In Situ Synchrotron Diffraction Analysis of Zn Additions on the Compression Properties of NK30.

In situ synchrotron radiation diffraction was performed during the compression of as-cast Mg-3Nd-Zn alloys with different amounts (0, 0.5, 1, and 2 wt %) of Zn addition at room temperature. During the tests, the acoustic emission signals of the samples were recorded. The results show that the addition of Zn decreased the strength of the alloys but, at the same time, increased their ductility. In the earlier stages of deformation, twin formation and basal slip were the dominant deformation mechanisms. The twins tended to grow during the entire compression stage; however, the formation of new twins dominated only at the beginning of the plastic deformation. In order to accommodate the strain levels, the alloys containing Zn underwent nonbasal slip in the later stages of deformation. This can be attributed to the presence of precipitates containing Zn in the microstructure, inhibiting twin growth.

Phase Formation during Solidification of Mg-Nd-Zn Alloys: An In Situ Synchrotron Radiation Diffraction Study.

Mg-4Nd base alloys with Zn additions of 3, 5 and 8 wt % were investigated with in situ synchrotron radiation diffraction during solidification. This method enabled the investigation of phase formation and transformation in the alloys. The diffraction results were supported with TEM observations on the as-solidified samples. The results show the effect of increased Zn addition on stabilizing the Mg3RE phase (RE-rare earth). The experimental results agree only partially with the theoretical calculations indicating the need to improve the existing thermodynamic database on the alloy system.

The Effect of Zn Content on the Mechanical Properties of Mg-4Nd-xZn Alloys (x = 0, 3, 5 and 8 wt.%).

The mechanical properties of as-cast Mg-4Nd-xZn (x = 0, 3, 5 or 8 wt.%) alloys were investigated both in situ and ex situ in as-cast and solution-treated conditions. The additions of 3 or 5 wt.% Zn in the base Mg-4Nd alloy did not improve yield strength in comparison to the binary Mg-4Nd alloy. Mechanical properties were shown to improve only with the relatively high concentration of 8 wt.% Zn to Mg-4Nd. The change in intermetallic morphology from a continuous intermetallic to a lamella-like intermetallic was the primary reason for the decreased mechanical properties in Mg-4Nd-3Zn and Mg-4Nd-5Zn compared with Mg-4Nd and Mg-4Nd-8Zn. The dissolution of intermetallic at grain boundaries following heat treatment further indicated the importance of grain boundary reinforcement as shown in both in situ and ex situ compression testing. Azimuthal angle-time plots indicated little grain rotation most noticeably in Mg-4Nd, which also indicated the influence of a strong intermetallic network along the grain boundaries.

Short-term corneal endothelial response to wear of silicone-hydrogel contact lenses in East Asian eyes.

OBJECTIVE: To evaluate corneal endothelial bleb response to wear of silicone-hydrogel contact lenses in eyes of East Asian subjects. METHODS: A total of 24 subjects of East Asian origin, attended 3 separate sessions for a prospective, single-centre, trial. The following contact lenses were used: ACUVUE ADVANCE with HYDRACLEAR (ADVANCE, -3 dioptres), ACUVUE OASYS with HYDRACLEAR Plus (OASYS, -3 dioptres), Focus NIGHT & DAY (NIGHT & DAY, -3 dioptres) and SofLens 38 (+3 dioptres). A modified Balaam's crossover design was used to randomize presentation of sessions and contact lenses within sessions. Session 1 was a comparison between OASYS and SofLens 38 under closed eye conditions, session 2 was a comparison between ADVANCE and NIGHT & DAY under open eye conditions, and session 3 was a comparison between OASYS and NIGHT & DAY worn under closed eye conditions. Corneal endothelial images were captured with the Topcon SP-3000P noncontact Specular Microscope before lens wear, after 20 mins of wear with lenses on and 5 and 10 mins later after lens removal. Blebs were manually identified on these digital images by a masked observer. The area of blebs and total area under consideration were derived using ImageNet software and used to calculate percentage area of blebs. A boundary of equivalence of 1% was used as a clinically significant bleb area difference, and two-sided 95% confidence intervals were utilized to evaluate differences between lenses within each session. RESULTS: In session 1, SofLens 38 produced a mean percentage area of blebs of 8.0% under closed eye conditions, which was significantly different to that produced by OASYS (1.6%). In session 2, both Advance and Night & Day produced a mean percentage bleb area of 0.4% under open eye conditions. In session 3, OASYS and NIGHT & DAY produced statistically similar mean percentage bleb areas of 1.7% and 2.0%, respectively. CONCLUSIONS: The similarity of bleb responses induced by the silicone-hydrogel lenses under the tested wearing conditions is consistent with the proposition that increases in Dk/t above a certain level will produce minimal change in corneal physiologic conditions compared with that when no lens is worn.