The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.
By means of dimensional selection of natural lignocellulosic fibers, based on precise diameter measurements, it was recently possible to obtain fibers with relatively higher tensile strength. The present article overviews works on the statistical evaluation, through the Weibull analysis, of the ultimate tensile stress of eight lignocellulosic fibers: sisal, ramie, curaua, jute, bamboo, coir, piassava and buriti. It is shown that, for all of these fibers, the tensile strength holds an inverse relationship with the fiber diameter. Statistically this relationship conforms to a hyperbolic type of analytical equation, which discloses the possibility of unusually high strength fibers to be selected in association with very small diameters. A structural analysis using scanning electron microscopy offered an explanation to the strengthening mechanisms responsible for the superior performance of these dimensionally selected fibers.
An optimal design of photonic crystal optical fibers for simultaneous dispersion compensation and Raman amplification is investigated by numerical simulation using the finite-difference simultaneous over-relaxation method. The proposed fiber was fabricated and experimental characterization results are presented. Figure 1 Raman gain, ␥, as a function of the pitch parameter, ⌳, for various d/⌳ values. The single star represents the C-band DC-PCF with physical parameters d/⌳ ϭ 0.89 and ⌳ ϭ 0.93 m.ABSTRACT: Refraction of obliquely incident plane waves due to the interface of a vacuous half-space and a half-space occupied by a simply moving, nondissipative, isotropic dielectric-magnetic medium is considered, when the medium's velocity lies parallel to the interface and in the plane of incidence. Counterposition of the refracted wave vector and time-averaged Poynting vector occurs when the medium's velocity is sufficiently large in magnitude and makes an obtuse angle with the incident wave vector. The counterposition induced by relative motion occurs whether the refraction is negative or positive when the medium is at rest.
An optimal design of photonic crystal optical fibers (PCFs) for simultaneous dispersion compensation and Raman amplification is demonstrated by numerical simulation using the finite-difference simultaneous over-relaxation (FD-SOR) method. Preliminary experimental results towards this design are presented.
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