charge distribution in the fission fragments. By comparing these values with the experimental results, it is revealed that those models are not appropriate for predicting the nuclear charge distribution in the fission fragments. The variation in the most probable charge, $Z_{P}$, of the isobaric distribution for the fission fragments and the charge for a mass given by unchanged charge density, $Z_{UCD}$, is turned out to be small as a function of mass. The parameter, $Z_{P}$ $-Z_{UCD}$, varies from 0.45 to 0.5 in charge units. The nuclear charge dispersion, $\sigma$, shows about 0.5 charge units for the fission fragments. Neutron odd-even effect in fission products could not be revealed clearly without considering the odd-even effect of prompt neutron emission.

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Analysis of Power Amplifier Nonlinear Response Based on Practical Circuit Parameters (회로 특성 파라미터에 근거한 전력 증폭기의 비선형 응답 특성)

  • Park, Yong-Kuk;Kim, Hyeong-Seok
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.61 no.5
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    • pp.721-725
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    • 2012
  • In this paper, a novel analysis on the nonlinear response of a power amplifier (PA) with the intermodulation distortion (IMD) asymmetry is proposed based on the mutislice behavioral model. The coefficients of the odd-order and even-order polynomial of that model are represented with the PA practical circuit parameters such as intercept points, gain and amplitudes of excitation inputs. We also develop the analytic expressions to distinguish baseband frequency effect from second harmonic effect on the IMD asymmetry. We also validate the derived analytic expressions through measurements.

Thermotropic Liquid Crystalline Behavior of α,ω-Bis(4-nitroazobenzene-4'-carbonyloxy)alkanes (α,ω-비스(4-니트로아조벤젠-4'-카보닐옥시)알칸들의 열방성 액정 거동)

  • Jeong, Seung Yong;Hwang, Dong Jun;Ma, Yung Dae
    • Applied Chemistry for Engineering
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    • v.21 no.2
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    • pp.230-237
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    • 2010
  • A homologous series of linear liquid crystal dimers, ${\alpha},{\omega}$-bis(4-nitroazobenzene-4'-carbonyloxy)alkanes (NATWESn, n = 2~8, 10, the number of methylene units in the spacer) have been synthesized, and the thermal behavior of the series has been investigated. All the dimers formed enantiotropic nematic phases. The nematic-isotropic transition temperatures of the dimers and their entropy variation at the phase transition showed a large odd-even effect as a function of n. This behavior was rationalized in terms of the change in the average shape of the spacer on varing the parity of the spacer. The thermal stability and degree of order in the nematic phase and the magnitude of the odd-even effect of NATWESn were very similar to those of the corresponding ether compounds, while they were significantly different from those of the monomesogenic compounds, 4-{4'-(nitrophenylazo)phenoxy}alkanoyl chlorides and the side-chain liquid-crystalline polymers, the poly[1-{4-(4'-nitrophenylazo) phenoxycarbonylalkanoyloxy}ethylene]s. The results were discussed in terms of the 'irtual trimer model'by Imrie.

Extraction of Design Parameters for Re-entrant Mode Microstrip Directional Coupler with High Directivity Using FE Calculation (유한요소계산을 이용한 고지향성을 갖는 재-진입모드 마이크로스트립 방향성 결합기의 설계 파라미터 추출)

  • Kim, Hyeong-Seok;Park, Jun-Seok;Ahn, Dal
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.50 no.5
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    • pp.238-242
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    • 2001
  • In this paper, we extracted design parameters for re-entrant mode microstrip directional coupler using FE(finite element) calculations. The microstrip directional coupler suffers from a poor directivity due to effect of the inhomogeneous dielectric including both dielectric substrate and air in microstrip transmission lines. Thus, the phase velocity of even mode is not equal to that of odd mode. In order to improve the directivity of microstrip directional coupler, a novel re-entrant mode microstrip directional coupler was employed. In microstrip configuration, the high directivity can be reached by matching the even- and odd-mode effective phase velocities. Through the values of capacitance obtained from 2-dimensional FE calculations, the phase velocities for each mode and the design parameter were extracted for the proposed parallel coupled-line configuration. Based on the extracted design parameter with phase matching condition, we designed and fabricated a 30dB directional coupler at 0.85GHz. Experimental results show good performance with excellent, isolation and directivity.

