请问这篇GRE阅读是什么意思Calculations of the density of alloys based on

请问这篇GRE阅读是什么意思
Calculations of the density of alloys based on
Bernal-type models of the alloy‘s metal component
agreed fairly well with the experimentall y determined
Line values from measurements on alloys
consisting of a
5 noble metal together with ametalloid,such as alloys of
palladium and silicon,or alloys consisting of iron,
phosphorus,and carbon,although small discrepancies
remained.One difference between real alloys and the
hard spheres used in Bernal models is that the
10 components of an alloy have different sizes,so that
models based on two sizes of spheres are more
appropriate for a binary alloy,for
example.The smaller
metalloid atoms of the alloy might fit into holes in the
dense,random-packed structure of the larger metal
atoms.
主要是最后两句不明白,“One difference between real alloys and the
hard spheres used in Bernal models is that the
10 components of an alloy have different sizes,so that
models based on two sizes of spheres are more
appropriate for a binary alloy,for example.The smaller
metalloid atoms of the alloy might fit into holes in the
dense,random-packed structure of the larger metal
atoms.”不太明白这两句话在说什么,