Materials scientists at Caltech seek to understand and control
the world of solids, liquids, and  gases around us. To understand
how this broad scope is narrowed to specific topics in materials
science, we need the concept of microstructure.
Some phenomena, such as the gravitational implosion of stars,
are obviously more appropriate for study in astrophysics.
Nevertheless, the packing of the neutrons in a neutron star
will affect its deformation during collisions with celestial
objects.
The idea that the internal structure of a neutron star will
affect its mechanical response to an applied force is very
much an idea that falls within the purview of materials science.
Materials scientists use the word "microstructure" to
identify the composite personality of the internal structure
of the material.
Frequently the implication is that materials scientists study
microstructures of "engineering materials", which
means materials of technological importance such as ion conductors
or doped silicon. The figure shows an idealized microstructure,
useful for the analysis of high frequency vibrations in some
solids. It depicts small crystallites attached together with
soft springs. This picture has been useful for understanding
relationships between electromagnetic absorption and the microstructure
of small magnetic crystallites. Is this an engineering material?
Not yet, but perhaps someday it will be.
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