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1.
The barrier properties of polymer-clay nanocomposites, with far less inorganic contents of layered-silicate fillers, are remarkably superior to those of neat polymers or their conventional counterparts. A simple renormalization group model is proposed to assess the influence of geometric factors (such as aspect ratio, orientation, and extent of exfoliation) of layered-silicate fillers on the barrier properties of polymer-clay nanocomposites. The results show that the aspect ratio of exfoliated silicate platelets has a critical role in controlling the microstructure of polymer-clay nanocomposites and their barrier properties. The estimated percolation thresholds of clay content for minimum permeability are in good agreement with experimental data. 相似文献
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利用T矩阵和离散坐标法研究了取向比对椭球粒子散射特性的影响, 计算了小尺度范围内椭球粒子的散射特征参量, 包括消光效率因子、不对称因子、单次散射反照率、散射相矩阵及双向反射函数(BRDF). 结果表明, 椭球粒子的散射特性与取向比密切相关, 粒子取向比会影响散射参量的振荡频率和振幅, 与球形粒子散射参量的相对差异也呈周期振荡趋势. 研究还发现, 某些特殊粒子尺寸的散射参量与粒子取向比基本无关. 在多次散射条件下, 分析不同取向比粒子群的BRDF随反射角和光学厚度的变化特性. 结果显示: 不同取向比粒子群的BRDF随反射角的变化趋势基本一致, 球形粒子群比非球形粒子群的BRDF曲线波动振幅更大; 球形-非球形粒子的BRDF相对差异随光学厚度和取向比的增大而减小, 随入射角的增大而增大. 相似文献
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The influence of systematic perturbation of input interaction parameters on thermodynamic equilibrium properties is studied employing dissipative particle dynamics (DPD) simulations. The values of both the excess pressure and the surface tension are found to be very sensitive to the values of the soft repulsion parameter between unlike DPD particles for high values of the coarse-graining level (number of water molecules per DPD particle). For the case in which a molecular surfactant is present at the interface we have determined the dependence of these properties on the values of the parameters that characterize the bonding force between polymer beads. No significant differences were found between linear and branched surfactants. 相似文献
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R. del Sole 《Solid State Communications》1981,37(7):537-540
Light-propagation equations at crystal surfaces are solved in the long-wavelength limit, fully accounting for surface anisotropy, inhomogeneity and non-locality of the dielectric susceptibility tensor. Local-field and excitonic effects are also accounted in principle. Equations allowing calculation of internal and external reflectivity coefficients are given and used to analyze experimental data. 相似文献
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Electronic structure and optical properties of BiSI crystal were investigated by the full potential linearized augmented plane wave (FL-LAPW) method with density functional theory (DFT). The complex dielectric function and optical constants, such as optical absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, were calculated. The optical properties of BiSI crystal were studied experimentally by spectroscopic ellipsometry. The experimental results were compared with the theoretical spectra of complex dielectric functions and with the spectra of a pseudo-dielectric function (PDF). This method shows that experimental spectra consist of four Laurence lines sum. 相似文献
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Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
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First-principles methods have been applied to explore the electronic and optical properties of BYF single crystals heavily doped with the Ho3+ ion (16.33 and 30.36 mol%). The electronic properties calculations manifest that the top of the valence band is dominated by 2p-orbitals of the F atoms and 4f-orbitals of the Ho atoms. The new defect states are dominated by 4f-orbitals of the Ho atoms which exist in the forbidden band. The principal absorptionat around 5.13 eV (241.7 nm) and 5.75 eV (215.7 nm) occurs in ultra-violet range owing to the electronic transitions from the occupied 2p-orbitalsof the F atoms as well as 4f-orbitals of the Ho atoms to empty 4f-orbitals of neighboring Ho atoms. Moreover, the influence of crystal field will split the energy levels of rare earth ions and easily release the parity forbidden condition of free rare earth ions resulting in f-f transition. Therefore, there may be a 2 μm luminescence in the Ho-doped BYF crystal. 相似文献
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C. Z. Bi J. Y. Ma J. Yan X. Fang D. Z. Yao B. R. Zhao X. G. Qiu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):167-171
Near-normal incident infrared reflectivity spectra of a
(001) YVO4 single crystal have been measured at different
temperatures in the frequency region between 100 and 6000 cm-1.
