  In an effort to understand nuclei in terms of quarks we develop an effective
theory to low-energy quantum chromodynamics in which a single quark contained
in a nucleus is driven by a mean field due to other constituents of the
nucleus. We analyze the reason why the number of $d$ quarks in light stable
nuclei is much the same as that of $u$ quarks, while for heavier nuclei
beginning with ${\rm Ca}^{40}$, the number of $d$ quarks is greater than the
number of $u$ quarks. To account for the finiteness of the periodic table, we
invoke a version of gauge/gravity duality between the dynamical affair in
stable nuclei and that in extremal black holes. With the assumption that the
end of stability for heavy nuclei is dual to the occurrence of a naked
singularity, we find that the maximal number of protons in stable nuclei is
$Z_{\max}^{\rm H}\approx 82$.