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Thermotropic Liquid Crystalline Properties of α,ω-Bis(4-cyanoazobenzene-4'-oxy)alkanes (α,ω-비스(4-사이아노아조벤젠-4'-옥시)알케인들의 열방성 액정 특성)

  • Jeong, Seung Yong;Kim, Hyo Gap;Ma, Yung Dae
    • Applied Chemistry for Engineering
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    • v.22 no.4
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    • pp.358-366
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    • 2011
  • A homologous series of linear liquid crystal dimers, the ${\alpha},{\omega}$-bis(4-cyano-azobenzene-4'-oxy)alkanes (CATWETn, where n, the number of methylene units in the spacer, is 2~10) were synthesized, and their thermotropic liquid crystalline phase behavior were investigated. The CATWETn with n of 3 and 6 exhibited monotropic nematic phases, whereas other derivatives showed enantiotropic nematic phases. The nematic-isotropic transition temperatures of the dimers and their entropy variation at the phase transition showed a large odd-even effect as a function of n. This phase transition behavior was rationalized in terms of the change in the average shape of the spacer on varying the parity of the spacer. The thermal stability and degree of order in the nematic phase and the magnitude of the odd-even effect of CATWETn were similar to those for the methoxy-, nitro-, and pentyl-substituted dimers, while they were significantly different from those for the monomesogenic compounds, 1-{4-(4'-cyanophenylazo)phenoxy}alkylbromides and the side-chain liquid-crystalline polymers, the poly[1-{4-(4'-cyanophenylazo)phenoxyalkyloxy}ethylene]s. The results were discussed in terms of 'virtual trimer model' by Imrie.

Thermotropic Liquid Crystalline Behaviors of 4-{4'-(nitrophenylazo)phenoxy}alkanoic Acids and 4-{4'-(nitrophenylazo)phenoxy}alkanoyl Chlorides (4-{4'-(니트로페닐아조)펜옥시}알칸 산들 그리고 4-{4'-(니트로페닐아조)펜옥시}알카노일 클로라이드들의 열방성 액정 거동)

  • Jeong, Seung Yong;Ma, Yung Dae
    • Applied Chemistry for Engineering
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    • v.19 no.5
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    • pp.504-511
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    • 2008
  • Two kinds of nitroazobenzene derivatives: 4-{4'-(nitrophenylazo)phenoxy}alkanoic acids (NAAn, n = 2~8, 10, number of methylene units in the alkyl chain) and 4-{4'-(nitrophenylazo)phenoxy}alkanoyl chlorides (NACn, n = 2~8, 10) were synthesized, and their thermotropic liquid crystalline behaviors were investigated. NAA6 formed an enantiotropic nematic phase, while the remainders, except NAA2, showed monotropic nematic phases. Isotropic-nematic transition temperature ($T_{iN}$) and change of entropy (${\Delta}S$) at $T_{iN}$ for both of NAAn and NACn varied by the change of n, and pronounced odd-even effects of n were also observed. However, the $T_{iN}$ and ${\Delta}S$ values of NAAn were much higher than those of NACn. This fact may be attributed to the hydrogen bonding between carboxyl groups. Thermal properties and degree of order in the mesophase and the magnitude of the odd-even effects of both NAAn and NACn were significantly different from those reported for 4-(alkoxy)-4'-nitroazobenzenes. It was discussed in terms of the differences in the molecular anisotropy and the temperature-dependent flexibility of the substituted groups.

Synthesis and Properties of Liquid Crystal Compounds and Epoxy Resin Based Side Chain Liquid Crystal Polymers II. Linear and Crosslinked Epoxy LC Polymers (방향족 액정동족체 및 Epoxy형 측쇄 액정고분자의 합성 및 성질 II. 선형 및 가교형 측쇄 액정고분자)

  • Ahn, Wonsool;Chang, Jin Gyu;Keum, Chang Dae;Park, Lee Soon
    • Applied Chemistry for Engineering
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    • v.9 no.1
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    • pp.71-75
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    • 1998
  • Liquid crystalline compounds with amine terminal group and related linear and cross-linked liquid crystal polymers with epoxy resin structure were synthesized and characterized to develope matrix materials for polymer dispersed liquid display applications. Both linear and crosslinked side chain type liquid crystal polymers made with aromatic amine mesogens and ethylene glycol diglycidyl ether exhibited nematic texture as shown by polarized optical microscope(POM) and their transition temperatures were determined both by DSC and POM. Liquid crystal polymer samples also showed even-odd effect as the spacer length of aromatic amine mesogens were varied, however, the effect was samller than that of low molecular weight mesogens. Changes of nematic-to-isotropic transition($T_{NI}$) of crosslinked type polymer liquid crystals were also disscussed in relation to the concentration change of crosslinking agent 1,10-diaminodecane.

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