PurposeThe continuous-text reading-acuity test MNREAD is designed to measure the reading performance of people with normal and low vision. This test is used to estimate maximum reading speed (MRS), critical print size (CPS), reading acuity (RA), and the reading accessibility index (ACC). Here we report the age dependence of these measures for normally sighted individuals, providing baseline data for MNREAD testing.MethodsWe analyzed MNREAD data from 645 normally sighted participants ranging in age from 8 to 81 years. The data were collected in several studies conducted by different testers and at different sites in our research program, enabling evaluation of robustness of the test.ResultsMaximum reading speed and reading accessibility index showed a trilinear dependence on age: first increasing from 8 to 16 years (MRS: 140–200 words per minute [wpm]; ACC: 0.7–1.0); then stabilizing in the range of 16 to 40 years (MRS: 200 ± 25 wpm; ACC: 1.0 ± 0.14); and decreasing to 175 wpm and 0.88 by 81 years. Critical print size was constant from 8 to 23 years (0.08 logMAR), increased slowly until 68 years (0.21 logMAR), and then more rapidly until 81 years (0.34 logMAR). logMAR reading acuity improved from −0.1 at 8 years to −0.18 at 16 years, then gradually worsened to −0.05 at 81 years.ConclusionsWe found a weak dependence of the MNREAD parameters on age in normal vision. In broad terms, MNREAD performance exhibits differences between three age groups: children 8 to 16 years, young adults 16 to 40 years, and middle-aged to older adults >40 years.

We observe "ghost" islands formed on terraces during homoepitaxial nucleation of GaN. We attribute the ghost islands to intermediate nucleation states, which can be driven into "normal" islands by scanning tunneling microscopy. The formation of ghost islands is related to excess Ga atoms on the surface. The excess Ga also affect island number density: by increasing Ga coverage, the island density first decreases, reaching a minimum at about 1 monolayer (ML) Ga and then increases rapidly for coverages above 1 ML. This nonmonotonic behavior points to a surfactant effect of the Ga atoms.

The most fundamental difference between oxide surfaces and those of metals and elemental semiconductors arises from the strong ionic character of the metal-oxygen bond. Polar oxide surfaces have a net charge in each plane and a net dipole moment in the repeat unit perpendicular to the surface, predicted by classical theory to lead to an 'electrostatic catastrophe'. Different surface stabilization models have been proposed and studied [1]; reconstruction [2] and hydrogen adsorption [3] being the two relevant mechanisms for the present study. We report the first observation of the marked effects that the polar MgO(111) surface termination can have on the growth and structure of iron oxide films grown by oxygen plasma-assisted molecular beam epitaxy (OPAMBE). We combine high resolution transmission electron microscopy (HRTEM), X-ray and electron diffraction (XRD, RHEED, SAD), vibrating sample magnetometry (VMS) and density functional theory (DFT) to elucidate the atomic and electronic structure of these novel polar oxide films and interfaces, and to develop an understanding of the polar interface stabilization mechanisms. Epi-polished single crystal MgO(111) surfaces were cleaned with solvents and annealed in a tube furnace under the flow of oxygen at 800°C and 1100°C for the preparation of unreconstructed and reconstructed surfaces, respectively. Upon insertion in ultrahigh vacuum, both surface types were treated with oxygen plasma (55mA at 2×10-5 torr O 2 partial pressure) at room temperature, then heated to ~500°C before exposing to a flux of Fe atoms corresponding to a growth rate of 0.1 Å Fe/s. Fig. 1 shows streaky RHEED patterns from the starting MgO(111) surfaces terminated with an unreconstructed 1×1-OH structure (a) and mixture of (√3×√3)R30° (dominant) and (2×2) reconstruction domains (d). Upon termination of the iron oxide growth, the in-situ RHEED patterns are spotty and consistent with hematite (Fe 2 O 3) bulk termination in both cases (Fig. 1b,e). The VMS results show marked differences in the saturation magnetization and coercivity (Fig. 1c,f), both parameters being unusually high for the film grown on the reconstructed surface. Cross sectional samples were prepared by tripod polishing and argon ion milling methods. HRTEM and SAD studies showed a single phase Fe 2 O 3 film on the unreconstructed surface (Fig. 2a,b,c) with epitaxial relationship: (0001)Fe 2 O 3 ||(111)MgO; [11-20] Fe 2 O 3 ||[1-10] MgO, consistent with XRD. An interfacial Fe 3 O 4 (111) band of ~6.2 nm thickness is found in the Fe 2 O 3 (0001) film grown on MgO(111)-(√3×√3)R30° surface under otherwise identical conditions. This buried magnetite band was not detected by lab source XRD, but it is clearly visible in HRTEM (Fig. 2d,e) and weekly visible in SAD (Fig. 2f). The interfacial magnetite provides an explanation for the mixed ferri-and antiferromagnetic behavior of the films grown on reconstructed polar MgO(111) surfaces. Theoretical modeling is under way to explain this phenomenon.