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This paper focuses on the space charge characteristics of epoxy resin and its nano-MgO composites exposed to UV irradiation. Compared with the pure epoxy resin samples, different space charge characteristics of the nanocomposites have been found. With the filler content increased (0.5 wt%~7 wt%), the total amount of charge first decreases, then increases, and then decreases again, then tend to be stable for samples experienced 200h UV ageing. Specimens with 3 wt%~5 wt% nano-MgO accumulate less space charge, while the 1 wt% nanocomposites accumulate the most. In addition, total charge of the composites with 3 wt%~5 wt% nanofiller appears almost stable after 50h UV ageing. Measurements of dielectric loss factor and volume resistivity also show that 3 wt%~5 wt% nano-MgO is benefit for the UV ageing resistance in epoxy-based materials.

Background: Vitamin D deficiency and secondary rises in parathyroid hormone (PTH) are highly prevalent in obese African-Americans. Endothelial dysfunction related to oxidative stress is more common in African-Americans compared to whites. Currently, the association of vitamin D (25-hydroxyvitamin D, 25-OH D) and PTH to nitric oxide metabolites (NOx) – nitrate and nitrite – and oxidative stress in African-Americans is unknown. Objective: A cross-sectional design was utilized to determine the association of 25-OH D and PTH with urinary NOx (UNOx) (n = 101) and plasma isoprostanes (n = 125), an oxidative stress marker, in overweight (body mass index of 25–39.9), normotensive African-Americans aged ≥35 years. Measurements: Multivariable linear regression analysis adjusted for age, sex, body mass index, and season was used to determine the relationship of 25-OH D and PTH to UNOx and isoprostanes. General linear models, adjusted for the same covariates, contrasted UNOx across three mutually exclusive vitamin D/PTH groups: (1) normal 25-OH D (51–249 nmol/l) and normal PTH (≤65 pg/ml); (2) low 25-OH D and normal PTH, and (3) low 25-OH D and high PTH. Results: 25-OH D was directly associated with UNOx before (p = 0.02) and after (p = 0.03) adjustment for PTH levels. A borderline significant association was observed between PTH and isoprostanes (p = 0.08). UNOx was 424, 290, and 270 µmol/8 h, respectively, across vitamin D/PTH groups 1–3 (p = 0.08). Conclusion: 25-OH D was directly associated with NO availability and PTH was positively, though borderline, associated with isoprostanes in overweight, normotensive adult African-Americans.