Soft contact lens extended wear affects corneal epithelial permeability: hypoxic or mechanical etiology?

Contact lens extended wear increases the permeability of epithelium to sodium fluorescein (P(dc)). The exact mechanism is not known. However, changes in P(dc) likely result from either corneal hypoxia or mechanical trauma, or both. We explored the effects of one-night continuous wear with either high- or low-Dk/t soft lenses on P(dc). The results show that corneal epithelial barrier function decreases significantly with both lens groups. We also observed that Asian eyes had higher P(dc) after overnight wear compared to non-Asian and that for both Asian and non-Asian eyes, the elimination of corneal hypoxia did not prevent changes in epithelial permeability.     

Development of an Active Packaging Film Based on a Methylcellulose Coating Containing Murta (<Emphasis Type="Italic">Ugni molinae</Emphasis> Turcz) Leaf Extract

A new active packaging film based on murta leaf extract was elaborated. The extract was incorporated into a methylcellulose layer which was coated on a low-density polyethylene (LDPE) film. Its antioxidant effectivity, antimicrobial activity, and physicochemical properties were evaluated. The active film was able to keep its antimicrobial and antioxidant properties for at least 60 days. During this time, the growth of Listeria (L.) innocua was reduced by 2 log cycles and free radical formation could be inhibited by about 90 % for films stored under light and dark conditions. The active coating on the LDPE film did not affect the thermal and water vapor transmission properties; however, slight changes in the mechanical, color, and optical properties were observed. Finally, a sensory analysis showed that active coating did not change the flavor and odor properties of a fatty food packed inside the active material. This suggests that this active packaging film could be used to extend the shelf-life of packaged food.     

Alternative Approach to Modeling of Nucleation and Remelting in Powder Bed Fusion Additive Manufacturing

In powder bed fusion (PBF) of metals, energy of a laser or electron beam is utilized to form near-net-shaped parts from a powder bed. A very promising application of PBF lies in the direct control of the resulting microstructure by adjusting process parameters. Especially the intentional tilting of grains in one certain direction offers a complete new field of activity for additively produced parts specially designed for a given load case. Nucleation is essential for utilization of this effect. Herein, an alternative approach for modeling nucleation in PBF of metals is introduced. The model is not intended to cover every physical effect of this extreme complex phenomenon. Based on observations reported from different researchers in the field of PBF, a heuristic approach is applied to consider new grains within a cellular automata (CA)-based crystal growth model for PBF. Utilizing the implicit capability of the CA to model competitive growth of grains, this approach does not require any additional computational capacities. The numerical calculations are carried out using a message–passing interface (MPI) parallelization on a high-performance computing (HPC) cluster located at the Regional Research Center Erlangen. The numerical results are validated by means of experiments and electron backscatter diffractometric measurements.     

Influence of Cu Addition and Microstructural Configuration on the Creep Resistance and Mechanical Properties of an Fe-Based α/α′/α″ Superalloy

Introducing Cu nanoparticles is an effective mechanism for strengthening and toughening Fe-based materials such as ultra-high-strength steels. Herein, the effect of Cu on the mechanical properties of a novel Fe-based α/α′/α″ superalloy is studied. Compared to a Cu-free reference alloy, nanoindentation reveals an increase in hardness, which was associated with the formation of Cu nanoparticles. Both alloys show room temperature (RT) compressive plastic strain at maximum stress greater than 8%, irrespective of the heat-treatment. At RT and at 750 °C, the Cu-containing alloy exhibits a slightly higher strength, but the heat treatment has a more significant impact: A configuration of α-matrix and intermetallic α′/α″-phases forming an interpenetrating network is superior to a state with isolated precipitates. This difference vanishes in monotonic creep experiments, and under the same conditions, the Cu-containing alloy exhibits a twice as high creep rate despite a slightly higher precipitate fraction. This is linked to a higher lattice misfit and faster-coarsening kinetics. Post-mortem transmission electron microscopy analysis of the creep-deformed specimens identifies dislocation bypass as the dominant deformation mechanism. However, the presence of <010>{110} dislocations in the interfacial networks and evidence of dislocation activity within α′/α″ precipitates suggest the occurrence of shearing events.     

Liquid‐selenium‐enhanced grain growth of nanoparticle precursor layers for CuInSe2 solar cell absorbers

Large‐grained CuInSe₂ absorber layers are synthesized using a non‐vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide‐based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H₂ or H₂Se gasses. Lateral grain sizes up to 4 µm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe₂ enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low‐cost, non‐vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes. Copyright © 2014 John Wiley & Sons, Ltd.     

Spin-Flip Raman Scattering on Electrons and Holes in Two-Dimensional (PEA)2PbI4 Perovskites

The class of Ruddlesden–Popper type (PEA)₂PbI₄ perovskites comprises 2D structures whose optical properties are determined by excitons with a large binding energy of about 260 meV. It complements the family of other 2D semiconductor materials by having the band structure typical for lead halide perovskites, that can be considered as inverted compared to conventional III–V and II–VI semiconductors. Accordingly, novel spin phenomena can be expected for them. Spin-flip Raman scattering is used here to measure the Zeeman splitting of electrons and holes in a magnetic field up to 10 T. From the recorded data, the electron and hole Landé factors (g-factors) are evaluated, their signs are determined, and their anisotropies are measured. The electron g-factor value changes from +2.11 out-of-plane to +2.50 in-plane, while the hole g-factor ranges between -0.13 and -0.51. The spin flips of the resident carriers are arranged via their interaction with photogenerated excitons. Also the double spin-flip process, where a resident electron and a resident hole interact with the same exciton, is observed showing a cumulative Raman shift. Dynamic nuclear spin polarization induced by spin-polarized holes is detected in corresponding changes of the hole Zeeman splitting. An Overhauser field of the polarized nuclei acting on the holes as large as 0.6 T can be achieved.     

Numerical and Experimental Investigation on the Self-Healing Potential of Interpenetrating Metal–Ceramic Composites

An interpenetrating metal ceramic composite (IMCC) has been investigated regarding the potential as well as the feasibility of self-healing. Triggered by heating, cracks in the damaged composite located mainly in the Al₂O₃ ceramic or at the interface could be filled and closed by the liquid AlSi10Mg metal alloy. This healing procedure promises to reduce stress concentrations at crack tips and to improve the mechanical properties compared to the predamaged composite. Two different numerical approaches have been introduced to investigate this assumption and the potential of self-healed IMCCs for a best case scenario: 1) A simple 2D model to analyze the reduction of stress concentrations in front of a crack tip within the ceramic due to healing and 2) a 3D model based on CT-scan reconstructed microstructures to study how macroscopic mechanical properties can be restored depending on the amount of predamage. Further, the self-healing approach has been investigated experimentally for the same composite. Despite the fact that experimental self-healing of the investigated IMCC is only moderately feasible so far, the study shows the great potential that can still be exploited in order to extend the service life time of IMCC engineering components.