Improving the Dielectric Properties of Polymers by Incorporating Nano-particles.

The paper presents a brief review of the promise of nanotechnology applied to polymeric insulation materials and discusses the electrical properties found. For a variety of nanocomposites, the dielectric behaviour has shown that the interface between the embedded particles and host matrix holds the key to the understanding of the bulk phenomena being observed. Dielectric spectroscopy verified the motion of carriers through the interaction zones that surround the particles. The obvious improvements in endurance and breakdown strength of nanocomposites may be due to a reduction of charge accumulation. PEA space charge tests confirm this charge dissipation. By examining the onset field of space charge accumulation, it may be possible to determine whether a system is likely to be useful

“Mirror Image Effect” Space Charge Distribution in XLPE Power Cable under Opposite Stressing Voltage Polarity

The paper presents space charge distributions under opposite voltage polarities in full size cross-linked polyethylene power cables using the pulsed electro-acoustic technique. Under both positive and negative polarities, space charge distributions possess similar profiles but opposite polarities. A similar phenomenon had been reported previously in plaque samples and was termed the “mirror image effect”. By comparing the results between cables treated by degassing under different conditions, the paper concludes that the “mirror image” charge distribution is mainly attributed to a bulk effect within the volume of the insulation, whilst electron transfer by tunneling through an electrode/insulator interface contributes to the generation of homo “mirror image” close to the electrodes

Subtropical middle atmosphere dynamics observed by the Chung Li radar

The Chung Li Radar (24.91 N; 121.24 E) has been operating since 1986. A five beam observational configuration was used on a regular basis to study the various dynamics processes in the atmosphere-lower stratosphere height region. Due to its geographical location, the annual Typhoon and Mei-Yu seasons provide good opportunities to study the various interesting dynamic processes such as instabilities, generation of gravity waves, wave mean field interaction, etc. Three dimensional air motions due to these fronts are presented. Special cases of gravity wave generation, propagation and their effects on the turbulent layers are discussed

Comparative study of Steel-FRP, FRP and steel reinforced coral concrete beams in their flexural performance

In this paper, a comparative study of Carbon Fiber Reinforced Polymer (CFRP) Bar and Steel-Carbon Fiber Composite Bar (SCFCB) reinforced coral concrete beams are made through a series experimental tests and theoretical analysis. The flexural capacity, crack development and failure modes of CFRP and SCFCB reinforced coral concrete were investigated in detail. They are also compared to ordinary steel reinforced coral concrete beams. The results show that under the same condition of reinforcement ratio, the SCFCB reinforced beam exhibits better performance than those of the CFRP reinforced beams, and its stiffness is slightly lower than that of the steel reinforced beam. Under the same load condition, the crack width of the SCFCB beam is between the steel reinforced beam and the CFRP bar reinforced beam. Before the steel core yields, the crack growth rate of SCFCB beam is similar to the steel reinforced beam. SCFCB has a higher strength utilization rate, about 70% -85% of its ultimate strength. The current design guidance was also examined based on the test results. It was found that the existing design specifications for FRP reinforced normal concrete is not suitable for SCFCB reinforced coral concrete structures

The Influence of Water on Dielectric Behavior of Silica-filled Epoxy Nano-composites and Percolation Phenomenon

The dielectric properties of epoxy resin were studied as a function of hydration by dielectric spectroscopy. The dielectric spectroscopy measurements show different conduction and quasi-DC behaviors at very low frequencies (<10-2 Hz) with activation energies dependent on the hydration. These observations lead to the development of a model in which a “water shell” is formed around the nano-particles. The multiple shell model, originally proposed by Lewis and developed by Tanaka, has been further developed to explain low frequency dielectric spectroscopy results in which percolation of charge carriers through overlapping water shells was shown to occur. At 100% relative humidity, water is believed to surround the nanoparticles to a depth of approximately 10 monolayers as the first layer. A second layer of water is proposed that is dispersed by sufficiently concentrated to be conductive. If all the water had existed in a single layer surrounding a nanoparticle, this layer would have been approximately 5 nm thick at 100% RH. Filler particles that have surfaces that are functionalized to be hydrophobic considerably reduce the amount of water absorbed in nanocomposites under the same conditions of humidity. PEA results show that the wetted epoxy specimens have a higher threshold field of space charge accumulation than such dry specimens since water enhances charge decay