The reflectivity spectra are analyzed with the factorized form of
the dielectric function, and the dielectric properties and optical
conductivity of the YVO4 crystal are obtained. From the TO/LO
splitting, effective charges at different temperatures are
calculated to study the ionicity of YVO4. The internal modes
of the VO43- ion and the external modes of the Y(VO4) lattice
are compared with SiO44- in zircon and with other rare-earth vanadates. 相似文献
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R. Fuchs 《Physics letters. A》1973,43(1):42-44
The optical absorption due to bulk vibrational modes in an ionic crystal film is calculated using a nonlocal dielectric function . 相似文献
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《Infrared physics》1990,30(3):265-269
Far-infrared reflectivity measurements on single crystal barium and strontium hexaferrite are presented. The infrared active TO, and the associated LO phonon frequencies and the dielectric permittivity functions for E ⊥c have been determined using a fitting procedure based on a four parameter model. The infrared active modes of these compounds (space group D46h have been determined by group theoretical analysis and the results compared with the spectroscopic measurements. 相似文献
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《Composite Interfaces》2013,20(3-4):325-339
It is well known that the bending test provides a simple and convenient way of measuring the strength of unidirectional composite materials and gives very repeatable results. The aim of this research work was to study and analyze the flexural properties of unidirectional reinforced carbon fiber/epoxy (UD) specimens subjected to three-point loading. The effect of span-to-thickness ratio (L/h) and width-to-thickness ratio (b/h) on the three-point bending of UD composites has been investigated. Results have shown that unidirectional composites exhibit a transition in the failure mode from shear delamination to fiber yield with the span-tothickness ratio (L/h) is increased. The observed experimental data are confirmed by theoretical considerations presented here. Using the classical beam theory the conclusions of the tests could be extended by applying some reasonable requirements and simple rational fractional functions identified. This made it possible to express the asymptotic values of the flexural strength, the flexural modulus and apparent shear stress in a form that is independent from the values of the span-to-thickness ratio applied, and characterize the bending behavior of the composite materials at a more exact level. 相似文献
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Dependence of film thickness on the electrical and optical properties of ZnO-Cu-ZnO multilayers 总被引:1,自引:0,他引:1
ZnO-Cu-ZnO multilayers were prepared by simultaneous RF magnetron sputtering of ZnO and DC magnetron sputtering of Cu. Cu films with different thickness were used as the intermediate metal layer. The optical and electrical properties of the multilayers studied by UV-vis spectrophotometer and four point probe method, respectively, shows that transmittance increases with decrease of copper thickness up to an optimum thickness of 5 nm and sheet resistance decreases with increase of thickness. Low resistivity and high transmission were obtained when the film structure has a thickness of ZnO/Cu/ZnO: 50/5/50 nm. The performance of the multilayers as transparent conducting material was better than the single layer ZnO of equal thickness. 相似文献
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We propose a method for calculation of the bandgaps in the cladding of hollow-core photonic crystal fibers, based on the Floquet
theorem. The effectiveness of the approach is confirmed by estimates of the effect of the number of air channels in the cladding
on attenuation of the fiber modes due to mode energy leakage from the core. We have studied the conditions for the existence
of eigenmodes in the indicated fibers.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 311–320, March–April, 2009. 相似文献
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SUNIST低环径比托卡马克的供电系统 总被引:1,自引:1,他引:0
介绍了SUNIST低环径比托卡马克的纵向场线圈、欧姆加热场线圈和平衡场线圈的电学参数。所用电容器组储能系统采用电容换流式准恒流充电回路。测量了这三组线圈中的放电电流,并将测量结果与回路计算结果作了比较。 相似文献