Water-Tree Resistant Characteristics of Crosslinker-Modified-SiO2/XLPE Nanocomposites.

Trimethylolpropane triacrylate (TMPTA) as a photoactive crosslinker is grafted onto hydrophobic nanosilica surface through click chemical reactions of mercapto double bonds to prepare the functionalized nanoparticles (TMPTA-s-SiO2), which are used to develop TMPTA-s-SiO2/XLPE nanocomposites with improvements in mechanical strength and electrical resistance. The expedited aging experiments of water-tree growth are performed with a water-knife electrode and analyzed in consistence with the mechanical performances evaluated by means of dynamic thermo-mechanical analysis (DMA) and tensile stress-strain characteristics. Due to the dense cross-linking network of polyethylene molecular chains formed on the TMPTA-modified surfaces of SiO2 nanofillers, TMPTA-s-SiO2 nanofillers are chemically introduced into XLPE matrix to acquire higher crosslinking degree and connection strength in the amorphous regions between polyethylene lamellae, accounting for the higher water-tree resistance and ameliorated mechanical performances, compared with pure XLPE and neat-SiO2/XLPE nanocomposite. Hydrophilic TMPTA molecules grafted on the nano-SiO2 surface can inhibit the condensation of water molecules into water micro-beads at insulation defects, thus attenuating the damage of water micro-beads to polyethylene configurations under alternating electric fields and thus restricting water-tree growth in amorphous regions. The intensified interfaces between TMPTA-s-SiO2 nanofillers and XLPE matrix limit the segment motions of polyethylene molecular chains and resist the diffusion of water molecules in XLPE amorphous regions, which further contributes to the excellent water-tree resistance of TMPTA-s-SiO2/XLPE nanocomposites.

Functionalization of Silica Nanoparticles to Improve Crosslinking Degree, Insulation Performance and Space Charge Characteristics of UV-initiated XLPE.

In order to inhibit the outward-migrations of photo-initiator molecules in the ultraviolet-initiated crosslinking process and simultaneously improve the crosslinking degree and dielectric properties of crosslinked polyethylene (XLPE) materials, we have specifically developed surface-modified-SiO2/XLPE nanocomposites with the silica nanofillers that have been functionalized through chemical surface modifications. With the sulfur-containing silanes and 3-mercaptopropyl trimethoxy silane (MPTMS), the functional monomers of auxiliary crosslinker triallyl isocyanurate (TAIC) have been successfully grafted on the silica surface through thiol-ene click chemistry reactions. The grafted functional groups are verified by molecular characterizations of Fourier transform infrared spectra and nuclear magnetic resonance hydrogen spectra. Scanning electronic microscopy (SEM) indicates that the functionalized silica nanoparticles have been filled into polyethylene matrix with remarkably increased dispersivity compared with the neat silica nanoparticles. Under ultraviolet (UV) irradiation, the high efficient crosslinking reactions of polyethylene molecules are facilitated by the auxiliary crosslinkers that have been grafted onto the surfaces of silica nanofillers in polyethylene matrix. With the UV-initiated crosslinking technique, the crosslinking degree, insulation performance, and space charge characteristics of SiO2/XLPE nanocomposites are investigated in comparison with the XLPE material. Due to the combined effects of the high dispersion of nanofillers and the polar-groups of TAIC grafted on the surfaces of SiO2 nanofillers, the functionlized-SiO2/XLPE nanocomposite with an appropriate filling content represents the most preferable crosslinking degree with multiple improvements in the space charge characteristics and direct current dielectric breakdown strength. Simultaneously employing nanodielectric technology and functional-group surface modification, this study promises a modification strategy for developing XLPE nanocomposites with high mechanical and dielectric performances.

[Correlation of DNA methylation status of imprinted gene H19 ICR with oligozoospermia and asthenozoospermia].

OBJECTIVE: To study the correlation of the DNA methylation status of the imprinted gene H19 imprinting control region (ICR) with oligozoospermia and asthenozoospermia. METHODS: We eliminated chromosomal abnormality as the cause of male infertility in the subjects by karyotype analysis and detection of Y-chromosome microdeletions, and identified 18 cases of single factor-induced oligozoospermia (sperm concentration < 15 x 10(6)/ml) and 20 cases of single factor-induced asthenozoospermia (progressively motile sperm <32%) by computer-aided sperm analysis (CASA). Then we extracted genome-wide sperm DNA, treated it with bisul- fite, subjected the target gene fragments to PCR amplification and sequencing. Lastly, we analyzed the DNA methylation status of the target genes with BIQ Analyzer and processed the data using SPSS17.0. RESULTS: The DNA methylation level of the H19 ICR was increased significantly in the oligozoospermia patients ([9.19 +/- 2.45]%, P < 0.05), especially in the severe oligozoospermia males with sperm concentration < 3 x 10(6)/ml (P < 0.01), as compared with that of the 20 fertile control men ([0.30 +/- 0.06]%). However, no significant differences were found in the level ([0.30 +/- 0.07]%) and pattern of the DNA methylation of the H19 ICR (P = 0.62). Further analysis of the DNA methylation status of the CTCF-6 binding sites indicated that the DNA methylation degree was significant higher in the oligozoospermia men ([2.67 +/- 0.75]%) than in the fertile control ([0.05 +/- 0.03]%) or the asthenozoospermia group ([0.03 +/- 0.02]%), with no significant differences between the latter two (P = 0.35). CONCLUSION: The reduced DNA methylation of the H19 ICR is negatively correlated with sperm concentration but not associated with sperm motility.

[Effects of Astragalus polysaccharide on nephritis induced by cationic bovine serum albumin in rats].

OBJECTIVE: To study the effects of Astragalus polysaccharide on nephritis induced by cationic bovine serum albumin in rats. METHODS: C-BSA induced nephritis model was utilized in rats. The effects of Astragalus polysaccharide on this model were investigated. RESULTS: Proteinuria of the Astragalus polysaccharide group was alleviated. The pathological damages of the Astragalus polysaccharide group were less severe in comparison with the model group. The Astragalus polysaccharide group could improve erythrocyte immune function and increase the CD35 and CD44s contents of red blood cells. CONCLUSION: Astragalus polysaccharide exerts a good effect in alleviating glomerular immune inflammation and improving erythrocyte immune function in the treatment of C-BSA induced nephritis.

[Mechanism of hedysari polysaccharide in the apoptosis of human hepatocellular carcinoma HEP-G2 cells].

OBJECTIVE: To study the effects of Hedysari polysaccharide (HPS) on the proliferation and apoptosis of human hepatocellular carcinoma HEP-G2 cells and its mechanism. METHODS: MTT assay, flow cytometry and fluorescence microscopy were used to the effects of HPS in anti-proliferation, cell cycle arresting and apoptosis induction. Flow cytometry was also used to detect the effects detect of HPS on protein expressions of Bcl-2 and Bax. RESULTS: HPS could cause apparent inhibition on cell growth, induce G2/M phase arrest and apoptosis on HEP-G2 cells. HPS could down-regulate bcl-2 protein expression and up-regulate Bax protein expression. CONCLUSION: HPS has anti-tumor effects, maybe by the way of inhibiting the cell growth, arresting the G2/M phase, inducing apoptosis, down-regulating bcl-2 and up-regulating Bax protein expression.