In microwave heating, the energy is directly introduced into the material resulting in a rapid and volumetric heating process with reduced thermal gradients, when the electromagnetic field is homogeneous. From those reasons, the microwave technology has been widely used in the industry to process dielectric materials. The capacity to heat with microwave radiation is related with the dielectric properties of the materials and the electromagnetic field distribution. The knowledge of the permittivity dependence with the temperature is essential to understand the thermal distribution and to minimize the non-homogeneity of the electromagnetic field. To analyse the history of the heating process, the evolution of the electromagnetic field, the temperature and the skin depth, were simulated dynamically in a ceramic sample. The evaluation of the thermal runaway has also been made. This is the most critical phenomenon observed in the sintering of ceramic materials because it causes deformations, or even melting on certain points in the material, originating the destruction of it. In our study we show that during the heating process the hot spot's have some dynamic, and at high temperatures most of the microwave energy is absorbed at the surface of the material. We also show the existence of a time-delay of the thermal response with the electromagnetic changes.

merical experiments showed that the gigabit Ethernet is suitable for a smaller cluster in terms of ratio of performance to price. The multiple core processors with OpenMP optimization will be good choice for the serial code.ABSTRACT: In this work we determine the elastic constant, the Young modulus, and the strain limit of commercial optical fibers. The fiber rupture limit in standard and Boron codoped photosensitive optical fibers, usually used in FBG-based sensors, is also quantified. The estimation of such values is extremely relevant, providing useful experimental values to be used in the design and modeling of the sensors.

β-Poly(vinylidene fluoride) (β-PVDF) exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The piezoelectric properties of the material can be optimised by poling the original stretched film. The main effect of the poling process is the alignment of the randomly organised dipolar moments against the applied field. In this work, poled and non-poled β-PVDF from the same batch are characterised by dielectric spectroscopy. The origin of the electrical and mechanical response of poled and non-poled β-PVDF were further explored by far IR spectroscopy and discussed on a molecular level. The main effect of the poling process on the dielectric response of the material is a small increase of the dielectric constant due to the preferential alignment of the main dipolar contribution and a slight decrease of the dielectric loss, due to the more organized amorphous structure. The conductivity is strongly increased by poling, especially the high-temperature conductivity, ascribed mainly to hopping conductivity due to free charges induced during poling. FTIR experiments indicate that the origin of these effects and also of the variations in the thermo-mechanical response of the material can be found in the reorientation of the crystalline dipoles along the poling field, together with a partial reduction of the amount of α phase and an increase of the amount of β phase. The α to β transformation, mainly due to the stretching process, seems to be optimized by the poling process.

The structural features of four different kraft papers were related to their surface properties and to the response upon industrial impregnation with phenol-formaldehyde (PF) resin. The chemical composition and the structure of paper were suggested to be important factors determining the interaction with PF resin, which was assessed by contact angle measurements and surface energy analysis. The presence of fatty matter (extractives) and inorganic fillers together with structural anisotropy of paper confers the difference in affinity of the face and backside of papers toward PF resin. This affects the resin distribution in impregnated precured kraft papers as revealed by microfluorescence spectroscopic analysis of transversal cuts.

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