Investigation of the Space Charge and DC Breakdown Behavior of XLPE/α-Al2O3 Nanocomposites.

This paper describes the effects of α-Al2O3 nanosheets on the direct current voltage breakdown strength and space charge accumulation in crosslinked polyethylene/α-Al2O3 nanocomposites. The α-Al2O3 nanosheets with a uniform size and high aspect ratio were synthesized, surface-modified, and characterized. The α-Al2O3 nanosheets were uniformly distributed into a crosslinked polyethylene matrix by mechanical blending and hot-press crosslinking. Direct current breakdown testing, electrical conductivity tests, and measurements of space charge indicated that the addition of α-Al2O3 nanosheets introduced a large number of deep traps, blocked the charge injection, and decreased the charge carrier mobility, thereby significantly reducing the conductivity (from 3.25 × 10-13 S/m to 1.04 × 10-13 S/m), improving the direct current breakdown strength (from 220 to 320 kV/mm) and suppressing the space charge accumulation in the crosslinked polyethylene matrix. Besides, the results of direct current breakdown testing and electrical conductivity tests also showed that the surface modification of α-Al2O3 nanosheets effectively improved the direct current breakdown strength and reduced the conductivity of crosslinked polyethylene/α-Al2O3 nanocomposites.

Spectroscopic insights into the Photoreduction of Cytochrome c with UVA-Vis Light Irradiation.

With the particular conjugation structure in the heme prosthetic group, Cyt c shows unusual functions similar to chlorophyll while irradiated by specific wavelength of UV-Vis lights. To further reveal mechanism of the photo-irradiation of Cyt c, we then studied various external factors that may influence the photo induced process. The absorbance intensity increase of band (317 nm) and Q band (520 nm and 549 nm)indicated Cyt c in phosphate-buffered saline within N2 atmosphere was photoreduced to Fe(II) Cyt c. Irradiated by 410 nm, the photoreduction process was facilitated by Met. But Trp, Tyr and Phe impeded the process due to their light absorbance abilities. In addition, the results of fluorescence and CD spectra indicated that the microenvironment polarity of Trp residue varied during the photoreduction process. And the secondary structure of Cyt c changed with lower α-helix/ßsheet ratio. The photoreduction mechanism of Cyt c was intramolecular electron transfer and porphyrin cation radicals were generated. The protein structure of Cyt c changed as well as part of the photoreduction.