Influence of Surface Conditions on Wear and Friction of Hardmetals

C

Self-consistent field predictions for quenched spherical biocompatible triblock copolymer micelles

We have used the Scheutjens-Fleer self-consistent field (SF-SCF) method to predict the self-assembly of triblock copolymers with a solvophilic middle block and sufficiently long solvophobic outer blocks. We model copolymers consisting of polyethylene oxide (PEO) as solvophilic block and poly(lactic-co-glycolic) acid (PLGA) or poly({\ko}-caprolactone) (PCL) as solvophobic block. These copolymers form structurally quenched spherical micelles provided the solvophilic block is long enough. Predictions are calibrated on experimental data for micelles composed of PCL-PEO-PCL and PLGA-PEO-PLGA triblock copolymers prepared via the nanoprecipitation method. We establish effective interaction parameters that enable us to predict various micelle properties such as the hydrodynamic size, the aggregation number and the loading capacity of the micelles for hydrophobic species that are consistent with experimental finding.Comment: accepted for publication in Soft Matte

In situ He⁺ irradiation of the double solid solution (Ti_0.5,Zr_0.5)₂(Al_0.5,Sn_0.5)C MAX phase:Defect evolution in the 350–800 °C temperature range

Thin foils of the double solid solution (Zr0.5,Ti0.5)2(Al0.5,Sn0.5)C MAX phase were in situ irradiated in a transmission electron microscope (TEM) up to a fluence of 1.3 × 1017 ions⋅cm-2 (∼7.5 dpa), using 6 keV He+ ions. Irradiations were performed in the 350–800 °C temperature range. In situ and post-irradiation examination (PIE) by TEM was used to study the evolution of irradiation-induced defects as function of dose and temperature. Spherical He bubbles and string-like arrangements thereof, He platelets, and dislocation loops were observed. Dislocation loop segments were found to lie in non-basal-planes. At irradiation temperatures ≥ 450 °C, grain boundary tearing was observed locally due to He bubble segregation. However, the tears did not result in transgranular crack propagation. The intensity of specific spots in the selected area electron diffraction patterns weakened upon irradiation at 450 and 500 °C, indicating an increased crystal symmetry. Above 700 °C this was not observed, indicating damage recovery at the high end of the investigated temperature range. High-resolution scanning TEM imaging performed during the PIE of foils previously irradiated at 700 °C showed that the chemical ordering and nanolamination of the MAX phase were preserved after 7.5 dpa He+ irradiation. The size distributions of the He platelets and spherical bubbles were evaluated as function of temperature and dose.</p

Cumulative ultraviolet radiation flux in adulthood and risk of incident skin cancers in women

Background: Solar ultraviolet (UV) exposure estimated based on residential history has been used as a sun exposure indicator in previous case–control and descriptive studies. However, the associations of cumulative UV exposure based on residential history with different skin cancers, including melanoma, squamous cell carcinoma (SCC), and basal cell carcinoma (BCC), have not been evaluated simultaneously in prospective studies. Methods: We conducted a cohort study among 108 578 women in the Nurses' Health Study (1976–2006) to evaluate the relative risks of skin cancers with cumulative UV flux based on residential history in adulthood. Results: Risk of SCC and BCC was significantly lower for women in lower quintiles vs the highest quintile of cumulative UV flux (both P for trend <0.0001). The association between cumulative UV flux and risk of melanoma did not reach statistical significance. However, risk of melanoma appeared to be lower among women in lower quintiles vs the highest quintile of cumulative UV flux in lag analyses with 2–10 years between exposure and outcome. The multivariable-adjusted hazard ratios per 200 × 10−4 Robertson–Berger units increase in cumulative UV flux were 0.979 (95% confidence interval (CI): 0.933, 1.028) for melanoma, 1.072 (95% CI: 1.041, 1.103) for SCC, and 1.043 (95% CI: 1.034, 1.052) for BCC. Conclusions: Associations with cumulative UV exposure in adulthood among women differed for melanoma, SCC, and BCC, suggesting a potential variable role of UV radiation in adulthood in the carcinogenesis of the three major skin cancers