At this hour after we have had two days of this extremely interesting and exciting Discussion Meeting, I do not want to keep you for very long. I will not even attempt to give you a summary─I cannot at this late hour. What I want to do instead is to give some impression of what this Discussion Meeting has meant to me and what general linking principles I have been able to see in it. Every one of you will also want to make his own evaluation. I feel that the value of a meeting like this is very great because it has brought together, both in the papers and in the discussion, people from hitherto almost exclusively separate disciplines. The metallurgists, the ceramic and glass experts, the polymer chemists and solid-state physicists have met and discussed many topics of common interest to them. We who were concerned with organizing this meeting had to be extremely restrictive to keep the scope within practical bounds. We had to exclude, for instance, all papers dealing with the chemistry of preparation of polymers or those on the different techniques of glass making, and there are other properties, fascinating properties like electrical and optical properties, which could have been touched on had there been more time. We had to stick to a very limited field of properties common to all these new or improved substances, namely, the mechanical properties, and even then not of mechanical properties in general, such as elasticity. It is quite clear from the way the discussion has gone that only the two major mechanical properties have come into the foreground, one being the yield point or beginning of plasticity, and the other the limit of fracture or total breakdown. These are essentially practical considerations because although the first of these, the yield point, may have some physical meaning, the second is really essentially a practical limitation of the material performance. The presence of preformed cracks, for instance, absolutely limits the use of some materials in different conditions of stress.
Up-conversion of sunlight by GaInP/GaAs/Ge cell stacks: Limiting efficiency, practical limitation and comparison with tandem cells
