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91.
Matthew Thompson Carolyn Carkner Adrian Bailey Nicholas J. Mosey Nadia Kapernaum 《Liquid crystals》2013,40(9):1246-1260
Two sterically equivalent series of phenoxy-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals were synthesised, and their mesogenic properties were characterised by polarised optical microscopy and differential scanning calorimetry (DSC). The phenoxy end-group causes a significant increase in melting point and inhibits – at least partially – the mesomorphism of these materials relative to the parent isomers; in most cases, the broad enantiotropic SmC phase formed by the parent isomers is suppressed by the addition of the phenoxy end-group. However, detailed analyses by small-angle X-ray scattering and monodomain 2D X-ray scattering suggest that these compounds form a SmA phase with a partially intercalated bilayer structure in which the phenoxy end-groups are nanosegregated. Such an intercalated bilayer structure might enable the tuning of smectogenic properties by appropriate substitution of the phenoxy end-groups. 相似文献
92.
We propose a method for fast switching of vertically aligned (VA) negative liquid crystals (LCs) by hiding the relaxation process of LCs. During the turn-off process, a strong in-plane electric field is applied for a short duration of time instead of relying solely on the slow relaxation of LCs. The LC molecules are rotated to the transmission axis of one of the polarisers by the applied in-plane electric field, resulting in turn-off switching that is 5.8 times faster than that of a conventional VA cell. By applying an overdriving scheme, we experimentally obtained a total response time of 3.3 ms. 相似文献
93.
The dissolution behavior of carbon steel in ammonium chloride (NH4Cl) solution containing sodium thiosulfate (Na2S2O3) of various concentrations (0.01 and 0.1 M) was investigated using electrochemical impedance spectroscopy (EIS) and other nonelectrochemical techniques. The weight loss and polarization measurements indicate a significant increase in the NH4Cl corrosion rate of carbon steel on addition of Na2S2O3. The EIS measurements exhibited two capacitive loops at multiple direct current (dc) potentials for both the concentrations. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to analyze the impedance data. A four-step mechanism with two intermediate adsorbate species of same charge was proposed to explain the dissolution behavior of carbon steel in the given system. The surface coverage values enumerated that the surface was entirely covered with adsorbed species unlike in the pure NH4Cl system. Charge transfer resistance and polarization resistance values estimated from RMA parameters indicate the increase in a dissolution rate with dc potential. The surface morphology was inspected via field emission scanning electron microscopy, and the corrosion products including surface state of carbon steel electrode were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. 相似文献
94.
Flash DSC crystallization study for blown film grade bimodal HDPE resins. I. Isothermal kinetics and its application of the blown film modeling
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Cecilia D. Treviño‐Quintanilla Ramanan Krishnamoorti Jaime Bonilla‐Ríos 《Journal of Polymer Science.Polymer Physics》2016,54(23):2425-2431
Isothermal ultra‐cooling crystallization tests were conducted on three blown film grade bimodal HDPE resins using an ultrafast scanning calorimeter, the Flash DSC. Isothermal tests were performed to study the regime transition, the thermal nucleation and the spherulitical growth using the Hoffman‐Lauritzen theory in a range between 90 °C and 116 °C. Temperature profile estimations using such data were in good agreement with actual blown film process data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2425–2431 相似文献
95.
96.
As the higher and higher frequency bands of existing metallic cables in access networks are being continuously exploited by modern transmission technologies, such as the G.fast, the necessity of providing accurate and suitable modeling of their transmission characteristics is evident. Therefore, this paper is focused on modeling of a propagation constant of twisted pairs and metallic cables at high frequencies up to 250 MHz, and an innovative arsinh model is proposed and described. This new model is based on an idea of adopting inverse hyperbolic sine function for modeling of both secondary line coefficients, attenuation constant and phase constant, and its main motivation is to provide their accurate estimations for G.fast frequencies up to 250 MHz for various types of metallic cables while maintaining a low computational complexity. The proposed model was compared with numerous characteristics measured for various real metallic cables as well as with several existing models in order to illustrate its potential. The results, which are presented within this paper, clearly illustrate that the proposed arsinh model generally outperforms existing standard models based on the equal number of required parameters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
97.
基于直升机卫星通信系统的特点,分析了卫星通信系统中姿态角提取、坐标变化及抗遮挡等关键技术,采用链路分析估算方法,提出了针对关键技术点的测试方案设计,通过工程案例验证,实现了对系统的测试与评估。 相似文献
98.
Hans Eliot Edling Matthew Vincent Herv Marand Samantha J. Talley Kevin Barr Robert B. Moore S. Richard Turner 《Journal of Polymer Science.Polymer Physics》2019,57(15):973-980
Structurally rigid copolyester thermoplastics were synthesized from 1,4‐cyclohexanedimethanol and the diesters dimethyl biphenyl‐4,4′‐dicarboxylate and dimethyl 2,6‐naphthalenedicarboxylate (DMN) via conventional melt transesterification. Conventional differential scanning calorimetry (CDSC) showed all compositions to exhibit multiple endotherms upon heating. Wide‐angle X‐ray diffraction analysis showed copolyester compositions to exhibit the crystalline structure of either the homopolyester Poly(1,4‐cyclohexylenedimethylene 2,6‐naphthalate) (PCN) or the homopolyester Poly(1,4‐cyclohexylenedimethylene 4,4′‐bibenzoate) (PCB), but not both simultaneously. Further thermal analysis using CDSC and fast DSC investigated the origin of the multiple endotherm behavior. While three endotherms are observed for low heating rates, the upper two endotherms appear to merge at heating rates about 1–5 °C s?1 and a single endotherm remains above heating rates about 10–50 °C s?1. While the behavior of the upper two endotherms is undeniably consistent with the mechanism of melting–recrystallization–remelting (MRR), we suggest that the low endotherm is likely associated with the melting of constrained secondary crystals, although MRR effects cannot be ruled out. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 973–980 相似文献
99.
Low-field nuclear magnetic resonance techniques are employed to extract information about the effects introduced by the interaction with the surface on the rotational and translational dynamics of molecules confined inside a mesoporous carbon xerogel. The molecules under study were water, cyclohexane, and hexane. They were chosen due to their different interaction strength with the carbonaceous matrix. Frequency dependent longitudinal relaxation measurements, using the fast field cycling technique, allowed extraction of the fractal dimension of the carbon xerogel surface. It was observed that the measured value is influenced by the molecule affinity to the surface. Diffusion measurements, using the pulse field gradient technique, have revealed that the stronger interaction with the surface of cyclohexane and hexane molecules leads to an increased diffusive tortuosity, as compared with water. 相似文献
100.