carbon nanocones
... that the opening angle of hollow carbon nanocones is not arbitrary, but has a few preferential values?
... that the opening angle of hollow <b id="mwDjU"><a href="./Carbon_nanocone" id="mwDjY" rel="mw:WikiLink" title="Carbon nanocone">carbon nanocones</a></b> <i id="mwDjc">(pictured)</i> is not arbitrary, but has a few preferential values?